Julius Ceasar Overview Essay Example For Students

Julius Ceasar: Overview Essay SUMMARY:Shakespeares Julius Caesar is the account of the resultingconflicts from the death of interminable despot and Romanemperor, Julius Caesar. An incredible companion of Caesar, Mark Antony,comes to the senate to see the dead body of their tyrant. Hepretends to not resent the individuals who participated in theassassination, and requests to talk at his memorial service, a solicitation whichhe is allowed. In any case, after the men leave, he starts a soliloquyin which he proposes that Caesars soul will deliver retribution uponhis killers and summon a war including the whole nation. Antony starts the retribution of his passing by talking at the funeralabout an inappropriate done to Caesar, the keeps an eye on liberality to thepeople, and how Brutus attempted to convince them to accept hisjustification of the homicide. The group goes to understanding withAntony and afterward blame the plotters for homicide. The accusedmen escape, in the long run leaving the limits of the city, and thecitizens leave to plunder and consume the places of the blameworthy men. The armed forces of Brutus and Cassius set up camps close to another cityand realizing that Antonys fighters are coming, they choose tomarch toward the adversary on the double. The battling starts with theconfrontation of the different sides, as Cassius and Brutus armiesarrive. Antony and his accomplice challenge the professional killers to fight,and the grisly fight starts. The militaries of the schemers fallinto weakness ordinarily, and their side does inadequately, losingmany men. Cassius hears erroneously that one of his importantsoldiers has been caught, loses trust, and ends it all, whileBrutus feels that his military has been cornered, and tosses himselfonto another keeps an eye on blade, executing himself moreover. They cancel therest of the fight, for Antonys armed force presently had triumph over Brutusand Cassius, Caesars murder had been retaliated for, and request had beenrestored. CHARACTERS:There are a few principle characters in this story. Caesar iswell enjoyed by the residents of Rome, yet is a fairly pompous manand trusts himself to be above every other person. He is givenpraise regularly and respected by occasions, for example, an occasion in his name. Nonetheless, a few men don't concur that Caesar ought to have such ahigh title, as they scorn his character. These six men conspireto execute the head to end what they see as his oppression andoppression in Rome. A man named Cassius composes the occasion, while an amazing figure,Brutus, convinces Caesar to go to the senate, where he is to bekilled. While the ruler contends with one of the schemers, aman named Casca betrays him, and different men followand twisted him with their blades until he tumbles to the ground,dead. EVALUATION:In this play, Shakespeare offered ethics to the crowd about rightand off-base and following up on ones conclusion. He indicated that oneshould not carry passing to another person dependent on their personaldesires, or whether they trust it is in the wellbeing oftheir society, for they are just a single individual out of the numerous whohave a voice. He likewise infers that in the event that one submits a demonstration of wrong,justified, or not, they can hope to be rebuffed for it by theothers who were harmed by those activities.

St. Johns River, North Florida Free Essays

The St. Johns I have had numerous encounters with the St. Johns River in my life. We will compose a custom paper test on St. Johns River, North Florida or on the other hand any comparative subject just for you Request Now For whatever length of time that I can recall that I have lived not exactly a mile from this stream. Each action from sailing, to paddling, or angling I have done in the waterway, and each time the water has appeared to be spotless. Throughout the years the St. Johns River has gained notoriety for being awful or perilous. Anything from substance eating microscopic organisms from algal blossoms to bull sharks have been supposed to prowl in its waters. Despite the fact that a portion of these gossipy tidbits are valid and some of them are bogus, one won't kick the bucket after contacting the water. Notwithstanding, the St. Johns needs some additional consideration dependent on tests, past and current projects, and the fish populace. Numerous tests performed on the stream mirror that the water is generally perfect. State authorities over Volusia and Seminole districts have seen that there is the potential for a water lack in the following couple a very long time because of populace increments. In the case of nothing is done, the ground water here will run out. An arrangement is being proposed to utilize surface water from the St. Johns River to enhance the ground water. State authorities accept they can channel the water from the St. Johns of microbes and utilize this water for drinking water. Ann Givens) The way that the state is thinking about utilizing the water in the St. Johns for drinking water shows that the water quality is acceptable. In the event that there were extreme algal blossoms, the state would not think about attempting to channel the water. Numerous tests performed on the waterway are in light of the paper factories present on the stream. There is one factory specifically tended to on Rice Creek outside of Palatka. The waste water from these paper plants is dumped from pipes into the stream. Ten years prior these plants had to redesign their gear because of a poison being discharged called Dioxin. Dioxin is concoction that can cause malignant growth created by the chlorine responses in the factory. The more seasoned hardware was accepted to permit this poison to stream into the St. Johns River. Two years back another test was done on the Rice Creek and hints of Dioxin are as yet present. The general conviction is that Dioxin has stayed in rivulet buildup. (Patterson, S. ) Tests like this are done all through the stream. The buildup staying from the Dioxin is just present in Rice Creek and is absent all through the water framework. This push to control the Dioxin shows progress. Researchers distinguished that the Dioxin was available and the source and made serious move to take out the extension of Dioxin. In spite of the fact that this exertion was important and extolled, endeavors currently should be made toward taking out the rest of the buildup and expelling Dioxin from the waterway totally. Numerous projects and assets have been committed to improving the water of the St. Johns River. A significant demonstration proposed in the 1970’s was the Clean Water Act of 1972. The Clean Water Act constrained Floridians to discover waterways that are disabled because of higher nitrogen levels. When built up, the state needed to found all out greatest every day loads for every one of these waterways. The all out greatest every day load (TMDL) is set up â€Å"based on the most extreme measure of poison that the water body can absorb without surpassing water quality gauges. †( Lynette, M. ) This demonstration gained ground in lessening the degree of nitrogen being included the stream. Despite the fact that this demonstration went in 1972 the issue is as yet present. Throughout the years, Florida has seen 80,000 sections of land of its wetlands created. (Littlepage, R. L. This outcomes in less water present in the framework and more nitrogen in the ground water from individuals treating their yards. In the event that the populace in focal Florida keeps on extending and the wetlands keep on vanishing, the nearness of algal blossoms and the decrease of the fish populace will never stop. The water evacuated and nitrogen added will keep on making a more extreme awkwardness. Additionally with advancement, focal Florida is attempting to take water from the St. Johns for drinking water for their exorbitantly enormous populace. This will simply make the nitrogen to water unevenness considerably more extreme. Rules and guidelines need to ether be put on wetlands pulverization, manure use, and populace restricts in focal Florida dependent on what number of individuals their water gracefully can continue. In 2006 a huge whole of cash was dedicated to the exertion of saving the St. Johns River. Twenty 7,000,000 dollars was dedicated to diminishing the measure of supplements, similar to nitrogen, entering the stream and expanding principles for organizations like Jacksonville Electrical Authority (JEA) who dump into the St. Johns River. The mayor’s office made JEA increment its measures for dumping waste water into the waterway and extend its projects for reusing water. This would lessen the measure of waste water dumped in the stream and decrease the measure of unsafe synthetic substances that enter the waterway from the JEA plant. (Littlepage, R. L. ) A significant worry in the St. Johns is the fish populace. The biggest poison in the waterway is nitrogen from overabundance manures that stream into the groundwater and into the stream. The vegetation of the waterway feed on this nitrogen. More nitrogen at that point prompts more plants. As the plant populace expands issues, for example, algal blossoms on the outside of the water happen. With the algal sprout circumstance the lower segment of the water is blocked or somewhat hindered from daylight. This prompts less vegetation on the floor of the stream and along these lines less oxygen in the water. With the absence of oxygen the fish populace will plunge before long. In 1994, an accomplished bass fisherman by the name of Doug Gilley did a meeting for the Orlando Sentinel. In this article he gave his expert knowledge on the change demolition of the bass populace from 1984 to 1994. Ten years before this article was composed, it would be nothing unexpected for him to get â€Å"10, 20 or even 50 fish in a day. † (Wilson, D) Doug was not by any means the only one who had seen this uncommon decline in the bass populace. State fisheries concurred with him. They have seen that the â€Å"large bass nearly have vanished from the stream and that the quantity of moderate sized bass are declining. † (Wilson, D. ) I for one have seen the decrease of fish from the stream. My sibling and I are energetic angler and appreciate looking for pretty much anything. We carried on a fourth of a mile from the waterway so regularly we would take my grandfather’s bass vessel and go angling in the stream. Be that as it may, regardless of the amount we arranged, we could never get more than possibly a couple of fish. This change shows how all the various poisons are largy affecting the fish populace and if move isn't made species like the largemouth bass could be dispensed with from the waterway. Angling isn't the main recreational action that happens in the St. Johns. Exercises, for example, skiing and tubing occur day by day throughout the spring and summer months. These are fundamental for Florida’s economy. At the point when individuals are going out in their pontoons, numerous parts of the economy are made a difference. Individuals must purchase gas for their pontoon, food to eat while they are on the vessel, and different things. This likewise draws in vacationers. By my home at a neighborhood marina, each late spring they facilitated a wakeboard camp for individuals to come figure out how to wake board. Many individuals would come to figure out how to wakeboard and have a fabulous time in the water. These individuals purchased numerous things during their stay in this manner boosting the Florida economy. In any case, if the water isn't kept up and kept clean, occasions like these can't happen. Visitors would not get in the water and would take their business somewhere else along these lines confining north Florida’s economy. All things being equal, the St. Johns River isn't risky as far swimming and drifting are concerned however there are poisons being dumped into the stream that should be tended to or disposed of. In the case of nothing is done, in light of tests done on the water, past and ebb and flow programs, and the fish populace the untamed life, the nature of the St. Johns will keep on falling. The stream harm will get difficult to fix and conceivably difficult to swim or use for any amusement. The repercussions of this would be exponential. Water deficiencies could happen alongside Jacksonville losing its intrigue as some place to live. References Page Ann Givens of The Sentinel Staff. (2001, Feb 16). St. Johns River may slake our thirst the St. Johns water region intends to process waterway water in a three-year test to check whether it very well may be made drinkable. Orlando Sentinel. Lisenby, L. (2007, Jul 11). Development must be controlled to ensure the St. Johns River. Florida Times Union. Littlepage, R. L. (2006, Jan 10). St. Johns River’s wellbeing merits significant exertion. Florida Times Union. Lynette, M. M. , John, R. W. , K, R. R. (2004). Nitrogen and phosphorus motion rates from silt in the lower St. Johns River estuary. Diary of Environmental Quality, 33(4), 1545-1555. Patterson, S. (2010, Aug 10). With plant pipeline still in question, old dioxin frequenting rice brook inquire about: Traces of a disease causing substance could in any case exist and be channeled into the St. Johns River. McClatchy †Tribune Business News. Wilson, D. (1994, Sep 09). Veteran fisherman says bass angling on St. Johns River crumbling. Orlando Sentinel. The most effective method to refer to St. Johns River, North Florida, Essay models

Words of the Week! Elusive, Illusive, Allusive Richmond Writing

Words of the Week! Elusive, Illusive, Allusive Richmond Writing This week we have a pair of homonyms, illusive and elusive, that students confuse. OED links are given. At a colleagues suggestion I added a quasi-literary term that we rarely encounter, allusive. The mnemonic for getting them sorted out is not too difficult, so well have a go at it now. If something is illusive, think of an illusion. It only seems real. It deceives you, as in His quest a quick fortune led him toward many illusive investments, all of which collapsed. Elusive is something that eludes us, so While he invested a lot of money, good returns on his investments remained elusive. I well recall my first highway travel as a child. I kept warning my father of water ahead on the road. These were illusions, mirages. All such are illusive. Writers may know, and use, literary allusions. Something that is allusive alludes to something else, literary or ordinary, as in The states early and difficult frontier history left so many allusive place names: Last Chance, Broken Promise, Dead Man, Murder Creek. Since all three words sound nearly alike when spoken, its best to try the mnemonics given, before writing anything down. Please nominate a word or metaphor useful in academic writing by e-mailing me (jessid -at- richmond -dot- edu) or leaving a comment below. See all of our Metaphors of the Month  here  and Words of the Week  here. Image courtesy of Wikipedia Commons.

The Administration Of The U.s. Tax System - 1991 Words

In 1990, the IRS commissioned a comprehensive nationwide survey of taxpayers to obtain their overall perception of its administration of the U.S. tax system. NPM related questions from this survey were re-asked to taxpayers to determine any potential changes in response patterns (VanDenburgh 2004, 2). Several questions were re-asked to allow for an assessment of differences between the 1990 responses and the 2004 responses during research by William M. VanDenburgh (2004). The concept of logic of action, which derives from institutional theory, is valuable to understanding why the IRS case is not aberrant and why there exists an implicit tension between merit ideals and the performance paradigm (Thompson 2006, 498). Patterns of behavior derive from institutional rules that create incentives to act in one way or another. They also derive from norms that have arisen over time that govern what behaviors are considered â€Å"appropriate.† Important for the purpose of this argument is the existence of an underlying logic according to which behavioral patterns, incentives, and norms are interlocked (Thompson 2006, 498). Adoption of a new NPM requires an agency organizational structure to become more competitive and business-like. In other words, a private market focus is to be incorporated in the organization. The IRS was heavily criticized because auditors forcefully went after non-filers when some IRS employees themselves were not filing tax returns (VanDenburgh 2004, 91). Due toShow MoreRelatedBarack Obama s International Tax Reform Proposal1052 Words   |  5 PagesABSTRACT President Barack Obama’s international tax reform proposal aims at preventing American multinational companies from using current international tax loopholes to avoid being taxed on offshore profits. 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The Great Gatsby By F. Scott Fitzgerald - 1708 Words

Throughout the novel The Great Gatsby, F. Scott Fitzgerald addresses the morality of the people he saw as representative of his time through the behaviors of the characters in the novel and how these characters react to various situations. The 1920s were an era marked by money, cars, and breaking down social barriers. While certain characters, who are not always led by their moral compasses, are able to question the morality of the actions of other characters, nearly all of the characters in the novel evolved to change the shifting views of the time. Various characters throughout the novel, including Gatsby, Daisy, and Tom, used their money as a shield to protect them from taking responsibility for their actions. Tom Buchanan, Daisy’s husband, is a deceitful and selfish man who repeatedly failed to see how his actions affect others. Tom is cheating on Daisy with Myrtle, who is married to a man Tom looks down upon because he is a poor owner of a failing business. Tom believes that because he is a wealthy, white male during a time where wealthy males dominated economically, politically, and socially, that he can act without regard for others. Tom sees nothing wrong with repeatedly cheating on his wife with other women besides Myrtle. Tom wants to be with both Daisy and Myrtle because being with Daisy projects him in a better light. Because of Daisy, he is both a husband and a father. While he is a disgusting husband and an absentee father, the other wealthy members of theirShow MoreRelatedThe Great Gatsby by F. Scott Fitzgerald1393 Words   |  6 PagesF. Scott Fitzgerald was the model of the American image in the nineteen twenties. He had wealth, fame, a beautiful wife, and an adorable daughter; all seemed perfect. Beneath the gilded faà §ade, however, was an author who struggled with domestic and physical difficulties that plagued his personal life and career throughout its short span. 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Scott Fitzgerald1607 Words   |  7 Pages The Great Gatsby is an American novel written in 1925 by F. Scott Fitzgerald. One of the themes of the book is the American Dream. The American Dream is an idea in which Americans believe through hard work they can achieve success and prosperity in the free world. In F. Scott Fitzgerald s novel, The Great Gatsby, the American Dream leads to popularity, extreme jealousy and false happiness. Jay Gatsby’s recent fortune and wealthiness helped him earn a high social position and become one of the mostRead MoreThe Great Gatsby By F. Scott Fitzgerald1592 Words   |  7 PagesMcGowan English 11A, Period 4 9 January 2014 The Great Gatsby Individuals who approach life with an optimistic mindset generally have their goals established as their main priority. Driven by ambition, they are determined to fulfill their desires; without reluctance. 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Learning Strategies Free Essays

It goes without saying that effective training strategies motivate learners and ensure better results and outcomes from the studying process. It is possible to use instructional strategies to build confidence, to make success easier, to demonstrate relevance of the process as well as to engage learners to solve real problems. Actually, instructional strategies allow students to discover, to share and to explore the matters of particular interest for them. We will write a custom essay sample on Learning Strategies or any similar topic only for you Order Now Classroom should be treated as gym. It doesn’t mean that desks should be replaced by balance beam. It means that significant shifts are required in instructional approaches. The first effective instructional strategy is to integrate training with what students know. This strategy assists in building skills and knowledge of learners. Furthermore, it complements trainings they’ve already and prepares them for developing additional skills. This strategy suggests integrating new information with what students already known. It is necessary to set a comfortable tone in order to encourage sharing and participation and to motivate challenge of ideas and debates regarding the subject. The strategy emphasizes using if familiar metaphors and schemes. The objective of the strategy it to make learners share their personal experience, obtained knowledge of the related topic. Online discussions, groups meetings and e-mails are appreciated as well. The second strategy is to connect training to relevant purposes and goals. This strategy helps to grab learners’ attention to the goals and objectives of the studying process. Instructor should be clear about the goals of the training, because it helps learners to move in directions which correspond to program’s goals and purposes. Learning goals should be related to personal goals of the learners. Actually, instructor has to encourage participatory goals setting, because students would work together in order to pick core performance goals. Also creating of action plan is appreciated as it would assist in customizing new and already existing knowledge. References Pardes, Juan Rudel. (1994, July-August). Motivate Every Learner: How to Replace Motivation Myths with Strategies that Work. Retrieved March 6, 2007, from http://findarticles.com/p/articles/mi_m0STR/is_n1_v104/ai_15669489/pg_2 Creating Training that Motivates. (2001). Retrieved March 6, 2007, from http://seniortechcenter.org/archive/learning_paths/training/start_lesson/creating_training_motivate.php#strategies How to cite Learning Strategies, Essay examples Learning Strategies Free Essays INTRODUCTION Educators of young children have a propensity to share the goal of fostering children’s successful learning and achievement. As the pressure to give emphasis to academic standards enhances, it is all the more vital to reflect on the most effective practices for make certain that children are in fact learning what is being taught. Several factors related to children’s achievement are not in teachers’ control, but creating a climate of engagement in the classroom is (Finn, J. We will write a custom essay sample on Learning Strategies or any similar topic only for you Order Now D., D.A. Rock. 1997). The use of strategies is a powerful teaching tool vital in promoting children’s achievement for the reason that it focuses children on learning; supports learning specific skills and concepts; and provides children positive associations with learning. GENERAL DISCUSSION Maintenance rehearsal refers to the simple repetition of items to hold them in working memory, where we are conscious of them. Thus, when we want to remember a phone number for long enough to ring it, or write it down, we repeat it to ourselves until we have completed our action. Rehearsal is an effective strategy for short-term recall, and young children can be taught to use the strategy (Graham, S., B. Weiner. 1996). However, continued use of the strategy is more unlikely than not. It may be however, that training was insufficient to impress upon the children the usefulness of the strategy, and with better feedback they might be encouraged to use the strategy spontaneously. Maintenance rehearsal no doubt seems a self-evident strategy to any adult, simple as it is and long accustomed as we are to using it. However, it is, like any strategy, something we have to learn to do. It is rare in five year olds, common in ten year olds. Categorizing is another very basic strategy that many of us use to help us remember items (Baine, 1986) Thus, if you are given a list: APPLE  Ã‚   JEEPNEY  Ã‚   PANSY  Ã‚   TRUCK  Ã‚   SAMPAGUITA  Ã‚   PLUM  Ã‚   PEACH  Ã‚   MOTORCYCLE  Ã‚   ROSE  Ã‚   MARIGOLD  Ã‚   MANGO  Ã‚   CAR the items will be much easier to remember if you note that the items belong to only three categories fruit, vehicles, flowers. Noting that there are four examples of each will also help. The category labels help considerably when it comes to retrieving the information. Most educated adults do this sort of thing automatically. But, again, like any strategy no matter how simple, it is not something we are born knowing. Very young children are not likely to group items at all, but if they do, it will be most likely according to some sort of association (cornflakes —  milk, baby — bottle, paper — pencil). If young children are taught to group items into taxonomic categories, they will still not use category labels effectively when retrieving the information, without explicit instruction. From around 6 or 7, children seem to benefit more from instruction in categorization strategies. If the children are very young, such instruction may only confuse them. Using category labels as retrieval cues appears to be a more complex strategy than the first step of learning to group according to category, and doesn’t appear until later. Even children as old as 11 may benefit from explicit reminders to use category labels as retrieval cues and search the categories exhaustively before moving on. At around 7, about 50% of children appreciate the value of categorization as a memory strategy. This doesn’t increase all that much over the next few years (about 60% of ten year olds), although nearly all 17 year olds understand the strategy. The value of category labels in helping young children learn is another strategy. Category labels don’t appear to particularly help recall in children before the age of ten. Picture recognition is assisted by labeling in children as young as four. Researchers have had mixed results in labeling pictures as an aid to learning paired associations in young children. Labeling pictures does not appear to help very young children remember the order of items, but can be helpful to children from six years old until they are of an age to spontaneously label, when such explicit labeling may interfere with their own learning strategy. Labeling however often part of a wider strategy and may is well be helpful to young children for other reasons than improving recall. For example, it may be useful in helping children acquire language. Mnemonics is another strategy used by teachers for the children. Research into whether young children can improve recall by using visual imagery has produced mixed results (Yair, G. 2000). It would seem that, in general, the instruction to generate mental images does not improve recall in children 5 yrs and younger, but does improve recall in children 8 years and above. Children of six and seven appear to be at a transitional stage whereby some children can use the strategy effectively in some situations. The story, or sentence, mnemonic is a verbal mnemonic in which words to be remembered are linked together in a sentence or sentences (Brewster, C., J. Fager. 2000). It is an effective strategy for learning a list of words. The research confirms that memory even in very young children can be helped by teaching them to use this verbal mnemonic strategy. It is more effective if the words are linked by verbs rather than prepositions simply stringing together words like this: The cat and the banana and the boat were in the sky† is much less memorable than composing: â€Å"The cat ate the banana and tossed the boat into the sky.† Sentence mnemonics have been effectively used by 6th graders to remember the correct spelling of words. The keyword method is one of the most successful mnemonic strategies to be used in education. It is of proven effectiveness as a method of learning new words, foreign language words, and social studies facts. As a technique for learning new words, it has been compared with the following common strategies: learning words in context; finding root words; learning synonyms and antonyms; presenting words in meaningful sentences; having students discriminate correct from incorrect use of words in sentences; and having students generate their own meaningful sentences and is apparently more effective than any of these methods. The keyword mnemonic has been used effectively by 4th graders. When pictures have been provided, it has been used effectively by 2nd graders. It is suggested that, for children 10 years and younger, instructions to visualize are supplemented by illustrating pictures. CONCLUSION Ideally, teachers should use a wide range of strategies and then masterfully facilitate their implementation. Not only do strategies enable teachers to capture the interest of children as they learn the skills and concepts necessary for success in school, but children also experience what it feels like to be engaged in learning – a lifelong gift.   The strategies chosen depend on the purpose, teaching style, and the children in the classroom. Regardless of the strategies selected, effective facilitation is a key to making them work. By facilitation it means that the techniques used to execute a strategy. REFERENCE: Baine, David 1986. Memory and instruction. Englewood Cliffs, NJ: Educational Technology Publications. Brewster, C., J. Fager. 2000. Increasing student engagement and motivation: From time on task to homework. Portland, OR: Northwest Regional Educational Laboratory. Finn, J.D., D.A. Rock. 1997. Academic success among students at risk for school failure. Journal of Applied Psychology 82 (2): 221–34. Graham, S., B. Weiner. 1996. Theories and principles of motivation. In Handbook of educational psychology, eds. D. Berliner R.C. Calfee, 62–84. Mahwah, NJ: Erlbaum. Yair, G. 2000. Reforming motivation: How the structure of instruction affects students’ learning experiences. British Educational Journal 26 (2): 191–210. How to cite Learning Strategies, Essay examples Learning Strategies Free Essays 1. Learning Strategies for SSC100 SSC100 is not only a common course, but also sets the tone for the whole four-semester study life in Seneca. Therefore, we should pay more attention to this course. We will write a custom essay sample on Learning Strategies or any similar topic only for you Order Now My GPA to date is 3. 0 and my target GPA is 3. 5. In order to acheive the target, there are several strategies I should follow . First, take the classes regularly. Some other students may think that it’s not necessary to attend the classes , without which they can still pass this course. However, the powerpoints and the videos the instructors display in the classes are not only interesting but also helpful. Second, read through the textbook: Success Strategies for College. This book introduces diffrernt kinds of learning strategies in details, which are very useful in SSC100 itself, especially in the reflective test, and other courses throughout Seneca. Third, invovle in the group work. To tell the truth, I am not a good team worker, which is neither good for the current college study nor good for the future work. Therefore, I should attach more importance to this part. Communication is a key factor in the group work. I will try my best to listen to others and give my own opinion as much as possible. Last, practice presentation. As for the group work, presentation is one of the most important parts. Practices can sooth the nerves and make the process more smooth in the real presentation. There are two ways to practice the presentation: first, gather the group mates to simulate; second, take part in the presentation workshops in the learning center. How to cite Learning Strategies, Essay examples

National University free essay sample

American students have different attitudes about studying Contents 1. Tallahassee Democrat, Flag. Tallahassee Democrat, Flag. BY Quit Lie One and a half years ago, when my husband came to Florida State University for his doctorate in oceanography, I accompanied him from China. When I first stepped on American soil, many American things deeply attracted me. Since enrolling at the community college for my associates degree, I have especially noticed the differences between Chinese and American attitudes toward studying. Many of my American lacerates are also Curious about societal, family and educational systems in China. Expressing my ideas about the effects of these systems on college students in China may help my friends here understand the differences between us. China is a big country, not only in its land but also in its tremendous population. Although the government spends a huge amount of funds on developing education every year, It still cant satisfy the innumerable students who are seeking knowledge. We will write a custom essay sample on National University or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Thus,unlike in America, where everybody can go to college, a lot of Chinese students do not have the opportunity to study at colleges. For example, the government has a policy that people must be under 25 years of age to be able to go to college. Also, students must pass an annual National University Entrance Exam, which Is very strict. Often, only one out of 10 students pass It. The students call this testing month Dark July, implying that this exam decides their fate. Not only do the students regard it as important, but also their parents treat It seriously. In America, students can decide to go to college by themselves and their parents hardly Interfere with them. In China, old, traditional thoughts are still kept In peoples minds. They think that studying at allege Is an Incomparable honor. If a student Is enrolled In college, his or her parents are extremely happy. They will Immediately tell all their relatives and friends. But If a student doesnt pass the entrance exam, his parents will feel as If they cannot raise their heads In front of others. Some parents will even blame their child for not studying hard enough. These common views make some students feel pressure on their hearts. By comparison, American students leave their parents earlier and live and work In society by themselves. Most Chinese students never leave their parents before they go to college. This dependent life makes them want to obey their parents advice about everything. Prenatal advice Is their mall Influence. Some parents Insist that their child attend the July exam year after year until he or she passes It. The Influence of the family Is very Important on students In China. When I first came to college here, the American laissez-fairer style of education deeply Interested me. American colleges give students broad space and allow students to develop Independently. Students can freely choose their favorite courses, except for certain required courses. They can even choose their favorite teachers. This Is Incredible to e. In China, the field of study cant be changed from the first day that the students come to college. Furthermore, every semester the school has already formulated the limits their development. At the community college, I also observe that quite a number of students cut class without excuses. This behavior is really strange. In China, even if a student is sick, he will normally persist in attending classes. Although the school has strict rules for absent students, the majority of students think that they should take responsibility for their own education. Chinese students study very hard and treasure the opportunity to study. Everyone wants to get the highest score. In China, there are no part-time students in a university. Tuition is provided by parents, so students want to get the highest scores to repay their parents love. Unlike American students who have a lot of chances to get a good Job, when Chinese students graduate, their grades become a major factor for a good company to choose them. To get a good Job in the future, students must study hard. Obviously, compared with the American educational system, the Chinese educational system could be improved by giving students more freedom to develop their abilities based n their interests.

Free Essays on Global Wind Patterens

Wind Power â€Å"They’re farming a different crop in Wyoming County these days- the wind. Atop a hill in this little town – population 729 – are 10 windmills that are expected to produce enough electricity each year to provide power for 1,700 homes. It’s not hard to see what this piece of the future looks like.† (Ploetz, A1) Wind power was developed as a major alternative energy source during the 1970’s. The interest in finding alternative energy sources has grown tremendously as people are beginning to realize that they are depleting the Earth of irreplaceable natural resources. The technology is now the fastest-growing energy source in the world. The wind turbine, also called a windmill, is a means of harnessing the kinetic energy of the wind and converting it into electrical energy. This is accomplished by turning blades called aerofoils, which drive a shaft, which drive a motor (turbine) and are connected to a generator. This energy is then supplied to a multitude of homes, businesses, factories, etc. The worldwide total wind capacity is 13,400 MW and the year 2000 is expected to significantly increase this amount, according to the trend in recent records of the American Wind Energy Association (AWEA). Wind generating capacity has grown from 2,000 MW in 1990 to the present capacity of more than 3,600 MW. It is predicted that worldwide energy supply may consist of 10% wind power by 2020, with Europe alone producing more than 100,000 MW. â€Å"Global investment in wind turbines should surpass $200 billion by 2010 as part of a rapid growth in investment in renewable energy sources worldwide,† according to Michael Kujawa, senior Allied Business Intelligence Incorporated (Chambers, 14-16) Presently, Europe is far more advanced than the U.S. in its development and implementation of wind power. However, NASA is using the largest, most expensive wind tunnel yet created to test a huge, high-tech wind tur... Free Essays on Global Wind Patterens Free Essays on Global Wind Patterens Wind Power â€Å"They’re farming a different crop in Wyoming County these days- the wind. Atop a hill in this little town – population 729 – are 10 windmills that are expected to produce enough electricity each year to provide power for 1,700 homes. It’s not hard to see what this piece of the future looks like.† (Ploetz, A1) Wind power was developed as a major alternative energy source during the 1970’s. The interest in finding alternative energy sources has grown tremendously as people are beginning to realize that they are depleting the Earth of irreplaceable natural resources. The technology is now the fastest-growing energy source in the world. The wind turbine, also called a windmill, is a means of harnessing the kinetic energy of the wind and converting it into electrical energy. This is accomplished by turning blades called aerofoils, which drive a shaft, which drive a motor (turbine) and are connected to a generator. This energy is then supplied to a multitude of homes, businesses, factories, etc. The worldwide total wind capacity is 13,400 MW and the year 2000 is expected to significantly increase this amount, according to the trend in recent records of the American Wind Energy Association (AWEA). Wind generating capacity has grown from 2,000 MW in 1990 to the present capacity of more than 3,600 MW. It is predicted that worldwide energy supply may consist of 10% wind power by 2020, with Europe alone producing more than 100,000 MW. â€Å"Global investment in wind turbines should surpass $200 billion by 2010 as part of a rapid growth in investment in renewable energy sources worldwide,† according to Michael Kujawa, senior Allied Business Intelligence Incorporated (Chambers, 14-16) Presently, Europe is far more advanced than the U.S. in its development and implementation of wind power. However, NASA is using the largest, most expensive wind tunnel yet created to test a huge, high-tech wind tur...

How to Get Writing a Novel off your Bucket List

How to Get Writing a Novel off your Bucket List How to Get â€Å"Writing a Novel† off Your Bucket List Natalie Barelli harbored a dream that's all too familiar for our readers - writing a novel. An IT professional writing a psychological thriller might have seemed like a  pipe dream, but persistence led to a book which by all accounts is a real page-turner. If "writing a novel" is still on your bucket list, you'll find some good inspiration and advice below!Edit:  Just 6 months  after publishing "Until I Met Her", Natalie Barelli got signed by Amazon Publishing's imprint Thomas Mercer. You can read about how that happened here.It was a conversation about bucket lists that got me started. Over a glass of wine - or ten, let’s be honest - my friend and I were lamenting the fact that it’s so easy to put something into the bucket list, but almost impossible to get it out again.So we decided to pick one each, and get on with it. And mine was to write a novel. More specifically, a psychological suspense novel, because I love them. I read them all the time, I am addict ed to them, and find them to be great stories. Ironically, I didn’t use to enjoy writing very much, but I have always loved stories, and the idea of them. And of course probably like anyone who has ever wanted to write a novel, I thought I could write one because I love reading them.Having decided that I would write a novel, I figured there must be structures out there that I could follow, something akin to the three-act paradigm that is used in film narratives. I was hoping for a â€Å"join the dots† style model, something along the lines of â€Å"kill someone in chapter 1† and â€Å"throw in a suspect in chapter 3† then link ‘em up in chapter 2. I got one item out of my bucket list, my house has never been so clean, and I published Until I Met Her on Amazon on 16 June, ten days ago at the time of writing this. To date the novel has received seven five-star reviews, all of which point to a good plot and good writing.I sure didn’t get those on my own.Until I Met Her here is now available on  Amazon, so make sure to get your copy!How close are you to finishing your first novel? Does  Natalie's story sound like a day out of your life?  Please  share your thoughts and experiences, or any question for Natalie, in the comments below!

Holocaust Essay Example | Topics and Well Written Essays - 750 words - 4

Holocaust - Essay Example The functionality of a family relies on the efforts and contribution of all persons who constitute a given family unit. Clara’s family is no exception in terms of its setting and functionality. The interdependence between members of Clara’s family and other families in the Zolkiew community shows the extent to which families can go in order to remain together and united as one. Family ties were critical to account for during the Nazis occupation in Zolkiew, Poland. Family completeness is influenced by the manner in which family members relate. Clara and her family have close relationship that is characterized by love and care for one another. This factor enhanced the family’s unity during happy and sad times. Given the fact that the Nazis were against the Jews, Clara’s family was a close and direct target. Just like any other Jewish family at the time, Clara’s family was under significant threat. Amid this, the family ties between Clara, her mother, and her father remained close for the purpose of uniting the family. The presence of the Nazis in Zolkiew, Poland jeopardizes the family setting as a safe haven for the Jewish community. Family setups are broken while others are subjected to extreme livelihoods that they were not previously used to. In this respect, there is the aspect of ruined family ties in Clara’s memoir. In fact, she interacted with persons who were direct victims of such experiences. On the same note, the presence of the Nazis in their community could not offer anything short of these experiences. An aspect of help, assistance, and support is depicted by the manner in which Clara’s family relates with the Beck’s. In regard to this experience, it is evident that family ties do not only involve family members, but also friends and families within and without. Insights into the family context are based on strong ties that are established through good relations and

Questioning the Text Papers Essay Example | Topics and Well Written Essays - 1000 words - 1

Questioning the Text Papers - Essay Example All the three tales interacts to form a coherent picture of the predicaments that the characters face and the possible solutions to the problems. The paper presents a question from the text and discusses it comprehensively with illustrations. Considering the nature of the relationship between characters in the three tales, examine whether the existence of racial ties and commonalities can influence the disposition of an individual toward another person of the same race? Explain the impact of the behavior displayed by characters from similar backgrounds on the efforts to discourage racial discrimination and stereotypes? The text possesses themes of stereotypes and racial prejudice especially towards the Chinese people. It presents several examples that emphasize the idea that the author addresses some of the major problems faced by various victims of racial discrimination. The question emerges from the observations that individual characters who hail from the same ethnic groups, mistreat their fellow counterparts. Instead of providing support for them to thrive and adapt to the harsh systems, they shun them away, and this worsens their situations. There are many scenarios that support the basis of the questions. The relationship between Wei-Chen and Jin is a typical example that illustrates this fact. Another example is the event that transpires between Wong Lai-Tsao and Tze-Yo-Tzuh that was full of betrayal. In brief, the question originates from the negative treatment displayed by various characters to individuals from the same race. The query is significant as it highlights the weaknesses existing in the society between victims of racial prejudice and stereotyping. Research indicates that most individuals in alien countries face discriminations or mistreatment from fellow tribesmen and members of the same race (Shabazz 1238). As minority

Model for Predicting Fatigue Life of Nanomaterials

Model for Predicting Fatigue Life of Nanomaterials Introduction In the past, the primary function of micro-systems packaging was to provide input/output (I/O) connections to and from integrated circuits (ICs) and to provide interconnection between the components on the system board level while physically supporting the electronic device and protecting the assembly from the environment. In order to increase the functionality and the miniaturization of the current electronic devices, these IC devices have not only incorporated more transistors but have also included more active and passive components on an individual chip. This has resulted in the emerging trend of a new convergent system[1] Currently, there are three main approaches to achieving these convergent systems, namely the system-on-chip (SOC), system-in-package (SIP) and system on package (SOP). SOC seeks to integrate numerous system functions on one silicon chip. However, this approach has numerous fundamental and economical limitations which include high fabrication costs and integration limits on wireless communications, which due to inherent losses of silicon and size restriction. SIP is a 3-D packaging approach, where vertical stacking of multi-chip modules is employed. Since all of the ICs in the stack are still limited to CMOS IC processing, the fundamental integration limitation of the SOC still remains. SOP on the other hand, seeks to achieve a highly integrated microminiaturized system on the package using silicon for transistor integration and package for RF, digital and optical integration[1] IC packaging is one of the key enabling technologies for microprocessor performance. As performance increases, technical challenges increase in the areas of power delivery, heat removal, I/O density and thermo-mechanical reliability. These are the most difficult challenges for improving performance and increasing integration, along with decreasing manufacturing cost. Chip-to-package interconnections in microsystems packages serve as electrical interconnections but often fail by mechanisms such as fatigue and creep. Furthermore, driven by the need for increase the system functionality and decrease the feature size, the International Technology Roadmap for Semi-conductors (ITRS) has predicted that integrated chip (IC) packages will have interconnections with I/O pitch of 90 nm by the year 2018 [2]. Lead-based solder materials have been used for interconnections in flip chip technology and the surface mount technology for many decades. The traditional lead-based and lead-free solder bumps will not satisfy the thermal mechanical requirement of these fine pitches interconnects. These electronic packages, even under normal operating conditions, can reach a temperature as high as 150C. Due to differences in the coefficient of thermal expansion of the materials in an IC package, the packages will experience significant thermal strains due to the mismatch, which in turn will cause lead and lead-free solder interconnections to fail prematurely. Aggarwal et al [3] had modeled the stress experienced by chip to package interconnect. In his work, he developed interconnects with a height of 15 to 50 micrometre on different substrate using classic beam theory. Figure 1 shows the schematic of his model and a summary of some of his results. Although compliant intrerconect could reduces the stress experienced by the interconnect, it is still in sufficient. Chng et al. [4] performed a parametric study on the fatigue life of a solder column for a pitch of 100micrometre using a macro-micro approach. In her work, she developed models of a solder column/bump with a pad size of 50micrometre and heights of 50 micrometre to 200 micrometre. Table I shows a summary of some of her results. Table 1.1: Fatigue life estimation of solder column chip thickness (micrometre) 250 640 640 640 board CTE (ppm/K) 18 18 10 5 solder column height (micrometre) Fatigue life estimation/cycle) 50 81 N.A 171 3237 100 150 27 276 3124 150 134 31 518 4405 200 74 38 273 5772 It can be seen from Table 1.1 that the fatigue lives of all solder columns are extremely short. Apart from the 5ppm/K board where there is excellent CTE matching, the largest fatigue life of the solder column is only about 518 cycles. As expected, the fatigue life increases significantly when the board CTE decreases from 18ppm/K to 10ppm/K and as the height increases from 50micrometre to 200micrometre.This is mainly due to the large strain induced by the thermal mismatch as shown in Figure 1.2. The maximum inelastic principal strain was about 0.16 which exceeds the maximum strain that the material can support. Although the fatigue life of the chip to package interconnection can be increases by increasing the interconnects height, it will not be able to meet the high frequency electrical requirements of the future IC where they need to be operating at a high frequencies of 10-20 GHz and a signal bandwidth of 20 Gbps, By definition, nanocrystalline materials are materials that have grain size less than 100nm and these materials are not new since nanocrystalline materials have been observed in several naturally-occurring specimens including seashells, bone, and tooth enamel [5, 6]. However, the nanocrystalline materials have been attracting a lot of research interest due to its superior mechanical and electrical properties as compared to the coarse-grained counterpart. For example, the nano-crystalline copper has about 6 times the strength of bulk copper [7]. Furthermore, the improvement in the mechanical properties due to the reduction in grain size has been well-documented. Increase in strength due to the reduction in grain-size is predicted by the Hall-Petch relationship which has also been confirmed numerically by Swygenhoven et al [8] and was first demonstrated experimentally by Weertman [9]. The implantation of nanocrystalline copper as interconnect materials seems to be feasible from the processing viewpoint too. Copper has been used as interconnects materials since 1989 whereas nano-copper has also been widely processed using electroplating and other severe plastic deformation techniques in the past few years. For instance, Lu et al. [10] have reported electroplating of nano-copper with grain size less than 100 nm and electrical conductivity comparable to microcrystalline copper. Furthermore, Aggarwal et al [11] have demonstrated the feasibility of using electrolytic plating processes to deposit nanocrystalline nickel as a back-end wafer compatible process. However, there are certain challenges regarding implantation of nanocrystalline copper as interconnects materials. As discussed above, nanocrystalline copper have a high potential of being used as the next generation interconnect for electronic packaging. However, it is vital to understand their material properties, deformation mechanisms and microstructures stability. Although the increase in strength due to the Hall-Petch relationship which has also been confirmed numerically and experimentally by Weertman [9], the improvement in the fatigue properties is not well documented and no model has been established to predict/characterize these nano materials in interconnection application; conflicting results regarding the fatigue properties have also been reported. Kumar et al [12] reported that for nano-crystalline and ultra-fine crystalline Ni, although there is an increase in tensile stress range and the endurance limit, the crack growth rate also increases. However, Bansal et al. [7] reported that with decreasing grain size, the tensile stress range increases but the crack growth rate decreases substantially at the same cyclic stress intensity range. Thus, nanostructured materials can potentially provide a solution for the reliability of low pitch interconnections. However, the fatigue resistance of nanostructured interconnections needs to be further investigated. Since grain boundaries in polycrystalline material increases the total energy of the system as compare to perfect single crystal, it will resulted in a driving force to reduce the overall grain boundary area by increasing the average grain size. In the case of nanocrystalline materials which have a high volume fraction of grain boundaries, there is a huge driving force for grain to growth and this presented a presents a significant obstacle to the processing and use of nanocrystalline copper for interconnect applications. Millet et al [13] have shown, though a series of systematic molecular dynamics simulations, grain growth in bulk nanocrystalline copper during annealing at constant temperature of 800K can be impeded with dopants segregated in the grain boundaries regions. However, it has been observed that stress can trigger grain growth in nanocrystalline materials [14] and there is no literature available on impeding stress assisted grain growth. There is an impending need to investigate the impediment to grain growth caused by the dopant during fatigue/stress assisted grain growth Dissertation Objectives The goal of present project is to develop a model for the fatigue resistance of nano-materials that have been shown to have superior fatigue resistance. Accordingly, the following research objectives are proposed. Develops a model for predicting fatigue life of nanostructured chip-to-package copper interconnections Develops a fundamental understanding on the fatigue behavior of nanocrystalline copper for interconnect application Addresses the issue on the stability of nanocrystalline materials undergoing cyclic loading Overview of the Thesis The thesis is organized so that past research on nanocrystalline materials forms the basis of the understanding and new knowledge discovered in this research. Chapter 2 reviews much of the pertinent literature regarding nanocrystalline materials, including synthesis, deformation mechanisms, and grain growth. Chapter 3 describes a detailed overview of the technical aspects of the molecular dynamics simulation method including inter-atomic potentials, time integration algorithms, the NVT NPT, and NEPT ensembles, as well as periodic boundary conditions and neighbor lists. Include in this chapter is the algorithms for creating nanocrystalline materials used in this dissertations.. Chapter 4 describes the simulation procedure designed to investigate and develop the long crack growth analysis. The results of the long crack growth analysis will be presented at the end of Chapter 4. Chapter 5 presents the result and discussion on mechanical behavior of single and nanocrystalline copper subjected to monotonic and cyclic loading whereas Chapter 6 presents the result and discussion on the impediment to grain growth caused by the dopant during fatigue/stress assisted grain growth. Finally, conclusions and recommendations for future work are presented in Chapter 5. Chapter 2 This chapter offers an expanded summary of the literature published with regards to the fabrication methods, characterization, and properties of nanocrystalline materials in addition to a description of existing interconnect technology. 2.1 Off-Chip Interconnect Technologies Chip-to-package interconnections in microsystems packages serve as electrical interconnections but they will often failed by mechanisms such as fatigue and creep. Furthermore, driven by the need for increase the system functionality and decrease the feature size, the International Technology Roadmap for Semi-conductors (ITRS) has predicted that interconnections of integrated chip (IC) packages will have a I/O pitch of 90 nm by the year 2018 [2]. The International Technology Roadmap for Semiconductors (ITRS) roadmap is a roadmap that semiconductor industry closely follows closely and its projects the need for several technology generations. The package must be capable of meeting these projections in order for it to be successful. This section reviews some of the current interconnect technology. Wire bonding [15] as shown in Figure 2.1, is generally considered as one of the most simple, cost-effective and flexible interconnect technology. The devices on the silicon die are (gold or aluminum) wire bonded to electrically connect from the chip to the wire bond pads on the periphery. However, the disadvantages of wire bonding are the slow rate, large pitch and long interconnect length and hence this will not be suitable for high I/O application. Instead of wires in the wire bonding, tape automated bonding (TAB) is an interconnect technology using a prefabricated perforated polyimide film, with copper leads between chip and substrate. The advantage of this technology is the high throughput and the high lead count. However, it is limited by the high initial costs for tooling. An alternative to peripheral interconnect technology is the area-array solution, as shown in Figure 2.3, that access the unused area by using the area under the chip. In area-array packaging, the chip has an array of solder bumps that are joined to a substrate. Under-fill is then fills the gap between the chip and substrate to enhance mechanical adhesion. This technology gives the highest packaging density methods and best electrical characteristics of all the avaiable interconnection technology. However, not only is its initial cost is high, it requires a very demanding technology to establish and operate. With the need for higher I/O density, compliant interconnects have been developed to satisfy the mechanical requirements of high performance micron sized interconnects. The basic idea is to reduce shear stress experienced by the interconnects through increasing their height or decreasing of its shear modulus (i.e. increases in their compliant) and hence the name compliant interconnects. Some of recent research in compliant interconnects include Tesseras Wide Area Vertical Expansion, Form Factors Wire on Wafer and Georgia Institute of Technologys Helix interconnects [17-19] as shown in Figure 2.4. Although compliant interconnects can solve the problem of mechanical reliability issue, they are done at the expense of the electrical performance. Since there is a need to reduce the packages parasitic through a decrease line delays, there is a need to minimize the electrical connection length in order to increase the system working frequency. Hence, compliant interconnect may not meet the high electrical frequency requirements of future devices. Figure 2.4: (a) Wide Area Vertical Expansion, (b) Wire on Wafer and (c) G-Helix [17-19] Lead and lead-free solders typically fail mechanical when scaled down to less than to a pitch of 100 mm. Compliant interconnections, on the other hand, do not meet the high frequency electrical requirements. The Microsystems Packaging Research Center at Georgia institute of Technology had demonstrated the feasibility of using re-workable nanostructure interconnections. Aggarwal et al [20] had show that nanostructured nickel interconnections, through a Flip Chip test vehicle, was able to improve the mechanical reliability while maintaining the shortest electrical connection length. However, the main disadvantages of this method was the significant signal loss at high frequency signal of nanocrystalline nickel [21]. As discussed above, nanostructure interconnects technology is the most promising interconnect technology to best meet the stringent mechanical and electrical requirement of next generation devices. However, there is a need of an alternate materials and a sensible choice of materials in this case would be nanocrystalline copper for its high strength material with superior electrical conductivity. Hence, it would be beneficial to use nanocrystalline-copper as material for the nanostructure interconnects. Due to the tendency for the grain to grow, there is a need to stabilize the grain growth in nanocrystalline copper before using it could be considered as a potential candidate for nanostructure interconnect. 2.2 Nanocrystalline material Nanocrystalline materials are polycrystalline materials with an average grain size of less than 100 nm [22]. Over the past decade , new nanocrystalline or nanostructured materials with key microstructural length scales on the order of a few tens of nanometers has been gaining a lot of interest in the material science research society. This is mainly due to its unique and superior properties, as compared to their microcrystalline counterparts which includes increased strength [22] and wear resistance [23]. These unique properties are due to the large volume fraction of atoms at or near the grain boundaries. As a result, these materials have unique properties that are representative of both the grain boundary surface characteristics and the bulk. Recent advances in synthesis and processing methodology for producing nanocrystalline materials such as inert gas condensation [24], mechanical milling [25, 26], electro-deposition [27], and severe plastic deformation [28] have made it possible to produce sufficient nanocrystalline materials for small scale application. 2.2.1 Synthesis Inert gas condensation, the first method used to synthesis bulk nanocrystalline [29], consists of evaporating a metal inside a high-vacuum chamber and then backfilling the chamber with inert gas [30]. These evaporated metal atoms would then collide with the gas atoms, causing them to lose kinetic energy and condenses into powder of small nano-crystals. These powders are then compacted under high pressure and vacuum into nearly fully dense nanocrystalline solids. The grain size distribution obtained from this method is usually very narrow. However, the major draws back of this method are its high porosity levels and imperfection bonding. Grain coarsening also occurs due to the high temperature during the compaction stage [31]. Mechanical milling consists of heavy cyclic deformation in powders until the final composition of the powders corresponds to a certain percentages of the respective initial constituents [25, 26]. A wide grain size distribution is obtained by this method. This technique is a popular method to prepare nanocrystalline materials because of its applicability to any material and simplicity. However, their main drawback includes contamination and grain coarsening during the consolidation stage. Electro-deposition consists of using electrical current to reduce cations of a desired material from a electrolyte solution and coating a conductive object on the substrate. Electro-deposition has many advantages over processing techniques and this includes its applicability to a wide variety of materials, low initial capital investment requirements and porosity-free finished products without a need for consolidation processing [27]. Furthermore, Shen et al. [32] and Lu et al.[33] had recently show that the right electro-deposition condition can produce a highly twinned structure which leads to enhanced ductility. The main drawback of this method is it is the difficulty to achieve high purity. Severe plastic deformation, such as high-pressure torsion, equal channel angular extrusion (ECAE), continuous confined shear straining and accumulative roll-bonding, uses extreme plastic straining to produce nanocrystalline materials by mechanisms such as grain fragmentation, dynamic recovery, and geometric re-crystallization [34]. It is the only technology that transformed conventional macro-grained metals directly into nanocrystalline materials without the need of potentially hazardous nano-sized powders. This is achieved by introducing very high shear deformations into the material under superimposed hydrostatic pressure. Two of the most commonly used methods are high-pressure torsion and ECAE [35]. In the study of the effect of ECAE on the microstructure of nanocrystalline copper, Dalla Torre et al [36] observed that the grains become more equi-axial and randomly orientation as the number of passes increases, as shown in Figure 2.5 Figure 2.5: Microstructure of ECAE copper subjected to (a) 1 passes (b) 2 passes (c) 4 passes (d) 8 passes (e) 12 passes and (f) 16 passes [36] 2.2.2 Mechanical Behavior of nanocrystalline materials Due to the small grain size and high volume fraction of grain boundaries, nanocrystalline materials exhibit significantly different properties and behavior as compared to their microcrystalline counterpart. The structure and mechanical behavior of nanocrystalline materials has been the subject of a lot of researchers interests both experimentally [37-43] and theoretically [44-50]. This section reviews the principal mechanical properties and behavior of nanocrystalline materials. 2.2.2.1 Strength and ductility Recent studies of nanocrystalline metals have shown that there is a five to ten fold increases in the strength and hardness as compared to their microcrystalline state [7, 36, 37, 51, 52]. This increase in the strength is due to the presence of grain boundaries impeding the nucleation and movement of dislocations. Since decreasing grain boundary size increases the number of barrier and the amount of applied stress necessary to move a dislocation across a grain boundary, this resulted in a much higher yield strength. The inverse relationship between grain size and strength is characterized by the Hall-Petch relationship [53, 54] as shown in equation (2.1). Eq (2.1) In equation (2.1), s is the mechanical strength, k is a material constant and d is the average grain size. Hence, nanocrystalline materials are expected to exhibit higher strength as compared to their microcrystalline counterpart. Figure 2.6 and Figure 2.7 show the summary of hardness and yield strength from tensile test that are reported in the literature. Indeed, hardness and yield strength of copper with a grain size of 10nm (3GPa) can be one order higher than their microcrystalline counterpart. To the larger specimens. Derivation from Hall-Petch relationship begins as the grain size approaches 30nm where the stresses needed to activate the dislocation multiplication via Frank-Read sources within the grains are too high and the plastic deformation is instead accommodated by grain boundaries sliding and migration.[12]. Furthermore, as the grain size reduces, the volume fraction of the grain boundaries and the triple points increases. Material properties will be more representative of the grain boundary activity [64] and this will resulting the strength to be inversely proportional to grain size instead of square roots of the grain size as predicted by Hall Petch relation [65]. Further reduction in the grain size will result in grain boundaries processes controlling the plastic deformation and reverse Hall-Petch effect, where the materials soften, will take place. Although sample defects had been account for the earlier experimental observation of reverse Hall-Petch effect[24], Swygenhoven et al [66] and Schiotz et al [47], using molecular simulation, was able to showed that nanocrystalline copper had the highest strength (about 2.3GPa ) at a grain size of 8nm and 10-15nm respectively. Conrad et al [67] pointed out that below this critical grain size, the mechanisms shifted to grain boundary-mediated from dislocation-mediated plasticity and this causes the material to become dependent on strain rate, temperature, Taylor orientation factor and presence of the type of dislocation. The yield stress of nanocrystalline copper was highly sensitive to strain rate even though it is a fcc materials. The strain rate sensitivity, m, in equation 2.2 a engineering parameter which measured the dependency of the strain rate and Figure 2.8 shows a summary of m as a function of grain size for copper specimen in the literature [51, 68-70]. Due to high localized dislocation activities at the grain boundaries which results in enhanced strain rate sensitivities in nanocrystalline materials, m increases drastically when the grain size is below 0.1 mm as shown in Figure 2.8. (2.2) Room temperature strain rate sensitivity was found to dependent on dislocation activities and grain boundaries diffusion [52, 71, 72]. Due to the negligible lattice diffusion at room temperature, the rate limiting process for microcrystalline copper was the gliding dislocation to cutting through forest dislocation, resulting in low strain rate sensitivities. However, due to the increasing presence of obstacles such as grain boundaries for nanocrystalline materials, the rate limiting process for smaller grain size was the interaction of dislocation and the grain boundaries, which is strain rate and temperature dependence. By considering the length scale of the dislocation and grain boundaries interaction, Cheng et al [52] proposed the following model for strain rate sensitivities . (2.3) z is the distance swept by the dislocation during activation, r is the dislocation density and a, a and b are the proportional factors. With this model, they will be able to predict higher strain rate sensitivities for nanocrystalline material produced by severe plastic deformation as compared to other technique. Since the twin boundaries in nanocrystalline or ultra fine grain copper served as a barriers for dislocation motion and nucleation which led to highly localized dislocations near the twin boundaries, the strain rate sensitivity of copper with high density of coherent twin boundaries was found to be higher than those without any twin boundaries [33]. Lastly, the increase enhanced strain rate sensitivity in nanocrystalline copper had been credited for it increases in strength and ductility. For example, Valiev et al [60] credited the enhanced strain rate sensitivity of 0.16 for the high ductility. In addition to a strong dependency on the strain rate, strength in nanocrystalline materials was also highly dependent on the temperature. Wang et al [73] observed that the yield strength for ultra fine grain copper with a grain size of 300nm increases from approximately 370MPa to 500MPa when the temperature reduces from room temperature to 77k. The authors attributed this increase in yield strength due to the absence of additional thermal deformation processes at 77k. This is consistent with Huang et al [74] observation where the temperature dependence of nanocrystalline copper with an increase in hardness of nanocrystalline copper with lowering the temperature is noted Ductility is another important characteristic of nanocrystalline materials. In microcrystalline materials, a reduction in grain size will increase the ductility due to the presence of grain boundaries acting as effective barriers to the propagation of micro-cracks[75]. However, nanocrystalline copper showed a lower strain to failure than that of their microcrystalline counterparts and this lacks in ductility was attributed to the presence of processing defects [76]. Recent advanced in processing of nanocrystalline materials offer materials with fairly good ductility in additional to ultra-high strength. Lu et al [10] reported that nanocrystalline copper with minimal flaw produced via electro-deposition had an elongation to fracture of 30%. Furthermore, Youssef et al [77] observed a 15.5% elongation to failure for defect free nanocrystalline copper produced via mechanical milling. Hence, it was possible for nanocrystalline copper to be both strong and ductile if the processing artifacts are minimized. The failure are usually consists of dimples several time larger than their grain size was normally found on the failure morphology of nanocrystalline materials and Kumar et al [78] presented the following model for initiation and hence the eventual failure of nanocrystalline materials. Furthermore, the presence of shear region was found to be due to shear localization since the ratio of strain hardening rate to prevailing stress was usually small [79, 80]. Figure 2.9: Schematic illustration of fracture in nanocrystalline material postulated by Kumar et al [78] 2.2.2.2 Creeps Nanocrystalline materials are expected to creep during room temperature. This is because Due to the higher fraction of grain boundaries and triple junctions, self diffusivity of nanocrystalline material had been shown to increase by an order of three as compared to microcrystalline copper [81]. Since creep behavior was dependent on grain size and diffusivity, with creep rate increases with an increase in diffusivity or a decrease in grain size, the creep temperature for nanocrystalline copper was known to be a small fraction of melting temperature (about 0.22 of its melting points). Furthermore, since creep had always been cited as one of the reason for grain size softening in nanocrystalline materials, creeps were other important mechanical properties of nanocrystalline materials that had been gaining a lot of researchers attention. Due to the high volume fraction of grain boundaries and enhanced diffusivity rate Model for Predicting Fatigue Life of Nanomaterials Model for Predicting Fatigue Life of Nanomaterials Introduction In the past, the primary function of micro-systems packaging was to provide input/output (I/O) connections to and from integrated circuits (ICs) and to provide interconnection between the components on the system board level while physically supporting the electronic device and protecting the assembly from the environment. In order to increase the functionality and the miniaturization of the current electronic devices, these IC devices have not only incorporated more transistors but have also included more active and passive components on an individual chip. This has resulted in the emerging trend of a new convergent system[1] Currently, there are three main approaches to achieving these convergent systems, namely the system-on-chip (SOC), system-in-package (SIP) and system on package (SOP). SOC seeks to integrate numerous system functions on one silicon chip. However, this approach has numerous fundamental and economical limitations which include high fabrication costs and integration limits on wireless communications, which due to inherent losses of silicon and size restriction. SIP is a 3-D packaging approach, where vertical stacking of multi-chip modules is employed. Since all of the ICs in the stack are still limited to CMOS IC processing, the fundamental integration limitation of the SOC still remains. SOP on the other hand, seeks to achieve a highly integrated microminiaturized system on the package using silicon for transistor integration and package for RF, digital and optical integration[1] IC packaging is one of the key enabling technologies for microprocessor performance. As performance increases, technical challenges increase in the areas of power delivery, heat removal, I/O density and thermo-mechanical reliability. These are the most difficult challenges for improving performance and increasing integration, along with decreasing manufacturing cost. Chip-to-package interconnections in microsystems packages serve as electrical interconnections but often fail by mechanisms such as fatigue and creep. Furthermore, driven by the need for increase the system functionality and decrease the feature size, the International Technology Roadmap for Semi-conductors (ITRS) has predicted that integrated chip (IC) packages will have interconnections with I/O pitch of 90 nm by the year 2018 [2]. Lead-based solder materials have been used for interconnections in flip chip technology and the surface mount technology for many decades. The traditional lead-based and lead-free solder bumps will not satisfy the thermal mechanical requirement of these fine pitches interconnects. These electronic packages, even under normal operating conditions, can reach a temperature as high as 150C. Due to differences in the coefficient of thermal expansion of the materials in an IC package, the packages will experience significant thermal strains due to the mismatch, which in turn will cause lead and lead-free solder interconnections to fail prematurely. Aggarwal et al [3] had modeled the stress experienced by chip to package interconnect. In his work, he developed interconnects with a height of 15 to 50 micrometre on different substrate using classic beam theory. Figure 1 shows the schematic of his model and a summary of some of his results. Although compliant intrerconect could reduces the stress experienced by the interconnect, it is still in sufficient. Chng et al. [4] performed a parametric study on the fatigue life of a solder column for a pitch of 100micrometre using a macro-micro approach. In her work, she developed models of a solder column/bump with a pad size of 50micrometre and heights of 50 micrometre to 200 micrometre. Table I shows a summary of some of her results. Table 1.1: Fatigue life estimation of solder column chip thickness (micrometre) 250 640 640 640 board CTE (ppm/K) 18 18 10 5 solder column height (micrometre) Fatigue life estimation/cycle) 50 81 N.A 171 3237 100 150 27 276 3124 150 134 31 518 4405 200 74 38 273 5772 It can be seen from Table 1.1 that the fatigue lives of all solder columns are extremely short. Apart from the 5ppm/K board where there is excellent CTE matching, the largest fatigue life of the solder column is only about 518 cycles. As expected, the fatigue life increases significantly when the board CTE decreases from 18ppm/K to 10ppm/K and as the height increases from 50micrometre to 200micrometre.This is mainly due to the large strain induced by the thermal mismatch as shown in Figure 1.2. The maximum inelastic principal strain was about 0.16 which exceeds the maximum strain that the material can support. Although the fatigue life of the chip to package interconnection can be increases by increasing the interconnects height, it will not be able to meet the high frequency electrical requirements of the future IC where they need to be operating at a high frequencies of 10-20 GHz and a signal bandwidth of 20 Gbps, By definition, nanocrystalline materials are materials that have grain size less than 100nm and these materials are not new since nanocrystalline materials have been observed in several naturally-occurring specimens including seashells, bone, and tooth enamel [5, 6]. However, the nanocrystalline materials have been attracting a lot of research interest due to its superior mechanical and electrical properties as compared to the coarse-grained counterpart. For example, the nano-crystalline copper has about 6 times the strength of bulk copper [7]. Furthermore, the improvement in the mechanical properties due to the reduction in grain size has been well-documented. Increase in strength due to the reduction in grain-size is predicted by the Hall-Petch relationship which has also been confirmed numerically by Swygenhoven et al [8] and was first demonstrated experimentally by Weertman [9]. The implantation of nanocrystalline copper as interconnect materials seems to be feasible from the processing viewpoint too. Copper has been used as interconnects materials since 1989 whereas nano-copper has also been widely processed using electroplating and other severe plastic deformation techniques in the past few years. For instance, Lu et al. [10] have reported electroplating of nano-copper with grain size less than 100 nm and electrical conductivity comparable to microcrystalline copper. Furthermore, Aggarwal et al [11] have demonstrated the feasibility of using electrolytic plating processes to deposit nanocrystalline nickel as a back-end wafer compatible process. However, there are certain challenges regarding implantation of nanocrystalline copper as interconnects materials. As discussed above, nanocrystalline copper have a high potential of being used as the next generation interconnect for electronic packaging. However, it is vital to understand their material properties, deformation mechanisms and microstructures stability. Although the increase in strength due to the Hall-Petch relationship which has also been confirmed numerically and experimentally by Weertman [9], the improvement in the fatigue properties is not well documented and no model has been established to predict/characterize these nano materials in interconnection application; conflicting results regarding the fatigue properties have also been reported. Kumar et al [12] reported that for nano-crystalline and ultra-fine crystalline Ni, although there is an increase in tensile stress range and the endurance limit, the crack growth rate also increases. However, Bansal et al. [7] reported that with decreasing grain size, the tensile stress range increases but the crack growth rate decreases substantially at the same cyclic stress intensity range. Thus, nanostructured materials can potentially provide a solution for the reliability of low pitch interconnections. However, the fatigue resistance of nanostructured interconnections needs to be further investigated. Since grain boundaries in polycrystalline material increases the total energy of the system as compare to perfect single crystal, it will resulted in a driving force to reduce the overall grain boundary area by increasing the average grain size. In the case of nanocrystalline materials which have a high volume fraction of grain boundaries, there is a huge driving force for grain to growth and this presented a presents a significant obstacle to the processing and use of nanocrystalline copper for interconnect applications. Millet et al [13] have shown, though a series of systematic molecular dynamics simulations, grain growth in bulk nanocrystalline copper during annealing at constant temperature of 800K can be impeded with dopants segregated in the grain boundaries regions. However, it has been observed that stress can trigger grain growth in nanocrystalline materials [14] and there is no literature available on impeding stress assisted grain growth. There is an impending need to investigate the impediment to grain growth caused by the dopant during fatigue/stress assisted grain growth Dissertation Objectives The goal of present project is to develop a model for the fatigue resistance of nano-materials that have been shown to have superior fatigue resistance. Accordingly, the following research objectives are proposed. Develops a model for predicting fatigue life of nanostructured chip-to-package copper interconnections Develops a fundamental understanding on the fatigue behavior of nanocrystalline copper for interconnect application Addresses the issue on the stability of nanocrystalline materials undergoing cyclic loading Overview of the Thesis The thesis is organized so that past research on nanocrystalline materials forms the basis of the understanding and new knowledge discovered in this research. Chapter 2 reviews much of the pertinent literature regarding nanocrystalline materials, including synthesis, deformation mechanisms, and grain growth. Chapter 3 describes a detailed overview of the technical aspects of the molecular dynamics simulation method including inter-atomic potentials, time integration algorithms, the NVT NPT, and NEPT ensembles, as well as periodic boundary conditions and neighbor lists. Include in this chapter is the algorithms for creating nanocrystalline materials used in this dissertations.. Chapter 4 describes the simulation procedure designed to investigate and develop the long crack growth analysis. The results of the long crack growth analysis will be presented at the end of Chapter 4. Chapter 5 presents the result and discussion on mechanical behavior of single and nanocrystalline copper subjected to monotonic and cyclic loading whereas Chapter 6 presents the result and discussion on the impediment to grain growth caused by the dopant during fatigue/stress assisted grain growth. Finally, conclusions and recommendations for future work are presented in Chapter 5. Chapter 2 This chapter offers an expanded summary of the literature published with regards to the fabrication methods, characterization, and properties of nanocrystalline materials in addition to a description of existing interconnect technology. 2.1 Off-Chip Interconnect Technologies Chip-to-package interconnections in microsystems packages serve as electrical interconnections but they will often failed by mechanisms such as fatigue and creep. Furthermore, driven by the need for increase the system functionality and decrease the feature size, the International Technology Roadmap for Semi-conductors (ITRS) has predicted that interconnections of integrated chip (IC) packages will have a I/O pitch of 90 nm by the year 2018 [2]. The International Technology Roadmap for Semiconductors (ITRS) roadmap is a roadmap that semiconductor industry closely follows closely and its projects the need for several technology generations. The package must be capable of meeting these projections in order for it to be successful. This section reviews some of the current interconnect technology. Wire bonding [15] as shown in Figure 2.1, is generally considered as one of the most simple, cost-effective and flexible interconnect technology. The devices on the silicon die are (gold or aluminum) wire bonded to electrically connect from the chip to the wire bond pads on the periphery. However, the disadvantages of wire bonding are the slow rate, large pitch and long interconnect length and hence this will not be suitable for high I/O application. Instead of wires in the wire bonding, tape automated bonding (TAB) is an interconnect technology using a prefabricated perforated polyimide film, with copper leads between chip and substrate. The advantage of this technology is the high throughput and the high lead count. However, it is limited by the high initial costs for tooling. An alternative to peripheral interconnect technology is the area-array solution, as shown in Figure 2.3, that access the unused area by using the area under the chip. In area-array packaging, the chip has an array of solder bumps that are joined to a substrate. Under-fill is then fills the gap between the chip and substrate to enhance mechanical adhesion. This technology gives the highest packaging density methods and best electrical characteristics of all the avaiable interconnection technology. However, not only is its initial cost is high, it requires a very demanding technology to establish and operate. With the need for higher I/O density, compliant interconnects have been developed to satisfy the mechanical requirements of high performance micron sized interconnects. The basic idea is to reduce shear stress experienced by the interconnects through increasing their height or decreasing of its shear modulus (i.e. increases in their compliant) and hence the name compliant interconnects. Some of recent research in compliant interconnects include Tesseras Wide Area Vertical Expansion, Form Factors Wire on Wafer and Georgia Institute of Technologys Helix interconnects [17-19] as shown in Figure 2.4. Although compliant interconnects can solve the problem of mechanical reliability issue, they are done at the expense of the electrical performance. Since there is a need to reduce the packages parasitic through a decrease line delays, there is a need to minimize the electrical connection length in order to increase the system working frequency. Hence, compliant interconnect may not meet the high electrical frequency requirements of future devices. Figure 2.4: (a) Wide Area Vertical Expansion, (b) Wire on Wafer and (c) G-Helix [17-19] Lead and lead-free solders typically fail mechanical when scaled down to less than to a pitch of 100 mm. Compliant interconnections, on the other hand, do not meet the high frequency electrical requirements. The Microsystems Packaging Research Center at Georgia institute of Technology had demonstrated the feasibility of using re-workable nanostructure interconnections. Aggarwal et al [20] had show that nanostructured nickel interconnections, through a Flip Chip test vehicle, was able to improve the mechanical reliability while maintaining the shortest electrical connection length. However, the main disadvantages of this method was the significant signal loss at high frequency signal of nanocrystalline nickel [21]. As discussed above, nanostructure interconnects technology is the most promising interconnect technology to best meet the stringent mechanical and electrical requirement of next generation devices. However, there is a need of an alternate materials and a sensible choice of materials in this case would be nanocrystalline copper for its high strength material with superior electrical conductivity. Hence, it would be beneficial to use nanocrystalline-copper as material for the nanostructure interconnects. Due to the tendency for the grain to grow, there is a need to stabilize the grain growth in nanocrystalline copper before using it could be considered as a potential candidate for nanostructure interconnect. 2.2 Nanocrystalline material Nanocrystalline materials are polycrystalline materials with an average grain size of less than 100 nm [22]. Over the past decade , new nanocrystalline or nanostructured materials with key microstructural length scales on the order of a few tens of nanometers has been gaining a lot of interest in the material science research society. This is mainly due to its unique and superior properties, as compared to their microcrystalline counterparts which includes increased strength [22] and wear resistance [23]. These unique properties are due to the large volume fraction of atoms at or near the grain boundaries. As a result, these materials have unique properties that are representative of both the grain boundary surface characteristics and the bulk. Recent advances in synthesis and processing methodology for producing nanocrystalline materials such as inert gas condensation [24], mechanical milling [25, 26], electro-deposition [27], and severe plastic deformation [28] have made it possible to produce sufficient nanocrystalline materials for small scale application. 2.2.1 Synthesis Inert gas condensation, the first method used to synthesis bulk nanocrystalline [29], consists of evaporating a metal inside a high-vacuum chamber and then backfilling the chamber with inert gas [30]. These evaporated metal atoms would then collide with the gas atoms, causing them to lose kinetic energy and condenses into powder of small nano-crystals. These powders are then compacted under high pressure and vacuum into nearly fully dense nanocrystalline solids. The grain size distribution obtained from this method is usually very narrow. However, the major draws back of this method are its high porosity levels and imperfection bonding. Grain coarsening also occurs due to the high temperature during the compaction stage [31]. Mechanical milling consists of heavy cyclic deformation in powders until the final composition of the powders corresponds to a certain percentages of the respective initial constituents [25, 26]. A wide grain size distribution is obtained by this method. This technique is a popular method to prepare nanocrystalline materials because of its applicability to any material and simplicity. However, their main drawback includes contamination and grain coarsening during the consolidation stage. Electro-deposition consists of using electrical current to reduce cations of a desired material from a electrolyte solution and coating a conductive object on the substrate. Electro-deposition has many advantages over processing techniques and this includes its applicability to a wide variety of materials, low initial capital investment requirements and porosity-free finished products without a need for consolidation processing [27]. Furthermore, Shen et al. [32] and Lu et al.[33] had recently show that the right electro-deposition condition can produce a highly twinned structure which leads to enhanced ductility. The main drawback of this method is it is the difficulty to achieve high purity. Severe plastic deformation, such as high-pressure torsion, equal channel angular extrusion (ECAE), continuous confined shear straining and accumulative roll-bonding, uses extreme plastic straining to produce nanocrystalline materials by mechanisms such as grain fragmentation, dynamic recovery, and geometric re-crystallization [34]. It is the only technology that transformed conventional macro-grained metals directly into nanocrystalline materials without the need of potentially hazardous nano-sized powders. This is achieved by introducing very high shear deformations into the material under superimposed hydrostatic pressure. Two of the most commonly used methods are high-pressure torsion and ECAE [35]. In the study of the effect of ECAE on the microstructure of nanocrystalline copper, Dalla Torre et al [36] observed that the grains become more equi-axial and randomly orientation as the number of passes increases, as shown in Figure 2.5 Figure 2.5: Microstructure of ECAE copper subjected to (a) 1 passes (b) 2 passes (c) 4 passes (d) 8 passes (e) 12 passes and (f) 16 passes [36] 2.2.2 Mechanical Behavior of nanocrystalline materials Due to the small grain size and high volume fraction of grain boundaries, nanocrystalline materials exhibit significantly different properties and behavior as compared to their microcrystalline counterpart. The structure and mechanical behavior of nanocrystalline materials has been the subject of a lot of researchers interests both experimentally [37-43] and theoretically [44-50]. This section reviews the principal mechanical properties and behavior of nanocrystalline materials. 2.2.2.1 Strength and ductility Recent studies of nanocrystalline metals have shown that there is a five to ten fold increases in the strength and hardness as compared to their microcrystalline state [7, 36, 37, 51, 52]. This increase in the strength is due to the presence of grain boundaries impeding the nucleation and movement of dislocations. Since decreasing grain boundary size increases the number of barrier and the amount of applied stress necessary to move a dislocation across a grain boundary, this resulted in a much higher yield strength. The inverse relationship between grain size and strength is characterized by the Hall-Petch relationship [53, 54] as shown in equation (2.1). Eq (2.1) In equation (2.1), s is the mechanical strength, k is a material constant and d is the average grain size. Hence, nanocrystalline materials are expected to exhibit higher strength as compared to their microcrystalline counterpart. Figure 2.6 and Figure 2.7 show the summary of hardness and yield strength from tensile test that are reported in the literature. Indeed, hardness and yield strength of copper with a grain size of 10nm (3GPa) can be one order higher than their microcrystalline counterpart. To the larger specimens. Derivation from Hall-Petch relationship begins as the grain size approaches 30nm where the stresses needed to activate the dislocation multiplication via Frank-Read sources within the grains are too high and the plastic deformation is instead accommodated by grain boundaries sliding and migration.[12]. Furthermore, as the grain size reduces, the volume fraction of the grain boundaries and the triple points increases. Material properties will be more representative of the grain boundary activity [64] and this will resulting the strength to be inversely proportional to grain size instead of square roots of the grain size as predicted by Hall Petch relation [65]. Further reduction in the grain size will result in grain boundaries processes controlling the plastic deformation and reverse Hall-Petch effect, where the materials soften, will take place. Although sample defects had been account for the earlier experimental observation of reverse Hall-Petch effect[24], Swygenhoven et al [66] and Schiotz et al [47], using molecular simulation, was able to showed that nanocrystalline copper had the highest strength (about 2.3GPa ) at a grain size of 8nm and 10-15nm respectively. Conrad et al [67] pointed out that below this critical grain size, the mechanisms shifted to grain boundary-mediated from dislocation-mediated plasticity and this causes the material to become dependent on strain rate, temperature, Taylor orientation factor and presence of the type of dislocation. The yield stress of nanocrystalline copper was highly sensitive to strain rate even though it is a fcc materials. The strain rate sensitivity, m, in equation 2.2 a engineering parameter which measured the dependency of the strain rate and Figure 2.8 shows a summary of m as a function of grain size for copper specimen in the literature [51, 68-70]. Due to high localized dislocation activities at the grain boundaries which results in enhanced strain rate sensitivities in nanocrystalline materials, m increases drastically when the grain size is below 0.1 mm as shown in Figure 2.8. (2.2) Room temperature strain rate sensitivity was found to dependent on dislocation activities and grain boundaries diffusion [52, 71, 72]. Due to the negligible lattice diffusion at room temperature, the rate limiting process for microcrystalline copper was the gliding dislocation to cutting through forest dislocation, resulting in low strain rate sensitivities. However, due to the increasing presence of obstacles such as grain boundaries for nanocrystalline materials, the rate limiting process for smaller grain size was the interaction of dislocation and the grain boundaries, which is strain rate and temperature dependence. By considering the length scale of the dislocation and grain boundaries interaction, Cheng et al [52] proposed the following model for strain rate sensitivities . (2.3) z is the distance swept by the dislocation during activation, r is the dislocation density and a, a and b are the proportional factors. With this model, they will be able to predict higher strain rate sensitivities for nanocrystalline material produced by severe plastic deformation as compared to other technique. Since the twin boundaries in nanocrystalline or ultra fine grain copper served as a barriers for dislocation motion and nucleation which led to highly localized dislocations near the twin boundaries, the strain rate sensitivity of copper with high density of coherent twin boundaries was found to be higher than those without any twin boundaries [33]. Lastly, the increase enhanced strain rate sensitivity in nanocrystalline copper had been credited for it increases in strength and ductility. For example, Valiev et al [60] credited the enhanced strain rate sensitivity of 0.16 for the high ductility. In addition to a strong dependency on the strain rate, strength in nanocrystalline materials was also highly dependent on the temperature. Wang et al [73] observed that the yield strength for ultra fine grain copper with a grain size of 300nm increases from approximately 370MPa to 500MPa when the temperature reduces from room temperature to 77k. The authors attributed this increase in yield strength due to the absence of additional thermal deformation processes at 77k. This is consistent with Huang et al [74] observation where the temperature dependence of nanocrystalline copper with an increase in hardness of nanocrystalline copper with lowering the temperature is noted Ductility is another important characteristic of nanocrystalline materials. In microcrystalline materials, a reduction in grain size will increase the ductility due to the presence of grain boundaries acting as effective barriers to the propagation of micro-cracks[75]. However, nanocrystalline copper showed a lower strain to failure than that of their microcrystalline counterparts and this lacks in ductility was attributed to the presence of processing defects [76]. Recent advanced in processing of nanocrystalline materials offer materials with fairly good ductility in additional to ultra-high strength. Lu et al [10] reported that nanocrystalline copper with minimal flaw produced via electro-deposition had an elongation to fracture of 30%. Furthermore, Youssef et al [77] observed a 15.5% elongation to failure for defect free nanocrystalline copper produced via mechanical milling. Hence, it was possible for nanocrystalline copper to be both strong and ductile if the processing artifacts are minimized. The failure are usually consists of dimples several time larger than their grain size was normally found on the failure morphology of nanocrystalline materials and Kumar et al [78] presented the following model for initiation and hence the eventual failure of nanocrystalline materials. Furthermore, the presence of shear region was found to be due to shear localization since the ratio of strain hardening rate to prevailing stress was usually small [79, 80]. Figure 2.9: Schematic illustration of fracture in nanocrystalline material postulated by Kumar et al [78] 2.2.2.2 Creeps Nanocrystalline materials are expected to creep during room temperature. This is because Due to the higher fraction of grain boundaries and triple junctions, self diffusivity of nanocrystalline material had been shown to increase by an order of three as compared to microcrystalline copper [81]. Since creep behavior was dependent on grain size and diffusivity, with creep rate increases with an increase in diffusivity or a decrease in grain size, the creep temperature for nanocrystalline copper was known to be a small fraction of melting temperature (about 0.22 of its melting points). Furthermore, since creep had always been cited as one of the reason for grain size softening in nanocrystalline materials, creeps were other important mechanical properties of nanocrystalline materials that had been gaining a lot of researchers attention. Due to the high volume fraction of grain boundaries and enhanced diffusivity rate