文献综述英文
开题报告文献综述范文英文
开题报告文献综述范文英文IntroductionThe purpose of this literature review is to provide a comprehensive overview of the existing research and literature in the field of open topic reports. Open topic reports refer to the initial stage of research where a proposal is made to investigate a particular topic. This review aims to identify the gaps and limitations in current research and highlight the significance of conducting further investigations in this area.MethodsA comprehensive search of various databases was conducted to identify relevant academic articles and research papers. The search terms included "open topic reports," "research proposal," and "literature review." The inclusion criteria required that the articles were published in English within the last ten years. After analyzing the titles and abstracts of the initial search results, a total of 50 articles were selected for the review.ResultsThe review of the literature identified several key themes and findings regarding open topic reports. Firstly, the process of developing a research proposal was highlighted as a critical step in research initiation. The literature emphasized the importance of clearly defined research objectives, research questions, and methodology. Additionally, the review revealed that the selection of an appropriateresearch topic is crucial and should consider relevancy, feasibility, and originality.Furthermore, the literature emphasized the need for a comprehensive literature review within open topic reports. It was highlighted that a thorough review of existing literature enables researchers to identify the current state of knowledge, potential research gaps, and opportunities for further exploration. Additionally, the literature review aids in refining the research questions and developing a theoretical framework.DiscussionBased on the literature review, it is evident that open topic reports play a vital role in the research process. They provide researchers with the opportunity to propose new research ideas, identify research gaps, and lay the foundation for future investigations. However, the literature also indicates certain limitations and challenges in the field. For instance, there is a lack of standardized guidelines or frameworks for developing open topic reports, which can lead to inconsistencies and variations in quality.ConclusionIn conclusion, the literature review highlights the importance of open topic reports as a precursor to conducting research. It underscores the significance of developing clear research objectives and asking relevant research questions. Additionally, it emphasizes the need for a comprehensive literature review to identify research gaps and refine the research focus. However, further research is required to address the limitations identified in the literature and establish standardizedguidelines for open topic reports. This review provides a foundation for future investigations in this area and contributes to the advancement of research practices.。
文献综述 英文作文
文献综述英文作文In recent years, there has been a growing interest in the impact of social media on mental health. Many studies have found that excessive use of social media can lead to feelings of loneliness, anxiety, and depression. This has raised concerns about the potential negative effects of social media on individuals' well-being.The concept of mindfulness has gained popularity as a potential intervention for improving mental health. Mindfulness involves paying attention to the present moment and accepting it without judgment. Research has shown that practicing mindfulness can reduce stress, improve mood, and enhance overall well-being.There is also a growing body of literature on the relationship between physical activity and mental health. Regular exercise has been found to have a positive impact on mood and can help reduce symptoms of anxiety and depression. This has led to an increased focus onincorporating physical activity into mental health treatment and prevention programs.The use of technology in mental health treatment has also been a topic of interest. With the development of digital mental health interventions, individuals can access therapy and support through online platforms and mobile apps. This has the potential to increase access to mental health care and provide support to those who may not have access to traditional in-person services.The role of genetics in mental health has been another area of research. Studies have shown that genetic factors can contribute to the development of mental health disorders. Understanding the genetic basis of mentalillness can help inform treatment approaches and improve outcomes for individuals with these conditions.In conclusion, there is a wide range of research on various aspects of mental health, including the impact of social media, the benefits of mindfulness, the relationship between physical activity and mental well-being, the use oftechnology in mental health treatment, and the role of genetics in mental illness. This diverse body of literature provides valuable insights into the complex nature of mental health and offers potential avenues for improving mental well-being.。
文献综述如何写(英文)
How to Write a Good Literature Review1. IntroductionNot to be confused with a book review, a literature review surveys scholarly articles, books and other sources (e.g. dissertations, conference proceedings) relevant to a particular issue, area of research, or theory, providing a description, summary, and critical evaluation of each work. The purpose is to offer an overview of significant literature published on a topic.2. ComponentsSimilar to primary research, development of the literature review requires four stages:▪Problem formulation—which topic or field is being examined and what are its component issues?▪Literature search—finding materials relevant to the subject being explored▪Data evaluation—determining which literature makes a significant contribution to the understanding of the topic▪Analysis and interpretation—discussing the findings and conclusions of pertinent literatureLiterature reviews should comprise the following elements:▪An overview of the subject, issue or theory under consideration, along with the objectives of the literature review▪Division of works under review into categories (e.g. those in support of a particular position, those against, and those offering alternative theses entirely) ▪Explanation of how each work is similar to and how it varies from the others▪Conclusions as to which pieces are best considered in their argument, are most convincing of their opinions, and make the greatest contribution to the understanding and development of their area of researchIn assessing each piece, consideration should be given to:▪Provenance—What are the author's credentials? Are the author's arguments supported by evidence (e.g. primary historical material, case studies, narratives, statistics, recent scientific findings)?▪Objectivity—Is the author's perspective even-handed or prejudicial? Is contrary data considered or is certain pertinent information ignored to prove the author's point?▪Persuasiveness—Which of the author's theses are most/least convincing?▪Value—Are the author's arguments and conclusions convincing? Does the work ultimately contribute in any significant way to an understanding of the subject?3. Definition and Use/PurposeA literature review may constitute an essential chapter of a thesis or dissertation, or may be a self-contained review of writings on a subject. In either case, its purpose is to:▪Place each work in the context of its contribution to the understanding of the subject under review▪Describe the relationship of each work to the others under consideration▪Identify new ways to interpret, and shed light on any gaps in, previous research▪Resolve conflicts amongst seemingly contradictory previous studies▪Identify areas of prior scholarship to prevent duplication of effort▪Point the way forward for further research▪Place one's original work (in the case of theses or dissertations) in the context of existing literatureHere are some of the questions your literature review should answer:1.What do we already know in the immediate area concerned?2. What are the characteristics of the key concepts or the main factors or variables?2.What are the relationships between these key concepts, factors or variables?3.What are the existing theories?4.Where are the inconsistencies or other shortcomings in our knowledge andunderstanding?5.What views need to be (further) tested?6.What evidence is lacking, inconclusive, contradictory or too limited?7.Why study (further) the research problem?8.What contribution can the present study be expected to make?9. What research designs or methods seem unsatisfactory?HOW CAN I WRITE A GOOD LITERATURE REVIEW?Remember the purpose: it should answer the questions we looked at above. Look at how published writers review the literature. You'll see that you should use the literature to explain your research - after all, you are not writing a literature review just to tell your reader what other researchers have done. You aim should be to show why your research needs to be carried out, how you came to choose certain methodologies or theories to work with, how your work adds to the research already carried out, etc.Read with a purpose:you need to summarize the work you read but you must also decide which ideas or information are important to your research (so you can emphasize them), and which are less important and can be covered briefly or left out of your review. You should also look for the major concepts, conclusions, theories, arguments etc. that underlie the work, and look for similarities and differences with closely related work. This is difficult when you first start reading, but should become easier the more you read in your area.Write with a purpose: your aim should be to evaluate and show relationships between the work already done (Is Researcher Y's theory more convincing than Researcher X's? DidResearcher X build on the work of Researcher Y?) and between this work and your own. In order to do this effectively you should carefully plan how you are going to organize your work.A lot of people like to organize their work chronologically (using time as their organizing system). Unless developments over time are crucial to explain the context of your research problem, using a chronological system will not be an effective way to organize your work. Some people choose to organize their work alphabetically by author name: this system will not allow you to show the relationships between the work of different researchers, and your work, and should be avoided!When you read for your literature review, you are actually doing two things at the same time (which makes things more difficult for you!):1. you are trying to define your research problem: finding a gap, asking a question,continuing previous research, counter-claiming;2. you are trying to read every source relevant to your research problem.Naturally, until you have defined your problem, you will find that there are hundreds of sources that seem relevant. However, you cannot define your problem until you read around your research area. This seems a vicious circle, but what should happen is that as you read you define your problem, and as you define your problem you will more easily be able to decide what to read and what to ignore.TRAPSSome traps to avoid:Trying to read everything! As you might already have discovered, if you try to be comprehensive you will never be able to finish the reading! The idea of the literature review is not to provide a summary of all the published work that relates to your research, but a survey of the most relevant and significant work.Reading but not writing! It's easier to read than to write: given the choice, most of us would rather sit down with a cup of coffee and read yet another article instead of putting ourselves in front of the computer to write about what we have already read! Writing takes much more effort, doesn't it? However, writing can help you to understand and find relationships between the work you've read, so don't put writing off until you've "finished" reading - after all, you will probably still be doing some reading all the way through to the end of your research project. Also, don't think of what you first write as being the final ornear-final version. Writing is a way of thinking, so allow yourself to write as many drafts as you need, changing your ideas and information as you learn more about the context of your research problem.Not keeping bibliographic information!The moment will come when you have to write your references page . . . and then you realize you have forgotten to keep the information you need, and that you never got around to putting references into your work. The only solution is to spend a lot of time in the library tracking down all those sources that you read, and going through your writing to find which information came from which source. If you're lucky, maybe you can actually do this before your defence - more likely, you will unable to find all your sources, a big headache for you and your committee. To avoid this nightmare, always keep this information in your notes. Always put references into your writing. Notice how on this course we have referenced the works that we have referred to - you should do the same.LITERATURE REVIEW: AN EXAMPLEHere is an example of using the literature to explain and define a problem. This example is taken from an introduction because most thesis literature reviews tend to be too long for us to easily look at. Although your literature review will probably be much longer than the one below, it is useful to look at the principles the writers have used.On the optimal container size in automated warehousesY. Roll, M.J. Rosenblatt and D. Kadosh, Proceedings of the NinthICPRAutomated storage and retrieval systems (AS/RS) are being introduced intothe industry and warehousing at an increasing rate. Forecasts indicate thatthis trend will continue for the foreseeable future (see [1]). Research in thearea of AS/RS has followed several avenues. Early work by Hausman,Schwarz and Graves [6, 7] was concerned with storage assignment andinterleaving policies, based on turnover rates of the various items. Elsayed [3]and Elsayed and Stern [4] compared algorithms for handling orders inAR/RS. Additional work by Karasawa et al. [9], Azadivar [2] and Parry et al.[11] deals with the design of an AS/RS and the determination of itsthroughput by simulation and optimization techniques.Several researchers addressed the problem of the optimal handling unit(pallet or container) size, to be used in material handling and warehousingsystems. Steudell [13], Tanchoco and Agee[14], Tanchoco et al. [15] andGrasso and Tanchoco [5] studied various aspects of this subject. The last tworeferences incorporate the size of the pallet, or unit load, in evaluation of theoptimal lot sizes for multi-inventory systems with limited storage space. In areport on a specific case, Normandin [10] has demonstrated that using the'best-size' container can result in considerable savings. A simulation modelcombining container size and warehouse capacity considerations, in anAS/RS environment, was developed by Kadosh [8]. The general results,reflecting the stochastic nature of the flow of goods, are similar to thosereported by Rosenblatt and Roll [12]. Nevertheless, container size was foundto affect strongly overall warehousing costs.In this paper, we present an analytical framework for approximating theoptimal size of a warehouse container. The approximation is based on seriesof generalizations and specific assumptions. However, these are valid for awide range of real life situations. The underlying assumptions of the modelare presented in the following section.Notice how the writers have:grouped similar information: "Steudell [13], Tanchoco and Agee[14], Tanchoco et al. [15] and Grasso and Tanchoco [5] studied various aspects of this subject."shown the relationship between the work of different researchers, showingsimilarities/differences: "The general results, reflecting the stochastic nature of the flow of goods, are similar to those reported by Rosenblatt and Roll [12]."indicated the position of the work in the research area history: "Early work by Hausman, Schwarz and Graves [6, 7] . . . "moved from a general discussion of the research in AS/RS to the more specific area (optimal container size) that they themselves are researching i.e. they relate previous work to their own to define it, justify it and explain it.。
literaturereview文献综述的写法（英文版）
literaturereview⽂献综述的写法（英⽂版）Literature ReviewThis packet details the steps necessary to produce a literature review that may be required for work in various disciplines, including English, history and psychology. This packet is not intended to replace instructor guidelines and should not be used in that manner. The packet’s intended use is as a supplement to classroom instruction on assembling a literature review. Therefore, it contains only general information that must be tailored to fit specific guidelines as required by your discipline and by your instructor.This packet is subdivided into six sections:I. General InformationStates what a literature review is and what purpose it serves.II. ProcessGives step-by-step instructions on how to get started on your literature review.III. OrganizationExplains the two most common ways of arranging information in a literature review.IV. FormatProvides descriptions for two of the most common formats used in a literature review, the item to item comparison and contrast (Format A) and the criteria to criteria comparison and contrast (Format B).V. ChecklistAllows appraisal of your completed literature review to assure that it follows all necessary guidelines.VI. ResourcesLists helpful resources used to compile this packet so that you may obtain further information.M General Information MDefinitionLiterature reviews can have two roles: In their first role, they function as a stand-alone paper. At other times they will actually be part of a larger research thesis. In this handout, literature reviews will be referred to in the stand-alone sense. As a stand-alone paper, literature reviews are multi-layered and are more formal and detailed than book reviews. As the author of a literature review, you must become familiar with a large amount of research on a specific topic. You will then develop your own thesis about the topic related to this research. After this, you will classify and critically analyze research on the topic by making a comparison between several different studies and by emphasizing how these studies and their comparison relate to your own thesis.In effect, a literature review is a paper that compiles, outlines and evaluates previously established research and relates it to your own thesis. It provides a context for readers as if theywere researching the topic on their own. Just from reading your paper, readers should be able to gain insight into the amountand quality of research on the topic. Your thesis and the literature reviewed serve several important functions within the paper:Your thesis creates a foundation for the literature review because it helps narrow the topic by providing a sense of direction; however, you will have to conduct some initial research and reading before deciding on an appropriate thesis. Your personal thesis may be a statement addressing some of the following situations: “why your research needs to be carried out, how you came to choose certain methodologies or theories to work with, how your work adds to the research already carried out”(Brightwell, G. and Shaw, J., 1997-98), or it may present some other logical perspective.Reviewed literature is organized in a logical manner that best suits the topic of the review and the hypothesis of the literature (see Organization and Format). The selected method of organization and style of format should draw attention to similarities and differences among the reviewed literature; these similarities and differences are based on specific criteria you revealed in the literature review’s introduction. According to Brightwell and Shaw (1997-98), your goal in the body of the review “. . . should be to evaluate and show relationships between the work already done (Is Researcher Y’s theory more convincing than Researcher X’s? Did Researcher X build on the work of Researcher Y?) and between this work and your own [thesis].” Additional information on these topics can be found in the Organization and Format sections of this packet. Therefore, carefully planned organization is an essential part of any literature review.PurposeAlthough literature reviews may vary according to discipline, their overall goal is similar. A literature review serves as a compilation of the most significant sources on a subject and relates the findings of each of these sources in a rational manner while supporting the literature review author’s own thesis. A literature review establishes which sources are most relevant to its author’s point and which sources are most credible to the discipline at hand.In a literature review, the results of previous research are summarized, organized and evaluated. Discipline-SpecificityA literature review’s organization, format, level of detail and citation style may vary according to discipline because different disciplines have different audiences. Examples here pertain to the natural sciences, social sciences and humanities.Natural and social sciences The author of a literature review in the natural or social sciences must pay close attention to measurements, study populations and technical aspects of experimental findings. Typically, a portion of the natural or social sciences literature review is set aside for reviewing sources on the primary topic. Then, a comparative analysis or discussion section is used to analyze the similarities and differences among the sources, tying them in with the literature review author’s original thesis.Humanities The author of a literature review in the humanities usually does not set aside a special section for reviewing the sources; instead, citations may be found randomly throughout the paper. The literature being reviewed is arranged according to paragraphs based on the author’s points, which in turn, support the author’s thesis. The paper itself may not be called a literature review at all. It is more likely to be called a critical analysis.Remember that the best bet for determining what type of literature review is appropriate for your course is checking with the instructor prior to beginning research.REVIEW1. What is the purpose of a literature review? What is the connection between theauthor’s thesis and the literature being reviewed?2. What discipline will your literature review be classified in?M Process M1. Find several articles that deal with your research topic. Sometimes it is helpful to review the bibliography of one of the first scholarly sources that you encounter and compare it to the bibliographies of other sources on the topic. If the same source is listed within several of these bibliographies, it is probably a fundamental, credible source that will aid you in your review.2. Before you begin reviewing literature, realize that you are looking to accomplish two things:A. Defining your research problem/thesis (examples: finding a flaw inresearch, continuing previous research, etc . . .)B. Reading and evaluating significant works that are relevant to yourresearch problem.You will be conducting Steps A and B simultaneously because the two form a circular pattern. As you read related sources (Step B), you define your problem, and as you define your problem (Step A) you will more easily be able to decide what material is relevant enough to be worthy of reading (Step B).3. Once you begin reviewing, make an entry with complete bibliographical information and comments for each work that you are going to include in the review.4. Compare the articles by evaluating the similarities and differences among them. This will be the initial stage in the formulation of your thesis.5. Form a thesis that is clearly written and can be logically supported by the literature you will include in your review.6. View the articles briefly again and jot down any notes that seem to relateto your thesis.7. Decide which organizational pattern and format are best for the topic of your review.8. Construct an appropriate outline for the literature review.9. Write an introduction that introduces the topic, reveals your thesis statement, and arranges key issues.10. Organize and write the body of your paper according to the appropriate format: topical or chronological.11. Write a conclusion that reconciles similarities and differences on the topic and reemphasizes the criteria used to arrive at this conclusion./doc/8b508cc25fbfc77da269b1c1.html plete the final draft of the literature review.13. Check over the final draft for grammar and punctuation errors.14. Use the checklist provided here to make sure that all parts of the literature review are addressed and focused. REVIEW1. What do you consider to be the most crucial step(s) in the process of your literature review ? Why? Justify your response(s).A literature review can be arranged either topically or chronologically.Topical organization occurs in reviews where previous research being evaluated is divided into segments with each one representing a part of some larger issue. In a topical review, the author begins by describing the characteristics of research shared by several studies and then moves on to analyze their similarities and differences. For more information, see the example below.ExampleThe organization of a literature review begins in the introduction. For example, in the introduction of a literature review about the effect of seating arrangements on peer tutoringcommunication, you would first introduce the topic and what your literature review will attempt to assess:…Writing centers can set the table for collaborative tutoring sessions through a careful consideration of spatial arrangement . . .Then state what angle is going to be explored:…These studies will be used to support the author’s claims that spatial arrangement is instrumental in encouraging collaborative environments in the writing center…Then, arrange key issues that will be addressed in this review by answering questions that you have personally developedand are tailored to fit your topic. In the introduction, give the audience a clear picture of how you will organize your paper: Establishing a Critical Response for a Literature ReviewYou may find this section helpful at Steps 3, 4 and 5 of the process. When reviewing your sources, explore the following areas to help develop your critical response:What is the purpose of the research or work?What research or literary methods are used?How do the major concepts operate?In a research study, how accurate are the measurements?In a literary work, is the author’s position objective or biased? What are the different interpretations of the results of the study or of the literary work itself?M Organization MIn the following, I1 first review some relevant research concerning spatial arrangement and then discuss some recommended and alternate seating arrangements to encourage a collaborative environment in the writing center. Finally, I include some other considerations.In the body of this literature review, you would organize the information topically around each point (or question) that you asked yourself:-Research Review-Recommended Spatial Arrangement-Alternative Spatial Arrangement-Other ConsiderationsThen, write a conclusion that explains the significance of your findings:…While the seating arrangements outlined above are generally a good ‘setting’ for peer tutoring sessions, we should remember that each tutoring session is unique. Not all students will be comfortable with a side-by-side spatial arrangement at a round table. Tutors should be perceptive of and receptive to students who may have other spatial needs…Chronological organization occurs when a review is organized in time order and is most often used when a historical context is needed for discussing a topic from its beginning to its current state; chronological organization is especially helpful when discussing inactive periods and shifts in perspective on a given topic.ExampleThe organization of a literature review begins in the introduction. For example, in the introduction of a literature review entitled Development of Social Science Research on Attitudes Towards Gender in America, you would first introduce the topic and what your review hopes to assess:…This literature review will assess the development of research designed to uncover gender attitudes in America during the latter part of the 20th Century…Then state what angle is going to be explored:..As research progressed throughout the 20th century, the methods that social scientists use for measuring these attitudes developed and changed as well…Then, chronologically arrange issues that will be addressed in this review:Gender stereotypes still exist today, and varying attitudes can be traced over the past fifty years. Survey instruments used to gather data on these varying attitudes have also changed drastically over the course of time.In the body of this literature review, you would organize the information chronologically, adressing each point (or question)that is being asked for a particular time period:-Stereotypes and Survey Instruments of the 1950’s-Stereotypes and Survey Instruments of the 1960’s-Stereotypes and Survey Instruments of the 1970’s-Stereotypes and Survey Instruments of the 1980’s-Stereotypes and Survey Instruments of the 1990’s-Current Advancements1 Always clear the use of I with your instructor. An alternative to this would be the use of third person wording, such as “This paper reviews some relevant research concerning spatial arrangement and then discusses some recommended and alternate seating arrangements to encourage a collaborative environment in the writing center.”Then, write a conclusion that explains the significance of your findings:Although the survey instruments used in the 1950’s and 1960’s developed an obvious bias when surveying Americans regarding gender attitudes, the 1970’s brought about great change. Today social scientists are more careful than ever about testing the quality of a survey instrument before using it on the general public.M Format MThere are also two suggested formats for composing your literature review. Format A is used when comparing several studies that have similar hypothesis but different findings. Each piece of research is summarized individually. Format A is good for reviews with a small number of entries; however, this format may confuse the audience when used with a large number of reviews because descriptions of so many studies may get in the way of the analysis. Keep in mind that each piece of research usually will not receive equal attention in the review.Format A OutlineI. Introduction consists of four parts that are usually discussed in one paragraph.a. Identify the general topic being discussed.b. Mention trends published about the topic.c. State thesis establishing the reason for writing the literaturereview.d. Explain criteria by giving a description of each of the criteria used in evaluating theliterature review and rationalizing its organizationII. Literature reviewed section is divided up according to study.a.First study is summarized and discussed.b.Second study is summarized and discussed.c. Third study is summarized and discussed.III. Comparative analysis acknowledges the similarities and differences between studies.a. Similarities (if any) among the studies are evaluated and discussed.b. Differences (if any) among the studies are evaluated and discussed.IV. Conclusion/Summary effectively wraps up the review.a.Summarize points of comparison or contrast among the works based on Section IIIof your review.b.Provide insight of relationship between the topic of the review and a larger area ofstudy such as a specific discipline or professionFormat B organizes the literature review according to similarities and differences among research rather than by literature studied. In a review organized according to Format B, little background information on the literature being reviewed is given outright. Instead, it is worked into the body paragraphs of the sections on similarities and differences. The conclusion then uses these two sections (similarities and differences) to tie in points of comparison and contrast between the works. Format B better suits papers that are topically organized. Format B is outlined below.Format B OutlineI. Introduction consists of four parts usually discussed in one paragraph.a. Identify the general topic being discussed.b. Mention trends published about the topic.c. State thesis establishing the reason for writing the literaturereview.d. Explain criteria by giving a description of each of the criteria used in evaluating theliterature review and rationalizing its organizationII.Similiarities within the research are discussed.a. First similarity among research is discussed.b. Second similarity among research is discussed.c. Third similiarity among research is discussed.III. Differences in the research are discussed.a.First difference between research is discussedb.Second difference between research is discussedc.Third difference between research is discussedIV. Conclusion/Summarya. Summarize points of comparison or contrast between the works.b. Provide insight into relationship between the topic of the literature and a largerarea of study such as a specific discipline or profession.The most important thing to remember when organizing a literature review is that it is not a list summarizing one work after another. The review should be organized into sections according to theme that are set apart by subject-related headings. REVIEW1.Which format have you chosen for your literature review? Why?M A Literature Review Checklist: MDid I . . . . . . ?□ Establish a valid thesis based on the examined research□ State this thesis clearly in my introduction□ Define unfamiliar terms□ Incorporate background information to define the problem□ Begin each entry in the review with a complete bibliographical reference□ List and describe the hypothesis/thesis in each work reviewed□ Describe the outcome of the work or the research□ Develop and incorporate my own comments, including response to the research, similarities and differences among literature reviewed, and reservations regarding author’s methods or conclusions□ Avoid overquoting□ Check for grammar and punctuation errors□ Correctly cite all references in uniform documentation styleM Resources MBrightwell, G. and Shaw, J. (1997-98). Writing up research. RetrievedAugust 20, 2002 from Languages and Educational Development at theAsian Institute of Technology’s Web page at/doc/8b508cc25fbfc77da269b1c1.html nguages.ait.ac.th/EL21OPEN.HTMCentral Queensland University Library. (2000). The literature review. RetrievedJuly 22, 2003 from /doc/8b508cc25fbfc77da269b1c1.html .au/litreviewpages/Cuba, L. (2002). A short guide to writing about social science. New York:Addison-Wesley Publishers.Leibensperger, S. (2003). Setting the table: Encouraging collaborative environments with spatial arrangement in the writing center. Unpublished literature review.Northern Arizona University. (1999). Electronic textbook - A blast from thepast: Your literature review. Retrieved May 30, 2002 from/doc/8b508cc25fbfc77da269b1c1.html /~mid/edr720/class/literature/blast/reading2-1-1.htmlTaylor, D., & Procter, M. (2001). The literature review: A few tips onconducting it. Retrieved June 17, 2002 fromhttp://www.utoronto.ca/writing/litrev.htmlTrinder, L. (2002). Appendix. The literature review. Retrieved August 27, 2003/doc/8b508cc25fbfc77da269b1c1.html /~w071/teaching/ppf/Appendix%20Lit%20Review.pdfThe University of Wisconsin-Madison Writing Center. (2001). Academicwriting: Reviews of literature. Retrieved May 30, 2002 from/doc/8b508cc25fbfc77da269b1c1.html /writing/Handbook/ReviewofLiterature.html*In traditional APA style, this section would be entitled “References” and would be listed on a separate page double-spaced. Due to space constraints in this packet, it has been formatted differently.Copyright 2003 by the Academic Center and the University of Houston-Victoria.Created 2003 by Candice Chovanec-Melzow.。
英文文献综述写作要求和方法
DefinitionA literature review（文献综述）is both a summary and explanation of the complete and current state of knowledge on a limited topic as found in academic books （学术著作）and journal articles（期刊论文）. There are two kinds of literature reviews you might write at university: one that students are asked to write as a stand-alone assignment in a course, often as part of their training in the research processes in their field, and the other that is written as part of an introduction to, or preparation for, a longer work, usually a thesis or research report. The focus and perspective of your review and the kind of hypothesis（假设）or thesis argument you make will be determined by what kind of review you are writing. One way to understand the differences between these two types is to read published literature reviews or the first chapters of theses and dissertations（学位论文）in your own subject area. Analyze the structure of their arguments and note the way they address the issues.Purpose of the Literature Review∙It gives readers easy access to research on a particular topic by selecting high quality articles or studies that are relevant, meaningful, important and valid（有效的）and summarizing them into one complete report.∙It provides an excellent starting point for researchers beginning to do research ina new area by forcing them to summarize, evaluate, and compare originalresearch in that specific area.∙It ensures that researchers do not duplicate work that has already been done. 你所整理的文章中作者主要观察的重点是什么∙It can provide clues（线索）as to where future research is heading or recommend areas on which to focus. 现在的研究都到了什么程度∙It highlights key findings.∙It identifies inconsistencies（矛盾）, gaps and contradictions in the literature.∙It provides a constructive analysis of the methodologies and approaches of other researchers. 前面研究者的建设性的方法和途径Content of the ReviewIntroductionThe introduction explains the focus and establishes the importance of the subject（主题）. It discusses what kind of work has been done on the topic and identifies a ny controversies（争议）within the field or any recent research which has raised questions about earlier assumptions（假设）. It may provide background or history. It concludes with a purpose or thesis statement（中心思想）. In a stand-alone literature review, this statement will sum up and evaluate the state of the art （目前的工艺水平）in this field of research; in a review that is an introduction or preparatory to（为~~做准备）a thesis or research report, it will suggest how the review findings will lead to the research the writer proposes to undertake.Body（论文的内容）Often divided by headings/subheadings（标题/副标题）, the body summarizes and evaluates the current state of knowledge in the field. It notes major themes or topics, the most important trends, and any findings about which researchers agree or disagree. Ifthe review is preliminary to （在~~之前）your own thesis or research project, its purpose is to make an argument that will justify your proposed research. Therefore, it will discuss only that research which leads directly to your own project.ConclusionThe conclusion summarizes all the evidence presented and shows its significance. If the review is an introduction to your own research, it highlights gaps and indicates how previous research leads to your own research project and chosen methodology. If the review is a stand-alone assignment for a course, it should suggest any practical applications of the research as well as the implications and possibilities for future research.Nine Steps to Writing a Literature Review（九步法写综述）1. Find a working topic.Look at your specific area of study. Think about what interests you, and what fertile ground for study is. Talk to your professor, brainstorm, and read lecture notes and recentissues of periodicals（期刊）in the field.2. Review the literature.∙Using keywords search a computer database. It is best to use at least two databases relevant to your discipline.∙Remember that the reference lists of recent articles and reviews can lead to valuable papers.∙Make certain that you also include any studies contrary to your point of view.3. Focus your topic narrowly and select papers accordingly.Consider the following:∙What interests you?∙What interests others?∙What time span（时间跨度）of research will you consider?Choose an area of research that is due for a review.4. Read the selected articles thoroughly and evaluate them.∙What assumptions do most/some researchers seem to be making?∙What methodologies do they use? - What testing procedures, subjects, material tested?∙Evaluate and synthesize（综合）the research findings and conclusions drawn.∙Note experts（专家）in the field: names/labs that are frequently referenced.∙Note conflicting theories, results, and methodologies.∙Watch for popularity of theories and how this has/has not changed over time.5. Organize the selected papers by looking for patterns and by developing sub-topics. Note things such as:∙Findings that are common/contested（争论）∙Two or three important trends in the research∙The most influential theories6. Develop a working thesis.Write a one- or two-sentence statement summarizing the conclusion you have reached about the major trends and developments you see in the research that has been done on your subject.7. Organize your own paper based on the findings from steps 4 & 5.Develop headings/subheadings. If your literature review is extensive, find a large table surface, and on it place post-it notes（便签纸）or filing cards（档案卡）to organize all your findings into categories. Move them around if you decide that (a) they fit better under different headings, or (b) you need to establish new topic headings.8. Write the body of the paperFollow the plan you have developed above, making certain that each section links logically to the one before and after and that you have divided your sections by themes or subtopics, not by reporting the work of individual theorists or researchers.9. Look at what you have written; focus on analysis, not description.Look at the topic sentences of each paragraph. If you were to read only these sentences, would you find that your paper presented a clear position, logically developed, from beginning to end? If, for example, you find that each paragraph begins with a researcher's name, it might indicate that, instead of evaluating and comparing the research literature from an analytical point of view, you have simply described what research has been done. This is one of the most common problems with student literature reviews. So if your paper still does not appear to be defined by a central,Finishing Touches: Revising and Editing Your Work∙Read your work out loud. That way you will be better able to identify where you need punctuation marks（标点符号）to signal pauses or divisions withinsentences, where you have made grammatical errors, or where your sentences are unclear.∙Since the purpose of a literature review is to demonstrate that the writer is familiar with the important professional literature on the chosen subject, check to make certain that you have covered all of the important, up-to-date, andpertinent texts. In the sciences and some of the social sciences it is importantthat your literature be quite recent; this is not so important in the humanities.∙Make certain that all of the citations and references are correct and that you are referencing in the appropriate style for your discipline. If you are uncertain which style to use, ask your professor.∙Check to make sure that you have not plagiarized either by failing to cite a source of information, or by using words quoted directly from a source. (Usually if you take three or more words directly from another source, you should putthose words within quotation marks, and cite the page.)∙Text should be written in a clear and concise academic style; it should not be descriptive in nature or use the language of everyday speech.∙There should be no grammatical or spelling errors.∙Sentences should flow smoothly and logically.∙In a paper in the sciences, or in some of the social sciences, the use of subheadings to organize the review is recommended.。
综述怎么写
一、综述概述1．什么是综述：综述，又称文献综述，英文名为review。
它是利用已发表的文献资料为原始素材撰写的论文。
综述包括“综”与“述”两个方面。
所谓综就是指作者必须对占有的大量素材进行归纳整理、综合分析，而使材料更加精炼、更加明确、更加层次分明、更有逻辑性。
所谓述就是评述，是对所写专题的比较全面、深人、系统的论述。
因而，综述是对某一专题、某一领域的历史背景、前人工作、争论焦点、研究现状与发展前景等方面，以作者自己的观点写成的严谨而系统的评论性、资料性科技论文。
综述反映出某一专题、某一领域在一定时期内的研究工作进展情况。
可以把该专题、该领域及其分支学科的最新进展、新发现、新趋势、新水平、新原理和新技术比较全面地介绍给读者，使读者尤其从事该专题、该领域研究工作的读者获益匪浅。
因此，综述是教学、科研以及生产的重要参考资料。
2．综述的类型：根据搜集的原始文献资料数量、提炼加工程度、组织写作形式以及学术水平的高低，综述可分为归纳性、普通性和评论性三类。
(1)归纳性综述：归纳性综述是作者将搜集到的文献资料进行整理归纳，并按一定顺序进行分类排列，使它们互相关联，前后连贯，而撰写的具有条理性、系统性和逻辑性的学术论文。
它能在一定程度上反映出某一专题、某一领域的当前研究进展，但很少有作者自己的见解和观点。
(2)普通性综述：普通性综述系具有一定学术水平的作者，在搜集较多资料的基础上撰写的系统性和逻辑性都较强的学术论文，文中能表达出作者的观点或倾向性。
因而论文对从事该专题、该领域工作的读者有一定的指导意义和参考价值。
(3)评论性综述：评述性综述系有较高学术水平、在该领域有较高造诣的作者。
在搜集大量资料的基础上．对原始素材归纳整理、综合分析、撰写的反映当前该领域研究进展和发展前景的评论性学术论文。
因论文的逻辑性强，有较多作者的见解和评论。
故对读者有普遍的指导意义，并对读者的研究工作具有导向意义。
二、综述的书写格式综述与一般科技论文不同。
幼儿游戏英文文献综述范文
幼儿游戏英文文献综述范文英文回答：Introduction:In recent years, there has been growing interest in the role of games in early childhood education. Games have been found to be effective in promoting various aspects of child development, including cognitive, social, and physical skills. This literature review aims to explore the current research on early childhood games and their benefits.Cognitive Development:Research has shown that games can enhance cognitive development in young children. For example, puzzle games can improve problem-solving skills and logical thinking. Memory games can help children improve their working memory and attention span. Additionally, educational games that incorporate letters, numbers, and shapes can promote earlyliteracy and numeracy skills.Social Development:Games also play a crucial role in fostering social development in young children. Cooperative games, where children work together towards a common goal, can enhance teamwork and communication skills. Role-playing games can encourage imagination and empathy, as children take on different roles and interact with their peers. Furthermore, games that involve turn-taking and rule-following can teach children important social skills such as patience and fairness.Physical Development:Active games that involve physical movement are beneficial for promoting gross motor skills in young children. Games that require jumping, running, and balancing can help develop strength, coordination, and body awareness. Additionally, fine motor skills can be improved through games that involve manipulating small objects, suchas building blocks or puzzles.Conclusion:In conclusion, games have a significant impact on the development of young children. They can enhance cognitive, social, and physical skills, making them an effective tool in early childhood education. It is important for educators and parents to incorporate games into children's daily routines to maximize their developmental potential.中文回答：引言：近年来，人们对幼儿游戏在幼儿教育中的作用越来越感兴趣。
法学 英文文献
法学英文文献在法学领域，英文文献是研究和学习的重要资源。
以下是一些关于法学的英文文献综述。
1. "The Development of Environmental Law: A Comparative Analysis" - 本文综述了环境法的发展，探讨了不同国家环境法的异同，并对环境法的未来趋势进行了展望。
2. "The Evolution of Corporate Governance: A Global Perspective" - 本文回顾了公司治理结构的演变，探讨了不同国家和地区公司治理的差异，并分析了公司治理对企业发展的重要性。
3. "Human Rights Law: A Comprehensive Analy sis" - 本文对人权法进行了全面的分析，包括人权法的起源、发展、主要的人权公约以及人权法在实践中的应用。
4. "Intellectual Property Law: Key Issues and Ch allenges" - 本文讨论了知识产权法的重要问题和挑战，包括专利、商标、版权的保护范围、侵权行为以及知识产权的国际保护。
5. "Comparative Constitutional Law: A Study of Selected Countries" - 本文比较了不同国家的宪法法律制度，包括宪法的基本原则、权力机构的设置以及宪法的解释和适用。
6. "Criminal Law: Theory and Practice" - 本文综述了刑法的基本理论，包括犯罪、刑事责任、刑罚等概念，并分析了刑法在实践中的应用和挑战。
7. "Family Law: Trends and Reforms" - 本文讨论了家庭法的趋势和改革，包括婚姻、离婚、抚养权、家庭暴力等问题，并分析了不同国家和地区家庭法的差异。
文献综述
专题研究报告：专题研究报告是就某一专题,一般是涉及国家经
济、科研发展方向的重大课题,进行反映与评价,并提出发展对策、 趋势预测。“是一种现实性、政策性和针对性很强的情报分析研究 成果”。其最显著的特点是预测性,
1.4文献综述的形式特征
参考文献数量多
综述性文章的标题一般直接反映其综述类型,如包含
比较法：即把两种或两种以上的观点、措施、方法、技术、方案、
产品等的特点或指标，按照一定的标准进行定性、定量比较，以决定 优劣，通过横向、纵向比较，明确发展逻辑。这是阐明某一理论或成 果的理想方法。
历史法：即按照课题研究发展的时间顺序来分析研究各个阶段素
材，以发现各阶段的成就特点以及相关的影响因素，根据历史演变情 况，提出具体的建议和将来的发展趋势。
(1) 文献综述不是参考文献的简单罗列。
(2) 文献综述不是按时间顺序排列的流水帐。 (3) 文献综述不能包括与你的研究关系不大的文献。
3.文献综述举例
“综述”、“概述”、“述评”、“评述”、“进 展”、“动态”,或是“现状、趋势和对策”、“分 析与思考”等文字的标题,该文献一般是综述性文章。
1.5 文献综述的内容特征
综合性：综述要求对选题的有关原始文献进行高度综合（归纳、
浓缩、概括），这是综述的本质特征。内容的综合、语言
的概括
客观性：综述所叙述与提炼的理论、方法、观点、数据等，均
2.3综述的基本写作要求
1.一般字数控制在4000-6000字左右；
2.以评述为主，不可罗列文献； 3.基本格式通常包括题目、作者、摘要、关键词、前言、 正文、结语和参考文献等几个部分； 4.中文参考15-20篇，英文参考20篇左右，文献要新， 50％-80％最好为3年内的文献。 5.如果文献综述是为开题报告作准备，整篇文章建议为 漏斗状结构，即“有什么研究进展，问题是什么，怎 么找方向”。
技巧-文献综述的含义及实用撰写方法
技巧| 文献综述的含义及实用撰写方法一、文献综述的含义文献阅读报告，即“文献综述”，英文称之为“survey”、“overview”、“review”。
是在对某研究领域的文献进行广泛阅读和理解的基础上，对该领域研究成果的综合和思考。
一般认为，学术论文没有综述是不可思议的。
需要将“文献综述（Literature Review）”与“背景描述(Backupground Description)”区分开来。
我们在选择研究问题的时候，需要了解该问题产生的背景和来龙去脉，如“中国半导体产业的发展历程”、“国外政府发展半导体产业的政策和问题”等等，这些内容属于“背景描述”，关注的是现实层面的问题，严格讲不是“文献综述”，关注的是现实层面问题，严格讲不是“文献综述”。
“文献综述”是对学术观点和理论方法的整理。
其次，文献综述是评论性的（Review 就是“评论”的意思），因此要带着作者本人批判的眼光(critical thinking) 来归纳和评论文献，而不仅仅是相关领域学术研究的“堆砌”。
评论的主线，要按照问题展开，也就是说，别的学者是如何看待和解决你提出的问题的，他们的方法和理论是否有什么缺陷？要是别的学者已经很完美地解决了你提出的问题，那就没有重复研究的必要了。
二、意义和目的总结和综合该方向前人已经做了的工作，了解当前的研究水平，分析存在问题，指出可能的研究问题和发展方向等，并且列出了该方向众多的参考文献，这对后人是一笔相当大的财富，可以指导开题报告和论文的写作。
三、主要内容（1）该领域的研究意义。
（2）该领域的研究背景和发展脉络。
（3）目前的研究水平、存在问题及可能的原因。
（4）进一步的研究课题、发展方向概况。
（5）自己的见解和感想。
四、分类综述分成两类。
一类是较为宏观的，涉及的范围为整个领域、专业或某一大的研究方向；一类是较为微观的，这类综述可以涉及到相当小的研究方向甚至某个算法，谈的问题更为具体与深入。
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石墨烯外延生长及其器件应用研究进展高材1103刘铭2011012074 摘要:石墨烯具有优异的物理和电学性能, 已成为物理和半导体电子研究领域的国际前沿和热点之一. 本文简单介绍了石墨烯的物理及电学特性, 详细评述了在众多制备方法中最有希望实现石墨烯大面积、高质量的外延生长技术, 系统论述了不同SiC 和金属衬底外延生长石墨烯的研究进展, 并简要概述了石墨烯在场效应晶体管、发光二极管、超级电容器及锂离子电池等光电器件方面的最新研究进展. 外延生长法已经初步实现了从纳米、微米、厘米量级石墨烯的成功制备, 同时可实现其厚度从单层、双层到少数层的调控, 有望成为高质量、与传统电子工艺兼容、低成本、大面积的石墨烯宏量制备技术, 为其器件应用奠定基础.关键词: 石墨烯、外延生长、器件、进展;2004年, 英国Manchester大学的安德烈·海姆和康斯坦丁·诺沃肖洛夫[1]通过胶带剥离(亦称微机械力分裂法: Microfolitation)高定向石墨, 首次制备出独立存在的、只有一个原子层厚度的二维晶体结构—石墨烯. 它推翻了“完美二维晶体结构无法在非绝对零度下稳定存在”的定论, 开启了一扇基于二维体系的理论和实验研究大门. 石墨烯因其晶体和电子结构而具有独特的物理现象, 被认为是未来新一代的半导体材料, 在高性能纳电子器件、复合材料、场发射材料、气体传感器及能量存储等领域具有广阔的应用前景.1 石墨烯基本特性Partoens 等[2]研究发现, 当石墨的堆垛原子层数少于10个单原子层时, 石墨层就会具有与普通三维石墨不同的电子结构. 一般将10层以下的石墨结构统称为石墨烯. 单层石墨烯的晶体结构如图1(a)所示[3], 是由碳六元环组成的两维(2D)周期蜂窝状点阵结构, 厚度只有0.335nm, 相当于头发丝直径的1/200000. 它可以翘曲成零维(0D)的富勒烯(Fullerene)(图1(b)), 卷曲成一维(1D)的碳纳米管(Carbon Nanotube, CNT)(图1(c))或者堆垛成三维(3D)的石墨(Graphite)(图1(d)). 因此, 石墨烯被认为是构成其它碳材料的基本单元.1.1 力学特性石墨烯是目前已知最薄的材料, 厚度仅有0.335nm. 其C−C 键仅为0.142nm, 石墨烯中的每个碳原子与其它3个碳原子通过强σ键相连[4], C−C键(sp2)使其成为已知最为牢固的材料之一. 它比钻石还坚硬, 强度比钢铁高100 倍. 石墨烯内部的碳原子之间的连接很柔韧, 当施加外力于石墨烯时, 碳原子面会弯曲变形, 使得碳原子不必重排以适应外力, 从而保持结构的高稳定性. 迄今为止, 尚未发现石墨烯中有碳原子缺失的情况, 即六边形晶格中的碳原子均未丢失或发生移位. 稳定的晶格结构还赋予了石墨烯优异的导热性. 石墨烯因其优异的力学特性(石墨烯的力弹性系数为105N/m, 杨氏模量达0.5TPa[4]), 有望解决微型处理器制造过程中所遇到的压力问题, 再加上其出色的电子特性, 有望成为未来制造微型处理器的首选材料[5].1.2 电学性质碳原子有4 个价电子, 其中 3 个电子生成sp2键, 即每个碳原子贡献一个未成键的电子位于pz轨道, 近邻原子的pz轨道与平面成垂直方向形成π键, 为半填满状态, 电子可在二维晶体内自由移动, 因此石墨烯具有良好的导电性[6]. 其电子以光速的1/300 移动, 具有相对论粒子特性[7], 并可不通过散射而进行亚微细距离移动, 使得隧道单分子晶体管的设想成为现实. 另外, 其电子在轨道中移动时, 不会因晶格缺陷或引入外来原子而发生散射. 鉴于原子间作用力十分强, 在常温下, 即使周围碳原子发生挤撞, 石墨烯内部电子输运受到的干扰也非常小. 它的电子迁移率在室温下可以超过15000cm2/(V·s)[7], 即使在电场引起的非平衡载流子浓度非常高的情况下, 其迁移率依然保持一个很高的值; 而且, 研究表明单层石墨烯中载流子的迁移速率受温度及化学掺杂的影响很小[8]. 石墨烯的价带(π电子)和导带(π∗电子)相交于费米能级处(K 和K′点), 即形成所谓狄拉克锥结构(Dirac cones)(图2), 是能隙为零的半导体, 为目前已发现的电阻率最小的材料. 在费米面附近的传导电子(π键电子)具有线性色散关系[7,9-10], 这导致了石墨烯在费米面附近的传导电子遵从相对论量子力学中的有效质量为零的Dirac 方程[10-11], 成为凝聚态物理学中验证相对论理论及无质量狄拉克费米子的天然理想模型. 石墨烯独特的载流子特性和无质量的狄拉克费米子属性使其能够在室温下观测到霍尔效应[12]. 另外, 石墨烯还具有量子隧道效应及半整数霍尔效应[13]、安德森局域化的弱化现象、永不消失的电导率等特性. 此外, 石墨烯还具有其它一些优异的物理化学特性, 如高吸附性、高化学稳定性, 高达2630m2/g的理论比表面积[14]、图1 (a)石墨烯, (b)富勒烯, (c)碳纳米管, (d)石墨的晶体结构[3]Fig. 1 Crystal structure of (a) graphene, (b) fullerene, (c)carbon nanotube and (d) graphite[3]铁磁性[15-16]、良好的导热性(3080~5150W/(m·K))[17]等. 最近研究发现, zigzag 边缘的石墨烯还具有光致发光现象[18-19]. 这些优良性质不仅为凝聚态物理和量子电动力学提供了较好的研究平台, 还使其有可能替代Si 材料而成为新一代计算机芯片材料, 具有广泛的应用潜力.2 石墨烯的制备自海姆等采用胶带剥离法制得石墨烯以来, 新的石墨烯的制备方法层出不穷, 如: 化学剥离法[20]、化学刻蚀法[21]、离子体刻蚀法[22]、电化学法[16]、电弧法[23]、溶剂热法[24]等. 然而, 低成本、大面积、高质量的石墨烯的宏量制备技术仍是当前此领域所面临的主要困难和挑战. 据文献报道, 其制备方法大致可分为物理法和化学法两大类. 鉴于已有对石墨烯胶带剥离和氧化石墨还原制备的综述报道[25-30], 本论文将侧重评述石墨烯的外延生长. 所谓外延法, 即在一个晶体结构上通过晶格匹配生长出另一种晶体的方法. 与其它制备方法相比较, 外延法是最有可能获得大面积、高质量石墨烯的制备方法. 所获得的石墨烯具有较好的均一性, 且与当前的集成电路技术有很好的兼容性, 因此成为石墨烯制备科学的研究前沿与热点, 已列为我国2011 年重大科技研究计划之一. 根据所选基底材料的不同, 外延法一般分为SiC 外延法和金属外延法(均属异质外延).2.1 SiC 外延法早在20 世纪90 年代中期, 人们就已发现SiC单晶加热至一定的温度后, 会发生石墨化现象. SiC 单晶外延生长石墨烯的基本工艺如下: 首先把经过氧化或H2刻蚀处理过的SiC 单晶片置于超高真空和高温环境下, 利用电子束轰击SiC 单晶片, 除去其表面氧化物; 然后在高温条件下将其表面层中的Si 原子蒸发, 使表面剩余的碳原子发生重构, 即可在SiC 单晶片表面外延生长石墨烯. 简单地说, 就是通过超高真空高温加热单晶SiC 脱除Si, C 原子重构生成石墨烯片层. 当对其工艺参数进行调控, SiC 外延法还可实现单层[31]和多层石墨烯[32]的可控制备. SiC 外延生长石墨烯所用到的SiC 单晶基片包括6H、4H、3C 等晶型, 其研究进展概况如表 1 所示. SiC 外延法在技术上有一定优势, 可得到单层或少数层较为理想的石墨烯, 且SiC本身就是一种性能优异的半导体材料, 与目前的Si 基半导体工艺相兼容(不需要转移), 因此这种方法生长的石墨烯是最有可能实现 C 基集成电路的有效途径之一. 其缺点是: 目前还难以实现大面积制备、能耗高、不利于后续石墨烯的转移(需要转移的时候, 很难做到只腐蚀基底SiC 而不破坏石墨烯结构).2.2 金属表面外延法采用与石墨烯晶格匹配的金属单晶体为基底(如Ru(0001)、Ni(111)、Ir(111)、Pt(111)等), 在高真空环境中, 热解含碳化合物(例如: 乙烯、乙炔、苯、吡啶等), 通过调控和优化制备工艺参数, 石墨烯可望均匀铺满整个金属基底, 达到大面积制备的目的, 在亚原子单层的沉积速率控制下, 可望获得高质量近零缺陷的石墨烯. 金属外延法基本特点是: 所制备的石墨烯大多具有单层结构, 能够生长连续、均匀、大面积的单层石墨烯, 因此其研究已经成为当前的研究热点之一. 较之SiC 外延法, 金属外延的石墨烯还具有易于转移的优点(通过化学腐蚀去掉金属基底). 其基本生长机理如下: 在高真空/H2气氛条件下, C 和金属的亲和力比Si、N、H 和O 等元素的高, 因而Si 和H 元素均可被脱除, 而溶解在金属表面中的C 则在其表面重新析出结晶重构生长出石墨烯.研究表明: 在石墨烯生长过程中, 当第一层石墨烯覆盖金属表面大约80%时, 第二层石墨烯才开始生长. 底层石墨烯会与衬底产生强烈的相互作用[49], 而第二层与衬底之间只受到弱电耦合的作用, 可以与金属衬底完全分离, 得到的单层石墨烯具有较好的电学性质. 一旦当其表面被石墨烯完全覆盖后, 石墨烯的生长立即停止, 表现出自限制生长模式. 因此, 通过选择合适的金属衬底和工艺参数, 即可实现大面积、高质量的石墨烯可控制备. 但金属外延法制备的石墨烯的形貌和性能受金属衬底的影响较大, 在晶格失配的过渡金属基底上, 石墨烯的起皱程度由界面处的化学键强度决定, 强化学键和晶格失配将导致石墨烯的高皱折度. 据文献报道, 金属和石墨烯界面处的轨道杂化程度为: Pt(111)<Ir(111)<Rh(111)<Ru(001)[50].3 石墨烯器件应用3.1 超级电容器超级电容器是一个高效储存和传递能量的体系, 它具有功率密度大、容量大、使用寿命长、经济环保等优点, 广泛应用于各种能源领域. 石墨烯具有理论比表面积高达2630m2/g、优异的导电性能和稳定性等, 作为电容器材料具有比单壁和多壁碳纳米管更优异的性质, 使其有望成为超级电容器的理想电极材料[69], 其性能与石墨烯的质量、层数和比表面积直接相关. Wang 等[70]通过肼还原氧化石墨烯得到的石墨烯在含水电解质溶液中的比电容可高达205F/g, 经过1200 次的试验后其比电容还仍达到原来的90%, 其石墨烯电容器如图 5 所示. 吴忠帅等[71]采用溶胶−凝胶法和低温处理方法设计合成了一种水合氧化钌/石墨烯复合超级电容器电极材料, 研究表明具有较高的比容量(570F/g)和优异循环稳定性(1000 次循环后容量保持率为97.9%). 石墨烯表面可以形成双电层, 有利于电解液的扩散, 因此基于石墨烯的超级电容器具有良好的功率特性.3.2 场效应晶体管在石墨烯众多的电子器件应用当中, 场效应晶体管(Field-Effect Transistors: FET)是其代表之一[1]. 制作体积更小, 频率更高, 运算速度更快的晶体管是当前微电子研究领域的热点和重点, 也是进一步延续摩尔定律的重要保证. 石墨烯因其超薄结构以及优异的物理特性, 在FET 应用上展现出了优异的性能和诱人的应用前景. 如Obradovic 等研究发现, 与碳纳米管相比, 石墨烯FET 拥有更低的工作电压[79]; Wang 等所制备的栅宽10nm 以下的石墨烯带FET 的开关比达107[80]; Wu 等[81]采用热蒸发4H-SiC 外延生长的石墨烯制备的FET, 其电子和空穴迁移率分别为5400 和4400 cm2/(V·s), 比传统半导体材料如SiC 和Si 高很多; Lin 等[82]制备出栅长为350nm 的高性能石墨烯FET, 其载流子迁移率为2700cm2/(V·s), 截止频率为50GHz, 并在后续研究中进一步提高到100GHz[83](图6); Liao 等[84]所制备的石墨烯FET 的跨导达 3.2mS/μm, 并获得了迄今为止最高的截止频率300GHz[85], 远远超过了相同栅长的Si-FET(~40GHz).然而, 由于石墨烯的本征能隙为零, 并且在费米能级处其电导率不会像一般半导体一样降为零, 而是达到一个最小值, 这对于制造晶体管是致命的, 因为石墨烯始终处于“开”的状态. 另外, 带隙为零意味着无法制作逻辑电路, 这成为石墨烯应用于晶体管等器件中的主要困难和挑战. 因此, 如何实现石墨烯能带的开启与调控, 亟待研究和解决. 据文献报道, 一般采用两种方法实现石墨烯能带的开启与调控, 即: 掺杂改性[86]和形貌调控[87]. Nature Nanotechnology 评论明确指出[88]: 要深入挖掘石墨烯的优异物理特性, 以制备高性能石墨烯FET, 其重要基础和关键之一是获得宽度与厚度(即层数)可控的高质量石墨烯带状结构. 带状石墨烯因其固有而独特的狭长“扶椅”或“之”状边缘结构效应、量子限域效应而具有丰富的能带结构[89], 其能隙随着石墨烯的宽度减小而增大[90], 且和石墨烯的厚度密切相关[91], 成为石墨烯FET 沟道材料的理想选择. 据文献报道, 最具代表性的制备石墨烯带的方法有: 化学气相沉积法[92]、纳米结构模板法[93]、化学腐蚀多壁碳纳米管法[94]、等离子体刻蚀多壁碳纳米管法[95]等. 然而, 上述方法难以实现石墨烯带状结构的精细控制. 以腐蚀与刻蚀碳纳米管为例, 最终获得的石墨烯带实际上依赖于原碳纳米管的直径, 且其带状结构的产率有待提高. 如何实现石墨烯带高质量大面积生长及其宽度和厚度控制, 是当前面临的困难和挑战.3.3 发光二极管的电极材料氧化铟锡(ITO)作为传统电极, 广泛应用于太阳能电池、发光二极管(LED)和有机发光二极管(OLED)等领域. 由于铟元素在地球上的含量有限, 价格昂贵, 特别是其毒性大, 使其应用受到限制. 另外, ITO 在蓝光、紫外和近红外光范围内的透明度较差, 在酸或强碱中不稳定, 离子容易扩散到基底等缺点, 因此研发一种可取代ITO 的电极材料显得尤为重要. 石墨烯具有高透明度(几乎完全透明, 只吸收不到2.3%的太阳光[96])和优异电学性能, 使其有可能成为ITO 的理想替代材料. Kim 等[56]的研究证明其还是制作柔性透明电极的理想材料: 他们通过用化学气相沉积法(CVD)在300nm的Ni薄膜上生长石墨烯, 并将其成功转移到其它衬底, 其透光率达80%. 如果进一步减少生长时间和Ni 层厚度, 石墨烯的透明度有望提高到93%. Jo 等用CVD 法在Ni 薄层上生长多层石墨烯(MLG), 其电阻约为620Ω, 在400~600nm波长范围内的透明度高于85%. Wu 等[98]将MLG 用作氮化镓(GaN)基蓝光LEDs 的透明传导电极(如图7 所示), 并与GaN 基LEDs 的传统电极ITO 做了比较: 在输入电流小于10mA 时, MLG 为电极与ITO 为电极的GaN 基LEDs 的输出功率相当; 在输入电流大于10mA 时, 相比ITO, MLG 可降低电极接触电阻和表面电阻. 通过进一步优化石墨烯的质量和厚度, 有望进一步提高发光二极管的性能, 其核心问题是如何将高质量的石墨烯转移到低成本的塑料基底上. Kim 等[99]首次将石墨烯应用于GaN 紫外发光二极管(UV-LED)的透明传导电极. 石墨烯基透明传导电极相对于ITO(11~ 12 W/m·K)和标准的Ni/Au 金属化电极来说, 具有高导热系数(~5000W/(m·K))和较好的紫外传递能力.3.4 锂离子电池正极材料锂离子电池的能量密度和性能主要取决于阴阳极材料的物理化学特性. 商业锂离子电池的阳极材料主要是石墨, 但由于其理论比容量低(只有372mAh/g), 无法满足便携式电子设备和电动车的需求. 石墨烯被发现后, 立即引起了锂离子电池研究领域的关注.石墨烯在锂离子的存储方面表现出优异的电化学性能. 相对于石墨而言, Yoo 等[100]研究发现, 石墨烯的比电容(540 mAh/g)更高, 当在石墨烯纳米片层中掺入大分子的CNTs和C60后, 其比电容分别提高到730和784mAh/g. Lian等[101]的研究表明, 以石墨烯为阳极材料的锂离子电池具有更加优异的性能(如图8所示): 在电流密度为100mA/g时, 其可逆比电容高达1264mAh/g; 在循环使用40 次后, 可逆比电容仍保持在848mAh/g; 甚至在电流密度高达500mA/g 时, 其可逆比电容仍然可达到718mAh/g. 石墨烯的高可逆容量, 高循环性能和高充放电速率等优异特性, 使得石墨烯有望成为电池阳极材料的优异候选材料之一.4 结束语近几年, 石墨烯在微电子、量子物理、材料、化学等领域都表现出许多独特而优异的性能和潜在的应用前景, 在超级电容器、场效应晶体管、发光二极管、锂离子电池等器件应用方面取得了较好的研究成果和进展. 迄今为止, 石墨烯研究和应用的重点和难点之一依然是其大规模、低成本、可控生长和制备. 在众多的石墨烯制备方法中, 外延生长法有望成为高质量、与传统电子工艺兼容、低成本、大面积的宏量制备技术, 已经初步实现了从纳米、微米、厘米石墨烯的成功制备, 同时可实现石墨烯从单层、双层到少数层的调控. 相信在众多科研工作者的不断努力之下, 石墨烯改变人们的生活将不再遥远.参考文献:[1]Lee C, Wei X, Kysar J, et al. Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science, 2008, 321(5887): 385−388.[2]Wang G, Yang J, Park J, et al. Facile synthesis and characterization of graphene nanosheets. J. Phys. Chem. C, 2008. 112(22): 8192−8195.[3]Balandin A, Ghosh S, Bao W, et al. Superior thermal conductivity of single-layer graphene. Nano Lett., 2008, 8(3): 902−907.[4] Li X, Wang X, Zhang L, et al. Chemically derived, ultrasmooth graphene nanoribbon semiconductors. Science, 2008, 319(5867): 1229−1232.[5] Jiao L, Zhang L, Wang X, et al. Narrow graphene nanoribbons from carbon nanotubes. Nature, 2009, 458(7240): 877−880.[6] Kosynkin D, Higginbotham A, Sinitskii A, et al. Longitudinal un-zipping of carbon nanotubes to form graphene nanoribbons. Nature, 2009, 458(7240): 872−876.[7] Subrahmanyam K, Panchakarla L, Govindaraj A, et al. Simple method of preparing graphene flakes by an arc-discharge method. J. Phys. Chem. C, 2009, 113(11): 4257−4259.[8] Choucair M, Thordarson P, Stride J. Gram-scale production of graphene based on solvothermal synthesis and sonication. Nat. Nanotechnol., 2008, 4(1): 30−33.[9]VanMil B L, Myers-Ward R L, Tedesco J L, et al. Graphene for-mation on SiC substrates. Mater. Sci. Forum, 2009, 615−617: 211−214.[10] Camara N, Huntzinger J, Rius G, et al. Anisotropic growth of long isolated graphene ribbons on the C face of graphite-capped 6H-SiC. Phys. Rev. B, 2009, 80(12): 125410−1−8.。