Ch.12 Quality

英语字母及字母组合的发音规则一元音字母的发音规则1. 字母Aa的发音：重读开音发/e / name face plane grape snake game classmate table baby sale重读闭音发/ / bag black thank panda rabbit apple grandpa and can lamp fan lamb carrot trash flat ant dad manfamily fat happy轻读发/ / about panda elephant America banana umbrella sofa vegetable轻读发/ / orange village cabbage重读发/ɑ:/ ask fast task answer after father giraffe class banana grass在/w/后面发/ / want what watch wash quality / kw l t / 质量;品质例外water / :/重读发/e/ any many anything anyone anybody anyway重读发/e / parents various / ve r s /各种各样的2. 字母Ee的发音：重读开音发/i:/ he she we these even complete完成 compete竞赛;竞技重读闭音发/e/ pen pencil ten red yellow elephant seven well yes very tell sell desk umbrella bed help chessmenu fresh set get轻读发/ / open problem children quiet science parents轻读发/ / eraser eleven because before decide report design prepare重读发/ / period/ p r d/ 时段;时期3. 字母i y的发音：重读开音发/a / fine five nine kite time like knife drive ride climb child kind nice write white type skywhy my try bye fly重读闭音发/ / six it is pig milk gift this sister fish big picture window fridge English thin ill dishriver visit listen tip shipy字母轻读时发/ / friendly usually happy easy healthy funny busy i轻读发/ / terrible possible pencil cousini重读发/i:/ police/p li:s/警察 magazine/m g zi:n/杂志machine/m i:n/ 机器 unique /ju: ni:k/唯一的;独特的technique /tek`ni:k/技巧4. 字母Oo的发音：重读开音发/ / nose go open yo-yo no photo phone home those over close重读闭音发/ / dog hot coffee doll from lock orange box long doctor sockshop God strong office not stop often hobby drop 重读闭音发/ / son monkey mother come some colour love doesmoney company become ton other another brother 轻读发/ / second to day com puter to day to morrow to mato重读发/u:/ do shoes to move移动 remove去除 tomb/tu:m/坟墓o不发音： season reason三个o特殊发音的单词：woman / / women / / one /w /5. 字母Uu的发音：重读开音发/ju:/ use useful usually cute duty music computer重读闭音发/ / bus but sun sunlight supper fun cut duck gun jump runhug study重读闭音发/ / pull push bush put full bull公牛轻读发/ / autumn succeed/s k si:d/成功动 success suggest/s d est/建议重读开音发/u:/ super blue ruller glue June true rude重读发/j / during/ dju r /在…期间 curious / kju r s/好奇的两个u特殊发音的单词: busy/ b z / 忙的 bury / ber / 埋葬二元音字母与r字母组合的发音规则1. ar字母组合的发音：重读发/ɑ:/ are car card farm arm start art garden sharpener smart far park hard alarm party March mark dark轻读发/ / sugar/ g /糖 dollar美元在w后发/ :/ warm warn war quarter/ kw :t /一刻钟；四分之一2. er字母组合的发音：重读发/ :/ certainly serve term person轻读发/ / sharpener hamburger under teacher tiger farmer driver summer3. ir字母组合的发音重读发/ :/ bird third thirteen thirty girl first dirty firm4. or字母组合的发音重读发/ :/ short fork sport morning report for born horse轻读发/ / doctor vistor actor for get monitor班长在w后发/ :/ work word world worth值得的 worm蠕虫5. ur字母组合的发音重读发/ :/ purple turn nurse hurt hamburger Thursday Saturday curtain帘子轻读发/ / surprise惊讶 surround/s raund/包围 survive存活三字母a与其它字母组合的发音规则1. ai字母组合的发音：重读发/e / paint rain rainbow tail wait train轻读不发音 certain certainly Britain curtain特殊发音：said /e/2. au字母组合的发音：重读发/ :/ August cause fault autumn pause sauce调味汁 sausage 香肠发/ / because Australia发/ɑ:/ aunt laugh3. al字母组合的发音：/ :/ small tall fall talk walk/ :l/ always almost already salt altogether/ɑ:/ half calm镇定;平静4. aw字母组合的发音：重读发/ :/ draw paw爪子 saw law法律 dawn黎明 crawl爬行5. air字母组合的发音：发/e / air chair hair airport repair pair upstair6. are字母组合的发音：发/e / prepare share care careful dare敢7. augh字母组合的发音：发/ :/ taught teach的过去式 caught catch的过去式 daughter女儿naughty淘气的发/ɑ:f/ laugh8. ay字母组合的发音：重读发/e / day today pay play say way away may May hoo ray好哇;万岁轻读发/ /holiday Monday Tuesday Wednesday Thursday Friday Saturday Sunday特殊发音：says /e/四字母e与其它字母组合的发音规则1. ea字母组合的发音：发/i:/ teacher teach peach seat team clean please read jeans cheap speak leave easy eat发/e/ bread dead head heavy health healthy ready weather weather发/e / great break steak牛排发/ / real really idea2. ee字母组合的发音：发/i:/ meet three queen jeep see sheep tree feel feet bee3. ear字母组合的发音：发/ / ear hear near dear clear fear year发/ :/ heard hear的过去式 learn early search寻找 research研究;调查发/e / pear bear wear穿;戴特殊发音的单词：heart /ɑ:/心脏;心4. ei字母组合的发音：重读发/e / neighbour / ne b /邻居重读发/i:/ receive收到 seize抓住 ceiling天花板轻读发/ / foreign/ f r n/外国的 foreigner外国人5. ew字母组合的发音：发/ju:/ few new news newspaper报纸发/u:/ blew吹blow的过去式 flew飞fly的过去式threw扔throw的过去式 crew全体船员发/ / sew 缝纫6. ere字母组合的发音：发/ / here sincere/s n s /真诚的 mere仅仅;只是发/e / there where7. eer字母组合的发音：发/ / deer beer cheer peer同龄人;同伴 engineer/ end n /工程师8. ey字母组合的发音：重读发/e / they hey obey遵守 grey灰色重读发/ i:/ key轻读发/ / honey monkey donkey money valley山谷 volleyball排球9. eigh字母组合的发音：发/e / eight eighteen eighty weigh weight特殊发音：height /a / 高度10. ex字母组合的发音：发/ ks/ ex press表达 ex pressoion ex plain解释 ex pensive贵的 ex periment实验发/eks/extra额外的excellent极好的exercise练习;运动exit出口发/ gz/ exam考试 exact确切的五字母i与其它字母组合的发音规则1. ie字母组合的发音：发/i:/ piece片;块 be lieve field田地 thief小偷 chief主要的;长官niece侄女发/a / die lie tie发/a / quiet diet饮食 science科学发/ / fierce凶猛的2. ire字母组合的发音：发/a / tire使累 hire雇佣 wire电线 in spire激励 desire渴望admire崇拜3. igh字母组合的发音：发/a / right fight high night bright light might may 的过去式六字母o与其它字母组合的发音规则1. oa字母组合的发音：发/ / boat goat goal coat road load载重;载入发/ :/ broad宽阔的 abroad在国外2. oar字母组合的发音：发/ :/ board板 blackboard roar咆哮;怒吼 soar高飞3. oi和oy字母组合的发音：发/ / boy toy joy enjoy oil油 noise吵闹声 noisy boil煮沸;沸腾;水开4. oo字母组合的发音：发/ / 记住这些单词：book good goodbye look cook煮;烹饪 wood木头foottook understood stood hook 钩子 hoo ray好哇;万岁发/u:/ afternoon ballnoon too food school noon room noodlespoon bootssoon cool tool fool moon发/ / 记住两个单词：flood洪水 blood血5. oor字母组合的发音：发/ :/ 记住两个单词：floor地板 door发/ / 记住这个单词：poor贫穷的6. ou字母组合的发音：发/a / mouth cloud mouse sound house mountain about countsouth round发/ / enough/ n f/ 足够的 cousin country发/u:/ you soup group routine/ru: ti:n/常规工作发/ / shoulder肩膀 soul心灵发/ /记住这个单词cough /k f/ 咳嗽轻读发/ / dangerous危险的 famous出名的 humorous幽默的7. ough字母组合的发音：发/ :/ foughtfight的过去式 thoughtthink的过去式 broughtbring的过去式boughtbuy的过去式记住这些特殊发音的单词：though/e /尽管;即使 plough /pla /耕地through/θru:/ 穿过;通过介词thorough / θ r / 彻底的;完全的8. our字母组合的发音：发/a / our hour flour面粉发/ / tour 旅途;旅行 tourist游客轻读发/ / humour幽默 colour favour赞同;喜爱 neighbour邻居9. ow字母组合的发音：发/a / brown how flower down now发/ / rainbow window know snow follow show flow水流;流动特殊发音的单词：knowledge / n l d / 知识10. ure字母组合的发音：重读发/ / sure确信的;的确 surely en sure使确信重读发/j / cure治愈 ma ture成熟的 se cure安全的轻读发/ / pleasure/ ple /高兴 measure/ me /尺寸;措施 treasure/ tre/财宝七辅音字母的发音规则Bb /b/ Cc 在a; o和u前发/k/；在e和i前发/s/ Dd /d/ Ff /f/ Gg /g//d /Hh /h/ Jj /d / Kk /k/ Ll / / Mm /m/ Nn /n/ / / Pp /p/ /k/Rr /r/ Ss /s/ /z/ / / / / Tt /t/ Vv /v/ Ww /w/ Xx /ks/ /gz/ Yy /j/ Zz /z/八需特别注意的辅音字母的发音规则1. c字母的特殊发音：c在单词中间;ia和ie前发/ / social社会的;社交的 official官方的mu sician音乐家 ancient/ e nt/古代的2. g字母的特殊发音：garage / g rɑ: / 车库；修车间3. s字母的特殊发音：/ / sure sugar Russia Asia/ / usual usually pleasure measure treasure4. n字母的特殊发音：n在/k/和/g/前面发/ / think thank angry bank language5. x字母的发音：在结尾或辅音前发/ks/ box fox text except expert export在元音前发/gz/ exam exact example发/k / anxious / k s/焦虑的；焦急的6. l字母的两种发音：l后面有元音就发/ / 了 look like fly love family live friendlyl后面没有元音就发/ /猴 apple people beautiful fall film salt help九需特别注意的辅音字母组合的发音规则1. ng字母组合在词尾发/ / thing something sing song long strong wrong young2. ch字母组合的发音：发/t / teacher peach chance church beach cheer cheap chip ouch 发/k/ school ache痛 technology /tek n l d /技术 chemistry / kem str /化学发/ / machine /m i:n/ 机器 moustache /m stɑ: / 小胡子发/d / sandwich 三明治3. ck字母组合发/k/ cock duck clock chicken kick Jack back black lock pick4. tch字母组合发/t / match 比赛；匹配 catch 抓住 fetch 去拿来5. th字母组合的发音：发/θ/ think thank fourth thing thin three third fifth发/e/ they this that with there these those father mother brother6. qu字母组合发/kw/ quite quiet quick quiz question quarter quality7. que字母组合发/k/ technique /tek ni:k/技巧 cheque /t ek/支票unique/ju: ni:k/ 唯一的;独特的8. ph字母组合发/f/ elephant photo telephone9. gh字母组合发/f/ enough 足够的 tough 强壮的;威猛的 rough 粗糙的cough咳嗽10. kn字母组合发/n/;k不发音 knife know knee膝盖 knit编织 knot结;打结11. wr字母组合发/r/;w不发音 wrong write wrap包裹 wrinkle皱纹；起皱12. wh字母组合的发音：发/w/ what white why which when where wheel车轮发/h/ who whose whom whole整个13. ture字母组合轻读发/t / picture culture/ k lt /文化 future/ fju:t /未来temperature/tempr t /温度14. tion字母组合的发音：发/ n/ station车站 nation国家;民族 action动作 education/ edju: ke发/t n/ 记住这两个单词：question suggestion /s d est n/ 建议15. ssion或sion字母组合的发音：发/ n/ expression/ ks pre n/表达;表情 impression/ m pre n/印象intension/ n ten n/专心致志发/ n/ decision/d si n/决定 explosion/ ks pl n/爆炸conclusion/k nk lu: n/结论 decision/d s n/决定十单词附加词尾的发音规则英语中单词的附加词尾主要有：名词的复数形式;动词的第三人称单数形式;动词的-ed形式;动词的-ing形式;和形容词的比较级和最高级形式..其中名词的复数和动词的三单形式在x; s; z; sh; ch结尾的单词后面加es; 其它直接加s..其中动词的-ed和-ing形式碰到重读闭音节时要双写最后一个辅音再加ed或ing;如：banned;hugged; beginning; digging..这些附加词尾的读音都有一定的读音规则..其中形容词的比较级和最高级略..备注：同学们;这是老师花了好几个晚上整理出来的;直到高中仍旧有用;希望你们能够妥善地保管这份资料;要经常抽空读一读;看一看;想一想..慢慢地;你们就能理解并掌握这些拼读规则了..学好英语;积累单词是关键那么就从掌握单词的拼读规则开始吧;它会让你学得轻松;记得牢固..。

2009年4月A pr il 2009岩 矿 测 试ROCK AND M I N ERA L ANALY SIS V o.l 28,N o .2157~160收稿日期:2008-04-30;修订日期:2008-09-03基金项目:国土资源地质大调查项目资助(200120190107-05);地质调查工作项目)))地下水有机污染物分析方法研究项目资助(121201063460);国家地质实验测试中心基本科研业务项目资助(2008CSJ02)作者简介:李松(1978-)男,北京市人,工程师,分析化学专业。

E -m ai:l ccagv ip @163.co m 。

文章编号:0254-5357(2009)02-0157-04地下水有机污染物分析测试技术专栏地下水中12项半挥发性有机污染物测定的质量控制李 松,饶 竹(国家地质实验测试中心,北京 100037)摘要:以正己烷液-液萃取、气相色谱(电子捕获检测器)和高效液相色谱(紫外、荧光检测器)检测地下水调查样品中12项半挥发性有机污染物组分的分析为例,从水样的储存、气相色谱进样口活性评定、试剂空白检查、萃取过程中乳化现象的消除等方面总结出一些经验。

参照美国EPA 方法中QA /QC 的经验,建立了全国地下水调查样品中半挥发性有机污染物分析过程的质量控制流程程序,通过引用质量控制图直观评价批量样品分析的满意度,实现了分析流程的受控状态。

关键词:半挥发性有机污染物;地下水;质量控制;经验交流中图分类号:O213.1;O656.31 文献标识码:BQuality Control for t he Deter m ination of 12Se m -i volatile Organic Poll utants i n Groundwater Sa mplesLI Song,RAO Zhu(Nati o nal Research C enter f o r Geoanal y si s ,Beiji n g 100037,Chi n a)Abst ract :L i q u i d -liquid Extraction (LLE )w ith n -hexane w as developed to ex tract 12k i n ds of se m -i vo latile organic co m pounds in groundw ater sa mp les .Gas chro m atography equipped w ith electron captured detector (ECD )and high perfor m ance li q u i d chro m atography equ i p ped w ith u ltrav iolet detecto r (UVD)and fluorescence detector (FLD )w ere used to ana lyze the tar get co m pounds .So m e facto rs affecti n g t h e deter m inati o ns inc l u d i n g t h e preservation o f the w ater sa m ples ,the activ ity eva l u ation o f the gas chro m atography i n j e ction ,inspection of reagent b lanks ,e li m i n ation of e m u lsifica ti o n i n w ater sa m ple ex traction ,etc .w ere d iscussed i n deta ils .Reference to the QA /QC protoco ls fro m EPA,a quality con tro l procedure for se m -i volatile organ ic co m pound analysi s i n groundw ater sa mp les w as proposed.By usi n g quality contro l charts fo r eval u ating batch analyti c al resu lts ,it ensures that the ana lytical procedure is under the qua lity contro.l K ey w ords :se m -i volatile o r gan ic po ll u tan;t groundw ater sa m ple ;quality contro;l experience exchange 利用正己烷液-液萃取地下水样中A -六六六、B -六六六、C -六六六、D -六六六、p ,p c -DDE 、p ,p c -DDD 、o ,p c -DDT 、p,p c -DDT 、六氯苯、苯并[a]芘,以气相色谱-电子捕获检测器(GC -ECD)、高效液相色谱-紫外-荧光检测器(H PLC-UV -FLD )分别检测特征化合物,方法检测限)157)低、精密度好、简便准确,缩短了样品的萃取时间,减少了样品的使用量,适用于批量样品分析[1-3]。

DOI: 10.1126/science.1171245, 1312 (2009);324Scienceet al.Xuesong Li,Graphene Films on Copper Foils Large-Area Synthesis of High-Quality and Uniform (this information is current as of June 8, 2009 ):The following resources related to this article are available online at/cgi/content/full/324/5932/1312version of this article at:including high-resolution figures, can be found in the online Updated information and services,/cgi/content/full/1171245/DC1 can be found at:Supporting Online Material /cgi/content/full/324/5932/1312#otherarticles , 2 of which can be accessed for free:cites 25 articles This article/cgi/collection/mat_sci Materials Science: subject collections This article appears in the following/about/permissions.dtl in whole or in part can be found at: this article permission to reproduce of this article or about obtaining reprints Information about obtaining registered trademark of AAAS.is a Science 2009 by the American Association for the Advancement of Science; all rights reserved. The title Copyright American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. 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for their help with the initial tests on the liquid cells.This project is supported by the Director,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division of the U.S.Department of Energy under contract DE-AC02-05CH11231.Supporting Online Material/cgi/content/full/324/5932/1309/DC1Materials and Methods Figs.S1to S3Movies S1and S2References10February 2009;accepted 8April 200910.1126/science.1172104Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper FoilsXuesong Li,1Weiwei Cai,1Jinho An,1Seyoung Kim,2Junghyo Nah,2Dongxing Yang,1Richard Piner,1Aruna Velamakanni,1Inhwa Jung,1Emanuel Tutuc,2Sanjay K.Banerjee,2Luigi Colombo,3*Rodney S.Ruoff 1*Graphene has been attracting great interest because of its distinctive band structure and physical properties.Today,graphene is limited to small sizes because it is produced mostly by exfoliating graphite.We grew large-area graphene films of the order of centimeters on copper substrates by chemical vapor deposition using methane.The films are predominantly single-layer graphene,with a small percentage (less than 5%)of the area having few layers,and are continuous across copper surface steps and grain boundaries.The low solubility of carbon in copper appears to help make this growth process self-limiting.We also developed graphene film transfer processes to arbitrary substrates,and dual-gated field-effect transistors fabricated on silicon/silicon dioxide substrates showed electron mobilities as high as 4050square centimeters per volt per second at room temperature.Graphene,a monolayer of sp 2-bonded car-bon atoms,is a quasi –two-dimensional (2D)material.Graphene has been attract-ing great interest because of its distinctive band structure and physical properties (1).Today,the size of graphene films produced is limited to small sizes (usually <1000m m 2)because the films are produced mostly by exfoliating graphite,which is not a scalable technique.Graphene has also been synthesized by the desorption of Si from SiC single-crystal surfaces,which yields a multilayered graphene structure that behaves like graphene (2,3),and by a surface precipitation process of carbon in some transition metals (4–8).Electronic application will require high-quality large-area graphene that can be manipu-lated to make complex devices and integrated in silicon device flows.Field-effect transistors (FETs)fabricated with exfoliated graphite have shown promising electrical properties (9,10),but these devices will not meet the silicon device scaling requirements,especially those for power reduction and performance.One device that could meet the silicon roadmap requirements beyond the 15-nm node was proposed by S.K.Banerjee et al .(11).The device is a “BisFET ”(bilayer pseudospin FET)that is made up of two graphene layers separated by a thin dielectric.The ability to create this device can be facilitated by the availability of large-area graphene.Making a transparent electrode,another prom-ising application of graphene,also requires large films (6,12–14).At this time,there is no pathway for the formation of a graphene layer that can be ex-foliated from or transferred from the graphene synthesized on SiC,but there is a way to growand transfer graphene grown on metal substrates (5–7).Although graphene has been grown on a number of metals,we still have the challenge of growing large-area graphene.For example,graphene grown on Ni seems to be limited by its small grain size,presence of multilayers at the grain boundaries,and the high solubility of car-bon (6,7).We have developed a graphene chem-ical vapor deposition (CVD)growth process on copper foils (25m m thick in our experiment).The films grow directly on the surface by a surface-catalyzed process,and the film is predominantly graphene with <5%of the area having two-and three-layer graphene flakes.Under our process-ing conditions,the two-and three-layer flakes do not grow larger with time.One of the major benefits of our process is that it can be used to grow graphene on 300-mm copper films on Si substrates (a standard process in Si technology).It is also well known that annealing of Cu can lead to very large grains.As described in (15),we grew graphene on copper foils at temperatures up to 1000°C by CVD of carbon using a mixture of methane and hydrogen.Figure 1A shows a scanning electron microscopy (SEM)image of graphene on a copper substrate where the Cu grains are clearly visible.A higher-resolution image of graphene on Cu (Fig.1B)shows the presence of Cu surface steps,graphene “wrinkles,”and the presence of non-uniform dark flakes.The wrinkles associated with the thermal expansion coefficient difference between Cu and graphene are also found to cross Cu grain boundaries,indicating that the graphene film is continuous.The inset in Fig.1B shows transmission electron microscopy (TEM)images of graphene and bilayer graphene.With the use of a process similar to that described in (16),the as-grown graphene can be easily transferred to alternative substrates,such as SiO 2/Si or glass (Fig.1,C and D),for further evaluation and for various applications;a detailed transfer process is described (15).The process and method used to transfer graphene from Cu was the same for the SiO 2/Si substrate and the glass substrate.Al-1Department of Mechanical Engineering and the Texas Materials Institute,1University Station C2200,The University of Texas at Austin,Austin,TX 78712–0292,USA.2Department of Electrical and Computer Engineering,Microelectronics Research Center,The University of Texas at Austin,Austin,TX 78758,USA.3Texas Instruments,Dallas,TX 75243,USA.*To whom correspondence should be addressed.E-mail:colombo@ (L.C.);r.ruoff@ (R.S.R.)5JUNE 2009VOL 324SCIENCE1312REPORTSo n J u n e 8, 2009w w w .s c i e n c e m a g .o r g D o w n l o a d e d f r o mthough it is difficult to see the graphene on the SiO 2/Si substrate,a similar graphene film from another Cu substrate transferred on glass clearly shows that it is optically uniform.We used Raman spectroscopy to evaluate the quality and uniformity of graphene on a SiO 2/Si substrate.Figure 2shows SEM and optical im-ages with the corresponding Raman spectra and maps of the D,G,and 2D bands providing in-formation on the defect density and film thick-ness.The Raman spectra are from the spots marked with the corresponding colored circles shown in the other panels (in Fig.2,A and B,green arrows are used instead of circles so as to show the trilayer region more clearly).The thickness and uniformity of the graphene films were evaluated via color contrast under optical microscope (17)and Raman spectra (7,18,19).The Raman spectrum from the lightest pink background in Fig.2B shows typical features of monolayer graphene:(i)a ~0.5G –to –2D inten-sity ratio and (ii)a symmetric 2D band centered at ~2680cm –1with a full width at half maxi-mum of ~33cm –1.The second lightest pink flakes (blue circle)correspond to bilayer graphene,and the darkest one (green arrow)represents trilayer graphene.This thickness variation is more clearly shown in the SEM image in Fig.2A.The D map in Fig.2D,which has been associated with defects in graphene,is rather uniform and near the background level,except for regions where wrinkles are present and close to few-layer regions.The G and the 2D maps clearly show the presence of more than one layer in the flakes.In the wrinkled regions,there are peak height variations in both the G and 2D bands,and there is a broadening of the 2D band.An analysis of the intensity of the optical image over the whole sample (1cm by 1cm)showed that the area with the lightest pink color is more than 95%,and all 40Raman spectra randomly collected from this area show monolayer graphene.There is only a small fraction of trilayer or few-layer (<10)graphene (<1%),and the rest is bilayer graphene (~3to 4%).We grew films on Cu as a function of time and Cu foil thickness under isothermal and iso-baric ing the process flow de-scribed in (15),we found that graphene growth on Cu is self-limited;growth that proceeded for more than 60min yielded a similar structure to growth runs performed for ~10min.For timesFig.2.(A )SEM image of graphene transferred on SiO 2/Si (285-nm-thick oxide layer)showing wrin-kles,as well as two-and three-layerregions.(B )Op-tical microscope image of the same regions as in (A).(C )Raman spectra from the marked spots with cor-responding colored circles or arrows showing the pres-enceofone,two,andthree layers of graphene.a.u.,ar-bitrary units.(D to F )Ra-man maps of the D (1300to 1400cm –1),G (1560to 1620cm –1),and 2D (2660to 2700cm –1)bands,re-spectively (WITec alpha300,l laser =532nm,~500-nm spot size,100×objector).CCD cts.,charge-coupled device counts.Scale bars,5mm.Fig.1.(A )SEM image of graphene on a copper foil with a growth time of 30min.(B )High-resolution SEM image showing a Cu grain boundary and steps,two-and three-layer graphene flakes,and graphene wrinkles.Inset in (B)shows TEM images of folded graphene edges.1L,one layer;2L,two layers.(C and D )Graphene films transferred onto a SiO 2/Si substrate and a glass plate,respectively. SCIENCE VOL 3245JUNE 20091313REPORTSo n J u n e 8, 2009w w w .s c i e n c e m a g .o r g D o w n l o a d e d f r o mmuch less than 10min,the Cu surface is usually not fully covered [SEM images of graphene on Cu with different growth time are shown in fig.S3(15)].The growth of graphene on Cu foils of varying thickness (12.5,25,and 50m m)also yielded similar graphene structure with re-gions of double and triple flakes,but neither discontinuous monolayer graphene for thinner Cu foils nor continuous multilayer graphene for thicker Cu foils,as we would have expected based on the precipitation mechanism.Accord-ing to these observations,we concluded that graphene is growing by a surface-catalyzed pro-cess rather than a precipitation process,as has been reported by others for Ni (5–7).Monolayer graphene formation caused by surface segrega-tion or surface adsorption of carbon has also been observed on transition metals such as Ni and Co at elevated temperatures by Blakely and coauthors (20–22).However,when the metal substrates were cooled down to room temper-ature,thick graphite films were obtained because of precipitation of excess C from these metals,in which the solubility of C is relatively high.In recent work,thin Ni films and a fast-cooling process have been used to suppress the amount of precipitated C.However,this process still yields films with a wide range of graphene layer thicknesses,from one to a few tens of lay-ers and with defects associated with fast cooling (5–7).Our results suggest that the graphene growth process is not one of C precipitation but rather a CVD process.The precise mechanism will require additional experiments to understand in full,but very low C solubility in Cu (23–25)and poor C saturation as a result of graphene sur-face coverage may be playing a role in limiting or preventing the precipitation process altogether at high temperature,similar to the case of im-peding of carburization of Ni (26).This provides a pathway for growing self-limited graphene films.To evaluate the electrical quality of the syn-thesized graphene,we fabricated dual-gated FETs with Al 2O 3as the gate dielectric and measured them at room temperature.Along with a device model that incorporates a finite density at the Dirac point,the dielectric,and the quantum ca-pacitances (9),the data are shown in Fig.3.The extracted carrier mobility for this device is ~4050cm 2V –1s –1,with the residual carrier concentra-tion at the Dirac point of n 0=3.2×1011cm –2.These data suggest that the films are of rea-sonable quality,at least sufficient to continue improving the growth process to achieve a ma-terial quality equivalent to the exfoliated natural graphite.References and Notes1.A.K.Geim,K.S.Novoselov,Nat.Mater.6,183(2007).2.C.Berger et al .,Science 312,1191(2006);published online 12April 2006(10.1126/science.1125925).3.K.V.Emtsev et al .,Nat.Mater.8,203(2009).4.P.W.Sutter,J.-I.Flege,E.A.Sutter,Nat.Mater.7,406(2008).5.Q.Yu et al .,Appl.Phys.Lett.93,113103(2008).6.K.S.Kim et al .,Nature 457,706(2009).7.A.Reina et al .,Nano Lett.9,30(2009).8.J.Coraux,A.T.N ’Diaye,C.Busse,T.Michely,Nano Lett.8,565(2008).9.S.Kim et al .,Appl.Phys.Lett.94,062107(2009).10.M.C.Lemme et al .,Solid-State Electron.52,514(2008).11.S.K.Banerjee,L.F.Register,E.Tutuc,D.Reddy,A.H.MacDonald,IEEE Electron Device Lett.30,158(2009).12.P.Blake et al .,Nano Lett.8,1704(2008).13.R.R.Nair et al .,Science 320,1308(2008);published online 3April 2008(10.1126/science.1156965).14.X.Wang,L.Zhi,K.Müllen,Nano Lett.8,323(2008).15.See supporting material on Science Online.16.A.Reina et al .,J.Phys.Chem.C 112,17741(2008).17.Z.H.Ni et al .,Nano Lett.7,2758(2007).18.A.C.Ferrari et al .,Phys.Rev.Lett.97,187401(2006).19.A.Das et al .,Nat.Nanotechnol.3,210(2008).20.M.Eizenberg,J.M.Blakely,Surf.Sci.82,228(1979).21.M.Eizenberg,J.M.Blakely,J.Chem.Phys.71,3467(1979).22.J.C.Hamilton,J.M.Blakely,Surf.Sci.91,199(1980).23.R.B.McLellan,Scr.Metal.3,389(1969).24.G.Mathieu,S.Guiot,J.Carbané,Scr.Metal.7,421(1973).25.G.A.López,E.J.Mittemeijer,Scr.Mater.51,1(2004).26.R.Kikowatz,K.Flad,G.Horz,J.Vac.Sci.Technol.A 5,1009(1987).27.We thank the Nanoelectronic Research Initiative(NRI –Southwest Area Nanoelectronics Center,grant no.2006-NE-1464),the Defense Advanced Research Projects Agency Carbon Electronics for RF Applications Center,and the University of Texas at Austin for support.Supporting Online Material/cgi/content/full/1171245/DC1Materials and Methods Figs.S1to S322January 2009;accepted 9April 2009Published online 7May 2009;10.1126/science.1171245Include this information when citing this paper.Superconductivity at the Two-Dimensional LimitShengyong Qin,Jungdae Kim,Qian Niu,Chih-Kang Shih *Superconductivity in the extreme two-dimensional limit is studied on ultrathin lead films down to two atomic layers,where only a single channel of quantum well states exists.Scanning tunneling spectroscopy reveals that local superconducting order remains robust until two atomic layers,where the transition temperature abruptly plunges to a lower value,depending sensitively on the exact atomic structure of the film.Our result shows that Cooper pairs can still form in the last two-dimensional channel of electron states,although their binding is strongly affected by the substrate.Studies of two-dimensional (2D)super-conductivities have been generally limited to the regime where the superconducting order parameter behaves as a 2D wave func-tion but the underline electrons are still three-dimensional (1–11).Recent advancements in materials synthesis have enabled the growth of epitaxial superconductor thin films with unprec-Fig.3.(A )Optical micro-scope imageofa graphene FET.(B )Device resistance versus top-gate voltage (V TG ),with different back-gate (V BG )biases,and ver-sus V TG -V Dirac,TG (V TG at the Dirac point),with a model fit (solidline).5JUNE 2009VOL 324SCIENCE1314REPORTSo n J u n e 8, 2009w w w .s c i e n c e m a g .o r g D o w n l o a d e d f r o m。

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