本文主要研究内容
作者刘然（2019）在《纳米结形成机制及其导电性能理论研究》一文中研究指出：随着功能半导体电子元器件小型化的不断发展,人们希望可以直接在纳米尺度上甚至单分子层次上搭建性能稳定且可操控的微型功能电子器件,即所谓的纳米器件和分子器件。纳米与分子功能器件的设计与性质研究是国际上的研究热点,近二十年来,人们在这一领域开展了大量的理论与实验研究工作。由于器件的尺寸只有纳米量级,极易受到外界的影响,其中,电极-纳米功能结构（或分子）连接界面的不可控性是影响器件功能与应用的重要因素。为了理解电极-纳米功能结构（或分子）间的相互作用以及界面结构控制规律,为实验制备性能稳定、可操控的功能器件提供理论支持,论文基于第一性原理计算,根据相关实验结果,研究了金纳米结界面原子的控制与转移机理、计算并模拟了纳米结中电极与分子作用形式及体系的演化过程,讨论了影响电极—分子界面接触的可能因素,不仅系统理解了相关实验测量结果,而且指导实验成功构建了功能纳米结构。研究主要包括以下五部分内容:（1）基于金纳米结的原子控制与原子“存储器”构建了金纳米结体系,并在密度泛函理论（Density Functional Theory,DFT）基础上结合非平衡格林函数（Non-Equilibrium Green’s Function,NEGF）方法计算了两电极连接处单个原子在金纳米结中的迁移过程以及由该过程引起的体系电导变化。通过分析电极接触点处表面原子迁移过程的最小能量路径,得到了电导约为1 G0和2 G0且能量大小相同的两个稳态结构和一个介于两稳态构型之间且能量较高的电导约为1 G0的亚稳态结构。计算显示,两电极连接处外侧的原子带有0.8 e电荷量,当电极偏压大于50 mV时,该原子在电场诱导下借助振动,越过亚稳态以及能量势垒,实现两个稳态构型间的转换。如果电极偏压小于该偏压阈值,该原子没有足够能量越过亚稳态以及能量势垒,体系的电导状态将保持在原稳态上。因此通过较高偏压进行原子转移可以完成“写”操作,而利用低偏压测量体系电导则可作为“读”操作,从而,在单原子尺度上利用金纳米结实现了纳米存储器功能。实验测量发现,金纳米结1 G0–2 G0间电导转换的偏压阈值为48 mV,与理论计算完全相符。由于振动在原子迁移过程中起到辅助作用,这导致了纳米存储器需要在适当的温度和压强下才能正常工作。（2）基于电场辅助原子迁移技术的纳米间隙制作机理在第一性原理计算基础上,建立了电场辅助原子迁移（Field-Aided Atom Migration,FAAM）方法,在金纳米电极之间精确构建了界面稳定的原子尺度间隙。为了理解这一技术手段的操作机理,计算了拉伸和压缩过程中金纳米结的构型演变。计算结果表明,在反复拉伸/压缩过程中,桥接在两个电极之间的部分金原子容易形成单原子链。而且在单原子链两端容易产生晶格空位,这使得通过FAAM方法产生电极间隙成为可能。在场辅助原子迁移中,外场施加定向驱动力,增加体系的初始能量,降低原子迁移路径中的势垒,从而推动原子完成迁移。电导和拉伸、压缩作用力作为拉伸和压缩过程中的可观测物理量,为场辅助原子迁移的执行时间点提供了非常有用的信号。这一方案解决了电极固定状态下如何构建尺寸确定的纳米间隙的难题,在基于分子器件的电路集成中具有潜在的应用价值。按照这一方案,向东教授课题组通过实验,在电极固定的情况下成功地制造了尺寸稳定在0.38±0.05 nm的金纳米间隙,与理论预测结果完全一致。（3）电极尖端构型对苯胺类分子结电输运性质的影响在密度泛函理论基础上计算了苯胺类分子在电极拉伸过程中的演化,结果显示,苯胺类分子的氨基（-NH2）末端与金电极间的连接方式受电极界面的几何构型影响明显。当分子末端的氨基与锥形堆积的金原子相连接时,在电极顶端Au原子的作用下,末端氨基中N原子的电子结构由sp2杂化部分转化为sp3杂化,由此导致了电极顶端金原子与分子末端氨基之间较强的配位相互作用。而当分子与平面电极相连时,分子末端的氨基仍然保持sp2杂化的平面结构,分子与电极间只能通过弱的范德瓦尔斯力相连接。此时,分子末端的氨基与电极间存在着较大的间隙,并形成明显的隧穿势垒,阻碍了电子从电极到分子再到电极的输运,降低了电子通过分子结的概率。根据一维透射结合三维修正近似（One-Dimension Transmission Combined with Three-Dimension Correction Approximation,OTCTCA）方法计算,锥形电极—苯胺分子—锥形电极类型分子结的电导约为平面电极—苯胺分子—平面电极类型分子结电导的1.5倍。因此,通过改变电极构型可以优化电极与苯胺类分子之间的连接方式,从而增强体系的导电性能,提高分子结的稳定性。（4）不同分子末端与电极界面相互作用的差异利用DFT结合OTCTCA方法,研究了以氨基为末端的1,4-二氨基丁烷分子和以吡啶为末端的4,4’-二吡啶分子分别在锥形和平面形电极之间形成分子结的能量、作用力、应变因子和体系电导。发现以吡啶为末端的分子在锥形电极之间的电导要比在平面电极之间的电导小约1个量级。如果平面电极的表面上存在孤立的金原子,该分子结的电导在拉伸过程中会出现双电导平台的现象。因此,吡啶分子可以用于识别电极界面的形貌。对于1,4-二氨基丁烷分子,其NH2末端中的N原子通过sp3杂化的配位键与电极表面的金原子相连,该末端N原子会抓住与其连接的Au原子,使之突出电极界面并出现滑移。但是,当分子结在1.1 nN的作用力下断裂时,被抓住的Au原子会回到初始的晶格状态。由1,4-二氨基丁烷分子与电极构成的分子结的电导平台随电极距离的增加、界面结构的变化没有出现显著的改变。因此,电极界面的结构变化对1,4-二氨基丁烷分子的电导性质几乎没有影响。（5）氢键重组引起双分子结体系电导振荡现象基于DFT计算结合OTCTCA方法,研究了由1,4-二氨基苯和4,4’-二氨基联苯组成的双分子体系随电极拉伸的演化过程,以及与过程相对应的体系电导。计算结果显示,如果双分子体系中连接两电极的为同一分子,则两分子末端氨基之间的H键作用对体系电导产生的影响可以忽略。这表明氨基间的H键作用对Au-NH2（类sp3杂化）间的耦合影响很弱。如果两电极分别连接两不同分子,两分子末端氨基间的H键将成为“电极-M1-M2-电极”电子输运通道的一部分。此时,氨基末端间的H键随电极距离变化将选择性地发生断裂和重组,并进一步影响体系电导,导致体系电导随电极的拉伸出现跃变。在特定电极距离下,氨基间H键的断裂和重组会在体系振动诱导下自发发生,进而导致体系电导的自发振荡现象。尽管在实验中能够观察到这一现象,由于电极距离的限制,大幅度的电导振荡在实验中出现的概率一般非常小。本文共有八章,第一章对分子电子学的发展和目前面临的问题进行了简要的综述;第二章介绍了计算纳米结体系结构及伏—安特性所用的密度泛函理论和电子输运理论;第三章着重讨论了纯金纳米线在电场作用下出现的表面原子迁移现象,并利用这一现象设计了原子尺度的“存储器”;第四章研究了金纳米线拉伸-压缩演化过程,讨论了电场辅助金原子迁移行为,给出了电极固定情况下构建确定尺寸纳米间隙的技术方案;第五章讨论了不同电极构型对苯胺分子电导性质的影响,阐明了电极构型影响分子末端氨基与电极间连接方式的内在原因及判断分子与电极间连接方式的方法;第六章对比了以不同杂化类型N原子为末端的分子在锥形电极、平面形电极之间的连接方式、单点能、作用力、体系应变和体系电导;第七章研究了分子末端之间的H键相互作用对含有1,4-二氨基苯和4,4’-二氨基联苯分子的双分子体系拉伸演化、电导平台的影响;第八章为上述几章进行了总结,并对后续工作进行了展望。
Abstract
sui zhao gong neng ban dao ti dian zi yuan qi jian xiao xing hua de bu duan fa zhan ,ren men xi wang ke yi zhi jie zai na mi che du shang shen zhi chan fen zi ceng ci shang da jian xing neng wen ding ju ke cao kong de wei xing gong neng dian zi qi jian ,ji suo wei de na mi qi jian he fen zi qi jian 。na mi yu fen zi gong neng qi jian de she ji yu xing zhi yan jiu shi guo ji shang de yan jiu re dian ,jin er shi nian lai ,ren men zai zhe yi ling yu kai zhan le da liang de li lun yu shi yan yan jiu gong zuo 。you yu qi jian de che cun zhi you na mi liang ji ,ji yi shou dao wai jie de ying xiang ,ji zhong ,dian ji -na mi gong neng jie gou （huo fen zi ）lian jie jie mian de bu ke kong xing shi ying xiang qi jian gong neng yu ying yong de chong yao yin su 。wei le li jie dian ji -na mi gong neng jie gou （huo fen zi ）jian de xiang hu zuo yong yi ji jie mian jie gou kong zhi gui lv ,wei shi yan zhi bei xing neng wen ding 、ke cao kong de gong neng qi jian di gong li lun zhi chi ,lun wen ji yu di yi xing yuan li ji suan ,gen ju xiang guan shi yan jie guo ,yan jiu le jin na mi jie jie mian yuan zi de kong zhi yu zhuai yi ji li 、ji suan bing mo ni le na mi jie zhong dian ji yu fen zi zuo yong xing shi ji ti ji de yan hua guo cheng ,tao lun le ying xiang dian ji —fen zi jie mian jie chu de ke neng yin su ,bu jin ji tong li jie le xiang guan shi yan ce liang jie guo ,er ju zhi dao shi yan cheng gong gou jian le gong neng na mi jie gou 。yan jiu zhu yao bao gua yi xia wu bu fen nei rong :（1）ji yu jin na mi jie de yuan zi kong zhi yu yuan zi “cun chu qi ”gou jian le jin na mi jie ti ji ,bing zai mi du fan han li lun （Density Functional Theory,DFT）ji chu shang jie ge fei ping heng ge lin han shu （Non-Equilibrium Green’s Function,NEGF）fang fa ji suan le liang dian ji lian jie chu chan ge yuan zi zai jin na mi jie zhong de qian yi guo cheng yi ji you gai guo cheng yin qi de ti ji dian dao bian hua 。tong guo fen xi dian ji jie chu dian chu biao mian yuan zi qian yi guo cheng de zui xiao neng liang lu jing ,de dao le dian dao yao wei 1 G0he 2 G0ju neng liang da xiao xiang tong de liang ge wen tai jie gou he yi ge jie yu liang wen tai gou xing zhi jian ju neng liang jiao gao de dian dao yao wei 1 G0de ya wen tai jie gou 。ji suan xian shi ,liang dian ji lian jie chu wai ce de yuan zi dai you 0.8 edian he liang ,dang dian ji pian ya da yu 50 mVshi ,gai yuan zi zai dian chang you dao xia jie zhu zhen dong ,yue guo ya wen tai yi ji neng liang shi lei ,shi xian liang ge wen tai gou xing jian de zhuai huan 。ru guo dian ji pian ya xiao yu gai pian ya yu zhi ,gai yuan zi mei you zu gou neng liang yue guo ya wen tai yi ji neng liang shi lei ,ti ji de dian dao zhuang tai jiang bao chi zai yuan wen tai shang 。yin ci tong guo jiao gao pian ya jin hang yuan zi zhuai yi ke yi wan cheng “xie ”cao zuo ,er li yong di pian ya ce liang ti ji dian dao ze ke zuo wei “dou ”cao zuo ,cong er ,zai chan yuan zi che du shang li yong jin na mi jie shi xian le na mi cun chu qi gong neng 。shi yan ce liang fa xian ,jin na mi jie 1 G0–2 G0jian dian dao zhuai huan de pian ya yu zhi wei 48 mV,yu li lun ji suan wan quan xiang fu 。you yu zhen dong zai yuan zi qian yi guo cheng zhong qi dao fu zhu zuo yong ,zhe dao zhi le na mi cun chu qi xu yao zai kuo dang de wen du he ya jiang xia cai neng zheng chang gong zuo 。（2）ji yu dian chang fu zhu yuan zi qian yi ji shu de na mi jian xi zhi zuo ji li zai di yi xing yuan li ji suan ji chu shang ,jian li le dian chang fu zhu yuan zi qian yi （Field-Aided Atom Migration,FAAM）fang fa ,zai jin na mi dian ji zhi jian jing que gou jian le jie mian wen ding de yuan zi che du jian xi 。wei le li jie zhe yi ji shu shou duan de cao zuo ji li ,ji suan le la shen he ya su guo cheng zhong jin na mi jie de gou xing yan bian 。ji suan jie guo biao ming ,zai fan fu la shen /ya su guo cheng zhong ,qiao jie zai liang ge dian ji zhi jian de bu fen jin yuan zi rong yi xing cheng chan yuan zi lian 。er ju zai chan yuan zi lian liang duan rong yi chan sheng jing ge kong wei ,zhe shi de tong guo FAAMfang fa chan sheng dian ji jian xi cheng wei ke neng 。zai chang fu zhu yuan zi qian yi zhong ,wai chang shi jia ding xiang qu dong li ,zeng jia ti ji de chu shi neng liang ,jiang di yuan zi qian yi lu jing zhong de shi lei ,cong er tui dong yuan zi wan cheng qian yi 。dian dao he la shen 、ya su zuo yong li zuo wei la shen he ya su guo cheng zhong de ke guan ce wu li liang ,wei chang fu zhu yuan zi qian yi de zhi hang shi jian dian di gong le fei chang you yong de xin hao 。zhe yi fang an jie jue le dian ji gu ding zhuang tai xia ru he gou jian che cun que ding de na mi jian xi de nan ti ,zai ji yu fen zi qi jian de dian lu ji cheng zhong ju you qian zai de ying yong jia zhi 。an zhao zhe yi fang an ,xiang dong jiao shou ke ti zu tong guo shi yan ,zai dian ji gu ding de qing kuang xia cheng gong de zhi zao le che cun wen ding zai 0.38±0.05 nmde jin na mi jian xi ,yu li lun yu ce jie guo wan quan yi zhi 。（3）dian ji jian duan gou xing dui ben an lei fen zi jie dian shu yun xing zhi de ying xiang zai mi du fan han li lun ji chu shang ji suan le ben an lei fen zi zai dian ji la shen guo cheng zhong de yan hua ,jie guo xian shi ,ben an lei fen zi de an ji （-NH2）mo duan yu jin dian ji jian de lian jie fang shi shou dian ji jie mian de ji he gou xing ying xiang ming xian 。dang fen zi mo duan de an ji yu zhui xing dui ji de jin yuan zi xiang lian jie shi ,zai dian ji ding duan Auyuan zi de zuo yong xia ,mo duan an ji zhong Nyuan zi de dian zi jie gou you sp2za hua bu fen zhuai hua wei sp3za hua ,you ci dao zhi le dian ji ding duan jin yuan zi yu fen zi mo duan an ji zhi jian jiao jiang de pei wei xiang hu zuo yong 。er dang fen zi yu ping mian dian ji xiang lian shi ,fen zi mo duan de an ji reng ran bao chi sp2za hua de ping mian jie gou ,fen zi yu dian ji jian zhi neng tong guo ruo de fan de wa er si li xiang lian jie 。ci shi ,fen zi mo duan de an ji yu dian ji jian cun zai zhao jiao da de jian xi ,bing xing cheng ming xian de sui chuan shi lei ,zu ai le dian zi cong dian ji dao fen zi zai dao dian ji de shu yun ,jiang di le dian zi tong guo fen zi jie de gai lv 。gen ju yi wei tou she jie ge san wei xiu zheng jin shi （One-Dimension Transmission Combined with Three-Dimension Correction Approximation,OTCTCA）fang fa ji suan ,zhui xing dian ji —ben an fen zi —zhui xing dian ji lei xing fen zi jie de dian dao yao wei ping mian dian ji —ben an fen zi —ping mian dian ji lei xing fen zi jie dian dao de 1.5bei 。yin ci ,tong guo gai bian dian ji gou xing ke yi you hua dian ji yu ben an lei fen zi zhi jian de lian jie fang shi ,cong er zeng jiang ti ji de dao dian xing neng ,di gao fen zi jie de wen ding xing 。（4）bu tong fen zi mo duan yu dian ji jie mian xiang hu zuo yong de cha yi li yong DFTjie ge OTCTCAfang fa ,yan jiu le yi an ji wei mo duan de 1,4-er an ji ding wan fen zi he yi bi ding wei mo duan de 4,4’-er bi ding fen zi fen bie zai zhui xing he ping mian xing dian ji zhi jian xing cheng fen zi jie de neng liang 、zuo yong li 、ying bian yin zi he ti ji dian dao 。fa xian yi bi ding wei mo duan de fen zi zai zhui xing dian ji zhi jian de dian dao yao bi zai ping mian dian ji zhi jian de dian dao xiao yao 1ge liang ji 。ru guo ping mian dian ji de biao mian shang cun zai gu li de jin yuan zi ,gai fen zi jie de dian dao zai la shen guo cheng zhong hui chu xian shuang dian dao ping tai de xian xiang 。yin ci ,bi ding fen zi ke yi yong yu shi bie dian ji jie mian de xing mao 。dui yu 1,4-er an ji ding wan fen zi ,ji NH2mo duan zhong de Nyuan zi tong guo sp3za hua de pei wei jian yu dian ji biao mian de jin yuan zi xiang lian ,gai mo duan Nyuan zi hui zhua zhu yu ji lian jie de Auyuan zi ,shi zhi tu chu dian ji jie mian bing chu xian hua yi 。dan shi ,dang fen zi jie zai 1.1 nNde zuo yong li xia duan lie shi ,bei zhua zhu de Auyuan zi hui hui dao chu shi de jing ge zhuang tai 。you 1,4-er an ji ding wan fen zi yu dian ji gou cheng de fen zi jie de dian dao ping tai sui dian ji ju li de zeng jia 、jie mian jie gou de bian hua mei you chu xian xian zhe de gai bian 。yin ci ,dian ji jie mian de jie gou bian hua dui 1,4-er an ji ding wan fen zi de dian dao xing zhi ji hu mei you ying xiang 。（5）qing jian chong zu yin qi shuang fen zi jie ti ji dian dao zhen dang xian xiang ji yu DFTji suan jie ge OTCTCAfang fa ,yan jiu le you 1,4-er an ji ben he 4,4’-er an ji lian ben zu cheng de shuang fen zi ti ji sui dian ji la shen de yan hua guo cheng ,yi ji yu guo cheng xiang dui ying de ti ji dian dao 。ji suan jie guo xian shi ,ru guo shuang fen zi ti ji zhong lian jie liang dian ji de wei tong yi fen zi ,ze liang fen zi mo duan an ji zhi jian de Hjian zuo yong dui ti ji dian dao chan sheng de ying xiang ke yi hu lve 。zhe biao ming an ji jian de Hjian zuo yong dui Au-NH2（lei sp3za hua ）jian de ou ge ying xiang hen ruo 。ru guo liang dian ji fen bie lian jie liang bu tong fen zi ,liang fen zi mo duan an ji jian de Hjian jiang cheng wei “dian ji -M1-M2-dian ji ”dian zi shu yun tong dao de yi bu fen 。ci shi ,an ji mo duan jian de Hjian sui dian ji ju li bian hua jiang shua ze xing de fa sheng duan lie he chong zu ,bing jin yi bu ying xiang ti ji dian dao ,dao zhi ti ji dian dao sui dian ji de la shen chu xian yue bian 。zai te ding dian ji ju li xia ,an ji jian Hjian de duan lie he chong zu hui zai ti ji zhen dong you dao xia zi fa fa sheng ,jin er dao zhi ti ji dian dao de zi fa zhen dang xian xiang 。jin guan zai shi yan zhong neng gou guan cha dao zhe yi xian xiang ,you yu dian ji ju li de xian zhi ,da fu du de dian dao zhen dang zai shi yan zhong chu xian de gai lv yi ban fei chang xiao 。ben wen gong you ba zhang ,di yi zhang dui fen zi dian zi xue de fa zhan he mu qian mian lin de wen ti jin hang le jian yao de zeng shu ;di er zhang jie shao le ji suan na mi jie ti ji jie gou ji fu —an te xing suo yong de mi du fan han li lun he dian zi shu yun li lun ;di san zhang zhao chong tao lun le chun jin na mi xian zai dian chang zuo yong xia chu xian de biao mian yuan zi qian yi xian xiang ,bing li yong zhe yi xian xiang she ji le yuan zi che du de “cun chu qi ”;di si zhang yan jiu le jin na mi xian la shen -ya su yan hua guo cheng ,tao lun le dian chang fu zhu jin yuan zi qian yi hang wei ,gei chu le dian ji gu ding qing kuang xia gou jian que ding che cun na mi jian xi de ji shu fang an ;di wu zhang tao lun le bu tong dian ji gou xing dui ben an fen zi dian dao xing zhi de ying xiang ,chan ming le dian ji gou xing ying xiang fen zi mo duan an ji yu dian ji jian lian jie fang shi de nei zai yuan yin ji pan duan fen zi yu dian ji jian lian jie fang shi de fang fa ;di liu zhang dui bi le yi bu tong za hua lei xing Nyuan zi wei mo duan de fen zi zai zhui xing dian ji 、ping mian xing dian ji zhi jian de lian jie fang shi 、chan dian neng 、zuo yong li 、ti ji ying bian he ti ji dian dao ;di qi zhang yan jiu le fen zi mo duan zhi jian de Hjian xiang hu zuo yong dui han you 1,4-er an ji ben he 4,4’-er an ji lian ben fen zi de shuang fen zi ti ji la shen yan hua 、dian dao ping tai de ying xiang ;di ba zhang wei shang shu ji zhang jin hang le zong jie ,bing dui hou xu gong zuo jin hang le zhan wang 。
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标签：金纳米结形成机制论文; 非平衡格林函数方法论文; 密度泛函理论论文; 分子存储器论文; 分子器件论文; 山东师范大学2019-08-27论文;