本文選題：密度泛函理論 + 非平衡格林函數(shù)方法��； 參考：《山東大學(xué)》2017年碩士論文

【摘要】：分子電子學(xué)由于其在納米功能材料領(lǐng)域的潛在應(yīng)用價(jià)值一直備受科研人員關(guān)注,主要研究?jī)?nèi)容為利用單分子及分子團(tuán)簇,如單壁或多壁的碳納米管、有機(jī)小分子以及高分子等來構(gòu)造各種功能性的電子器件,并且研究這些分子電子器件的電特性或光特性。近年來,隨著實(shí)驗(yàn)技術(shù)和理論方法的進(jìn)步和發(fā)展,使得人們?cè)O(shè)計(jì),測(cè)量并計(jì)算具有不同功能的分子電子的器件成為可能。這些基于單分子的電子器件具有獨(dú)特的物理性質(zhì),包括負(fù)微分電阻效應(yīng),分子整流現(xiàn)象,開關(guān)效應(yīng),存儲(chǔ)器和二極管等等。其中,由于分子開關(guān)具有存儲(chǔ)信息和傳遞信息的特質(zhì),對(duì)于分子開關(guān)的研究成為了前沿課題。根據(jù)觸發(fā)因素的不同,分子開關(guān)可以分為兩類:電開關(guān)和光開關(guān)。前者在電場(chǎng)或者電流脈沖等外部觸發(fā)因素下實(shí)現(xiàn)開態(tài)和關(guān)態(tài)的轉(zhuǎn)化,而后者則是在光的觸發(fā)下實(shí)現(xiàn)電流開/關(guān)狀態(tài)的相互轉(zhuǎn)化。由于光的反應(yīng)時(shí)間短而且容易獲得,光是非常理想的外部觸發(fā)因素,因此光開關(guān)引起了科學(xué)家們的廣泛關(guān)注。本文,我們利用密度泛函理論與非平衡格林函數(shù)相結(jié)合的辦法,系統(tǒng)地研究了旋轉(zhuǎn)分子馬達(dá)和二芳基乙烯分子的電子輸運(yùn)性質(zhì),探討其作為分子光開關(guān)的可能性。研究?jī)?nèi)容和主要結(jié)論有:1.光驅(qū)動(dòng)旋轉(zhuǎn)分子馬達(dá)光分子開關(guān)Feringa第二代光驅(qū)動(dòng)分子馬達(dá)在360°旋轉(zhuǎn)過程中,兩種異構(gòu)體分別為anti-folded和syn-folded,計(jì)算發(fā)現(xiàn),通過順勢(shì)異構(gòu)體的電流總是大于通過反式異構(gòu)體的電流,這意味著在一個(gè)旋轉(zhuǎn)周期中,分子的導(dǎo)電性改變了四次。這種光引起的周期性電導(dǎo)改變特質(zhì)使得分子馬達(dá)具有光分子開關(guān)潛質(zhì)。兩種異構(gòu)體的不同的輸運(yùn)特性主要是由于分子的有效共軛長(zhǎng)度。順勢(shì)異構(gòu)體費(fèi)米能級(jí)附近的透射峰來源于HOMO軌道,順勢(shì)異構(gòu)體的HOMO軌道相對(duì)于反式異構(gòu)體來說更加離域。而且反式異構(gòu)體的透射峰距離費(fèi)米能級(jí)較遠(yuǎn),因此相對(duì)于順勢(shì)異構(gòu)體,反式異構(gòu)體的導(dǎo)電性較差。2.二芳基乙烯光分子開關(guān)實(shí)驗(yàn)上發(fā)現(xiàn)了二芳基乙烯分子吸收可見光可以實(shí)現(xiàn)雙向轉(zhuǎn)變。通過我們的計(jì)算模擬發(fā)現(xiàn),通過閉環(huán)化合物的電流遠(yuǎn)遠(yuǎn)大于通過開環(huán)化合物的電流。電流比高達(dá)2700,使其呈現(xiàn)出良好的開關(guān)特性。另外,在我們的閉環(huán)態(tài)器件中還出現(xiàn)了負(fù)微分電阻現(xiàn)象(NDR)。開環(huán)化合物在費(fèi)米能級(jí)附近沒有透射峰是其導(dǎo)電能力弱的原因。開環(huán)化合物的HOMO和LUMO軌道都是局域的,而閉環(huán)化合物的LUMO軌道是離域的,在費(fèi)米能級(jí)附近的透射峰來自LUMO軌道,因此LUMO軌道是主要的電子輸運(yùn)軌道。閉環(huán)化合物在偏壓0.8V時(shí),偏壓窗內(nèi)的的透射峰積分大于其在偏壓為0.9V時(shí)的透射峰積分,這是其出現(xiàn)NDR的原因。
[Abstract]:Molecular electronics has attracted the attention of researchers because of its potential application value in the field of nano-functional materials. It is mainly concerned with the use of single-molecule and molecular clusters, such as single-walled or multi-walled carbon nanotubes. Organic small molecules and polymers are used to construct various functional electronic devices, and the electrical or optical properties of these molecular electronic devices are studied. In recent years, with the development of experimental technology and theoretical methods, it is possible to design, measure and calculate molecular electronic devices with different functions. These electronic devices based on single molecule have unique physical properties, including negative differential resistance effect, molecular rectification, switching effect, memory and diode, and so on. Among them, because molecular switches have the characteristics of storing and transferring information, the research of molecular switches has become a frontier topic. According to the trigger factors, molecular switches can be divided into two categories: electrical switches and optical switches. The former realizes the transition of open and off states under external triggering factors such as electric field or current pulse, while the latter realizes the mutual conversion of current on / off states under the trigger of light. Light is an ideal external trigger because the reaction time of light is short and easy to obtain, so optical switch has attracted wide attention of scientists. In this paper, using density functional theory and non-equilibrium Green's function, we systematically study the electron transport properties of rotating molecular motors and diarylethylene molecules, and discuss the possibility of using them as molecular optical switches. The contents and main conclusions of the study are as follows: 1. The two isomers are anti-folded and syn-fold, respectively. It is found that the current of the homeoisomer is always greater than that of the trans-isomer during the rotation of the second generation of the photo-driven molecular motor Feringa. This means that the conductivity of the molecule changes four times in a rotation cycle. The characteristic of periodic conductance change caused by light makes the molecular motor have the potential of photomolecular switch. The different transport properties of the two isomers are mainly due to the effective conjugation length of the molecules. The transmission peak near the Fermi energy level of homeoisomer originates from Homo orbitals, and Homo orbitals of homeoisomers are more delocalized than trans isomers. Moreover, the transmission peak of trans isomer is far away from Fermi energy level, so the conductivity of trans isomer is lower than that of homeopathic isomer. It is found that the visible light absorption of the diaryl ethylene molecule can realize the bidirectional transition in the experiment of the diaryl ethylene photomolecular switch. Our simulations show that the current through the closed loop compound is much larger than that through the open loop compound. The current ratio is as high as 2700, which makes it show good switching characteristics. In addition, the negative differential resistance (NDR) phenomenon appears in our closed-loop devices. The absence of a transmission peak near the Fermi level is the reason for the weak conductivity of the ring opening compounds. The Homo and LUMO orbitals of the open ring compounds are local, while the LUMO orbitals of the closed loop compounds are delocalized. The transmission peaks near the Fermi energy level come from the LUMO orbitals, so the LUMO orbitals are the main electron transport orbits. When the bias voltage is 0.8 V, the transmission peak integral in the bias window is larger than the transmission peak integral at the bias voltage of 0.9 V, which is the reason for the NDR.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O469

【參考文獻(xiàn)】

相關(guān)期刊論文 前1條

1 華中一;分子尺寸器件與單分子器件[J];微納電子技術(shù);2002年07期

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本文編號(hào)：2065060