本文選題：石墨烯 + 電場(chǎng)效應(yīng)�。� 參考：《太原理工大學(xué)》2015年碩士論文

【摘要】：自2004年在實(shí)驗(yàn)中成功制備出石墨烯以來(lái)，由于其具有特殊的物理和化學(xué)性質(zhì)，因此在復(fù)合材料、電子元件和晶體管、傳感器、太陽(yáng)能電池、吸附劑等方面都有廣泛的應(yīng)用前景。 石墨烯是碳原子以六邊形形式排列的超薄片狀納米材料，其厚度僅有碳原子大小，是到現(xiàn)階段為止世界上已知的最薄、最堅(jiān)硬的物質(zhì)，它接近全透明，且電阻率與其他材料相比較低，電子遷移速度也相對(duì)較快。本文主要是利用基于密度泛函理論的第一性原理計(jì)算方法的CASTEP軟件包，采用模守恒贗勢(shì)和超胞模型，系統(tǒng)地研究石墨烯納米帶的電場(chǎng)效應(yīng)以及石墨烯吸附不同濃度的氫原子的色散曲線和聲子振動(dòng)譜。具體完成的工作如下： 首先，利用第一性原理計(jì)算含有三個(gè)或四個(gè)Z型碳鏈的超窄石墨烯納米帶的電場(chǎng)效應(yīng)，其導(dǎo)電機(jī)制隨所加的垂直電場(chǎng)的改變而變化。在電場(chǎng)效應(yīng)下，超窄石墨烯納米帶的最高價(jià)帶與寬型石墨烯納米帶類(lèi)似，而最低導(dǎo)帶卻有兩種情況：自旋退化和自旋劈裂，這兩種最低導(dǎo)帶在量子空間是獨(dú)立的。隨著電場(chǎng)強(qiáng)度的增加，導(dǎo)電機(jī)制由最低導(dǎo)帶的自旋退化轉(zhuǎn)化成自旋劈裂。利用LDA和GGA泛函可以得到相同的理論結(jié)果，在實(shí)際計(jì)算中LDA和GGA通常都低估帶隙，而利用GGA計(jì)算得到的帶隙比LDA大。 其次，利用密度泛函微擾理論計(jì)算不同氫原子覆蓋度下石墨烯的聲子色散曲線和聲子振動(dòng)譜。根據(jù)聲子色散曲線以及聲子態(tài)密度的特征頻率可以識(shí)別氫原子的覆蓋度。由氫原子的化學(xué)性質(zhì)可知，氫原子在石墨烯上最穩(wěn)定的吸附位是碳原子正上方，即頂位。隨著氫原子覆蓋度的降低，高頻特征頻率值逐漸增大，振動(dòng)強(qiáng)度逐漸減小，最后趨于無(wú)限大石墨烯吸附單個(gè)氫原子的情形。當(dāng)覆蓋度為50%時(shí)，由于氫原子間的相互作用強(qiáng)，使石墨烯的晶格結(jié)構(gòu)發(fā)生大的形變，破壞了原有對(duì)稱(chēng)性，，改變了石墨烯的本征振動(dòng)模式，出現(xiàn)了兩支高頻特征振動(dòng)頻率，這是超高覆蓋度的特征。當(dāng)覆蓋度降低時(shí)，石墨烯自身結(jié)構(gòu)沒(méi)有大的形變，本征對(duì)稱(chēng)性基本保持不變，于是雙特征頻率恢復(fù)簡(jiǎn)并，雙特征峰變成單特征峰。這一理論預(yù)言可以幫助指導(dǎo)實(shí)驗(yàn)中對(duì)石墨烯上氫原子覆蓋度的測(cè)量和表征。 最后，在附錄部分我們基于第一性原理，研究了鹵素原子轟擊萘分子開(kāi)環(huán)裂解成鏈、以及負(fù)電和溶液效應(yīng)的反應(yīng)動(dòng)力學(xué)，分析了以產(chǎn)物的碳鏈長(zhǎng)度、結(jié)合能、存在時(shí)間和燃燒熱為參數(shù)的成本模型。結(jié)果表明：(1)萘分子和鹵素原子之間的電荷轉(zhuǎn)移是萘環(huán)開(kāi)環(huán)裂解的物理原因；(2)對(duì)于不同的轟擊位置，萘分子的碳碳鍵可以選擇性斷裂成不同長(zhǎng)度的碳鏈，生成的碳鏈可以進(jìn)一步通過(guò)加氫形成液體燃料；(3)負(fù)電效應(yīng)可以降低成本，乙醚溶液效應(yīng)對(duì)成本的影響是雙重的。
[Abstract]:Because of its special physical and chemical properties, graphene has been widely used in composite materials, electronic components and transistors, sensors, solar cells, adsorbents and so on since it was successfully prepared in 2004. Graphene is an ultrathin sheet material with carbon atoms arranged in hexagonal form. Its thickness is only the size of carbon atoms. It is the thinnest and hardest material known in the world so far, and it is close to full transparency. The resistivity is lower than that of other materials, and the electron migration rate is relatively fast. In this paper, we mainly use the CASTEP software package based on density functional theory (DFT) to calculate the first principles, and adopt the modular conserved pseudopotential and supercell model. The electric field effect of graphene nanobelts and the dispersion curves and phonon vibrational spectra of different concentrations of hydrogen atoms adsorbed by graphene were studied systematically. The work accomplished is as follows: First, the electric field effect of ultranarrow graphene nanobelts containing three or four Z-type carbon chains is calculated by first principles, and the conduction mechanism changes with the change of the vertical electric field. Under the electric field effect, the highest valence band of ultra-narrow graphene nanobelts is similar to that of broad graphene nanoribbons, but the lowest conduction bands have two conditions: spin degradation and spin-splitting, which are independent in quantum space. With the increase of electric field intensity, the conduction mechanism changes from the spin degradation of the lowest conduction band to the spin splitting. The same theoretical results can be obtained by using LDA and GGA Functionals. In practical calculations, LDA and GGA usually underestimate the band gap, but the band gap calculated by GGA is larger than that by LDA. Secondly, the phonon dispersion curves and phonon vibration spectra of graphene with different hydrogen atomic coverage are calculated by density functional perturbation theory. According to the phonon dispersion curve and the characteristic frequency of phonon density of states, the covering degree of hydrogen atom can be recognized. According to the chemical properties of hydrogen atom, the most stable adsorption site of hydrogen atom on graphene is the top position of carbon atom. With the decrease of hydrogen atomic coverage, the high frequency characteristic frequency increases gradually, the vibration intensity decreases gradually, and finally tends to the case of infinite graphene adsorbing a single hydrogen atom. When the covering degree is 50, because of the strong interaction between hydrogen atoms, the lattice structure of graphene is deformed greatly, the original symmetry is destroyed, the intrinsic vibration mode of graphene is changed, and two high frequency characteristic vibration frequencies appear. This is the characteristic of high coverage. When the coverage degree decreases, there is no big deformation in graphene structure, and the intrinsic symmetry remains basically unchanged, so the double characteristic frequency is degenerate and the double characteristic peak becomes a single characteristic peak. This theoretical prediction can help to guide the measurement and characterization of hydrogen atomic coverage on graphene in experiments. Finally, in the appendix, based on the first principle, we study the reaction kinetics of halide atom bombarding naphthalene molecules by ring opening and cracking, as well as the reaction kinetics of negative charge and solution effect. The length of carbon chain and binding energy of the product are analyzed. Cost model with time of existence and combustion heat as parameters. The results show that the charge transfer between naphthalene molecules and halogen atoms is the physical reason for the ring-opening cracking of naphthalene rings. For different bombardment sites, the carbon bond of naphthalene molecules can be selectively broken into carbon chains of different lengths. The resulting carbon chain can be further hydrogenated to form a liquid fuel, the negative charge effect can reduce the cost, and the effect of ether solution on the cost is dual.
【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TQ127.11;O647.3

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