本文選題：第一性原理　切入點：石墨烯　出處：《哈爾濱工業(yè)大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：石墨烯自從出現(xiàn)便掀起了納米科技領(lǐng)域的風(fēng)暴,有關(guān)它的應(yīng)用也日益增加。石墨烯獨特而出色的特性讓它成為了合成材料界的神奇焦點。雖然石墨烯被認(rèn)為是21世紀(jì)的一種很有潛力的材料,但是它仍然具有一些缺陷,比如,零帶隙、非磁性以及在可見光范圍只有2%的吸收率。單層石墨烯的電子結(jié)構(gòu)、磁學(xué)和光學(xué)特性可以通過在它的二維(2D)結(jié)構(gòu)中摻雜其他原子或團簇來進行調(diào)控。為了克服以上提到的純石墨烯的缺點并且調(diào)控其特性使其滿足工程應(yīng)用的需要,本文研究了在石墨烯晶格中引入其他的原子(比如,硼(B),氮(N),堿土金屬(AEM)和5d過渡金屬(TM))或團簇(比如,3d過渡金屬三氧化物和四氧化物(TMO_3(4)))。通過運用基于密度泛函理論(DFT)的第一性原理計算,本文研究了石墨烯以及雜質(zhì)原子或團簇?fù)诫s的石墨烯材料的結(jié)構(gòu)、電學(xué)、磁學(xué)和光學(xué)特性。純石墨烯和雜質(zhì)原子摻雜的石墨烯結(jié)構(gòu)的光學(xué)性質(zhì)是在隨機相位近似(RPA)下進行計算的。計算中采用了溫度為T=0 K下的參數(shù)。通過在石墨烯中摻入BN環(huán),可以觀察到,BN環(huán)摻雜的石墨烯結(jié)構(gòu)表現(xiàn)為直接帶隙,而且?guī)秾挾入S著石墨烯中BN環(huán)數(shù)量的增加而增加,同時隨著BN環(huán)數(shù)量的增加,吸收光譜呈現(xiàn)明顯的紅移趨勢,14 e V處的吸收峰幅值減小。對于AEM原子(比如,Be、Mg、Ca、Sr和Ba)摻雜的石墨烯,計算結(jié)果表明,Be、Mg和Ca原子摻雜的石墨烯結(jié)構(gòu)呈現(xiàn)半金屬特性,并分別帶有大小為0.00μB、1.86μB和4.00μB的磁矩。而Sr和Ba原子摻雜的石墨烯結(jié)構(gòu)呈現(xiàn)間接帶隙半導(dǎo)體特性,并分別帶有大小為3.16μB和0.46μB的磁矩。通過研究電子態(tài)密度,我們發(fā)現(xiàn)摻雜石墨烯結(jié)構(gòu)的磁矩是由雜質(zhì)原子的sp軌道引起的。計算結(jié)果表明,AEM元素的摻雜可以增加0到3 e V的吸收,并且減小14 e V處的吸收峰。另外在7到11 e V之間出現(xiàn)了第三個較小的吸收峰值,此峰值在純石墨烯吸收光譜中并未出現(xiàn)�？梢悦黠@觀察出吸收光譜朝著可見光范圍的紅移趨勢。同時可以發(fā)現(xiàn)AEM原子的摻雜引起了低能量區(qū)反射峰值的增加。同樣地,在5d TM原子(比如,Hf,Ta,W,Os,Re,Ir和Pt)替換雙空位的石墨烯中,Hf,Ta和W摻雜的石墨烯結(jié)構(gòu)在高對稱K點自旋向上和自旋向下的軌道處產(chǎn)生了帶隙,并分別帶有0.783μB、1.65μB和2.00μB的磁矩。Ir和Pt摻雜的結(jié)構(gòu)表現(xiàn)出了間接帶隙半導(dǎo)體性質(zhì)。有趣的是,Os摻雜的石墨烯結(jié)構(gòu)在自旋向上軌道處呈現(xiàn)直接帶隙半導(dǎo)體特性,并帶有1.5μB的磁矩。從態(tài)密度圖我們可以推測摻雜石墨烯結(jié)構(gòu)的磁性與5d TM原子的d軌道有關(guān)。所有雜質(zhì)原子(比如,AEM和5d TM元素)都被石墨烯緊緊地束縛,具有較大的結(jié)合能,并且電荷轉(zhuǎn)移的方向是從雜質(zhì)原子到石墨烯。之后,本文研究了用兩種不同的方法在石墨烯中嵌入3d TMO_3(TM=Ti、V、Cr、Fe、Co、Mn和Ni)。第一種是用TMO_3團簇直接替換了石墨烯中的四個碳(C)原子。在第二種方法中石墨烯環(huán)中的三個C原子被氧(O)原子替換而TM原子吸附在三個O原子的空位。在Cr、Fe、Co和Ni原子摻雜的情況下,費米能級向?qū)б苿?從而引起狄拉克錐向價帶移動,并且在高對稱K點產(chǎn)生了帶隙。在Ti O_3和VO_3摻雜的情況下,摻雜的結(jié)構(gòu)表現(xiàn)出半導(dǎo)體性質(zhì)。有趣的是,Ti O_3摻雜的結(jié)構(gòu)表現(xiàn)出稀磁半導(dǎo)體(DMS)性質(zhì)并帶有2.0μB的磁矩。相應(yīng)地,Co O_3、Cr O_3、Fe O_3和Mn O_3摻雜分別產(chǎn)生了1.015μB、2.347μB、2.084μB和3.584μB的磁矩。在第二種方法中O原子摻雜在石墨烯中,而TM原子吸附在空位,對于所有的摻雜結(jié)構(gòu)費米能級向?qū)б苿?狄拉克錐向價帶移動。在Cr和Ni吸附的情況下,體系表現(xiàn)為間接帶隙半導(dǎo)體,磁矩為0.0μB。Co吸附表現(xiàn)為DMS并產(chǎn)生了0.916μB的磁矩。Fe、Mn、Ti和V吸附在高對稱K點產(chǎn)生了帶隙,并分別產(chǎn)生了1.54μB、0.9909μB、1.912μB和0.98μB的磁矩。最后,我們分別用3d TMO_4替換石墨烯中的單空位和雙空位,然后研究了它們的性質(zhì)。計算結(jié)果表明,CrO_4和Mn O_4摻雜的單空位石墨烯結(jié)構(gòu)在自旋向下軌道表現(xiàn)出稀磁半導(dǎo)體性質(zhì)并分別具有2.15μB和3.51μB的磁矩。但是,Co O_4、Fe O_4、Ti O_4和Ni O_4摻雜的單空位石墨烯中,費米能級向?qū)б苿?引起了狄拉克錐向價帶移動,從而在高對稱K點產(chǎn)生帶隙。有趣的是,Co O_4、CrO_4,、Fe O_4和Mn O_4摻雜的雙空位石墨烯結(jié)構(gòu)在其自旋向上軌道表現(xiàn)出稀磁半導(dǎo)體性質(zhì),并分別具有1.74μB、3.27μB、3.09μB和1.99μB的磁矩。我們發(fā)現(xiàn),對于所有的TMO_3(4)團簇?fù)诫s,所有雜質(zhì)原子都被石墨烯緊緊地束縛,具有較大的結(jié)合能,并且電荷轉(zhuǎn)移的方向是從石墨烯到TMO_3(4)團簇。對TMO_3(4)團簇?fù)诫s石墨烯結(jié)構(gòu)態(tài)密度圖的深入分析表明摻雜石墨烯的磁矩是由3d TM原子的d軌道引起的。本文進行的研究以及得到的結(jié)論可以促進納米電子、自旋力學(xué)、能量存儲以及光電設(shè)備等應(yīng)用中以石墨烯為基礎(chǔ)的器件的設(shè)計和優(yōu)化。本文的研究還為未來本領(lǐng)域的研究指明了方向。同時對于本文提出的石墨烯摻雜結(jié)構(gòu)還需要進行進一步的實驗工作,從而和本文的理論預(yù)測結(jié)果進行對比。
[Abstract]:Since the emergence of graphene nano science and technology has set off a storm, the application is also increasing. The unique and outstanding characteristics of graphene makes it a focus of magical materials. Although the synthesis of graphene is believed to be a potential material in twenty-first Century, but it still has some defects, for example. The zero band gap, nonmagnetic and in the visible light absorption rate of only 2%. The electronic structure of graphene, magnetic and optical properties through its two-dimensional (2D) structure doped with other atoms or clusters to carry out regulation. In order to overcome the above mentioned pure graphene defects and control because of its characteristics to meet the needs of engineering application, the other atoms in the graphene lattice (for example, boron (B), nitrogen (N), alkaline earth metal and transition metal (AEM) 5D (TM)) or clusters (e.g., transition metal oxides and 3D three Four oxide (TMO_3 (4))). By using the density functional theory (DFT) based on the first principle calculation is studied in this paper, electrical and structure of graphene, graphene materials doped with impurity atoms or clusters, magnetic and optical properties. The optical properties of pure and impurity atoms of graphene doped graphene the structure is in the random phase approximation (RPA) was calculated. In the calculation of temperature parameters T=0 and K. The graphene doped BN ring can be observed, the graphene structure of BN doped ring for direct band gap and the band gap width increases with the increase of graphite by BN ring number at the same time, with the increase of BN ring number, the absorption spectra showed obvious red shift, 14 e V peak amplitude for AEM atoms (e.g., Be, Mg, Ca, Sr and Ba) doped graphene, the calculation results show that Be, Mg and graphene Ca doped The structure presents half metallic properties, and respectively provided with a size of 0 B, the magnetic moment of 1.86 B and 4 B. The graphene structure of Sr and Ba atoms present indirect bandgap semiconductor properties, and respectively provided with a magnetic moment size of 3.16 B and 0.46 B. Through the research on the electronic density of States, we that moment doped graphene structure is caused by impurity atoms SP orbit. The calculation results show that the AEM doping can be increased by 0 to 3 E V absorption, and reduce the 14 e absorption peak at V. In addition, between 7 to 11 e V the absorption peak appeared third smaller, the peak the values in the pure graphene absorption does not appear in the spectrum. It can be observed that the absorption spectra in the range of visible light. The red shift can be found at the same time the doping of the AEM atom caused an increase in the low energy region of the reflection peak. Similarly, in the 5D (for example, Hf, TM atoms Ta, W, Os, Re, Ir replace and Pt) 鍙岀┖浣嶇殑鐭沖ⅷ鐑腑,Hf,Ta鍜學(xué)鎺烘潅鐨勭煶澧ㄧ儻緇撴瀯鍦ㄩ珮瀵圭ОK鐐硅嚜鏃嬪悜涓婂拰鑷棆鍚戜笅鐨勮建閬撳浜х敓浜嗗甫闅，

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