First-principles Study Based On Graphene And Armchair Graphene Nanoribbons

Graphene,a "single-layer graphite sheet",is a new type of two-dimensional six-membered ring structure.Its special electronic structure makes graphene have excellent physical and chemical properties.Due to the special zero band gap structure of graphene,the application of graphene in semiconductor devices is limited.Based on the first-principles principle,the electronic structures and optical properties of graphene and graphene nanobelts doped at different concentrations were calculated.The electronic structure and optical properties of the armchair-type graphene nano-doped boron atoms were studied and analyzed,which provided a theoretical basis for the application of graphene in semiconductor devices.In the paper the main work is divided into the following:1.The electronic structure and optical properties of intrinsic graphene and graphene at different doping concentrations were obtained by first-principles calculation based on density functional theory.The results show th at the intrinsic graphene is a special material with zero band gap,and the conduction band and the valence band are compared with the Dirac point.The graphene system doped with boron atoms is strongly p-type doped,the Dirac point is not zero,and as the doping concentration increases,the Fermi level enters the valence band,making the valence band a non-full band.Thereby exhibiting the characteristics of the metal.The doped nitrogen atom doping system is a strong n-type doping.As the doping concentration increases,the Fermi level enters the conduction band,causing the conduction band to change from empty to non-full.The boron-nitrogen diatomic co-doped graphene system and the intrinsic graphene system are isoelectronic systems,and the 2p orbital electrons of the boron atom and the 2p orbital electrons of the nitrogen atom are strongly hybridized,so that the band gap at the Fermi level is opened.The band gap value of the para-doped system is 1.28 7eV,the band gap value of the meta-doping system is 0.167e V,and the band gap of the ortho-doping system is 1.2eV.The doping systems of the three different positions have different static dielectric functions,wherein the value of the static dielectric function of the meta-doping is the largest.The absorption peak of the ortho doping system in the low frequency region is the largest,and the absorption peak of the paramagnetic doping in the high frequency region is the largest.The para-doping has the high,est intensity of reflection in the far-ultraviolet band and a wider reflection band in the infrared and visible bands.The meta-doping system is more effective for the reflection of longer wavelength infrared light bands.2,Graphene nanoribbon models with different widths were established on the MS computing software platform to calculate their electronic structure and optical properties.It can be known from the calculation results that the graphene is made into a nanobelt model of a certain width,and the band gap of the band is also opened.As the bandwidth of the nanobelt increases,the bandgap value shows a variation characteristic of period 3;in an oscillation period,the magnitude relationship of the bandgap value can be Eg(Na=3m+1)>Eg(Na=3 m)>Eg(Na=3 m+2),and a simple explanation is given for this..3.based on the first-principles principle,the formation energy of graphene nanobelts doped with boron atoms at different positions was obtained by MS calculation software platform.The results show that the structure of graphene nanoribbons with edge-doped boron atoms is more stable.The electronic structure and optical properties of the edge-doped boron atoms were calculated.As a result,the graphene nanoribbons with edge-doped boron atoms formed a band gap of about 05 eV,and the peak of the optical absorption spectrum was weakened after doping.The use of doping to modulate the performance of graphene nanoribbons is a very useful method.Therefore,it is very important to further and extensively study the doping performance of graphene nanoribbons and the development of devices.