掺杂石墨烯吸附特性的第一性原理研究

利用第一性原理方法研究了一氧化碳分子在本征和硼、氮、铝、磷掺杂的有限尺寸石墨烯上的吸附机理.结果表明,石墨烯作为一氧化碳传感器时的性能依赖于掺杂元素.本征、硼和氮掺杂石墨烯吸附一氧化碳时的吸附能较低,为物理吸附.铝、磷掺杂石墨烯的吸附能显著提高,比本征、硼和氮掺杂时高出约一个数量级,且铝和磷原子从石墨烯中突出,使其发生局部弯曲.铝掺杂石墨烯增强了石墨烯与一氧化碳分子之间的相互作用,可以提高石墨烯的气敏性和吸附能力,是一氧化碳传感器的最佳候选材料之一.     

氮掺杂双层石墨烯吸附钠的第一性原理研究

采用密度泛函理论(DFT)的第一性原理方法,对Na在本征双层石墨烯(PBLG)和不同掺杂浓度的N掺杂石墨烯(NBLG)表面的吸附性质进行了研究.确定了不同N掺杂浓度时NBLG的最稳定N分布结构,计算了Na在PBLG和不同掺杂浓度的NBLG表面的吸附能.计算结果表明,N原子掺杂倾向于取代对位或次临近位置的C原子,并与下层C原子相对;随着N掺杂浓度的增加,吸附高度逐渐增加,且与掺杂N原子分布相匹配; Na在PBLG表面吸附使平均层间距增加,而在NBLG表面吸附使之减小; Na与C_(27)N_9表面的结合最稳定.     

硼掺杂双层石墨烯吸附钠的第一性原理研究

采用密度泛函理论(DFT)的第一性原理方法,对Na在本征双层石墨烯(PBLG)和不同掺杂浓度的B掺杂石墨烯(BBLG)表面的吸附性质进行了研究.确定了不同B掺杂浓度时BBLG的最稳定B分布结构,计算了Na在PBLG和不同掺杂浓度的BBLG表面的吸附能.计算结果表明,B原子掺杂倾向于占据上层中对位或次临近位置,并与下层中六边形碳环中心相对,B_4C_(32)的形成能最小;B掺杂浓度的增加使BBLG中上层石墨烯片层结构起伏增大,而对下层影响较小;Na在BBLG表面吸附高度和平均层间距受上层结构起伏影响显著;Na倾向于吸附在B_9C_(27)表面B原子的上方,使原始平面结构产生起伏,Na与B_9C_(27)表面的结合最稳定.     

Na在B掺杂的空位石墨烯上吸附性能的第一性原理研究

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯和B掺杂的空位石墨烯吸附Na原子的电荷密度、吸附能、态密度、储存量以及电极电压.结果表明,两种石墨烯中,Na原子的最佳吸附位置都是H位.B掺杂的空位石墨烯对Na原子的吸附能是-2.08 eV,比本征石墨烯对Na原子的吸附能(-0.71eV)低很多.B掺杂的空位石墨烯中Na原子与B原子发生轨道杂化,本征石墨烯中没有杂化现象.B掺杂的空位石墨烯能够吸附12个Na原子,较本征石墨烯多.因此,B掺杂的空位石墨烯更适合储钠.     

B、N掺杂对钠在石墨烯上吸附性能的影响

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯及缺陷石墨烯对Na原子的吸附行为。主要研究了三种石墨烯：本征石墨烯、B掺杂的石墨烯和N掺杂的石墨烯。结果表明,与本征石墨烯相比,B掺杂的石墨烯和N掺杂的石墨烯在吸附能、电荷密度、态密度和储钠量方面表现出很大的差异。B掺杂的石墨烯对Na原子的吸附能是-1.93 eV,约为本征石墨烯对Na原子吸附能的2.7倍;与本征石墨烯相比,N掺杂的石墨烯对Na原子的吸附能明显增大。态密度计算结果表明,Na原子与B掺杂的石墨烯中的B原子发生轨道杂化,而本征石墨烯和N掺杂的石墨烯中不存在轨道杂化现象。B掺杂的石墨烯对Na原子的吸附量是3个,与本征石墨烯相比显著提高。因此,B掺杂的石墨烯有望成为一种新型的储钠材料。     

B、N掺杂对钠在石墨烯上吸附性能的影响

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯及缺陷石墨烯对Na原子的吸附行为.主要研究了三种石墨烯:本征石墨烯、B掺杂的石墨烯和N掺杂的石墨烯.结果表明,与本征石墨烯相比,B掺杂的石墨烯和N掺杂的石墨烯在吸附能、电荷密度、态密度和储钠量方面表现出很大的差异.B掺杂的石墨烯对Na原子的吸附能是-1.93 e V,约为本征石墨烯对Na原子吸附能的2.7倍;与本征石墨烯相比,N掺杂的石墨烯对Na原子的吸附能明显增大.态密度计算结果表明,Na原子与B掺杂的石墨烯中的B原子发生轨道杂化,而本征石墨烯和N掺杂的石墨烯中不存在轨道杂化现象.B掺杂的石墨烯对Na原子的吸附量是3个,与本征石墨烯相比显著提高.因此,B掺杂的石墨烯有望成为一种新型的储钠材料.     

Y掺杂空位石墨烯对NO及CO气体表面吸附的第一性原理研究

摘　要：基于第一性原理的计算方法,建立了本征石墨烯、空位石墨烯及钇( Y)掺杂空位石墨烯模型,并计算了CO、NO在三类石墨烯表面的吸附过程. 从表面能、吸附结构、吸附能和态密度四个方面进行分析讨论,研究掺杂Y对CO、NO气体吸附性能的影响. 结果表明：CO、NO与本征石墨烯之间的吸附为弱的物理吸附,掺杂Y后增强了材料表面对CO、NO的吸附效果,最大吸附能分别为7.414eV、6.702eV,属于化学吸附;掺杂Y使空位石墨烯费米能级附近有了更多的活跃电子,其吸附NO后体系由半金属转变为金属特性,该特性能为开发更加优良的石墨烯气敏材料提供理论支持.     

五角石墨烯吸附H2S的第一性原理计算

硫化氢作为一种神经毒物和腐蚀性气体污染物,严重威胁人体健康并限制工业的发展.本文采用第一性原理计算的方法,研究了H₂S气体分子在原始五角石墨烯、非金属掺杂及金属掺杂五角石墨烯上的吸附行为.详细计算了H₂S气体分子与五角石墨烯之间的吸附构型、吸附能及电荷转移.结果表明:1)原始五角石墨烯和非金属元素掺杂五角石墨烯与H₂S气体分子间仅为微弱的物理吸附,无法直接用于吸附H₂S气体;2) Co、Ni、Cu及Ti掺杂的五角石墨烯对H₂S气体的吸附作用显著增强.当金属掺杂在sp~2C位置时,掺杂五角石墨烯对H₂S气体的吸附效果较好,此时的吸附均为化学吸附;3) Co、Ni、Cu及Ti掺杂的五角石墨烯均可作为H₂S气体的传感/捕获材料.其中Cu掺杂五角石墨烯吸附H₂S气体的效果最好.本文的研究结果对设计开发基于五角石墨烯的H₂S气体传感/捕获材料提供了理论指导.     

碱金属在石墨烯表面吸附，迁移行为的第一性原理研究

利用基于密度泛函理论的第一性原理方法计算了3种碱金属（Li,Na,K）在石墨烯表面的吸附性质,迁移行为和电学性质。结果表明：3种碱金属在石墨烯表面的最稳定吸附位都是H位;吸附过程中电荷由碱金属原子向石墨烯片层转移。Li→Na→K,吸附能先减小再增大,吸附的强弱顺序为Li−石墨烯体系强于K −石墨烯体系和Na−石墨烯体系;体系的离子性逐渐增强;碱金属原子在石墨烯表面的迁移激活能逐渐降低,迁移行为更容易实现。     

碱金属在石墨烯表面吸附，迁移行为的第一性原理研究

利用基于密度泛函理论的第一性原理方法计算了3种碱金属（Li,Na,K）在石墨烯表面的吸附性质,迁移行为和电学性质。结果表明：3种碱金属在石墨烯表面的最稳定吸附位都是H位;吸附过程中电荷由碱金属原子向石墨烯片层转移。Li→Na→K,吸附能先减小再增大,吸附的强弱顺序为Li−石墨烯体系强于K −石墨烯体系和Na−石墨烯体系;体系的离子性逐渐增强;碱金属原子在石墨烯表面的迁移激活能逐渐降低,迁移行为更容易实现。     

Electronic and magnetic behaviors of graphene with 5d series transition metal atom substitutions: A first-principles study

The electronic structures and magnetic behaviors of graphene with 5d series transition metal atom substitutions are investigated by performing first-principles calculations. All the impurities are tightly bonded to single vacancy in a graphene sheet. The substitutions of La and Ta lead to Fermi level shifting to valence and conduction band, respectively. Both the two substitutions result in metallic properties. Moreover, the Hf, Os and Pt-substituted systems exhibit semiconductor properties, while the Re and Ir-substituted ones exhibit robust half-metallic properties. Interestingly, W-substituted system shows dilute magnetic semiconductor property. On the other hand, the substitution of Ta, W, Re and Ir induce 0.86 μ_B, 2 μ_B, 1 μ_B and 0.99 μ_B magnetic moment, respectively. Our studies demonstrate that the 5d series transition metal substituted graphene have potential applications in nanoelectronics, spintronics and magnetic storage devices.     

Enhanced gas-sensing performance of graphene by doping transition metal atoms: A first-principles study

By performing the first-principles calculations, we investigated the sensitivity and selectivity of transitional metal (TM, TMSc, Ti, V, Cr and Mn) atoms doped graphene toward NO molecule. We firstly calculated the atomic structures, electronic structures and magnetic properties of TM-doped graphene, then studied the adsorptions of NO, N₂ and O₂ molecules on the TM-doped graphene. By comparing the change of electrical conductivity and magnetic moments after the adsorption of these molecules, we found that the Sc-, Ti- and Mn-doped graphene are the potential candidates in the applications of gas sensor for detection NO molecule.     

Fe,Co,Ni掺杂石墨烯表面吸附C_2H_4的第一性原理研究

基于密度泛函理论(DFT)的广义梯度近似(GGA),本文对本征石墨烯以及掺杂Fe,Co,Ni石墨烯的几何结构和电子性质进行了优化计算,并计算了C_2H_4在本征石墨烯以及掺杂石墨烯表面的吸附过程,讨论了体系的吸附能、稳定性、DOS及掺杂对键长的影响.结果表明C_2H_4在本征石墨烯B位的吸附和掺杂石墨烯的吸附为化学吸附,在本征石墨烯T和H位的吸附为物理吸附;掺杂后石墨烯的比表面积增大,与本征石墨烯相比,掺杂使费米能级附近的态密度积分显著提高,表明掺杂石墨烯的电导性会发生变化,从而影响对C_2H_4的气敏度..C_2H_4在Fe、Co、Ni分别掺石墨烯的最佳吸附位为T位、H位和B位;掺杂Fe,Ni后体系的吸附能力显著提高,且掺杂Ni时体系的吸附能力最好.     

Manipulation of inherent characteristics of graphene through N and Mg atom co-doping; a DFT study

First-principles calculations were performed to investigate the structural, electronic, magnetic and optical properties of nitrogen (N) and magnesium (Mg) atom co-doped graphene systems. We observed that, N and Mg atom co-doping in graphene, introduces half-metallic properties in the electronic structure of graphene, introduces ferromagnetism behavior along with new trends in optical properties of graphene. Doping site and concentration of N and Mg atoms in graphene was changed and resulting effects of these changes on aforementioned properties were investigated. Through density of states plots we observed that, Mg atom sp orbitals mainly induced magnetic moments in graphene. It was revealed that, N/Mg atoms substitution in graphene introduces a red shift in absorption spectrum towards visible range and a finite absorption coefficient quantity value in 0 to 3 eV and 7 to 11 eV energy intervals is also produced, that is unavailable for absorption spectrum of intrinsic graphene. Moreover, N/Mg atoms co-doping produces increment in the reflectivity parameter of graphene in low lying energy region, while producing diminishing behavior in the higher energy range. These results offer a possibility to tune electronic, magnetic and optical characteristics of graphene sufficiently for utilization in graphene based spintronic and optoelectronic devices.     

Structures of Pt clusters on graphene by first-principles calculations

The interactions between Pt_n clusters (n?13) and a graphene sheet have been investigated by first-principles calculations based on density functional theory. For single Pt-atom and Pt₂-dimer adsorptions, the stable adsorption sites are bridge sites between neighboring carbon atoms. When the number of Pt atoms in a cluster increases, the Pt-C interaction energy per contacting Pt atom becomes smaller. For smaller clusters (3?n?7), the adsorption as a vertical planar cluster is more stable than that as parallel planar or three-dimensional (3D) clusters, due to the stability of a planar configuration itself and the stronger planar-edge/graphene interaction, while the adsorption as a parallel planer cluster becomes stable for larger cluster (n?7) via the deformation of the planar configuration so as to attain the planar-edge/graphene contact. For much larger clusters (n?10), the adsorption as a 3D cluster becomes the most stable due to the stability of the 3D configuration itself as well as substantial Pt-C interactions of edge or corner Pt atoms. The interfacial interaction between a Pt cluster and graphene seriously depends on the shape and size of a cluster and the manner of contact on a graphene sheet.     

Aluminum and nitrogen impurities in Wurtzite ZnO: first-principles studies

First-principles calculations have been performed to investigate the doping behaviors of Al and N dopant impurities in ZnO. According to the results, in the Al mono-doping case, the impurity states are quite delocalized, the corresponding effective masses are small, and the formation energy is as low as −9.71 eV. In the N mono-doping case, the impurity states are localized, the effective masses are large, and the formation energy is high (4.55 eV in the most favorable extreme O-rich conditions). In the Al-N codoping case, the corresponding effective masses are marked decreased compared to the N mono-doping situations, and the formation energy of the N-Al-N system is as low as −2.54 eV in the O-rich condition. The above results can explain the electrical behaviors of the doped or codoped ZnO systems observed in experiments.     

Vibrational properties and Raman spectra of different edge graphene nanoribbons,studied by first-principles calculations

The vibrational properties and Raman spectra of graphene nanoribbons with six different edges have been studied by using the first-principles calculations. It is found that edge reconstruction leads to the emergence of localized vibrational modes and new topological defect modes, making the different edges identified by polarized Raman spectra. The radial breathing-like modes are found to be independent of the edge structures, while the G-band-related modes are affected by different edge structures. Our results suggest that the polarized Raman spectrum could be a powerful experimental tool for distinguishing the GNRs with different edge structures due to their different vibrational properties.     

Intermediate band insertion by group-IIIA elements alloying in a low cost solar cell absorber CuYSe2: A first-principles study

By using first-principles calculations based on HSE06 hybrid functional, the structural, electronic, and optical properties of CuYSe₂ as a low cost absorber material have been studied. Our results show that CuYSe₂ is a semiconductor with indirect band gap of 1.46 eV and optical band gap of 2.00 eV. Especially, an intermediate band has been found in Ga and In alloyed CuYSe₂, respectively, which can be served as a stepping stone to optical absorption on low energy photons. Therefore, Ga and In alloyed CuYSe₂ with an intermediate band as a new absorber material have been proposed.     

Exploration the p-type doping mechanism of GaAs nanowires from first-principles study

Using first-principle calculations, we present a systematic investigation upon the influence of p-type doping on the structural and electronic properties of H-passivated GaAs nanowires with wurtzite structure. The GaAs nanowire models of different doping types, different doping elements, different doping positions and different doping concentrations are established. The calculated formation energies show that Zn element becomes more competitive or even slightly favored in realizing p-type doping compared to Be element. For an individual Zn incorporation model, Zn atom tends to substitute the subsurface Ga atom. As increasing Zn doping concentration, the p-type doping process becomes more and more difficult. Besides, both interstitial and substitutional doping lead to the distortion of atomic structure near impurity atoms and cause the ionicity of GaAs nanowires enhanced. The p-type doped GaAs nanowires models are all direct band gap semiconductors. After substitutional doping, the total density of state curves shift toward higher energy sides and the Fermi level entering valence bands. Our calculations provide a significant reference for the preparation of p-type doping GaAs nanowire, which has a promising potential application in the field of photocathodes.