标题： 利用应变和表面功能物种工程化扶手椅形石墨烯纳米带的功函数：第一性原理研究 显示英文标题

标题： Engineering the work function of armchair graphene nanoribbons using strain and surface functional species: a first principles study

摘要： 通过第一性原理密度泛函理论计算研究了应变、边缘钝化和表面功能物种对扶手椅形石墨烯纳米带（AGNRs）结构和电子性质的影响，特别关注功函数。发现功函数随着单轴拉伸应变的增加而增加，随着压缩而减少。功函数在应变下的变化主要是由于费米能级随应变的变化。此外，讨论了功函数变化与核心能级位移之间的关系。发现了拉伸和压缩应变下核心能级位移的不同趋势。对于边缘碳原子被氧钝化的AGNRs，在中等应变下其功函数高于边缘被氢钝化的纳米带。在足够大的拉伸（压缩）应变下，这两种边缘钝化方式的功函数差异会增大（减小）。这与约4%的拉伸应变下的直接-间接带隙转变有关，并与约-12%的大压缩应变下的结构转变有关。此外，还研究了表面物种修饰（如不同覆盖密度的H、F或OH）的影响。发现功函数随表面功能物种的类型和覆盖率而变化。F和OH修饰会增加功函数，而H会降低它。表面功能物种被修饰在AGNRs的一侧或两侧。发现一侧和两侧修饰之间的功函数差异相对较小，这可能表明引入的表面偶极子起次要作用。 显示英文摘要

摘要： First principles density-functional theory calculations were performed to study the effects of strain, edge passivation, and surface functional species on the structural and electronic properties of armchair graphene nanoribbons (AGNRs) with a particular focus on the work function. The work function was found to increase with uniaxial tensile strain while decreasing with compression. The variation of the work function under strain is primarily due to the shift of the Fermi energy with strain. In addition, the relationship between the work function variation and the core level shift with strain is discussed. Distinct trends of the core level shift under tensile and compressive strain were discovered. For AGNRs with the edge carbon atoms passivated by oxygen, the work function is higher than for nanoribbons with the edge passivated by hydrogen under a moderate strain. The difference between the work functions in these two edge passivations is enlarged (reduced) under a sufficient tensile (compressive) strain. This has been correlated to a direct-indirect band gap transition for tensile strains of about 4% and to a structural transformation for large compressive strains at about -12%. Furthermore, the effect of the surface species decoration, such as H, F, or OH with different covering density, was investigated. It was found that the work function varies with the type and coverage of surface functional species. F and OH decoration increase the work function while H decreases it. The surface functional species were decorated on either one side or both sides of AGNRs. The difference in the work functions between one-side and two-side decorations was found to be relatively small, which may suggest an introduced surface dipole plays a minor role.