碱(土)金属/双层α-硼烯纳米复合体的结构和功函性质的理论研究

Structure and Work Function of Alkaline(Earth)Metal-Bilayer α-Borophene Nanocomposite:A Theoretical Study

功函可调硼烯基电极材料可有效提升载流子的迁移效率,因此对于最大化器件的能量转换效率及性能至关重要.基于第一性原理密度泛函理论,研究了碱(土)金属吸附双层α-硼烯(M/DBBP;M=Li~Cs;Be~Ba)纳米复合材料的几何、稳定性、电子结构和功函随M电离能(IP)的变化规律.结果表明,所研究的10个M/DBBP体系均是热、动力学稳定的.M/DBBP体系的M—B键长、结合能、吸附原子与DBBP之间的电子转移和功函均与吸附原子IP呈(近)线性关系.由于Li和Be的尺寸非常小,其大幅增加的M—B成键区域导致Li/DBBP和Be/DBBP的结合能偏离了与其吸附原子IP之间的线性关系.由于Ca/DBBP中层间区域形成了独特的多中心键,使得Ca/DBBP的层间相互作用强度显著高于其余9个体系.M/DBBP保持了金属性,碱(土)金属原子与DBBP之间的成键方式均为离子键.此外,吸附原子向基体转移的电荷数和诱导偶极矩均随吸附原子IP的减小而增加,是碱(土)金属/DBBP功函降低的主要原因.本研究揭示了M/DBBP复合体的几何、稳定性、电子结构和功函的变化规律,为深入认识上述科学问题,以及实验上设计功函可调的硼烯基电极材料提供理论依据.

Work function-adjustable borophene-based electrode materials are of significant importance for achieving the max-imum energy conversion efficiency of electronic devices owing to their vital role in efficient transferring of carriers.Accord-ingly,understanding the regularity in the gradation of the work function for adatom-borophene nanocomposites with diverse adatoms will facilitate the design of such materials.Herein,the structural stabilities,electronic structures,and work functions of M-decorated experimentally available bilayer α-borophene(M/DBBP;M=Li~Cs;Be~Ba)are investigated systemati-cally.The results obtained indicate that M/DBBP are all thermodynamically and kinetically stable.Moreover,M—B bond length,binding energy(E_(b)),electron transfer between M and DBBP,and work function(ϕ)are linearly dependent on the ioni-zation potential(IP)in the same adatom family for these investigated systems.Furthermore,we report the two exceptional binding energies of Li/DBBP and Be/DBBP,which deviate from abovementioned IP dependence,owing to their extremely small adatoms and the resulting significantly enhanced effective M—B bonding areas.Impressively,the forming interlayer multi-centered B—B bonds lead to a significantly enhanced interlayer interaction of Ca/DBBP relative to other nine M/DBBP systems.In addition to interpreting that the metallic M/DBBP possesses ionic sp-p and dsp-p bonds for M_(1)/DBBP(M_(1)=Li,Na,Be,Mg,Sr,and Ba)and M_(2)/DBBP(M_(2)=K,Rb,Cs,and Ca),respectively,in particular,we confirm that the positive IP dependence of ϕ for alkali(earth)metal/DBBP originates from the synergistic effect of charge rearrangement and the increasing induced dipole moment.Our predictions not only provide guidance to the experimental efforts towards the realization of work function-adjustable borophene-based electrodes,which can be utilized as cathode materials in electronic devices,but also pre-sent a rational understanding of the bonding rules between varying alkali(earth)metal adatoms and bilayerα-borophene.