卷曲方式对Rh原子在单壁碳纳米管内外吸附的影响

Helicity effects on Rh adsorption behavior inside and outside the single-wall carbon nanotubes

碳纳米管曲率与卷曲方式是同时存在并影响金属原子在碳纳米管内外吸附行为的重要因素,单独研究卷曲方式对金属吸附行为的影响较困难.选取曲率相近、卷曲方式不同的扶手椅型(6,6)、锯齿型(10,0)与手性(8,4)单壁碳纳米管(SWCNT),利用密度泛函理论研究了Rh原子在SWCNT内外的吸附行为.构型优化表明:由于SWCNT卷曲方式不同,导致Rh原子在(6,6),(10,0)与(8,4)SWCNT内外吸附的稳定构型不同;不同卷曲方式亦使SWCNT与Rh原子相互作用的C原子不同,导致Rh在不同管型内外吸附能的差异.电荷密度分析表明,SWCNT管外的电荷密度大于SWCNT管内的电荷密度,不同卷曲方式SWCNT电荷密度变化不同.差分电荷密度显示卷曲方式不同导致Rh原子与C原子相互作用时轨道取向不同,得失电子情况略有差异.能带结构分析表明,Rh原子吸附后的SWCNT在费米能级附近出现掺杂能带.吸附Rh原子后的(6,6)SWCNT仍呈金属性;当Rh原子在(10,0)SWCNT管内吸附时,SWCNT由半导体性转变为金属性,而Rh原子在SWCNT管外吸附时,SWCNT带隙降低;吸附Rh原子的(8,4)SWCNT带隙降低.

The curvature and the helicity of single-wall carbon nanotube （SWCNT） are the important factors which influence the adsorption behaviors of metal atoms inside and outside carbon tubes.However,it is difficult to investigate the separate effects of SWCNT helicity on the adsorption behaviors of metal atoms.In the present work,the armchair （6,6）,zigzag （10,0）,and chiral （8,4） tubes with similar curvature are selected,then the Rh adsorption behaviors inside and outside the tubes are systematically investigated using the density functional theroy.Due to the different SWCNT helicities,the stable configurations of Rh atoms on tubes are different.The neighbor carbon atoms interacting with Rh atoms vary with tube helicity,therefore,the Rh adsorption energies for a similar configuration are also different.It indicates that the outer charge density of SWCNT is higher than the inner one.Different helicities lead to different charge density variations along the radial direction.Charge density difference shows that the orbital orientations of Rh adatom and the electrons obtained and lost are slightly different due to the different helicities.The bandstructure indicates that the doping band appears near the Fermi energy level.The （6,6） tube with Rh adatom still exhibits metallicity.When Rh atoms are adsorbed inside the （10,0） tube,the nanotube transforms from the semiconducting into the metallic one.However,the band gap reduces when Rh atoms adsorbed outside the tube.After the Rh adsorption,the （8,4） tube band gap reduces.