密度泛函理论研究十二烷硫醇在Au(111)面上的吸附

采用第一性原理方法研究了十二烷硫醇(C₁₂H₂₅SH)分子在Au(111)面上未解离和解离吸附的结构、能量和吸附性质,在此基础上分析判断长链硫醇分子在Au(111)面吸附时S―H键的解离, 以及分子链长度对吸附结构和能量的影响. 计算了S原子在不同位置以不同方式吸附的系列构型, 结果表明在S―H键解离前和解离后,均存在两种可能的表面结构, 直立吸附构型和平铺吸附构型; 未解离的C₁₂H₂₅SH分子倾向于吸附在top位, 吸附能为0.35-0.38 eV; H原子解离后C₁₂H₂₅S基团倾向于吸附在bri-fcc位, 吸附能量为2.01-2.09 eV. 比较分析未解离吸附和解离吸附, 发现C₁₂H₂₅SH分子未解离吸附相较于解离吸附要稳定, 未解离吸附属于弱化学吸附.局域电子态密度和差分电荷密度分析进一步验证了S―H解离后S原子与表面之间成键的数目增加, 而且键合更强. 同时我们发现长链硫醇的吸附能量较短链硫醇的吸附能量略大, S原子与表面Au原子之间的距离略小.

Density Functional Theory Study on the Adsorption of Dodecylthiol on Au(111) Surface

By applying the first-principles methods based on density functional theory and the slab model, we have studied the non-dissociative and dissociated adsorptions of a dodecylthiol (C₁₂H₂₅SH) molecule on Au(111) surface. Based on the calculated results, the fate of the H atom has been analyzed, and the longchain adsorption and short-chain adsorption have been compared. We have performed structure optimizations for a series of initial structures with the S atom located on different sites with different tilt angles. This structure optimizations gave two surface structures before and after the dissociation of S―H; the standing-up and lying-down adsorption structures. Our calculations indicate that the C₁₂H₂₅SH molecule prefers to stay on the top site, the corresponding adsorption energies are 0.35-0.38 eV. The dissociated C12H25S group prefers to adsorb on the bri-fcc site, with adsorption energies of 2.01-2.09 eV. We have compared the non-dissociative C₁₂H₂₅SH/Au(111) and dissociated C₁₂H₂₅S/Au(111) with the H atom adsorbing onto Au and desorbing as H₂, and found that the non-dissociative adsorption is more stable. The formation energy and the electronic structure showed that the non-dissociative adsorption belongs to the weak chemisorption, whereas the interaction between the S atom and Au surface becomes much stronger following cleavage of the S―H. A comparison of the adsorption of long-chain thiols on Au(111) surface with that of the short-chain thiols, indicates that the adsorption energies of the long-chain thiols are slightly larger, and the distances between the S atomand the surface Au atoms are slightly shorter.