苯并咪唑苝与金属Ag的界面电子结构研究

Study of electronic structure of 3,4,9,10-perylenetetracarboxylic bisimidazole/Ag interface by photoemission

利用同步辐射光电子能谱实验技术考察了苯并咪唑苝(BZP)和Ag的界面形成过程与电子结构.单层覆盖度以下时,BZP分子与Ag有弱相互作用,在有机分子禁带中出现明显界面反应态,结合能位于0.9eV.单层铺满后,BZP分子呈现三维岛式生长,且与Ag的相互作用逐渐减弱,同时最高占据分子轨道由于终态效应逐渐向高结合能方向位移至体相结合能位置(2.3eV).Ag衬底上BZP分子的生长导致样品表面功函数减小,表明形成了表面偶极势(Δ=0.3eV),且电子从有机分子向金属Ag偏移.最后,考察了BZP/Ag界面受温度和O2的影响,发现BZP/Ag界面在250℃以下退火后,其特征峰与带隙态的位置保持不变,但在O2气氛中暴露后带隙态消失,价带电子能级向低结合能位移.

Synchrotron radiation photoemission was used to investigate the interface between the organic semiconductor （BZP） and polycrystalline silver film. Before complete coverage by one monolayer, the BZP molecules interacted weekly with silver and a gap state appeared at 0.9 eV below Fermi level. After the coverage is complete, the growth of BZP is inferred to be in the 3D- island mode and the interaction with the substrate gradually diminishes. Because of the final state effect, the highest occupied molecular orbital （HOMO） level shifts to higher binding energy and reaches ultimately 2.3 eV of the HOMO level in the bulk. The deposition of BZP on silver surface resulted in the decrease of sample work function, which demonstrats interfacial dipoles forming on the BZP/Ag contact （△= 0.3 eV） and indicats the electrons being deviated from the organic molecules to the metal substrate. In addition, the effect of annealing and exposure to oxygen on the BZP/Ag interface has been taken into account. It is found that the binding energies of the characteristic peaks of BZP and the gap state hardly change after interface annealing at 250℃, but after being exposed to oxygen, the gap state disappears and the valence bands shift to lower binding energies.