单层硅烯表面的CoPc分子吸附研究

由于低维材料表面上的单原子和分子具有丰富的物理化学性质,现已经成为量子器件及催化科学等领域的研究热点.单层硅烯在不同的衬底制备温度下,表现出丰富的超结构,这些超结构为实现有序的单原子或分子吸附提供了可靠的模板.利用原位硅烯薄膜制备,分子沉积,超高真空扫描隧道显微镜以及扫描隧道谱,本文研究了Ag(111)衬底上3种硅烯超结构((4×4),(■×■),(2■×2■))的电子态结构,表面功函数随超结构的变化,以及CoPc分子在这3种超结构硅烯上的吸附行为.研究结果表明,这3种超结构的硅烯具有类似的电子能带结构,且存在电子从Ag(111)衬底转移到硅烯上的可能性,从而导致硅烯的表面功函数增大,表面功函数在原子级尺度上的变化对分子的选择性吸附起着重要作用.此外,还观察到分子与硅烯的相互作用导致CoPc分子的电子结构发生对称性破缺.

Adsorption of CoPc molecules on silicene surface

As their characteristic dimensions are reduced to the nanoscale regime,such as single layer and single atom,the materials exhibit novel physical and chemical properties.Both the two-dimensional materials and the ordered array of single atoms or molecules have become cutting-edge research topics in the area of modern quantum devices and catalytic science.Silicene prepared on the Ag(111)substrate exhibits abundant superstructures at different substrate temperatures and coverages.These superstructures can be reliable templates for fabricating the ordered array of single atoms or molecules.Using in-situ silicene preparation,molecular deposition,ultra-high vacuum scanning tunneling microscope(STM),and scanning tunneling spectroscopy(STS),the electronic structures,surface work functions and adsorption behaviors of CoPc molecules on three silicene superstructures((4×4),(√13×√13),and(2√3×2√3))are studied.Firstly,the three silicene superstructures have similar electronic structures according to the characterization from the dI/dV curve at 77 K.The electronic structure varies on an atomic scale.With the disordering increasing,the full width at half maximum of the+0.6 V states broadens from(4×4)to(√13×√13)to(2√3×2√3).Secondly,the average surface work functions of the three superstructures of silicene also vary on an atomic scale and are all higher than those on the Silver surface.So,electrons are probably transferred from the Ag substrate to the single-layer silicene.The number of the transferred electrons increases from(4×4)structure,(√13×√13)structure,to(2√3×2√3)structure.Thirdly,the change of the surface work function on an atomic scale plays an important role in selectively adsorbing the CoPc molecules,which causes the symmetry of CoPc electronic structure to break.It indicates that none of the three silicene superstructures belongs to a completeπ-bond system.Especially,on the(4×4)superstructure,all CoPc molecules are divided into two halves.One half is similar to the free standing ones,in which there are HOMO(–0.45 V)and LUMO(+0.7 V)state.The other half has strong interaction with the silicene.The HOMO state is suppressed and there is a hybrid state at 1.0 V according to the dI/dV characterization.