物理学报2025，Vol.74Issue(8)：178-185,8.DOI:10.7498/aps.74.20250076
Cd(0001)表面上苉分子的薄膜生长及电子透射现象
Thin film growth and electronic transmission of picene molecules on Cd(0001)surface
摘要
Abstract
The thin films of picene on the Cd(0001)surface are investigated by scanning tunneling microscopy(STM)in this work.Compared with conventional noble metal substrates such as Au,Ag,and Cu,Cd(0001)has low electronegativity and small work function,which can effectively weaken the molecule-substrate interactions,thereby promoting the intermolecular van der Waals attraction.The experiments are conducted by ultrahigh vacuum low-temperature STM combined with a molecular beam epitaxy system.The crystalline Cd(0001)films are grown on a surface of Si(111)-7×7 by depositing 15-20 monolayers of Cd atoms,followed by being annealed.The picene molecules are deposited on the Cd(0001)surface at 100-120 K,where monolayer(ML)is defined as the critical coverage before second-layer nucleation.All STM measurements are acquired in constant-current mode. It is observed that,in the submonolayer regime,the picene molecules occupy the entire substrate surface and form disordered two-dimensional molecular gas,indicating the existence of electrostatic repulsive interaction among picene molecules.With the coverage increasing,the first layer of molecules undergoes the disorder-order transition,forming the parallel array of molecular stripes of flat-lying molecules.The high-resolution STM images show that the building block of molecular stripes is a picene dimer with the opposite dipole moments.More importantly,under a specific bias voltage,the first layer of molecular stripes exhibits electronic transmission:not only can the underlying Cd substrate atoms be observed,but also the standing waves of scattered electrons can be observed near the defects.When the coverage exceeds 1.0 ML,the second picene layer also forms the stripe array composed of picene dimers of a flat-lying and a side-on molecules,similar to the(110)plane in picene crystals.The above results show that the electrons from the quantum-well states of Cd(0001)thin film have very strong penetration ability,and their vertical tunneling length reaches to the distance of two molecular layers.关键词
苉分子/扫描隧道显微镜/偶极-偶极相互作用/电子透射现象Key words
picene molecules/scanning tunneling microscopy/dipole-dipole interaction/electronic transmission引用本文复制引用
余涛,付诗润,鲁鸿平,王俊忠..Cd(0001)表面上苉分子的薄膜生长及电子透射现象[J].物理学报,2025,74(8):178-185,8.基金项目
国家自然科学基金(批准号:11874304,11574253)资助的课题. Project supported by the National Natural Science Foundation of China(Grant Nos.11874304,11574253). （批准号:11874304,11574253）
