2,7-二辛基[1]苯并噻吩并[3,2-b]苯并噻吩(C8-BTBT)与MoS_2界面的能级匹配与薄膜生长

Energy Level Bending and Molecular Packing Mode of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene(C8-BTBT) on MoS_2

结合紫外光电子能谱(UPS)、X射线光电子能谱(XPS)和原子力显微镜(AFM)等实验手段系统研究了C8-BTBT沉积在层状Mo S2基底上的界面能级匹配、薄膜生长和分子取向。研究发现C8-BTBT分子竖直生长在Mo S2上,生长过程中界面的真空能级(VL)、最高占据态轨道(HOMO)和电离能(IP)都出现了非常规的弯曲现象。这种能级弯曲行为可归因于直立分子从界面相到体相的转变过程中,其分子倾斜角(θ)存在一定的渐变,这种渐变会在沿表面法线方向诱导出一系列的层间电偶极,最终导致能级的弯曲。同时θ的变化也会改变薄膜的表面极化强度,引起IP的逐渐减小。能级的弯曲在界面处形成类P-N结的效应会对C8-BTBT基电子器件的性能有很大的影响。

The energy level alignment, film growth and molecular orientation of C8-BTBT on MoS2 were studied by ultraviolet photoemission spectroscopy ( UPS ) , X-ray photoemission spectroscopy ( XPS) and atomic force microscopy ( AFM) . The molecules adopt standing-up orientation on MoS2 and the island growth mood were confirmed. The ionization potential ( IP) decrease and highest oc-cupied orbital ( HOMO) down-shift were observed as the film thickness increased. IP decrease is as-cribed to the gradual increase of the surface electric dipole pointing inwards when the molecular tilt angle (θ) about the substrate normal decreases with the increasing of film thickness. The energy level shift results in an analogy P-N junction effect, which provides important guidance for C8-BTBT based electronic device design.