Conducting Probe Atomic Force Microscopy Investigation of Anisotropic Charge Transport in Solution Cast PBD Single Crystals Induced by an External Field

摘要

2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-l,3,4-oxdiazole (PBD) is a good electron-transporting material and can form single crystals from solution.In this work,solution cast PBD single crystals with different crystallographic axes (b,c) perpendicular to the Au/S substrates in large area are achieved by controlling the rate of solvent evaporation in the presence and absence of external electrostatic field,respectively.The orientation of these single crystals on Au/S substrate was characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM).Conducting probe atomic force microscopy (CP-AFM) was used to measure the charge transport characteristics of PBD single crystals grown on Au/S substrates.Transport was measured perpendicular to the substrate between the CP-AFM tip and the Au/S substrate.The electron mobility of 3 x 10~3 cm~2/(V s) for PBD single crystal along crystallographic b-axis is determined.And the electron mobility of PBD single crystal along the c-axis is about 2 orders of magnitude higher than that along the b-axis due to the anisotropic charge transport at the low voltage region.We demonstrate that CP-AFM may be applied successfully to measuring the anisotropic charge transport of single crystals over nanoscopic length scales.