Epitaxial Growth of Pentacene on Alkali Halide Surfaces Studied by Kelvin Probe Force Microscopy

TL;DR

This study investigates the epitaxial growth and electronic properties of pentacene on alkali halide surfaces using Kelvin probe force microscopy, revealing molecular orientations, charge transfer effects, and defect structures relevant for molecular electronics.

Contribution

It provides new insights into the epitaxial growth mechanisms and electronic properties of pentacene on insulating surfaces, combining experimental microscopy with theoretical calculations.

Findings

Molecular islands of upright pentacene form on KBr and KCl surfaces.

Large local contact potential differences indicate partial charge transfer.

Line defects observed reveal epitaxial growth patterns.

Abstract

In the field of molecular electronics thin films of molecules adsorbed on insulating surfaces are used as the functional building blocks of electronic devices. A control of the structural and electronic properties of the thin films is required for a reliable operating mode of such devices. Here, noncontact atomic force and Kelvin probe force microscopies have been used to investigate the growth and electronic properties of pentacene on KBr(001) and KCl(001) surfaces. Mainly molecular islands of upright standing pentacene are formed, whereas a new phase of tilted molecules appear near step edges on some KBr samples. Local contact potential differences (LCPD) have been studied with both Kelvin experiments and density-functional theory calculations. Large LCPD are found between the substrate and the differently oriented molecules, which may be explained by a partial charge transfer from the pentacene to the surface. The monitoring of the changes of the pentacene islands during dewetting shows that multilayers build up at the expense of monolayers. Moreover, in the Kelvin images, previously unknown line defects appear, which unveil the epitaxial growth of pentacene crystals.