Pentacene islands grown on ultra-thin SiO2

TL;DR

This study demonstrates the growth and detailed characterization of pentacene islands on ultra-thin SiO2 films, revealing molecular structure, orientation, and surface morphology at room temperature.

Contribution

It provides new insights into pentacene film growth on ultra-thin oxide substrates, including molecular resolution and surface morphology analysis.

Findings

Pentacene forms standing-up grains in the first layer.

Molecular resolution achieved in subsequent layers.

Surface morphology follows substrate step structure.

Abstract

Ultra-thin oxide (UTO) films were grown on Si(111) in ultrahigh vacuum at room temperature and characterized by scanning tunneling microscopy. The ultra-thin oxide films were then used as substrates for room temperature growth of pentacene. The apparent height of the first layer is 1.57 +/- 0.05 nm, indicating standing up pentacene grains in the thin-film phase were formed. Pentacene is molecularly resolved in the second and subsequent molecular layers. The measured in-plane unit cell for the pentacene (001) plane (ab plane) is a=0.76+/-0.01 nm, b=0.59+/-0.01 nm, and gamma=87.5+/-0.4 degrees. The films are unperturbed by the UTO's short-range spatial variation in tunneling probability, and reduce its corresponding effective roughness and correlation exponent with increasing thickness. The pentacene surface morphology follows that of the UTO substrate, preserving step structure, the long range surface rms roughness of ~0.1 nm, and the structural correlation exponent of ~1.