The influence of substrate temperature on growth of para-sexiphenyl thin films on Ir{111} supported graphene studied by LEEM

TL;DR

This study investigates how substrate temperature affects the growth and structure of para-sexiphenyl thin films on Ir{111} supported graphene using LEEM, revealing defect sites as nucleation points and different growth modes at various temperatures.

Contribution

It provides real-time insights into the growth mechanisms of para-sexiphenyl films on graphene, highlighting the role of defects and temperature in determining molecular orientation and film morphology.

Findings

Defects on graphene serve as nucleation sites for 6P growth.

Different growth modes observed at various temperatures.

Wetting layer and needles have similar molecular structures.

Abstract

The growth of para-sexiphenyl (6P) thin films as a function of substrate temperature on Ir{111} supported graphene flakes has been studied in real-time with Low Energy Electron Microscopy (LEEM). Micro Low Energy Electron Diffraction (\mu LEED) has been used to determine the structure of the different 6P features formed on the surface. We observe the nucleation and growth of a wetting layer consisting of lying molecules in the initial stages of growth. Graphene defects -- wrinkles -- are found to be preferential sites for the nucleation of the wetting layer and of the 6P needles that grow on top of the wetting layer in the later stages of deposition. The molecular structure of the wetting layer and needles is found to be similar. As a result, only a limited number of growth directions are observed for the needles. In contrast, on the bare Ir{111} surface 6P molecules assume an upright orientation. The formation of ramified islands is observed on the bare Ir{111} surface at 320 K and 352 K, whereas at 405 K the formation of a continuous layer of upright standing molecules growing in a step flow like manner is observed.