Controlling the growth of Bi(110) and Bi(111) films on an insulating substrate

TL;DR

This study demonstrates the controlled growth of Bi(110) and Bi(111) thin films on an insulating substrate using synchrotron X-ray techniques, revealing temperature-dependent orientation transitions and film quality improvements.

Contribution

It introduces a method to control the crystallographic orientation and quality of bismuth films on insulating substrates through temperature regulation.

Findings

Bi(110) films can be grown at 40 K with pseudo-cubic structure.

Heating reduces roughness and induces a transition from Bi(110) to Bi(111).

High-quality, ultrasmooth Bi(111) films are achieved above 450 K.

Abstract

Here we demonstrate the controlled growth of Bi(110) and Bi(111) films on an (insulating) $\alpha$-Al$_2$O$_3$(0001) substrate by surface X-ray diffraction and X-ray reflectivity using synchrotron radiation. At temperatures as low as 40 K, unanticipated pseudo-cubic Bi(110) films are grown having a thickness ranging from a few to tens of nanometers. The roughness at the film-vacuum as well as at the film-substrate interface, can be reduced by mild heating, where a crystallographic orientation transition of Bi(110) towards Bi(111) is observed at 400 K. From 450 K onwards high quality and ultrasmooth Bi(111) films are formed. Growth around the transition temperature results in the growth of competing Bi(110) and Bi(111) thin film domains.