Nano scale phase separation in Au-Ge system on ultra clean Si(100) surfaces

TL;DR

This study investigates the formation of bi-lobed Au-Ge nanostructures on ultra-clean Si(100) surfaces under UHV conditions, revealing the necessity of gold-silicide formation for phase separation and detailed structural analysis.

Contribution

It demonstrates that gold-silicide nanoalloy formation is essential for Au-Ge phase separation into bi-lobed nanostructures on Si(100).

Findings

Gold-silicide nanoalloy formation is necessary for phase separation.

Au-Ge nanostructures form with side-by-side lobes after annealing.

Gold diffuses into the substrate, Ge remains localized.

Abstract

We report on the formation of lobe-lobe (bi-lobed) Au-Ge nanostructures under ultra high vacuum (UHV) conditions (\approx 3\times 10^{-10} mbar) on clean Si(100) surfaces. For this study, \approx 2.0 nm thick Au samples were grown on the substrate surface by molecular beam epitaxy (MBE). Thermal annealing was carried out inside the UHV chamber at temperature \apprx 500{\deg}C and following this, nearly square shaped Au_{x}Si_{1-x} nano structures of average length \approx 48 nm were formed. A \approx 2 nm Ge film was further deposited on the above surface while the substrate was kept at a temperature of \approx 500{\deg}C. Well ordered Au-Ge nanostructures where Au and Ge residing side by side (lobe-lobe structures) were formed. In our systematic studies, we show that, gold-silicide nanoalloy formation at the substrate (Si) surface is necessary for forming phase separated Au-Ge bilobed nanostructures. Electron microscopy (TEM, STEM-EDS, SEM) studies were carried out to determine the structure of Au - Ge nano systems. Rutherford backscattering Spectrometry measurements show gold inter-diffusion into substrate while it is absent for Ge.