Substrate pre-sputtering for layer-by-layer van der Waals epitaxy of 2D materials

TL;DR

This paper introduces a substrate pre-treatment method using low-energy noble gas plasma to significantly improve layer-by-layer growth of 2D transition metal chalcogenides via molecular-beam epitaxy, enabling better control of the growth process.

Contribution

It presents a novel plasma-based substrate pre-treatment technique that enhances nucleation and growth control in MBE of 2D materials, addressing previous synthesis challenges.

Findings

Enhanced nucleation of 2D layers on treated substrates

Achieved true layer-by-layer epitaxial growth

Tunable growth dynamics through plasma exposure parameters

Abstract

Two-dimensional transition metal chalcogenides, with their atomically layered structure, favourable electronic and mechanical properties, and often strong spin-orbit coupling, are ideal systems for fundamental studies and for applications ranging from spintronics to optoelectronics. Their bottom-up synthesis via epitaxial techniques such as molecular-beam epitaxy (MBE) has, however, proved challenging. Here, we develop a simple substrate pre-treatment process utilising exposure to a low-energy noble gas plasma. We show how this dramatically enhances nucleation of an MBE-grown epilayer atop, and through this, realise a true layer-by-layer growth mode. We further demonstrate the possibility of tuning the resulting growth dynamics via control of the species and dose of the plasma exposure.