# Growth of large crystals of Janus phase RhSeCl using self-selecting vapour growth

## TL;DR

This paper introduces a new method to grow large, high-quality Janus RhSeCl crystals, which are important for advanced electronic devices.

## Contribution

A novel two-step self-selecting vapour growth method for large-scale synthesis of phase-pure Janus RhSeCl crystals.

## Key findings

- Crystals up to 6 mm in size were successfully synthesized using the new method.
- A previously unreported impurity was identified and strategies to avoid it were demonstrated.
- The method allows reproducible production of high-quality monolayer flakes for device fabrication.

## Abstract

In recent years, interest in 2D Janus materials has grown exponentially, particularly with regard to their applications in spintronics and optoelectronic devices. The defining feature of Janus materials is the ordered arrangement of different layer terminations – creating chemically distinct surfaces and an inherent out-of-plane polarity. Among the few known Janus materials, RhSeCl is particularly intriguing as a rare example of an intrinsic Janus compound. Owing to its exceptional chemical stability, RhSeCl offers a promising platform for exploring the physics related to the Janus-structure. However, synthesising large, high-quality crystals of this compound remains a significant challenge. Here, we report a novel synthetic pathway for growing crystals up to 6 mm in lateral size via a two-step self-selecting vapour growth reaction. We further present a comprehensive comparison of newly developed synthesis routes with all previously reported methods for RhSeCl. During these investigations, we identified a previously unreported impurity that forms in specific growth pathways and demonstrate how it can be avoided to obtain phase-pure few- and monolayer flakes. We showcase the reproducibility of the process to obtain high-quality, large single-crystals and flakes.

Large Janus RhSeCl crystals grown via a two-step self-selecting vapour growth approach starting from SeCl4 and their exfoliation down to a monolayer for device fabrication.