New strategy for black phosphorus crystal growth through ternary clathrate

TL;DR

This paper introduces a novel low-temperature, low-pressure method for synthesizing high-quality black phosphorus crystals using a ternary clathrate, emphasizing a vapor-solid-solid growth mechanism and resulting in high mobility crystals.

Contribution

The study presents a new synthesis strategy for black phosphorus crystals via ternary clathrate, highlighting the role of P vacancies and a vapor-solid-solid growth model.

Findings

Black-P crystals grow in situ at the original clathrate site.

P vacancies are crucial for Black-P formation.

High mobility (~350 cm^2/Vs) indicates high-quality crystals.

Abstract

We are reporting a new synthetic strategy to grow large size black phosphorus (Black-P) crystals through a ternary clathrate Sn$_{24}$P$_{22-x}$I$_8$, under lower synthetic temperature and pressure. The Black-P crystals are found grown in situ at the site where the solid clathrate originally resides, which suggests chemical vapor mineralizer does not play a critical role for the Black-P formation. More detailed systematical studies has indicated the P vacancies in the framework of ternary clathrate Sn$_{24}$P$_{22-x}$I$_8$ is important for the subsequent Black-P from phosphorus vapors, and a likely Vapor-Solid-Solid (VSS) model is responsible for the Black-P crystal growth. The obtained room temperature mobility {\mu} is ~ 350 $cm^2/Vs$ from Hall measurements at mechanically-cleaved flake, where noticeable micro-cracks are visible. The obtained high mobility value further suggest the high quality of the Black-P crystals synthesized through this route.