Direct observation of structural phase transformations during continuous phosphorus deposition on Cu(111)

TL;DR

This study uses advanced microscopy techniques to observe the real-time transformation of phosphorus on Cu(111), revealing a new growth pathway for phosphorene involving an intermediary copper phosphide phase.

Contribution

It provides the first direct observation of the structural phase transformations during phosphorus deposition, uncovering a novel growth mode for phosphorene on metal surfaces.

Findings

Phosphorus initially intermixes with Cu forming copper phosphide.

A transition from phosphide to blue phosphorene occurs as P concentration increases.

Multilayer phosphorene growth proceeds via self-assembly of phosphorus clusters.

Abstract

Blue phosphorene -- two-dimensional, hexagonal-structured, semiconducting phosphorus -- has gained attention as it is considered easier to synthesize on metal surfaces than its allotrope, black phosphorene. Recent studies report different structures of phosphorene, for example, on Cu(111), but the underlying mechanisms of their formation are not known. Here, using a combination of in situ ultrahigh vacuum low-energy electron microscopy and in vacuo scanning tunneling microscopy, we determine the time-evolution of the surface structure and morphology during the deposition of phosphorus on single-crystalline Cu(111). We find that during early stages of deposition, phosphorus intermixes with Cu, resulting in copper phosphide structures. With increasing surface concentration of phosphorus, the phosphide phase disappears and a blue phosphorene layer forms, followed by self-assembly of highly ordered phosphorus clusters that eventually grow into multilayer islands. We attribute the unexpected transformation of stable phosphide to a phosphorene layer, and the previously unreported multilayer growth, to the presence of a large concentration of P2 dimers on the surface. Our results constitute direct evidence for a new growth mode leading to a phosphorene layer via an intermediary phase, which could underpin the growth of other 2D materials on strongly interacting substrates.