Size, Shape, and Phase Control in Ultrathin CdSe Nanosheets

TL;DR

This study presents a solution-based method to synthesize ultrathin CdSe nanosheets with tunable size, shape, and phase by using halogenated alkanes as additives, enabling precise control over their properties.

Contribution

The paper introduces a novel hot-injection synthesis approach utilizing halogenated alkanes to control the morphology and crystal phase of CdSe nanosheets.

Findings

Shape can be tuned from sexangular to triangular.

Phase can be switched from zinc blende to wurtzite.

Halide ions influence geometry and crystal structure evolution.

Abstract

Ultrathin two-dimensional nanosheets raise a rapidly increasing interest due to their unique dimensionality-dependent properties. Most of the two-dimensional materials are obtained by exfoliation of layered bulk materials or are grown on substrates by vapor deposition methods. To produce free-standing nanosheets, solution-based colloidal methods are emerging as promising routes. In this work, we demonstrate ultrathin CdSe nanosheets with controllable size, shape and phase. The key of our approach is the use of halogenated alkanes as additives in a hot-injection synthesis. Increasing concentrations of bromoalkanes can tune the shape from sexangular to quadrangular to triangular and the phase from zinc blende to wurtzite. Geometry and crystal structure evolution of the nanosheets take place in the presence of halide ions, acting as cadmium complexing agents and as surface X-type ligands, according to mass spectrometry and X-ray photoelectron spectroscopies. Our experimental findings show that the degree of these changes depends on the molecular structure of the halogen alkanes and the type of halogen atom.