Size, Shape, and Phase Control in Ultrathin CdSe Nanosheets

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.Comment: 24 pages, 6 figure

Ligand Displacement Exposes Binding Site Heterogeneity on CdSe Nanocrystal Surfaces

“…1,2 The specific binding of organic ligands to nanocrystal surfaces is used to control the size and shape of NCs as they grow in a reaction mixture. [3][4][5][6] Moreover, the resulting ligand capping stabilizes NC dispersions by steric hindrance and facilitates the homogeneous dispersion of NCs in solvents or polymer matrices. 7,8 In addition, ligands play a role in the physical properties of NCs.…”

A comparative study demonstrates strong size tunability of carrier–phonon coupling in CdSe-based 2D and 0D nanocrystals

“…Optoelectronic properties of semiconductor nanoparticles attract increasing interest because of their promising application potential. Particularly 2D semiconductors in the form of nanoplatelets and sheets [1][2][3][4][5][6] receive growing attention due to fast radiative lifetimes 7,8 related to strong exciton correlation and the giant oscillator strength effect 4,9,10 allowing high quantum yields, 11,12 promising lasing properties [13][14][15] and high two-photon absorption. [15][16][17] Furthermore, their directed emission 18 and polarization 19 and well-width dependent high dark-bright splitting 20,21 of 3-6 meV are of direct interest.…”

Self‐Limited Epitaxial Growth of Ultrathin Nonlayered CdS Flakes for High‐Performance Photodetectors

“…Here, only through restraining the growth of special crystallographic facets can we realize the anisotropic growth, resulting in 2D morphology . Based on this, some nonlayered 2D structures have been obtained via wet chemistry methods (i.e., TiO 2 , PbS, CdSe, CdS). However, the small size (below 1 µm), low crystal quality, and unavoidable residual organics will bring myriad fabrication challenges for further optoelectronic applications .…”