Mid-IR band gap engineering of CdxPb1−xS nanocrystals by mechanochemical reaction

Guo-Long Tan,Weibing Wu,Limin Liu

doi:10.1063/1.4881878

Abstract

Composition-tunable ternary CdxPb1−xS nanocrystals (NCs) are very important materials for remote sensing and detecting in the infrared (IR) wavelength region. They are, however, almost exclusively prepared by wet chemical routes which lead to surface-capped nanoparticles. The surface capping molecules could move their absorption peaks from mid-IR to near IR wavelength region. However, surface clean CdxPb1−xS nanocrystals (NCs) would demonstrate intrinsic optical spectrum in the mid-IR region. Herein, we present a physical mechanical alloying (MA) process being applied to prepare tens of grams of surface clean CdxPb1−xS nanocrystals within the composition range of x = 0.0 to 0.4. The average particle size is smaller than 9 nm. The as-milled nanocrystals are chemically homogenous. The CdxPb1−xS nanocrystals show a continuous lattice contraction with Cd content. There is an exponential indirect band gap-composition relationship. This MA method shows the ability to continuously and precisely tune the band gap energies of ternary CdxPb1−xS semiconductor nanocrystals from mid-IR region (2638 nm) to NIR wavelength region (1240 nm) through chemical composition.

Highlights

Over the past two decades, with their unique size-dependent optical properties and potential for a wide range of applications, more and more people pay attention to semiconductor nanocrystals
Ternary alloys prepared out of binary semiconductors provide a class of semiconductors in which the lattice parameter, band gap energy, and other operational parameters could be continuously varied within specified limits by alloying appropriate binary constituents with changes in their relative concentrations.[1,2,3]
The structural evolution of as-milled powders upon different ball milling period was monitored by Rigaku powder X-ray diffraction machine as well as JEOL 2100F high resolution transmission electronic microscopy (HRTEM)

Summary

INTRODUCTION

Over the past two decades, with their unique size-dependent optical properties and potential for a wide range of applications, more and more people pay attention to semiconductor nanocrystals. It is significant to take an alternative physical method to prepare surface clean and homogeneous alloyed CdxPb1−xS nanocrystals, which could demonstrate tunable intrinsic optical spectrum or band gap energies at mid IR wavelength region and continuous lattice parameter change with variation of chemical composition (x). Mechanical alloying process is such a physical method for mass fabrication of surface clean semiconductor NCs. A certain number of semiconductor nanocrystals, such as PbS,[19] CdSe,[20] CdTe,[21] CdS,[22] ZnS,[23] and CdSe1−xSx (x = 0∼1),[24] have been prepared by this top-down approach with average sizes smaller than 10 nm. We are going to present the synthesis of ternary CdxPb1−xS NCs with clean surface and homogeneous composition by mechanical alloying process.

EXPERIMENTAL PROCEDURE

Structure feature

Findings

CONCLUSION