High temperature mediated rocksalt to wurtzite phase transformation in cadmium oxide nano-sheets and their theoretical evidence

TL;DR

This study demonstrates a high-temperature phase transformation in cadmium oxide nano-sheets from rocksalt to wurtzite structure, supported by experimental characterization and theoretical calculations revealing the underlying electronic and structural changes.

Contribution

It provides new experimental evidence and theoretical insights into the temperature-induced phase transition in CdO thin films, combining multiple advanced techniques and simulations.

Findings

Phase transformation confirmed by XRD and TEM

Optical band gap increases from 2.2 to 3.2 eV after annealing

Structural evolution into nano-sheet network observed

Abstract

In the paper, high temperature induced phase transformation in chemically grown CdO thin films has been demonstrated whereas their corresponding electronic origin is further investigated by density functional theory. In particular, cubic rocksalt to hexagonal wurtzite PT in 900 degree centigrade annealed CdO thin films is confirmed by Xray diffraction , consistent with High Resolution Transmission Electron Microscopy. Such high temperature treatment also leads to significant enhancement in optical band gap from 2.2 to 3.2 eV as manifested by UV-Visible spectroscopy. Moreover, atomic force microscopy and scanning electron microscopy clearly evidence the structural evolution via formation of nano-sheet network in wurtzite phased CdO films. Furthermore, Xray Absorption spectra at oxygen k edge revealed a notable shift in inflection point of absorption edge while X-ray Photoelectron spectroscopy of Cd 3d and O 1s suggested the gradual reduction in CdO2 phase with increasing annealing temperature. In addition, different complementary techniques including Rutherford Backscattering, Raman Spectroscopy have also been exploited to understand the aforementioned PT and their structural correlation. Finally, molecular dynamics simulation along with density functional theory calculations suggest that symmetry modification at Brillouin zone boundary provides a succinct signature for such PT in CdO thin film.