Keywords :
Phase transformation; X-ray absorption near edge spectroscopy; X-ray photoelectron spectroscopy; Annealing temperatures; B2 phase; Cd concentrations; CdO-nanoparticles; Composite thin films; Film-substrate interfaces; Phases transformation; Structural phase transformations; X-ray photoelectrons; Electronic, Optical and Magnetic Materials; Surfaces and Interfaces; Surfaces, Coatings and Films; Metals and Alloys; Materials Chemistry
Abstract :
[en] This study explores the influence of willemite Zn2SiO4 phase upon the structural phase transformation from the B1 (NaCl) to B2 (CsCl) phase in CdxZn1-xO (x = 0.20, and 0.60) composite thin films. X-ray diffraction and Raman spectroscopy analyses show that at an annealing temperature of 900 °C, the B2 phase of CdO nanoparticles becomes achievable with a relative atomic concentration of 60 % Cd, whereas it is absent with 20 % Cd concentration. The presence of the willemite Zn2SiO4 phase for 60 % Cd concentration at 900 °C annealing temperature, which plays an important role in this transformation, was confirmed by analyzing the Zn L3,2 and O K edges X-ray absorption near edge spectroscopy, Si 2p edge X-ray photoelectron spectroscopy, and a broad emission in the green spectral region of the photoluminescence spectra. Electron microscopy indicates the out-diffusion of Zn2SiO4 nanoparticles from the film-substrate interface to the film surface, facilitated by the kinetic energy gained during high-temperature thermal annealing. The larger unit cell volume of the trigonal Zn2SiO4 phase was identified as inducing the necessary local pressure to trigger the B1 to B2 phase transformation in the CdO nanoparticles. Additionally, simulations using Zn K edge extended absorption fine structure suggest that the local environment around the Zn atoms remain unchanged during phase transition. Cross-sectional transmission electron microscopy images reveal the presence of an amorphous SiOx layer at the film-substrate interface, facilitating atomic inter-diffusion and leading to the formation of the Zn2SiO4 nanoparticles. It is shown that a Cd concentration exceeding 40 % in the ZnO matrix enables the achievement of the experimentally challenging high-pressure B2 phase.
Funding text :
A. Das acknowledges Wallonie Bruxelles International's post-doctoral grant. A. Das acknowledges Dr. Xavier Noirfalise for his support during XPS measurements and Dr. Damien Cossement for his support during Raman spectroscopic measurements. C.B. is a Research Associate of the FRS-FNRS, Belgium This publication was partly developed under the provision of the Polish Ministry and Higher Education project Support for research and development with the use of research infrastructure of the \u201CNational Synchrotron Radiation Centre SOLARIS\u201D under contract No 1/SOL/2021/2. We acknowledge SOLARIS Centre for providing access to the PIRX Beamline. Authors acknowledge \u201CNational Synchrotron Radiation Research Centre\u201D, Taiwan for EXAFS measurements.A. Das acknowledges Wallonie Bruxelles International's post-doctoral grant. A. Das acknowledges Dr. Xavier Noirfalise for his support during XPS measurements and Dr. Damien Cossement for his support during Raman spectroscopic measurements. C.B. is a Research Associate of the FRS-FNRS, Belgium This publication was partly developed under the provision of the Polish Ministry and Higher Education project Support for research and development with the use of research infrastructure of the \" National Synchrotron Radiation Centre SOLARIS \" under contract No. 1/SOL/2021/2 . We acknowledge SOLARIS Centre for providing access to the PIRX Beamline. Authors acknowledge \u201CNational Synchrotron Radiation Research Centre\u201D, Taiwan for EXAFS measurements.
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