Amun Amri

Near-edge X-ray absorption fine structure studies of Cr1-xMxN coatings

M. Mahbubur Rahman, Alex Duan, Zhong-Tao Jiang, Zonghan Xie, Alex Wu, Amun Amri, Bruce Cowie, Chun-Yang Yin

Chemical bonding states and solar selective characteristics of unbalanced magnetron sputtered TixM1−x−yNy films

Transition metal nitride TixM1−x−yNy (M = Al or AlSi) based thin films are evaluated as solar selective surfaces by correlating their spectral selective features with their crystal structure and chemical bonding state including mechanical strength. Ti0.5N0.5, Ti0.25Al0.25N0.5, and Ti0.25Al0.2Si0.05N0.5 films were synthesized on AISI M2 steel substrates via closed field unbalanced magnetron sputtering technology. These were investigated using XRD, SEM, XPS, UV-Vis, FTIR and nanoindentation techniques. Analysis of the optical properties showed the solar absorptance, in the visible range, of the TixM1−x−yNy films improved significantly from 51% to 81% with AlSi-doping and an increase of solar absorptance of up to 66% was recorded from films doped with Al. Moreover, the Al doping can reduce the thermal emittance in the infrared range from 6.06% to 5.11%, whereas doping with AlSi reduces the emittance to ca. 3.58%. The highest solar selectivity of 22.63 was achieved with TiAlSiN films. Mechanical studies showed enhanced hardness by ∼32%; enhanced yield strength by ∼16% and enhanced plastic deformation by ∼110% of Al and AlSi doped TiN matrix.

Investigation of the post-annealing electromagnetic response of Cu–Co oxide coatings via optical measurement and computational modelling

The optical frequency response and changes to the dielectric and optical parameters due to annealing temperature variation (200–500 °C) of sol–gel derived CuCoOx thin film coatings were investigated. The optical constants such as absorption coefficient, band-gaps, Urbach energy, complex refractive index, complex dielectric constants, optical dispersion parameters, and energy loss functions were determined from reflectance data analysis recorded in the ultraviolet to near-infrared (190–2200 nm) range. The absorption coefficient and the broadening of absorption edge (steepness parameter), energy band-gaps, Urbach energy, loss tangent and energy loss functions decreased with the increase in annealing temperatures. The refractive index displayed normal dispersion behaviors at higher frequency with the maximum value at a temperature of 500 °C. First-principles simulations, density functional theory (DFT+U) as implemented in the Cambridge Serial Total Energy Package (CASTEP), based on a cluster structure of Cu0.5Co2.5O4 system, optimized the crystalline structure and calculated the electronic structure of the framework. The calculated density of states (DOS) and associated absorption coefficient and dielectric constant results reasonably support the experimental findings.

3d Transition Metal Oxide based Sol-gel Derived Coatings for Photothermal Applications

Photothermal devices require high performance solar selective materials for the surface of solar energy converters. A good solar selective surface exhibits high spectral absorptance in the visible range and low thermal emittance in the infrared to far-infrared range of the solar spectrum. 3d transition metal oxide based thin film coatings are explored as high solar selective material to be used in solar energy harvesting devices. Solar selectivity of such coatings depends on the deposition conditions, crystal structure, chemical composition, microstructural morphology, composition uniformity and stoichiometry. This report highlights and summarizes the optical properties and mechanical characteristics of some recently developed sol-gel dip- coating derived from CuxCoyOz transition metal oxides based solar selective surfaces thinfilms. X-ray photoelectron spectroscopy (XPS), UV-Vis spectrometer, FTIR spectrophotometer, nanoindentation and Synchrotron radiation X-ray diffraction (SR-XRD) techniques are utilized to realize various features involved in such coatings.

Near-edge X-ray absorption fine structure studies ofCr1−xMxN coatings

M. Mahbubur Rahman, Alex Duan, Zhong-Tao Jiang, Zonghan Xie, Alex Wu, Amun Amri, Bruce Cowie, Chun-Yang Yin

Near-edge X-ray absorption fine structure studies of Cr₁₋ₓMₓN coatings

M. Mahbubur Rahman, Alex Duan, Zhong-Tao Jiang, Zonghan Xie, Alex Wu, Amun Amri, Bruce Cowie, Chun-Yang Yin