Faculty Publications

Now showing 1 - 3 of 3

Electron beam deposited multilayer optical interference coatings using oxide composites
(Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2012) Nayak, A.N.; Sahoo, N.K.; Tokas, R.B.; Biswas, A.; Kamble, N.M.
Optical multilayer interference coatings are not only the key elements/components of the lasers, synchrotron (beam lines), and solar devices but also serve to propagate, deliver and manipulate electromagnetic radiations involved there for materials science experiments. Composite oxide thin film materials have added several promising dimensions with respect to the design, development of such precision devices related to such applications. Binary ZrO2MgO and ternary ZrO2-MgO-Al2O3 oxide composite thin films have been deposited using electron beam physical vapor deposition (EB-PVD) technique and nano-metric multilayer devices utilizing such films in a regular periodic layered design have been developed. As a specific objective, a multilayer high-reflection (HR) laser mirror having a designated bandwidth has been designed and developed for the Nd:YAG second harmonic laser wavelength of 532 run. These composite thin films and multilayers have been characterized using various microstructural probing techniques.
Optical properties of TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber coatings by phase-modulated spectroscopic ellipsometry
(Springer Verlag service@springer.de, 2017) Jyothi, J.; Biswas, A.; Sarkar, P.; Soum-Glaude, A.; Nagaraja, H.S.; Barshilia, H.C.
TiAlC, TiAlCN, TiAlSiCN, TiAlSiCO, and TiAlSiO layers of thicknesses ~2.2 ?m, 755, 491, 393, and 431 nm, respectively, were deposited on stainless steel, silicon, and glass substrates to study their refractive indices and extinction coefficients using the phase-modulated spectroscopic ellipsometry in the wavelength range of 300–1200 nm. Absorption coefficient of each layer was calculated from the extinction coefficient of the layer. The results indicate that the first three layers (i.e., TiAlC, TiAlCN, and TiAlSiCN) are absorbing in nature, while TiAlSiCO and TiAlSiO act as intermediate and antireflection layers. Subsequently, a tandem absorber of TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO with layer thicknesses of 62, 20, 18, 16, and 27 nm, respectively, was deposited on stainless steel substrates to fabricate a spectrally selective coating with absorptance of 0.961 and emittance of 0.15 at 82 °C. The obtained refractive indices and extinction coefficients of the tandem absorber were used to simulate the reflectance of the deposited tandem absorber using SCOUT software. Simulated reflectance data of the tandem absorber showed a good agreement with the experimental data measured by UV–Vis–NIR and FTIR spectrophotometry. The angular dependence of the selective properties of the tandem absorber was studied by measuring the reflectance spectra of the tandem absorber at different incident angles. © 2017, Springer-Verlag GmbH Germany.
Structural and Thermophysical Anomalies of Liquid Water: A Tale of Molecules in the Instantaneous Low- And High-Density Regions
(American Chemical Society service@acs.org, 2020) Priyadarsini, A.; Biswas, A.; Chakraborty, D.; Mallik, B.S.
Water is believed to be a heterogeneous liquid comprising multiple density regions that arise because of the presence of interstitial molecules and can be differentiated by their structure as well as the existence of hydrogen-bonded pairs with varying strengths. First-principles molecular dynamics studies were performed at six different temperatures to investigate the effect of temperature on the thermophysical, structure, dynamics, and vibrational spectral properties of the water molecules using dispersion-corrected density functional theory. The variation of properties like density, cohesive energy, and compressibility with a change in temperature produces a trend that matches with the experiments and resembles the experimentally observed anomalous behavior. We explore the possibility of explaining the trends in calculated properties by analyzing the structure and dynamics of the water molecules in terms of instantaneous low- and instantaneous high-density regions that are found during the simulation time. The dynamics of these two types of water molecules were studied by calculating the lifetime from the proposed autocorrelation functions. The lifetime of formation of instantaneous low-density water is found to decrease with an increase in temperature, whereas the lifetime of instantaneous high-density water is found to be maximum at 298 K among all the considered temperatures. The presence of more interstitial water molecules is observed at this temperature. The signature of these water molecules is found in the radial distribution function, spatial distribution function, void distribution, configurational space, orientational dynamics, and spectral diffusion calculations. It is also found that around 298 K, these water molecules are present distinctively that mix up with the first and second solvation shells with the rise of the temperature. The outlook of the reported results can be extended to other thermodynamic conditions to explain some of the anomalous properties, which can be related to the presence of the interstitial molecules in water. © © 2020 American Chemical Society.

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