Harish C. Barshilia

Raman spectroscopy studies on the thermal stability of TiN, CrN, TiAlN coatings and nanolayered TiN/CrN, TiAlN/CrN multilayer coatings

About 1.5-um-thick single-layer TiN, CrN, TiAlN coatings and nanolayered TiN/CrN, TiAlN/CrN multilayer coatings were deposited on silicon (111) substrates using a13; reactive direct current magnetron sputtering process. Structural characterization of the coatings was done using x-ray diffraction (XRD) and micro-Raman spectroscopy. All13; the coatings exhibited NaCl B1 structure in the XRD data. Raman spectroscopy data of as-deposited coatings exhibited two broad bands centered at 230x2013;250 and 540x2013;630 cmx2212;1.13; These bands have been assigned to acoustical and optical phonon modes, respectively. Thermal stability of the coatings was studied by heating the coatings in air in a13; resistive furnace for 30 min in the temperature range 400x2013;900 xB0;C. Structural changes as a result of heating were characterized using Raman spectroscopy and XRD. Raman13; data showed that TiN, CrN, TiN/CrN, TiAlN, and TiAlN/CrN coatings started to oxidize at 500, 600, 750, 800, and 900 xB0;C, respectively. To isolate the oxidation-induced spectral changes as a result of heating of the coatings in air, samples were also annealed in vacuum at 800 xB0;C under similar conditions. The Raman data of vacuum-annealed coatings showed no phase transformation, and intensity of the optical phonon mode increased and shifted to lower frequencies. The origin of these spectral changes is discussed in terms of defect structure of the coatings. Our results indicate that the thermal stability of nanolayered multilayer coatings is superior to the13; single-layer coatings.

TiAlN∕TiAlON∕Si3N4 tandem absorber for high temperature solar selective applications

A tandem absorber of TiAlN∕TiAlON∕Si3N4 is prepared using a magnetron sputtering process. The graded composition of the individual component layers of the tandem absorber produces a film with a refractive index increasing from the surface to the substrate, which exhibits a high absorptance (0.95) and a low emittance (0.07). The tandem absorber is stable in air up to 600°C for 2h, indicating its importance for high temperature solar selective applications. The thermal stability of the tandem absorber is attributed to high oxidation resistance and microstructural stability of the component materials at higher temperatures.

Characterization of Cu/Ni multilayer coatings by nanoindentation and atomic force microscopy

Cu/Ni multilayer coatings prepared by RF/DC magnetron sputtering process were characterized using x-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) techniques. Films deposited under certain deposition conditions showed the appearance of satellite reflections around the principal reflections in the XRD data, indicating the formation of superlattice structure. Nanohardness measurements were performed on the films prepared under different deposition conditions, e.g. modulation wavelength (x39B;), copper to nickel thickness ratio (tCu/tNi) and substrate temperature (Ts). Nanohardness data revealed that the hardness was enhanced by a factor of 2.5 times that of the rule-of-mixtures value. This enhancement in hardness occurred over a limited range of x39B;. The results indicated that the hardness also depends on the copper to nickel thickness ratio and for tCu/tNi0.30 the films exhibited a maximum hardness. The hardness increased almost linearly with substrate temperature up to 200 xB0;C and got saturated at 250 xB0;C. No considerable change in the hardness was observed after vacuum annealing of the coatings. Imaging of the residual imprints by AFM revealed pile-up formation after indentation. The extent of pile-up, a measure of plastic flow of the material, was dependent on the preparation conditions of the multilayer coatings.

Structure and optical properties of pulsed sputter deposited CrxOy/Cr/Cr2O3 solar selective coatings

Spectrally selective CrxOy∕Cr∕Cr2O3 multilayer absorber coatings were deposited on copper (Cu) substrates using a pulsed sputtering system. The Cr targets were sputtered using asymmetric bipolar-pulsed dc generators in Ar+O2 and Ar plasmas to deposit a CrxOy (bottomlayer)∕Cr∕Cr2O3 (top layer) coating. The compositions and thicknesses of the individual component layers have been optimized to achieve high absorptance (0.899–0.912) and low emittance (0.05–0.06). The x-ray diffraction data in thin film mode showed that the CrxOy∕Cr∕Cr2O3 coating consists of an amorphous phase; the Raman data of the coating, however, showed the presence of A1g and Eg modes, characteristic of Cr2O3. The x-ray photoelectron spectroscopy (XPS) data from near-surface region of the absorber suggested that the chemical state of Cr was in the form of Cr3+ and no phases of CrO2 and CrO3 were present. The experimental spectroscopic ellipsometric data have been fitted with theoretical models to derive the dispersion of the optical const...

Microstructural modifications in diamond-like carbon thin films caused by high energy ion irradiation

Abstract The effect of high energy (85 MeV) nickel ions on diamond-like carbon thin films, deposited by microwave discharge of acetylene and methane gases mixed with hydrogen, has been investigated. IR, Raman and spectroscopic ellipsometry studies of irradiated and as-deposited films show large changes in their microstructural features. The effects of irradiation on films prepared from acetylene-hydrogen and methane-hydrogen gas mixtures are very different. Such a behaviour is proposed to be due to the microstructural variations in the as-deposited films.

Study of hydrogen in DLC film by ERDA with 58Ni ions

Abstract The content of hydrogen and its depth profile in diamond like carbon (DLC) films deposited by the microwave plasma deposition technique is determined by Elastic Recoil Detection Analysis (ERDA) using 85 MeV 58 Ni ions. Simultaneous detection of hydrogen and carbon recoils provided a method to determine the relative number of hydrogen: carbon atoms without using a standard H sample for quantitative calibration.

Carbon Nanotube‐Based Tandem Absorber with Tunable Spectral Selectivity: Transition from Near‐Perfect Blackbody Absorber to Solar Selective Absorber

CVD grown CNT thin film with a thickness greater than 10 μm behaves like a near-perfect blackbody absorber (i.e., α/ε = 0.99/0.99). Whereas, for a thickness ≤ 0.4 µm, the CNT based tandem absorber acts as a spectrally selective coating (i.e., α/ε = 0.95/0.20). These selective coatings exhibit thermal stability up to 650 °C in vacuum, which can be used for solar thermal power generation.

Growth and characterization of TiAlN∕CrAlN superlattices prepared by reactive direct current magnetron sputtering

TiAlN and CrAlN coatings were prepared using a reactive direct current magnetron sputtering system from TiAl and CrAl targets. Structural characterization of the coatings using x-ray diffraction (XRD) revealed the B1 NaCl structure of TiAlN and CrAlN coatings with a prominent reflection along the (111) plane. The XPS data confirmed the bonding structures of TiAlN and CrAlN single layer coatings. Subsequently, nanolayered multilayer coatings of TiAlN∕CrAlN were deposited on silicon and mild steel (MS) substrates at different modulation wavelengths (Λ) with a total thickness of approximately 1.0μm. The modulation wavelengths were calculated from the x-ray reflectivity data using modified Bragg’s law. TiAlN∕CrAlN multilayer coatings were textured along (111) for Λ<200A and the XRD patterns showed the formation of superlattice structure for coatings deposited at Λ=102A. The x-ray reflectivity data showed reflections of fifth and seventh orders for multilayer coatings deposited at Λ=102 and 138A, respectively,...

Deposition of TiN/CrN hard superlattices by reactive d.c. magnetron sputtering

Multilayer superlattice coatings of TiN/CrN were deposited on silicon substrates using a reactive d.c. magnetron sputtering process. Superlattice period, also known as modulation wavelength (A), was controlled by controlling the dwell time of the substrate underneath Ti and Cr targets. X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the films. The XRD data showed 1st and 2nd order satellite reflections along the principal reflection for films having 132 Å > Å > 84 Å, thus confirming the formation of superlattice. The multilayer coatings exhibited hardness(H) as high as 3200 kg/mm2, which is 2 times the rule-of-mixtures value (i.e.)HTiN= 2200 kg/mm2 andHCrN= 1000 kg/mm2). Detailed investigations on the effects of various process parameters indicated that hardness of the superlattice coatings was affected not only by modulation wavelength but also by nitrogen partial pressure and ion bombardment during deposition.

Effect of substrate roughness on the apparent surface free energy of sputter deposited superhydrophobic polytetrafluoroethylene coatings: A comparison of experimental data with different theoretical models

We have studied the effect of substrate roughness on the wettability and the apparent surface free energy (SFE) of sputter deposited polytetrafluoroethylene (PTFE) coatings deposited on untreated glass (average roughness, Ra=2.0 nm), plasma etched glass (Ra=7.4 nm), and sandblasted glass (Ra=4500 nm) substrates. The wettability of the PTFE coatings deposited on substrates with varying roughnesses was evaluated by measuring the apparent contact angle (CA) using a series of probe liquids from nonpolar aprotic to polar protic. The wettability measurements indicate that an apparent water CA of 152° with a sliding angle of 8° was achieved for PTFE coatings deposited on a substrate with Ra=4500 nm. The superhydrophobicity observed in these coatings is attributed to the presence of dual scale roughness, densely packed microstructure and the presence of CF3 groups. Unlike the bulk PTFE which is mainly dispersive, the sputter deposited PTFE coatings are expected to have some degree of polar component due to the pl...