D.C. Kothari

Tribological properties of (Ti,Al)N coatings deposited at different bias voltages using the cathodic arc technique

Abstract A study was carried out to see the effect of substrate bias voltage on various tribological properties of (Ti,Al)N films deposited using the arc-PVD technique. Films were deposited at substrate biases of −30, −50, −100, −300 and −500 V. It has been found that the Al at.% decreases with an increase in bias voltage. The wear rate measured using a calo-wear test is at a minimum for the films deposited at −100 V bias voltage. Lattice strain and microhardness show a maxima at −100 V. It is observed that the number of macro particles on the surface increases with bias voltage for −30 and −50 V and decreases after −100 V. The Glancing-angle XRD shows the presence of the h -(Ti,Al)N phase at lower bias voltages. The color varies from bluish black ( L =46.2, a *=−0.13, b *=−3.06) to brownish black ( L =43.84, a *=2.39, b *=−1.53) as the bias voltage is increased. Oxidation and corrosion properties show marginal change with bias voltage.

Hybrid Perovskite Quantum Nanostructures Synthesized by Electrospray Antisolvent–Solvent Extraction and Intercalation

Perovskites based on organometal lead halides have attracted great deal of scientific attention recently in the context of solar cells and optoelectronic devices due to their unique and tunable electronic and optical properties. Herein, we show that the use of electrospray technique in conjunction with the antisolvent-solvent extraction leads to novel low-dimensional quantum structures (especially 2-D nanosheets) of CH3NH3PbI3- and CH3NH3PbBr3-based layered perovskites with unusual luminescence properties. We also show that the optical bandgaps and emission characteristics of these colloidal nanomaterials can be tuned over a broad range of visible spectral region by compositional tailoring of mixed-halide (I- and Br-based) perovskites.

Effect of ion implantation on corrosion resistance and high temperature oxidation resistance of Ti deposited 316 stainless steel

Corrosion and oxidation studies of Ti coated on 316 SS have been performed after 30 keV N + 2 ion implantation. Thirty nanometer of Ti was coated on 316 SS by thermal evaporation method. The implantations were carried out at doses ranging from 1×10 16 to 5×10 17 ions/cm 2 . Glancing angle X-ray diffraction was used to check nitride formation after ion implantation. RBS and secondary ion mass spectroscopy were employed to find concentration and depth profile of Ti and nitrogen. The aqueous corrosion studies were carried out in 0.5 N H 2 SO 4 and 0.5 N HNO 3 solutions. The oxidation resistance studies were carried out in air at 800 °C using continuous and discontinuous method. The oxidation and corrosion resistance increase after nitrogen implantation. The oxidation resistance is maximum at a dose of 5×10 16 ions/cm 2 . It is also observed that the dose affects the initial period of nucleation. In case of aqueous corrosion it was found that corrosion resistance has improved substantially with respect to the untreated substrates. Saturation in corrosion improvement is noticed at higher doses.

XPS studies of N + implanted aluminium

Abstract 30 keV N+ ions are implanted in polycrystalline aluminium foils, at various doses. XPS spectra are recorded at various depths. For the specimens implanted at a dose of 1 × 1016 and 1 × 1017 ions cm 2 , the Al 2p 3 2 , binding energy (BE) is 75, 74.2 and 73 eV at different depths up to about 855 A. The N 1s 1 2 spectra recorded at various depths exhibit three distinct species corresponding to three binding energies equal to 399, 397.5 and 396.5 eV, for the signals coming from increasing depths. These species may be of adsorbed nitrogen, nonstoichiometric nitride and stoichiometric nitride respectively, formed due to bombardment induced N loss. However, such behaviour is not exhibited by specimen implanted at a higher dose of 1 × 1018 ions cm 2 . Therefore, for the nitrogen implanted aluminium system, the surface precipitation model seems to work.

XPS studies at various temperatures of nitrogen implanted 304 stainless steel

Abstract Thermal stability of the nitrides formed by ion implantation of nitrogen on 304 stainless steel (304 SS), is studied using X-ray photoelectron spectroscopy (XPS). Nitrogen implantation has been carried out at room temperature (RT) at a dose of 1 ×10 18 ions/cm 2 on 304 SS foils. XPS spectra have been recorded at RT, 150°C, 250°C, 350°C and 500°C. It is observed that various nitride phases are formed. The major redistribution of N atoms takes place above 250°C. At higher temperatures, possibly, Fe 2 + x N phases decompose and CrN concentration increases. The evolution of nitrogen gas is also observed. The method for determining the charge transfer from the XPS shift in the case of nitrides is developed and is applied in the present work. Microhardness changes in the implanted samples were also registered and their possible correlation with the nitride formation is discussed.

Recent trends in surface engineering using cathodic arc technique

Abstract The paper describes the developmental work of single layer and multilayer TiN, m-TiCN, (Ti,Al)N and m-(Ti,Al)N coatings for industrial applications (where the prefix ‘m’ stands for multilayer). The cathodic arc technique was used to deposit these coatings on high speed steel substrates (M2 grade) and cutting tools. For multi-layer m-TiCN deposition, (N 2 +CH 4 ) gas mixture was used. For (Ti,Al)N and m-(Ti,Al)N coatings, sintered-TiAl targets with 70 at.% aluminum were used. Thickness, hardness, abrasive wear and adhesion strength of the coatings were measured for a large number of samples (∼50) from different cycles and average values are presented in this paper. X-Ray diffraction (XRD) measurements reveal that all the coatings have (111) orientation. (Ti,Al)N coating has a better oxidation resistance than the other coatings under investigation. The corrosion resistance of the coatings under investigations is found to be comparable, (Ti,Al)N being marginally superior amongst the coatings studied. Wear constant measured using Calo-wear equipment for TiN, m-(Ti,Al)N, m-TiCN, and (Ti,Al)N are 2.7, 1.9, 1.7 and 0.7×10 −13 m 2 N −1 , respectively, indicating lowest wear resistance for TiN and highest for (Ti,Al)N amongst the coatings under investigation. A good correlation has been observed between the wear constant and the tool wear during machining.

XPS studies at various depths of low energy N2+ ions implanted on 304 stainless steel

Abstract We report here the effect of implantation at two doses, i.e. 1×1017 ions cm−2 (specimen-1) and 1×1018 ions cm−2 (specimen-2) of N2+ ions implanted on 304 stainless steel (304-ss) foils. It was observed that the microhardness increased with done. Surface analysis of the specimen was carried out using X-ray photoelectron spectroscopy (XPS) in order to understand the mechanism responsible for reduction in wear, reported by various groups. The presence of Fe2N seems to play a major role in microhardness and reduction in wear. Depth profiles of specimen 1 were carried out using the XPS technique. The concentration of nitrogen shows a near gaussian profile centring at about 30 nm whereas nickel and chromium segregate at the near surface region, showing higher concentration at about 20 nm. The concentration of iron is depleted at the near-surface region.

NiS1.97: A New Efficient Water Oxidation Catalyst for Photoelectrochemical Hydrogen Generation.

NiS1.97, a sulfur-deficient dichalcogenide, in nanoscale form, is shown to be a unique and efficient photoelectrochemical (PEC) catalyst for H2 generation by water splitting. Phase pure NiS1.97 nanomaterial is obtained by converting nickel oxide into sulfide by controlled sulfurization method, which is otherwise difficult to establish. The defect states (sulfur vacancies) in this material increase the carrier density and in turn lead to favorable band line-up with respect to redox potential of water, rendering it to be an effective photoelectrochemical catalyst. The material exhibits a remarkable PEC performance of 1.25 mA/cm(2) vs NHE at 0.68 V in neutral pH, which is almost 1000 times superior as compared with that of the stoichiometric phase of NiS2. The latter is well-known to be a cocatalyst but not as a primary PEC catalyst.

Glancing-angle X-ray diffraction and X-ray photoelectron spectroscopy studies of nitrogen-implanted tantalum☆

Abstract Polycrystalline tantalum thin foils are implanted with molecular nitrogen ions at an energy of 30 keV and with doses 1 × 1017, 2 × 1017 and 5 × 1017 N atoms cm−2 at room temperature. Different phases formed as a result of implantation are identified using glancing-angle X-ray diffraction. The specimen with dose 1 × 1017 N atoms cm−2 shows the presence of f.c.c. TaN, f.c.c. TaN0.04 and h.c.p. Ta5N6 phases. The specimen with dose 5 × 1017 N atoms cm−2 shows the formation of h.c.p. Ta2N and h.c.p. TaN in addition to the phases present in the specimen with the lower dose. X-ray photoelectron spectroscopy results show preferential nitrogen loss during implantation and argon sputtering.

X-ray diffraction peak profile analysis of TiNx films prepared on silicon by reactive ion beam assisted deposition

Abstract Reactive ion beam assisted deposition (RIBAD) was used to prepare TiN x films having different concentrations of nitrogen, on silicon. X-ray diffraction (XRD) was used to determine microstructural disorder parameters, i.e. the crystallite size and the microstrain of the phases present in the specimens. During film growth, initially [002] oriented titanium film was formed and was then replaced by the [111] oriented TiN x film on introduction of nitrogen. The crystallite size was found to be less than 10 nm and decreased as the nitrogen concentration increased. Microstrain was observed to increase with nitrogen concentration. The main cause for the increase in microstrain is suggested to be lattice parameter fluctuations induced by ion bombardment.