R. S. Rawat

Rapid Synthesis of Cobalt Nitride Nanowires: Highly Efficient and Low‐Cost Catalysts for Oxygen Evolution

Electrochemical splitting of water to produce hydrogen and oxygen is an important process for many energy storage and conversion devices. Developing efficient, durable, low-cost, and earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is of great urgency. To achieve the rapid synthesis of transition-metal nitride nanostructures and improve their electrocatalytic performance, a new strategy has been developed to convert cobalt oxide precursors into cobalt nitride nanowires through N2 radio frequency plasma treatment. This method requires significantly shorter reaction times (about 1 min) at room temperature compared to conventional high-temperature NH3 annealing which requires a few hours. The plasma treatment significantly enhances the OER activity, as evidenced by a low overpotential of 290 mV to reach a current density of 10 mA cm(-2) , a small Tafel slope, and long-term durability in an alkaline electrolyte.

Deposition of titanium nitride thin films on stainless steel—AISI 304 substrates using a plasma focus device

Abstract A 3.3 kJ pulsed plasma focus device was used to deposit thin films of titanium nitride (TiN) at room temperature onto the stainless steel—AISI 304 substrates. The small plasma focus device, fitted with solid titanium anode instead of the usual hollow copper anode, was operated with nitrogen as the filling gas for deposition of TiN thin films. Films were deposited with different numbers of focus shots, at different distances from the top of the anode, and at different angular positions with respect to the anode axis. Deposited films have been characterized for their structure by X-ray diffractometry (XRD), surface morphology by scanning electron microscopy (SEM), elemental composition and distribution mapping by energy dispersive X-ray (EDX) analysis and hardness using a nanoindenter. XRD patterns show the growth of as-deposited polycrystalline TiN thin film. Diffraction patterns for films deposited along the anode axis show induction of a phase corresponding to iron chromium nickel on the film–substrate interface. SEM pictures confirm uniformly distributed TiN grains with hardly any crack over the film surface. Conglomeration of smaller TiN grains, to form bigger size grains, is seen to occur at the films deposited with higher total ion flux. The EDX spectra show the presence of expected constituent elements. EDX mapping confirms the uniform distribution of TiN on the film surface. The variation in structure, morphology, thickness and hardness of the deposited films with the variation of film deposition parameters is explained, qualitatively, on the basis of ion emission characteristics of the focus device. Polycrystalline, smooth and hard thin films of TiN are successfully deposited at room temperature stainless steel—AISI 304 substrates using the plasma focus device.

Soft X-ray optimization studies on a dense plasma focus device operated in neon and argon in repetitive mode

This paper investigates the emission characteristics of a high-performance low-energy (3-kJ) repetitive dense plasma focus device, NX2, operated at up to 1-Hz repetition rate to develop it as an intense source of soft X-rays (SXR) for microlithography and micromachining. Various SXR yield optimization studies with argon and neon as filling gases were performed under different operating conditions (charging voltage, filling pressure, anode length, and insulator sleeve length). The SXR yield was computed using signals obtained from a PIN diode SXR spectrometer with appropriate filters. When operated in neon, the average optimum SXR (/spl lambda//spl sim/1 nm) yield in 4/spl pi/ steradians was found to be up to 140 J/shot, which corresponded to a wall plug efficiency of 5.6%. Operation in argon showed that optimized SXR (/spl lambda//spl sim/0.4 nm) yield was up to 1.3 J/shot. While operating with neon under optimized conditions with a water-cooled anode in repetitive mode, the NX2 device was used as a SXR source to imprint a test lithograph on a highly sensitive chemically-amplified resist SU-8. Test structures showing the effect of a stepper with aspect ratio 3:1 on 10-/spl mu/m-thick SU-8 resist film were obtained.

Oxygen rich p-type ZnO thin films using wet chemical route with enhanced carrier concentration by temperature-dependent tuning of acceptor defects

This paper reports the temperature-dependent tailoring of acceptor defects in oxygen rich ZnO thin films, for enhanced p-type conductivity. The oxygen rich p-type ZnO thin films were successfully grown by pulsed laser deposition on silicon substrate at different postdeposition annealing temperatures (500–800 °C). The oxygen rich ZnO powder was synthesized by wet chemical method using zinc acetate dihydrate [Zn(CH3COO)2·2H2O] and potassium hydroxide (KOH) as precursors. The powder was then compressed and sintered to make pellets for pulsed laser deposition system. The x-ray diffraction analysis exhibits an improved crystallinity in thin films annealed at elevated temperatures with a temperature-dependent variation in lattice constants. An analysis of Auger Zn L3M4,5M4,5 peak reveals a consistent decrease in interstitial zinc (Zni) exhibiting its temperature-dependent reversion to zinc lattice sites. Room temperature photoluminescence of the p-type ZnO shows a dominant deep level emission peak at ∼3.12 eV r...

Computing plasma focus pinch current from total current measurement

The total current Itotal waveform in a plasma focus discharge is the most commonly measured quantity, contrasting with the difficult measurement of Ipinch. However, yield laws should be scaled to focus pinch current Ipinch rather than the peak Itotal. This paper describes how Ipinch may be computed from the Itotal trace by fitting a computed current trace to the measured current trace using the Lee model. The method is applied to an experiment in which both the Itotal trace and the plasma sheath current trace were measured. The result shows good agreement between the values of computed and measured Ipinch.

Optimization of the high pressure operation regime for enhanced neutron yield in a plasma focus device

The average total neutron yield is measured, using an indium foil activation detector, at various combinations of filling gas pressures (including the higher pressure operation regime) of deuterium, capacitor bank charging voltages, anode lengths and insulator sleeve lengths to optimize the neutron yield from the NX2 Plasma Focus device. A remarkable six-fold increase in the average maximum total neutron yield, to a record value of (7 ± 1) × 108 neutrons per shot, compared to the similar energy UNU-ICTP Plasma Focus device is achieved for deuterium at a relatively much higher filling gas pressure of 20 mbar. The average peak neutron energy for the axial direction (0°), radial direction (90°) and backward direction (180°) is estimated to be 2.89 ± 0.25 MeV, 2.49 ± 0.20 MeV and 2.11 ± 0.12 MeV, respectively. The average forward to radial neutron yield anisotropy is found to be 1.46 ± 0.28. The neutron energy and anisotropy measurements suggest that the neutron production mechanism may be predominantly beam target.

Effect of energetic ion irradiation on CdI2 films

The effect of plasma irradiation is studied systematically on a 4H polytype (002) oriented

Optimizing UNU/ICTP PFF Plasma Focus for Neon Soft X-ray Operation

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Effect of insulator sleeve length on soft x-ray emission from a neon-filled plasma focus device

stoichiometric film having compressive residual stress. Plasma irradiation was found to change the orientation to (110) of the film at certain moderate irradiation distances. A linear decrease in grain size and residual stress was observed with decreasing irradiation distance (or increasing ion energy) consistent with both structural and morphological observations. The direct optical energy gap

Numerical experiments on plasma focus pinch current limitation

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