Raj Kumar

Bio: Raj Kumar is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Semiconductor & Wafer. The author has an hindex of 2, co-authored 3 publications receiving 19 citations.

Selective determination of ammonia, ethanol and acetone by reduced graphene oxide based gas sensors at room temperature

Abstract: This work reports a new technique for the selective determination of three organic vapors– ammonia, ethanol and acetone by employing two resistive sensors. These two resistive sensors are based on reduced graphene oxide (RGO) and RGO– rosebengal (RB) composites. The chemically synthesized RGO and RGO–RB based sensors were tested for four different concentrations of ammonia (400–2800 ppm) and two different concentrations (1000, 2000 ppm) of ethanol and acetone each, at room temperature. The RGO sensor was found to exhibit response of 10.3% to 25.3% to 400–2800 ppm of ammonia, 1.01% to 1.15% to 1000 and 2000 ppm of acetone respectively, and 1.05% to 1.56% to 1000 and 2000 ppm of ethanol respectively. The RGO–RB composite-based sensor exhibited an enhanced response ranging from ~17% to 36.6% for 400–2800 ppm of ammonia, 1.6% to 3.2% for 1000 and 2000 ppm of acetone and 1.1% to 1.7% for 1000 and 2000 ppm of ethanol at room temperature. An algorithm, based on the soft margin classifier was developed to accurately determine the concentrations of all the three organic vapors. The initial 100 s of the response values of both the sensors for all the targeted vapors were considered for this purpose. This resulted into classification of all the concentrations of the three organic vapors much before the full-scale response of the sensors. It is believed that this work will aid in development of portable devices comprising of array of sensors having the capability of determining the vapors and their concentrations accurately.

Relativistic cross-focusing of two coaxial Gaussian laser beams in a plasma

Abstract: The paper presents a paraxial theory of the relativistic cross-focusing of two coaxial Gaussian laser beams of different frequencies in a homogeneous plasma. We discuss the self-focusing of a weaker laser beam in the plasma due to the optical inhomogeneities introduced by another stronger copropagating laser beam. In the presence of the second stronger beam (P cr21 < P 2 < P cr22 ), the plasma behaves as an oscillatory waveguide for the first, weaker, beam (P 1 < P cr11 ) as it propagates in the plasma. When both the beams are strong (P cr11,21 < P 1,2 < P cr12,22 ), the nonlinearities introduced by the relativistic effect are additive in nature, such that one beam can undergo oscillatory self-focusing and the other simultaneously defocusing, and vice versa. A comparison reveals that cross-focusing due to relativistic nonlinearity is possible for a wider range of powers of the laser pulses than is cross-focusing due to ponderomotive nonlinearity. Relativistic cross-focusing is important in plasma beat-wave excitation and collective laser particle accelerators.

Effects of nitrogen plasma immersion ion implantation in silicon

Abstract: Silicon wafers of p and n-types of 1 to 10 ohm-cm resistivity were implanted with nitrogen ions employing Plasma Immersion Ion Implantation (PIII) technique. Implantation were carried out at three doses corresponding to low (approximately 1013 /cm2), moderate (approximately 1015 /cm2) and high (approximately 1017 /cm2) dose regimes. Metal-silicon devices were fabricated using conventional semiconductor processing techniques. One set of the samples was annealed in forming gas ambient. Electrical characterization was done on all the devices. Change in reverse and forward current was observed with dose of implanted ions. The barrier height of the n- type sample decreases with increase in implanted ion dose, where as in the case of p-type silicon, barrier height was found increasing with dose. At high doses the top layer of both n and p-type silicon become nitrogen rich and exhibits optical properties different from that of unimplanted silicon as measured by ellipsometry. With the nitrogen rich layer, the device behaved like metal-insulator-silicon structure whose electrical characteristics have been studied. Sputtering effects of the nitrogen ions during implantation were also studied.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A Review on Functionalized Graphene Sensors for Detection of Ammonia.

Abstract: Since the first graphene gas sensor has been reported, functionalized graphene gas sensors have already attracted a lot of research interest due to their potential for high sensitivity, great selectivity, and fast detection of various gases. In this paper, we summarize the recent development and progression of functionalized graphene sensors for ammonia (NH3) detection at room temperature. We review graphene gas sensors functionalized by different materials, including metallic nanoparticles, metal oxides, organic molecules, and conducting polymers. The various sensing mechanism of functionalized graphene gas sensors are explained and compared. Meanwhile, some existing challenges that may hinder the sensor mass production are discussed and several related solutions are proposed. Possible opportunities and perspective applications of the graphene NH3 sensors are also presented.

Focusing of electromagnetic beams in collisional plasmas, with finite thermal conduction

Abstract: In this paper we present a theoretical investigation of the focusing of coaxial Gaussian electromagnetic beams and of a Gaussian ripple on an electromagnetic beam of uniform irradiance in a collisional plasma (in thermal equilibrium in the absence of the beams). A self consistent solution of the electromagnetic wave equation, the energy balance equation, and Fourier’s equation of heat conduction has been obtained in the paraxial approximation. The nonuniform distribution of the electron density and thereby the dielectric function on account of the nonuniform electron temperature/density distribution causes the focusing/defocusing of the beams. The effect of thermal conduction on the temperature distribution of the electrons, on the critical curves, and the nature of focusing has been specifically studied. In common with earlier studies, three regions in the initial beam width—initial axial irradiance plane, corresponding to steady divergence, self focusing and oscillatory divergence have been characterize...

Cross focusing of two laser beams and plasma wave excitation

Abstract: This article presents the cross focusing of two high power laser beams in a plasma when relativistic and ponderomotive nonlinearities are operative. The effect of electron density modification changes the critical power significantly in contrast to (only) relativistic case. The plasma wave generation at the difference frequency and particle acceleration has also been studied. In a typical case when laser wavelengths are 1047 and 1064nm and electron density 1.9×1019cm−3, the maximum electron plasma wave power flux comes out to be 6×1017W∕cm2 (laser power P1=3.6×1018W∕cm2 and P2=3.2×1018W∕cm2).

Self-focusing and cross-focusing of Gaussian electromagnetic beams in fully ionized collisional magnetoplasmas

Abstract: This paper presents an analysis and subsequent discussion of the phenomena of self-focusing of single electromagnetic Gaussian beams and cross-focusing of multiple coaxial beams in fully ionized magnetoplasma, taking into account the Ohmic heating of the electrons by the beams and loss of energy by electrons due to collision with the ions and electronic thermal conduction; the energy gained by ions in collision with the electrons has been equated to the energy lost on account of ionic thermal conduction. It is seen that the inclusion of the ionic thermal conduction reduces self/cross-focusing for high values of the magnetic field (νe≪Ωc) and enhances the same for low values of the magnetic field (νe≫ωc); here νe is the electron collision frequency and ωc,Ωc are the cyclotron frequencies of electrons and ions, respectively. The wave frequency is assumed to be much higher than the cyclotron frequency of the electrons. The results lead to the conclusion that considerable error occurs by neglecting ionic ther...

Mutual focusing/defocusing of Gaussian electromagnetic beams in collisional plasmas

Abstract: In this paper the authors have considered the mutual focusing/defocusing of a number of coaxial Gaussian electromagnetic beams in a singly ionized collisional plasma (initially in thermal equilibrium) and the ionosphere (with singly charged ions). Starting from the expression of the electron temperature in terms of the irradiance of the waves, expressions for the electron density and the dielectric function in the form ∊o(z,E∙E*)−r2∊2(z,E∙E*) have been derived; the power loss by electrons to heavy particles is assumed to be much larger than that due to thermal conduction. The dominant nonlinearity considered herein is the radial redistribution of the electron density on account of the radial dependence of the electric field of the waves and consequently of the electron temperature. Using this expression for the dielectric function, the coupled wave equations corresponding to different beams have been solved in the paraxial approximation, yielding a system of coupled second-order differential equations for...