Showing papers by "Mukul Gupta published in 2018"
TL;DR: In this article, the performance of fabricated photodetectors was studied by current voltage, spectral photoresponse, and temporal response measurements, and the values of peak responsivity were 0.4, 0.15 and 0.20, respectively.
Abstract: Mg x Zn1– x O ( $x = 0.05$ , 0.15 and 0.20) based metal–semiconductor–metal ultraviolet (UV) photodetectors were fabricated on Si substrate using dual-ion-beam sputtering. The performances of fabricated photodetectors were studied by current–voltage, spectral photoresponse, and temporal response measurements. The values of peak responsivity of photodetectors were 0.4, 0.31, and 0.27 A/W with corresponding external quantum efficiency of 146%, 110%, and 105% for $x = 0.05$ , 0.15 and 0.20, respectively. The cutoff wavelength and UV/visible rejection ratio of fabricated photodetectors decrease over 360–330 nm and 341.8–115.3, respectively, with increase in Mg concentration. The variation in specific detectivity and noise equivalent power with Mg concentration variation is also reported.
33 citations
TL;DR: In this article, the evolution of the structure and magnetic properties of an amorphous CoFeB layer in a heterostructure consisting of HM/CoFeB/HM (Hf, W), with thermal annealing has been studied using magneto-optical Kerr effect (MOKE) and synchrotron based Grazing incidence x-ray diffraction (GIXRD) measurements.
15 citations
TL;DR: In this article, the authors used time of flight (ToF) neutron reflectivity (NR) to measure the density of a-C thin films and found that the determination of density of carbon thin films, especially those with a thickness of few tens of nm, may not be accurate with XRR due to a poor scattering contrast between the film and substrate.
14 citations
TL;DR: In this article, the local structure and magnetization of Co 4 N thin films deposited by a reactive dc magnetron sputtering process were studied and the interstitial incorporation of N atoms in a fcc Co lattice is expected to expand the structure.
11 citations
TL;DR: In this paper, temperature and pressure dependent Raman spectroscopic studies are presented which showed signatures of spin-reorientation transition in SmFeO3 and x-ray diffraction study as a function of pressure is also presented that shows the variation in structural parameters like interatomic distances, bond angles and degree of octahedral tilt.
8 citations
TL;DR: In this article, the effect of magnetic field on the absorptive optical nonlinearity in ion beam sputtered as-deposited and annealed NiO thin films have been studied and the magnetic field dependent nonlinear absorption coefficients are obtained.
8 citations
TL;DR: In this paper, the evolution of magnetic properties of thin FeCoB films sandwiched between two Mo layers has been studied as a function of thermal annealing at different temperatures.
7 citations
TL;DR: In this paper, the microstructural origin of enhanced radial growth in magnesium-doped single crystalline wurtzite gallium nitride (w-GaN) nanorods (NRs) grown by MBE was discussed.
Abstract: We discuss the microstructural origin of enhanced radial growth in magnesium (Mg) doped single crystalline wurtzite gallium nitride (w-GaN) nanorods (NRs) grown by MBE, using electron microscopy and first-principles Density Functional Theory calculations. Experimentally, we observe that Mg incorporation increases the surface coverage of the grown samples as a consequence of an increase in the radial growth rate of the NRs. We also observe that the coalescence of NRs becomes prominent and the height at which coalescence between proximal rods occurs decreases with increase in Mg concentration. From first-principles calculations, we find that the surface free energy of the Mg doped surface reduces with increasing Mg concentration in the samples. The calculations further suggest a reduction in the adsorption energy and the diffusion barrier of Ga adatoms along [ 11 2 ¯ 0 ] on the side wall surface of the NRs as the underlying mechanism for the observed enhancement in the radial growth rate of GaN NRs. The physics and chemistry behind reduction of the adsorption energy of Ga ad-atoms on the doped surface are explained in the light of electronic structure of the relevant surfaces.
7 citations
TL;DR: In this article, the effects of selenization time on the microstructural, optical, and electrical properties of stacked (Cu/Se/ZnSe/ Se/Ge/Se) × 4 layers of CZGSe thin films were studied.
Abstract: We have studied the effects of selenization time on the microstructural, optical, and electrical properties of stacked (Cu/Se/ZnSe/Se/Ge/Se) × 4 layers to demonstrate growth of Cu2ZnGeSe4 (CZGSe) thin films. Electron beam evaporation was used to deposit CZGSe films on glass substrates for selenization in high vacuum at 450°C for different times (15 min, 30 min, 45 min, and 60 min). The incomplete reaction of the precursor layers necessitates selenization at higher temperature for different durations to achieve desirable microstructural and optoelectronic properties. Energy-dispersive spectroscopic measurements revealed that the stacked layers selenized at 450°C for 30 min were nearly stoichiometric with atomic ratios of Cu/(Zn + Ge) = 0.88, Zn/Ge = 1.11, and Se/(Cu + Zn + Ge) = 1.03. X-ray diffraction analysis revealed that the stacks selenized at 450°C for 30 min crystallized in tetragonal stannite structure. Selenization-time-dependent Raman measurements of the selenized stacks are systematically presented to understand the growth of CZGSe. The elemental distribution through depth as a function of selenization time was investigated using secondary-ion mass spectroscopy. The ionic valency of the constituent elements in CZGSe films selenized at 450°C for 30 min was examined using high-resolution x-ray photoelectron spectroscopy. Significant changes were observed in the surface morphology of the stacked layers with increase in selenization time. The effects of defects on the electrical properties and of binary phases on the optical properties are discussed.
6 citations
TL;DR: In this article, the electronic structure of double perovskite Pr2MnNiO6 was studied using core x-ray photoelectron spectroscopy and xray absorption spectra.
Abstract: The electronic structure of double perovskite Pr2MnNiO6 was studied using core x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. The 2p x-ray absorption spectra show that Mn and Ni are in 4+ and 2+ states respectively. Based on charge transfer multiplet analysis of the 2p XPS spectra of both ions, we find charge transfer energies [Formula: see text] of 3.5 and 2.5 eV for Ni and Mn respectively. The ground state of Ni2+ and Mn4+ ions reveal a higher d electron count of 8.21 and 3.38 respectively as compared to the ionic values. The partial density of states clearly show a charge transfer character of the system for U - J [Formula: see text] 2 eV. The O 1s edge absorption spectra reveal a band gap of 0.9 eV, which is close to the value estimated from analysis of Ni and Mn 2p photoemission and absorption spectra. The combined analysis of nature of spectroscopic data and first principles calculations reveal that the material is a p - d type charge transfer insulator with an intermediate covalent character according to the Zannen-Sawatzy-Allen phase diagram.
6 citations
TL;DR: In this article, the effect of isochronal annealing on the evolution of structural and magnetic properties of FePt was studied using XRD and Magneto Optic Kerr Effect (MOKE) measurements.
Abstract: Enhancement in L10 transformation kinetics in FePt is achieved by incorporating an optimum concentration of ternary element Cu, which has limited solubility in the fcc FePt phase, into the FePt multilayer stack. Two different multilayer structures were deposited. In first multilayer Cu is deposited at one interface of Fe/Pt and in other Cu is alloyed with Fe and Pt layers by co-sputtering. One Fe42.5Pt42.5Cu15 alloy film is also prepared and detailed study of evolution of structural and magnetic properties as a function of isochronal annealing is done using XRD and Magneto Optic Kerr Effect (MOKE) measurements respectively. Annealing up to 200oC results only in intermixing in the multilayer structure, with no sign of L10 transformation. Annealing at 300oC for 1h results in partial transformation to L10 phase as evidenced by appearance of (001) superlattice peak as well as large increase in the coercivity. It is found that in the Fe(Cu)/Pt(Cu) multilayer exhibits significantly faster L10 transformation as compared to Fe/Pt/Cu multilayer or FePtCu alloy film. Inter-diffusion study using x-ray reflectivity measurements reveals that constant for interdiffusion in Fe(Cu)/Pt(Cu) is only marginally higher than that in Fe/Pt/Cu multilayer. The observed enhancement in L10 transformation rate in Fe(Cu)/Pt(Cu) multilayer is discussed in terms of possible enhancement of diffusivities of constituent species in fcc FePt phase.Enhancement in L10 transformation kinetics in FePt is achieved by incorporating an optimum concentration of ternary element Cu, which has limited solubility in the fcc FePt phase, into the FePt multilayer stack. Two different multilayer structures were deposited. In first multilayer Cu is deposited at one interface of Fe/Pt and in other Cu is alloyed with Fe and Pt layers by co-sputtering. One Fe42.5Pt42.5Cu15 alloy film is also prepared and detailed study of evolution of structural and magnetic properties as a function of isochronal annealing is done using XRD and Magneto Optic Kerr Effect (MOKE) measurements respectively. Annealing up to 200oC results only in intermixing in the multilayer structure, with no sign of L10 transformation. Annealing at 300oC for 1h results in partial transformation to L10 phase as evidenced by appearance of (001) superlattice peak as well as large increase in the coercivity. It is found that in the Fe(Cu)/Pt(Cu) multilayer exhibits significantly faster L10 transformation as ...
TL;DR: In this article, the role of the state of the MgO surface in controlling the interface structure was investigated using soft x-ray absorption spectroscopy, which is capable of detecting even a sub monolayer of a given phase, combined with in situ measurements as a function of iron layer thickness.
Abstract: Interfacial reaction between iron and MgO has been studied in situ during deposition of iron on MgO surface, using soft x-ray absorption spectroscopy High sensitivity of the technique which is capable of detecting even a sub monolayer of a given phase, combined with in situ measurements as a function of iron layer thickness, allowed one to make a quantitative estimate of interfacial phases Two different substrates namely, MgO (001) single crystal, and a polycrystalline MgO film on Si substrate have been used in order to elucidate the role of the state of MgO surface in controlling the interface structure It is found that at the interface of iron and MgO film, about two monolayers of Fe3O4 is formed Fe3O4 being the oxide of iron with the highest heat of formation, the reaction appears to be controlled thermodynamically On the other hand, on the interface with MgO (001) surface, FeO is formed, suggesting that the reaction is limited by the availability of oxygen atoms Magnetic behaviour of the FeO layer gets modified significantly due to proximity effect of the bulk ferromagnetic iron layer
TL;DR: In this article, thin films of titanium oxide (TiO2) were prepared by ion beam sputtering at room temperature under various oxygen partial pressure and annealed at 350°C and higher.
TL;DR: In this paper, the authors reported the growth of Cu2Zn(Sn,Ge)Se4 (CZTGSe) thin films by incorporation of germanium during the deposition of precursor film consisting of multiple stacks of (Sn/Se/Ge/Se,Se/ZnSe/S/Cu/Se), which were sequentially evaporated onto soda lime glass substrates held at 100°C in high vacuum.
TL;DR: In this paper, the role of stacking order on the growth and properties of six possible multiple stacks of Cu-ZnSe-Ge with selenium incorporation at a precursor stage were prepared using electron beam evaporation followed by vacuum selenization at 475 °C for 30 minutes.
TL;DR: In this article, the authors reported the preparation of 5.5μm wide and 10μm grating periodicity patterned [ F e ( 2.0 n m ) / P t (2.5 n m ] X 10 multilayer and its thermal annealing behavior.
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TL;DR: In this article, the authors studied amorphous carbon ($a$-C) thin films deposited using direct current (dc) and high power impulse magnetron sputtering (HiPIMS) techniques and found that determination of density of carbon thin films, specially those with a thickness of few tens of nm, may not be accurate with XRR due to a poor scattering contrast between the film and substrate.
Abstract: In this work, we studied amorphous carbon ($a$-C) thin films deposited using direct current (dc) and high power impulse magnetron sputtering (HiPIMS) techniques. The microstructure and electronic properties reveal subtle differences in $a$-C thin films deposited by two techniques. While, films deposited with dcMS have a smooth texture typically found in $a$-C thin films, those deposited with HiPIMS consist of dense hillocks surrounded by a porous microstructure. The density of $a$-C thin films is a decisive parameter to judge their quality. Often, x-ray reflectivity (XRR) has been used to measure the density of carbon thin films. From the present work, we find that determination of density of carbon thin films, specially those with a thickness of few tens of nm, may not be accurate with XRR due to a poor scattering contrast between the film and substrate. By utilizing neutron reflectivity (NR) in the time of flight mode, a technique not commonly used for carbon thin films, we could accurately measure differences in the densities of $a$-C thin films deposited using dcMS and HiPIMS.
10 Apr 2018
TL;DR: In this paper, Mn and Co doped TiO2 thin films are prepared by rf magnetron sputtering technique and GIXRD measurements shows anatase phase for pure TiO 2 and Mn dopedTiO2, however mixed anatase and rutile phase for Co dopTiO 2, which is attributed to the oxygen vacancy mediated interaction between the TM ions.
Abstract: Mn and Co doped TiO2 thin films are prepared by rf magnetron sputtering technique. GIXRD measurements shows anatase phase for pure TiO2 and Mn doped TiO2, however mixed anatase and rutile phase for Co doped TiO2. XANES and EXAFS measurements at dopant and host site confirm the substitution of host site by dopant ions. O K edge measurements and EXAFS results at the dopant site confirms the presence of oxygen vacancies. Ferromagnetism obtained in the doped TiO2 thin films is attributed to the oxygen vacancy mediated interaction between the TM ions.