Showing papers by "Mukul Gupta published in 2014"

Development of soft X-ray polarized light beamline on Indus-2 synchrotron radiation source

Abstract: This article describes the development of a soft x-ray beamline on a bending magnet source of Indus-2 storage ring (2.5 GeV) and some preliminary results of x-ray absorption spectroscopy (XAS) measurements using the same. The beamline layout is based on a spherical grating monochromator. The beamline is able to accept synchrotron radiation from the bending magnet port BL-1 of the Indus-2 ring with a wide solid angle. The large horizontal and vertical angular acceptance contributes to high photon flux and selective polarization respectively. The complete beamline is tested for ultrahigh vacuum (UHV) ∼ 10−10 mbar. First absorption spectrum was obtained on HOPG graphite foil. Our performance test indicates that modest resolving power has been achieved with adequate photon flux to carry out various absorption experiments.

Influence of annealing temperature on ZnO thin films grown by dual ion beam sputtering

Abstract: We have investigated the influence of in situ annealing on the optical, electrical, structural and morphological properties of ZnO thin films prepared on p-type Si(100) substrates by dual ion beam sputtering deposition (DIBSD) system. X-ray diffraction (XRD) measurements showed that all ZnO films have (002) preferred orientation. Full-width at half-maximum (FWHM) of XRD from the (002) crystal plane was observed to reach to a minimum value of 0.139° from ZnO film, annealed at 600 °C. Photoluminescence (PL) measurements demonstrated sharp near-band-edge emission (NBE) at ~ 380 nm along with broad deep level emissions (DLEs) at room temperature. Moreover, when the annealing temperature was increased from 400 to 600 °C, the ratio of NBE peak intensity to DLE peak intensity initially increased, however, it reduced at further increase in annealing temperature. In electrical characterization as well, when annealing temperature was increased from 400 to 600 °C, room temperature electron mobility enhanced from 6.534 to 13.326 cm2/V s, and then reduced with subsequent increase in temperature. Therefore, 600 °C annealing temperature produced good-quality ZnO film, suitable for optoelectronic devices fabrication. X-ray photoelectron spectroscopy (XPS) study revealed the presence of oxygen interstitials and vacancies point defects in ZnO film annealed at 400 °C.

Growth and characterizations of dual ion beam sputtered CIGS thin films for photovoltaic applications

Abstract: The growth of CIGS thin films on soda-lime glass substrates at different substrate temperatures by dual ion beam sputtering system in a single-step route from a single quaternary sputtering target with the composition of Cu (In0.70 Ga0.30) Se2 was reported. The effects of the substrate temperature on structural, optical, morphological and electrical properties of CIGS films were investigated. Stoichiometry of one such film was investigated by X-ray photoelectron spectroscopy. All CIGS films had demonstrated a strong (112) orientation located at 2θ ~26.70o, which indicated the chalcopyrite structure of films. The value of full-width at half-maximum of (112) peak was reduced from 0.58° to 0.19° and crystallite size was enlarged from 14.98 to 43.05 nm as growth temperature was increased from 100 to 400 °C. However, atomic force microscope results showed a smooth and uniform surface at lower growth temperature and the surface roughness was observed to increase with increasing growth temperature. Hall measurements exhibited the minimum film resistivity of 0.09 Ω cm with a hole concentration of 2.42 × 1018 cm−3 and mobility of 28.60 cm2 V−1 s−1 for CIGS film grown at 100 °C. Film absorption coefficient was found to enhance nominally from 1 × 105 to 2.3 × 105 cm−1 with increasing growth temperature from 100 to 400 °C.

Influence of ion-beam sputtering deposition parameters on highly photosensitive and transparent CdZnO thin films

Abstract: CdZnO thin films with a nominal thickness of ~200 nm were grown on c-plane sapphire substrates by dual ion-beam sputtering deposition technique. The effect of substrate temperature (300–600 °C) and gas ambience on structural, morphological, compositional and opto-electronic properties was studied. X-ray diffraction patterns confirmed that all the films were polycrystalline in nature and were preferentially oriented along the c-axis. It was revealed that the films grown at Ar/O2 ratio of 4:1 were structurally more ordered and the film quality was found to be the best at 500 °C. The compositional studies specify that approximately 11.8 at.% of cadmium were present in the film deposited at 300 °C in Ar–O2 mixture. Investigations on optical properties by photoluminescence and absorption studies indicate band gap shrinkage with the increase in argon partial pressure and substrate temperature. It was found that photosensitivity of the deposited films was highly dependent on growth conditions. The photosensitivity was found to be 5000-fold higher for CdZnO film grown at 600 °C in Ar–O2 ambience compared to the best reported result, and this was promising to realize high-performance opto-electronic devices on such CdZnO films.

Effect of dopants on thermal stability and self-diffusion in iron-nitride thin films

Abstract: We studied the effect of dopants (Al, Ti, Zr) on the thermal stability of iron nitride thin films prepared using a dc magnetron sputtering technique. Structure and magnetic characterization of deposited samples reveal that the thermal stability together with soft magnetic properties of iron nitride thin films get significantly improved with doping. To understand the observed results, detailed Fe and N self-diffusion measurements were performed. It was observed that N self-diffusion gets suppressed with Al doping whereas Ti or Zr doping results in somewhat faster N diffusion. On the other hand Fe self-diffusion seems to get suppressed with any dopant of which heat of nitride formation is significantly smaller than that of iron nitride. Importantly, it was observed that N self-diffusion plays only a trivial role, as compared to Fe self-diffusion, in affecting the thermal stability of iron nitride thin films. Based on the obtained results effect of dopants on self-diffusion process is discussed.

Phonons, lithium diffusion and thermodynamics of LiMPO4 (M = Mn, Fe)

Abstract: We report phonon studies using neutron inelastic scattering experiments, ab initio density functional theory calculations and potential model calculations on LiMPO4 (M = Mn, Fe) at ambient and high temperature to understand the microscopic picture of a Li sub-lattice. The experiments are in good agreement with calculations. Here for the first time we have correlated the diffusion of lithium and dynamical instability in LiMPO4. The lattice dynamics calculations indicate the instability of the zone-centre as well as zone-boundary phonon modes along the [100] direction at unit cell volumes corresponding to elevated temperature. Under ambient conditions, eigen vectors of Li corresponding to these modes exhibit displacement only in the x–y plane. However with initiation of phonon instability Li atoms exhibit displacement along all the three directions with the highest component along the x direction. Molecular dynamics simulations with increasing temperature indicate large mean square displacement of Li as compared to other constituent atoms. The computed pair-correlations between various atom pairs show that there is local disorder occurring in the lithium sub-lattice with increasing temperature, while other pairs show minimal changes.

Behavior of dual ion beam sputtered MgZnO thin films for different oxygen partial pressure

Abstract: Mg-doped ZnO (MgZnO) films were grown on p-Si (001) substrates by dual ion beam sputtering deposition system at a constant growth temperature of 600 °C for different oxygen partial pressure. The impact of oxygen partial pressure on the structural, electrical, elemental and morphological properties was thoroughly investigated. X-ray diffraction (XRD) spectra revealed that the deposited MgZnO films were polycrystalline in nature with preferred (002) crystal orientation. The peak of MgZnO (101) plane was reduced significantly as oxygen partial pressure was increased and disappeared completely at 80 and 100 % O2. The maximum electron concentration was evaluated to be 5.79 × 1018 cm−3 with resistivity of 0.116 Ω cm and electron mobility of 9.306 cm2/V s at room temperature, for MgZnO film grown with 20 % O2. Raman spectra shows a broad peak at 434 cm−1 corresponded to E 2 high phonons mode of MgZnO wurtzite structure. The peak at 560 cm−1 corresponded to the E1 (LO) mode and was associated with oxygen deficiency in MgZnO films. Raman intensity at 560 cm−1 reduced, on increasing oxygen partial pressure. A correlation between structural, electrical, elemental and morphological properties with oxygen partial pressure was also established.

Identification of a kinetic length scale which dictates alloy phase composition in Ni-Al interfaces on annealing at low temperatures

Abstract: Ni-aluminides are an important class of intermetallics from technological point of view. Ni-Al phase diagram has been studied in detail experimentally as well as theoretically. It is known that if annealed at low temperature, the first alloy phase is usually NiAl3 according to Bene's rule. It is also understood that heat of formation may get modified by local densities of the constituents forming the alloy. In this regard, it is important to identify a kinetic length scale for defining “local density” in a system. We have deposited ultrathin multilayers of Ni and Al of layer thickness in tens of nanometres with Ni:Al stoichiometric ratio as 3:1 and 1:3, respectively. Considering these stoichiometry, Ni3Al and NiAl3 are the thermodynamically favoured alloy phases in these samples. We used x-ray reflectivity, polarized neutron reflectivity, x-ray diffraction, and secondary ion mass spectroscopy to follow the alloy formation after annealing and identified the alloy phases at interfaces with nanometre resolut...

Optical And Surface Morphology Study of Zinc Phthalocyanine Langmuir Blodgett Thin Film.

Abstract: The UV-Vis absorption spectroscopy analysis reveals that prominent J-aggregation of ZnPc molecules was observed in the LB films while no such aggregation was found in the solution. Change in fluorescence color of ZnPc LB film from its solution confirms the appearance of new aggregation.

Synthesis and characterization of pulsed laser deposited SnO2-Fe2O3 composite thin films for TCO application

Abstract: SnO2-Fe 2 O 3 composite thin films were deposited on quartz substrate at 650 °C by pulsed laser deposition with Fe 2 O 3 content varying between 0 and 50 wt.%. The effect of increasing Fe 2 O 3 content on structural, optical and electrical properties of SnO 2 -Fe 2 O 3 films were investigated. X-ray diffraction analysis indicates that the nature of deposited composite films can be tune from crystalline to amorphous with increase in the Fe 2 O 3 content. X-ray photoelectron spectroscopy studies confirm the presence of SnO 2 and Fe 2 O 3 in the microstructure. Atomic force microscopy studies of the deposited films indicate that RMS roughness vary between 114.4 and 1.48 nm. The average optical transmittance decreases from 92 to 72% with increasing Fe 2 O 3 content of the deposited films. The optical bandgap was decreased from 3.69 to 3.31 eV with increase in Fe 2 O 3 content. The minimum resistivity was observed 3.71 × 10 −2 Ω cm for the 30 wt.% Fe 2 O 3 composite film. The low resistivity and high transmittance in the visible region enables these films suitable for optoelectronic applications.

Study of iron mononitride thin films

Abstract: In this work we have studied the crystal structural and local ordering of iron and nitrogen in iron mononitride thin films prepared using dc magnetron sputtering at sputtering power of 100W and 500W. The films were sputtered using pure nitrogen to enhance the reactivity of nitrogen with iron. The x-ray diffraction (XRD), conversion electron Mossbauer spectroscopy (CEMS) and soft x-ray absorption spectroscopy (SXAS) studies shows that the film crystallizes in ZnS-type crystal structure.

Inelastic neutron scattering investigations of negative thermal expansion behavior in semiconductors and framework solids

Abstract: Negative thermal expansion (NTE) is known in simple compounds like ZnSe as well as framework compounds like Zn(CN)2 [1] and Cu2O [2]. In Cu2O, the Cu atoms are linearly coordinated by two oxygen at...

Study of magnetic iron nitride thin films deposited by high power impulse magnetron sputtering

Abstract: In this work, we studied phase formation, structural and magnetic properties of iron-nitride (Fe-N) thin films deposited using high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (dc-MS) The nitrogen partial pressure during deposition was systematically varied both in HiPIMS and dc-MS Resulting Fe-N films were characterized for their microstructure, magnetic properties and nitrogen concentration We found that HiPIMS deposited Fe-N films show a globular nanocrystalline microstructure and improved soft magnetic properties In addition, it was found that the nitrogen reactivity impedes in HiPIMS as compared to dc-MS Obtained results can be understood in terms of distinct plasma properties of HiPIMS

CIGS thin film Deposition by Dual Ion Beam Sputtering (DIBS) system for Solar cell Applications

Abstract: Currently in solar cell market the cost effective Copper Indium Gallium Selenide (i.e. Cu(In,Ga)Se2 or CIGS) thin film solar cells are showing most promising result among all other thin film solar cell technology. Typically, CIGS thin films for photovoltaic devices are deposited by co-evaporation or by deposition of the metals with or followed by treatment in a selenium environment. These methods have several disadvantages and complications. In this article, we describe an alternative of the same. We described the CIGS thin films of 1 μm thickness grown onto soda lime glass substrates by Dual Ion Beam Sputtering (DIBS) system from a single quaternary target with the composition of Cu (In0.70Ga0.30)Se2 in a single step route without any additional selenization at different temperatures from 100 °C to 400 °C. These CIGS thin films are characterized for the solar cell application. The effects of the substrate temperature, on the structural and optical property of the CIGS layers were studied at room temperature using X-Ray Diffraction and UV–Vis-NIR spectrophotometer. The obtained results of the thin films includes the crystallinity, grain size, absorption coefficient and band gap energy etc. In structural property the preferred orientation of grains along highly oriented the (112) plane is observed. Crystallinity of the films improved with increasing substrate temperature as evidenced by the decrease of FWHM from 0.64 °C to 0.29 °C The strong influence of growth temperature on these properties were observed. We demonstrated that growth temperature can be varied in order to optimize the film properties and improve device performance.