G. Mohan Rao

Indian Institute of Science, Department of Instrumentation and Applied Physics, Faculty Member

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Papers by G. Mohan Rao

Hydrogen plasma-treated 1D/3D TiO2 nanorod array photoanode for efficient photoelectrochemical water splitting

Ceramics International

Rapid thermal processed thin films of reactively sputtered Ta2O5

Thin Solid Films

Rapid thermal processed thin films of reactively sputtered tantalum pentoxide Ta,O, thin films ha... more Rapid thermal processed thin films of reactively sputtered tantalum pentoxide Ta,O, thin films have been deposited on silicon and platinum coated silicon substrates by reactive magnetron sputtering. The as-deposited films were amorphous and showed good electrical properties in terms of a dielectric permittivity of about 24 and leakage current density of 9 x 10 ' A cm-*. A rapid thermal annealing process at temperatures above 700 "C crystallized the films, increased the dielectric relative permittivity, and decreased the leakage current. The dielectric constant for a film rapidly annealed at 850 "C increased to 45 and its leakage current density lowered to 2 x lo-' A cm-*. The dielectric measurements in the MIS configuration showed that Ta,O, might be used as a dielectric material instead of SiO, or S&N, for integrated devices. The current voltage characteristics observed at low and high fields suggested different conduction mechanisms.

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Superhydrophobic and high SERS performance of Ag coated CuO nanostructured thin films prepared by successive ionic layered adsorption reaction (SILAR) process

Journal of Colloid and Interface Science, 2016

The present work demonstrates the superhydrophobic and Surface Enhanced Raman Spectroscopy (SERS)... more The present work demonstrates the superhydrophobic and Surface Enhanced Raman Spectroscopy (SERS) active substrate performance of silver coated copper oxide (Ag@CuO) nanostructured thin films prepared by the SILAR process. Super hydrophobic substrates that combine super hydrophobic condensation effect and high enhancement ability of Ag@CuO nanoflowers are investigated for SERS studies. The possible growth mechanism for the formation of nanoflower arrays from nanospindles has been discussed. Morphology and crystallinity of the Ag@CuO thin films are confirmed using FESEM and XRD. The results obtained in the present study indicate that the as-deposited hydrophobic nanospindles structure converts to super hydrophobic nanoflower arrays on annealing at 200°C. The Ag@CuO super hydrophobic nanoflowers thin film based SERS substrates show highly enhanced Raman spectra with an EF value of 2.0×10(7) for (Rhodamine 6G) R6G, allowing a detection limit from a 10(-10)molL(-1) solution. The present study may provide a new perception in fabricating efficient super hydrophobic substrates for SERS, suggesting that the fabricated substrates are promising candidates for trace analysis of R6G dye and are expected to be widely used as highly sensitive SERS active substrates for various toxic dyes in the future.

Bulk Synthesis of Reduced Graphene Oxide Cakes

Graphene, 2015

Effect of Substrate temperature on the microstructure variation in sputter-deposited hydrogenated amorphous silicon thinfilms

International Conference on Advanced Nanomaterials Emerging Engineering Technologies, 2013

ABSTRACT Vacancy, void incorporation and Si-Hx configuration in hydrogenated amorphous silicon (a... more ABSTRACT Vacancy, void incorporation and Si-Hx configuration in hydrogenated amorphous silicon (a-Si:H) thin films was studied. Films were grown by Direct Current (DC), pulsed DC and Radio Frequency (RF) magnetron sputtering. Fourier Transform Infrared (FTIR) spectroscopic analysis has been carried out on the films and found that, the a-Si:H films grown by DC magnetron sputtering are of good quality compared to pulsed DC and RF deposited films. The effect of Substrate temperature (TS) on the total hydrogen concentration (CH), configuration of hydrogen bonding, density (decided by the vacancy and void incorporation) and the microstructure factor (R*) was studied. TS is found to be an active parameter in affecting the above said properties of the films. The films contain both vacancies and voids. At low hydrogen dilutions the films are vacancy dominated and at high hydrogen dilutions they are void dominated. It is found that TS favors monohydride (Si-H) bonding at the cost of dihydride (Si-H2) bonding. This dividing line is at CH=14 at.%H for DC sputter deposited films. The microstructure structure factor R* is found to be zero for as deposited DC films at TS=773K. The threshold CH for void dominated region is found to be CH=23 at.%H for RF, CH=18 at.%H for PDC and CH~14 at.%H for DC sputter deposited films.

Process parameter dependent property studies on CdO films prepared by DC reactive magnetron sputtering

Materials Chemistry and Physics, 2001

... sputtering. TK Subramanyam a , G. Mohan Rao b and S. Uthanna Corresponding Author Contact Inf... more

Influence of oxygen partial pressure on the glow discharge characteristics during dc reactive magnetron sputtering

Vacuum, 1991

SnO 2 nanowire anchored graphene nanosheet matrix for the superior performance of Li-ion thin film battery anode

J. Mater. Chem. A, 2015

All solid state batteries are essential candidate for miniaturizing the portable electronics devi... more

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Effect of substrate temperature on the properties of ZrO2 films prepared by d.c. reactive magnetron sputtering

Effect of post-deposition annealing on composition and electrical properties of dc reactive magnetron sputtered Al2O3 thin films

Effect of Post-Deposition Annealing on the Al<SUB>2</SUB>O<SUB>3</SUB>/Si(100) Interface Properties

Science of Advanced Materials, 2014

ABSTRACT In the present investigation, Al2O3 thin films were deposited onto Si &lt; 100 &... more ABSTRACT In the present investigation, Al2O3 thin films were deposited onto Si &lt; 100 &gt; substrates by DC reactive magnetron sputtering. The films were annealed in vacuum for one hour at 623, 823 and 1023 K. The composition of the films was quantitatively estimated using X-ray photoelectron spectroscopy (XPS) and the O/Al ratio was found be in the range 1.19 to 1.43. Grazing incidence X-ray diffraction (GIXRD) results revealed that the annealed films are amorphous in nature. Cross sectional transmission electron microscopy (X-TEM) analysis was carried out to study the microstructure and nature of the Al2O3-Si interface as a function of post-deposition annealing. TEM results revealed the presence of nanocrystalline gamma-Al2O3 in the annealed films and an amorphous interface layer was observed at the Al2O3 Si interface. The thickness of the amorphous interface layer was determined from the TEM analysis and the results are discussed.

Substrate temperature influenced physical properties of silicon MOS devices with TiO2 gate dielectric

Surface and Interface Analysis, 2012

a DC reactive magnetron sputtering technique was employed for deposition of titanium dioxide (TiO... more a DC reactive magnetron sputtering technique was employed for deposition of titanium dioxide (TiO 2) films. The films were formed on Corning glass and p-Si (100) substrates by sputtering of titanium target in an oxygen partial pressure of 6Â10 À2 Pa and at different substrate temperatures in the range 303-673 K. The films formed at 303 K were X-ray amorphous whereas those deposited at substrate temperatures ≥ 473 K were transformed into polycrystalline nature with anatase phase of TiO 2. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic bonding configuration of TiO 2. The surface morphology of the films was significantly influenced by the substrate temperature. MOS capacitor with Al/TiO 2 /p-Si sandwich structure was fabricated and performed current-voltage and capacitance-voltage characteristics. At an applied gate voltage of 1.5 V, the leakage current density of the device decreased from 1.8 Â 10 À6 to 5.4 Â 10 À8 A/cm 2 with the increase of substrate temperature from 303 to 673 K. The electrical conduction in the MOS structure was more predominant with Schottky emission and Fowler-Nordheim conduction. The dielectric constant (at 1 MHz) of the films increased from 6 to 20 with increase of substrate temperature. The optical band gap of the films increased from 3.50 to 3.56 eV and refractive index from 2.20 to 2.37 with the increase of substrate temperature from 303 to 673 K.

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Studies of process parameter controlled composition variation in sputtered YBa2Cu3O7 − x films

Vacuum, 1997

YBazCu307_X films have been deposited on (100) MgO substrates by a high pressure oxygen sputterin... more YBazCu307_X films have been deposited on (100) MgO substrates by a high pressure oxygen sputtering technique. Optical emission spectroscopic study of the sputter plasma indicates that the sputtered species are atomic in nature. Based on the atomic nature of the sputtered species, a model has been used to estimate the atomic flux of different constituents reaching the substrate considering the thermalisation and diffusion of the sputtered atoms. The change in composition of the films deposited with different inter-electrode spacing from 15 to 20mm and sputtering pressure in the range 'l.O-2.6mbar has been explained on the basis of atomic flux of constituent atoms reaching the substrate and resputtering rates of individual constituents from the deposited films. The reasons for realising films with stoichiometric composition at a pressure 2.0mbar and inter-electrode distance 79mm have been explained on the basis of the above model.

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Sputter deposited LiPON thin films from powder target as electrolyte for thin film battery applications

Thin Solid Films, 2011

Lithium phosphorus oxynitride (LiPON) thin films as solid electrolytes were prepared by reactive ... more Lithium phosphorus oxynitride (LiPON) thin films as solid electrolytes were prepared by reactive radio frequency (rf) magnetron sputtering from Li 3 PO 4 powder compact target. High deposition rates and ease of manufacturing powder target compared with conventional ceramic Li 3 PO 4 targets offer flexibility in handling and reduce the cost associated. Rf power density varied from 1.7 Wcm − 2 to 3 Wcm − 2 and N 2 flow from 10 to 30 sccm for a fixed substrate to target distance of 4 cm for best ionic conductivity. The surface chemical analysis done by X-ray photoelectron spectroscopy showed incorporation of nitrogen into the film as both triply, N t and doubly, N d coordinated form. With increased presence of N t , ionic conductivity of LiPON was found to be increasing. The electrochemical impedance spectroscopy of LiPON films confirmed an ionic conductivity of 1.1 × 10 − 6 Scm − 1 for optimum rf power and N 2 flow conditions.

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Rapid thermal processed thin films of niobium pentoxide (Nb2 O5) deposited by reactive magnetron sputtering

Thin Solid Films, 1995

Niobium pentoxide thin films have been deposited on silicon and platinum-coated silicon substrate... more Niobium pentoxide thin films have been deposited on silicon and platinum-coated silicon substrates by reactive magnetron sputtering. The as-deposited films were amorphous and showed good electrical properties in terms of a dielectric permittivity of about 30, and leakage current density of IO-' A cm-' at a field of 120 kV cm-'. A rapid thermal annealing process at 800 "C further increased the dielectric constant to 90 and increased the leakage current density to 5 x IO-" A cm-'. The currentPvoltage characteristics observed at low and high fields suggested a combination of phenomena at different regimes of applied electric field. The capacitance-voltage characteristics performed in the metal-insulator-semiconductor configuration indicated good electronic interfaces with a nominal trap density of 4.5 x 10" cnP2 eV_ '. which is consistent with the behavior observed with conventional dielectrics such as SiO, on silicon surfaces.

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Vacuum emissivity meter for thermal emittance measurements of coatings

Review of Scientific Instruments, 1988

The problems in measuring thermal emittance by steady-state calorimetric technique have been anal... more

Electron cyclotron resonance plasma source for ion assisted deposition of thin films

Review of Scientific Instruments, 2000

An electron cyclotron resonance (ECR) plasma source (10 cm in diameter) has been developed for io... more An electron cyclotron resonance (ECR) plasma source (10 cm in diameter) has been developed for ion assisted sputter deposition of thin films. Variation of plasma parameters like ion density, electron temperature, plasma potential, and floating potential as a function of pressure and microwave power has been studied using Langmuir probe analysis. The ECR source gives an ion density of 1.01×1011/cm3 at a distance of 8 cm from the source exit at a pressure of 8×10−4 mbar and 400 W of microwave power. The uniformity of the plasma parameters at the substrate position was found to be ±2% over a diameter of 12 cm. Thin films of copper and silicon nitride have been deposited by rf sputtering in the presence of ECR plasma. The properties showed a significant change at an ECR power of 100 W.

Structure-composition-property dependence in reactive magnetron sputtered ZnO thin films

Optical Materials, 2002

Thin films of zinc oxide (ZnO) were prepared by dc reactive magnetron sputtering on glass substra... more Thin films of zinc oxide (ZnO) were prepared by dc reactive magnetron sputtering on glass substrates at various oxygen partial pressures in the range 1 Â 10 À4-6 Â 10 À3 mbar and substrate temperatures in the range 548-723 K. The variation of cathode potential of zinc target on the oxygen partial pressure was explained in terms of target poisoning effects. The stoichiometry of the films has improved with the increase in the oxygen partial pressure. The films were polycrystalline with wurtzite structure. The films formed at higher substrate temperatures were (0 0 2) oriented. The temperature dependence of Hall mobility of the films formed at various substrate temperatures indicated that the grain boundary scattering of charge carriers was predominant electrical conduction mechanism in these films. The optical band gap of the films increased with the increase of substrate temperature. The ZnO films formed under optimized oxygen partial pressure of 1 Â 10 À3 mbar and substrate temperature of 663 K exhibited low electrical resistivity of 6:9 Â 10 À2 X cm, high visible optical transmittance of 83%, optical band gap of 3.28 eV and a figure of merit of 78 X À1 cm À1 .

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Synthesis and magnetic studies of flower-like nickel nanocones

Materials Science and Engineering: B, 2009

Flower-like nickel nanocone structures are synthesized by a simple chemical reduction method usin... more Flower-like nickel nanocone structures are synthesized by a simple chemical reduction method using hydrazine hydrate as the reducing agent. The structure, morphology and magnetic properties of as synthesized products are studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and SQUID magnetometer. The morphology evolution is studied by varying the reaction temperature and concentration of nickel chloride keeping other conditions unchanged.

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Bias induced structural changes in tungsten nitride films deposited by unbalanced magnetron sputtering

Materials Science and Engineering: B, 2004

Tungsten nitride thin films were deposited using unbalanced magnetron sputtering system. The effe... more Tungsten nitride thin films were deposited using unbalanced magnetron sputtering system. The effect of the ratio of nitrogen partial pressure to the total pressure during deposition and the substrate bias on the tungsten nitride formation has been studied. The glow discharge characteristics of the process have been studied in order to determine the deposition parameters. It is observed that nitrogen partial pressure ratio 0.4 and cathode current of 200mA favors the formation of the W2N films. The variation in the electrical resistivity of the ...

G. Mohan Rao

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