28 results on '"S R Sarath Kumar"'
Search Results
2. Electrocatalysts for Hydrogen Evolution Reaction
- Author
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R. Shilpa, K. S. Sibi, S. R. Sarath Kumar, R. K. Pai, and R.B. Rakhi
- Published
- 2023
3. Reductive Ring Opening of a Cyclo-Tri(phosphonio)methanide Dication to a Phosphanylcarbodiphosphorane: In Situ UV-Vis Spectroelectrochemistry and Gold Coordination
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Sivathmeehan Yogendra, Felix Hennersdorf, Jan J. Weigand, Stephen Schulz, Roland Fischer, and S R Sarath Kumar
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In situ ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,010402 general chemistry ,Ring (chemistry) ,Photochemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,3. Good health ,Dication ,Inorganic Chemistry ,Ultraviolet visible spectroscopy ,Yield (chemistry) ,Physical and Theoretical Chemistry ,Lone pair ,Bond cleavage - Abstract
The formal two-electron reduction of the cyclo-tri(phosphonio)methanide dication 12+ results in a ring-opening reaction via C–P bond cleavage to yield the unique phosphanyl-functionalized carbodiphosphorane 2. In situ spectroelectrochemical investigations of the reduction of dication 12+ and the oxidation of 2 give insights into the mechanism of this unusual and reversible bond cleavage reaction. Compound 2 features in total three lone pairs of electrons, facilitating the preparation of mono-, di-, and trigold complexes.
- Published
- 2017
4. Ultralow lattice thermal conductivity in monolayer C3N as compared to graphene
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Vasudeo Pandurang Babar, S. R. Sarath Kumar, Sanjib Kumar Sharma, and Udo Schwingenschlögl
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Materials science ,Condensed matter physics ,Renewable Energy, Sustainability and the Environment ,Phonon ,Graphene ,Anharmonicity ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Boltzmann equation ,0104 chemical sciences ,law.invention ,Thermal conductivity ,law ,Thermoelectric effect ,Monolayer ,General Materials Science ,Density functional theory ,0210 nano-technology - Abstract
Using density functional theory and the Boltzmann transport equation for phonons, we demonstrate that the thermal conductivity is massively reduced in monolayer C3N as compared to isostructural graphene. We show that larger phase space for three-phonon scattering processes is available in monolayer C3N, which results in much shorter phonon life-times. Although both materials are characterized by sp2 hybridisation, anharmonicity effects are found to be enhanced for the C–N and C–C bonds in monolayer C3N, reflected by a Gruneisen parameter of −8.5 as compared to −2.2 in graphene. The combination of these properties with the fact that monolayer C3N is organic, non-toxic, and built of earth abundant elements gives rise to great potential in thermoelectric applications.
- Published
- 2017
5. Enhanced high temperature thermoelectric response of sulphuric acid treated conducting polymer thin films
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Husam Niman Alshareef, R.B Rakhi, S R Sarath Kumar, and Narendra Kurra
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Conductive polymer ,Quenching ,Materials science ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,symbols.namesake ,PEDOT:PSS ,Electrical resistivity and conductivity ,Seebeck coefficient ,Thermoelectric effect ,Materials Chemistry ,symbols ,Composite material ,Thin film ,0210 nano-technology ,Raman spectroscopy - Abstract
We report the high temperature thermoelectric properties of solution processed untreated and sulphuric acid treated poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (or PEDOT:PSS) films. The acid treatment is shown to simultaneously enhance the electrical conductivity and the Seebeck coefficient of the metal-like films, resulting in a five-fold increase in the thermoelectric power factor (from 0.01 to 0.052 W m−1 K−1) at 460 K, compared to the untreated film. By using atomic force micrographs, Raman and impedance spectra and using a series heterogeneous model for electrical conductivity, we demonstrate that acid treatment results in the removal of PSS from the films, leading to the quenching of accumulated charge-induced energy barriers, facilitating metal-like conduction. The continuous removal of PSS and changes in morphology of the PEDOT grains upon acid treatment may alter the local band structure of PEDOT:PSS, in such a way as to simultaneously enhance the Seebeck coefficient.
- Published
- 2016
6. Enhanced Thermoelectric Figure-of-Merit in Thermally Robust, Nanostructured Superlattices Based on SrTiO3
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Husam N. Alshareef, Terry M. Tritt, Arash Mehdizadeh Dehkordi, S. R. Sarath Kumar, Kun Li, and Anas Abutaha
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Materials science ,Ionic radius ,Dopant ,Annealing (metallurgy) ,business.industry ,General Chemical Engineering ,Superlattice ,General Chemistry ,Pulsed laser deposition ,Thermal conductivity ,Seebeck coefficient ,Thermoelectric effect ,Materials Chemistry ,Optoelectronics ,business - Abstract
Thermoelectric (TE) metal oxides overcome crucial disadvantages of traditional heavy-metal-alloy-based TE materials, such as toxicity, scarcity, and instability at high temperatures. Here, we report the TE properties of metal oxide superlattices, composed from alternating layers of 5% Pr3+-doped SrTiO3−δ (SPTO) and 20% Nb5+-doped SrTiO3−δ (STNO) fabricated using pulsed laser deposition (PLD). Excellent stability is established for these superlattices by maintaining the crystal structure and reproducing the TE properties after long-time (20 h) annealing at high temperature (∼1000 K). The introduction of oxygen vacancies as well as extrinsic dopants (Pr3+ and Nb5+), with different masses and ionic radii, at different lattice sites in SPTO and STNO layers, respectively, results in a substantial reduction of thermal conductivity via scattering a wider range of phonon spectrum without limiting the electrical transport and thermopower, leading to an enhancement in the figure-of-merit (ZT). The superlattice comp...
- Published
- 2015
7. Thermoelectric Response of Bulk and Monolayer MoSe2 and WSe2
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S. R. Sarath Kumar and Udo Schwingenschlögl
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Materials science ,Condensed matter physics ,General Chemical Engineering ,Semiclassical physics ,Transport theory ,General Chemistry ,Thermoelectric materials ,Lattice thermal conductivity ,Condensed Matter::Materials Science ,symbols.namesake ,Monolayer ,Boltzmann constant ,Thermoelectric effect ,Materials Chemistry ,symbols - Abstract
We study the thermoelectric properties of bulk and monolayer MoSe2 and WSe2 by first-principles calculations and semiclassical Boltzmann transport theory. The lattice thermal conductivity is calcul...
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- 2015
8. Arsenene and Antimonene: Two-Dimensional Materials with High Thermoelectric Figures of Merit
- Author
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S. R. Sarath Kumar, Suraj Sharma, and Udo Schwingenschlögl
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Materials science ,Graphene ,Phonon ,General Physics and Astronomy ,Semiclassical physics ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,01 natural sciences ,Engineering physics ,0104 chemical sciences ,law.invention ,law ,Head start ,Thermoelectric effect ,Figure of merit ,Density functional theory ,0210 nano-technology - Abstract
Graphene has a big head start, but other two-dimensional (2D) materials continue to pique interest---and not just for electronics. These systems also might be good, for example, in thermoelectric devices to scavenge wasted energy, and many basic questions need to be addressed. The authors use density functional theory plus semiclassical Boltzmann transport to study As and Sb monolayers, and find that both show excellent thermoelectric response. With low phonon group velocities and vibrational frequencies reducing lattice thermal conductivity, they outperform all known 2D materials, and are serious competition even for well-established thermoelectrics.
- Published
- 2017
9. Doping site dependent thermoelectric properties of epitaxial strontium titanate thin films
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Husam N. Alshareef, Terry M. Tritt, Anas Abutaha, S. R. Sarath Kumar, and Arash Mehdizadeh Dehkordi
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Materials science ,business.industry ,Doping ,General Chemistry ,Epitaxy ,chemistry.chemical_compound ,Thermal conductivity ,chemistry ,Electrical resistivity and conductivity ,Seebeck coefficient ,Thermoelectric effect ,Materials Chemistry ,Strontium titanate ,Optoelectronics ,Thin film ,business - Abstract
We demonstrate that the thermoelectric properties of epitaxial strontium titanate (STO) thin films can be improved by additional B-site doping of A-site doped ABO3 type perovskite STO. The additional B-site doping of A-site doped STO results in increased electrical conductivity, but at the expense of Seebeck coefficient. However, doping on both sites of the STO lattice significantly reduces the lattice thermal conductivity of STO by adding more densely and strategically distributed phononic scattering centers that attack wider phonon spectra. The additional B-site doping limits the trade-off relationship between the electrical conductivity and total thermal conductivity of A-site doped STO, leading to an improvement in the room-temperature thermoelectric figure of merit, ZT. The 5% Pr3+ and 20% Nb5+ double-doped STO film exhibits the best ZT of 0.016 at room temperature.
- Published
- 2014
10. Thermoelectric Properties of Strontium Titanate Superlattices Incorporating Niobium Oxide Nanolayers
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Terry M. Tritt, S. R. Sarath Kumar, Husam N. Alshareef, Mohamed N. Hedhili, and Dongkyu Cha
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Materials science ,General Chemical Engineering ,Superlattice ,Analytical chemistry ,General Chemistry ,chemistry.chemical_compound ,chemistry ,X-ray photoelectron spectroscopy ,Electrical resistivity and conductivity ,Seebeck coefficient ,Thermoelectric effect ,Materials Chemistry ,Strontium titanate ,Niobium oxide ,Orthorhombic crystal system - Abstract
A novel superlattice structure based on epitaxial nanoscale layers of NbOx and Nb-doped SrTiO3 is fabricated using a layer-by-layer approach on lattice matched LAO substrates. The absolute Seebeck coefficient and electrical conductivity of the [(NbOx)a/(Nb-doped SrTiO3)b]20 superlattices (SLs) were found to increase with decreasing layer thickness ratio (a/b ratio), reaching, at high temperatures, a power factor that is comparable to epitaxial Nb-doped SrTiO3 (STNO) films (∼0.7 W m–1 K–1). High temperature studies reveal that the SLs behave as n-type semiconductors and undergo an irreversible change at a varying crossover temperature that depends on the a/b ratio. By use of high resolution X-ray photoelectron spectroscopy and X-ray diffraction, the irreversible changes are identified to be due to a phase transformation from cubic NbO to orthorhombic Nb2O5, which limits the highest temperature of stable operation of the superlattice to 950 K.
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- 2014
11. Thermoelectric performance of functionalizedSc2CMXenes
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Udo Schwingenschlögl and S. R. Sarath Kumar
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Materials science ,Condensed matter physics ,Mean free path ,Phonon ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Electrical resistivity and conductivity ,Seebeck coefficient ,Thermoelectric effect ,Thermal ,Surface modification ,0210 nano-technology ,MXenes - Abstract
Functionalization of the MXene ${\mathrm{Sc}}_{2}\mathrm{C}$, which has the rare property to realize semiconducting states for various functionalizations including O, F, and OH, is studied with respect to the electronic and thermal behavior. The lowest lattice thermal conductivity is obtained for OH functionalization and an additional 30% decrease can be achieved by confining the phonon mean free path to 100 nm. Despite a relatively low Seebeck coefficient, ${\mathrm{Sc}}_{2}\mathrm{C}({\mathrm{OH})}_{2}$ is a candidate for intermediate-temperature thermoelectric applications due to compensation by a high electrical conductivity and very low lattice thermal conductivity.
- Published
- 2016
12. Lattice thermal conductivity in layered BiCuSeO
- Author
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S. R. Sarath Kumar and Udo Schwingenschlögl
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Materials science ,Condensed matter physics ,Mean free path ,Scattering ,Phonon ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Thermal conduction ,01 natural sciences ,Condensed Matter::Materials Science ,0103 physical sciences ,Thermal ,Dispersion (optics) ,Figure of merit ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,Anisotropy - Abstract
We quantify the low lattice thermal conductivity in layered BiCuSeO (the oxide with the highest known figure of merit). It turns out that the scattering of acoustical into optical phonons is strongly enhanced in the material because of the special structure of the phonon dispersion. For example, at room temperature the optical phonons account for an enormous 42% of the lattice thermal conductivity. We also quantify the anisotropy of the lattice thermal conductivity and determine the distribution of the mean free path of the phonons at different temperatures to provide a guide for tuning the thermal properties.
- Published
- 2016
13. Pulsed laser deposition and thermoelectric properties of In- and Yb-doped CoSb3 skutterudite thin films
- Author
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Jennifer Graff, Husam N. Alshareef, Terry M. Tritt, S. R. Sarath Kumar, and A. Alyamani
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Materials science ,Mechanical Engineering ,Analytical chemistry ,Atmospheric temperature range ,engineering.material ,Conductivity ,Condensed Matter Physics ,Pulsed laser deposition ,Mechanics of Materials ,Seebeck coefficient ,Thermoelectric effect ,Surface roughness ,engineering ,General Materials Science ,Skutterudite ,Thin film - Abstract
In- and Yb-doped CoSb3 thin films were prepared by pulsed laser deposition. Process optimization studies revealed that a very narrow process window exists for the growth of single-phase skutterudite films. The electrical conductivity and Seebeck coefficient measured in the temperature range 300–700 K revealed an irreversible change on the first heating cycle in argon ambient, which is attributed to the enhanced surface roughness of the films or trace secondary phases. A power factor of 0.68 W m−1 K−1 was obtained at ∼700 K, which is nearly six times lower than that of bulk samples. This difference is attributed to grain boundary scattering that causes a drop in film conductivity.
- Published
- 2011
14. Orthorhombic Ti2O3: A Polymorph-Dependent Narrow-Bandgap Ferromagnetic Oxide
- Author
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Stephen J. Pennycook, Tom Wu, S. R. Sarath Kumar, Husam N. Alshareef, Haijun Wu, Shuai Dong, Mark B. H. Breese, Jingsheng Chen, Nimer Wehbe, Xiaojiang Yu, Xinmao Yin, Yangyang Li, and Yakui Weng
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Materials science ,Band gap ,Foundation (engineering) ,Oxide ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Engineering physics ,Electronic, Optical and Magnetic Materials ,Biomaterials ,chemistry.chemical_compound ,chemistry ,Ferromagnetism ,0103 physical sciences ,Electrochemistry ,Natural science ,Orthorhombic crystal system ,010306 general physics ,0210 nano-technology - Abstract
This work was supported by the King Abdullah University of Science and Technology (KAUST). Y.K.W. and S.D. were supported by National Natural Science Foundation of China (Grant No. 11674055). J.S.C. was supported by the Singapore National Research Foundation under CRP Award No. NRF-CRP10-2012-02 and IIP award No. NRF-IIP001-001.
- Published
- 2017
15. Transparent ITO-Mn:ITO Thin-Film Thermocouples
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R.B Rakhi, S R Sarath Kumar, and Subbiah Kasiviswanathan
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Materials science ,business.industry ,Doping ,Thin film thermocouples ,Optical transparency ,chemistry.chemical_element ,Manganese ,Indium tin oxide ,chemistry ,Thermocouple ,Electrical resistivity and conductivity ,Thermoelectric effect ,Electronic engineering ,Optoelectronics ,Electrical and Electronic Engineering ,business ,Instrumentation - Abstract
Transparent thin-film thermocouples have been fabricated with indium tin oxide (ITO) and manganese doped indium tin oxide (Mn:ITO) as the positive and negative legs, respectively. Optical transparency of the thermocouples was above 85% in the visible region of the spectrum. Presence of Mn has been found to enhance the thermoelectric response, without significantly increasing the resistivity. Seebeck voltages of ~ 20 mV and ~ 31 mV have been obtained at 625 K, respectively, for the thermocouples with Mn:ITO legs having 1.6 at.% and 4.3 at.% Mn. The response has been found to be reproducible with an error of plusmn2%.
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- 2009
16. High temperature thermoelectric properties of strontium titanate thin films with oxygen vacancy and niobium doping
- Author
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Husam N. Alshareef, S. R. Sarath Kumar, and Abeer Z. Barasheed
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Materials science ,Dopant ,Annealing (metallurgy) ,Inorganic chemistry ,Doping ,Analytical chemistry ,Thermoelectric materials ,chemistry.chemical_compound ,Lattice constant ,chemistry ,Seebeck coefficient ,Thermoelectric effect ,Strontium titanate ,General Materials Science - Abstract
We report the evolution of high temperature thermoelectric properties of SrTiO3 thin films doped with Nb and oxygen vacancies. Structure-property relations in this important thermoelectric oxide are elucidated and the variation of transport properties with dopant concentrations is discussed. Oxygen vacancies are incorporated during growth or annealing in Ar/H2 above 800 K. An increase in lattice constant due to the inclusion of Nb and oxygen vacancies is found to result in an increase in carrier density and electrical conductivity with simultaneous decrease in carrier effective mass and Seebeck coefficient. The lattice thermal conductivity at 300 K is found to be 2.22 W m(-1) K(-1), and the estimated figure of merit is 0.29 at 1000 K.
- Published
- 2013
17. Correlation of Mn charge state with the electrical resistivity of Mn doped indium tin oxide thin films
- Author
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R.B Rakhi, Husam Niman Alshareef, S R Sarath Kumar, Mohamed Nejib Hedhili, and Subbiah Kasiviswanathan
- Subjects
Manganese compounds ,Photolithography ,Materials science ,Physics and Astronomy (miscellaneous) ,Binding energy ,Analytical chemistry ,chemistry.chemical_element ,Manganese ,Indium ,Electric conductivity ,Electrical resistivity and conductivity ,Indium compounds ,Charge state ,Core levels ,Mn doped ,Thin film ,Oxide films ,Three component ,Tin oxides ,Electrical resistivity ,Charge (physics) ,Charge compensation ,Satellite peaks ,Indium tin oxide ,Indium Tin Oxide films ,chemistry ,Indium tin oxide thin films ,Tin ,Core level ,Mn-doped ,Mn concentrations ,Titanium compounds ,Bonding analysis - Abstract
Correlation of charge state of Mn with the increase in resistivity with Mn concentration is demonstrated in Mn-doped indium tin oxide films. Bonding analysis shows that Mn 2p3/2 core level can be deconvoluted into three components corresponding to Mn2+ and Mn4+ with binding energies 640.8 eV and 642.7 eV, respectively, and a Mn2+ satellite at ?5.4 eV away from the Mn2+ peak. The presence of the satellite peak unambiguously proves that Mn exists in the +2 charge state. The ratio of concentration of Mn2+ to Mn4+ of ?4:1 suggests that charge compensation occurs in the n-type films causing the resistivity increase. � 2010 American Institute of Physics.
- Published
- 2010
18. Role of oxygen vacancies in the high-temperature thermopower of indium oxide and indium tin oxide films
- Author
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R.B Rakhi, S R Sarath Kumar, and Subbiah Kasiviswanathan
- Subjects
Electric resistance ,Photolithography ,Materials science ,Optical absorptions ,Absorption spectroscopy ,Inorganic chemistry ,Oxide ,Analytical chemistry ,chemistry.chemical_element ,High temperatures ,Indium oxides ,Indium ,Electrical resistivities ,Absorption ,chemistry.chemical_compound ,Sputtering ,Electrical resistivity and conductivity ,Ito films ,Materials Chemistry ,Light absorption ,Electrical and Electronic Engineering ,Thin film ,Oxide films ,Thermopower measurements ,Condensed Matter Physics ,Tin oxide ,Room temperatures ,Electronic, Optical and Magnetic Materials ,Indium tin oxide ,Oxygen ,Oxygen loss ,chemistry ,Indium tin oxide thin films ,Oxygen vacancies ,Tin ,Thermopower ,DC sputtering ,Titanium compounds ,As-grown ,Indium tin oxide films ,Electric network analysis - Abstract
Thermopower measurements in a range of 300-650 K along with room temperature optical absorption and electrical resistivity studies were performed on indium oxide (IO) and indium tin oxide (ITO) thin films grown by reactive dc sputtering. The thermopower of as-grown and oxygen-annealed IO and ITO films measured in Ar ambient displayed characteristics attributable to oxygen loss. The observations were substantiated with optical absorption and electrical resistivity results. � 2009 IOP Publishing Ltd.
- Published
- 2009
19. Thermopower and optical studies on undoped and manganese doped indium tin oxide films
- Author
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S. R. Sarath Kumar, V. Damodara Das, and S. Kasiviswanathan
- Subjects
Manganese compounds ,Photolithography ,Materials science ,Band gap ,Band-gap tuning ,Inorganic chemistry ,Analytical chemistry ,Indium ,Absorption ,Magnetic semiconductors ,Electric conductivity ,Electrical resistivity and conductivity ,Materials Chemistry ,Transparent conducting oxides ,Light absorption ,Thin film ,Oxide films ,Room temperature ,Manganese ,Thermopower measurements ,Thermoelectric power ,Optical absorption ,Thermopowers ,Doping ,Metals and Alloys ,Electrical resistivity ,Surfaces and Interfaces ,Indium tin oxide ,Sputter deposition ,Tin oxide ,Optical study ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Oxygen ,Indium Tin Oxide films ,Oxygen loss ,Oxygen vacancies ,Tin ,Physical vapor deposition ,Thermopower ,DC sputtering ,Diluted magnetic semiconductors ,Carrier concentration ,Mn concentrations - Abstract
Thermopower measurements in the range of 300-650 K along with room temperature optical absorption and electrical resistivity studies have been performed on indium tin oxide (ITO) and manganese doped indium tin oxide (Mn:ITO) thin films grown by reactive DC sputtering. The thermopower of the films measured in Ar ambient displayed irreversible changes attributable to oxygen loss. Thermopower, carrier concentration and resistivity of the films have been found to depend on oxygen vacancies and Mn concentration. The observations have been substantiated with optical absorption and room temperature electrical resistivity results. It has also been observed that band gap tuning in these films is possible by the introduction of Mn as well as oxygen vacancies. � 2009 Elsevier B.V. All rights reserved.
- Published
- 2009
20. Ion beam studies on reactive DC sputtered manganese doped indium tin oxide thin films
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Thomas Osipowicz, P. Malar, S. Kasiviswanathan, Swarnadeep Banerjee, and S. R. Sarath Kumar
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Nuclear and High Energy Physics ,Materials science ,Silicon ,Analytical chemistry ,chemistry.chemical_element ,Manganese ,Rutherford backscattering spectrometry ,Indium tin oxide ,chemistry ,Sputtering ,Indium compounds ,Ion beams ,Magnetoelectronics ,Rutherford backscattering spectroscopy ,Saturation magnetization ,X ray diffraction ,Magnetic elements ,Spin-based electronics ,Thin films ,Thin film ,Tin ,Instrumentation ,Indium - Abstract
Indium based transparent conducting oxides doped with magnetic elements have been studied intensively in recent years with a view to develop novel ferromagnetic semiconductors for spin-based electronics. In the present work, we have grown manganese doped indium tin oxide (Mn:ITO) thin films, onto Si and Si/SiO2 substrates by DC reactive sputtering of a composite target containing indium-tin alloy and manganese, in a gas mixture of oxygen and argon. Glancing angle X-ray diffraction (GXRD) studies reveal the polycrystalline nature of the films. Magnetic measurements carried out using vibrating sample magnetometer (VSM) suggest that the films are ferromagnetic at room temperature, with a saturation magnetization of ?22.8 emu/cm3. The atomic percentages of In, Sn, Mn and O, as estimated using Rutherford backscattering spectrometry (RBS) are 37.0, 4.0, 1.6 and 57.4, respectively. RBS measurements reveal that the interface of the films with Si substrate has a ?30 nm thick intermediate layer. This layer consists of oxygen, silicon, indium, tin and manganese, in the ratio 1:0.56:0.21:0.07:0.03, indicative of diffusion of elements across the interface. The films on Si/SiO2, on the other hand, have a sharp interface. � 2007 Elsevier B.V. All rights reserved.
- Published
- 2008
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21. A hot probe setup for the measurement of Seebeck coefficient of thin wires and thin films using integral method
- Author
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R.B Rakhi, S R Sarath Kumar, and Subbiah Kasiviswanathan
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Materials science ,business.industry ,Constantan ,Rod ,Copper ,Indium compounds ,Seebeck coefficient ,Thermal effects ,Wire ,Electrical transport measurements ,Indium tin oxide (ITO) thin films ,Thin films ,Indium tin oxide ,Thermocouple ,Thermoelectric effect ,Optoelectronics ,Thin film ,business ,Instrumentation ,Voltage - Abstract
An experimental setup is developed for the measurement of the Seebeck coefficient of thin wires and thin films in the temperature range of 300-650 K. The setup makes use of the integral method for measuring the Seebeck voltage across the sample. Two pointed copper rods with in-built thermocouples serve as hot and cold probes as well as leads for measuring the Seebeck voltage. The setup employs localized heating and enables easy sample loading using a spring loaded mounting system and is fully automated. Test measurements are made on a constantan wire and indium tin oxide (ITO) thin film for illustration. The Seebeck voltage obtained for constantan wire is in agreement with the NIST data for copper constantan couple with an error of 1%. The calculated carrier concentration of ITO film from the Seebeck coefficient measurement is comparable with that obtained by electrical transport measurements. The error in the Seebeck coefficient is estimated to be within 3%. � 2008 American Institute of Physics.
- Published
- 2008
22. In situ growth of p and n-type graphene thin films and diodes by pulsed laser deposition
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M. A. Khan, Husam N. Alshareef, S. R. Sarath Kumar, Mohamed N. Hedhili, and Pradipta K. Nayak
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Materials science ,Physics and Astronomy (miscellaneous) ,Graphene ,Doping ,technology, industry, and agriculture ,Analytical chemistry ,Electron spectroscopy ,Pulsed laser deposition ,law.invention ,Surface coating ,symbols.namesake ,X-ray photoelectron spectroscopy ,law ,symbols ,Thin film ,Raman spectroscopy - Abstract
We report the in situ growth of p and n-type graphene thin films by ultraviolet pulsed laser deposition in the presence of argon and nitrogen, respectively. Electron microscopy and Raman studies confirmed the growth, while temperature dependent electrical conductivity and Seebeck coefficient studies confirmed the polarity type of graphene films. Nitrogen doping at different sites of the honeycomb structure, responsible for n-type conduction, is identified using X-ray photoelectron spectroscopy, for films grown in nitrogen. A diode-like rectifying behavior is exhibited by p-n junction diodes fabricated using the graphene films.
- Published
- 2013
23. Ultraviolet laser deposition of graphene thin films without catalytic layers
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Husam Niman Alshareef, R.B Rakhi, and S R Sarath Kumar
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Laser ablation ,Materials science ,Physics and Astronomy (miscellaneous) ,Graphene ,business.industry ,Graphene foam ,Nanotechnology ,law.invention ,Pulsed laser deposition ,law ,Optoelectronics ,Pyrolytic carbon ,Thin film ,business ,Graphene nanoribbons ,Graphene oxide paper - Abstract
In this letter, the formation of nanostructured graphene by ultraviolet laser ablation of a highly ordered pyrolytic graphite target under optimized conditions is demonstrated, without a catalytic layer, and a model for the growth process is proposed. Previously, graphene film deposition by low-energy laser (2.3 eV) was explained by photo-thermal models, which implied that graphene films cannot be deposited by laser energies higher than the C-C bond energy in highly ordered pyrolytic graphite (3.7 eV). Here, we show that nanostructured graphene films can in fact be deposited using ultraviolet laser (5 eV) directly over different substrates, without a catalytic layer. The formation of graphene is explained by bond-breaking assisted by photoelectronic excitation leading to formation of carbon clusters at the target and annealing out of defects at the substrate.
- Published
- 2013
24. Temperature dependent thermoelectric properties of chemically derived gallium zinc oxide thin films
- Author
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Husam N. Alshareef, S. R. Sarath Kumar, and Abeer Z. Barasheed
- Subjects
Materials science ,Dopant ,Annealing (metallurgy) ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,Zinc oxide thin films ,Oxygen ,chemistry ,Chemical engineering ,Thermoelectric effect ,Materials Chemistry ,Thin film ,Gallium - Abstract
In this study, the temperature dependent thermoelectric properties of sol–gel prepared ZnO and 3% Ga-doped ZnO (GZO) thin films have been explored. The power factor of GZO films, as compared to ZnO, is improved by nearly 17% at high temperature. A stabilization anneal, prior to thermoelectric measurements, in a strongly reducing Ar/H2 (95/5) atmosphere at 500 °C was found to effectively stabilize the chemically derived films, practically eliminating hysteresis during thermoelectric measurements. Subtle changes in the thermoelectric properties of stabilized films have been correlated to oxygen vacancies and excitonic levels that are known to exist in ZnO-based thin films. The role of Ga dopants and defects, formed upon annealing, in driving the observed complex temperature dependence of the thermoelectric properties is discussed.
- Published
- 2013
25. Effect of oxygen vacancy distribution on the thermoelectric properties of La-doped SrTiO3 epitaxial thin films
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R.B Rakhi, Anas Abutaha, Husam Niman Alshareef, S R Sarath Kumar, and Mohamed Nejib Hedhili
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Condensed Matter::Materials Science ,Effective mass (solid-state physics) ,Materials science ,Ellipsometry ,Electrical resistivity and conductivity ,Condensed Matter::Superconductivity ,Seebeck coefficient ,Doping ,Thermoelectric effect ,Analytical chemistry ,General Physics and Astronomy ,Electrical measurements ,Thin film - Abstract
A detailed study of the role of oxygen vacancies in determining the effective mass and high temperature (300–1000 K) thermoelectric properties of La-doped epitaxial SrTiO3 thin films is presented. It is observed that at intermediate temperatures, a transition from degenerate to non-degenerate behavior is observed in the Seebeck coefficient, but not electrical conductivity, which is attributed to heterogeneous oxygen non-stoichiometry. Heikes formula is found to be invalid for the films with oxygen vacancies. By fitting the spectroscopic ellipsometry (SE) data, obtained in the range 300–2100 nm, using a Drude-Lorentz dispersion relation with two Lorentz oscillators, the electrical and optical properties of the films are extracted. Using the excellent agreement between the transport properties extracted from SE modeling and direct electrical measurements, we demonstrate that an increase in concentration of oxygen vacancies results in a simultaneous increase of both carrier concentration and electron effecti...
- Published
- 2012
26. Enhanced carrier density in Nb-doped SrTiO3thermoelectrics
- Author
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Husam N. Alshareef, Kemal Özdoğan, S. R. Sarath Kumar, Udo Schwingenschlögl, and M. Upadhyay Kahaly
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Materials science ,Condensed matter physics ,chemistry ,Band gap ,Ab initio quantum chemistry methods ,Seebeck coefficient ,Thermoelectric effect ,Niobium ,General Physics and Astronomy ,chemistry.chemical_element ,Density functional theory ,Thermoelectric materials ,Epitaxy - Abstract
We study epitaxial SrTiO3 interfaced with Nb-doped SrTi1-xNbxO3 (x = 0, 0.125, 0.25, 0.375, and 0.5) by full-potential density functional theory. From the electronic band structures obtained by our ab-initio calculations we determine the dependence of the induced metallicity on the Nb concentration. We obtain a monotonous increase of the carrier density with the Nb concentration. The results are confirmed by experiments for SrTi0.88Nb0.12O3 and SrTi0.8Nb0.2O3, demonstrating the predictive power and limitations of our theoretical approach. We also show that the Seebeck coefficient decreases monotonously with increasing temperature.
- Published
- 2012
27. Modeling the transport properties of epitaxially grown thermoelectric oxide thin films using spectroscopic ellipsometry
- Author
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R.B Rakhi, Anas Abutaha, Husam Niman Alshareef, S R Sarath Kumar, and Mohamed Nejib Hedhili
- Subjects
chemistry.chemical_compound ,Materials science ,Physics and Astronomy (miscellaneous) ,chemistry ,Ellipsometry ,Annealing (metallurgy) ,Seebeck coefficient ,Thermoelectric effect ,Oxide ,Analytical chemistry ,Electrical measurements ,Thin film ,Thermoelectric materials - Abstract
The influence of oxygen vacancies on the transport properties of epitaxial thermoelectric (Sr,La)TiO3 thin films is determined using electrical and spectroscopic ellipsometry (SE) measurements. Oxygen vacancy concentration was varied by ex-situ annealing in Ar and Ar/H2. All films exhibited degenerate semiconducting behavior, and electrical conductivity decreased (258–133 S cm−1) with increasing oxygen content. Similar decrease in the Seebeck coefficient is observed and attributed to a decrease in effective mass (7.8–3.2 me), as determined by SE. Excellent agreement between transport properties deduced from SE and direct electrical measurements suggests that SE is an effective tool for studying oxide thin film thermoelectrics.
- Published
- 2012
28. Lattice dynamics and substrate-dependent transport properties of (In, Yb)-doped CoSb3 skutterudite thin films
- Author
-
Husam N. Alshareef, Dongkyu Cha, and S. R. Sarath Kumar
- Subjects
Materials science ,Dopant ,Condensed matter physics ,Band gap ,Doping ,General Physics and Astronomy ,engineering.material ,Pulsed laser deposition ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,engineering ,Direct and indirect band gaps ,Grain boundary ,Skutterudite ,Thin film - Abstract
Lattice dynamics, low-temperature electrical transport, and high-temperature thermoelectric properties of (In, Yb)-doped CoSb3 thin films on different substrates are reported. Pulsed laser deposition under optimized conditions yielded single-phase polycrystalline skutterudite films. Raman spectroscopy studies suggested that In and Yb dopants occupy the cage sites in the skutterudite lattice. Low-temperature electrical transport studies revealed the n-type semiconducting nature of the films with extrinsic and intrinsic conduction mechanisms, in sharp contrast to the degenerate nature reported for identical bulk samples. Calculations yielded a direct bandgap close to 50 meV with no evidence of an indirect gap. The carrier concentration of the films was identical to that reported for the bulk and increased with temperature beyond 250 K. The higher resistivity exhibited is attributed to the enhanced grain boundary scattering in films with a high concentration of grains. The maximum power factor of ∼0.68 W m−1...
- Published
- 2011
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