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- 저자 : Seetawan, Tosawat (검색결과 4 건)
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Kumar, M.,Vora-ud, A.,Seetawan, T.,Han, J.G. Elsevier Ltd 2016 Materials & Design Vol.98 No.-
<P>Thermoelectric measurement is an exhaustive exercise for the case of thin films, requiring meticulous attention to the thermal contact interfaces and the instrumentation. Usually, different set-ups are combined for the temperature dependent measurement of different thermoelectric key quantities. Here, a facile 6-probe measurement set-up is presented, which can measure Seebeck coefficients and electrical properties of thin films in the temperature range of 300 K-600 K. Using this set-up, the thermoelectric properties of Ge2Sb5Te5 thin films, prepared with pulsed DC magnetron sputtering method are studied. The effects of working pressure, post-deposition thermal treatment and variation of film thickness on the microstructure, surface, electrical and thermoelectric properties are investigated systematically. Plasma diagnostics, performed using optical emission spectroscopy provided the information about various radicals' excitations and the electron temperature. Microstnictural studies show the phase transformation from amorphous to metastable cubic phase. FESEM study exhibits highly dense films with uniform grains compactness. It has been found that lowering average crystallite size by optimum electron temperature and pressure conditions governs the enhancement in Seebeck coefficient. The throughput of process >400 nm/min, and obtained Seebeck coefficients values 271.50 mu V/K are highly promising for industrial utilization. (C) 2016 Elsevier Ltd. All lights reserved.</P>
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Athorn Voraeud,Somporn Thaowonkaew,Meena Rittiruam,Mati Horprathum,Tosawat Seetawan 한국물리학회 2016 Current Applied Physics Vol.16 No.3
GeSbTe0.5 hexagonal phase thin film (heGeSbTe0.5) has been deposited on silicon wafer with 1 mm thick silicon dioxide (SiO2/Si) by pulsed dc magnetron sputtering using a 99.99% of 1: 1: 1 ratio of Ge: Sb: Te target at ambient temperature. The asedeposited thin film has been deposited time for 60 min and annealed at temperature 673 K each for 15, 30, 45 and 60 min at high vacuum state. The effected annealing time treatment (ta) on phase preferred orientation, morphology and film thickness (d), atomic composition, carrier concentration (n) and mobility (m) and Seebeck coefficient have been investigated by Xeray diffraction (XRD), fieldeemission scanning electron microscopy (FEeSEM), Auger electron microscopy (AES), Hall Effect measurement and steady state method, respectively. The obtained results of as edeposited thin film is amorphous with Ge:Sb:Te; 1:0.7:0.5 atomic ratio and showed the crystal phases of hexagonal structure with Ge:Sb:Te; 1:1:0.5 atomic ratio after annealing at 673 K. The annealed time 45 min of heGeSbTe0.5 thin film was yielded good thermoelectric properties with highest carrier concentration 3.35 1021 cm3, Seebeck coefficient 78.50 mV K1and power factor 3.95 104 Wm1 K2.
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Vora-ud, A.,Rittiruam, M.,Kumar, M.,Han, J.G.,Seetawan, T. Elsevier Ltd 2016 Materials & Design Vol.89 No.-
<P>Using a combination of molecular orbital and molecular dynamics simulations, electronic and thermoelectric properties of GeSbTe model clusters are presented. The unit cells of Ge13Sb20Te52, Ge7Sb12Te40 and Ge14Sb6Te26 model clusters are designed corresponding to GeSb2Te4, GeSb4Te7 and Ge2Sb2Te5 compositions in hexagonal phase, oriented in the c-axis direction. The electronic structures of clusters have been simulated by discrete-variational molecular orbital calculation using Hartree-Fock-Slater approximation to determine the electrical conductivity and Seebeck coefficients in Mott expression. For thermal properties, molecular dynamics simulations have been employed on clusters in amorphous, cubic and hexagonal phases using Verlet's algorithm and subsequently using Green-Kubo relation for lattice thermal conductivity. We assumed inter-atomic interaction, defined by the Morse-type potential function added to Busing-Ida potential function, which considers partial electronic charges on the ions, bond length of the cation-anion pair, and depth and shape of the potential. Based on our simulations, detailed variation of electrical conductivity, carrier thermal conductivity, lattice thermal conductivity, Seebeck coefficients, power factor and figure of merit, are presented as a function of temperature in 300-700 K range. Thermoelectric parameters obtained in present study were compared and explained with those of experimentally results of Ge2Sb2Te5 composition in hexagonal phase. (C) 2015 Elsevier Ltd. All rights reserved.</P>
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Vora-ud, Athorn,Kumar, Manish,Jin, Su bong,Muthitamongkol, Pennapa,Horprathum, Mati,Thaowonkaew, Somporn,Chao-moo, Watchara,Thanachayanont, Chancana,Thang, Phan Bach,Seetawan, Tosawat,Han, Jeon Geon Elsevier 2018 Journal of alloys and compounds Vol.763 No.-
<P><B>Abstract</B></P> <P>Optimization of substrate heating during sputtering processes is essential to obtain desired microstructures of deposited thin films, as it provides the required energy flux during the nucleation and growth. In this work, Ge<SUB>2</SUB>Sb<SUB>2</SUB>Te<SUB>5</SUB> thin films were prepared by a pulsed-DC magnetron sputtering process at optimized plasma conditions (pulsed frequency and pulse reversal time). The effect of substrate heating, in temperature range of 250–450 °C, was systematically investigated on the process throughput and various properties i.e. microstructure, morphology, atomic composition, carrier concentration, mobility and Seebeck coefficient of deposited films. The substrate heating was found to be required to obtain films in cubic crystalline phase. Through the optimization of substrate temperature, process throughput and surface properties, electrical properties as well as thermoelectric power factors were enhanced. The maximum power factor value of thin films was achieved as 0.77 mW m<SUP>–1</SUP> K<SUP>–2</SUP> for the substrate temperature as 400 °C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ge<SUB>2</SUB>Sb<SUB>2</SUB>Te<SUB>5</SUB> thin films were successfully microstructural controlled by substrate heating. </LI> <LI> Microstructural of Ge<SUB>2</SUB>Sb<SUB>2</SUB>Te<SUB>5</SUB> thin films were controlled for thermoelectric properties. </LI> <LI> Thermoelectric properties were discussed based on temperature of substrate heating. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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