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Author: search.filters.author.Nuthongkum, PilaiponSubject: search.filters.subject.Flexible Bi2Te3

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    Comparison of thermoelectric properties of flexible bismuth telluride thin films deposited via DC and RF magnetron sputtering
    (2019-11-18)
    Jitthamapirom, Piya
    ;
    Wanarattikan, Pornsiri
    ;
    Nuthongkum, Pilaipon
    ;
    Sakdanuphab, Rachsak
    ;
    Sakulkalavek, Aparporn
    Bi<inf>2</inf>Te<inf>3</inf> thin films were deposited onto polyamide sheets with direct current (DC) or radio frequency (RF) magnetron sputtering techniques. The films were prepared using a Bi<inf>2</inf>Te<inf>3</inf> target at a varying pre-heating temperature from 150 to 350 °C. It was observed that the type of plasma excitation and pre-heating temperature can significantly change the composition, preferred orientation, crystallinity, and thermoelectric properties of the films. The pre-heat treatment significantly affected the non-stoichiometric composition. In addition, it was shown that crystallinity and (0 0 l) planes were enhanced in the DC sputtered coatings at a high pre-heating temperature. The maximum power factor of 3.5 × 10<sup>−3</sup> W/m K<sup>2</sup> at 285 °C was obtained for the films deposited using DC magnetron sputtering and a pre-heating temperature of 350 °C. The carrier concentration and mobility of the film were 5.40 × 10<sup>20</sup> cm<sup>−3</sup> and 13.04 cm<sup>2</sup>/V s, respectively. Compared with an ordinary Bi<inf>2</inf>Te<inf>3</inf> film, the power factor of such film has been greatly increased. The results indicated that DC magnetron sputtering can enhance the (0 0l) plane orientation in the Bi<inf>2</inf>Te<inf>3</inf> film.
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    [Bi]:[Te] Control, Structural and Thermoelectric Properties of Flexible BixTey Thin Films Prepared by RF Magnetron Sputtering at Different Sputtering Pressures
    (2017-11-01)
    Nuthongkum, Pilaipon
    ;
    Sakdanuphab, Rachsak
    ;
    Horprathum, Mati
    ;
    Sakulkalavek, Aparporn
    In this work, flexible Bi<inf>x</inf>Te<inf>y</inf> thin films were prepared by radio frequency (RF) magnetron sputtering using a Bi<inf>2</inf>Te<inf>3</inf> target on polyimide substrate. The effects of sputtering pressures, which ranged between 0.6 Pa and 1.6 Pa on the [Bi]:[Te] ratio, and structural and thermoelectric properties were investigated. The [Bi]:[Te] ratio of thin film was determined by energy-dispersive spectrometry (EDS). The EDS spectra show the variation of the [Bi]:[Te] ratio as the sputtering pressure is varied. The film deposited at 1.4 Pa almost has a stoichiometric composition. The selective films with different [Bi]:[Te] ratios and sputtering pressures were characterized by their surface morphologies, crystal and chemical structures by field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD) and Raman spectroscopy, respectively. Electrical transport properties, including carrier concentration and mobility, were measured by Hall effect measurements. Seebeck coefficients and electrical conductivities were simultaneously measured by a direct current four-terminal method (ZEM-3). The XRD and Raman spectroscopy results show a difference in microstructure between BiTe and Bi<inf>2</inf>Te<inf>3</inf> depending on the [Bi]:[Te] ratio. Electrical conductivity and Seebeck coefficient are related to the crystal and chemical structures. The maximum power factor of the Bi<inf>2</inf>Te<inf>3</inf> thin film is 9.5 × 10<sup>−4</sup> W/K<sup>2</sup> m at room temperature, and it increases to 12.0 × 10<sup>−4</sup> W/K<sup>2</sup> m at 195°C.
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    RSM Base Study of the Effect of Argon Gas Flow Rate and Annealing Temperature on the [Bi]:[Te] Ratio and Thermoelectric Properties of Flexible Bi-Te Thin Film
    (2017-05-01)
    Nuthongkum, Pilaipon
    ;
    Sakulkalavek, Aparporn
    ;
    Sakdanuphab, Rachsak
    Bismuth telluride (Bi-Te) thin films coated on a flexible substrate were prepared by RF (radio frequency) magnetron sputtering technique. A response surface methodology based on a central composite design was used to optimize deposition parameters, including the amount of Ar gas flow rate (100.5–106.5 sccm) in the sputtering process and the annealing temperature (250–320°C) for stoichiometric Bi<inf>2</inf>Te<inf>3</inf> thin films. The mathematical model was validated and proven to be statistically sufficient and accurate in predicting a response (Te content). The stoichiometric Bi<inf>2</inf>Te<inf>3</inf> thin films can be prepared on terms appropriate to the Ar flow rate and annealing temperature under several conditions, such as at the Ar flow rate of 103.5 sccm followed by an annealing temperature of 285°C. The characterization of the crystal structure and surface morphology of selected samples with different [Bi]:[Te] content were analyzed by x-ray diffraction (XRD) and a field emission scanning electron microscope, respectively. The XRD spectra showed Bi-Te and Bi<inf>2</inf>Te<inf>3</inf> structures that corresponded with the ratio of [Bi]:[Te]. The Seebeck coefficient and electrical conductivity were simultaneously measured at room temperature and up to 300°C by a direct current four-terminal method. The maximum power factor of the stoichiometric Bi<inf>2</inf>Te<inf>3</inf> thin film was 61×10<sup>−5</sup> W/K<sup>2</sup>m at 243°C.