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Effects of substrate rotational speed and phase transition on β-V2O5 for temperature-sensitive thin films
(2025-12-01)
Fungfuang, Natasia
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Khlayboonme, S. Tipawan
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Kitiwan, Mettaya
The phase stability and reversibility of V<inf>2</inf>O<inf>5</inf> are crucial for smart, contactless optical thermal sensors. Controlling phase characteristics optimizes device performance, particularly by achieving lower phase-transition temperatures with reversible properties. This study examines the effects of substrate rotational speed on the phase content and homogeneity of V<inf>2</inf>O<inf>5</inf> thin films deposited via radiofrequency magnetron sputtering using an inclined magnetron head and an O<inf>2</inf>-reactive process. Characterized using X-ray diffraction, electron microscopy, Hall effect measurements, and ultraviolet–visible spectroscopy, the films exhibited a mixture of β-monoclinic and β-tetragonal phases. Increasing the substrate rotational speed from 0 to 40 rpm increased the film thickness from 125 to 220 nm but reduced the crystallite size from 16.8 to 7.9 nm for the β-monoclinic phase. The direct bandgap energy decreased from 3.582 to 2.56 eV, and the electron density decreased from 2.92 × 1018 to 5.2 × 1017 cm−3, suggesting suppressed depletion of vanadyl oxygen in the film structure. Optical analysis revealed that the dispersive energy for the β-monoclinic phase increased from 24.7 to 30.3 eV as the rotational speed increased—attributed to stronger polarization due to lattice vibrations. The responses of the annealed and as-deposited films to thermally induced stimuli were investigated. During cooling to 100 °C, the β-tetragonal phase content continued to increase, whereas the β-monoclinic phase content decreased and appeared to revert to levels observed before heating. This result revealed a reversible β-monoclinic phase transformation during cooling, indicating the potential of amorphous β-monoclinic V<inf>2</inf>O<inf>5</inf> films for chromic and temperature-sensitive sensors with repeatable performance.
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Transition between monoclinic and tetragonal β phases induced by reactive oxygen gas in RF-sputtered V2O5 thin films
(2022-11-01)
Khlayboonme, S. Tipawan
Thin films of V<inf>2</inf>O<inf>5</inf> are promising materials for applications in chromogenic devices, such as gas sensors and contactless optical thermal sensors. Therefore, controlling the formation of the various phases of V<inf>2</inf>O<inf>5</inf> is important. The device performance, in relation to satisfactory coloration efficiency and fast response, strongly depends on the characteristics of the phase incorporated in the film structure. To better understand the phase formation in these films, thin films of V<inf>2</inf>O<inf>5</inf> were deposited by RF magnetron sputtering using an O<inf>2</inf>-reaction technique from a metallic V target, and the influence of RF power and O<inf>2</inf> levels on the transition between the β-monoclinic and β-tetragonal phase structures was investigated by X-ray diffractometer. The films were also evaluated using Auger-electron, Raman-, and UV-vis spectrometers to determine their composition, chemical, and electronic properties to assess the effects of the two sputtering parameters. The mechanism underlying the development of film properties is related to the plasma characteristics and species observed by optical emission spectroscopy. Increasing the RF power resulted in a higher phase content of the β-monoclinic and α-orthorhombic phase, whereas an increasing the oxygen levels induced a phase transition towards the β-tetragonal phase of V<inf>2</inf>O<inf>5</inf>. Films with different phase contents exhibited different optical energy bandgaps. Plasma diagnostics showed that increasing the RF power increased the thickness of plasma sheaths on the target surface. The thinner sheath on the target surface further increased the β-tetragonal phase content. The variation between β-monoclinic and β-tetragonal phase content was expected because of the bombardment of energetic O− ions that were accelerated from the plasma sheath toward the growth surface. A deeper understanding of the transition between β phases in V<inf>2</inf>O<inf>5</inf> films can enable better phase control, which can improve film application towards various sensing devices, particularly chromic- or temperature-sensors.
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Understanding the effect of sputtering pressures on the thermoelectric properties of GeTe films
(2022-02-10)
Daichakomphu, Noppanut
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Abbas, Suman
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Chou, Ta Lei
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Chen, Li Chyong
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Chen, Kuei Hsien
In this work, we study the effect of sputtering pressures on the thermoelectric properties of GeTe films. The working pressures were differentiated from 3 to 30 mTorr, and the as-deposited films were annealed at 623 K for 10 min in Ar atmosphere. The results show that the working pressure has a significant effect on the Ge content and crystalline size. The turning trend of the Seebeck coefficient with different sputtering pressures corresponds to the Ge content. The surface morphology of annealed film will change from cracks to voids with increasing sputtering pressure. This behavior can be explained by the growth mechanisms model. The voids and relatively low crystalline size of GeTe films affect to the reduction of the electrical conductivity. In addition, the void content decreased as film thickness was increased. Therefore, controlling the working pressures in the sputtering process and film thickness is important for the thermoelectric performance of GeTe thin film. In our work, we prove that the thermoelectric properties of GeTe films could be optimized effectively by simply tuning different sputtering conditions.
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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
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Sakdanuphab, Rachsak
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Horprathum, Mati
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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 × 10−4 W/K2 m at room temperature, and it increases to 12.0 × 10−4 W/K2 m at 195°C.
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Microstructure and Electrical Properties of Antimony Telluride Thin Films Deposited by RF Magnetron Sputtering on Flexible Substrate Using Different Sputtering Pressures
(2017-05-01)
Khumtong, T.
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Sukwisute, P.
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Sakulkalavek, A.
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Sakdanuphab, R.
The microstructural, electrical, and thermoelectric properties of antimony telluride (Sb<inf>2</inf>Te<inf>3</inf>) thin films have been investigated for thermoelectric applications. Sb<inf>2</inf>Te<inf>3</inf> thin films were deposited on flexible substrate (polyimide) by radiofrequency (RF) magnetron sputtering from a Sb<inf>2</inf>Te<inf>3</inf> target using different sputtering pressures in the range from 4 × 10−3 mbar to 1.2 × 10−2 mbar. The crystal structure, [Sb]:[Te] ratio, and electrical and thermoelectric properties of the films were analyzed by grazing-incidence x-ray diffraction (XRD) analysis, energy-dispersive x-ray spectroscopy (EDS), and Hall effect and Seebeck measurements, respectively. The XRD spectra of the films demonstrated polycrystalline structure with preferred orientation of (015), (110), and (1010). A high-intensity spectrum was found for the film deposited at lower sputtering pressure. EDS analysis of the films revealed the effects of the sputtering pressure on the [Sb]:[Te] atomic ratio, with nearly stoichiometric films being obtained at higher sputtering pressure. The stoichiometric Sb<inf>2</inf>Te<inf>3</inf> films showed p-type characteristics with electrical conductivity, carrier concentration, and mobility of 35.7 S cm−1, 6.38 × 1019 cm−3, and 3.67 cm2 V−1 s−1, respectively. The maximum power factor of 1.07 × 10−4 W m−1 K−2 was achieved for the film deposited at sputtering pressure of 1.0 × 10−2 mbar.
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Chemical characterization and electrical properties of indium oxynitride grown by reactive gas-timing RF magnetron sputtering
(2010-02-05)
Sungthong, A.
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Khomdet, P.
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Porntheeraphat, S.
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Hruanun, C.
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Poyai, A.
This work investigates changes in the chemical composition of InON thin films, grown by reactive gas-timing rf magnetron sputtering with different O<inf>2</inf>:N<inf>2</inf> timing ratio characterized by Auger Electron Microscope (AES), Raman Spectroscopy which are well correlated with the electrical properties of films. The existence of nitrogen and oxygen in the deposited InON thin films was revealed by AES. Two Raman active optical phonons have been clearly observed and assigned to InN E<inf>1</inf>(TO) at ∼470 cm-1 and E<inf>1</inf>(LO) at ∼570 cm-1 and also shifted with different O<inf>2</inf>:N<inf>2</inf> timing ratio. The carrier mobility of InON thin films was decreased when the ratio of O<inf>2</inf>:N <inf>2</inf> timing is increased. © (2010) Trans Tech Publications.
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An extreme change in structural and optical properties of indium oxynitride deposited by reactive gas-timing RF magnetron sputtering
(2008-09-30)
Sungthong, A.
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Porntheeraphat, S.
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Poyai, A.
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Nukeaw, J.
The indium oxynitride (InON) films were achieved by reactive RF magnetron sputtering indium target which has the purity of 99.999% with a novel reactive gas-timing technique. The structural, optical and electrical properties in a series of polycrystalline InON films affected by gas-timing of reactive N <inf>2</inf> and O <inf>2</inf> gases introduced to the chamber were observed. The X-ray photoelectron spectroscopy revealed that the oxygen content in thin films that compounded to indium and nitrogen, which increased from 10% in indium nitride (InN) to 66% in indium oxide (In <inf>2</inf> O <inf>3</inf> ) films. The X-ray diffraction peaks show that the phase of deposited films changes from InN to InON and to In <inf>2</inf> O <inf>3</inf> with an increasing oxygen timing. The hexagonal structure of InN films with predominant (0 0 2) and (0 0 4) orientation was observed when pure nitrogen is only used as sputtering gas, while InON and In <inf>2</inf> O <inf>3</inf> seem to demonstrate body-center cubic polycrystalline structures depending on gas-timing. The surface morphologies investigated from atomic force microscope of deposited films with varying gas-timing of O <inf>2</inf> :N <inf>2</inf> show indifferent. The numerical algorithm method was used to define the optical bandgap of films from transmittance results. The increasing oxygen gas-timing affects extremely to the change of crystallinity phase from InN to InON and to In <inf>2</inf> O <inf>3</inf> , the increase of optical bandgap from 1.4 to 3.4 eV and the rise of sheet resistance from 15 Ω/□ to insulator. © 2008 Elsevier B.V. All rights reserved.
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Characterization of ITO thin films on PET substrates prepared by gas-timing RF magnetron sputtering
(2005-11-09)
Klamchuen, Annop
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Pornteeraphat, Nisaporn
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Nukeaw, Jiti
Indium tin oxide (ITO) thin films were deposited on polyethylene terephthalate (PET) substrates at room temperature by RF magnetron sputtering with a new technique, called gas-timing. The influence of RF power on properties of ITO thin films was investigated. From the x-ray diffraction measurement of the ITO thin films grown by this technique, cubic, nano-crystalline structure with predominant (222) and (400) orientation was observed. It was found that the increasing of RF power yielded to decrease in the sheet resistance of ITO thin films. The sheet resistance of ITO thin films deposited by RF power of 40 watts had the lowest value of 8 Ω/□. By the gas-timing technique, the ITO thin films on PET substrates were achieved with high transmittance in visible region of 90%. Therefore, the gas-timing RF magnetron sputtering is a promising technique to achieve the ITO thin film on PET substrate with low resistivity and high transmittance in visible region without substrate heating and post-deposition annealing. © 2005 The Surface Science Society of Japan.

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