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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
;
Khlayboonme, S. Tipawan
;
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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Comparative study of non-annealing and annealing on properties of ITO deposited by RF magnetron sputtering
(2015-01-01)
Khlayboonme, S. Tipawan
;
Warawoot, Thowladda
A comparison of the properties for two ITO thin films was performed. The two films were as follows - as-deposited and annealed ITO films. The influence of annealing on the structural, morphological, electrical, and optical properties was studied. The post-annealing treatment was done at a temperature of 400 for 1 h in air. The ITO thin films were deposited onto glass substrates by RF magnetron sputtering of a ceramic In<inf>2</inf>O<inf>3</inf>: SnO<inf>2</inf> target in pure argon atmosphere at a low base pressure of <10-6 mbar and a RF power of 50 W. The films were characterized by XRD, FTIR, contact angle measurements, FE-SEM combined with EDX, Halleffect measurements and UV-Vis transmission spectroscopy. The ITO films showed a crystalline structure with a predominant orientation (400) and its intensity was increased after the film was annealed. The structure of the annealed film became reformed in more perfect columnar structure. The annealed film showed a decrease in contact angle and increase in FTIR spectra intensity. The annealing induced more tin incorporated into the film from 0.51 to 2.62 at%. The resistivity decreased from 2.7×10-3 to 1.1×10-3 Ω cm with increasing mobility from 7.5 to 27.5 cm2 V-1 s-1 but decreasing carrier concentration from 3.0×1020 to 2.0 × 1020 cm-3. The optical band gap increased from 3.43 to 3.50 eV. All films showed highly transparency (×85%) in the visible light region. Compared with the non-annealed ITO film, the air-annealed ITO film revealed the better properties except for carrier concentration.

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