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Reversible thermally stimulated phase transition in amorphous–nanocrystalline β-V2O5 thin films for temperature-sensitive electronics
(2026-01-01)
Tipawan Khlayboonme, S.
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Fungfuang, Natasia
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Kitiwan, Mettaya
V<inf>2</inf>O<inf>5</inf> thin films are significant for next-generation temperature-sensitive electronic devices owing to notable phase stability and reversibility. Optimizing phase characteristics toward reversible low-temperature transitions enhances device performance. In this study, thin films of amorphous–nanocrystalline β-V<inf>2</inf>O<inf>5</inf> were deposited on glass substrates using the inclined magnetron head in radio-frequency magnetron sputtering under an O<inf>2</inf> reactive gas. The effects of thermal stimulation (heating to 400 °C, followed by cooling) were investigated for an as-deposited film prepared at 7.5 % O<inf>2</inf> and for two annealed films deposited at 7.5 % and 10 % O<inf>2.</inf> The annealed films were annealed at 300 °C before thermal stimulation. The films were characterized by X-ray diffractometry (XRD), Auger-electron spectroscopy, field-emission electron microscopy, Van der Pauw and Hall effect measurements, and ultraviolet–visible spectroscopy. The as-deposited film exhibited insulating behavior, whereas the annealed films at 7.5 % and 10 % O<inf>2</inf> demonstrated n-type and p-type conductivities, respectively, accompanied by decreased intensity of the V LMM Auger peak. Before thermal stimulation, the as-deposited film was highly amorphous, whereas the annealed films comprised the β-monoclinic phase. Thermal stimulation caused mixed β-monoclinic and β-tetragonal symmetries for all films and induced significant changes in surface morphology, except for the annealed film at 7.5 % O<inf>2</inf>. Variations in carrier density and bandgap energy indicated that thermal energy promoted oxygen vacancies but reduced vanadium vacancies in the film structure. In situ XRD analysis demonstrated the phase stability and reversible formation of the nanocrystalline β-monoclinic phase, revealing potential for thermally responsive applications requiring repeatable phase behavior.
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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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Preparation of CdSe thin films: annealing effects on structure and optical properties
(2025-01-01)
Hankoy, Montree
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Kitiwan, Mettaya
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Tunthawiroon, Phacharaphon
In this work, we prepared well−crystallized CdSe thin films onto glass substrates using vacuum thermal evaporation method (VTE). The CdSe thin film was deposited on the substrate for 10 min in a vacuum chamber where the pressure was maintained at 5⋅10-5 Torr. To further increase the crystallinity, the as-deposited CdSe films were next thermally annealed in the air at annealing temperatures between 200 and 400 °C. The CdSe films were then investigated for phase composition, morphology, and optical properties. X-ray diffraction (XRD) examinations demonstrated a hexagonal phase of CdSe with preferential orientation along the (002) direction. The morphology analysis showed a homogeneous morphology with an average grain of approximately 65.55–90.25 nm in size. Chemical analysis confirmed the stoichiometric presence of Cd and Se. In addition, the optical band gap, determined from Tauc’s plot, using UV-Vis spectroscopic data, was found to be in the range of 1.66–1.69 eV. An annealing temperature of 300 °C resulted in the most favorable condition with the lowest optical band gap value of 1.66 eV, indicating a narrower band gap in the annealed CdSe thin film. The high deposition rate of VTE presents a significant advantage for this technique, potentially facilitating its use in creating optoelectronics and solar cells that are highly efficient and cost-effective.

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