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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 × 10<sup>18</sup> to 5.2 × 10<sup>17</sup> cm<sup>−3</sup>, 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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    RF-sputtered V2O5 thin films on two different glass substrates
    (2021-01-01)
    Khlayboonme, S. Tipawan
    ;
    Thowladda, Warawoot
    Thin V<inf>2</inf>O<inf>5</inf> films were deposited on two different commercial soda-lime glass substrates (A and B) by O<inf>2</inf> reactive radio frequency magnetron sputtering using a vanadium target. The influences of the surface energy and roughness of the substrates on the structure and atomic bonding of the films were examined. The film on substrate A was polycrystalline, with eight crystal orientations, whereas the film on substrate B yielded an intense (001) diffraction peak of α-V<inf>2</inf>O<inf>5</inf> and a weak (200) peak of β-V<inf>2</inf>O<inf>5</inf>, indicating preferred orientation along these planes. Structural analyses indicated that substrate B with lower surface energy and higher roughness enhanced the formation of a layered a-V<inf>2</inf>O<inf>5</inf> structure.