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Author: search.filters.author.Khlayboonme, S. TipawanSubject: search.filters.subject.V2O5 thin film

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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<sup>−</sup> 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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    Influence of the rf power and oxygen content on structural, electrical, and optical properties of V2O5 thin films prepared via reactive radio frequency sputtering
    (2022-07-01)
    Khlayboonme, S. Tipawan
    ;
    Thedsakhulwong, Amorn
    Herein, V<inf>2</inf>O<inf>5</inf> thin films were deposited through O<inf>2</inf>-reactive radio frequency (RF) magnetron sputtering using a metallic vanadium arget without external heating on a glass substrate. The influence of the RF power and O<inf>2</inf> content on phase formation was investigated, and the percentage of the phase volume was related to the electrical and optical properties of the films. These films were composed of a mixture of α and β phases of V<inf>2</inf>O<inf>5</inf>, and the coexistence of monoclinic (βм) and tetragonal (βт) symmetries of the β-phase structure was observed. The phase of the film deposited at 100 W RF power with 10% O<inf>2</inf> was βт. Increasing the RF power to 150 W led to the development of the βм phase in the film. At 200 W, the obtained film was a mixture of βм- and α-V<inf>2</inf>O<inf>5</inf> phases, and the film produced with an O<inf>2</inf> content of more than 10% was a mixture of three phases: βт-, βм-, and α-V<inf>2</inf>O<inf>5</inf>. Further increase in the O<inf>2</inf> content decreased the βм-phase volume but increased the βт-phase volume. The electrical resistivity and optical properties depended on the phase volume. Furthermore, the relationship between the phase volume and film properties is presented.