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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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Underlying mechanism of Al incorporation in sol-gel-based dip-coated ZnO:Al thin films
(2024-07-15)
Khlayboonme, S. Tipawan
Al-doped ZnO films were applied to glass substrates using a sol-gel-based dip-coating method. The chemical composition, surface morphology, crystal structure, and optical and electrical properties were examined to elucidate the mechanism underlying doping efficiency. The optimum Al-doping was 1.00 at%. Al doping induced an increase in the crystallite size, light transmission, optical band gap energy, and carrier concentration but decreased the resistivity of the films. Excessive doping level beyond 1.00 at% degraded all the characteristics of the films. The underlying mechanism of the Al dopant atoms in the ZnO lattice is related to the growth units. The addition of aluminum nitrate promoted the formation of Zn(OH)<inf>2</inf> growth units in the solution, whereas its further addition resulted in the formation of additional Zn(OH)<inf>2</inf>, along with the Zn(OH)<inf>4</inf>2−. The deterioration in the characteristics of the films was attributed to the Zn(OH)<inf>4</inf>2− formation. Understanding the relation between the film characteristics and growth-unit formation is a base tool to increase the optimum Al-doping level, improving film application towards high performance of optoelectronic devices.
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Insights into the properties and possible bonding states of radiofrequency-magnetron-sputtered indium tin oxide thin films acquired using ultraviolet–visible spectroscopy data for cost-effective material characterization
(2023-12-01)
Khlayboonme, S. Tipawan
Indium tin oxide (Sn-doped In<inf>2</inf>O<inf>3</inf>) is an optical material that is widely utilized in designing modern optoelectronic devices. To demonstrate the efficiency of ultraviolet–visible spectroscopy as a primary analysis tool for thin-film characterization, Sn-doped In<inf>2</inf>O<inf>3</inf> films were deposited under untreated and annealed conditions. The optical parameters of these films were determined based on the transmission–reflection spectra recorded by an ultraviolet–visible spectroscopy laboratory setup. Through four-point probing, energy dispersive spectroscopy, and contact angle measurements, the electronic-band structures and chemical bonding states of the thin films were estimated. The transmission spectra confirmed that the post-annealing treatment promoted film homogeneity. Deeper insights into the optical parameters revealed that annealing encouraged Sn atom incorporation into the film structure and better stable phase formation. The incorporation of Sn atoms resulted in the substitution of Sn4+ into the In3+ sites of the In<inf>2</inf>O<inf>3</inf> lattice and formation of the SnO phase. Notably, our evaluation of the film properties based on data acquired from ultraviolet–visible spectroscopy revealed good consistency with the data acquired from Hall-effect, X-ray diffractometry, and X-ray photoelectron spectroscopy investigations.
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Optical Properties of CuCdS Thin Film Prepared by Vacuum Thermal Evaporation Technique
(2023-01-01)
Hankoy, Montree
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Treetornkeerati, Paramapat
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Fungfuang, Natasia
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Khlayboonme, S. Tipawan
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Kitiwan, Mettaya
This study reports on the synthesis and characterizations of copper cadmium sulfide (CuCdS) thin films prepared using the vacuum thermal evaporation technique with copper sulfide and CdS as precursors in a 1:1 molar ratio. The structural properties of the thin films were analyzed using X-ray diffraction (XRD) which revealed that the main composition of the thin film was CdS with the preferred orientation of the (101) plane. The optical properties were examined using UV–Vis spectrophotometry. The photosensitivity of the films was determined using I–V measurements performed with a two-probe technique. The prepared CuCdS thin films have high optical transmittance of 92%.
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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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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
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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.
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Impact of Al-doping on structural, electrical, and optical properties of sol-gel dip coated ZnO:Al thin films
(2021-07-01)
Khlayboonme, S. Tipawan
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Thowladda, Warawoot
Aluminum-doped ZnO (AZO) thin films were coated on glass substrates using the sol-gel dip-coating technique. We investigated the effect of Al-doping level on the surface morphology, crystal structure, atomic bonding, and optical and electrical properties of the AZO films. The Al-doping levels in the sol-gel solution were 0, 0.25, 0.50, 1.0, 1.5, and 3.0% with a Zn precursor concentration of 0.50 M. The results show that the grain boundary increased with the doping level, while the crystallite size decreased from 27.2 to 14.2 nm. The AZO films were subjected to tensile stress. The Al-doping levels ≤ of 1.5% encouraged the intensity of the (002) x-ray diffraction peak. The center of the (002) peak shifted from 34.46° to 34.51°, and that of the E2highRaman mode shifted from 435.0 to 432.4 cm-1. Doping with 1.5% Al resulted in a maximum electron concentration of 4.7 × 1018 cm-3 with a minimum resistivity of 2.6 × 10-1 Ω cm and a mobility of 5.14 cm2/V.s. The Urbach energy increased from 88 to 120 meV with increasing doping level. For the AZO films doped with Al (≤1.5%), the analysis of the UV-vis spectra reveals that the position of the conduction band (CB) minimum of the films shifted from -0.16 to -0.21 eV and shifted outward from the valence band (VB). Further Al doping to 3.0% resulted in a VB shift toward CB. The optical band gap reached a maximum of 3.33 eV at 1.5% Al. The combination of tensile stress and electron density due to Al doping influences the shift in the optical band gap of the AZO films. The crystal structure, atomic bonding, and electronic band structure of ZnO films can be modified by Al doping.
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Influence of reactive oxygen gas on sputtered-vanadium oxide films under post-annealing in vacuum
(2021-01-01)
Khlayboonme, S. Tipawan
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Thowladda, Warawoot
Vanadium oxide thin films were deposited on glass substrates by O2 reactive-RF magnetron sputtering from a vanadium (V) target without substrate-heating. The percentages of O2 gas were 10%, 7.5%, 6.0%, 5.0% and 2.5%. The total gas flow rate (O2/Ar) was kept at 25 sccm. As-deposited films were experienced post-annealing process at different temperatures and times. The crystallinity and chemical bonding states of films were examined by X-ray diffraction and Raman spectroscopy. The condition in annealing to active crystallinity depended on an earlier composition of the films. As O2-gas percentages were 10% and 7.5%, after annealing, the as-deposited VxOy films were transformed into crystalline V2O5 films. With decreasing in O2 percentage to 5.0% and 2.5%, the films were transformed into V2O3 and VO films, respectively. The films deposited with 6.0% O2 were crystallized to VO2 with phase B after annealing with 500 °C 15 h. By applying a longer time to 30 h at the high temperature 500 °C in annealing, VO2 films revealed only phase M formation.
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RF-sputtered V2O5 thin films on two different glass substrates
(2021-01-01)
Khlayboonme, S. Tipawan
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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.
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Phase transformation of nanocrystalline diamond films: Effect of methane concentration
(2020-01-01)
Khlayboonme, S. Tipawan
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Thowladda, Warawoot
Ultra-nanocrystalline diamond films were prepared by a microwave plasma-enhanced chemical vapor deposition reactor using CH4/H2 gas mixture with a power as low as 650 W. The effects of CH4 concentration on nanostructure of the films and gas-phase species in plasma were investigated. The CH4 concentrations of 1.5%, 3.0%, 3.5%, and 4.0% were used and balanced with H2 to a total flow rate of 200 sccm. Morphology and composition of the films were characterized by SEM, Raman spectroscopy and Auger spectroscopy. The gas-phase species and electron density in the plasma were explored by optical emission spectroscopy and plasma-impedance measurement. The increasing CH4 concentration from 1.5% to 4.0% increased C2Hx species and decreased electron density. Phase of the film transform from nano-into ultranano-diamond phase but the growth rate revealingly decreased from 300 to 210 nm/h. Raman spectra indicate the higher CH4 concentration promted phase of the film transiton from NCD to UNCD. While Auger spectra revealed that UNCD film deposited with 4.0%CH4 was composed of 90.52% diamond phase but only 9.48% of graphite phase. The relation between phase transformation of the films and growth mechnism controlled by gas-phase species in the plasma will be dissused.

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