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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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Effect of pyrazine in PEDOT:PSS thin films: Structural, optical, optoelectrical, and electrical analysis
(2023-02-01)
Teesetsopon, Pichanan
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Treewut, Pattaraporn
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Sripetch, Sasithorn
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Nasomjai, Piyatida
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Tubtimtae, Auttasit
The pristine PEDOT:PSS and different weight amounts of pyrazine in PEDOT:PSS thin films were prepared using the doctor-blading technique on a borosilicate glass substrate. The structural, optical, and electrical properties of the effect of pyrazine in PEDOT:PSS thin films were presented for the first time of this admixed solution. More accuracy in the surface of thin films was observed by atomic force microscopy (AFM) which revealed the granular deposits on the film surfaces. Some hill shapes and the distribution of agglomerated grains were also observed on the thin films. The PEDOT:PSS with pyrazine has a preferred orientation to be an orthorhombic crystal structure. The crystallite sizes were reduced from 230.40 nm to 101.81 nm for 30–60 mg pyrazine in the PEDOT:PSS. The energy band gap (E<inf>g</inf>) value of pristine PEDOT:PSS is of 3.50 eV with Urbach energy (E<inf>U</inf>) of 336.10 meV. The alteration E<inf>g</inf> values from 3.52 to 3.67 eV was obtained with the estimated E<inf>U</inf> values in the range of 283.16–324.62 meV depends on various amounts of pyrazine. The linear optical parameters, i.e., the refractive index, optical electronegativity, real/imaginary dielectric constants, extinction coefficient, and optical conductivity were investigated and explained by the changes in the formation, nucleation, growth of clusters, and particle arrangement. As the spectrum increased, the highest χ(1), χ(3), and n<inf>2</inf> values were obtained for the 80 mg pyrazine in PEDOT:PSS of 0.110, 2.562 × 10−14 esu, and 6.219 × 10−13 esu, respectively. The electrical conductivity was clearly increased for pyrazine exceeding 40 mg from 1.85 × 102 to 3.84 × 102 S/cm and the figure of merit was in the range of 4.34 × 10−2 to 4.68 × 10−2 Ω−1. Thus, the novelty of this work can show that pyrazine in the range of 40 mg–80 mg is the optimum condition to synthesize non-linear optical (NLO) materials, organic light-emitting diodes (OLEDs), and organic light-emitting transistors (OLETs).
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Structural, optical and electrical properties of the microcrystalline structure of (Ba1-xY2x/3)(Zr0.20Ti0.80)O3 ceramics
(2020-07-01)
Sumang, Rattiphorn
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Thongmee, Navavan
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Bongkarn, Theerachai
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Prasertpalichat, Sasipohn
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Kidkhunthod, Pinit
Yttrium (Y3+) doped barium zirconate titanate, (Ba<inf>1-x</inf>Y<inf>2x/3</inf>)(Zr<inf>0.20</inf>Ti<inf>0.80</inf>)O<inf>3</inf>; BYZT ceramics with varying x (0 = x ≤ 0.10) were prepared by the solid-state reaction method. These samples were analyzed by X-ray diffraction (XRD) and the XRD patterns were fitted using the Rietveld refinement. The local structural changes of the BYZT ceramics were investigated by synchrotron X-ray absorption spectroscopy. The results showed that an increase in the x content in the BYZT lattice structure significantly affected the phase transition behavior and the local structure around the Ti absorbing atoms, which corresponds with the phase transition from a tetragonal to a cubic structure. SEM images showed a uniform and highly dense microstructure with increasing x values. The optical band gap (E<inf>gap</inf>) values measured from the UV–visual diffuse reflectance spectra, showed a decrease from ~3.55 eV to ~2.90 eV with increasing values of x. The modified Curie-Weiss law showed that a normal ferroelectric phase transition is observed in the unmodified BZT ceramic and as the concentration of x increased, it induces diffuseness in the phase transition behavior. The largest dielectric constant (ε<inf>r</inf> = 13,200), the highest recoverable energy-storage density (W<inf>rec</inf> = 1.76 J/cm3) with an excellent energy storage efficiency (η = 91%) under a lower electric field of 50 kV/cm and lowest dielectric loss (tanδ = 0.01) were found in the composition of Ba<inf>0.98</inf>Y<inf>0.01337</inf>Zr<inf>0.2</inf>Ti<inf>0.8</inf>O<inf>3</inf> (x = 0.02 mol.%).
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Processing and characterization of amorphous copper oxide thin films prepared by reactive magnetron sputtering
(2018-01-01)
Gaewdang, Thitinai
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Wongcharoen, Ngamnit
In this paper, copper oxide (CuO<inf>x</inf>) thin films with amorphous phase were prepared on glass substrates by reactive dc magnetron sputtering. The influence of the flow rate of O<inf>2</inf> on the structural, optical and electrical properties of the as-deposited films was systematically studied. XRD revealed that the as-deposited films remained amorphous in the whole range of adjusted oxygen flow rate. Surface morphology and nanoparticle size of the films were observed by AFM. Electrical resistivity and Hall effect measurements were performed on the films with van der Pauw configuration. The positive sign of the Hall coefficient confirmed the p-type conductivity in all studied films. From temperature-dependent electrical conductivity of the films prepared at R(O<inf>2</inf>) of 1.5 sccm, it was show that three types of behavior can be expected, nearest-neighbor hopping at high temperature range (200-300 K), the Mott variable range hopping at low temperature (110-190 K) and Efros-Shklovskii variable range hopping at very low temperature (65-100 K). Some important parameters corresponding to Mott-VRH and ES-VRH like density of localized states near the Fermi level (N(E<inf>F</inf>)), localization length (ξ), degree of disorder(T<inf>0</inf>), hopping distance (R) and hopping energy (W) were determined. These parameters would be helpful for optimizing the performance of photovoltaic applications.
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Effect of excess oxygen for CuFeO2.06 delafossite on thermoelectric and optical properties
(2017-12-01)
Rudradawong, Chalermpol
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Ruttanapun, Chesta
This work presents the role of excess oxygen in CuFeO<inf>2.06</inf> compounds on thermoelectric and optical properties. The CuFeO<inf>2.06</inf> specimens were synthesized by solid state reaction method. X-ray diffraction technique has confirmed the CuFeO<inf>2</inf> structure for the specimens. In particularly, CuFeO<inf>2.06</inf> specimen revealed the structural extension of lattice parameter: a and c. Also, the specimen found increasing excess oxygen of approximately 3% as a resulted enhancement of mixed valence state of Cu+ and Cu2+ ions. XPS showed mixed valence state of the Cu+/Cu2+ ions, and Fe3+ and Fe2+ ions was also found in the CuFeO<inf>2.06</inf> specimen. Mixed valence states contributed the co-existence of hole and electron carriers for conduction. Consequently, electrical conductivity of the CuFeO<inf>2.06</inf> specimen increased up to 23 S/cm at 873 K. Also, increasing Seebeck coefficient was shown to be approximately 302 μV/K at 873 K. The CuFeO<inf>2.06</inf> specimen was found power factor to be approximately 2.1 × 10−4 W/m∙K2 at 873 K. The indirect optical gap of CuFeO<inf>2.06</inf> (2.40 eV) was lower than that of the CuFeO<inf>2</inf> (2.60 eV). Thus, thermoelectric and optical properties were governed by an existence of excess oxygen.
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Direct synthesis and growth mechanism of metal molybdate (AMoO4; A = Ca and Ba) fine particles via the mechanochemical method
(2017-08-01)
Janbua, Wanwisa
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Bongkarn, Theerachai
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Vittayakorn, Wanwilai
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Vittayakorn, Naratip
Metal molybdate (AMoO<inf>4</inf>; Ca and Ba) fine particles were synthesized successfully in a simple way using the mechanochemical method under ambient conditions, without surfactants or any capping agents. The effect of milling time on phase formation and morphology was investigated. The functional group and phase formation analyses were carried out using Fourier transform infrared (FT-IR), Raman spectroscopy and X-ray diffraction (XRD) methods. XRD revealed that all samples were of a pure tetragonal scheelite structure. FT-IR and Raman analysis exhibited a Mo-O stretching peak of molecular [MoO<inf>4</inf>]2-, which related to the scheelite structure. Difference in growth mechanism and morphology was observed significantly in CaMoO<inf>4</inf> and BaMoO<inf>4</inf> particles. The primary CaMoO<inf>4</inf> nanocrystalline was formed in its initial state at 80–100 nm, and tended to aggregate into a peach-like shaped morphology with increasing milling time, while a space shuttle-like morphology formed directly via an oriented attachment mechanism for the BaMoO<inf>4</inf> particle. A possible mechanism for the formation of metal molybdate, with a different milling time, was discussed in detail. It is interesting that this work was able to present a simple way of synthesizing complex oxide materials on a large scale.
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Highly-transparent multi-layered spin-coated silk fibroin film
(2017-01-01)
Wasapinyokul, Kamol
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Kaewpirom, Supranee
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Chuwongin, Santhad
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Boonsang, Siridech
In this study, the silk fibroin films with different numbers of layers were fabricated by the spin-coating method and their optical transmittances were observed. The process to synthesise the silk fibroin solution was explained - starting from the silk cocoon until the silk-fibroin solution, approximately 7.5% concentration wt/vol, was obtained. The solution was spin-coated onto clean glass substrates to fabricate samples. Totally 10 samples with different numbers of layers, from 1 to 5 layers, were obtained. All samples can be separated into two groups: those left dried at room temperature after spin-coating and those heated at 60°C. They were then measured for their transmittance over the visible-to-near-infrared region. All samples exhibited the high transmittance where the values were at 95% and 98%, for the samples at room temperature and those at 60°C, respectively. This was believed to be due to the heating effect that caused the silk fibroin to arrange itself after being heated, hence the higher transmittance. These high transmittances were maintained regardless of the number of layers and length of heating time. Results from this study could be used to fabricate a silk fibroin film with high optical transmittance and adjustable other properties.
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Modification of optical properties of spin-coated TiO2 film by heat treatments
(2017-01-01)
Chunarom, Chutinat
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Yontrarak, Tanapat
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Wipopcharoenkul, Puttinan
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Wasapinyokul, Kamol
In this report, effects of heat treatment conditions on the transmittance of titanium dioxide, TiO<inf>2</inf>, films were examined. The colloidal solution of TiO<inf>2</inf> in two different solvents - isopropanol, IPA, and sulfuric acid, H<inf>2</inf>SO<inf>4</inf>, were deposited via a spin-coating method onto clean glass substrates. The films were subsequently annealed and cooled down, either quickly or slowly, before being measured for their optical transmittances in the visible region. Three points were noted: Firstly, when the films were quickly cooled down after annealed, their transmittance depended on their annealing temperature. In IPA and H<inf>2</inf>SO<inf>4</inf>, the transmittance decreased and increased, respectively, when the annealing temperature increased. Secondly, when the films were slowly cooled down after annealed, their transmittance seemed to be independent from the annealing temperature, where the films had roughly equal transmittance regardless of annealing temperature. Lastly, the TiO<inf>2</inf> films with H<inf>2</inf>SO<inf>4</inf> provided higher transmittance than those with IPA. All the three stated characteristics were the same for all wavelengths in the visible region. These results were believed to result from the dispersibility of the TiO<inf>2</inf> in each solvent and the cooling-down processes. Such results could be further developed to select a suitable heat treatment process for a spin-coated TiO<inf>2</inf> film with a desired optical transmittance.

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