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Tailoring the structural and optical properties of fabricated TiO2 thin films by O2 duty cycle in reactive gas-timing magnetron sputtering
(2023-08-01)
Chittinan, Donyawan
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Buranasiri, Prathan
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Lertvanithphol, Tossaporn
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Eiamchai, Pitak
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Tantiwanichapan, Khwanchai
Titanium dioxide (TiO<inf>2</inf>) thin films were deposited on silicon (100) and glass substrates via conventional reactive sputtering and reactive gas-timing (RGT) sputtering techniques. The duty cycle of supplied O<inf>2</inf> gas determined its effect on the properties of the TiO<inf>2</inf> films through spectroscopic ellipsometry (SE). With the best triple-layer model for SE fitting, the films' structure and optical properties were analyzed and compared. The high-resolution transmission electron microscope (HR-TEM) showed good agreement with the structure of the SE model, while the grazing-incidence X-ray diffraction (GIXRD) confirmed the crystallinity of the films. The results showed that the duty cycle was a crucial factor in the deposition rate and crystalline phase of the TiO<inf>2</inf> films. The optical reflectance (%R) spectra were measured by a UV-VIS-NIR spectrophotometer, representing anti-reflection properties at a specific wavelength related to the duty cycle. Moreover, the omnidirectional optical transmittance (Omni-T) profiles were also determined. The results showed that the transmittances (%T) of TiO<inf>2</inf> film near those specific wavelengths were enhanced over the bare glass substrate at a wide angle. In addition, photoelectron spectroscopy (PES) was used to confirm the chemical states and atomic compositions.
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Formation of HfOxNy nanorod GLAD films growth by rapid thermal oxidation
(2023-01-01)
Phae-ngam, W.
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Prathumsit, J.
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Chananonnawathorn, C.
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Nakajima, H.
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Lertvanithphol, T.
In this work, the hafnium oxynitride (HfON) nanorod films on p-type silicon (Si) wafer substrate have been fabricated by reactive magnetron sputtering with glancing angle deposition (GLAD) technique, subsequently with a rapid thermal oxidation process at 500–900 °C under low-vacuum state. The crystallinity and morphology were investigated by glazing-incident X-ray diffraction (GIXRD) and field-emission scanning electron microscopy (FE-SEM), respectively. As-deposited films were amorphous nanorod films. The surface-sensitive X-ray photoelectron spectroscopy (XPS) analytical technique revealed that nitrogen atoms are increasingly replaced with oxygen atoms at the surface. The distribution of nitrogen atoms investigated by X-ray absorption spectroscopy (XAS) revealed the substitution of nitrogen with oxygen at the film surface and molecular nitrogen trapped in the film as the annealing temperature was increased.
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Tailoring Properties of Hafnium Nitride Thin Film via Reactive Gas-Timing RF Magnetron Sputtering for Surface Enhanced-Raman Scattering Substrates
(2022-01-01)
Sucheewa, Nguentra
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Wongwiriyapan, Winadda
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Klamchuen, Annop
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Obata, Michiko
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Fujishige, Masatsugu
This study successfully demonstrated the tailoring properties of hafnium nitride (HfN) thin films via reactive gas-timing (RGT) RF magnetron sputtering for surface-enhanced Raman spectroscopy (SERS) substrate applications. The optimal RGT sputtering condition was investigated by varying the duration time of the argon and nitrogen gas sequence. The RGT technique formed thin films with a grain size of approximately 15 nm. Additionally, the atomic ratios of nitrogen and hafnium can be controlled between 0.24 and 0.28, which is greater than the conventional technique, resulting in a high absorbance in the long wavelength region. Moreover, the HfN thin film exhibited a high Raman signal intensity with an EF of 8.5 × 104 to methylene blue molecules and was capable of being reused five times. A superior performance of HfN as a SERS substrate can be attributed to its tailored grain size and chemical composition, which results in an increase in the hot spot effect. These results demonstrate that the RGT technique is a viable method for fabricating HfN thin films with controlled properties at room temperature, which makes them an attractive material for SERS and other plasmonic applications.
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Synergistic effect of nickel nanoparticles and carbon nanotubes buckypaper for enhancement of microwave shielding properties
(2020-01-01)
Sukgorn, Nuttaya
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Yordsri, Visittapong
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Thanachayanon, Chanchana
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Horprathum, Mati
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Chudpooti, Nonchanutt
Carbon nanotubes (CNTs) are considered as the most promising materials to solve the electromagnetic interference (EMI) issue. Various forms of CNTs including CNTs/polymer composites, metal nanoparticles-decorated CNTs and freestanding CNT buckypapers (CNT BPs) have been proposed to enhance shielding effectiveness. In this study, the synergistic effect of nickel nanoparticles (NPs) and relatively short CNTs for the enhancement of microwave shielding properties was investigated. CNT BPs were prepared by vacuum filtration of well-dispersed multi-walled CNTs and subsequently nickel was decorated on the CNT BPs (Ni/CNT) by pulsed DC sputtering technique with different deposition times of 0, 5, 10 and 15 min (hereinafter referred to as CNi0, CNi05, CNi10 and CNi15, respectively). The diameter of Ni/CNT increased from 8.74±0.53 to 72.5±3.2 nm and the conductivity improved from 9.57±0.87 to 12.57±0.59 S/cm when the nickel deposition time was 15 min. Nickel NPs were the mixed phases of nickel and nickel oxide with a dominant nickel phase. The shielding effectiveness at the frequency of 9.5 GHz achieved to-34.1 dB for CNi15. The enhancement of shielding effectiveness of CNi15 is attributed to the synergistic effect of CNTs and nickel NPs on wave dissipation.
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Spectroscopic study on amorphous tantalum oxynitride thin films prepared by reactive gas-timing RF magnetron sputtering
(2019-10-30)
Lertvanithphol, T.
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Rakreungdet, W.
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Chananonnawathorn, C.
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Eiamchai, P.
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Limwichean, S.
The amorphous tantalum oxynitride (TaO<inf>x</inf>N<inf>y</inf>) thin films were prepared on silicon (100) substrates by magnetron sputtering system with different techniques of conventional reactive sputtering and reactive gas-timing (RGT). The films were studied via spectroscopic ellipsometry (SE) measured in the range of 0.75–5.0 eV with 0.025 eV interval at 70° incident angle, and the optical model based on Tauc-Lorentz function was constructed to extract the properties of the films. The SE results indicated that all prepared films were grown homogeneously and show different optical properties upon their deposition conditions and techniques. The optical properties of film prepared by conventional reactive sputtering were close to the tantalum oxide film (TaO). The refractive index and optical band gap (E<inf>g</inf>) of RGT samples changed with the oxygen timing and correlated with the change of oxygen and nitrogen concentration of the films. In addition, the morphologies, crystallinities, atomic concentrations and distributions of nitrogen atoms in the films analyzed by field-emission scanning electron microscopy, glazing-incident X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy are also discussed.
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Simultaneous O2 plasma and thermal treatment for improved surface conductivity of Cu-Doped SnO2 films
(2019-08-01)
Somjaijaroen, Natthawirot
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Sakdanuphab, Rachsak
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Chanlek, Narong
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Chirawatkul, Prae
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Sakulkalavek, Aparporn
Cu-doped SnO<inf>2</inf> thin films were deposited on a glass substrate using radio frequency magnetron sputtering. The effects of varying the O<inf>2</inf> partial pressure during the deposition process and post-O<inf>2</inf> plasma treatment at 420 °C were investigated. Bulk and surface oxidation states were measured by X-ray absorption near-edge structure spectroscopy and X-ray photoelectron spectroscopy. The as-deposited films exhibited oxygen deficient compositions and Cu+ or Cu2+ ions, which depend on the deposited O<inf>2</inf> partial pressure. After the post-plasma treatment, the films changed from an amorphous structure into a low crystalline film. X-ray diffraction results indicated substitutional doping, wherein some Sn4+ ions were replaced with Cu+ or Cu2+ ions. The O<inf>2</inf> plasma treatment can remove Cu2+ and O2− from the film surface. The oxygen deficiency defects and Cu+- or Cu2+- doped present at the surface are the key factors in controlling the sheet resistance of the Cu-doped SnO<inf>2</inf> film. The minimum sheet resistance was obtained after the plasma treatment of the films deposited at a 2% O<inf>2</inf> partial pressure.
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Observations of the initial stages on reactive gas-timing sputtered TaO thin films by dynamic in situ spectroscopic ellipsometery
(2019-06-01)
Chittinan, D.
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Buranasiri, P.
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Lertvanithphol, T.
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Eiamchai, P.
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Patthanasettakul, V.
Dynamic in-situ spectroscopic ellipsometry (iSE) was employed to investigate the growth mechanism of the tantalum oxide (TaO) film on silicon wafer substrate deposited by reactive gas-timing RF magnetron sputtering compared with conventional reactive sputtering. The effect of reactive gas timing parameter on physical structure and optical property were analyzed by both the continuous and island film growth model with Tauc-Lorentz optical model. The variation of refractive index, film thickness and void volume fraction were obtained from dynamic fits of iSE data indicated that the growth process of the amorphous TaO thin films was divided into two regimes: the nucleation stage and continuous-layer stage. These stages were observed during deposition although the initial film growth stage corresponds to the island film growth model. The study demonstrates that sputtered TaO by the RGT technique at the O<inf>2</inf> on-off gas timing has played a crucial factor in improving the formation of nucleation stage and that the deposited TaO thin films were high deposition rate with high refractive index. The complementary field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) showed a good agreement with the film thickness and morphology obtained from dynamic iSE measurement. The real-time monitoring of iSE offers important evidences to understand the growth mechanism of reactive gas-timing technique.
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Empirical modelling and optimization of pre-heat temperature and Ar flow rate using response surface methodology for stoichiometric Sb2Te3 thin films prepared by RF magnetron sputtering
(2017-01-01)
Khumtong, Tanakorn
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Sakulkalavek, Aparporn
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Sakdanuphab, Rachsak
In this work, a flexible antimony telluride thin film was deposited by RF magnetron sputtering. The response surface methodology based on central composite design was used to study the influence of the Ar flow rate (A) and the pre-heat temperature of the substrate (T) on the Te content (%Te). The %Te of the thin film tended to increase with an increase in both the Ar flow rate and the pre-heat temperature. Stoichiometric Sb<inf>2</inf>Te<inf>3</inf> thin films were obtained that agreed with the model equation of %Te = 59.22 + 0.070 A - 0.098 T + 5.580 × 10−4AT – 7.212 × 10−4A2 + 1.05 × 10−4 T2. Micro-strainand dislocation density were enhanced using high Ar flow rate and low pre-heat temperature. The dislocation density and stoichiometry contributed to the substantially enhanced Seebeck coefficient and electrical conductivity of the films, respectively. The temperature dependence of the power factor is strongly dominated by electrical conductivity, leading to the highest value for a stoichiometric film of 2.0 × 0−3 W/m.K2 at 250 °C. During process optimization, several conditions can be prepared by RF magnetron sputtering with an Sb<inf>2</inf>Te<inf>3</inf> target in order to obtain stoichiometric Sb<inf>2</inf>Te<inf>3</inf> films. However, the expected condition to obtain highest power factor was the highest Ar gas flow rate and the lowest pre-heat temperature.
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Determination of thickness and optical properties of tantalum oxide thin films by spectroscopic ellipsometry
(2014-01-01)
Chananonnawathorn, Chanunthorn
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Khemasiri, Narathon
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Srichaiyaperk, Thanat
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Samransuksamer, Benjarong
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Horprathum, Mati
Tantalum oxide (Ta<inf>2</inf>O<inf>5</inf>) thin films were prepared, at different deposition time, by a DC reactive magnetron sputtering. During the deposition, a high-quality tantalum target was sputtered under argon and oxygen ambience on to silicon (100) and glass substrates. The prepared thin films were systematically characterized for both physical and optical properties based on spectroscopic ellipsometry (SE), and consequently confirmed by several methods. With the SE physical models, we could determine the thin film thickness as well as their inhomogeneity. The films thickness results were directly confirmed by field-emission scanning electron microscopy (FE-SEM) used to observe cross-sections, and surface profiler used to measure the physical thickness of the films. With the SE optical models, we applied both the Cauchy and Tauc-Lorentz dispersions in order to obtain the optical constants, to be directly compared with those from the Swanepoel method (SM). Our result showed that from the SE analyses, the SE physical model was obtained as the multi-layer configurations. The obtained Ta<inf>2</inf>O<inf>5</inf> thin film thickness was closely related with the measured result from the FE-SEM cross-sectional micrographs and the surface profiler. For the optical characteristic, the double layer physical model was best optimized with the Tauc Lorentz dispersion model for the most accurate results. In comparison, the SM technique also demonstrated a capability to determine both the film thickness and its refractive index only from some samples. Therefore, this study proved that the SE technique successfully and accurately determine both the physical and optical properties of the Ta<inf>2</inf>O<inf>5</inf> thin films. © (2014) Trans Tech Publications, Switzerland.
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Diode parameters of heterojunctions comprising p-type si substrate and n-type β-FeSi2 thin films
(2014-01-01)
Promros, Nathaporn
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Funasaki, Suguru
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Takahara, Motoki
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Shaban, Mahmoud
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Yoshitake, Tsuyoshi
N-Type β-FeSi<inf>2</inf>/p-type Si heterojunctions have been successfully fabricated by facingtargets direct-current sputtering at a substrate temperature of 600 °C without post-annealing and their current-voltage characteristics were measured at low temperatures ragne from 300 K down to 50 K. The ideality factor, saturation current and series resistance were estimated by the thermionic emission theory and Cheung’s method. By the thermionic emission theory, we calculated the ideality factor from the slope of the linear part from the forward lnJ-V and estimated the saturation current density from the straight line intercept of lnJ-V at a zero voltage. As decreasing temperatures from 300 down to 50 K, the value of ideality factor increased from 1.2 to 15.6, while the value of saturation current density decreased from 1.6 × 10-6 A/cm2 to 3.8 × 10-10 A/cm2. From the plots of dV/d(lnJ)-J and H(J)-J by Cheung’s method, the obtained values of series resistances are consistent with each other. The series resistances analyzed from both plots increased as decreasing temperatures.

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