Radio-frequency Sputtering Method Research Articles

Photoelectrical performances of semiconductor-based devices having CoFe and CoFeNi magnetic interlayers

This study was designed to examine the photoelectric device performances of cobalt-iron (CoFe) and cobalt-iron-nickel (CoFeNi) materials with good magnetic properties, specifically to investigate the effect of the Ni element on the electrical properties. In this context, Al/CoFe/p-Si and Al/CoFeNi/p-Si devices were produced by coating both materials between the semiconductor and the metal using the radio frequency (RF) sputtering method. First of all, to investigate the structural properties of the coated films, the content analysis was carried out by x-ray diffraction (XRD) analysis. To determine the photoelectrical properties of the produced devices, current–voltage and transient photocurrent measurements were performed and analyzed under different light intensities. While the ideality factor (barrier height) values of the devices produced using CoFe and CoFeNi materials were found to be 11.45 (0.487 eV) and 9.86 (0.513 eV), respectively, in the dark, they were obtained as 13.29 (0.446 eV) and 11.02 (0.484 eV) under 100 mW cm−2 illumination. It was determined that both devices are sensitive to light, with the sensitivity of the device with the CoFeNi interlayer being much higher. In addition, photocapacitance and photoconductivity measurements were carried out to examine the photocapacitor performance of the devices. As a result of the investigations, both current–voltage, photocurrent, and photo-capacitance/conductivity measurements showed that the device with the CoFeNi interface layer showed better performance than the device with the CoFe interface. Therefore, it has been determined that the Ni element has a positive effect on electrical properties. The results obtained show that the prepared materials and produced devices can be used in photovoltaic applications.

Investigation of the Effect of Vacuum and Air Annealing on the Structural, Optical and Electrical Properties of Radio Frequency Sputtered WO<sub>3</sub> Thin Films

Thin films of tungsten oxide were deposited on glass substrates by the radio frequency (RF) reactive sputtering from a high purity tungsten metal target (99.9%) with a diameter of 10 cm. The reactive sputtering was carried out in an argon-oxygen gas mixture containing 20% of O2 and 80% of Ar. The used RF power is 200 W while fixing the deposition time at 120 min. Finally, the prepared films were annealed at different temperatures (350 °C, 400 °C, 450 °C, 500°C and 550 °C) for 1 hour under air and under vacuum. X-ray diffractograms showed that the deposited thin films crystallized in Hexagonal/Monoclinic WO3 phase. It was found that the crystallite size varies with the annealing temperature and the lattice parameters is a= 7.3064Å, b = 7.5292Å, c = 7.6875Å and a=b= 7.3242Å, c= 7.6624 Å, for h-WO3 and m-WO3 structures, respectively. Scanning Electron Microscopy (SEM), Raman spectra confirmed the formation of WO3 thin films. In addition, optical transmittance data revealed that the optical bandgap of the films decreases with increasing the annealing temperature. Electrical measurements revealed that annealing in air results in more resistive samples, which should be taken into account in future investigations, especially as buffer layers for efficient photovoltaic solar cells. Keywords: Vacuum, Tungsten oxide, Raman spectroscopy, RF Sputtering method, RF Power, Annealing temperature.

Structural and optical properties of smooth radio frequency sputtered XTe (X=Cd, Zn) thin films

Zinc telluride (ZnTe) and cadmium telluride (CdTe) thin films, with smooth surfaces, were prepared by the radio frequency sputtering method. X-ray diffaction patterns revealed the formation of pure cubic phases and allowed the access of the structural properties. The lattice mismash between the two compounds is found to be around 6%.UV–visible spectroscopy showed a significant absorption coefficient within the visible spectrum, accompanied by an energy band gap measuring 1.9 eVfor the ZnTe film and 1.42 eV for the CdTe film. This study may be benificial for using these materials together of separately in photovoltaic and photocatalytic devices.

Investigation of Contact Resistance Between Sputter-Deposited ITO and Mist-CVD-Deposited InSnZnO for Transparent Thin-Film Transistors Applications

The transparent thin-film transistors based on InSnZnO are investigated in this study. The Al2O3 and InSnZnO thin films deposited using mist chemical vapor deposition (mist CVD) are respectively used as the gate insulating and channel layers. The indium tin oxide (ITO) thin films deposited using the radio frequency (RF) sputtering method are served as the source/drain and gate electrodes. When the RF power of 45 W is used to deposit the ITO film, the lowest specific contact resistance of 9.7 × 10−3 Ω-cm2 and high optical transmittance of 72.4% are obtained. Furthermore, the thin-film transistor with ITO as the source/drain electrodes exhibits more stable electrical characteristics than the one with Al.

Thermoluminescence properties of TiO2/Cu/TiO2 multilayer thin films fabricated by (RF/DC) sputtering for radiation dosimetry

The most popular TLDs are composed of phosphors, ceramics, and crystals. Despite having a high light output per unit of absorbed dose, they suffer from rapid signal fading, light scattering, saturation at higher doses, and difficulties annealing for re-use. Here, we report the characteristics of a novel TiO2/Cu/TiO2 multilayer thin film dosimeter fabricated using radio-frequency (RF) and direct current (DC) sputtering methods with a faster deposition rate, high purity, and uniformity. The multilayer sequence was set to TiO2 (150 nm)/Cu (x)/TiO2 (50 nm), at varying Cu thicknesses (x = 5, 10, 25, 40, and 50 nm). The structure, morphology, elemental composition, and optical properties of the films were characterized by the XRD, FESEM, EDX, and UV–Vis, respectively. Next, the best TiO2 multilayer films with 5 nm Cu were tested for morphological, structural, and optical properties at 600 and 1200 mGy of x-ray radiation. The dosimetric properties of samples irradiated with X-ray doses ranging from 100 to 1500 mGy were then investigated. The best annealing time, reproducibility, fading, low minimum detectable dose as well as the effect of different heating rates on the TL glow curve have all been studied. Our results indicate that the films are amorphous, porous with spherically shaped nanoparticles, have a uniform distribution of elements, and are transparent in the visible region. The optimum TL intensity was found at TiO2 (445 nm)/14.2 nm Cu/TiO2 (130 nm) sequence. The dose-response has a good linear correlation to x-ray radiation with a sensitivity that is 0.444 times less than that of TLD-100 sensitivity within the dose range 100–1500 mGy. Upon irradiation, the band gap decreases, crystallinity increases, pores increase, films become rougher, and the absorption band edge extends to higher wavelengths. The single and multilayer TiO2 films have high-intensity peaks at 270 and 274 ∘C, respectively, which is typical of TL glow curve peaks used in TLD applications. There were no significant changes in the TL reading after six times of reuse, and the fading was observed at 49.57% after 15 days of irradiation. The findings indicate that TiO2/Cu/TiO2 multilayer films are appropriate for thermoluminescence dosimetric applications.

The impact of multi-layered dielectrics on the electrical performance of ZnO thin-film transistors

The electrical performance of ZnO thin film transistors (TFTs) fabricated on three different dielectric layers is investigated using an inverted staggered bottom gate thin film transistor structure. This work demonstrated the potential of integrating high-k dielectrics in ZnO TFTs in a dielectric multi-layered stack using SiO2 as the support layer for all the hero-dielectrics layers. In order to achieve this, ZnO thin film semiconducting layers were deposited at room temperature by radio frequency (RF) sputtering method and with no post deposition heat treatment, making them suitable candidates for low cost large area electronics on low temperature substrates (such as plastics). The dielectric films investigated were aluminium nitride (AlN), silicon nitride (SiN) and silicon dioxide (SiO2). The effective mobility of SiN devices was about half that observed in AlN devices. However, the dielectric layers exhibited hysteresis of approximately 0 V, 2 V and 7 V for the SiO2, AlN and SiN respectively. In addition, SiO2 TFTs have lowest threshold voltage (VT) and turn-on voltage (Von). The capacitance-voltage measurement for these device show that the flatband and threshold voltage of SiN and AlN MOS capacitors shifted towards more negative voltages instead when compared with the single layer SiO2 devices.

Effect of Gamma Radiation on Structural and Optical Properties of ZnO and Mg-Doped ZnO Films Paired with Monte Carlo Simulation

In space, geostationary electronics located within the outer van Allen radiation belt are vulnerable to gamma radiation exposure. In terms of application, implementing an electronic system in a high radiation environment is impossible via conventional engineering materials such as metal alloys as they are prone to radiation damage. Exposure to such radiation causes degradation and structural defects within the semiconductor component, significantly changing their overall density. The changes in the density will then cause electronic failure, known as the single event phenomena. Thus, the radiation response of material must be thoroughly investigated before the material is applied in a harsh radiation environment, specifically for flexible space borne electronic application. In this work, potential candidates for space-borne application devices: zinc oxide (ZnO) and Mg-doped ZnO thin film with a film thickness of 300 nm, were deposited onto an indium tin oxide (ITO) substrate via radio frequency (RF) sputtering method. The fabricated films were then irradiated by Co-60 gamma ray at a dose rate of 2 kGy/hr. The total ionizing dose (TID) effect of ZnO and Mg-doped ZnO thin films were then studied. From the results obtained, degradation towards the surface morphology, optical properties, and lattice parameters caused by increasing TID, ranging from 10 kGy–300 kGy, were evaluated. The alteration can be observed on the morphological changes due to the change in the roughness root mean square (RMS) with TID, while structural changes show increased strain and decreased crystallite size. For the optical properties, band gap tends to decrease with increased dose in response to colour centre (Farbe centre) effects resulting in a decrease in transmittance spectra of the fabricated films.

Growth morphology and phase composition of hierarchically self-organized oxyspinel composite films deposited by radio frequency magnetron sputtering

Multicomponent Al 0.1 Si 0,05 Ti 0,1 Mn 1.45 Co 0.7 Ni 0.6 O 4 oxyspinel solid solution ceramics was synthesized to be subsequently used as a target for the deposition of thin films onto silicon and metallized silicon substrates by means of radio frequency sputtering method. Temporal evolution of chemical and phase compositions of the deposited layers, as well as their structure and surface morphology for the different substrate temperatures, have been systematically investigated using energy dispersive X-ray (EDS) analysis, secondary ion mass spectroscopy (SIMS) profiling, Raman spectroscopy, and atomic force microscopy (AFM). The samples revealed a uniform chemical composition throughout their whole depth, corresponding well with the formula unit of the spinel. Across the film depth, progressive developing of a self-organized, two-scale hierarchical composite structure was observed, which is composed of the main oxide grains decorated with spinel nanocrystallites.

Vertically Aligned CdO-Decked α-Fe2O3 Nanorod Arrays by a Radio Frequency Sputtering Method for Enhanced Photocatalytic Applications.

Green hydrogen production is one of the most desirable sustainable goals of the United Nations. Thus, for that purpose, we developed hematite (α-Fe2O3), an n-type semiconductor, a desirable candidate for photoelectrochemical (PEC) water splitting, enabling hydrogen evolution. High recombination losses, low efficiency, and large-scale production hinder its potential. To address these issues, we have fabricated optimized bare and cadmium oxide (CdO)-decorated hematite thin film nanorod arrays using a throughput radio frequency (RF) sputtering with efficient water splitting behavior. To the best of our knowledge, no work has been done so far on the synthesis of CdO/α-Fe2O3 via RF sputtering for PEC application. Bare α-Fe2O3 samples, with a morphology of vertically aligned nanorods, were fabricated with optimized parameters such as as-deposited 70 nm of Fe, an angle of deposition of 70°, and an annealing temperature of 600 °C, which showed a photocurrent density of 0.38 mA/cm2 at 1.65 V vs reversible hydrogen electrode (RHE). Characterizations depicted that this unique morphology with high crystallinity directly enhanced the performance of hematite photoanodes. Further, deposition of 30 nm of cadmium (CdO) on the α-Fe2O3 nanorods produced a corn-like morphology with CdO nanoparticles (∼2 nm), resulting in 4-times enhancement of the PEC performance (1.2 mA/cm2 at 1.65 V vs RHE). CdO acted as a co-catalyst, responsible for satisfactory suppression of recombination and facilitating the hole transfer, directly enhancing the overall photocurrent density. This photoanode showed an extremely stable behavior over a period of 26 h when kept under constant illumination. Furthermore, the CdO-modified photoanode showed a better dye degradation (98% in 40 min) than the bare hematite (60% in 40 min), proving to be an efficient photoanode.

Production of high-transparent MgO films by radio-frequency sputtering method

Magnesium oxide (MgO) thin films were deposited on silicon and glass substrates by the radio frequency (RF) sputtering method. The MgO films were annealed at 400 ⁰C for 4h. The effect of working pressure on the structure and optical properties of MgO films was investigated. Structural characterization of thin films was determined using the X-ray diffraction (XRD) method. XRD results showed the presence of dominant peaks corresponding to the (200) and (220) lattice planes of MgO. However, peaks corresponding to (111), (311) and (222) lattice planes of the MgO also appeared in the films deposited at low pressure. It was determined that the average crystal size decreased as the working pressure reduced, while the deposition rate increased. SEM analysis showed that the microstructure of the nano-spherical MgO film transformed into a coarse-grained nano-pyramidal shape after annealing. The optical properties of MgO films were investigated by UV-Vis spectroscopy. Accordingly, it was determined that the absorption threshold of the films was around 310 nm wavelength and the optical band gap of the films varied between 4.07 and 4.14 eV. As a result, MgO films with high transmittance reaching an average of 95% in the visible region were obtained.

Bandgap modulation and electrical characteristics of (AlxGa1−x)2O3/4H-SiC thin film heterostructures

In this work, (AlxGa1−x)2O3 thin films were grown on a 4H-SiC substrate by radio frequency (RF) sputtering. (AlxGa1−x)2O3 targets with different nominal Al content xt: 0, 0.1, 0.4, 0.8, and 1 were used for RF sputtering. Samples were subsequently annealed at 800 °C to enhance film crystallinity. X-ray diffraction analysis revealed the improved crystallinity for increased Al content (xt), ranging from a ratio of 0 to 0.4 (in relation to Al+Ga content). The films with Al content of 0.8 and 1 exhibited poor crystallinity. The chemical compositions of the Al, Ga, and O atoms were consistent with those of the sputtering targets. Furthermore, the analysis of the inelastic energy loss from X-ray photoelectron spectroscopy confirmed that bandgap tuning is possible for (AlxGa1−x)2O3 using the RF sputtering method. Hall mobility improved up to 17.1%, from 21.90 (xt: 0) to 25.65 (xt: 0.4) cm2V−1s−1. I−V characteristics corresponded well with the Hall measurement. Therefore this study effectively demonstrated the tuning of the bandgap of (AlxGa1−x)2O3 by varying the Al composition. Further, the electrical properties of the (AlxGa1−x)2O3 can be improved or maintained from that of conventional Ga2O3 devices by optimizing the growth ambient.

ZrO2/ZnO/TiO2 Nanocomposite Coatings on Stainless Steel for Improved Corrosion Resistance, Biocompatibility, and Antimicrobial Activity.

The ultrathin nanocomposite coatings made of zirconium oxide (ZrO2), zinc oxide (ZnO), and titanium oxide (TiO2) on stainless steel (SS) were prepared by the radio frequency sputtering method, and the effects of the nanocomposite coating on corrosion protection and antibacterial activities of nanocomposite coated SS were investigated. Scanning electron microscopy was conducted to observe surface morphology of nanocomposite coatings with distinct distribution of grains with the formation on SS substrate. From the electrochemical impedance spectroscopy results, ZrO2/ZnO/TiO2 nanocomposite coating showed excellent corrosion protection performance at 37 °C during immersion in simulated body fluid and saliva solution for 12 and 4 weeks, respectively. The impedance of ZrO2/ZnO/TiO2 (40/10/50) nanocomposite coated SS exhibited values about 5 orders of magnitude higher than that of uncoated SS with polarization at the low-frequency region. Cell viability of ZrO2/ZnO/TiO2 nanocomposite coated SS was examined under mouse fibroblasts culture (L929), and it was observed that the nanocomposite coating improves proliferation through effective cellular attachment compared to uncoated SS. From the antimicrobial activity results, ZrO2/ZnO/TiO2 nanocomposite-coated SS showed killing efficiency of 81.2% and 72.4% against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, respectively.

Study of the relationship between magnetic anisotropy and composition ratio of Fe oxide to Fe at CoFeB/MgO film interface

Ta (5)/CoFeB (1)/MgO (2)/Ta (2) (in nm) multilayers were deposited on silicon substrates by magnetron sputtering, and the MgO layer was prepared by two methods at the same argon gas flow rate: the radio frequency (RF) sputtering method of MgO target and the reactive sputtering method of direct current (DC) sputtering Mg target with introducing oxygen at the same time. The sample prepared by the former method was denoted as Sample A, and the latter was denoted as Sample B. The results indicate that as-deposited Sample A shows in-plane magnetic anisotropy (IMA) with Keff = -0.79 × 106erg/cm3. However, the as-deposited Sample B shows perpendicular magnetic anisotropy (PMA) with Keff = 1.69 × 106erg/cm3, and the Keff value increases to 3.17 × 106erg/cm3 after annealing at 250℃. X-ray photoelectron spectroscopy (XPS) results illustrate that the films show PMA when the composition ratio (ε) of Fe oxide to Fe in CoFeB/oxide interface of Sample A and B annealed below 300 ℃, is approximately in the range of 0.65–0.75. When ε is beyond the above range, the film shows IMA. Moderate oxidation state at the interface results in the formation of PMA and it was improved by forming effective orbital hybridization of Fe 3d and O 2p. High resolution transmission electron microscopy (HRTEM) analysis reveals that no crystallization appears in CoFeB and MgO layer of the film before and after annealing, and crystallization has no effect on the interface chemical states in this system.

Production of high-transparent MgO films by radio-frequency sputtering method

Magnesium oxide (MgO) thin films were deposited on silicon and glass substrates by the radio frequency (RF) sputtering method. The MgO films were annealed at 400 ⁰C for 4h. The effect of working pressure on the structure and optical properties of MgO films was investigated. Structural characterization of thin films was determined using the X-ray diffraction (XRD) method. XRD results showed the presence of dominant peaks corresponding to the (200) and (220) lattice planes of MgO. However, peaks corresponding to (111), (311) and (222) lattice planes of the MgO also appeared in the films deposited at low pressure. It was determined that the average crystal size decreased as the working pressure reduced, while the deposition rate increased. SEM analysis showed that the microstructure of the nano-spherical MgO film transformed into a coarse-grained nano-pyramidal shape after annealing. The optical properties of MgO films were investigated by UV-Vis spectroscopy. Accordingly, it was determined that the absorption threshold of the films was around 310 nm wavelength and the optical band gap of the films varied between 4.07 and 4.14 eV. As a result, MgO films with high transmittance reaching an average of 95% in the visible region were obtained.

Fabrication of Ag embedded−SnS films via the RF approach: First study on NO2 gas–sensing performance

We report on the synthesis of 5-nm thick-Ag embedded−SnS (Ag/SnS) films by the radio frequency (RF) sputtering method as an absorbent layer to detect NO2 gas. Structure, morphology, elements, and optical properties of the Ag/SnS films were studied by X − ray diffraction, scanning electron microscopy, energy−dispersive spectroscopy, Raman and photoluminescence techniques, respectively. We firstly investigated the sensitivity of 5 – 20 ppm concentration of the Ag/SnS films to NO2 gas at an operating temperature ranging 30 – 100 °C. It was indicated that the Ag/SnS film–based sensor got good response and recovery at an operating temperature of 80 °C for NO2 gas. The 100 nm thick SnS film−based sensor made a faster response time (40 s) and recovery time (1320 s) to 20 ppm NO2 gas at 30 °C than those of other SnS films−based sensors. The result shows that the Ag/SnS film might be suitable for improving NO2 sensor properties due to the enhanced hole mobility, and more defectiveness of the SnS monolayer (Sn–vacancy). Based on these findings, we propose the fabrication of nanometals on SnS film for the high sensitive and selective NO2 gas−sensing a lower detection limit and at room temperature.

A Study on the ZnO Thin Film Deposited by RF Sputtering Method as an Electron Transport Layer in Quantum Dot Light-Emitting Diodes

We report a highly efficient quantum dot light emitting diode (QLEDs) with a radio frequency (RF) sputtered ZnO thin film as an electron transport layer (ETL) instead of the conventional ZnO nanoparticles (NPs) by solution process. ZnO NPs have been used as a key material to improve the performance of QLEDs, but the charge imbalance in ZnO NPs resulting from fast electron injection, and their limited uniformity are significant disadvantages. In this study, ZnO layers were deposited by RF sputtering with various O2 partial pressures. All of the ZnO films showed preferential growth along the (002) direction, smooth morphology, and good optical transmittance. To test their feasibility for QLEDs, we fabricated devices with RF sputtered ZnO layers as an ETL, which has the inverted structure of ITO/RF sputtered ZnO/QDs/CBP/MoO3/Al. The optical/electrical characteristics of two devices, comprised of RF sputtered ZnO and ZnO NPs, were compared with each other. QLEDs with the sputtered ZnO ETL achieved a current efficiency of 11.32 cd/A, which was higher than the 8.23 cd/A of the QLEDs with ZnO NPs ETL. Next, to find the optimum ZnO thin film for highly efficient QLEDs, deposition conditions with various O2 partial pressures were tested, and device performance was investigated. The maximum current efficiency was 13.33 cd/A when the ratio of Ar/O2 was 4:3. Additional oxygen gas reduced the O vacancies in the ZnO thin film, which resulted in a decrease in electrical conductivity, thereby improving charge balance in the emission layer of the QLEDs. As a result, we provide a way to control the ZnO ETL properties and to improve device performance by controlling O2 partial pressure.

A Study on the ZnO Thin Film Deposited by RF Sputtering Method as an Electron Transport Layer in Quantum Dot Light-Emitting Diodes

We report a highly efficient quantum dot light emitting diode (QLEDs) with a radio frequency (RF) sputtered ZnO thin film as an electron transport layer (ETL) instead of the conventional ZnO nanoparticles (NPs) by solution process. ZnO NPs have been used as a key material to improve the performance of QLEDs, but the charge imbalance in ZnO NPs resulting from fast electron injection, and their limited uniformity are significant disadvantages. In this study, ZnO layers were deposited by RF sputtering with various O2 partial pressures. All of the ZnO films showed preferential growth along the (002) direction, smooth morphology, and good optical transmittance. To test their feasibility for QLEDs, we fabricated devices with RF sputtered ZnO layers as an ETL, which has the inverted structure of ITO/RF sputtered ZnO/QDs/CBP/MoO3/Al. The optical/electrical characteristics of two devices, comprised of RF sputtered ZnO and ZnO NPs, were compared with each other. QLEDs with the sputtered ZnO ETL achieved a current efficiency of 11.32 cd/A, which was higher than the 8.23 cd/A of the QLEDs with ZnO NPs ETL. Next, to find the optimum ZnO thin film for highly efficient QLEDs, deposition conditions with various O2 partial pressures were tested, and device performance was investigated. The maximum current efficiency was 13.33 cd/A when the ratio of Ar/O2 was 4:3. Additional oxygen gas reduced the O vacancies in the ZnO thin film, which resulted in a decrease in electrical conductivity, thereby improving charge balance in the emission layer of the QLEDs. As a result, we provide a way to control the ZnO ETL properties and to improve device performance by controlling O2 partial pressure.

Effects of Substrates on Structural and Morphological Characteristics of Radio Frequency Sputtered ZnO Layers

High quality Zinc Oxide nanostructures (ZONSs) with customized traits became demanding for diverse applications. Based on this fact, some ZONSs with varied layer thicknesses (100 to 400 nm) were deposited on three types of Si (plain, polished and etched) and borosilicate glass substrates using the radio frequency (RF) sputtering method. Asdeposited samples were characterized systematically using various techniques to determine the effects of the substrates on their structures and morphologies. The XRD analyses of the sample showed the formation of high quality nanocrystallites with varying sizes where the crystallinity was improved with the increase of layer thickness and change of substrates. The FESEM and AFM images exhibited the nucleation of dense nanocrystallites with some pores/voids with enhanced surface roughness. In addition, the EDX spectra displayed the presence of appropriate chemical elements in the ZONSs layers. Sample grown on the etched Si substrate at layer thickness of 300 nm was found to be optimum. The results for the etched Si were presented. It was demonstrated that by optimizing the RF sputtering parameters (power of 100 W, Argon flow of 10 sccm and pressure of 10-5 mb) the structural and morphological traits of the layered ZONSs can be tailored. The proposed ZONSs may be useful for various optoelectronic applications including the metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors fabrication.

Optimization of post-deposition annealing temperature for improved signal-to-noise ratio in In2O3 gas sensor

This paper investigates the effects of post-deposition annealing (PDA) temperature on H2S gas sensing and low-frequency noise characteristics of In2O3 gas sensors. In2O3 thin-films are deposited using the radio frequency (RF) sputtering method at an RF power of 150 W and post-annealed at various temperatures (200, 300, and 400 °C). The response of the In2O3 gas sensor to H2S decreases with increasing PDA temperature due to the increase of grain size. However, the In2O3 post-annealed at 200 °C shows the largest 1/f noise since the damaged sensing material-substrate interface is not fully recovered by the PDA. The sensors post-annealed at a higher temperature (300 °C and 400 °C) recover the damaged interface. Thanks to its moderate response and noise level, the sensor post-annealed at 300 °C shows the largest signal-to-noise ratio.

Unprecedented Thermal Stability of Plasmonic Titanium Nitride Films up to 1400 °C

AbstractTitanium nitride (TiN) has emerged as one of the most promising refractory materials for plasmonic and photonic applications at high temperatures due to its prominent optical properties along with mechanical and thermal stability. From a high temperature standpoint, TiN is a substitution for Au and Ag in the visible to near‐infrared wavelength range, with potential applications including thermophotovoltaics, thermoplasmonics, hot‐electron and high temperature reflective coatings. However, the optical properties and thermal stability of TiN films strongly depend on the growth conditions, such as temperature, partial pressure of the reactive ion gas, ion energy, and substrate orientation. In this work, epitaxial TiN films are grown at 835 °C on an Al2O3 substrate using a radio frequency sputtering method. The oxidization behavior of TiN is investigated at 1000 °C under a medium vacuum condition of 2 × 10–3 mbar, which is relevant for practical technical applications, and the thermal stability at 1400 °C under a high vacuum condition of 2 × 10–6 mbar. The TiN film structure shows an unprecedented structural stability at 1000 °C for a minimum duration of 2 h under a medium vacuum condition, and an exceptional thermal stability at 1400 °C, for 8 h under a high vacuum condition, without any protective coating layer. The work reveals, for the first time to the authors’ knowledge, that the TiN film structure with columnar grains exhibits remarkable thermal stability at 1400 °C due to low‐index interfaces and twin boundaries. These findings unlock the fundamental understanding of the TiN material at extreme temperatures and demonstrate a key step towards fabricating thermally stable photonic/plasmonic devices for harsh environments.