DC Magnetron Sputtering Technique Research Articles

Investigations of TiC and SiC films synthesized by DC magnetron sputtering and thermal annealing

In this research article, two-dimensional thin films of titanium, hierarchical titanium-carbon, titanium carbide, hierarchical silicon-carbon, and silicon carbide films were synthesized on the plates of AISI 304 stainless steel and glass slides, individually, using DC magnetron sputtering techniques. During the sputtering process, the creation of stable plasma was affected by the vacuum level, DC potential, plasma current, and Argon gas. The results showed that the coatings of titanium, titanium-carbon, and titanium carbide modified the optical properties of stainless steel. Additionally, titanium carbide coatings displayed a shiny gold appearance with a hardness of 1500 HV. Besides this, X-ray diffraction studies revealed a hexagonal Ti in the metallic films and C60, and diamond-like structures dispersed on its surface after the carbon coating. The spherical particulates of Ti and C60/diamond-like carbon particulates anchored on its surface were observed using scanning electron microscope analysis. The structural analysis indicated C vacant sites, which are available for ionic/electronic charge diffusion, thereby rendering these structures suitable for making Li storage batteries as electrode material.

Sputtered vanadium carbon nitride (VCN) thin films: a potential electrode for supercapacitors

The preparation of efficient thin film-based electrode materials is a vital prerequisite for practical energy storage devices. Herein, we have prepared unique vanadium carbon nitride (VCN) thin films on FTO substrates by pulsed DC magnetron sputtering technique for competent supercapacitor electrodes. XRD analysis confirmed the crystalline nature of VCN thin films. SEM and AFM revealed a smooth morphology with an average grain size of 30 nm. Raman spectra showed two broad peaks around 1346 and 1589 cm−1, belonging to the D-band and G-band of VCN. The surface electronic states of VCN were investigated by XPS analysis, which confirmed the formation of pure VCN films without any impurities. The electrochemical performance of the thin film electrode was evaluated using cyclic voltammetry (CV), Galvanostatic charge–discharge (GCD), and Electrochemical impedance analysis (EIS). The electrochemical results showed the VCN thin films exhibited super capacitive behaviours. The maximum specific capacitance (Cs) value of 78.2 F g−1 was obtained from GCD studies. A variation in charge transfer resistance is detected from the EIS study, which arises due to the partial oxidation of the active nitride component. The VCN electrode showed good cycling stability, retaining 87% of its capacitance at a current density of 5 A g−1 even after 2000 cycles. The sputtered VCN films have been demonstrated as potential thin film electrodes for electrochemical supercapacitors for practical energy storage devices.

Magnetic Anisotropy of FeNi Multilayer Films with Different Orientations of the Magnetic Anisotropy Axes in Adjacent Layers

FeNi films were prepared using the DC magnetron sputtering technique with an oblique deposition arrangement. Multilayers with different orientations of the magnetic anisotropy axes were obtained thanks to a rotary sample holder inside the vacuum chamber. Magnetic properties were studied using magneto–optical Kerr microscopy and a vibrating sample magnetometer. Single-layered FeNi films having thicknesses as high as 10 nm and 40 nm show in-plane uniaxial easy magnetization axes produced by the oblique incidence of incoming components of the beams. Magnetic anisotropy field for four-layered samples with orthogonal uniaxial magnetic anisotropy axes in the adjacent layers and the thickness of individual layers of 10 nm and 40 nm turned out to be less than in single-layered films. The magnetic properties peculiarities of the eight-layered sample FeNi (10 nm) × 8 obtained by rotation of the sample holder by 45° before deposition of each subsequent layer suggest the formation of a helix-like magnetic structure through the thickness of the multilayered sample similar to the magnetization arrangement in the Bloch-type magnetic domain wall.

Mechanical and tribological properties of (AlCoCrNiSi)100−xNx thin films

High entropy thin films of (AlCoCrNiSi)100−xNx were deposited on silicon wafers using a pulsed DC magnetron sputtering technique, with nitrogen gas flow ratios (RN) of 0, 0.33, and 0.50. The structure and properties of these films were analyzed for elemental composition, surface and cross-sectional morphologies, microstructure, roughness, and mechanical properties. The coatings were primarily composed of an amorphous structure with a minor presence of a BCC structure and exhibited periodic variations in chemical composition from the substrate to the free surface. An increase in RN enhances crystallinity of the materials. Nanoindentation results showed that the films deposited at RN = 0.50 displayed the highest hardness (10.7 ± 0.5 GPa) and reduced modulus (176 ± 5 GPa), which were the highest among the films. Microtribology testing was conducted using a 20 μm radius spherical diamond tip under ambient air and normal loads ranging from 0.5 to 9 mN. Worn surfaces were characterized using atomic force microscopy. The coefficient of friction was evaluated to investigate the elastic and plastic behaviors of films using Schiffmann’s model. The coating without nitrogen displayed a predominant plastic behavior during the initial cycles, while the coating deposited at RN = 0.33 demonstrated a more elastic behavior, particularly at lower loads.

Sputter Grown Hexagonal WSe2@Graphite Nanoflakes for Electrochemical Energy Storage

In the pursuit of sustainable and efficient energy storage solutions, researchers have continuously explored novel materials and technologies to enhance the performance of energy storage devices. Recently, transition metal dichalcogenide (TMDCs) such as molybdenum disulfide (MoS2), molybdenum diselenides (MoSe2), and tungsten disulfide (WS2) with a honeycomb-like structure has sparked considerable interest in utilization as electrode material for supercapacitor (SCs) applications due to their unique layered structures. Generally, the small surface area of TMDCs in their bulk form restricts their practical usage in the SCs applications. Whereas TMDC in thin 2D form exhibits high surface area and flexibility to the electrode material which allows more charge storage and results in high capacitance and energy density. In the present work, high-quality tungsten diselenide (WSe2) thin film electrodes were deposited over graphite sheets (WSe2@Graphite) using DC magnetron sputtering technique at an elevated temperature of around 200 0C under the controlled argon atmosphere. The electrochemical properties of these WSe2@Graphite electrode were investigated in three electrodes configuration using 1M Na2SO4 aqueous electrolyte by recording CV, GCD, and EIS spectra. The hexagonal WSe2@graphite nanoflakes were found to exhibit an exceptionally high areal capacitance of 88.05 mF/cm2 and energy density of 7.83 µWh/cm2 at a scan rate of 5 mV/s. Further, GCD was performed, and the WSe2@graphite electrode exhibits a high areal capacitance of 37.5 mF/cm2 at the current density of 0.5 mA/cm2. The WSe2 thin film electrode shows a high energy density of 3.3 µWh/cm2 at a power density of 199.98 µW/cm2. Additionally, the WSe2@graphite thin film electrode demonstrates high cyclic stability with retaining ~ 90.33% capacitance even after 2000 consecutive GCD cycles. The obtained hexagonal nanoflakes-like morphology provides a high surface area and porous structure that helps to improve the electrochemical performance of the WSe2 thin film. The obtained results demonstrate that the WSe2@graphite thin film exhibit excellent electrochemical performance and can be utilized as a potential material for supercapacitor electrodes. Keywords- Transition metal dichalcogenide (TMDCs), tungsten diselenide (WSe2), DC magnetron sputtering, supercapacitor, and nanoflakes Figure 1

Impact of sputtering gas on the microstructural, mechanical and wetting properties of vanadium nitride coatings

Vanadium nitride (VN) coatings were deposited via reactive DC magnetron sputtering technique on a hot substrate (400 °C) with varying partial pressure of N2. The impact of nitrogen partial pressure on the crystal structure, microstructure, elemental composition, surface topography, mechanical and wetting properties of VN coatings was investigated using grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, field emission scanning electron microscope (FESEM), energy dispersive spectroscopy (EDS), atomic force microscope (AFM), nano-indentation, and drop shape analyzer (DSA). The variation in the N2 partial pressure leads the significant changes in the microstructure, mechanical and wetting properties of the coatings. The GIXRD spectra reveals the formation of crystalline FCC phase in the deposited VN coatings. However, at 100% N2 partial pressure, the preferred orientation of crystal planes changes from (200) to (220). The FESEM image reveals that at low N2 partial pressure, the coating exhibits well-separated grains with clearly visible grain boundaries. As the N2 partial pressure increases, the agglomeration of grains becomes more pronounced, and the grain boundaries become less discernible. However, at 100% N2 partial pressure, the structure transforms into triangular nanoflake-like prismatic structures with voids. The VN coatings with 60% N2 partial pressure exhibits the highest mechanical properties whereas at 100% N2 partial pressure, the VN coatings reveal super-hydrophilic character.

Thermoelectric properties of sputter deposited Bi2Te3–PbTe multilayer thin films

Pristine Bi2Te3, PbTe, and multilayer of Bi2Te3/PbTe thin films were deposited on a glass substrate using the DC magnetron sputtering technique. XRD, FE-SEM, AFM, Raman, electrical, and thermal properties were analyzed to understand the structural, surface, electrical resistivity, Seebeck coefficient, and electrical part of thermal conductivity of the films. The structural analysis by XRD confirms the phase purity of the pristine films and the mixed phase for the multilayer films. FE-SEM morphology images showed a significant variation in the surface structure. The Seebeck coefficient, resistivity, and power factor analysis were carried out to understand the charge transfer processes. Multilayer films exhibited a high absolute Seebeck coefficient (S) value of −140.6 μV/K for BPB-5 film and −130.6 μV/K for BP-6 film compared to −92.9 μV/K of Bi2Te3 film with n-type behavior at 370 K. Similarly; the power factor value is also higher for multi-layer films compared to pristine film.

Investigation of resonant properties of metamaterial THz filters fabricated from vanadium dioxide thin films

Vanadium dioxide (VO2) is a promising candidate for electronic and optical switching applications in the terahertz frequency range due to the metal to insulator transition (MIT). In this study, the use of VO2 patterned as a metamaterial surface or coupled as a homogeneous layer with a metallic metamaterial surface on top is investigated in terms of performance. High-quality VO2 thin films were deposited on c-cut sapphire substrates by using the dc magnetron sputtering technique. A change in resistivity by a factor of 104 MIT in VO2 was observed allowing to investigate its use as a controllable metamaterial. The layer was patterned using a unique geometry (four-cross shaped) that operates in the THz frequency range. To understand its performance as a tunable THz filter, the four-cross structure fabricated from VO2 is compared to one fabricated from Au on VO2 bare film using UV lithography and ion beam etching techniques. The spectral performances of metamaterials were assessed using THz-Time Domain Spectroscopy (THz-TDS) and results were compared with simulations based on CST Microwave Studio. Absence of the resonant effects in the purely developed VO2 device, while clear observation of the MIT behavior shows the strong dependency of the inductive and/or capacitive effects of the four-cross structure on conductivity of the surface metamaterial, which is clearly observable for the Au-based device. In the latter case, the resonant transmittance of the filter can be effectively modulated by change in temperature.

Optical and Magnetic Response of Pure and CU-Ions Substituted Dysprosium Oxide Thin Films for Various Applications

Dysprosium oxide (Dy2O3) and Cu/Dy2O3 thin films of thickness 117.14 nm and 258.30 nm, respectively were successfully deposited via a well-known DC-magnetron sputtering technique. Field emission scanning electron microscopy clarifies the growth of uniform and fine granular particles on silicon substrate. The hexagonal closed pack structure for both the thin films has been observed by the x-ray diffraction analysis and it was observed that by inclusion of copper the HCP structure of thin film was retain with a slight shift in the main peak. The reduction from 3.9 eV to 3.8 eV in the energy band gap value was observed by incorporation of copper ions Dy2O3 thin films. The M-H loops obtained through Vibrating Sample Magnetometer (VSM) shows that Dy2O3 thin film behave ferromagnetically at low temperature with a saturation magnetization value of 2860 emu/cc and evolves through its phase transition temperatures and behave paramagnetically at room temperature. In Cu/Dy2O3 case, the diamagnetic response of Cu dominates and produces reverse hysteresis loop at both temperatures make it a suitable candidate for energy and memory storage devices applications.

Understanding the Role of Underlying Substrates on Hydrogen Evolution Reaction (HER) Catalytic Activity of Atomically Dispersed Pt Atoms

Electrochemical water splitting is an environmentally friendly way of producing hydrogen, but this process requires highly efficient catalysts. Platinum (Pt) is known the best catalyst for hydrogen evolution reaction (HER) in acidic media, but the scarcity and high cost of Pt limits its applicability in widespread technologies. In this work, we have uncovered the role of underlying substrate on the HER activity of atomically dispersed Pt atoms. A DC magnetron sputtering technique has been utilized to deposit transition metal (Cu, Mo, W, Ti and Ta) thin films as underlying substrates for atomically dispersed and extremely low loading of Pt (< 1.5 at%). As synthesized samples were characterized as electrocatalysts for the HER in both alkali and acidic media. In combination of standard electrochemical experiments (e.g., CV), the differential electrochemical mass spectrometry (DEMS) results show that despite low loading of Pt, the prepared catalysts produce hydrogen at a rate comparable with that of a pristine Pt. Based on the XPS study, the excellent performance is attributed to the modified electronic properties of the Pt atoms due to interaction with underlying substrates. Additionally, the performance of the Pt atoms is significantly governed by the physical properties of underlying substances. Our catalysts also displayed good stability for HER activity and found to be stable after 1000 cycles of continuous operation.

Tunable band-selective photodetector based on sputter-deposited SnOx thin-films: Effect of reactive gas pulsing process

In this work, high-performance SnOx band-selective photodetectors (PDs) were realized by DC magnetron sputtering technique. The reactive gas pulsing process (RGPP) was implemented with pulsing period fixed at P = 20 s to adjust tin and oxygen concentrations in the film. The impact of pulsed oxygen time on the structural, morphological and photosensing properties of SnOx-based PDs was investigated. The fabricated SnOx-based PD at a high duty cycle of 80% of P demonstrated high UV photodetection capabilities and solar-blind characteristic with a high responsivity of 21.8 mA/W, a high signal to noise ratio of 6 × 104 and a specific detectivity of about 5 × 1011 Jones. It was also revealed that the use of a short oxygen pulsing time 8 s paves the way for the realization of multispectral SnOx PD, demonstrating a high responsivity values of 36.45 mA/W, 36.4 mA/W and 34 mA/W over UV, Visible and NIR bands, respectively. This is attributed to the role of using RGPP in modulating the film optoelectronic properties from metallic to insulator when the duty cycle and thus oxygen concentration in the films changed from pure tin to overstoichiometric SnO2 compound. The prepared SnOx PDs demonstrated many advantageous features like low-noise, cost effective and high sensitivity. The obtained results proved that SnOx can be used as an alternative material for developing high-performance band-selective sensing devices.

Topological surface state induced spin pumping in sputtered topological insulator (Bi2Te3)–ferromagnet (Co60Fe20B20) heterostructures

Topological insulators with high spin–orbit coupling and helically spin-momentum-locked topological surface states (TSSs) can serve as efficient spin current generators for modern spintronics applications. We used the industrial-friendly DC magnetron sputtering technique to fabricate magnetic heterostructures consisting of Bi2Te3 (BT) as a topological insulator and Co60Fe20B20 (CFB) as a magnetic layer and studied the temperature-dependent spin pumping, utilizing out-of-plane ferromagnetic resonance spectroscopy. These results demonstrate that the effective spin-mixing conductance is significantly affected by the contribution of two-magnon scattering (TMS). It is found that the TMS-free effective spin-mixing conductance increases with decreasing temperature. Additionally, results from magneto-transport measurements indicate that the surface coherence length of BT is in accordance with the temperature-dependent effective spin-mixing conductance. This enhancement of effective mixing conductance correlated with the enhancement in the contribution of the TSSs as evaluated using the weak-anti-localization effect. This study provides a deeper understanding of the temperature-dependent spin dynamics in sputtered BT/CFB heterostructures which can serve as a guide for further exploration of such bilayers for topological-based spintronic applications.

Fabrication of Zr-Ti-Si glassy metallic overlay on 3D printed Ti-6Al4V implant prototypes for enhanced biocompatibility

Implantable materials with enhanced corrosion resistance and bioactivity are highly desired for biomedical application. A 3D metal printed prototype surface was coated with amorphous alloy components of elements Zr, Ti and Si (Zr54Ti35 Si11) as a novel biomedical grade ternary system for the implants. A DC magnetron sputtering technique was used to sputter the films on Ti-6Al-4 V implant prototypes, exhibiting a smooth and denser coating with root means square surface roughness of 1.4 nm. Surface morphology and structural integrity of the thin film metallic glass (TFMG) was studied from electron microscopic techniques and X-ray diffraction analysis. The TFMG is thermally stable with a large supercooled liquid region (∆Tx) of 81.2 °C. Mechanical characteristics of the coatings were studied using the nanoindentation method to correlate the hardness and modulus of the implant materials. Under the simulated body fluid condition, Ti-6Al-4 V implant with 500 nm thickness coatings (Zr54Ti35Si11) exhibited the superior corrosion resistance rate 1 × 10−6 mpy with a charge transfer resistance of 34 kΩ promising for practical application. Electrochemical impedance spectra and Tafel analysis revealed that the corrosion resistance was prominent in the 500 nm thickness TFMG system than the 250 nm and uncoated bare counterparts. The in-vitro biocompatibility and cytotoxicity studies of the as-coated 3D printed implants were studied using the human osteoblast and L929 fibroblast cell lines, respectively. A hemocompatibility study on the implant materials revealed that erythrocytes remain biconcave without aggregation, platelet activation and thrombogenesis, supporting the biocompatibility of the implants. The integration of such unique properties makes these TFMG system ideal candidates for biomedical implants.

Tuning microstructure and mechanical and wear resistance of ZrNbTiMo refractory high-entropy alloy films via sputtering power

Introduction: Recently, great efforts have been dedicated to tailoring the microstructure of the RHEA films to further optimize the performance of the films. However, there is still a lack of in-depth study on their wear mechanism and microstructure evolution.Methods: In this work, the novel ZrNbTiMo RHEA films were prepared by DC magnetron sputtering and splicing target techniques. The effects of sputtering power on the microstructure, hardness, toughness, and wear resistance of ZrNbTiMo RHEA films were investigated in detail.Results: The ZrNbTiMo films possess the nanocomposite structure, the bcc nanocrystal is wrapped in an amorphous phase. The wear resistance of the film is expected to be improved by finding an appropriate ratio between the amorphous phase and the nanocrystal phase. The nanocrystal structure ensures the high hardness (6.547 ∼ 7.560 GPa) of the ZrNbTiMo film. In addition, the nanocrystals hinder crack propagation, this toughness mechanism effectively improves the toughness of the film. The ZrNbTiMo film prepared at 150 W possesses excellent mechanical properties, hardness of 7.240 GPa and toughness of 0.437 ± 0.040 MPa × m1/2, exhibits better wear resistance (wear rate: 5.223 × 10−7 mm3/N m).Discussion: The wear resistance of ZrNbTiMo film is controlled by both hardness and toughness. The nanocomposite structure makes the ZrNbTiMo films possess a composite fracture which could improve the toughness of the ZrNbTiMo film. The wear-resistant ZrNbTiMo RHEA films with wear rates of the order of 10−6 mm3/N m have been prepared by tuning the sputtering power, this film can be used as a potential candidate for wear-resistant coatings.

Tribological behavior of Cr/a-C multilayered coating against PEEK under dry sliding condition

PEEK is of increasing interest as self-lubricating material for high temperature applications due to its remarkable mechanical properties. However, PEEK is apt to be worn out under dry sliding condition. In this work, the amorphous carbon(a-C) coating interleaved with Cr layer was deposited by a DC magnetron sputtering technique. The friction behavior of the Cr/a-C multilayered coating against PEEK pair was performed in dry atmosphere using a pin-on-disk tribometer. The tribochemical reactions was discussed in terms of evolution of surface morphology and chemical composition of wear debris. Results showed that the tribological behavior of Cr/a-C coating against PEEK pair is dominated by a synergistic effect arisen from inherent graphitization of a-C layer and suppressed adhesive reaction of transferred Cr layer.

Investigation of Structure and Optical Properties for Copper Oxide Thin Films on Plastic Substrate by Helicon Plasma DC Magnetron Sputtering Technique

As we move towards a decarbonized society, transparent solar cells have recently become an important means of increasing power generation in familiar locations. Copper oxide has been attracting attention as a candidate material for the production of transparent solar cells. In order to further expand the range of applications, it is believed that it will be necessary to develop flexible, transparent plastic substrates. For the purpose of optical applications, copper oxide thin films with CuO, Cu2O, or both phases were fabricated on highly transparent plastics such as poly-methyl methacrylate (PMMA) and polycarbonate (PC), as well as on a glass substrate as a comparable sample. The helicon plasma DC magnetron sputtering method was used to fabricate thin films at a low deposition temperature due to the low heat resistance of plastic substrates. In addition, the helicon plasma DC magnetron sputtering method is capable of depositing films at low vacuum pressure, which enables the preparation of thin films with high crystallinity. The structure, surface shape, and optical properties of fabricated films were investigated using X-ray diffraction (XRD), a laser microscope, and a UV-Vis spectrophotometer, respectively. In this study, the formation of copper oxide thin films on plastic substrates at low temperatures has been verified, as have the crystal structure and optical properties, which is considered a rare study in this field.

Structural and Oxidation Behavior of Nanocomposite TiCrN Thin Films

The structural and oxidation behavior of nanocomposite titanium chromium nitride (TiCrN) thin films has been investigated by using x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDS), and field emission scanning electron microscopy (FE-SEM). The TiCrN thin films were deposited on Si substrates by using the reactive DC magnetron sputtering technique from the Ti-Cr mosaic target. After that, the as-deposited thin films were annealed in the air at 500 - 900°C for 2 h. The XRD results showed that the formation oxidation of anataseTiO2, rutile-TiO2, and Cr2O3 which diffraction peak appear from 500°C. The relative intensity of these oxide peaks varied with the annealed temperatures. By observing from FE-SEM, the aggregation of the grain increased with the annealing temperature. The cross-sectional results showed that the thin dense oxide overlayer occurred at 700°C and the oxide thickness increased gradually with the annealing temperature. Meanwhile, underneath the TiCrN grain grew above 700°C and become more void structure after annealing at 700°C. The dramatically increase of the oxygen content was found at 700°C and the evolution of Ti, Cr, N, and O with different elements compositions at various annealing temperatures were investigated from the EDS technique. The oxide layer obviously grows inward indicating the oxidation of TiCrN thin films belongs to inward oxidation. The oxidation rate of the films was increased with the increase of annealing temperature. The activation energy of the oxidation as evaluated by the Arrhenius-type relation was 168 kJ/mol.

Sputtered (Fe,Mn)3O4 Spinel Oxide Thin Films for Micro-Supercapacitor

The scaling up of wireless operating microelectronics for upcoming Internet of Things (IoT) applications demands high-performance micro-supercapacitors (MSCs) with corresponding high-energy and power capabilities. Indeed, this necessitates the quest for MSC’s electrode materials capable of delivering high energy density at high charge/discharge rates. Many multicationic oxides, such as spinel manganese-iron compounds, demonstrate good pseudocapacitive properties as positive electrodes in conventional supercapacitors. However, fulfilling the required fabrication techniques is a challenge for their applications in MSCs. Hence, this study, for the first time, demonstrates the successful deposition of spinel Mn-Fe thin films on a functional platinum-based current collector. The deposition is achieved in a reactive oxygen environment via reactive DC magnetron sputtering techniques and subsequently annealed ex situ at 600 °C in a nitrogen environment. The electrochemical signature in neutral 1 M Na2SO4 aqueous electrolyte is comparable to those reported for spinel type Mn-Fe bulk counterparts. The areal capacitance at 10 mV.s−1 is 15.5 mF.cm−2 for 1 μm thick film, exhibiting excellent coulombic efficiency (close to 100%) and long-term cycle stability after 10,000 cycles. Thus, the synthesis of the multicationic pseudocapacitive oxides via compatible microelectronic deposition methods has set a prospective path to achieve very high-performance MSCs for future IoT applications.

X-ray Photoelectron Spectroscopy (XPS) Analysis of Ultrafine Au Nanoparticles Supported over Reactively Sputtered TiO2 Films.

The impact of a titania (TiO2) support film surface on the catalytic activity of gold nanoparticles (Au NP) was investigated. Using the reactive dc-magnetron sputtering technique, TiO2 films with an amorphous, anatase, and nitrogen-doped anatase crystal structure were produced for a subsequent role as a support material for Au NP. Raman spectra of these TiO2 films revealed that both vacuum and NH3 annealing treatments promoted amorphous to anatase phase transformation through the presence of a peak in the 513–519 cm−1 spectral regime. Furthermore, annealing under NH3 flux had an associated blue shift and broadening of the Raman active mode at 1430 cm−1, characteristic of an increase in the oxygen vacancies (VO). For a 3 to 15 s sputter deposition time, the Au NP over TiO2 support films were in the 6.7–17.1 nm size range. From X-ray photoelectron spectroscope (XPS) analysis, the absence of any shift in the Au 4f core level peak implied that there was no change in the electronic properties of Au NP. On the other hand, spontaneous hydroxyl (–OH) group adsorption to anatase TiO2 support was instantly detected, the magnitude of which was found to be enhanced upon increasing the Au NP loading. Nitrogen-doped anatase TiO2 supporting Au NP with ~21.8 nm exhibited a greater extent of molecular oxygen adsorption. The adsorption of both –OH and O2 species is believed to take place at the perimeter sites of the Au NP interfacing with the TiO2 film. XPS analyses and discussions about the tentative roles of O2 and –OH adsorbent species toward Au/TiO2 systems corroborate very well with interpretations of density functional theory simulations.

Performance evaluation of transparent self-powered n-ZnO/p-NiO heterojunction ultraviolet photosensors

We have constructed NiO/ZnO thin film heterojunction diodes by dc magnetron sputtering technique and evaluated their performance for ultraviolet sensor applications. The constructed device configuration, ITO/ZnO/NiO/Ag exhibited excellent current-voltage rectifying characteristics in the order of 10 5 at room temperature. The effect of rapid thermal annealing treatment on the fabricated ITO/ZnO/NiO thin film stack was evaluated for their photodetector characteristics. The structural, optical, and spectroscopic properties were also investigated. Further, the ITO/ZnO/NiO/Ag diodes were tested under 365 nm UV light illumination having a power density of 0.06 mW/cm 2 . Remarkably, a speed of response with rise/fall time of 197.29/537.10 ms has been recorded at self-powered mode. Interestingly, the photodiode device has exhibited a spectral responsivity of 13.01 mA/W and stable photo detectivity of 5.66 × 10 11 Jones at room temperature. The n-ZnO/p-NiO heterojunction photodetector has shown its ability to detect a faint UV light in a self-powered mode. • Fabricated transparent p-NiO/n-ZnO heterojunction by dc magnetron sputtering with an excellent photo-to-dark current ratio. • It operated in a self-powered mode under 365 nm wavelength of a low optical power source i.e., 0.06 mW/cm 2 . • Achieved excellent speed of response of rising and fall time of 197.29 ms and 537.10 ms respectively. • At Zero bias, responsivity varied from 13.01 mA/W to 6.52 mA/W and EQE 4.42 % to 2.21 % as a function of rapid thermal annealing.