Dual-target Magnetron Sputtering Research Articles

Studies on Dual Sputtered CuGaO2 Thin Films

There has been extensive research conducted on n-type transparent conducting oxide (TCO) films like Sn-doped In2O3 (ITO) [1], Al-doped ZnO (AZO) [2], etc. P-type transparent conducting oxides are yet to be researched extensively. Active devices such as p-n junction devices and transistors are required to make progress in the development of transparent electronics. In this effort, research in p-Type TCOs is important. Most of the p-Type TCOs are copper-based ternary oxides [3].In this work, CuGaO2 thin films were prepared using the dual-target RF magnetron sputtering technique. Cu2O and Ga2O3 targets were simultaneously sputtered on quartz substrates. The sputtering power of Cu2O was kept constant at 50 W and the sputtering power of Ga2O3 was varied. The films were deposited at room temperature and were subsequently annealed in nitrogen ambiance at 900 °C. The X-ray diffraction and optical studies were performed to analyze the films to optimize their properties.[1] Fallah, H.; Ghasemi, M.; Hassanzadeh, A.; Steki, H. The effect of annealing on structural, electrical and optical properties of nanostructured ITO films prepared by e-beam evaporation. Mater. Res. Bull. 2007, 42, 487–496[2] Shantheyanda, B.P.; Todi, V.O.; Sundaram, K.B.; Vijayakumar, A.; Oladeji, I. Compositional study of vacuum annealed Al doped ZnO thin films obtained by RF magnetron sputtering. J. Vac. Sci. Technol. A 2011, 29, 051514.[3] Sundaresh, S.; Bharath, A.H.; Sundaram, K.B. Effect of Cu2O Sputtering Power Variation on the Characteristics of Radio Frequency Sputtered p-Type Delafossite CuCrO2 Thin Films. Coatings 2023, 13, 395.

Improvement of the mechanical and tribological behaviors by Ti-C interlayer for diamond-like carbon films on nitrile butadiene rubber

To improve the mechanical and tribological properties of diamond-like carbon (DLC) film on nitrile butadiene rubber, the DLC/Ti-C bilayer films are fabricated by a dual-target magnetron sputtering method. The morphological characterization results indicate that the roughness of DLC/Ti-C first decreases and then increases slightly with the increase of Ti content and surface roughness of all modified samples is lower than that of nitrile butadiene rubber (NBR). Raman spectra show that the change of Ti content in the Ti-C interlayer has no effect on the ratio of sp2 to sp3 bonds of surface DLC film. The nanoindentation results show that the Ti content significantly affects the hardness, Young’s modulus, hrex/hmax and elastic recovery (%). Notably, the DLC/Ti-C films with a Ti content of 12.32 ∼ 14.77 at. % show the lowest coefficient of friction (CoF, 0.1 ∼ 0.2) and superior wear resistance due to the increased transformation of sp2 into sp3 in the films. This study unravels that the DLC films' superior mechanical and tribologic performance could be realized by regulating the Ti content in the Ti-C interlayer.

Effect of Annealing Temperature on Radio Frequency Sputtered p-Type Delafossite Copper Chromium Oxide (CuCrO2) Thin Films and Investigation of Diode Characteristics Forming Transparent pn-Heterojunction

For the first time, the deposition of CuCrO2 thin films was carried out using a dual-target RF magnetron sputtering technique using Cu2O and Cr2O3 targets. The deposited films were subsequently annealed in N2 ambiance from 600–900 °C. This work reports that the electrical, optical, structural, and morphological properties of CuCrO2 thin films are significantly affected due to the variation in the annealing temperature. XRD analysis confirms the presence of single-phase CuCrO2 in the films annealed at 650 °C. The presence of Cu in the 1+ oxidation state in the phase pure CuCrO2 thin films was confirmed through XPS analysis. Further, through XPS analysis, the oxidation states of Cu and Cr, the full-width half maximum (FWHM), the peak positions, and their respective binding energies have been elucidated. SEM analysis confirms the promotion of nanocrystalline growth in the thin films as the annealing temperature was increased from 600 °C. The average grain size increased from 40.22 nm to 105.31 nm as the annealing temperature was increased from 600 to 900 °C. Optical studies conducted in the wavelength range of 200 nm to 800 nm revealed a decrease in the optical transmission and optical bandgap with an increase in the annealing temperature. The highest optical transmission of ~81% and an optical bandgap of 3.21 eV were obtained for the films depicting the delafossite nature of CuCrO2. The optical bandgap was found to vary between 3.16 eV and 3.74 eV for the films studied in this research. The lowest resistivity of 0.652 Ω cm was obtained for the films annealed at 650 °C. Transparent heterojunction diodes involving p-type delafossite copper chromium oxide (CuCrO2) and n-type indium tin oxide (ITO) were fabricated. The best diode depicted a cut-in voltage of 0.85 V, a very low leakage current of 1.24 x 10-8, an ideality factor of 4.13, and a rectification ratio of 2375.

Influence of neutron/gamma irradiation on damage and scintillation of Ga-doped ZnO thin films

As a new type of inorganic scintillator, ZnO crystal doped with Ga has been used for Ultra-fast scintillating detectors with fast response to detect X-ray, gamma, neutron, and charged particles. Moreover, due to the large bandgap energy and high threshold displacement energy, ZnO: Ga has a strong radiation resistance in theory. However, there is a lack of experimental studies on the change of scintillation properties of ZnO: Ga under an intense irradiation environment. This study deposited thin Ga-doped ZnO films on α-Al2O3(0001) substrate by dual-target reactive magnetron sputtering. The ZnO: Ga samples were irradiated by neutrons from 1010 to 7.1 × 1014 neutrons/cm2 (1 MeV neutron equivalent fluence) and γ rays from 500 to 10,000 Gy, respectively. The structural and optical properties of all irradiated samples were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), optical transmittance (TS), and effective light output at room temperature. The results indicated that all the irradiated samples are still in both hexagonal wurtzite structure and c-axis orientation. Compared with unirradiated samples, it is found that the samples' optical transmittance, energy resolution, and effective light output have little change due to irradiation, which has fully proved that the ZnO: Ga scintillation films have good radiation resistance under neutron and gamma irradiation. Hence, ZnO: Ga is an attractive candidate for radiation detectors with ultra-fast responses under extreme radiation environments.

F, Mg and Ga co-doped ZnO transparent conductive thin films by dual-target magnetron sputtering: Fabrication, structure, and characteristics

F, Mg and Ga co-doped ZnO (FMGZO) films are deposited on glass substrates at room temperature by magnetron sputtering using MgF2 and ZnO:Ga targets. The effects of RF sputtering power applied to the MgF2 target on structure, morphology, composition, electrical and optical properties of the films are investigated in detail. The experimental results show that all samples are polycrystalline films with hexagonal wurtzite structure and low surface roughness. The FMGZO film deposited at RF sputtering power of 15 W exhibits the highest figure of merit of 5.66 × 10−2 Ω−1 with the resistivity of 6.5 × 10−4 Ω cm, the carrier concentration of 4.12 × 1020 cm−3 and the Hall mobility of 23.38 cm2/V s, while the average optical transmittance is as high as 95.23% in the visible range. The photoelectric performance of the FMGZO film is significantly higher than that of previously reported co-doped ZnO films, which makes it suitable for various high-efficiency optoelectronic devices.

Preparation of Al-Al2O3 composite coating by dual-target magnetron sputtering and study on deuterium permeability

In this study, Al-Al2O3 double-layer coating and Al-Al2O3 fusion coating were prepared on 316L stainless steel substrate by double target and double frequency magnetron sputtering. It was found that the Al/Al2O3 transition layer was formed between Al and Al2O3 by CO sputtering deposition, which effectively reduces the interlayer microstructure defects, and makes the Al-Al2O3 fusion coating have a denser interlayer structure than the Al-Al2O3 double-layer coating. The deuterium permeation test of the coating was carried out at 823–1023 K. The deuterium resistance reduction factor of Al-Al2O3 fusion coating was 8–72, which was 2–3 times that of Al-Al2O3 double-layer coating. The deuterium permeation diffusion time of Al-Al2O3 fusion coating was 1/10 of that of Al-Al2O3 double-layer coating. With the increase of penetration test temperature, it was found that the deuterium resistance reduction factor of Al-Al2O3 fusion coating increases significantly, which was because amorphous Al2O3 was transformed into more dense γ-Al2O3 in high temperature test.

Room-Temperature Formation of Hard BCx Films by Low Power Magnetron Sputtering

Boron carbide is one of the most important non-metallic materials. Amorphous BCx films were synthesized at room temperature by single- and dual-target magnetron sputtering processes. A B4C target and C target were operated using an RF signal and a DC signal, respectively. The effect of using single- and dual-target deposition and process parameters on the chemical bonding and composition of the films as well as their functional properties were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray energy dispersive analysis, X-ray diffraction, ellipsometry, and spectrophotometry. It was found that the film properties depend on the sputtering power and the used targets. EDX data show that the composition of the samples varied from B2C to practically BC2 in the case of using an additional C target. According to the XPS data, it corresponds to the different chemical states of the boron atom. A nanoindentation study showed that the film with a composition close to B2C deposited with the highest B4C target power reached a hardness of 25 GPa and Young’s modulus of 230 GPa. The optical properties of the films also depend on the composition, so the band gap (Eg) of the BCx film varied in the range of 2.1–2.8 eV, while the Eg of the carbon-rich films decreased to 1.1 eV.

On the adhesion and wear resistance of DLC films deposited on nitrile butadiene rubber: A Ti-C interlayer

To promote the adhesion strength between diamond-like carbon (DLC) films and nitrile butadiene rubber (NBR) substrates, titanium-doped carbon (Ti-C) films prepared by dual-target magnetron sputtering under varied substrate bias voltages were used as an interlayer on the rough NBR. The surface topography and structure of Ti-C films were investigated by atomic force microscopy (AFM) and Raman spectra. Raman analysis indicates that the increase of substrate bias voltage leads to an increase of the number or the size of sp2 clusters in the Ti-C interlayer. The adhesion strength and tribological properties of DLC films coated on NBR substrate were scrutinized by a scratch tester and a ball-on-disk tribometer, respectively. It was found that DLC film with a Ti-C interlayer at a certain bias voltage exhibited superior wear resistance with a low coefficient of friction (CoF) during the sliding of 6000 laps. No clear damages in the coatings were observed from the wear tracks. Besides, the scratch test also revealed a reliable adhesion when the interlayer was prepared at −150 V, as confirmed by a scratch crack width of ~50 μm as compared to that of the pure DLC film increasing to ~ 120 μm. Therefore, a Ti-C interlayer could significantly enhance the adhesion and wear resistance of DLC thin films deposited on NBR.

Enhancement of the Hydrogen Evolution Reaction from Ni-MoS2 Hybrid Nanoclusters.

This report focuses on a novel strategy for the preparation of transition metal–MoS2 hybrid nanoclusters based on a one-step, dual-target magnetron sputtering, and gas condensation process demonstrated for Ni-MoS2. Aberration-corrected STEM images coupled with EDX analysis confirms the presence of Ni and MoS2 in the hybrid nanoclusters (average diameter = 5.0 nm, Mo:S ratio = 1:1.8 ± 0.1). The Ni-MoS2 nanoclusters display a 100 mV shift in the hydrogen evolution reaction (HER) onset potential and an almost 3-fold increase in exchange current density compared with the undoped MoS2 nanoclusters, the latter effect in agreement with reported DFT calculations. This activity is only reached after air exposure of the Ni-MoS2 hybrid nanoclusters, suggested by XPS measurements to originate from a Ni dopant atoms oxidation state conversion from metallic to 2+ characteristic of the NiO species active to the HER. Anodic stripping voltammetry (ASV) experiments on the Ni-MoS2 hybrid nanoclusters confirm the presence of Ni-doped edge sites and reveal distinctive electrochemical features associated with both doped Mo-edge and doped S-edge sites which correlate with both their thermodynamic stability and relative abundance.

Sputter-Deposited Indium–Tin Oxide Thin Films for Acetaldehyde Gas Sensing

Reactive dual-target DC magnetron sputtering was used to prepare In–Sn oxide thin films with a wide range of compositions. The films were subjected to annealing post-treatment at 400 °C or 500 °C for different periods of time. Compositional and structural characterizations were performed by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Rutherford backscattering and scanning electron microscopy. Films were investigated for gas sensing at 200 °C by measuring their resistance response upon exposure to acetaldehyde mixed with synthetic air. We found that the relative indium-to-tin content was very important and that measurable sensor responses could be recorded at acetaldehyde concentrations down to 200 ppb, with small resistance drift between repeated exposures, for both crystalline SnO2-like films and for amorphous films consisting of about equal amounts of In and Sn. We also demonstrated that it is not possible to prepare crystalline sensors with intermediate indium-to-tin compositions by sputter deposition and post-annealing up to 500 °C.

Enhancement of the electrical characteristics of thin-film transistors with indium–zinc–tin oxide/Ag/indium–zinc–tin oxide multilayer electrodes

Transparent indium–zinc–tin oxide (IZTO)-based thin-film transistors (TFTs) with IZTO/Ag/IZTO multilayer electrodes were fabricated on glass substrates using a tilted dual-target radio-frequency magnetron sputtering system. The IZTO TFTs with IZTO/Ag/IZTO multilayer electrodes exhibited a high optical transmittance in a visible region. The threshold voltage, the mobility, and the on/off-current ratio of the TFTs with IZTO/Ag/IZTO multilayer electrodes were enhanced in comparison with those of the TFTs with ITO electrodes. The source/drain contact resistance of the IZTO TFTs with IZTO/Ag/IZTO multilayer electrodes was smaller than that of the IZTO TFTs with ITO electrodes, resulting in enhancement of their electrical characteristics.

Enhancement of the electrical characteristics of indium–zinc tin-oxide thin-film transistors utilizing dual-channel layers

Thin film transistors (TFTs) with indium–zinc tin-oxide (IZTO) dual-channel layers were fabricated on heavily-doped p-type Si substrates by using a tilted dual-target radio-frequency magnetron sputtering system. The number of oxygen vacancies in the IZTO channel layer decreased with increasing oxygen partial pressure, resulting in a decrease in the conductivity. The threshold voltage (Vth) shifted toward positive gate-source voltage with increasing oxygen partial pressure for the growth of the IZTO layer because of a decrease in the carrier concentration. The Vth, the mobility, the on/off-current ratio, and the subthreshold swing of the dual-channel IZTO TFTs were 3.5 V, 7.1 cm2/V s, 1.3 V/decade, and 8.2 × 106, respectively, which was enhanced by utilizing dual-channel layers consisting of a top channel deposited at a high oxygen partial pressure and a bottom channel deposited at a low oxygen partial pressure.

Structure characteristic and its evolution of Cu-W films prepared by dual-target magnetron sputtering deposition

Immiscible Cu-W alloy thin films were prepared using dual-target magnetron sputtering deposition process. The structure evolution of Cu-W thin films during preparation was investigated by X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy. In the initial stage of dual-target magnetron sputtering deposition process, an amorphous phase formed; then it crystallized and the analogy spinodal structure formed due to the bombardment of the sputtered particles during sputtering deposition process, the surface structure of the film without the bombardment of the sputtered particles was the amorphous one, the distribution of the crystalline and amorphous phase showed layer structure. The solid solubility with the analogy spinodal structure was calculated using the Vegard law. For Cu-13.7%W (mole fraction) film, its structure was composed of Cu-11%W solution, Cu-37%W solution and pure Cu; for Cu-14.3%W film, it was composed of Cu-15%W solution, Cu-38%W solution, and pure Cu; for Cu-18.1%W film, it was composed of Cu-19%W solution, Cu-36% W solution and pure Cu.

Ion-induced transformations of a W–Si interface

Tungsten silicide formation in multilayer tungsten/silicon structure was investigated. The W–Si multilayers were deposited on thermally oxidized silicon wafers using the dual-target magnetron sputtering. Deposition of the whole stack of sublayers was carried out without breaking vacuum in order to eliminate contamination or oxidation of the interfaces between sublayers. Samples were annealed in the RTA furnace at temperatures ranging from 700 °C up to 1050 °C. Some of the structures were irradiated with argon ion beam before annealing. Reactions between sublayers were studied using SEM imaging of cross-sectional cleavages and by X-ray diffraction analysis. Influence of the irradiation with argon ion beam on structural transformations was investigated using RBS analysis. It has been found that tungsten silicide formation depends on the deposition sequence. The reaction was more effective on interfaces between silicon layer deposited on tungsten then on interface between tungsten deposited on silicon. Ion beam mixing experiment showed that ion–target interaction promotes formation of the WSi 2 phase.

Field-emission properties of carbon nanotubes grown using Cu–Cr catalysts

In addition to Ni, Co, and Fe, the authors show that a copper (Cu) chromium (Cr) alloy can be a good catalyst for controlled growth of carbon nanotubes (CNTs). A thermal chemical vapor deposition was used at 600°C to deposit the CNTs, and a dual-target magnetron sputtering system was used to control the ratio of the Cu∕Cr alloy. The material properties of the CNTs, such as concentration, diameter, and density, are directly affected by the ratio of Cu∕Cr alloy, which subsequently affect the field-emission properties. Their results showed that Cr can be used to effectively control the catalytic effects of the Cu catalysts, where the quality of the CNTs could vary while the density could be controlled from 4×107to5×1010tubes∕cm2. The field-emission current density of the CNT film increases with Cu∕Cr ratio from 1∕6.4 to 4.6∕1 and decreases when the Cu∕Cr ratio is more than 4.8∕1 in the alloy film. When the Cu∕Cr ratio is at 4.6∕1, the average current density peaks at 5129μA∕cm2 at the applied field of 3.53V∕μm, showing an optimized field-emission property.

Effect of FGM on Film Quality of Al onto Cu(001) Substrate by Considering Incident Energy and Deposition Rate

A molecular dynamic (MD) method is used to simulate Al atom depositing on Cu substrate by controlling the incident energy and the deposition rate for dual-target magnetron sputtering. At the interface, functional graded material (FGM) will be created to reduce the residual stress after the deposition process. The results indicate that the surface roughness of the deposited film will be reduced with the assistance of FGM, and more layers of FGM will reduce more the root-mean-square (RMS) value and the residual stress to obtain excellent quality of the deposited film.

Nc-VO 2/Al 2O 3 nanocomposite films prepared by dual target magnetron sputtering

A dual target magnetron sputtering system was used to synthesize nanocomposite films with VO 2 nanocrystals embedded in Al 2O 3 matrix. Glancing incidence X-ray diffraction and high-resolution transmission electron microscopy reveal the formation of VO 2 nanocrystallites with monoclinic structure. X-ray photoemission analysis confirmed that oxide particles predominantly possess VO 2 stoichiometry. Valence band spectra acquired below and above transition temperature demonstrate that embedded VO 2 particles exhibit a first-order monoclinic-to-tetragonal phase transition, however the band shape in a metallic state exhibits feature that is not characteristic for bulk material.

Electrical, optical, and structural properties of ITO co-sputtered IZO films by dual target magnetron sputtering

We have investigated electrical, optical, and structural properties of indium tin oxide (ITO) co-sputtered indium zinc oxide (IZO) film prepared by a dual target direct current (DC) magnetron sputtering at room temperature in pure Ar ambient. It was shown that the resistivity and sheet resistance of ITO co-sputtered IZO films monotonically increased with increasing DC power of ITO target at constant DC power of IZO target. Synchrotron X-ray scattering and scanning electron microscope examination results show that addition of ITO in the IZO film lead to crystallization of IZTO film due to low transition temperature of the ITO from amorphous to crystalline. However, ITO co-sputtered IZO film (ITO/IZO power = 100 W:100 W) exhibit higher work function than those of pure IZO and ITO film. It was found that the work function as well as the electrical, optical, and surface properties of the IZTO film could be controlled by varying the DC power of IZO and ITO targets, respectively.

Study on the Structure and Electrochromism of WO<sub>3</sub> and Ti-Doped WO<sub>3</sub> Films

WO3 and Ti-doped WO3 electrochromic films were prepared by mid-frequency dual-target magnetron sputtering method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and spectrophotometer were used to characterize the structure, morphology, composition and transmittance properties of the films, respectively. The results show that this method is available to deposit WO3 and Ti-doped WO3 electrochromic films. The as-deposited films prepared at room temperature are amorphous and display good transmittance. The difference value of transmittance between the bleached and coloration states of WO3 film is above 60% at 633nm. Ti-doped WO3 films have smoother surface and smaller grains than undoped ones. Moreover, the crystalline temperature increases after doping titanium, because the titanium atoms influence the lattice distortion of the WO3 films. So it is more convenient for Li+ ions to inject into films and can enhance the response speed and stability of Ti-doped WO3 electrochromic films.

Electrochromic Properties of Sputtered Ti-Doped WO3 Films

Ti-doped WO3 films were prepared by the mid-frequency dual-targetmagnetron sputtering method. The structure and electrochromicproperties of the Ti-doped WO3 films were analysed by X-Raydiffraction (XRD), Raman spectroscopy, spectrophotometer, cyclicchronoamperometry and atomic force microscopy (AFM). The resultsindicate that the crystallinity decrease after the doping oftitanium, the channels for ion injection and extraction increase,the responding speed with 5.1% titanium doped becomes faster, andits circle life increases more than four times compared with theundoped WO3 film. In the coloured state, the W-O-W bondsdecrease, but the W = O bonds increase. Since the W-O-W bonds breakdown for Li+ ions' injection and more W = O bonds form, it ismore convenient to inject Li+ ions into the Ti-doped film thanundoped film because more W-O-W bonds break down in the colouredstate.