Sputtering Process Research Articles

Development of photocatalytic nanostructured TiO2 and NiO/TiO2 coatings by DC magnetron sputtering for photocatalytic applications

High photocatalytic activity layers were obtained by combining a TiO2 nanostructured coating support with 10 nm and 20 nm NiO layers synthesized by direct current (DC) magnetron sputtering. In order to improve the TiO2 crystallinity several sputtering process parameters were studied. The TiO2 and NiO/TiO2 coatings were characterized through XPS, XRD, FESEM, AFM and UV transmittance measurements, in the latter case, for band gap determination. The photocatalytic activity of the coatings was tested through methylene blue degradation under UV light. The formation of a p-n heterojunction between the TiO2 and NiO layers improved the degradation rates, compared to the bare TiO2 layers; however, almost no difference can be seen when increasing the NiO sputtering power and subsequently the coating thickness to higher values than 20 nm.

The effects of Ar + N2 plasma power-based attachment of metal nanoparticles on the electron field emission properties of carbon nanotubes

An ideal vacuum-based electron emitter requires a low turn-on field and quick emission processes. Carbon nanotubes (CNTs) have great potential for emission applications, but have some limitations that affect their performance. Consequently, they can benefit from the alteration of their surface morphology upon decoration with plasma-based metal nanoparticles. In this work, we have attached iron nanoparticles on the CNTs surface via a radio frequency (rf) sputtering process using Ar + N2 gas with various plasma power in steps of 50 W. Field emission scanning electron microscopy (FESEM) micrographs have confirmed the attachment of the iron nanoparticles and etching of the nanotubes surface at high plasma power. The Raman spectra strongly confirm the formation of defects in the carbon sheet of the nanotubes. In the plasma treatment process, the increase in the Dband intensity enhanced the degree of disorder and may be beneficial for enhanced emission properties. The field electron emission properties are significantly enhanced after the Fe nanoparticles attached with plasma incorporated in terms of the reduction in Eto (1.64 from 2.02 V/μm) &Eth (1.98 from 2.64 V/μm), and increase in J (391.11–1179.24 μA/cm2) and β (1419–2900), respectively. The field emission parameters of the field emitters are modified due to incorporation of nitrogen species, attached Fe nanoparticles, and reduction in the nanotube density. The as-prepared field emitters also qualified the orthodox field emission hypothesis test by exhibiting fextr values in an acceptable range. Therefore, we can use the Ar + N2 plasma-based Fe nanoparticles decorated CNT field emitters in vacuum electronic device applications.

Enhanced photocatalysis and photohydrophilicity in TiO2–W5O14 nanocomposite thin films grown by in-lay sputtering

Investigation on the photocatalytic and photoinduced hydrophilic properties of pure and nitrogen doped TiO2–W5O14 nanocomposite thin films grown by in-lay sputtering process is reported. For comparison, similar properties of reactively sputtered nanocrystalline titanium dioxide (TiO2) and nanowire tungsten oxide (W18O49) thin films are studied as well. Structurally, TiO2–W5O14 thin films are highly crystalline and strongly multiphased while TiO2 and W18O49 thin films are anatase, monoclinic, respectively. The band gap of nitrogen doped TiO2–W5O14 thin film is ∼2.82 eV while that of TiO2 and W18O49 thin films are ∼3.27 eV. Surface morphology of TiO2–W5O14 and TiO2 films show nanocrystalline particulates of sizes 15–70 nm, 20–50 nm, respectively while W18O49 films show randomly dispersed nanowires with average diameter of ∼50 nm and maximum length of ∼30 μm. Owing to bandgap shift in visible range, porous surface structures and crystallinity, the nitrogen doped TiO2–W5O14 nanocomposite thin films are found to exhibit better (i) photohydrophilicity with water contact angle of ∼7° in 2 h under UV-A irradiation and (ii) photocatalytic efficiency with methylene blue degradation rate of −1.12μmol/(l.d), −0.78 μmol/(l.d) under ultraviolet and visible light sources, respectively.

Highly Flexible Electroluminescent Devices Based on Super Durable AlN‐Dispersed Ag Ultrathin Films

AbstractHigh performance and durable electrodes are prerequisites for the stable operation of various optoelectronic devices, such as alternating current electroluminescence (ACEL) applications. As for the flexible electrodes based on ultrathin metals, which have attracted much attention in recent years, stability problems as evidenced by optically lossy and electrical degradation of the silver (Ag) layer in the service environment are the key issues to be solved before its practical application. This work prepares ultrathin and stable doped silver films by introducing a small amount of AlN during the sputtering process. The Ag‐AlN thin films exhibit a comprehensive stability promotion in terms of high temperature (250 °C in the air) and damp‐heat (85 °C, 85% relative humidity (RH) for 12 h) test compared with pure Ag counterpart. In addition, flexible ACEL devices based on AZO/Ag‐AlN/AZO/polyethylene terephthalate (PET) films with a luminance of 176.1 cd m−2 at 300 V and 400 Hz and excellent luminescence performance and mechanical flexibility under operating conditions are developed. Such ACEL devices based on these ultrathin and durable Ag‐AlN films are up‐and‐coming in practical, flexible electronics applications.

AWafer-Scale Nanoporous 2D Active Pixel Image Sensor Matrix with High Uniformity, High Sensitivity, and Rapid Switching.

2D transition-metal dichalcogenides (TMDs) havebeen successfully developed as novel ubiquitous optoelectronics owing to their excellent electrical and optical characteristics. However, active-matrix image sensors based on TMDs have limitations owing to the difficulty of fabricating large-area integrated circuitry and achieving high optical sensitivity. Herein, a large-area uniform, highly sensitive, and robust image sensor matrix with active pixels consisting of nanoporous molybdenum disulfide (MoS2 ) phototransistors and indium-gallium-zinc oxide (IGZO) switching transistors is reported. Large-area uniform 4-inch wafer-scale bilayer MoS2 films are synthesized by radio-frequency (RF) magnetron sputtering and sulfurization processes and patterned to be a nanoporous structure consisting of an array of periodic nanopores on the MoS2 surface via block copolymer lithography. Edge exposure on the nanoporous bilayer MoS2 induces the formation of subgap states, which promotes a photogating effect to obtain an exceptionally high photoresponsivity of 5.2 × 104 A W-1 . A 4-inch-wafer-scale image mapping is successively achieved using this active-matrix image sensor by controlling the device sensing and switching states. The high-performance active-matrix image sensor is state-of-the-art in 2D material-based integrated circuitry and pixel image sensor applications.

Influence of magnetron sputtering process on the stability of WO3 thin film gas sensor

Influence of magnetron sputtering process on the stability of WO3 thin film gas sensor

Effective low‐frequency EMI conformal shielding for system‐in‐package (SiP) modules

AbstractThis letter presents several low‐frequency electromagnetic interference shielding solutions by using the conformal shielding technology with the sputtering process. The shielding effectiveness (SE) is verified by the near‐field test method with a transmission line (TL) as the radiating source. On the basis of the test condition and scenario, the TL‐based modeling method is applied to quickly predict the SE performance. Detailed measurement environment, setup, and procedures are also thoroughly introduced in this letter. Four copper (Cu) solutions with 5, 10, 20, and 30 μm shielding thicknesses and two hybrid copper/nickel‐iron (Cu/NiFe) solutions with 5/5 and 13/5 μm shielding thicknesses are tested. Among these solutions, a minimum of 15 dB and a maximum of 35 dB of measured SE at 10 MHz are seen. Moreover, the simulated and measured SE results are in good agreement. It is also noticed that the hybrid Cu/NiFe solution provides a comparable SE performance with a thinner thickness compared with the pure Cu solution.

Hybrid Wetting Surface with Plasmonic Alloy Nanocomposites for Sensitive SERS Detection.

In this paper, a hybrid wetting surface (HWS) with Au/Ag alloy nanocomposites was proposed for rapid, cost-effective, stable and sensitive SERS application. This surface was fabricated in a large area by facile electrospinning, plasma etching and photomask-assisted sputtering processes. The high-density 'hot spots' and rough surface from plasmonic alloy nanocomposites promoted the significant enhancement of the electromagnetic field. Meanwhile, the condensation effects induced by HWS further improved the density of target analytes at the SERS active area. Thus, the SERS signals increased ~4 orders of magnitude compared to the normal SERS substrate. In addition, the reproducibility, uniformity, as well as thermal performance of HWS were also examined by comparative experiments, indicating their high reliability, portability and practicability for on-site tests. The efficient results suggested that this smart surface had great potential to evolve as a platform for advanced sensor-based applications.

A niobium pentoxide waveguide sensor for on-chip mid-infrared absorption spectroscopic methane measurement

The advantages of integrating infrared (IR) waveguide gas sensors on a chip include compactness, low power consumption, and high selectivity. Mid-IR waveguide sensors could be made of a variety of metal oxides with merits of low cost, high stability, transparency in the visible-IR spectrum, and non-toxicity. However, because most metal oxides have low refractive index, they are rarely used as waveguide core materials. To overcome this limitation, we chose niobium pentoxide (Nb2O5), a transparent material with high refractive index in the 0.35–10 µm wavelength range, as the core layer. We fabricated a Nb2O5 rectangular waveguide gas sensor using magnetron sputtering and lift-off process. The Nb2O5 waveguide with an external confinement factor of 11.5% was used for on-chip methane measurement at 3.291 µm based on wavelength modulation spectroscopy. A detection limit of 348 parts per million was achieved with an optimal averaging time of 61.2 s for a 2 cm long waveguide. The reported Nb2O5 waveguide gas sensor not only broadens the waveguide sensor core material family from silicon, chalcogenide (ChG) glass to metal oxides, but also provides detailed preparation and characterization methods for such kind of waveguide device.

Secondary ion mass spectrometry quantification of boron distribution in an array of silicon nanowires

The development of non-planar structures such as arrays of nanowires (NWs), poses a significant challenge for dopant concentration determination. Techniques that can be readily used for 3D structures usually lack the desired sensitivity whereas secondary ion mass spectrometry (SIMS), known for its excellent detection limits, is designed to analyze flat samples. In this work, we overcome the limitation of standard SIMS approaches. NWs are covered with photoresist forming a flat surface. For high incident angle bombardment, the sputtering process becomes self-flattening, i.e. the ions collide with the sidewalls of the exposed tips of NWs at much lower angles and sputter them significantly faster. Thus, reliable information about the dopant distribution along the height of NWs can be obtained. The SIMS analysis can be performed on an array of 1000 x 1000 nanowires with a detection limit of about 5 x 1016 atoms/cm3 and a reasonable signal-to-noise ratio of about 10 dB.

Physicochemical model for reactive sputtering of a sandwich target

A non-isothermal physicochemical model of reactive sputtering is extended in this work. The new version is used in this work to simulate reactive sputtering of a sandwich target with two plates of different metals located on the same axis. The external plate contains cut-outs through which the internal plate is sputtered. The main independent process parameters are the reactive gas flow introduced into the vacuum chamber, the discharge current density, and the total area of cut-outs in the external plate. The physical model of the process is described by a system containing 14 algebraic equations. Only its numerical solution is possible, which allows studying the sputtering process in detail. The model can be used to estimate the conditions that ensure the deposition of a compound film in a real technological process. The model was used to analyze sputtering of a target with internal titanium and external tantalum plates in oxygen. Application of the model in particular cases of sputtering of single targets showed that it is adequate.

MODELING AND SIMULATION OF MAGNETRON-SPUTTERRED NiTi THIN FILM DEPOSITION BY SRIM/TRIM

Nickel-Titanium (Ni-Ti) thin films have gained a lot of attention due to their unique features, such as the shape memory effect. Micro-actuators, micro-valve, micro-fluid pumps, bio-medical applications, and electronic applications have a lot of interest in these smart thin films. Sputter-deposited NiTi thin films have shown the potential to be very useful as a powerful actuator in micro-electro-mechanical systems (MEMS) because of their large recovery forces and high recoverable strains. Despite the advancement of improved deposition methods for the NiTi thin films, there are still certain unsolved challenges that impede accurate composition control throughout the deposition process. Many applications, spanning from the aerospace industries to a range of nanotechnologies, require knowledge of the sputtering characteristics of the materials that are subjected to bombardment, ejection, and deposition of ions. In recent decades, atomic scale modeling has been given a high emphasis in ion sputtering research, providing an adequate and precise description of collision cascades in solids using the Stopping and Range of Ions in Matter (SRIM) and Transport of Ions in Matter (TRIM). In this paper, SRIM is used to address how the heavy ions interact with the target materials. A variety of ion-solid interaction characteristics, including the sputter yield, have been determined by simulating collision cascades in the solids. On the other hand, TRIM was used to describe the range of ions that enter into the matter and cause damage to the target throughout the process. The simulation was carried out to compare the sputtering yield of Ni and Ti by varying the energy input (from 300[Formula: see text]V to 1300[Formula: see text]V). SRIM simulation was conducted by varying the thickness of the film, the angle of incidence of ions, and the energy involved in the sputtering process. The characterization of the films has been carried out using Field Emission Scanning Electron Microscopy (FESEM) to comprehend the surface and interface morphologies of the films and to validate the simulated results. With an increase in energy input (target voltage), the sputtering yield increased. The sputtering yield of the Ni target was higher than the Ti target indicating that Ni can be removed relatively easier than Ti.

Sputtering of micro-carbon-silver film (μC-Ag) for endotracheal tubes to mitigate respiratory infections

Polyurethane (PU) substrates are biocompatible materials widely used to manufacture endotracheal tubes. However, in common with other biomedical materials, they are liable to the formation of microbial films. The occurrence of pneumonia in intubated patients treated at intensive care units often takes the form of ventilator-associated pneumonia (VAP). The issue relates to the translocation of pathogenic microorganisms that colonize the oropharyngeal mucosa, dental plaque, stomach, and sinuses. New protective materials can provide a more effective therapeutic approach to mitigating bacterial films. This work concerns microcrystalline carbon film containing dispersed silver nanoparticles (μC-Ag) deposited on PU substrates using a physical vapor deposition sputtering process. For the first time, carbon paper was used to produce a carbon target with holes exposing a silver disk positioned under the carbon paper, forming a single target for use in the sputtering system. The silver nanoparticles were well distributed in the carbon film. The adherence characteristics of the μC-Ag film were evaluated using a tape test technique, and electron dispersive x-ray mapping was performed to analyze the residual particles after the tape test. The microbicidal effect of the thin film was also investigated using species S. aureus, a pathogenic microorganism responsible for most infections of the lower respiratory tract involving VAP and ventilator-associated tracheobronchitis (VAT). The results demonstrated that μC-Ag films on PU substrates are promising materials for mitigating pathogenic microorganisms on endotracheal tubes.

Synthesis of CuO thin films by a direct current reactive sputtering process for CO gas sensing application

A direct current magnetron reactive sputtering, one of the well-known physical vapour deposition (PVD) techniques, was employed for the preparation of CuO thin films at room temperature for CO gas sensing application. The effect of the O2 gas flow ratio on the phase formation of copper oxide was studied by varying the O2 flow rate in the total flow of Ar/O2 gas mixture. Cu2O phase was found to form at a low O2 flow ratio of 10% and gradually converted into stable CuO phase with an increase in O2 flow ratio through the intermediate phase of Cu4O3. The films exhibited a granular morphology, and the average grain size increased with an increase in the O2 partial flow. Single-phase CuO thin film has been obtained with 40% of O2 gas flow ratio. The evolution of the copper oxide phases with increasing O2 partial flow was also confirmed using the Cu 2p and O 1s core-levels of X-ray photoelectron spectroscopy. The CO gas sensing characteristics of the CuO thin film were examined by varying the operating temperature in the range of 200 °C–400 °C. An optimized CO sensing response of 127% has been obtained at 375 °C towards 91 ppm concentration with a response/recovery time of 161 s/99 s.

Report on the 171st Seminar of Sputtering and Plasma Processes Division

Report on the 171st Seminar of Sputtering and Plasma Processes Division

Coupling effects of W alloying with preparation temperature on microstructures and irradiation tolerance of nanostructured Cu films

Grain size is a critical factor determining materials properties but is challenging to be quantitatively controlled especially in nanoscale. Here, we found the average grain size of pure Cu film can be enhanced from 23 to 557 nm with the preparation temperature increasing from 298 to 773 K during magnetron sputtering. The temperature effect is weakened after W addition to Cu matrix and the grain size of Cu96W4 samples just exhibits slight increase from 30 to 145 nm. The coupling effect of W alloying with temperature is related to the decreased diffusion of Cu atoms after W addition during magnetron sputtering process. Cu–W supersaturated solid solution is formed at low temperatures (below 773 K for Cu96W4 or 573 K for Cu94W6) but W atoms could be agglomerated at elevated temperatures. Moreover, after He ions irradiation at 673 K, fewer and smaller cavities are formed in Cu96W4 samples compared to pure Cu, indicating that W addition could significantly enhance irradiation tolerance.

Physics-separating artificial neural networks for predicting initial stages of Al sputtering and thin film deposition in Ar plasma discharges

Simulations of Al thin film sputter depositions rely on accurate plasma and surface interaction models. Establishing the latter commonly requires a higher level of abstraction and means to dismiss the fundamental atomic fidelity. Previous works on sputtering processes addressed this issue by establishing machine learning surrogate models, which include a basic surface state (i.e. stoichiometry) as static input. In this work, an evolving surface state and defect structure are introduced to jointly describe sputtering and growth with physics-separating artificial neural networks. The data describing the plasma–surface interactions (PSIs) stem from hybrid reactive molecular dynamics/time-stamped force bias Monte Carlo simulations of Al neutrals and Ar+ ions impinging onto Al(001) surfaces. It is demonstrated that the fundamental processes are comprehensively described by taking the surface state as well as defect structure into account. Hence, a machine learning PSI surrogate model is established that resolves the inherent kinetics with high physical fidelity. The resulting model is not restricted to input from modeling and simulation, but may similarly be applied to experimental input data.

Gradient Variation Oxygen-Content Vanadium-Oxygen Composite Films with Enhanced Crystallinity and Excellent Durability for Smart Windows.

Vanadium dioxide (VO2)-based smart windows show excellent promise for energy-saving and have been extensively researched. However, for the glass industry-compatible magnetron sputtering process, VO2 films are difficult to obtain and have homogeneous crystalline state, leaving them lacking the ideal solar modulation (ΔTsol) and sensitivity (narrow hysteresis loop). More importantly, the instability of VO2 hinders its commercialization. Multilayer structures have been repeatedly investigated to solve these problems. Unfortunately, the mediocre thermochromic properties as well as the complex and expensive manufacturing steps still hinder its commercialization. In this work, we prepared gradient variation oxygen-content vanadium-oxygen composite films (V2O3/VO2/V2O5, VOgv) with enhanced crystallinity and excellent durability by one-step continuous sputtering. According to optical measurements, the ΔTsol of the VOgv films was significantly increased by 145% (from 6.85 to 16.80%) compared to VO2 films, and the width of the hysteresis loop was reduced by 67% (from 19.34 to 6.36 °C), while the VOgv films exhibited a wider preparation window. The accelerated tests have shown that the film has an equivalent service life of approximately 20 years. We exploited the intrinsic similarity in properties of homologous compounds of vanadium oxide and simplified the preparation process, which is supposed to break the existing application bottlenecks and increase the commercializing possibility of VO2-based thermochromic smart windows.

Materials Based on Amorphous Al2O3 and Composite W-Al2O3 for Solar Coatings Deposited by High-Rate Sputter Processes

In parabolic trough technology, the development of thermally and structurally stable solar coatings plays a key role in determining the efficiency, durability, and economic feasibility of tube receivers. A cermet-based solar coating is typically constituted by a thin film stratification, where a multilayer graded cermet is placed between an infrared metallic reflector and an antireflection filter. This work reports the realization of materials based on Al2O3 and W characterized by high structural and chemical stability in vacuum at high temperature, obtained through the optimization of high-deposition-rate processes. Al2O3 material, employed as the antireflection layer, was deposited through a reactive magnetron sputtering process at a high deposition rate. Cermet materials based on W-Al2O3 were deposited and employed as absorber layers by implementing reactive magnetron co-sputtering processes. An investigation into the stability of the realized samples was carried out by means of several material characterization methods before and after the annealing process in vacuum (1 × 10−3 Pa) at high temperature (620 °C). The structural properties of the samples were evaluated using Raman spectroscopy and XRD measurements, revealing a negligible presence of oxides that can compromise the structural stability. Spectrophotometric analysis showed little variations between the deposited and annealed samples, clearly indicating the high structural stability.

Basic Characterization and Sputtering Processing of Diatom‐Based Anode Materials

AbstractSilicon‐based anode materials are advantageous because of its high specific capacity, rich resources and appropriate lithium deintercalation potential. However, it is also limited by some disadvantages including large volume expension, poor electronic conductivity and low Initial Coulomb Efficiency(ICE). Benefitting from the original hierarchical porous structure of diatom and amorphous framework of SiO2, we explore the diatoms cultured on a large scale as the anode materials of lithium batteries. Herein, we obtain a suitable diatom‐based anode material with particle diameter D50 4.065 μm, BET specific surface area 228.28 m2/g and biomass of carbon approximately 25 %, while it successfully solves the problems of volume expansion and electronic conductivity. Furthermore, after facile sputtering processing, we successfully introduced metallic elements into the diatom‐based anode. The elements include 3.40 % of Al, 0.75 % of Ti, 10.40 % of Ni, etc. The charge‐dischare results show that the introduction of both Al and Ti lead to performance improvement in some extend.