Vacuum Magnetron Sputtering Research Articles

An experimental study on the effect of salt spray testing on the optical properties of solar selective absorber coatings produced with different manufacturing technologies

Solar selective absorber coating (SSAC) is one of the key components of a solar collector, with its optical properties having a significant impact on the collector’s thermal performance. The key parameters characterizing the optical properties of an SSAC are the solar absorptance (absorptance of solar radiation) and the thermal emittance (emittance for long-wave radiation). However, some of high-performing SSACs suffer from some drawbacks, such as lower durability, lower resistance to corrosion and abrasion, which is particularly harmful for SSACs, as, for example, chlorides in the atmosphere have become a main contributor to corrosion in coastal areas with the increasing trend of global warming. In this paper, salt spray tests have been conducted on the SSACs manufactured by three common manufacturing technologies, i.e., the anode oxidation (AO) technology, the vacuum magnetron sputtering (VMS) technology, and the black chromium plating (BCP) technology, over the testing durations of 12 h, 24 h, 36 h, and 48 h, respectively, to examine the effect of the salt spray testing on the optical properties of SSACs manufactured by different manufacturing technologies. The salt spray testing is an accelerated aging testing method for evaluating the SSAC’s resistance to corrosion when it is under an extended exposure to a saline, or salted, spray (fog). The experimental results show that, in general, the SSACs manufactured by the BCP technology have excellent resistance to salt spray (i.e., to corrosion) and those manufactured by the AO technology have only reasonable resistance to corrosion, whereas the SSACs manufactured by the VMS technology have very poor resistance to corrosion. The results also demonstrate that there are noticeable differences in the optical properties of the SSAC samples even manufactured by the same technology but by different manufacturers, with some having significant differences. The causes for the differences have been further examined through the inspection of the physical appearance of the selected SSAC samples and the experimentally measured distributions of the monochromatic reflectance of solar radiation of the samples over the solar spectrum before and after the salt spray testing over different durations.

Effect of tungsten based coating characteristics on microstructure and thermal conductivity of diamond/Cu composites prepared by pressueless infiltration

Tungsten coatings were deposited on diamond particles by vacuum magnetron sputtering. The coated diamond particles were firstly heat treated at different temperatures, and diamond/copper (Cu) composites were fabricated by using a pressureless infiltration method afterwards. The influences of heat treatment on the microstructure and composition of tungsten based coating surface and diamond/copper composites were analysed. Notable differences were found in the microstructure with heating temperatures. Moreover, the tungsten based coating surface contained large quantities of oxidised tungsten, and the phase composition of the coatings varied within the range of tungsten–W2C–WC as the heat treatment temperature increased. The fracture surface morphologies in the copper matrix composites reinforced with diamond particles with coatings were identically characterised with the presence of ductile fracture of matrix accompanied by dissociation of diamond particles from the matrix. The thermal conductivity (TC) and gas tightness behaviours of the diamond/copper composites were also explored. A maximum TC of 768 W m−1 K−1 and a fine gas tightness of 2.5 × 10-10 Pa m3/s were obtained with reinforcement of tungsten-coated diamond particles treated at 800 °C. The value of the interface thermal resistance between copper and diamond particles was also estimated and specifically discussed.

Fe40Co40Se20 Glassy Films Supported on Carbon Fiber Paper as Electrocatalysts in the Oxygen Evolution Reaction

We report a type of transition metal selenide (Fe40Co40Se20) thin films supported on carbon fiber paper (CFP) (Fe40Co40Se20/CFP) and study the effects of the substrate temperature during thin film deposition on the electrocatalytic performance of the films in the oxygen evolution reaction. Fe40Co40Se20/CFP thin films were deposited by vacuum magnetron sputtering at substrate temperatures of 308, 393, and 573 K. In 1 M KOH, the amorphous film deposited at 393 K exhibited better comprehensive electrocatalytic activity and stability than that of the Fe40Co40Se20/CFP thin films deposited under other conditions, achieving a low overpotential of 307 mV at a current density of 10 mA cm−2 and low Tafel slope of 35 mV dec−1. These results reveal that an appropriate substrate temperature during film formation improves the catalytic performance of thin film catalysts to some extent. A combination of low charge resistance and large electrochemically active surface area contributes to the electrocatalytic performance of the Fe40Co40Se20/CFP thin films.

Influence of crystal orientation on the magnetostriction behavior of Fe films formed on MgO single-crystal substrates

Abstract Fe thin films are prepared on MgO substrates of (001), (110), and (111) orientations by ultra-high vacuum magnetron sputtering. The magnetostriction behaviors under rotating magnetic fields are observed by using a cantilever method. The relationship between in-plane magnetic anisotropy and magnetostriction behavior is investigated. An Fe(001)bcc single-crystal film is obtained on MgO(001) substrate. A four-fold symmetry in in-plane magnetic anisotropy is observed for the Fe(001)bcc film, where the easy magnetization directions are parallel to bcc[100] and bcc[010]. An Fe(211)bcc bi-crystalline film is formed on MgO(110) substrate and the film also shows an almost four-fold symmetric magnetic anisotropy. The reason is interpreted to be due to an influence of overlap of magnetic anisotropies of two bcc(211) variants with two effective easy magnetization directions which are obtained by projecting bcc[010] and bcc[001] on the bcc(211) plane. An Fe(110)bcc film is epitaxially grown on MgO(111) substrate with two types of variant with the crystallographic orientation relationships similar to Nishiyama-Wasserman and Kurdjumov-Sachs. The Fe(110) film shows an isotropic in-plane magnetic property due to an influence of the variant structure. Usual sinusoidal waveforms of magnetostriction are observed for the Fe(110) film. On the other hand, waveforms measured for the Fe(001) and the Fe(211) films are deformed from sinusoidal shape under low in-plane rotating magnetic fields and the magnetostriction behaviors are similar between the two films. Rectangular waveforms are observed for the bending parallel to easy magnetization directions, whereas triangular waveforms are recognized for the bending parallel to hard directions. The phenomenon is related to the direction difference between applied magnetic field and magnetization in magnetically unsaturated films with in-plane anisotropies. The magnetostriction behavior is influenced by the symmetry of in-plane magnetic anisotropy.

Technologies of Metallization of Carbon Fabric and the Properties of the Related Carbon Fiber Reinforced Plastics

Two technologies of metallization of carbon ribbons in vacuum deposition and magnetron sputtering setups are considered. Titanium is used as a metallic coating. Carbon fiber reinforced plastic samples with a coupling agent based on aminopropyl triethoxysilane are prepared for comparison. The coupling agent is also applied using the following two technologies: in the first technology, it is applied onto a ribbon and is then dried; in the second technology, it is introduced into the composition of a binder. A LUP carbon ribbon and an epoxy binder are used for investigations. The carbon fiber reinforced plastics for all technologies under study are prepared using vacuum infusion. The increase in the interlayer shear strength is found to be maximal for the metallization of the carbon on a Bulat-6 setup.

Thermo-barrier nanostructure microplasma coatings of ZrO2

This work shows the formation of oxide ceramic coating ZrO2. The coating is formed on a copper substrate in the series of layers. Two different methods are used for deposition of metallic layers: vacuum arc deposition (PVD) and magnetron sputtering. The last metal layer is converted into oxide by microplasma oxidation. As a result, microplasma nanostructured coating is formed on the surface. Morphology and elemental composition of these coatings are investigated by means of a scanning electron microscope with attachment for element analysis. Thermocyclic stability of coatings is determined. Thermal cycling tests for the coatings have demonstrated promising results of lifetimes more than 1000 cycles.

Magnetic hardening of Nd-Ce-Fe-B films with high Ce concentration

Partial substitution of Ce in Nd-Fe-B magnets is a feasible way to cope with the crisis of Nd and Dy in Nd-Fe-B production and reduce the cost of Nd-Fe-B magnets. In the present paper, the Nd-Ce-Fe-B films with high performance have been successfully fabricated by using an ultra-high vacuum (UHV) magnetron sputtering system. High magnetic performance with a ceorcivity of 13.3 kOe, a remanence of 11.4 kGs and a maximum energy product of 29.4 GMOe is obtained with the Ce substitution for more than 50 wt.% Nd without Dy addition. The high coercivity and (BH)max achieved in this work are much larger than those of previously reported Nd-Ce-Fe-B magnets with the same Ce concentration. The phase structure, microstructure and coercivity mechanism are analyzed. The coercivity mechanism is determined to be mainly dominated by nucleation. Based on the microstructure observation and coercivity mechanism analysis, the fine and well separated grains, smooth grain surface, small and less inhomogeneities should be responsible for the high coercivity. Our results encourage the further improvement of magnetic properties in Ce magnets including the bulk material with high Ce concentration.

Ni deposited onto MWCNTs buckypapers for improved broadband EMI shielding

Highly flexible, mechanically robust and ultra-thin Ni deposited onto multi-walled carbon nanotubes (MWCNTs) buckypapers (BPs) were fabricated via vacuum filtration and magnetron sputtering. The samples were characterized structurally using scanning electron microscopy and X-ray Diffraction. Electromagnetic interference (EMI) shielding effectiveness (SE) of Ni deposited onto MWCNTs BPs with different deposition time (0, 30 and 60 min) were tested in frequency range of 2–18 GHz, including S-band, C-band, X-band and Ku-band. The 60 min Ni deposited onto MWCNTs BPs exhibited much higher EMI SE of average value up to 42.59 dB with the thickness of only 0.105 mm. Based on reliability study, the 60 min Ni deposited onto MWCNTs BPs retains 94.3% of its EMI SE after 500 cycles of mechanical bending. Therefore, the results and techniques promise a simple and effective approach to achieve light-weight and ultra-thin composite films for a wide application at the prospect of the field of EMI shielding.

The magnetic properties of CoFeB and CoFeB/Ag nanodot arrays fabricated by a template transfer imprinting method

In this study, a practical method for fabricating size-tunable and periodic CoFeB and CoFeB/Ag nanodot arrays on glass substrate was developed using a template transfer imprinting method, which consisted of nanoimprint lithography and vacuum magnetron sputtering. It was found that the coercivity could be distinctly enhanced by introducing periodic CoFeB nanodot arrays. Also, the coercivity of the CoFeB/Ag nanodot arrays could be flexibly tuned over a wide range by tailoring the thickness of the Ag layer, due to the interfacial magneto-electric coupling effect. Investigations such as those conducted in this study will provide promising references for the future fabrications of high performance nanostructured magnetic materials, which can be potentially utilized in many fields.

Specific electric polarizability of copper nanoparticles in the optical range of the spectrum

Work is devoted to a research of dimensional changes in optical properties of nanosized copper particles with sizes less than 10 nm in statistically inhomogeneous systems. Experimental spectral and dimensional dependences of the complex specific electric polarizability of nanosized copper particles with experimental-analytical method are determined in the optical spectral range from 0.2 to 1.1 μm. The values of the complex specific electric polarizability were determined by analytical solution of Rosenberg’s spectrophotometric equations with the use of experimental results of spectrophotometric measurements of transmission and reflection coefficients of copper islet films and the results of electron microscopic studies of their morphological microstructure, taking into account the statistical analysis of the particle size distribution. Nanosized copper particles with a statistically inhomogeneous structure in the system of islet films on quartz substrates were obtained by vacuum-magnetron sputtering. An analysis of function of copper nanoparticles distribution in size in a system with a statistically inhomogeneous structure was carried out using the Pearson’s consensus criterion.To find out the features of optical absorption of nanosized copper particles, their experimental spectral and dimensional dependences of the complex specific electric polarizability are compared with the corresponding characteristics for model particles with properties characteristic for macroscopic volumes of copper. It was found that the optical properties of nanosized copper particles differ from optical properties of copper in a macroscopic volume. An increase in the absolute values of the components of the complex specific electric polarizability of spherical nanosized copper particles with decreasing their diameter within the range from 8 nm to 3.2 nm for wavelengths of 0.2 - 1.1 μm is established.The spectral dependences of optical parameters of nanosized copper particles according to well-known theories of classical and quantum dimensional effects are calculated. In order to study the nature of dimensional dependences of optical parameters of copper nanoparticles, a comparative analysis of calculated and experimental spectral and dimensional dependences of their optical parameters was carried out. It is shown that the experimental dimensional changes in the complex specific electric polarizability of copper particles in the investigated range of sizes not be due to the classical or quantum dimensional effect in the dipole approximation.Ref. 36, fig. 3.

Surface oxidation of as-deposit uranium film characterized by X-ray photoelectron spectroscopy

Uranium film is a main functional component to realize the high efficiency conversion of laser to X-ray in the study on laser inertial confinement fusion. It also has important applications in relevant physics experiments. Due to its active chemical properties, the metal uranium film is extremely difficult to preserve in the atmosphere. A variety of methods may help to avoid the oxidation of uranium film, such as coating protective layer, vacuum or inert atmosphere protection. But under these conditions, the oxidation property of uranium film still needs experimental investigation. In this paper, the oxidation processes of uranium films under different atmospheres are studied by X-ray photoelectron spectroscopy (XPS) and depth profiling. Firstly, uranium films and gold-uranium multilayer films are prepared by ultra-high vacuum magnetron sputtering deposition, and then they are exposed to atmosphere, high purity argon and ultrahigh vacuum for a period of time. Finally, the distributions and valence states of oxygen and uranium elements are investigated by XPS depth profiling. The oxidation mechanism is analyzed according to the oxidation products and the microstructure characteristics of samples. The results show that the oxygen element is undetectable in the initial films. In the Au-U multilayer film, the protective ability of Au layer is greatly weakened by the micro-defects. The defect is not only the micro channel of oxygen entering into the sample directly, but also the origin of the interlaminar cracks at the Au/U interface. In about three weeks, the uranium layer is severely oxidized and large area lamination occurs. The oxidation products consist of a dense oxide thin film on uranium surface and corrosion pitting around the defects, which are mainly UO2. For the pure uranium film, the surface of the film is completely oxidized when it is exposed to high purity argon only for 6 h. The UO2 layers with different thickness values are formed on their surface, which is due to the rapid diffusion of oxygen atoms at the columnar grain boundaries of the film. After the sample is exposed to the ultra-high vacuum for 12 h, UO2 layer with a thickness of less than 1 nm is generated on the surface of the pure uranium film. In the etching of oxide by argon ion beams, the preferential sputtering effect of O is produced, and UO2 is reduced into non-stoichiometric UO2-x. The effect of preferential sputtering is weakened with the decrease of oxide content. When the oxide content is less than 10%, the reduction of UO2 can hardly be detected.

Multiple thermal cycling and phase transitions in Ge-Sb-Te materials

Structural transformations in Ge2Sb2Te5 thin films fabricated by the thermal evaporation in vacuum (TEV) and DC magnetron sputtering (MS) were studied by the differential scanning calorimetry (DSC). Multiple DSC measurements revealed the appearance of reproducible endothermic peaks in all samples in the temperature range of 390–425°C (one for TEV and two for MS films, respectively). Investigations by X-ray diffraction, scanning and transmission electron microscopes were carried out, and the natures of these endothermic peaks were discussed.

Improved interfacial adhesion between TiAlN/DLC multi-layered coatings by controlling the morphology via bias

By combining the advantages of the thermo-mechanical properties of TiAlN and self-lubricating properties of diamond-like carbon (DLC), a multi-layered TiAlN/DLC coating is fabricated by filtered cathodic vacuum arc and magnetron sputtering. According to the different morphology and mismatch between the physical and chemical properties of TiAlN and DLC, multiple methods are used to study the growth mechanism of crystalline TiAlN and amorphous DLC in the combined system. The morphology evolution depending on the bias is studied and the brittle interface is assessed by scratch experiments. The results show that an interlamination failure occurs at the top of first DLC layer due to the cluster morphology obtained by small bias, however, the failure moves to the interface above the substrate when the clusters are refined by increasing bias. By adopting the stepwise decreased bias, the 4.5μm thick TiAlN/DLC multi-layer coating is fabricated and does not exhibit interfacial failure at any interface between TiAlN and DLC in the scratch experiments up to a load of 100N. Excellent adhesion (Lc=63N) is also achieved from coatings deposited on high-speed steel with optimized Cr/CrCx/CrC interlayers prepared by high-power impulse magnetron sputtering.

Post-Annealing Effects on Surface Morphological, Electrical and Optical Properties of Nanostructured Cr-Doped CdO Thin Films

Nanostructured Cr-doped CdO thin films were deposited on glass substrates by reactive direct current magnetron sputtering and post-annealed in vacuum from 200°C to 500°C. X-ray diffraction studies confirmed that the films exhibit cubic nature with preferential orientation along the (111) plane. The crystallite size, lattice parameters, unit cell volume and strain in the films were determined from x-ray diffraction analysis. The surface morphology of the films has been characterized by field emission scanning electron microscopy and atomic force microscopy. The electrical properties of the Cr-doped CdO thin films were measured by using a four-probe method and Hall effect system. The lowest electrical resistivity of 2.20 × 10−4 Ω cm and a maximum optical transmittance of 88% have been obtained for the thin films annealed at 500°C. The optical band gap of the films decreased from 2.77 eV to 2.65 eV with the increase of annealing temperature. The optical constants, packing density and porosity of Cr-doped CdO thin films were also evaluated from the transmittance spectra.

Metallized Nonwoven Electrospun Polyamide-6 Nanofibers for Energy Production and Storage

Nonwoven polymer materials based on polyamide-6 coated with stainless steel that are used as electrodes to produce energy and batteries to store it were investigated. Nanofibers were prepared by capillary-free electrospinning. The metal coating was applied using vacuum magnetron sputtering. Continuous metallized nonwoven material coated with sputtered stainless steel was formed after 4-10 min of magnetron sputtering. The resistance of the metallized nonwoven material was seven orders of magnitude less than that of uncoated material and five orders less than that of heat-treated nonwoven material. It was found that vacuum sputtering of the conducting stainless-steel coating reduced the nanofiber diameter by an average of 1.5 times due to evaporation of residual solvent.

Spin-Valve based magnetoresistive nanoparticle detector for applications in biosensing

A magnetoresistive sensor platform for the detection of individual magnetic reporter particles is presented. The sensing scheme is based on the detection of the shift in the sensor’s magnetoresistance-switching field in the presence of magnetic particle(s). A bottom-pinned spin-valve multilayer (Co/Ru/Co)/Cu/(Co/Ru/Co) device structure (with Ta/Ru seed and Ta capping layers) used for the sensor was deposited using ultra-high vacuum magnetron sputtering and patterned using conventional microfabrication techniques. Inexpensive electronics to measure device magnetoresistance (using DC currents) was used for testing. The detection of individual 500nm Fe3O4 nanoparticles as well as the detection of up to ten (10) nanoparticles was demonstrated and verified using scanning electron microscopy (SEM). The developed sensors are readily integratable into a biosensing platform for the detection of biomolecules at ultra-low concentration using magnetic nanoparticles as reporters.

Influence of chemical composition of electrode material on the differential capacitance characteristics of the ionic liquid | electrode interface

The electrical double layer structure at polycrystalline metal|ionic liquid interface has been studied using cyclic voltammetry, electrochemical impedance spectroscopy and in situ infrared methods. Polycrystalline Bi(PC), Pb(PC), Au(PC) and Pt(PC) electrodes have been prepared using ultra-high vacuum magnetron sputtering method. Noticeable dependence of differential capacitance on the electrode potential has been observed. For all electrodes, a wide well-expressed minimum in capacitance, potential (C, E) curve has been shown. For graphene, C(0001), carbide-derived carbon and Bi(PC) U-shaped curves and for Pb(PC), Au(PC) and Pt(PC) M-shaped C, E curves have been measured. Dependence of the C, E curve shape on the electrode chemical composition has been explained by the different position of the image plane of surface charge, dependent on the electronic characteristics of the electrodes under study.

Nano mechanical and wear properties of multi-layer Ti/TiN coatings deposited on Al 7075 by high-vacuum magnetron sputtering

Super-hard coatings are frequently applied to improve the mechanical properties and abrasive properties of light alloys such as titanium and aluminum. In this work, single-layer TiN and multi-layer Ti/TiN coatings are deposited on Al 7075 by ultra-high vacuum magnetron sputtering and the structure, morphology, and triobological properties are investigated. The impact of the Ti layer on the microstructure, mechanical, and abrasive properties are also studied in details. The coatings containing the single TiN layer and Ti/TiN multi-layer crystal have the (111) and (002) preferred orientations. The hardness values of the single-layer and multi-layer coatings are 45.93 and 35.54, which are about 25 and 19 times larger than that of the substrate, respectively. The coefficients of friction of the multi-layer and single-layer coatings are 0.48 and 0.54, respectively. In the multi-layer coating, the Ti interlayer has smaller shear strength and acts as a lubricant during the abrasion test to reduce the friction. The TiAlNxOy and TiNxOy tribolayers may be formed in the single-layer and multi-layer coatings, respectively and compared with the single-layer coatings, the multilayer ones have better tribological properties.

Formation of biocompatible surface layers depending on the sputtering distance

Nano- and micro-dimensional surface layers of silver and tantalum on flat and wire NiTi substrates by the method of magnetron sputtering in vacuum were produced. The structure and composition of the samples were determined using SEM and Auger spectroscopy. With an increase in the sputtering distance, the thickness of the surface layers decreases, and the thickness of the transition layer and the dependence of the thickness change as a whole depend on the nature of the sputtered substance.

Fabrication of titanium carburizing electrodes for capacitive deionization.

Titanium carburizing electrodes were used as the electrodes in a capacitive deionization (CDI) process for desalination in this study. Two methods of high vacuum magnetron sputtering and chemical deposition were used for the preparation of nano-titanium carburizing electrodes (named Ti-C* and Ti-C**). By comparing the adsorption capacities of different kinds of electrode material, combined with physical and chemical characteristics and electrochemical analysis, the method of high vacuum magnetron sputtering to prepare Ti-C* electrodes have been proved successful for the CDI process. The results show that under the same conditions, the adsorption capacity of Ti-C* and Ti-C**were 9.6 mg/g and 7.12 mg/g, respectively. The Ti-C* electrodes showed a higher ion electrosorption capacity than Ti-C** and the electrodes can be easily regenerated, indicating excellent recyclability. This study provided a novel method to fabricate titanium carburizing electrodes in CDI process and might lead to the improvement of the CDI desalination performance in an industrial practical application.