Pulsed Direct Current Magnetron Sputtering Research Articles

Return of target material ions leads to a reduced hysteresis in reactive high power impulse magnetron sputtering: Experiment

Titanium and aluminum targets have been reactively sputtered in Ar +O2 or Ar +N2 gas mixtures in order to systematically investigate the effect of reduced hysteresis in reactive high power impulse magnetron sputtering (HiPIMS) as compared to other sputtering techniques utilizing low discharge target power density (e.g., direct current or pulsed direct current mid-frequency magnetron sputtering) operated at the same average discharge power. We found that the negative slope of the flow rate of the reactive gas gettered by the sputtered target material as a function of the reactive gas partial pressure is clearly lower in the case of HiPIMS. This results in a lower critical pumping speed, which implies a reduced hysteresis. We argue that the most important effect explaining the observed behavior is covering of the reacted areas of the target by the returning ionized metal, effectively lowering the target coverage at a given partial pressure. This explanation is supported by a calculation using an analytical model of reactive HiPIMS with time and space averaging (developed by us).

Influence of Substrate Temperature and Film Thickness on Thermal, Electrical, and Structural Properties of HPPMS and DC Magnetron Sputtered Ge Thin Films

Ge was deposited as thickness gradient films at temperatures up to 800 °C by direct current (DC) and high power pulsed magnetron sputtering (HPPMS). Structural characterization shows increased crystallization with increasing substrate temperature and film thickness. Thermal conductivity was measured by a novel high‐throughput time‐domain thermo‐reflectance method. Thermo‐electrical properties correlate to the degree of crystallization. Conductivities increase with increasing substrate temperature up to 500 °C. For higher temperatures the trend reverses. A room temperature deposited/annealed film displays smaller crystallites (10 nm) and lower thermal conductivity (5 Wm−1 K−1) compared to 25 Wm−1 K−1 for hot DC deposition. Compared to DC, HPPMS films show higher thermal conductivities up to 45 Wm−1 K−1.

Recent Developments in Accelerated Antibacterial Inactivation on 2D Cu-Titania Surfaces under Indoor Visible Light

This review focuses on Cu/TiO2 sequentially sputtered and Cu-TiO2 co-sputtered catalytic/photocatalytic surfaces that lead to bacterial inactivation, discussing their stability, synthesis, adhesion, and antibacterial kinetics. The intervention of TiO2, Cu, and the synergic effect of Cu and TiO2 on films prepared by a colloidal sol-gel method leading to bacterial inactivation is reviewed. Processes in aerobic and anaerobic media leading to bacterial loss of viability in multidrug resistant (MDR) pathogens, Gram-negative, and Gram-positive bacteria are described. Insight is provided for the interfacial charge transfer mechanism under solar irradiation occurring between TiO2 and Cu. Surface properties of 2D TiO2/Cu and TiO2-Cu films are correlated with the bacterial inactivation kinetics in dark and under light conditions. The intervention of these antibacterial sputtered surfaces in health-care facilities, leading to Methicillin-resistant Staphylococcus Aureus (MRSA)-isolates inactivation, is described in dark and under actinic light conditions. The synergic intervention of the Cu and TiO2 films leading to bacterial inactivation prepared by direct current magnetron sputtering (DCMS), pulsed direct current magnetron sputtering (DCMSP), and high power impulse magnetron sputtering (HIPIMS) is reported in a detailed manner.

Low temperature pulsed direct current magnetron sputtering technique for single phase β-In2S3 buffer layers for solar cell applications

This work explores the possibilities of using the pulsed direct current (dc) magnetron sputtering (PDCMS) process to deposit an alternative to the cadmium sulphide buffer layer in copper indium gallium diselenide – based solar cells. The main problems with the CdS layer are its toxic nature and its deposition using a chemical bath technique. These factors make it difficult to incorporate into in-line production and significant effort has been expended to find a suitable alternative buffer layer with in-line manufacturing capability. Towards this aim, the material properties of an In2S3 film, sputtered from a powder target, have been investigated. Films were deposited at different substrate temperatures ranging from “no additional substrate heating” to 250°C. The deposition of a single phase β-In2S3 without substrate heating/annealing has not previously been reported. The films deposited by the ion-enhanced PdcMS technique without any additional heating were found to be single phase. The grain size increased with increase in substrate temperature. However, this led to a decrease in the sulphur content; as a result the band gap decreased. For solar cell applications, the CdS buffer layer (optical band gap ∼2.4eV) needs to be replaced with a material which has a band gap wider than 2.4eV for improved performance and reduction of absorption loss in the blue wavelength region. Ideally the band gap should be between 2.6 and 3.0eV. Our PdcMS room temperature deposited In2S3 had a measured band gap of 2.77eV.

Superhydrophobic photocatalytic PTFE – Titania coatings deposited by reactive pDC magnetron sputtering from a blended powder target

The production of photocatalytic coatings with superhydrophobic properties, as opposed to the conventional hydrophilic properties, is desirable for the prevention of adhesion of contaminants to photocatalytic surfaces with subsequent deterioration of photocatalytic properties. In this work polytetrafluoroethylene (PTFE) – TiO2 composite thin films were deposited using a novel method of reactive pulsed direct current (pDC) magnetron sputtering of a blended PTFE – titanium oxide powder target. The surface characteristics and photocatalytic properties of the deposited composite coatings were studied. The as-deposited coatings were annealed at 523 K in air and analysed with Raman spectroscopy, optical profilometry and scanning electron microscopy. Hydrophobicity was assessed though measurements of water contact angles, and photocatalytic properties were studied via methylene blue dye degradation under UV irradiation. It was found that variations of gas flow and, hence, process pressures allowed deposition of samples combining superhydrophobicity with stable photocatalytic efficiency under UV light irradiation. Reversible wettability behaviour was observed with the alternation of light-dark cycles.

The multi-functional stack design of a molybdenum back contact prepared by pulsed DC magnetron sputtering

The purpose of this work is to study the effect of deposition parameters on the properties of molybdenum (Mo) films based on direct-current (DC) pulsed magnetron sputtering and to develop a suitable Mo back contact structure with the requisite properties for Cu(In, Ga)Se2 (CIGS) thin films fabricated by post-selenization of electrodeposited Cu/In/Ga stack precursors. The electrical, microstructural and stress properties of the Mo films were investigated as a function of two deposition parameters: the working pressure and film thickness. First, the resistivity of the Mo films decreased with decreasing working pressure or increasing film thickness. Second, the films deposited at higher pressures with porous microstructures are under compressive stress, whereas those films deposited at lower pressures with densely packed networks are under tensile stress. Third, the films deposited at low pressure beyond a certain thickness exhibit tensile stress cracks. Given the above results, a multi-functional stack of Mo films was introduced as the back contact. In this process, it was determined that a bilayer Mo back contact with opposing stress contributions could simultaneously eliminate surface flaws and achieve low resistivity; however, electrodeposition of Cu/In/Ga stack precursors from a chemical solution onto the Mo layer failed and the Mo film fell off the substrate during the high temperature selenization process. To improve adhesion at the interface, the surface and bottom of the bilayer Mo stack were designed to contain different Mo functional structures and a four-layer Mo back contact was created for post-selenized CIGS thin film.

The investigation of band gap and N chemical bond structure of N–TiO2 film prepared by N ion beam implantation

Titanium dioxide (TiO2) film was deposited by the direct current pulse magnetron sputtering technique. Then the surface of TiO2 film was implanted by the N ion beam at room temperature. Through this way, N-doped TiO2 (N–TiO2) film was obtained and the band gap of N–TiO2 film was decreased to 2.97 eV. XPS result revealed that N ion was doped into TiO2 film as Ti–N and Ti–NO bonds. N ion was substitutionally/interstitially doped into TiO2 crystal lattice and Ti–N bond was formed. N ion was doped into amorphous TiO2 and Ti–ON bond was formed. The polycrystal TiO2 film could result in that more N ion was substitutionally/interstitially doped into TiO2 crystal lattice, which could effectively narrow the band gap of N–TiO2 film. This work provides a potential N doping method which could be applied commercially.

(Cr,Al)N/(Cr,Al)ON Oxy-nitride Coatings deposited by Hybrid dcMS/HPPMS for Plastics Processing Applications

In plastics industry injection molding and extrusion tools are subjected to adhesive and abrasive wear by the flowing hot melt during extrusion process and adhering solidified melt. Due to their beneficial properties, Cr-based nitride hard coatings deposited by physical vapor deposition (PVD) are applied as protective coatings. In this regard, especially Cr-based oxy-nitride coatings with increased oxygen contents have a high potential to be used on plastic processing tools. In the presented work, five different oxy-nitride monolayer and bilayer coatings (Cr,Al)N/(Cr,Al)ON were synthesized on tool steel substrate AISI 420 (X42Cr13, 1.2083) by means of a hybrid direct current and high power pulsed magnetron sputtering (dcMS/HPPMS) process. Further, the coating architecture was varied in order to compare oxy-nitride monolayers with nitride coatings comprised of thin oxy-nitride top layers. All coatings were investigated with regard to their coating properties and, as defined by the corresponding coating/substrate interactions, with regard to their compound properties. The interactions between the coatings and Makrolon® 2408 polycarbonate (PC2408) were also characterized by means of high temperature contact angle and adhesive tensile strength measurements. Complementary, in-depth chemical analysis of the surface oxide regions of the coatings by means of X-ray photoelectron spectroscopy (XPS) was performed and revealed that the surface oxide composition is primarily determined by the oxygen concentration in the coating bulk. Further, this resulted into high contact angles of the polycarbonate melt, which is desirable for injection molding. All coated samples exhibited a better demolding behavior of the solidified plastic melt as compared to uncoated AISI 420.

On the plastic deformation of chromium-based nitride hard coatings deposited by hybrid dcMS/HPPMS: A fundamental study using nanoscratch test

Tribological behavior and elastic-plastic deformation of hard coatings deposited by physical vapor deposition (PVD) under normal and lateral loads can be investigated using innovative nanoscratch tests. However, a comprehensive study of thin PVD coatings requires a precise insight into mechanisms of the observed plastic deformation. Nanoscratch analyses on nanostructured PVD hard coatings and investigations of the mechanisms of resulted plastic deformation are the subjects of current research. In the presented work, two coatings CrN and (Cr,Al)N deposited on quenched and tempered AISI 420 steel substrate were investigated. The coatings were synthesized using a hybrid technology, consisting of direct current and high power pulse magnetron sputtering dcMS/HPPMS. Nanoscratch tests were performed with constant normal loads applying Berkovich and conical indenters. Despite significant hardness, these coatings deformed plastically under applied forces. Plastic deformation of the coatings was investigated by means of confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were applied to explore the mechanism of plastic deformation of the investigated coatings. Based on the results of CLSM and SEM, (Cr,Al)N exhibited a higher resistance against plastic deformation compared to CrN. The TEM investigations furthermore revealed that neither micro-crack formation nor dislocation motion inside the individual grains led to the observed plastic deformation. The dominating mechanism of the plastic deformation of investigated coatings is explained by sliding of grain boundaries (GBS) as the main reason.

An experimental investigation on the machining characteristics of Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills

We report the machining characteristics and machinability of a nickel based superalloy in this study. A micro-milling operation is loaded on Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills. A full factorial design of experiments was devised to optimize the machining conditions to reduce the flank wear on the tool surface. The optimized machining conditions for uncoated micro-tools were found to be a cutting speed (vc) of 13m/min and a feed rate (fz) of 6mm/min. Following this, the tools were coated with TiAlN using a semi-industrial four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. Further experiments were then performed using these optimized machining conditions using both uncoated and TiAlN coated micro-tools in order to ascertain the tool wear and surface integrity. The change in geometry of the machined slot was estimated based on the variation in tool radius of the micro-end mill with progression of the operation. A direct comparison was made between the results observed using both uncoated and TiAlN coated tungsten carbide to illustrate the effect of the nanocomposite TiAlN coating. It was seen that TiAlN coated micro-tools exhibited a superior performance as compared to the uncoated ones with respect to tool life and micro-burr formation.

The properties of chromium oxide coatings on NdFeB magnets by magnetron sputtering with ion beam assisted deposition

The coatings of Cr2O3 were deposited on sintered NdFeB magnets by direct current (DC) pulse magnetron sputtering with and without ion beam at different O2 pressures. The coatings were compact and had a thickness of 1.8–2.2 μm. The coatings achieved a hardness up to 29 GPa and a wear rate of 1.78 × 10−7 mm3/Nm when ion-beam-assisted-deposition (IBAD) was used. Excellent anti-corrosion properties were obtained in the coating prepared by IBAD while the good magnetic properties of NdFeB substrate were retained. Electrochemical measurements revealed that the corrosion current density of the sample decreased from 4.66 × 10−6 A/cm2 (bare NdFeB) to 2.87 × 10−7 A/cm2 when O2 flux was 17 sccm during IBAD process.

Pulsed-Plasma Physical Vapor Deposition Approach Toward the Facile Synthesis of Multilayer and Monolayer Graphene for Anticoagulation Applications.

We demonstrate the growth of multilayer and single-layer graphene on copper foil using bipolar pulsed direct current (DC) magnetron sputtering of a graphite target in pure argon atmosphere. Single-layer graphene (SG) and few-layer graphene (FLG) films are deposited at temperatures ranging from 700 °C to 920 °C within <30 min. We find that the deposition and post-deposition annealing temperatures influence the layer thickness and quality of the graphene films formed. The films were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and optical transmission spectroscopy techniques. Based on the above studies, a diffusion-controlled mechanism was proposed for the graphene growth. A single-step whole blood assay was used to investigate the anticoagulant activity of graphene surfaces. Platelet adhesion, activation, and morphological changes on the graphene/glass surfaces, compared to bare glass, were analyzed using fluorescence microscopy and SEM techniques. We have found significant suppression of the platelet adhesion, activation, and aggregation on the graphene-covered surfaces, compared to the bare glass, indicating the anticoagulant activity of the deposited graphene films. Our production technique represents an industrially relevant method for the growth of SG and FLG for various applications including the biomedical field.

Low-temperature synthesis of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering

Thermochromic (TC) vanadium dioxide thin films provide means for controlling solar energy throughput and can be used for energy-saving applications such as smart windows. One of the factors limiting the deployment of VO2 films in TC devices is the growth temperature τs. At present, temperatures in excess of 450°C are required, which clearly can be an impediment especially for temperature-sensitive substrates. Here we address the issue of high τs by synthesizing VO2 thin films from highly ionized fluxes of depositing species generated in high power impulse magnetron sputtering (HiPIMS) discharges. The use of ions facilitates low-temperature film growth because the energy of the depositing species can be readily manipulated by substrate bias. For comparison, films were also synthesized by pulsed direct current magnetron sputtering. Structural and optical characterization of VO2 thin films on ITO-coated glass substrates confirms previous results that HiPIMS allows τs to be reduced from ~500 to ~300°C. Importantly, we demonstrated that HiPIMS permits the composition and TC response of the films to be tuned by altering the energy of the deposition flux via substrate bias. An optimum ion energy of 100eV was identified, which points at a potential for further reduction of τs thereby opening new possibilities for industrially-relevant applications of VO2-based TC thin films. Weak TC activity was observed even at τs≈200°C in HiPIMS-produced films.

Simulation, fabrication, and application of transparent conductive Mo-doped ZnO film in a solar cell

In this study, Mo-doped ZnO (MZO) films were investigated using first-principles calculations based on density functional theory and magnetron sputtering technology. The theoretical results predicted that after Mo was incorporated into ZnO, the MZO film would present n-type metallic properties and the optical band gap would widen, which predicts that MZO films possess favorable electrical and optical properties. An MZO film with high conductivity and a wide spectral range was fabricated at various substrate temperatures (TS) using pulsed direct-current magnetron sputtering. From 400 to 1200nm, a lower resistivity of 7.68×10−4Ωcm and a higher average transmittance (exceeding 80%) were observed when the MZO film was deposited at the optimal TS of 280°C. Thin-film solar cells consisting of hydrogenated microcrystalline silicon germanium fabricated on textured MZO films demonstrated a strong enhancement of 7.24% in the conversion efficiency because of their improved short-circuit current density (Jsc) and open-circuit voltage (Voc) compared with a commercial Al-doped ZnO film applied to a reference solar cell.

Optical and electrical properties of ITO thin films sputtered on flexible FEP substrate as passive thermal control system for space applications

ITO thin films were deposited on flexible fluorinated ethylene propylene (FEP) substrates by pulsed direct current reactive magnetron sputtering system using an In:Sn (90%–10% wt.) alloy target. The influence of the deposition parameters (argon and oxygen flow rates, and substrate temperature) and effect of coating thickness on the optical, electrical, structural and microstructural properties of ITO thin films deposited on FEP was investigated. The thickness of the ITO coatings was varied from 5 to 180nm. The optimized ITO coating (10nm thick) exhibited high IR emittance (79%) on FEP substrate with high average solar transmittance (94.0%) and moderate sheet resistance (3kΩ/sq.). We also investigated in detail the angular dependence of reflectance as well as haze factor of thin ITO coatings. Our results suggest that 10nm thick ITO coating exhibits an average haze factor of 8.6%. The high value of IR emittance, moderate sheet resistance and high solar transmittance along with low haze factor indicate the suitability of ITO thin films on FEP substrates as flexible optical solar reflector for space applications.

Piezoresistive properties of diamond like carbon films containing copper

In the present study diamond like carbon films containing copper (DLC:Cu) were deposited by reactive magnetron sputtering. Direct current (DC) sputtering and high power pulsed magnetron sputtering (HIPIMS) were used. The influence of the composition and structure on piezoresistive properties of DLC:Cu films was investigated. Structure of DLC:Cu films was investigated by Raman scattering spectroscopy and transmission electron microscopy (TEM). Chemical composition of the films was studied by using energy-dispersive X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). Particularly analysis of XPS O1s spectra revealed oxidation of Cu nanoparticles. Piezoresistive gauge factor of DLC:Cu films was in 3–6 range and decreased with the increase of copper atomic concentration. Tendency of the decrease of the gauge factor of DLC:Cu films with the increased D/G peak area ratio (decreased sp3/sp2 carbon bond ratio) was observed. It was found that resistance (R) of DLC:Cu films decreased with the increase of Cu atomic concentration by logarithmic law. It is shown that a quasilinear increase of piezoresistive gauge factor with log(R) is in good accordance with percolation theory. Temperature coefficient of resistance (TCR) of DLC:Cu films was negative and decreased with copper amount in Cu atomic concentrations ranging up to ~40%. Very low TCR values (zero TCR) were observed only for DLC:Cu films with low gauge factor that was close to the gauge factor of the metallic strain gauges. Role of some possible mechanisms: copper amount as well as Cu cluster size on the value of gauge factor is discussed.

Influence of discharge power and annealing temperature on the properties of indium tin oxide thin films prepared by pulsed-DC magnetron sputtering

Indium tin oxide (ITO) films, prepared by a pulsed direct current magnetron sputtering system, are investigated at powers from 0.4 to 2.0 kW (power density in the range 0.8–4.1 W/cm2). It is found that the carrier concentration and crystallinity of the ITO films increase with increasing discharge power, while the electron mobility decreases from 49.2 cm2/Vs at 0.4 kW to 30.3 cm2/Vs at 2.0 kW. X-ray photoelectron spectroscopy measurements demonstrate that the ITO films prepared at high powers have more oxygen deficient and Sn4+ bonding states. These two types of bonding states are most relevant to the oxygen vacancies and substitutional tin atoms, which are the dominant electron donors in ITO. This observation explains why highly conductive ITO films are achieved at high deposition powers. Besides the investigation of the as-deposited ITO properties, annealing induced changes are explored in air ambient. The ITO properties are maintained for most of the samples when annealed at 150 °C, while degraded ITO properties are observed when annealed at 200 °C, especially for films grown at low powers. The annealing induced changes are most probably related to changes of the film crystallinity. A clear improvement of the crystallinity is observed for low power deposited ITO films after annealing at 200 °C for 240 min.

Deposition and characterization of AlN thin films on ceramic electric insulators using pulsed DC magnetron sputtering

Abstract Porcelain electric insulators are fundamental support devices to act as holders for transmission lines. The exposition to pollutants environments such as industrial areas, deserts and sea air, containing carbon, sand and salt are examples that can reduce the devices dielectric property. The present investigation aims to develop and characterize hydrophobic aluminum nitride thin films, deposited on porcelain insulators surfaces, using a pulsed direct current magnetron sputtering (PDMS). An aluminum target with 99.999% purity was used as precursor and nitrogen 99.999% purity was employed. The film characterization was performed using AFM, FEG and FTIR. The surface resistivity was evaluated by four-point probe method. Different deposition times lead to different wettability characteristics, verified by the sessile drop method using a goniometer. The experimental results show the formation of a low roughness aluminum nitride film with hydrophobic properties over the glazed surface of a commercial porcelain electrical insulator.

Structural and mechanical properties of reactively sputtered TiAlC nanostructured hard coatings

TiAlC nanostructured hard coatings have been deposited on Si(100) substrates by four-cathode reactive pulsed direct current unbalanced magnetron sputtering at various process conditions. The effects of Al and C on the compositional, mechanical and micro-structural properties of TiAlC coatings have been investigated using X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, atomic force microscopy and nanoindentation hardness tester. Furthermore, the effect of substrate bias on the surface morphology, micro-structure and mechanical properties of TiAlC coatings is examined in detail. Formation of Ti3AlC(111) phase along with inclusion of TiC and amorphous carbon phases has been confirmed by XRD and micro-Raman spectroscopy studies. The optimized TiAlC coating exhibited a maximum hardness of ~30GPa and elastic modulus of 288GPa. Analysis of the nanoindentation data indicated that the resistance to plastic deformation (H3/E*2) and elastic strain to failure (H/E*) decrease with C and Al contents in the TiAlC coatings, whereas, these properties increase with an increase in the substrate bias due to grain size refinement. Lastly, fracture toughness of TiAlC coating has also been calculated using a cube corner indenter and the optimized coating exhibited a maximum toughness of ~1.38MPam1/2 at a load of 50mN.

Light trapping properties of surface textured ZnO:Al films deposited at various working pressures

Surface textured ZnO:Al (AZO) films with good optoelectronic and light trapping properties were prepared on glass substrates by direct current pulse magnetron sputtering followed by a wet chemical etching process in NaOH solution (5wt%) at room temperature. The influence of working pressure on different properties of AZO films including etching rate, structural and optoelectronic properties, light trapping ability as well as etching behavior was studied in detail. Different surface features were observed with the increasing of working pressure. The relationship between surface textured structure and working pressure was discussed. The etched AZO film deposited at 0.8Pa exhibited uniformly and distinctly crater-like surface textured structure, which is an effective textured surface for light trapping. Correspondingly, for the etched AZO film deposited at 0.8Pa, high visible optical transparence, electrical conductivity and haze value were also achieved.