Plasma-assisted Sputtering Research Articles

Synthesis and optimization of photocatalytic performance of WO3-loaded TiO2 nanotube array layers

TiO2 nanotube arrays were grown by anodic oxidation of the surface of Ti metal foils in an electrochemical cell with organic electrolyte containing fluorine, using constant bias voltage, 30 V. The average typical diameter and length of the as-prepared tubes were 87 nm and 3.8 μm, respectively. The titania nanotube arrays surface was subsequently loaded with WO3 non-contiguous thin layers by plasma-assisted RF sputtering. The addition of WO3 on the nanotube surface resulted in the formation of semiconductor heterojunctions, which lead to supplementary spatial separation of electron–hole pairs and reduced the recombination rate. Macroscopically, this is certified by increased lifetime of the photocatalytic activation and associated increase of surface wettability. In the current experiments, four sample sets with increasing WO3 coverage were prepared by increasing the sputter-deposition time of the WO3 material. Nanotube array morphology, structure and elemental composition were investigated by high-resolution scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and energy-dispersive x-ray spectroscopy. A comparison was made between the characteristics of the WO3-loaded nanotube layers and a reference bare TiO2 nanotube arrays layer. Annealing the samples at 420 °C led to the development of predominant anatase. The effects of UV irradiation and the presence of dopant fluorine species were further investigated and discussed as means to modifying the generation of hydroxyl radicals. Optimal conditions for the best photocatalytic performance of titania nanotube arrays were established via monitoring the degradation of methylene blue pollutant.

Concentration limits of niobium and cadmium alloys existence, formed by ultrafine particles

Cd metals are established to form an alloy with a body-centered cubic structure up to a 64.5 at. % concentration as a result of determining the limits existence of Cadmium in Niobium solid solutions, obtained by plasma-assisted ion sputtering and ultrafine particles co-precipitation to a critical size. At this, two linear dependence sections in the range of 0 – 50.0 at. % and 50.0 – 64.5 at. % of Cadmium (the rest is Niobium) are found described by the equations a [nm] = 8•10-5x +0.3306 and a [nm] = 3•10-4x +0.32188 (respectively), where x is the Cadmium content in the alloy, at. %. At 68 at. % of Cadmium, an unknown phase was identified; no solid solutions of Niobium in the Cadmium were detected. The growth of the lattice parameter is due to the fact, that Cadmium atoms have a larger radius than Niobium atoms: (ra)Cd = 0,1727 нм, (ra)Nb = 0,1625 nm. The kink on the linear dependence of the lattice parameter of the Cadmium in Niobium solid solution as a result of Cadmium concentration in the alloy is explained by the fact that Cadmium first replaces the Niobium atom in the center of the unit cell, then is also embedded in the Niobium lattice with increasing its concentration replacing the Niobium atom in one of the cube vertices. The latter causes a more intense increase in the size of the unit cell. The possibility of the alloys formation in a wide range of concentrations as a result of thermal-fluctuation melting and the merging of very small unlike particles that have significant differences in physical properties, metal particles was confirmed, which is unattainable with the traditional thermal production method.

Properties of tungsten thin film deposited using inductively coupled plasma assisted sputtering for next-generation interconnect metal

Tungsten (W) is actively investigated as one of the future metallization materials which can replace Cu for the metal thickness lower than tens of nanometer due to its sfmall electron mean free path of 19 nm and high melting temperature of 3673 K. In this study, inductively coupled plasma (ICP) assisted DC magnetron sputtering of W has been investigated for the lower resistivity of nm scale W film (30 nm). When the characteristics of W thin films deposited with and without ICP assistance were investigated, the decrease of the W thin film resistivity with the increase of deposition rate was observed as the ICP power is increased regardless of substrate heating. The decrease of W thin film resistivity by the ICP assisted DC sputter deposition was related to the change of crystal structure from A-15 to BCC, decreased oxygen incorporation in the film, decreased surface roughness, and increased grain size due to the increased ion flux to the substrate.

Optimised Performance of Non-Dispersive Infrared Gas Sensors Using Multilayer Thin Film Bandpass Filters

In this work, performance improvements are described for a low-power consumption non-dispersive infrared (NDIR) methane (CH4) gas sensor using customised optical thin film bandpass filters (BPFs) centered at 3300 nm. BPFs shape the spectral characteristics of the combined mid-infrared III–V based light emitting diode (LED)/photodiode (PD) light source/detector optopair, enhancing the NDIR CH4 sensor performance. The BPFs, deposited using a novel microwave plasma-assisted pulsed DC sputter deposition process, provide room temperature deposition directly onto the temperature-sensitive PD heterostructure. BPFs comprise germanium (Ge) and niobium pentoxide (Nb2O5) alternating high and low refractive index layers, respectively. Two different optical filter designs are progressed with BPF bandwidths (BWs) of 160 and 300 nm. A comparison of the modelled and measured NDIR sensor performance is described, highlighting the maximised signal-to-noise ratio (SNR) and the minimised cross-talk performance benefits. The BPF spectral stability for various environmental temperature and humidity conditions is demonstrated.

Thin films as model system for understanding the electrochemical reaction mechanisms in conversion reaction of MgH2 with lithium

Metal hydrides are promising high-capacity anode materials for Li-ion batteries but their conversion reaction with lithium suffers from low reversibility at room temperature (RT). Irreversibility issues in magnesium hydride MgH2 thin films are investigated, as well-defined model system. Films are deposited over Cu current collectors by means of microwave plasma-assisted sputtering and coated with aluminum to minimize formation of passivating MgO native oxide. Structural and chemical properties of the electrodes have been analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). Galvanostatic cycling reversibility at RT and C/50 regime is limited to 25% in the first cycle for 1 μm thick films. The lithiation of the thin film is complete and doubles its thickness. Despite drastic volume changes, neither cracks, voids, nor detachment of the thin film from the substrate are noticed. Moreover, electronic resistivity decreases upon lithiation due to the formation of metallic Mg. The origin of irreversibility phenomena in MgH2 films is attributed to sluggish mass transport of species within the electrode at RT.

Reliable Multivalued Conductance States in TaO x Memristors through Oxygen Plasma-Assisted Electrode Deposition with in Situ-Biased Conductance State Transmission Electron Microscopy Analysis.

Transition metal oxide-based memristors have widely been proposed for applications toward artificial synapses. In general, memristors have two or more electrically switchable stable resistance states that device researchers see as an analogue to the ion channels found in biological synapses. The mechanism behind resistive switching in metal oxides has been divided into electrochemical metallization models and valence change models. The stability of the resistance states in the memristor vary widely depending on: oxide material, electrode material, deposition conditions, film thickness, and programming conditions. So far, it has been extremely challenging to obtain reliable memristors with more than two stable multivalued states along with endurances greater than ∼1000 cycles for each of those states. Using an oxygen plasma-assisted sputter deposition method of noble metal electrodes, we found that the metal-oxide interface could be deposited with substantially lower interface roughness observable at the nanometer scale. This markedly improved device reliability and function, allowing for a demonstration of memristors with four completely distinct levels from ∼6 × 10-6 to ∼4 × 10-8 S that were tested up to 104 cycles per level. Furthermore through a unique in situ transmission electron microscopy study, we were able to verify a redox reaction-type model to be dominant in our samples, leading to the higher degree of electrical state controllability. For solid-state synapse applications, the improvements to electrical properties will lead to simple device structures, with an overall power and area reduction of at least 1000 times when compared to SRAM.

Gallium incorporation into phosphate based glasses: Bulk and thin film properties.

The osteogenic ions Ca2+, P5+, Mg2+, and antimicrobial ion Ga3+ were homogenously dispersed into a 1.45 µm thick phosphate glass coating by plasma assisted sputtering onto commercially pure grade titanium. The objective was to deliver therapeutic ions in orthopaedic/dental implants such as cementeless endoprostheses or dental screws. The hardness 4.7 GPa and elastic modulus 69.7 GPa, of the coating were comparable to plasma sprayed hydroxyapatite/dental enamel, whilst superseding femoral cortical bone. To investigate the manufacturing challenge of translation from a target to vapour condensed coating, structural/compositional properties of the target (P51MQ) were compared to the coating (P40PVD) and a melt-quenched equivalent (P40MQ). Following condensation from P51MQ to P40PVD, P2O5 content reduced from 48.9 to 40.5 mol%. This depolymerisation and reduction in the P-O-P bridging oxygen content as determined by 31P NMR, FTIR and Raman spectroscopy techniques was attributed to a decrease in the P2O5 network former and increases in alkali/alkali-earth cations. P40PVD appeared denser (3.47 vs. 2.70 g cm-3) and more polymerised than it's compositionally equivalent P40MQ, showing that structure/ mechanical properties were affected by manufacturing route.

Design and manufacture of super-multilayer optical filters based on PARMS technology

Abstract Three multilayer interference optical filters, including a UV band-pass, a VIS dual-band-pass and a notch filter, were designed by using Ta2O5, Nb2O5, Al2O3 and SiO2 as high- and low-index materials. During the design of the coating process, a hybrid optical monitoring and RATE-controlled layer thickness control scheme was adopted. The coating process was simulated by using the optical monitoring system (OMS) Simulator, and the simulation result indicated that the layer thickness can be controlled within an error of less than ±0.1%. The three filters were manufactured on a plasma-assisted reactive magnetic sputtering (PARMS) coating machine. The measurements indicate that for the UV band-pass filter, the peak transmittance is higher than 95% and the blocking density is better than OD6 in the 300–1100 nm region, whereas for the dual-band-pass filter, the center wavelength positioning accuracy of the two passbands are less than ±2 nm, the peak transmittance is higher than 95% and blocking density is better than OD6 in the 300–950 nm region. Finally, for the notch filter, the minimum transmittance rates are >90% and >94% in the visible and near infrared, respectively, and the blocking density is better than OD5.5 at 808 nm.

Atomically flat platinum films grown on synthetic mica

Atomically flat platinum thin films were heteroepitaxially grown on synthetic fluorophlogopite mica [KMg3(AlSi3O10)F2] by van der Waals epitaxy. Platinum films deposited on a fluorophlogopite mica substrate by inductively coupled plasma-assisted sputtering with oxygen introduction on a synthetic mica substrate resulted in the growth of twin single-crystalline epitaxial Pt(111) films.

Characterisation of Cu2O/CuO thin films produced by plasma-assisted DC sputtering for solar cell application

For large-scale implementation of devices magnetron sputtering is a practical method of producing metal oxides, however sputtered copper oxides tend to form as a mixture of Cu2O, Cu4O3, and CuO, with Cu2O being particularly difficult to produce reliably in pure form. In this study, nanostructured thin films of Cu2O, Cu4O3, and CuO were prepared using a novel reactive sputtering system, based on plasma-assisted DC magnetron sputtering with deposition and plasma assisted reaction zones spatially separated enabling separate control of film oxidation. X-ray diffraction, optical spectroscopy, and Raman spectroscopy were used to characterise the physical and optical properties and it is shown that plasma-assisted DC sputtering is a suitable technique for reliable production of CuO and Cu2O films in large areas at room temperature without the necessity of further processing. The results also indicate that solar cell performance may relate positively to the presence of crystalline Cu4O3 (200) and/or Cu2O (111) over other crystalline forms of copper oxide or amorphous copper oxide thin films.

Single crystalline epitaxial platinum film on Al2O3(0001) prepared by oxygen-doped sputtering deposition

We have deposited platinum by inductively coupled plasma-assisted radio frequency sputtering on an Al2O3(0001) substrate annealed at approximately 700 °C with and without oxygen blend. The surface morphology and crystallinity of the obtained Pt films with a thickness of approximately 200 nm were subjected to atomic force microscope (AFM) and X-ray diffraction (XRD) investigations. Without oxygen being introduced during the sputtering process, a (111)-oriented polycrystalline film was obtained. The introduction of oxygen led to the generation of twin single crystalline epitaxial Pt(111) films with a typical fcc(111) surface morphology of hexagonal symmetry.

Single-crystalline epitaxial platinum film on yttrium-stabilized zirconia (111) prepared by sputtering deposition

Sputtering is an important film deposition method that has been used for the fabrication of thin films used in basic research to the mass production process in factories. However, single-crystalline epitaxial platinum film has not been successfully prepared on yttria-stabilized zirconia (YSZ) (111) substrates by the sputtering method. We have deposited platinum by inductively coupled plasma-assisted sputtering on YSZ(111) with postdeposition annealing at 750–850 °C. As a result, single-crystalline epitaxial films with a root mean square roughness better than 0.2 nm were successfully fabricated.

The microstructure and mechanical properties of tantalum nitride coatings deposited by a plasma assisted bias sputtering deposition process

Abstract In this study, two tantalum nitride-based coatings were synthesized onto Ti-6Al-4V substrates with two different Ar/N 2 flux ratios using a form of plasma assisted bias sputtering deposition termed the double cathode glow discharge deposition technique. Their microstructures and mechanical properties were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy and nanoindentation tests. At a low nitrogen partial pressure, the tantalum nitride coating consists of a hexagonal Ta 2 N phase, with a preferred (101) orientation, while at a high nitrogen partial pressure, the as-deposited coating is composed of a face-centered cubic (fcc) TaN phase with a strongly (200) oriented texture. The two as-deposited coatings exhibited striated nanostructured composed of equiaxed grains about ~ 10 nm in diameter, embedded with an array of homogenously distributed nanopores. The mechanical properties and damage resistance of the coatings were evaluated by nanoindentation techniques. The hardness and elastic modulus of the Ta 2 N coating was higher than those of the TaN coating, indicating that the Ta 2 N coating may offer better protection ability for the underlying metal substrate under load-bearing conditions. In addition, the presence of nanopores is beneficial to the contact damage resistance for both coatings.

The effect of alloying on the structure and peculiarities of tribological behavior of vacuum-deposited diamond-like coatings

In this work, we report the results of a study of the atomic and crystalline structures, phase and chemical compositions and tribological properties of DLC coatings deposited by plasma-assisted (PA) CVD (a-C:H:Si and a-C:H:Si:Mo) and magnetron reactive sputtering (a-C:H:Cr). The a-C:H:Si:Mo coatings revealed the formation of ultra-dispersed inclusions of either molybdenum carbides or silicides, whereas no such inclusions were found in the a-C:H:Si compound. The a-C:H:Cr coatings that were deposited in an acetylene–nitrogen gas mixture exhibited a nanocomposite structure composed of chromium, its carbide and nitride phases. The tribological tests showed that the DLC coatings with silicon and silicon–molybdenum have a high friction coefficient and a low working performance, while the chromium-containing coatings have high levels of their mechanical and tribological characteristics, making them promising materials for operation under high contact pressures.

Process controllability of inductively coupled plasma-enhanced reactive sputter deposition for the fabrication of amorphous InGaZnOx channel thin-film transistors

The process controllability of inductively coupled plasma-enhanced reactive sputter deposition for the fabrication of amorphous InGaZnOx (a-IGZO) channel thin-film transistors (TFTs) was investigated. a-IGZO film deposition with the addition of H2 gas was performed using a plasma-assisted reactive sputtering system to control the oxidation process during a-IGZO film formation by balancing the oxidation and reduction reactions. Optical emission spectroscopy measurements indicate the possibility for the oxidation reaction to be inhibited by a decrease in the density of oxygen atoms and the reduction effect of hydrogen during a-IGZO film deposition due to the addition of H2 gas. The characteristics of TFTs fabricated using a-IGZO films deposited with a plasma-enhanced magnetron sputtering deposition system were investigated. The results indicate the possibility of expanding the process window by controlling the balance between oxidation and reduction with the addition of H2 gas. TFTs with a-IGZO films that were deposited with the addition of H2 gas exhibited good performance with a field-effect mobility (μFE) of 15.3 cm2 V−1 s−1 and a subthreshold gate voltage swing (S) of 0.48 V decade−1.

Enhancement of the crystalline Ge film growth by inductively coupled plasma-assisted pulsed DC sputtering.

The effect of pulsed DC sputtering on the crystalline growth of Ge thin film was investigated. Ge thin films were deposited on the glass substrates using ICP-assisted pulsed DC sputtering. The Ge target was sputtered using asymmetric bipolar pulsed DC sputtering system with and without assistance of ICP source. The pulse frequency of 200 Hz and the pulse on time of 500 μsec (duty cycle = 10%) were kept during sputtering process. Crystal structures were studied from X-ray diffraction. The X-ray diffraction patterns clearly showed crystalline film structures. The Ge thin films with randomly oriented crystalline were obtained using pulsed DC sputtering without ICP, whereas they had well aligned (220) orientation crystalline using ICP source. Moreover, the combination of ICP assistance and pulsed DC sputtering enhanced the growth of crystalline Ge thin films without hydrogen and metal by in situ deposition. The structure and lattice of the films were studied from TEM images. The cross-sectional TEM images revealed the deposited Ge films with columnar structure.

MgH2 thin films deposited by one-step reactive plasma sputtering

The morphology, crystal structure, hydrogen content, and sorption properties of magnesium hydride thin films prepared by reactive plasma-assisted sputter deposition were investigated. Few micrometers-thick films were deposited on Si and SiO2/Si substrates, at low pressure (0.4 Pa) and close to room temperature using (Ar + H2) plasma with H2 fraction in the range 15–70%. The microstructure and hydrogen content of the films are closely related to the surface temperature and hydrogen partial pressure during the deposition process. Operating in pulsed-plasma mode allows the hydrogenation rate of the MgH2 thin film to top up to 98%, thereby producing a nearly fully hydrogenated film in a single-step process. The positive effect of the pulsed process is explained by the significant decrease in the whole energy flux incident on the surface and the favourable impact of the transient process for the rearrangement/relaxation of the materials. As for the hydrogen storage properties, desorption experiments and cycling of the films show the destabilizing effect of Mg2Si formation at the interface between the film and the Si substrate resulting in a drastically increased desorption kinetics compared to less reactive SiO2 substrate. However, the reaction is regrettably not reversible upon hydrogenation and the hydrogen storage capacity is consequently reduced upon cycling. Nevertheless, the deposition process carried out on inert substrates would offer true potential for reversible storage. Finally, our experimental results, which show the possibility to preferentially grow the metastable medium pressure γ-MgH2 phase, open possibilities for the synthesis of more complex metastable phases such as magnesium-based ternary compounds.

Numerical Modeling of an Inductively Coupled Plasma Sputter Sublimation Deposition System

Fluid model based numerical simulation was carried out for an inductively coupled plasma assisted sputter deposition system. Power absorption, electron temperature and density distribution was modeled with drift diffusion approximation. Effect of an electrically conducting substrate was analyzed and showed confined plasma below the substrate. Part of the plasma was leaked around the substrate edge. Comparison between the quasi-neutrality based compact model and Poisson equation resolved model showed more broadened profile in inductively coupled plasma power absorption than quasi-neutrality case, but very similar Ar ion number density profile. Electric potential was calculated to be in the range of 50 V between a Cr rod source and a conductive substrate. A new model including Cr sputtering by Ar+was developed and used in simulating Cr deposition process. Cr was modeled to be ionized by direct electron impact and showed narrower distribution than Ar ions.

Coating diamond-like carbon films on polymer substrates by inductively coupled plasma assisted sputtering

In this paper, a new sputtering technique for coating hydrogen-free diamond-like carbon (DLC) films on polytetrafluoroethylene (PTFE) substrates in an inductively coupled plasma (ICP) will be reported. The ICP has the advantages of producing high-density plasma (HDP) for DLC deposition at low substrate temperatures (<50°C). The method developed in this work is particularly advantageous for coating on substrates with low melting points such as polymers. Various characterization techniques have been used to investigate the chemical, tribological, and electronic features of the deposited films. Raman spectroscopy revealed two broad peaks at 1386cm−1 and 1573cm−1 corresponding to the D and G peaks respectively. The DLC films produced by this method have less than 20% sp3 carbon bonds. The average grain size of the hydrogen-free DLC was ~57nm. The roughness of the uncoated PTFE substrate surfaces decreased dramatically (from 662 to 179nm) with DLC coating.

Effect of conductive TiN buffer layer on the growth of stoichiometric VO2 films and the out-of-plane insulator–metal transition properties

A TiN buffer film is used with a conductive interfacial layer for stoichiometric vanadium dioxide (VO2) film growth, creating a layered device with a VO2 insulator–metal transition. Low-temperature growth (&amp;lt;250 °C) of the VO2 film on a Ti layer on a Si substrate is achieved using inductively coupled plasma-assisted sputtering. It is found that Ti diffusion and oxidation degrades the VO2 film quality at higher temperatures, but the introduction of a TiN buffer layer suppresses the degradation and enables growth of a stoichiometric VO2 film even at 400 °C. The high resistance of the VO2 film grown on the TiN layer suggests the benefit of using the intrinsic insulator–metal transition of VO2. The voltage-triggered switching properties of the layered devices are examined, and the cause of the high out-of-plane resistance in this layered structure is discussed based upon the dependence of the initial resistance as a function the electrode area.