Pulsed Reactive Magnetron Sputtering Research Articles

Superior high-temperature oxidation resistance of magnetron sputtered Hf–B–Si–C–N film

A hard and optically transparent amorphous Hf7B23Si17C4N45 film with a contamination level less than 4at%, prepared by reactive pulsed dc magnetron sputtering, was subjected to systematic investigation of high-temperature oxidation behavior in air up to 1700°C. We focus on thermogravimetric analysis of the film in air and on the evolution of the film structure, microstructure and elemental composition with an annealing temperature ranging from 1100°C to 1700°C. The film exhibits a superior oxidation resistance up to 1600°C due to a formation of a nanocomposite protective oxide layer on the surface above 1000°C. The layer consists of monoclinic and tetragonal (or orthorhombic) HfO2 nanocrystallites surrounded by a SiO2-based amorphous matrix, most probably containing boron. The HfO2 nanocrystallites exhibit a gradient in size with a dense population of small (a couple of nm) crystallites next to the interface and larger but dispersed crystallites close to the surface.

Al in ZnO — From doping to alloying: An investigation of Al electrical activation in relation to structure and charge transport limits

The electrical activation of Al in ZnO thin films grown by pulsed reactive magnetron sputtering is quantified experimentally for a wide range of Al concentrations. We find that the activation does not exceed 35% remaining constant for growth temperatures below a certain optimum value at which the highest free electron density and mobility are achieved. Above this temperature, the Al activation decreases rapidly, while Al is accumulating in the films and their micro-structure as well as electrical properties deteriorate significantly. The analysis of possible mechanisms of Al deactivation suggests that the observed effects may be explained only by considering Al doped ZnO as metastable solid solution showing a tendency to segregation of Al into secondary phases.

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.

Magnetron discharge sputtering for fabrication of nanogradient optical coatings

The technology of the middle frequency pulse reactive magnetron sputtering for fabrication of nanogradient optical coatings with smooth variation of refractive index was developed and studied. The technology is based on programmable motion of a substrate over two magnetrons with targets of different materials. The feature of the deposition process is a constant composition of reactive gas medium and an invariable magnetron operation mode. To realize this technology, an automatic computer-controlled sputtering system additionally comprising a gas discharge activator of reactive gas (oxygen) and an in situ optical monitor- spectrovisor has been built. The dielectric oxide-based nanogradient coatings of photon-barrier type were successfully fabricated. The obtained results confirm the high potential of the middle frequency pulse reactive magnetron sputtering of silicon and metal targets for fabrication of nanogradient dielectric optical coatings with excellent properties.

Enhancement of bioactivity of pulsed magnetron sputtered TiCxNy with bioactive glass (BAG) incorporated polycaprolactone (PCL) composite scaffold

Titanium carbonitride (TiCxNy) thin films were fabricated on SS 316 L by pulsed reactive DC magnetron sputtering using titanium and graphite targets. The sputtered film was characterized microstructurally by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). The XRD pattern revealed that the film was preferentially oriented along (200) axis with a grain size of 20 nm. A globular morphology was observed from electron micrograph while Energy dispersive X-ray spectroscopy (EDS) showed the compositional purity of the film. To improve the bioactivity, bioactive glass (BAG) nanopowders of size 60 nm, synthesized by sol–gel method, was incorporated into a polycaprolactone (PCL) scaffold (BAG-PCL), which was applied over TiCxNy/SS (BAG-PCL/TiCN/SS). In-vitro bioactivity studies of BAG-PCL showed the apatite formation, which was confirmed from fourier transform infrared (FTIR) spectrum and SEM. In-vitro corrosion studies in simulated body fluid (SBF) solution showed that the coated specimen had a higher charge transfer resistance than stainless steel (SS) bare. The enhancement of bioactivity was monitored by hemocompatibility and cytocompatibility, where an improved cell attachment and lower thrombus formation was observed for the coatings with BAG-PCL.

Nanocrystalline Low‐Refractive Magnesium Fluoride Films Deposited by Reactive Magnetron Sputtering: Optical and Structural Properties

In this work, we study MgF2 thin‐film synthesis by reactive pulsed DC magnetron sputtering from a metallic magnesium target in a gas mixture of argon, oxygen, and carbon tetrafluoride (CF4). Nanocrystalline films on silicon and glass substrates with excellent properties for optical application are achieved. The plasma discharge is analyzed with a differentially pumped mass spectrometer before and during the deposition process. Without breaking the vacuum, monochromatic photoelectron spectroscopy (XPS) is performed for in situ determination of the atomic C and O concentration. Film microstructure, topography, and thickness are investigated by electron microscopy (SEM and TEM), atomic force microscopy (AFM), and X‐ray diffraction (XRD). The optical constants n and k are determined by spectroscopic ellipsometry and spectrophotometry: a consistent parametric fit of the ellipsometric angles and spectral transmittance and reflectance based on three Lorentz oscillators to determine n and k is achieved for a wide spectral range (300–2 300 nm). At 550 nm, a refractive index of 1.382 and near‐zero absorption is obtained, which is in excellent agreement with n = 1.383 of polycrystalline MgF2. The measured light reflection at 760 nm is reduced by 3% for a quarter‐wave nanocrystalline MgF2 coating on glass compared to the uncoated glass substrate.

Photocatalytic properties of titania thin films prepared by sputtering versus evaporation and aging of induced oxygen vacancy defects

In order to understand the variations in photocatalytic efficiencies of titania thin films prepared by different physical vapor deposition techniques, we studied the microstructure and resulting properties for the two widely used PVD methods, electron beam evaporation and reactive pulsed DC magnetron sputtering. In addition, we investigated the effect of oxygen vacancy defects induced by tempering in reducing atmospheres and the aging behavior. After deposition, several tempering series in oxygen, air, argon, and forming gas were carried out to control the amount of oxygen vacancy defects. The films were characterized with respect to crystallinity, texture, grain growth, grain structure, surface roughness, light transmission as well as band gap energy; the photocatalytic efficiency was measured via methylene blue degradation. The results show different nucleation and growth mechanisms between evaporated and sputtered titania thin films, resulting in severe influence on photocatalytic efficiency. The evaporated thin films exhibited homogeneous nucleation and growth, and stayed in the anatase structure even after tempering at 800°C for 1h. In contrast, the sputtered thin films started to form grains at the interface to the substrate and showed heterogeneous nucleation and growth. Moreover, the sputtered films already formed rutile when tempered at 600°C for 1h. The gain in surface area due to tempering, which promotes adsorption of photocatalytic reactants, was more pronounced in sputtered thin films (+29%) compared to evaporated thin films (+6%). Films with oxygen vacancy defects, preserved by tempering in argon or induced by tempering in forming gas, showed a large improvement in photocatalytic efficiency. However, aging of the samples over a period of 19 months lead to a progressive decline in efficiency, finally reaching the level of thin films tempered in air, which had remained stable over the same 19 month period. This strongly questions widely applied concepts based on improving the photocatalytic efficiency via oxygen vacancy defects.

Photoanodes with Fully Controllable Texture: The Enhanced Water Splitting Efficiency of Thin Hematite Films Exhibiting Solely (110) Crystal Orientation.

Hematite, α-Fe2O3, is considered as one of the most promising materials for sustainable hydrogen production via photoelectrochemical water splitting with a theoretical solar-to-hydrogen efficiency of 17%. However, the poor electrical conductivity of hematite is a substantial limitation reducing its efficiency in real experimental conditions. Despite of computing models suggesting that the electrical conductivity is extremely anisotropic, revealing up to 4 orders of magnitude higher electron transport with conduction along the (110) hematite crystal plane, synthetic approaches allowing the sole growth in that direction have not been reported yet. Here, we present a strategy for controlling the crystal orientation of very thin hematite films by adjusting energy of ion flux during advanced pulsed reactive magnetron sputtering technique. The texture and effect of the deposition mode on the film properties were monitored by XRD, conversion electron Mössbauer spectroscopy, XPS, SEM, AFM, PEC water splitting, IPCE, transient photocurrent measurements, and Mott-Schottky analysis. The precise control of the synthetic conditions allowed to fabricate hematite photoanodes exhibiting fully textured structures along (110) and (104) crystal planes with huge differences in photocurrents of 0.65 and 0.02 mA cm(-2) (both at 1.55 V versus RHE), respectively. The photocurrent registered for fully textured (110) film is among record values reported for thin planar films. Moreover, the developed fine-tuning of crystal orientation having a huge impact on the photoefficiency would induce further improvement of thin hematite films mainly if cation doping will be combined with the controllable texture.

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.

Toughness measurement of thin films based on circumferential cracks induced at conical indentation

In the present study, circumferential ring cracks were produced in two types of alumina coatings under conical indentation. The alumina coatings were produced using reactive dual pulsed magnetron sputtering. The coatings were deposited at 150 and $$530\,^\circ \hbox {C}$$ which resulted in coatings with hardness values of $$9.1\pm 0.2$$ and $$20.7\pm 1.1$$ GPa, respectively. The coating fractures were studied using scanning electron microscopy and the critical parameters for fracture: load, depth and crack radius, were determined for a range of coating thicknesses for both series. The crack behavior is compared to a numerical finite element model of the system. The model assumes the coating to be linear elastic while plasticity was included in the substrate. The critical parameters for different values of fracture toughness were extracted from the FEM stress field using closed-form expressions. The behavior of the simulated data and the experimental data was found to follow similar trends for all the investigated critical parameters. Furthermore, it was found that the critical load is the fracture parameter from which a measure for the fracture toughness is most accurately obtained. The hard coatings were observed to have higher fracture toughness than the softer coatings (200 vs. $$75 \, \hbox {J/m}^{2}$$ ).

Photocatalytic effects of reactively sputtered N-doped anatase upon irradiation at UV-A and UV-A/VIS threshold wavelengths

In biomedicine, light induced photocatalysis at implant surfaces has been gaining increasing interest during the last years. In the fields of biofilm attack at dental implant sites, photocatalytic decomposition of proteinaceous conditioning films could be shown recently on polycrystalline anatase coatings. However, for clinical treatments directly at the patient, the commonly applied UV-A is unwanted due to possible cell damage at host tissues. Therefore, in this study, anatase thin films were N-doped during reactive pulse magnetron sputtering, and the respective modifications were investigated for red-shifting, hydrophilization, and efficiency of photocatalytic organic decomposition upon UV-A compared to irradiation at the UV-A/VIS threshold around 400nm wavelengths. Generally, with increasing nitrogen flow during anatase sputtering, the ability of gaining superhydrophilicity or decomposing methylene blue decreased. Anatase sputtered under lowest nitrogen flow rates≤1sccm decomposed human serum albumin films more efficiently upon 405nm irradiation than anatase variants sputtered under higher nitrogen flow rates. Furthermore, undoped anatase could be activated similarly to low-doped variants even upon irradiation at 405nm peak wavelength enabling significant protein decomposition. These findings open the way for clinical applications of undoped and low-doped anatase modifications in cases where biocompatibility requires longer wavelengths than UV-A. Further research is still needed to clarify possible functional advantages of undoped and low-doped anatase modifications for specific biomedical applications at the UV-A/VIS threshold region around 400nm.

Semiconducting WO3 thin films prepared by pulsed reactive magnetron sputtering

WO3 crystalline semiconductor thin films for water-splitting applications were prepared by pulsed unbalanced reactive magnetron sputtering with W target and Ar + O2 gas mixture. Postdeposition annealing at temperature of 450 °C was applied to the WO3 samples to improve their crystallinity and semiconductor properties. Various pulsing modes were tested in deposition experiments with different pulsing frequencies, discharge power applied in pulse, and average applied power. To determine the influence of the plasma parameters on the deposition process, the pulsed and average ion flux density on the substrate were measured using an ion probe. The WO3 films had monoclinic crystalline structure after the annealing process. Different crystallite orientations were found for different modes of discharge pulsing. Preferential orientation of the (200) plane parallel to the substrate surface was identified for higher frequency of discharge pulsing with lower substrate pulsed ion flux but higher average substrate ion flux. The WO3 films with this type of texture had the highest photocurrents in photoelectrochemical (PEC) measurements.

Photocatalytic visible-light active bismuth tungstate coatings deposited by reactive magnetron sputtering

Photocatalytic bismuth tungstate thin films with visible-light activity were deposited via reactive pulsed DC magnetron sputtering onto soda-lime glass substrates. Varying the power delivered to the bismuth and tungsten targets allowed control over the Bi/W ratio in the coatings, and therefore the structural and optical properties of the coatings. As-deposited coatings were characterised with amorphous microstructures and were annealed at 673 K to develop crystallinity. The visible light photocatalytic activity of the coatings, which was analysed using the methylene blue degradation test, was found to be superior to that of a commercial titania-based photocatalytic product.

Effect of oxygen partial pressure on properties of ZnO/Al thin films prepared by pulsed dc reactive magnetron sputtering with SpeedFlo controller

Transparent conductive aluminium doped zinc oxide (ZnO: Al, AZO) films have been prepared on glass substrate by pulsed direct current reactive magnetron sputtering at room temperature. The dependence of oxygen partial pressure on the optical, electrical and structural properties was investigated. The oxygen partial pressure was accurately controlled by a closed loop SpeedFlo controller with a λ sensor. X-ray diffraction analysis indicated that the AZO films deposited at various oxygen partial pressures presented a polycrystalline wurtzite structure with a (002) preferred orientation perpendicular to the substrates. The densely packed AZO films with columnar structure were observed on the plan view by scanning electron microscope. The AZO film that was deposited at oxygen partial pressure of 3·36×10−2 Pa has superior performance with minimal resistivity of 1·14×10−3 Ω cm. Optical transmittance was obtained ∼80% in the visible region.

Effect of Si additions on thermal stability and the phase transition sequence of sputtered amorphous alumina thin films

Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at. % were deposited by combinatorial reactive pulsed DC magnetron sputtering of Al and Al-Si (90-10 at. %) split segments in Ar/O2 atmosphere. The effect of Si alloying on thermal stability of the as-deposited amorphous alumina thin films and the phase formation sequence was evaluated by using differential scanning calorimetry and X-ray diffraction. The thermal stability window of the amorphous phase containing 2.7 at. % of Si was increased by more than 100 °C compared to that of the unalloyed phase. A similar retarding effect of Si alloying was also observed for the α-Al2O3 formation temperature, which increased by more than 120 °C. While for the latter retardation, the evidence for the presence of SiO2 at the grain boundaries was presented previously, this obviously cannot explain the stability enhancement reported here for the amorphous phase. Based on density functional theory molecular dynamics simulations and synchrotron X-ray diffraction experiments for amorphous Al2O3 with and without Si incorporation, we suggest that the experimentally identified enhanced thermal stability of amorphous alumina with addition of Si is due to the formation of shorter and stronger Si–O bonds as compared to Al–O bonds.

Stable production of TiOx nanoparticles with narrow size distribution by reactive pulsed dc magnetron sputtering

The pulsed dc magnetron technique was used for generating TiOx nanoparticles by sputtering from a titanium target in a gas aggregation source. It was observed that the deposition rate (DR) of nanoparticles shows a peak followed by a broad tail, even for constant operation conditions. As a key finding of the present investigation, we show that nanoparticle deposition can be stabilized at nonzero DR for the pulsed power regime. Monitoring the oxygen concentration by mass spectrometry provides insight into nanoparticle generation in different processes. Characterization of the nanoparticle film morphology based on transmission electron microscopy reveals a very narrow size distribution. Furthermore, the oxygen admixture has a significant influence on the size distribution and also on the mean size of the formed nanoparticles. In situ analysis of the chemical composition of the deposited films directly after preparation by x-ray photoelectron spectroscopy shows a major contribution by sub-oxide titanium compounds to nanoparticle production.

Investigation of the structure, elemental and phase composition of coatings on the basis of oxynitride titanium deposited by reactive magnetron sputtering

The structure, morphology and properties of titanium-oxynitride coatings deposited by pulsed reactive magnetron sputtering were investigated. The methods of X-ray diffractometry, Raman spectroscopy, secondary ion mass-spectrometry and scanning electron microscopy are used. It is established that the structure, and the elemental and phase composition of coatings depend on the size of the ratio of oxygen/nitrogen in the composition of the reactive gas, and also on the magnitude of the negative bias applied to the substrate. The increase in the fraction of nitrogen leads to a reduction in the speed of sputtering, to a reduction in the contact angle of wetting, an increase in hardness and a reduction in Young’s modulus when a negative offset was used.

Rugate filters used in slit-lamp delivery to improve color rendering of illumination for retinal photocoagulation.

Laser filters and color filters used in slit-lamp delivery have been developed by the rugate approach to improve color rendering of illumination for retinal photocoagulation. The double-notch laser filter is designed according to the required laser lines and incident angle. Based on the transmission spectrum of a double-notch laser filter and the spectral power distribution (SPD) of the light source of a slit lamp, a scanning search algorithm is applied to find the optimal transmission spectrum of a multi-notch color filter for the best color rendering index of illumination. Open-source software is used to design the refractive index profile of the rugate filters, which are deposited by the reactive pulse magnetron sputtering. Both the theoretical analysis of SPD of slitlamp delivery with consideration of the deposited rugate filters and the experimental results demonstrate that the color rendering property of illumination can be improved remarkably, thus making fundus observation and retinal laser photocoagulation more reliable and efficient.

Structure and Optical Property of Cu<sub>2</sub>O:N Thin Film Deposited by Reactive Pulse Magnetron Sputtering

N-doped Cu2O (Cu2O:N) thin films were deposited on glass substrate by reactive pulse magnetron sputtering method using Cu target. Crystalline phases of thin films were controlled by adjusting N2/ O2flow rate ratio and sputtering power precisely during the sputtering process, and the single phase of Cu2O(111) thin films were obtained at room temperature. The thin films deposited at different sputtering powers were characteristics of 2D growth and the root mean square (RMS) of surface roughness of thin films gradually increased with the increasing of sputtering power. The optical band gap (Eg) of thin films were in the range 2.18-2.35 eV, and slightly decreased with increasing of sputtering power from 45 W to 90 W.

Effect of Substrate Bias in Copper Sputtering Plasma Measured by Langmuir Probe

There are several techniques to deposit the metal oxide thin film such as electron beam evaporator, pulse laser deposition and reactive magnetron sputtering deposition. In this experiment, magnetron sputtering deposition techniques will be used to produce a copper oxide thin film due to its simplicity and repeatability performance. Recently, copper oxide thin film has been studied because of its low cost material, sensitivity to ambient condition and easiness to produce oxide thin film. It is one of the p-type semiconductor oxides materials that are suitable to be used as a gas sensing material. In order to increase the sensitivity and to optimize the properties of copper oxide thin film, it is essential to study on the plasma properties during the deposition of copper oxide. In current studies, Langmuir probe was used to investigate the effect of substrate bias towards the fabrication of copper oxide thin film at rf dissipation power of 400 W. The oxygen flow rate was fixed at 8sccm. The Langmuir probe tip was focus at roughly 2 cm above the substrate holder. The ion and electron current were collected from the plasma environment. Then the electron temperature, electron density, ion density, ion flux, Debye length and plasma potential at various substrate biases were evaluated from the current-voltage curve. The electron temperature at various oxygen flow rates was almost unchanged. The effect of substrate bias toward the electron temperature was also almost unseen, except that the electron temperature at-40 V bias voltage was slightly lower than others. In addition, the ion flux at the same plasma condition shows that the ion flux was higher at-40 V substrate bias voltage. The results suggest that the ion bombardment effect toward the deposited copper oxide thin film would be higher at low oxygen flow rate. Thus it will create a rough surface morphology or nanostructured copper oxide thin film. This is a potential ways to improve the sensitivity of copper oxide gas sensor.