Pulsed DC Magnetron Sputtering Research Articles

Grain-wise piezoelectric response of polycrystalline aluminum nitride thin films: an empirical investigation using piezo force microscopy

Abstract Local mapping of piezoelectric response across grains with different crystal planes is crucial to enhance the level of understanding of the piezoelectric behavior of wurtzite hexagonal (WH) AlN thin films. To investigate this phenomenon, polycrystalline WH-AlN thin films were deposited by pulsed-DC magnetron sputtering using a mixture of argon (Ar) and nitrogen (N2) with varying N2 content as 5%, 10%, and 20% in the form of the AlN/Ti/Si (100) heterostructure. Piezo force microscopy (PFM) was used to establish a correlation among piezo-response (PR) phase contrast, polarity, and crystal planes constituting the film surface. A phenomenological model is also presented to correlate the distribution of interface sheet charges with polar (0002)-, semi-polar (10 1 ¯ 1)-, and non-polar (10 1 ¯ 0)-planes present on the film surface. This interdependence eventually regulates the phase between piezoelectric oscillations and modulation voltage, which is ultimately translated into a grain-wise contrast obtained from PR-phase images.

Analysis of pulsed direct current reactive magnetron sputtering on a silicon target

Reactive sputtering is a very useful technique, particularly, for producing inhomogeneous interference filters, where the refractive index changes smoothly during deposition. In such a context, precise control of deposition parameters is crucial for replicating the desired optical properties. This study employed a pulsed DC power source to investigate the influence of a duty cycle on target poisoning, sputtering plasma characteristics, electric signals, and optical and morphological properties of synthesized films. Reactive pulsed DC magnetron sputtering was characterized by analyzing the behavior of plasma emission via optical emission spectroscopy and voltage-current signals, while modulating parameters such as the oxygen content within the vacuum chamber. A set of thin films was coated on glass substrates under different system conditions. These films underwent characterization employing spectroscopic ellipsometry to ascertain their optical constants, atomic force microscopy for surface morphology analysis, and x-ray diffraction for the determination of crystalline structures. The results indicate that longer duty cycles required higher oxygen levels to poison the target. Additionally, a detailed analysis of electrical signals revealed nonsquare waveforms, whose characteristics were influenced by both the duty cycle and the oxygen content within the sputtering chamber, resulting in higher effective voltages during the on-time of the voltage pulse. Grown films via reactive pulsed DC magnetron sputtering were also compared to films grown via conventional DC magnetron sputtering at equivalent conditions of target poisoning.

In-situ optimization of lateral film uniformity in PVD system by using Fiber Bragg grating temperature sensors

Fiber Bragg grating (FBG) based temperature sensing method has been employed in this work for measuring the lateral temperature distribution on substrate plane during pulse DC magnetron sputtering deposition for optimization of lateral film uniformity. The evolution of temperature distribution with the variation of important process parameters like pulse width (496–1616 ns), deposition pressure (3.1 × 10−3–1.9 × 10–2 mbar) and sputtering power (25–250 W) have been measured over 40 mm radial distance on glass substrate horizon. To investigate the effect of substrate height on the temperature distribution, the later has been measured at two different substrate heights (60 mm and 90 mm) for varying sputtering power. Finally, the effect of variation in temperature distribution on uniformity of thickness and optical, morphological and structural properties have been investigated by separately depositing two HfO2 thin films at two representative extreme deposition powers (75 W and 200 W). The correlation of film non-uniformity of the above properties with the temperature distribution suggests that FBG based multipoint temperature sensing can be possibly used as an indicative tool for in situ optimization of the lateral film uniformity. In addition, the fast response and workability in plasma environment of FBG sensors enables precise in situ mapping of temperature distribution in sputtering process.

Modeling of cracking behavior of CrAlN coatings on silicon during micro- and nanoindentation

The deformation and failure behavior of any coating governs the performance of the resulting coating system. In the present work, we numerically and experimentally examine the fundamental deformation mechanisms of CrAlN coating on Si substrate, particularly its cracking behavior under indentation processes. For this purpose, CrAlN coatings deposited on monocrystalline Si substrates by pulsed DC magnetron sputtering were subject to indentation procedures with different depths. Subsequent characterization of top surface and cross-sectional morphologies demonstrates a strong dependence of coating profile and microstructures on the initial surface condition of the substrate. Specifically, uniform CrAlN coatings with a thickness of 1.1 μm and densified columnar microstructures were prepared on a polished Si substrate. Berkovich nanoindentation test with an indentation depth of 530 nm derives the mechanical properties of the prepared CrAlN coating. The corresponding finite element simulation reveals the propensity of cracking initiation accompanied by the stress concentration at three edge corners of the dent. Subsequent microindentation test with an indentation depth of 1.09 μm demonstrates the coexistence of plastic deformation and brittle fracture of CrAlN coating. In particular, surface radial cracks within CrAlN coating are experimentally and theoretically observed, and the cracking processes are analyzed in detail by finite element simulations.

Photocatalytic degradation of methylene blue by anatase TiO2 coating

AbstractPhotocatalytic coatings have the potential to contribute to the purification of water via an advanced oxidation process (AOP). A commonly used method for analyzing the mechanism of the photocatalytic performance of a given reactor type is to document the degradation behavior in a solution containing methylene blue. However, since methylene blue is rather unstable, the degradation results should be viewed critically. In this work, the degradation behavior of a test solution with methylene blue on quartz glass surfaces coated with photocatalytic titanium dioxide (TiO2) of the anatase modification was investigated through a variety of different light sources. The coating was deposited by physical vapor deposition (PVD) with the reactive pulsed DC magnetron sputtering ion plating (MSIP) method described in the study by Desch and Lake, while the quartz glasses were coated with a 100 nm thick TiO2 coating on the outside. The same glasses were used for all experiments with TiO2. In the determination of the degradation rate, additional experiments were performed using pure quartz glass without any coating, which made it possible to examine the influence of different light sources on the degradation rate of methylene blue in general. Three different light sources, namely UV‐A, UV‐C, and simple fluorescent lamps were used in this study. The concentration of methylene blue was recorded by photo spectrometer in 10‐min increments throughout the experiment and the experiments were performed for 24 h in all cases. Our data indicates that the methylene blue test is a poor method because the degradation rate is not clearly differentiable due to the low stability of the test substance. Without including reference testing in the absence of a catalyst, data may be subject to misinterpretation.

Effect of rapid thermal annealing on microstructure, mechanical and tribological properties of amorphous SiC hard coatings

Herein, a-SiC hard coatings were prepared by pulsed DC magnetron sputtering followed by rapid thermal annealing (RTA) at various temperatures. The influence of the RTA temperature on the coatings’ microstructure, mechanical and tribological properties was investigated. The results show that the surface morphology of a-SiC coatings almost unchanged and remains amorphous within 973 K annealing temperature. The content of sp3 first increases and then decreases with increasing annealing temperature, and reaches the maximum value at 773 K. The hardness (H) and elastic modulus (E) of the a-SiC coatings also increase firstly and then decrease due to the variation of sp3 content, while average friction coefficient decreases first and then increases. As the annealing temperature is 823 K, the maximal H, E of 25.02 GPa, 243.63 GPa are obtained. At 773 K annealing temperature, the minimum friction coefficient of 0.107 is realized, a-SiC coating exhibits higher H/E, H3/E2 and tribological properties.

Structural and Optical Properties of Aluminium Nitride Thin Films Fabricated Using Pulsed Laser Deposition and DC Magnetron Sputtering on Various Substrates

Abstract Aluminium nitride thin films were fabricated using pulsed laser deposition and DC magnetron sputtering. Different technological parameters and the effects of different substrates on the optical and structural parameters of AlN samples were studied. An X-ray diffraction study was performed for the layer deposited on the Si3N4 substrate. A high-energy electron diffraction study was also carried out for the layer deposited on a KCl substrate. Transmission spectra of layers on quartz, sapphire, and glass substrates were obtained. An evaluation of the optical band gap of the obtained layers was carried out (Eg form 3.81 to 5.81 eV) and the refractive index was calculated (2.58). The relative density of the film (N1TN-AlN sample) is 1.26 and was calculated using the Lorentz-Lorentz relationship. Layers of aluminium nitride show an amorphous character with a polycrystalline region. It was shown that the properties of AlN films strongly depend on the method, growth conditions, and substrate used.

Tribological properties of silver coatings prepared by low temperature pulsed DC magnetron sputtering and electroplating for aero-engines fasteners

In this work, the causes of failure of electroplating silver coatings on aero-engine nuts were explored. And the microhardness of low temperature pulsed DC magnetron sputtering silver coatings was increased by 25%, and the bonding force was increased by about 1.2 times. At high temperature, the friction coefficients of magnetron sputtering silver coatings was about 20% lower than that of electroplating silver coatings, and the wear volume was about 90% lower than that of it at maximum. The wear mechanism of magnetron sputtering silver coatings was mainly abrasive wear, while that of electroplating silver coatings was mainly adhesive wear. Besides, the results of molecular dynamics showed that silver coatings would move and aggregate in layers during the friction.

Investigation of W-SiC compositionally graded films as a divertor material

W-SiC composite material is a promising plasma-facing material candidate alternative to pure W due to the low neutron activation, low impurity radiation, and low tritium diffusivity of SiC while leveraging the high erosion resistance of the W armor. Additionally, W and SiC have high thermomechanical compatibility given their similar thermal expansion rates. The present study addresses the synthesis and performance of compositionally graded W-SiC films fabricated by pulsed-DC magnetron sputtering. Compositional gradients were characterized using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS), and crystallographic information was obtained using electron diffraction and X-ray diffraction (XRD). Samples were exposed to L-mode deuterium plasma discharges in the DIII-D tokamak using the Divertor Material Evaluation System (DiMES). Post-mortem characterizations were performed using scanning electron microscopy (SEM) and XRD. Electron diffraction and XRD showed that the compositionally graded W-SiC films were composed of polycrystalline W and amorphous SiC with amorphous W+SiC interlayers. No macroscopic delamination or microstructural changes were observed under mild exposure conditions. This study serves as a preliminary examination of W-SiC compositionally graded composites as a potential candidate divertor material in future tokamak devices.

Sputtered vanadium carbon nitride (VCN) thin films: a potential electrode for supercapacitors

The preparation of efficient thin film-based electrode materials is a vital prerequisite for practical energy storage devices. Herein, we have prepared unique vanadium carbon nitride (VCN) thin films on FTO substrates by pulsed DC magnetron sputtering technique for competent supercapacitor electrodes. XRD analysis confirmed the crystalline nature of VCN thin films. SEM and AFM revealed a smooth morphology with an average grain size of 30 nm. Raman spectra showed two broad peaks around 1346 and 1589 cm−1, belonging to the D-band and G-band of VCN. The surface electronic states of VCN were investigated by XPS analysis, which confirmed the formation of pure VCN films without any impurities. The electrochemical performance of the thin film electrode was evaluated using cyclic voltammetry (CV), Galvanostatic charge–discharge (GCD), and Electrochemical impedance analysis (EIS). The electrochemical results showed the VCN thin films exhibited super capacitive behaviours. The maximum specific capacitance (Cs) value of 78.2 F g−1 was obtained from GCD studies. A variation in charge transfer resistance is detected from the EIS study, which arises due to the partial oxidation of the active nitride component. The VCN electrode showed good cycling stability, retaining 87% of its capacitance at a current density of 5 A g−1 even after 2000 cycles. The sputtered VCN films have been demonstrated as potential thin film electrodes for electrochemical supercapacitors for practical energy storage devices.

Effect of V/Mo Atomic Ratio on the Microstructure and Mechanical Properties of MoVCuN Coatings.

To improve the gas ionization ratio, the Mo-V-Cu-N coatings were deposited by pulsed dc magnetron sputtering with assistance from an anode layer ion source, and the influence of the V/Mo atomic ratio was explored with regard to the microstructure and mechanical properties of the coatings. The findings of this study indicated that the MoVCuN coatings exhibited a solid solution phase of FCC B1-MoVN with a prominent (220) preferred orientation, and the deposition rate was found to decrease from 4.7 to 1.8 nm/min when the V/Mo atomic ratio increased. The average surface roughness of the MoVCuN coatings gradually decreased, and the lowest surface roughness of 6.9 nm was achieved at a V/Mo atomic ratio of 0.31. Due to the enhanced ion bombardment effect, the coatings changed from a coarse columnar to a dense columnar crystal structure, and promoted grain refinement at higher V/Mo atomic ratios, contributing to a gradual improvement in the compressive residual stress, hardness and adhesion strength of the coatings.

Mechanical and tribological properties of (AlCoCrNiSi)100−xNx thin films

High entropy thin films of (AlCoCrNiSi)100−xNx were deposited on silicon wafers using a pulsed DC magnetron sputtering technique, with nitrogen gas flow ratios (RN) of 0, 0.33, and 0.50. The structure and properties of these films were analyzed for elemental composition, surface and cross-sectional morphologies, microstructure, roughness, and mechanical properties. The coatings were primarily composed of an amorphous structure with a minor presence of a BCC structure and exhibited periodic variations in chemical composition from the substrate to the free surface. An increase in RN enhances crystallinity of the materials. Nanoindentation results showed that the films deposited at RN = 0.50 displayed the highest hardness (10.7 ± 0.5 GPa) and reduced modulus (176 ± 5 GPa), which were the highest among the films. Microtribology testing was conducted using a 20 μm radius spherical diamond tip under ambient air and normal loads ranging from 0.5 to 9 mN. Worn surfaces were characterized using atomic force microscopy. The coefficient of friction was evaluated to investigate the elastic and plastic behaviors of films using Schiffmann’s model. The coating without nitrogen displayed a predominant plastic behavior during the initial cycles, while the coating deposited at RN = 0.33 demonstrated a more elastic behavior, particularly at lower loads.

Tribocorrosion behaviors of VNbMoTaWCr high entropy alloy coatings

In this work, four BCC-structured VNbMoTaW and VNbMoTaWCr high entropy alloy (HEA) coatings with different Cr contents were fabricated on the surface of 304 stainless steel (304SS) plates by a pulsed DC magnetron sputtering system. In addition to the dry pin-on-disk wear test and pure corrosion test, two kinds of tribocorrosion tests were performed. For the tribocorrosion test without applied potential, the HEA coatings were immersed in a 3.5 wt% NaCl aqueous solution at room temperature under 1 N load using a pin-on-disk tribometer. For the tribocorrosion test with applied potentials, the potentiodynamic polarization test was conducted to investigate the effects of external potentials and sliding loads on the corrosion current density, polarization resistance, and wear rates of HEA coatings. The hardness, corrosion resistance, and tribocorrosion (without applied potential) resistance of VNbMoTaWCr HEA coatings increased with increasing Cr content. The VNbMoTaWCr coatings with higher than 24.7 at.% Cr had a high hardness of 16.4 to 16.5 GPa and excellent corrosion resistance in pure corrosion and tribocorrosion without applied potential. On the other hand, as the tribocorrosion was executed with an applied potential higher than the breakdown potential and high current density, the tribocorrosion resistance of HEA coatings was greatly influenced by its protection degradation ratio, Pdr (the polarization resistance ratio between pure corrosion and tribocorrosion setup 2). Finally, the lowest wear rate of 2.55 × 10−5 mm3N−1 m−1, which was 1.4 times better than 304SS, was obtained for the VNbMoTaWCr coating containing 11.65 at.% Cr after the tribocorrosion test with applied high potential because of its lower Pdr value and less decay of corrosion protection ability.

Deposition of gold on a PET film by pulsed DC magnetron sputtering

Pulsed DC magnetron sputtering was employed to deposit gold onto polyethylene terephthalate (PET) film. The optical properties of the gold coating were evaluated through reflectance and transmittance measurements using a Jasco V-770/SLM-907 spectrophotometer. Spectral analysis provides information about the colour, impurities, surface quality, and coating thickness. In sputtering experiments with a circular target, the gold coating exhibits a relatively uniform colour in the area opposite the target, with a thickness (df) greater than 60 nm and a resistance lower than 6 Ω. The coating thickness gradually decreases away from the center, therefore affecting other physical properties, so it should be considered and used for calculations when coating on a large substrate. The fabricated gold coating passes tests for adhesion, friction resistance and resistance to cleaning agents, making it suitable for industrial and daily applications such as decoration or making electrodes for biosensors and electronic components.

Characterization of Structural, Optical, Corrosion, and Mechanical Properties of HfO2 Thin Films Deposited Using Pulsed DC Magnetron Sputtering.

Various properties of HfO2, such as hardness, corrosion, or electrical resistance, depend on the method and the conditions of deposition. In this work, a thorough comparison of scarcely investigated mechanical properties of HfO2 thin films deposited with different conditions of reactive magnetron sputtering process is presented. Four thin films were sputtered in processes that varied in plasma ignition method (continuous or sequential) and target-substrate distance. The structural characteristics of the HfO2 thin films were examined using Raman spectroscopy and X-ray diffraction measurements. Furthermore, the optoelectronic properties were determined based on transmittance and current-voltage characteristics. The mechanical properties of the HfO2 thin films were determined using nanoindentation and scratch test. In turn, the corrosion properties were determined by analyzing the voltametric curves. The transparent HfO2 thin films deposited in the continuous process are characterized by better corrosion resistance than the same layer formed in the sequential process, regardless of the target-substrate distance (8 cm or 12 cm). Furthermore, these samples are also characterized by the highest value of Young's modulus and scratch resistance. The combination of good corrosion and scratch resistance could contribute to the new application of HfO2 as a corrosion protective material.

Investigation and Band Gap Analysis of Pulsed Dc Magnetron Sputtered Diamond‐Like Carbon to Enhance Contact‐Electrification and Durability of Triboelectric Nanogenerators

AbstractThis work details the triboelectric characteristics of diamond‐like carbon (DLC) film where a proportioned sp3:sp2 bond ratio is engineered through a patented pulsed DC magnetron sputtering process to achieve a durable commercial energy harvesting material. A triboelectric nanogenerator (TENG) is fabricated by creating the triboelectric interface between DLC and PTFE. The presence and synchronization of σ – σ and σ – π bonds between DLC‐PFTE contact surface amplify the electronic cloud overlap between their atoms leading to an enhancement of the triboelectric surface charge density. The inherent hardness and reduced friction achieved through DLC and PTFE respectively prevent the mass transfer, and consequent power loss upon consecutive mechanical contact and achieves a stable electric power output of 141 mW m−2. The DLC durability achieved with PTFE in TENG demonstrates its significant potential as low frequency (1 – 10 Hz) energy harvesting devices and self‐/low‐power electronic devices and sensors. The paper uniquely contributes to a better understanding of the triboelectrification mechanism by insightfully detailing the band‐to‐band transition of electrons between the PTFE and DLC tribo‐interface, as well as discussing gap and frequency limitation of the tribo‐pair on the triboelectric charge yield, storage, transfer, and on the friction layer electric field.

Enhanced emission from hBN in sputtered microcavities.

In this observational study, we embed few-layer hexagonal boron nitride (hBN) inside a planar Fabry-Perot cavity fabricated using a pulsed DC magnetron sputtering system and show that the hBN retains its inherent visible range, defect-based luminescent properties following relatively energetic deposition processing. The observed surface-normal emission enhancement factor of ∼40 is in good agreement with theoretical predictions. We also found that embedded hBN subjected to a rapid thermal annealing treatment exhibits a cracking effect where the edges of the material glow distinctly brighter than adjacent regions. Our results might inform future efforts involving monolithic integration of hBN active layers.

Si–Sn codoped n-GaN film sputtering grown on an amorphous glass substrate

DC-pulse magnetron sputtering was utilized to deposit a 300 nm-thick n-type GaN thin film that was co-doped with Si–Sn onto an amorphous glass substrate with a ZnO buffer layer. The deposited thin films were then subjected to post-growth thermal annealing at temperatures of 300 °C, 400 °C, or 500 °C to enhance their crystal quality. Hall measurements revealed that the film annealed at 500 °C had the lowest thin-film resistance of 0.82 Ω cm and the highest carrier concentration of 3.84 × 1019 cm−3. The thin film surface was studied using atomic force microscopy; the film annealed at 500 °C had an average grain size and surface roughness of 25.3 and 2.37 nm, respectively. Furthermore, the x-ray diffraction measurements revealed a preferential (002) crystal orientation and hexagonal wurtzite crystal structure at 2θ ≈ 34.5°. The thin film had a full width at half maximum value of 0.387°, it was also found to be very narrow. Compositional analysis of the films was conducted with x-ray photoelectron spectroscopy and verified that both Si and Sn were doped into the GaN film utilizing covalent bonding with N atoms. Finally, the film annealed at 500 °C had a high optical transmittance of 82.9% at 400–800 nm, a high figure of merit factor of 490.3 × 10−3 Ω−1, and low contact resistance of 567 Ω; these excellent optoelectronic properties were attributed to the film’s high electron concentration and indicate that the material is feasible for application in transparent optoelectronic devices.

Photocatalytic activity of TiO2 deposited by reactive HiPIMS with long target-to-substrate distance

Reactive High Power Impulse Magnetron Sputtering (HiPIMS) of TiO2 thin films was carried out to investigate the influence of ion parameters and the deposition temperature on the film crystallinity and photocatalytic performance. In order to limit unintentional substrate heating, a deposition setup with long target-to-substrate distance was used. Different HiPIMS pulse configurations, deposition temperatures and substrate bias were evaluated. TiO2 films prepared by pulsed dc magnetron sputtering were used as reference. Films deposited at room temperature were all found to be X-ray amorphous, and a minimum temperature of 200 °C was needed for film crystallization irrespective of the mode of operation. This is attributed to the relatively long target-to-substrate distance of 180 mm used in this work. The growth of a specific polymorph was shown to be dependent on the operation mode, where a high oxygen partial pressure was ideal for anatase formation. The photodegradation rates were, as expected, found to be highest for crystalline samples, where single- and mixed-phase films yielded similar rates. Furthermore, the photodegradation rates of HiPIMS films deposited without substrate heating could be enhanced up to 3 times as compared to the corresponding pulsed dc reference film. The ion assistance in HiPIMS is also beneficial at moderate temperatures, here 200 °C, where an improved crystallinity as compared to pdcMS, was observed.

STRUCTURAL AND MECHANICAL PROPERTIES OF TiAlN AND TiAlN GRADIENT FILMS DEPOSITED BY REACTIVE PULSED DC MAGNETRON SPUTTERING

TiAlN and TiAlN gradient films were deposited on Si substrates by reactive pulsed DC magnetron sputtering. The crystal structure and morphology of TiAlN films were characterized via X-ray diffraction (XRD), and field emission scanning electron microscope (FE-SEM), respectively. Moreover, elemental composition, hardness, and adhesion of TiAlN films were analyzed by energy-dispersive X-ray spectroscopy (EDS), nanoindentation test, and scratch test, respectively. The TiAlN films and TiAlN gradient films showed columnar structure and cubic crystal structure with different orientation planes. The elemental mapping of TiAlN gradient films clearly demonstrated the TiAlN gradient films. TiAlN gradient films have slightly lower hardness compared to TiAlN films while adhesion of the films increases.