Direct Current Magnetron Sputtering Research Articles

Structure Modulation and Self-Lubricating Properties of Porous TiN–MoS2 Composite Coating Under Humidity–Fluctuating Conditions

To improve the friction performance and service life of protective coatings in humidity-fluctuating environments, porous hard titanium nitride (TiN)–molybdenum disulfide (MoS2) composite coatings were prepared by using direct current magnetron sputtering (DCMS) with the mode of oblique angle deposition (OAD) and chemical vapor deposition (CVD) technologies. The structure and chemical component were characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The tribological properties of these TiN–MoS2 composite coatings were investigated. The results indicate that the porous TiN–MoS2 composite coating exhibited outstanding friction performance and long service life under humidity-fluctuating environments. At the initial 20% relative humidity (RH) stage, the MoS2 on the porous TiN–MoS2 composite coating surface worked as an effective lubricant; thus, the coating demonstrated excellent lubrication performance, and the friction coefficient (COF) was about 0.05. As the humidity was alternated to 70% RH, the lubrication effect diminished due to the production of molybdenum oxide (MoO3), and the COF was about 0.2, which was attributed to the degradation of MoS2 on the wear track and the release of fresh MoS2 from the porous TiN matrix. After the environmental conditions shifted from 70% to 20% RH, the MoO3 was removed, and the lubrication effect was restored. In summary, TiN–MoS2 porous composite coating offers a promising approach for lubrication in humidity-fluctuating environments.

Influence of substrate orientation and pre-annealing treatment on the metal–insulator transition in V2O3 films: Insights from Al2O3r, a, c, and m-plane substrates

We investigate the structural and metal–insulator transition (MIT) behavior of epitaxial V2O3 films fabricated by reactive direct current magnetron sputtering on r, a, c, and m-plane Al2O3 substrates, in both as-received and annealed states. Characterization of MIT of the V2O3 films grown on annealed substrates demonstrated significant changes in observed MIT properties, i.e., r-plane films showed ≈2 order increase in transition magnitude, m-plane ≈6 orders, and c-plane films exhibited a reduction of ≈3 orders, compared to un-annealed substrates, whereas for V2O3 on annealed a-plane, it revealed a shift in the transition to higher values, with reduction in hysteresis width. Structural characterization conducted via x-ray diffraction and atomic force microscopy revealed a reduction in out-of-plane compressive strain for annealed substrates, along with decreased lateral grain size. Additionally, the correlation between the V2O3 MIT and its underlying structural phase transition was verified by temperature-dependent x-ray diffraction analysis. These findings highlight the role of substrate orientation and pre-annealing in tuning the MIT behavior of V2O3 films grown on the Al2O3 substrate.

Decoration of Silver Nanoparticles on WS2-WO3 Nanosheets: Implications for Surface-Enhanced Resonance Raman Spectroscopy Detection and Material Characteristics

This study investigates the chemical and structural modifications of vertically aligned tungsten disulfide–tungsten trioxide (WS2-WO3) nanosheets decorated with silver nanoparticles (Ag(NPs)) under nitrogen plasma conditions. The synthesized vertically aligned WS2-WO3 nanosheets were functionalized through direct-current (DC) magnetron sputtering, forming silver-decorated samples. Structural changes, as well as the size and distribution of Ag(NPs), were characterized using scanning electron microscopy (SEM). Chemical state analysis was conducted via X-ray photoelectron spectroscopy (XPS), while Raman spectroscopy was employed to investigate vibrational modes. The findings confirmed the successful decoration of Ag(NPs) and identified unexpected compound transformations that were dependent on the duration of functionalization. The synthesized and functionalized samples were evaluated for their sensing capabilities towards Rhodamine B (RhB) through surface-enhanced resonance Raman scattering (SERRS). This study discusses the impact of substrate morphology and the shape and size of nanoparticles on the enhancement of SERRS mechanisms, achieving an enhancement factor (EF) of approximately 1.6 × 106 and a limit of detection (LOD) of 10−9 M.

Preparation of sandwich-structured V6O13via direct current magnetron sputtering for high-capacity zinc-ion batteries.

Aqueous zinc-ion batteries are an appealing electrochemical energy storage solution due to their affordability and safety. Significant attention has been focused on vanadium oxide cathode materials for ZIBs, owing to their high specific capacity, unique layered or tunnel structures, and low cost. Compared to traditional methods for preparing and assembling electrode materials, direct current (DC) magnetron sputtering allows direct synthesis and uniform deposition on current collectors, offering advantages such as simplicity, mild reaction conditions, and strong film adhesion. Therefore, we synthesized sandwich-structured vanadium oxides (V6O13) with a V-O framework on stainless steel using this method, and for the first time, employed them as cathode materials for zinc-ion batteries. The unique crystal structure of V6O13 features numerous ion diffusion channels, providing ample sites for zinc ion embedding. Additionally, the multiple valence states of vanadium in V6O13 contribute to its high specific capacity and excellent coulombic efficiency during the charge/discharge process. The V6O13 synthesized at 400 °C in 3% O2 exhibits the highest specific capacity (550 mA h g-1 at 100 mA g-1). This synthesis strategy demonstrates significant application potential and offers a new pathway for the fabrication of other oxide thin-film electrode materials.

Localized surface plasmon resonance of Ag nanoparticle thin films deposited by direct-current magnetron sputtering

This study investigates the localized surface plasmon resonance (LSPR) of Ag nanoparticle (NP) thin films deposited by magnetron sputtering on an alkaline-free aluminosilicate-glass substrate at a substrate temperature of 600 °C. The equivalent film thickness was controlled to be 5, 10, 20, and 50 nm by adjusting the deposition time. The deposited Ag thin films formed NPs with uniform diameter and spacing for all Ag thicknesses. The NP diameters ranged approximately from 16 to 88 nm, corresponding to the equivalent film thickness. Due to the formation of isolated NPs, all Ag thin films exhibited a singlet LSPR peak in their extinction spectra. The LSPR peak position in the extinction spectra shifted with the refractive index of the environmental solvent media when the Ag NP thin films were immersed in these media. In addition, the insertion of a MgO, Nb2O3, or TiO2 underlayer shifted the LSPR peak position in the extinction spectra according to the refractive index of each underlayer material. A peak shift corresponding to the refractive index of the environmental solvent media was also observed for Ag NP thin films deposited on underlayers. The relatively low sensitivity of the LSPR peak shift to the refractive index of the environmental solvent media suggests that the solvent media only covered the top surface of the Ag NPs distributed on the substrate but did not infiltrate the spaces between them. The results of this study demonstrate the applicability of sputter-deposited Ag NP thin films to solid LSPR devices.

Optimizing the properties of In-N dual-doped SnO2 films: incorporation of nitrogen into the SnO2 lattice at the optimal content via direct current sputtering.

Direct current magnetron sputtering was employed to fabricate In-N dual-doped SnO2 films, with varying concentrations of N2 in a mixed sputtering gas of N2 and argon (Ar). The quantity of N-substituted O elements in the SnO2 lattice was confirmed through energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). A comprehensive investigation of properties of the In-N dual-doped SnO2 films was conducted using various techniques, including X-ray diffraction analysis, field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), ultraviolet absorption spectroscopy, Hall effect measurements, and current-voltage (I-V) characteristic assessments. The results indicated that when the ratio of N2 to the mixed gas (Ar + N2) exceeded 15%, the films exhibited p-type conductivity. The films demonstrated optimal electrical and structural properties at an N2 content of 45%, with a resistivity of 5.1 × 10-3 Ω cm, hole mobility of 12.75 cm2 V-1 s-1, crystal grain size of 25.74 nm, and a root mean square (RMS) roughness of 0.61 nm, resulting in the highest photocurrent at the INTO-45/Si interface.

Thermal conductivity of AlN thin films deposited by reactive DC magnetron sputtering on different substrates using ultra-fast transient hot strip technique

In the frame of this work, we report a profound insight into the thermal conductivity (k) of aluminum nitride (AlN) thin films deposited on AlN-molecular beam epitaxy (MBE)/Si(111) and AlN-Kyma/Si(111) substrates at low temperatures (<200 °C) using reactive direct current magnetron sputtering (DCMS). Our concern is not on the thermal properties at the nanoscale, but rather on relating thermal macroscopic properties to the microstructure for submicronic to micronic AlN films. As the mean free path for AlN material is about 100 nm, the thickness of our films lies between 400 nm and 2 μm. The k measurements were conducted using the ultra-fast transient hot strip technique. It was found that the k values of the deposited films change depending on both the substrate type and the film thickness. For the 500 nm AlN thick film, k value was about 250 W m−1 K−1 for AlN-DCMS films grown on 10 nm AlN-MBE/Si against 90 W m−1 K−1 for those deposited on 200 nm AlN-Kyma/Si. The thermal boundary resistance has been computed equal to (0.25 ± 0.08) × 10−9 K m2 W−1 on 10 nm AlN-MBE/Si against (3.56 ± 1.50) × 10−9 K m2 W−1 on 200 nm AlN-Kyma/Si. Additionally, both pole figures and high resolution transmission electron microscopy confirm k results. In fact, pole figures confirm the good crystal quality of the film on both substrates, but HR-TEM analyses show that the AlN films grown on 10 nm AlN-MBE/Si template exhibit good crystalline quality with an epitaxial regrowth and abrupt interface compared to those obtained for 200 nm AlN-Kyma/Si. It also appears that the thermal boundary resistance plays a major role in the thermal properties of AlN films.

Effects of bias voltage on microstructure and properties of vanadium dioxide films deposited by DC magnetron sputtering

Applying an appropriate bias voltage during direct current magnetron sputtering can optimize the valence state, facilitate phase transition, and improve the performance of deposited VO2 film.

A Review of Transparent Conducting Films (TCFs): Prospective ITO and AZO Deposition Methods and Applications.

This study offers a comprehensive summary of the current states as well as potential future directions of transparent conducting oxides (TCOs), particularly tin-doped indium oxide (ITO), the most readily accessible TCO on the market. Solar cells, flat panel displays (FPDs), liquid crystal displays (LCDs), antireflection (AR) coatings for airbus windows, photovoltaic and optoelectronic devices, transparent p-n junction diodes, etc. are a few of the best uses for this material. Other conductive metals that show a lot of promise as substitutes for traditional conductive materials include copper, zinc oxide, aluminum, silver, gold, and tin. These metals are also utilized in AR coatings. The optimal deposition techniques for creating ITO films under the current conditions have been determined to be DC (direct current) and RF (radio frequency) MS (magnetron sputtering) deposition, both with and without the introduction of Ar gas. When producing most types of AR coatings, it is necessary to obtain thicknesses of at least 100 nm and minimum resistivities on the order of 10-4 Ω cm. For AR coatings, issues related to less-conductive materials than ITO have been considered.

Evolution of Chemical, Structural, and Mechanical Properties of Titanium Nitride Films with Different Thicknesses Fabricated Using Pulsed DC Magnetron Sputtering.

Considering the application of titanium nitride (TiN) films as a release layer in producing Wolter-I X-ray telescope mirror shells by the electroformed nickel replication (ENR) technique, this research pays attention to the influence of nanometer-scale thickness variation in the microstructure and physical properties of TiN films deposited by the pulsed direct current (DC) magnetron sputtering method. This topic has received limited attention in the existing literature. TiN films (9.8 nm to 42.9 nm) were fabricated to comprehensively analyze the evolution in microstructure, depth distribution of elements, surface morphology, and intrinsic stress. With increasing thickness, TiN transitioned from amorphous to (200) and (111)-(200) mixed-oriented crystallization, explaining inflection points in the increasing roughness curve. Elements (C, N, O, Si, and Ti) and chemical bond proportions (Ti-N, Ti-N-O, and Ti-O) varied with film depth, and the fitting of film density can be optimized according to these variations. Crystallite size increased with thickness, which led to a reduction in intrinsic stress. It is evident that as film thickness increases, TiN forms a stable crystal structure, thereby reducing intrinsic stress, but resulting in increased roughness. Considering the impact of changes in thin film thickness on physical properties such as roughness, crystallinity, and intrinsic stress, a TiN film with a thickness of approximately 25 nm is deemed suitable for application as a release layer.

Annealing Temperature Effect on the Properties of CoCe Thin Films Prepared by Magnetron Sputtering at Si(100) and Glass Substrates

This study explores cobalt–cerium (Co90Ce10) thin films deposited on silicon (Si) (100) and glass substrates via direct current (DC) magnetron sputtering, with thicknesses from 10 nanometer (nm) to 50 nm. Post-deposition annealing treatments, conducted from 100 °C to 300 °C, resulted in significant changes in surface roughness, surface energy, and magnetic domain size, demonstrating the potential to tune magnetic properties via thermal processing. The films exhibited hydrophilic behavior, with thinner films showing a stronger substrate effect, crucial for surface engineering in device fabrication. Increased film thickness reduced transmittance due to photon signal inhibition and light scattering, important for optimizing optical devices. Furthermore, the reduction in sheet resistance and resistivity with increasing thickness and heat treatment highlights the significance of these parameters in optimizing the electrical properties for practical applications.

Influence of Sputtering DC Sputtering Power on the Surface Evolution of Ti Thin Films: A Fractal Description

The power supplied to the target during a sputtering process affects surface evolution. As such, the influence of sputtering power on the growth of titanium (Ti) thin films was studied. The Ti thin films were deposited using a direct current (DC) magnetron sputtering system from a pure Ti target on a glass substrate at varying sputtering powers of 15% (54.12 W), 30% (109.70 W), and 50% (188.17 W) of the maximum system capacity. The thin films were then characterised for topography using atomic force microscopy (AFM), morphology using a field emission scanning electron microscope (FESEM), and crystallinity using an x-ray diffractometer (XRD). Furthermore, fractal analysis based on the AFM imaging was undertaken to evaluate the growth mechanisms of the Ti thin films. The thickness, grain size, and roughness of the thin films increased with the deposition power. The samples were mostly amorphous, although at 30% and 50%, a weak peak of Ti (002) was observed via x-ray diffraction. The fractal dimension (Df) decreased with increasing power. The multifractality strength increased with increasing power. Based on the fractal study, Volmer-Weber and Stranski-Krastanov's modes describe the growth mechanism of Ti thin films deposited at varying sputtering power.

Structural and magnetic properties of Co2FeGa full-Heusler alloy thin films with low Gilbert damping

Highly ordered Co2FeGa thin films were successfully prepared using direct current magnetron sputtering by adjusting the film growth conditions. This involved making modifications to substrate and annealing temperatures. Structural, chemical, and magnetic properties were systematically studied using global and surface techniques. The results showed a transition from a partially ordered film grown at 300 °C to a highly ordered L21 full-Heusler phase at 600 °C. X-ray photoelectron spectroscopy confirmed a stoichiometric Co2FeGa alloy for the films, while 57Fe conversion electron Mössbauer spectroscopy revealed the atomic disorder–order transition induced by high substrate temperatures and/or annealing temperatures. The magnetic properties were found to be strongly influenced by the thermal history of the films. Saturation magnetization reached 1200 kA/m and coercivity was as low as 0.8 mT for the film growth at 600 °C. Ferromagnetic resonance showed that the α-Gilbert damping parameter was significantly affected by growth conditions with a value of 0.0015(3) measured in films grown at the highest temperature. This study demonstrates that precise control over film crystallinity and atomic ordering can lead to low α-damping values in polycrystalline Co2FeGa thin films, making them promising materials for use in spintronic devices.

Evaluation of Performance and Longevity of Ti-Cu Dry Electrodes: Degradation Analysis Using Anodic Stripping Voltammetry.

This study aimed to investigate the degradation of dry biopotential electrodes using the anodic stripping voltammetry (ASV) technique. The electrodes were based on Ti-Cu thin films deposited on different polymeric substrates (polyurethane, polylactic acid, and cellulose) by Direct Current (DC) magnetron sputtering. TiCu0.34 thin films (chemical composition of 25.4 at.% Cu and 74.6 at.% Ti) were prepared by sputtering a composite Ti target. For comparison purposes, a Cu-pure thin film was prepared under the same conditions and used as a reference. Both films exhibited dense microstructures with differences in surface topography and crystalline structure. The degradation process involved immersing TiCu0.34 and Cu-pure thin films in artificial sweat (prepared following the ISO standard 3160-2) for different durations (1 h, 4 h, 24 h, 168 h, and 240 h). ASV was the technique selected to quantify the amount of Cu(II) released by the electrodes immersed in the sweat solution. The optimal analysis conditions were set for 120 s and -1.0 V for time deposition and potential deposition, respectively, with a quantification limit of 0.050 ppm and a detection limit of 0.016 ppm. The results showed that TiCu0.34 electrodes on polyurethane substrates were significantly more reliable over time compared to Cu-pure electrodes. After 240 h of immersion, the TiCu0.34 electrodes released a maximum of 0.06 ppm Cu, while Cu-pure electrodes released 16 ppm. The results showed the significant impact of the substrate on the electrode's longevity, with cellulose bases performing poorly. TiCu0.34 thin films on cellulose released 1.15 µg/cm2 of copper after 240 h, compared to 1.12 mg/cm2 from Cu-pure films deposited on the same substrate. Optical microscopy revealed that electrodes based on polylactic acid substrates were more prone to corrosion over time, whereas TiCu thin-film metallic glass-like structures on PU substrates showed extended lifespan. This study underscored the importance of assessing the degradation of dry biopotential electrodes for e-health applications, contributing to developing more durable and reliable sensing devices. While the study simulated real-world conditions using artificial sweat, it did not involve in vivo measurements.

Structural evolution and mechanical properties of Cr coatings deposited by magnetron sputtering on PCrNi1MoA steel

Cr coatings were prepared by direct current magnetron sputtering on PCrNi1MoA steel, a substrate that has received limited attention in previous studies. The influence of deposition temperature on the microstructure and mechanical properties of Cr coatings was clarified. A comparative analysis was also performed to assess their performance relative to Cr coatings on the stainless steel substrate. All coatings on PCrNi1MoA steel exhibited densely packed fibrous grains in the cross section and a faceted triangular pyramid shape on the surface. Generally, increasing the deposition temperature led to enhanced mechanical properties, primarily due to the reduction of flaws and microporosity, facilitated by the increased mobility of adatoms at higher temperatures. The maximum values of hardness (H), elastic modulus (E), ratios of H/E and H3/E2, and adhesion strength are 4.1 GPa, 117.8 GPa, 0.43, 0.45 GPa, and 27 N, respectively. Compared to the Cr coatings on stainless steel, those on PCrNi1MoA steel exhibited a higher (110) texture coefficient, more uniform grain structures at high deposition temperatures, smoother surfaces, and better adhesion to the substrate.

Wear and Corrosion Resistance of ZrN Coatings Deposited on Ti6Al4V Alloy for Biomedical Applications

Zirconium nitrides films were synthesized on Ti6Al4V substrates at a bias voltage of −50 V, −80 V, −110 V and −150 V by the direct current (DC) reactive magnetron sputtering technique. The as-deposited coatings were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The wear and corrosion resistance of the obtained ZrN coatings were evaluated to determine the possibility for their implementation in modern biomedical applications. It was found that the intensity of the diffraction peak of the Zr-N phase corresponding to the (1 1 1) crystallographic plane rose as the bias voltage increased, while the ZrN coatings’ thickness reduced from 1.21 µm to 250 nm. The ZrN films’ surface roughness rose up to 75 nm at −150 V. Wear tests showed an increase in the wear rate and wear intensity as the bias voltage increased. Corrosion studies of the ZrN coatings were carried out by three electrochemical methods: open circuit potential (OCP), cyclic voltammetry (polarization measurements) and electrochemical impedance spectroscopy (EIS). All electrochemical measurements confirmed that the highest protection to corrosion is the ZrN coating, which was deposited on the Ti6Al4V substrate at a bias voltage of −150 V.

Visible Light-Driven Photocatalysis and Antibacterial Performance of a Cu-TiO2 Nanocomposite.

A Cu-TiO2 nanomaterial with unique antibacterial and photocatalytic properties is introduced in this study. Cu-TiO2 nanocomposites were obtained using an adapted direct current magnetron sputtering apparatus, where TiO2 anatase nanoparticles (NPs) were used as the substrates and copper as the sputtering target. The obtained powder was characterized by physical and chemical methods. Copper was deposited on TiO2 NPs for 30 and 60 min, resulting in two samples with different copper contents of 3 and 5 wt %, respectively. The photocatalysis test evaluated the degradation of rhodamine B (RhB) dye under a specific wavelength (405 nm LED) and a complete degeneration occurred in 120 min, ∼ 33% faster when compared to pristine TiO2. The antibacterial assays were performed for Escherichia coli and Staphylococcus aureus in dark and visible-light conditions, using a 405 nm LED and a wide-spectrum white LED, reaching an inactivation of 99.9999% for both bacteria. The magnetron sputtering is an ecofriendly way to form heterojunctions with photocatalytic and bactericidal properties in the absence of wet chemical methods or residues. This work may open new pathways for enhancing the fungicidal and virucidal activities of nanocomposites under the action of visible light.

Nanostructure of TiO\(_{2}\) and WO\(_{3}\) multilayer films deposited on ITO glass for electrochromic enhanced photocatalytic activity

The photocatalytic activity (PA) by electrochromic (EC) enhancement of single and multilayer films of TiO2, WO3, TiO2/WO3, and WO3/TiO2 was investigated. All films were deposited from metal on an ITO glass substrate using direct current (DC) magnetron sputtering via an oblique angle deposition (OAD) technique at 85°. Subsequently, a thermal oxidation (TO) process at 500℃ was applied for the samples to form metal oxide films. The morphology, elemental composition, crystal structure, and optical properties were studied by using field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD), and UV-vis spectroscopy, respectively. The photocatalytic properties were investigated by showing the degradation rate of methylene blue (MB) solution as an organic pollutant that was examined under ultraviolet irradiation of 300 µW∙cm‒2. The film samples were investigated by comparing the pre-color and colored states that were achieved through the EC process. The EC properties of WO3 led to increased charge insertion on the film surface. This observation was further supported by cyclic voltammetry (CV) testing, which revealed a higher current density for the thin film samples. The photodegradation results showed that the samples in the colored state exhibited a significantly higher degradation rate of MB compared to the pre-color state.

Passivation Effect of Rock-Salt Nitride Materials on a Planar p-Si Photocathode for Solar Water Reduction.

Photoelectrochemical water splitting, which uses sunlight to produce clean hydrogen fuel, is gaining traction with rising concerns about fossil fuels and pollution. Silicon (Si) photocathodes are promising for this process due to their light absorption and favorable band alignment for hydrogen production. However, limitations such as reflectance, low photovoltage, and rapid photocorrosion hinder their overall performance and stability. An interfacial insulating layer such as SiOx ensures superior durability to p-Si photocathodes. However, the inherent heterogeneity and intrinsic defects pose challenges to effective surface passivation. This study investigates the challenges of photocorrosion and utilization of a thin titanium nitride (TiN) passivation layer deposited using direct-current magnetron sputtering to protect the native silicon oxide (SiOx) layer. Additionally, a molybdenum oxynitride (Mo(O,N)x) bifunctional layer is employed to enhance both the electrocatalytic activity and durability of the photocathode. The presence of oxygen and nitrogen within this cocatalyst layer modifies the surface chemistry of the p-Si photocathode, promoting favorable interfacial interactions with electrolyte species during PEC reactions. This modification facilitates efficient charge transfer processes and accelerates reaction kinetics, ultimately optimizing the performance and operational lifetime of the photocathode. The resulting Mo(O,N)x/TiN/p-Si photocathode exhibited a remarkable onset potential of +0.46 VRHE in harsh acidic conditions under simulated sunlight (AM 1.5G illumination, 100 mW·cm-2). Notably, the photocathode demonstrated exceptional long-term stability exceeding 140 h, highlighting the combined TiN passivation and Mo(O,N)x cocatalyst as a protection strategy.

Microscopic examination of rf-cavity-quality niobium films through local nonlinear microwave response

The performance of superconducting radio-frequency (SRF) cavities is sometimes limited by local defects. To investigate the rf properties of these local defects, especially those that nucleate rf magnetic vortices, a near-field magnetic microwave microscope is employed. Local third-harmonic response (P3f) and its temperature dependence and rf power dependence are measured for one Nb/Cu film grown by direct current magnetron sputtering (DCMS) and six Nb/Cu films grown by high-power impulse magnetron sputtering (HiPIMS) with systematic variation of deposition conditions. Five out of the six HiPIMS Nb/Cu films show a strong third-harmonic response that is likely coming from rf vortex nucleation due to a low-Tc surface defect with a transition temperature between 6.3 and 6.8 K, suggesting that this defect is a generic feature of air-exposed HiPIMS Nb/Cu films. A phenomenological model of surface-defect grain boundaries hosting a low-Tc impurity phase is introduced and studied with time-dependent Ginzburg-Landau (TDGL) simulations of probe-sample interaction to better understand the measured third-harmonic response. The simulation results show that the third-harmonic response of rf vortex nucleation caused by surface defects exhibits the same general features as the data, including peaks in third-harmonic response with temperature, and their shift and broadening with higher microwave amplitude. We find that the parameters of the phenomenological model (the density of surface defects that nucleate rf vortices and the depth an rf vortex travels through these surface defects) vary systematically with film deposition conditions. From the point of view of these two properties, the Nb/Cu film that is most effective at reducing the nucleation of rf vortices associated with surface defects can be identified. Published by the American Physical Society 2024