Metal Films Research Articles

Exploring Structural Anisotropy in Amorphous Tb-Co via Changes in Medium-Range Ordering.

Amorphous thin films grown by magnetron co-sputtering exhibit changes in atomic structure with varying growth and annealing temperatures. Structural variations influence the bulk properties of the films. Scanning nanodiffraction performed in a transmission electron microscope (TEM) is applied to amorphous Tb17Co83 (a-Tb-Co) films deposited over a range of temperatures to measure relative changes in medium-range ordering (MRO). These measurements reveal an increase in MRO with higher growth temperatures and a decrease in MRO with higher annealing temperatures. The trend in MRO indicates a relationship between the growth conditions and local atomic ordering. By tilting select films, the TEM measures variations in the local atomic structure as a function of orientation within the films. The findings support claims that preferential ordering along the growth direction results from temperature-mediated adatom configurations during deposition, and that oriented MRO correlates with increased structural anisotropy, explaining the strong growth-induced perpendicular magnetic anisotropy found in rare earth-transition metal films. Beyond magnetic films, we propose the tilted FEM workflow as a method of extracting anisotropic structural information in a variety of amorphous materials with directionally dependent bulk properties, such as films with inherent bonding asymmetry grown by physical vapor deposition.

Preferential Stripping Analysis of Post-Transition Metals (In and Ga) at Bi/Hg Films Electroplated on Graphene-Functionalized Graphite Rods

In this study, we introduce a novel electrochemical sensor combining reduced graphene oxide (rGO) sheets with a bismuth–mercury (Bi/Hg) film, electroplated onto pencil graphite electrodes (PGEs) for the high-sensitivity detection of trace amounts of gallium (Ga3+) and indium (In3+) in water samples using square wave anodic stripping voltammetry (SWASV). The electrochemical modification of PGEs with rGO and bimetallic Bi/Hg films (ERGO-Bi/HgF-PGE) exhibited synergistic effects, enhancing the oxidation signals of Ga and In. Graphene oxide (GO) was accumulated onto PGEs and reduced through cyclic reduction. Key parameters influencing the electroanalytical performance, such as deposition potential, deposition time, and pH, were systematically optimized. The improved adsorption of Ga3+ and In3+ ions at the Bi/Hg films on the graphene-functionalized electrodes during the preconcentration step significantly enhanced sensitivity, achieving detection limits of 2.53 nmol L−1 for Ga3+ and 7.27 nmol L−1 for In3+. The preferential accumulation of each post-transition metal, used in transparent displays, to form fused alloys at Bi and Hg films, respectively, is highlighted. The sensor demonstrated effective quantification of Ga3+ and In3+ in tap water, with detection capabilities well below the USEPA guidelines. This study pioneers the use of bimetallic films to selectively and simultaneously detect the post-transition metals In3+ and Ga3+, highlighting the role of graphene functionalization in augmenting metal film accumulation on cost-effective graphite rods. Additionally, the combined synergistic effects of Bi/Hg and graphene functionalization have been explored for the first time, offering promising implications for environmental analysis and water quality monitoring.

High-Performance Ga2O3 Solar-Blind Photodetector Based on Thermal Oxidized Ga Buffer-Layer.

High-performance Ga2O3 solar-blind photodetectors are critical for applications due to their selective solar-blind ultraviolet sensitivity. The quality of the Ga2O3 film has a significant impact on the performance of photodetectors. This study presents an innovative approach to enhancing the quality of Ga2O3 films through the introduction of a naturally graded buffer layer, which is formed by the oxidation of a metallic Ga film and significantly improves interface stability by accommodating lattice mismatches and reducing defects. The structural and compositional characteristics of Ga2O3 films were comprehensively analyzed using UV-vis (ultraviolet-visible) spectroscopy, AFM (Atomic Force Microscope), PL (Photoluminescence Spectroscopy), TEM (Transmission Electron Microscope), and XPS (X-ray Photoelectron Spectroscopy). The photodetectors fabricated from these films demonstrate responsivity of 99.8 mA/W and a solar-blind UV/UV ratio of 1.17 × 103, with significant improvement compared to direct deposited films. This research highlights the potential of natural buffering layers to advance the performance of Ga2O3-based solar-blind UV detectors.

Graphene‐Induced Surface Softening and Nanostructure Evolution of Platinum Foils

While it has been previously accepted that graphene growth on metal films by chemical vapor deposition (CVD) protects the surfaces by stiffening and hardening, in this study, an unusual opposite effect is reported. Herein, we use nanoindentation to study the mechaniported. Herein, we use nanoindentation to study the mechanical behavior of graphene‐covered platinum foils. Two graphene growth recipes using undiluted and diluted methane flow are studied, aiming to achieve a bulk or a surface‐mediated graphene growth mechanism, respectively. Contrary to previous reports, a 17% decrease is observed in the elastic modulus of the Pt surfaces when covered by graphene compared to graphene‐free regions for both recipes, when using the real indentation contact area extracted via atomic force microscopy (AFM) for the estimation. By performing cross‐sectional transmission electron microscopy (TEM), subsurface multilayers responsible for the decrease in stiffness are revealed and these observations and the mechanism of layer formation are explained. Hence, in this study, it is highlighted that surface stiffening of metals by graphene CVD has exceptions, especially in the case of metals with high carbon solubility. Moreover, in this study, approaches for combining cross‐sectional TEM, topological scans from AFM, and raw load–displacement data from nanoindentation to provide a complete, multiscale elucidation of the mechanical behavior of a material surface are described.

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.

Tailoring Second Harmonic Generation via Strong Coupling in a One‐Dimensional Photonic Crystal Heterostructure

Controlling harmonic generation is crucial for nonlinear optics and nanophotonic devices. Herein, a 1D photonic crystal heterostructure is theoretically proposed comprising a metal film, a lithium niobate layer, and a distributed Bragg reflector with a defect layer. The Tamm state and the defect state for dual‐band second‐harmonic generation (SHG) enhancement simultaneously are numerically investigated. Finite‐element method simulations indicate that SHG efficiencies based on Tamm plasmons and the defect state are 6.85 × 10−6 and 3.28 × 10−4, respectively. Intriguingly, the strong coupling between the defect state and Tamm plasmons enables spatial energy exchange, leading to the SHG switching between them. In the strong coupling region with Rabi splitting energy up to 5.5 meV, the SHG conversion efficiency reaching 5 × 10−5 is observed for both two new hybridized states. During the entire anticrossing Rabi splitting process, the SHG efficiency difference between two resonances can be modulated by up to two orders of magnitude. The coupling strength between two resonances is adjusted by varying the position of the defect layer. Simulation results are consistent with the coupled oscillator model. This work not only offers a platform for studying nonlinear frequency conversion but also establishes a new method of using strong coupling to tailor SHG.

Dragonfly‐Inspired Compound Eye Lens with Biomimetic Structural Design

AbstractCompound eye biomimetics are extensively studied owing to their high level of functionality. However, optimizing material‐dependent parameters, such as refractive index, is essential for maximizing lens function. Therefore, metal films are deposited on Pantala flavescens compound eyes using a magnetic mirror magnetron cathode, which deposits films at low temperatures without plasma impingement. By increasing the thickness of the film on the compound eye surface, a compound eye mold is successfully fabricated with high heat tolerance. Lens fabrication is achieved using a high‐temperature‐curable resin. The resulting lens comprises numerous uniformly shaped functional units. This method offers a highly reproducible lens‐pouring molding technique using various materials, marking a significant advancement in developing imaging devices and sensors that accurately replicate the functionalities of dragonfly eyes.

Tilted columnar metal film as transducer of transverse coherent acoustic phonons in picosecond acoustics

Picosecond acoustics has been widely used to study thin film elasticity, hypersound attenuation, and adhesion of thin films to substrates. A major limitation of the technique is its restriction to only longitudinal waves. Although work has been reported on the ultrafast generation and detection of transverse waves, a general method compatible with thin films deposited on silicon is still missing. In this work, we show that by depositing a tilted columnar metal film and using an optical detection sensitive to light polarization, it is possible to excite and detect optically both types of bulk acoustic waves in thin films. The protocol is first established on metalized glass substrates, then applied to a range of transparent films deposited on silicon (silica, AlN, AlScN, and SiC). In each case, Brillouin oscillations are detected at two frequencies, one being the longitudinal mode, the other the transverse. The film thickness and two sound velocities are measured in each thin film. Transverse coherent phonons as high as 116 GHz are observed in the SiC thin film.

Tailoring the structure of Al50Mo50 alloy films towards realizing the well match between mechanical and electrical performance by controlling the growth mode

Metal films that combine superior mechanical properties with good conductivity are crucial for fulfilling the structural and functional requirements for MEMS applications. To achieve this, single-phase supersaturated solid solution Al50Mo50 alloy films were synthesized using magnetron sputtering at room temperature. By varying the deposition rate, the growth mode of these films was systematically controlled. The results demonstrate that there is no segregation in any of the films, which maintain homogeneity in composition and exhibit unexpected thermal stability at 550℃. As the deposition rate increases, the growth mode of the films transitions from a nano-columnar crystal structure to a layered + island structure. The supersaturated solid solution Al50Mo50 alloy film featuring a layered + island structure exhibits notable properties: high hardness (11.86GPa), high elastic modulus (194.27GPa), excellent ductility with a critical strain of 1.5%, and exceptionally low resistivity (100.95 μΩ cm). This combination of mechanical and electrical properties ensures a well-balanced performance suitable for MEMS applications. Moreover, the controlled process of the growth model and the optimization mechanism for enhanced ductility are systematically elucidated. These findings identify Al50Mo50 alloy films as an ideal candidate material for the design and development of MEMS/NEMS devices.

Corrosion resistance properties and hydrogen embrittlement protection efficiency of single-layer and multi-layer metal and ceramic films deposited on SS316L substrates

Hydrogen is a promising source of clean energy. However, the tanks used to store hydrogen fuel are prone to hydrogen embrittlement and are thus at risk of stress cracking and catastrophic failure. Accordingly, this study deposited single-layer and double-layer Zr, Al, SiO2, Al2O3, Al@Al2O3, and Al@SiO2 films on 316L stainless steel substrates and examined their feasibility as protective coatings by measuring their anti-corrosion properties and hydrogen permeation currents. The results showed that the single-layer Al2O3 film had a higher corrosion resistance than the single-layer SiO2 film and bare 316L substrate. Among all the coatings, the Al@Al2O3 double-layer coating exhibited the highest protection efficiency of 95%. Moreover, it showed the lowest hydrogen penetration current density (1.08 x 10-3 A/cm2), the longest hydrogen embrittlement time (16000 s), and the lowest hydrogen content (0.008 mol/cm3). In other words, the Al@Al2O3 double-layer coating combined superior corrosion resistance with excellent hydrogen permeation suppression. Consequently, it is a promising material for enhancing the safety and longevity of hydrogen storage tanks in practical applications.

Investigation of arc spot splitting behavior on aluminum, titanium, and their alloy cathodes under different gas flows

This paper presents an experimental study on the spot splitting behavior of aluminum, titanium, and their alloy cathodes during electric arc discharge. Utilizing high-speed digital cameras, we dynamically captured the splitting motion of cathode arc spots and analyzed their behavior under different pressures of argon, nitrogen, and oxygen. The study also examined the effects of pulsed arc current parameters on spot splitting. We observed a ringlike expansion of pulsed arc spots during splitting, with aluminum cathodes showing better performance than titanium in promoting spot splitting and stabilizing the subsequent motion of the split spots. Oxygen was found to enhance spot splitting more effectively than nitrogen. Furthermore, the parameters of the pulsed arc can control the extent of spot splitting and expansion. These findings provide valuable insights for optimizing arc parameter control in metal film deposition processes.

Tunable Graphene‐Based Absorber Using Nanoscale Grooved Metal Film at Telecommunication Wavelengths

Graphene‐based absorbers have various modern applications across industries due to their exceptional properties. Some common applications include: thermal management and energy storage. Herein, the design and simulation of a broadband tunable absorber based on graphene with perfect absorption spectra in the near‐infrared region are reported. The proposed structure consists of an MgF2 layer and golden disc surrounded by L‐shaped golden arms placed on single layer of graphene. The structure guarantees polarization‐insensitive (PI) performance under normal incident due to the symmetrical design. The investigation of the PI of the structure reveals almost similar absorption for oblique incident angles up to 55° for TM and up to 60° for TE polarization. The desirable resonance wavelength is achievable by tuning the geometrical parameters. By changing the chemical potential of graphene, the absorption and bandwidth of absorber are controllable. A full width at half maximum of 330 nm is another superiority of this absorber. These considerable aspects of the proposed structure make it practical for varieties of applications such as cloaking, sensing, switching, and so on.

Detection of Serratia marcescens and Mierococcus lysodeikticus Bacterial Cells Using Cerium Oxide/Transition Metal Dichalcogenides Heterostructure‐Based Surface Plasmon Resonance Sensor

This article explores a novel surface plasmon resonance sensor for detecting the Serratia marcescens and Mierococcus lysodeikticus bacteria cells employing the cerium oxide (CeO2) and transition metal dichalcogenides heterostructure. The proposed sensor is designed based on the Kretschmann configuration, where silver (Ag) is deposited over a prism's surface to excite the surface plasmons. The transfer matrix method and angular interrogation technique are exploited for analyzing the sensor's performance at a wavelength of 633 nm. Firstly, the optimization of the prism and metal film is analyzed by selecting the minimum reflectance, better sensitivity, and quality factor. Secondly, the influence of the proposed structure in the sensor is executed by the performances of different structures, which are made with defined layers. Thirdly, different sensing parameters are analyzed for the considered bacterial cells, resulting in the maximum attained parameters being a sensitivity of 369.40° RIU−1, QF of 151.35 RIU−1, and detection accuracy of 7.57. Finally, the comparative study also shows the noteworthy enhancement using the proposed sensor compared with existing work. Therefore, the proposed sensor can be used as a carrier for detecting the bacterial cells and establishing a new platform for biomolecular and biomedical applications.

Ambient pressure x-ray photoelectron spectroscopy study on the initial atomic layer deposition process of platinum

The initial adsorption of MeCpPtMe3 is investigated using synchrotron-based ambient pressure x-ray photoelectron spectroscopy (XPS). The experiments are done on a native oxide-covered Si substrate. In addition, a reaction with O2 and the created Pt surface was investigated. Inspiration for the reaction studies was found from atomic layer deposition of metallic Pt, process that uses the same compounds as precursors. With time-resolved XPS, we have been able to observe details of the deposition process and especially see chemical changes on the Pt atoms during the initial deposition of the Pt precursor. The change of the binding energy of the Pt 4f core level appears to occur on a different timescale than the growth of the active surface sites. The very long pulse of the Pt precursor resulted in a metallic surface already from the beginning, which suggest chemical vapor deposition-like reactions occurring between the surface and the precursor molecules in this experiment. Additionally, based on the XPS data measured after the Pt precursor pulse, we can make suggestions for the reaction pathway, which point toward a scenario that leaves carbon from the MeCpPtMe3 precursor on the surface. These carbon species are then efficiently removed by the subsequent coreactant pulse, leaving behind a mostly metallic Pt film.

Deposition of thin refractory-metal-films onto glasses through diaphragms at plasma focus facility

The results of experiments are presented on the deposition onto silicate glasses of thin refractorymetal- films: molybdenum, tantalum and tungsten. The technique used for manufacturing films was based on the deposition of metal-containing plasma formed when exposing the surface of foils made of refractory metals to high-power plasma and ion pulses. For generation of such pulses, the facility of plasma focus type was used, which makes it possible to obtain ion beams and plasma flows with the energy flux density in the range of 1010—1012 W/cm2. The most intense central part of the ion-plasma flow was separated using metal diaphragms with aperture diameters of 2.5, 3.5, and 4.5 mm. Metal Mo, Ta and W films with dimensions of ∅ 3—5 mm were obtained on the surfaces of glasses. Metal films are characterized by good adhesion, since they coalesce with the glass surface. It was discovered that the planarity of films becomes violated due to the drift of molten metal particles under the glass surface. The relief of films is non-uniform, which can be explained by the presence of micrometer-sized metal particles in the plasma flow.

Evaluating size effects on the thermal conductivity and electron-phonon scattering rates of copper thin films for experimental validation of Matthiessen’s rule

As metallic nanostructures shrink towards the size of the electronic mean free path, thermal conductivity decreases due to increased electronic scattering rates. Matthiessen’s rule is commonly applied to assess changes in electron scattering rates, although this rule has not been validated experimentally at typical operating temperatures for most of the electronic systems (e.g., near room temperature). In this study, we experimentally evaluate the validity of Matthiessen’s rule in determining the thermal conductivity of thin metal films by measuring the in-plane thermal conductivity and electronic scattering rates of copper (Cu) films with varying thicknesses (27 nm — 5 µm), microstructures, and grain boundary segregation. Comparing total electron scattering rates measured with infrared ellipsometry to infrared ultrafast pump-probe measurements, we find that the electron-phonon coupling factor is independent of film thickness, whereas the total electronic scattering rate increases with decreasing film thickness. Our findings provide experimental validation of Matthiessen’s rule for electron transport in thin metal films at room temperature and also introduce an approach to discern critical heat transfer processes in thin metal interconnects, which holds significance for the advancement of future CMOS technology.

Phonon Drag Contribution to Thermopower for a Heated Metal Nanoisland on a Semiconductor Substrate.

The possible contribution of phonon drag effect to the thermoelectrically sustained potential of a heated nanoisland on a semiconductor surface was estimated in a first principal consideration. We regarded electrons and phonons as interacting particles, and the interaction cross-section was derived from the basic theory of semiconductors. The solution of the equation of motion for average electrons under the simultaneous action of phonon drag and electric field gave the distributions of phonon flux, density of charge carriers and electric potential. Dimensional suppression of thermal conductance and electron-phonon interaction were accounted for but found to be less effective than expected. The developed model predicts the formation of a layer with a high density of charge carriers that is practically independent of the concentration of dopant ions. This layer can effectively intercept the phonon flow propagating from the heated nanoisland. The resulting thermoEMF can have sufficient magnitudes to explain the low-voltage electron emission capability of nanoisland films of metals and sp2-bonded carbon, previously studied by our group. The phenomenon predicted by the model can be used in thermoelectric converters with untypical parameters or in systems for local cooling.

Synthesis of ZnO NWs via Thermal Evaporation Technique

Zinc oxide nanowires ZnONWs were successfully synthesized on glass slides. The synthesis was conducted firstly by the deposition of 12 µm a thin film of Zn metal by thermal evaporation. Secondly,the coated film was annealed at a temperature of 600 ºC in air for four hours to grow the ZnO nanowires. It have been observed that the produced nanowires were grown in a vertical orientation and having a high density, very long, and a minimal aspect ratio. The crystal structure and morphology of ZnO nanowires were investigated with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The UV-visible spectrophotometer was also used to calculate the optical parameters from the absorption spectrum and show a band gap energy around 3.25 eV. The crystal structure of the material was revealed to be polycrystalline with a preferred orientation in the direction of [101]. Small average crystallite size was calculated about 17nm The wires can be measured to have a length of around 10 µm with diameters ranging from 50 to 100 nm. This could be used for gas sensor applications. In addition, this ZnONWs structure has a maximum transmittance (100%) which can be a good candidate for many optoelectronic apllications.

Parametric Excitation and Instabilities of Spin Waves Driven by Surface Acoustic Waves

AbstractThe parametric excitation of spin waves by coherent surface acoustic waves in metallic magnetic thin film structures is demonstrated experimentally using Brillouin light scattering spectroscopy. Complementary micromagnetic simulations and analytical modeling reveal that, depending on the experimental conditions, the spin‐wave instabilities originate from different phonon‐magnon and magnon‐magnon scattering processes. This opens novel ways to create micro‐scaled nonlinear magnonic systems for logic and data processing that profit from the efficient excitation of phonons using piezoelectricity.

Control resonant excitation of surface plasmon polariton in quantum-dot molecule system via tunneling induced transparency and Autler–Townes splitting

Electromagnetic induced transparency (EIT) and Autler–Townes splitting (ATS) both produce a transparency window in an absorption profile, yet EIT is distinct in that it can create a transparency window for a weak control field. To elucidate the distinct physical mechanisms underlying EIT and ATS effects, we explore the controlled resonant excitation of surface plasmon polaritons (SPPs) within these regimes. Our setup is composed of three layers: a top vacuum or air layer, a central metal film, and a bottom layer of dielectric medium based on the quantum-dot molecules (QDMs) system. Unlike typical systems, that employ prism or grating coupling scheme, our setup takes advantage of the unique features of the QDMs medium to investigate the direct resonance excitation of SPPs. A weak probe and a strong control field are carried through air or vacuum to the top layer. Our results demonstrate that the permittivity of the bottom medium displays tunneling induced transparency (TIT) if the tunneling strength (Te) and the decay rate of the direct exciton (Γ1) follow the condition Te/Γ1⩽0.5; otherwise, it represents the ATS effect. In both instances, the permittivity of the QDMs medium satisfy the low-loss (high transmission) criteria, i.e., Re [ɛd]<1 and Im [ɛd]≪1, providing a framework for exploring the control resonant excitation of SPPs. We simulate the reflection and transmission spectra using the Fresnel’s formula and noticed sharp dips in reflection and peaks in the transmission spectra, which are the signature of coupler free resonance excitation of SPPs. We noticed that the narrow peak in TIT allows for strong light transmission and thus a high peak in SPP resonance excitation, resulting in higher sensitivity in plasmonic sensors. Conversely, the large spacing between the two peaks in the ATS effect broadens the range of effective excitation frequencies for SPPs, increasing the system’s adaptability and efficiency in applications requiring broad spectrum responses.