Glass Thin Films Research Articles

Tailoring nanostructured Ni-Nb metallic glassy thin films by substrate temperature

Improving the thermostability and mechanical properties of metastable amorphous materials are critical for their potential applications. Here we report the achievement of a wide variety of nanostructures and properties in Ni-Nb metallic glass thin films (MGTFs) by tuning the substrate temperature (Tsub) during magnetron sputtering. By gradually increasing Tsub close to glass transition temperature (Tg) from room temperature, we evidence the transition from the hierarchical nanostructure with microcracks to the denser nanostructure with a smoother surface and smaller column/particle size. This transition contributes to the enhanced plastic deformation stability and nanomechanical properties, thermal stability, and optical reflectivity in the visible light wavelength. We explain the nanostructure evolution with Tsub based on the competition between the shadowing effect and surface diffusion. The shadowing effect is dominant in low-Tsub films and promotes the voided boundaries, while surface diffusion is remarkably enhanced at high Tsub (0.76–0.87 Tg) to form dense intergrain boundaries. This finding provides a promising avenue towards producing novel functional MGTFs with controllable nanostructures and properties without any post-treatment.

Observation of yttrium oxide segregation in a ZrO2‐SiO2 glass‐ceramic at nanometer dimensions

AbstractDopant segregation at grain boundaries (GBs) in ceramics has been widely reported, while whether similar segregation behavior occurs in glass‐ceramics remains unknown. The distribution of dopant in glass‐ceramics may be totally different due to the existence of glass phase. This study examines the distribution of Y3+ ions in a ZrO2‐SiO2 glass‐ceramic. Two samples were prepared by hot pressing, yttrium oxide‐doped, and undoped 65 mol% ZrO2‐35 mol% SiO2 nanocrystalline glass‐ceramics (NCGCs). The NCGCs had the same microstructure, that is, ZrO2 nanoparticles (NPs) embedded in an amorphous SiO2 matrix. XRD results showed that the undoped NCGC was composed of 20.9 wt% (weight percentage) monoclinic ZrO2 (m‐ZrO2) and 79.1 wt% tetragonal ZrO2 (t‐ZrO2), while the yttrium oxide‐doped NCGC was composed of 9.6 wt% m‐ZrO2 and 90.4 wt% t‐ZrO2. X‐ray energy‐dispersive spectrometry (EDS) results in scanning electron transmission microscopy (STEM) mode demonstrated that Y3+ ions segregated both on the surface of ZrO2 NPs and within the thin intergranular glass film (with a thickness of approximately 7 Å) between ZrO2 NPs in the yttrium oxide‐doped NCGC. Interestingly, no obvious Y signals were detected in the amorphous SiO2 matrix. Density functional theory calculation results showed that Y3+ ions had a strong segregation tendency in the GB area and the segregation of Y3+ ions increased the work of separation of GB layer. These findings provide new understanding of the segregation behavior of dopant in glass‐ceramics, which may offer useful guidance for other researchers to tailor the properties of glass‐ceramics through GB engineering.

Metallic glass thin film integrated with flexible membrane for electromagnetic micropump application

In this work, metallic glass (MG) thin film integrated with flexible membrane for use in an electromagnetic micropump was proposed and developed. Fe-based MG thin film deposited on a flexible membrane was employed as the actuation membrane. The electromagnetic force generated between the electromagnetic coil and the magnetized thin film was used to excite the actuation membrane. The actuation membrane was integrated with a microchannel for the micropump application. The fluid in the microchannel was driven by the pressure change resulting from the membrane deflection. Membrane deflection of 45 μm was achieved when a current of 0.12 A was applied to the electromagnetic coil. In addition, a maximum flow rate of 0.17 μl min−1 was achieved and driven by the electromagnetic micropump. The Fe-based MG integrated with the flexible membrane actuated by electromagnetic force could be applied to the actuation membrane for the electromagnetic micropump.

Study and fabrication of a flexible Zr-based metallic glass thin film strain gauge

Metallic glass is an amorphous structure and has excellent mechanical properties such as high strength, hardness and elastic strain limitation. In this study, a Zr-based metallic glass thin film was deposited on a polymer substrate using the sputter technique for strain gauge applications. A copper thin film strain gauge was fabricated to compare with the properties of the Zr-based strain gauge. Different thicknesses of the thin films were fabricated for comparison. The gauge factor of the Zr-based strain gauge is 2.4 times higher than that of the copper strain gauge. The temperature coefficient of resistance of the Zr-based metallic glass thin film is extremely low, 8 × 10−6 °C−1, which is essential to reduce thermal drift for strain gauge applications.

Crack and its interaction with defects in Al coated with Cu50Zr50 metallic glass thin film: an MD simulation study.

Molecular dynamics (MD) simulation studies are carried out to investigate the crack propagation behavior and crack-void interactions in Al coated with Cu50Zr50 metallic glass (MG) thin film model. The model thin film is subjected to mode I and mode II loading conditions at a temperature of 300K and a strain rate of 1010s-1. The simulations are carried out in the framework of EAM (embedded atom method) potential based on the CZM (cohesive zone model). The model size is 435Å (x-axis) × 174Å (y-axis) × 17Å (z-axis). Nine models are investigated containing an edge crack (length, L = 43Å, and 118Å) located at the interface and voids (diameter, ϕ = 10-36Å) located in the Al region and at the interface. The results show that crack propagation occurs by dislocation emission and blunts the crack tip. The presence of void ahead of the crack tip restricts the crack propagation due to the stress field resulting in bowing out of the crack and is effective with an increase in the void size which grows normal and parallel to the loading direction. The estimated crack speeds in mode I and mode II are 366m/s and 370m/s during stable crack growth. Separation of the interface occurs by fracture of the ligaments between the voids. Shockley partial dislocations are found nucleating from the void surfaces; twinned regions are found between the voids. The work of separation is found to be 11.56J/m2 for mode I and 3.7J/m2 in mode II, indicating that failure occurs in mode II. Graphical abstract.

Enhancement of electrical performance of ZnSe thin films via Au nanosandwiching

Abstract In this work, we report the effect of sandwiching of Au nanosheets on the structural and electrical properties of ZnSe thin films. The ZnSe films which are grown by the thermal evaporation technique onto glass and yttrium thin film substrates exhibit lattice deformation accompanied with lattice constant extension, grain size reduction and increased defect density upon Au nanosandwiching. The temperature dependent direct current conductivity analysis has shown that the 70 nm thick Au layers successfully increased the electrical conductivity by three orders of magnitude without causing degeneracy. On the other hand, the alternating current conductivity studies in the frequency domain of 10 MHz to 1800 MHz have shown that the alternating current conduction in ZnSe is dominated by both of quantum mechanical tunneling and correlated barrier hopping of electrons over the energy barriers formed at the grain boundaries. The Au nanosheets are observed to increase the density of localized states near Fermi level and reduce the average hopping energy by ~5 times. The conductivity, capacitance, impedance and reflection coefficient spectral analyses have shown that the nanosandwiching of Au between two layers of ZnSe makes the zinc selenide more appropriate for electronic applications and for applications which need microwave cavities.

Impact of substrate nature and film thickness on physical properties of antimony trisulphide (Sb2S3) thin films for multifunctional device applications

Sb 2 S 3 thin films were deposited with various thickness on glass and flexible polymer Polyetherimide (PEI) substrates by simple chemical bath deposition. X-ray diffraction patterns reveal the formation of polycrystalline films with orthorhombic structure. The Sb 2 S 3 thin films grown on the PEI substrate are rougher. The enhancement of roughness for Sb 2 S 3 /PEI thin films leads to improve their hydrophobic character. Furthermore, they show high values of contact angle ( CA ) around 162°. The absorption coefficient of thin films is determined to be higher than 10 4 cm −1 . The band-gap energy has been found to be between 1.6 and 2.1 eV as a function of thickness which related to the variation of structural defects. Thus, the growth of these films significantly depends on the nature of the substrate and its thickness. The obtained results show that all Sb 2 S 3 on glass and PEI thin films have potential applications in the self-cleaning windows and solar cells. • Substrate nature affects the growth orientation, microstructural and surface morphology of Sb 2 S 3 thin films. • PEI flexible substrate leads the obtainment of Sb 2 S 3 super-hydrophobic surfaces. • The physical properties of Sb 2 S 3 thin films are very sensitive to the film thickness.

Size dependent hidden serration behaviors of shear banding in metallic glass thin films

Serration usually observed in metallic glass (MG) is attributed to the shear band propagation and reflects the heterogeneous deformation in a large-length scale. However, the knowledge concerned small length scale heterogeneous deformation intrinsically related to shear transformation zones (STZ) in metallic glass is inadequate, for the difficulty to probe the variable in deformation process on small spatial scales. In this study, we investigated the small length scale hidden serration upon nanoindentation on metallic glass film. The hidden serration was attributed to STZs evolution, instead of shear band propagation. More heterogeneous structure which contains more STZs with larger volume, getting more possibilities to be activated and percolated, result in small-scale serration in the slope curve of load-displacement. The hidden serration patterns established a correlation between load-displacement curve and shear banding process down to microscopic level. It offers a deep understanding of heterogeneous structures dependent plasticity in metallic glasses.

Processing technologies for sealing glasses and glass‐ceramics

AbstractThis paper embraces two different approaches for the joining of materials through glass sealants. First, the conventional method of furnace sealing in which paste technology is normally employed. The glass sealant is applied in powder form mixed with agglomerant and with the help of dispenser robots, tape casting, or screen printing. Glass‐ceramics for sealing of solid oxide fuel cells (SOFC) are described as an example of this type of processing. Glass composition, thermal properties, particle size of the glass powder, sintering and crystallization competition, and final crystalline phases together with a suitable chemical compatibility with the metallic and ceramic elements to be sealed need to be carefully adjusted for this specific application. Second, laser welding is presented as an alternative sealing technology. A general overview about laser welding through glass sealants is presented. Particularly, the welding of sapphire and fused silica glass through a BTS.2SiO2 thin film glass sealant by employment of a nanosecond‐pulsed laser is detailed. Laser parameters (frequency, power, scan speed, and number of passes) were optimized to get the best molten conditions of the BTS thin film, while allowing its crystallization. BTS crystallization upon laser welding leads to a strong blue emission upon UV excitation. Finally, both processing technologies were compared.

Terahertz and Infrared Spectroscopy of Dense and Porous Organosilicate Glass Thin Films

Wide-range measurements of thin films of SiCxOyHz organosilicate glasses, both dense and porous, deposited on dielectric sapphire substrates and conductive layers of platinum and aluminum, were performed in the THz–IR (5–5000 cm–1) range. This method can be used not only to analyze the evolution of absorption bands in amorphous dielectric films but also to evaluate static conductivity in the framework of the Drude model of conductive layers and to determine the electrodynamic characteristics of organosilicate films with low dielectric permittivity. The original approach proposes a comprehensive analysis of experimental broadband data in order to determine not only the parameters of the individual bands of lattice and molecular vibrations but also the integrated electrodynamic characteristics of the samples obtained.

A Novel Non-enzymatic Biosensor Based on Ti-Metallic Glass Thin Film: The Blood Glucose Oxidation Approach.

Background:Material selection is a key issue for the fabrication of non-enzymatic electrode in glucose biosensors. Metallic glass (MG) as an advanced innovative material can provides many basic structural requirements of electrodes. A novel non-enzymatic biosensor based on Ti57Cu28{Zr0.95−Hf0.05}XSi15-X MG (Ti-MG) thin film was introduced for glucose oxidation.Methods:The Ti-MG thin film was deposited on the carbon substrate of screen-printed carbon electrode (SPCE), and the Ti-MG modified SPCE was fabricated as Ti-MG/SPCE. The morphology and structure of the Ti-MG thin film were characterized by field emission scanning electron microscope and X-ray diffraction. Electrochemical evaluations were studied by electrochemical impedance spectroscopy and cyclic voltammetry.Results:The Ti-MG was sputtered on the carbon substrate in the form of a porous spongy thin film with 285 nm thickness and nanoparticles with average diameter size of 110 nm. The Ti-MG/SPCE showed low charge transfer resistance to the electron transfer and high electrocatalytic activity toward the oxidation of glucose in PBS (pH = 7.4) solution. This biosensor exhibited good analytical performance with a linear range from 2 to 8 mM glucose and sensitivity of 0.017 μA mM−1.Conclusion:The experimental results indicate that Ti-MG thin film has a high ability to electron transfer and glucose oxidation for the development of non-enzymatic glucose biosensors.

Proton-conducting BaO-P2O5 and BaO-La2O3-Al2O3-P2O5 glass thin films

BaO-P2O5 (BP) and BaO-La2O3-Al2O3-P2O5 (BLAP) glass thin films with a thickness of 80–160 nm, which have a high content of residual moisture and a high concentration of non-bridging oxygen (NBO) as a medium for proton movement, were fabricated through sol-gel spin coating using water as a solvent. All the fabricated glass thin films exhibited amorphous phase and glassy, defect-free surfaces. The thickness of the BP thin films decreased as the annealing temperature increased. The increase in the annealing temperature led to a decrease in NBO/BO ratio which is thought to affect proton mobility and an increase in mobile proton concentration. Therefore, it seems that high proton concentration by residual water appears to have a dominant effect on fast proton conduction. The calculated proton concentrations of the fabricated BP thin films were decreased from 55.9 mol/l to 45.5 mol/l as the annealing temperature increased from 300 °C to 400 °C. The conductivity of BP and BLAP thin films annealed at 400 °C were 2.52 × 10−6 S/cm and 1.32 × 10−5 S/cm, respectively, at 300 °C. BLAP thin film showed significantly improved conductivity compared to those of BP glass thin films due to its high proton concentration.

Electrocatalytic Behavior of Hydrogenated Pd-Metallic Glass Nanofilms: Butler-Volmer, Tafel, and Impedance Analyses

Electrocatalytic activity and sorption behavior of hydrogen in nanosized Pd–Si–(Cu) metallic glass thin film and Pd thin film electrodes sputtered on a Si/SiO2 substrate were investigated by linear sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrode MG4 (Pd69Si18Cu13) exhibits the best performance with the highest electrocatalytic activity in the hydrogen evolution region with less than half of the Tafel slope of Pd thin film of the same thickness and lowest overpotential at 10 mA cm−2. A new approach has been adopted by a nonlinear fitting of the entire region of the polarization curve (far- and near-equilibrium cathodic and anodic regions) to the Butler-Volmer model. α parameter is lowest for the MG2 electrode (Pd79Si16Cu5), marking that nonequilibrium conditions change the reaction kinetics. Together with MG2, MG4 shows the lowest Bode magnitude values for hydrogen sorption and evolution regions, indicating that the bonding and release of hydrogen atoms to the electrode is easier. MG4 electrode shows a dramatic decrease of the overpotential after 100 cycles, yielding an increase in hydrogen activity. Besides, MG4 exhibits the sharpest current density drop in the HER region in cyclic voltammetry compared with other MG and Pd electrodes, indicating higher electrocatalytic activity towards hydrogen evolution. The findings highlight the influence of the selected metallic glasses for the design and development of metal catalysts with higher sorption kinetics and/or electrocatalytic turnover.

Fabrication, Corrosion, and Mechanical Properties of Magnetron Sputtered Cu-Zr-Al Metallic Glass Thin Film.

The appearance of thin film metallic glasses (TFMGs) is gaining increasing interest because of their unique mechanical and anticorrosion properties and potential engineering applications. In this study, Cu–Zr–Al ternary thin film metallic glasses were fabricated by using DC magnetron sputtering equipment with various target powers. The evolution of the structure was systematically investigated by grazing incidence X-ray diffractometer, scanning electron microscopy, and transmission electron microscopy. The deposition rate increases with the increasing of applied target power. The as-deposited thin films show an amorphous structure. The compositional fluctuations on the nanometer scale indicate the presence of two Cu- and Zr-rich amorphous phases. The electrochemical corrosion measurements indicated that Cu–Zr–Al thin film metallic glasses had good corrosion resistance in the sulfuric acid solution. Nanoindentation results showed that the mechanical deformation was found to be homogenous and reproducible with a high value range for the hardness and modulus.

Thermal poling induced second-order optical nonlinearity in phosphosilicate glass thin films

ABSTRACTA phosphosilicate glass (PSG) nonlinear film is prepared on a fused silica plate using plasma- enhanced chemical vapour deposition (PECVD) and thermal poling. Under all poling conditions, the second-harmonic generation (SHG) signals of the PSG thin-film samples are stronger than those of pristine fused silica. The poling mechanism can be well explained qualitatively by the electric-field induced second-harmonic generation (EFISH) and dipole reorientation models. The hindering effect of the film-glass interface is also observed. Besides, the threshold poling temperature (To), poling voltage (Vo) and poling duration (to) of the PSG thin-film samples are all smaller than those of pristine fused silica, which may be ascribed to less dense PSG films. The nonlinear profile of the PSG thin-film sample is distributed in the whole film and the partial glass substrate on the anodic side of the sample. The second-order nonlinear susceptibility (χ(2)) is around 0.58 and 0.32 pm/V, respectively.

Preparation and characterization of sol-gel derived highly transparent aluminosilicate glass thin films with ultrahigh doping level of Yb3+ ions

A series of highly transparent aluminosilicate glass films with ultrahigh doping level of Yb3+ ions have been prepared by Sol-Gel method and deposited on transparent silica glass substrates with thickness ranging from 0.901 μm to 1.314 μm and doping level of Yb3+ ions up to 30 mol%. Each film exhibits a characteristic photoluminsecence spectrum of Yb3+ ions with a maximum at 975 nm and high transmission in VIS-NIR region. The refractive index for the film has been measured by spectroscopic ellipsometry. AFM images and EPMA cross-sectional images have presented the formation of film surface and cross section respectively and a uniform film formation has been achieved with the composition of 10YbO1.5-15AlO1.5-75SiO2 and 20YbO1.5-12AlO1.5-58SiO2. It has been verified that multilayer films get a major improvement in photoluminescence intensity still with high transmission in VIS-NIR region.

Surface-Bulk Interplay in Vapor-Deposited Glasses: Crossover Length and the Origin of Front Transformation.

Thin film stable glasses transform into a liquid by a moving front that propagates from surfaces or interfaces with higher mobility. We use calorimetric data of vapor-deposited glasses of different thicknesses and stabilities to identify the role of glassy and liquid dynamics on the transformation process. By invoking the existence of an ultrathin intermediate layer whose transformation strongly depends on the properties of both the liquid and the glass, we show that the recovery to equilibrium is driven by the mismatch in the dynamics between glass and liquid. The lifetime of this intermediate layer associated with the moving front is the geometric mean between the bulk transformation time and the alpha relaxation time. Within this view, we explain the observed dependencies of the growth front velocity and the crossover length with both stability and temperature. Extrapolation of these results points towards ordinary thin film glasses transforming via a frontlike transformation mechanism if heated sufficiently fast, establishing a close connection between vapor-deposited and liquid-cooled glasses.

Variations in the linear and nonlinear refractive indices of chalcogenide glass thin films for photonic applications

In this paper, we report the variations in linear and nonlinear refractive indices of Ge20Ga5Sb10S65, Ge20Ga5Sb10Se65, Ge25Sb10S65 and, Ge16As24S60 chalcogenide glass thin films. The linear refractive index (n) has been determined and analyzed by the Swanepoels method and the Wemple-DiDomenico model(WDD). The theoretical formulation by Fournier and Snitzer has been used to study the nonlinear refractive index (n2) which is compared with the modified Boling model. The compositional dependence of various parameters such as the optical band gap(Eg), linear refractive index, extinction coefficient(k), optical conductivity(σ) and dielectric parameters(εr, εi) was also analyzed. Results on variations of linear and nonlinear refractive indices are interpreted on the basis of the optical polarizability of the materials. The n2 of the prepared chalcogenide glass thin films are found to be two orders greater than that of pure and doped silica glasses which make them ideal candidates for all-optical networks.

Broadband Optical Absorber Based on Nanopatterned Metallic Glass Thin Films.

Applications of metallic glass thin films (MGTFs) in the optical area have seldom been reported. We successfully design and fabricate a broadband and durable absorber with MGTFs. It is found that the absorber, with a total thickness of only ∼230 nm smaller than the light wavelength, exhibits excellent performance, that is, an average absorption of >90% from the visible to the near-infrared range (500-1300 nm). This is of significance for the optical application of MGTFs with the potential for large-scale fabrication using superplastic deformation in the supercooled liquid region of MGTFs.

Atomic-scale viscoplasticity mechanisms revealed in high ductility metallic glass films

The fundamental plasticity mechanisms in thin freestanding Zr65Ni35 metallic glass films are investigated in order to unravel the origin of an outstanding strength/ductility balance. The deformation process is homogenous until fracture with no evidence of catastrophic shear banding. The creep/relaxation behaviour of the films was characterized by on-chip tensile testing, revealing an activation volume in the range 100–200 Å3. Advanced high-resolution transmission electron microscopy imaging and spectroscopy exhibit a very fine glassy nanostructure with well-defined dense Ni-rich clusters embedded in Zr-rich clusters of lower atomic density and a ~2–3 nm characteristic length scale. Nanobeam electron diffraction analysis reveals that the accumulation of plastic deformation at room-temperature correlates with monotonously increasing disruption of the local atomic order. These results provide experimental evidences of the dynamics of shear transformation zones activation in metallic glasses. The impact of the nanoscale structural heterogeneities on the mechanical properties including the rate dependent behaviour is discussed, shedding new light on the governing plasticity mechanisms in metallic glasses with initially heterogeneous atomic arrangement.