Amorphous Silica Substrates Research Articles

Ion-induced surface effects on soda-lime, amorphous silica (aSiO2) and silicon (100) substrates with 1.5 MeV Cu ion implantation

Soda-lime, silica and silicon (100) substrates were implanted with 1.5 MeV Cu+ ions with observable macroscopic surface effects. All substrates were irradiated at 70°, at 200-nA currents, in room temperature conditions, and for a total ion fluence between 3×1016 and 2×1017 ions cm−2. Surface characterization was carried out using SEM and AFM. Changes on the morphology result in the emergence of surface structures resembling ripples in the early stage which evolve into complex wrinkling structures at high ion doses. The formation and growth of surface patterns may be elucidated in terms of low and medium energies theories.

Reduced thermal resistance of amorphous Al2O3 thin films on β-Ga2O3 and amorphous SiO2 substrates via rapid thermal annealing

The impact of rapid thermal annealing (1000 °C for 1 min) on the thermal transport properties of amorphous alumina (a-Al2O3) thin films grown by atomic layer deposition on β−Ga2O3 and amorphous silica (a-SiO2) substrates is determined using frequency-domain thermoreflectance measurements. The annealing more than doubles the a-Al2O3 thermal conductivity for both substrates (1.54 ± 0.13 to 3.14 ± 0.27 W m−1 K−1 for β−Ga2O3 and 1.60 ± 0.14 to 3.87 ± 0.33 W m−1 K−1 for a-SiO2) while keeping the film amorphous. The thermal conductivity increase is attributed to partial recrystallization and off-gassing of embedded impurities. Annealing halves the thermal boundary resistance of the a-Al2O3/a-SiO2 interface (10.5 ± 1.0 to 4.47 ± 0.42 m2 K GW−1), which is attributed to compositional mixing and structural reorganization that are enabled by the elastic matching of these two materials. The thermal boundary resistance of the a-Al2O3/β−Ga2O3 interface is not affected by annealing due to the elastic mismatch. Reducing the thermal resistance of a-Al2O3 dielectric films and adjacent interfaces by annealing will promote lateral heat spreading adjacent to hot spots and improve device longevity.

Study on properties of diamond-like carbon films deposited by RF ICP PECVD method for micro- and optoelectronic applications

In this paper, a comparison of Diamond-like Carbon (DLC) films with different sp3 fraction content prepared by Radio Frequency Inductively Coupled Plasma Enhanced Chemical Vapour Deposition (RF ICP PECVD) was presented. Structural, surface, optical, and mechanical properties of deposited DLC films were analyzed with the use of awide range of measurement techniques. The investigated films were deposited on silicon (Si), amorphous silica (SiO2), and metallic (Ti6Al4V) substrates at room temperature. The deposited DLC films have sp3 fraction content ranging from 35 % to 70 %, uniform, compact and dense microstructure. The investigation indicates that the properties of DLC films required for micro- and optoelectronic applications improve with the sp3 fraction content. The refractive index (n) increased from 1.976 to2.086, packaging density (PD) from 0.964 to 0.744, electrical resistivity (ρ) from 2.1 ∙ 1010 to 4.4 ∙ 1011 Ωcm, hardness (H) from 16.4 19.1 to GPa and elastic modulus (E) from 109 to 129 GPa. However, the 50 % sp3 DLC thin film exhibited the highest resistance to cracking (H3/E2 = 0.44). The decrease of Urbach energy (EU) from 0.75 to 0.46 eV was observed for the DLC film with the highest sp3 fraction content, while all investigated DLC samples had similar optical bandgap energy (Egopt ≈ 1.3 eV). The research has shown that it is possible to obtain DLC coatings using the RF ICP PECVD technique that has better properties than films deposited by the classic PECVD technique.

Influence of annealing on selected properties of mixed copper and titanium oxides

This work presents an investigation of the effects of post-process annealing on the morphologyof mixed copper and titanium oxides and on their electrical and hydrogen sensing properties. (CuTi)Oxthin films were deposited by magnetron sputtering on amorphous silica and ceramic substrates withinterdigitated electrodes. In addition, post-process thermal treatment was applied at the temperaturesof 200C and 250C.The transformation of the thin film structure during the thermal oxidation process was studied byX-ray diffraction, while the morphology of the thin films was determined using an optical profilometer.Current-voltage and thermoelectric characteristics were measured to determine electrical properties,from which the resistance and conduction type were determined. The post-treatment (CuTi)Ox thinfilms exhibited hole-type conduction and, additionally, strongly responded to hydrogen atmosphere.Keywords: electronics, hydrogen gas sensors, mixed copper and titanium oxides, thin films, magnetronsputtering

Atomistic prediction on the degradation of vinylester-based composite under chloride and elevated temperature

Vinylester resin is widely used as matrix for fabricating glass fiber reinforced polymer in marine applications. Even though vinylester based material is understood to be durable in general, the interface between vinylester and the bonded additive can be degraded when subjected to various environmental conditions. Here, the degradation at vinylester/glass interface in chloride environment under elevated temperature is studied through molecular dynamics simulations. The atomistic model consists of a cross-linked vinylester matrix and an amorphous silica substrate. The results show that environmental condition of chloride and elevated temperature leads to the largest loss of interfacial adhesion, which correlates with structural and mechanical degradation of bonded interface. The degradation mechanism is indicated by reduced interfacial stress, decreased vinylester density close to interface, and formation of H-bond. Softened polymer matrix and deteriorated interface inhibit the stress transfer between fiber and matrix, eventually leading to deteriorated macroscopic properties. The performance of degraded vinylester is also compared with other polymer matrixes to provide guidance for designing more durable polymeric composites. This study provides fundamental information on interfacial deterioration in vinylester based composites, which forms the basis for predicting degradation of macroscopic performance.

Effect of the Substrate on MoS2 Monolayer Morphology: An Integrated Computational and Experimental Study.

Synthesis of two-dimensional materials, specifically transition metal dichalcogenides (TMDs), with controlled lattice orientations is a major barrier to their industrial applications. Controlling the orientation of as-grown TMDs is critical for preventing the formation of grain boundaries, thus reaching their maximum mechanical and optoelectronic performance. Here, we investigated the role of the substrate's crystallinity in the growth orientation of 2D materials using reactive molecular dynamics (MD) simulations and verified with experimental growth using the chemical vapor deposition (CVD) technique. We considered MoS2 as our model material and investigated its growth on crystalline and amorphous silica and sapphire substrates. We revealed the role of the substrate's energy landscape on the orientation of as-grown TMDs, where the presence of monolayer-substrate energy barriers perpendicular to the streamlines hinder the detachment of precursor nuclei from the substrate. We show that MoS2 monolayers with controlled orientations could not be grown on the SiO2 substrate and revealed that amorphization of the substrate changes the intensity and equilibrium distance of monolayer-substrate interactions. Our simulations indicate that 0° rotated MoS2 is the most favorable configuration on a sapphire substrate, consistent with our experimental results. The experimentally validated computational results and insight presented in this study pave the way for the high-quality synthesis of TMDs for high-performance electronic and optoelectronic devices.

In silico study of substrate chemistry effect on the tethering of engineered antibodies for SARS-CoV-2 detection: Amorphous silica vs gold

The influence of the properties of different solid substrates on the tethering of two antibodies, IgG1-CR3022 and IgG1-S309, which were specifically engineered for the detection of SARS-CoV-2, has been examined at the molecular level using conventional and accelerated Molecular Dynamics (cMD and aMD, respectively). Two surfaces with very different properties and widely used in immunosensors for diagnosis, amorphous silica and the most stable facet of the face-centered cubic gold structure, have been considered. The effects of such surfaces on the structure and orientation of the immobilized antibodies have been determined by quantifying the tilt and hinge angles that describe the orientation and shape of the antibody, respectively, and the dihedrals that measure the relative position of the antibody arms with respect to the surface. Results show that the interactions with amorphous silica, which are mainly electrostatic due to the charged nature of the surface, help to preserve the orientation and structure of the antibodies, especially of the IgG1-CR3022, indicating that the primary sequence of those antibodies also plays some role. Instead, short-range van der Waals interactions with the inert gold surface cause a higher degree tilting and fraying of the antibodies with respect to amorphous silica. The interactions between the antibodies and the surface also affect the correlation among the different angles and dihedrals, which increases with their strength. Overall, results explain why amorphous silica substrates are frequently used to immobilize antibodies in immunosensors.

Correlation between Electrostatic and Hydration Forces on Silica and Gibbsite Surfaces: An Atomic Force Microscopy Study.

The balance between hydration and Derjaguin–Landau–Verwey–Overbeek (DLVO) forces at solid–liquid interfaces controls many processes, such as colloidal stability, wetting, electrochemistry, biomolecular self-assembly, and ion adsorption. Yet, the origin of molecular scale hydration forces and their relation to the surface charge density that controls the continuum scale electrostatic forces is poorly understood. We argue that these two types of forces are largely independent of each other. To support this hypothesis, we performed atomic force microscopy experiments using intermediate-sized tips that enable the simultaneous detection of DLVO and molecular scale oscillatory hydration forces at the interface between composite gibbsite:silica–aqueous electrolyte interfaces. We extract surface charge densities from forces measured at tip–sample separations of 1.5 nm and beyond using DLVO theory in combination with charge regulation boundary conditions for various pH values and salt concentrations. We simultaneously observe both colloidal scale DLVO forces and oscillatory hydration forces for an individual crystalline gibbsite particle and the underlying amorphous silica substrate for all fluid compositions investigated. While the diffuse layer charge varies with pH as expected, the oscillatory hydration forces are found to be largely independent of pH and salt concentration, supporting our hypothesis that both forces indeed have a very different origin. Oscillatory hydration forces are found to be distinctly more pronounced on gibbsite than on silica. We rationalize this observation based on the distribution of hydroxyl groups available for H bonding on the two distinct surfaces.

Self-organization mechanisms in a Fe-Au film: from isolated core-shell to multicore nanoparticles

Many nanotechnological applications necessitate a high density of nanoparticles (NPs), making NP morphology control highly challenging. In this work, the morphology of bimetallic NPs formed by magnetron sputtering deposition of a Fe(3 nm)-Au(2 nm) bilayer film on an amorphous silica substrate is analyzed using high-angle dark-field scanning transmission electron microscopy (HAADF-STEM). While all the NPs adopt a Fe-Au core-shell chemical order, they can be sorted into three different types. Isolated NPs, displaying either a highly symmetric centered core geometry (CC-type) or an asymmetrical off-centered core geometry (OC-type), are observed despite the rather large metallic volume. The majority of the NPs however displays a multicore geometry, with Fe cores in the 10-12 nm range, larger than the NPs observed in a pure Fe (3nm) film grown under identical conditions. The driving forces leading to the different morphologies are discussed together with the role played by the environnement.

Deposited Mono-component Cu Metallic Glass: A Molecular Dynamics Study

In this work, the simulation of the physical vapor deposition process of Cu on amorphous silica substrate was performed. The resultant Cu thin layer is amorphous. In addition, the liquid quenching of Cu from 2000 K to 50 K was simulated with different cooling rates to allow the comparison of Cu metallic glass formation. Copper glasses from the two different processes (PVD and quenching) showed comparable radial distribution functions. However, the Voronoi tessellation analyses revealed different local structures. The Cu glass obtained by PVD process exhibited higher densities and lower potential energies when compared to its melt-quenched counterpart, which resembles the properties of ultrastable glasses.

Degradation of epoxy/glass interface in hygrothermal environment: An atomistic investigation

The degradation at the glass fiber/matrix interface through molecular dynamics simulations in hygrothermal environment is investigated. The glass fiber reinforced polymer composite has been modeled using a cross-linked epoxy matrix and amorphous silica substrate. The degradation mechanism in hygrothermal environment is indicated through the reduction of decreased adhesion energy and the weakened intermolecular interactions with the consideration of hydration bond. Furthermore, softened epoxy molecules in hygrothermal conditioning possess a lower density near the fiber surface, which inhabits the stress transfer between fiber and matrix, eventually leading to the deteriorated interfacial adhesion. Our simulation results echo with the experimental measurements, which can be further calibrated and utilized as inputs in micromechanical models to bridge the gap between the macroscopic and microscopic behavior of civil infrastructures.

Atomistic investigation of GFRP composites under chloride environment

Fiber reinforced polymer composites have paved the way for the evolution of the engineering materials. Glass fiber reinforced polymer (GFRP) has become one of the most promising materials among the novel composites due to its low price and high performance. Here, the GFRP composite in investigated by fill atomistic molecular dynamics, which contains the epoxy matrix and amorphous silica substrate. The degradation in chloride environment is revealed through the interfacial interactions, the structural changes of the epoxy matrix and hydrogen bonding in the composites. Compared to dry and aqueous environment, the simulation results show that chloride environment leads to the worst deterioration of interfacial adhesion, which correlates with structural and mechanical degradation of bonded interface, as indicated by the decreased epoxy density close to interface. It is indicated by examining the nano-structures of the interface during the pulling process that the chloride environment hinders the formation of intramolecular and intermolecular hydrogen bonds in the GFRP composites. These findings indicate the deterioration towards bond and matrix is critical in the presence of the chloride environment, which provides the fundamental insight for designing and predicting performance degradation of macroscopic GFRP composites in the marine application.

Deposition of Single Phase Polycrystalline α-Fe2O3 Thin Film on Silicon and Silica Substrates by Spray Pyrolysis

Thin films of polycrystalline single phase α-Fe2O3 have been deposited on single crystal silicon and amorphous silica (silica) substrates by spray pyrolysis technique in a single step using a mixture of water and ferrocene dissolved in xylene. The films have been characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy techniques. The uniformity of the grown films was evident from the electron microscopic images on both the substrates. The crystallinity and band gap were investigated using X-ray diffraction and absorption spectroscopy respectively. Raman measurements of the prepared films have been carried out using two excitation wavelengths of 633 nm and 785 nm to investigate the depth of homogeneity of the films. The wavelength dependent Raman measurements reveal that the film is uniform across the thickness of the film on both the substrates.

Titanium Carbide MXene Nucleation Layer for Epitaxial Growth of High-Quality GaN Nanowires on Amorphous Substrates.

Growing III-nitride nanowires on 2D materials is advantageous, as it effectively decouples the underlying growth substrate from the properties of the nanowires. As a relatively new family of 2D materials, MXenes are promising candidates as III-nitride nanowire nucleation layers capable of providing simultaneous transparency and conductivity. In this work, we demonstrate the direct epitaxial growth of GaN nanowires on Ti3C2 MXene films. The MXene films consist of nanoflakes spray coated onto an amorphous silica substrate. We observed an epitaxial relationship between the GaN nanowires and the MXene nanoflakes due to the compatibility between the triangular lattice of Ti3C2 MXene and the hexagonal structure of wurtzite GaN. The GaN nanowires on MXene show good material quality and partial transparency at visible wavelengths. Nanoscale electrical characterization using conductive atomic force microscopy reveals a Schottky barrier height of ∼330 meV between the GaN nanowire and the Ti3C2 MXene film. Our work highlights the potential of using MXene as a transparent and conductive preorienting nucleation layer for high-quality GaN growth on amorphous substrates.

Thermophysical properties of refractory W-50.4%Re and Mo-39.5%Re thin alloy layers deposited on silicon and silica substrates

The examined samples were W-Re and Mo-Re thin alloy layers with high content of Rhenium, applied in industry as protective coatings. The 550 nm of W-50.4%Re and 580 nm of Mo-39.5%Re alloys were deposited on crystalline silicon and amorphous silica substrates by magnetron sputtering method. For thermal characterization of investigated layers the scanning thermal microscopy (SThM) and high frequency photothermal radiometry (HF-PTR) measurements were carried out. The thermal methods were supported by the microstructural studies performed by the atomic force microscopy (AFM) and X-ray diffraction (XRD). The SThM method allowed determining the thermal conductivity (κ) of the alloy layers. From the HF-PTR the effective thermal conductivity (κeff) was determined directly. Estimation of the thermal boundary resistance (Rth) between particular alloy layer and its substrate enabled determination of the real κ of the layer with its thermal diffusivity (α) and effusivity (ε) from the HF-PTR fitting. The results showed, that W-Re and Mo-Re layers deposited on Si are characterized by higher κ, α, and ε values, and lower Rth in comparison to those deposited on SiO2. The κ values for W-Re and Mo-Re layers deposited on Si and SiO2 substrates were estimated in the range from 7 W·m−1 K−1 to 12 W·m−1 K−1, and 1.6 W·m−1 K−1 to 4 W·m−1 K−1, respectively. The correlation between the alloy layer structure, it's thermophysical properties and substrate structure was observed. The AFM and XRD measurements confirmed the short range order formation in Mo-Re layers deposited on Si.

Interfacial thermal resistance between few-layer MoS2 and silica substrates: A molecular dynamics study

Interfacial thermal resistance (ITR) between molybdenum disulfide (MoS2) and crystalline or amorphous silica as a substrate was studied using molecular dynamics (MD) simulation. To do so, pump–probe method, which is a MD technique inspired by an experimental method, was employed. The effects of substrate type, temperature, number of layers of MoS2 and van der Waals (vdW) coupling strength on ITR between MoS2 and its silica substrates were explored. It was observed that, obtained ITR values for crystalline or amorphous silica substrate were close to one another. Our findings showed that, by increasing the temperature from 200 K to 400 K, ITR between a single-layer MoS2 and its crystalline or amorphous silica substrate decreases by about 20%, which might be due to better phonons couplings at the interface in higher temperatures. We also showed that, ITR between multilayer MoS2 and crystalline or amorphous silica substrate does not differ by increasing the number of layers of MoS2. It has been found that, by increasing Lennard-Jones coupling strength from 0.5 to 2, ITR between a single-layer MoS2 and crystalline/amorphous silica substrate decreases by around 80%, showing better phonons couplings at the interface between the two structures.

Kinetics and crystal texture improvements on thin germanium layers obtained by aluminium induced crystallization using oxygen plasma

The fabrication of strongly-textured thin crystalline germanium layers on amorphous silica substrates can be achieved by aluminium induced crystallization using the ‘aluminium induced layer exchange’ mechanism. This requires a diffusion barrier, or interlayer, between the Al and Ge layers with a specific chemistry. We investigate here the effect of oxygen plasma on this interlayer as an alternative route to the standard air-exposure process. We find that the plasma treatment strongly slows down the kinetics of the crystallization. This can be compensated by a higher process temperature, after which the defect density becomes similar to that of air-oxidized but with defects of smaller size. This substantially improves the overall texture of the Ge layer and a near complete (111) orientation is obtained.

Organic-Silica Interactions in Saline: Elucidating the Structural Influence of Calcium in Low-Salinity Enhanced Oil Recovery

Enhanced oil recovery using low-salinity solutions to sweep sandstone reservoirs is a widely-practiced strategy. The mechanisms governing this remain unresolved. Here, we elucidate the role of Ca2+ by combining chemical force microscopy (CFM) and molecular dynamics (MD) simulations. We probe the influence of electrolyte composition and concentration on the adsorption of a representative molecule, positively-charged alkylammonium, at the aqueous electrolyte/silica interface, for four electrolytes: NaCl, KCl, MgCl2, and CaCl2. CFM reveals stronger adhesion on silica in CaCl2 compared with the other electrolytes, and shows a concentration-dependent adhesion not observed for the other electrolytes. Using MD simulations, we model the electrolytes at a negatively-charged amorphous silica substrate and predict the adsorption of methylammonium. Our simulations reveal four classes of surface adsorption site, where the prevalence of these sites depends only on CaCl2 concentration. The sites relevant to strong adhesion feature the O− silica site and Ca2+ in the presence of associated Cl−, which gain prevalence at higher CaCl2 concentration. Our simulations also predict the adhesion force profile to be distinct for CaCl2 compared with the other electrolytes. Together, these analyses explain our experimental data. Our findings indicate in general how silica wettability may be manipulated by electrolyte concentration.

Hydrogen production over the hetero-junction MnO2/SiO2

The motivation of this work is the hydrogen production as a non-polluting renewable energy under visible light. For this purpose, the hetero-junction 2%MnO2/SiO2 was synthetized by the impregnation method and characterized by X-ray diffraction, scanning electron microcopy (MEB), FTIR spectroscopy, diffuse reflectance and electrical conductivity. The X-ray analysis shows the amorphous silica substrate and the rutile phase MnO2. The optical curve (αhν)2 as a function of hν shows a direct transition of 1.83 eV for MnO2. The capacitance measurement of the rutile indicates a flat band potential of −0.027 VSCE, more negative than the hydrogen evolution in SO32− aqueous solution. As application, hydrogen was successfully evolved over the hetero-junction MnO2/SiO2. A good H2 production was obtained after 30 min of irradiation corresponding to 5.1 mmol h−1 g−1 under visible light (29 mWcm−2). The improved photocatalytic performance is due to the sensitizer MnO2 homogeneously supported on porous SiO2 substrate acting as templating agent.

YIG Films Through Synthesis by Means of the Polymeric Precursor Method: Correlation Between the Structural and Vibrational Properties with Magnetic Behavior

Yttrium iron garnet (YIG, Y3Fe5 O 12) films were synthesized from a polymeric precursor and they were deposited by spin coating onto amorphous silica substrates; where the films were annealed at T a = 450, 600, 700, 800, and 900 ∘C under air. Vibrational and magnetic properties of YIG films were followed by means of Raman spectroscopy, vibrant sample magnetometry (VSM), and ferromagnetic resonance (FMR), respectively. X-ray diffraction and Raman spectroscopy indicated that the YIG films are crystalline after annealing at T a ≥ 800 ∘C, but they are amorphous below T a. The amorphous films have a broad Raman band to 670 cm−1, due to higher states in the phonon state density of YIG, suggesting the existence of a short order around tetrahedral Fe3+ ions. Magnetic hysteresis measurements are indicative of a superparamagnetic behavior in amorphous YIG films and with a soft magnetic behavior in the crystalline ones. The deconvolution in FMR spectra shows that the amorphous precursor films have two different absorption modes corresponding to different sites for Fe3+ ions: the first is associated with magnetic local ordering around tetrahedral Fe3+ centers corresponding with superexchange interactions J aa in tetrahedral sites, while the other absorption is associated with an amorphous matrix in the paramagnetic state. Finally, FMR spectra in crystalline films show the presence of two different sites for Fe3+ ions, and that they are associated with magnetic local ordering around tetrahedral and octahedral Fe3+ centers.