Silica Films Research Articles

Dual-band dielectric metamaterial absorber and sensing applications

We present numerically a dual-band dielectric metamaterial absorber where a silica film layer is inserted between the top asymmetric silicon dimer array and the bottom metal substrate. The simulation results show that we can get two resonance peaks (labeled A and B) with near-perfect absorption in the near-infrared regime. Peak A, which is originated from the cavity resonance in the gaps of the dimers, has a full width at half-maximum (FWHM) of 4.8 nm and quality factor of 407. And peak B, which is originated from the destructive interfering of the asymmetric dimers, has an ultra-narrow bandwidth of 0.0014 nm and quality factor of 1.38×106which are much superior to those of the existing metamaterial absorbers. In addition, the simulations also show that the absorption bandwidths can be further narrowed by adjusting the silica layer thickness. Due to the ultra-narrow bandwidths, peaks A and B have the high figure of merits (FOMs) of 51.4 and 6.0×104. Such high FOMs indicate that the proposed dual-band absorber can be applied as a high-performance refractive index sensor.

Low-temperature re-oxidation of near-interface defects and voltage stability in SiC MOS capacitors

We proposed a solution to improve the interface property and voltage instability of silicon carbide metal–oxide–semiconductor (SiC MOS) capacitors by eliminating near-interface defects with a single oxygen element. Results indicated that the quality of the silicon dioxide (SiO2) film and SiC/SiO2 interface and the voltage stability of SiC MOS capacitors were simultaneously improved by the proposed process. The mechanism underlying the improvement in the electrical performance of SiC MOS capacitors by oxygen plasma re-oxidation annealing (OP-ROA) could be elaborated by analysing the results of secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. We believe that the OP-ROA process can eliminate C- and Si-related defects and silicon oxycarbide (SiOxCy) and reduce the thicknesses of the interface–transition region, thereby decreasing relative Si and C contents near the SiC/SiO2 interface. The evolution of C-related defect structures was simulated through density functional theory calculation, which was performed as a supplemental analysis.

An environmentally friendly approach to produce single-layer anti-reflective coatings on large surfaces using wet chemical method

Sustainable production of anti-reflective coatings demands environmentally friendly approaches. This paper introduces a novel method of preparing thin films from an aqueous medium using a sol-gel technique. Single-layer anti-reflective coatings, from water-based silica sols, were prepared and characterized. The thicknesses of thin films were found to be between 75 and 135 nm with refractive indexes between 1.23 and 1.41 and porosities between 7 and 53%. The maximum transmissions of manufactured coatings reached from 99.85% to 99.03% in the visible region. The ageing of silica particles in the aqueous medium was studied using TEM. The transparent water-based sol consisted of individual silicon-dioxide nanoparticles with narrow size distribution (15–20 nm). The TEM images showed, that the silica nanoparticles become uniform and distinguishable within two weeks and no aggregation occurs within 46 days. It was found, that the aqueous silica sol is stable and clear for more than 6 months. The aqueous silica films deposited onto large glass surfaces were found to be homogeneous, with excellent adhesion (Cross Hatch Test is 0; ISO 2409 test standard) and hardness equal to 2H. We present a schematic illustration of the adsorption mechanism of non-ionic silicone surfactant and Pluronic surfactant on the silica surface.

Phenylboronic acid-functionalized vertically ordered mesoporous silica films for selective electrochemical determinationof fluoride ion in tap water.

Theselective electrochemical determination of fluoride is reported by phenylboronic acid-functionalized vertically ordered mesoporous silica film attached to the indium tin oxide electrode, designed as PBA-VMSF/ITO. Fluoride ion can selectively bind to phenylboronic acid to generate boronate anions, leading to negative charges inside the ultrasmall nanochannel of VMSF and ultimately rejecting the access of potassium ferricyanideions to the electrode surface. By recording the reduced electrochemical signal of potassium ferricyanide, determinationof fluoride ion in aqueous solution was achieved with a fast response, wide response range, and high selectivity. Furthermore, with the specific recognition of PBA and anti-fouling ability of VMSF, the PBA-VMSF/ITO sensor has been successfully used to detect fluoride ion in tap water.

Spectroscopic Properties of Si-nc in SiOx Films Using HFCVD.

In the present work, non-stoichiometric silicon oxide films (SiOx) deposited using a hot filament chemical vapor deposition technique at short time and simple parameters of depositions are reported. This is motivated by the numerous potential applications of SiOx films in areas such as optoelectronics. SiOx films were characterized with different spectroscopic techniques. The deposited films have interesting characteristics such as the presence of silicon nanoclusters without applying thermal annealing, in addition to a strong photoluminescence after applying thermal annealing in the vicinity of 1.5 eV, which may be attributed to the presence of small, oxidized silicon grains (less than 2 nm) or silicon nanocrystals (Si-nc). An interesting correlation was found between oxygen content, the presence of hydrogen, and the formation of defects in the material, with parameters such as the band gap and the Urbach energies. This correlation is interesting in the development of band gap engineering for this material for applications in photonic devices.

Large temperature range model for the atmospheric pressure chemical vapor deposition of silicon dioxide films on thermosensitive substrates

Coating complex surfaces by functional amorphous silica films for new applications including energy harvesting and health depends on the operating range and robustness of their deposition process. In this paper, we propose a new kinetic model for the atmospheric pressure chemical vapor deposition of SiO2 films from TEOS/O2/O3 valid in the 150−520 °C temperature range, thus allowing for treating thermally sensitive substrates. For this, we revisit reported chemical schemes in Computational Fluid Dynamics simulations considering original experimental data on the deposition rate of SiO2 films from a hot-wall reactor. The new model takes into account for the first time a thermal dependency of the direct formation of SiO2 from TEOS and O3 and yields excellent agreement in both shape and value between experimental and calculated local deposition rate profiles. The model provides non-measurable information such as local distributions of species concentration and reaction rates, which are valuable for developing optimized CVD reactor designs. Original solutions for the introduction of the reactants are proposed, to uniformly coat complex and/or large parts at a wide temperature range.

Structural and optical properties of Zn-implanted silica: effect of fluence and annealing

The phase-structural composition of a silica film grown on Si substrate implanted with Zn ions at room temperature with different fluences has been studied using transmission electron microscopy and electron diffraction. The small clusters (1–2 nm) and the large clusters (5–7 nm) have been formed in as-implanted silica films with the Zn concentration of 6–7 at % and 16–18 at %, respectively. Furnace annealing at 750 °С for two hours results both in the formation of the orthorhombic Zn2SiO4 phase (space group R-3) in the case of low fluence (5 · 1016 cm–2) and in the formation of the cubic ZnO phase (space group F-43m) in the case of high fluence (1 · 1017 cm–2). It has been shown that impurity loss during implantation and subsequent annealing increase with fluence of implanted ions. The fraction of Zn atoms in clusters has been estimated to be 15 % and 18 % for fluences (5 · 1016 cm–2) and (1 · 1017 cm–2), respectively. It has been shown that residual Zn impurities dissolved in silica matrix noticeably suppress the light-emitting properties of silica with embedded Zn2SiO4 and ZnO nanocrystals.

Structurally coloured organic–inorganic hybrid silica films with a chiral nematic structure prepared through a self-templating approach

ABSTRACT Structural coloured organic–inorganic hybrid silica films are prepared through a self-templating approach using a liquid crystalline organosilane and a chiral dopant under the catalysis of HCl. The reflective band is tunable by changing the concentration of the chiral dopant. Field-emission scanning electron microscopy images indicated that the layer structure is constructed by right-handed packed nanofibers.

Cross-Plane Thermal Conductance of Phosphonate-Based Self-Assembled Monolayers and Self-Assembled Nanodielectrics.

Self-assembled nanodielectrics (SANDs) consist of alternating layers of polarized phosphonate-functionalized azastibazolium π-electron (PAE) and high-k dielectric metal oxide (ZrO2 or HfOx) films. SANDs are desirable gate dielectrics materials for thin-film transistor applications because of their excellent properties such as low-temperature fabrication, large dielectric strength, and large capacitance. In this paper, we investigate the cross-plane thermal boundary conductance of SANDs using the frequency domain thermoreflectance (FDTR) technique. First, we characterize the thermal conductance of PAE self-assembled monolayers (SAMs), inverted-PAE (IPAE) SAMs, and mixed PAE-IPAE SAMs, sandwiched between thin gold and silica (SiO2) films at the top and bottom surfaces. Next, we quantify the thermal conductance of SAND-n with different numbers (n) of PAE-ZrO2 layers and thicknesses ranging between 4.7 and 11.3 nm. From the FDTR measurements, we observe that the thermal boundary conductance of the SAMs can be tuned between 42.1 ± 4.6 MW/(m2 K) and 52.4 ± 2.5 MW/(m2 K), based on the relative density of the PAE and IPAE chromophores. In the SAND-n samples, we observe a monotonic decrease in the thermal conductance with increasing n. We use the measured thermal conductance data in a series resistance model to estimate a thermal interface conductance of 695 MW/(m2 K) for the contact between the PAE chromophore and the zirconium dioxide films, which is an order of magnitude larger than the SAMs. We attribute the improved thermal conductance to stronger adhesion between the PAE chromophore and the zirconium dioxide films, as compared to the weakly bonded SAMs to the gold and silicon dioxide films.

Phonon-assisted electron tunneling between traps in silicon oxide films treated in hydrogen plasma

The charge transport in thin thermal silicon oxide films treated in electron cyclotron resonance hydrogen plasma at different exposure times was investigated. X-ray photoelectron studies show that such treatment leads to the oxygen deficiency of the films. It was established that the treatment of the films in plasma leads to an increase of their conductivity by a factor of about 102. The film charge transport properties were studied at different temperatures and analyzed within four theoretical dielectric conductivity models. It was found that the charge transport mechanism is described by Fowler-Nordheim model in the initial silicon oxide and by the model of phonon-assisted electron tunneling between neutral traps after the treatment in hydrogen plasma. The thermal trap ionization energy value (Wt = 1.6 eV) measured from transport experiments is in agreement with that obtained from ab initio calculations for the oxygen vacancy (Si-Si bond) in SiO2.

Preparation and Magnetic Properties of Nano-Sized Iron Powder Particles Coated with Silica Film by Calcium Hydride Reduction Method

Preparation and Magnetic Properties of Nano-Sized Iron Powder Particles Coated with Silica Film by Calcium Hydride Reduction Method

Apparent relaxation of in-plane residual stress of sol–gel-derived crystalline and glass oxide thin films

Crystalline or glass oxide thin films with thickness of ca. 50–210 nm and porosity of ca. 5–17% were prepared on Si(100) wafers by the sol–gel method. The films were left standing at room temperature in dry and humid atmosphere as well as in water for varying periods of time. We measured the in-plane residual stress of the films as a function of time during storing at room temperature by measuring the radius of curvature of the substrate surface. The anatase, silica, and ceria films had tensile in-plane residual stress when fired at 1000 °C, 600 °C, and 800 °C, respectively. Such tensile stress was found to decrease with time, finally becoming constant, at room temperature, where the rate and extent of stress reduction were larger in the order, “in water” > “in humid atmosphere” > “in dry atmosphere.” On the other hand, the silica films had compressive in-plane residual stress when fired at 1000 °C. Such compressive stress was stable, not decreasing with time, at room temperature. The ceria film, after showing a decrease in tensile stress in humid atmosphere, exhibited an increase in stress when heated at 300 °C. When stored again at room temperature in humid atmosphere, the film showed a decrease in stress with time over again. Then we excluded the structural relaxation as the origin of the tensile stress reduction at room temperature, considering the stability of the compressive stress and the reversibility of the tensile stress. The ceria films showed a decrease in tensile stress even when stored in acetone and n-heptane vapors, suggesting that the film expansion resulting from the vapor-molecule adsorption may be the origin of the decrease in tensile stress. Yttria-stabilized zirconia films fired at 1000 °C also had tensile stress. The stress, however, was constant with time at room temperature, the reason for which is unknown, and further studies should be made.

Production of low-energy fragment-ion beams from hexamethyldisiloxane and the irradiation of SiO+ ion beam to substrates with supplemental oxygen gas for SiO2 film formation

In this work, low-energy fragment-ion beams were produced from hexamethyldisiloxane (HMDSO) used as a source material and substrates were irradiated by these beams with supplemental oxygen gas for the formation of silicon dioxide (SiO2) film. During this process, SiO+ ions having an energy of 50 eV were mass-selected from various fragments derived from the decomposition of HMDSO. These ions were subsequently transferred to a Si substrate at room temperature in conjunction with a supplemental oxygen flow. The resulting film was assessed by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy to confirm SiO2 deposition. The bonding of incident SiO+ ions with a quartz crystal microbalance (QCM) was assessed at ion energies of 50, 100 and 200 eV, and the sticking probability of incident SiO+ ions to the QCM crystal substrate was found to decrease monotonically with increasing energy.

Medium-Pressure Reactivity of Acetylene on Pd-Cu Alloy Nanoparticles Supported on Thin Silica Films.

The ability to correlate industrial high-pressure catalysis with high-vacuum research has been of great interest for decades. We employed a double-chamber vacuum system to study the self-hydrogenation of acetylene to ethylene and its trimerization to benzene at medium pressures to compare the reactivity in this pressure range to the known model catalytic acetylene reactivity in ultrahigh vacuum (UHV). We measured the reactivity of Pd-Cu bimetallic alloy nanoparticles (ANPs) with different elemental compositions deposited on top of native SiO2/Si(100) and on bilayer SiO2/Ru(0001) surfaces, where the latter was shown to contribute to ANP stability. Following exposure to 0.5 mbar of acetylene, ANPs on both surfaces catalyze the formation of ethylene and benzene, with ethylene as the more probable product. The ANPs on bilayer SiO2/Ru(0001) were highly selective toward ethylene formation, with an ethylene/benzene ratio of more than 2 orders of magnitude, whereas on the native SiO2/Si(100) there was a significantly lower selectivity (about 5) at the same temperature range and catalyst elemental composition. Interestingly, these selectivity values are similar to those found under UHV conditions. In addition, ANPs grown on native SiO2/Si(100), unlike SiO2/Ru(0001), revealed an optimal temperature for ethylene and benzene formation due to the limited stability of the particles.

Window Layer Thickness Effect on Amorphous Silicon Oxide Solar Cell Performances

The recent research and developments of a-Si:H based solar cells have greatly promoted its position as low cost solar cell. Unfortunately, a-Si:H solar cells suffer appreciable light induced degradation for thickness greater than 200nm. It has been reported that boron doped hydrogenated amorphous silicon oxide (p-a-SiOx:H) films have a low temperature coefficient compared to those based on hydrogenated amorphous silicon (p-a-Si:H) . Moreover, the solar cells with a p-a-SiOx: H generate more electricity than the solar cells with p-a-Si: H window layer due to the wider band gap (Eg) of these films. We present in this paper a computer simulation on the effects of window layer thickness on the performances of single junction amorphous silicon oxide solar cells. We varied the thickness of the window layer from 5 nm to 25 nm and our simulation results showed that cells parameters are significantly affected window layer thickness. However, the film thickness of the p-a-SiOx:H window layer increased from 5 nm to 25 nm, the power conversion efficiency (PCE) of the solar cells respectively decreased in the ranges of 5.733% to 5.271% .the simulation data are in good agreement with the literature

Deuterated silicon dioxide for heterogeneous integration of ultra-low-loss waveguides.

Ultra-low-loss waveguide fabrication typically requires high-temperature annealing beyond 1000°C to reduce the hydrogen content in deposited dielectric films. However, realizing the full potential of an ultra-low loss will require the integration of active materials that cannot tolerate high temperature. Uniting ultra-low-loss waveguides with on-chip sources, modulators, and detectors will require a low-temperature, low-loss dielectric to serve as a passivation and spacer layers for complex fabrication processes. We report a 250°C deuterated silicon dioxide film for top cladding in ultra-low-loss waveguides. Using multiple techniques, we measure propagation loss below 12 dB/m for the entire 1200-1650 nm range and top-cladding material absorption below 1 dB/m in the S, C, and L bands.

Photonic crystal films with high reflectance based on mesoporous silica in the extreme ultraviolet range

In the present work, mesoporous silica films with hexagonally packed perpendicular nanochannels treated as a 2D photonic crystal in extreme ultraviolet (EUV) range are explored by combining theories and experiments. The simulation results show that this film structure exhibits high reflectivities in a wide band range from 5 nm to 11 nm and at broad incidences angle range. The better reflective properties can be ascribed to its excellent photonic crystal structure corresponding to short spectral region. Experimentally, highly ordered mesoporous silica films with vertical mesochannels were fabricated by electrochemically assisted self-assembly method. Moreover, the reflectances of the fabricated film at 5–11 nm region were also tested using synchrotron radiation, which can reach up to 80.4% at 2°from grazing incidence direction. Meanwhile, a relative high reflectance can be maintained at 5–11 nm at incidence angles of 2–7°. This research results offer a new strategy to developing a promising extreme ultraviolet optical film with high reflectance and broad band range.

Improving Mechanical Properties of Glass Fiber Reinforced Polymers through Silica-Based Surface Nanoengineering

Glass fiber reinforced polymer (GFRP) composites are widely used materials in structural and transport applications owing to their excellent strength-to-weight ratio. In GFRPs, mechanical properties are mainly governed by the filler-to-matrix interphase region, which need to be rationally designed and carefully engineered to optimize the composite performance. However, the structural and chemical parameters that optimize mechanical performance are partially unknown. Here, we report on different surface nanoengineering strategies and their effect on the mechanical properties of GFRPs. Commercial woven glass fibers (wGFs) are modified with several distinct silica-based nanostructured coatings that provide different pore sizes, surface areas, and adhesion energies. To study their mechanical properties, epoxy–wGF laminated composites are manufactured and characterized using sliding contact, tensile, and three-point bending tests. Composites based on coated wGFs generally show improved mechanical performance over those based on bare wGFs. In particular, wGFs coated with mesoporous silica films display the highest specific surface areas, pore sizes and adhesion energies and provide the highest Young’s and flexural modulus, with up to 31% improvement with respect to composites based on bare wGFs. The improvement of the composite’s mechanical properties with the wGFs coating is related to a better stress distribution and a homogeneous loading transfer at the polymer–GF interphase. Overall, this study provides insights on how GFRP’s mechanical properties can be boosted beyond the current state-of-the-art by the rational design of its interphase.

Highly Selective Polishing Rate Between a Tungsten Film and a Silicon-Dioxide Film by Using a Malic-Acid Selectivity Agent in Tungsten-Film Chemical-Mechanical Planarization

For achieving a highly selective polishing rate between a tungsten (W) film and a silicon-dioxide (SiO2) film in W chemical-mechanical planarization (CMP), we designed W-film CMP slurry by mixing a small-molecule having two carboxylic functional groups (i.e., malic acid) as a selectivity agent. The selectivity was principally controlled by the malic acid concentration: it rapidly increased with increasing malic acid concentration in the W-film CMP slurry, and a W-film polishing rate:SiO2-film polishing rate of >100:1 was achieved. We found that the selectivity was mainly determined by the chemical properties, such as the corrosion and the chemical reaction between the films and malic acid rather than by the mechanical property, i.e., the electrostatic force between the ZrO2 abrasive and the films.

Development of a Selective and Sensitive Chlorogenic Acid Fluorimetric Sensor Using Molecularly Imprinted Polymer ZnO Quantum Dots

In this work, an optical sensor based on zinc oxide quantum dots (ZnO-QDs) was used to determine the chlorogenic acid (CGA). First, ZnO-QDs were prepared using a sol-gel method. Next, a thin film of silica was formed on the surface of ZnO-QDs using a reverse microemulsion technique. To prepare the molecularly imprinted polymer (MIP), 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) were employed as a functional monomer and a cross-linker, respectively. Finally, the ZnO-QDsMIP composite was used to measure CGA. Different variables, affecting the optical signal of the sensor, were optimized. Under the optimal conditions, the linear dynamic range of the optical sensor was from 0.2 to $5.3~\mu \text{g}$ mL−1 CGA with a detection limit as $0.06~\mu \text{g}$ mL−1. The effect of several potentially interfering species was investigated, and the results confirmed an excellent selectivity of the sensor for the measurement of CGA. Using this sensor to measure CGA in human plasma samples showed that the sensor is also capable of measuring CGA in complex matrix samples.