Thickness Of Silica Layer Research Articles

Atomic layer deposited titanium dioxide coatings on KD-II silicon carbide fibers and their characterization

To provide oxidation protection and/or to act as an interfacial coating, titanium oxide (TiO2) coatings were deposited on KD-II SiC fibers by employing atomic layer deposition (ALD) technique with tetrakis(dimethylamido)titanium (TDMAT) and water (H2O) as precursors. The average deposition rate was about 0.08nm per cycle, and the prepared coatings were smooth, uniform and conformal, shielding the fibers entirely. The as-deposited coatings were amorphous regardless of the coating thickness, and changed to anatase and rutile crystal phase after annealing at 600°C and 1000°C, respectively. The oxidation measurement suggests that the TiO2 coating enhanced the oxidation resistance of SiC fibers obviously. SiC fibers coated with a 70-nm-thick TiO2 layer retained a relatively high tensile strength of 1.66GPa even after exposition to air at 1400°C for 1h, and thick silica layer was not observed. In contrast, uncoated SiC fibers were oxidized dramatically through the same oxidation treatment, covered with a macro-cracked thick silica film, and the tensile strength was not measurable due to interfilament adhesion. The above results indicate that TiO2 films deposited by ALD are a promising oxidation resistance coating for SiC fibers.

Production of silver-silica core-shell nanocomposites using ultra-short pulsed laser ablation in nanoporous aqueous silica colloidal solutions

Ultra-short pulsed laser ablation of materials in liquid has been demonstrated to be a versatile technique for nanoparticles production. In a previous paper, it has been described, for the first time, how by laser ablation in a liquid system, silver nanoparticles can be loaded onto SBA-15 and MCM-41 supports which show promising catalytic properties for the oxidation of Volatile Organic Compounds (VOCs). The aim of the present research is to demonstrate the formation of stable silver-silica core-shell nanoparticles by direct laser ablation (Ti:Sa; 800 nm; pulse duration: 120 fs; repetition rate: 1 kHz, pulse energy: 3.6 mJ, fluence: 9 J cm − 2) of a Ag target submerged in a static colloidal solution of MCM-41 or SBA-15 silica nanoporous materials. In previous studies, it was discovered that a side and negligible product of the laser ablation process of silver performed in water-silica systems, could be related to the formation of silver-silica core-shell nanoparticles. In order to emphasize this side process some modifications to the laser ablation experimental set-up were performed. Among these, the most important one, in order to favor the production of the core-shell systems, was to keep the liquid silica suspension firm. The laser generated nanomaterials were then analyzed using TEM morphologic characterization. By UV–vis absorption spectra the observed features have been related to components of the colloidal solution as well as to the number of the incident laser pulses. In this manner characterizations on both the process and the resulting suspension have been performed. Significant amount of small sized silver-silica core-shell nanoparticles have been detected in the studied systems. The size distribution, polydispersivity, UV–vis plasmonic bands and stability of the produced silver-silica core-shell nanocomposites have been related to the extent of damage induced in the nanoporous silica structure during the ablation procedure adopted here. In presence of SBA-15 the silver-silica core-shell nanoparticles observed by TEM are smaller and more homogeneously dispersed if compared with the core-shell system obtained when the MCM-41 mesoporous silica was used. The outcomes show that the choice of the mesoporous silica material can affect the silica shell thickness in addition to the Ag NPs size distribution. With this regard, TEM images evidence that in MCM-41 the silver-silica core-shell nanostructures display a silica layer thickness between 1–10 nm; conversely, for SBA-15, the silver-silica core-shell nanoparticles are finely dispersed and the silica shell shows, when present, an average thickness of about 5 nm.

Synergic combination of the sol-gel method with dip coating for plasmonic devices.

Biosensing technologies based on plasmonic nanostructures have recently attracted significant attention due to their small dimensions, low-cost and high sensitivity but are often limited in terms of affinity, selectivity and stability. Consequently, several methods have been employed to functionalize plasmonic surfaces used for detection in order to increase their stability. Herein, a plasmonic surface was modified through a controlled, silica platform, which enables the improvement of the plasmonic-based sensor functionality. The key processing parameters that allow for the fine-tuning of the silica layer thickness on the plasmonic structure were studied. Control of the silica coating thickness was achieved through a combined approach involving sol–gel and dip-coating techniques. The silica films were characterized using spectroscopic ellipsometry, contact angle measurements, atomic force microscopy and dispersive spectroscopy. The effect of the use of silica layers on the optical properties of the plasmonic structures was evaluated. The obtained results show that the silica coating enables surface protection of the plasmonic structures, preserving their stability for an extended time and inducing a suitable reduction of the regeneration time of the chip.

Structural and microwave properties of silica-coated NiFeMo flakes/polymer composites

The microwave properties of sheets containing silica-coated NiFeMo flakes are investigated and discussed according to the sheet structure, the silica layer uniformity and thickness. Commercial NiFeMo flakes are coated using the Stoeber method and embedded in polymer using the doctor blade process. The silica layer thickness is estimated by transmission electron microscopy (TEM) and the coating quality is probed by scanning electron microscopy (SEM). The in-plane orientation of magnetic moments within the sheet is evidenced by 57Fe Mössbauer spectrometry. As a result, the permittivity of composites is strongly reduced when the NiFeMo flakes are completely coated, whereas the permeability level is weakly and progressively altered when the silica thickness increases. We show that the frequency range for microwave absorption can be tuned according to the silica thickness and the flake loading. Reflection losses of −13 dB are obtained in the 1–2 GHz range for a normal incident electromagnetic wave interacting with 3 mm sheets backed by a perfect conductor and loaded with silica (90 nm width)-coated NiFeMo flakes.

Influence of silicon dioxide capping layers on pore characteristics in nanocrystalline silicon membranes

Porous nanocrystalline silicon (pnc-Si) membranes are a new class of membrane material with promising applications in biological separations. Pores are formed in a silicon film sandwiched between nm thick silicon dioxide layers during rapid thermal annealing. Controlling pore size is critical in the size-dependent separation applications. In this work, we systematically studied the influence of the silicon dioxide capping layers on pnc-Si membranes. Even a single nm thick top oxide layer is enough to switch from agglomeration to pore formation after annealing. Both the pore size and porosity increase with the thickness of the top oxide, but quickly reach a plateau after 10 nm of oxide. The bottom oxide layer acts as a barrier layer to prevent the a-Si film from undergoing homo-epitaxial growth during annealing. Both the pore size and porosity decrease as the thickness of the bottom oxide layer increases to 100 nm. The decrease of the pore size and porosity is correlated with the increased roughness of the bottom oxide layer, which hinders nanocrystal nucleation and nanopore formation.

Average Physical Enhancement by Nanomaterials under X-ray Irradiation

We for the first time used highly water-soluble silica-covered gold nanoparticles (AuNP@SiO2) in water to successfully isolate average physical enhancement from other enhancements such as nanoscale physical enhancement, chemical enhancement, and antienhancement and obtained the highest enhancement slope of 1.03 per weight percent (wp–1) and the highest experimental enhancement factor of 4.5-fold (εexpt = 4.5 and εexpt= 0 for no enhancement) at 7.5 wp of gold in water. The slope and εexpt agree with the theoretically predicted values obtained from simulation of enhancement of X-rays by gold nanoparticles in water, and the experimental enhancement coefficient (γ = εexpt/εtheo, 0 ≤ γ ≤ 1) is approximately 0.90. The enhancement dependency on X-ray energy, silica layer thickness, and sample thickness were studied experimentally and theoretically. The results presented here elucidate the mechanism of the average physical enhancement by nanomaterials under X-ray irradiation.

Monolithic Composite Electrodes Comprising Silicon Nanoparticles Embedded in Lignin‐derived Carbon Fibers for Lithium‐Ion Batteries

AbstractWe report direct manufacturing of high‐capacity carbon/silicon composite fiber electrodes for lithium‐ion batteries produced via a flexible low‐cost melt processing route, yielding low‐cost stable silicon particles coated in situ by a 10 nanometer thick protective silica layer. The core–shell silicon/SiO2 islands are embedded in electrochemically active and electronically conductive carbon fiber derived from lignin precursor material. The silicon–silica–carbon composites exhibit capacities exceeding 700 mAh g−1 with Coulombic efficiencies in excess of 99.5 %. The high efficiency, stability, and rate capability are linked to the nanocrystalline structure and abundant, uniform nanometer‐thick SiO2 interfaces that are produced during the spinning and subsequent pyrolysis of the precursor blend.

Experimental fossilization of the Thermophilic Gram-positive Bacterium Geobacillus SP7A: A Long Duration Preservation Study

Recent experiments to fossilize microorganisms using silica have shown that the fossilization process is far more complex than originally thought; microorganisms not only play an active role in silica precipitation but may also remain alive while silica is precipitating on their cell wall. To better understand the mechanisms that lead to the preservation of fossilized microbes in recent and ancient rocks, we experimentally silicified a Gram-positive bacterium, Geobacillus SP7A, over a period of five years. The microbial response to experimental fossilization was monitored with the use of LIVE/DEAD staining to assess the structural integrity of the cells during fossilization. It documented the crucial role of silicification on the preservation of the cells and of their structural integrity after several years. Electron microscopy observations showed that initial fossilization of Gram-positive bacteria was extremely rapid, thus allowing very good preservation of Geobacillus SP7A cells. A thick layer of silica was deposited on the outer surface of cell walls in the earliest phase of silicification before invading the cytoplasmic space. Eventually, the cell wall was the only recognizable feature. Heavily mineralized cells thus showed morphological similarities with natural microfossils found in the rock record.

Optical properties of silica-coated Y2O3:Er,Yb nanoparticles in the presence of polyvinylpyrrolidone

The optical properties of polyvinylpyrrolidone (PVP)-adsorbed and silica-coated Y2O3:Er,Yb nanoparticles produced by using PVP were studied for potential bio-applications of upconversion nanoparticles. We utilized PVP to better disperse Y2O3:Er,Yb nanoparticles in solution and to prepare silica-coated Y2O3:Er,Yb nanoparticles. The fluorescent intensity of PVP-adsorbed Y2O3:Er,Yb nanoparticles was 1.25 times higher than non-adsorbed Y2O3:Er,Yb nanoparticles, which was probably due to surface defects in Y2O3:Er,Yb nanoparticles being covered by the PVP. However, the fluorescent intensity of silica-coated Y2O3:Er,Yb nanoparticles decreased as silica layer thickness increased. This could be ascribed to the higher vibrational energy of PVP than that of the silica structure. Therefore, the optimum silica layer thickness is important in bio-applications to avoid deterioration of the optical properties of Y2O3:Er,Yb nanoparticles.

Effect of Using Ethanol as the Oxygen Source on the Growth and Dielectric Behavior of Atomic Layer Deposited Hafnium Oxide

Hafnium oxide (HfO2) is widely identified as a suitable high-k material to replace conventionally used low-k silicon oxide for gate dielectric layers in complementary metal-oxide semiconductor (CMOS) devices. High dielectric constant (~ 25) and compatibility with silicon substrate makes HfO2 an ideal candidate for future scaling of transistors.1 HfO2 has been deposited using various methods. Of all, atomic layer deposition (ALD) seems to be the suitable method to deposit ultra-thin conformal layers on deep trenches and future 3D transistor structures. ALD is a vapor phase deposition technique, in which sequential exposure and purging of a surface to reactive elements in vapor phase is used to grow thin films in layer-by-layer fashion with excellent control on film thickness and composition down to Å level.2 There were numerous studies on ALD of HfO2 using different precursor and oxygen source combinations.3 The property of the resultant HfO2films depends on the precursor combination, deposition conditions, post deposition treatment conditions etc.ALD of HfO2 is traditionally performed using oxygen, ozone or water as the oxygen source. These oxidizers oxidize the underlying silicon substrates during the initial ALD cycles and form thick interfacial silicon oxide layer. This layer reduces the dielectric constant of the structure. To reduce the risk of forming such thick interfacial layer we used ethanol as the ALD oxygen source. Ethanol showed good reactivity towards the hafnium precursor, tetrakis(diethylamino)hafnium, and displayed clean ALD growth behavior with a wide ALD process temperature window of 200-280 °C (Fig. 1). In this paper, ALD growth behavior, ALD process temperature window and dielectric characterization of the ALD HfO2films will be discussed in detail along with film compositional analysis.

Atomistic modeling of bending properties of oxidized silicon nanowires

In this work, we have modeled a three point bending test of monocrystalline Si nanowires using molecular dynamics simulations in order to investigate their elastic properties. Tested nanowires were about 30 nm in length and had diameters from 5 to 9 nm. To study the influence of a native oxide layer, nanowires were covered with a 1 nm thick silica layer. The bending force was applied by a carbon diamond half-sphere with a 5 nm diameter. The Si-O parametrization for the Tersoff potential was used to describe atomic interactions between Si and O atoms. In order to remove the indentation effect of the diamond half-sphere and to obtain a pure bending behavior, we have also performed a set of simulations with fixed bottoms of the nanowires. Our results show that the oxide layer reduces the nanowire stiffness when compared with a pure Si nanowire with the same number of silicon atoms—in spite of the fact that the oxidized nanowires had larger diameters.

Fabrication of a micro-cantilever gold plated beams array

Purpose – The processing techniques and materials utilized in the fabrication of a two-terminal electrostatically actuated micro-electro-mechanical cantilever-arrayed device used for radio frequency tuning applications are presented in this work. The paper aims to discuss these issues. Design/methodology/approach – The process, which is based on silicon surface micromachining, uses spin-coated photoresist as the sacrificial layer underneath the electroplated gold structural material and an insulating layer of silicon dioxide, deposited using plasma enhanced chemical vapour deposition (PECVD), to avoid a short circuit between the cantilever and the bottom electrode in a total of six major fabrication steps. These included the PECVD of the silicon dioxide insulating layer, optical lithography to transfer photomask layer patterns, vacuum evaporation to deposit thin films of titanium (Ti) and gold (Au), electroplating of Au, the dry release of the cantilever beam arrays, and finally the wafer dicing to split the different micro devices. These process steps were each sub-detailed to give a total of 14 micro-fabrication processes. Findings – Scanning electron microscope images taken on the final fabricated device that was dry released using oxygen plasma ashing to avoid stiction showed 12 freely suspended micro-cantilevered beams suspended with an average electrostatic gap of 2.29±0.17 μm above a 4,934±3 Å thick silicon dioxide layer. Preliminary dimensional measurements on the fabricated devices revealed that the cantilevers were at least 52.06±1.93 μm wide with lengths varying from 377.97±0.01 to 1,491.89±0.01 μm and were at least 2.21±0.05 μm thick. Originality/value – The cantilever beams used in this work were manufactured using electroplated gold, and photoresist was used as a sacrificial layer underneath the beams. Plasma ashing was used to release the beams. The beams were anchored to a central electrode and each beam was designed with varying length.

Deposition of silica nanoparticles onto alumina measured by optical reflectometry and quartz crystal microbalance with dissipation techniques

Understanding of the interactions between particles and the substrate is important for successful sol–gel deposition of thin films. We have studied the deposition of silica nanoparticles on alumina coated surfaces in aqueous electrolytes by optical reflectometry (OR) and a quartz crystal microbalance with dissipation (QCM-D). The deposition of negatively charged silica nanoparticles on positively charged alumina was primarily controlled by the electric diffuse double layer interactions between the substrate and the deposited particles, modulated by the counter-ion release. The build-up of a negative charge on the positively charged substrate resulted in a decrease in the deposition rate with increasing surface coverage. Higher surface coverage of silica nanoparticles was obtained at low pH than at high pH conditions, due to reduced electric diffuse double layer repulsion between the silica nanoparticles. The deposition was enhanced at high pH by increasing the concentration of NaCl due to compression of the electric diffuse double layer. In particular, the repulsion between the silica nanoparticles was efficiently screened at a concentration of NaCl higher than 100mM and thick silica layers could be deposited at pH=6 and 8.

Piezoelectric excited millimeter sized cantilever sensors for measuring gas density changes

Rapid, in-situ measurement of gas density is valuable for monitoring industrial processes. We show that piezoelectric-excited millimeter-sized cantilever (PEMC) sensors exhibit precision for measuring gas density changes as small as 0.088g/l with sensitivity equivalent to 0.049g/(lHz). PEMC sensors were fabricated by bonding 127μm thick piezoelectric layer (lead zirconate titanate) to a base 160μm thick silica layer. Gases (He, N2, Ar) were passed continuously through an isothermally maintained flow cell, in which the PEMC sensors were mounted and the steady state resonant frequency values were monitored. The changes in observed resonant frequencies were collected and compared in multiple experiments with well-established theory for the frequency response of a dynamic cantilever surrounded by an inviscid fluid and were found to be in reasonable agreement. A finite element model of the PEMC sensor showed good agreement with the measured resonant frequency values.

Silica-Coated Gold Nanorod Arrays for Nanoplasmonics Devices

A facile method for growing silica layer on lithographically designed gold nanorod arrays (GNRAs) using a convenient sol-gel method is presented herein. The silica layer thickness was controlled on GNRAs with the reaction time. The localized surface plasmon resonance (LSPR) spectra of these hybrid metal/dielectric nanoparticles were recorded before and after the coating and the effect of different solvents on the LSPR were also assessed. The change in the fluorescence and SERS intensities of a probe molecule (Rh6G) deposited on GNRAs and silica-coated GNRAs revealed that the as-fabricated silica layer does inhibit the quenching of molecular excited states and enhances photophysical/photochemical processes. This kind of hybrid metal/dielectric nanoparticle arrays hence turn out to be real good candidates to design new "plasmonic-active" devices.

Hot-wire polysilicon waveguides with low deposition temperature

We fabricated and measured the optical loss of polysilicon waveguides deposited using hot-wire chemical vapor deposition at a temperature of 240°C. A polysilicon film 220 nm thick was deposited on top of a 2000 nm thick plasma-enhanced chemical vapor deposition silicon dioxide layer. The crystalline volume fraction of the polysilicon film was measured by Raman spectroscopy to be 91%. The optical propagation losses of 400, 500, and 600 nm waveguides were measured to be 16.9, 15.9, and 13.5 dB/cm, respectively, for transverse electric mode at the wavelength of 1550 nm. Scattering loss is expected to be the major contributor to the propagation loss.

Fluorescence enhancement of [formula omitted] by core–shell Ag@SiO2 nanocomposites

Enhancement of the light emission of dye molecules (Ru(bpy)32+) was studied by coating dye-doped SiO2 layer on Ag core. The enhancement ratio was found to be relative to the thickness of dye-doped silica layer. The core–shell Ag@dye-SiO2 nanocomposites have the strongest fluorescence intensities when the thickness of dye-SiO2 layer was tuned to 10nm. It was found that an 11-fold enhancement of fluorescence signal was realized with Ag@dye-SiO2 nanoparticles, compared to the sample without silver core.

The Key Technologies of SOI Micro-Accelerometer Front Release Process

In order to develop the SOI micro-accelerometer front release process, this paper discusses in details the key technologies of the process. There are three problems need to be resolved: the corrosion of the electrode, the corrosion rate of the buried silicon dioxide layer as well as the anti-adhesion of the micro-structure. The corrosion characteristic of the electrode is studied, and a metal electrode of high ability of anti-HF acid corrosion is designed, after release of the micro-structure, the electrode does not fall off. The corrosion property of the buried silicon dioxide is studied, and the corrosion rate is exactly known for 2um and 5um thick buried silicon dioxide layer. Based on this, the buried silicon dioxide layer etching time can be controlled, preventing over-etching of the oxide layer. The adhesion of comb fingers and the mass with the substrate is settled at last. By electron microscopy tests, found that the process can get a good micro-structure surface, with smaller footing effects. By test, the sensitivity of the accelerometer is about 144.5mv/g.

Enhanced light trapping for the silver nanoparticles embedded in the silica layer atop the silicon substrate

The optical properties of the structures with silver nanoparticles embedded in the silica layer atop the silicon substrate are simulated by the finite-difference time-domain method. The effects of nanoparticle size, period, silica layer thickness, and the angle of incidence of the illuminated light on optical transmissions are studied. It is found that there is the red-shift for the maximum of the total light transmitting into the silicon substrate as the silica layer thickness increases. The electric field intensity distributions and the average power densities for the structure with largest optical transmission is studied, and the strong electric field intensities are found in the silica regions surrounding to the silver nanoparticles, which can help the light energy going into the silicon substrate. By controlling the structure parameters, the optical transmissions of the structures with the silica layer can have higher optical transmissions than the cases without the silica layer. The silica layer plays the role as the graded refractive index layer between the air and the silicon substrate, and the light power from the incident wave can transmit into the silicon substrate with less optical reflections for choosing a suitable silica layer thickness. A guideline to design the structures with high optical transmissions for the solar spectra is given. This study cannot only be useful for the solar cells applications, but also other antireflection applications.

Structural Investigation of Cr(Al)N/SiOx Films Prepared on Si Substrates by Differential Pumping Cosputtering

Analytical electron microscopy revealed the structure and growth of hard coating Cr(Al)N/SiOx nanocomposite films prepared in a differential pumping cosputtering (DPCS) system, which has two chambers to sputter different materials and a rotating substrate holder. The substrate holder was heated at 250 °C and rotated at a speed as low as 1 rpm. In order to promote the adhesion between the substrate and composite film, transition layers were deposited on a (001) Si substrate by sputtering from the CrAl target with an Ar flow and a mixture flow of Ar and N2 (Ar/N2) gases, subsequently, prior to the composite film deposition. Then, the Cr(Al)N/SiOx nanocomposite film was fabricated on the transition layers by cosputtering from the CrAl target with the Ar/N2 gas flow and from the SiO2 target with the Ar gas flow. The film had a multilayer structure of ∼1.6 nm thick crystallite layers of Cr(Al)N similar to NaCl-type CrN and ∼1 nm thick amorphous silicon oxide layers. The structure of the transition layers was also elucidated. These results can help with the fabrication of new hard nanocomposite films by DPCS.