SiO2 Islands Research Articles

Improving Bond Strength of Translucent Zirconia Through Surface Treatment With SiO2-ZrO2 Coatings.

Translucent monolithic zirconia ceramics have been applied in dental clinics due to their esthetic translucent formulations and mechanical properties. Considering inherent ceramic brittleness, adhesive bonding with resin composite increases the fracture resistance of ceramic restorations. However, zirconia is a chemically stable material that is difficult to adhesively bond with resin. To investigate the influences of SiO2-ZrO2 coatings on adhesive bonding of zirconia and the surface characterization of those coatings. Translucent zirconia discs were classified into groups based on surface treatments: CT (control), SB (sandblasting), C21(SiO2:ZrO2=2:1), C11(SiO2:ZrO2=1:1), and C12 (SiO2:ZrO2=1:2) (n=10). Surface characterization of coatings on zirconia were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), surface roughness assessment (Ra), X-ray diffraction (XRD), water contact angle (WCA), translucency parameter (TP), and shear bond strength (SBS). Two-way ANOVA for shear bond strength results and ANOVA for Ra and WCA were performed. SEM images revealed SiO2 islands on zirconia disks coated with SiO2-ZrO2. Surface roughness of C12, C11, and C21 groups was significantly larger than those of groups SB and CT (p<0.05). XRD results showed that phase transformation of zirconia disks was detected only in the SB group. In addition, SiO2-ZrO2 coatings reduced WCA. The translucency decreased only in group C21. Group C11 showed the highest shear bond strength under both aging conditions. SiO2-ZrO2 coating is a promising method to enhance the adhesive resin bonding of translucent zirconia without causing phase transformation of translucent zirconia.

Suppression of pesting failure in MoSi2 film by doping of Si

MoSi2 usually suffers pesting failure at 400– 700 °C due to severe oxidation of Mo, which has been a great hindrance for industrial applications. To address this issue, this work grew MoSi2(Si) thin films via magnetron co-sputtering of a Si single element target and a MoSi2 compound target on Si wafer substrates at room temperature, followed by annealing at 950 °C in an argon atmosphere. The as-annealed thin films were heated in a muffle furnace at 700 °C in air to experience different duration of oxidation. After that, the oxidation resistance was evaluated by examining the thickness, morphology, structure and composition of the as-heated thin films using field emission scanning electron microscopy and X-ray diffraction, respectively. In comparison with the MoSi2 without doping of Si, the MoSi2(Si) film is denser and exhibits a C11b crystalline structure with a smaller crystal size of 30 nm. The oxidation of Mo is effectively inhibited. There is no big bulge on the film surface after 1 h oxidation. But the oxidation of Si is severe, resulting in the continuous growth of grey SiO2 layer which help preventing the further oxidation of Mo. SiO2 islands are observed after oxidation for 9 h. The early pesting sites gradually become healed by the grown SiO2 layer during oxidation for 60 h. The mechanism for suppressing the pesting failure of MoSi2 by Si doping is discussed in details. A model is developed to explain the process.

Microstructural and chemical constitution of the oxide scale formed on a pesting-resistant Mo-Si-Ti alloy

The oxidation behaviour of the pesting-resistant eutectic alloy Mo-20Si-52.8Ti was investigated by addressing the microstructural and chemical constitution by grazing incidence X-ray diffraction GIXRD and atom probe tomography APT of oxide scales formed at 800 and 1200 °C in order to understand their protective character. The duplex Si-Ti-oxide scale formed at 800 °C in air, i.e. within the so-called “pesting regime”, is considerably slow growing with a scale thickness of (11 ± 3) μm after 1000 h of exposure. It is composed of a Ti(+IV)-oxide with the chemical composition of approximately TiO2.1 confirmed by APT and SiO2 islands, which are most likely amorphous. The oxide scale formed at 1200 °C, a potential application temperature, is characterised by a top single-phase scale and an underlying duplex scale with a considerably increased thickness of (68 ± 11) μm in total. It consists of rutile TiO2 and some cristobalite SiO2 as determined by GIXRD. APT analysis of the top Ti-oxide scale confirms the stoichiometry TiO2.2. The underlying duplex scale comprising Ti- and Si-oxide is characterised by strongly off-stoichiometric compounds, namely TiO1.4 and SiO1.6. Initial linear oxide scale growth kinetics are found at 800 °C, which change to cubic kinetics for exposure times longer than 100 h. At higher temperatures of 1100 and 1200 °C, diffusion-controlled, almost parabolic kinetics prevail.

Formation Process of the Integrated Core(Fe-6.5wt.%Si)@Shell(SiO2) Structure Obtained via Fluidized Bed Chemical Vapor Deposition

As electromagnetic functional materials, soft magnetic composites (SMCs) have great potential for applications in high-energy electromagnetic conversion devices. The most effective way to optimize the performance of an SMC is to incorporate it into insulated ferromagnetic core-shell particles with high structural uniformity and integrity. Fluidized bed chemical vapor deposition (FBCVD) is a facile and efficient technique for the synthesis of ferromagnetic/SiO2 core-shell particles. However, the formation mechanism and conditions of integrated ferromagnetic/SiO2 core-shell structures during the FBCVD process are not fully understood. On this basis, the formation process and the deposition time required for transformation of the Fe-6.5wt.%Si substrate into the Fe-6.5wt.%Si/SiO2 composite, and finally into the Fe-6.5wt.%Si/SiO2 core-shell structure, were investigated. Deposition of the insulative SiO2 coating onto the Fe-6.5wt.%Si particles was described by the three-dimensional island nucleation theory. The SiO2 islands were initially concentrated in rough areas on the Fe-6.5wt.%Si particle substrates owing to the lower heterogeneous nucleation energy. Deposition for at least 960 s was necessary to obtain the integrated ferromagnetic/SiO2 core-shell structure. The uniformity, integrity, and thickness of the insulative SiO2 coating increased with the increasing deposition time. The results in this study may provide a foundation for future kinetics investigations and the application of FBCVD technology.

The growth mechanism and characterization of few-layer diphenyl dinaphthothienothiophene films prepared by vacuum deposition

The growth mechanism of 2,9-diphenyl-dinaphtho [2,3-b:2′,3′-f]thieno [3,2-b]thiophene (DPh-DNTT) thin-films prepared by vacuum deposition was investigated based on the morphological crystallinity of the obtained films. In addition to atomic force microscopy, which is commonly used for imaging surface morphology, optical microscopy was also positively used for the same purpose. The technique allows the quick and easy evaluation of thin films. The optical microscopy images show that DPh-DNTT films grew according to a layer-by-layer growth mode. Each layer grew as flat two-dimensional (2D) islands with a thickness of about 2.3 nm, where DPh-DNTT molecules stand almost vertically on the substrate. The height difference between layers provided a color contrast in these images, which visualizes the initial 2D island on the Si substrate with thermally grown SiO2 and fractal-shape 2D islands on top surface. By using the method, a monolayer of isolated and round 2D islands, with a diameter of approximately 4 μm, formed at a high substrate temperature on a SiO2 surface that had been previously treated with O2 plasma or UV-O3. The presence of a DPh-DNTT layer on the substrate was also confirmed by micro-Raman measurement.

Structure and Strain Relaxation of GaN Nanorods Grown on Homoepitaxial Surface via Controlling Irregular Mask

We propose a simple and low-cost approach using irregular mask for growing GaN nanorods (NRs) bottom up on a freestanding GaN substrate through hydride vapor-phase epitaxy. The irregular mask consists of uncoalesced SiO2 islands deposited by plasma-enhanced chemical vapor deposition to isolate growth. The selection of the SiO2 amount is investigated to achieve reasonable NR density (high coverage), desired morphology (flat side walls and uniform diameters), and lattice quality (single crystalline; better quality than that of an as-grown layer under the same growth ambient). Using this growth approach with appropriate parameters, we successfully synthesize high coverage of uncoalesced NRs on a homoepitaxial surface in a short growth duration. The morphology, density, and growth rate are controlled by adjusting V/III ratios. The cathodoluminescence and photoluminescence measurements of GaN show that luminescence was obtained near 3.4 eV while the structure was grown with mask but contained defect signals wh...

Copper vapor-assisted growth of hexagonal graphene domains on silica islands

Silica (SiO2) islands with a dendritic structure were prepared on polycrystalline copper foil, using silane (SiH4) as a precursor, by annealing at high temperature. Assisted by copper vapor from bare sections of the foil, single-layer hexagonal graphene domains were grown directly on the SiO2 islands by chemical vapor deposition. Scanning electron microscopy, atomic force microscopy, Raman spectra, and X-ray photoelectron spectroscopy confirm that hexagonal graphene domains, each measuring several microns, were synthesized on the silica islands.

Evolution of thin protecting Si-layer on Mn0.5Si0.5 layer at low temperatures

Evolution of 2-nm-thick protecting Si-layer on amorphous Mn0.5Si0.5 films at elevated temperatures was investigated by using conductive atom force microscopy (CAFM) and other structure and composition characterization methods. At a temperature of 300°C, a dramatic change was observed in surface morphology with many islands forming on the surface. Those islands were SiO2 islands rather than Si ones. Further studies showed that those islands formed via first oxidation of the Si cap layer followed by the agglomeration of this SiO2 layer. Because Si cap layer has widely been used as protecting materials to prevent the surface from oxidizing and contamination, this study provides an insight on the effectiveness of thin protecting Si-layer at low temperatures.

Dissolution mechanism of dolomite in converter slag at 1873 K

The mechanism of dolomite dissolution in converter slag was studied and found to proceed by two steps: decomposition of dolomite into CaO and MgO and dissolution of the product into the slag. The first step was found to be controlled by heat transfer, which was confirmed by theoretical calculation. The decomposed dolomite had many pores, which allowed easy slag penetration. A discontinuous 2CaO.SiO2 layer along with MgO.Fe2O3 particles was found on the surface of the samples. Some 2CaO.SiO2 islands were found in the vicinity of the samples in the slag, revealing that the dissolution was dominated by peeling-off of the layer of 2CaO.SiO2–MgO.Fe2O3 mixture. 2CaO.SiO2, (Mg, Fe)Oss along with super cooled liquid phases were found inside dolomite samples close to the surface. 2CaO.SiO2 phase was replaced gradually by 3CaO.SiO2 towards the centre of the decomposed sample. While addition of small amounts of dolomite directly into the slag could be considered in steelmaking converter, too much would result in slow dissolution and waste of the raw materials.

Characterization of InGaN/GaN Multiple Quantum Wells Grown on Sapphire Substrates by Nano-scale Epitaxial Lateral Overgrowth Technique

ABSTRACTHigh-quality InGaN/GaN multiple quantum wells (MQWs) were fabricated on nano-scale epitaxial lateral overgrown (NELO) GaN layers which was prepared using nanometer-scale SiO2 islands, with an average diameter and interdistance of 300nm and 200nm respectively, as the growth mask. The active region of the device consists of five periods of GaN/InGaN MQWs were grown on top of the NELO layer using MOCVD technique. It is observed that some of the dislocations from the undoped GaN were blocked by the SiO2 growth mask and typical threading dislocation (TD) density found in the NELO samples is ~7.5×107cm-2. Significant improvement in the electroluminescence (EL) is observed which is believed to partly arise from the improvement in the internal quantum efficiency (ηi). The experimental data on the temperature dependence of the photoluminescence (PL) were fitted to a proposed model using Levenberg-Marquardt approximation. Based on our analyses it is found that the relative improvement in ηi at 300K over a control device grown in the same growth condition but without the NELO layer to a NELO device is only 0.59. It is generally accepted that TD is the non-radiative recombination center which affects the IQE. Therefore, room-temperature IQE values also support that NELO device exhibits lower TD density.

Characterization of GaN/InGaN multiple quantum wells grown on sapphire substrates by nano-scale epitaxial lateral overgrowth technique

High-quality GaN/InGaN multiple quantum wells (MQWs) were fabricated on nano-scale epitaxial lateral overgrown (NELO) GaN layers. To grow the NELO layer first a 200nm-thick SiO2 was deposited on a 2μm-thick undoped GaN layer. A 10nm-thick Ni layer was then deposited on the SiO2 film followed by an annealing process to form nano-scale Ni clusters. These Ni clusters will serve as a dry etch mask for the underlying SiO2 layer, resulting in the formation of SiO2 islands of diameter and inter-distance of 300 and 200nm, respectively. Undoped NELO GaN layer of thickness 2μm was grown on the template with SiO2 growth mask using metal organic chemical vapor deposition technique. A 2μm-thick n-GaN epilayer and a 5-period GaN/InGaN MQWs were grown on top of the NELO layer. It is found that the overgrown GaN epilayers exhibit a significant reduction in threading dislocation (TD). From the atomic force microscopy characterizations, the TD density reduces from 3×108 to 6×107cm−2 by utilizing the NELO technique. Optical properties of the MQWs deposited on the NELO layer (type N) were characterized by temperature-dependent photoluminescence (PL). The results are compared to a control structure (type C) grown in the same growth run as the type N structures but without the NELO layer. It is found that type N sample exhibits three-fold improvement in PL intensity at room temperature. The increase in external quantum efficiency arises from both enhanced extraction efficiency and internal quantum efficiency. Detailed temperature-dependent PL studies were conducted to evaluate the relative improvement in internal quantum efficiency to account for the improved material quality when MQWs were grown on top of NELO epilayers.

Determination of migration of ion-implanted helium in silica by proton backscattering spectrometry

Understanding the processes caused by ion implantation of light ions in dielectric materials such as silica is important for developing the diagnostic systems used in fusion and fission environments. Recently, it has been shown that ion-implanted helium is able to escape from SiO2 films. To study this process in details, helium was implanted into the central part of a buried SiO2 island up to a fluence of 4×1017He/cm2. The implanted helium could be detected in the SiO2 island, if the oxide was insulated properly from the vacuum. The shape of the helium depth distributions was far from SRIM simulation because helium distributed in the whole 1μm thick oxide layer. After the ion implantation, helium was observed only on the implanted spot. After nine months the implanted helium filled out the whole oxide island as it was expected from the high diffusivity.

Rearrangement of the oxide-semiconductor interface in annealed Al2O3∕4H-SiC structures

Al 2 O 3 films with different thicknesses have been deposited on n-type (nitrogen-doped) 4H-SiC(0001) epitaxial samples by atomic layer chemical vapor deposition at 300°C and subsequently annealed in Ar atmosphere at temperatures up to 1000°C. The Al2O3∕4H-SiC structures were analyzed by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and transmission electron microscopy (TEM). The XPS and SIMS results indicate that the average composition in the wider interface area does not significantly change due to the annealing. However, as revealed by the TEM investigations in combination with XPS, the as-grown samples exhibit a double interface created by an intermediate suboxide SiOx layer (x&amp;lt;2). After annealing, this intermediate suboxide layer breaks up and transforms into SiO2 islands, resulting in a rather rough interface region and a high concentration of pure Si in the Al2O3 film. Furthermore, a pronounced accumulation of H is found in the rough interface region and this may play a key role for the low density of shallow electron states reported for annealed Al2O3∕4H-SiC structures.

The changes in morphology of Si(1 0 0) surface upon dipping in ultrapure water

The changes in morphology and chemical states of Si(1 0 0) surface upon dipping in ultrapure water were investigated by using atomic force microscope and X-ray photoelectron spectroscopy. The oxidation and the etching competitively progressed at the HF-treated Si(1 0 0) surface in ultrapure water, which made the smooth surface rough. However, the surface covered with a thick native oxide film was not etched at all. During the repetition of the oxidation and the etching, the SiO 2-nuclei was, by chance, able to grow up to some size of islands and worked as the protective barrier against the water etching. Thus, the SiO 2-islands would remain without being etched off, whereas rest parts of the surface could be etched off. This selective etching leads the surface morphology to become rough. Both the oxidation and the etching progressed violently as the water temperature and the dipping time increased.

Orthogonal Self-Assembly of Carbon Nanotube Crossbar Architectures by Simultaneous Graphoepitaxy and Field-Directed Growth

Crossbar arrays of single-wall carbon nanotubes are produced spontaneously in a single step of chemical vapor deposition by simultaneous graphoepitaxy along faceted nanosteps and field-directed growth, perpendicular to each other. The two alignment mechanisms take place selectively on miscut C-plane sapphire and patterned amorphous SiO2 islands, respectively, without mutual interference, producing dense nanotube grids, with up to 12 junctions per square micrometer. This one-step method of orthogonal self-assembly may open up new possibilities for nanotube circuit integration.

Dose-window dependence on Si crystal orientation in separation by implanted oxygen substrate formation

Separation by implemented oxygen (SIMOX)(111) substrates have been formed by oxygen-ion (16O+) implantation into Si(111), showing that a so-called “dose-window” at 16O+-implantation into Si differs from Si(100) to Si(111). In SIMOX(100), an oxygen dose of 4 × 1017/cm2 into Si(100) is widely recognized as the dose-window when the acceleration energy is 180 keV. For the first time, our work shows that an oxygen dose of 5 × 1017/cm2 into Si(111) is the dose-window for the formation of SIMOX(111) substrates when the acceleration energy is 180 keV. The difference between dose-windows is caused by anisotropy of the crystal orientation during growth of the faceted buried SiO2. We also numerically analyzed the data at different oxidation velocities for each facet of the polyhedral SiO2 islands. Numerical analysis results show good agreement with the experimental data.

Optical emission from silicon-based SiO2 islands fabricated by anodic alumina templates

We have investigated the photoluminescence spectra of silicon-based nanoscale SiO2 islands obtained by anodization of silicon-based aluminum membranes in a 0.3m sulfuric acid solution under a constant voltage of 25V. Two ultraviolet emission bands were observed at 290 and 370nm. After annealing the samples in 900°C in O2, the 290nm band vanishes, but the 370nm band still exists. We suggest that the 290nm band originates from optical transition in the E′ centers in the SiO2 islands according to its annealing behavior. The 370nm band is considered to be from Al-related luminescence centers, [AlO4]0, because a decrease of intensity of the 370nm band is in agreement with that of amount of the Al ion impurities located in the SiO2 islands. This work shows a clear understanding of the light-emitting mechanism of silicon-based SiO2 island array. The obtained result can be expected to have important applications in modem optoelectronics.

Nanoscale islands and color centers in porous anodic alumina on silicon fabricated by oxalic acid

Anodic oxidation of Al film on silicon substrate in oxalic acid is investigated through the j–t curves and its photoluminescence (PL). Their growth is analyzed with three typical stages according to j–t curve, which is agreed with the growth of nanoscale SiO2 islands at the interface between Al film and Si substrate. The violet and blue peaks of PL were due to F+ and F centers, respectively. The evolvement from F+ to F centers during the late stage of anodization was revealed by the PL behavior at different stage.

Silicon-based field-effect-transistor cantilever for surface potential mapping

A silicon-based scanning probe with a field effect transistor (FET) has been developed. The FET is integrated onto an atomic force microscope cantilever with a sharpened tip. The commonly used complementary-metal–oxide–semiconductor process has been employed to construct the FET using a silicon-on-insulator wafer. The probe is used to measure a surface potential with a resolution of &amp;lt;300 nm when determined by the edge of patterned SiO2 islands. The probe can be also used to detect local properties on semiconductor surfaces, such as isolated charge distributions on a surface or at subsurface.

Si-based nanoscale SiO 2 islands and light-emitting source array

A SiO2 nanoscale island array was fabricated on a Si substrate by using anodic porous alumina as a mask. Transmission electron microscopy observation and the atomic force microscopy pattern show that the arrangement of SiO2 islands has a quasi-hexagonal symmetry. Ge ions with a dose of 1×1017 cm-2 were subsequently implanted into the SiO2 island array to form Ge-related light-emitting centers. The photoluminescence (PL) spectra of as-implanted and annealed samples show three PL bands at 370, 400 and 415 nm. Their intensities reach maximums in the sample with an annealing temperature of 700 °C. Spectral analysis suggests that the 370 and 415 nm PL bands arise from ≡Ge-Ge≡ and ≡Ge-Si defect centers, while the 400 nm PL is related to GeO color centers in the SiO2 islands. The existence of these PL bands indicates the formation of a Si-based nanoscale light source array.