Mixed Silicon Research Articles

Field tests of a self-sintering, anti-soiling, self-cleaning, nanoporous metal oxide, transparent thin film coating for solar photovoltaic modules

Nanoporous metal oxide ceramic coatings, deposited using sol-gel techniques, have the potential to impart self-sintering and self-cleaning coatings to silicon oxide glass. When used on solar photovoltaic modules, these coatings can impart anti-static properties, improve wetting behavior, and degrade soiling deposits through photocatalytic activity. This paper reports on a field trial of a mixed silicon and titanium oxide thin film coating conducted in the upper midwestern U.S. Coated modules demonstrated increased electrical generation relative to uncoated controls. The results are encouraging for the commercialization of this coating technology, and provide a strong motivation for further research and development efforts.

Combustion of suspensions of mixed aluminum and silicon carbide in the products of hydrocarbon flames

A stabilized methane/air Bunsen flame is seeded with powder fuel mixtures containing various combinations of spherical, micron-sized aluminum (Valimet H-2 with nominal d50 = 3.5 µm and H-15 with nominal d50 = 20 µm) and silicon carbide (SiC) at different mass ratios over a ∼0-400 g/m3 concentration range. It is observed that in dispersions of only H-2 aluminum, a bright white aluminum flame front forms and couples to the methane-air flame, resulting in a sustained flame speed even at concentrations beyond 400 g/m3. In contrast, dispersions of only H-15 powder decrease flame speed rapidly and cause an open-tipped methane-air flame at concentrations beyond 200 g/m3, similar to inert SiC powder. When blended together into H-2:H-15 1:1 (mass ratio) mixture dispersions, an aluminum flame front forms and couples to the methane-air flame, with a flame speed comparable to unitary H-2 aluminum in contrast to mixtures of H-2:SiC 3:1 which produce no noticeable difference in flame speed from purely inert mixtures of SiC at nearly 200 g/m3. Mixtures of H-2:SiC 3:1 demonstrate an aluminum flame coupling to the methane flame, but with an increased separation between the fronts that was not observed in previous hybrid flames studies. The flame temperatures, flame coupling, and aluminum combustion efficiency behaviors are attributed to the effective amount of slowly reacting or inert solid material in the mixed powder fuels. The behaviors are consistent with a simple hybrid flames model, developed in previous work, where the effectively reduced heat of reaction of the powder fuel is unable to support sufficient heat feedback to the methane-air flame permitting effective secondary flame front formation and flame-coupling. From this understanding, a method for determining the relative energy contribution of a lower reactivity component in a fuel mixture when it is thermally driven by a higher reactivity fuel is demonstrated using the secondary front formation and flame coupling as a benchmark for reaching a certain heat of reaction of the fuel solid mixture. It is estimated that the H-15 component of a H-2:H-15 1:2 mixture contributes to approximately 55% of the thermal energy required to achieve the same behavior as a H-2:SiC 3:1 fuel mixture.

Understanding silicon monoxide gas evolution from mixed silicon and silica powders.

Silicon on silica materials are ubiquitous in 21st century technology. From nanoparticles to integrated circuits, these systems are integral for modern semiconductor fabrication. While the Si-SiO2 interface is often (incorrectly) presumed to be stable, the direct reduction of silica by silicon is possible at high temperatures, resulting in the evolution of silicon monoxide (SiO) gas. Under appropriate conditions, this somewhat unexpected reaction can complicate solid state nanomaterial syntheses by etching away the desired products. This report describes an investigation into the SiO evolution reaction by interrogation of powdered Si-SiO2 mixtures before and after thermal treatment. The impacts of processing temperature, time, and sample composition are examined and discussed. Of particular importance, this investigation reveals the underappreciated role of silica crystallinity (cristobalite) in this solid-state reaction under comparatively low temperature conditions (ca. 1200 °C). With an improved understanding of SiO evolution, we hope to inspire new creative pathways for Si-SiO2 interface manipulation.

Ultra-light 3D bamboo-like SiC nanowires felt for efficient microwave absorption in the low-frequency region

Nonmagnetic ceramics are ideal microwave absorbing materials used in high-temperature and oxidizing environments. However, low-frequency absorbing properties of this material are rarely reported because low-frequency absorbing requires nonmagnetic materials to have much higher permittivity. In this research, a series of three-dimensional architectures formed by SiC nanowires with different microstructures felt were fabricated to address this issue. The morphology of the SiCnw (linear, bamboo-shaped, and worm-like) dominated by the VLS growth mechanism can be manipulated by the silicon vapor concentration, which is governed by the vaporization temperature of the mixed silicon source (Si and SiO2) in different sintering processes. The spontaneously overlapped bamboo-shaped SiC nanowires in these felt enhance the permittivity and conductivity loss and produce multiple scattering effects on the incident EM waves, thus increasing the low-frequency wave absorption ability. The RLmin of the bamboo-shaped SiCnw felt reaches −44.3 dB at 3.85 GHz with the corresponding EAB of 0.64 GHz (3.6–4.24 GHz) at a thickness of 3.5 mm. The density of the SiCnw felt is as low as 0.022 g/cm3 due to the high porosity (99.3%) of 3D networks, which fulfills lightweight requirements and highly efficient electromagnetic wave absorption.

Effect of Pre-Harvest Foliar Calcium and Silicon Fertilization on Pineapple Quality and Fruit Collapse Incidence

Pineapple can be affected by fruit collapse, a disease caused by the bacterium Dickeya zeae. However, adequate fertilization can increase the fruit’s resistance to this illness. Therefore, the impact of preharvest foliar calcium and silicon fertilization on pineapple quality and fruit collapse incidence was assessed in this study. The experiment implemented a split-plot design with two factors. The first factor has two terms of inoculation (flower induction and before harvest). The second factor uses a control with three foliar fertilization treatments, A (control: No foliar fertilizers applied), B (Ca from 13 to 11 weeks before harvest/from 6 weeks to harvest), C (Si from 13 to 11 weeks before harvest/from 6 weeks to harvest), and D (Ca + Si from 13 to 11 weeks before harvest/from 6 weeks to harvest). Treatment D gave the best response. It had the lowest fruit collapse incidence (21.70%), highest ascorbic acid (71.64 mg/kg), elevated β-carotene (4.87 mg/kg) and mineral content (Ca: 1851.10 mg/kg, Si: 1164.87 mg/kg), essentially under the before harvest term of inoculation, which was more harmful for the fruit. In conclusion, mixed foliar calcium and silicon fertilization manage to improve the tolerance to fruit collapse incidence, impacting the pineapple quality positively

Unsaturated amido-substituted six-vertex mixed silicon germanium clusters.

The synthesis of mixed silicon and germanium clusters SixGe6-x{N(SiMe3)Dipp}41-3 (x = 3.7, 3.1, 2.1) with amido-substituents and two unsubstituted germanium atoms was achieved in co-reductions using the tribromosilane {N(SiMe3)Dipp}SiBr3 and the tribromogermane {N(SiMe3)Dipp}GeBr3 in three different ratios. The ratio of Si and Ge used for the synthesis of 1-3 approximately corresponds to that in the final products. All compounds were characterized by single crystal X-ray diffraction and EI mass spectrometry. In addition, 1 and 2 were characterized by solid-state 29Si{1H} CP/MAS NMR spectroscopy and multinuclear NMR spectroscopy in solution.

Impurity element analysis of aluminum hydride using PIXE, XPS and elemental analyzer technique

Aluminum hydride (AlH3), an attractive hydrogen storage material, plays an important role in rocket and aerospace industry. The impurities in aluminum hydride may seriously cause the deterioration in its properties and stability. Mixing AlH3 sample with the known content of silicon, we distinguish the elements in AlH3 and determine their concentration by using PIXE, XPS and elemental analyzer. Al, Si, Cl, Ca and Fe were identified by PIXE. XPS technique was used to measure the oxidized product of the mixed silicon. C, H content were obtain from the elemental analyzer. The results of the impurity concentration show the effectiveness of the synergy among these techniques except carbon. The XPS result from the pristine sample shows the concentration of carbon is 6 times larger than the major element Al while the result from the elemental analyzer is only 0.620 wt%. It suggests that the XPS technique is surface-sensitive and not well suited to the determination of the bulk concentration of carbon. The mass fraction ratio of Al to H is μAl/H=8.718<273, which indicates that the product partly decomposes.

The mixed silicon and cadmium synergistically impact the allelopathy of Solidago canadensis L. on native plant species Lactuca sativa L.

Several invasive alien plants (IAP) can trigger evidently allelopathy on the seed germination and seedling growth (SgSg) of native plant species (NPS). The getting worse condition with heavy metal pollution (e.g., cadmium) can significantly impact SgSg of plant species. Silicon can offset the adverse effects of environmental pressure on the growth and development of plant species. Thus, it is important to evaluate the influences of silicon on the allelopathy of IAP on SgSg of NPS under cadmium stress to better understand the mechanism driving the successful colonization of IAP. This study focuses on the allelopathy of the infamous IAP Solidago canadensis L. (Canada goldenrod; by using leaf extracts) on SgSg of NPS Lactuca sativa L. under the separated and mixed silicon and cadmium addition. S. canadensis triggers notably allelopathy on SgSg of L. sativa and gradually upsurges with increasing leaf extract concentration. Thus, the growth performance of NPS will be gradually reduced with an increasing degree of S. canadensis invasion. Cadmium evidently declines SgSg of L. sativa due to the broken balance of plant species for nutrient absorption. The mixed S. canadensis leaf extracts and cadmium synergistically impact seed germination of L. sativa but antagonistically affect seedling growth of L. sativa. The mixed silicon and cadmium intensify the allelopathy of S. canadensis on SgSg of L. sativa probably due to the increased effective content of cadmium in plant roots under silicon addition. Thus, the mixed silicon and cadmium will be advantageous to the following invasion process of IAP largely via the depressed SgSg of NPS.

A facile strategy for the core-shell FeSiAl composites with high-efficiency electromagnetic wave absorption

Novel electromagnetic wave absorber with strong absorption and excellent oxidation resistance composed of a FeSiAl core and nitride coating shell was synthesized by surface nitriding process in terms of its simplicity and efficiency. Uniform nitride coatings with bilayer structure have been obtained and the inner layer mainly consists of silicon nitrides while the outer layer contains mixed iron and silicon nitrides due to selective nitridation. Detailed microstructure and composition distribution of the coating correlated to the absorption performance have been systematically investigated. The interaction between the FeSiAl alloy and N element has been defined to consider the energetics of the formation for different nitrides. Enhanced wave absorption is achieved with wide absorption bandwidth (8.11 GHz), covering almost the entire X and Ku band.

Mixed-Phase nc-SiOX:H Interlayer to Improve Light Trapping and Shunt Quenching in a-Si:H Solar Cell

By using radio frequency plasma enhanced chemical vapor deposition method (13.56 MHz), a mixed phase nanocrystalline silicon oxide (nc-SiOX:H) interlayer has been developed. The optoelectronic properties of the nc-SiO:H layer was optimized by varying gas flow ratio. An interlayer has been inserted between the silicon layer and back contact. The nc-SiO:H interlayer has served as a dual-function layer in the solar cell, i.e., act as a rear reflector layer for light trapping and also minimized the local leakage and quenching the shunt effect. The fabricated solar cells with and without nc-SiOX:H interlayer showed efficiencies of 7.84% and 9.35%, respectively, with an i-layer thickness of 250 nm. Efficient light trapping and suppressed parasitic losses by adopting nc-SiOX:H interlayer resulted in a relative increase in the efficiency of about 19.26%. Light-induced degradation study of the solar cells with and without an interlayer has also been presented here. After shunt quenching effect, the relative degradation in conversion efficiency for an interlayer cell is ∼7.27% after 1000 h of light soaking, whereas, under the same experimental conditions, the relative degradation is ∼10.82% for the solar cell without an interlayer. The possible origin of higher degradation in the latter device has been addressed in this work.

Mechanistic Study on Water Splitting Reactions by Small Silicon Clusters Si3X, X = Si, Be, Mg, Ca.

Interaction, dissociation, and dehydrogenation reactions of water monomer and dimer with pure and mixed tetrameric silicon clusters Si3X with X = Si, Be, Mg, Ca were investigated using high accuracy quantum chemical calculations. While geometries were optimized using the DFT/B3LYP functional with the aug-cc-pVTZ basis set, reaction energy profiles were constructed making use of the coupled-cluster theory with extrapolation to complete basis set, CCSD(T)/CBS. Cleavage of the O-H bond in water dimer is found to be more favored than that of water monomer in the reaction with Si4. The water acceptor monomer in water dimer performs as an internal catalyst facilitating H atom transfer to form H2. Adsorption of water dimer on Si3X clusters mostly takes place upon interaction of the donor water molecule with Si cluster. Water dimer adsorbs more strongly on Si3M than on Si4. The most stable complexes obtained upon interaction of water dimer with Si3M mainly arise from M-O interaction in preference over a Si-O connection. Substitution of a Si atom in Si4 by an earth alkaline metal induces a substantial reduction of the energy barrier for the (rate-limiting) first O-H bond cleavage of water dimer. The most remarkable achievement upon doping is a disappearance of the overall energy barrier for the initial O-H bond cleavage in water dimer. Of the three binary Si3M clusters considered, dehydrogenation of water dimer driven by Si3Be is the most kinetically and thermodynamically favorable pathway. In comparison to another cluster such as Al6 and nanoparticles Ru55, energy barriers for water dimer dissociation on Si3M are much lower. The mixed clusters Si3M turn out to be as efficient alternative reagents for O-H dissociation and hydrogen production from water dimer. This study proposes further searches for other mixed silicon clusters as realistic gas phase reagents for crucial dehydrogenation processes in such a way they can be prepared and conducted in experiment.

Molten salt thermal conductivity enhancement by mixing nanoparticles

Fluoride molten salts are considered candidate of a coolant nuclear fusion reactors. However, heat transfer performance of the molten salts is not as high as liquid metals. Therefore, it is necessary to enhance thermophysical properties of the molten salts to get higher heat removal efficiency. This study aim is to enhance molten salt thermal conductivity by mixing nanoparticles. We employed molten salt HTS (Heat Transfer Salt), which is a mixed salt of NaNO2, NaNO3 and KNO3, as a surrogate of the fluoride molten salts. We measured the HTS thermal conductivity mixed silicon carbide nanoparticles at from approximately 150–250 °C, and then evaluated a rate of thermal conductivity enhancement. The method to measure the thermal conductivity was a transient hot-wire method. We found that the HTS thermal conductivity increased due to mixing the nanoparticles. In conclusion, it was demonstrated that mixing nanoparticles was able to enhance molten salt thermal conductivity. Moreover, we concluded that, in the present temperature range except near melting point of the sample, an amount of thermal energy that the nanoparticles stored did not significantly change even at the higher temperature.

The Li-storage capacity of SiOC glasses with and without mixed silicon oxycarbide bonds

Mixed bonds in SiOCs lead to a more disordered/defect-free carbon phase with high capacity for reversible storage of Li ions.

Comparative Study of Methanol Activation by Different Small Mixed Silicon Clusters Si2M with M = H, Li, Na, Cu, and Ag.

High-accuracy quantum chemical calculations were carried out to study the mechanisms and catalytic abilities of various mixed silicon species Si2M with M = H, Li, Na, Cu, and Ag toward the first step of methanol activation reaction. Standard heats of formation of these small triatomic Si clusters were determined. Potential-energy profiles were constructed using the coupled-cluster theory with extrapolation to complete basis set CCSD(T)/CBS, and CCSD(T)/aug-cc-pVTZ-PP for Si2Cu and Si2Ag. The most stable complexes generated by the interaction of methanol with the mixed clusters Si2M possess low-spin states and mainly stem from an M–O connection in preference to Si–O interaction, except for the Si2H case. In two competitive pathways including O–H and C–H bond breakings, the cleavage of the O–H bond in the presence of all clusters studied becomes predominant. Of the mixed clusters Si2M considered, the dissociation pathways of both O–H and C–H bonds with Si2Li turns out to have the lowest energy barriers. The most remarkable finding is the absence of the overall energy barrier for the O–H cleavage with the assistance of Si2Li. The breaking of O–H and C–H bonds with the assistance of Si2H, Si2Li, and Si2Na is kinetically preferred with respect to the Si2Cu and Si2Ag cases, apart from the case of Si2Na for O–H cleavage. In comparison with other transition-metal clusters with the same size, such as Cu3, Pt3, and PtAu2, the energy barriers for the O–H bond activation in the presence of small Si species, especially Si2H and Si2Li, are found to be lower. Consequently, these small mixed silicon clusters can be regarded as promising alternatives for the expensive metal-based catalysts currently used for methanol activation particularly and other dehydrogenation processes of organic compounds. The present study also suggests a further extensive search for other doped silicon clusters as efficient and more realistic gas-phase catalysts for important dehydrogenation processes in such a way that they can be experimentally prepared and implemented.

CW-Laser-Induced Solid-State Reactions in Mixed Micron-Sized Particles of Silicon Monoxide and Titanium Monoxide: Nano-Structured Composite with Visible Light Absorption

Silica–titania mixed oxides and composites have been broadly examined for their physical and catalytic properties, but titanium monoxide–silicon monoxide counterparts have yet drawn very little attention. Here we report that laser-induced processing of mixed silicon and titanium monoxides results in reactions yielding a nanostructured Ti/Si/O composite absorbing visible light. Changes in the composition of intimately mixed μm-sized particles of silicon monoxide (SiO) and titanium monoxide (TiO) induced by scanning of a cw CO2 laser beam along the TiO–SiO pellet surface were examined by FTIR and Raman spectroscopy, X-ray diffraction and electron microscopy. They are shown to consist in the evolution of TiO2 (rutile and anatase), titanium suboxides (Ti4.5O5, Ti2O3), silica and amorphous binary SiOx, TiOx and ternary SixTiyOz nano-phases which contain less or more O than SiO and TiO monoxides. These products are ascribed to concurrent silicothermal reduction of TiO and O-transfer between SiO and TiO due to interdiffusion of Si- and Ti-based species. These reactions taking place under transient localized heating are not inhibited by passivation shells around SiO and TiO particles. The laser-produced Ti/Si/O composite shows absorption band at 425 nm tailing up to 1100 nm. Its solar-light photocatalytic activity in decolorization of Methylene Blue is compared to that of the unheated SiO and TiO powders absorbing only in UV region.

Making and Breaking Bonds in Superconducting SrAl4–xSix (0 ≤ x ≤ 2)

We explored the role of valence electron concentration in bond formation and superconductivity of mixed silicon–aluminum networks by using high-pressure synthesis to obtain the BaAl4-type structural pattern in solid solution samples SrAl4–xSix where 0 ≤ x ≤ 2. Local ordering of aluminum and silicon in SrAl4–xSix was evidenced by nuclear magnetic resonance experiments. Subsequent bonding analysis by quantum chemical techniques in real space demonstrated that the strong deviation of the lattice parameters in SrAl4–xSix from Vegard’s law can be attributed to the strengthening of interatomic Al–Al and Al–Si bonds within the layers (perpendicular to [001]) for 0 ≤ x ≤ 1.5, followed by the breaking of the interlayer bonds (parallel to [001]) for 1.5 < x ≤ 2 and leading to the structural transition from the BaAl4 structure type with three-dimensional anionic framework at lower x values to the two-dimensional anion of the BaZn2P2 structure type with increasing x values. Low-temperature measurements of the resisti...

MuTRiG: a mixed signal Silicon Photomultiplier readout ASIC with high timing resolution and gigabit data link

MuTRiG is a mixed signal Silicon Photomultiplier readout ASIC designed in UMC 180 nm CMOS technology for precise timing and high event rate applications in high energy physics experiments and medical imaging. It is dedicated to the readout of the scintillating fiber detector and the scintillating tile detector of the Mu3e experiment. The MuTRiG chip extends the excellent timing performance of the STiCv3 chip with a fast digital readout for high rate applications. The high timing performance of the fully differential SiPM readout channels and 50 ps time binning TDCs are complemented by an upgraded digital readout logic and a 1.28 Gbps LVDS serial data link. The design of the chip and the characterization results of the analog front-end, TDC and the LVDS data link are presented.

Dissolution and Passivation of a Silicon-Rich Austenitic Stainless Steel during Active-Passive Cycles in Sulfuric and Nitric Acid

The high Si containing X1CrNiSi18-15-4 stainless steel (SS) spontaneously forms a protective oxide film that is mostly composed of mixed chromium and silicon oxides. This film ensures a good durability of the industrial facilities the alloy was designed for, containing very acidic electrolytes such as hot and concentrated nitric acid, HNO3, in presence of oxidizing species. In the present work, the chemistry of the oxide formed and the passivation kinetics of the alloy in sulfuric acid, H2SO4, and for the first time in HNO3, were monitored by atomic emission spectroelectrochemistry (AESEC) over successive activation and passivation cycles of the material. X1CrNiSi18-15-4 SS was compared to a low Si containing SS, the X2CrNiN18-10 SS. It was found that a similar quantity and rate of passive film was formed during passivation, and dissolved during activation. Reproducible results were obtained over several active-passive cycles. The excess Cr was correlated with the dissolution rate decay during passivation. The Si/Cr ratio of the passive film was determined by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy (performed using transmission electron microscopy), and AESEC giving similar results within experimental error. The EDX profile suggest that the passive film consists of a Si rich outer and Cr rich inner layer.

Dual mechanism of photoresponse in composite Si–Au nanolayers on crystalline silicon

Silicon‐based structures comprised of crystalline silicon substrates and active layers of mixed silicon and gold nanoparticles were fabricated and characterized. Several layer compositions were studied. The investigated structures demonstrate very large spectral sensitivity (more than 10 A W−1) in the wide spectral range (400–1000 nm). Such large sensitivity implies presence of photocurrent amplification. A model which involves dual mechanism of the photoresponse was proposed in order to explain the appearance of the photocurrent amplification in the investigated structures.Spectral sensitivity of the structure with composite layer of Si and Au nanoparticles on Si substrate (Au volume fraction is ∼50%) at reverse bias voltage of −0.4 V.

Mixed titanium, silicon, and aluminum oxide nanostructures as novel adsorbent for removal of rhodamine 6G and methylene blue as cationic dyes from aqueous solution

Mixed oxide nanoparticles containing Ti, Si, and Al of 8–15 nm size range were synthesized using a combined sol-gel - hydrothermal method. Effects of composition on the structure, morphology, and optical properties of the nanoparticles were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), microRaman spectroscopy, and diffuse reflectance spectroscopy (DRS). Dye removal abilities of the nanoparticles from aqueous solutions were tested for different cationic dyes. While all the mixed oxide nanoparticles revealed high and fast adsorption of cationic dyes, the particles containing Ti and Si turned out to be the best. The adsorption kinetics and equilibrium adsorption behavior of the adsorbate - adsorbent systems could be well described by pseudo-second-order kinetics and Langmuir isotherm model, respectively. Estimated thermodynamic parameters revealed the adsorption process is spontaneous, driven mainly by the electrostatic force between the cationic dye molecules and negative charge at nanoparticle surface. Highest dye adsorption capacity (162.96 mg MB/g) of the mixed oxide nanostructures containing Ti and Si is associated to their high specific surface area, and the presence of surface Si-Oδ- groups, in addition to the hydroxyl groups of amorphous titania. Mixed oxide nanoparticles containing 75% Ti and 25% Si seen to be the most efficient adsorbents for removing cationic dye molecules from wastewater.