Surface Silicon Atoms Research Articles

Large-capacity adsorption of the organic dye with surface-silanol-rich hybrid nano silica

Surface-silanol-rich hybrid nano silica was synthesized with a reverse-phase microemulsion method. Exposure ratio of the surface silicon atom reached 81.4 % with the mildest drying method of air-drying at room temperature, which enabled a large amount of amino (5.8 mmol g−1) and silanol (8.0 mmol g−1) to be simultaneously generated on the surface. Abundant surface groups enabled the present material to efficiently remove various anionic dyes from the wastewater with a maximum adsorption capacity of 2048 mg g−1. The reported result supplied good reference for the designing of the adsorbent through modulating the surface groups’ composition and amount.

Simulating and Analyzing the Electronic Structure of a Spherical Amorphous SiO2 Nanoparticle of Finite Radius

This study focuses on the electronic structure and properties of amorphous SiO2 nanoparticle with a radius of 18 Å using Density Functional Theory and the Orthogonalized Linear Combination of Atomic Orbital method. Through employing appropriate statistical techniques, three distinct models (I, II, and III) of amorphous SiO2 nanoparticle with an 18 Å radius are generated based on the continuous random network structure incorporating periodic boundaries. The calculated Total Density of States and Partial Density of States reveal insights into the electronic interactions within the nanoparticle. The band gap values are assessed at both less accurate and more accurate potentials such that the band gap increases from 2 eV to 4.2 eV with higher potentials for Model I, where surface atoms has dangling bonds stabilized by hydrogen atoms. Model II, consisting of all surface silicon atoms bonded to four oxygen atoms, exhibits a band gap of 1 eV, increasing to 1.8 eV with higher potentials. Model III, saturated with hydrogen atoms, shows a band gap of 4 eV, decreasing to 3.75 eV at higher potentials. The introduction of the more accurate potential serves to minimize the gap states initially observed with the less accurate potential. The electronic structure calculations provide crucial information for understanding the electronic interactions within the amorphous SiO2 nanoparticle with implications for their applications in various fields such as biomedicine, catalysis, electronics, and nanotechnology.

Does repeated autoclave sterilization cause changes in the color and fragility of fiberglass reinforced resin crowns?

BackgroundSince the effects of sterilization on the Fiberglass Reinforced Resin Crowns (FRRCs) is not well-known the aim of current study was to evaluate the effects of autoclave sterilization on the fracture resistance, color stability, and surface composition of FRRCs.MethodsA total of 48 crowns were used. The crowns were divided into three groups according to the sterilization number: no sterilization (Control Group), one sterilization (Group 1), and four sterilizations (Group 2). The microstructure of the three crowns from each group was evaluated using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. Thirteen FRRCs from each group were first used for color stability testing and then for the fracture resistance analysis. One-way analysis of variance (ANOVA), one-way repeated measures ANOVA, and paired t-tests were used in the statistical analysis.ResultsEDX results revealed that the weight% of surface silicon atoms in group 2 was significantly higher. Some crack lines could be observed on the SEM images. Statistically significant differences were found in color stability following the first and fourth sterilization cycles (p < .01). The increase in the sterilization cycle did not statistically decrease the fracture resistance of the FRRCs (p = .055); however, overall, a decreasing trend was observed in fracture resistance as the sterilization cycle increased.ConclusionsAutoclave sterilization caused some changes in the surface elemental composition and surface morphology of FRRCs. Avoiding unnecessary FRRC trials is important to reduce the number of sterilizations.

Theoretical study of the initial stages of Ba growth on Si(100) substrate

We present theoretical study based on DFT calculations of the initial stages of Ba growth on Si(100) substrate. The obtained results indicate the possibility of coexistence of the inter-row and intra-row Ba monomers, as predicted by reported earlier STM measurements – the inter-row configuration has only 0.15 eV lower energy than the intra-row system. The detailed analysis of the atomic and electronic structures of both monomers have been performed. It was found that in all cases Ba adatom tends to interact with silicon surface atoms with higher vertical position.Presented study shows that the presence of both types of Ba monomer increases the local chemical reactivity of silicon surface, however this effect is stronger for the inter-row configuration. It was shown that such modification of substrate reactivity influences the form of the further aggregation of Ba adatoms. The obtained results indicate the tendency to formation by adatoms of linear-zigzag chains across the surface dimer rows, which seems to be in the agreement with reported earlier STM data.

Fusion bonding of copper and silicon at -70 °C by electrochemistry

Wafer bonding processing typically employs thermal energy to fuse two surfaces by stimulating atomic interdiffusion at high temperatures. However, we found that the fusion bonding of copper and silicon can occur at an extremely low temperature in cryo-electrochemical processing cooled by dry-ice (-20 °C) or even by liquid nitrogen (-70 °C). The results demonstrate that electrical energy can replace the thermal energy that must be used in semiconductor processes. The bonding phenomenon reproducibly occurred, and even the copper surface was not favorable for spontaneous bonding. Notably, the bonding strength of Cu/Si was very high. Even after forcibly inserting a razor at the bonding interface, a copper layer was split from the Cu host substrate to enable a transfer onto silicon. The secondary-ion mass spectrometry (SIMS) analysis revealed that the bonding was caused by nanoscale interdiffusion between surface copper and silicon atoms. We propose a possible mechanism where holes are driven into the bonding interface of Cu/Si under bias, positively charge the Cu atoms and form cations (i.e., surface activation). The electric field continuously drives Cu cations to bond with the dangling bonds on the mating silicon to form Si-Cu bonds. The Cu cations that arrive later can pass over the bonding interface and quickly diffuse into the silicon interstitials. This study of fusion bonding at -70 °C by electrochemistry-assisted interdiffusion instead of thermal energy has profound implications for wafer bonding processes and applications.

Fusion Bonding of Copper and Silicon at -70°C by Electrochemistry

Wafer bonding processing typically employs thermal energy to fuse two surfaces by stimulating atomic interdiffusion at high temperatures. However, we found that fusion bonding of copper and silicon can occur at an extremely low temperature in cryo-electrochemical processing cooled by dry-ice (-20°C) or even by liquid nitrogen (-70°C). The results demonstrate that electrical energy can replace the thermal energy that must be used in semiconductor processes. The bonding phenomenon occurred repeatedly, even the copper surface was not favorable for spontaneous bonding. Notably, the bonding strength of Cu/Si was very high. Even after forcibly inserting a razor at the bonding interface, a copper layer was split from the Cu host substrate to transfer onto silicon. Secondary-ion mass spectrometry (SIMS) analysis revealed that the bonding was caused by nanoscale interdiffusion between surface copper and silicon atoms. We propose a possible mechanism in which holes are driven into the bonding interface of Cu/Si under bias, positively charge the Cu atoms and form cations (that is, surface activation). The electric field continuously drives Cu cations to bond with the dangling bonds on the mating silicon to form Si-Cu bonds. The late-forming Cu cations can pass over the bonding interface and quickly diffuse into the silicon interstitials. This study of fusion bonding at -70oC by electrochemistry-assisted interdiffusion rather than by thermal energy has profound implications for the bonding mechanism.

2D SiC/Si Structure: Electron States and Adsorbability

A model of a heterostructure consisting of a silicon-carbide single layer formed on a massive silicon substrate is proposed. The problem of the adsorption of alkali metal atoms and halogen atoms on the carbon and silicon surface atoms of a 2D SiC/Si heterostructure is considered. Analytical estimates for charge transfer and the adsorption energy are reported.

Highly effective esterification of lignin to produce a pharmaceutical intermediate using novel silica mesoporous molecular sieves as catalysts

The use of lignin to prepare fine chemicals is a hot research topic. Here, we propose a strategy for esterification of the syringyl group, which is abundant in lignin, to produce 3,4-dimethoxyphenyl acetic acid ester. Lignin reacts with alcohols over acidic pure silica catalyst, L-MCM-41, to generate 3,4-dimethoxyphenyl acetic acid esters. The esterification yield from alkali lignin (Indulin AT) reached more than 60%. Furthermore, L-MCM-41 was easily and quickly prepared using hydroxyl free radicals. The obtained L-MCM-41 exhibited enhanced Lewis acidity and stability compared to silica MCM-41 derived from a traditional hydrothermal system. The enhanced Lewis acidity of the surface silicon atoms of L-MCM-41 can be attributed to the electron-withdrawing effect of abundant geminal hydroxyl groups that they bear. Based on spectroscopic data and the concentration of hydroxyl free radicals, the mechanism underpinning the enhanced acidity and stability of the mesoporous silica molecular sieves is proposed. This work enables production of fine chemicals using lignin as feedstock and provides a reliable and simple method for the synthesis of strongly acidic mesoporous silica molecular sieves.

INFLUENCE OF SILICON WAFER CRYSTALLOGRAPHIC ORIENTATION ON ANODIZATION MECHANISM

The influence of silicon wafer crystallographic orientation on the formation of porous silicon during anodization in an HF solution is studied. Cross-section SEM image comparison of samples with different crystallographic orientations has shown that (111) Si samples exhibit a more branching, tree-like pore structure with a higher porosity value compared to (100) Si samples. This phenomenon is explained by pointing out differences in crystal structure and numbers of Si-Si chemical bonds in different crystallographic directions. Namely, in (100)-oriented silicon crystals every surface Si atom has two bonds connecting it to atoms underneath it, as well as two broken bonds able to interact with Fions. Through electron injection into silicon, enough energy is applied to break the underlying bonds, forming SiF as a result. The presence of two Fions bonded with every surface silicon atom leads to weakening the bonds of surface silicon atoms with the underlying atoms, thus making the process of breaking the Si-Si bonds more energy efficient. As for (111)-oriented crystals, silicon atoms only have one broken surface bond, and breaking backbonds with underlying silicon atoms requires a higher value of activation energy due to their larger amount (three as opposed to two for (100) silicon). It is concluded that this very reason leads to slower etching speeds of (111)-oriented silicon wafers. The results help evaluate the way the silicon crystal structure affects the etching process, including its speed and direction, which is an especially important factor to consider when forming (111)-oriented porous silicon.

Гетероструктура 2D SiC/Si: электронные состояния и адсорбционная способность

Abstract A model of a heterostructure consisting of a silicon-carbide single layer formed on a massive silicon substrate is proposed. The problem of the adsorption of alkali metal atoms and halogen atoms on the carbon and silicon surface atoms of a 2D SiC/Si heterostructure is considered. Analytical estimates for charge transfer and the adsorption energy are reported.

Initiating and Monitoring the Evolution of Single Electrons Within Atom-Defined Structures.

Using a noncontact atomic force microscope, we track and manipulate the position of single electrons confined to atomic structures engineered from silicon dangling bonds on the hydrogen terminated silicon surface. An attractive tip surface interaction mechanically manipulates the equilibrium position of a surface silicon atom, causing rehybridization that stabilizes a negative charge at the dangling bond. This is applied to controllably switch the charge state of individual dangling bonds. Because this mechanism is based on short range interactions and can be performed without applied bias voltage, we maintain both site-specific selectivity and single-electron control. We extract the short range forces involved with this mechanism by subtracting the long range forces acquired on a dimer vacancy site. As a result of relaxation of the silicon lattice to accommodate negatively charged dangling bonds, we observe charge configurations of dangling bond structures that remain stable for many seconds at 4.5K. Subsequently, we use charge manipulation to directly prepare the ground state and metastable charge configurations of dangling bond structures composed of up to six atoms.

Oxidative reactivity of alkali-like superatoms of group 5 metal-encapsulating Si16 cage nanoclusters

It is crucial to control the reactivity of surface silicon atoms for applications in miniaturized silicon-based nanodevices. Here we demonstrate that reactive silicon atoms are made unreactive by forming a Si16 cage that encapsulates a metal atom. Specifically, group 5 metal-encapsulating Si16 nanoclusters (M@Si16: M = V, Nb, and Ta) exhibit alkali-like superatomic behavior on n-type C60 substrates, where charge transfer between M@Si16 and C60 satisfies the 68-electron shell closure as M@Si16+. The oxidation properties of M@Si16+ are investigated by X-ray photoelectron spectroscopy, revealing that the chemical stability of the caged silicon surface towards oxygen is enhanced by a factor of 104 compared to a crystalline silicon surface, and that M@Si16 are oxidized stepwise from the outer Si16 cage to the central metal atom. While the nanoclusters share a common Si16 cage, their chemical robustness depends on a superatomic “periodicity” (Ta@Si16 > V@Si16 > Nb@Si16) which is explained by the electron density distributions of M@Si16 investigated by DFT calculations.

An Optimized FinFET Channel With Improved Line-Edge Roughness and Linewidth Roughness Using the Hydrogen Thermal Treatment Technology

Evolutionary process of a nanoscale FinFET channel during rapid hydrogen thermal treatment is modeled using a kinetic Monte Carlo simulation. In this paper, a novel model of nanoscale FinFET channel is proposed based on the surface diffusion theory of silicon fin structures. The evolution characteristics of fin surface morphology, including line edge roughness (LER), line width roughness, and the cross-correlation coefficient ρ, are investigated in the diffusion process of silicon fin structures at different temperatures and time. All the characteristic parameters can directly affect the carrier transport performance of FinFET. The LER of a silicon fin has been effectively reduced by at least 60%. The linewidth roughness and ρ was also investigated in the evolution of FinFET channel. The results indicate that an optimized nanoscale FinFET channel can be achieved by controlling the migration of surface silicon atoms in rapid hydrogen thermal treatment technology application, yielding atomically smooth sidewall surfaces. The present experimental results are coincided with the simulation results. Thus, such technology plays a crucial role in the application of nanoscale FinFET.

Boronic Acid-Functionalized Oxide-Free Silicon Surfaces for the Electrochemical Sensing of Dopamine.

Boronic acid monolayers covalently bound to hydrogen-terminated Si(111) surfaces have been prepared from the UV-directed hydrosilylation reaction of 4-vinylbenzeneboronic acid. X-ray photoelectron spectroscopy (XPS) analysis of the modified surface revealed characteristic peaks from the attached organic molecule with the expected molecular composition and without the oxidation of underlying silicon. From XPS data, the surface coverage was estimated to be ca. 0.34 ± 0.04 ethylbenzene boronic acid chain per surface silicon atom (i.e., (4.4 ± 0.5) × 10-10 mol cm-2), which is consistent with a densely packed monolayer. The electrochemical impedance spectroscopy measurements performed at pH 7.4 in the presence of the Fe(CN)63-/Fe(CN)64- reporter couple showed specific dopamine-induced changes as a result of the binding of the guest molecule to the immobilized boronate species. The charge-transfer resistance (Rct) was found to decrease from 4.9 MΩ to 14 kΩ upon increasing the dopamine concentration in the range of 10 μM-1 mM. Furthermore, the presence of the interfering ascorbic acid until a concentration of 10 mM did not significantly change the electrochemical response of the functionalized surface. Comparative electrochemical data obtained at the reference ethylbenzene monolayer provided clear evidence that the immobilized boronic acid units were responsible for the observed changes.

Fluorine Etching in Porous Silicon: An Ab-Initio Molecular Dynamics Study

Surface atom removal by fluorine in porous silicon is studied by using the first-principles molecular dynamics based on the density functional theory. The results confirm the preferential <100> crystalline etching direction, in agreement with the experimental results. Moreover, surface silicon atoms are mostly captured by two fluorine and two hydrogen atoms, producing difluorosilane (SiH2F2), in contrast to the widely accepted four fluorine-atom capture model. This new capture process could be verified by the infrared spectroscopy.

Surface Structure and Silicon Nanocrystal Photoluminescence: The Role of Hypervalent Silyl Groups

We report a combined experimental and theoretical study of the relationship between the surface structure of silicon nanocrystals synthesized in a nonthermal plasma reactor and their photoluminescence (PL) yields. Upon heating to 160 °C, a significant change in the SiH stretch region of the vibrational spectrum is observed indicating a decrease in surface SiH3 groups, which correlates with an increase in the PL yield. Effusion of SiHx and Si2H2x from the material is detected by residual gas analysis upon heating to temperatures below 200 °C, suggesting a weakly bound species. Analysis of electron paramagnetic resonance spectra before and after heating points to a small reduction in the density of dangling bonds upon heating but this reduction does not correlate with the increase in PL yield. Electronic structure calculations indicate that SiH3– groups may hypervalently bond to fully coordinated surface silicon atoms, resulting in a relatively weak (0.70 eV) bond that is consistent with the experimentally ...

Dynamic Observation of Confined Molecules in Self-Assembled Molecular Corrals

Molecular corrals self-assembled on a Si(111)-(7 × 7) surface after pyrrole exposure, enclosing silicon adatom sites where trimethylphosphine (TMP) was then datively adsorbed. The phosphine’s dynamic motion was investigated by scanning tunneling microscopy. The TMP was confined by the corral, hopping on adatom sites within it. Density functional theory calculations showed covalent bonding between the pyrroles and surface silicon atoms because of N–H dissociative adsorption. An electropositive potential around the TMP/Si cluster may induce electrostatic repulsion between the adsorbed molecules.

ChemInform Abstract: Laser Flash Synthesis of Graphene and Its Inorganic Analogues: An Innovative Breakthrough with Immense Promise

AbstractReview: 109 refs.

Cavity-assisted quantum computing in a silicon nanostructure

We present a scheme of quantum computing with charge qubits corresponding to one excess electron shared between dangling-bond pairs of surface silicon atoms that couple to a microwave stripline resonator on a chip. By choosing a certain evolution time, we propose the realization of a set of universal single- and two-qubit logical gates. Due to its intrinsic stability and scalability, the silicon dangling-bond charge qubit can be regarded as one of the most promising candidates for quantum computation. Compared to the previous schemes on quantum computing with silicon bulk systems, our scheme shows such advantages as a long coherent time and direct control and readout.

Growth of silicon oxynitride films by atmospheric pressure plasma jet

Ultra-thin silicon oxynitride (SiOxNy) layers were deposited by direct interaction of plasma species formed in an atmospheric pressure plasma jet (APPJ) with a silicon wafer. APPJs have been ignited in mixtures of helium (He) together with several nitrogen-based compounds. The chemical composition of the APPJ treated silicon surfaces was analysed by ultra-high vacuum x-ray photoelectron spectroscopy (XPS). The obtained N 1s XPS spectra showed that even 5 min of APPJ treatment is sufficient to fabricate SiOxNy films with a few nanometre thickness. A Si substrate exposed to an APPJ generated in a mixture of He/NH3 resulted in the most efficient growth of SiOxNy films, indicated by the strongest N 1s XPS signal among all studied gas mixtures. Moreover, the N 1s spectra exhibited two major characteristics of chemical bonding structures attributed to nitrogen bonded to three silicon surface atoms, N–(S)3, and nitrogen bonded to two silicon surface atoms and one oxygen atom, (Si)2–N–O.