Si-OH Bonds Research Articles

Thermal expansion of hydrated six-coordinate silicon in thaumasite, Ca3Si(OH)6(CO3)(SO4)�12H2O

Thaumasite, Ca3Si(OH)6(CO3)(SO4)12H2O, occurs as a low-temperature secondary alteration phase in mafic igneous and metamorphic rocks, and is recognized as a product and indicator of sulfate attack in Portland cement. It is also the only mineral known to contain silicon in six-coordination with hydroxyl (OH)− that is stable at ambient P–T conditions. Thermal expansion of the various components of this unusual structure has been determined from single-crystal X-ray structure refinements of natural thaumasite at 130 and 298 K. No phase transitions were observed over this temperature range. Cell parameters at room temperature are: a= 11.0538(6) A, c=10.4111(8) A and V=1101.67(10) A3, and were measured at intervals of about 50 K between 130 and 298 K, resulting in mean axial and volumetric coefficients of thermal expansion (×10−5K−1); α a =1.7(1), α c =2.1(2), and α V =5.6(2). Although the unit cell and VIIICaO8 polyhedra show significant positive thermal expansion over this temperature range, the silicate octahedron, sulfate tetrahedron, and carbonate group show zero or negative thermal expansion, with α V (VISiO6) = −0.6 ± 1.1, α V (IVSO4)=−5.8 ± 1.4, and α R (C–O)= 0.0 ± 1.8 (×10−5 K−1). Most of the thermal expansion is accommodated by lengthening of the R(O...O) hydrogen bond distances by on average 5σ, although the hydrogen bonds involving hydroxyl sites on VISi expand twice as much as those on molecular water, causing the [Ca3Si(OH)6(H2O)12]4+ columns to expand in diameter more than they move apart over this temperature range. The average Si–OH bond length of the six-coordinated Si atom 〈R(VISi–OH)〉 in thaumasite is 1.783(1) A, being about 0.02 A (˜20σ) shorter than VISi–OH in the dense hydrous magnesium silicate, phase D, MgSi2H2O6.

The effect of photo-irradiation in hydrolysis and condensation of silicon alkoxide

A silicon alkoxide–water–ethanol mixed solution was irradiated with ultraviolet rays, and the change of the silicon alkoxide molecular structure was evaluated by 29Si nuclear magnetic resonance and Fourier transform infrared spectroscopies. Silicon alkoxide was hydrolyzed and the Si–OH bonds were produced by UV irradiation without any chemical catalyst for hydrolysis. The Si–O–Si bonds were also produced, and viscosity of the alkoxide solution became higher due to condensation of alkoxide.

Spectroscopic characterization of intrinsic losses in an organic–inorganic hybrid waveguide synthesized by the sol–gel process

A promising way of fabricating integrated optics components is based on the sol–gel synthesis and photocuring of hybrid materials. However, the presence of OH groups in these materials is a major factor in optical amplification inhibition. In particular, high losses at 1550 nm are mainly due to non-condensed OH groups originating from the sol–gel process at low temperature. Thus, improvement of the final properties of these materials is correlated with the inhibition of OH group concentration. In this study, we used 29Si NMR and near infrared spectroscopy to demonstrate the catalytic effect of zirconium (IV) n-propoxide on the condensation reactions of silanol groups. 29Si NMR showed the absence of silanol species at the end of the synthesis. This result is attributed to the zirconate hydrophilic effect which consumes OH groups by catalysing the polycondensation of Si–OH bonds. In parallel, near-infrared experiments showed the presence of a high proportion of OH species at the end of the synthesis showing that the remaining OH groups are only present in the zirconium species.

Formation of self-assembly and the mechanism of Si nanoquantum dots prepared by low pressure chemical vapor deposition

Si nanoquantum dots have been formed by self-assembled growth on the both Si—O—Si and Si—OH bonds terminated SiO2 surfaces using the low-pressur e chemical vapor deposition (LPCVD) and surface thermal decomposition of pure SiH4 gas. We have experimentally studied the variation of Si dot density with Si—OH bonds density, deposition temperature and SiH4 pressure, and analyzed qu alitatively the formation mechanism of the Si nanoquantum dots based on LPCVD surface thermal dynamics principle. The results are very important for the control of the density and size of Si nanoquantum dots, and have potential applications in the new quantum devices.

<I>In-situ</I> Photoluminescence, Raman, and IR Spectral Study of Porous Silicon during Exposure to Thermoelectrons/H atoms, /H<SUB>2</SUB>O and /O<SUB>3</SUB>

Photoluminescence (PL), Raman, and transmission IR spectral measurements of porous silicon (PS) have been carried out during exposure to thermoelectrons and also subsequent exposure to H atoms, H 2 O and O 3 . The PL band of as-anodized PS was significantly decreased by the first exposure to thermoelectrons accompanied by the intensity reduction of the IR bands due to hydrogenated Si species (Si-H x ; x = 1-3). Upon subsequent exposure to H atoms the PL band intensity was almost recovered but never exceeded its original intensity. This PL recovery was accompanied by re-generation of Si-H x bottds. In contrast, an overshooting recovery in the PL intensity took place when thermoelectron-treated PS was exposed to H 2 O or O 3 . The obtained IR spectra showed that Si-O and/or Si-OH bonds were formed at the PS surface. These results demonstrate that the PL of the PS is quite sensitive to the oxygen-included surface bonds.

Plasma enhanced chemical vapor deposition of low dielectric constant SiCFO thin films

Low dielectric constant SiCFO films were grown on oxidized p-type Si (1 0 0) using SiH 4 and CF 4 in plasma enhanced chemical vapor deposition reactor. The film showed good water resistance and quite low dielectric constant in a range of 1.3–2.0. The growth rate, chemical structure, and dielectric constant were quite dependent on the plasma source power. Fourier transform infrared spectroscopy (FT-IR) spectra showed SiO, CF and CC bonds, but no CH, HOH and SiOH bonds formed. The as-grown film also showed good adhesion at the interface and smooth surface morphology.

Multiple internal reflection spectroscopy for quantitative infrared analysis of thin-film surface coating for biological environment

A study of silica surface preparation for covalent grafting of biological molecules is made by Multiple Internal Reflection (MIR) infrared spectroscopy. The samples are composed of silicon substrate covered with a thick silica layer submitted to various chemical steps. The two-prism coupling geometry is used. Compared to bevelled angle, this configuration allows the analysis with variable distance propagation and the sample act as its own reference. As a consequence, quantitative results are presented.The samples are modified by silane chemistry to introduce a specific function such as an aldehyde for covalent attachment of an NH2-modified oligonucleotide or protein. The successive chemical steps are followed and quantified in terms of reaction efficiency. In these conditions, we could characterize the silica surface hydroxylation, the silanisation and the transformation of the epoxy final function into an aldehyde. Because process characterization shows that silanisation is the more critical step, an additional study is made about the type and quantity of Si–OH bonds present on the silica surface for various hydroxylation steps.This study demonstrates that MIR method using variable propagation distance is a powerful tool for process characterization and allows the optimisation of a reliable process for biochips.

Diffusion and reactions of hydrogen in F2-laser-irradiated SiO2 glass.

The diffusion and reactions of hydrogenous species generated by single-pulsed F2 laser photolysis of SiO-H bond in SiO2 glass were studied in situ between 10 and 330 K. Experimental evidence indicates that atomic hydrogen (H0) becomes mobile even at temperatures as low as approximately 30 K. A sizable number of H0 dimerize by a diffusion-limited reaction into molecular hydrogen (H2) that may migrate above approximately 200 K. Activation energies for the diffusion, inherently scattered due to the structural disorder in glass, are separated into three bands centered at approximately 0.1 eV for free H0, approximately 0.2 eV presumably for shallow-trapped H0, and approximately 0.4 eV for H2.

Recovering Dielectric Loss of Low Dielectric Constant Organic Siloxane during the Photoresist Removal Process

The interaction between low dielectric constant (low-k) hybrid organic siloxane polymer (HOSP) and plasma ashing has been investigated. plasma ashing is commonly performed to remove the photoresist (PR) during integrated circuit fabrication. However, dielectric loss usually occurs in the HOSP films during the PR removal process. In order to eliminate dielectric loss originating from an plasma attack, hexamethyldisilazane (HMDS) treatment is proposed to repair the damage in the HOSP film. HMDS can react with Si-OH bonds and reduce moisture uptake. Moreover, the leakage current and the dielectric constant is decreased significantly when damaged HOSP film undergoes HMDS treatment. For this reason, HMDS treatment is a promising method to apply to the photoresist removal. © 2002 The Electrochemical Society. All rights reserved.

Structure, collective hydrogen transfer, and formation of Si(OH)4 in SiO2–(H2O)n clusters

SiO 2 –water clusters are studied using first-principles Born–Oppenheimer molecular dynamics based on density functional theory and generalized gradient approximations. Systematic investigations of structure and energetics as functions of cluster size demonstrate the roles of water molecules in chemical reactions. The water-assisted formation of a Si(OH)4 molecule from a single SiO2 molecule is revealed at the atomic level. The dynamics of dissociation of water molecules and formation of Si–OH bonds is investigated via simulations at finite temperature. A complex process that involves double and triple hydrogen atom transfer is discovered to be the reaction path.

High-quality SiO 2 film deposition using active reaction by oxygen radical

A novel film deposition method called radical shower chemical vapor deposition (RS-CVD) has been developed for high-quality gate-oxide (SiO 2) film formation on low-temperature poly-Si TFT-LCD. RS-CVD is characterised by a plasma damage-free deposition on a large area substrate at a low temperature, although discharge is used to generate the activated species of oxygen radicals. In film deposition, by using a reaction of SiH 4 with oxygen radicals, it is possible to grow SiO 2 films under low substrate temperature at low deposition pressure. Dependencies of film properties on deposition parameters are investigated to optimize the RS-CVD process. The parameter dependencies are interpreted with consideration of the gas phase reaction mechanisms, which account for the observable consequences of Si–OH bonds quantity incorporated in the films. Throughout this study, it is concluded that it is necessary for the film quality to reduce the contamination of intermediate species containing Si–OH bonds in the films and to control the excess reaction in the gas phase. Besides, the increase in the oxygen radical quantity is effective for the improvement of film properties.

Enhancing the resistance of low- k hydrogen silsesquioxane (HSQ) to wet stripper damage

The interaction between low- k hydrogen silsesquioxane (HSQ) film and wet stripper was investigated. The wet stripper has been commonly used to remove photoresister in IC integration processing. However, the high content of alkalinity in the stripper solution often leads to the hydrolysis of HSQ film, forming dangling bonds in the HSQ. The dangling bonds in the HSQ film can easily react with hydroxide ion (OH −) in wet stripper solution and form Si–OH bonds. The resultant HSQ film will tend to uptake water and consequently increase both the leakage current and dielectric constant. In this study, H 2-plasma pre-treatment was applied to the HSQ film. The hydrogen plasma treatment passivates the HSQ surface and prevent HSQ from water uptake during photoresist stripping. Therefore, dielectric degradation can be avoided with the H 2-plasma pre-treatment.

Electrical and Structural Properties of Catalytic-Nitrided SiO2 Films

ABSTRACTThis paper reports structural and electrical properties of catalytic-nitrided silicon dioxide (SiO2) films. The surface of SiO2/Si(100) was nitrided at temperatures below 573 K. It was found that the incorporated N atoms are bound to Si atoms and O atoms and located on the top-surface of SiO2. Catalytic-nitrided SiO2 films have small amounts of Si-OH bonds and adequate resistance to boron (B) penetration.

Defect formation and structural alternation in modified SiO2 glasses by irradiation with F2 laser or ArF excimer laser

The formation and restoration of defects by F2 laser irradiation with high laser fluence were investigated for modified silica glasses, and the results were compared with those by ArF excimer laser irradiation. F2 laser irradiation induced oxygen deficient centers (ODCs) and E′ centers via one-photon-absorption processes, while ODC and E′ defects are generated by two-photon-absorption processes by an ArF excimer laser. As-doped SiOHs and photoinduced SiOHs enhanced the formation of defects markedly in the case of F2 laser irradiation. F2 laser light transformed isolated SiOH bonds into hydrogen-bonded SiOHs, while such a process did not occur under ArF excimer laser light. These results suggest that silica glass networks were dissociated by two types of processes. The dominant process is the formation of pairs of E′ centers and NBOHCs, followed by conversion to the SiHs and SiOHs as a result of chemical reactions with hydrogen molecules in silica glass at room temperature. The other is the generation of ODC defects accompanied by interstitial oxygen molecules, which are also decomposed partly into E′ centers with the aid of F2 laser light.

H2O Outgassing Properties of Fumed and Precipitated Silica Particles by Temperature-Programmed Desorption

Temperature-programmed desorption was performed at temperatures up to 850 K on as-received fumed and precipitated silica particles. Physisorbed water molecules on both types of silica had activation energies in the range of 38–61 kJ/mol. However, the activation energies of desorption for chemisorbed water varied from ∼80 to >247 kJ/mol for fumed silica, Cab-O-Sil-M-7D, and ∼96 to 155 kJ/mol for precipitated silica, Hi-Sil-233. Our results suggest that physisorbed water can be effectively pumped away at room temperature (or preferably at 320 K) in a matter of hours. Chemisorbed water with high activation energies of desorption (>126 kJ/mol) will not escape silica surfaces in 100 years even at 320 K, while a significant amount of the chemisorbed water with medium activation energies (80–109 kJ/mol) will leave the silica surfaces in that time span. Most of the chemisorbed water with activation energies <126 kJ/mol can be pumped away in a matter of days in a good vacuum environment at 500 K. We had previously measured about 0.1–0.4 wt% of water in silica-reinforced polysiloxane formulations containing ∼21% Cab-O-Sil-M-7D and ∼4% Hi-Sil-233. Comparing present results with these formulations, we conclude that the adsorbed H2O and the Si–OH bonds on the silica surfaces are the major contributors to water outgassing from these types of silica-filled polymers.

Control of self-assembling formation of nanometer silicon dots by low pressure chemical vapor deposition

The formation of nanometer-scale silicon dots on ultrathin SiO2 layers has been studied by controlling the early stages of low-pressure chemical vapor deposition (LPCVD) of a monosilane gas. It has been suggested that the thermal dissociation of surface Si–O bonds plays a role in creation of nucleation sites on as-grown SiO2 and that surface Si–OH bonds formed by a dilute HF treatment or pure water immersion act as nucleation sites during LPCVD. By spatially controlling OH-termination on the SiO2 surface before LPCVD, the selective growth of Si dots has been demonstrated.

Bond strain, chemical induction, and OH incorporation in low-temperature (350–100 °C) plasma deposited silicon dioxide films

New device concepts are being considered with very demanding requirements for low-temperature processing. In this article, infrared transmission and ellipsometry is used to compare silicon oxide films formed by plasma chemical vapor deposition using SiH4, N2O, and either He or H2 dilution gas between 350 and 100 °C. The Si–O asymmetric stretching mode is affected by bond strain and chemical induction, and monitoring the Si–O peak position gives insight into the effect of process conditions on local bond structure. Hydrogen is expected to affect surface processes during growth, for instance, to enable the removal of surface SiOH bonds through H-mediated abstraction, leading to improved bonding structure at low temperature. We find that exposing the surface to hydrogen atoms during growth helps eliminate isolated SiOH bonds, leading to Si–Si bond formation. However, an increase in associated SiOH bonding groups, stabilized by hydrogen bonding, is also observed. The density of associated SiOH groups is larger at low temperature where the rate of water desorption is reduced, suggesting that the associated OH is formed by physisorbed water produced during OH removal. Films deposited with hydrogen dilution show somewhat improved electrical performance at &amp;lt;200 °C, but further work is required to produce high quality films at very low temperatures.

Controlled Synthesis of Perfluoroaryl Functionalized Hybrid Materials for Optical Applications based on NMR Spectroscopy and Molecular Modeling

ABSTRACTThe synthesis of ORMOCER®*s (inorganic-organic polymers) for optical applications is studied in detail. Producing waveguide materials with the desired low optical losses at wavelengths of 1310 and 1550 nm requires a thorough control of the initial inorganic network formation, because absorption losses are particularly due to Si-OH bonds beside aliphatic C-H bonds. Therefore, the synthesis of UV- or thermally curable organopolysiloxane resins with minimized Si-OH content is crucial. The investigation of the sol-gel reaction of organoalkoxysilanes by 29Si-NMR spectroscopy provides a detailed insight into the influence of reaction conditions on the species and networks formed. Reaction parameters were optimized towards the formation of ORMOCER® resins suitable for waveguide applications. Finally, the material synthesis is completed by crosslinking organically polymerizable units present in the ORMOCER® resin to establish the inorganic-organic hybrid network. The experimental work is accompanied by computational chemistry. Calculating electronic properties is of value in predicting silane reactivities as well as spectroscopic data of intermediates. Molecular modeling is a convenient tool for the visualization of structural details on the molecular level.

Changes in Orientational Polarization and Structure of Silicon Dioxide Film by Fluorine Addition

Use of F‐doped silicon dioxide film as a low dielectric constant intermetal film for ultralarge scale integrated circuits (ULSI) is useful from the viewpoint of product cost and compatibility with present processing technologies. By adding to plasma‐enhanced chemical vapor deposition, we obtained F‐doped films with a dielectric constant as low as 2.6. The mechanism behind this decrease was investigated by estimating the dielectric constants due to the polarization components using capacitance‐voltage measurements, Kramers‐Kronig transformation, and spectroscopic ellipsometry. Fluorine addition lowers the orientational polarization by decreasing the number of ‒OH bonds, and this decrease in Si‒OH concentration is a key factor which is responsible for the lower dielectric constant in the F‐doped film. Orientational polarization due to the Si‒OH bond disappears in the far infrared with increasing frequency, thus the dielectric constant is composed only of ionic and electronic polarization components in the frequency range beyond the far infrared. The quantitative analysis of fluorine and OH shows that excess Si‒F bonds replace Si‒O and form . We suggest that the water absorption for F‐doped film can be minimized by suppressing fluorine addition at the time that the Si‒OH bonds vanish in order to avoid forming and destroying the threefold rings. © 1999 The Electrochemical Society. All rights reserved.

Effects of O2- and N2O-Plasma Treatments on Properties of Plasma-Enhanced-Chemical-Vapor-Deposition Tetraethylorthosilicate Oxide

The high quality silicon oxide films were prepared by plasma-enhanced chemical vapor deposition (PECVD) using tetraethylorthosilicate (TEOS)-oxygen based chemistry. The O2- or N2O-plasma treatments were performed on the as-deposited films as an attempt to improve the properties of the TEOS oxide films. TEOS oxide film deposited at lower pressure had lower Si–OH content, less carbon impurity, and flatter surface, and hence had better electrical properties. Both O2- and N2O-plasma would decrease the oxygen content of the oxide film, which led the composition of the film to deviate from the stoichiometric SiO2. The O2-plasma treatment did not show the encouraging effect on the chemical structure and electrical properties of the TEOS oxide films. In contrast, the N2O-plasma treatment could be a promising means to improve the breakdown field and leakage current density of the TEOS oxide films, which was accomplished by the N2O-plasma effect to facilitate the passivation of dangling bonds, linking reaction of Si–OH bonds, nitridation reaction and densification of the amorphous silicon oxide network.