Dissociation Of Si Research Articles

Lewis Base/Acid Coordination Stabilizes Planar 6π Aromatic Si6/P6

We have developed a strategy for designing planar all-Si and all-P 6π aromatics based on experimentally available building blocks. A Si6 hexagon coordinated by three phosphines at the 1,3,5-positions, Si6(PH3)3, which has three lone-pair-carrying Si atoms is nearly planar and aromatic. Replacing PH3 by NH3 induces perfect planarity. Two-electron reduction of Si6(PH3)3 results in doubly aromatic Si62– with the dissociation of Si–P bonds, instead of a nonaromatic system such as the benzene dianion. Similarly to base-coordinated Si6, Lewis acid coordination to P6 can give planar 6π aromatics. P6(BH3)3 is a nearly planar minimum. Replacing BH3 with a stronger Lewis acid, B(CN)3, gives a perfectly planar structure. A PH3-coordinated all-Si diene resembling butadiene is predicted. A concerted 4 + 2 cycloaddition between this all-Si diene and ethylene is proposed here and has a computed barrier of only 22 kcal/mol.

Influence of structural Al and Si vacancies on the interaction of kaolinite basal surfaces with alkali cations: A molecular dynamics study

Point defects, particularly vacancies, exist abundantly in the structure of a variety of clay minerals (e.g., kaolinite). Such defects significantly alter the physical/chemical characteristics of the minerals. Dissolution of kaolinite in an alkali medium is a critical step in the geopolymerization process and it determines the properties of the final product. In this work, a series of molecular dynamics (MD) simulations were carried out in the isothermal-isobaric (NPT) ensemble at 298K and 1atm to study the influence of structural vacancies (Al and Si vacancies in particular) on the interaction/dissolution of the two basal surfaces of kaolinite (partially deprotonated octahedral and tetrahedral surfaces) exposed to alkali media. Two different alkali media were used. One contained sodium cation (Na+) only while the other potassium cation (K+) and their concentrations were 3M and 5M. The MD results showed that regardless of the type of cation and cation concentration, Al vacancies on the octahedral surface promoted the dissolution of Al into the solution compared to the surface without Al vacancies. However, there existed a vacancy concentration (2 Al vacancies per 576 Al atoms) at which the dissolution amount was the maximum and above which the dissolution decreased with increasing Al vacancy concentration. The presence of Si vacancies in the tetrahedral surface did not show significant effect on the dissociation of Si. Radial distribution function (RDF) analyses indicated that the degree of crystallinity of the octahedral surface decreased as the number of Al vacancies increased but this was not the case for the tetrahedral surface.

NMR and Quantum‐Chemical Studies of Electrostatically Stabilized 1‐(N,N‐Substituted‐aminiomethyl)spirobi[3‐oxo(2,5‐dioxa‐1‐silacyclopentan)]ates (ES‐Silanates)

ABSTRACT1‐(N,N‐substituted‐aminiomethyl)spirobi[3‐oxo(2,5‐dioxa‐1‐silacyclopentan)]ates were investigated using NMR, X‐ray, and quantum‐chemical methods. The free activation parameters for the inversion of “ammonium‐amine nitrogen” and the chirality change at the pentacoordinated silicon were determined by dynamic NMR spectroscopy. The latter proceeds via the dissociation of SiO bonds. The results were confirmed by quantum‐chemical calculations, the experimental observation of cross‐peaks in 2D‐EXSY NMR spectra, and the spirocycle exchange reactions. Transition pathways between the different diastereomers in solution were analyzed.

Effect of an Ultrathin SiN Cap Layer on the Bias Temperature Instability in Metal–Oxide–Semiconductor Field-Effect Transistors with HfSiON Gate Stacks

The negative-bias temperature instability (NBTI) and positive-bias temperature instability (PBTI) of HfSiON/SiO2 metal–oxide–semiconductor field-effect transistors (MOSFETs) with and without an ultrathin SiN cap layer were investigated. For the PBTI of n-channel MOSFETs, the dominant degradation mechanism is the electron tunneling from the Si channel and electron trapping in the pre-existing traps in HfSiON. The SiN cap layer does not make a significant difference in PBTI. For the NBTI of p-channel MOSFETs, on the other hand, both the electron trapping in HfSiON and the dissociation of Si–H bonds at the SiO2/channel-Si interface (i.e., the interface trap generation) play a role and the SiN cap layer makes a significant difference in NBTI: the dominant degradation mechanism for the devices without the SiN cap layer is the electron trapping in HfSiON, whereas that for the devices with the SiN cap layer is the interface trap generation. This indicates that the interfacial SiN cap layer can effectively suppress the electron tunneling from the polycrystalline silicon (polySi) gate to HfSiON under the NBT stress.

SiOC 박막에서 Si-O 결합의 증가와 유전상수의 관계

ICP-CVD 방법에 의해 제작된 SiOC 박막을 유전상수와 화학적 이동의 상관성에 대하여 조사하였다. SiOC 박막은 플라즈마 에너지에 의해서 해리작용과 재결합작용에 의해서 cross link 구조를 갖게 되는 Si-O 와 C-O 결합으로 구성된 <TEX>$930{\sim}1230\;cm^{-1}$</TEX> 영역에서 혼합된 Si-O-C 주 결합으로 이루어졌다. C-O 결합은 <TEX>$1270cm^{-1}$</TEX>에서 보여지는 Si-<TEX>$CH_3$</TEX> 결합의 말단부분인 C-H 결합이 전기음성도가 큰 산소에 의해서 끌리는 효과로부터 만들어진 결합이다. 그러나 Si-O 결합은 Si-<TEX>$CH_3$</TEX> 결합이 분해되고 난뒤 2차 이온결합에 의해서 만들어진 결합이다. Si-O 결합의 증가는 주결합에서 오른쪽 결합이 증가하기 때문이며, FTIR 스펙트라에 의해서 red shift로 나타났다. 이러한 결과는 SiOC 박막이 보다 더 안정되고 강한 박막임을 의미한다. 그래서 SiOC 박막은 열처리 후 비정질도가 높고 거칠기가 감소되는 것을 확인하였다. SiOC films made by the inductively coupled plasma chemical vapor deposition were researched the relationship between the dielectric constant and the chemical shift. SiOC film obtained by plasma method had the main Si-O-C bond with the molecule vibration mode in the range of <TEX>$930{\sim}1230\;cm^{-1}$</TEX> which consists of C-O and Si-O bonds related to the cross link formation according to the dissociation and recombination. The C-O bond originated from the elongation effect by the neighboring highly electron negative oxygen atoms at terminal C-H bond in Si-<TEX>$CH_3$</TEX> of <TEX>$1270cm^{-1}$</TEX>. However, the Si-O bond was formed from the second ionic sites recombined after the dissociation of Si-<TEX>$CH_3$</TEX> of <TEX>$1270cm^{-1}$</TEX>. The increase of the Si-O bond induced the redshift as the shift of peak in FTIR spectra because of the increase of right shoulder in main bond. These results mean that SiOC films become more stable and stronger than SiOC film with dominant C-O bond. So it was researched that the roughness was also decreased due to the high degree of amorphous structure at SiOC film with the redshift after annealing.

Effect of temperature on layer separation by plasma hydrogenation

We have studied hydrogen diffusion in plasma hydrogenated Si∕SiGe∕Si heterostructure at different temperatures. At low temperature, intrinsic point defects in the molecular beam epitaxy grown Si capping layer are found to compete with the buried strain SiGe layer for hydrogen trapping. The interaction of hydrogen with point defects affects the hydrogen long-range diffusion, and restricts the amount of hydrogen available for trapping by the SiGe layer. However, hydrogen trapping by the capping layer is attenuated with increasing hydrogenation temperature allowing more hydrogen to be trapped in the strain SiGe layer with subsequent surface blister formation. A potential temperature window for plasma hydrogenation induced layer separation is identified based on the combined considerations of trap-limited diffusion at low temperature and outdiffusion of H2 molecule together with the dissociation of Si–H bonds inside of H platelet at high temperature.

Dissociation of Si+ ion implanted and as-grown thin SiO2 layers during annealing in ultra-pure neutral ambient by emanation of SiO

We have observed a very inhomogeneous dissociation of stoichiometric and non-stoichiometric thin SiO2 layers (thermally grown on Si substrates) during high temperature annealing at a low partial pressure of oxygen. During this process some silicon of the (100)Si substrate and, in case of Si ion implantation, and additionally, excess Si is consumed. The SiO2 dissociation has been studied by electron microscopy and Rutherford backscattering spectrometry. Large holes (&amp;gt;1 μm) in non-implanted oxide layers have been observed which evolve probably from defects located at the Si∕SiO2 interface. For Si implanted SiO2 additionally the formation of voids within the oxide during annealing has been observed preferably at the position of the implanted Si excess. Oxygen vacancies are possibly emitted from Si∕SiO2 interfaces into the oxide and migrate through SiO2 with long-range distortions of the oxide network. In that way the hole and void formation in the oxide can be explained by oxygen-vacancy formation, migration and silicon-monoxide (SiO) emanation. As a driving force for growth of the large holes we identified oxygen diffusion from the Si∕SiO2 interface to the bare Si surface. This surface is a sink of oxygen diffusion due to the emanation of volatile SiO, whereas the Si∕SiO2 interface serves as an oxygen source. The predicted mechanism is consistent with the geometry of the holes in the SiO2 layer.

SiH 4 adsorption on SiGe(0 0 1)

The adsorption process of silane (SiH 4) on a SiGe(0 0 1) surface has been investigated by using infrared absorption spectroscopy in a multiple internal reflection geometry. We have observed that SiH 4 dissociatively adsorbs on a SiGe(0 0 1) surface at room temperature to generate Si and Ge hydrides. The dissociation of Si- and Ge-hydride species is found to strongly depend on the Ge concentration of the SiGe crystal. At a low Ge concentration of 9%, Si monohydride (SiH) and dihydride (SiH 2) are preferentially produced as compared to the higher Si hydride, SiH 3. At higher Ge concentrations of 19%, 36%, on the other hand, monohydrides of SiH and GeH and trihyderide SiH 3 are favorably generated at the initial stage of the adsorption. We interpret that when SiH 4 adsorbs on the SiGe surface, hydrogen atoms released from the SiH 4 molecule stick onto Ge or Si sites to produce Si or Ge monohydrides and the remaining fragments of –SiH 3 adsorb both on Si and Ge sites. The SiH 3 species is readily decomposed to lower hydrides of SiH and SiH 2 by releasing H atoms at low Ge concentrations of 0% and 9%, while the decomposition is suppressed by Ge in cases of 19% and 36%.

Analysis of the Photochemical Reaction on the Surface for Room Temperature Deposition of SiO2 Thin Films by Photo-CVD using Vacuum Ultraviolet Light

We have analyzed the photochemical reaction for the deposition of SiO2 thin films at room temperature in photo-CVD using a vacuum ultraviolet (VUV) excimer lamp with reflection-absorption spectroscopy using a Fourier transform infrared spectrometer (RAS-FTIR). Tetraethoxyorthosilicate (TEOS) was used as a precursor and two types of excimer lamps were used as light sources. The reaction in VUV-CVD is divided into two stages: the reaction in the vapor phase, and the reaction on the surface of the substrate. In this work, we analyzed the latter stage. As a result of analyzing the spectra obtained, it was found that the main reaction for the formation of the SiO2 film was in the latter stage, in which the dissociation of Si–O bonds in Si–O–CH2 in the adsorbed fragments was preceded by the photo-dissociation of C2H5.

Power dependence of defect formation in SiO2 glass by F2 laser irradiation

The dependence of defect formation in a high-purity synthetic SiO2 glass on F2 laser power was studied. Above the threshold value of ∼10 mJ cm−2 pulse−1 (∼0.5 MW cm−2), the concentration of the laser-induced E′ center created by the dissociation of Si–O–Si bond increased as a function of the F2 laser power squared. The quantum yield of the E′ center formed by the high-power F2 laser irradiation was ∼3 orders of magnitude larger than that formed via two-photon absorption processes of KrF or ArF laser pulses. This strongly suggests that irradiating with the high-power F2 laser creates the E′ center via two-step absorption processes.

Mechanisms of Electrical Stress-Induced Degradation in H2/Plasma Hydrogenated n- and p-Channel Polysilicon Thin Film Transistors

The degradation characteristics under various bias stress conditions are systematically investigated in hydrogenated n- and p-channel polysilicon thin film transistors (poly-Si TFTs) with a sidewall spacer. The device characteristics after a relatively long stress in the p-channel TFTs exhibit more serious degradation than those in the n-channel TFTs. Moreover, the stress time dependence of the threshold voltage shift in the former devices shows more complicated behavior than that in the latter. These serious and complicated time-dependent degradation characteristics (induced only in p-channel devices) can be explained by the generation of two defect states in which hydrogen plays an important role: one is positively charged traps that correspond to Si+ atoms generated by the injection of H+ ions into the gate oxide near the source and appear after a certain stress time. The other is deep traps that correspond to dangling bonds generated by the dissociation of Si–H bonds at/near the interface near the source and appear after a long stress time.

CO2Laser Photochemical Hole Burning in the IR Reflection Spectra of Crystalline Natural Silicates

Structural and chemical transformations induced on the surface of crystalline natural silicates by pulse СО2laser radiation with a pulse length of 200 ns and an energy per pulse of 2 J were examined. The IR reflection spectra of nepheline KNa3[AlSiO4]4and rhodonite CaMn4[Si5O15] were measured before and after exposure to laser radiation. An increase in the reflectance at the laser frequency used was observed, which was named “hole burning” in the IR reflection spectra of specimens. A 50-cm–1wide hole was shown to be burnt at a frequency coinciding with that of a laser radiation line within this width. At the incident laser frequency, a narrow, 5-cm–1wide hole is also burnt in the IR spectra of the irradiated samples. The burning of the 50-cm–1hole was assumed to be due to the selective sublimation of SimOncomplexes. The burning of the narrow hole of 5 cm–1width is associated with the laser-induced selective dissociation of Si–O bonds in the near-surface layer at the frequency employed.

Hydrogen in silicon: Fundamental properties and consequences for devices

The interactions between hydrogen and silicon are investigated based on first-principles calculations. After a comprehensive overview of various configurations attention is focused on the energetics and dissociation of Si–H bonds. An examination of the dissociation mechanism of Si–H bonds suggests an explanation for the observed difference in stability between hydrogen and deuterium at dangling bonds. Connections between the phenomena at surfaces, interfaces, and in amorphous materials will be pointed out.

Structural Changes of Sol–Gel‐Derived TiO2–SiO2 Coatings in an Environment of High Temperature and High Humidity

Structural changes in sol–gel‐derived TiO2–SiO2 coatings were found to proceed in an environment of high temperature and high humidity as follows: (1) dissociation of Si–O–Ti bonds in the coating by the attack of water vapor, (2) formation of Ti–O–Ti bonds, and (3) nucleation and growth of anatase TiO2. The coating obtained with the addition of poly(ethylene glycol), PEG, reacts with water vapor more easily than the coating obtained without PEG, since the former is more porous than the latter due to the decomposition of PEG during heat treatment.