Theoretical study of the reaction of acrylonitrile on Si(001)

Two recent experiments for adsorbed acrylonitrile on the Si(001) surface reported different adsorption structures at 110 and 300 K. We investigate the reaction of acrylonitrile on Si(001) by first-principles density-functional calculations. We find that the so-called [4+2] structure in which acrylonitrile resides between two dimer rows is not only thermodynamically favored over other structural models but also easily formed via a precursor where the N atom of acrylonitrile is attached to the down atom of the Si dimer. The additional initial-state theory calculation for the C 1s core levels of adsorbed acrylonitrile provides an interpretation for the observed low- and room-temperature adsorption configurations in terms of the precursor and [4+2] structures, respectively.     

Theoretical Studies on the Si（001）-SiO2 Interface Structure

1 INTRODUCTION Silicon and its alloy have been widely applied in such fields as electronic industry, high-temperature structural ceramics, etc. In addition, the researches on silicon and its relevant materials greatly promote the rapid development of modern optics and infor- mation technology. Therefore, more and more at- tention is focused on the structure of silicon, oxide of silicon and the interfaces between silicon and metal or nonmetal. As an ideal passive film on the Si surface, S…     

Theoretical prediction of heterogeneous molecular wires on the Si(001) surface

Using first-principles density-functional calculations, we propose a self-assembly technique for fabrication of the heterogeneous molecular wire on the dangling-bond wire generated on a H-passivated Si(001) surface. Here, we choose pyridine and borine as Lewis base and acid molecules, respectively, to demonstrate different behaviors in the chemical reactivity and selectivity on the dangling-bond wire, leading to formation of the heterogeneous pyridine-borine wire.     

A new Si tetramer structure on Si (001)

Interactions between Si ad-dimers on Si (001) have been studied by molecular dynamics simulations using the Stillinger–Weber potential. The interactions determine the formation of clusters from diffusing dimers. We show different pathways for the formation of multiple-dimer clusters and propose a new tetramer (T_CC) structure formation by two diffusing dimers interacting. This tetramer structure has been found to be energetically stable with respect to isolated ad-dimers. Moreover, their local bonding configuration is very similar to the B-type step edge which is known to be the favoured adsorption site for epitaxial growth. The proposed tetramer may play a crucial role as the nucleus of the new epitaxial layer on Si (001).     

Different adsorption structures of pyridine on Si(001) and Ge(001) surfaces

The adsorption and reaction of pyridine on the Si(001) and Ge(001) surfaces are investigated by first-principles density-functional calculations within the generalized gradient approximation. On both surfaces the N atom of pyridine initially reacts with the down atom of the dimer, forming a single bond between the N atom and the down atom. On Ge(001) such an adsorption configuration is most favorable, but on Si(001) a further reaction with a neighboring dimer occurs, resulting in formation of a bridge-type configuration. Especially we find that on Ge(001) the bridge-type configuration is less stable than the gas phase. Our results provide an explanation for a subtle difference in the adsorption structures of pyridine on Si(001) and Ge(001), which was observed from recent scanning tunneling microscopy experiments.     

Adsorption dynamics of ethylene on Si(001)

The dynamics of ethylene adsorption on the Si(001) surface was investigated by means of molecular beam techniques. A constant decrease of initial sticking probability s(0) was observed with increasing kinetic energy indicating a non-activated adsorption channel. With increasing surface temperature, s(0) decreases as well, pointing towards adsorption via a precursor state. Quantitative evaluation of the temperature dependence of s(0) via the Kisliuk model was possible for surface temperatures above 250 K; below that value, the temperature dependence is dominated by the adsorption dynamics into the precursor state. Maximum surface coverage was found to be reduced with increasing surface temperature, which is discussed on the basis of a long lifetime of the precursor state at low temperatures.     

Structure and binding energies of unsaturated hydrocarbons on Si(001) and Ge(001)

The adsorption of acetylene, ethylene, and benzene on the Si(001) and Ge(001) surfaces is investigated by first-principles density-functional calculations within the generalized-gradient approximation. We find that the adsorption energies of the three hydrocarbons containing a triple bond, a double bond, and a pi-conjugated aromatic ring decrease as the sequence of C2H2>C2H4>C6H6. We also find that the bondings of acetylene, ethylene, and benzene to Ge(001) are much weaker than those to Si(001). As a result, benzene is weakly bound to Ge(001) while it is chemisorbed on Si(001), consistent with temperature-programmed desorption data.     

Molecular beam investigation of hydrogen dissociation on Si(001) and Si(111) surfaces

The influence of molecular vibrations on the reaction dynamics of H2 on Si(001) as well as isotopic effects have been investigated by means of optical second-harmonic generation and molecular beam techniques. Enhanced dissociation of vibrationally excited H2 on Si(001)2 x 1 has been found corresponding to a reduction of the mean adsorption barrier to 390 meV and 180 meV for nu=1 and nu=2, respectively. The adsorption dynamics of the isotopes H2 and D2 show only small differences in the accessible range of beam energies between 50 meV and 350 meV. They are traced back to different degrees of vibrational excitation and do not point to an important influence of quantum tunneling in crossing the adsorption barrier. The sticking probability of H2 on the 7 x 7-reconstructed Si(111) surface was found to be activated both by H2 kinetic energy and surface temperature in a qualitatively similar fashion as H2/Si(001)2 x 1. Quantitatively, the overall sticking probabilities of H2 on the Si(111) surface are about one order of magnitude lower than on Si(001), the influence of surface temperature is generally stronger.     

Theoretical modeling of oxygen adsorption on the PbTe(001) surface

For the semiconducting compound PbTe, the initial stages of oxidation, which are important for technology of IR-and thermoelectric devices, have been theoretically studied. The structure, stability, and changes in the electrostatic potentials at the oxidized sites in lead telluride have been calculated in the framework of the cluster approach by the hybrid density functional theory B3LYP method. Different variants of attachment of one to six oxygen atoms to the atoms of the surface and subsurface layers have been considered. The most stable oxidation products have been found. The calculation results are quantitatively consistent with experimental XPS data on chemical shifts.     

Structural analysis of the reconstructed Si(001)-C surface

The atomic structure of reconstructed Si(001)c(4 x 4)-C surface has been studied by coaxial impact collision ion scattering spectroscopy. When the 100L of ethylene (C(2)H(4)) molecules have been exposed on Si(001)-(2 x 1) surface at 700 degrees C, it is found that C atoms cause the ordering of missing Si dimer defects and occupy the fourth layer of Si(001) directly below the bridge site. Our results provide the support for the previous model in which a missing dimer structure is accompanied by C incorporation into the subsurface.     

Peierls instability in one-dimensional borine wire on Si(001)

We present a theoretical study of the Peierls instability in the 1D borine wire formed on the Si(001) surface. Our first-principles density-functional theory calculations show that this molecular wire is stabilized by formation of a 1D-CDW, accompanying a structural distortion with a double periodicity and a band-gap opening at the Fermi level. Such a 1D molecular wire on the 2D substrate provides a surface CDW system to allow a real-space observation of CDWs, their fluctuations or critical behaviors at atomic scale.     

2,2＇－二磺酸基联苯氨的合成

间硝基苯磺酸盐;;葡萄糖;甲醛;2;2＇－二磺酸基联苯氨的合成     

Self-directed growth of benzonitrile line on H-terminated Si(001) surface

Using first-principles density-functional calculations we predict a self-directed growth of benzonitrile molecular line on a H-terminated Si(001) surface. The C[triple bond]N bond of benzonitrile reacts with a single Si dangling bond which can be generated by the removal of a H atom, forming one Si-N bond and one C radical. Subsequently, the produced C radical can be stabilized by abstracting a H atom from a neighboring Si dimer, creating another H-empty site. This H-abstraction process whose activation barrier is 0.65 eV sets off a chain reaction to grow one-dimensional benzonitrile line along the Si dimer row. Our calculated energy profile for formation of the benzonitrile line shows its relatively easier formation compared with previously reported styrene and vinylferrocene lines.     

Effects of adsorbed bismuth on Si(001) surface electronic states

It is shown that depositing Bi on an Si(001) surface fills the free broken-bond surface states, whose concentration decreases linearly as the bismuth coating 8 increases up to _st, = 0.6 monolayer. The bismuth desorption activation energy is constant < _st, (E_d = 2.77 ± 0.1 eV) and decreases for > _st.Taras Shevachenko Kiev National University, ul. Vladimirskaya 64, 252601 Kiev-17, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 168–171, May–June, 1996. Original article submitted September 19, 1995.     

Structural determination of the low-coverage phase of Al on Si(001) surface

The atomic structure of Al layer on Si(001)-(2 x 1) surface has been studied by coaxial impact collision ion scattering spectroscopy. When 0.5 monolayer (ML) of Al atoms are adsorbed on Si(001) at room temperature, it is found that Al adatoms are dimerized and Al ad-dimers are oriented parallel to the underlying Si dimers at the position of centering T3 site with a height of 1.02 Angstroms from the first layer of Si(001). The bond length of the Al dimer is 2.67 Angstroms. With increasing Al coverage up to one ML, Al ad-dimers still occupied near T3 site and the next favorable site is near HH site.     

Formation of GeO2 under Graphene on Ge(001)/Si(001) Substrates Using Water Vapor

The problem of graphene protection of Ge surfaces against oxidation is investigated. Raman, X-Ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements of graphene epitaxially grown on Ge(001)/Si(001) substrates are presented. It is shown that the penetration of water vapor through graphene defects on Gr/Ge(001)/Si(001) samples leads to the oxidation of germanium, forming GeO₂. The presence of trigonal GeO₂ under graphene was identified by Raman and XRD measurements. The oxidation of Ge leads to the formation of blisters under the graphene layer. It is suggested that oxidation of Ge is connected with the dissociation of water molecules and penetration of OH molecules or O to the Ge surface. It has also been found that the formation of blisters of GeO₂ leads to a dramatic increase in the intensity of the graphene Raman spectrum. The increase in the Raman signal intensity is most likely due to the screening of graphene by GeO₂ from the Ge(001) surface.     

Molecular dynamics simulations of hydration shell on montmorillonite (001) in water

Molecular dynamics simulations (MDS) of montmorillonite (001)/water interface system were used for studying the hydration shell on the montmorillonite surface in this work. The study was performed on the simulation of concentration profile and self‐diffusion coefficients. The results have shown that there was a hydration shell on the surface with the thickness of approximately 1.74 nm, which was composed of six ordered water molecule layers, including ordered layers and transition layers. The water molecules in the shell were closely and orderly arranged than those in bulk water, leading to a higher concentration of water molecules. Copyright © 2016 John Wiley & Sons, Ltd.     

Ultra-clean Si(111) and Si(001) Surfaces Prepared by Advanced Wet Chemical Cleaning

Wet chemical cleaning of silicon is a critical step, e.g., pre-gate clean, in the semiconductor manufacturing^[1]. For example, pre-gate oxide cleaning demands ultra-clean silicon surface with least surface roughness. It is well known that metallic infinities and roughness cause the lower breakdown voltage in gate dielectric^[2]. It has stringent requirements for ultra-clean and atomically flat silicon surface as the thickness of gate oxide is decreasing. In the present work, we have extended our study on Si(100) surface13] and extensively investigated wet chemical cleaning of Si(111) and Si(100) surfaces in NH₄F-based solutions by using scanning tunneling microscopy (STM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and total reflection X-ray fluorescence spectrometry (TXRF). Surface roughness, organic contamination, metallic impurities and surface termination on the silicon surfaces after wet chemical cleaning with various NH₄F-based solutions have been determined and compared with those treated with RCA cleans, HF solutions and other industrially used solutions. Our results indicate that ultra-clean and smooth Si(111) and Si(001) surfaces are obtained by treatment with NH4F-based solutions.