A theoretical examination of the chemisorption of benzene on Si(100)−(2 × 1)

A theoretical examination of the structure of the adsorbed state of benzene on the Si(100)-(2 × 1) surface is discussed. A number of potential candidate structures are examined. The local minimum in the total energy for each structure has been calculated with respect to variations in the atomic coordinates for the adsorbed benzene structure and the first four layers of the substrate. The preferred structure is the one with the lowest value for the total energy. This structure, in agreement with the experimental observations, describes a topology for the adsorbed benzene with no Si-H bonds and all the C-H bonds remaining intact. The benzene ring is oriented at an angle of 24° from the surface plane. Four of the carbon atoms are bonded to the silicon surface. Two silicon atoms are each bonded to two carbon atoms.     

Density functional theory study of the near edge X-ray absorption fine structure and infrared spectroscopy of acetylene and benzene on group IV semiconductor surfaces

The near edge X-ray absorption fine structure and infrared spectroscopy of acetylene and benzene adsorbed on C(1 0 0)-2 × 1, Si(1 0 0)-2 × 1 and Ge(1 0 0)-2 × 1 surfaces is studied with density functional theory calculations. Time dependent density functional theory calculations of the near edge X-ray absorption fine structure with a modified exchange-correlation functional agree well with experiment, and show that the spectral features arise from excitation to π^∗, and orbitals, where X represents C, Si or Ge. The excitation energies are dependent on the surface, and for acetylene, the location of the π^∗ band also varies with the surface. Calculations of the vibrational modes show the CH stretching frequencies for carbon atoms bonded directly to the surface vary significantly between the three surfaces, while those for carbon atoms not bonded to the surface do not change significantly.     

Effects of subsurface Na,H and C on the bonding of carbon to nickel surfaces

This paper reports the results of a theoretical study of Na, H and C subsurface atomic species in nickel and demonstrates how these interstitial atoms influence the reactivity of the Ni(111) surface and the structure of carbon species adsorbed on the surface. The benzene molecule, C₆H₆, in planar and nonplanar geometries, is used to probe bonding at the surface. Adsorption energies are calculated by ab initio configuration interaction techniques modelling the surface as an embedded cluster. Adsorption energies of planar C₆H₆ at the most stable, three-fold, adsorption site are 18 kcal/mol for the Ni(111) surface, and 10, 19 and 44 kcal/mol in the presence of the Na, H and C interstitials, respectively. The energies required for the planar to puckered distortion are 99 kcal/mol on Ni(111), 69 kcal/mol with the Na interstitial, 83 kcal/mol with H, and 134 kcal/mol with C compared to 198 kcal/mol for distortion of C₆H₆ in the gas phase. The possible relevance of these results to the nucleation of diamond on nickel are discussed. The results indicate that subsurface Na stabilizes tetrahedrally bonded carbon subunits of the diamond structure while subsurface C may make it easier for the overlayer to revert to a planar graphite structure.     

Molecular dynamics simulation of CH3 interaction with Si(1 0 0) surface

Molecular dynamics simulations of the CH₃ interaction with Si(1 0 0) were performed using the Tersoff-Brenner potential. The H/C ratio obtained from the simulations is in agreement with available experimental data. The results show that H atoms preferentially react with Si. SiH is the dominant form of SiH_x generated. The amount of hydrogen that reacts with silicon is essentially energy-independent. H atoms do not react with adsorbed carbon atoms. The presence of C-H bonds on the surface is due to molecular adsorption.     

入射能量对H2+与SiC表面相互作用影响的分子动力学模拟

用分子动力学方法研究了入射能量对 H2+与 SiC 样品表面相互作用的影响.模拟结果表明,在 H2+轰击 SiC 样品表面的初始阶段,样品中 H 原子的滞留量增加较快,其后,增加的速率减慢,并逐渐趋于饱和.入射能量越大,样品中 H 原子的滞留量也就越大.样品在 H2+的轰击下,样品 Si、C 原子会发生刻蚀.入射能量越...     

Diamond-like C2H nanolayer, diamane: Simulation of the structure and properties

We consider a new C₂H nanostructure based on bilayer graphene transformed under the covalent bond of hydrogen atoms adsorbed on its external surface, as well as compounds of carbon atoms located opposite each other in neighboring layers. They constitute a “film” of the 〈111〉 diamond with a thickness of less than 1 nm, which is called diamane. The energy characteristics and electron spectra of diamane, graphene, and diamond are calculated using the density functional theory and are compared with each other. The effective Young’s moduli and destruction thresholds of diamane and graphene membranes are determined by the molecular dynamics method. It is shown that C₂H diamane is more stable than CH graphane, its dielectric “gap” is narrower than the band gap of bulk diamond (by 0.8 eV) and graphane (by 0.3 eV), and is harder and more brittle than the latter.     

Quasiparticle effects on tunneling currents: a study of C2H4 adsorbed on the Si(001)- (2 x 1) surface

We present a first-principles calculation of the quasiparticle electronic structure of ethylene adsorbed on the dimer reconstructed Si(001)-(2x1) surface. Within the GW approximation, the self-energy corrections for the adsorbate states are found to be about 1.5 eV larger than those for the states derived from bulk silicon. The calculated quasiparticle band structure is in excellent agreement with photoemission spectra. Finally, the effects of the quasiparticle corrections on the scanning tunneling microscope images of the adsorbed molecules are shown to be important as the lowering of the C2H4 energy levels within GW strongly reduces their tunneling probability.     

Hydrogen-induced surface metallization of beta-SiC(100)-(3x2) revisited by density functional theory calculations

Recent experiments on the silicon terminated (3 x 2)-SiC(100) surface indicated an unexpected metallic character upon hydrogen adsorption. This effect was attributed to the bonding of hydrogen to a row of Si atoms and to the stabilization of a neighboring dangling bond row. Here, on the basis of density-functional calculations, we show that multiple-layer adsorption of H at the reconstructed surface is compatible with a different geometry: in addition to saturating the topmost Si dangling bonds, H atoms are adsorbed at rather unusual sites, i.e., stable bridge positions above third-layer Si dimers. The results thus suggest an alternative interpretation for the electronic structure of the metallic surface.     

The adsorption of acetylene on W(100) at room temperature: An electron spectroscopic study

The adsorption of acetylene on W(100) at room temperature has been studied by AES, ELS, thermal desorption, mass spectrometry, work function and LEED in one vacuum chamber. AES line profile analysis shows that there are at least two adsorption processes occurring at room temperature. Further, it is possible to explain all the AES results by assuming non-sequential adsorption into just two states, denoted by α and β. This picture was substantiated and embellished by comparison with other standard surface techniques. The α-state comprises either a C₂H₂ unit with an activation energy for desorption of $\text{2.3}\text{eV}\text{molecule}\text{(53}\text{kcal mole}{}^{\mathrm{?1}}\text{)}$ or CH units bounded through the carbon of the β-state. Saturation coverage for the α-state is 3 × 10¹⁴ molecules cm^?2. The β-state is dissociative at low acetylene exposures and comparison between a carbon covered surface and the β-state suggest the latter to be dissociative up to saturation. There also appears to be ca. 10¹⁴ hydrogen atoms cm^?2 on W(100) on room temperature acetylene saturation, the carbon content of the β-state being 9 × 10¹⁴ atoms cm^?2. The residual C?C bond from the molecule in the β-state remains unknown. No sign of ordering in the adsorbed species was detected, save the possibility of (1 × 1) in the β-state. Acetylene adsorption at 580 K showed hydrogen from the β-state to block acetylene adsorption by 15% at saturation. A two-site adsorption model for the β-state is proposed to explain the results. The α-state is bonded through the carbon of the β-state and it is speculated that the former adsorbs onto “β” domains where there is a critical minimum size for the latter.     

XPS and RBS investigations of Si–Er–O interactions on a Si(1 0 0)-2x1 surface

The interactions among erbium, oxygen and silicon atoms on a Si(1 0 0)-2x1 reconstructed surface have been studied by means of X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. Erbium and oxygen were deposited at 600 °C on the Si surface and their behavior has been observed after different thermal processes. It was found that at 600 °C, the formation of a stable surface complex Er–O–Si is obtained together with Si oxidation; after an 800 °C annealing, the amount of oxygen bound to Si decreases and the remaining O atoms are mainly bonded to Er. An abrupt change was observed after 900 and 1000 °C annealings, which bury the Er atoms about 60 Å below the substrate surface. Our results give some hints to hypotise the O diffusion towards the Si bulk.     

Initial Processes of Hydrogen Adsorption on Si（100） Surface

The adsorption of one monolayer H atoms on an ideal Si(100) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of adsorption systems of H atoms on different sites are calculated.It is found that the adsorbed H atoms are more favorable on B1 site (bridge site) with a distance 0.056 nm above the Si surface. There does not exist reaction barrier at the Si surface. The layer projected density states are calculated and compared with those of the clean surface. The charge transfers are also investigated.     

Initial Processes of Hydrogen Adsorption on Si(100) Surface

The adsorption of one monolayer H atoms on an ideal Si(100) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of adsorption systems of H atoms on different sites are calculated.It is found that the adsorbed H atoms are more favorable on B1 site (bridge site) with a distance 0.056 nm above the Si surface. There does not exist reaction barrier at the Si surface. The layer projected density states are calculated and compared with those of the clean surface. The charge transfers are also investigated.     

Thermal-hydrogen promoted selective desorption and enhanced mobility of adsorbed radicals in silicon film growth

Car-Parrinello simulations and static density-functional theory calculations reveal how hydrogen promotes growth of epitaxial, ordered Si films in plasma-enhanced chemical vapor deposition at low-temperature conditions where the exposed Si(001)-(2x1) surface is fully hydrogenated. Thermal H atoms, indeed, are shown to selectively etch adsorbed silyl back to the gas phase or to form adsorbed species which can be easily incorporated into the crystal down to T approximately 200 degrees C and start diffusing around T approximately 300 degrees C. Our results are well consistent with earlier experiments.     

Molecular dynamical simulations on a-C:H film growth from atomic flux of C and H: Effect of H fraction

Molecular dynamical simulations are carried out to studying the hydrogenated amorphous carbon (a-C:H) film growth from C and H atoms. The effects of the H fraction in source atoms and incident energy on the film formation are investigated. Our simulations show that almost all the H atoms incorporating into the films bond to carbon and the amount of H₂ molecules is very slight. Increasing the H fraction in source atoms raises the sp³-C fraction, leads to a linear increase of H concentration in film, but decreases the film growth rate. The influence of H fraction on the film growth mechanism is also discussed.     

Low-energy D scattering from Cs and CsCl adsorbed on the Si(100)2 × 1 surface

On the basis of neutralization and inelastic scattering of low-energy D⁺ ions, the bond nature of Cs and CsCl adsorbed on the Si(100)2 × 1 surface has been investigated. In a low-coverage regime ( < 0.2 ML), Cs is adsorbed ionically on Si(100) and subsequent oxygen adsorption readily causes the ionic Cs---O bond. CsCl is dissociatively adsorbed on the surface in a low-coverage regime due to the preferential reaction of Cl with the Si dangling bond and the resultant Cs is ionically bonded to Si.     

2(1H)喹啉酮化合物及其开环衍生物的13C NMR研究

本文报道了16种2(1H)喹啉酮及其开环衍生物的碳谱研究,归属了取代喹啉酮母核骨架及侧链上每个碳原子的化学位移,并就卤素取代对母核骨架碳的化学位移影响规律进行了探讨.文中所有化合物的核磁数据迄今未见文献报道.     

金刚石表面无定形碳氢薄膜生长的分子动力学模拟

利用分子动力学模拟方法研究了CH₂基团轰击金刚石(111)面所形成的无定形碳氢薄膜(a-C:H)的生长过程. 结构分析表明, 得到的无定形碳氢薄膜中碳原子的局域结构(如C–C第一近邻数)与其中氢原子的含量密切相关. CH₂ 基团入射能量的增加会导致得到的薄膜的氢含量降低, 从而改变薄膜中类sp³成键碳原子的比例.     

Fast ortho-para conversion of H2 adsorbed at copper surface step atoms

Ortho-para conversion of H2 adsorbed at the step atoms of a Cu(510) surface proceeds with a short conversion time constant around 1 s as observed in electron-energy-loss measurements of rotational populations. We suggest that this rapid conversion is related to the special character of the adsorption state, which involves a short H2-Cu bond length of 1.8 A. On the flat Cu(100) surface, conversion is found to occur at active sites, most likely step atoms.     

分子动力学模拟H原子与Si的表面相互作用

通过分子动力学模拟了入射能量对H原子与晶Si表面相互作用的影响. 通过模拟数据与实验数据的比较, 得到H原子吸附率随入射量的增加 呈先增加后趋于平衡的趋势. 沉积的H原子在Si表面形成一层氢化非晶硅薄膜, 刻蚀产物(H₂, SiH₂, SiH₃和SiH₄)对H原子吸附率趋于平衡有重要影响, 并且也决定了样品的表面粗糙度. 当入射能量为1 eV时, 样品表面粗糙度最小. 随着入射能量的增加, 氢化非晶硅薄膜中各成分(SiH, SiH₂, SiH₃)的量以及分布均有所变化. 关键词： 分子动力学 吸附率 表面粗糙度 氢化非晶硅薄膜     

H2在Li掺杂Al6Si+上吸附的理论研究

本文利用密度泛函理论的B3LYP/6-31G(d, p)和组态相互作用的QCISD/6-31G(d, p)研究了Al6Si+和Al6SiLi+团簇的几何和电子结构及其对H2分子的吸附,两种不同方法计算的H2分子在团簇上的吸附能非常一致。H2分子在Al6Si+团簇上的吸附能仅为-0.018 eV,Al6Si+团簇中掺杂Li原子可以明显增强其对H2分子的吸附。Al6SiLi+团簇吸附一个H2分子的吸附能可以达到-0.157 eV,吸附五个H2分子的平均吸附能为-0.088 eV。态密度和自然键轨道分析表明,电荷从Li原子向Si原子转移,H2分子在带正电的Li离子产生的电场中发生极化,从而在静电相互作用下吸附在Li原子周围。