金刚石(111)面上乙炔合成金刚石薄膜的成核机理

运用量子力学半经验分子轨道AMl方法计算乙炔作为生长基在金刚石(111)附氢表面上的吸附和成核过程,提出了两种可能的由乙炔合成金刚石薄膜的成核机理,探讨了其生长基作用.     

金刚石附氢(100)面脱氢势垒的量子化学研究

采用MNDO（UHF）方法计算了金刚石（100）－（1×1）：2H双氢化表面和（100）－（2×1）：H单氢化表面的脱氢势垒，论证了决定金刚石附氢表面脱氢势垒大小的主要因素是气相－表面吸附氢原子间的相互排斥大小，得出（100）面两种表面结构脱氢势垒的理论预言值分别为71和59kJ·mol-1，均大于（111）面脱氢势垒的理论预言值42kJ·mol-1．揭示了在同等生长条件下金刚石（111）面可供成核和生长的反应基多于（100）面，与实验上得到的同等生长条件下（111）面的相对生长率大于（100）面的结论是一致的。     

金刚石(111)氢化表面脱氢势垒的量子化学研究

采用MNDO(UHF)方法,计算金刚石(111)面的脱氢势垒。在与气相有机分子脱氢活化能实验值系统比较的基础上,在一组尺度不同的金刚石表面团簇模型上进行了计算,结果收敛于42±4kJ/mol.并与MNDO(RHF)和AM1(UHF、RHF)方法给出的相应结果进行了比较。     

金刚石晶形显露的化学控制

采用热丝化学气相沉积法（HPCV），研究了N2、O2对金刚石晶形显露的影响。发现微量的氮气的加入（[N2]／[CH4]＜1％）有利于金刚石（100）晶面的显露，且不会降低金刚石晶形的完整性；微量氧的加入有利于金刚石（111）面显露．采用氧辅助控制金刚石膜（111）织构生长，可以使X射线（111）峰摇摆曲线的半宽降到6．2°．氮或氧的加入扩大了织构生长金刚石（100）或（111）膜的基片温度范围．     

金刚石（111）清洁／附氢表面与甲基的相互作用

利用Ａｍｌ分子轨道法计算了金刚石（１１１）清洁／附氢表面与甲基相互作用的特殊势能曲线，深入研究了清洁、附氢表面与甲基相互作用下基底弛豫重建、四甲基构型及成键能的差别，进而得到附氢表面较清洁表面更适合于甲基吸附，是更好的金刚石薄膜生长址的结论。在距基底表面０．５ｎｍ内，甲基与清洁、附氢表面皆有强烈的相互作用。     

金刚石(111)面上乙炔生长金刚石薄膜的机理

运用量子力学半经验分子轨道ＡＭ１方法，计算乙炔作为生长基在金刚石（１１１）附氢表面上存在核结构时的外延生长过程，结果表明，乙炔是金刚石（１１１）表面外延生长的有效生长基之一。     

毫秒脉冲激光合成超细纳米金刚石

通过热力学和动力学的基本理论, 分析了毫秒脉冲激光照射石墨悬浮液合成超细纳米金刚石的机理. 在毫秒脉冲激光与石墨颗粒相互作用形成的碳蒸气羽中, 通过碳蒸气凝聚形成了金刚石核. 与纳秒脉冲激光相比, 毫秒脉冲激光具有较低的功率密度和较长的脉宽, 为金刚石核的生长提供了较小的过冷度, 使得金刚石核的生长速率减小; 而较小的生长速率也为金刚石表面形成sp2杂化结构提供了机会, 它可以有效降低金刚石核的表面能, 促使金刚石核稳定, 但表面的sp2杂化也阻止了金刚石核的外延. 以上两个原因决定了毫秒激光辐照石墨颗粒过程中只能获得超细的纳米金刚石.     

碳纳米管向金刚石纳米晶粒的转变

在碳60（C60）[1]和碳纳米管(CNTs)[2]发现之前,人们知道碳通常显示石墨和金刚石两种晶体结构.自从C60和碳纳米管发现后,由于其独特的纳米结构而具有广泛的应用前景,国内外许多学者致力于研究它们的物理和化学特性,而C60、巴基葱（多层碳纳米球）、碳纳米管和金刚石之间的转变是所研究的焦点之一.目前,由碳的其他形式向金刚石转变的主要方法有：Meilunas等人[3]以C60和C70薄膜为基底气相生长多晶金刚石,C60和C70的稳定性和微平面结构在外界条件下,有利于金刚石成核和外延生长;Banhart[4]小组研究了在电子束辐射作用下巴基葱转变…     

Cl/Ag体系研究 Ⅱ.Cl吸附引起的表面结构变化

运用LEED,UPS和HREELS等表面技术研究了氯吸附至(c)阶段的Ag(111)表面结构.结果表明,表面上有三维的AgCl(111)生成,其生长按修正的Stranski-Krastanov模式进行.伴随着AgCI(111)生长的同时,表面上产生缺陷.这种缺陷只有在氯吸附至(c)阶段时表面上形成三维AgCI的过程中才能产生,它一旦在表面上形成后,表面上氯的存在与否对其不产生影响.本文提出了一个(c)阶段时的Cl/Ag(111)体系的结构模型.     

酪氨酸酶在硼掺杂金刚石薄膜电极上的固定及酚类化合物的检测

以硼掺杂金刚石(boron-doped d iamond,BDD)薄膜作基底,利用光化学反应将含有碳碳双键的烯丙胺化合物修饰在BDD表面,形成氨基单分子层,再经过酰胺键的连接使酪氨酸酶固定在氨基化的金刚石表面,从而制得酪氨酸酶修饰的电极.应用循环伏安法研究该电极用于酚类化合物(包括苯酚、对甲基苯酚和对苯二酚等)检测的灵敏度、线性范围及其稳定性.     

甲烷在清洁 Pd(111) 及氧改性的 Pd(111) 表面解离的密度泛函理论研究

 采用广义梯度近似 (GGA) 的密度泛函理论 (DFT) 并结合平板模型, 研究了 CH4 在清洁 Pd(111) 及 O 改性的 Pd(111) 表面发生 C朒 键断裂的反应历程. 优化了裂解过程中反应物、过渡态和产物的几何构型, 获得了反应路径上各物种的吸附能及反应的活化能. 结果表明, CH4 采用一个 H 原子指向表面的构型在 Pd(111) 表面的顶位吸附, CH3 的最稳定的吸附位置为顶位, OH, O 和 H 的最稳定吸附位置均为面心立方. CH4 在清洁 Pd(111) 表面裂解的活化能为 0.97 eV, 低于它在 O 原子改性 (O 没有参与反应) 的 Pd(111) 表面的活化能 1.42 eV, 说明表面氧原子抑制了 CH4 中 C朒 键的断裂. 当亚表面 O 原子和表面 O 原子 (O 参与反应) 共同存在时, C朒 键断裂的活化能为 0.72 eV, 低于只有表层氧存在时的活化能 (1.43 eV), 说明亚表面的 O 原子对 CH4 分子的活化具有促进作用. CH4 在 O 原子改性的 Pd(111) 表面裂解生成 CH3 和 H, 以及生成 CH3 和 OH 的反应活化能分别为 1.42 和 1.43 eV, 说明 CH4 在 O 原子改性的 Pd(111) 表面发生这两种反应的难易程度相当.     

Dissociation of CH3I on the Al111 surface--an STM and density functional theory study

The reaction of methyl iodide with the Al(111) surface was studied by room-temperature scanning tunneling microscopy (STM) and by first principles calculations. It was found that at 300 K methyl iodide decomposes on the Al(111) surface, forming methyl (CH(3)), methylidyne (CH), and adsorbed iodine. Methyl groups are observed to occupy atop sites by STM. The occupation of the hollow site by methylidyne was observed in STM measurements. Total energy density functional theory calculations have shown that methyl species occupy atop Al sites (E(A) = 45.3 kcal/mol), methylidyne species adsorb on fcc hollow sites (E(A) = 155.0 kcal/mol), while individual iodine atoms can bind on both on-top or hollow sites with adsorption energies between 54 and 56 kcal/mol.     

Effect of coadsorbed dopants on diamond initial growth processes: CH3 adsorption

An investigation based on an ultrasoft pseudopotential density functional theory (DFT) method, using the generalized gradient approximation (GGA) under periodic boundary conditions, has been performed in order to investigate how the presence of a neighboring dopant is affecting the CH 3 adsorption reaction (regarded to be an initial growth process). For this study, both the (100) and (111) diamond surface orientations have been considered, and various dopants in two different hydrogenated forms AH X (A = N, B, S, P, or C; X = 0 or 1 for S, X = 1 or 2 for N, B, and P, and X = 2 or 3 for C) were especially scrutinized. For most of the cases studied, the presence of a coadsorbed dopant was found to disfavor CH 3 adsorption with an efficiency that depends on the surface orientation as well as dopant type and position. The NH 2, PH 2, and SH species have the strongest effect in counteracting the CH 3 adsorption to the diamond (111) surface. This is also the situation with the dopants adsorbed on either of two specific surface sites (out of three positions studied) on the diamond (100)-2 x 1 surface. The main reasons for these observations are induced steric hindrances between the two coadsorbates. The BH 2 species, adsorbed to the third type of surface site on diamond (100), has been found to affect the adsorption reaction by formation of a C surf-B bond prior to CH 3 adsorption. The dopants in their radical forms are generally shown to always strongly disfavor the CH 3 adsorption reaction by formation of a C surf-X bond prior to adsorption. However, the NH radical will only form this new bond with the radical surface C site when it is adsorbed to position 3 on the surface.     

Infrared spectroscopic investigation of the reaction of hydrogen-terminated, (111)-oriented, silicon surfaces with liquid methanol

Fourier transform infrared spectroscopy and first principles calculations have been used to investigate the reaction of atomically smooth, hydrogen-terminated Si(111) (H-Si) surfaces with anhydrous liquid methanol. After 10 min of reaction at room temperature, a sharp absorbance feature was apparent at approximately 1080 cm(-1) that was polarized normal to the surface plane. Previous reports have identified this mode as a Si-O-C stretch; however, the first principles calculations, presented in this work, indicate that this mode is a combination of an O-C stretch with a CH3 rock. At longer reaction times, the intensity of the Si-H stretching mode decreased, while peaks attributable to the O-C coupled stretch and the CH3 stretching modes, respectively, increased in intensity. Spectra of H-Si(111) surfaces that had reacted with CD3OD showed the appearance of Si-D signals polarized normal to the surface as well as the appearance of vibrations indicative of Si-OCD3 surface species. The data are consistent with two surface reactions occurring in parallel, involving (a) chemical attack of hydrogen-terminated Si(111) terraces by CH3OH, forming Si-OCH3 moieties having their Si-O bond oriented normal to the Si(111) surface and (b) transfer of the acidic hydrogen of the methanol to the silicon surface, either through a direct H-to-D exchange mechanism or through a mechanism involving chemical step-flow etching of Si-H step sites.     

氢终止金刚石表面的形成机理

为考察金刚石形成氢终止表面的反应机制,采用微波氢等离子体处理以及电阻丝氢气气氛加热处理进行对比研究.利用光发射谱(OES)和漫反射傅里叶变换红外光谱(DRIFTS)分别表征了微波氢等离子体中的活性基团和金刚石表面氢终止浓度.结果表明,微波氢等离子体环境下,随着衬底温度、等离子体密度和能量的增加,温度至700 ℃ (800 W/3 kPa)时,等离子体中出现了明显的CH基团;相应地,金刚石表面氢终止浓度随温度、等离子体密度和能量的增加而增加.采用氢气气氛下电阻丝加热的方法同样形成了氢终止金刚石表面,表明微波等离子体处理金刚石表面形成氢终止主要源于由温度控制的表面化学反应,而非等离子体的物理刻蚀作用.氧终止金刚石表面形成氢终止的机制是表面C=O键在高于500 ℃时分解为CO,相应的悬挂键由氢原子或氢分子占据.