密度泛函理论方法研究6H-SiC(0001)表面对氧分子和水分子的吸附

本文通过密度泛函方法计算6H-SiC(0001)表面对氧分子和水分子的吸附. 在6H-SiC(0001)表面上吸附的O₂分子自发地解离成O^*,并被吸收在C与Si原子之间的空位上. 吸附的H₂O自发地分解成OH^*和H^*,它们都被吸附在Si原子的顶部,OH^*进一步可逆地转化为O^*和H^*. H^*可以使Si悬键饱和并改变O^*的吸附类型,并进一步稳定6H-SiC(0001)表面并防止其转变为SiO₂.     

Ru(0001)表面氮分子和钡原子的相互作用

本文采用密度泛函理论方法研究了Ru(0001)表面氮分子和钡原子的相互作用.计算结果表明,钡原子的作用弱化了氮分子键.氮分子键长从Ru(001)-N2表面的0.113 nm伸长互Ru(001)-N2/Ba表面的0.120 nm;分子的拉伸振动频率从2221 cm-1减小到1746 cm-1;氮分子得到的电荷数从清洁表面的0.3e增加到1.1 e.电荷从钡原子6s轨道向钌原子4d轨道转移,转移电荷增强了氮分子2π空轨道和钌原子4d轨道间的杂化作用,导致5σ分子轨道和dπ杂化轨道发生极化.轨道极化使分子电偶极矩增加了约-0.136 e(A).金属钡在Ru(0001)表面氮分子活化过程中具备电子型助催剂的特征.     

Ru(0001)表面氮分子和钡原子的相互作用

本文采用密度泛函理论方法研究了Ru(0001)表面氮分子和钡原子的相互作用。计算结果表明,钡原子的作用弱化了氮分子键。氮分子键长从Ru(001)-N2表面的0.113 nm伸长至Ru(001)-N2/Ba表面的0.120 nm;分子的拉伸振动频率从2221 cm-1减小到1746 cm-1;氮分子得到的电荷数从清洁表面的0.3 e增加到1.1 e。电荷从钡原子6s轨道向钌原子4d轨道转移,转移电荷增强了氮分子 空轨道和钌原子4d轨道间的杂化作用,导致 分子轨道和 杂化轨道发生极化。轨道极化使分子电偶极矩增加了约-0.136 eÅ。金属钡在Ru(0001)表面氮分子活化过程中具备电子型助催剂的特征。     

BaxOy小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质

为了说明钡助剂的存在形式, 本文采用第一性原理方法研究了Ba_xO_y小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质. 基于总能的热力学分析发现, 在实验条件下(500 K, P_H2O/P_H2<10^-3), Ba₂O团簇比BaO₂, BaO, Ba和O等团簇(原子)更加稳定. 这证实含有金属性钡原子的团簇也是氧化钡助剂可能的工作状态. 表面电荷差分密度说明Ba₂O团簇的氧和钡原子与衬底的作用不同. 不过Ba₂O团簇氧和钡原子附近的氮分子吸附行为相似, Ba₂O团簇增强了氮分子和衬底的相互作用. Ba₂O团簇氧和钡原子附近的氮分子吸附能分别为0.78 和0.88 eV, 均大于清洁表面的0.67 eV. 氮分子间距和氮分子的拉伸振动频率都表明Ba₂O团簇在一定程度上活化了吸附氮分子. Ba₂O团簇氧和钡原子附近的N–N键长分别为0.117和0.116 nm, 大于清洁表面的0.114 nm. 氧和钡原子附近氮分子的拉伸振动频率分别为 1888 和1985 cm^-1, 小于清洁表面的2193 cm^-1. 电荷差分密度的计算结果说明, 削弱作用主要来自于Ba₂O团簇中钡离子和氮分子间的静电作用. 两者间的静电作用增加了氮分子π 反键轨道的占据数, 促进了氮分子极化, 从而削弱氮分子键.     

Ag(100)表面氧吸附的密度泛函理论和STM图像研究

用密度泛函理论研究了氧原子的吸附对于Ag(100)表面结构和电子态的影响.通过PAW总能计算研究了p(1×1)、c(2×2)和(2^1/2×22^1/2)R45°等几种原子氧覆盖度下的吸附结构，以及在上述结构下Ag(100)表面的弛豫特性、吸附能量、功函数等一系列物理量.研究表明：在(2^1/2×22^1/2)R45°-2O吸附Ag(100)表面的情况下，每格两列就会缺失     

C2H4在清洁和有Cs覆盖的Ru(0001)表面吸附的TDS研究

用热脱附谱(TDS)方法研究了乙烯(C₂H₄)在Ru(0001)表面上的吸附.在低温下(200K以下)乙烯可以在清洁及有Cs的Ru(0001)表面上以分子状态稳定吸附,在衬底温度升高至200K以上时,乙烯发生了脱氢分解反应,乙烯分解后的主要产物为乙炔(C₂H₂).在清洁的Ru(0001)表面,乙烯有两种吸附状态,脱附温度分别为275K和360K.而乙炔的脱附温度为350K.在Ru(0001)表面有Cs的存在时,乙烯分解 关键词： 乙烯 钌(0001)表面 铯钌(0001)表面乙烯 钌(0001)表面 铯钌(0001)表面     

温度对GaN(0001)表面生长吸附SrO、BaO和TiO_2影响的理论研究

采用基于第一性原理的从头计算分子动力学方法,模拟了300、400、500、600和700℃下SrO、BaO和TiO_2分子在GaN(0001)表面吸附的动力学过程,研究了温度对原子运动轨迹、吸附能、界面电荷分布、稳定吸附方位和扩散系数的影响.温度不同,O-Ga成键时间不同,SrO分子中的O原子与GaN基底成键的Ga原子不同; TiO_2分子中O原子与GaN表面Ga原子成键的顺序也不同.温度对SrO、BaO和TiO_2分子在GaN(0001)表面的最终吸附形态和吸附方位有显著的影响.温度对不同吸附体系吸附能的影响也不相同;小分子在GaN(0001)基片表面优先吸附的顺序依次为TiO_2、SrO和BaO分子.数据分析显示SrO和BaO分子的最优生长温度是600℃,TiO_2分子的最优生长温度是500℃.     

Cl原子在γ-TiAl(111)表面吸附的第一性原理研究

基于密度泛函理论,在广义梯度近似下研究了Cl在γ-TiAl(111)表面的吸附.计算结果表明:γ-TiAl(111)表面的面心立方位置(fcc)和六角密排位置(hcp)为Cl吸附的稳定位置,当覆盖度Θ小于一个单层(ML)时,Cl原子倾向于吸附在γ-TiAl(111)表面近邻为多Ti的位置.电子结构分析发现,Cl原子同表面金属原子形成较强的离子键,并且成键具有一定的方向性.当Cl原子和O原子共同在γ-TiAl(111)表面吸附时,二者都趋     

α-Al2O3(0001)表面原子缺陷对ZnO吸附影响

采用基于密度泛函理论的分子动力学方法，对α-Al₂O₃(0001)表面 Al，O原子空位缺陷及其对ZnO吸附进行了理论计算.电子局域函数显示了表面空位处的电子密度变化，表面Al原子空缺处有非常明显的缺电子区域，悬挂键临近O的电子密度增大，有利于对Zn的吸附；O原子空缺处的Al原子处存在孤立电子，其ELF值为005—03，将有利于同电负性较大的O或O^2-结合.通过吸附动力学模拟与体系能量的计算发现，表面缺陷显著增强了表面 的化学吸附，空缺原子处都被吸附原子填补，吸附结合能远大于单晶表面的情况.在Al空缺的表面，由于ZnO的O与表面O形成双键，破坏了α-Al₂O₃(0001)表面O六 角对称结构，减小了 O的表面扩散，从而不利于规则的ZnO薄膜生长.相反，O的空缺表面，弥补了α-Al_{2O3(0001)表面O空位缺陷，不影响基片表面O六角对称结构.}     

二氧化钛薄膜表面甲醇吸附的和频振动光谱

自行搭建了用于研究表面光催化的宽带红外和频振动光谱并可以原位紫外光激发的装置. 利用自制的结构紧凑小巧的高真空样品池,可以在10 kPa氧气氛围下经原位紫外光照除掉 射频磁控溅射制备的二氧化钛薄膜表面的有机污染物. 通过在室温下改变甲醇气压和指认吸附在薄膜表面的甲醇的和频振动光谱,发现薄膜表面有两种吸附的甲醇,分子形式吸附的甲醇(CH₃OH)和解离吸附的甲醇(CH₃O). 当甲醇的覆盖度由低变高时,分子形式吸附的甲醇的CH₃的对称伸缩振动和费米共振峰红移了6～8 cm^-1. 真空下,薄膜表面的甲氧基和表面的氢原子可以重新结合并以甲醇分子的形式脱附. 研究表明二氧化钛薄膜体系存在两个平衡：气相甲醇和表面吸附的甲醇分子之间,以及表面吸附的甲醇分子和甲氧基之间.     

Effect of van der Waals interactions on H<Subscript>2</Subscript> dissociation on clean and defected Ru(0001) surface

Ab initio computational methods are used to study the relevance of van der Waals interactions in the case of a hydrogen molecule adsorption on the Ru(0001) surface. In addition to the clean surface, the effects of ruthenium adatom and vacancy on the process are studied. The adsorption characteristics are analyzed in terms of two dimensional cuts of the potential energy surface (PES). Based on the earlier studies for such systems, we mostly concentrate on the trajectories where the hydrogen molecule approaches the surface in parallel orientation. The results indicate that for a clean Ru(0001) the calculations applying the non-local van der Waals potentials yield higher barriers for the dissociation of the H₂ molecule. Of the high symmetry sites on Ru(0001), the top site is found to be the most reactive one. The vacancy and ruthenium adatom sites exhibit high dissociation barriers compared with the clean surface.     

IR spectroscopy of adsorbed dinitrogen: a sensitive probe of defect sites on Pt(111)

Fourier transform infrared reflection absorption spectroscopy (FT-IRAS) has been used to probe the non-dissociative adsorption of N₂ on an atomically clean Pt(111) single crystal. In contradiction to a previous IRAS study of nitrogen adsorption on a Pt(111) foil at 120 K, no nitrogen infrared (IR) band was observed on a fully annealed Pt(111) surface at 90 K. Following Ar⁺ ion bombardment, adsorption of nitrogen at 90 K produces an intense IR band at 2222 cm⁻¹ attributed to the N---N stretching mode of molecular nitrogen adsorbed on defect sites produced by ion bombardment. Annealing the Ar⁺ ion sputtered surface to a temperature above 750 K completely suppresses the adsorption of nitrogen at 90 K. Based on these and other results, we postulate that nitrogen adsorbs at 90 K mainly on monovacancies on platinum. We suggest that this specific adsorption occurs by sigma donation from nitrogen to the base of monovacancy sites which possess a low d-electron density compared to surface Pt atoms.     

Chemisorption and decomposition of nitric oxide on ruthenium

Nitric oxide, strongly chemisorbed on ruthenium, is desorbed almost completely as oxygen and nitrogen. Oxygen, nitrogen, and nitric oxide were observed singly on ruthenium with field emission microscopy. Thermal desorption spectroscopy from Ru(101&#x0304;0) showed that molecular nitrogen is only physisorbed but nitrogen from NO decomposition is strongly chemisorbed. Nitrogen from NO shows three binding states, the most strongly bound being present to only a small extent. NO shows three and two binding states when adsorbed at 120 K and 295 K respectively. Work function measurements gave Δφ = 1.3 eV for a monolayer of NO. NO is dissociatively adsorbed above 250 K but a lower temperature limit was not established. The decomposition of NO on $\text{Ru}\text{(10}\text{1}\text{0)}$ under high vacuum conditions is catalytic in that no oxides of ruthenium were observed to form in the process.     

Electronic structures and vibrational properties of coronene on Ru(0001): first-principles study

We calculate the configurations, electronic structures, vibrational properties at the coronene/Ru(0001) interface, and adsorption of a single Pt atom on coronene/Ru(0001) based on density functional theory calculations. The geometric structures and electronic structures of the coronene on Ru(0001) are compared with those of the graphene/Ru(0001). The results show that the coronene/Ru(0001) can be a simplified model system used to describe the interaction between graphene and ruthenium. Further calculations of the vibrational properties of coronene molecule adsorbed on Ru(0001) suggest that the phonon properties of differently corrugated regions of graphene on Ru(0001) are different. This model system is also used to investigate the selective adsorption of Pt atoms on graphene/Ru(0001). The configurations of Pt on coronene/Ru(0001) with the lowest binding energy give clues to explain the experimental observation that a Pt cluster selectively adsorbs on the second highest regions of graphene/Ru(0001). This work provides a simple model for understanding the adsorption properties and vibrational properties of graphene on Ru(0001) substrate.     

Pd对O吸附在ZnO（0001）面上的影响的第一性原理研究

本文用第一性原理方法计算了Pd 在ZnO(0001)面上的吸附、Pd对O吸附的影响及Pd替代表面Zn原子能量的变化.结果表明：(1) Pd的吸附位置不随覆盖度变化,Pd稳定吸附位为H3位;(2)Pd在1/4单层吸附时比1个单层吸附时稳定;(3)Pd的存在增强了氧在ZnO(0001)面上的吸附,O原子可以扩散到Pd吸附层的下,Pd处于最上面, 具有催化作用.     

Binding energies and K-edge spectra of NO chemisorbed on Ru(0001)

The electronic structures, adsorption energies and equilibrium geometries of chemisorbed NO on the Ru(0001) surface for several adsorption sites were determined using cluster models and employing the first principles, local density theory. Ground state one-electron eigenvalues and wave functions were obtained using the discrete variational method with numerical atomic bases. K-edge X-ray absorption spectra of both nitrogen and oxygen for each geometry were obtained using a scattered wave method. The effects of the surface on these spectra were studied by comparison with results from an isolated NO molecule and with the XPS and UPS experiments of Umbach et al. Both the NO and the NO-substrate vibration frequencies were calculated. Comparison between these theoretical results, recent electron energy loss spectra of Conrad et al. and early experiments of Thomas et al. suggests that NO is adsorbed only at threefold and top sites.     

Electronic structures and coronene on Ru（0001）： vibrational properties of first-principles study

We calculate the configurations,electronic structures,vibrational properties at the coronene/Ru(0001) interface,and adsorption of a single Pt atom on coronene/Ru(0001) based on density functional theory calculations.The geometric structures and electronic structures of the coronene on Ru(0001) are compared with those of the graphene/Ru(0001).The results show that the coronene/Ru(0001) can be a simplified model system used to describe the interaction between graphene and ruthenium.Further calculations of the vibrational properties of coronene molecule adsorbed on Ru(0001) suggest that the phonon properties of differently corrugated regions of graphene on Ru(0001) are different.This model system is also used to investigate the selective adsorption of Pt atoms on graphene/Ru(0001).The configurations of Pt on coronene/Ru(0001) with the lowest binding energy give clues to explain the experimental observation that a Pt cluster selectively adsorbs on the second highest regions of graphene/Ru(0001).This work provides a simple model for understanding the adsorption properties and vibrational properties of graphene on Ru(0001) substrate.     

The influence of crystallographic steps on coadsorption: CO---O/Ni(119)

On low index nickel surfaces, repulsive interactions between atomic oxygen and CO drive the phase separation of these species into oxygen-rich and CO-rich islands. Because these adsorbates interact differently with crystallographic steps, the size and the structure of these islands are modified on stepped surfaces. We have monitored coadsorption-induced changes in the distribution of CO with IRRAS, observing six different CO stretching bands which are assigned to distinct local chemisorption environments. When oxygen fully saturates sites along the step edge, the steps are completely blocked from CO adsorption and virtually all the CO population on the terraces shifts from atop to bridge sites. This terrace site shift is similarly accomplished by atomic oxygen chemisorbed at terrace sites. From these coadsorption-induced changes in CO site distributions, constrained by the 10 Å terrace width, we conclude the through-metal O---CO interaction responsible for this CO site shift must be operative over a range of 5 Å. At θ_o = 0.18 ML, when oxygen occupies, but does not fully saturate the step edge, a new CO adsorption site is created, with a characteristic frequency of 1750 cm⁻¹. This new site is assigned to CO bonded to kinks along the step edge based upon its low intensity ( geometric kink density), enhanced binding strength and sensitivity to oxygen coverage. At higher oxygen coverages, compression of the CO adlayer is observed, with CO shifting to asymmetric bridge sites. As saturation coverage is approached, CO occupies weakly bound sites in close proximity ( 3 Å) to O adatoms, with high characteristic frequencies of 2100 cm⁻¹.