Direct measurement of the growth mode of graphene on SiC(0001) and SiC(0001¯)

We have determined the growth mode of graphene on SiC(0001) and SiC(0001ˉ) using ultrathin, isotopically labeled Si(13)C "marker layers" grown epitaxially on the Si(12)C surfaces. Few-layer graphene overlayers were formed via thermal decomposition at elevated temperature. For both surface terminations (Si face and C face), we find that the (13)C is located mainly in the outermost graphene layers, indicating that, during decomposition, new graphene layers form underneath existing ones.     

(0001)SiC衬底MgB_2超薄膜的制备和性质研究

利用混合物理化学气相沉积法(Hybrid physical-chemical vapor deposition简称为(HPCVD)在(0001)SiC衬底上制备了干净的MgB2超导超薄膜.在背景气体、压强、载气氢气流量以及B2H6的流量一定的情况下,改变沉积时间,制得一系列MgB2超薄膜样品。通过观察样品的表面形貌变化探究了MgB2超薄膜的生长过程.该系列超薄膜的生长遵循Volmer-Weber岛状生长模式且沿c轴外延生长.以20nm超薄膜作为例子,可知其表面连接性良好,超导转变温度Tc(0)≈38.5K,临界电流密度Jc≈0.82×107 A/cm2,表明了利用HPCVD在(0001)SiC衬底上制备的MgB2超薄膜有很好的性能.这预示其在超导电子器件上具有广阔的应用前景.     

Influence of defects in SiC （0001） on epitaxial graphene

Defects in silicon carbide(SiC) substrate are crucial to the properties of the epitaxial graphene(EG) grown on it. Here we report the effect of defects in SiC on the crystalline quality of EGs through comparative studies of the characteristics of the EGs grown on SiC(0001) substrates with different defect densities. It is found that EGs on high quality SiC possess regular steps on the surface of the SiC and there is no discernible D peak in its Raman spectrum. Conversely, the EG on the SiC with a high density of defects has a strong D peak, irregular stepped morphology and poor uniformity in graphene layer numbers. It is the defects in the SiC that are responsible for the irregular stepped morphology and lead to the small domain size in the EG.     

Raman Spectrum of Epitaxial Graphene on SiC （0001） by Pulsed Electron Irradiation

We report new Raman features of epitaxial graphene （EG） on Si-face 4H-SiC prepared by pulsed electron irradiation （PEI）. With increasing graphene layers, frequencies of G and 2D peaks show blue-shifts and approach those of bulk highly-oriented pyrolytic graphite. It is indicated that the EG is slightly tension strained and tends to be strain-free. Meanwhile, single Lorentzian line shapes are well fitted to the 2D peaks of EG on SiC（O001） and their full widths at half maximum decrease with the increasing graphene layers, which indicates that the multilayer EG on Si-face can also contain turbostratic stacking by our PEI route instead of only AB Bernal stacking by a traditional thermal annealing method. It is worth noting that the stacking style plays an important role on the charge carrier mobility. Therefore our findings will be a candidate for growing quality graphene with high carrier mobility both on the Si- and C-terminated SiC substrate. Mechanisms behind the features are studied and discussed.     

Interaction of water with stepped Co(0001): how is it different from flat Co(0001)?

The adsorption and dissociation of water monomer and dimer on stepped Co(0001) surface were studied by means of first-principles calculations. Present results indicate that the adsorption strength of water is greatly enhanced by the presence of step, while the activity of water monomer dissociation does not exhibit a noticeable improvement. Nevertheless, water dimer partial dissociation on stepped Co(0001) is more active than on flat Co(0001), and the promotion of oxygen atom on O–H bond cleavage of H₂O is more prominent on stepped surface than on flat Co(0001). The findings reveal the importance of low coordinated surface atoms on metallic catalysts and the vital role of surface rippling on water dissociation. Together with previous reports, the activity of water dissociation on cobalt-based catalytic surfaces depends dominantly on O-containing species like oxygen atom, H₂O or hydroxyl.     

GaN(0001)表面的电子结构研究

报道了纤锌矿WZ(wurtzite)GaN(0001)表面的电子结构研究.采用全势线性缀加平面波方法计算得到了GaN分波态密度,与以前实验结果一致.讨论了Ga3d对GaN电子结构的影响.利用同步辐射角分辨光电子能谱技术研究了价带电子结构.通过改变光子能量的垂直出射谱勾画沿ΓA方向的体能带结构,与计算得到的能带结构符合得较好.根据沿ΓK和ΓM方向的非垂直出射谱,确定了两个表面态的能带色散 关键词： GaN 角分辨光电发射 全势线性缀加平面波 电子结构     

Passivation of carbon dimer defects in amorphous SiO_2/4H–SiC(0001) interface:A first-principles study

An amorphous SiO_2/4 H–Si C(0001) interface model with carbon dimer defects is established based on density functional theory of the first-principle plane wave pseudopotential method.The structures of carbon dimer defects after passivation by H_2 and NO molecules are established,and the interface states before and after passivation are calculated by the Heyd–Scuseria–Ernzerhof(HSE06) hybrid functional scheme.Calculation results indicate that H_2 can be adsorbed on the O_2–C = C–O_2 defect and the carbon–carbon double bond is converted into a single bond.However,H_2 cannot be adsorbed on the O_2–(C = C) –O_2 defect.The NO molecules can be bonded by N and C atoms to transform the carbon–carbon double bonds,thereby passivating the two defects.This study shows that the mechanism for the passivation of Si O_2/4 H–SiC(0001) interface carbon dimer defects is to convert the carbon–carbon double bonds into carbon dimers.Moreover,some intermediate structures that can be introduced into the interface state in the band gap should be avoided.     

Temperature dependence of the thickness and morphology of epitaxial graphene grown on SiC （0001） wafers

Epitaxial graphene is synthesized by silicon sublimation from the Si-terminated 6H–SiC substrate. The effects of graphitization temperature on the thickness and surface morphology of epitaxial graphene are investigated. X-ray photoelectron spectroscopy spectra and atomic force microscopy images reveal that the epitaxial graphene thickness increases and the epitaxial graphene roughness decreases with the increase in graphitization temperature. This means that the thickness and roughness of epitaxial graphene films can be modulated by varying the graphitization temperature. In addition, the electrical properties of epitaxial graphene film are also investigated by Hall effect measurement.     

氧原子在Zr(0001)表面附近的扩散

在密度泛函理论计算的基础上,利用微动弹性带（nudged elastic band）方法研究了氧原子在Zr（0001）表面附近的扩散.首先计算了氧原子从稳定的表面面心立方（SFCC）位置向表面六角密排位置的扩散激活能（0.77 eV）;然后计算了氧原子从稳定的SFCC位置扩散到表面下第1层与第2层之间的八面体间隙位置,再继续向表面下第2层与第3层之间的八面体间隙位置扩散的激活能,在此过程中氧原子需克服两个能垒,其激活能分别为2.14和2.57 eV.结果表明,氧原子在Zr（0001）表面上方的扩散比较容易,而氧原子向Zr（0001）表面下的扩散相对较难. 关键词： Zr（0001）表面 微动弹性带 氧的扩散     

有机半导体在金属Ru(0001)上的界面特性研究

关键词：     

6H-SiC(0001)表面graphene逐层生长的分子动力学研究

利用经典分子动力学方法和模拟退火技术分析研究了6H-ＳiC（0001）表面graphene的逐层生长过程及其形貌结构特点．研究表明,经过高温蒸发表面硅原子后,6H-ＳiC（0001）表面的碳原子能够通过自组织过程生成稳定的局部单原子层graphene结构．这种过程类似于6H-ＳiC（0001）表面graphene的形成,其生长和结构形貌演化主要取决于退火温度和表面碳原子的覆盖程度． 研究发现,当退火温度高于1400K时,6H-ＳiC（0001）表面碳原子能形成局部的单原子层graphene结构．这一转变温 关键词： graphene 碳化硅 分子动力学     

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。     

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.     

Ge在Ru(0001)表面上生长及其性质研究

报道Ge在Ru(0001)表面上生长以及相互作用行为的扫描隧道显微镜（STM）和x射线光电子能谱（XPS）研究. STM的实验结果表明Ge在Ru(0001)表面的生长呈典型的Stranski_Krastanov生长模式，Ge的覆盖度小于单原子层时呈层状生长，而从第二层开始呈岛状生长. XPS测量显示衬底Ru(0001)与Ge的相互作用很弱. Ru(0001)表面的Ru 3d5/2和Ru 3d3/2芯态结合能分别处于2798和2840 eV. 随着Ge的生长，到Ge层的厚度为20个单原子层，衬底Ru 3d芯态结合能减小了约02 eV，而Ge 3d芯态结合能从Ge低覆盖度时的289 eV增加到了290 eV，其相对位移约为01 eV. 关键词： Ge Ru表面 生长 相互作用     

Fe/ZnO(0001)界面的同步辐射光电子能谱研究

利用同步辐射光电子能谱研究了Fe/ZnO生长模式、界面化学反应和电子结构.结果表明，Fe在ZnO(0001)表面以类SK模式生长(单层加岛状生长).当沉积约2?的Fe后，生长模式开始从二维层状生长转变成混合模式生长.界面价带谱和Fe3p芯能级谱的分析表明，在低覆盖度下，约有一个原子层(约1.5?)的Fe被ZnO(0001)面的外层O原子氧化，随着沉积厚度的增加，金属态Fe的信号逐渐增强.当吸附了5.1?的Fe时，出现了较强的金属Fe的Fermi边，说明出现了Fe的金属态.此外，在Fe原子吸附过程中，样品功函数在Fe厚度为0.2?时达到最小值4.5eV，偶极层形成后逐渐稳定在4.9eV.     

C60分子与石墨(0001)、硅(111)面的碰撞

用分子动力学模拟的方法和Tersoff多体势函数对以一定能量入射的C 60在石墨(0001)表面以及硅(111)表面碰撞的过程进行模拟研究.结果发现:碰撞过程是高度非弹性的,在弹回过程中,C60分子质心的运动可被看作是在准谐势下的运动 .C60以240 eV初始能量入射到石墨表面时,C60分子有严重的扭曲,最终将平铺在石墨表面形成薄膜;C60分子以30 eV初始动能入射到石墨表面时,将保持完好球形沉积在石墨表面;C60分子以60 eV的初始动能碰撞硅(111)表面时,C60分子最终沉积在硅表面,碰撞过程中C60分子有形变.     

Si(100)和蓝宝石(0001)衬底上3C-SiC的Raman研究

单晶Si和蓝宝石(0001)是两种重要的3C-SiC异质外延衬底材料，然而，由于Si及蓝宝石和3C-SiC之间大的晶格失配度和热膨胀系数失配度，在3C-SiC中会产生很大的内应力，直接影响3C-SiC的电学特性。Raman散射测试是一个功能很强的测试方法，其强度、宽度、Raman位移等有关Raman参数可以给出有关SiC晶体质量的信息，其中包括内应力。利用背散射几何构置的Raman方法研究了Si(100)和蓝宝石(0001)村底上LPCVD方法生长的SiC外延薄膜，在生长的所有样品中均观察到了典型的3C-SiC的TO和LO声子峰，在3C-SiC／Si材料中，这两个声子峰分别位于970．3cm-l和796．0cm-1，在3C-SiC／蓝宝石材料中，分别位于965．1cm^-1和801．2cm-1，这一结果表明这两种外延材料均为3C-SiC晶型。利用一个3C-SiC自由膜作为无应力标准样品,并根据3C-SiC／Si和3C-SiC／蓝宝石的TO和LO声子峰Raman位移相对于自由膜的移动量，得到3C-SiC中的内应力约分别为1GPa和4GPa。实验发现在这两种材料的TO声子峰的Raman位移移动方向相反，通过比较3C-SiC、Si和蓝宝石的热膨胀系数，预期Si衬底上的3C-SiC外延膜受到的应力为张应力，而蓝宝石衬底上3C-SiC受到的应力则为压应力。     

Fe/ZnO(0001-)界面的同步辐射光电子能谱研究

利用同步辐射光电子能谱研究了Fe／ZnO生长模式、界面化学反应和电子结构．结果表明，Fe在ZnO（0001^-）表面以类SK模式生长（单层加岛状生长）．当沉积约2A的Fe后，生长模式开始从二维层状生长转变成混合模式生长．界面价带谱和Fe3p芯能级谱的分析表明，在低覆盖度下，约有一个原子层（约1．5A）的Fe被ZnO（0001）面的外层0原子氧化，随着沉积厚度的增加，金属态Fe的信号逐渐增强．当吸附了5．1A的Fe时，出现了较强的金属Fe的Fermi边，说明出现了Fe的金属态．此外，在Fe原子吸附过程中，样品功函数在Fe厚度为0．2A时达到最小值4．5．eV，偶极层形成后逐渐稳定在4．9eV．