GaAs(111)衬底上生长的GaN的极性与生长方法和生长条件的关系

研究了在GaAs(111)衬底上生长的六角相GaN的极性的相关关系.在高Ⅴ/Ⅲ比的条件下用MOVPE和MOMBE方法生长的GaN的极性和GaAs衬底的极性一致;在(111)A-Ga表面上的生长层呈现Ga的极性,而在(111)B-As表面上的生长层呈现N的极性.然而,在低的Ⅴ/Ⅲ比,或采用一个AIN中间层的条件下,用HVPE和MOMBE方法在GaAs(111)B表面上生长的GaN呈现出Ga的极性.目前,其原因尚不清楚,但是这些结果表明采用HVPE生长方法或用一高温AlN阻挡层可以得到高质量的GaN.     

Ib型金刚石大单晶的限形生长

金刚石的限形生长有利于其后续加工.对于磨料级金刚石限形生长的研究已经比较透彻,但金刚石大单晶的限形生长尚缺乏全面系统的研究.本文以Fe Ni(64wt%:36wt%)合金为触媒,利用高温高压下的温度梯度法在5.6 GPa时对不同温度下分别沿(100)面和(111)面生长的Ib型金刚石大单晶的晶形进行了研究.研究表明:随着温度的升高,沿(100)晶面生长的金刚石大单晶的晶形分别为板状、塔状直至尖塔状,而沿(111)面生长的金刚石大单晶的晶形则分别为塔状和板状;分析了不同温度下分别沿(100)面和(111)面生长金刚石大单晶不同晶形高径比的变化情况.利用不同压力和温度下的金刚石大单晶合成实验绘制了沿(100)和(111)面生长金刚石大单晶的晶形在V形生长区域内的分布示意图,表明沿(111)面生长的金刚石大单晶V形区温度下限明显比以(100)面生长的高,而沿这两面生长金刚石大单晶的V形区温度上限差别并不明显.对不同生长面V形区温度上下限的差别进行了解释,据此实现了Ib型金刚石大单晶的限形生长.     

Si_3N_4/Si表面Si生长过程的扫描隧道显微镜研究

利用原位扫描隧道显微镜和低能电子衍射分析了Si的纳米颗粒在Si3N4 /Si(111)和Si3N4 /Si(10 0 )表面生长过程的结构演变 .在生长早期T为 35 0— 10 75K范围内 ,Si在两种衬底表面上都形成高密度的三维纳米团簇 ,这些团簇的大小均在几个纳米范围内 ,并且在高温退火时保持相当稳定的形状而不相互融合 .当生长继续时 ,Si的晶体小面开始显现 .在晶态的Si3N4 (0 0 0 1) /Si(111)表面 ,Si的 (111)小面生长比其他方向优先 ,生长方向与衬底Si(111)方向一致 .最后在大范围内形成以 (111)为主的晶面 .相反 ,在非晶的Si3N4 表面 ,即Si3N4 /Si(10 0 ) ,Si晶体的生长呈现完全随机的方向性 ,低指数面如 (111)和 (10 0 )面共存 ,但它们并不占据主导地位 ,大部分暴露的小面是高指数面如 (113)面 .对表面生长过程进行了探讨并给出了合理的物理解释     

温度对Si衬底上低压MOCVD外延生长ZnS薄膜质量的影响

用低压MOCVD系统在(111)Si衬底上,用两步生长方法(改变/流量比)在300～400℃时外延生长了ZnS单晶薄膜。随着衬底温度的降低,ZnS薄膜结晶质量提高,并在300℃生长时获得结晶完整性较好的(111)ZnS单晶薄膜。文中讨论了衬底温度对薄膜质量的影响。     

石墨烯在Ni(111)表面生长机理的紧束缚计算研究

本文采用SCC-DFTB方法,研究了石墨烯在Ni金属(111)表面上的生长机理及在台阶面生长情况.结果分析表明,苯环在Ni表面吸附时以界面fcc构型总能最低,结构最为稳定.边缘生长时,附着在衬底表面上的石墨烯层中C原子活性从边缘向中间逐渐降低.在由(111)晶面和(111)晶面相交形成的台阶面上,石墨烯片层可连续生长,同时相对衬底表面发生一定偏转,在较大面积时将出现缺陷.改善石墨烯与衬底台阶处的界面不匹配情况将有利于其大面积高质量生长.     

Ge/Si(111)与Si/Ge(111)体系的生长特性与表面再构研究

本文利用RHEED和AES对Ge/Si(111)和Si/Ge(111)体系的生长特性与表面再构进行了研究。由此提出了其生长模式,并讨论了应力对生长特性、界面特性和表面再构的作用。     

Ag(111)和Au(111)上铋的初始生长行为

半金属铋(Bi)的表面合金具有的Rashba效应,和其具体结构性质有重要关联.本文结合扫描隧道显微镜(STM)和密度泛函理论(DFT),系统地研究了Bi原子在Ag(111)和Au(111)上的不同初始生长行为.在室温Ag(111)上,连续的Ag2Bi合金薄膜会优先在Ag台阶边缘形成;在570 K Ag(111)上,随着...     

Si(111)分子束外延的生长动力学过程研究

本文用反射式高能电子衍射(RHEED)强度振荡研究了不同生长温度下Si(111)分子束外延的生长动力学过程,生长温度高于520℃(生长速率约0.15?/S)时,Si(111)外延为“台阶流”生长模式,生长温度低于475℃时,外延为“二维成核”双原子层生长模式,在较低温,甚至室温时,其外延仍为双原子层模式,但是镜向弹性散射束振荡和非弹性散射束振荡的叠加会造成RHEED强度在生长的最初阶段出现“类单原子层”模式的振荡特性。 关键词：     

分子束外延生长[111]晶向CdTe的研究

本文采用分子束外延(MBE)方法在BaF₂衬底上直接外延生长了CdTe(111)薄膜. 反射高能电子衍射(RHEED)实时监控生长表面, 衍射图样揭示了CdTe(111)在BaF₂表面由二维生长向三维生长的变化过程．XRD表征验证了外延生长的CdTe薄膜的单晶性质．由红外透射光谱测量和理论拟合相结合, 得到了CdTe外延薄膜室温带隙宽度E_g=1.511 eV.     

离轴生长的MgB_2超导薄膜的研究

通过混合物理化学沉积法(hybrid physical-chemical vapor deposition,简称为HPCVD),我们在多种单晶衬底上制备出了MgB2超导薄膜.经测量发现MgB2薄膜在6H-SiC、c-Al2O3、MgO(111)和YSZ(111)衬底上基本是沿c轴外延生长的,形成单晶薄膜;在MgO(211)、MgO(100)和钇稳定氧化锆(YSZ)(110)衬底上,MgB2晶粒的生长表现出明显的择优取向生长方式,并与晶格常数匹配关系所预言的结果一致。     

热壁外延与Ⅳ-Ⅵ族半导体红外器件

文章介绍了热壁外延（ＨＷＥ）技术及其应用。主要介绍了用热壁外延技术制作的几种Ⅳ－Ⅵ族半导体红外探测器和激光器,介绍了这方面国际上近年来的一些新进展,同时也介绍了我们自己的工作。     

X-ray photoelectron spectroscopy of Se films grown by hot wall epitaxy

The X-ray photoelectron spectroscopy (XPS) performed on Se films obtained by vacuum deposition and hot wall epitaxy (HWE) indicated shifts in the binding energies of the core-levels. The observed shift of 3.5 eV in the XPS spectrum of 3d level towards the higher binding energy in vacuum deposited film was associated with the Se₈ molecular state. On the other hand, the 3d-level XPS spectrum of Se films grown by HWE indicated an assymmetrical doublet. From the peak positions it was ascertained that the film was retained its bulk characteristic and a partial shift of 2.6 eV was interpretated for the presence of Se₆ molecules.     

Nuclear magnetic resonance study of epitaxial Co layers on single-crystal substrates

Nuclear magnetic resonance (NMR) is a powerful tool to study the local structure of ultrathin magnetic films and multilayers. This is demonstrated with an NMR study of ultrathin molecular beam epitaxy-grown Co layers on single-crystal Cu(111), Cu(110) and Pd(111) substrates. Co on Cu(111) results in a mixture of fcc and hep phases and the Cu(111)/Co interface is near to perfect. Co on Cu(110) grows mainly fcc in long stripe-shaped islands with rough Co/Cu interfaces. Finally, Co on Pd(111) gives a (111)-oriented fcc structure. The top surface is flat, but the Pd(111)/Co surface is intermixed.     

Oscillating indirect coupling of perpendicular magnetized Co(111)-monolayers through Cu(111)

Oscillating indirect coupling has been observed between perpendicularly magnetized Co(111)-monolayers on Cu(111). through a Cu(111)-interlayer. Contrarily, a weak indication of oscillation only was observed between in-plane magnetized Co(111)-films containing 5 monolayers each. Possible mechanisms for the strongly differing coupling behaviour observed in the Cu/Co(111) system are discussed.     

用扫描隧道显微镜测量局域功函数

用扫描隧道显微镜在Cu（111）-Au和Pt（111）-Ag表面上对局域功函数进行了测量．在扫描的同时通过测量隧道电流对针尖样品间距离变化的响应，可以在得到扫描隧道显微镜（STM）图的同时得到功函数图．用这种方法，成功地观察到Au，Ag覆盖层与Cu，Pt衬底间的功函数的差别．结果表明：Au覆盖层的功函数介于Cu（111）和Au（111）的功函数之间，这与其它方法的结果一致．在Pt（111）-Ag表面观察到了局域功函数随覆盖层厚度的变化．本工作表明：扫描隧道显微镜在研究功函数与表面结构的关系方面是十分有用的；用测量局域功函数的方法还可以区分表面不同种的物质 关键词：     

Al吸附在Pt,Ir和Au的(111)面的低覆盖度研究

应用密度泛函理论,系统研究了Al原子在Pt(111),Ir(111)和Au(111)表面的桥位、顶位、三重面心立方(fcc)洞位和六角密排(hcp)洞位这四个典型位置的吸附情况. 主要计算了三吸附体系的几何结构、平均结合能和差分电荷密度,并系统讨论了相关原子的密立根电荷布居数和投影态密度.研究发现,对于Pt(111)和Ir(111)表面,Al原子在hcp洞位最稳定,但是对于Au(111)表面,Al原子在fcc洞位最稳定. 关键词： 吸附 密度泛函理论 结合能 电子结构     

A LEED, TPD and HREELS investigation of NO adsorption on Sn/Pt(111) surface alloys

The adsorption of NO on Pt(111), and the (2 × 2)Sn/Pt(111) and (√3 × √3)R30°Sn/Pt(111) surface alloys has been studied using LEED, TPD and HREELS. NO adsorption produces a (2 × 2) LEED pattern on Pt(111) and a (2√3 × 2√3)R30° LEED pattern on the (2 × 2)Sn/Pt(111) surface. The initial sticking coefficient of NO on the (2 × 2)Sn/Pt(111) surface alloy at 100 K is the same as that on Pt(111), S₀ = 0.9, while the initial sticking coefficient of NO on the (√3 × √3)R30°Sn/Pt(111) surface decreases to 0.6. The presence of Sn in the surface layer of Pt(111) strongly reduces the binding energy of NO in contrast to the minor effect it has on CO. The binding energy of β-state NO is reduced by 8–10 kcal/mol on the Sn/Pt(111) surface alloys compared to Pt(111). HREELS data for saturation NO coverage on both surface alloys show two vibrational frequencies at 285 and 478 cm⁻¹ in the low frequency range and only one N-O stretching frequency at 1698 cm⁻¹. We assign this NO species as atop, bent-bonded NO. At small NO coverage, a species with a loss at 1455 cm⁻¹ was also observed on the (2 × 2)Sn/ Pt(111) surface alloy, similar to that observed on the Pt(111) surface. However, the atop, bent-bonded NO is the only species observed on the (√3 × √3)R30°Sn/Pt(111) surface alloy at any NO coverage studied.     

Ar adsorptions on Al (111) and Ir (111) surfaces: a first-principles study

We investigate the adsorptions of Ar on Al (111) and Ir (111) surfaces at the four high symmetry sites, i.e., top, bridge, fcc- and hcp-hollow sites at the coverage of 0.25 monolayer (ML) using the density functional theory within the generalized gradient approximation of Perdew, Burke and Ernzerhof functions. The geometric structures, the binding energies, the electronic properties of argon atoms adsorbed on Al (111) and Ir (111) surfaces, the difference in electron density between on the Al (111) surface and on the Ir (111) surface and the total density of states are calculated. Our studies indicate that the most stable adsorption site of Ar on the Al (111) surface is found to be the fcc-hollow site for the (2 × 2) structure. The corresponding binding energy of an argon atom at this site is 0.538 eV/Ar atom at a coverage of 0.25 ML. For the Ar adsorption on Ir (111) surface at the same coverage, the most favourable site is the hcp-hollow site, with a corresponding binding energy of 0.493 eV. The total density of states (TDOS) is analysed for Ar adsorption on Al (111) surface and it is concluded that the adsorption behaviour is dominated by the interaction between 3s, 3p orbits of Ar atom and the 3p orbit of the base Al metal and the formation of sp hybrid orbital. For Ar adsorption on Ir (111) surface, the conclusion is that the main interaction in the process of Ar adsorption on Ir (111) surface comes from the 3s and 3p orbits of argon atom and 5d orbit of Ir atom.     

Photoexcited processes at metal and alloy surfaces: electronic structure and adsorption site

Photoexcited processes of NO and CO at photon energies ranging from 2.3 to 6.4 eV are investigated on Pt(111), Ni(111) and Pt(111)---Ge surface alloys by reflection-absorption infrared spectroscopy and resonance-enhanced multiphoton ionization. The branching between three competitive processes of desorption, recapture and dissociation upon laser irradiation is dramatically changed on the three surfaces. On Pt(111), NO is either photodesorbed or photodissociated depending on the coverage, while NO is exclusively photodissociated on Ni(111). UV-photon irradiation of NO on Pt(111)---Ge, on the other hand, induces only desorption of NO. Desorption of CO bound at the on-top site of Pt(111) is induced by laser irradiation. The electronic mechanism for photodesorption and competitive branching is discussed in terms of the electronic structure of the substrate and the adsorbate.     

原位二次谐波研究Si(111)电极/电解液界面

本文利用电势依赖的原位二次谐波方法(SHG)研究Si(111)电极界面. 研究发现Si(111)电极在不同方位角下,其不同的偏振组合的SHG强度曲线随外加电势的变化呈现直线型或抛物线型两种不同的线型. 这种电势依赖的SHG响应曲线的差别可以用Si(111)电极的各向异性和各向同性对SHG信号的贡献来解释. Si(111)电极的各向异性和各向同性的贡献主要源于Si(111)电极掺杂浓度的增加.