C90分子单层膜在Au(111)表面的STM研究

在超高真空中使用热蒸发方法,在Au(111)表面上制备了C90分子的分子单层膜,并利用超高真空低温扫描隧道显微镜在120 K温度下对其结构进行研究.观察到C90分子在Au(111)表面上先是沿着台阶边缘生长,分子铺满一层后,会在薄膜上形成岛状结构.本文对岛状结构进行了原位高分辨表征,观察到C90分子在正偏压和负偏压下的...     

Au(111)表面Dy@C82分子单层膜的STM研究

利用超高真空扫描隧道显微镜(UHV-STM),在低温(78K)下研究了不同覆盖度下Dy@C82(Ⅰ)膜在Au(111)表面的生长和结构.Dy@C82分子首先吸附于金台阶,进而延伸至金台面上形成紧密排列的一维分子链或二维分子岛.高分辨STM图像显示ZDy@C82分子具有多种不同的内部结构,表明Dy@C82分子在金表面的取向是无序的.     

激光对吸附在Si(111)7×7和Si(100)2×1表面上的C60的不同作用

本文利用超高真空扫描隧道显微镜(UHV STM),在室温下研究沉积了约0.005ML的C60分子的Si(111)7×7和Si(100)2 × 1再构表面在波长为266nm的激光束轰击前后的表面形貌的变化.结果表明,在266nm的激光作用下,Si(111)7×7表面上的C60分子保持完好,表面缺陷明显增加,但并没有完全破坏7×7再构形貌;而Si(100)2×1表面上的C60分子却被打碎,样品表面变得杂乱无章.     

Si(100)和Si(111)衬底上的同质分子束外延

用超高真空电子束蒸发系统进行了硅的同质分子束外延.发现采用适当的表面化学处理方法,然后在超高真空中加热,可以在较低温度下(800—814℃)获得清洁和平整的有序表面.Si(100)和Si(111)的外延分别在520℃和714℃进行,外延膜的结构和电学特性良好.     

Au(111)表面自组装硫醇单分子膜的STM成像机理

本文利用基于密度泛函理论的算法模拟Au(111)表面紧密堆构型的烷烃硫醇自组装单分子层膜(SAMs)中单分子的扫描隧道显微镜(STM)图像，发现图像细节依赖于偏压和烃链链长，主要由受电子效应影响的形貌效应决定。同时进行了电子结构分析以研究硫醇SAMs的STM成像机制，还发现烷烃硫醇分子中的S原子在Au表面的吸附模式也明显地影响着STM图像细节。     

以金属为缓冲层在Si(111)上分子束外延GaN及其表征

用电子束蒸发方法在Si(111)衬底上蒸发了Au/Cr和Au/Ti/Al/Ti 两种金属缓冲层,然后在金属缓冲层上用气源分子束外延(GSMBE)生长GaN. 两种缓冲层的表面都比较平整和均匀,都是具有Au(111)面择优取向的立方相Au层. 在Au/Cr/Si(111)上MBE生长的GaN,生长结束后出现剥离. 在Au/Ti/Al/Ti/Si(111)上无AlN缓冲层直接生长GaN,得到的是多晶GaN;先在800℃生长一层AlN缓冲层,然后在710℃生长GaN,得到的是沿GaN(0001)面择优取向的六方相GaN. 将Au/Ti/Al/Ti/Si(111)在800℃下退火20min,金属层收缩为网状结构,并且成为多晶,不再具有Au(111)方向择优取向.     

以金属为缓冲层在Si(111)上分子束外延GaN及其表征

用电子束蒸发方法在Si(111)村底蒸发了Au/Cr和Au/Ti/AI/Ti两种金属缓冲层,然后在金属缓冲层上用气源分子束外延(GSMBE)生长GaN.两种缓冲层的表面部比较平整和均匀,都是具有Au(111)面掸优取向的立方相Au层.在Au/Cr/Si(111)上MBE生长的GaN,生长结束后出现剥离.在Au/Ti/Al/Ti/Si(111)上无AIN缓冲层直接生长GaN,得到的是多品GaN;先在800℃生长一层AIN缓冲层,然后在710℃生长GaN,得到的足沿GaN(0001)面择优取向的六方相GaN.将Au/Ti/Al/Ti/Si(111)在 800℃下退火20min,金属层收缩为网状结构,并且成为多晶,不再具有Au(111)方向择优取向.     

InAs和InSb(111)清洁表面存在In岛的实验证据

用电子能量损失谱证实了,在超高真空中用氩离子刻蚀所获得的 InAs(111)和 InSb(111)清洁表面上会形成In岛.而生成In岛的容易程度按InP、IuAs、InSb的次序递减.     

a-Si∶H/Au/a-Si∶H膜的退火行为

Tsai等人发现180℃退火后在a-Si:H/Au薄膜内生成了雪花状结晶Si岛,类似的结果也被Hultman等人报导过。本文利用透射电子显微镜(TEM)研究了a-Si:H/Au/A-Si:H(10nm/30nm/10nm)三层膜的真空退火行为并对退火后形成的枝叉状晶化Si岛的结构和形成机理进行了研究和探讨。电镜观察结果表明,Au与Si在室温下形成一互混层,这可通过Au(111)衍射环分裂成d值为0.236和0.248nm的二个衍射环来证实。150℃热处理导致了Au_2Si这一亚稳相的生成。在200和250℃退火一小时后,膜中出现了枝叉状组织。图a显示了在250℃退火后样品中出现的一枝叉状组织的形貌,其内存在的大量弯曲消光条纹表明晶体快速生长在膜内造成了很大的应力状态。图b和c分别是图a中基体区和枝叉区的电子衍     

二氧化硅超薄膜的扫描隧道显微镜和扫描隧道谱研究

用超高真空热氧化方法在Si(111)清洁衬底上生长了二氧化硅超薄膜，并利用超高真空扫描隧道显微镜和扫描隧道谱技术对超薄膜的表面形貌和局域电学特性进行了研究。结果显示，在超薄范围二氧化硅呈层状生长，不同层的微分电导谱所测禁带宽度差别可以达到约3eV，形貌对二氧化硅带宽的影响小于膜厚的影响。     

Structural Dynamics of Ultrathin Cobalt Oxide Nanoislands under Potential Control

Cobalt oxide is a promising earth abundant electrocatalyst and one of the most intensively studied oxides in electrocatalysis. In this study, the structural dynamics of well-defined cobalt oxide nanoislands (NIs) on Au(111) are investigated in situ under potential control. The samples are prepared in ultra-high vacuum and the system is characterized using scanning tunneling microscopy (STM). After transfer into the electrochemical environment, the structure, mobility, and dissolution is studied via in situ electrochemical (EC) STM, cyclic voltammetry, and EC on-line inductively coupled plasma mass spectrometry. Cobalt oxide on Au(111) forms bilayer (BL) and double-bilayer NIs (DL), which are stable at the open circuit potential (0.8 V_RHE). In the cathodic scan, the cobalt oxide BL islands become mobile at potentials of 0.5 V_RHE and start dissolving at potentials below. In sharp contrast to the BL islands, the DL islands retain their morphology up to much lower potential. The re-deposition of Co aggregates is observed close to the reduction potential of Co²⁺ to Co³⁺. In the anodic scan, both the BL and DL islands retain their morphology up to 1.5 V_RHE. Even under these conditions, the islands do not show dissolution during the oxygen evolution reaction (OER) while maintaining their high OER activity.     

NiAl(110)和Cu-Al(111)合金表面生长超薄氧化铝膜的畴界和厚度的STM研究

利用低温超高真空扫描隧道显微术研究了在NiAl(110)和Cu-Al( 111)合金衬底上氧化生长的超薄氧化铝膜的畴界和厚度.在这两种氧化铝薄膜上均观察到两种不同类型的畴界:反相畴界(antiphase domain boundary)和反射畴界( reflection domain boundary).结果显示Cu-...     

Simultaneous STM and UHV electron microscope observation of silicon nanowires extracted from Si(111) surface

A miniaturized scanning tunnelling microscope (STM) was fitted in a side-entry holder of an ultra-high vacuum electron microscope. The clean Si(111)7 x 7 surface was observed by both STM and reflection electron microscopy (REM) at atomic resolution. The tungsten tips were often rounded off upon tip-approach with a constant current, through a gentle touch with the sample surface. The apices of such rounded tips had radii of several tens of granometre with widths of about 3 x 3 nm. Atomically resolved STM of the Si(111)7 x 7 surface was obtainable when an atom or an atomic cluster sits on the tip surface. The rounded tips were used for fabrication of Si nanowires by the touch-and-away operation of the tip. The nanowires grew longer at higher substrate temperature and they reached as long as several tens of nanometre at 700 degrees C. The nanowire had many twins and the (111) twin lamellae were stacked in the direction of the wire axis. In another case, the twin planes were oblique to the wire axis so that the (112) direction was nearly parallel to the wire axis.     

Uniform Ag Thin Film Growth on an Sb-terminated Si(111) Surface

We report on the room-temperature-growth of highly uniform and ultrathin Ag films on Sb-terminated Si(111) surfaces, as evidenced from a scanning tunneling microscopy (STM) study in an UHV system. With predeposition of one monolayer (ML) of Sb, uniform growth of Ag islands was observed at room temperature. The Sb layer suppresses the surface diffusion of Ag atoms on Si surface and increases the Ag island density, and then the increased island density is believed to cause coalescence of Ag islands before the beginning of multilayer growth in higher coverages, resulting in the growth of atomically flat and uniform islands on the Sb surfactant layer.     

Binary Molecular Layers of C60 and Copper Phthalocyanine on Au(111): Self‐Organized Nanostructuring

The binary molecular system of C₆₀ and copper phthalocyanine(CuPc) molecules has been investigated by scanning tunneling microscopy (STM) at room temperature and at 50 K. As substrate Au(111) was chosen. When C₆₀ and CuPc molecules are sequentially deposited, it is found that well‐ordered domains of both molecules may coexist simultaneously. Hence hexagonal ordering of C₆₀ and quadratic ordering of CuPc is observed side by side but no ordered mixed layer of both molecules or heteroepitaxy from one molecule on the other is found. Instead the boundaries of the CuPc domains are often decorated by C₆₀ molecules and for a particular choice of parameters, with regard to the film preparation, individual CuPc molecules may adsorb on top of a C₆₀ layer. The interaction with the underlying C₆₀ layer permits the molecules to perform a localized, hindered rotation. At room temperature the hopping frequency is so high that only the time average of the rotation is seen by STM while at 50 K the rotation is frozen and the CuPc molecule is trapped in one definite position.     

Highly Ordered 2D Hydrogen‐Bonded Structures of a Tetralactam Macrocycle on the Au(111) Surface

Monolayers of a tetralactam macrocycle, which are commonly used as building blocks in the synthesis of rotaxanes or catenanes, are deposited on a Au(111) surface by using vapor deposition. Due to self‐organization, 2D highly ordered supramolecular networks form. From scanning tunneling microscopy (STM) and concomitant density‐function theory calculations, two structurally different phases are found. In both phases, pairs of hydrogen bonds between the amide groups of next‐neighbor macrocycles are responsible for the structural arrangement of the macrocycles. The structure of both phases differs from that of bulk lattice planes, which reveals that the Au(111) surface acts as a template for the growth of the specific 2D structures. These networks of tetralactam macrocycles possibly open a route to study mechanical interlocking processes or guest/host interactions of the molecules in further detail by using STM.     

Heteroepitaxial growth of InAs on GaAs(0 0 1) by in situ STM located inside MBE growth chamber

The growth of InAs on GaAs(0 0 1) is of great interest primarily due to the self-assembly of arrays of quantum dots (QDs) with excellent opto-electronic properties. However, a basic understanding of their spontaneous formation is lacking. Advanced experimental methods are required to probe these nanostructures dynamically in order to elucidate their growth mechanism. Scanning tunneling microscopy (STM) has been successfully applied to many GaAs-based materials grown by molecular beam epitaxy (MBE). Typical STM–MBE experiments involve quenching the sample and transferring it to a remote STM chamber under arsenic-free ultra-high vacuum. In the case of GaAs-based materials grown at substrate temperatures of 400–600 °C, operating the STM at room temperature ensures that the surface is essentially static on the time scale of STM imaging. To attempt dynamic experiments requires a system in which STM and MBE are incorporated into one unit in order to scan in situ during growth. Here, we discuss in situ STM results from just such a system, covering both QDs and the dynamics of the wetting layer.     

STM Lithography in an Organic Self‐Assembled Monolayer

We describe the suitability of ultra‐high vacuum scanning tunneling microscopy (UHV‐STM) based nanolithography by using highly ordered monomolecular organic films, called self‐assembled monolayers (SAMs), as ultrathin resists. Organothiol‐type SAMs such as hexadecanethiol (SH–(CH₂)₁₅–CH₃) and N‐biphenylthiol (SH–(C₆H₆)₂–NO₂) monolayers have been prepared by immersion on gold films and Au(111) single crystals. Organosilane‐type SAMs such as octadecyltrichlorosilane (SiCl₃–(CH₂)₁₇–CH₃) monolayers have been prepared on hydroxylated Si(100) surfaces as well as hydroxylated chromium film surfaces. Dense line patterns have been written by UHV‐STM in constant current mode for various tunneling parameters (gap voltage, tunneling current, scan speed, and orientation) and transferred into the underlying substrate by wet etch techniques. The etched structures have been analyzed by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). Best resolution has been achieved without etch transfer for a 20 nm × 20 nm square written in hexadecanethiol/Au(111) with an edge definition of about 5 nm. Etch transfer of the STM nanopatterns in Au films resulted in 55 nm dense line patterns (15 nm deep) mainly broadened by the isotropic etch characteristic, while 35 nm wide and 30 nm deep dense line patterns written in octadecyltrichlorosilane/Si(100) and anisotropically etched into Si(100) could be achieved.