Time evolution of adatom and vacancy clusters on Ag(110)

The time evolution of adatom and vacancy islands on an Ag(110) surface is studied by using a variable-temperature ultrahigh vacuum scanning tunneling microscope. The islands are created by Ar⁺ ion sputtering at low temperatures and at very low fluxes (0.004 ML s⁻¹). The area of both kinds of island decreases linearly as a function of time, at least for small islands. The experimental results are compared with kinetic Monte Carlo simulations.     

Theory of inelastic tunneling spectroscopy of a single molecule - Competition between elastic and inelastic current

A theory of inelastic electron tunneling spectroscopy of a single molecule with scanning tunneling microscope is presented using the Keldysh Green’s function method for an adsorbate-induced resonance coupled to the molecular vibration. It is found that the correction to the tunneling current is expressed in terms of the transmission probability; the correction is negative for the elastic part of the current and positive for the inelastic one. The differential conductance (dI/dV) exhibits an increase or decrease at the threshold corresponding to the opening of inelastic channel depending on the sign of the correction, and the size of this conductance jump is scaled with the vibrational damping due to electron-hole pair excitation. The lineshape of d²I/dV²-spectra calculated using a renormalized adsorbate Green’s function evolves from an antisymmetric dip to a peak through the derivative-like one as the position of the adsorbate resonance recedes from the Fermi level of the substrate.     

Electron transport and shell structures of single InAs quantum dots probed by nanogap electrodes

We have investigated electron transport and electron filling in single InAs quantum dots (QDs) using nanogap electrodes. Elliptic InAs QDs with diameter of 60/80 nm exhibited clear shell filling up to 12 electrons. Shell-dependent charging energies and level quantization energies for the s, p, and d states were determined from the addition energy spectra. Furthermore, it is found that the charging energies and the tunneling conductances strongly depend on the shell, reflecting that the electron wave functions for higher shells are more extended in space.     

Quantum transport of the single metallocene molecule

The Quantum transport of three single metallocene molecule is investigated by performing theoretical calculations using the non-equilibrium Green's function method combined with density functional theory. We find that the three metallocen molecules structure become stretched along the transport direction, the distance between two C_p rings longer than the other theory and experiment results. The lager conductance is found in nickelocene molecule, the main transmission channel is the electron coupling between molecule and the electrodes is through the Ni d_xz and d_yz orbitals and the s, d_xz, d_yz of gold. This is also confirmed by the highest occupied molecular orbital resonance at Fermi level. In addition, negative differential resistance effect is found in the ferrocene, cobaltocene molecules, this is also closely related with the evolution of the transmission spectrum under applied bias.     

扫描隧道显微镜在单分子科学中的应用

单分子科学是一门新兴的交叉科学,在当前的科技发展中具有重要意义.扫描隧道显微镜是研究单分子的一种强有力而独特的工具.文章以作者所在研究组近年来在单分子表征、操控和原型器件设计等方面的研究工作进展为例,概述了扫描隧道显微镜在单分子科学中的应用,重点介绍了以下成果：在硫醇分子自组装单层膜上观测到C60分子的本征笼状结构,并发现了一种新颖的由C60分子取向产生的拓扑序;结合实验图像和理论模拟,确定了单个C60分子在Si(111)-7×7表面的吸附取向;通过对金属富勒烯分子Dy@C82进行空间和能量分辨成像及相关理论模拟,确定了金属原子相对碳笼的位置及分子的取向;利用扫描隧道显微镜针尖对吸附在Au(111)表面的单个CoPc分子操作“分子手术”,以实现其吸附态和自旋态的量子调控;发现了一种由单电子隧穿和C59N分子的特殊能级结构产生的新的整流机制;发现了一种由针尖电子态和CoPc分子中Co原子轨道的空间对称性匹配产生的负微分电阻效应.     

STM and AFM of bio/organic molecules and structures

Applications of scanning tunneling and atomic force microscopes in bio/organic researches are reviewed with a special emphasis on the types of researches that are expected to contribute to the creation of a new field of “single molecule biochemistry” in the near future. The reviewed articles within the scope as stated above actually include a fairly broad spectrum of researches. It is, therefore, a hope of the author that this review will be useful to those who are considering biological applications of the probe microscopy techniques but are not quite familiar with the types of experiments that have been done in the past. In the section on scanning tunneling microscopy, identification of chemically distinct functional groups by the difference in their tunneling properties will be discussed as a main focus because it is fundamental for biochemists to identify molecules by their shapes and properties. In the section on atomic force microscopy, recent progresses in the imaging techniques of proteins and DNAs are closely reviewed, and rapidly advancing technologies of single molecule measurements and manipulation of nanometer sized structures are given extensive coverage because the author considers that such new applications are extremely promising to open an entirely new field in biological sciences.     

单硫醇分子结的几何结构和电输运性质:压力效应与末端基团效应

利用杂化密度泛函理论,研究了以甲基、醇基、羧基为末端基团的烷烃硫醇分子与金电极形成分子结的过程,得到了分子结的几何结构与外加压力的关系. 并在此基础上,利用弹性散射格林函数方法研究了烷烃硫醇分子的电输运性质. 研究结果表明,对于C₁₁S分子来说,当两电极距离大于2.1 nm时,该分子结断裂;对于C₁₁SOH和C₁₀SCOOH来说,相应的分子结断裂的电极距离基本相同(2.15 nm). 在相同的外加压力(4.0 nN)下,C_{11关键词： 压力 末端基团 烷烃硫醇分子 电输运性质}     

Preferential heights in the growth of Ag islands on Si(1 1 1)-(7 × 7) surfaces

Growth behavior of thin Ag films on Si substrates at room temperature has been investigated by scanning tunneling microscopy and reflection high energy electron diffraction. In the layer-plus-island growth Ag islands show strongly preferred atomic scale heights and flat top. At low coverage (1 ML), islands containing two atomic layers of Ag are overwhelmingly formed. At higher coverages island height distribution shows strong peaks at relative heights corresponding to an even number (2, 4, 6, …) of Ag atomic layers. Beyond some coverage the height preference vanishes due to the appearance of screw dislocations and spiral growth.     

Interaction of O2 with Pd single crystals in the range 1-150 Torr: Surface morphology transformations

The interaction of O₂ with Pd single crystals including Pd(1 1 1), Pd(1 1 0) and Pd(1 0 0) in the pressure range 1-150 Torr was studied using scanning tunneling microscopy (STM). The Pd single crystal surface morphologies were determined by the oxidation conditions: O₂ pressure, exposure time and treatment temperature. Oxygen dissolution into Pd metal followed by the formation of bulk oxide was observed. The dissolution of oxygen resulted in the increase of the inter-planar spacing between the first two layers, 9-14% increase after an exposure of Pd(1 1 1) to 10-25 Torr O₂ at 600 K for 10 min, and 10-20% increase after exposing Pd(1 1 0) and Pd(1 0 0) to 1 Torr O₂ at 600 K for 10 min. Elongated or semi-spherical oxide agglomerates along the steps nucleated and grew on both Pd(1 1 0) and Pd(1 0 0) surfaces after oxidation in 5-25 Torr O₂ at 600 K. When bulk PdO was formed, the single crystal surface was covered with semi-spherical agglomerates 2-4 nm in size, which tended to aggregate to form a “cauliflower-like” structure. The single crystal surface area also increased during oxidation.     

存在固有偶极矩的 型三能级单分子体系发射光子统计性质研究

用最近发展的产生函数（Generating Function）方法,研究了在连续激光场和射频场作用下存在固有偶极矩的 型三能级单分子体系发射光子的统计性质。主要讨论了不同激光场强度和不同射频场,激光场失谐频率对系统平均发射光子数 ,线型 和Mandel 参数的影响,以及射频场对系统发射光子等待时间分布 的影响等。结果表明：外加激光场和射频场对单分子发射光子都具有很好的调控作用,可以选择合适的激光场参数和射频场参数来操纵单分子发射光子。     

金属电极对有机分子非弹性电子隧穿谱的影响

利用第一性原理计算金属电极下1,6-己二硫醇和1,4-二巯基苯分子结的非弹性电子隧穿谱,发现非弹性电子隧穿谱对金属电极的变化十分灵敏,并且非弹性电子隧穿谱的振动峰位置和强度与硫原子和金属电极表面的距离密切相关.结果表明电极材料和分子与金属成键的情况是影响分子结的非弹性电子输运的重要因素.理论分析进一步表明不同金属电极和有机分子的耦合能不同导致了谱峰强弱的调整.     

The adsorption of and reaction of NO2 on Ag(1 1 1)-p(4 × 4)-O and formation of surface nitrate

The adsorption and reaction of nitrogen dioxide on the Ag(1 1 1)-p(4 × 4)-O surface has been investigated with RAIRS, TPRS and STM. At 300 K NO₂ initially reacts with the oxygen overlayer to form nitrate in p(3 × 3) and p(4 × 4) structures, which convert to a new p(3 × 3) at saturation coverage. Surface pitting during nitrate adsorption is suggestive of the incorporation of silver atoms into the NO₃ structure. With heating NO₃ decomposes into NO₂ and O at 396 K and 497 K, and oxygen desorbs at 578 K.     

并五苯分子在Ag(110)表面成膜过程中的结构研究

采用低能电子衍射原位研究了并五苯分子（C₂₂H₁₄）在Ag(110)单晶表面的生长，观察了在初期沉积过程及随后基底变温过程中分子层结构的形成和变化.室温下并五苯分子在Ag(110)基底表面具有高的迁移性，从开始无序的亚单层膜结构逐渐形成有序的单层膜结构．实验和理论分析表明：并五苯分子平铺在Ag(110)表面，形成了与基底构成有关的有序结构，存在沿基底晶向成镜面对称的两种畴界取向，在基底温度从室温升高到接近并五苯升华温度的过程中，基底上的有序分子层结构保持稳定不变 关键词： 并五苯 低能电子衍射图案 分子层结构 Ag(110)     

Observation of stable mixed alkanethiolate-chloride adlayer on Ag(1 1 1): structural correlation with pure alkanethiolate monolayers

The self-assembly of 1-alkanethiols, CH₃(CH₂)_n−1SH (n=2-16), on Ag(1 1 1) film initially covered with a native oxide monolayer and that on a chloride-covered Ag(1 1 1) were comparatively studied by X-ray photoelectron spectroscopy and scanning tunneling microscopy. The native oxide monolayer was readily substituted completely by thiolates irrespective of chain length, leading to a dense (√7×√7)R19.1° monolayer for n<3, or a distorted (√7×√7)R19.1° structure for n>3 accompanied by distinct island and fine domain structures previously reported by other groups. In contrast, the chloride-to-thiolate conversion was far from complete for long alkanethiols (n?8), and at sufficiently high conversion temperature (>50 °C), we found a highly stable mixed thiolate-chloride monolayer with a well-defined 2:1 S/Cl atomic ratio, suggesting the occurrence of a mixed (√7×√7)R19.1° adlayer ordering. The combined effects of substrate-molecule and intermolecular interactions behind these contrastive phenomena are discussed.     

Reliable lateral manipulation of a single Ag adatom on a Ag(1 1 1) surface with a trimer-apex tip

We study the reliability of the lateral manipulation of a single Ag adatom on a Ag(1 1 1) surface with the single-atom and trimer-apex tips based on molecular statics simulations using surface embedded-atom-method potential. The dependence of the manipulation reliability on tip height and orientation is investigated. For the single-atom tip the manipulation reliability increases monotonically with decreasing tip height, which is owing to the strengthened lateral tip-adatom interaction as the tip height lowers. For the trimer-apex tip, the manipulation reliability is sensitive to the tip orientation in the lower tip-height range, while in the higher tip-height range the manipulation reliability is independent of the tip orientation and moreover can be greatly improved due to the strong vertical attraction of the tip on the adatom as compared to the single-atom tip. We also compare these results to those for manipulating single Cu adatoms on the Cu(1 1 1) surface, reveal the underlying physics, and propose the method to improve the manipulation reliability for different systems.     

CO和O2分子与TiO2(110)表面负载Pt单原子的相互作用

Pt单原子在低温CO氧化反应中具有很高的催化活性. 利用扫描隧道显微术与密度泛函理论,研究了Pt单原子在还原性TiO₂(110)表面的吸附行为及其与CO和O₂分子的相互作用. 研究发现在80 K低温下,TiO₂表面的氧空位缺陷是Pt单原子的最优吸附位. 将CO和O₂分子分别通入Pt单原子吸附后的TiO₂表面,研究相应的吸附构型. 实验表明在低覆盖度下,单个Pt原子会俘获一个CO分子,CO分子同时与表面次近邻的五配位Ti原子(Ti_5c)成键,进而形成非对称的Pt-CO 复合物构型. 将样品从80 K升温到100 K后,TiO₂表面的CO分子会迁移到Pt-CO处形成Pt-(CO)₂的复合结构. 对于O₂分子,单个Pt原子同样会吸附一个O₂分子,O₂分子也会与最近邻或次近邻的Ti_5c原子成键形成两种Pt-O₂构型. 这些结果在单分子尺度上揭示了CO和O₂与Pt单原子的相互作用,呈现了CO与O₂反应中的初始状态.     

Role of Phe‐D5 isotopically labeled analogues of bradykinin on elucidation of its adsorption mode on Ag,Au, and Cu electrodes. Surface‐enhanced Raman spectroscopy studies

Raman (RS), surface‐enhanced Raman scattering (SERS), electrochemistry, and isotopic effect methods were used to characterize selective adsorption of two isotopically labeled bradykinin analogues, [(Phe‐D₅)⁵]BK and [(Phe‐D₅)⁸]BK, a hormone which is known to be involved in small‐cell and non‐small‐cell lung carcinoma and prostate cancer. The investigated analogues contain Phe residue, at position 5 or 8 in the amino acid sequence, substituted by Phe‐D₅ (five protons of L‐phenylalanine ring substituted by deuterium). [(Phe‐D₅)⁵]BK and [(Phe‐D₅)⁸]BK were immobilized onto electrochemically roughened Ag, Au, and Cu electrode surfaces under different applied electrode potentials (−1.000 V to 0.200 V) in an aqueous solution containing 0.01 M phosphate buffer (pH = 7.0) and 0.1 M Na₂SO₄. Based on the analyses of the spectral profiles in the 920 – 1050 cm⁻¹ spectral range, specific conclusions were drawn with respect to the Phe⋅⋅⋅metal interactions and changes in the interaction that occurred when the adsorption conditions were varied. Copyright © 2013 John Wiley & Sons, Ltd.     

Self-assembly formation of the ordered nanostructure arrays induced by Be interaction with Si(1 1 1) surface

Formation of the beryllium (Be) submonolayers on the Si(1 1 1)7 × 7 surface has been studied using scanning tunneling microscopy. It has been found that Be interaction with Si(1 1 1) at 500-700 °C results in a self-assembly formation of the four various types of the highly-ordered nanostructure arrays. The nanostructure arrays develop on top of the “soft” silicide layer, which period and orientation alter with the nanostructure growth: the shorter the nanostructure period, the larger the rotation angle. The main structural parameters of the silicide layer and nanostructure arrays have been established.     

纳米银粒子表面增强拉曼光谱在宠物饲料中三聚氰胺的速测研究

研究将制备的纳米银粒子作为表面增强拉曼光谱的增强试剂,实现对宠物饲料中三聚氰胺的快速定性定量分析。以709与1542cm-1处拉曼位移作为定性依据,以1149cm-1峰强度作为归一化标准,在1.0～10.0mg·kg-1浓度范围实现定量计算,检测限0.5mg·kg-1。研究发现,纳米银粒子对三聚氰胺具有较强的拉曼增强效应,特征峰信号强度与纳米银粒子加入时间,溶液涡旋强度有很大的关系,同时也受提取溶剂的种类、提取方式及样品加入量的影响。本方法中每个样品5min内完成分析,与现有方法相比,快速简便,对宠物饲料中三聚氰胺实现现场、快速检测。