表面分子手性识别与组装结构的STM研究

表面手性现象是物理化学科学研究的重要内容之一,研究表面手性现象,将有助于对分子吸附,分子间相互作用,多相手性催化,手性分离与拆分等科学和实际应用问题的深入理解.在表面手性现象和手性结构的研究中,扫描隧道显微技术（STM）发挥着重要作用,成为研究表面手性现象的重要手段.该综述文章以本课题组近年已发表的研究工作为主,重点介绍利用STM研究固体表面分子吸附组装体系中关于手性问题的部分结果,包括固有手性分子在固体表面的吸附,非手性分子组装形成手性结构,以及表面手性结构的转化和调控.还结合实验结果分析探讨了表面手性的结构形成、放大和传递等,展望了该研究领域的发展趋势.     

Observations of image contrast and dimerization of decacyclene by low temperature scanning tunneling microscopy

Low temperature scanning tunneling microscopy studies revealed both monomer and dimer forms of decacyclene (DC) on atomically clean Cu(100) and Cu(111). The observed image contrast in DC is strongly bias dependent and also influenced by tip modifications. Alternatively, dimers appear solely as protrusions and are nearly bias independent. We provide evidence of both dimer formation and dissociation and suggest that two DC molecules stack by aligning their molecular planes in a parallel fashion with respect to the surface. Dimers and their surface-dependent properties demonstrate the interplay between surface-molecule and molecule-molecule interactions.     

Two-dimensional supramolecular self-assembly probed by scanning tunneling microscopy

Supramolecular chemistry has a very large impact on chemistry of current interest and the use of non-covalent but directional forces is appealing for the construction of 'supramolecular architectures'. The invention of scanning probe microscopy techniques has opened new doorways to study these concepts on surfaces. This review deals with recent progress in the study of two-dimensional supramolecular self-assembly on surfaces probed by scanning tunneling microscopy, with a special emphasis on structure, dynamics and reactivity of hydrogen bonded systems.     

Determination of relative binding affinities of labeling molecules with amino acids by using scanning tunneling microscopy

The binding behaviour of labeling molecule copper phthalocyanine tetrasulfonate sodium (PcCu(SO(3)Na)(4)) on the assemblies of representative polyamino acids has been studied by using scanning tunneling microscopy (STM). By directly visualizing the adsorption and distribution of the labeling species on the peptide assemblies in STM images, one could obtain relative binding affinities of the labeling molecule with different amino acid residues.     

Luminescence from 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(111) surface excited by tunneling electrons in scanning tunneling microscopy

The electronic excitations induced with tunneling electrons into adlayers of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on Ag(111) have been investigated by in situ fluorescence spectroscopy in scanning tunneling microscopy (STM). A minute area of the surface is excited by an electron tunneling process in STM. Fluorescence spectra strongly depend on the coverage of PTCDA on Ag(111). The adsorption of the first PTCDA layer quenches the intrinsic surface plasmon originated from the clean Ag(111). When the second layer is formed, fluorescence spectra are dominated by the signals from PTCDA, which are interpreted as the radiative decay from the manifold of first singlet excited state (S(1)) of adsorbed PTCDA. The fluorescence of PTCDA is independent of the bias polarity. In addition, the fluorescence excitation spectrum agrees with that by optical excitation. Both results indicate that S(1) is directly excited by the inelastic impact scattering of electrons tunneling within the PTCDA adlayer.     

The effect of electrochemical surface treatments of carbon fibers using scanning tunneling microscopy

Scanning tunneling microscopy (STM) has been applied to the study of the topography of polyacrylonitrile (PAN)-based carbon fibers before and after electrochemical surface treatments. The results show that the electrical anodic oxidation only changes the surface aspects; at nanometric resolution; the nanostructure and nanotexture such as the step-like crystallite stacking are decreased with increasing electric current densities.     

Identification of single-strand DNA by in situ scanning tunneling microscopy

We report here in situ scanning tunneling microscopy imaging of hexaammineruthenium (II)/(III) (RuHex) binding to single-strand DNA oligonucleotide with 13 bases immobilized in a mixed monolayer on a single-crystal Au(111) surface. RuHex does not bind to the other component in the monolayer, mercaptohexanol. Images before and after addition of RuHex show a strong contrast increase, suggesting that single-stranded DNA is, indeed, conducting when a redox group is bound to the strand. When compared with previous results, the data also suggest that the mechanism of domain formation of the immobilized DNA is independent of the sequence.     

Construction of tunable supramolecular networks studied by scanning tunneling microscopy

In this review we describe a family of organic-based host frameworks which can accommodate guest molecules. The aim of the study is to test the adjustability of this class of mimic structures that may lead to new interesting functions. Emphasis of our research is placed upon four aspects: 1) thermal properties, 2) surface photochemistry, 3) fullerene adsorption, and 4) guest inclusion. It is envisioned that such approach of nanoporous molecular networks might be developed into a new family of useful soft fr...     

Self-assembled monolayers on Pt(111): molecular packing structure and strain effects observed by scanning tunneling microscopy

Self-assembled monolayers (SAMs) of octanethiol and benzeneethanethiol were deposited on clean Pt(111) surfaces in ultrahigh vacuum (UHV). Highly resolved images of these SAMs produced by an in situ scanning tunneling microscope (STM) showed that both systems organize into a super-structure mosaic of domains of locally ordered, closely packed molecules. Analysis of the STM images indicated a (square root 3 x square root 3)R30 degrees unit cell for the octanethiol SAMs and a 4(square root 3 x square root 3)R30 degrees periodicity based on 2 x 2 basic molecular packing for the benzeneethanethiol SAMs under the coverage conditions investigated. SAMs on Pt(111) exhibited differences in molecular packing and a lower density of disordered regions than SAMs on Au(111). Electron transport measurements were performed using scanning tunneling spectroscopy. Benzeneethanethiol/Pt(111) junctions exhibited a higher conductance than octanethiol/Pt(111) junctions.     

Microscale temperature measurement by scanning thermal microscopy

Scanning thermal microscopy (SThM) can measure thermal image with a nano-scale spatial resolution. However, there remains an issue in quantitative temperature measurement. We proposed an active temperature measurement method that provides a real temperature image by compensating a variation in contact thermal conductance. Performance of the active method was examined by a multi-function cantilever made with micro-fabrication process. Response test of the cantilever showed about 50 Hz cut off frequency for both passive and active method. Temperature measurement test indicated that sensitivity of heat flow detection was not enough to measure real temperature regardless of the thermal contact conductance. Imaging test demonstrated that the active method takes temperature image closer to real temperature distribution than the passive method. This revised version was published online in August 2006 with corrections to the Cover Date.     

A single molecule view of bistilbene photoisomerization on a surface using scanning tunneling microscopy

The advent of scanning tunneling microscopy (STM) has permitted a detailed atomic view of organic molecules adsorbed on solid surfaces. In this work, we make use of the STM to provide an unprecedented direct single-molecule perspective on the cis-trans photoisomerization of stilbene molecules within ordered monolayers physisorbed on the Ag/Ge(111)-( radical3x radical3)R30 degrees surface. The STM view of the molecular structure transformation upon irradiation provides direct evidence for the generally accepted one-bond-flip mechanism proposed for the photoisomerization process. We also find that the surface environment produces a profound effect on the reaction mechanism. The reaction is observed to proceed mainly through pairs of co-isomerizing molecules situated at domain boundaries. To explain these observations, we propose a mechanism whereby excitation migrates to the domain boundary and the reaction occurs through a biexciton reaction pathway.     

Physical structure of standing-up aromatic SAMs revealed by scanning tunneling microscopy

Long-range-ordered aromatic SAMs are formed on Au(111) using 4-nitrophenyl sulfenyl chloride as a precursor. Although the main structure is a √3 × √3 with a molecular density similar to that usually found for aliphatic SAMs, particular spots presenting specific shapes are also observed by STM. These include hexagons, partial hexagons, parallelograms, and zigzags resulting from specific arrangements of adsorbed molecules. These molecular arrangements are reversible as they form and dissociate or "vanish" in various areas on the surface. STM shows that these particular structures provide some order to their surrounding because areas void of these structures look less ordered. More interestingly, STM shows submolecular details of the molecules involved in forming these structures, hence providing direct experimental evidence for the ability of the STM to provide physical structure information of standing up SAMs. This is indeed a heavily debated question, and this work reports the first experimental example where submolecular physical structure is revealed by STM for standing-up SAMs.     

Selective internal manipulation of a single molecule by scanning tunneling microscopy

We have studied the adsorption of the polyaromatic molecule 1,4"-paratriphenyldimethylacetone, which we have nicknamed Trima. The originality of this linear molecule is that it was designed and synthesized to have two functionalities. First, chemisorb itself to the surface by its two ends rather like a bridge. Second, the central part of the molecule could then be rotated by injecting electrons with the tip of the scanning tunneling microscope (STM). The length of the molecule corresponds exactly to the spacing between five dimers in a row on the Si(100)-2 x 1 surface. We found that the molecule adsorbs as expected on the clean silicon surface by using complementary STM and synchrotron radiation studies. Manipulation of individual molecules with the STM tip showed selective internal modifications that were highly voltage dependent. These manipulations were found to be compatible with an electronic excitation of the pi-pi* transition of the molecule.     

Organic monolayers chemisorbed on gold observed by scanning probe microscopy

Scanning force (SFM) and scanning tunneling (STM) microscopies are suitable techniques for the investigation of the structure of organic monolayers. Results are presented on thioalkane monolayers and thiolipid monolayers on gold. Both molecules attach covalently to the gold surface. STM images of the self assembled dodecanethiol layer display the molecular order of the film and reveal the presence of defects at the molecular scale. Moreover, domains and domain boundaries can be distinguished. Thiolipid layers on gold have been observed by SFM. The monolayer separates in solid-analogous star shaped domains and fluid-analogous domains. Imaging under water demonstrates the stability of the layer.     

扫描隧道显微镜在有机化学中的应用

扫描隧道显微镜的最大优点是可达到原子量级的分辨率。本文综述了STM对有机分子的结构、聚集形态及其反应过程的研究。     

Solvent effects on two-dimensional molecular self-assemblies investigated by using scanning tunneling microscopy

Self-assembly structures investigated by using scanning tunneling microscopy (STM) at liquid/solid interface have been a topic of broad interest in surface science, molecular materials, molecular electronics. The delicate balance among the adsorbate–solvent, adsorbate–adsorbate, solvent–solvent interactions would give rise to the coadsorption or competitive deposition of solvent with adsorbate. The solvents at the interface enable dynamic absorption and desorption of the adsorbates leading to the controlled assembly of the molecular architectures. The solvent-induced polymorphism, coadsorption effect, as well as solvent effects on chirality and electronic structures are discussed in this report in view of the polarity, solubility and viscosity of the solvent, the hydrogen bonding formation between solute and solvent, and the solvophobic and solvophilic effects. The systematic studies on the solvent effects would shed light on better control of assembly structures for design of new molecular materials and molecular electronics.     

Fully adiabatic dissociative electrochemical electron transfer reactions induced by scanning tunneling microscopy

A theory of fully adiabatic dissociative electrochemical processes of the electron transfer that are induced by scanning tunneling microscopy is constructed. Adiabatic free energy surfaces are calculated and properties of their symmetry are examined under various conditions. Diagrams of kinetic regimes, which characterize possible kinetic processes, which may proceed in the system under consideration, are constructed in the space of model parameters. Dependence of activation free energy on the bias voltage, overvoltage, physical properties of a molecule, and intensity of interaction of a molecule with an electrode and the tip of the scanning tunneling microscope is explored.     

Single carbon dioxide molecules on surfaces studied by low-temperature scanning tunneling microscopy

The chemical conversion of carbon dioxide (\(\hbox {CO}_2\)) has been intensively studied because the molecule is responsible for global warming. Rational design of catalysts plays an important role in converting \(\hbox {CO}_2\) into value-added compounds. Understanding the interaction between \(\hbox {CO}_2\) and surfaces of catalysts is a prerequisite to preparing high-performance catalysts. This review focuses on the investigations of \(\hbox {CO}_2\) molecules on single crystalline surfaces studied by low-temperature scanning tunneling microscopy. Molecular adsorption, diffusion, and conversion on metal surfaces, metal oxide surfaces, and surfaces decorated by metal-organic frameworks are summarized.     

Isolated supramolecules on surfaces studied with scanning tunneling microscopy

To date, supramolecular chemistry is an ever growing research field owing to its crucial role in molecular catalysis, recognition, medicine, data storage and processing as well as artificial photosynthetic devices.Different isolated supramolecules were prepared by molecular self-assembly on surfaces. This review mainly focuses on supramolecular aggregations on noble metal surfaces studied by scanning tunneling microscopy, including dimers, trimers, tetramers, pentamers, wire-like assemblies and Sierpin′ ski triangular fractals. The variety of self-assembled structures reflects the subtle balance between intermolecular and molecule–substrate interactions, which to some extent may be controlled by molecules, substrates and the molecular coverage. The comparative study of different architectures helps identifying the operative mechanisms that lead to the structural motifs. The application of these mechanisms may lead to novel assemblies with tailored physicochemical properties.     

Rough silver films studied by surface enhanced raman spectroscopy and low temperature scanning tunnelling microscopy

The surface topography of Ag films and surface enhanced Raman scattering (SERS) from benzene on Ag films have been simultaneously recorded. The Ag films were formed by vacuum deposition at temperatures ranging from 100 K to 500 K. Analysis of scanning tunnelling microscopy (STM) images shows that films formed below 250 K are fractal structures with Hausdorff-Besicovitch dimension 2.55 < D < 2.72, while for those formed above 250 K, D≈2. The lower temperature, rough films exhibit strong surface enhanced Raman scattering but the higher temperature, smooth films do not. We consider the consequences of fractal character and the possible correlation between this and the SERS activity of these films.