粘胶基碳纤维表面结构的STM研究

本文建立了用具有原子级分辨能力的扫描隧道显微镜 (STM)研究粘胶基碳纤维 (RCF)表面结构的方法。在较大尺度的STM图像上 ,RCF表面显得很粗糙 ,“峰”和“谷”的特征非常明显。增大放大率时 ,发现了约10nm宽的条状结构 ,其排列与纤维轴成一定角度 (45°～ 90°)。首次获得了RCF原子级的STM图像 ,在原子级尺度上 ,其原子排列并不规则 ,相邻原子间距为 0 .14 2nm ,最近六元环中心的距离是 0 .2 5 3nm。与高定向降解石墨 (HOPG)的对比研究进一步表明RCF表面的碳网是变形的六元环结构     

Scanning tunneling microscopy study of fullerenes

Scanning tunneling microscopy investigations of adsorption and film growth of various fullerenes on semiconductor and metal surfaces are reviewed. The fullerenes being studied are C₆₀, C₇₀, C₈₄, Sc@C₈₂ and Y@C₈₂ and the substrates being used for adsorption are Si (111), Si (100), Ge (111), GaAs (110), GaAs (001), Au (111), Au (110), Au (100), Cu (111) and Ag (111) surfaces.     

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.     

Investigation of structures of micelles of a fullerene derivative of alanine in aqueous solutions by tunneling scanning microscopy

Structures of micelles ofN-(monohydrofullerenyl)-l-alanine and their associates were studied by tunneling scanning microscopy in the regime of a profilometer with a 10-nm resolution along the vertical line. The data obtained show that the micelles of the compound studied are anisodiametric particles 0.5–10 m in size containing negligible amounts of water. The thickness of the micelles depends on their lengths.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 876–878, April, 1996.     

Some Unusual Features of Highly Oriented Pyrolytic Graphite Observed by Electrochemical Scanning Tunneling Microscopy

HOPGisoneofthemostcommonlyusedsubstratesinSTMforitiseasilycleavedtoalargeatondcallyflatareaonthebasalplane.ExceptforO.246nmperiodicityrelatedregularatomicstructure,thedefectsandothervarious5e,t,,,,nativetothebasa1planeofHOPGcancoverasmuchasl-lO%ofthesurface.'Ofthesefeatures,stepsarethe'mostconunonlyobserved.'ThewidespreaduseofthissubstratehasledtothediscoveryofsomecrystalimperfectionsnativetothebasalplaneofHOPG',includingstackingfaults,graphitestrandsandfibers,brokenorflakedIayersandsup…     

Scanning force microscopy and amplitude versus distance measurements on single‐crystal oxide surfaces

Dynamic mode imaging and investigations on amplitude versus distance measurements were carried out on surfaces of single‐crystal; SrTiO₃, Al₂O₃ and LaAlO₃. Experiments were performed to optimize the imaging parameters for surfaces having varying elastic properties. The dependence of the amplitude–distance curve on different materials and the amplitude of oscillation was investigated. For SrTiO₃, a low‐drive amplitude provided the linear region necessary for imaging. A large amplitude of oscillation, however, created dips in the amplitude–distance curves, presumably due to complications in the tip dynamics such as bifurcation, period doubling, etc. In the case of Al₂O₃ and LaAlO₃, amplitude–distance curves were characterized by oscillations for lower tip sample separations and step‐like discontinuities in the stiff region. The magnitude of the oscillations and discontinuities was found to decrease with amplitude and eventually could be eliminated. Thus, for these samples a large amplitude of the cantilever provided the linear region required for imaging. It was observed also that two different surfaces of Al₂O₃ (c‐cut and r‐cut) yield totally different amplitude–distance curves consistent with their standard differences. The results indicate the complex behaviour of amplitude–distance curves, which not only vary from one sample to another but from one surface to another for a given sample. Copyright © 2004 John Wiley & Sons, Ltd.     

Scanning tunneling microscopy study of DNA-chromophore motif on solid surfaces

We focus our studies on DNA-chromophore motif on surfaces using samples prepared by the synthetic methods described by Wang and Li in a recent publication (J. Am. Chem. Soc. 2003, 125, 5248-5249). Scanning tunneling microscope (STM) was used to investigate the DNA-chromophore hybrids adsorbed on Au(111) and highly oriented pyrolytic graphite (HOPG) surfaces at room temperature in air. Experiments found that the DNA-chromophore hybrid molecules easily formed multimolecule aggregations on gold surface. On HOPG surfaces, however, DNA-chromophore hybrids were usually adsorbed as single molecules. STM images further showed DNA-chromophore hybrids adsorbed on Au(111) surfaces existed in the form of single molecule, dimer, trimer, tetramer, etc. The occurrence of molecular aggregations indicates that molecular interactions are comparable or stronger than molecule-substrate interactions; such weak interactions control the geometrical sizes and topographical shapes of the self-assembled DNA-chromophore hybrids on surfaces.     

Surface characterization of laser-treated poly(ethylene terephthalate) by optical profilometry and scanning tunneling microscopy

Characteristic changes in the surface topography due to UV laser treatment are of high significance for the determination of material destruction thresholds and surface structure development. E.g. irradiation of poly(ethylene terephthalate) (PET) film with pulsed UV laser light of 248 nm modifies the smoth surface of the polymer into a well oriented structured surface. The development of these structures were studied with scanning tunneling microscopy (STM) and high resolution optical profilometry. Three dimensional data of the surface were taken from the samples after each laser pulse. A change of topographic data was found in relation to fluence and number of pulses applied. © 1993 John Wilcy & Sons, Inc.     

Structure and topography of molecular assemblies on solid substrates by infrared spectroscopy and scanning tunneling microscopy

Recently we have combined infrared spectroscopy and atomic resolution scanning tunneling microscopy (STM) to probe the local structure and intermolecular arrangement of molecules within thin films. IR spectroscopy provides spatially averaged information about orientation of the molecules with respect to the surface and about intermolecular arrangement within the crystallographic unit cell. STM data yields a local picture of molecular packing within the film. The requirements of an atomically flat (over distances of hundreds of angstroms) conducting substrate for the STM are fulfilled by an epitaxially grown film of gold on a cleaved mica substrate which also provides a good infrared reflective surface, enabling IR and STM measurements on identical samples. Systems investigated include Langmuir-Blodgett films of cadmium arachidate and self-assembled films of octadecyltrichlorosilane.     

Scanning electrochemical microscopy for direct imaging of reaction rates

Not only in electrochemistry but also in biology and in membrane transport, localized processes at solid-liquid or liquid-liquid interfaces play an important role at defect sites, pores, or individual cells, but are difficult to characterize by integral investigation. Scanning electrochemical microscopy is suitable for such investigations. After two decades of development, this method is based on a solid theoretical foundation and a large number of demonstrated applications. It offers the possibility of directly imaging heterogeneous reaction rates and locally modifying substrates by electrochemically generated reagents. The applications range from classical electrochemical problems, such as the investigation of localized corrosion and electrocatalytic reactions in fuel cells, sensor surfaces, biochips, and microstructured analysis systems, to mass transport through synthetic membranes, skin and tissue, as well as intercellular communication processes. Moreover, processes can be studied that occur at liquid surfaces and liquid-liquid interfaces.     

Visualization of atomic processes on ruthenium dioxide using scanning tunneling microscopy.

The visualization of surface reactions on the atomic scale provides direct insight into the microscopic reaction steps taking place in a catalytic reaction at a (model) catalyst's surface. Employing the technique of scanning tunneling microscopy (STM), we investigated the CO oxidation reaction over the RuO2(110) and RuO2(100) surfaces. For both surfaces the protruding bridging O atoms are imaged in STM as bright features. The reaction mechanism is identical on both orientations of RuO2. CO molecules adsorb on the undercoordinated surface Ru atoms from where they recombine with undercoordinated O atoms to form CO2 at the oxide surface. In contrast to the RuO2(110) surface, the RuO2(100) surface stabilizes also a catalytically inactive c(2 x 2) surface phase onto which CO is not able to adsorb above 100 K. We argue that this inactive RuO2(100)-c(2 x 2) phase may play an important role in the deactivation of RuO2 catalysts in the electrochemical Cl2 evolution and other heterogeneous reactions.     

Scanning tunneling microscopy and spectroscopy of donor-acceptor-donor triads at the liquid/solid interface.

By means of scanning tunneling microscopy (STM), the self-assembly of two organic donor-acceptor-donor triads (donor=oligo(p-phenylene vinylene) (OPV); acceptor=perylene diimide (PDI)) and their mixtures has been investigated at the liquid/solid interface. Both triads differ in the nature of the substituents and, therefore, in the redox properties of the central perylene diimide unit (H or Cl). Thanks to the submolecular resolution, the distinct electronic properties of the units, within a triad and between the two triads, are reflected by the relative STM contrast in the bias-dependent imaging experiments. Moreover, scanning tunneling spectroscopy reveals an inverse rectifying behavior of the OPV and H-substituted PDI units, which is discussed in the framework of quasi-resonant tunneling. A striking difference is observed for the Cl-substituted triad.     

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.     

Symmetry properties of adiabatic free energy surfaces and a diagram of kinetic modes in the case of electrochemical tunneling microscopy of redox systems

The symmetry properties of adiabatic free energy surfaces, which describe redox and dissociative electron transfer reactions in systems of the type in situ STM, are investigated. A notion of an effective overvoltage, which is a generalization of a traditional overvoltage to the case where the bias voltage is other than zero, is introduced. Diagrams of kinetic modes, which describe processes that can occur in systems of the type in situ STM under consideration, are constructed in the space of model parameters. It is shown that, in some cases, with the bias voltage other than zero, there may emerge DKR of a sufficiently complicated structure with several critical regions.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 419–432.Original Russian Text Copyright © 2005 by Medvedev.     

Calculation of adiabatic free energy surfaces in the case of electrochemical tunneling microscopy of redox systems

A method of adiabatic (infinitely slow) switching-on of interaction of the reactant with the electrode and the tip of a tunneling microscope at a bias voltage other than zero is used to derive expressions for the average number of electrons in the valence orbital of the reactant, the current passing through the valence orbital of the reactant at fixed values of coordinates of the slow subsystem of the solvent, and the electronic contribution to an expression that describes the adiabatic free energy surface (AFES) of the electrode-reactant-tip of the tunneling microscope system. The derived expressions are the same that had already been obtained in a Kuznetsov-Schmickler work, by a not-quite-correct method, though. Relationships that link the AFES corresponding to the opposite signs of the bias voltage are deduced. Examples of calculations of AFES and a current for a number of characteristic sets of parameters of the system are presented.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 259–272.Original Russian Text Copyright © 2005 by Medvedev.     

In situ scanning probe microscopy and new perspectives in analytical chemistry

The resolution of scanning tunnelling microscopy (STM) and other scanning probe microscopies is unprecedented but the techniques are fraught with limitations as analytical tools. These limitations and their relationship to the physical mechanisms of image contrast are first discussed. Some new options based on in situ STM, which hold prospects for molecular- and mesoscopic-scale analytical chemistry, are then reviewed. They are illustrated by metallic electro-crystallisation and -dissolution, and in situ STM spectroscopy of large redox molecules. The biophysically oriented analytical options of in situ atomic force microscopy, and analytical chemical perspectives for the new microcantilever sensor techniques are also discussed.     

Effect ofn-octyl acetate on the microstructure of corn starch sols studied by scanning tunneling microscopy

The microstructure of a corn starch sol was studied by scanning tunneling microscopy. The influence ofn-octyl acetate on the microstructure was found. The original starch sol contains compact anisodiametric particles 500–800 nm in size. The addition ofn-octyl acetate produces friable oval associates consisting of fine spherical particles 50–20 nm in size. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1478–1480, August, 2000.     

Topography Structure and Scanning Tunneling Spectrum of Nickel(Ⅱ)-tetraphenylporphyrin Molecules on Au(111)

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were performed on monolayer film of NiTPP supported on Au(111) under ultrahigh vacuum (UHV) conditions. The constant current STM images show remarkable bias dependence. High resolution STM data clearly show the individual NiTPP molecules and allow easy differentiation between NiTPP and CoTPP reported before. Scanning tunneling spectra, as a function of molecule-tip separation, were acquired over a range of tip motion of 0.42 nm. Spectra do not show the variation in band splitting with tip distance. It appears for molecules such as NiTPP that the average potential at the molecule is essentially the same at the same metal substrate. For molecules of the height of NiTPP, the scanning tunneling spectra should give reliable occupied and unoccupied orbital energies over a wide range of tip-molecule distances.