Atomic resolution imaging of electrode surfaces in solutions containing reversible redox species

Procedures are described for insulating metal scanning tunneling microscope (STM) tips with either glass or polymer coatings. In solutions containing 0.10 M of a reversible redox couple, Fe(CN) - 3/-46 , the faradaic limiting current to polymer coated tips was 200–500 pA and that for glass coated tips was <10 pA. For polymer insulated tips, steady-state currents of 10–100 pA were observed at tip-sample displacements less than 0.3 µm. The suppression of faradaic current achieved by these coating procedures enabled the collection of the first atomic resolution STM images of highly ordered pyrolytic graphite electrodes in contact with redox-active electrolytes. Preliminary data for the in situ electrochemical characterization of these tips are also discussed

Design of a scanning tunneling microscope for electrochemical applications

A design for a scanning tunneling microscope that is well suited for electrochemical investigations is presented. The construction of the microscope ensures that only the tunneling tip and the sample participate in electrochemical reactions. The design also allows rapid replacement of the tip or sample, and enables facile introduction of auxiliary electrodes for use in electrochemical experiments. The microscope utilizes stepper motor driven approach mechanics in order to achieve fully remote operation and to allow reproducible coarse control of tip/sample spacings for electrochemical experiments. Highly ordered pyrolytic graphite images at atomic resolution in air and aqueous solutions can be obtained with this microscope

Imaging of liquid crystals with tunneling microscopy

We have used the scanning tunneling microscope (STM) to image a wide variety of organic liquid crystal molecules adsorbed onto a graphite substrate. From the images it is apparent that the STM is resolving individual liquid crystal molecules, as well as the different functional groups within the molecules. The high resolution allows direct observation of features that were not previously known, or had to be inferred from X-ray diffraction, neutron scattering, dilatometry, and other means. In this work, we image four diverse examples of liquid crystal molecules, and measure their packing arrangement and internal bond angles. We find that liquid crystal phases occur at the substrate boundary which have a higher degree of order and stability than the corresponding bulk phase. This surface phase remains intact even when heated 10-15 °C above the bulk isotropic transition temperature.Nous avons utilisé un microscope à effet tunnel (STM) pour visualiser une grande variété de molécules de cristaux liquides organiques adsorbées sur un substrat en graphique. D'après les images, on voit que le STM a la résolution correspondant aux molécules individuelles et aux divers groupes fonctionnels à l'intérieur des molécules. La haute résolution permet l'observation directe de détails par encore connus ou qui étaient seulement déduits à partir d'expériences de rayons X, neutrons, dilatométrie, etc... Dans ce travail, nous analysons les images de plusieurs exemples de molécules de cristaux liquides, mesurons leurs arrangement et angles de liaisons. On en déduit que les phases de cristal liquide apparaissant à la frontière du substrat ont un degré d'ordre et une stabilité supérieure à ceux de la phase massique. Cette phase en surface reste intacte, même après un réchauffement de 10 à 15 °C au-dessus de la température de transition isotrope de la phase massique