No abstract

No abstract

No abstract

We report in situ scanning tunneling microscopy at atomic-layer resolution of the topographic changes accompanying electrochemical reactions. In dilute perchloric acid, Au(l 11) terraces roughen during the electrochemical formation and reduction of more than a monolayer of gold oxide, but anneal in minutes at moderate potential. Trace chloride enhances step motion, prevents the observation of roughening, and promotes the dissolution of gold during oxidation and rereduction. These observations illustrate the role adsorbates have in determining the surface mobility of substrate atoms.PACS numbers: 61.16.Di, 66.30.Lw, 81.60.Bn, 82.45.+ZThe microscopic details underlying important interfacial electrochemical processes such as electron transfer, plating, passivation, and corrosion are traditionally inferred from in situ measurements of macroscopic quantities: charge, potential, concentrations, surface tension, etc. Recently, various groups have demonstrated the feasibility of using ex situ electron spectroscopies, microscopies, and diffraction techniques 1 " 5 and in situ techniques such as glancing angle x-ray absorption and diffraction 6 " 8 and infrared reflection-absorption spectroscopy 9 to obtain structural information about the electrochemical interface at the atomic level. Scanning tunneling microscopy (STM) could offer a microscopic, realspace view of the electrochemical interface to complement these other tools. 10 One immediate target for investigation with the STM is the growth, dissolution, or rearrangement of crystalline surfaces due to electrochemical reactions. A prototypical example of electrochemically induced change at a crystalline surface is the electrochemical oxidation and rereduction of gold. 11 " 16 Recently, Wiechers et al. have demonstrated resolution of monatomic gold layers at the interface of Au(lll) and aqueous solutions while controlling the electrochemical potential of the gold surface. 17 Here, we report the first in situ STM observations with atomic-layer resolution of the consequences of an electrochemical surface reaction: the roughening, annealing, and dissolution accompanying the oxidation and rereduction of the Au(lll) surface.Gold (111) films on mica were prepared by evaporation of gold onto mica at 225 °C as reported earlier. 18 The samples were clamped to the base plate of a Nanoscope I STM (Digital Electronics) with a Teflon ring, which also formed the electrochemical cell. The counter electrode was a Pt wire, and the reference electrode was an Ag wire in an AgClC>4 solution separated from the cell by a length of Teflon tubing. All electrochemical potentials are reported with respect to the normal hydrogen electrode (NHE). HCIO4 was Ultra grade (Hopkin and Williams Co.), HC1 was reagent grade, water was from a Milli-Q purification train (Millipore Corp.), and oxygen was not removed from the cell. The sample potential was controlled relative to the reference electrode by driving the potential of the counter electrode, and the tip-tosample bias was fixed at -10 mV.The tunnelin...

Abstract. In the last years disturbances in VLF/LF radio signals related to seismic activity have been presented. The radio data were collected by receivers located on the ground or on satellites. The ground-based research implies systematic data collection by a network of receivers. Since 2000 the "Pacific VLF network", conducted by Japanese researchers, has been in operation. During 2008 a radio receiver was developed by the Italian factory Elettronika (Palo del Colle, Bari). The receiver is equipment working in VLF and LF bands. It can monitor 10 frequencies distributed in these bands and, for each of them, it saves the power level. At the beginning of 2009, five receivers were made for the realization of the "European VLF/LF Network"; two were planned for Italy and one for Greece, Turkey and Romania, respectively. In 2010 the network was enlarged to include a new receiver installed in Portugal. In this work, first the receiver and its setting up in the different places are described. Then, several disturbances in the radio signals related to the transmitters, receivers, meteorological/geomagnetic conditions are presented and described.