A direct scanning tunneling microscopy ex-situ determination on the nanometer scale of the topography of electrochemically highly activated platinum electrodes is presented. A correlation between catalytic activity and surface microtopography becomes evident. This result gives support to a structural model for the activated electrode surface. In the model, a volume with a pebble-like structure allows electrocatalytic processes to occur practically free of diffusion relaxation contributions under usual voltammetric conditions. Catalytic activity and surface roughness are of the outmost importance in heterogeneous catalysis, including electrocatalysis. The term roughness usually implies the existence of both macropores (macroroughness), which to a great extent are responsible for additional diffusional relaxation,' and micropores (microroughness), which concern the effective catalytic area.2 Despite the close relationship between microroughness and catalytic activity, many real systems involve complex macro-and micropore structures which make the direct determination of microroughness a difficult task. A new approach to overcome this drawback is forseen by using metal surfaces which offer large catalytic activity, negligible micropore diffusional relaxation, and distribution of active sites very close to that of the starting materiaL3 This is the case, among others, with platinum electrodes in acid solutions, which have been subjected to a relatively fast square potential cycling, over a potential range such that a hydrous metal oxide multilayer is formed and immediately afterwards is electroreduced to yield a substantially increased active area. The new surface
This work presents the physical realisation of metallic ion beams from atomic emitters with currents of approximately 105 ions per second. It also puts forward the idea of field surface melting at approximately one third of the bulk melting temperature. Under cooling this melted surface, experiments show pyramidal structures of nanometer dimensions ending in one atom also separated by nanometers, then shaping surface grain boundaries. Furthermore, this reveals why it is possible to have atomic resolution in STM experiments. The formation of double, triple, etc. atomic teton tips is also possible. All this is shown by field ion and field emission microscopies and atomic metallic ion emission experiments presented here for tungsten tips
Electron field emission calculations on atomic-size microtips are presented. Models inorporating the atomic size and the particular geometrical shape of the tip are proposed. Theoretical analysis explain the remarkable properties observed experimentally : strong electron beam focusing and anomalous I-V characteristics. We present a first series of experiments and quantum mechanical calculations that suggest the possibility of atomic resolution in Electron Field Emission
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