Superlattices formed by interaction of hydrogen iodide with Pt(111) and Pt(100) studied by LEED, Auger and thermal desorption mass spectroscopy

Electrochemistry at well-characterized surfaces

“…The first UPD process forms a (3X3) epitaxial layer of hexagonal close-packed Ag having a layer of iodine atoms adsorbed on top of the layer, resembling the (111) plane of Agl in the usual zinc blend structure. Later stages of UPD produce structures having (3X3)R30°local geometry arranged in domains of sufficiently small width (11)(12)(13)(14)(15)(16)(17) Pt unit mesh distances) to give characteristic LEED beams. In the course of LEED studies of electrodeposition it was discovered that the surfaces of oriented Pt single crystals that have been disordered by ion bombardment or electrochemical oxidation and reduction can be restored to a well-defined state by annealing under an atmosphere of Ar containing I2 vapor.15,23 The ordered layer of I atoms is removed quantitatively by subsequent heating in the absence of I2 to yield an ordered, clean Pt surface.…”

“…r*+i = (Qfc+2 -Q*+i)/(rc.FA) (14) where n = number of Faradays per mole electrolyzed, and F; = Faraday's constant. The final (k + 2) filling leads to no further adsorption and is used to determine the bulk solute concentration, C°: C°= (Qk+2-Qb)/(nFV)…”

Unequal-sphere packing model for the structural arrangement of the well-ordered adsorbate-substrate system

“…The result of this comparison is astonishing. Using our model of the unequal spheres we have been able to identify and determine as the most probable, all structural arrangements of the iodine atoms adsorbed at the Pt(111) surface, previously found in experiments by STM, 18,23-30 low-energy electron diffraction (LEED), 5,[31][32][33][34][35][36] and some other techniques. 9,[37][38][39][40][41][42][43][44] In other words, our question, "Up to which level (how far) a system like chemisorbed iodine on the Pt (111) surface can be described in terms of the possible atomic arrangements, by our model based on geometrical principles?"…”

“…It is the so-called ͑3 ϫ 3͒-asym structure. [24][25][26][27][28][29][30][31][32][33][34][35][36][37]41,42 We believe that our model based on geometrical principles can also explain the appearance of this particular structure. Note that the arrangement of ͑3 ϫ 3͒-asym iodine adlayer on Pt(111) has been described in many papers, so far.…”

“…In case of ͑3 ϫ 3͒-asym, each threefold iodine atoms is surrounded by six neighboring adatoms positioned at a higher level. [24][25][26][27][28][29][30][31][32][33][34][35][36][37] In order to understand the conditions for appearance and differences between ͑3 ϫ 3͒-sym and ͑3 ϫ 3͒-asym structures we employ our model, looking for a full range of possible FIG. 4.…”