Ghaleb N. Salaita

Cation competition in the electrical double-layer at a well-defined electrode surface: Li+,Na+,K+,Cs+,H+,Mg2+,Ca2+,Ba2+,La3+, tetramethylammonium, choline and acetylcholine cations at Pt (111) surfaces containing an ordered layer of cyanide

Immersion of the Pt (111) surface into aqueous KCN solution produced an ordered ionic layer, Pt (111)(2√3×2√3)R30°−KCN. The adlattice consisted of isolated adsorbed CN− anions surrounded by adsorbed HCN molecules, and a layer of K+ counter-ions. When immersed at open circuit into aqueous solutions of simple chloride salts this surface underwent cation exchange without loss or rearrangement of the CN−/HCN layer, based upon Auger spectroscopy and LEED. Experiments in which cations were made to adsorb competitively from mixtures of chloride salts revealed that a remarkable degree of selectivity exists in the interaction of cations with this CN− layer. Highly charged cations predominated, followed by cations of relatively small size and those least strongly hydrated. Strength of cation retention varied in the order: La3+ ≫ Ba2+ > Ca2+ ≫ Mg2+ ≫ K+ > Na+ = Cs+ > NH4+ > H+ ≫ Li+ ≫ NH4+. Quaternary ammonium cations (tetramethylammonium, choline, acetylcholine), even when present in large excess, were unable to compete with other cations for retention by the double-layer.

Films formed on well-defined stainless steel single-crystal surfaces in oxygen and water: studies of the (111) plane by LEED, Auger and XPS

Abstract Reported here are studies by LEED, Auger and X-ray photo-electron spectroscopy of the (111) plane of a face-centered cubic Fe-Cr-Ni alloy single-crystal of composition (70 at% Fe, 18 at% Cr, 12 at% Ni) resembling type 304 stainless steel. Surface films resulting from treatment with O 2 , water vapor or liquid water at ambient temperature or with annealing were characterized. A disordered oxygen-containing layer was formed at ambient temperature. When formed from water, the layer contained oxide and undissociated water. Some of the water was co-ordinated and the remainder hydrogen bonded within the film. Annealing, or formation of the film at temperatures above 1000 K, produced an ordered oxide film consisting primarily of chromium oxides in the form of hexagonal meshes of Cr 2 O 3 (001), square meshes of CrO and an antiphase-domain adlattice of chemisorbed oxygen.