Ordered layers (adlattices) formed spontaneously when the Pt(lll) surface was immersed into aqueous ionic solutions. On the basis of Auger spectroscopy and LEED, the following salts formed adlattices as indicated: KCN, Pt(lll) (2\/3X2\/3)R30°-KCN; KSCN, Pt(lll) (2X2)-KSCN; K2S, Pt(lll) (diffuse 1X1)-K2S; KI, Pt(lll) (3X3)-I; KBr, Pt(lll) (3X3)-KBr. KI solution yielded a layer of neutral I atoms requiring no cationic counterion, in agreement with previous studies of HI vapor and aqueous electrosorption. All ionic concentrations studied (1CT4 to 10-1 M) gave similar results. The adsorbed layer of anions functioned as a cation exchanger: K+ ions were quantitatively replaced when the surface was rinsed with 10-4 M HC1 or CaCl2. Exchange of cations did not change the LEED pattern at room temperature; however, reconstruction occurred on heating to about 100 °C in some cases. Auger spectra indicated that hydroquinonesulfonate (KHQS) displayed a packing density transition as a function of concentration, as expected from electrochemical data; LEED patterns displayed no fractional-index beams due to the KHQS layer.
Studies by low energy electron diffraction (LEED) and Auger spectroscopy of copper electrodeposited on well‐characterized platinum (111) surfaces from aqueous sodium perchlorate solutions are reported. Prior to electrodeposition, the platinum (111) surface was pretreated with
I2
vapor in ultrahigh vacuum to form a Pt(111)
false(√7×√7false)
R19.1°‐I superlattice, which protected the platinum surface and the surface of the electrodeposit from attack by the electrolyte and contamination by residual gases. The results were as follows: electrodeposition took place in two narrow, overlapping underpotential deposition linear scan voltammetric peaks followed by one conventional bulk copper deposition peak. Underpotential deposition produced an ordered layer. The first underpotential deposition peak formed a
false(3×3false)
superlattice in which the unit cell contained four iodine atoms and a comparable number of Cu atoms per nine surface Pt atoms
false(θnormalCu=θI=4/9false)
. At completion of the underpotential deposition process a
false(10×10false)
coincidence lattice was present in which
θnormalCu=8/9
and
θI=4/9
. The iodine Auger signal was not appreciably affected by Cu deposition, indicating that the iodine atoms were present in the topmost layer of the surface at all Cu coverages.
Reported here are studies by LEED, Auger spectroscopy, and electrochemistry which show that Pt(100) monocrystal surfaces purposely disordered by electrochemical oxidation and reduction (as in the procedure commonly employed to clean or "activate" Pt electrodes) are restored to an ordered state by programmed heating under an Ar atmosphere containing iodine vapor. A nearly hexagonal, centered-rectangular adlattice of I atoms was formed, containing three I and five Pt atoms in the surface unit cell, 6l = 0.6, Pt(100)[c(v/2X5V'2)]R45°-I. Programmed heating of this adlattice led to stepwise desorption of halogen and produced a series of related adlattices. One of these, Pt(100)[(cv/2X2v/2)]R45°-I, at 0] = 0.50, is particularly amenable to identification, without LEED, by means of its characteristic cyclic voltammogram for silver electrodeposition. The behavior of each iodine adlattice toward silver electrodeposition and programmed temperature desorption is reported. These atmospheric iodine pretreatment and voltammetric procedures for preparing and verifying a well-defined electrode surface do not require vacuum equipment, although demonstration of the ordered structures in this work employed LEED and related techniques under ultrahigh vacuum. This basic approach should be applicable to a wide range of metals and adsorbates.
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