Ordered ionic layers formed on platinum(111) from aqueous solutions

Abstract

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.

Induced Adsorption of Chloride and Bromide by Submonolayer Amounts of Copper Underpotentially Deposited on Pt(111)

“…Fig 1 shows (1 11), as observed previously, by Hubbard and co-workers [30]. As expected, because of its stronger adsorption, the presence of bromide causes a shift of the entire voltammetric profile towards more negative potentials (with a peak at about -0.07 V) in relation to the case of chloride.…”

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.…”

Detailed characterization of (3×3) iodine adlayer on Pt(111) by unequal-sphere packing model

“…These lattices have been characterized by LEED, [6][7][8][9][10][11][12] ADAM, 13 STM, [14][15][16] and Surface X-ray Scattering ͑SXS͒. [17][18][19][20][21] The same type of iodine adlayer on Pt͑111͒ was found for preparations from gas phase [12][13][14] and from aqueous solution.…”