Interaction of Silver, Cesium, and Zinc with Alumina Surfaces:  Thermal Desorption and Photoemission Studies

Abstract

Cs, Ag, and Zn behave in a different way when deposited on surfaces of ultrathin (15-20 Å) films of alumina. In the case of Cs/Al 2 O 3 , the alkali atoms wet the oxide, forming strong chemisorption bonds. At small coverages of Cs, desorption of the alkali occurred between 600 and 1000 K. As the amount of Cs deposited increased, there was a reduction in the Cs desorption temperature to ∼350 K. This broad range of desorption temperatures reflects a continuous decrease in the Cs adsorption energy from 63 to 18 kcal/mol with increasing Cs coverage. The deposition of small amounts of Cs induced large (0.9-1.1 eV) positive shifts in the binding energies of the O KVV, O 1s, and Al 2p features of the alumina films. This is consistent with a transfer of electrons from Cs into surface states of alumina that produces a transformation similar to a change from p-type to n-type semiconductors. Ag and Zn do not wet the surface of alumina well and form three-dimensional clusters or particles. In these systems, the activation energies for desorption of the admetal increase with cluster size (20 kcal/mol for Ag, 10 kcal/mol for Zn). The deposition of Ag and Zn induces only minor perturbations in the electronic properties of alumina. Small silver clusters supported on alumina exhibit an incompletely developed metallic band structure. The differences in the behavior of the Cssystems are explained in terms of variations in the surface free energy of the admetals and in the nature of the admetal-oxide bonds.

X-Ray Photoelectron Spectroscopy Study of the Composition of Polyphenol Films Formed on Pt by Electropolymerisation of Phenol in the Presence of Sulphide in Carbonate Medium

“…[26][27][28][29][30][31][32][33] Rather it matches fairly well with that found for multilayers of sulphur deposited on Au after oxidation of sulphide at pHs ranging from acidic to highly alkaline. 30,[34][35][36][37] Moreover, a photoelectronic core level at 162.4 eV was found in the spectra of Pt samples emersed at various potentials (0.8, 1.1, and 1.3 V) during a potential linear sweep from 0.0 to 1.5 V/RHE run in a 10-4 M Na 2 S + 0.1 M Na 2 CO 3 solution free of bulk phenol ( Figure 7).…”

Use and limitations of electron flood gun control of surface potential during XPS: two non‐homogeneous sample types

“…For example, Cl 17 was observed to decrease the BE of oxidized Al but Cs was found to increase it. 28 The ability to trap charge and to change the apparent oxidation state of an oxide is dependent on the nature of the film or oxide layer and the nature of the contaminant, as well as sample history including thermal or other processing. If carbon is used as a reference the chemical nature of the surface and the carbon source will influence the measurement, as will the total amount of carbon present.…”

X-ray photoelectron spectroscopy study of thiols adsorbed on Pt(111) with and without the presence of a copper monolayer

“…The presence of the Cu adlayer seems to promote dimer formation and to hinder N-Pt interaction, as is observed in Figs 1 The oxidative adsorption process for thiols has been proved by open-circuit potential (OCP) measurements as well as current-time transients, 27 confirming a net electron transfer from sulphur to the metal as part of the monolayer formation process. However, the sulphur behaves as an electron acceptor when it is bonded to gold 27 or platinum, 28 due to the large difference between the electronegativities of sulphur and gold or platinium. 29 For thiols adsorbed on gold the OCP changes to less negative values, after the initial stages of adsorption, due to a gradual retro-donation of the negative charge that is accumulated on the electrode towards the sulphur adatom.…”

“…S 3p electron transfer. 28 As the negative charge on the sulphur becomes larger, the S 2p binding energy becomes smaller. 30 The S 2p BE for 4-MP is smaller (162.7 eV) than for 2-MP (163.1 eV).…”

“…Studies of aliphatic thiols adsorbed on gold 31 show two peaks in the S 2p spectrum located at 163.6 and 163.3 eV, depending on whether the sulphur atom adsorption is on step sites or on terraces sites. In the case of sulphur adsorbed on Pt(111), 28 the S 2p spectrum shows two peaks located at 162.31 and 161.37 eV for hollow and bridge sites, respectively. Following this result, it could be possible that 2-MP could be adsorbed on sites of higher interaction energy (two platinum atoms) than 4-MP (one platinum atom).…”