M.A. Karolewski

On the growth of Ni on Cu(100)

The growth of Ni on Cu(100) has been studied by X-ray photoelectron spectroscopy (XPS). The thermal stability of the submonolayer phase was investigated using XPS forward scattering measurements. The results suggest that the surface alloying starts already around 260–300 K. The variations of Ni2p32 binding energy and line profile with coverage were studied in order to obtain information about the Ni growth mode and lateral morphology of the Ni overlayer. Furthermore, CO titration was used to study the distribution of Ni atoms in the initial stages of overlayer growth. The experiments lend support to a model of Ni monolayer development based on the gradual compression of isolated Ni adatoms.

SIMS study of Cs/MoS2(0001) : II. Chemisorption of O2, H2O, HCOOH, CO2 and CS2

Abstract Chemisorption of a number of small molecules (O2, H2O, HCOOH, CO2, CS2) on cesiated surfaces of MoS2(0001) has been investigated at room temperature using low-flux SIMS. Chemisorption appears to involve dissociation in every instance. The compositions of adsorbed species can be inferred on the basis of their SIMS emission. O2, H2O and HCOOH gave rise to adsorbed O, OH and HCOO species respectively. The adsorbed species (CO3?) resulting from CO2 exposure could not be identified unambiguously because of mass interferences. CS2 dissociation appears to involve sulphur elimination with loss of the volatile CS radical back to the gas phase. Adsorption kinetics were monitored via adsorbate induced attenuations (“quenching”) of negative substrate ion emission. The rate and extent of this process varied considerably between the different adsorbates. The reactivities and SIMS behaviours of adsorbed species on Cs/MoS2 are discussed in terms of electron transfer processes occurring during chemisorption. We find some evidence for catalytic oxidation of the normally inert MoS2 substrate following exposure of Cs/MoS2 to O2 or H2O.

Coadsorption of cesium and water on MgO(100)

Abstract The room temperature chemisorption of isotopically labelled water (H 2 18 O) on clean and Cs-dosed MgO(100) surfaces has been investigated using secondary ion mass spectrometry (SIMS). Both clean and cesiated MgO surfaces show qualitative similarities in chemisorption behaviour, namely rapid dissociative adsorption of H 2 O with retention of liberated hydrogen at the surface as hydroxyl. Two adsorption regimes are identified, the first of these being completed after only 2 L of H 2 O exposure. Addition of Cs to MgO(100) appears to increase the total surface H 2 O uptake by 50–100% relative to clean MgO(100).

SIMS characterisation of chemisorbed pyridine, pyrrole and formate on pyrite (100)

Chemisorption of pyridine, pyrrole and formic acid on the (100) surface of pyrite (FeS2) at 320 K has been studied using SIMS. Pyridine adsorbs molecularly on FeS2 with saturation occurring after 2 L exposure; pyrrole chemisorption is also molecular but the adsorption state is reversible, pressure dependent, and only transiently occupied at 320 K; formic acid chemisorption is dissociative, resulting in adsorbed formate, but does not proceed to saturation unless activated by ion-induced removal of the carboxylic hydrogen atom. The chemisorption behaviours and secondary ion emissive properties of these systems can be rationalized in terms of the electronic donor capability (“basicity”) and character of each adsorbate species.

An ion-induced crystal current study of clean, sulphided and oxidized Cu(100)

Abstract The non-induced secondary emissive properties of clean, sulphided and oxidized Cu(100) surfaces have been investigated using the ion-induced crystal current (ICC) method described earlier [Surface Sci. 180 (1987) L113]. We have studied the effects of ion channelling and surface structure on the anisotropic properties of the ICC of clean and sulphided Cu(100) at H 2 S exposures of up to 10 8 L. We have also monitored the initial uptake kinetics and structural development of oxygen on Cu(100), and H 2 S on clean and oxidized Cu(100) surfaces using the same method. Analytical applications of ICC methods in surface science and technology are considered in some detail.

SIMS study of Cs/MoS2(0001): I. Cs deposition and chlorocarbon dissociation

The vapour deposition of Cs on MoS2(0001) and the chenusorption of chlorocarbons on Cs/MoS2 have been characterized by SIMS under low primary ion flux conditions. The Cs+ intensity passes through a maximum at approximately 0.25 τs, where τs is the dosing time required for Cs saturation, and thereafter declines towards a lower, constant value. Cs deposition leads to an enhancement of all negative ion intensities to the extent that their combined yield may approach unity per incident primary Ar+ ion and may contribute to the ion-induced crystal current (ICC) variation. The chenusorption of CH2Cl2 1,2-C2H4Cl2 and trans-1,2-C2H2Cl2 on the cesiated basal plane of MoS2 is studied at 330 K. Elimination of chlorine occurs in every instance with loss of the organic molecular fragment into the gas phase. Chlorine uptake by Cs/MoS2 leads to a progressive decline in negative secondary ion intensities. Chemisorption proceeds rapidly, particularly at high Cs coverages where it is essentially complete after reagent exposures of (1−2) × 10−6 mbar.s.

SIMS study of the interaction of methanol with clean Cu(100)

Abstract The interaction of MeOD (= M) with the clean Cu(100) surface at ~125 K was examined by low-flux (static) SIMS. The molecular character of the adsorption process was evident in the structure of the major secondary ion progressions detected, namely CuMn+, MnD+, MnOD− and MnMeO− (n=0,1,…). Above ~0.6 L exposure, MeOD adsorption was found to be spontaneously re and dependent on the partial pressure of MeOD. At this same exposure a threshold for enhanced emission of OH− (relative to OD−) and the larger secondary ion clusters was reached. It is suggested that typical MeOD condensation on Cu(100) proceeds initially by dispersion of an isolated dimeric species, rather than by nucleative growth as polymeric clusters, and that the ~0.6 L exposure threshold marks the onset of lateral inter-site adsorbate interactions, which are apparently repulsive in character. For MeOD partial pressures in excess of 5 × 10−8 mbar, a preferential attenuation of the yields of all clusters containing Cu takes place, which is attributed to multilayer MeOD condensation.

SIMS study of Cs/MoS2(0001). III: Chemisorption of acetone, propanal, 2-propanol and pyridine

Abstract The chemisorption of acetone (2-propanone), propanal (1-propanone), 2-propanol and pyridine on cesiated surfaces of MoS 2 (0001) has been investigated at room temperature using low-flux (“static”) secondary ion mass spectrometry (SIMS). Acetone and propanal are found to adsorb on Cs/MoS 2 without appreciable dissociation, probably as molecular species. However, in principle, conversion of these adsorbates to enolate species cannot be ruled out. On adsorption 2-propanol also undergoes dehydrogenation to produce a chemisorbed species identical to that obtained from acetone, i.e., a tautomer of molecular acetone or its enolate derivative. A molecularly adsorbed 2-propanol species has also been observed in dynamic equilibrium with the gas-phase species at higher partial pressure (2 × 10 −6 mbar) of the gaseous reactant. Pyridine adsorbs in small but detectable amounts on clean MoS 2 , probably at acidic defect sites. However, even trace pyridine uptake is efficiently suppressed in the presence of Cs.

SIMS study of elemental sulphur and sulphur chemisorbed on Fe and Cu

Abstract Static SIMS data for sulphur chemisorbed on polycrystalline Fe and Cu, and Cu(100) surfaces are reported. Also dynamic SIMS measurements have been made on elemental sulphur. Data are discussed in terms of substrate structure and bonding interactions. Results from surface sulphides of Fe and Cu are compared with SIMS data for bulk sulphides measured by the present authors in an earlier work.

Secondary ion mass spectra of metal sulphides

Abstract Secondary ion mass spectra of 12 mineral metal sulphides of copper, iron, silver, zinc and nickel have been measured. The influence of surface crystallography on cluster ion abundances has been determined for some low index surfaces of pyrite (FeS2). Polymorphic α—β phase transformations of Ag2S, Cu2S and Cu5FeS4 have been monitored in situ using SIMS. Data have been discussed with reference to sample surface crystallography, bulk structure, stoichiometry and intrinsic ion stability effects.