H. Raza

Growth of copper and palladium on α-Al2O3(0001)

Non-contact atomic force microscopy (NC-AFM) has been used to image the room-temperature growth of copper and palladium on the (1 x 1) and (root 31 x root 31) R +/- 9 degrees terminations of alpha-Al2O3(0001). Three-dimensional (3D) clusters of palladium are observed on both the (1 x 1) and the (root 31 x root 31) R +/- 9 degrees terminations, with 3D clusters of copper observed on the reconstructed surface. There is evidence of step-edge-dominated growth of palladium on the (root 31 x root 31) R +/- 9 degrees termination

Imaging reconstructed TiO2 surfaces with non-contact atomic force microscopy

Abstract We have used non-contact atomic force microscopy (NC-AFM) to study TiO2(110), identifying a row with twice the thickness of a TiO2(110)1×2 row. This can be explained by a [110] extension of the added row model of TiO2(110)1×2. In the [001] direction, this reconstruction narrows into a 1×2 row giving strong evidence that the two structures are very closely related. For the TiO2(100) surface, we present NC-AFM data which supports the intermediate 1×3-β model previously proposed on the basis of an STM experiment.

Non-contact atomic force microscopy imaging of TiO2(100) surfaces

Abstract Atomically resolved non-contact fm mode atomic force microscopy images have been obtained from TiO2(100) surfaces. The 1×1 surface is observed, as well as the 1×3 phase previously imaged with STM. The morphology of the latter reconstruction consists of (110) microfacets. An additional reconstruction with 1×3 symmetry is observed, which is assigned to a phase intermediate between the 1×1 and 1×3-microfacet terminations.

X-ray and electron beam modification of thiophene overlayers on TiO2(100)1 × 1 and 1 × 3

The effects of electron and X-ray beams on thiophene overlayers on TiO2(100) 1 × 1 and 1 × 3 surfaces have been investigated using AES, UPS and XPS. Mg Kα X-rays were found to polymerise a thiophene multilayer condensed at 120 K. The evidence points to a substrate-secondary-electron mediated process. A 3 keV electron beam also modifies a condensed thiophene overlayer, probably by polymerisation.

NEXAFS studies of the reaction of SO2 with TiO2(100)-(1 × 1) and -(1 × 3)

Abstract S K-edge NEXAFS has been used to monitor the thermally-activated reaction of SO2 with TiO2(100)-(1 × 3) and TiO2(100)-(1 × 1) in order to investigate the influence of surface structure and oxygen vacancies on the reactivity. In each case SO2 chemisorbs at 110 K, reacting further to form a sulphite-like intermediate species at higher temperatures (110–;400 K). This intermediate transforms to a sulphate-like species as the temperature is further increased (130–;500 K). The polarisation dependence of the NEXAFS for the sulphate-like species on both substrates at 130–;220 K evidences a lowering of the expected Td molecular symmetry. Overall, the data indicate that the mesoscopic morphology of the substrate has little influence on the adsorption site or reaction pathway for SO2. In addition, the only discernable effect of oxygen vacancies on the reaction is that 0.03 ML of sulphide is formed on TiO2(100)-(1 × 3) following SO2 exposure.

A non-contact atomic force microscopy and ‘force spectroscopy’ study of charging on oxide surfaces

Force spectroscopy curves from a number of oxide surfaces have been recorded. Contact potential difference (CPD) curves recorded from two different areas of an MgO(100) surface are shifted in a manner consistent with local surface charging. This charging is removed by deposition of Fe or Cu. On an NiAl(110) supported alumina film we have investigated the use of frequency shift (Δf) versus distance curves as an analytical tool for chemical identification. Curves recorded from the bare substrate are clearly different to those recorded over adsorbates. This difference is likely to be due to local surface charging, since such differences are not observed in detuning curves recorded from domain boundaries of similar apparent height to the adsorbates.

Photoemission studies of the reaction of benzene with TiO2(100)1×1 and 1×3

Abstract The adsorption and polymerisation of benzene on TiO 2 (100)1×1 and 1×3 surfaces has been investigated using AES, UPS and XPS. Benzene was found to adopt a tilted configuration on the 1×3 surface, and a near parallel orientation on the 1×1 surface at sub-monolayer coverages. Polymerisation is observed on benzene-dosed surfaces after X-ray irradiation. In addition, polymerisation or dissociation is also observed after exposure of the benzene overlayer to an electron beam.