Adsorption of Au and Pd over bilayer SiO₂/Ru has been investigated using scanning-probe microscopy, X-ray photoemission spectroscopy (XPS), and density functional theory (DFT). Low temperature (∼5 K) atomic force (AFM) and scanning tunneling microscopy (STM) measurements reveal the presence of small adsorption features after exposing the samples to small doses of either metal. In the case of Pd, we note a homogeneous distribution of adsorbates across the entire surface, which consists of both amorphous and crystalline phases. Au, however, adsorbs only over amorphous areas and domain boundaries, which possess larger pores than can be found in the ordered portions of the film. DFT calculations reveal that this difference is rooted in the pore-size-dependent barriers for diffusion of the two metals into the film, where they can then bind stably at the Ru interface. Auger parameter analysis of the Pd 3d and Au 4f core-levels from atoms binding in this manner show upward orbital-energy shifts, which, according to the results of theoretical calculations, originate from effects similar to those causing surface core-level-shifts for such metals. Further analysis of the computational results shows that such atoms donate electron density to the Ru support, which is consistent with XPS results that show band-bending effects related to decreases in the work-function of the sample after adsorbing either metal. Additional features in the XPS studies suggest that a secondary binding mechanism, mediated by cluster formation over the SiO₂ film, becomes increasingly favorable as temperature and loading increase

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Real space image data of two-dimensional amorphous networks have become available in high resolution. We review a number of systems regarding ring size distribution, pair correlation function and characteristic structural clusters. We present similarities and differences that can help identify general descriptors for amorphousness.

Auger parameter ( α) measurements have been employed to determine the extent to which initial-and final-state effects govern surface core-level shifts in x-ray photoelectron spectroscopy (XPS) measurements of Pd atoms confined between a bilayer SiO 2 film and its Ru(0001) support. For atoms bound in this manner, we note negative binding energy shifts ( BEs) of ß0.3 eV, relative to the Pd 3d peak position in the bulk, and attribute these shifts to large variations in the initial-state orbital energies of the supported atoms (ß1.1 eV towards E F ), coupled with decreased final-state relaxation contributions (ß0.8 eV). Theoretical calculations reveal that, despite small partial positive charges and decreased final-state screening, the decreased 4d-5sp hybridization of the undercoordinated Pd atoms results in large enough upward 3d orbital-energy shifts to yield the net-negative BE noted by XPS.

We present a local spectroscopy study of thin MgO films on Mo(001), investigated with a combined noncontact atomic force microscope (nc-AFM) and scanning tunneling microscope (STM). The work function of Mo(001) and MgO/Mo(001) was measured with field emission resonance (FER) spectroscopy. The work function of the clean Mo(001) surface Φ_Mo was determined to be 4.5 eV. After the deposition of an 8 atomic layer thick MgO film, it decreased to Φ_MgO/Mo = 3.2 eV (ΔΦFER = −1.3 eV). This work function shift ΔΦ_FER, introduced by the oxide film on the metal work function, was also investigated with contact potential difference (CPD) measurements. Here, a lowering of the work function by ΔΦ_CPD = −1.1 eV was measured. Furthermore, the influence of line defects, present in the MgO film, on the local work function was investigated and compared to pristine terrace sites of the oxide film. Here, we measured a slightly higher local work function of +200 meV above line defects as compared to pristine oxide terrace sites