Au nanoparticles on a templating TiOx/Pt(111) ultrathin polar film: a photoemission and photoelectron diffraction study

Abstract

We present an in-depth investigation of Au nanoparticles self-assembled on a zigzag-like TiO(x)/Pt(111) ultrathin polar film, whose structure is known in great detail. The peculiar pattern of defects (picoholes) templates a linear array of size-selected (ca. 1 nm) Au nanoparticles without disruption of the titania layer, as observed by scanning tunneling microscopy. Their structure and electronic properties have been investigated by several large-area spectroscopic tools, i.e. high-resolution core and valence level photoemission and angle-scanned and energy-scanned photoelectron diffraction. The comparison between experimental data and density functional theoretical calculations indicates that the Au atoms landing on the oxide film are rather mobile, and that the picoholes can act as effective trapping and nucleation centers for the growth of the Au nanoparticles. All the experimental results are in concord in indicating that the Au NPs are flat islands with a maximum thickness of 2-3 layers exposing the (111) surface.

Interaction of iron with a wagon wheel-like ultrathin TiOx film grown on Pt(111)

“…[12][13][14] In contrast, scanning tunneling microscopy (STM) studies of Pd on FeO/Pt(111) showed the wetting behavior of the metal, because of its strong interaction with the substrate. [12][13][14] In contrast, scanning tunneling microscopy (STM) studies of Pd on FeO/Pt(111) showed the wetting behavior of the metal, because of its strong interaction with the substrate.…”

Stability and chemisorption properties of ultrathin TiOx/Pt(111) films and Au/TiOx/Pt(111) model catalysts in reactive atmospheres

“…These play an active role as preferential nucleation sites for the growth of metal NPs (see below). 17,18 For the w 0 -TiO x film, having a stoichiometry close to that of the z 0 -TiO x phase, 22 the STM data do not show any evidence of ordered arrays of defects. 32 In the fully stoichiometric rect 0 -TiO 2 phase, 24 a Pt-O-Ti interface is formed, and, as a consequence of the weaker Pt-O interaction with respect to the Pt-Ti one, 33 a partial dewetting of the film occurs which drives the system toward the formation of flat and regularly shaped rect 0 -TiO 2 islands (with a minimum thickness of two bilayers), which progressively increase their lateral size and thickness as a function of the Ti coverage.…”

“…When an ordered array of point defects is present on the UT film, it can act as a template for a directed assembling process, eventually providing an ordered array of NPs. [10][11][12][13][14][15][16][17][18][19] However, the extrapolation of the properties obtained on such UHV model catalysts to realistic catalytic conditions is an operation which is not necessarily legitimate, and studies checking the validity over the so-called material and pressure gaps are certainly needed. 20 In recent years, some of us focused the attention on UT TiO x films deposited on a Pt(111) single crystal.…”

“…24 In addition, the structure and morphology of the Au/TiO x /Pt(111) model catalysts obtained after evaporation of Au in UHV conditions were investigated in depth by using scanning tunnelling microscopy (STM). 17,18,25 In particular, the capability of the z 0 -TiO x UT film to produce an ordered array of size-selected Au NPs as a consequence of the ordered defectivity (see below) has been demonstrated. 17,18 In this paper we want to address the stability of both the TiO x /Pt(111) UT films and Au/TiO x /Pt(111) model catalysts at high pressure (HP) (in the mbar range) by comparing X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED) and STM measurements carried out before and after the exposure to an elevated pressure of pure CO or a CO-O 2 (1 : 1) gas mixture (up to 100 mbar), so partially filling the pressure gap.…”

“…17,18,25 In particular, the capability of the z 0 -TiO x UT film to produce an ordered array of size-selected Au NPs as a consequence of the ordered defectivity (see below) has been demonstrated. 17,18 In this paper we want to address the stability of both the TiO x /Pt(111) UT films and Au/TiO x /Pt(111) model catalysts at high pressure (HP) (in the mbar range) by comparing X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED) and STM measurements carried out before and after the exposure to an elevated pressure of pure CO or a CO-O 2 (1 : 1) gas mixture (up to 100 mbar), so partially filling the pressure gap. In addition, we also analyse their chemisorption properties toward CO by in situ polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) during gas exposure.…”