Reactive deposition of NiO ultrathin films on Pd(100)

NiO ultrathin films have been grown on Pd(100) following a reactive deposition procedure. Ni has been dosed at room temperature on the substrate surface in an oxygen partial pressure of 4 · 10-6 mbar. The electronic and structural evolution of the resulting NiO(100) ultrathin films has been followed by means of X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD), low energy electron diffraction (LEED), and scanning tunnelling microscopy (STM). XPS, XPD and STM data indicate a 2D growth of the first NiO monolayer, while further growth leads to the nucleation of 3D islands, in a Stranski–Krastanov growth scheme. Combined XPD and LEED data indicate an initially pseudomorphic growth, characterised by in-plane compressive tetragonal strain of the NiO film, with a consequent out-of-plane interlayer expansion. Partial strain relaxation occurs abruptly, very likely between the second and the third atomic layer of the 3D islands, while a completely bulk-like cubic environment is reached only gradually as a function of thickness. NiO(100) films even ca 50 equivalent monolayers thick can be grown with good long-range order, as shown by (1 · 1) LEED images

STM study of the initial stages of C60 adsorption on the Pt(1 1 0)-(1 2) surface.

International audienceWe have studied the initial stages of adsorption of C60 on the Pt (1 1 0)-(1 2) surface by means of STM. At room temperature, fullerene molecules adsorb in the troughs between two adjacent Pt rows of the missing row reconstruction. Mobility over the terraces is negligible, denoting strong bonding with the surface, also testified by a well-defined orientation of fullerene monomers with respect to the substrate. Upon annealing at 750 K, molecular migration towards kinks and step edges occurs, where small islands nucleation begins. A commensurate registry with the substrate is maintained by small (5–10 molecules) C60 aggregates, leading to expanded nearest-neighbour distances with respect to those found in hexagonal close packed fullerene ad-islands grown on other metallic substrates

STM study of the initial stages of C60 adsorption on the Pt(1 1 0)-(1 7 2) surface

We have studied the initial stages of adsorption of C60 on the Pt (1 1 0)-(1 7 2) surface by means of STM. At room temperature, fullerene molecules adsorb in the troughs between two adjacent Pt rows of the missing row reconstruction. Mobility over the terraces is negligible, denoting strong bonding with the surface, also testified by a well-defined orientation of fullerene monomers with respect to the substrate. Upon annealing at 750 K, molecular migration towards kinks and step edges occurs, where small islands nucleation begins. A commensurate registry with the substrate is maintained by small (5\u201310 molecules) C60 aggregates, leading to expanded nearest-neighbour distances with respect to those found in hexagonal close packed fullerene ad-islands grown on other metallic substrates

Bottom-up Assembly of Single-Domain Titania Nanosheets on (1x2)-Pt(110)

A bottom-up route towards the synthesis of titania nanosheets is explored, alternative to the exfoliation of layered titanates. Nanosheets are assembled from the constituent elements and epitaxially matched to a suitable substrate: (1x2)-Pt110. Their basic lepidocrocite structure is modulated at the nanoscale due to coincidence with the substrate. Density functional calculations reveal the structure details of the nanosheet, which is also shown to be in close relationship with a (001)-oriented anatase bilayer

Temperature-Dependent Self-Assemblies of C60 on (1X2)- Pt(110): A STM/DFT Investigation

Thermal self-assembly of C60 on (1 7 2)-Pt(110) following room-temperature deposition has been studied by means of scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density functional theory (DFT) calculations. Two distinct C60 chemisorption phases have been identified and characterized as a function of the annealing temperature. After a thermal treatment at 700 K, islands of a C60 quasi-hexagonal lattice form. These islands are characterized by the highest surface density so far reported for a two-dimensional surface-supported fullerene phase (the surface area per molecule is 87.0 \uc52), with intermolecular nearest-neighbor distances equal to 9.6 \ub1 0.1 \uc5. Embedded nanowires of fullerene dumbbell dimers (with an intermolecular distance equal to 9.2 \ub1 0.1 \uc5) occasionally nucleate within this high-density phase following a \u201cmolecular zip\u201d mechanism. Highly site selective chemisorption driven by the particularly strong overlayer 12substrate bonding is proposed to be responsible for the first reported example of surface-templated chemical bond formation between fullerene molecules. After annealing at 850 K, an oblique C60 chemisorption phase forms. This is characterized by a tetramolecular basis associated to each lattice point of the two-dimensional superstructure and by a peculiar bright 12dim contrast in STM images acquired at positive sample bias values. The combination of high- resolution STM images with LEED data and DFT calculations leads to the conclusion that the (1 7 2) substrate reconstruction is lifted at the fullerene 12platinum interface and also provides a detailed description of the molecular bonding sites and orientations found within the phase. It is proposed that the main factor ruling the interconversion of chemisorption phases is the variation of substrate atom mobility as a function of temperature

Ultrathin TiO2 Films on (1x2)-Pt(110): a LEED, Photoemission, STM, and Theoretical Investigation

The preparation and characterization of fully oxidized TiO2 ultrathin films obtained by reactive deposition of Ti in an O2 background on the (1 72)-Pt(110) reconstructed surface is described in details. The structure, the electronic properties, and the morphology of the epitaxial films giving rise to a (14 74) coincidence superstructure are discussed on the basis of low-energy electron diffraction, photoemission (both core and valence band), angle-scanned X-ray photoelectron diffraction, scanning tunneling microscopy data, and density functional theory calculations. We show that the oxide overlayer is a stoichiometric lepidocrocite-like single-domain nanosheet. This can be thought of as originating from a (100) oriented anatase bilayer which spontaneously restructure by a uniaxial relative sliding of one single layer with respect to the other by half a unit cell. According to the results of theoretical calculations, the process is self-driven by the spatial confinement, whereas a minor role is played by the interaction with the substrate. The occurrence of the (14 74) coincidence between the overlayer and the substrate is fully rationalized on the basis of the reported data

Reactive growth of NiO ultrathin films on Pd(100): a multitechnique approach

Reactivegrowth of NiO ultrathin films on Pd(1 0 0) has been performed by evaporating metallic Ni in an oxygen atmosphere. The evolution of the ultrathin film is followed by means of low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD) and scanning tunnelling microscopy (STM). The first monolayer (ML) of the deposited oxide develops as a completely wetting 2D overlayer with a c(4 7 2) periodicity, as shown by sharp LEED patterns and atomically resolved STM images. Further NiO deposition results in 3D NiO(1 0 0) islands formation on-top the c(4 7 2) superstructure, as shown by STM images and XPD data. Two layers thick islands are shown to be pseudomorphic to the substrate, i.e. characterised by in-plane compressive strain and interlayer expansion. LEED, XPD and STM give independent yet converging evidence that partial strain relaxation occurs within the third monolayer

Strong Bonding of Single C60 Molecules to (1 x 2)-Pt(110): An STM/DFT Investigation

The interaction of single C60 molecules with the (1 7 2)- Pt(110) surface has been studied by scanning tunneling microscopy and density functional theory (DFT) calculations on slab models. Molecules are observed to be frozen at room temperature and are found to be almost exclusively in the same configuration. Extensive DFT calculations show that this configuration is the global energy minimum, suggesting that adsorbed molecules have enough rototranslational freedom to escape from the numerous local minima. The adsorption energy (3.81 eV) is the strongest ever found for C60, and it is roughly proportional to the number of the Pt and C atoms at contact distance. Analysis of DFT results shows that the surface 12adsorbate interaction is covalent in nature. A minority fraction of C60 molecules appear to be adsorbed on surface defects. A careful investigation of their registry and height with respect to the regularly adsorbed units leads to an indirect structural characterization of the nanopits which act as their adsorption sites