F. Patthey

Fluorescence and Phosphorescence from Individual C60 Molecules Excited by Local Electron Tunneling

Using the highly localized current of electrons tunneling through a double barrier scanning tunneling microscope junction, we excite luminescence from a selected C60 molecule in the surface layer of fullerene nanocrystals grown on an ultrathin NaCl film on Au(111). In the observed fluorescence and phosphorescence spectra, pure electronic as well as vibronically induced transitions of an individual C60 molecule are identified, leading to unambiguous chemical recognition on the single-molecular scale.

Magnetic remanence in single atoms

Stable magnets from single atoms An important goal in molecular magnetism is to create a permanent magnet from a single atom. Metal atoms adsorbed on surfaces can develop strong magnetization in an applied field (paramagnetism). Donati et al. show that single holmium atoms adsorbed on a magnesium oxide film grown on a silver substrate show residual magnetism for temperatures up to 30 K and bistabilty that lasts for 1500 s at 10 K (see the Perspective by Khajetoorians and Heinrich). The atom avoids spin relaxation by a combination of quantum-state symmetry and by the oxide film preventing the spin from interacting with the underlying metal via tunneling. Science, this issue p. 318; see also p. 296 A single holmium atom on a magnesium oxide film can retain its magnetic moment up to 30 kelvin. [Also see Perspective by Khajetoorians and Heinrich] A permanent magnet retains a substantial fraction of its saturation magnetization in the absence of an external magnetic field. Realizing magnetic remanence in a single atom allows for storing and processing information in the smallest unit of matter. We show that individual holmium (Ho) atoms adsorbed on ultrathin MgO(100) layers on Ag(100) exhibit magnetic remanence up to a temperature of 30 kelvin and a relaxation time of 1500 seconds at 10 kelvin. This extraordinary stability is achieved by the realization of a symmetry-protected magnetic ground state and by decoupling the Ho spin from the underlying metal by a tunnel barrier.

Giant Hysteresis of Single-Molecule Magnets Adsorbed on a Nonmagnetic Insulator

TbPc2 single-molecule magnets adsorbed on a magnesium oxide tunnel barrier exhibit record magnetic remanence, record hysteresis opening, perfect out-of-plane alignment of the magnetic easy axes, and self-assembly into a well-ordered layer.

Two‐Dimensional Tiling by Rubrene Molecules Self‐Assembled in Supramolecular Pentagons, Hexagons, and Heptagons on a Au(111) Surface

Keywords: rubrene ; scanning probe microscopy ; self-assembly ; supramolecular chemistry ; Crystals ; Symmetry ; Graphite Reference EPFL-ARTICLE-161210doi:10.1002/anie.200704479View record in Web of Science Record created on 2010-11-30, modified on 2016-08-09

Plasmon enhanced luminescence from fullerene molecules excited by local electron tunneling

Tunneling electrons from a scanning tunneling microscope (STM) induce luminescence from C(60) and C(70) molecules forming fullerene nanocrystals grown on ultrathin NaCl films on Au(111). Intramolecular fluorescence and phosphorescence associated with the transitions between the lowest electronic excited state and ground state of C(70) molecules are identified, leading to unambiguous chemical recognition on the nanoscale. Moreover we demonstrate that the molecular luminescence is selectively enhanced by localized surface plasmons in the STM tip-sample gap.

Growth study of silver on Mgo(100)/Mo(100)

We report on ultra-high-vacuum depositions of thermally evaporated silver at different temperatures and coverages on a well-characterized thin magnesium oxide film, which is supported on a molybdenum single crystal. From electron energy loss (EELS, HREELS) and photoemission spectra (UPS, XPS), we propose a three-dimensional growth mode at room temperature. From temperature-dependent measurements between T=100 and 500 K, we deduce the sticking probability, S, for this system.

Coverage-dependent self-organization: from individual adatoms to adatom superlattices

The coverage-dependent self-organization of Ce-adatoms on a Ag(111) surface is studied by scanning tunnelling microscopy at temperatures ranging from 3.9 to 10 K. At a coverage of 0.03% of a Ce monolayer individual Ce-adatoms and Ce dimers are observed, the mutual interatomic distances of which are clearly related to multiples of the Fermi wavelength λF/2, reflecting surface-state-mediated electronic interactions. At a coverage of 0.2% the formation of chains and small islands with hexagonal structure prevails. At a coverage of 1% a hexagonal superlattice with a periodicity of 3.2 nm is observed. At a coverage of 2% the superlattice of Ce-adatoms is found to be compressed, showing an interatomic distance of 2.2 nm. At higher coverage the number of dimers increases considerably and the superlattice collapses into compact islands. An increase in the temperature towards about 10 K at a coverage of 1% also causes the collapse of the hexagonal Ce superlattice. These experimental findings are rationalized within the electron scattering model of Hyldgard and Persson, which specifically takes into account the electronic surface-state on Ag(111). The experimentally derived two-body interaction potential is able to account for the observed phenomena as a function of concentration and temperature.

Electronic-Structure of Supported Mass-Selected Transition-Metal Clusters - a Photoemission-Study

Note: Part B Reference LPS-ARTICLE-1992-001doi:10.1016/0039-6028(92)91400-6 Record created on 2007-06-20, modified on 2016-08-08

An ultrahigh vacuum sputter source for in situ deposition of size-selected clusters: Ag on graphite

The investigation of supported size-selected clusters by different surface science techniques requires stringent ultrahigh vacuum (UHV) conditions during cluster deposition especially at low temperatures. The existing high-energy sputter sources used for cluster production in general do not fulfil this demand. We therefore have developed, built and tested a new fully bakeable ultrahigh vacuum-compatible version of the cluster source CORDIS (Cold Reflex Discharge Ion Source). As a first application, we present ultraviolet photoemission spectra (UPS) of size-selected clusters generated by this new cluster source and deposited on highly oriented pyrolytic graphite (HOPG). We show evidence for cluster diffusion and island formation even down to low temperature (T = 70 K). These islands display a polycrystalline structure. After a short annealing, they are transformed into Ag films with (111) surface orientation.

Distinction of nuclear spin states with the scanning tunneling microscope.

We demonstrate rotational excitation spectroscopy with the scanning tunneling microscope for physisorbed H(2) and its isotopes HD and D(2). The observed excitation energies are very close to the gas phase values and show the expected scaling with the moment of inertia. Since these energies are characteristic for the molecular nuclear spin states we are able to identify the para and ortho species of hydrogen and deuterium, respectively. We thereby demonstrate nuclear spin sensitivity with unprecedented spatial resolution.