Time-correlations as a contrast mechanism in scanning-tunneling-microscopy-induced photon emission

We have developed an experimental technique based on scanning-tunneling microscope (STM) which permits to record simultaneously topography, STM-induced photon emission and a map of two-photon auto-correlations for time resolutions down to the sub-nanosecond range. In the case of a gold surface at air, we show that the tip-induced luminescence exhibits a photon-bunching phenomenon at a 10-ns time scale which depends both on bias and on local topography. The photon bunching was exclusively observed at specific bumps of the surface.     

A Magnetic Resonance Investigation of the Process of Corundum Formation Starting from Sol–Gel Precursors

²⁷Al–MAS (magic angle spinning)–NMR and Fe³⁺ EPR measurements have been performed to follow the local process of corundum formation starting from xerogel on the Al³⁺ and Fe³⁺ sites yielding complementary information. Different heat treatments have been applied to the samples: an isochronous procedure and thermoanalytical measurements stopped by quenching. Despite the different mechanisms of the phase transitions deduced, both seeding and Fe³⁺ doping under the conditions of isochronous procedure favor the formation of α-Al₂O₃ at remarkably low temperatures. The first observed temperature of corundum formation following the isochronous procedure with iron-doped samples is as low as 750°C. The transition alumina, which could be clearly evidenced, is the γ-Al₂O₃ phase (four- and six-fold Al coordination). In undoped or unseeded samples, intermediate Fe species could be detected by ESR and evidence for θ-Al₂O₃ was obtained from ²⁷Al–NMR spectroscopy.     

Nanochemistry at the atomic scale revealed in hydrogen-induced semiconductor surface metallization

Passivation of semiconductor surfaces against chemical attack can be achieved by terminating the surface-dangling bonds with a monovalent atom such as hydrogen. Such passivation invariably leads to the removal of all surface states in the bandgap, and thus to the termination of non-metallic surfaces. Here we report the first observation of semiconductor surface metallization induced by atomic hydrogen. This result, established by using photo-electron and photo-absorption spectroscopies and scanning tunnelling techniques, is achieved on a Si-terminated cubic silicon carbide (SiC) surface. It results from competition between hydrogen termination of surface-dangling bonds and hydrogen-generated steric hindrance below the surface. Understanding the ingredient for hydrogen-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides a means to develop electrical contacts on high-bandgap chemically passive materials, particularly for interfacing with biological systems, and gives control of surfaces for lubrication, for example of nanomechanical devices.     

Controlled surface ordering of endohedral fullerenes with a SrTiO(3) template

The ability to select the way in which atoms and molecules self-organize on a surface is important for synthesizing nanometre scale devices. Here we show how endohedral fullerenes (Er(3)N@C(80)) can be assembled into four distinctive arrangements on a strontium titanate surface template. Each template pattern correlates to a particular reconstruction on n-doped SrTiO(3)(001), made in whole or in part by self-assembled arrays of non-stoichiometric oxide nanostructures. Close-packed assemblies of Er(3)N@C(80) molecules are formed, as well as one-dimensional chains and two-dimensional grids. This method of template-assisted molecular ordering provides a new platform for the development of experimental schemes of classical and quantum information processing at the molecular level.     

Moiré pattern induced by the electronic coupling between 1-octanol self-assembled monolayers and graphite surface

Two-dimensional self-assembly of 1-octanol molecules on a graphite surface is investigated using scanning tunneling microscopy (STM) at the solid/liquid interface. STM images reveal that this molecule self-assembles into a compact hydrogen-bonded herringbone nanoarchitecture. Molecules are preferentially arranged in a head-to-head and tail-to-tail fashion. A Moiré pattern appears in the STM images when the 1-octanol layer is covering the graphite surface. The large Moiré stripes are perpendicular to the 1-octanol lamellae. Interpretation of the STM images suggests that the Moiré periodicity is governed by the electronic properties of the graphite surface and the 1-octanol layer periodicity.