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Register a new userMillikelvin LEED apparatus: a feasibility study
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A low-energy electron diffraction (LEED) apparatus which works at temperatures down to about 100 mK is designed to obtain structural information of 2D helium on graphite. This very low temperature system can be realized by reducing the thermal inflow from the LEED optics to the sample which is cooled by cryogen-free dilution refrigerator. The atomic scattering factor of He is also estimated using a kinematical model, which suggests that the diffraction signal from He atom can well be obtained by using a delay-line detector instead of a fluorescent screen.
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A new instrument for spot profile analysis of electron diffraction - SPA-LEED - has been set up. The instrument works either with a transparent phosphor screen for visual inspection of the pattern or in its main mode with a channeltron for the measurement of the intensity. The diffraction pattern is recorded with a fixed channeltron position by scanning the beam over the channeltron aperture using two sets of electrostatic deflection plates. The scanning range covers about 30{deg}. The intensity may vary over five orders of magnitude. The SPA-LEED system was checked with the Si 111 7 x 7 surface. A full width at half maximum of 0.3% of the normal reflex distance corresponding to a transfer width of 110 nm is reproducibly obtained. Under optimum conditions the transfer width rose up to about 200 nm. Initial high resolution measurements have been performed on the system Pb on Cu 111. The results demonstrate the possibilities of the new instrument for qualitative and quantitative analysis.
We present a comprehensive study of the adsorption behavior of iron phthalocyanine on the low-index crystal faces of silver. By combining measurements of the reciprocal space by means of photoelectron momentum mapping and low energy electron diffraction, the real space adsorption geometries are reconstructed. At monolayer coverage ordered superstructures exist on all studied surfaces containing one molecule in the unit cell in case of Ag(100) and Ag(111), and two molecules per unit cell for Ag(110). The azimuthal tilt angle of the molecules against the high symmetry directions of the substrate is derived from the photoelectron momentum maps. A comparative analysis of the momentum patterns on the substrates with different symmetry indicates that both constituents of the twofold degenerate FePc lowest unoccupied molecular orbital are occupied by charge transfer from the substrate at the interface.
Using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), scanning tunnelling microscopy (STM) and high resolution photo-electron spectroscopy (HR-PES) techniques we have studied the annealing effect of one silicon monolayer deposited at room temperature onto a Ni (111) substrate. The variations of the Si surface concentration, recorded by AES at 300{deg}C and 400{deg}C, show at the beginning a rapid Si decreasing followed by a slowing down up to a plateau equivalent to about 1/3 silicon monolayer. STM images and LEED patterns, both recorded at room temperature just after annealing, reveal the formation of an ordered hexagonal superstructure(rot3xrot3)R30{deg}-type. From these observations and from a quantitative analysis of HR-PES data, recorded before and after annealing, we propose that the (rot3 x rot3)R30{deg}superstructure corresponds to a two dimensional (2D) Ni2Si surface silicide.
Light Emitting Diodes emits no IR and no UV and their spectrum is fully in the visible part. But LEDs are not cold and all energy losses are thermal losses. The aim of this paper is to prove the feasibility to reuse the thermal losses to produce light through a thermoelectric module. Papers where Peltier modules are included in LEDs systems are all the time used for cooling [1-6]. At the knowledge of the authors, this the first time that thermal losses are used to increase the global efficiency of a high power LED lighting system by using Peltier modules to produce light.
The adsorption geometry of 1,3,5-tris(4-mercaptophenyl)benzene (TMB) on Cu(111) is determined with high precision using two independent methods, experimentally by quantitative low energy electron diffraction (LEED-I(V)) and theoretically by dispersion corrected density functional theory (DFT-vdW). Structural refinement using both methods consistently results in similar adsorption sites and geometries. Thereby a level of confidence is reached that allows deduction of subtle structural details such as molecular deformations or relaxations of copper substrate atoms.
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