1,721,054 research outputs found
Diffusive atom transport along step edges on Ag(111) at 295 K
No full textThe entropy-driven relaxation of a unique, non-equilibrium step edge configuration on the Ag(111) surface was observed using time-resolved STM imaging at room temperature. Using the Gibbs-Thomson relation, the relaxation process is quantitatively described as diffusive mass transport in terms of a gradient in the chemical potential along the monoatomic step edge. The STM data directly show that mass transport on Ag(111) is dominated by step edge diffusion at 295 K, and allow an estimate of the corresponding effective energy barrier. We obtain E-eff = 0.49 +/- 0.05 eV and compare this value with recent results on island diffusion studies. (C) 2003 Elsevier B.V. All rights reserved
Controlling the screening process of a nanoscaled space charge region by minority carriers
No full textThe miniaturization of future electronic devices is intimately connected to the ability to control electric fields on the atomic scale. In a nanoscopic system defined by a limited number of charges, the combined dynamics of bound and free charges become important. Here we present a model system based on the electrostatic interaction between a metallic tip of a scanning tunnelling microscope and a GaAs(110) semiconductor surface. The system is driven out of equilibrium by optical excitation, which provides ambipolar free charge carriers, and by an optically induced unipolar tunnel current. This combination enables the active control of the density and spatial distribution of free and bound charge in the space-charge region, that is, modifying the screening processes. Temporal fluctuations of single dopants are modified, meaning we are able to control the noise of the system. It is found that free charge carriers suppress the noise level in field-controlled, nanoscopic systems.[CRC1073]; [C4
Asymmetry of acceptor wave functions caused by surface-related strain and electric field in InAs
No full textThe spatial distribution of the local density of states at Mn acceptors near the (110) surface of p-doped InAs is investigated by scanning tunneling microscopy. The shapes of the acceptor contrasts for different dopant depths under the surface are analyzed. Acceptors located within the first ten subsurface layers of the semiconductor show a lower symmetry than expected from theoretical predictions for the bulk acceptor wave function. They exhibit a (001) mirror asymmetry. The degree of asymmetry depends on the acceptor atoms' depths. The measured contrasts for acceptors buried below the tenth subsurface layer closely match the theoretically derived shape. Two effects are able to cause the observed symmetry reduction, i.e., the strain field of the surface relaxation and the tip-induced electric field. While both effects induce similar asymmetries, a comparison of their relative strengths indicates that surface-related strain is the dominant effect for Mn in InAs
From time-resolved atomic-scale imaging of individual donors to their cooperative dynamics
No full textPulsed optical excitation in combination with scanning tunnel microscopy resolves charge dynamics at the gallium arsenide surface.</jats:p
Mapping Itinerant Electrons around Kondo Impurities
No full textWe investigate single Fe and Co atoms buried below a Cu(100) surface using low temperature scanning tunneling spectroscopy. By mapping the local density of states of the itinerant electrons at the surface, the Kondo resonance near the Fermi energy is analyzed. Probing bulk impurities in this well-defined scattering geometry allows separating the physics of the Kondo system and the measuring process. The line shape of the Kondo signature shows an oscillatory behavior as a function of depth of the impurity as well as a function of lateral distance. The oscillation period along the different directions reveals that the spectral function of the itinerant electrons is anisotropic.Deutsche Forschungsgemeinschaft [SFB 602
Fixing the Energy Scale in Scanning Tunneling Microscopy on Semiconductor Surfaces
Full text linkIn scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptor-related conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard model is used to rationalize our findings, capturing the crossover between the acceptor state being part of an impurity band for zero band bending and the acceptor state being split off and localized for strong negative or positive band bending, respectively
Mesoscopic scale study of lateral dynamics of Sn intercalation of the graphene buffer layer on SiC
No full texthttp://dx.doi.org/10.13039/501100001659 Deutsche Forschungsgemeinschaf
Magnetotransport on the nano scale
No full textAbstractTransport experiments in strong magnetic fields show a variety of fascinating phenomena like the quantum Hall effect, weak localization or the giant magnetoresistance. Often they originate from the atomic-scale structure inaccessible to macroscopic magnetotransport experiments. To connect spatial information with transport properties, various advanced scanning probe methods have been developed. Capable of ultimate spatial resolution, scanning tunnelling potentiometry has been used to determine the resistance of atomic-scale defects such as steps and interfaces. Here we combine this technique with magnetic fields and thus transfer magnetotransport experiments to the atomic scale. Monitoring the local voltage drop in epitaxial graphene, we show how the magnetic field controls the electric field components. We find that scattering processes at localized defects are independent of the strong magnetic field while monolayer and bilayer graphene sheets show a locally varying conductivity and charge carrier concentration differing from the macroscopic average.</jats:p
Monatomic steps on reconstructed
No full textThe interference pattern of surface state electrons which are
scattered from monatomic steps on the \chem{Au(111)} surface is
studied with Scanning Thermovoltage Microscopy at 80 kelvin. The
step contours are periodically modulated by the underlying
herringbone surface reconstruction and act like
a long-period diffraction grating. This leads to a characteristic
rhomb-shaped interference pattern in front of the step (Talbot
effect). A simulation of electron scattering from such steps
shows good agreement with our experiments and allows the
interpretation of earlier data in a new and consistent way. We
rule out the confinement of surface states due to the
reconstruction potential is responsible for the observed wave
pattern
Graphene-metal contact resistivity on semi-insulating 6H-SiC(0001) measured with Kelvin probe force microscopy
No full textWe present Kelvin probe force microscopy measurements and resistance network simulations of the lateral charge transport across few-layer graphene on the semi-insulating 6H-SiC(0001) surface. After preparation of the SiC crystal by thermal decomposition, gold electrodes were prepared on the top of the graphene layers. The transport field is extracted by subtracting measurements of reverse lateral bias applied to the gold electrodes. Graphene sheet resistances as low as 0: 75 k Omega/sq were observed. By comparing the experimental transport measurements with a resistance network simulation the contact resistivity between graphene and a gold electrode can be determined to be < 1 x 10(-6) Omega cm(2). (C) 2013 AIP Publishing LLC
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