Showing papers on "Scanning tunneling spectroscopy published in 1992"
IBM1
TL;DR: A coherent-state path-integral calculation shows that quantum tunneling of magnetization direction is spin-parity dependent, and that this topological effect results from interference between tunneling paths.
Abstract: Within a wide class of ferromagnetic and antiferromagnetic systems, quantum tunneling of magnetization direction is spin-parity dependent: it vanishes for magnetic particles with half-integer spin, but is allowed for integer spin. A coherent-state path-integral calculation shows that this topological effect results from interference between tunneling paths.
208 citations
TL;DR: In some spin tunneling problems there are several different but symmetry-related tunneling paths that connect the same initial and final configurations but the topological phase factors of the corresponding tunneling amplitudes can lead to destructive interference between the different paths, so that the total tunneling amplitude is zero.
Abstract: In some spin tunneling problems there are several different but symmetry-related tunneling paths that connect the same initial and final configurations The topological phase factors of the corresponding tunneling amplitudes can lead to destructive interference between the different paths, so that the total tunneling amplitude is zero In the study of tunneling between different ground-state configurations of the Kagom\'e-lattice quantum Heisenberg antiferromagnet, this occurs when the spin s is half odd integer
164 citations
TL;DR: The measured I-V characteristics show the magnetic field qualitatively alters the tunneling density of states, creating both a wide gap at the Fermi level and a much broader density of final states than is present at zero field.
Abstract: Tunneling between parallel two-dimensional electron gases in double quantum wells is examined at both zero and high perpendicular magnetic field. The measured I-V characteristics show the magnetic field qualitatively alters the tunneling density of states, creating both a wide gap at the Fermi level and a much broader density of final states than is present at zero field. We suggest the origin of these effects lies in the strong Coulomb correlations characteristic of Landau quantized two-dimensional systems.
148 citations
TL;DR: In this paper, an experimental study of charge transport in nanometer-scale double-barrier resonant-tunneling devices was performed, where asymmetric heterostructure material was used so that one barrier is substantially less transparent than the other.
Abstract: We report a systematic experimental study of charge transport in nanometer-scale double-barrier resonant-tunneling devices. Asymmetric heterostructure material was used so that one barrier is substantially less transparent than the other. Resonant tunneling through size-quantized well states and single-electron charging of the well are thus largely separated in the two bias polarities. When the emitter barrier is more transparent than the collector barrier, electrons accumulate in the well; incremental electron occupation of the well, starting from zero, is accompanied by Coulomb blockade, which leads to sharp steps of the tunneling current. The voltage extent of the steps is affected by the intrawell electron-electron interaction. When the emitter barrier is less transparent, the current reflects resonant tunneling of just one electron at a time through size-quantized well states; the current peaks and/or steps (depending on experimental parameters) appear in current-voltage characteristics. Experimental results on magnetic field and temperature dependence of the current-voltage curves are also reported. Good agreement is achieved in comparison of many features of the experimental data with simple theoretical models.
110 citations
TL;DR: In this paper, the authors found that the ferromagnetic coupling between electrodes of the junction strongly modified the domain structures and magnetization reversal processes in the area of tunnel junction, and that the hysteresis of tunneling resistance was closely connected with magnetization processes.
99 citations
Journal Article•
97 citations
TL;DR: In this paper, the authors used the transfer Hamiltonian mechanism to determine the dependence of tunneling current on various system parameters like the bias voltage, the energy of reorganization, and electronic coupling of the redox centre to the tip and the substrate.
87 citations
TL;DR: In this paper, the surface structure of reduced TiO2−x(110) has been studied in ultrahigh-vacuum by scanning tunneling microscopy and tunneling spectroscopy.
79 citations
IBM1
TL;DR: In this article, the scanning tunneling microscope is used to image GaAs pn-doping superlattices, cleaved in ultrahigh vacuum, and currentvoltage measurements provide a detailed view of the variation in Fermi-level position across the super-lattice.
Abstract: The scanning tunneling microscope is used to image GaAs pn‐doping superlattices, cleaved in ultrahigh vacuum. Current‐voltage (I‐V) measurements provide a detailed view of the variation in Fermi‐level position across the superlattice. The I‐V curves show the clear signature of nondepleted n‐ and p‐type material, with depleted regions appearing at the interfaces between n‐ and p‐type layers. The number of states available for tunneling is found to provide the major source of contrast in the images.
76 citations
TL;DR: In this article, high-resolution images reveal a modulation in the topography of individual arsenic dimers measured with the tunneling microscope in the constant current mode, attributed to an increased tunneling probability out of the occupied electronic lone pair states of the As dimers.
Abstract: Scanning tunneling microscopy and scanning tunneling spectroscopy have been used to investigate the structure and current–voltage [I(V)] characteristics of the molecular‐beam epitaxially grown, As‐rich GaAs(001)‐(2×4) surface. High‐resolution images reveal a modulation in the topography of the individual arsenic dimers measured with the tunneling microscope in the constant current mode. The observed features are attributed to an increased tunneling probability out of the occupied electronic lone pair states of the As dimers. The I(V) spectroscopy performed on the (001) surface of low doped n‐type GaAs samples differs considerably from the results obtained on the (110) surface of this semiconductor. This is attributed to band bending that is due to a lower doping concentration below the surface. The electrostatics involved in imaging with a tunneling microscope are described in a simple model, based on the depletion approximation, that accounts for the experimental results.
01 Jan 1992
TL;DR: In this article, it is shown that any process that is not forbidden by fundamental symmetries should take place, although the rate of some Processes can be small. But it is well known from the high-energy physics that the most basic property of quantum mechanical particles is that they always can find the way around the lower-level restrictions.
Abstract: As it is well known from the high-energy physics, the most basic property of quantum mechanical particles is that they obey only fundamental symmetries, and always can find the way around the lower-level restrictions. It means that any process that is not forbidden by fundamental symmetries should take place, although the rate of some Processes can be small.
TL;DR: In this paper, the surface acceptors of the (2×4)/c(2×8) surface were investigated by spatially resolved tunneling spectroscopy, showing that negative charge is located at the kink sites.
Abstract: The compensating defects on the GaAs(001)‐(2×4)/c(2×8) surface that are induced by Si doping have been studied by spatially resolved tunneling spectroscopy. Previous scanning tunneling microscopy studies have shown that as the Si doping level of molecular‐beam epitaxially grown GaAs is increased, an increasing number of kinks form in the dimer‐vacancy rows of the (2×4)/c(2×8) surface reconstruction. These kinks are believed to act as surface acceptors and result in pinning of the surface Fermi level. In this work, both voltage dependent imaging and spectroscopy show that negative charge is located at the kink sites. This confirms that they are surface acceptors. The spectroscopy is consistent with each acceptor being occupied by one electron. The surface Fermi level is found to be pinned near midgap. While no peak in the state density centered on the Fermi level is observed, gap states in the form of tails extending in from the band edges are observed near some kinks.
TL;DR: In this article, a cross-sectional surface of Si(100) prepared by an ex situ cleave HF-dip technique is used to investigate the tunneling properties of the surface.
Abstract: Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are used to investigate a cross‐sectional surface of Si(100) prepared by an ex situ cleave HF‐dip technique. The agreement between the measured current–voltage spectra (I/Vs) and those calculated with an unpinned surface for both n‐ and p‐type bulk surfaces is good, thus indicating that the prepared surface is unpinned and the model is valid. Both the experimental and calculated I/Vs show three components of current: tunneling out of valence‐band states (VB), tunneling through dopant states (D), and tunneling into conduction‐band states (CB). As demonstrated by experiment, in agreement with the model, the shape of the I/Vs allows the discrimination of n‐type from p‐type surfaces. Furthermore, the model indicates that by measuring the dopant state current D‐component STM/STS is sensitive to the carrier density within the range of 1018–1021 cm−3. This suggests that this ex situ cleave sample preparation can be used to produce unpi...
TL;DR: In this article, the effect of reduction on the topographic and electronic structure of TiO2(110) surfaces was investigated in ultra-high vacuum using scanning tunneling microscopy (STM), in conjunction with conventional surface analytical techniques.
TL;DR: In this article, a spin-polarized scanning tunneling microscope (STM) was used for low energy electron diffraction on magnetite in air and in ultra high vacuum.
Abstract: Solutions to the main problems in operating a spin‐polarized scanning tunneling microscope are discussed. Preliminary experimental results obtained in the course of implementing these solutions are reported. Atomic resolution on Si(111) and Si(100) is achieved with a scanning tunneling microscope (STM) using chromium and iron tips. Fabrication of antiferromagnetic tips of Cr, MnNi, and MnPt is described. A technique of preparation of clean (100) surfaces of Fe3O4 (magnetite) is given. Low‐energy electron diffraction patterns were obtained on Fe3O4 for the first time. The first STM experimental results obtained on magnetite in air and in ultrahigh vacuum are reported. Atomic resolution is obtained on Fe3O4 (100) with an ultrahigh vacuum scanning tunneling microscope using iron and tungsten tips. This is the first successful observation of atomic resolution on a ferromagnetic sample using a ferromagnetic tip.
TL;DR: In this paper, the incorporation of an AlAs/GaAs resonant tunneling structure inside a GaAs pn junction leads to strong quantum-well electroluminescence originating from electron and hole tunneling into the resonance structure.
Abstract: The incorporation of an AlAs/GaAs resonant tunneling structure inside a GaAs p‐n junction leads to strong quantum‐well electroluminescence originating from electron and hole tunneling into the resonant tunneling structure. A large peak‐to‐valley ratio of 10:1 in the electroluminescence intensity is achieved at the electron resonance at 4.2 K, which decreases but persists (1.45:1) at room temperature. Resonant tunneling of holes is also apparent from the electroluminescence at low temperature.
TL;DR: In this paper, the authors discuss the tunneling characteristics of an anisotropic metal using the marginal-Fermi liquid phenomenology, and show that tunneling matrix elements lead to a conductance typically V-shaped for c-axis tunneling, and almost Aat for in-plane tunneling.
Abstract: We discuss the tunneling characteristics expected within an anisotropic metal using the marginal-Fermi-liquid phenomenology. Although there is no modification of the density of states, we show it to be natural that tunneling matrix elements lead to an anisotropic conductance, which is typically V-shaped for c-axis tunneling, and almost Aat for in-plane tunneling. We suggest that this behavior is directly related to the observation of resistive upturns in the c-axis conductivity of disordered samples
TL;DR: In this article, the authors used scanning tunneling spectroscopy (STS) to determine the band structure of polypyrrole films, which were electropolymerized onto a highly oriented pyrolytic graphite surface using a rotating disk electrode.
Abstract: Scanning tunneling spectroscopy (STS) has been used to determine the band structure of polypyrrole. The polypyrrole films were electropolymerized onto a highly oriented pyrolytic graphite surface using a rotating disk electrode. Differential conductance spectra measurements allowed us to follow the evolution of the band gap as a function of doping level. Before and after the STS measurements, the film structure was imaged by scanning tunneling microscopy. The STS results agree with data obtained by inverse photoemission spectroscopy
TL;DR: Photon emission from gold surfaces stimulated by electron tunneling under application of scanning tunneling microscopy has been detected in air and a correlation between the light emitted and the topographic features could be observed.
Abstract: Photon emission from gold surfaces stimulated by electron tunneling under application of scanning tunneling microscopy has been detected in air. At low voltages, a correlation between the light emitted and the topographic features could be observed. The influence of various parameters on the light emission has been investigated. As a secondary phenomenon, the light emission was observed to decay in an irreversible way, at high voltages (2 V).
TL;DR: In this paper, a scanning tunneling microscope (STM) was applied to a DC bias voltage an RF voltage at a frequency f of about 300 MHz, and observed the frequency components of the tip current at the second (2 f ) and third harmonic (3 f ) of the fundamental frequency f.
TL;DR: In this article, atomic force microscope and scanning tunneling microscope images of photoluminescent anodically etched porous silicon are presented and the development of the porous structure due to different etching stages is investigated.
Abstract: Atomic force microscope and scanning tunneling microscope images of photoluminescent anodically etched porous silicon are presented and the development of the porous structure due to different etching stages is investigated. These measurements show that the vertical surface roughness increases with etching while the lateral dimensions remain almost constant, in agreement with known etching models. In addition, the results give strong evidence for an amorphous surface layer that partially covers the porous structure. Tunneling spectroscopy of porous silicon and unetched silicon are also presented. The surface density of states (DOS) measurements of porous silicon are compared with its photoluminescence spectrum. The DOS measurements do not show a peak corresponding to the 1.8 eV photoluminescent peak energy nor do they show an increase in the band gap energy of porous silicon compared with crystalline silicon. However, these measurements do show that while the unetched silicon surface remains p type, the p...
TL;DR: In this paper, the Coulomb gap and Coulomb staircase were found at room temperature, in good agreement with the semi-classical theory of single-electron tunneling.
Abstract: Ultrasmall (5 nm in lateral diameter) double-barrier tunnel junctions have been realized using metal particles (2-5 nm in diameter) sandwiched in between a metallic substrate and the metallic tip of a scanning tunneling microscope (STM). The particles were either grown by e-beam evaporation or prepared using colloid chemistry. Two electrical transport effects, in good agreement with the semi-classical theory of single-electron tunneling, have been found at room temperature: the Coulomb gap and the Coulomb staircase. The interpretation in terms of single-electron tunneling is further supported by liquid helium temperature STM measurements on identical samples.
TL;DR: The shot noise and I-V characteristics of multilevel resonant-tunneling systems are investigated in a stochastic description including strong time correlation derived from the Pauli exclusion of tunneling electrons.
Abstract: The shot noise and I-V characteristics of multilevel resonant-tunneling systems are investigated in a stochastic description including strong time correlation derived from the Pauli exclusion of tunneling electrons. In the first resonance regime, one tunneling electron occupying a quantum-well quasibound state blocks one channel for the follow-up electrons. This correlation suppresses the shot noise. In the second (and higher) resonance regime, the tunneling electrons in the quantum well, when experiencing strong inelastic scatterings, fall immediately to occupy the low-lying off-resonance subband states and thus do not block the tunneling channels of others. There the noise power density may approach the full shot-noise level and the tunneling current can be enhanced.
IBM1
TL;DR: In this article, light emission from Cu(111) and Au(110) surfaces in the scanning tunneling microscope has been characterized, and fluorescence spectra are interpreted as arising from inelastic tunneling excitation of radiative tip-induced plasmon modes.
TL;DR: In this article, the I-V curves were calculated using the free electron and the WKB approximation, and the curves showed a characteristics change when the adsorbate has the highest occupied molecular orbital or the lowest unoccupied molecular orbital near the Fermi level.
TL;DR: A method for simulating scanning tunneling microscopy and spectroscopy at realistic tip-to-surface distances of 5-10 A is proposed, and its application is reported for Si(100) reconstructed surfaces.
Abstract: A method for simulating scanning tunneling microscopy (STM) and spectroscopy (STS) is proposed, which is effective at realistic tip-to-surface distances of 5--10 \AA{}, and its application is reported for Si(100) reconstructed surfaces. The vacuum tails of wave functions cannot be accurately described either by linear combination of atomic orbitals or by pure plane-wave expansion. An attempt is made to effectively describe the tail parts by combining this method with realistic calculations of the sample surface electronic states. The method is applied to Si(100) reconstructed surfaces and the features of the STM images and STS spectra of 2\ifmmode\times\else\texttimes\fi{}1 dimer structures are clarified. This method confirms that the experimental c(4\ifmmode\times\else\texttimes\fi{}2) image of STM is actually obtained from the c(4\ifmmode\times\else\texttimes\fi{}2) structure and reveals how the buckling of dimers is reflected on the STM image.