Showing papers on "Scanning tunneling spectroscopy published in 1990"
TL;DR: The transition from 2D to 3D growth of Ge on Si(001) has been investigated with scanning tunneling microscope and a metastable 3D cluster phase with well-defined structure and shape is found.
Abstract: The transition from 2D to 3D growth of Ge on Si(001) has been investigated with scanning tunneling microscopy. A metastable 3D cluster phase with well-defined structure and shape is found. The clusters have a {105} facet structure. Results suggest that these clusters define the kinetic path for formation of ``macroscopic'' Ge islands.
1,226 citations
TL;DR: Topographic STM images of the Cr(001) surface using a tungsten tip confirm the model of topological antiferromagnetism between ferromagnetic terraces separated by monatomic steps of 0.144 nm height.
Abstract: Vacuum tunneling of spin-polarized electrons from a ferromagnetic ${\mathrm{CrO}}_{2}$ tip into a Cr(001) single crystal has been observed by means of a scanning tunneling microscope (STM) operated in UHV. Topographic STM images of the Cr(001) surface using a tungsten tip confirm the model of topological antiferromagnetism between ferromagnetic terraces separated by monatomic steps of 0.144 nm height. With ${\mathrm{CrO}}_{2}$ tips, the measured step-height values alternate around the mean value of 0.144 nm due to an additional contribution from spin-polarized-electron tunneling.
466 citations
TL;DR: The rate of the elastic macroscopic quantum tunneling of the electric charge in a system of two small-area, normal, tunnel junctions in the Coulomb blockade regime is calculated.
Abstract: We calculate the rate of the elastic macroscopic quantum tunneling of the electric charge (q-MQT) in a system of two small-area, normal, tunnel junctions in the Coulomb blockade regime. Despite the fact that the intermediate electron state on the central electrode of the system during the tunneling is virtual, the rate of the q-MQT depends crucially on the character of real electron motion through this electrode. Typically this motion is diffusive, so that the tunneling rate is determined by the process of ``virtual diffusion'' of electrons on the time scale of the inverse Coulomb energy of the system, \ensuremath{\Elzxh}/${\mathit{E}}_{\mathit{C}}$.
393 citations
TL;DR: In this article, the authors used a scanning tunneling microscope to directly imaged n−alkane layers adsorbed at the liquid/graphite interface using a high degree of two-dimensional ordering.
Abstract: We have directly imaged n‐alkane layers adsorbed at the liquid/graphite interface using a scanning tunneling microscope. The layers possessed a high degree of two‐dimensional ordering. The adsorbate was observed to enhance the tunneling current, and the atomic structure of the images was dominated by features associated with the substrate. These systems are excellent vehicles for studies concerning the imaging mechanism of adsorbed organic layers because of their stability and simplicity.
340 citations
TL;DR: In this paper, the authors calculated the rate of light emission from a scanning tunneling microscope with an Ir tip probing a silver film and found a considerable enhancement of the spontaneous light emission compared with inverse-photo-emission experiments.
Abstract: We have calculated the rate of light emission from a scanning tunneling microscope with an Ir tip probing a silver film. We find a considerable enhancement of the rate of spontaneous light emission compared with, for example, inverse-photoemission experiments. This enhancement is the result of an amplification of the electromagnetic field in the area below the microscope tip due to a localized interface plasmon. One can estimate that one out of ${10}^{4}$ tunneling electrons will emit a photon. We also find that the experimentally observed maximum in the light emission as a function of bias voltage is directly related to the detailed behavior of tip-sample separation versus bias voltage.
257 citations
233 citations
IBM1
TL;DR: A theory of atomic resolution of scanning tunneling microscopy in terms of actual tip states, for example, d z 2 tip states on tungsten tips is presented, which shows clear contradiction to the resolution limits previously predicted.
Abstract: Scanning tunneling microscopy has repeatedly resolved individual atoms on a number of metal surfaces with atomic distances 2.5--3 \AA{}. This is in sharp contradiction to the resolution limits previously predicted, 6--9 \AA{}. We present a theory of such atomic resolution in terms of actual tip states, for example, ${\mathit{d}}_{\mathit{z}}^{2}$ tip states on tungsten tips. Quantitative interpretation of the observed images is obtained with no adjustable parameters. We predict that to achieve atomic resolution, the tip material should be either a d-band metal or certain semiconductor.
189 citations
TL;DR: An anomalously large periodicity has been observed in scanning tunneling microscope images of a (00.1) graphite sample as mentioned in this paper, which has hexagonal symmetry, a periodicity of 7.7±0.2 nm and is superimposed on the usual a=0.246 nm atomic spacing of graphite.
Abstract: An anomalously large periodicity has been observed in scanning tunneling microscope images of a (00.1) graphite sample. The unusual contrast has hexagonal symmetry, a periodicity of 7.7±0.2 nm and is superimposed on the usual a=0.246 nm atomic spacing of graphite. Current‐voltage curves recorded in the scanning tunneling spectroscopy mode from the region showing the superperiodicity exhibit slightly more metallic behavior than those from neighboring normal regions. One possible explanation for the observed periodicity is that it is a rotational moire pattern resulting from the overlap between a misoriented layer of graphite and the underlying graphite single crystal.
171 citations
TL;DR: At low temperature, evidence is found for macroscopic quantum tunneling of the electric charge (q-MQT) through the Coulomb energy barrier.
Abstract: The conductance of linear arrays of two and three normal-metal small tunnel junctions is studied for bias voltages V below the Coulomb-blockade threshold. At low temperature, we find evidence for macroscopic quantum tunneling of the electric charge (q-MQT) through the Coulomb energy barrier. For double junctions the tunneling rate scales as V 3 , and approximately as the product of the junction conductances, as predicted by the theory of inelastic q-MQT
113 citations
TL;DR: The scanning tunneling microscope has been used to image a reduced TiO2(110) surface in ultrahigh vacuum, demonstrating that atomic resolution imaging of an ionic, wide band gap (3.2 electron volts) semiconductor is possible.
Abstract: The scanning tunneling microscope has been used to image a reduced TiO(2)(110) surface in ultrahigh vacuum. Structural units with periodicities rangng from 21 to 3.4 angstroms have been clearly imaged, demonstrating that atomic resolution imaging of an ionic, wide band gap (3.2 electron volts) semiconductor is possible. The observed surface structures can be explained by a model involving ordered arrangements of two-dimensional defects known as crystallographic shear planes and indicate that the topography of nonstoichiometric oxide surfaces can be complex.
110 citations
TL;DR: In this article, the first observation of GaAs/AlGaAs compound multilayers and interfaces at atomic scale resolution using a scanning tunneling microscope was reported. And the atomic registry in the epitaxial layers and their interfaces was observed.
Abstract: We report the first observation of GaAs/AlGaAs compound multilayers and interfaces at atomic scale resolution. Using a scanning tunneling microscope, the atomic registry in the epitaxial layers and their interfaces was observed. The semiconductor band gaps and valence‐band offsets relative to the Fermi level are obtained via local spectroscopy in the GaAs and AlGaAs multilayers.
TL;DR: In this article, the invers problem is considered for the reconstruction of the real surface topography based on the corresponding STM image and the tip shape, using a simple, straightforward formalism.
Abstract: This letter critically discusses the topographical information obtained by scanning tunneling microscopy (STM) on surfaces with a mesoscopic roughness, i.e., in the range of some nm’s. In a foregoing publication [J. Appl. Phys. 67, 1156 (1990)], we already treated the evaluation of constant current images based on the knowledge of the real surface and the shape of the tunneling tip (‘‘tip shape limited resolution’’). Now we deal with the invers problem: the reconstruction of the real surface topography based on the corresponding STM image and the tip shape, using a simple, straightforward formalism.
TL;DR: In this article, a scanning tunneling microscope was used to directly deposit nanometer-scale structures into the input coil of a planar dc superconducting quantum interference device microsusceptometer.
Abstract: A scanning tunneling microscope has been used to directly deposit nanometer‐scale structures into the input coil of a planar dc superconducting quantum interference device microsusceptometer. Iron pentacarbonyl was used as the source gas for the deposits, yielding dots with diameters ranging from 10 to 30 nm and heights from 30 to 100 nm. Measurements on the particles at low temperatures show them to be magnetic and reveal macroscopic spin properties.
TL;DR: In this paper, a resonant tunneling model is proposed to explain the phenomenon of the graphite lattice being seen by STM without touching or disturbing the adsorbed molecules on it.
Abstract: Voltage‐dependent images of liquid crystals on graphite were observed in air by scanning tunneling microscopy (STM). Molecular rows of liquid crystals and the atomic pattern of the graphite substrate were imaged with high (above 1 V) and low (below 0.1 V) bias voltages, respectively. Patterns of molecules, grain boundaries, and distinguishable defects of the liquid crystal arrangement were reproduced even after imaging the substrate in the same area. This indicates that the graphite lattice can be seen by STM without touching or disturbing the adsorbed molecules on it. A resonant tunneling model is proposed to explain the phenomenon.
TL;DR: In this paper, the (001) surface of a highly doped n-type TiO sub 2 crystal was imaged in air with a Pt-Ir tip with a scanning tunneling microscope (STM).
Abstract: The (001) surface of a highly doped ({approximately} 10{sup 19} cm{sup {minus}3}) n-type TiO{sub 2} crystal, following polishing, wet etching, and cleaning, was imaged in air with a Pt-Ir tip with a scanning tunneling microscope (STM). Good images of the surface could be obtained with the sample held at negative voltage (positive tip bias), with the high-resolution image showing only Ti atoms. Tunneling spectroscopy, involving the recording of i-V curves and dynamic conductance (di/dV)-V curves with the tip held over a given spot on the TiO{sub 2} surface, was also carried out. The resulting curves show electron tunneling into the conduction band and from the valence band, as well as a prominent peak identified as a surface state about 0.3 eV below the conduction band edge.
TL;DR: A small, atomically varying signal of 3--5 mV is observed on both metal and semiconductor samples and demonstrated to arise not from variation in photovoltage but from spatial variations in rectification efficiency.
Abstract: Surface bias voltages induced on a scanning-tunneling-microscope junction illuminated with laser radiation are spatially measured for both metal and semiconductor samples. A surface photovoltage of \ensuremath{\sim}0.3 eV is observed for Si(111)-(7\ifmmode\times\else\texttimes\fi{}7), with large reductions in the vicinity of surface (subsurface) defects having midgap states. These reductions, attributed to a change in the recombination rate, have a typical surface screening distance of 15--25 \AA{}. A small, atomically varying signal of 3--5 mV is observed on both metal and semiconductor samples and demonstrated to arise not from variation in photovoltage but from spatial variations in rectification efficiency.
TL;DR: The dependence of the oscillations observed in scanning tunneling microscopy of the tunneling conductance with applied bias voltage on the tip's curvature and the interface potential has been studied in this article.
TL;DR: In this paper, nonresonant carrier tunneling is investigated by time-resolved and time-averaged optical methods for a series of samples with various barrier thicknesses.
Abstract: Nonresonant carrier tunneling is investigated by time‐resolved and time‐averaged optical methods for a series of samples with various barrier thicknesses. The electron tunneling times decrease exponentially with the decrease of barrier thickness from 8 to 3 nm, and the trend is well described by a semiclassical model. Additional efficient hole tunneling is observed in the 3 nm barrier sample, and the time constant is of the order of 50 ps.
TL;DR: Tunneling spectroscopy of Au(100) and Fe(5×20) surfaces has been studied in this paper, using a well-defined tunneling tip, I−S, I-V, and V/I*dI/dV-V spectra were obtained.
Abstract: Tunneling spectroscopy of Au(100)‐(5×20) and Fe on Au(100) surfaces has been studied. Using a well‐defined tunneling tip, I–S, I–V, and V/I*dI/dV–V spectra were obtained. The results confirm that the characteristics of the spectra resemble those of previously reported semiconductors. From I–S relations, it was found that the tunneling barrier decreases abruptly when the tunneling gap is <6 A.
Abstract: A remarkably stable microscopic tunnel junction can be made with two crossed wires separated by a monolayer of adsorbed molecules. Inelastic tunneling peaks of hydrocarbons are clearly resolved. A wide Coulomb blockade of single-electron tunneling is observed, indicating that stray capacitance does not influence the microscopic junction.
TL;DR: In this paper, Williams and Wickramasinghe measured thermopower on the atomic scale by using different tip and sample temperatures in a scanning tunneling microscope (STM) with different tip temperatures.
Abstract: Recently Williams and Wickramasinghe (1990a) have measured thermopower on the atomic scale by using different tip and sample temperatures in a scanning tunneling microscope (STM).
TL;DR: A novel approach to measure rotational tunneling in condensed phases using high-resolution optical spectroscopic methods to unravel the tunneling level structure and to measure the rate of the nuclear-spin conversion.
Abstract: We report a novel approach to measure rotational tunneling in condensed phases. High-resolution optical spectroscopic methods are used to unravel the tunneling level structure and to measure the rate of the nuclear-spin conversion. The method is demonstrated in experiments on the rotational motion of methyl groups in a crystal of durene doped with di-methyl-s-tetrazine but it can readily be transposed to other tunneling systems.
TL;DR: In this paper, the structural and electronic effects of lead substitution in high-temperature superconducting materials PbxBi2-xSr2CaCu2O8 have been characterized by scanning tunneling microscopy (STM).
Abstract: The structural and electronic effects of lead substitution in the high-temperature superconducting materials PbxBi2-xSr2CaCu2O8 have been characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Large-area STM images of the Bi(Pb)—O layers show that lead substitution distorts and disorders the one-dimensional superlattice found in these materials. Atomic-resolution images indicate that extra oxygen atoms are present in the Bi(Pb)—O layers. STS data show that the electronic structure of the Bi(Pb)—O layers is insensitive to lead substitution within ±0.5 electron volt of the Fermi level; however, a systematic decrease in the density of states is observed at ≈1 electron volt above the Fermi level. Because the superconducting transition temperatures are independent of x(Pb) (x ≤ 0.7), these microscopic STM and STS data suggest that the lead-induced electronic and structural changes in the Bi(Pb)—O layer do not perturb the electronic states critical to forming the superconducting state in this system.
TL;DR: In this paper, tunneling microscopy measurements of the influence of externally applied stress in Si(001) showed that strain modifies the relative areas of the p(2×1) and p(1×2) domains, in agreement with low energy electron diffraction (LEED) results.
Abstract: Scanning tunneling microscopy measurements of the influence of externally applied stress in Si(001) show that strain modifies the relative areas of the p(2×1) and p(1×2) domains, in agreement with low‐energy electron diffraction (LEED) results. Strain produces a striped phase of majority and minority domains. The total repeat length between domains of the same type, given by the vicinal miscut of the surface, is conserved.
IBM1
TL;DR: In this article, the authors used tunneling microscopy and spectroscopy for the detection of trapped molecules of copper phthalocyanine (CuPc) and liquid crystals on graphite.
Abstract: Adsorbed molecules of copper phthalocyanine (CuPc) and liquid crystals on graphite were measured by scanning tunneling microscopy (STM) and spectroscopy (STS) in air. The islands of molecules of CuPc were detected by STM. Tunneling spectra taken simultaneously with STM showed characteristic peaks correlated with local topographic features. In the observation of a nematic liquid crystal on graphite, one reproducible molecular pattern was found, for which a model of molecular ordering is proposed. Ordinary spectroscopy was found to be difficult due to a large polarization current caused by the liquid surrounding the tip. Bias voltage dependent images of the molecules which demonstrate electronic structure effects were obtained.
TL;DR: Quantum percolation theory explains anomalies in Raman-scattering and tunneling data which indicate intrinsic states below the energy gap of Y-Ba-Cu-O that are compatible with the observed linear temperature dependence of the planar resistivity.
Abstract: Quantum percolation theory explains anomalies in Raman-scattering and tunneling data which indicate intrinsic states below the energy gap of Y-Ba-Cu-O. Separation of these states into localized and extended components shows that the tunneling and Raman-scattering data are compatible with the observed linear temperature dependence of the planar resistivity.
TL;DR: In this article, it was shown that a scanning tunneling microscope with a magnetic tip gives us the possibility to determine the spin directions of surface magnetic ions with atomic resolution, but the tip should not necessarily be a ferromagnet.