Showing papers on "Scanning tunneling spectroscopy published in 2002"
TL;DR: In this article, the authors show that quasiparticle interference, due to elastic scattering between characteristic regions of momentum-space, provides a consistent explanation for the conductance modulations, without appeal to another order parameter.
Abstract: Scanning tunneling spectroscopy of the high-Tc superconductor Bi2Sr2CaCu2O8+delta reveals weak, incommensurate, spatial modulations in the tunneling conductance. Images of these energy-dependent modulations are Fourier analyzed to yield the dispersion of their wavevectors. Comparison of the dispersions with photoemission spectroscopy data indicates that quasiparticle interference, due to elastic scattering between characteristic regions of momentum-space, provides a consistent explanation for the conductance modulations, without appeal to another order parameter. These results refocus attention on quasiparticle scattering processes as potential explanations for other incommensurate phenomena in the cuprates. The momentum-resolved tunneling spectroscopy demonstrated here also provides a new technique with which to study quasiparticles in correlated materials.
497 citations
TL;DR: Detailed calculations using the InAlAs/InGaAs material system reveal that a splitting of a peak should be observed in the I-V curve of this device as a result of the spin-filtering effect.
Abstract: We propose an electronic spin-filter device that uses a nonmagnetic triple barrier resonant tunneling diode (TB-RTD). This device combines the spin-split resonant tunneling levels induced by the Rashba spin-orbit interaction and the spin blockade phenomena between two regions separated by the middle barrier in the TB-RTD. Detailed calculations using the InAlAs/InGaAs material system reveal that a splitting of a peak should be observed in the I-V curve of this device as a result of the spin-filtering effect. The filtering efficiency exceeds 99.9% at the peak positions in the I-V curve.
477 citations
TL;DR: In this article, a self-assembly pyrolytic route to large arrays of aligned n-type nanotubes (15-80 nm OD and <100 μm in length) is presented.
Abstract: Self-assembly pyrolytic routes to large arrays (<2.5 cm2) of aligned CNx nanotubes (15–80 nm OD and <100 μm in length) are presented. The method involves the thermolysis of ferrocene/melamine mixtures (5:95) at 900–1000 °C in the presence of Ar. Electron energy loss spectroscopy (EELS) reveals that the N content varies from 2–10%, and can be bonded to C in two different fashions (double-bonded and triple-bonded nitrogen). The electronic densities of states (DOS) of these CNx nanotubes, using scanning tunneling spectroscopy (STS), are presented. The doped nanotubes exhibit strong features in the conduction band close to the Fermi level (0.18 eV). Using tight-binding and ab initio calculations, we confirm that pyridine-like (double-bonded) N is responsible for introducing donor states close to the Fermi Level. These electron-rich structures are the first example of n-type nanotubes. Finally, it will be shown that moderate electron irradiation at 700–800 °C is capable of coalescing single-walled nanotubes (SWNTs). The process has also been studied using tight-binding molecular dynamics (TBMD). Vacancies induce the coalescence via a zipper-like mechanism, which has also been observed experimentally. These vacancies trigger the organization of atoms on the tube lattices within adjacent tubes. These results pave the way to the fabrication of nanotube heterojunctions, robust composites, contacts, nanocircuits and strong 3D composites using N-doped tubes as well as SWNTs.
405 citations
TL;DR: The study of the anisotropic superconductor MgB2 using a combination of scanning tunneling microscopy and spectroscopy reveals two distinct energy gaps with both gaps vanishing at the bulk T(c) with the data confirming the importance of Fermi-surface sheet dependent superconductivity proposed in the multigap model.
Abstract: The study of the anisotropic superconductor MgB2 using a combination of scanning tunneling microscopy and spectroscopy reveals two distinct energy gaps at Delta(1)=2.3 meV and Delta(2)=7.1 meV at 4.2 K. Different spectral weights of the partial superconducting density of states are a reflection of different tunneling directions in this multiband system. Temperature evolution of the tunneling spectra follows the BCS scenario [Phys. Rev. Lett. 3, 552 (1959)]] with both gaps vanishing at the bulk T(c). The data confirm the importance of Fermi-surface sheet dependent superconductivity in MgB2 proposed in the multigap model by Liu et al. [Phys. Rev. Lett. 87, 087005 (2001)]].
282 citations
TL;DR: The scaling of the Kondo temperature T(K) with the host electron density at the magnetic impurity is demonstrated and it is revealed that at the Cu(100) surface both tunneling into the hybridized localized state and into the substrate conduction band contribute to theKondo resonance.
Abstract: The Kondo resonance of Co adatoms on the Cu(100) and Cu(111) surfaces has been studied by scanning tunneling spectroscopy. We demonstrate the scaling of the Kondo temperature ${T}_{\mathrm{K}}$ with the host electron density at the magnetic impurity. The quantitative analysis of the tunneling spectra reveals that the Kondo resonance is dominated by the Cu bulk electrons. While at the Cu(100) surface both tunneling into the hybridized localized state and into the substrate conduction band contribute to the Kondo resonance, the latter channel is found to be dominant for Cu(111).
257 citations
TL;DR: This study demonstrates how the atomic arrangement of a nontrivial incommensurate surface can be solved by molecular dynamics in a case where experimental techniques alone give no solution.
Abstract: The oxidation of Pd(111) leads to an incommensurate surface oxide, which was studied by the use of scanning tunneling microscopy, surface x-ray diffraction, high resolution core level spectroscopy, and density functional calculations. A combination of these methods reveals a two-dimensional structure having no resemblance to bulk oxides of Pd. Our study also demonstrates how the atomic arrangement of a nontrivial incommensurate surface can be solved by molecular dynamics in a case where experimental techniques alone give no solution.
251 citations
TL;DR: Scanning tunneling spectroscopy imaging of the vortex lattice in single crystalline MgB2 suggests that superconductivity in the pi band is, at least partially, induced by the intrinsically superconducting sigma band.
Abstract: We report scanning tunneling spectroscopy imaging of the vortex lattice in single crystalline ${\mathrm{M}\mathrm{g}\mathrm{B}}_{2}$. By tunneling parallel to the $c$ axis, a single superconducting gap ($\ensuremath{\Delta}=2.2\text{ }\text{ }\mathrm{m}\mathrm{e}\mathrm{V}$) associated with the $\ensuremath{\pi}$ band is observed. The vortices in the $\ensuremath{\pi}$ band have a large core size compared to estimates based on ${H}_{c2}$ and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. These results suggest that superconductivity in the $\ensuremath{\pi}$ band is, at least partially, induced by the intrinsically superconducting $\ensuremath{\sigma}$ band.
212 citations
TL;DR: In this paper, the (0, 0, 1) surface atomic structure of Nb-doped SrTiO3 single crystals which were annealed in ultra high vacuum was investigated using scanning tunneling microscopy (STM).
200 citations
TL;DR: Both optical and tunneling spectra show that the level structure depends primarily on the diameter of the rod and not its length, and with increasing diameter, the band gap and the excited state level spacings shift to the red.
Abstract: Photoluminescence excitation spectroscopy and scanning-tunneling spectroscopy are used to study the electronic states in CdSe quantum rods that manifest a transition from a zero-dimensional to a one-dimensional quantum-confined structure. Both optical and tunneling spectra show that the level structure depends primarily on the diameter of the rod and not its length. With increasing diameter, the band gap and the excited state level spacings shift to the red. The level structure was assigned using a multiband effective-mass model, showing a similar dependence on rod dimensions.
199 citations
TL;DR: A review of light-induced effects in tunneling microscopy can be found in this article, where the authors discuss thermal effects, nonlinear effects, field enhancement at the STM tip, various effects on semiconductor surfaces, excitation of surface plasmons, detection of photoelectrons, spin-polarized tunneling, local optical spectroscopy, the use of ultrashort laser pulses for time-resolved STM, and the combination of STM and scanning near-field optical microscopy.
Abstract: The combination of scanning tunneling microscopy (STM) with optical excitation adds new information to STM. A review is presented covering the work done on light-induced effects in STM during the past 15 years. Effects discussed include thermal effects, nonlinear effects, field enhancement at the STM tip, various effects on semiconductor surfaces, excitation of surface plasmons, detection of photoelectrons, spin-polarized tunneling, as well as light-induced nanomodifications, local optical spectroscopy, the use of ultrashort laser pulses for time-resolved STM, and the combination of STM and scanning near-field optical microscopy.
197 citations
TL;DR: By combining the spatial resolution of a scanning-tunneling microscope (STM) with the electronic spin sensitivity of electron-spin resonance, it is possible to detect the presence of localized spins on surfaces as mentioned in this paper.
Abstract: By combining the spatial resolution of a scanning-tunneling microscope (STM) with the electronic spin sensitivity of electron-spin resonance, we show that it is possible to detect the presence of localized spins on surfaces The principle is that a STM is operated in a magnetic field, and the resulting component of the tunnel current at the Larmor (precession) frequency is measured This component is nonzero whenever there is tunneling into or out of a paramagnetic entity We have succeeded in obtaining spectra from free radical molecules from which the g factor of a spin entity may be inferred For the molecules studied here, α,γ-bisdiphenylene-β-phenylallyl, g was found to be 2±01
TL;DR: In this article, a controlled chemical reaction of single trans-2-butene molecules on the Pd(110) surface was realized by dosing tunneling electrons from the tip of a scanning tunneling microscope at 4.7 K. The reaction product was identified as a 1,3-butadiene molecule by inelastic electron tunneling spectroscopy.
Abstract: Controlled chemical reaction of single trans-2-butene molecules on the Pd(110) surface was realized by dosing tunneling electrons from the tip of a scanning tunneling microscope at 4.7 K. The reaction product was identified as a 1,3-butadiene molecule by inelastic electron tunneling spectroscopy. Threshold voltage for the reaction is $\ensuremath{\sim}365\text{ }\mathrm{m}\mathrm{V}$, which coincides with the vibrational excitation of the C-H stretching mode. The reaction was ascertained to be caused by C-H bond dissociation by multiple vibrational excitations of the C-H stretching mode via inelastic electron tunneling process.
TL;DR: Low temperature spin-polarized scanning tunneling microscopy of two monolayers Fe on W(110) using tungsten tips coated with different magnetic materials resolves the problem of the disturbing influence of a ferromagnetic tip in the investigation of soft magnetic materials and superparamagnetic particles.
Abstract: We have performed low temperature spin-polarized scanning tunneling microscopy (SP-STM) of two monolayers Fe on W(110) using tungsten tips coated with different magnetic materials. We observe stripe domains with a magnetic period of 50 +/- 5 nm. Employing Cr as a coating material we recorded SP-STM images with an antiferromagnetic probe tip. The advantage of its vanishing dipole field is most apparent in external magnetic fields. This new approach resolves the problem of the disturbing influence of a ferromagnetic tip in the investigation of soft magnetic materials and superparamagnetic particles.
TL;DR: This report describes synthesis and characterization of a molecular diode based upon a diblock conjugated oligomer system that exhibits a built-in electronic asymmetry, much like a semiconductor p-n junction.
Abstract: This report describes synthesis and characterization of a molecular diode based upon a diblock conjugated oligomer system. This system consists of two conjugated blocks with opposite electronic demand. The molecular structure exhibits a built-in electronic asymmetry, much like a semiconductor p−n junction. Electrical measurements by scanning tunneling spectroscopy (STS) clearly revealed a pronounced rectifying effect. Definitive proof for the molecular nature of the rectifying effect in this conjugated diblock molecule is provided by control experiments with a structurally similar reference compound.
01 Jan 2002
TL;DR: In this article, a simulation of STM images and STS Spectra of carbon nanotubes using an Arc Discharge is presented, along with an analysis of the effect of defects and polyhedral caps.
Abstract: Part I: Morphology, Characterization, and Formation of Nanotubes Filling Carbon Nanotubes Using an Arc Discharge A Loiseau, et al Simulation of STM Images and STS Spectra of Carbon Nanotubes Ph Lambin, et al Applications Research on Vapor-Grown Carbon Fibers GG Tibbetts, et al The Growth of Carbon and Boron Nitride Nanotubes: A Quantum Molecular Dynamics Study J-C Charlier, et al Nanoscopic Hybrid Materials: The Synthesis, Structure and Properties of Peapods, Cats and Kin DE Luzzi, BW Smith Linear Augmented Cylindrical Wave Method for Nanotubes: Band Structure of [Cu@C20] PN D'yachkov, OM Kepp Comparative Study of a Coiled Carbon Nanotube by Atomic Force Microscopy and Scanning Electron Microscopy and Scanning Electron Microscopy P Simonis, et al Investigation of the Deformation of Carbon Nanotube Composites Through the Use of Raman Spectroscopy CA Cooper, RJ Young Electronic States, Conductance and Localization in Carbon Nanotubes with Defects T Kostyrko, et al Physics of the Metal-Carbon Nanotube Interfaces: Charge Transfers, Fermi-Level `Pinning' and Application to the Scanning Tunneling Spectroscopy Y Xue, S Datta Single Particle Transport Through Carbon Nanotube Wires: Effect of Defects and Polyhedral Cap MP Anantram, TR Govindan Carbon Nanotubes from Oxide Solid Solution: A Way to Composite Powders, Composite Materials and Isolated Nanotubes C Laurent, et al Impulse Heating an Intercalated Compound Using a 2712 MHz A (Part contents)
TL;DR: Thin films of La0.7Sr0.3MnO3 on MgO show a metal insulator transition and colossal magnetoresistance that can be explained by intrinsic spatial inhomogeneities and undergo a percolation transition.
Abstract: Thin films of ${\mathrm{L}\mathrm{a}}_{0.7}{\mathrm{S}\mathrm{r}}_{0.3}{\mathrm{M}\mathrm{n}\mathrm{O}}_{3}$ on MgO show a metal insulator transition and colossal magnetoresistance. The shape of this transition can be explained by intrinsic spatial inhomogeneities, which give rise to a domain structure of conducting and insulating domains at the submicrometer scale. These domains then undergo a percolation transition. The tunneling conductance and tunneling gap measured by scanning tunneling spectroscopy were used to distinguish and visualize these domains.
TL;DR: In this article, the adsorption of C60 molecules on a Au(111) surface by using scanning tunneling microscopy and spectroscopy at room temperature was studied.
Abstract: We have performed a careful study of the adsorption of C60 molecules on a Au(111) surface by using scanning tunneling microscopy and spectroscopy at room temperature In coincidence with results from other techniques, differential conductance spectra give a value of 23 eV for the HOMO–LUMO gap of a monomolecular layer, with the LUMO level located at 06 eV above the Fermi level as a consequence of electronic charge transfer from the substrate into the molecule Small differences in position (and shape) of the LUMO-derived resonance, in the order of 01 eV, are found on molecules adsorbed at step edges We consider the Smoluchowski effect, ie, the interaction of the molecules with a charge-depleted region, to explain the observed differences in their bonding nature On some molecules forming part of bidimensional fullerene islands, similar differences were also detected with spatially resolved scanning tunneling spectroscopy, giving rise to a 2×2 commensurate structure of the molecular adlayer with resp
TL;DR: In this article, the local interfacial electronics between multiwalled carbon nanotubes and several supporting substrates has been investigated by utilizing the current transients in scanning tunneling spectroscopy, and a systematic variation in this local potential, as a function of tube diameter, is observed for both metallic and semimetallic substrates.
Abstract: By utilizing the current transients in scanning tunneling spectroscopy, the local interfacial electronics between multiwalled carbon nanotubes and several supporting substrates has been investigated. Voltage offsets in the tunneling spectra are directly correlated with the formation of a dipole layer at the nanotube-substrate interface, strongly suggesting the formation of interface states. Further, a systematic variation in this local potential, as a function of tube diameter, is observed for both metallic substrates (Au) and semimetallic substrates (graphite). In both cases, for tubes with diameters between \ensuremath{\sim}5 nm and 30 nm, the interfacial potential is nearly constant as a function of tube diameter. However, for tube diameters 5 nm, a dramatic change in the local potential is observed. Using ab initio techniques, this diameter-dependent electronic interaction is shown to derive from changes in the tube-substrate hybridization that results from the curvature of the nanotubes.
TL;DR: In this paper, the authors consider the form of the currentvoltage curves generated when tunneling spectroscopy is used to measure the energies of individual electronic energy levels in nanometer-scale systems.
Abstract: We consider the form of the current-voltage curves generated when tunneling spectroscopy is used to measure the energies of individual electronic energy levels in nanometer-scale systems. We point out that the voltage positions of the tunneling resonances can undergo temperature-dependent shifts, leading to errors in spectroscopic measurements that are proportional to the temperature. We do this by solving the set of rate equations that can be used to describe electron tunneling via discrete quantum states, for a number of cases important for comparison to experiments, including (1) when just one spin-degenerate level is accessible for transport, (2) when two spin-degenerate levels are accessible, with no variation in electron-electron interactions between eigenstates, and (3) when two spin-degenerate levels are accessible, but with variations in electron-electron interactions. We also comment on the general case with an arbitrary number of accessible levels. In each case we analyze the voltage positions, amplitudes, and widths of the current steps due to the quantum states.
TL;DR: The total decay rate is obtained which is valid over the entire range of temperatures and reduces to the appropriate results for the classical thermal activation at high temperatures, the thermally assisted tunneling at intermediate temperatures, and the pure quantum tunneling in optical lattices under gravity at low temperatures.
Abstract: We investigate the quantum tunneling of Bose-Einstein condensates in optical lattices under gravity in the "Wannier-Stark localization" regime and "Landau-Zener tunneling" regime. Our results agree with experimental data [B. P. Anderson et al., Science 282, 1686 (1998); F. S. Cataliotti et al., Science 293, 843 (2001)]. We obtain the total decay rate which is valid over the entire range of temperatures, and show how it reduces to the appropriate results for the classical thermal activation at high temperatures, the thermally assisted tunneling at intermediate temperatures, and the pure quantum tunneling at low temperatures. We design an experimental protocol to observe this new phenomenon in further experiments.
TL;DR: In this paper, the spin-parity effect of magnetization tunneling has been investigated and it is shown that the tunnel splitting is suppressed at zero transverse field if the total spin of the magnetic system is half-integer (Kramer degeneracy) but is allowed in integer spin systems.
Abstract: Single-molecule magnets facilitate the study of quantum tunneling of magnetization at the mesoscopic level. The spin-parity effect is among the fundamental predictions that have yet to be clearly observed. It is predicted that quantum tunneling is suppressed at zero transverse field if the total spin of the magnetic system is half-integer (Kramers degeneracy) but is allowed in integer spin systems. The Landau-Zener method is used to measure the tunnel splitting as a function of transverse field. Spin-parity dependent tunneling is established by comparing the transverse field dependence of the tunnel splitting of integer and half-integer spin systems.
TL;DR: Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained in the measurements of light tunneling through individual subwavelength pinholes in a gold film covered with a layer of polydiacetylene.
Abstract: Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained in the measurements of light tunneling through individual subwavelength pinholes in a gold film covered with a layer of polydiacetylene. The transmission of some pinholes reached saturation because of the optical nonlinearity of polydiacetylene at a very low light intensity of a few thousand photons per second. This result is explained theoretically in terms of a "photon blockade," similar to the Coulomb blockade phenomenon observed in single-electron tunneling experiments. Single-photon tunneling may find applications in the fields of quantum communication and information processing.
TL;DR: Water adsorbed in submonolayer coverage on Ag(111) at 70 K forms hydrogen-bonded networks and scanning tunneling spectroscopy indicates that the bond length within the two-dimensional hydrogen- bonded water layer is shortened.
Abstract: Water adsorbed in submonolayer coverage on Ag(111) at 70 K forms hydrogen-bonded networks. High resolution images in combination with calculation reveal that single protrusions represent a cyclic water hexamer with the intermolecular bond stretched to the silver lattice constant of 0.29 nm. Scanning tunneling spectroscopy indicates that the bond length within the two-dimensional hydrogen-bonded water layer is shortened. The spectra contain further information about the vibrational modes of water molecules.
TL;DR: Scanning tunneling spectroscopy of thin Fe films on W(110) shows that the electronic structure of domains and domain walls is different, and nanometer-scale magnetic structure information is obtained even by using nonmagnetic probe tips.
Abstract: Scanning tunneling spectroscopy (STS) of thin Fe films on W(110) shows that the electronic structure of domains and domain walls is different. This experimental result is explained on the basis of first-principles calculations. A detailed analysis reveals that the spin-orbit induced mixing between minority ${d}_{xy+xz}$ and minority ${d}_{{z}^{2}}$ spin states depends on the magnetization direction and changes the local density of states in the vacuum detectable by STS. As a consequence nanometer-scale magnetic structure information is obtained even by using nonmagnetic probe tips.
TL;DR: Linear Au chains two to 20 atoms long were constructed on a NiAl(110) surface via the manipulation of single atoms with a scanning tunneling microscope to reveal one-dimensional electronic density oscillations at energies 1.0 to 2.5 eV above the Fermi energy.
Abstract: Linear Au chains two to 20 atoms long were constructed on a NiAl(110) surface via the manipulation of single atoms with a scanning tunneling microscope. Differential conductance ($dI/dV$) images of these chains reveal one-dimensional electronic density oscillations at energies 1.0 to 2.5 eV above the Fermi energy. The origin of this delocalized electronic structure is traced to the existence of an electronic resonance measured on single, isolated Au atoms. Variations in the wavelength in $dI/dV$ images of an eleven-atom chain taken at different energies revealed an effective electronic mass of $0.4\ifmmode\pm\else\textpm\fi{}0.1$ times the mass of a free-electron.
TL;DR: In this article, a tight-binding model of single-wall carbon nanotubes with curvature-modified hopping parameter was presented, from which an analytical relation of band gaps to both chirality and diameter was derived by developing a transfer matrix method.
Abstract: We present a tight-binding model of single-wall carbon nanotubes with curvature-modified hopping parameter ${\ensuremath{\gamma}}_{i},$ from which an analytical relation of band gaps to both chirality and diameter is derived by developing a transfer matrix method. The results are in agreement with the experimental results obtained from scanning tunneling microscopy and scanning tunneling spectroscopy measurements by three groups.
TL;DR: Scanning tunneling spectroscopy measurements of the CuO chain plane in YBa(2)Cu(3)O(6+x) show an approximately 25 meV gap in the local density of states (LDOS) filled by numerous intragap resonances: intense peaks in LDOS spectra associated with one-dimensional, Friedel-like oscillations.
Abstract: We present scanning tunneling spectroscopy measurements of the CuO chain plane in YBa2Cu3O6+x, showing a similar to25 meV gap in the local density of states (LDOS) filled by numerous intragap resonances: intense peaks in LDOS spectra associated with one-d
TL;DR: In this paper, the structure and the electronic properties of a series of CH3 and CF3-terminated alkanethiol monolayers on Au(1 1 1) have been studied by scanning tunneling microscopy (STM) and surface X-ray and helium scattering.
TL;DR: In this article, a simple tight-binding model was proposed to explain the geometry of the defect states in the tunneling spectroscopy images of a single-input single-output (SISO) device.
Abstract: Scanning tunneling spectroscopy images of ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ doped with excess Bi reveal electronic defect states with a striking shape resembling clover leaves. With a simple tight-binding model, we show that the geometry of the defect states in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ can be directly related to the position of the originating impurities. Only the Bi defects at the Se sites five atomic layers below the surface are experimentally observed. We show that this effect can be explained by the interplay of defect and surface electronic structure.