Search results for "scanning tunneling microscope"
showing 10 items of 127 documents
Optical Near-Field Properties of Lithographically Designed Metallic Nanoparticles
1999
ABSTRACTWe report on the experimental observation of localized surface plasmons sustained by small metallic particles using a photon scanning tunneling microscope (PSTM). The surface plasmons are excited in gold nanostructures tailored by electron beam lithography. The constant height operation of the PSTM allowed a direct comparison with theoretical computations of the distribution of the optical near-field intensity. Plasmon coupling above a chain of Au particles and electromagnetic energy transfer from a resonantly excited nanoparticle to a nanowire are demonstrated. Our experimental results appear to be in good agreement with theoretical computations based on the Green's Dyadic Techniqu…
Electrical excitation of surface plasmons
2011
We exploit a plasmon mediated two-step momentum down-conversion scheme to convert low-energy tunneling electrons into propagating photons. Surface plasmon polaritons (SPPs) propagating along an extended gold nanowire are excited on one end by low-energy electron tunneling and are then converted to free-propagating photons at the other end. The separation of excitation and outcoupling proves that tunneling electrons excite gap plasmons that subsequently couple to propagating plasmons. Our work shows that electron tunneling provides a nonoptical, voltage-controlled, and low-energy pathway for launching SPPs in nanostructures, such as plasmonic waveguides.
Spin scattering and spin-polarized hybrid interface states at a metal-organic interface
2011
Spin scattering at the interface formed between metallic Fe and Cu-phthalocyanine molecules is investigated by spin-polarized scanning tunneling spectroscopy and spin-resolved photoemission. The results are interpreted using first-principles electronic structure theory. The combination of experimental and theoretical techniques allows us to shed light on the role of hybrid interface states for the spin scattering. We show that Cu-phthalocyanine acts, via hybrid interface states, as a local spin filter up to room temperature both below and above the Fermi energy, ${E}_{\mathrm{F}}$. At the same time, the molecule behaves as a featureless scattering barrier in a region of about 1 eV around ${…
Electrodynamics in complex systems
1996
This paper discusses recent theoretical efforts to develop a general and flexible method for the calculation of the field distributions around and inside complex optical systems involving both dielectric and metallic materials. Starting from the usual light-matter coupling Hamiltonian, we derive a self-consistent equation for the optical field in arbitrary optical systems composed of N different subdomains. We show that an appropriate solving procedure based on the real-space discretization of each subdomain raises the present approach to the rank of an accurate predictive numerical scheme. In order to illustrate its applicability, we use this formalism to address challenging problems relat…
Analysis of photon-scanning tunneling microscope images of inhomogeneous samples: determination of the local refractive index of channel waveguides
1995
Channel waveguides are imaged by a photon-scanning tunneling microscope (PSTM). The polarization of the light and its orientation with respect to the guide axis are shown to be very important parameters in the analysis of the images of such samples. We simulated image formation for the plane of incidence parallel to the axis of the guide. Our theoretical results are qualitatively in agreement with our measurements. These results show the ability of the PSTM to give information about the local refractive-index variations of a sample.
Disorder and localization effects on the local spectroscopic and infrared optical properties ofGa1−xMnxAs
2015
We study numerically the influence of disorder and localization effects on the local spectroscopic characteristics and infrared optical properties of ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{As}$. We treat the band structure and disorder effects at an equal level by using an exact diagonalization supercell simulation method. This method accurately describes the low-doping limit and gives a clear picture of the transition to higher dopings, which captures the localization effects inaccessible to other theoretical methods commonly used. Our simulations capture the rich in-gap localized states observed in scanning tunneling microscopy studies and reproduce the observed features of t…
Detection of the optical magnetic field by circular symmetry plasmons
2000
We report on the influence of coating a sharpened optical fiber tip with Au when observing nanofabricated dielectric structures with a Photon Scanning Tunneling Microscope (PSTM) in constant-height mode. For well-defined incident wavelengths and coating thicknesses, we found that such tips detect the distribution of the magnetic field associated with the optical wave in the near-field zone. A simple tip model indicates that this phenomenon is related to the excitation of circular symmetry plasmons in Au coated tips.
Simultaneous observation of light localization and confinement in near-field optics
2001
We report on the observation, in direct space, of both light localization and confinement effects near lithographically designed structures. The sample is observed in the optical near-field zone with a Photon Scanning Tunneling Microscope (PSTM). Several patterns composed of a few periods of TiO2 dots, arranged as a hexagonal lattice, have been investigated. When the central dot of the pattern is removed, a phenomenon of light localization above the vacancy can be observed in the PSTM image. The occurrence of this phenomenon can be related to the variation of the electromagnetic local density of state.
Imaging of test quartz gratings with a photon scanning tunneling microscope Experiment and theory
1995
We use the differential formalism of the electromagnetic theory of gratings to interpret the images of test sinusoidal or lamellar quartz gratings obtained with a photon scanning tunneling microscope. The period of the grating is 0.5 μm, and the height of the rule is 0.2 μm. It is shown that the images depend strongly on several parameters, such as polarization or angle of incidence, with respect to the ruling direction. A systematic study of the isointensity lines above the gratings as a function of polarization is presented, and it is shown that the image contrast can be increased or decreased depending on the sample–probe distance. To model the interaction of the fiber probe with the ele…
Electronic and mechanical characterization of self-assembled alkanethiol monolayers by scanning tunneling microscopy combined with interaction-force-…
1993
We have used scanning tunneling microscopy to study self-assembled monolayers of mercaptohexadecanol in ultrigh vacuum. In addition to tunneling, the interaction force gradient acting between tip and sample was measured. Analysis of the force-gradient data shows that the tip is in mechanical contact with the surface of the monolayer which, in turn, is elastically compressed. The lateral dimensions of the mechanical contact are substantially (approximately five times) larger than the width of the tunneling-current filament. The results suggest that the compression of the monolayer constitutes an integral part of tunneling through the molecules