Th. Schimmel

Surface plasmon polariton absorption modulator.

A new compact electrically controlled surface plasmon polariton (SPP) absorption modulator operating at communication wavelengths is introduced. The modulator is controlled by changing the free carrier density and thereby the propagation loss of the SPP.

DC-conductivity on a new type of highly conducting polyacetylene, N-(CH)x

Abstract We present precision conductivity measurements on a new type of stretch-aligned, iodine doped polyacetylene, yielding a room temperature conductivity σ of about 80 000 ω −1 cm −1 . The temperature dependence of σ was investigated between 3 K and 300 K parallel (σ | ) and perpendicular (σ⊥) to the stretching axis using both MONTGOMETRY- and standard four-probe techniques. For freshly prepared samples, the results indicate a common limiting mechanism for σ | and σ⊥ andare perfectly described by the SHENG model within the entire temperature range. Deliberate ag ing gives information about the influence of chemical defects on the conductivity mechanism.

Properties of Highly Conducting Polyacetylene

During the past 15 years, the synthesis and characterization of conducting polymers has attracted the attention of numerous groups of scientists /1/, stimulating a close cooperation of experimental and theoretical physicists, chemists, physico-chemists, materials research scientists and engineers.

Nanometer‐size surface modifications with preserved atomic order generated by voltage pulsing

We report on the generation of atomically resolved nanometer‐size surface modifications by applying voltage pulses at predefined locations on the surface of the layered semiconductor tungsten diselenide (WSe2). Time‐stable structures with diameters between 8 nm and less than 1 nm have been reproducibly written both in air and under vacuum. For small diameters, the resulting structures have the shape of mounds, whereas for diameters in excess of about 4 nm, a ring‐like appearance is observed. In both cases, the atomic order of the formerly undisturbed surface is preserved and no defects in the lateral atomic order of the surface layer are found.

Stochastic analysis of different rough surfaces

Abstract.This paper shows in detail the application of a new stochastic approach for the characterization of surface height profiles, which is based on the theory of Markov processes. With this analysis we achieve a characterization of the scale dependent complexity of surface roughness by means of a Fokker-Planck or Langevin equation, providing the complete stochastic information of multiscale joint probabilities. The method is applied to several surfaces with different properties, for the purpose of showing the utility of this method in more detail. In particular we show evidence of the Markov properties, and we estimate the parameters of the Fokker-Planck equation by pure, parameter-free data analysis. The resulting Fokker-Planck equations are verified by numerical reconstruction of the conditional probability density functions. The results are compared with those from the analysis of multi-affine and extended multi-affine scaling properties which is often used for surface topographies. The different surface structures analysed here show in detail the advantages and disadvantages of these methods.

EXPERIMENTS ON THE DEPOLARIZATION NEAR-FIELD SCANNING OPTICAL MICROSCOPE

We demonstrate the operation of an apparatus which we call the depolarization near-field scanning optical microscope. It delivers subwavelength resolution with uncoated optical fiber tips without the need for additional modulation techniques. We show that—in the near field—the edges perpendicular to the incident optical polarization are imaged. This dependence on the orientation of the linear polarization as well as the influence of small ellipticities of the polarization state on the imaging process are measured on a well-defined test sample. The transition from near- to far-field imaging as a function of the tip height is demonstrated. The results are in good agreement with recent theoretical predictions.

COMPUTER SIMULATIONS ON NEAR-FIELD SCANNING OPTICAL MICROSCOPY : CAN SUBWAVELENGTH RESOLUTION BE OBTAINED USING UNCOATED OPTICAL FIBER PROBES?

Recent experiments claim that subwavelength resolution can be obtained with an optical scanning microscope using uncoated optical fiber probes. In these experiments, linearly polarized light is sent down the fiber which is reflected and depolarized in the tip-sample region. The internally reflected signal in the orthogonal polarization is detected. Here, numerical solutions of the vector Maxwell equations for a model are discussed. In this model, subwavelength resolution can indeed be obtained in the above mode, while this is not possible without polarization sensitivity. The influence of parameters such as polarization, different scanning modes and tip-sample distance is discussed.

Independently switchable atomic quantum transistors by reversible contact reconstruction.

The controlled fabrication of actively switchable atomic-scale devices, in particular transistors, has remained elusive to date. Here, we explain the operation of an atomic-scale three-terminal device by a novel switching mechanism of bistable, self-stabilizing reconstruction of the electrode contacts at the atomic level: While the device is manufactured by electrochemical deposition, it operates entirely on the basis of mechanical effects of the solid-liquid interface. We analyze mechanically and thermally stable metallic junctions with a predefined quantized conductance of 1-5 G0 in experiment and atomistic simulation. Atomistic modeling of structural and conductance properties elucidates bistable electrode reconstruction as the underlying mechanism of the device. Independent room temperature operation of two transistors at low voltage demonstrates intriguing perspectives for quantum electronics and logics on the atomic scale.

On the nature of nanometer-scale islands formed by cadmium selenide deposition on hexagonal cadmium sulfide (0001)A

Using ex situ atomic force microscopy, nanometer-scale islands were observed on CdS(0001)A surfaces to appear after deposition of small amounts of CdSe. The sizes of these islands are similar to those reported in atomic force microscopy (AFM) studies of uncapped CdSe/ZnSe structures. Investigations by force modulation microscopy and photoluminescence spectroscopy show, however, that they are difficult to assign to a CdSe Stranski–Krastanow growth. Instead, AFM points to an onset of the island formation with the exposure of the samples to atmosphere. By use of electron microprobe analysis, it is suggested that these islands consist of selenium.

Preselectable integer quantum conductance of electrochemically fabricated silver point contacts

The controlled fabrication of well-ordered atomic-scale metallic contacts is of great interest: it is expected that the experimentally observed high percentage of point contacts with a conductance at noninteger multiples of the conductance quantum G0=2e2∕h in simple metals is correlated to defects resulting from the fabrication process. Here we demonstrate a combined electrochemical deposition and annealing method that allows the controlled fabrication of point contacts with preselectable integer quantum conductance. The resulting conductance measurements on silver point contacts are compared with tight-binding-like conductance calculations of modeled idealized junction geometries between two silver crystals with a predefined number of contact atoms.