Dynamics of Spontaneous Electric Field Domains in a Two-Dimensional Electron System Irradiated by Microwaves and the Conductance of a Donor Layer

The temperature dependence of the switching frequency of a microwave-induced spontaneous electric field forming a domain structure and the conductance of a doping layer that provides electrons to the two-dimensional electron system have been measured on samples fabricated from the same GaAs/AlGaAs heterostructure. Both quantities have been found to obey the thermally activated dependence (Arrhenius law) with close activation energies. This result indicates a relation between the quantities and confirms a hypothesis that the observed dynamics of the domain structure originates from the dynamical screening of the spontaneous electric field of domains by charges in the doping layer.     

Influence of After-Growth Treatments on the Optical Parameters of Teraherz ZnGeP2 Crystals

Russian Physics Journal - Results of investigations are presented of the THz spectra of the refractive index n(v) and of the extinction coefficient k(v) for ZnGeP2 single crystals with different...     

Equilibrium Chiral Edge Currents of the Landau Spin Sublevels

Journal of Experimental and Theoretical Physics - Equilibrium edge currents emerging due to the variation of occupation of individual Landau spin sublevels near the sample edge are calculated for...     

The structure and dynamics of the layer arising at the surface of superconducting aluminium on switching off the magnetic field H0 large values H0/Hc

The increase of the ratio of H₀/H_c is experimentally foound to result in changing the configuration and motion of the normal and superconducting regions in the layer.     

Structure,transport and field-emission properties of compound nanotubes: CN<Subscript>x</Subscript> vs. BNC<Subscript>x</Subscript> (<Emphasis Type="Italic">x</Emphasis><0.1)

Transport and field-emission properties of as-synthesized CN_x and BNC_x (x<0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CN_x nanotubes displayed well-defined metallic behavior and low resistivities of ∼10–100 kΩ or less at room temperature, whereas those made of BNC_x nanotubes exhibited semiconducting properties and high resistivities of ∼50–300 MΩ. Both types of ropes revealed good field-emission properties with emitting currents per rope reaching ∼4 μA(CN_x) and ∼2 μA (BNC_x), albeit the latter ropes se- verely deteriorated during the field emission. Macrofilms made of randomly oriented CN_x or BNC_x nanotubes displayed low and similar turn-on fields of ∼2–3 V/μm. 3 mA/cm² (BNC_x) and 5.5 mA/cm² (CN_x) current densities were reached at 5.5 V/μm macroscopic fields. At a current density of 0.2–0.4 mA/cm² both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing the current density to 0.2–0.4 A/cm², only CN_x films continued to emit steadily, while the field emission from BNC_x nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating. Received: 29 October 2002 / Accepted: 1 November 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp     

Coexistence of collective and single-particle effects in the photoresponse of a 2D electron gas to microwave radiation

The photoresponse of magnetoresistance of a high-density two-dimensional electron system to microwave electromagnetic radiation is studied. The damping of the Shubnikov-de Haas oscillation by radiation with a non-monotonic dependence of this effect on the magnetic field and the radiation-induced oscillations of magnetoresistance are observed. The damping is most pronounced within isolated narrow magnetic field intervals that closely correspond to the expected positions of magnetoplasma resonances in the sample under study and also near the cyclotron resonance position. A “window” is observed in the photoresponse near the field value predicted on the basis of a single-particle electron spectrum consisting of broadened Landau levels. The radiation-induced oscillations, the window in the photoresponse, and the damping of the Shubnikov-de Haas oscillations near the cyclotron resonance are described in terms of the theory based on the concept of the nonequilibrium filling of single-electron states. Thus, it is demonstrated that the photoresponse pattern observed in the experiment is formed by both single-particle and collective (magnetoplasma) effects.     

Subwavelength-resolution near-field Raman spectroscopy

The resolution capabilities of near-field Raman spectroscopy based on a giant enhancement of the electric field near a nanosized metal probe are studied. As a test sample, bundles of single-walled carbon nanotubes deposited on glass substrates are used. It is shown that this method ensures a subwavelength spatial resolution of about 50 nm and demonstrates a Raman scattering enhancement of the order of 10⁴.     

Incompressible electron phase in field-effect transistors

The formation of regions of compressible and incompressible phases in the quantum Hall effect regime has been considered for a two-dimensional (2D) electron system that is created in a field-effect transistor. This effect arises from long-period fluctuations of the density of ionized donors supplying electrons to the 2D system. It is shown that the motion of these regions caused by variations of the average electron density gives rise to minima in the capacitance of the capacitor formed by the 2D electron system and the transistor gate. When the corrections to the capacitance are small, the shape of the minima reproduces the donor density distribution function. Experimental data are presented that demonstrate good agreement with the predictions of the model.     

Acoustic Wave Chemical Sensors for Gases

A great number of publications devoted to the physicochemical principles of the operation of acoustic wave chemical sensors for gases, the state of the art, and the prospects for further development were surveyed and analyzed.