Conductance of a multiterminal ballistic wire

JETP Letters - An experimental study of the two-, three-, and four-terminal resistance of a ballistic wire is carried out. The wire is fabricated on the basis of high-mobility 2D electron gas in an...     

Direct synthesis of nitrogen-containing filamentous carbon on a high-percentage Ni-Cu catalyst

Nitrogen-containing catalytic filamentous carbon (N-CFC) of chemical composition NC₁₈-NC₁₀₄ has been synthesized by the decomposition of pyridine (Py) from gaseous mixtures with argon or H₂ at 550–800°C on Ni/Al₂O₃ (Ni) and Ni-Cu/Al₂O₃ (Ni-Cu) high-percentage catalysts. The activity of the Ni-Cu catalyst in Py decomposition in mixtures with H₂ is about one order of magnitude higher than its activity in Py/Ar mixtures (more than 70 g N-CFC per metal gram in 4.5 h at 750°C), which is interpreted as arising from the nickel-catalyzed hydrogenation of Py. The formation and growth of carbon fibers occurs through the decomposition of Py (from Ar/Py mixtures) and/or Py hydrodenitrification products (from H₂/Py mixtures). The carbon material has been characterized by elemental analysis, low-temperature nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The effect of the noncatalytic reactions of Py and its transformation products on the composition and texture of N-CFC is discussed.     

Temperature dependence of Aharonov-Bohm oscillations in small quasi-ballistic interferometers

The temperature dependence of the Aharonov-Bohm oscillations of small quasi-ballistic ring interferometers (effective radius R = 90–110 nm) is studied in a wide temperature range of (0.34–9) K. It is found that this dependence is determined not only by the size of the interferometer, but also by its microscopic state. It is shown that the effect may be associated with the influence of the fluctuation potential leading to different, but not completely stochastic, realizations of the scattering potential in conducting channels of the ring.     

Coulomb blockade in triangular lateral small-size quantum dots

An AlGaAs/GaAs lateral quantum dot of triangular shape with a characteristic size L<100 nm containing less than ten electrons was studied. Single-electron oscillations of the conductance G of this dot were measured at G<e²/h. When going from Ge²/h to G≈0.5e²/h, a decrease was found not only in the amplitude but also in the period of the oscillations. A calculation of the 3D-electrostatics demonstrated that this effect is due to a change in the dot size produced by control voltages.     

Identification of nitrogen-containing species obtained by nitric oxide adsorption on the surface of model gold catalysts

Nitric oxide adsorption at 300–500 K on gold particles supported on an alumina film has been investigated for the first time by in situ X-ray photoelectron spectroscopy. Two nitrogen-containing adsorption species can form on the surface of gold particles. By test experiments on NO adsorption on the stepped face (533) of a gold single crystal, these species have been identified as adsorbed nitrogen atoms (which are detected throughout the temperature range examined) and a surface complex with N₂O stoichiometry (which is stable in a narrow temperature range of 325–425 K).     

Quantum corrections to the conductance of AlGaAs/GaAs-based quasiballistic quantum wires

Quantum conductance corrections (QCCs) due to weak localization and interaction effects of quantum quasiballistic wires are investigated for the first time. At temperatures in the range 2 K<T<12 K a crossover of these corrections from one-dimensional behavior to zero-dimensional behavior is observed. It is shown that the phase coherence length in the wires studied is less than the length L _T =(ℏD/kT)^1/2 at all temperatures. It is found that the conventional theory of QCCs describes correctly the experimental temperature dependence of the QCCs but gives a much lower value than the experimental one. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 973–976 (25 June 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Conductance of short quantum wires with sharp boundaries

The conductance of short ballistic wires with boundaries, whose curvature radius is comparable to the electron wavelength, is investigated. It is found that, in such wires, no conductance quantization takes place. Instead, pronounced interference effects are observed. These effects are related to the Fabry-Perot interference by the wire edges and with the mesoscopic interference caused by the coherent scattering of electrons by the wire edges and by the impurities located in the near-wire regions of the 2D electron gas.     

Low-Frequency Microwave Response of a Quantum Point Contact

JETP Letters - The low-frequency microwave photoconductance of a short (100 nm) quantum point contact based on a high-mobility two-dimensional electron gas in the frequency range of 2–3 GHz...