C. Gustin

Structural and electrical characterization of hybrid metal-polypyrrole nanowires.

We present here the synthesis and structural characterization of hybrid Au-polypyrrole-Au and Pt-polypyrrole-Au nanowires together with a study of their electrical properties from room temperature down to very low temperature. A careful characterization of the metal-polymer interfaces by transmission electron microscopy revealed that the structure and mechanical strength of bottom and upper interfaces are very different. Variable temperature electrical transport measurements were performed on both multiple nanowires-contained within the polycarbonate template-and single nanowires. Our data show that the three-dimensional Mott variable-range-hopping model provides a complete framework for the understanding of transport in polypyrrole nanowires, including nonlinear current-voltage characteristics and magnetotransport at low temperatures.

Sign reversal and tunable rectification in a ballistic nanojunction

Low-temperature measurements show that an asymmetric mesoscopic junction patterned in a two-dimensional electron gas can exhibit tunable rectification, including sign reversal. Strikingly, we observe that the amplitude and sign of the effect are governed by the conductances of the channels and that rectification is reversed without reversing the asymmetry of the device. Based on the temperature dependence of the rectified voltage, we show that the effect is ballistic and exhibits unexpected features with respect to predictions of available models.

Two-dimensional self-consistent simulation of a triangular p-channel SOI nano-flash memory device

This paper presents the simulation of an SOI nano-flash memory device. The device is composed of a triangular quantum wire channel p-MOSFET with a self-aligned nano-floating gate embedded in the gate oxide. The simulation is carried out by combining TSUPREM-4 and a two-dimensional (2-D) self-consistent solution of the Poisson and Schrodinger equations. The fabrication process as well as quantum physics are taken into account. Hole distribution in the inversion layer of the triangular channel section is calculated in terms of wave functions and energy subbands. The threshold voltage shift between the programming and erasing of the device is investigated. In this paper, we show that the channel shape plays a crucial role in the programming voltage and the threshold voltage shift. Based on the fact that the holes are confined mainly at the top of the triangular channel section, we explain why our triangular channel device can be operated at relatively low programming voltage despite of a thick gate oxide and tunnel oxide. The threshold voltage shift in the triangular channel device is compared with that in a rectangular channel device. The result shows that the triangular channel device exhibits the larger threshold voltage shift.

Evidence for spin–orbit effects in an open ballistic quantum dot

We report on magnetoconductance measurements of an open two-dimensional ballistic cavity in a tilted magnetic field. In agreement with Folk et al. (Phys. Rev. Lett. 86 (2001) 2102), we show that, due to an increasing spin-orbit interaction, the variance of conductance fluctuations decreases when a large in-plane magnetic field is applied. When the magnetic field is applied parallel to the 2DEG, we observe a negative magnetoconductance peak around zero total field, which is reminiscent of the weak antilocalization effect induced by spin-orbit interaction

Evidence for universal conductance fluctuations in an open quantum dot under a strictly parallel magnetic field

We investigate the transport properties of semiconductor ballistic cavities subject to a parallel magnetic field. Universal conductance fluctuations are observed on two GaAs/AlGaAs quantum well samples with one and two occupied carrier subbands, respectively. Large differences between the two open quantum dots in both the amplitude and frequency distribution of these fluctuations are analyzed in terms of electron orbital motion and magnetic subband depopulation

Weak antilocalization and UCFs in an open bismuth quantum dot

We report on the observation of weak antilocalization and universal conductance fluctuations in the magnetoconductance of an open quasi-ballistic bismuth nano-cavity. The electron decoherence length is comparable to sample dimensions at low temperature, while the spin-orbit coupling length is smaller. The temperature dependence of both the conductance and the dephasing length are consistent with two-dimensional electron-electron interactions being the dominant decoherence process

The effect of Zeeman energy on heat capacity of GaAs/AlGaAs heterostructures near nu = 1.

By controlling the ratio eta between the Zeeman and Coulomb energies, the heat capacity of a multilayer two-dimensional electron system (2DES) is measured near Landau level filing v = 1 at 60 mK. The data reveal the disappearance of the nuclear spin contribution of GaAs quantum wells to the heat capacity as eta exceeds a critical value eta(c) approximate to 0.03. This result is interpreted as the effect of the transition from Skyrmions to single electron spin flips at large Zeeman energy