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An in situ doping approach was adopted to synthesize single-crystalline Sn-doped In2O3 [indium tin oxide (ITO)] nanowhiskers. Similar synthesis strategy could be used in the production of various doped metal oxide nanowhiskers. The growth mode of ITO nanowhiskers was discussed based on a self-catalytic vapor–liquid–solid growth mechanism. At room temperature, a photoluminescence peak at 510nm was observed, which was likely related to the surface defects of ITO nanowhiskers. In air ambient, the resistivity of individual ITO whisker was measured to be 0.40Ωcm, which was much higher than that of ITO films. A possible explanation for the high resistivity was proposed based on the influence of surface oxygen absorption.

By self-consistently solving two-dimensional Schrodinger and Poisson equations, we have studied electron quantum wires formed by etching two shallow trenches in GaAs/InGaAs/AlGaAs and GaAs/AlGaAs heterostructures for single-electron-transistor applications. Two-dimensional electron gases (2DEGs) form in the InGaAs layer in GaAs/InGaAs/AlGaAs and at the GaAs/AlGaAs interface in GaAs/AlGaAs heterostructure, the two etched trenches deplete the carriers of the 2DEGs underneath and thus effectively define an electron quantum wire. It has been determined that two etched trenches with a depth of 50 nm and a spatial separation of 250 nm are optimal to create an electron quantum wire in a GaAs/InGaAs/AlGaAs heterostructure with a cross section of 80×10 nm2 and a peak electron concentration of 1.5×1018 cm−3 at 4.2 K.

A parallel dot structure, which is not conductively coupled but capacitively coupled, is fabricated. Both of the respective single dots show clear Coulomb blockade oscillations (CBOs) as their gate voltages are scanned. Single-electron charging in one dot causes oscillations of the current through another dot, even in the regime of more negative gate voltages where the CBOs cannot be observed due to a too weak current. In addition, information on the energy levels in one dot can be obtained.

Effects of a finite drain voltage and a finite temperature on coherent transport in the single electron tunneling regime are investigated for a novel quantum dot structure defined by two shallow etched trenches and two line Schottky gates. A regular amplitude modulation of Coulomb blockade oscillations is observed and attributed to coherent resonant transport. Increasing drain voltage disturbs the amplitude modulation more significantly than raising the temperature. This is explained in terms of the effects of nonmonochromatic electrons on the interference condition.

We have investigated photoluminescence of double‐barrier diodes under various bias voltages and observed the saturation of the broadening of the photoluminescence lines. We have also studied the integrated photoluminescence intensity with increasing applied voltages near resonant voltages for high quality samples at low temperature (4.2 K). The results of the 77 K photoluminescence experiments confirm those at 4.2 K. The saturation of the broadening is due to weak hole localization; however, the saturation of the integrated photoluminescence intensity is mainly due to reduced nonradiative recombination. Our results suggest that the hole localization may arise from interface roughness.

Dielectric permittivity (e) and conductivity (σ) have been measured in (1 − x)BiFeO3-(x)BaTiO3 (BFO-xBT) multiferroic ceramics for x = 0.0, 0.05, and 0.10 as functions of temperature and frequency. A one-dimensional across-barrier model with intrinsic barriers B every lattice constant a and extrinsic barriers B + Δ every distance d is introduced to describe the dielectric response and conductivity. The across-barrier hopping is responsible for the high-temperature conductivity and dielectric relaxation in the lower temperature region. Good qualitative fits of dielectric permittivity and conductivity are obtained as functions of temperature and frequency. BaTiO3 substitution can enhance the intrinsic barrier and reduce the hopping conductivity.

Structure, magnetization, and dielectric permittivity of (1-x)BiFeO3-xBaTiO3 (BFO-BT) ceramics have been studied as a function of BT content (x = 0.0, 0.1, 0.2, and 0.3). In situ synchrotron x-ray diffraction result of BFO reveals a rhombohedral (R)–orthorhombic (O)–cubic (C) phase transition near 820 and 850 °C upon heating. BFO-10%BT and BFO-20%BT exhibit a R–C transition near 760 and 740 °C, respectively. A C(R)–C transition takes place near 680 °C in BFO-30%BT. C(R) represents that a minor R phase coexists in the C matrix. A local minimum of R distortion angle αR occurs upon heating and implies ionic displacements. This anomaly is likely resulted from the antiferromagnetic (AFM)–paramagnetic (PM) transition and is responsible for the broad frequency-dependent dielectric maximum. BFO and BFO-10−30%BT ceramics exhibit a similar AFM behavior with magnetic susceptibility of about 8.2 × 10-6 emu/g·Oe at room temperature. This work suggests that BTO-substitution can enhance dielectric response and reduce th...

In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO3)0.95(BaTiO3)0.05 (BFO–5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)–orthorhombic (O)–cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO–5%BT exhibits a R–C transition near 830 °C. The BaTiO3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO–5%BT remains less than 0.04 below 150 °C.

The magnetic-induced dielectric responses of BiFeO3 (BFO) thin films were measured at the X-band microwave frequency ranged from 7 to 12.5 GHz. The measurement was given initially by a high-precision cavity microwave resonator without magnetic field. Both the real and imaginary parts of the permittivity showed its dielectric property as a function of the measuring frequency. The X-band dielectric responses of the BFO thin film were then measured by a controlled magnetic field at room temperature. The data demonstrated up to 2.2% dielectric tunability by using only 3.46 kOe magnetic field at TE107 mode (9.97705 GHz).

We have theoretically studied two types of two-dimensional electron gases (2DEGs) in GaAs/InGaAs/AlGaAs and δ-doped-AlGaAs/GaAs heterostructures for single-electron transistor applications by self-consistently solving the Schrodinger and Poisson equations. Assuming the dominant effect of the ionized impurity scattering in determining the low-field carrier mobility, it has been shown that introducing an InGaAs layer to the conventional GaAs/AlGaAs heterostructure greatly increases the sheet density of the 2DEG and the corresponding carrier mobility. The δ-doped AlGaAs/GaAs and AlGaAs/InGaAs/GaAs heterostructures provide us with an even better control of the 2DEG with higher sheet density and carrier mobility.