Gate-controlled spin-orbit coupling in InAs/InGaAs quantum well structures.

We have investigated gate electric field controlled Rashba spin-orbit coupling (SOC) constant (alpha) in In0.53Ga0.47As and InAs-inserted quantum well (QW) structures. More than three times larger gate controllability of a in the InAs-inserted QW has been observed compared to the In0.53Ga0.47As QW. The enhanced gate controllability of alpha directly results from the larger zero-field SOC in narrow band gap InAs QW. Furthermore, the lower contact resistance and higher electron mobility imply that the InAs QW is a more promising channel for spintronic device applications.

Complementary spin transistor using a quantum well channel.

In order to utilize the spin field effect transistor in logic applications, the development of two types of complementary transistors, which play roles of the n- and p-type conventional charge transistors, is an essential prerequisite. In this research, we demonstrate complementary spin transistors consisting of two types of devices, namely parallel and antiparallel spin transistors using InAs based quantum well channels and exchange-biased ferromagnetic electrodes. In these spin transistors, the magnetization directions of the source and drain electrodes are parallel or antiparallel, respectively, depending on the exchange bias field direction. Using this scheme, we also realize a complementary logic operation purely with spin transistors controlled by the gate voltage, without any additional n- or p-channel transistor.

Large spin accumulation and crystallographic dependence of spin transport in single crystal gallium nitride nanowires.

Semiconductor spintronics is an alternative to conventional electronics that offers devices with high performance, low power and multiple functionality. Although a large number of devices with mesoscopic dimensions have been successfully demonstrated at low temperatures for decades, room-temperature operation still needs to go further. Here we study spin injection in single-crystal gallium nitride nanowires and report robust spin accumulation at room temperature with enhanced spin injection polarization of 9%. A large Overhauser coupling between the electron spin accumulation and the lattice nuclei is observed. Finally, our single-crystal gallium nitride samples have a trigonal cross-section defined by the (001), () and () planes. Using the Hanle effect, we show that the spin accumulation is significantly different for injection across the (001) and () (or ()) planes. This provides a technique for increasing room temperature spin injection in mesoscopic systems.

Crystalline Direction Dependence of Spin Precession Angle and Its Application to Complementary Spin Logic Devices.

In a semiconductor channel, spin-orbit interaction is divided into two terms, Rashba and Dresselhaus effects, which are key phenomena for modulating spin precession angles. The direction of Rashba field is always perpendicular to the wavevector but that of Dresselhaus field depends on the crystal orientation. Based on the individual Rashba and Dresselhaus strengths, we calculate spin precession angles for various crystal orientations in an InAs quantum well structure. When the channel length is 1 µm, the precession angle is 550° for the [110] direction and 460° for the [1-10] direction, respectively. Using the two spin transistors with different crystal directions, which play roles of n- and p-type transistors in conventional charge transistors, we propose a complementary logic device.

Magnetic In x Ga 1 - x N nanowires at room temperature using Cu dopant and annealing.

Single-crystal, Cu-doped In x Ga1 - x N nanowires were grown on GaN/Al2O3 substrates via a vapor-liquid-solid (VLS) mechanism using Ni/Au bi-catalysts. The typical diameter of the Cu:In x Ga1 - x N nanowires was 80 to 150 nm, with a typical length of hundreds of micrometers. The as-grown nanowires exhibited diamagnetism. After annealing, the nanowires exhibited ferromagnetism with saturation magnetic moments higher than 0.8 µB (1 µB × 10(-24) Am(2)) per Cu atom at room temperature by the measurements using a superconducting quantum interference device (SQUID) magnetometer. X-ray absorption and X-ray magnetic circular dichroism spectra at Cu L 2,3-edges indicated that the doped Cu had a local magnetic moment and that its electronic configuration was mainly 3d (9). It possessed a small trivalent component, and thus, the n-type behavior of electrical property is measured at room temperature.

Electric-field-induced spin injection enhancement.

The spin diffusion process can be modified by the electric field in a semiconductor channel. The electric field generated by the bias current improves the spin injection efficiency as well as the spin diffusion length at a ferromagnet-semiconductor hybrid system. Spin-polarized electrons from the ferromagnetic electrode were electrically investigated in an inverted heterostructure with an In0.53Ga0.47As active layer. Using local and non-local spin valve geometries, the interfacial spin polarizations with and without an electric field are extracted from the magnitude of spin transport signals. The interfacial spin polarization is increased from 3.2% to 7.0% with a current of 1 mA at T = 20 K. When the electric field assists the spin injection at the junction, the interfacial spin polarization remains 7% at the temperature ranged from 20 K to 200 K. Temperature dependence of the injected polarization shows that the electric field can compensate the thermal smearing of injection efficiency even at higher temperature.

Synthesis of p-type GaN nanowires.

GaN has been utilized in optoelectronics for two decades. However, p-type doping still remains crucial for realization of high performance GaN optoelectronics. Though Mg has been used as a p-dopant, its efficiency is low due to the formation of Mg-H complexes and/or structural defects in the course of doping. As a potential alternative p-type dopant, Cu has been recognized as an acceptor impurity for GaN. Herein, we report the fabrication of Cu-doped GaN nanowires (Cu:GaN NWs) and their p-type characteristics. The NWs were grown vertically via a vapor-liquid-solid (VLS) mechanism using a Au/Ni catalyst. Electrical characterization using a nanowire-field effect transistor (NW-FET) showed that the NWs exhibited n-type characteristics. However, with further annealing, the NWs showed p-type characteristics. A homo-junction structure (consisting of annealed Cu:GaN NW/n-type GaN thin film) exhibited p-n junction characteristics. A hybrid organic light emitting diode (OLED) employing the annealed Cu:GaN NWs as a hole injection layer (HIL) also demonstrated current injected luminescence. These results suggest that Cu can be used as a p-type dopant for GaN NWs.

Thermal spin injection and accumulation in CoFe/MgO/n-type Ge contacts.

Understanding the interplay between spin and heat is a fundamental and intriguing subject. Here we report thermal spin injection and accumulation in CoFe/MgO/n-type Ge contacts with an asymmetry of tunnel spin polarization. Using local heating of electrodes by laser beam or electrical current, the thermally-induced spin accumulation is observed for both polarities of the temperature gradient across the tunnel contact. We observe that the magnitude of thermally injected spin signal scales linearly with the power of local heating of electrodes, and its sign is reversed as we invert the temperature gradient. A large Hanle magnetothermopower (HMTP) of about 7.0% and the Seebeck spin tunneling coefficient of larger than 0.74 meV K(-1) are obtained at room temperature.

Mouse model of Aspergillus and Alternaria induced rhinosinusitis.

OBJECTIVE: Fungi are known to induce the production of chemical mediators from respiratory epithelial cells and have been increasingly recognized as important pathogens in sinusitis. However, the exact role of fungi in the pathogenesis of rhinosinusitis has not been clearly established. This study was performed to improve our understanding of the role of fungi in the pathogenesis of rhinosinusitis by developing an animal model of fungus induced rhinosinusitis. METHODS: Fifty mice (C57BL6/J) were divided into five groups. Sham-operated group was the first group. In the second group, Aspergillus versicolor (Group IIa) and Alternaria alternata (Group IIb) (10(6)spores/ml) were inoculated into the nasal cavity. In the third group, fungi were inoculated into the nasal cavity in the presence of mucosal scratch (Group IIIa,b) and the fourth group was a nasal mucosal scratch only (Group IV). The fifth was a negative control (Group V). The fungi were inoculated once a week on six occasions and then the animals were sacrificed at 7 weeks. The histological sections were examined in a blind manner for the appearance of neutrophil clusters and epithelial thickness with hematoxylin-eosin stain, and mucus secreting glands using the Alcian blue/periodic acid Schiff stain. RESULTS: Non-invasive fungal sinusitis had been induced with increased numbers of neutrophil clusters after Aspergillus and Alternaria exposure. The mice with the mucosal scratch wounds had significantly more inflammatory cell infiltration and epithelial thickening; but eosinophils were not commonly found. The mice with fungal sinusitis had goblet cell hyperplasia and increased mucus secretion in the sinonasal cavity. CONCLUSIONS: Inoculation of fungi in the nasal cavity induced rhinosinusitis in C57BL6/J mice. This mouse model may be used for better understanding of the role of fungi in the pathogenesis of rhinosinusitis.