Electrical spin injection from an organic-based ferrimagnet in a hybrid organic/inorganic heterostructure

We report the successful extraction of spin polarized current from the organic-based room temperature ferrimagnetic semiconductor V[TCNE]x (x~2, TCNE: tetracyanoethylene; TC ~ 400 K, EG ~ 0.5 eV, s ~ 10-2 S/cm) and its subsequent injection into a GaAs/AlGaAs light-emitting diode (LED). The spin current tracks the magnetization of V[TCNE]x~2, is weakly temperature dependent, and exhibits heavy hole / light hole asymmetry. This result has implications for room temperature spintronics and the use of inorganic materials to probe spin physics in organic and molecular systems

Dissipation in nanocrystalline-diamond nanomechanical resonators

We have measured the dissipation and frequency of nanocrystalline-diamond nanomechanical resonators with resonant frequencies between 13.7 MHz and 157.3 MHz, over a temperature range of 1.4–274 K. Using both magnetomotive network analysis and a time-domain ring-down technique, we have found the dissipation in this material to have a temperature dependence roughly following T^(0.2), with Q^(–1) ≈ 10^(–4) at low temperatures. The frequency dependence of a large dissipation feature at ~35–55 K is consistent with thermal activation over a 0.02 eV barrier with an attempt frequency of 10 GHz

Whimbrel Tracked with Satellite Transmitter on Migratory Flight Across North America

Two disjunct breeding populations of Whimbrel Numenius phaeopus have been described in the western hemisphere (American Ornithologists’ Union 1983). The western population breeds in portions of Alaska and across the Yukon and Northwest Territories of Canada while the eastern population breeds west and south of Hudson Bay (Skeel & Mallory 1996). Most of what we believe we know about the migratory pathways of these populations has been pieced together from circumstantial evidence gleaned from decades of field observations (Skeel & Mallory 1996, Taverner 1942). The populations have been thought to have separate migratory routes with little mixing where the western and eastern populations were confined to the Pacific and Atlantic Coasts, respectively. Here we present evidence of a transcontinental migration route that brings portions of the two Whimbrel populations into contact during spring migration..

Constraints on the Mode and Extent of Sedimentary Rock Alteration in Hyper-Arid and Hypo-Thermal Environments

Geologic evidence suggests that the surface of Mars has been dominated by cold, dry, and relatively stable environmental conditions over the past ~3.5 Ga. These conditions differ from those pre-sumed to be present prior to ~3.5 Ga, when observa-tions indicate that the martian surface was at least in-termittently able to support the prolonged flow of liq-uid water. Despite the more than 75% of martian his-tory dominated by cold, dry, and stable conditions, few investigations have studied weathering and alteration processes that may influence the martian surface dur-ing this time. Please see attachment

Linear and nonlinear coupling between transverse modes of a nanomechanical resonator

We measure both the linear and nonlinear coupling between transverse modes in a nanomechanical resonator. The nonlinear coupling is due to the displacement dependent tension of the resonator and leads to a frequency shift (“pulling”) of each mode proportional to the square of the orthogonal mode's displacement amplitude. The linear coupling is apparent as an avoided crossing of the resonant frequencies that occurs when one electrostatically tunes the modes into degeneracy via a nearby DC gate. We consider the possibility that the linear coupling results from an electrostatic interaction and find that this effect can only partially explain the magnitude of the observed coupling. By measuring the coupled amplitudes magnetomotively at various angles to the applied field, we find that as the modes are tuned through the degeneracy point, they remain linearly polarized, while their planes of vibration rotate by 90°

Coulomb Blockade in a Silicon/Silicon-Germanium Two-Dimensional Electron Gas Quantum Dot

We report the fabrication and electrical characterization of a single electron transistor in a modulation doped silicon/silicon-germanium heterostructure. The quantum dot is fabricated by electron beam lithography and subsequent reactive ion etching. The dot potential and electron density are modified by laterally defined side gates in the plane of the dot. Low temperature measurements show Coulomb blockade with a single electron charging energy of 3.2 meV.Comment: Typos corrected; to appear in Appl. Phys. Let