Ultranarrow conducting channels defined in GaAs-AlGaAs by low-energy ion damage

We have laterally patterned the narrowest conducting wires of two-dimensional electron gas (2DEG) material reported to date. The depletion induced by low-energy ion etching of GaAs-AlGaAs 2DEG structures was used to define narrow conducting channels. We employed high voltage electron beam lithography to create a range of channel geometries with widths as small as 75 nm. Using ion beam assisted etching by Cl2 gas and Ar ions with energies as low as 150 eV, conducting channels were defined by etching only through the thin GaAs cap layer. This slight etching is sufficient to entirely deplete the underlying material without necessitating exposure of the sidewalls that results in long lateral depletion lengths. At 4.2 K, without illumination, our narrowest wires retain a carrier density and mobility at least as high as that of the bulk 2DEG and exhibit quantized Hall effects. Aharonov–Bohm oscillations are seen in rings defined by this controlled etch-damage patterning. This patterning technique holds promise for creating one-dimensional conducting wires of even smaller sizes

The extraordinary Hall effect in coherent epitaxial tau (Mn,Ni)Al thin films on GaAs

Ultrathin coherent epitaxial films of ferromagnetic tau(Mn,Ni)0.60Al0.40 have been grown by molecular beam epitaxy on GaAs substrates. X-ray scattering and cross-sectional transmission electron microscopy measurements confirm that the c axis of the tetragonal tau unit cell is aligned normal to the (001) GaAs substrate. Measurements of the extraordinary Hall effect (EHE) show that the films are perpendicularly magnetized, exhibiting EHE resistivities saturating in the range of 3.3-7.1 muOMEGA-cm at room temperature. These values of EHE resistivity correspond to signals as large as +7 and -7 mV for the two magnetic states of the film with a measurement current of 1 mA. Switching between the two magnetic states is found to occur at distinct field values that depend on the previously applied maximum field. These observations suggest that the films are magnetically uniform. As such, tau(Mn,Ni)Al films may be an excellent medium for high-density storage of binary information

The development of a DNA analysis system for pollen

Abstract. The DNA analysis technique tRFLP (terminal restriction fragment length polymorphism) was utilised to develop an alternative to the traditional microscopic examination of pollen in order to facilitate the use of this valuable forensic evidence type. The gene chosen for this study was the alcohol dehyrogenase 1 gene. Statistical analysis established that the tRFLP technique was a reliable and reproducible technique that could provide considerable discriminating power between both plant and pollen species. This indicates that the tRFLP could be a suitable technique for the analysis of pollen communities as forensic evidence.

Motivated to retrieve: How often are you willing to go back to the well when the well is dry?

Despite the necessity of the decision to terminate memory search in many real-world memory tasks, little experimental work has investigated the underlying processes. In this study, the authors investigated termination decisions in free recall by providing participants an open-ended retrieval interval and requiring them to press a stop button when they had finished retrieving. Three variables important to assessing one’s willingness to search memory were examined: (a) the time spent searching memory after the last successful retrieval before choosing to quit (the exit latency); (b) task difficulty; and (c) individual differences in motivation, as measured by Webster and Kruglanski’s (1994) Need for Closure Scale. A strong negative correlation was found between individual differences in motivation and participants ’ exit latencies. This negative correlation was present only when the retrieval task started out as relatively difficult

Microfabrication of vertical-cavity surface-emitting laser cavities

We have reduced the threshold voltages and currents of vertical cavity surface emitting lasers by using dielectric high reflectivity mirrors which were deposited after the diode fabrication step. This device fabrication sequence is able to correct for inaccuracies in the crystal growth and allows the future development of more complex laser structures. The quantum-well based laser diodes were demonstrated at 0.72 µm, 0.85 µm, and 1.55 µm. Threshold currents and voltages of our 0.85 µm lasers were 2.8 mA at 1.7 V pulsed, and 4 mA when cw-pumped. The threshold currents of 5x7 µm^2 area 1.55 µm devices were 17 mA