Multiplex detection of mutations in clinical isolates of rifampin-resistant Mycobacterium tuberculosis by short oligonucleotide Ligation assay on DNA chips

A new approach, short-oligonucleotide-ligation assay on DNA chip (SOLAC), is developed to detect mutations in rifampin-resistant Mycobacterium tuberculosis. The method needs only four common probes to detect 15 mutational variants of the rpoB gene within 12 h. Fifty-five rifampin-resistant M. tuberculosis isolates were analyzed, resulting in 87.3% accuracy and 83.6% concordance relative to DNA sequencing.

Compact Reconfigurable Binary-Decision-Diagram Logic Circuit on a GaAs Nanowire Network

We describe a reconfigurable binary-decision-diagram logic circuit based on Shannon's expansion of Boolean logic function and its graphical representation on a semiconductor nanowire network. The circuit is reconfigured by using programmable switches that electrically connect and disconnect a small number of branches. This circuit has a compact structure with a small number of devices compared with the conventional look-up table architecture. A variable Boolean logic circuit was fabricated on an etched GaAs nanowire network having hexagonal topology with Schottky wrap gates and SiN-based programmable switches, and its correct logic operation together with dynamic reconfiguration was demonstrated.

Small-Signal Equivalent-Circuit Model and Characterization of 1.55-mu m Buried Tunnel Junction Vertical-Cavity Surface-Emitting Lasers

The work was supported in part by the National Natural Science Foundation of China under Grant 60536010, Grant 60606019, Grant 60777029, and Grant 60820106004, and in part by the National Basic Research Program of China under Grant 2006CB604902, Grant 2006CB302806, and Grant 2006dfa11880.

High repetition rate Q-switched microchip Nd:YVO4 laser with pulse duration as short as 1.1 ns

We have demonstrated a compact and an efficient passively Q-switched microchip Nd:YVO4 laser by using a composite semiconductor absorber as well as an output coupler. The composite semiconductor absorber was composed of an LT (low-temperature grown) In0.25Ga0.75As absorber and a pure GaAs absorber. To our knowledge, it was the first demonstration of the special absorber for Q-switching operation of microchip lasers. Laser pulses with durations of 1.1 ns were generated with a 350 mu m thick laser crystal and the repetition rate of the pulses was as high as 4.6 MHz. The average output power was 120 mW at the pump power of 700 mW. Pulse duration can be varied from 1.1 to 15.7 ns by changing the cavity length from 0.45 to 5 mm. Pulses with duration of 1.67 and 2.41 ns were also obtained with a 0.7 mm, thick laser crystal and a 1 mm thick laser crystal, respectively. (C) 2007 Elsevier GmbH. All rights reserved.

Proposal for the direct optical detection of pure spin currents in semiconductors

We suggest a different practical scheme for the direct detection of pure spin current by using the two-color Faraday rotation of optical quantum interference process (QUIP) in a semiconductor system. We demonstrate theoretically that the Faraday rotation of QUIP depends sensitively on the spin orientation and wave vector of the carriers, and can be tuned by the relative phase and the polarization direction of the omega and 2 omega laser beams. By adjusting these parameters, the magnitude and direction of the spin current can be detected.

Spin states and persistent currents in a quantum ring with an embedded magnetic impurity

Spin states and persistent currents are investigated theoretically in a quantum ring with an embedded magnetic ion under a uniform magnetic field including the spin-orbit interactions. The magnetic impurity acts as a spin-dependent delta-potential for electrons and results in gaps in the energy spectrum, consequently suppressing the oscillation of the persistent currents. The competition between the Zeeman splittings and the s-d exchange interaction leads to a transition of the electron ground state in the ring. The interplay between the periodic potential induced by the Rashba and Dresselhaus spin-orbit interactions and the delta-potential induced by the magnetic impurity leads to significant variation in the energy spectrum, charge density distribution, and persistent currents of electrons in the ring.

InAs/GaSb superlattices for photodetection in short wavelength infrared range

The first report of a short wavelength infrared detector based on type II InAs/GaSb superlattices is presented. Very short period superlattices containing InAs (2ML)/GaSb (8ML) superlattices (SLs) were grown by molecular-beam epitaxy on GaSb substrates. The photoluminescence showed a cut-off wavelength at 2.1 mu m at 10 K and 2.6 mu m at 300 K. Room-temperature optical transmittance spectra shows obvious absorption in InAs (2ML)/GaSb (8ML) SL in the range of 450-680 meV, i.e. 1.8-2.7 mu m. The cut-off wavelength moved from 2.3 mu m to 2.6 mu m with temperature rising from 77 K to 300 K in photoresponse spectra. The blackbody response R-v exponentially decreased as a function of 1/T in two temperature sections (130-200 K and 230-300 K). The blackbody detectivity D-bb(center dot) was beyond 1 x 10(8) cmHz(1/2)/W at room temperature. (C) 2009 Elsevier B.V. All rights reserved.

Transient Reorientation of a Doped Liquid Crystal System under a Short Laser Pulse

The transient optical nonlinearity of a nematic liquid crystal doped with azo-dye DR19 is examined. The optical reorientation threshold of a 25-mu m-thick planar-aligned sample of 5CB using a 50 ns pulse duration 532 nm YAG laser pulse is observed to decrease from 800 mJ/mm(2) to 0.6 mJ/mm(2) after the addition of 1 vol% azo dopant, a reduction of three orders of magnitude. When using a laser pulse duration of 10 ns, no such effect is observed. Experimental results indicate that the azo dopant molecules undergo photoisomerization from trans-isomer to cis-isomer under exposure to light, and this conformation change reorients the 5CB molecules via intermolecular coupling between guest and host. This guest-host coupling also affects the azo photoisomerization process.

SHORT PERIOD InAs/GaSb SUPERLATTICE INFRARED DETECTOR ON GaAs SUBSTRATES

Two type II superlattices (SLs) InAs(2ML)/GaSb(8ML) and InAs(8ML)/GaSb(8ML) were grown on GaAs substrates by molecular-beam epitaxy. High resolution X-ray diffraction showed the periods of the two SLs were 31.2 angstrom and 57.3 angstrom, respectively. Room-temperature optical transmittance spectra showed that there were clear absorption edges at 2.1 mu m and 5 mu m for the two SLs. The SWIR and MWIR photoconductor devices were fabricated by standard lithography and etched by tartaric acid solution. The spectral response and blackbody tests were carried out at low and room temperatues. The results show that the 50% cutoff wavelengths of the two photoconductors are 2.1 mu m and 5.0 mu m respectively and D-bb* is above 2 x 10(8) cmHz(1/2)/W for two kinds of photoconductors at 77K. D-bb* is above 10(8) cmHz(1/2)/W for SWIR photoconductor at room temperature.

GaAs Based InAs/GaSb Superlattice Short Wavelength Infrared Detectors Grown by Molecular Beam Epitaxy

InAs/GaSb superlattice (SL) short wavelength infrared photoconduction detectors are grown by molecular beam epitaxy on GaAs(001) semi-insulating substrates. An interfacial misfit mode AlSb quantum dot layer and a thick GaSb layer are grown as buffer layers. The detectors containing a 200-period 2ML/8ML InAs/GaSb SL active layer are fabricated with a pixel area of 800 x 800 mu m(2) without using passivation or antireflection coatings. Corresponding to the 50% cutoff wavelengths of 2.05 mu m at 77K and 2.25 mu m at 300 K, the peak detectivities of the detectors are 4 x 10(9) cm.Hz(1/2)/W at 77K and 2 x 10(8) cm.Hz(1/2)/W at 300 K, respectively.

Comparison of short period InAs/GaSb superlattices on GaSb and GaAs substrates

Type II superlattices (SLs) short period InAs(4ML)/GaSb(8ML) were grown by molecular-beam epitaxy on lattice-mismatched GaAs substrates and on GaSb substrates. A smooth GaSb epilayer was formed on GaAs substrates by inserting mulit-buffer layers including an interfacial misfit mode AlSb quantum dot layer and AlSb/GaSb superlattices smooth layer. SLs grown on GaAs substrates (GaAs-based SLs) showed well-resolved satellite peaks in XRD. GaSb-based SLs with better structural quality and smoother surface showed strong photoluminescence at 2.55 mu m with a full width at half maximum (FWHM) of 20 meV, narrower than 31 meV of GaAs-based SLs. Inferior optical absorption of GaAs-based SL was observed in the range of 2-3 mu m. Photoresponse of GaSb-based SLs showed the cut-off wavelength at 2.6 mu m.

Charge and spin currents in a three-terminal mesoscopic ring

We theoretically investigate the charge and spin currents in a three-terminal mesoscopic ring in the presence of a uniform and nonuniform Rashba spin-orbit interaction (SOI). It is shown that a fully spin-polarized charge current and a pure spin current can be generated by tuning the probe voltages and/or the strength of the Rashba SOI. The charge and spin currents oscillate as the strength of the Rashba SOI increases induced by the spin quantum interference. The ratio of probe voltages oscillates synchronously with the pure spin current as the strength of the Rashba SOI increases in a nonuniform Rashba ring, while it remains constant in a uniform Rashba ring. We demonstrate theoretically that a three-terminal uniform Rashba ring can be used as a spin polarizer and/or spin flipper for different spin injections, and a nonuniform Rashba ring could allow us to detect the pure spin current electrically. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3054322]

Optical characteristics of InAs quantum dots capped with short period GaAs/InAs superlattices and InGaAs combination layers

Long wavelength light emission was realized by capping InAs quantum dots (QDs) with short period GaAs/InAs superlattices (SLs) and an InGaAs strain-reducing layer (SRL). The optical properties were systematically investigated by photoluminescence tests. With increasing the periods of SLs, the emission wavelength of InAs QDs shifts from 1.27 to 1.53 mum. We explain the redshift as a result of the increased QD height with the SLs and the reduced strain in the dot caused by InGaAs SRL. (C) 2004 Published by Elsevier Ltd.

Tandem electroabsorption modulators integrated with DFB laser by ultra-low-pressure selective-area-growth MOCVD for 10 GHz optical short pulse generation

　

Spin and charge currents through a quantum dot connected to ferromagnetic leads

We investigate the spin polarized current through a quantum dot connected to ferromagnetic leads in the presence of a finite spin-dependent chemical potential. The effects of the spin polarization of the leads p and the external magnetic field B are studied. It is found that both the magnitude and the symmetry of the current are dependent on the spin polarization of the leads. When the two ferromagnetic leads are in parallel configuration, the spin polarization p has an insignificant effect on the spin current, and an accompanying charge current appears with the increase of p. When the leads are in antiparallel configuration, however, the effect of p is distinct. The charge current is always zero regardless of the variation of p in the absence of B. The peaks appearing in the pure spin current are greatly suppressed and become asymmetric as p is increased. The applied magnetic field B results in an accompanying charge current in both the parallel and antiparallel configurations of the leads. The characteristics of the currents are explained in terms of the density of states of the quantum dot.