Volume 91, Issue 22, 26 November 2007
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
high electron mobility transistors(HEMTs) were used to detect kidney injury molecule-1 (KIM-1), an important biomarker for early kidney injury detection. The gate region consisted of golddeposited onto the AlGaNsurface. The gold was conjugated to highly specific KIM-1 antibodies through a self-assembled monolayer of thioglycolic acid. The HEMT source-drain current showed a clear dependence on the KIM-1 concentration in phosphate-buffered saline solution. The limit of detection was using a gate sensing area. This approach shows potential for both preclinical and clinical kidney injury diagnosis with accurate, rapid, noninvasive, and high throughput capabilities.
- LASERS, OPTICS, AND OPTOELECTRONICS
91(2007); http://dx.doi.org/10.1063/1.2803756View Description Hide Description
We demonstrate the emission at room temperature from a metamorphic quantum well laser grown on GaAs by molecular beam epitaxy. The large lattice mismatch was accommodated through growth of a linearly graded buffer layer to create a high quality virtual substrate. Careful growth optimization ensured good optical and structural qualities. For a broad area laser, a minimum threshold current density of was achieved under pulsed operation. This result indicates that metamorphic InGaAsquantum wells can be an alternative approach for GaAs-based lasers.
91(2007); http://dx.doi.org/10.1063/1.2814042View Description Hide Description
Symmetrical optical power T-splitters were fabricated using miniaturized 90° bends with a curvature radius of and a high transmittance of almost 99% per bend. A constant excess loss of only was achieved at a photonic wire width of over the wide wavelength range from . The dependence of the transmittance on the width of the photonic wires of the T-splitter was investigated experimentally and theoretically, and good agreement between experiments and three-dimensional finite-difference time-domain simulations was obtained.
91(2007); http://dx.doi.org/10.1063/1.2817594View Description Hide Description
We report on electrical and optical properties of InGaN violet laser diodes,grown on high-pressure grown, almost dislocation free GaN substrates. In these structures, mechanical strain has been reduced by a partially relaxed AlN mask with stripe shaped windows. The dislocation density of the mask was . In the window areas, where we located the laser stripes, the dislocation density was below . We fabricated three types of laser diodes with aluminum composition in the cladding of 8%, 13%, and 16%. All devices remained crack-free. The laser threshold current decreased with increasing Al composition in the cladding.
91(2007); http://dx.doi.org/10.1063/1.2817331View Description Hide Description
In this letter, we report on the experimental observation of a complete in-plane photonic band gap for transverse-electric-like polarized modes in a polymerphotonic crystal slab with a triangular array of holes. We performed transmission measurements on two-dimensional photonic crystal slabs in both principal directions of the triangular lattice. For a propagation distance of 40 lattice constants, the transmission was effectively suppressed regardless of propagation direction below over a bandwidth of . The experimental results are in excellent agreement with theoretical predictions obtained from band diagram calculations and finite integration time domain techniques.
91(2007); http://dx.doi.org/10.1063/1.2815914View Description Hide Description
This letter investigates the focusing characteristics of lightwaves emitted from photonic crystal waveguide aperture using a concave corrugated surface. Based on Rowland’s theory, the concave structure is applied to the photonic crystal output surface. The field distribution pattern of the emitted lightwaves demonstrates the focusing effect. The focusing distance agrees with Rowland’s theory. By optimizing the surface structures, the focused beam has a full wave at half maximum width of . This suggests that the concave corrugated surface could substitute conventional optical lens for focusing and coupling subwavelength devices. Similarly, by inverting the surface structures, the lightwaves splits at the same focusing location.
ZnO nanoparticle size-dependent excitation of surface Raman signal from adsorbed molecules: Observation of a charge-transfer resonance91(2007); http://dx.doi.org/10.1063/1.2817529View Description Hide Description
By observing the Raman intensity of several molecules (4-mercaptopyridine and 4-mercaptobenzoic acid) adsorbed on the surface of ZnOnanocrystals as a function of particle size in the range of diameter, we show that a large increase in intensity is observed near . This is an indication of a size-dependent charge-transfer resonance. We interpret this effect as due to formation of a charge-transfer complex between a surface-bound exciton and the adsorbed molecule.
Enhancement of light extraction efficiency of InGaN quantum wells light emitting diodes using /polystyrene microlens arrays91(2007); http://dx.doi.org/10.1063/1.2816891View Description Hide Description
Improvement of light extraction efficiency of InGaNquantum wellslight emitting diodes(LEDs) using /polystyrene microspheres was demonstrated experimentally. The utilization of /polystyrene microlens arrays on InGaNquantum wellsLEDs, deposited via rapid convective deposition, allows the increase of the effective photon escape cone and reduction in the Fresnel reflection. Improvement of output power by 219% for InGaNquantum wellsLEDs emitting at peak wavelength of with /polystyrene microspheres microlens arrays was demonstrated.
91(2007); http://dx.doi.org/10.1063/1.2817744View Description Hide Description
We experimentally demonstrate that four-wave mixing(FWM) and six-wave mixing (SWM) processes can be selectively turned on and off in a close-cycled four-level atomic system. Under certain laser beam configuration, the FWM and SWM processes can be made to coexist with similar signal amplitudes and transmit through the same electromagnetically induced transparency window in such folded four-level atomic system. By introducing an additional pumpinglaser beam connecting to the fifth energy level, both FWM and SWM signals can be greatly enhanced.
91(2007); http://dx.doi.org/10.1063/1.2817964View Description Hide Description
Infiltration of planar two-dimensional siliconphotonic crystals with nanocomposites using a simple yet effective melt processing technique is presented. The nanocomposites that were developed by evenly dispersing functionalized nanoparticles into a photoconducting polymer were completely filled into photonic crystals with hole sizes ranging from . The infiltrated devices show tuning of the photonic band gap that is controllable by the adjustment of the nanoparticle loading level. These results may be useful in the development of tunable photonic crystal based devices and hybrid light emitting diodes and solor cells.
Second harmonic generation of green light with thermoelectrically oxidized undoped congruent lithium niobate crystals below91(2007); http://dx.doi.org/10.1063/1.2819076View Description Hide Description
We demonstrate that thermoelectric oxidization suppresses unwanted light-induced refractive index changes in undoped congruent periodically poled lithium niobate crystals used for single-pass continuous-wave frequency doubling of light. The maximum second harmonic output power shows a strong dependence on the phase matching temperature. For , a total of green light is generated with an efficiency of 22% corresponding to a normalized conversion efficiency of .
91(2007); http://dx.doi.org/10.1063/1.2819534View Description Hide Description
We have studied the sensitivity of a superconducting NbN hot electronbolometer mixer integrated with a spiral antenna at . Using hot/cold blackbody loads and a beam splitter all in vacuum, we measured a double sideband receiver noisetemperature of at the optimum local oscillator (LO) power of , which is about 12 times the quantum noise. Our result indicates that there is no sign of degradation of the mixing process at the superterahertz frequencies. Moreover, a measurement method is introduced which allows us for an accurate determination of the sensitivity despite LO power fluctuations.
Modifications of the exciton lifetime and internal quantum efficiency for organic light-emitting devices with a weak/strong microcavity91(2007); http://dx.doi.org/10.1063/1.2819610View Description Hide Description
A comprehensive analysis is given on the modifications of the exciton lifetime and internal quantum efficiency for organic light-emitting devices(OLEDs). A linear relation is derived between the exciton lifetime and , which is difficult to measure directly. The internal quantum efficiency can thus be estimated easily through the measurement of the exciton lifetime. The exciton lifetimes for OLEDs with weak or strong microcavity are studied experimentally and theoretically. The modification of the exciton lifetime is well explained through the microcavity effect and surface plasmon resonance. An excellent agreement between the experimental and theoretical results is achieved.
A liquid crystalline polymer microlens array with tunable focal intensity by the polarization control of a liquid crystal layer91(2007); http://dx.doi.org/10.1063/1.2813638View Description Hide Description
We propose a focal intensity tunable microlens array by using a birefringent liquid crystalline polymer for lensing action. Due to the difference of effective refractive indices, it acts as a positive or negative microlens with respect to the polarization state. As we control the incident polarization by adding a liquid crystal layer, the focal intensity can be tuned by an applied voltage. Twisted nematic and bistable ferroelectric liquid crystal modes were applied to demonstrate the possibility of various driving features such as a continuously tunable focal intensity or fast switching with memory effect.
91(2007); http://dx.doi.org/10.1063/1.2819611View Description Hide Description
Complex dynamics of femtosecond terawatt laser pulses in air is investigated theoretically and numerically by considering both susceptibility and multiphoton ionization. Our investigation shows that these two high-order nonlinearities, acting as a Hamiltonian perturbation, can destroy homoclinic orbit connection of phase trajectory and result in spatial chaos and complex pattern of laser wave field. Due to the chaotic behavior of laser field, laser filamentation appears when laser intensity increases close to the ionization threshold.
All-optical demultiplexing of signals with Mach-Zehnder interferometric switch utilizing intersubband transition in quantum well91(2007); http://dx.doi.org/10.1063/1.2820382View Description Hide Description
We have developed a Mach-Zehnder interferometric all-optical switch employing intersubband transition in an -coupled double quantum wellwaveguide. The recently discovered cross-phase modulation phenomenon was utilized as the switching mechanism; the nonlinear index of refraction for transverse electric polarized light is induced by intersubband optical excitation using transverse magnetic pump light. We demonstrate the demultiplexing operation of data signals to using this switch. At the input control pulse energy of , the demultiplexed signals showed an extinction ratio better than , and an error-free demultiplexing was achieved.
- PLASMAS AND ELECTRICAL DISCHARGES
91(2007); http://dx.doi.org/10.1063/1.2805032View Description Hide Description
A study on the dependence of electron energy distribution function(EEDF) on discharge gap size in capacitive rf discharges was conducted. The evolution of the EEDF over a gap size range from in Ar discharges was investigated both experimentally and theoretically. The measured EEDFs exhibited typical bi-Maxwellian forms with low energy electron groups. A significant depletion in the low energy portion of the bi-Maxwellian was found with decreasing gap size. The results show that electron heating by bulk electric fields, which is the main heating process of the low-energy electrons, is greatly enhanced as the gap size decreases, resulting in the abrupt change of the EEDF. The calculated EEDFs based on nonlocal kinetic theory are in good agreement with the experiments.
91(2007); http://dx.doi.org/10.1063/1.2817965View Description Hide Description
In this letter, an experimental study is presented to characterize a room-temperature plasma jet in atmospheric argon generated with submicrosecond voltage pulses at . Distinct from sinusoidally produced argon discharges that are prone to thermal runaway instabilities, the pulsed atmospheric argon plasma jet is stable and cold with an electron density 3.9 times greater than that in a comparable sinusoidal jet. Its optical emission is also much stronger. Electrical measurement suggests that the discharge event is preceded with a prebreakdown phase and its plasma stability is facilitated by the short voltage pulses.
91(2007); http://dx.doi.org/10.1063/1.2817950View Description Hide Description
Amplitude oscillation of the current modulation in an electron beam propagating through background plasma is investigated. An analytical calculation of the beam current modulation indicates amplitude oscillation at the beginning of propagation due to the perturbed space-charge fluctuation of the beam. It was also found that the mode strength of the beam current modulation further downstream grows exponentially from half, , of the initial perturbation instead of its value of , in contrast with the conventional understanding of two-stream instability. The analytical results are in good agreement with earlier simulation data.
Observation of the transition from a Townsend discharge to a glow discharge in helium at atmospheric pressure91(2007); http://dx.doi.org/10.1063/1.2819073View Description Hide Description
Dielectric barrier discharge in helium at atmospheric pressure was studied by taking fast images of the discharge during one current pulse using an intensified charge couple device. It was observed that there appears a weakly luminous layer close to the anode at the very beginning of the discharge, then the luminous area gradually expands into the entire gap as the anode layer moves toward the cathode, and finally a highly luminous layer forms close to the cathode at the time around the maximum of the current pulse. The evolution of the discharge pattern indicates a transition from Townsend discharge to glow discharge.
91(2007); http://dx.doi.org/10.1063/1.2815923View Description Hide Description
A noninvasive method to measure the ion flux from the current flowing through the substrate (substrate current) in a capacitive discharge is proposed. The substrate current consists of a displacement current and a conduction current. In a high frequency capacitively coupled plasma, the displacement current is usually much higher than the conduction current. However, the displacement current becomes negligible at a moment that the second time derivative of the substrate current becomes zero (the first time derivative reaches its minimum), and from the measured substrate current at that time, the ion flux can be obtained. The measured ion flux from this method is compared with the flux measured by another diagnostic method.