Volume 92, Issue 25, 23 June 2008
- 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
- organic electronics and photonics
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
We employ a combination of optical and electron-beam lithography to create an atom chip combining submicron wire structures with larger conventional wires on a single substrate. The multilayer fabrication enables crossed wire configurations, greatly enhancing the flexibility in designing potentials for ultracold quantum gases and Bose–Einstein condensates. Large current densities of and high voltages of up to across gaps are supported by even the smallest wire structures. We experimentally demonstrate the flexibility of the next generation atom chip by producing Bose–Einstein condensates in magnetic traps created by a combination of wires involving all different fabrication methods and structure sizes.
- LASERS, OPTICS, AND OPTOELECTRONICS
92(2008); http://dx.doi.org/10.1063/1.2951621View Description Hide Description
This letter presents the thermo-optic switching characteristics of an optical double-well structure, which has a high-low-high-low-high refractive index construct formed by micromachined siliconprisms and air gaps. Analysis shows such structure features full transmission (i.e., on state) and requires low refractive index change for switching function. The device is fabricated on silicon-on-isolator wafer using deep etching process. In experiment, it measures a switching speed of and an extinction ratio of . Compared with the other micromachined switches, this device utilizes different physical principle and processes various merits such as fast switching speed and low power consumption.
92(2008); http://dx.doi.org/10.1063/1.2949318View Description Hide Description
4H-silicon carbide (SiC) metal-semiconductor-metal (MSM) ultraviolet (UV)photodetectors with (A/S) films employed as antireflection/passivation layers have been demonstrated. The devices showed a peak responsivity of at and maximum external quantum efficiency of 50% at under electrical bias, which were much larger than conventional MSM detectors. The redshift of peak responsivity and response restriction effect were found and analyzed. The A/S/4H-SiC MSM photodetectors were also shown to possess outstanding features including high UV to visible rejection ratio, large photocurrent, etc. These results demonstrate A/S/4H-SiC photodetectors as a promising candidate for OEIC applications.
Influence of tip-sample interaction in a time-domain terahertz scattering near field scanning microscope92(2008); http://dx.doi.org/10.1063/1.2949858View Description Hide Description
Apertureless near field measurements with a metallic tip are performed in the terahertz frequency range. Lateral scans are recorded for different time delays within a terahertz pulse. The forward scattered terahertz signal strongly depends on the time delay. At larger time delays, the tip-sample interaction leads to additional structures in the scan that do not correspond to a change in topography or dielectric function.
Silicon resonant cavity enhanced photodetector based on the internal photoemission effect at : Fabrication and characterization92(2008); http://dx.doi.org/10.1063/1.2952193View Description Hide Description
In this paper, the realization and the characterization of a resonant cavity enhanced (RCE) photodetector, completely silicon compatible and working at , are reported. The detector is a RCE structure incorporating a Schottky diode and its working principle is based on the internal photoemission effect. Taking advantage of a Schottky diode fed on a high reflectivity Bragg mirror, an improvement in responsivity at is experimentally demonstrated.
92(2008); http://dx.doi.org/10.1063/1.2952194View Description Hide Description
Calculations show that electron states are not confined in the dashes in quantum dash-in-a-well laser structures. The combination of strain and three-dimensional confinement reduces the calculated density of states (DOS) near the valence band maximum, with the conduction and valence DOS then almost equal close to the band edges. Calculations and photoabsorption measurements show strongly polarized spontaneous emission and gain spectra. Experimental analysis shows the room temperature threshold current is dominated by nonradiative current paths.
Intensity-dependent enhancement of saturable absorption in nanohybrid composites: Evidence for resonant energy transfer by Auger recombination92(2008); http://dx.doi.org/10.1063/1.2952273View Description Hide Description
Intensity-dependent enhancement of saturable absorption in a film of nanohybrid composites has been observed by femtosecond time-resolved transient absorption measurement at . The nonlinear absorption coefficient of saturable absorption in nanohybrid composites is found to be dependent on excitation irradiance and it is determined to be at , an enhancement of nearly fourfold in comparison with that of pure PbSquantum dots(QDs). The enhancement is attributed to the excitation of surface plasmon by resonant energy transfer between PbSQDs and Aunanoparticles through Auger recombination.
92(2008); http://dx.doi.org/10.1063/1.2952275View Description Hide Description
A series of Zr and Fe codoped crystals was grown and their photorefractive properties have been investigated. Compared with , the concentration of ions is strongly increased in . As a result, the photorefractive response speed of these as-grown crystals is only and the sensitivity is larger than while the saturation diffraction efficiency still remains at a high level. These findings prove that is an excellent choice for volume holographic storage.
Multilayer white polymer light-emitting diodes with deoxyribonucleic acid-cetyltrimetylammonium complex as a hole-transporting/electron-blocking layer92(2008); http://dx.doi.org/10.1063/1.2948864View Description Hide Description
Using a thin film of deoxyribonucleic acid-cetyltrimetylammonium (DNA-CTMA) complex as a hole-transporting/electron-blocking layer, we have developed a sequential solution-processing approach for constructing multilayer (up to five layers) white polymer light-emitting diodes, incorporating the poly(9,9-dioctylfluorene-2,7-diyl)/poly[2-methoxy-5( -ethyl-hexyloxy)-1, 4-phenylene vinylene] emissive layer. These devices were demonstrated to show a low turn-on voltage , high efficiency , and high brightness with an improved white-color stability.
Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes92(2008); http://dx.doi.org/10.1063/1.2951599View Description Hide Description
We show that when a microsphere is illuminated by an evanescent wave, the optical forces on- and off-whispering gallery mode (WGM) resonance can differ by several orders of magnitude. Such size-selective force allows one to selectively manipulate the resonating particles, while leaving those particles at off-resonance untouched. As WGM resonances have very high-’s, this kind of force could be deployed for size-selective manipulation with a very high accuracy , as well as simultaneous particle-sorting according to their size or resonant frequency.
Enhanced emission efficiency of multiple quantum well light-emitting diode with an embedded photonic crystal92(2008); http://dx.doi.org/10.1063/1.2948851View Description Hide Description
A photonic crystal(PC)structure of periodic pillar cubic array is embedded in layer of multiple quantum well(MQW) blue light-emitting diode(LED). The diameter, period, and depth of pillar are , , and , respectively. The increments of 70% for external quantum efficiency, 17% for internal quantum efficiency, and 45% for light extraction efficiency from photoluminescence measurement, and 33% for optical output power at are observed for LEDs with an embedded PC layer. This improvement can be attributed to the increased extraction efficiency by PC effect as well as increased internal quantum efficiency due to the decrease of dislocation density in layer because of an epitaxial lateral over-growth process.
92(2008); http://dx.doi.org/10.1063/1.2952462View Description Hide Description
Pockel’s effect and optical rectification are demonstrated in the charge space region of a (111)-cut near-intrinsic silicon crystal by the use of a planar metal-insulator-semiconductor structure. The results show that both Pockel’s effect and optical rectification are so considerable that these effects should be taken into account for designing silicon-based photonic devices. The anisotropy of optical rectification is measured too, and experimental results are in good accordance with the theoretical analysis. These effects can also be used as a tool to investigate the properties of the charge space region of silicon devices in future.
92(2008); http://dx.doi.org/10.1063/1.2952486View Description Hide Description
We report on the first experimental observation of Tamm plasmonpolaritons (TPPs) formed at the interface between a metal and a dielectric Bragg reflector (DBR). In contrast to conventional surface plasmons, TPPs have an in-plane wavevector less than the wavevector of light in vacuum, which allows for their direct optical excitation. The angular resolved reflectivity and transmission spectra of a DBR covered by Au films of various thicknesses show the resonances associated with the TPP at low temperatures and room temperature. The in-plane dispersion of TTPs is parabolic with an effective mass of of the free electron mass.
92(2008); http://dx.doi.org/10.1063/1.2952488View Description Hide Description
We study the optical output power of a semiconductor laser, which exploits tunneling-injection of electrons and holes into quantum dots(QDs) from two separate quantum wells. Even if there is out-tunneling leakage of carriers from QDs, the intensity of parasitic recombination outside QDs remains restricted with increasing injection current. As a result, the light-current characteristic becomes increasingly linear, and the slope efficiency grows closer to unity at high injection currents—a fascinating feature favoring the use of tunneling-injection of both electrons and holes into QDs for high-power lasing.
92(2008); http://dx.doi.org/10.1063/1.2952509View Description Hide Description
We investigate theoretically the spin splitting of the exciton states in semiconductor coupled quantum dots (CQDs) containing a single magnetic ion. We find that the spin splitting can be switched on/off in the CQDs via the exchange interaction using the electric field. An interesting bright-to-dark exciton transition can be found and it significantly affects the photoluminescence spectrum. This phenomenon is induced by the transition of the ground exciton state, arising from the hole mixing effect, between the bonding and antibonding states.
Experimental demonstration of phase locking of a two-dimensional fiber laser array using a self-imaging resonator92(2008); http://dx.doi.org/10.1063/1.2952508View Description Hide Description
Phase locking of a two-dimensional fiber laser array is experimentally demonstrated by using a self-imaging resonator and a spatial filter. The stable beam profiles of in-phase mode and out-of-phase mode are observed by controlling the position of spatial filter. The phase locking fiber array with in-phase mode has produced coherent output. An antisymmetric eigenmode is also observed in our experiments. The phase locking is not sensitive to power variations among the pump beams and the configuration has the ability to repair a missing element.
Tunable surface plasmons for emission enhancement of silicon nanocrystals using Ag-poor cermet layer92(2008); http://dx.doi.org/10.1063/1.2953085View Description Hide Description
To improve the quantum efficiency from silicon nanocrystals, a structure with -poor cermet layers is proposed. Due to large permittivity of Ag-poor cermet and its dispersion characteristic, density of states can be enhanced at the energy much lower than the plasmon energy of Ag. By properly choosing the component of the Ag-poor cermet, the dispersion of surface plasmons can be engineered to increase radiative emission rate significantly at the emission energy of silicon nanocrystals. Effective enhancement is theoretically demonstrated using Ag, which was generally recognized as nonideal material for emission enhancement in silicon nanocrystals due to its high plasmon energy.
92(2008); http://dx.doi.org/10.1063/1.2950322View Description Hide Description
The dependence of the negative refraction of a simple Fabry–Perot system as a function of the sign of materialpermittivity and permeability is analyzed. It is shown that negative refraction is possible every time the transmission phase of the system shows an anomalous behavior. However if the permittivity or the permeability are complex the anomalous phase is no longer univocally related to the presence of a negative refractive index.
- PLASMAS AND ELECTRICAL DISCHARGES
92(2008); http://dx.doi.org/10.1063/1.2951595View Description Hide Description
The effect of pulse duration on in-band (2% bandwidth) conversion efficiency (CE) from a laser to extreme ultraviolet(EUV) light was investigated for Sn plasma. It was found that high in-band CE, 2.6%, is consistently obtained using a laser with pulse durations from . Employing a long pulse, for example, , in a laser system used in an EUV lithography source could make the system significantly more efficient, simpler, and cheaper as compared to that using a short pulse of or shorter.
92(2008); http://dx.doi.org/10.1063/1.2945283View Description Hide Description
The interaction of laser pulses with plasma is studied to scale the high-field physics from high power laser systems to low-energy, high-repetition-rate lasers. For this purpose, , Ti:sapphire laser pulses were focused in a spot of with a maximum intensity of . Efficient generations of energetic electrons and hard x-rays with energies of over were obtained by irradiating the low-energy, tightly focused laser pulses on a massive Cu target.
92(2008); http://dx.doi.org/10.1063/1.2952496View Description Hide Description
Positive pulsed corona discharge has been applied for the oxidation of gaseous elemental mercury from a simulated flue gas. The oxidation of to HgO and can significantly enhance the mercury removal from flue gas. At a gas condition of (10%), (3%), and (balance), oxidation efficiency of 84% was achieved at an input energy density of . The presence of NO, however, hinders oxidation due to the preferential reaction of NO with O and . On the contrary, shows little effect on oxidation due to its preferential reaction with OH. It has been also observed that the HCl in gas stream can be dissociated to Cl and and can induce additional oxidation to .