Volume 85, Issue 22, 29 November 2004
- lasers, optics, and optoelectronics
- 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:
An array of microcantilever beams, coated with a self-assembled monolayer of bistable, redox-controllable rotaxane molecules, undergoes controllable and reversible bending when it is exposed to chemical oxidants and reductants. Conversely, beams that are coated with a redox-active but mechanically inert control compound do not display the same bending. A series of control experiments and rational assessments preclude the influence of heat, photothermal effects, and variation as potential mechanisms of beam bending. Along with a simple calculation from a force balance diagram, these observations support the hypothesis that the cumulative nanoscale movements within surface-bound “molecular muscles” can be harnessed to perform larger-scale mechanical work.
- LASERS, OPTICS, AND OPTOELECTRONICS
Internal light source technique free from reabsorption losses for optical characterization of planar photonic crystals85(2004); http://dx.doi.org/10.1063/1.1826234View Description Hide Description
An optimization of the internal light source (ILS) technique for optical characterization of planar photonic crystals (PPhCs) is presented. The approach makes use of a double planar waveguidestructure that separates the region where the light emitting layers are embedded from the region where the PPhCs are fabricated. This technique is demonstrated to be free from reabsorption losses, thus combining the advantages of standard optical techniques with the versatility of the ILS setup. We validate this method by comparison with standard ILS measurements on several PPhC structures.
Efficient optical parametric oscillation based on periodically poled 1.0 mol % MgO-doped stoichiometric85(2004); http://dx.doi.org/10.1063/1.1828211View Description Hide Description
Effective optical parametric oscillation (OPO) at room temperature was demonstrated by a periodically poled 1.0 mol% MgO-doped stoichiometric lithium tantalate crystal. The slope conversion efficiency of total output power was and the maximum output power was 655 mW at 1.3 W pumping without photorefraction. The difference of the OPO performance was investigated between 0.5 and 1.0 mol % crystals, and a 1.0 mol % MgO-doped device exhibited better OPO performance and high resistance of photorefraction. The effective nonlinear coefficient of was found to be by single-pass first-order quasiphase matched second-harmonic generation at 1064 nm.
85(2004); http://dx.doi.org/10.1063/1.1828578View Description Hide Description
We report optical signal amplification in a solid-state dye-doped polymer with a rib waveguidestructure. A pulsed signal and a collinear pump are coupled into a poly(methyl methacrylate) waveguidedoped with 1% by weight Rhodamine 640 dye. Depending on the signal intensity, a maximum optical gain in the range is obtained from a -long device, accompanied by a signal-to-noise ratio in the range.
85(2004); http://dx.doi.org/10.1063/1.1825067View Description Hide Description
ZnOsingle-crystal microtubes were fabricated using an encapsulated microwavegrowth method. The ZnO crystals are grown in hexagonal hollow tube form with a well faceted end and side surfaces, which have cross-sectional dimensions of , lengths of , and wall thickness of . Under optical excitation, a strong near-band-edge emission was obtained at a peak wavelength of with a full width at half maximum of . The ZnO microtubes exhibited a highly selective UV light response with a cut-off wavelength at , and excellent electron field emission properties with an emission current density of at an applied field of .
Nonpolar emitters on reduced-defect lateral epitaxially overgrown -plane GaN with drive-current-independent electroluminescence emission peak85(2004); http://dx.doi.org/10.1063/1.1825612View Description Hide Description
Nonpolar -plane multiple-quantum-welllight-emitting diodes were grown by metalorganic chemical vapor deposition on reduced-defect density hydride-vapor-phase-epitaxy lateral epitaxially overgrown -plane GaN templates. Direct current output power of 240 μW was measured at 20 mA for a device, and dc output powers as high as 1.5 mW were measured at 250 mA. DCelectroluminescence(EL)measurements yielded a peak at 413.5 nm, corresponding with the room-temperature photoluminescence peak. The EL peak position was independent of drive current and a 23.5 nm linewidth was realized at 20 mA. The current–voltage characteristics of these diodes showed a forward voltage of 3.3 V with a series resistance of 7.8 Ω.
Multimode transflective liquid crystal display with a single cell gap using a self-masking process of photoalignment85(2004); http://dx.doi.org/10.1063/1.1828223View Description Hide Description
We demonstrate a transflective liquid crystal display(LCD),doped with a chiral agent to produce a low helical twisting power, in a multimode configuration consisting of the homogeneous alignment and the hybrid alignment. The multimode transflective LCD was fabricated by a single-step exposure of the UV light through an array of metal reflectors used as an amplitude photomask which gives an alternating homogeneous and homeotropic LC geometry. This single-step UV exposure produces no cell gap variations. In our configuration, the electro-optical disparity between the transmissive region and the reflective region was found to be significantly reduced by the low helical twisting power of the chiraldopant.
85(2004); http://dx.doi.org/10.1063/1.1828596View Description Hide Description
Ridge waveguide InGaAsN triple-quantum-well strain-compensated lasers grown by metal-organic chemical vapor deposition were fabricated with pulsed anodic oxidation. Laser output power reached in cw mode at room temperature from stripe lasers with a wavelength of . The threshold-current density was . The characteristic temperature of the lasers was in the linear region .
85(2004); http://dx.doi.org/10.1063/1.1828233View Description Hide Description
This letter discusses theoretical studies of optical properties of goldnanospheres and nanorods with various aspect ratios; these are embedded in a porous anodic alumina matrix. The nanoparticles have potential applications in optical filters and sensors.
85(2004); http://dx.doi.org/10.1063/1.1828235View Description Hide Description
Poly(-phenylene vinylene) (PPV) is a promising material, but shows poor processability, such as doping, due to its insolubility and infusibility. Therefore, the development of a standard and easy method of dye doping into PPV is important for device fabrication using PPV. We developed a simple method for the dispersal of dyes into PPV without deformation. Using this method, it was possible to change the color of PPV from yellow to green by doping with the blue dye 1,4-(’-diethylamino)anthraquinone (SV59). The amount of SV59 doped into PPV was . The fluorescencecolor of PPV could be changed from green to red by 2 min dispersal of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)--pyran.
85(2004); http://dx.doi.org/10.1063/1.1830076View Description Hide Description
It was found that the decrease of the multiple quantum well(MQW) growth temperature from 865 to 810 °C leads to a MQW emission wavelength shift from the violet to the green spectral region. The lowering of the growth temperature also promotes a decrease of the MQWphotoluminescence(PL) intensity at high excitation and a disappearance of the excitonic features from the low-temperature reflection and PLspectra of GaN barriers and claddings. The laser threshold dependence on is not monotonic, with the lowest value of at . High-temperature annealing (900 °C, 30 min) leads to a twofold increase of the PL efficiency only from the InGaNQWs grown at the lowest temperature. The results allow one to explain the laser threshold behavior in terms of the heterostructure quality, the defect concentration, In clusterization, and the piezoelectric field dependence on the MQW growth temperature.
85(2004); http://dx.doi.org/10.1063/1.1830071View Description Hide Description
By the two-dimensional triangular holey structure, a high-power stable single-mode operation was demonstrated in oxide confined vertical-cavity surface-emitting lasers. For two types of hole alignments, the lasing operation was observed with different near field patterns, i.e., a single spot pattern and a floral pattern. The former showed an output power of with a high side-mode suppression ratio (SMSR) of , which is explained by the selective loss mechanism. The latter showed a high power of with a SMSR of . The observed lasing spectrum and far field pattern indicate that it is a deformed fundamental mode whose bright spots extending over the device are in-phase oscillating. This device structure will be effective for the enhancement of single-mode power in devices with any material system.
The role of Auger recombination in the temperature-dependent output characteristics of -doped 1.3 μm quantum dot lasers85(2004); http://dx.doi.org/10.1063/1.1829158View Description Hide Description
Temperature invariant output slope efficiency and threshold current in the temperature range of 5–75 °C have been measured for 1.3 μm -doped self-organizedquantum dot lasers. Similar undoped quantum dot lasers exhibit in the same temperature range. A self-consistent model has been employed to calculate the various radiative and nonradiative current components in -doped and undoped lasers and to analyze the measured data. It is observed that Auger recombination in the dots plays an important role in determining the threshold current of the -doped lasers.
85(2004); http://dx.doi.org/10.1063/1.1827336View Description Hide Description
Buried and stacked planar as well as buried single and parallel channel waveguides are fabricated in sapphire by protonimplantation. Good control of the implantation parameters provides excellent confinement of the guided light in each structure. Low propagation losses are obtained in fundamental-mode, buried channel waveguides without postimplantation annealing. Choice of the implantation parameters allows one to design mode shapes with different ellipticity and∕or mode asymmetry in each orthogonal direction, thus demonstrating the versatility of the fabrication method. Horizontal and vertical parallelization is demonstrated for the design of one- or two-dimensional waveguide arrays in hard crystalline materials.
Improved device efficiency and color purity: Spectral redshift and line narrowing for poly via blending with phenyl-substituted poly [-phenylene vinylene] derivatives85(2004); http://dx.doi.org/10.1063/1.1828594View Description Hide Description
Highly efficient light-emitting diodes with redshifted narrow emission were realized based on blends of poly (MEH-PPV) and phenyl-substituted poly [-phenylene vinylene] derivative (P-PPV). EL emissions of blend device were redshifted about from the peak emission of for neat MEH-PPV device to around for devices from the blend film. The full width at half maximum of MEH-PPV emission from blend film was reduced from 91 to . The external quantum and luminous efficiencies of devices from blend films reached 5.27% and , respectively. The effective energy transfer and solid-state dilution effect of MEH-PPV in P-PPV host were thought of as the origin of the performance enhancement.
85(2004); http://dx.doi.org/10.1063/1.1829798View Description Hide Description
A metallic photonic crystalfilter has been demonstrated at terahertz frequencies, with the passband tunable over the range of 365–386 GHz. Tuning is achieved by a relative lateral shift of two metallic photonic crystal plates. Each plate is comprised of two orthogonal layers of gratings and integral mounting lugs. The plates are micromachined from silicon wafers then coated in gold to provide metallic electromagnetic behavior. An insertion loss of 3–7 dB and in the range of 20–30 was achieved. A shift of gave a tuning range of 21 GHz, tuning sensitivity of 150 GHz/mm, and a fractional tuning range of 6%.
gain in a hybrid silicate/phosphate glasses optical amplifier made by wafer bonding and ion-exchange techniques85(2004); http://dx.doi.org/10.1063/1.1829141View Description Hide Description
In this letter, we present the realization of a hybrid optical amplifier composed of an erbium/ytterbium co-doped phosphate glass wafer bonded on a silicate glass substrate. Indeed, a thin guiding phophate glass layer has been reported on an ion-exchanged channel passive waveguide by the wafer bonding technique creating a hybrid guiding structure. A gain for launched pump has been demonstrated with a -long hybrid amplifier.
85(2004); http://dx.doi.org/10.1063/1.1829167View Description Hide Description
GaN-based, mushroom-shaped microdisk lasers were fabricated using band-gap selective photoelectrochemical etching. The optically pumped microdisks had well-defined, distinct modes at excitation powers ranging from about . Modal linewidths of were reported, which was near the resolution of the measurement equipment. Quality factors for the microdisks were . The observed lasing threshold was . At higher excitation powers, heating effects and degradation were observed in the optical response of the microdisks.
85(2004); http://dx.doi.org/10.1063/1.1828593View Description Hide Description
We develop a method for the fabrication of functional microstructured optical fibers(MOFs) by selectively filling the air holes with liquid phase materials, where we utilize the dependence of filling speed on the size of the air holes. As a demonstration, we construct a hybrid MOF by filling the center hollow core of a triangular lattice photonic crystal fiber with dye-doped curable polymer, and experimentally observe the two-photon fluorescence from the hybrid MOF.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
85(2004); http://dx.doi.org/10.1063/1.1827331View Description Hide Description
In order to assess transverse elastic modulus of lead zirconate titanate(PZT)thin films, we used a nanoindenter with constant monitoring of the force. It is shown that the true elastic modulus, i.e., the low pressure elastic modulus, can be measured by this method. This permitted a determination that sputter depositedPZTfilms display a Young modulus close to a ferroelectric hard type PZT bulk ceramic. Moreover, this low pressure modulus is independent of grain size and thickness of the film, but this is no more true for high pressure modulus. This provides a step toward a better understanding of the properties of these PZTfilms and the possibility to better use them in microsystems.
Determination of the coefficient of friction between metal and diamond under high hydrostatic pressure85(2004); http://dx.doi.org/10.1063/1.1828579View Description Hide Description
We have developed an experimental method to obtain the coefficient of friction between diamond and metal under high confining pressure in the diamond anvil cell. A metal ring is compressed between the diamond anvils and its inner and outer diameters are measured as a function of the compression. Measured dimensions are then compared to the results of finite element simulations, in which the coefficient of friction is a free parameter. As an example, we apply the method to polycrystallinemolybdenum up to a hydrostaticpressure of .