Volume 91, Issue 1, 02 July 2007
- 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:
Monolithic mass sensors for ultrasensitive mass detection in air conditions have been fabricated using a conventional complementary metal-oxide-semiconductor(CMOS) process. The mass sensors are based on electrostatically excited submicrometer scale cantilevers integrated with CMOS electronics. The devices have been calibrated obtaining an experimental sensitivity of equivalent to for locally deposited mass. Results from time-resolved mass measurements are also presented. An evaluation of the mass resolution have been performed obtaining a value of in air conditions, resulting in an improvement of these devices from previous works in terms of sensitivity, resolution, and fabrication process complexity.
- LASERS, OPTICS, AND OPTOELECTRONICS
91(2007); http://dx.doi.org/10.1063/1.2754365View Description Hide Description
The authors demonstrate broadband efficient quasiphase matched second harmonic generation(SHG) in nonlinear crystals. The distribution of ferroelectric domains in a short-range order provides the possibility for broadband second harmonic generation in the visible range. This process is similar to the broadband SHG in random media, but it results in much higher conversion efficiency. The unique distribution of reciprocal vectors provided by the structuralshort-range order plays an important role in the enhancement. The achieved broadband SHG with high conversion efficiency will aid in the development of optics integration and multiple-channel devices.
Terahertz wave emission and detection using photoconductive antennas made on low-temperature-grown InGaAs with pulse excitation91(2007); http://dx.doi.org/10.1063/1.2754370View Description Hide Description
Photoconductive antennas made on low-temperature-grown Be doped have been investigated focusing on the terahertz emission properties. In the antenna of , the resistance as high as enabled us to increase the bias field up to , and the terahertz waves emitted from the antenna were significantly enhanced. In addition, terahertz waves with the spectral range over and the peak to noise ratio of were generated and detected using only pulses.
91(2007); http://dx.doi.org/10.1063/1.2753492View Description Hide Description
The dynamic behavior for the splay to bend transition of pi cell is investigated numerically in detail. When a pi cell has asymmetric pretilt angles, the initial splay configuration changes to asymmetric state driven by a low voltage, then to bend configuration driven by a pulse voltage that is larger than a transition voltage. The author’s results show that the transition voltage decreases with the increasing pretilt angle, and increases with the increasing anchoring energy and surfaceviscosity. The transition time is less than which is much faster than that of other methods.
91(2007); http://dx.doi.org/10.1063/1.2754356View Description Hide Description
Silicon-based light emitters have been fabricated on silicon-on-insulator substrates by embedding Geself-assembledquantum dots in microdisk resonators. Strong room-temperature resonantluminescence is observed from the microdisks under optical pumping. Photoluminescence from Gequantum dots is significantly enhanced by the microdisk resonators. Different kinds of cavity modes, whispering-gallery modes, and Fabry-Pérot modes are observed in the wavelength range from for microdisks with different diameters.
91(2007); http://dx.doi.org/10.1063/1.2753542View Description Hide Description
Amplification of three short light pulses in a time window at repetition rate has been demonstrated using a compact amplifier based on the conjugated polymer poly(9,-dioctylfluorene-co-benzothiadiazole). The amplifier was optically pumped and gratings were used to couple the signal into and out of the film. A gain of was observed for a signal pulse temporally aligned with the pump pulse in a waveguide. For a signal pulse delayed by , the maximum gain achieved was . The results are a step towards the use of polymeramplifiers in data communications.
91(2007); http://dx.doi.org/10.1063/1.2753697View Description Hide Description
Scalable fabrication of electrowetting displays with self-assembled oil dosing is reported. Electrowetting pixel structures consisted of flexible substrate/electrode/hydrophobic dielectric/hydrophilic grid. 20 electrowetting display prototypes were constructed with four pixel sizes ranging from and with five grid thicknesses ranging from . Self-assembled oil dosing was achieved by dip coating the substrate through an oil film suspended on water. The oil films in pixels were geometrically flat. Operating voltage increased with pixel aspect ratio. Electrical capacitance and optical absorption calculations confirm that oil thickness is within of the hydrophilic grid height.
91(2007); http://dx.doi.org/10.1063/1.2753746View Description Hide Description
Optical phonons assisted infrared absorption in based bolometer is demonstrated to be free, low, or over damping oscillation over different spectral ranges depending on the passivation thickness. In particular, it will become saturated due to the over damping oscillation in the spectral range corresponding to the absorption bands from strong phonon vibrations. The device reaches a peak absorbance of 99.9% at wavelength of and shows a broadband absorption, independent of metal-insulator transition and radiation incident angle up to 30° in the long wavelength infrared region.
91(2007); http://dx.doi.org/10.1063/1.2753747View Description Hide Description
The authors report on the terahertz time-domain spectroscopy of single-walled carbon nanotubes(SWCNTs) dispersed in a polymer film in a broad frequency range from . The complex dielectric function of the compositefilm is obtained without using Kramers-Kronig analysis, from which the dielectric function of SWCNTs is extracted by using the effective medium theory. The real part of the dielectric function exhibits very large values at low frequency below . The conductivity spectrum shows a peak around . The spectral behavior is consistent with overdamped Lorentzoscillator model, indicating the response of curvature-induced small-gap SWCNTs.
91(2007); http://dx.doi.org/10.1063/1.2753763View Description Hide Description
The authors demonstrate a novel atomic magnetometer that uses differential detection of the spatially diverging components of a light field to monitor the Larmor precession frequency of atoms in a thermal vapor. The design is implemented in compact form with a micromachined alkali vapor cell and a naturally divergent light field emitted by a vertical-cavity surface-emitting laser. Operating the magnetometer in differential mode cancels common-mode noise and improves the sensitivity by a factor of 26 over single-channel operation. They also suggest ways in which the current sensitivity of may be improved further without sacrificing size or simplicity.
91(2007); http://dx.doi.org/10.1063/1.2754363View Description Hide Description
A multikilowatt chemical oxygen-iodine laser (COIL) using molecular iodine generated chemically as the iodine source was developed and tested. The COIL, with a gain length of , was energized by a square pipe-array jet singlet oxygen generator (JSOG), with a nozzle bank having a designed Mach number of 2.5. The JSOG, operating without a primary buffer gas, has a much better operation stability during basic hydrogen peroxide pumping circulations. Iodine injectors/nozzles made of polyimide were used. An output power of and a chemical efficiency of 24.5% were achieved with a chlorine flow rate of .
Aggregation-induced emissions of tetraphenylethene derivatives and their utilities as chemical vapor sensors and in organic light-emitting diodes91(2007); http://dx.doi.org/10.1063/1.2753723View Description Hide Description
Nonemissive tetraphenylethene (TPE) 1 and its diphenylated derivative 2 were induced to emit intensely by aggregate formation. Crystalline aggregates of the dyes emitted bluer lights than their amorphous counterparts. The emissions of the TPE dyes could be switched off and on continuously and reversibly by wetting and dewetting with solvent vapors, respectively, manifesting their ability to optically sense volatile organic compounds. The light-emitting diodes fabricated from 1 and 2 were turned on at and and emitted blue lights with maximum luminance of and , respectively.
Differential phase shift quantum key distribution using single-photon detectors based on a sinusoidally gated avalanche photodiode91(2007); http://dx.doi.org/10.1063/1.2753767View Description Hide Description
The authors report a quantum key distribution experiment, in which they implemented a differential phase shift quantum key distribution protocol, using single-photon detectors based on avalanche photodiodes operated with a sinusoidal gating. The single-photon detectors were operated at a repetition frequency of with low after pulsing probabilities and low dark counts. A sifted key generation rate of was achieved over a communication distance of . Taking account of the security of the protocol against general individual attacks, secure keys can be generated with a rate of .
Low driving voltage and high stability organic light-emitting diodes with rhenium oxide-doped hole transporting layer91(2007); http://dx.doi.org/10.1063/1.2754635View Description Hide Description
The authors report a promising metal oxide-doped hole transporting layer (HTL) of rhenium oxide -doped -diphenyl--bis (-biphenyl)--diamine (NPB). The tris(8-hydroxyquinoline) aluminum-based organic light-emitting diodes with -doped NPB HTL exhibit driving voltage of and power efficiency of at , which is significantly improved compared to those ( and , respectively) obtained from the devices with undoped NPB. Furthermore, the device with -doped NPB layer reveals the prolonged lifetime than that with undoped NPB. Details of doping effects are described based on the UV-Vis absorption spectra and characteristics of hole-only devices.
91(2007); http://dx.doi.org/10.1063/1.2754641View Description Hide Description
Correlation between the rectilinear polarizations of the photons emitted from the biexciton decay in a single quantum dot is investigated in a device which allows the charge state of the dot to be controlled. Optimizing emission from the neutral exciton states maximizes the operating efficiency of the biexciton decay. This is important for single dot applications such as a triggered source of entangled photons. As the bias on the device is reduced correlation between the two photons is found to fall dramatically as emission from the negatively charged exciton becomes significant. Lifetime measurements demonstrate that electronic spin-scattering is the likely cause.
91(2007); http://dx.doi.org/10.1063/1.2754360View Description Hide Description
The authors describe the fabrication of low loss rib waveguides. Pulsed laser deposition was used to obtain high quality, dense films with the same stoichiometry as the bulk glass, while standard semiconductor processing was used to pattern the waveguides. They obtained rib waveguides of 3, 4, and wide with propagation losses ( at ) more than ten times lower than previously reported for this material.
91(2007); http://dx.doi.org/10.1063/1.2751586View Description Hide Description
The influence of fabrication-induced imperfections and material absorption on the quality factor of a microcavity pillar is studied numerically. The dependence on sidewall inclination, selective underetch, and intrinsic loss is quantified. The authors show that imperfections can lead to an improvement in and that a sidewall inclination angle of less than 1° causes a dramatic change in the factor. The variations in can be attributed to a delicate balance between effective index contrasts, mode overlap, and higher-order mode contributions.
91(2007); http://dx.doi.org/10.1063/1.2749427View Description Hide Description
Computed tomography of diffraction enhanced imaging (DEI-CT) based on synchrotron radiationsource has extremely high sensitivity of weakly absorbing low- samples in medical and biological fields. The authors propose a modified backprojection filtration(BPF)-type algorithm based on PI-line segments to reconstruct region of interest from truncated refraction-angle projection data in DEI-CT. The distribution of refractive index decrement in the sample can be directly estimated from its reconstruction images, which has been proved by experiments at the Beijing Synchrotron Radiation Facility. The algorithm paves the way for local reconstruction of large-size samples by the use of DEI-CT with small field of view based on synchrotron radiationsource.
91(2007); http://dx.doi.org/10.1063/1.2754357View Description Hide Description
An analytical model based on the diffraction-induced transformation [A. E. Kaplan, J. Opt. Soc. Am. B15, 951 (1998)] for an ultrashort subcycle laser pulse propagating in vacuum is considered. The pulse is initially Gaussian. To the lowest order of the diffraction angle its evolution satisfies Maxwell’sequations. The model is used to study the motion of charged particles in the pulse. It is shown that the delta-function representation is an excellent approximation of a subcycle pulse for studying charged-particle dynamics in subcycle pulse.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
91(2007); http://dx.doi.org/10.1063/1.2753494View Description Hide Description
Dimensional stability and structural reliability are major concerns for thermoplastics due to their nature of high mobility of polymer chains. Here the authors report the creep experiments on polypropylene filled with nanoparticles with diameter of 21 or at different load levels and temperatures, which show that the dimensional stability of the nanocomposites is significantly improved, especially by loading small sized nanoparticles. The creep strain and creep rate of nanoparticle-filled polypropylene are reduced by 46% and 80%, respectively, compared to those of the neat matrix. Additionally, creep lifetime is extended by 330% due to the addition of small nanoparticles.
Influence of temperature and photoexcitation density on the quantum efficiency of defect emission in ZnO powders91(2007); http://dx.doi.org/10.1063/1.2753540View Description Hide Description
The effect of laser excitation power density on the efficiency of intrinsic defect emission in ZnOpowders was characterized by varying the laser irradiance over three orders of magnitude and monitoring changes in the samples’ photoluminescence. The external quantum efficiency of the visible wavelength, broadband defect photoluminescence was found to depend not only on laser irradiance but also on temperature and prior annealing conditions. This material system is potentially useful as an ultraviolet-photoexcited, white light phosphor under low-power excitation at room temperature and below.