By Topic

Applied Physics Letters

Issue 14 • Date Apr 2005

Filter Results

Displaying Results 1 - 25 of 86
  • Issue Cover

    Page(s): c1
    Save to Project icon | PDF file iconPDF (455 KB)  
    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
    Save to Project icon | PDF file iconPDF (47 KB)  
    Freely Available from IEEE
  • Tuning of spontaneous emission of two-dimensional photonic crystal microcavities by accurate control of slab thickness

    Page(s): 141101 - 141101-3
    Save to Project icon | PDF file iconPDF (165 KB)  

    We have found a blueshift in the cavity modes confined in two-dimensional photonic crystal microcavities when the thickness of the slab was varied uniformly by accurate dry etching. The shifts in the wavelength of the cavity modes were around 2 nm towards shorter wavelengths per nanometer reduced in the thickness of the slab. Three-dimensional plane wave expansion calculations showed that the observed shifts are inside the calculated photonic band gap of the structures. The variation in the energy position of the peaks with the thickness has been analyzed by three-dimensional finite difference time domain calculations for a one missing hole microcavity. This tuning of the emission wavelength with the change in the thickness slab shows the important effect of the third dimension in photonic crystals made out of semiconductor slabs and it can be of interest for its application in the final processed photonic devices like photonic crystal lasers. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Transmission properties of terahertz pulses through an ultrathin subwavelength silicon hole array

    Page(s): 141102 - 141102-3
    Save to Project icon | PDF file iconPDF (106 KB)  

    We demonstrate extraordinary THz transmission of an array of subwavelength apertures patterned on ultrathin highly doped silicon by reactive ion etching. The zero-order transmission spectra exhibit well-defined maxima and minima which are attributed to the excitation of surface-plasmon polaritons and Wood’s anomaly. The transmission anisotropy is investigated with respect to the orientation of the elliptical hole array in the frequency range from 0.2 to 3.5 THz, and we notice that the transmission increases significantly when the major axis of the elliptical hole is perpendicular to the polarization of THz beam. In addition, redshift and reduction in transmission amplitude are observed when the surrounding dielectric permittivity is increased. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electronic control of nonresonant random lasing from a dye-doped smectic A* liquid crystal scattering device

    Page(s): 141103 - 141103-3
    Save to Project icon | PDF file iconPDF (198 KB)  

    The electronic control of the excitation threshold for random lasing in a dye-doped smectic A* liquid crystal is demonstrated. Random lasing is the term given to the nonlinear amplification of light which is the result of feedback due to multiple scattering. With the application of an electric field the smectic A* phase forms a highly scattering texture for which the nonlinear amplification of light occurs at an excitation threshold of 10 μJ/pulse. In comparison, nonlinear amplification is not observed in the field induced homeotropic texture. As a result, a device has been conceived and demonstrated whereby random lasing is switched “on” or “off” with an applied electric field. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Design, fabrication, and characterization of a two-dimensional photonic-crystal symmetric Mach-Zehnder interferometer for optical integrated circuits

    Page(s): 141104 - 141104-3
    Save to Project icon | PDF file iconPDF (383 KB)  

    We report on the design, fabrication, and optical characterization of a GaAs two-dimensional photonic-crystal-based symmetric Mach-Zehnder interferometer (PC-SMZ) aimed at all-optical switches in planar photonic integrated systems. The directional couplers that constitute the PC-SMZ interferometer prevent the occurrence of ring resonance which degrades the interference, and allow control pulses for the switching operation to be received. We show 50%- and 100%-power couplings from the transmission characteristics of the directional couplers, thus demonstrating their operation as 3-dB dividers in the PC-SMZ. We also show experimentally wavelength selectivity between signal and control pulses with a separation of ∼7 nm. These results indicate that the structure is promising as an all-optical switch when a nonlinear material such as a quantum dot is introduced into both arms of the interferometer. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Regenerated surface plasmon polaritons

    Page(s): 141105 - 141105-3
    Save to Project icon | PDF file iconPDF (206 KB)  

    We discuss a way to increase surface plasmon polariton (SPP) propagation lengths and intensities. It involves reflecting radiation loss back to the propagation surface, regenerating SPPs. This is achieved with a metal-dielectric structure, which is also designed to efficiently couple in external light. Flexibility in the design of the structure allows for optimization of SPP properties. Extensive finite-difference time-domain simulations, including coupling external light into the system, demonstrate the approach. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Tetracene light-emitting transistors on flexible plastic substrates

    Page(s): 141106 - 141106-3
    Save to Project icon | PDF file iconPDF (122 KB)  

    We report on organic light-emitting (field-effect) transistors (LETs) fabricated on a flexible and transparent plastic foil (Mylar), acting both as substrate and gate dielectric. The foil is patterned on one side with bottom-contact gold source and drain electrodes, while a thin film of gold is evaporated on the opposite side of the foil to form the gate electrode. A vacuum sublimed tetracene film is employed as an active layer for charge transport and light emission. Atomic force microscopy shows that tetracene films have a good adhesion on Mylar and exhibit a granular structure. The transistor shows unipolar p-type behavior with mobilities typically of 5×10-4 cm2/V s. Drain-source current and electroluminescence have been simultaneously measured. Provided a suitable gate bias is applied, light emission occurs at drain-source voltages (Vds) above saturation. LETs on plastic substrates could open the way to flexible devices combining the switching function of a transistor and the light emission. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Decay of photorefractive gratings in LiNbO3:Fe by neutron irradiation

    Page(s): 141107 - 141107-3
    Save to Project icon | PDF file iconPDF (141 KB)  

    The effect of neutron irradiation on photorefractive gratings in LiNbO3:Fe single crystals is studied experimentally. The observed phenomena result from the large effective cross section of 6Li for thermal and cold neutrons and from the large number of the electrons excited to the conduction band by the high kinetic energy that is released during the neutron generated fission of 6Li nuclei. The excited electrons erase the previously recorded holographic grating. The sensitivity threshold of the effect is better than 160 mSv (1.2×1010 cm-2 fluence) at neutron energy of 0.17 eV. Potential applications of the phenomena are discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Heteroepitaxial Bi3Fe5O12/La3Ga5O12 films for magneto-optical photonic crystals

    Page(s): 141108 - 141108-3
    Save to Project icon | PDF file iconPDF (273 KB)  

    Epitaxial La3Ga5O12 (LGG) garnet films and Bi3Fe5O12/La3Ga5O12 (BIG/LGG) heteroepitaxial film structures have been synthesized on the Gd3Ga5O12(GGG,111) single crystal. LGG films were grown by pulsed laser deposition technique whereas rf-magnetron sputtering was used to grow BIG films. LGG has a lattice constant 12.768 Å that is bigger than that in GGG (12.384 Å) and closer to that in BIG (12.626 Å). We demonstrate feasibility of integration lanthanum gallium garnet with a giant Faraday rotator Bi3Fe5O12 in magneto-optical photonic crystals. Heteroepitaxial Bi3Fe5O12(1.9 μm)/La3Ga5O12(300 nm)/GGG(111) structures show Faraday rotation as high as 5.74 degm compared to 5.46 degm in BIG/GGG at λ=655 nm. Fitting LGG reflectivity spectra to Fresnel formulas yields LGG refractive index no=1.981 compared to 1.963 in GGG at 655 nm. Dispersion of LGG refraction index follows S- - ellmeier formula no2=1+2.77/[1-(143 nm/λ)2] in the range from 400 nm to 1000 nm. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Terahertz wideband spectroscopic imaging based on two-dimensional electro-optic sampling technique

    Page(s): 141109 - 141109-3
    Save to Project icon | PDF file iconPDF (253 KB)  

    We extended the bandwidth of a terahertz (THz) spectroscopic imaging system based on two-dimensional electro-optic sampling. By using an optical-rectification emitter, formed by a ZnTe crystal, a high-frequency component of more than 2.0 THz was detected. A calibration-free procedure with polarity inversion of the THz beam ensures us precise spectroscopy: the polarity was inverted by rotating the emitter crystal. The spatial patterns of the chemicals were extracted from the THz multispectral images in the extended spectral region. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Polarization-independent phase modulation using a polymer-dispersed liquid crystal

    Page(s): 141110 - 141110-3
    Save to Project icon | PDF file iconPDF (318 KB)  

    Polarization-independent phase-only modulation of a polymer-dispersed liquid crystal (PDLC) is demonstrated. In the low voltage region, PDLC is translucent because of light scattering. Once the voltage exceeds a saturation level, PDLC is highly transparent and exhibits phase-only modulation capability. Although the remaining phase is not too large, it is still sufficient for making adaptive microdevices, such as microlens. A tunable-focus microlens for arrays using PDLC is demonstrated. This kind of microlens is scattering free, polarization independent, and has fast response time. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electron imaging of charge-separated field on a copper film induced by femtosecond laser irradiation

    Page(s): 141501 - 141501-3
    Save to Project icon | PDF file iconPDF (432 KB)  

    An instantaneous charge-separated field, built up at the femtosecond-laser-irradiated surface of a copper film, was observed by time-resolved electron imaging using an energy-chirped electron probe-beam. The probe beams with effective energies of 170 keV were generated by intense femtosecond laser irradiation onto a molybdenum target at an intensity of 1017 W/cm2. From the deflection of the probe electrons, the electric field was estimated to be 1.5 MV/m at a pump-laser intensity of 1015 W/cm2. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Microdischarges of xenon sustained by microwaves: Determination of scaling laws

    Page(s): 141502 - 141502-3
    Save to Project icon | PDF file iconPDF (123 KB)  

    The threshold conditions to maintain millimeter and submillimeter-size discharges of xenon with microwaves are experimentally determined. The threshold electric field required to sustain the plasma is reported as a function of gas pressure. The influence of the size of the dielectric cell in which the discharge is produced is also shown. The scaling laws are deduced from the threshold electric field measurements, assuming a few additional simplifying assumptions. The results are compared with data obtained with argon discharges sustained by surface waves in capillary tubes and the hypotheses assumed for the calculations are discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Temporal phenomena in inductively coupled chlorine and argon–chlorine discharges

    Page(s): 141503 - 141503-3
    Save to Project icon | PDF file iconPDF (58 KB)  

    Reproducible modulations in low-pressure, inductively coupled discharges operating in chlorine and argon–chlorine mixtures have been observed and studied. Changes in the light output, floating potential, negative ion fraction, and charged particle densities were observed. Here we report two types of unstable operational modes in an inductively coupled discharge. On the one hand, when the discharge was matched, to minimize reflected power, instabilities were observed in argon–chlorine plasmas over limited operating conditions of input power and gas pressure. The instability window decreased with increasing chlorine content and was observed for chlorine concentrations between 30% and 60% only. However, when operating at pressures below 5 mTorr and the discharge circuit detuned to increase the reflected power, modulations were observed in a pure chlorine discharge. These modulations varied in nature from a series of sharp bursts to a very periodic behavior and can be controlled, by variation of the matching conditions, to produce an apparent pulsed plasma environment. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Strong photoluminescence of nanostructured crystalline tungsten oxide thin films

    Page(s): 141901 - 141901-3
    Save to Project icon | PDF file iconPDF (266 KB)  

    Strong photoluminescence (PL) is observed in nanostructured crystalline tungsten oxide thin films that are prepared by thermal evaporation. Two kinds of films are investigated—one made of nanoparticles and another of nanowires. At room temperature, strong PL emissions at ultraviolet-visible and blue regions are found in both of the films. Compared with the complete absence of emission of bulk phase tungsten oxide powder under the same excitation conditions, our results clearly demonstrate the quantum-confinement-effect-induced photoluminescence in nanostructured tungsten oxides. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Activation volume for phosphorus diffusion in silicon and Si0.93Ge0.07

    Page(s): 141902 - 141902-3
    Save to Project icon | PDF file iconPDF (57 KB)  

    The hydrostatic pressure dependence of the diffusivity of P in compressively strained Si0.93Ge0.07 and unalloyed Si has been measured. In both cases the diffusivity is almost independent of pressure, characterized by an activation volume V* of (+0.09±0.11) times the atomic volume Ω for the unalloyed Si, and (+0.01±0.06) Ω for Si0.93Ge0.07. The results are used in conjunction with the reported effect of biaxial strain on diffusion normal to the surface to test the prediction for an interstitialcy-based mechanism of Aziz’s phenomenological thermodynamic treatment of diffusion under uniform nonhydrostatic stress states. The prediction agrees well with measured behavior, lending additional credence to the interstitial-based mechanism and supporting the nonhydrostatic thermodynamic treatment. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dual ring laser emission of conducting polymers in microcapillary structures

    Page(s): 141903 - 141903-3
    Save to Project icon | PDF file iconPDF (55 KB)  

    We have demonstrated photopumped multimode laser emission from cylindrical microcavities of conducting polymer thin films, which were formed by deposition on the inside surface of the glass microcapillary with capillary action. The laser emission was characterized by narrow emission lines and a well-defined excitation threshold. We also fabricated dual ring cavities on inner and outer surfaces of microcapillaries, and laser emission from both sides of capillaries was observed by photopumping with one excitation source. Fabricating two cylindrical microcavities on inner and outer surfaces of the microcapillary by utilizing a different sort of conducting polymers, dual laser emissions, blue and red in color, were obtained concurrently. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dynamic evolution of nanoscale shear bands in a bulk-metallic glass

    Page(s): 141904 - 141904-3
    Save to Project icon | PDF file iconPDF (356 KB)  

    Dynamic shear-band-evolution processes in a bulk-metallic glass (BMG), an emerging class of materials, were captured by a state-of-the-art, high-speed, infrared camera. Many shear bands initiated, propagated, and arrested before the final fracture in tension, each with decreasing temperature, and shear-strain profiles. A free-volume-exhaustion mechanism was proposed to explain the phenomena. The results contribute to understanding and improving the limited ductility of BMGs, which otherwise have superior mechanical properties. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electronic and atomic structures of quasi-one-dimensional K0.3MoO3

    Page(s): 141905 - 141905-3
    Save to Project icon | PDF file iconPDF (80 KB)  

    The electronic and atomic structures of quasi-one-dimensional blue bronze K0.3MoO3 were investigated by polarization-dependent O K-edge x-ray absorption near-edge structure (XANES) and Mo K-edge extended x-ray absorption fine structure (EXAFS) measurements at various temperature and applied voltages. The O K-edge XANES spectra suggest that the number of unoccupied O 2p–Mo 4d hybridized states increases and decreases with temperature, respectively, below and above a critical temperature of 180 K. The along b-axis electric current measurements show a threshold applied voltage, beyond which the current increases rapidly. The Mo K-edge EXAFS measurements show that the Mo–O bond lengths are insensitive to the temperature even beyond 180 K. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dense arrays of Co nanocrystals epitaxially grown on ion-patterned Cu(110) substrates

    Page(s): 141906 - 141906-3
    Save to Project icon | PDF file iconPDF (162 KB)  

    We report on the growth of {111}-faceted Co nanocrystals endowed with fcc structure during multilayer epitaxial deposition on a flat Cu(110) substrate. Lateral ordering of the Co nanocrystals into a periodic array is achieved if the Co deposition is performed on a Cu(110) substrate, prepatterned by ion sculpting. While for low coverages the Co film growth is conformal, reproducing the underlying arrangement of the Cu substrate pattern, for film thicknesses above 16 monolayers, size-selected {111}-faceted Co nanocrystals nucleate in registry with the underlying pattern periodicity. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Anomalous gap dependence of stretched Teflon/poly(p-phenylene vinylene) films

    Page(s): 141907 - 141907-2
    Save to Project icon | PDF file iconPDF (58 KB)  

    We have performed an experimental study of the anomalous increase of the gap energy (Egap) in stretched Teflon/poly (p-phenylene vinylene) films. Photoluminescence experiments, show that Egap initially undergoes an increase and then a decrease, as the film is stretched further. Polarized absorbance experiments reveal orientational ordering of chains with the stretching. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Band-gap discontinuity in GaN0.02As0.87Sb0.11/GaAs single-quantum wells investigated by photoreflectance spectroscopy

    Page(s): 141908 - 141908-3
    Save to Project icon | PDF file iconPDF (59 KB)  

    GaN0.02As0.87Sb0.11/GaAs single-quantum wells have been investigated by photoreflectance (PR) at room temperature. PR features related to the ground and excited state transitions have been clearly observed. The experimental data have been compared with the calculations in the envelope function formalism taking account the effect of strain. The band gap lowering and the increase in the electron effective mass due to the incorporation of nitrogen atoms into GaAsSb have been included. Excellent agreement between experimental data and calculation results have been found for band structure Type-I with the conduction-band offset ratio of 50%. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Oxygen tracer diffusion in Pb(Zr,Ti)O3 thin film enhanced by catalytic platinum

    Page(s): 141909 - 141909-3
    Save to Project icon | PDF file iconPDF (163 KB)  

    The self-diffusion of 18O into Pb(Zr,Ti)O3 [PZT] thin films on Pt/TiO2 coated Si wafers from an ambient of 99% 18O2 gas tracer was investigated by secondary ion mass spectroscopy (SIMS) when annealed at 450 °C, 550 °C, and 650 °C for up to 30 min. The results show that the 18O profile in PZT changed significantly with anneal temperature and the highest concentration of exchanged oxygen was at the PZT/Pt interface when annealed at 650 °C. Modeling of the oxygen tracer diffusion profiles from the 450 °C and 550 °C data yielded an activation energy of 0.83 eV when assuming 1D diffusion. Simulation of the 650 °C SIMS data indicated that the oxygen was dissociating on the catalytic Pt film underneath the PZT and then back diffusing into the PZT causing a higher concentration of oxygen at the PZT/Pt interface than at the surface. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Aluminum nanoscale order in amorphous Al92Sm8 measured by fluctuation electron microscopy

    Page(s): 141910 - 141910-3
    Save to Project icon | PDF file iconPDF (53 KB)  

    Fluctuation electron microscopy (FEM) measurements and simulations have identified nanoscale aluminum-like medium-range order in rapidly quenched amorphous Al92Sm8 which devitrifies by primary Al crystallization. Al92Sm8 amorphized by plastic deformation shows neither Al nanoscale order, nor primary crystallization. Annealing the rapidly quenched material below the primary crystallization temperature reduces the degree of nanoscale Al order measured by FEM. The FEM measurements suggest that 10–20 Å diameter regions with Al crystal-like order are associated with primary crystallization in amorphous Al92Sm8, which is consistent with the quenched-in cluster model of primary crystallization. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

Full Aims & Scope

Meet Our Editors

Editor
Nghi Q. Lam
Argonne National Laboratory