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Applied Physics Letters

Issue 25 • Date Dec 2005

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Displaying Results 1 - 25 of 113
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Highly efficient tunable tapered-polymer-fiber lasers

    Page(s): 251101 - 251101-3
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    A highly efficient tunable tapered-polymer-fiber (TPF) laser was demonstrated by use of a compound parabolic TPF doped with Rhodamine-6G (R6G) dye. The tuning ranges over 40 nm at the visible region for laser output with the maximum output energy of 600 μJ at 570 nm and the optical-optical conversion efficiency of 23% were achieved by a prism as a spectrally selective element. Moreover, the coupling efficiency for the taper exceeded 90%. Compared to traditional polymer fibers with a micrometer-size core diameter, the taper allows for a higher pump to be launched without damaging the fiber endfaces, and it can efficiently couple the light into the fiber and alleviate the alignment difficulty. So, the TPF laser not only possesses all of the advantages of traditional polymer-fiber lasers, and it can also obtain higher output energy and higher efficiency. Additionally, it is insensitive to geometrical displacements. View full abstract»

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  • All optically tunable wavelength-selective reflector consisting of coupled polymeric microring resonators

    Page(s): 251102 - 251102-3
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    We present an all optically tunable wavelength-selective reflector for planar lightwave technology based on coupled microring resonators. By employing the Vernier effect, we demonstrate narrow-band reflection and strong side-lobe suppression in an optical polymer device fabricated by soft lithography. Wide and simple tuning of the reflection peak using an external control beam is demonstrated. View full abstract»

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  • Quasiphase matched harmonic generation in a two-dimensional octagonal photonic superlattice

    Page(s): 251103 - 251103-3
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    We have fabricated LiNbO3 nonlinear photonic crystals with a two-dimensional octagonal quasilattice. The effective collinear quasiphase matched second-harmonic orange and green lights, with conversion efficiencies of ∼38% and 23%, were realized. The noncollinear harmonic processes at multiple wavelengths were also observed with the conversion efficiency of around 5%. All the-same results can be obtained when the crystal is rotated by the integral multiples of π/4. View full abstract»

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  • Dual localizations for second-harmonic generations using left-handed materials

    Page(s): 251104 - 251104-3
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    We show that dual localized modes can be achieved in defective one-dimensional photonic crystals containing left-handed materials. By inserting a nonlinear defect into a photonic crystal formed by stacked alternating left-handed materials and air layers, defective modes for fundamental wave and second-harmonic signal inside the zero-n gap and a Bragg gap are formed, respectively. We present a theory in designing the whole structure, and show that a giant enhancement of second-harmonic generation is achieved. The merits and character of such a scheme comparing with that in ordinary photonic crystals are discussed. View full abstract»

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  • Coded excitation of broadband terahertz using optical rectification in poled lithium niobate

    Page(s): 251105 - 251105-3
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    We demonstrate coded excitation of broadband terahertz for imaging applications. The encoded transmitter uses optical rectification of femtosecond laser pulses in poled lithium niobate patterned with a 53-bit binary phase code. The terahertz wave forms are detected by electro-optic sampling in zinc telluride. A digital pulse compression filter decodes the binary wave forms, producing broadband pulses at 1.0 THz. A two-dimensional imaging experiment shows comparable performance between the encoded transmitter and a zinc telluride emitter. View full abstract»

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  • Optimization of tapered semiconductor optical amplifiers for picosecond pulse amplification

    Page(s): 251106 - 251106-3
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    We present results of a fundamental device simulation study aimed at an optimization of high-power tapered semiconductor optical amplifiers for picosecond pulse amplification. Thereby, the microscopic light-matter coupling is described on the basis of a spatially resolved Maxwell–Bloch–Langevin description that takes into account many-body-carrier interactions, energy transfer between the carrier and phonon systems and, in particular, the spatiotemporal interplay of stimulated and amplified spontaneous emission and the noise caused by spontaneous emission. Extensive simulation runs reveal the microscopic physical processes which are responsible for the beam quality of the amplified picosecond pulses and allow us to give concrete suggestions for the optimization of the amplifier structure and geometry. We discuss the influence of a curved waveguide or spatially patterned current contact, and identify the length of the unpumped area as the most critical parameter to be carefully optimized. View full abstract»

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  • Design for a triply resonant vertical-emitting micro-optical parametric oscillator

    Page(s): 251107 - 251107-3
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    An approach is proposed for the realization of a vertical-cavity surface-emitting semiconductor micro-optical parametric oscillator that relies on the use of third-order excitonic nonlinearity in isotropic semiconductors. We demonstrate that a planar triple microcavity structure can be designed to provide triple resonance for the parametric frequencies together with built-in cavity phase-matching for all waves at normal incidence. An example is given of a monolithic structure consisting of three strongly coupled AlGaAs/GaAs lambda microcavities including single InGaAs quantum wells. Applications to the generation of twin photons or entangled photon pairs are discussed. View full abstract»

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  • Optical gain from InAs nanocrystal quantum dots in a polymer matrix

    Page(s): 251108 - 251108-3
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    We report on the observation of optical gain from InAs nanocrystal quantum dots which emit at 1.55 microns and are imbedded in a novel polymer platform. The measurements are based on a three-beam time resolved pump-probe technique, which enables extracting the intrinsic gain cross section, lifetime, and recovery time. These experiments are another step toward the realization of active optical devices based on InAs nanocrystals. View full abstract»

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  • Impact of N on the lasing characteristics of GaInNAs/GaAs quantum well lasers emitting from 1.29 to 1.52 μm

    Page(s): 251109 - 251109-3
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    The origin of the degradation with N of the threshold current density (Jth) and external differential quantum efficiency d) of 1.29 to 1.52 μm GaInNAs/GaAs laser diodes is analyzed. Adding N to InGaAs leads to a ∼25% reduction of the carrier injection efficiency and thus to an increase of Jth and a decrease of ηd. This effect is likely related to carrier recombination losses in the barriers and is independent of the N content. The optical absorption losses and the internal transparency current density are found to increase with N content, accounting for the rest of the degradation in Jth. Modeling of the transparency carrier and radiative current densities identifies the increase of the defect-related recombination coefficient in GaInNAs as the dominant effect leading to the N dependence of Jtr. View full abstract»

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  • Cadmium telluride bulk crystal as an ultrafast nonlinear optical switch

    Page(s): 251110 - 251110-3
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    A semiconductor bulk crystal has several advantages as a nonlinear optical material, such as low processing cost, long interaction length, and alleviation of the free-carrier absorption caused by two-photon absorption (TPA). We examine optical properties of semiconductor bulk crystals with different orientations at 1.55 μm and find that CdTe[111] has favorable capabilities, such as nonlinear refractive index of 5.23×10-17 (m2 W), TPA coefficient of 18.3 (mm GW), and consequent figure of merit of 0.54. Optical three-dimensional measurements of reflective material are carried out using CdTe[111] as ultrafast optical Kerr shutter and clear images corresponding to surface steps are obtained. View full abstract»

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  • Scaling of domain size during spinodal decomposition: Dislocation discreteness and mobility effects

    Page(s): 251901 - 251901-3
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    In this letter, we examine the effects of discrete mobile dislocations on spinodal decomposition kinetics in lattice mismatched binary alloys. By employing a novel continuum model, we demonstrate that the effects of dislocation mobility on domain coarsening kinetics can be expressed in a unified manner through a scaling function, describing a crossover from t1/2 to t1/3 behavior. View full abstract»

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  • High-quality nanothickness single-crystal Sc2O3 film grown on Si(111)

    Page(s): 251902 - 251902-3
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    High-quality single-crystal Sc2O3 films a few nanometer thick have been grown epitaxially on Si (111) despite a huge lattice mismatch. The films were electron-beam evaporated from a Sc2O3 target. Structural and morphological studies were carried out by x-ray diffraction and reflectivity, atomic force microscopy, high-resolution transmission electron microscopy, and medium-energy ion scattering, with the initial epitaxial growth monitored by in situ reflection high-energy electron diffraction. The films have the cubic bixbyite phase with a remarkably uniform thickness and high structural perfection. The film surfaces are very smooth and the oxide/Si interfaces are atomically sharp with a low average roughness of 0.06 nm. The films are well aligned with the Si substrate with an orientation relationship of Si(111)||Sc2O3(111), and an in-plane expitaxy of Si[110]||Sc2O3[101]. View full abstract»

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  • Electron energy-loss spectrometry studies of bonding in nanoscale NiSiO2 multilayers

    Page(s): 251903 - 251903-3
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    Electron energy-loss spectrometry in the transmission electron microscope is used to directly assess the nature of bonding at interfaces formed during alternating deposition of nanoscale Ni and SiO2 multilayers. Interfacial Ni–O bond formation near the interface is revealed by energy-loss near-edge structure preceding the O K edge threshold, indicating hybridization of O 2p with Ni 3d orbitals, and by characteristic white line structure associated with the Ni L2,3 edge. Interface spectra are compared to reference NiO spectra, verifying local Ni–O bonding at the Ni/SiO2 interface. View full abstract»

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  • Optical properties of thin films of [Ru(bpy)3][NaCr(ox)3] polymeric networks

    Page(s): 251904 - 251904-3
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    The optical properties of a thin film of the [Ru(bpy)3][NaCr(ox)3] network structure obtained by pulsed laser deposition are described. The luminescence shows the characteristic doublet of R lines at 14 400 cm-1 of the spin-forbidden ligand field transition 2E(t2g3)→4A2(t2g3) of the [Cr(ox)3]3- chromophore. The resonant energy migration within the R1 line shows that the three-dimensional crystallographic structure is preserved during the coating process. The observation of the R lines of [Cr(bpy)3]3+ at 13 710 cm-1 indicates that a small fraction of Cr3+ ions migrate from the oxalate network to the tris-bipyridine cation site in the cavities of the network. View full abstract»

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  • Nanoindentation of HgCdTe prepared by molecular beam epitaxy

    Page(s): 251905 - 251905-3
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    Nanoindentation has been used to investigate the elastoplastic behavior of Hg0.7Cd0.3Te prepared by molecular beam epitaxy. It was found that Hg0.7Cd0.3Te had a modulus of elasticity of ∼50 GPa and hardness of ∼0.66 GPa. The HgCdTe response to nanoindentation was found to be purely elastic for low loads and developed into ∼10% elastic and ∼90% plastic response for higher-load indentation exhibiting significant amounts of creep. The onset of plasticity has been observed to be marked by discontinuities or “pop-in” events in the indenter load-penetration curves at sheer stresses of ∼1.8 GPa, and has been correlated with the homogeneous nucleation and propagation of dislocations. View full abstract»

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  • Two-staged sorption isotherm of a nanoporous energy absorption system

    Page(s): 251906 - 251906-3
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    To selectively absorb impact energy, the profiles of sorption isotherms of protection systems must be adjusted in a broad spectrum. In this article, a N-Lauroylsarcosine sodium salt (sarcosyl) of intermediate molecular size is used to control the pressure induced infiltration of a nanoporous silica. The experimental result shows that the infiltration plateau of this system is two-staged; that is, not only the activation pressure but also the infiltration volume can be modified. It is noticed that the sarcosyl molecule demands a “free volume” to enter a nanopore. The free volume size decreases nearly linearly as the sarcosyl concentration increases. View full abstract»

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  • Strain-facilitated process for the lift-off of a Si layer of less than 20 nm thickness

    Page(s): 251907 - 251907-3
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    We report a process for the lift-off of an ultrathin Si layer. By plasma hydrogenation of a molecular-beam-epitaxy-grown heterostructure of Si/Sb-doped-Si/Si, ultrashallow cracking is controlled to occur at the depth of the Sb-doped layer. Prior to hydrogenation, an oxygen plasma treatment is used to induce the formation of a thin oxide layer on the surface of the heterostructure. Chemical etching of the surface oxide layer after hydrogenation further thins the thickness of the separated Si layer to be only 15 nm. Mechanisms of hydrogen trapping and strain-facilitated cracking are discussed. View full abstract»

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  • Self-assembly of steps and vacancy lines during the early stages of Ge/Si(001) heteroepitaxy

    Page(s): 251908 - 251908-3
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    The wetting layer formed during the early stages of Ge/Si(001) growth has been found in recent experiments to undergo a roughening process, where the SA surface steps affect the spatial organization of vacancy lines (VLs) by increasing (stretching) or decreasing (squeezing) their average spacing. Using a combination of atomistic simulations and elastic theory of surface defects, we have computed the interaction energy of the SA steps and VLs for each of the observed defect configurations. We find that the repulsive SA-VL interactions lead to an increase in the spacing of the VLs in the “stretch” arrangement, but do not significantly affect the VL spacing in the “squeeze” configuration, providing an explanation for the observed correlations in the wetting layer roughness. View full abstract»

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  • Effect of local ordering on the decomposition of an amorphous Cu–Zr–Ti alloy

    Page(s): 251909 - 251909-3
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    We present free-energy calculations based on the random solution model. These calculations support the fact that the Cu-based solid solution observed to form during decomposition in amorphous Cu60Zr30Ti10 alloy is an ordered metastable L12 Cu3(Zr,Ti) phase which can nucleate due to its small unit cell and high mixing preference of Zr with Cu atoms. View full abstract»

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  • Optical spectroscopy of trivalent chromium in sol-gel lithium niobate

    Page(s): 251910 - 251910-3
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    We report on the characterization of sol-gel derived lithium niobate via trivalent chromium probe ions, a study that is motivated by recent reports on the synthesis of high quality sol-gel lithium niobate (LiNbO3). In order to assess the quality of sol-gel derived LiNbO3, we incorporate Cr3+ during the hydrolysis stage of the sol-gel process. A comparison of the Cr3+ emission and photoexcitation data on both sol-gel and melt-grown LiNbO3 shows that the sol-gel derived material is highly stoichiometric. View full abstract»

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  • Photoluminescence of Si nanocrystal memory devices obtained by ion beam synthesis

    Page(s): 251911 - 251911-3
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    In this letter, we propose an original method to investigate Si nanocrystal-based nonvolatile memory devices, taking benefit of the photoluminescence (PL) spectroscopy and the specific optoelectronic properties of Si nanocrystals (Si-NCs). Ordered two-dimensional-arrays of Si-NCs were synthesized by ultralow-energy ion implantation in 7-nm-thick SiO2 and subsequent annealing. The Si-NCs population characteristics (size and density) were adjusted by different oxidizing annealing. This allowed, at the same time, the progressive healing of the oxide matrix. The analysis of the spectra revealed the presence of two PL bands, one due to quantum confinement effects in Si-NCs, and the other one attributed to silicon-rich oxide. Therefore, the evolution in energy and intensity of the PL bands was correlated to the oxidizing conditions, thus to the change of the Si-NCs size and density, and to the formation of stoichiometric SiO2. These results are of great interest as being the first step in using PL spectroscopy as a nondestructive method to assess or monitor the electrical performances of the future memory devices, before any step of contact fabrication. View full abstract»

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  • Optical properties of nanocluster-assembled ZnO thin films by nanocluster-beam deposition

    Page(s): 251912 - 251912-3
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    Nanocluster-assembled ZnO thin films have been synthesized by nanocluster-beam deposition, and the films exhibit a band-gap energy at 323.7 nm (3.84 eV) and ultraviolet (UV) light emission at 373 nm (3.32 eV) with an average particle size of 6 nm. A comparison of the optical properties of the annealed films with that of as-grown one is presented. It is found that, after the film is annealed, the shoulder in the absorbance spectra turns steeper and the intensity of UV light emission band becomes stronger. Moreover, blueshifts of band-gap energy and a UV emission band are both observed as decreasing the annealing temperature and ascribed to the quantum-confinement effect. View full abstract»

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  • Role of substrate and transparent conducting oxide in impurity evolvement in polycrystalline thin-film devices

    Page(s): 251913 - 251913-3
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    A comparison of as-grown and processed CdTe/CdS solar cell structures deposited on sapphire substrate has been undertaken with those grown on glass. The device structures were depth-profiled using quantitative secondary ion mass spectrometry. It was shown that while Si concentration profiles are similar to those for structures grown on glass, Na was more than one order of magnitude lower when sapphire was used instead of glass, showing that Na diffused from the glass. It was also found that there was no measurable diffusion of Sn from the SnO2 layer into CdTe, and that the former played an important role in preventing the diffusion of In from In-containing transparent conducting oxide layer. Cl, O, Br, and F species were also investigated and while Cl and O were found to be independent of the nature of the substrate used, Br and F were shown to be affected by the processing. View full abstract»

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

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Nghi Q. Lam
Argonne National Laboratory