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Applied Physics Letters

Issue 13 • Date Sep 2005

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Displaying Results 1 - 25 of 78
  • Issue Cover

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

    Page(s): toc1
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  • Thermal inhibition of high-power second-harmonic generation in periodically poled LiNbO3 and LiTaO3 crystals

    Page(s): 131101 - 131101-3
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    A coupled thermo-optical model shows strong thermal inhibition of second-harmonic generation (SHG) in periodically poled (PP) LiNbO3 (PPLN) and stoichiometric LiTaO3 (PPSLT) crystals. Three-dimensional simulations performed for a 1.064 μm fundamental wavelength pulsed nanosecond laser beam 150 μm in radius show the onset of significant temperature nonuniformities along and across the irradiated zone, and strong thermal dephasing and inhibition of SHG in these crystals for input powers ≫10 W. PPSLT is found to have a significant advantage over PPLN due to the higher heat conductance, decreasing these temperature nonuniformities and allowing one to maintain the irradiated zone within the corresponding SHG temperature tolerance range (ΔT≈3 K). View full abstract»

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  • Bends and splitters in metal-dielectric-metal subwavelength plasmonic waveguides

    Page(s): 131102 - 131102-3
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    We investigate the performance of bends and splitters in metal-dielectric-metal subwavelength plasmonic waveguides. We show that bends and splitters with no additional loss over a very wide frequency range can be designed for metal-dielectric-metal waveguides with center layer thickness small compared to the wavelength. We also introduce the concept of characteristic impedance for such systems to account for their behavior. View full abstract»

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  • Room temperature continuous wave operation of a heterojunction bipolar transistor laser

    Page(s): 131103 - 131103-3
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    Continuous wave laser operation at 25 °C, with simultaneous electrical gain, of an InGaP–GaAs heterojunction bipolar transistor laser, with AlGaAs optical confining layers and an InGaAs recombination quantum well incorporated into the p-type base region, is demonstrated. At laser threshold (IB=40 mA, VCB=0, 25 °C), the transistor current gain β=ΔIC/ΔIB in common-emitter operation changes abruptly (2.3→1.2,β≫1), with laser modes developing at wavelength λ∼1006 nm. Direct three-port modulation of the transistor laser at 3 GHz is demonstrated for a device with a 2.2 μm emitter width and a 850 μm length between cleaved Fabry–Perot facets (which is the performance of an exploratory device and not near the limits). View full abstract»

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  • Waveguide array-grating compressors

    Page(s): 131104 - 131104-3
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    We show that efficient optical pulse compression can be achieved when normally dispersive nonlinear waveguide arrays are used in conjunction with dispersive elements such as gratings or other programmable phase filters. Our computations indicate that the compression resulting from such discrete arrays can be of better quality as compared to that obtained traditionally from a single nonlinear waveguide element. The performance of the array-grating compression method is assessed in normally dispersive highly nonlinear AlGaAs array systems. View full abstract»

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  • Picosecond time-resolved imaging by nonscanning fluorescence Kerr gate microscope

    Page(s): 131105 - 131105-3
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    A nonscanning picosecond fluorescence Kerr gate microscope has been developed. By applying the optical Kerr gate technique to the fluorescence imaging of microscopic samples, picosecond time-resolved fluorescence images were obtained with 1.4-ps time resolutions and 1-μm space resolutions, without XY scanning of the sample or the excitation light. A demonstrational measurement on an organic microcrystal, perylene, is presented. View full abstract»

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  • Efficient second harmonic generation from large band gap II-VI semiconductor photonic crystal

    Page(s): 131106 - 131106-3
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    Dramatic enhancement of second harmonic generation (SHG) near the photonic band edge was observed in a one-dimensional ZnSe/ZnMgS semiconductor photonic crystal (PC) structure. Over two orders of magnitude increase in SHG intensity was observed at the photonic band edge at ∼1400 nm compared to the nonphase matching region. The maximum SHG conversion efficiency of 0.8% is observed in only seven micrometers length of crystal. This enhancement came from a combination of large ZnSe second order susceptibility coefficient (2)), high density of optical modes and phase matching of the fundamental and second harmonic waves near the photonic band edge due to modification of the dispersion curve by the PC structure. View full abstract»

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  • Curved-microfiber photon coupling for photonic crystal light emitter

    Page(s): 131107 - 131107-3
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    Highly-efficient evanescent coupling between a photonic crystal resonator and a curved fiber taper is demonstrated. The coupling is utilized to pump the photonic crystal laser and funnel its output photons through a single optical fiber, making it an all-fiber photon source. Photon collection efficiency of ∼70% into the fiber and output power of 27 nW are achieved. Highly local pumping results in the record-low threshold of ∼35 μW. This scheme provides an ideal platform for an on-demand single photon source based on two-dimensional photonic crystal. View full abstract»

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  • Pseudospark electron beam as an excitation source for extreme ultraviolet generation

    Page(s): 131501 - 131501-3
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    A xenon pseudospark device is used to generate energetic and intense electron beams (e-beams) that induce extreme ultraviolet (EUV) emission in the range of 11–17 nm. This e-beam-based EUV source is compact, and the device is of interest because it has potentially attractive EUV conversion efficiency and pulse energy requirement, with potential for long lifetime and high repetition-rate operation. The role of e-beam-induced inelastic electronic collisions is considered. View full abstract»

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  • Effect of multistep ionizations on the electron temperature in an argon inductively coupled plasma

    Page(s): 131502 - 131502-3
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    Electron energy distribution functions (EEDFs) are measured in an argon inductively coupled plasma. It is observed that the measured EEDFs are nearly Maxwellian distributions, and the electron temperature derived from the EEDFs decreases with increasing input radio-frequency (rf) power. It appears that additional ionization processes exist. To investigate this decrease in the electron temperature, multistep ionizations are taken into account. An analytical particle balance equation, including the multistep ionizations, are derived. According to the new balance equation, to balance between the total volume ionization and the total surface particle loss, the electron temperature should be decreased with increasing rf power. The comparison between the model and the experiment are presented, and the model agrees well with the experiment. View full abstract»

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  • Ion mass dependence of the etch yield of SrTiO3 films in reactive plasmas

    Page(s): 131503 - 131503-3
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    The influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO3 films in Ar/SF6 plasmas is investigated using a parametric approach. The etch yield is found to decrease as the concentration fraction of molecular ions increases. Introducing the concept of effective mass for both ions and SrTiO3, these experimental results are quantitatively explained in the framework of a well-established model originally developed to describe the sputtering of single-atom materials by noble monoatomic ions. View full abstract»

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  • Mechanisms for sustaining the free-standing plasma beam

    Page(s): 131504 - 131504-3
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    A two-dimensional model of a free-standing plasma beam is presented in the letter. Results for spatial distribution of the charged particles and the excited atoms are discussed with stress on the mechanisms sustaining the beam. View full abstract»

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  • A technique to study the lattice location of hydrogen atoms in silicon by channeling elastic recoil detection analysis

    Page(s): 131901 - 131901-3
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    By combining elastic recoil detection analysis with the channeling technique, energy analysis of forward-scattered 1H permits determination of the 1H lattice location. We have used this technique to study the lattice location of hydrogen in a crystalline Si containing a buried boron-doped layer. We showed that hydrogen atoms are trapped at the boron-doped Si layer after hydrogenation and that the majority of the trapped hydrogen atoms are located near bond-center sites. View full abstract»

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  • Atomic-scale structure of self-assembled In(Ga)As quantum rings in GaAs

    Page(s): 131902 - 131902-3
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    We present an atomic-scale analysis of the indium distribution of self-assembled In(Ga)As quantum rings (QRs) which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. We find that the size and shape of QRs as observed by cross-sectional scanning tunneling microscopy (X-STM) deviate substantially from the ring-shaped islands as observed by atomic force microscopy on the surface of uncapped QR structures. We show unambiguously that X-STM images the remaining quantum dot material whereas the AFM images the erupted quantum dot material. The remaining dot material shows an asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and is responsible for the observed electronic properties of QR structures. These quantum craters have an indium concentration of about 55% and a diameter of about 20 nm which is consistent with the observed electronic radius of QR structures. View full abstract»

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  • Direct experimental observation of a general pattern at the beginning of brittle fracture

    Page(s): 131903 - 131903-3
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    The failures of brittle and ductile materials are governed by the microscopic response around a flaw extremity; but the experimental access to this region of atomic dimensions is extremely difficult. Here we access experimentally this region by using a developed magnetic solid with atomistic characteristics that simulate the crack tip of brittle materials. We show that the general pattern for the beginning of all the ruptures is the reaching of a specific maximum value of the local stress between the unit cells at the extremity of the critical flaw. This work may help simulations of brittle fracture where a criterion is needed to determine when a bond is broken, corresponding to an experimental foundation to those works that use the criterion of a critical atomic snapping distance, starting from which the bond is considered broken. View full abstract»

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  • Microphotoluminescence mapping of laterally overgrown GaN layers on patterned Si (111) substrates

    Page(s): 131904 - 131904-3
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    Spatial distribution of optical properties of GaN layers grown on patterned Si (111) substrates by maskless metalorganic chemical vapor deposition has been investigated. The Si substrates were prepared with a pattern of 1.5 μm diameter holes at a 3.5 μm distance from each other. The holes were overgrown by GaN until coalescence, creating GaN areas with no substrate underneath. Microphotoluminescence mapping measurements with 0.8 μm lateral resolution show a five-fold increase in luminescence intensity coming from the overhang areas as compared to the layer directly over the substrate. This is accompanied by a slight redshift of the luminescence peak wavelength. Photoelectrochemical etching shows that the dislocation density is much lower in those areas while the photoluminescence redshift is attributed to lesser strain relaxation resulting from a lower dislocation density. View full abstract»

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  • Effect of Brownian coagulation on the microstructure evolution in rapidly solidified immiscible alloys

    Page(s): 131905 - 131905-2
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    The microstructure evolution during a liquid-liquid phase transformation was calculated. The effect of Brownian coagulation on the microstructure development was investigated. The results indicate that Brownian coagulation has a weak effect on the nucleation of the minority phase droplets. For a given alloy composition, its effect on the coalescence of droplets increases with the cooling rate until a critical cooling rate is reached. After that, its effect decreases with the cooling rate. Brownian coagulation leads to a wider and multipeak size distribution of minority phase droplets. View full abstract»

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  • Observation of nanoindentation rosettes on {0001}ZnO using scanning Kelvin probe microscopy

    Page(s): 131906 - 131906-3
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    Nanoindentation rosettes have been observed by scanning Kelvin probe microscopy on chemomechanical polished and etched {0001}ZnO while under illumination by a broadband light source. The rosette pattern consisted of a central region with a lower surface potential extending beyond the indentation and six arms emanating from this region along the <1120> directions. The length of the longest rosette arm was found to be proportional to the square root of the maximum force of indentation minus the average load at which pop-in occurred. View full abstract»

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  • Vacancy distribution around isolated implantation sites

    Page(s): 131907 - 131907-3
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    Microscopic experimental data on the distribution of vacancies created in isolated implantation events are reported for the model system B in Cu. An interstitial-to-substitutional conversion process of the implanted 12B ions is utilized to detect lattice damage. We observe vacancy clouds with well-defined edges and a mean radius of 13.5(9) nm. The radial profile of the local vacancy concentration never exceeds 10-4; it is almost flat in the central region before it falls off rapidly, a behavior which cannot be explained by simple binary-collision computer models. View full abstract»

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  • Interface structure and phase of epitaxial SrTiO3 (110) thin films grown directly on silicon

    Page(s): 131908 - 131908-3
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    The interface structure and phase between SrTiO3 (110) on Si (100) have been investigated using high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. The SrTiO3/Si interface was found to be epitaxially crystallized without any amorphous oxide layer. The formation of Sr silicate at the interface was suggested by considering the fact of the core-level spectra of the Si 2p, O 1s, and Sr 3d. Our results suggest that the presence of a coincident site lattice at the interface between Si and a Sr silicate and/or SrTiO3 may help to stabilize SrTiO3 in the epitaxial orientation reported in the work. View full abstract»

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  • Infrared-to-visible upconversion in thin films of LaEr(MoO4)3

    Page(s): 131909 - 131909-3
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    LaEr(MoO4)3 thin films have been grown by pulsed laser deposition. The films were characterized by x-ray diffraction, Rutherford backscattering, and fluorescence measurements. The results show that the deposited films were epitaxial with their c axis oriented along the surface normal. Films illuminated with 980 nm laser light show visible emission spectra. This visible emission arises as a result of the Er 4f-4f transitions and their lifetimes. Such so-called “upconverting phosphors” are important to the development of new chemical and biological sensing applications. View full abstract»

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  • Global method for measuring stress in polymer fibers at elevated temperatures

    Page(s): 131910 - 131910-3
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    In this work, a methodology is presented for evaluating the interfacial shear stress as well as the corresponding axial stress in full polymer fiber reinforced materials under elevated temperatures. Its validity was confirmed by deriving interfacial shear and axial stress expressions for embedded Kevlar® 29 fibers within an epoxy matrix by means of Raman microscopy. This approach can be established to other systems such as carbon or polyethylene fiber composites, for which the observed Raman bands are both stress and temperature sensitive. View full abstract»

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  • Polychromatic light emission from single InGaN quantum wells grown on pyramidal GaN facets

    Page(s): 131911 - 131911-3
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    We have studied the properties of InGaN/GaN quantum wells grown on epitaxially laterally overgrown GaN stripes. The stripes have a triangular cross section due to {1122} crystalline facets. We have observed that the integrated light emission from such structures is uniformly polychromatic over a wide range of the visible spectrum. Using cathodoluminescence techniques, we find that the local emission wavelength increases steadily along the facets, in the direction away from the substrate. The gradient in the emission wavelength is related to the dependence of the quantum well width on the relative position along the facet. The continuous variation of the quantum well properties causes a uniform, polychromatic luminescence band. For some conditions, such distribution can resemble solar-white light emission. This approach can be used to produce an integrated white light source for monolithically integrated white light-emitting diodes. View full abstract»

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  • Room-temperature stimulated emission from microcrystalline CsPbCl3 films

    Page(s): 131912 - 131912-3
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    Photoluminescence from microcrystalline CsPbCl3 films prepared by crystallization from the amorphous phase is measured under N2 laser excitation. Stimulated emission due to free exciton-free exciton inelastic collision occurs not only at 77 K (as reported very recently) but also at room temperature (RT). The intensity of the stimulated emission more rapidly increases with pumping intensity at RT than at 77 K, although the threshold is higher at the former temperature (600 kW cm-2) than at the latter (240 kW cm-2). This demonstration of the stimulated emission at RT from metal halides encourages us to explore laser media in metal halides because of their material abundance. 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