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Applied Physics Letters

Issue 7 • Date Aug 2008

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Displaying Results 1 - 25 of 94
  • Issue Cover

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

    Page(s): toc1
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    Freely Available from IEEE
  • Efficient single-photon frequency upconversion at 1.06 μm with ultralow background counts

    Page(s): 071101 - 071101-3
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    We demonstrated an efficient single-photon frequency upconversion system for the infrared photons at 1.06 μm with ultralow background counts. By pumping the system at a longer wavelength than that of the single-photon signal, the background counts caused by the pump-induced parametric fluorescence in the nonlinear crystal were reduced markedly. We achieved so far the lowest noise of ∼150 /s for a near unity conversion efficiency. View full abstract»

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  • Simultaneous interfacial misfit array formation and antiphase domain suppression on miscut silicon substrate

    Page(s): 071102 - 071102-3
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    The authors describe simultaneous interfacial misfit (IMF) array formation along with antiphase domain (APD) suppression in highly mismatched (Δa0/a0=13%) AlSb grown on a miscut Si (001) substrate. Strain energy from the AlSb/Si heterojunction is accommodated by a self-assembled two-dimensional array of pure 90° dislocations confined to the interface. The 13% lattice mismatch establishes the AlSb/Si IMF period of ∼3.46 nm. This IMF spacing is well matched to the step length of the miscut Si (001) substrate. Furthermore, the miscut substrate geometry suppresses APD formation due to the double step height. The resulting bulk material has both very low defect density (∼7×105/cm2) and very low APD density (∼103/cm2) confirmed by transmission electron microscope images. This material is expected to be desirable for electronic III-V devices on Si substrates. View full abstract»

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  • Frequency stabilization of an ultraviolet laser to ions in a discharge

    Page(s): 071103 - 071103-3
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    We stabilize an ultraviolet diode laser system at 369.5 nm to the optical absorption signal from Yb+ ions in a hollow-cathode discharge lamp. The error signal for stabilization is obtained by Zeeman spectroscopy of the 3 GHz wide absorption feature. The frequency stability is independently measured by comparison to the fluorescence signal from a laser-cooled crystal of 174Yb+ ions in a linear Paul trap. We measure a frequency fluctuation of 1.7 MHz over 1000 s and a frequency drift of 20 MHz over 7 days. Our method is suitable for use in quantum information processing experiments with trapped ion crystals. View full abstract»

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  • Tunable upconversion photon detector

    Page(s): 071104 - 071104-3
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    We introduce a simple approach for a tunable upconversion detector. This scheme is relevant for both single photon detection or anywhere where low light levels at telecom wavelengths need to be detected with a high degree of temporal resolution or where high count rates are desired. A system combining a periodically poled lithium niobate waveguide for the nonlinear wavelength conversion and a low jitter silicon avalanche photodiode is used in conjunction with a tunable pump source. We report more than a tenfold increase in the detectable bandwidth using this tuning scheme. View full abstract»

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  • Fabrication of three-dimensional photonic crystal structures by interferometric lithography and nanoparticle self-assembly

    Page(s): 071105 - 071105-3
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    We report a simple approach to fabrication of three-dimensional photonic crystal structures. One-dimensional photoresist patterns (lines) are defined as templates using interferometric lithography and silica nanoparticles are self-assembled around the photoresist patterns using spin coating. Multiple-layer structures are formed by repeating these processing steps. The photoresist patterns are removed through high temperature calcination to fabricate three-dimensional photonic crystals with void channels in a woodpile structure. The optical properties of as-prepared photonic crystal structures are in good agreement with simulation results. This approach provides a versatile and facile technology to fabricate photonic bandgap materials and photonic crystals with defects. View full abstract»

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  • ArF laser-based quantum well intermixing in InGaAs/InGaAsP heterostructures

    Page(s): 071106 - 071106-3
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    Radiation from a 193 nm ArF laser was investigated to modify surface properties of InGaAs/InGaAsP quantum well (QW) heterostructures and introduce defects required to enhance intermixing during the annealing process. A top 200 nm thick sacrificial layer of InP served as a reservoir for laser generated defects. The irradiation with up to 90 pulses at 65–150 mJ/cm2 allowed to generate an array of 1.2×1 mm2 sites of QW intermixed material, with bandgap energy blueshifted up to 107 nm. We discuss the mechanism and advantages of this approach for postgrowth wafer level fabrication of multibandgap QW material. View full abstract»

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  • Optically induced transport properties of freely suspended semiconductor submicron channels

    Page(s): 071107 - 071107-3
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    We report on optically induced transport phenomena in freely suspended channels containing a two-dimensional electron gas. The submicron devices are fabricated in AlGaAs/GaAs heterostructures by etching techniques. The photoresponse of the devices can be understood in terms of the combination of photogating and a photodoping effect. The hereby enhanced electronic conductance exhibits a time constant in the range of 1–10 ms. View full abstract»

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  • Low-cost and high-gain silicide Schottky-barrier collector phototransistor integrated on Si waveguide for infrared detection

    Page(s): 071108 - 071108-3
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    A two-terminal silicide Schottky-barrier collector phototransistor (SBCPT) integrated on a silicon-on-insulator waveguide was proposed and demonstrated using low-cost standard silicon processing technology. Owing to the current gain through the transistor action, the SBCPT at 5 V bias achieves a responsivity around 1550 nm of ∼150 mA/W, which is approximately 17.6-fold larger than the corresponding Schottky-barrier photodiode (SBPD) having the same silicide absorber. The current gain thereby the responsivity of SBCPT may be further improved simply by reducing the base width. Moreover, the SBCPT at negative bias exhibits a very low dark current of ∼12 pA owing to the presence of a reversely biased Si p-n junction while with the responsivity and speed only slightly degraded as compared to the SBPD counterpart. The proposed detector can be utilized as an in-line or terminal optical monitor in low-cost all-silicon electronic-photonic integrated circuits. View full abstract»

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  • Intervalley carrier transfer in short-wavelength InP-based quantum-cascade laser

    Page(s): 071109 - 071109-3
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    The scattering of electrons out of the upper laser state into indirect valleys in quantum-cascade lasers is demonstrated by investigating the operation of the laser under the influence of magnetic fields up to 45 T. A quantum-cascade laser based on strain-compensated AlAs barriers and In0.73Ga0.27As/InAs wells, emitting with wavelength 3.1 μm, is investigated as a function of magnetic field normal to the surface. Minima in emission power are observed when Landau levels of the upper laser state are brought into resonance with states derived from the indirect valleys, leading to the partial depopulation of the upper laser level. The energy for the indirect valley states is determined to be about 640 meV above the bottom of the In0.73Ga0.27As Γ valley, about 70 meV above the upper laser level. View full abstract»

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  • Intelligent multiparameter sensing with fiber Bragg gratings

    Page(s): 071110 - 071110-3
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    An approach to achieve intelligent sensing of multiple environmental parameters with a single-fiber sensor system is demonstrated through the use of multiplexed fiber Bragg gratings (FBGs) with coatings of different polymers and specifications. Using three FBGs of either acrylate or polyimide coating and polyimide coatings of different thicknesses, in situ discrimination of saccharinity, salinity, and temperature from the changes in the optical responses of the Bragg wavelengths of the gratings has been realized with sensitivities of 1.10×10-3 nm/%, 3.80×10-3 nm/% (blueshift), and 1.10×10-2 nmC (redshift), respectively. View full abstract»

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  • Tunable interband and intersubband transitions in modulation C-doped InGaAs/GaAs quantum dot lasers by postgrowth annealing process

    Page(s): 071111 - 071111-3
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    A bandgap and intersublevel spacing tuned laser has been realized by using a modulation C-doped InGaAs/GaAs quantum dot structure, which utilizes a postgrowth annealing process. The intermixed laser exhibits comparable light-current characteristics, indicating little detrimental change to the quantum dot laser material, and show a ground state bandgap blueshift of ∼13 nm and intersublevel energy spacing reduction of ∼30 nm compared to the unannealed device. The differences in the samples during annealing are attributed to the suppression of Ga vacancy propagation for samples with modulation C doping. View full abstract»

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  • Direct measurement of spatial electron density oscillations in a dual frequency capacitive plasma

    Page(s): 071501 - 071501-3
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    The spatio-temporal electron density oscillation in a narrow gap dual frequency (27.12 and 1.937 MHz) capacitive discharge has been measured for the first time by using a floating microwave hairpin resonance probe. By measuring the probe’s resonance frequency in a space and phase-resolved manner, we observe significant oscillation in electron density at both drive frequencies throughout the region between the parallel plate electrodes. The observed phenomenon is attributed to the influence of presheath electric fields of the opposing electrodes in alternate fashion. View full abstract»

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  • Temporal-spatial-resolved spectroscopic study on the formation of an atmospheric pressure microplasma jet

    Page(s): 071502 - 071502-3
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    Temporal-spatial-resolved optical emission spectroscopy was employed to shed light on the dynamic behavior and the propagation mechanism of a plasma, originating from a dielectric barrier discharge in helium inside a quartz tube for microplasma jet formation. The plasma propagated, regardless of the gas flow direction, in an accelerating manner at a high velocity up to 17 km/s, suggesting that the propagation was sustained by photoionization. A theoretical analysis demonstrated that the enhancement of the local electric field ahead of the ionization front was mainly responsible for the acceleration of the plasma near the electrode. View full abstract»

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  • Control of the discharge chemistry of CHF3 in dual-frequency capacitively coupled plasmas

    Page(s): 071503 - 071503-3
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    The discharge chemistry of CHF3 in 27/2, 60/2, and 60/13.56 MHz dual-frequency capacitively coupled plasmas (DF-CCPs) is studied with actinometric optical emission spectroscopy and mass spectrometry. The frequency effect on the generation of reactive species was investigated. The reactive radicals and the density ratio of F/CF2 could be controlled by the 2 MHz rf power in 27/2 and 60/2 MHz DF-CCPs. The density ratios of F/CF2 in 27/2 and 60/2 MHz DF-CCPs are observed to increase with an increase in low-frequency power. However, this control could not be obtained in 60/13.56 MHz DF-CCP. View full abstract»

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  • Observation of Ti4+ ions in a high power impulse magnetron sputtering plasma

    Page(s): 071504 - 071504-3
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    Multiply charged titanium ions including Ti4+ were observed in high power impulse magnetron sputtering discharges. Mass/charge spectrometry was used to identify metal ion species. Quadruply charged titanium ions were identified by isotope-induced broadening at mass/charge 12. Due to their high potential energy, Ti4+ ions give a high yield of secondary electrons, which in turn are likely to be responsible for the generation of multiply charged states. View full abstract»

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  • Spatial retarding field energy analyzer measurements downstream of a helicon double layer plasma

    Page(s): 071505 - 071505-3
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    Spatial ion energy measurements using a retarding field energy analyzer are performed in the exhaust of a 0.30 mTorr, 250 W helicon double layer plasma to investigate the divergence of the argon ion beam formed by acceleration in the double layer. Various divergence angles are computed by considering the radial distribution of beam density; the average beam ion diverging by 9°. The efficiency at which momentum is imparted parallel to the longitudinal axis of the thruster is calculated to be 98%. The results show that a few centimeters downstream of the source, the beam ions do not follow the magnetic field lines. View full abstract»

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  • A method to measure the electron temperature and density of a laser-produced plasma by Raman scattering

    Page(s): 071506 - 071506-3
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    A method is proposed to investigate the electron temperature and density of a laser-produced plasma simultaneously, using the temperature dependence difference of the Raman forward scattering (RFS) and backward scattering (RBS). Density and temperature dependence of spectra from the RBS and the RFS in a laser produced plasma were investigated by one-dimensional particle-in-cell simulations in the nonrelativistic regime. This technique has a great advantage as a simple diagnostic of plasma characteristics in the sense that it can be performed only with the pump laser, without any additional probe laser. View full abstract»

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  • Use of zeolites in the capture of charged particles from plasma

    Page(s): 071507 - 071507-3
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    The zeolites NaA and 13X were introduced to a coplanar discharge cell to investigate the behavior of charged particles from plasma. The zeolite crystals were attached to the surface without blocking their nanopores. The memory margin related to the accumulated charged particles on the surface indicated that the zeolites absorb charged particles. This phenomenon was also observed at the displacement and discharge current plots. Zeolites with a different window size cause abnormally high displacement and a saturation phenomenon of discharge currents. Note in particular that NaA seems to not only absorb charged particles but also capture gas molecules. View full abstract»

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  • Effect of limiting the cathode surface on direct current microhollow cathode discharge in helium

    Page(s): 071508 - 071508-3
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    This paper describes how to light several microdischarges in parallel without having to individually ballast each one. The V-I curve of a microhollow cathode discharge is characterized by a constant voltage in the normal glow regime because the plasma is able to spread over the cathode surface area to provide the additional secondary electrons needed. If one limits the cathode surface area, the V-I characteristic can be forced into an abnormal glow regime in which the operating voltage must increase with the current. It is then possible to light several microdischarges mounted in parallel without ballasting them individually. View full abstract»

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  • Three-dimensional atom probe investigation of boron distribution in CoFeB/MgO/CoFeB magnetic tunnel junctions

    Page(s): 071901 - 071901-3
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    Significant lateral compositional variations have been revealed in a three-dimensional atom probe (3DAP) study of the MgO barriers of magnetic tunnel junctions. High resolution electron microscopy of the CoFeB/MgO/CoFeB/Ru/CoFe/PtMn multilayer indicates that the MgO barrier is smooth, uniform, and with good crystallinity. Nevertheless, the 3DAP data show lateral variations in the MgO composition over length scales on the order of tens of nanometers. Boron is not uniformly distributed within the CoFeB layers, but has tended to segregate to the interfaces. Annealing has no significant effect on the distribution of B, indicating that the segregation occurring during growth is relatively stable. View full abstract»

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  • Thermophysical properties of Si, Ge, and Si–Ge alloy melts measured under microgravity

    Page(s): 071902 - 071902-3
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    We have investigated density, thermal expansion, and surface tension of Si, Ge, and Si–Ge alloys in the melt and undercooled state under microgravity conditions. The experiments were conducted in the TEMPUS facility on board a Zero-G aircraft. The density of the liquid alloys as a function of composition show a nonideal behavior. Thermal expansion coefficients were found to be in the order of 10-4 K-1 and was highest for Si75Ge25 melt. The surface tension is lowered with the addition of 25 at. % Si in Ge. The further addition of Si increases the surface tension almost linearly with composition. View full abstract»

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  • Resonance effects in broadband acoustic cloak with multilayered homogeneous isotropic materials

    Page(s): 071903 - 071903-3
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    The frequency response of the multilayered acoustic cloak made of isotropic materials is analyzed by the acoustic scattering theory. When concealing a rigid cylinder, the acoustic total scattering cross section (TSCS) monotonically increases with frequency. If concealing penetrable materials, the cloak-induced reverse-phase monopole and dipole resonances can increase the TSCS around the resonant frequencies, while the in-phase monopole resonance decreases the TSCS. The results are confirmed by numerical simulations of the finite element method. View full abstract»

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  • Spatially resolved strain measurements in Mo-alloy micropillars by differential aperture x-ray microscopy

    Page(s): 071904 - 071904-3
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    Spatially resolved strain distributions in the NiAl matrix and the ∼550–1000 nm Mo fibers of a NiAl–Mo eutectic were investigated by microbeam x-ray diffraction. Position sensitive d-spacings for the individual phases were obtained from spatially resolved and energy-resolved Laue patterns. For embedded Mo fibers, the measured elastic strain is consistent with the predicted thermal mismatch strain between the NiAl and Mo phases. However, when the NiAl matrix is etched back to expose Mo micropillars, the d-spacing increases to that of unconstrained Mo, indicating release of the compressive residual strain in the Mo fibers. 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