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Applied Physics Letters

Issue 23 • Date Jun 1999

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Displaying Results 1 - 25 of 53
  • 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
  • All-optical focal length converter using large optical nonlinearity in guest-host liquid crystals

    Page(s): 3429 - 3431
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    We present an all-optical focal length converter using both large optical nonlinearity and anisotropic complex refractive indices in guest-host nematic liquid crystals (GHLCs). The nonlinear phase modulation was generated by irradiating the GHLCs with a He–Ne laser beam (wavelength; 633 nm) having a Gaussian profile. A laser diode (LD) beam (wavelength; 788 nm) passed at the same point as the He–Ne laser beam spot. The phase of the LD beam was modulated and the LD beam was focused due to the phase modulation. The focal length of the LD beam was varied over a range of several centimeters by controlling the intensity of the He–Ne laser beam. © 1999 American Institute of Physics. View full abstract»

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  • Far-infrared laser oscillation from a very small p-Ge crystal under uniaxial stress

    Page(s): 3432 - 3434
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    We report on pulse laser oscillation from a p-Ge intervalence band (IVB) laser composed of a Ga-doped Ge crystal measuring about 1×1×5 mm3 which is a very small volume compared with those reported so far for shallow-acceptor-doped Ge. Laser oscillation is only achieved under uniaxial stresses greater than 1300 kg/cm2. We find that the optimum stress for lasing is around 3500–4100 kg/cm2 when the p-Ge IVB lasers are operated at liquid helium temperature. The minimum electric power needed for lasing is only 280 W at a peak period of pulse emission. © 1999 American Institute of Physics. View full abstract»

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  • Polarization modulation in optoelectronic generation and detection of terahertz beams

    Page(s): 3435 - 3437
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    Compared with the conventional laser amplitude modulation with a lock-in amplifier, the optical polarization modulation in optoelectronic generation and detection of a free-space terahertz (THz) radiation provides up to twofold increase of the dynamic range. The total laser power for the optoelectronic generation of THz beams can be fully utilized. © 1999 American Institute of Physics. View full abstract»

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  • InAsSb/InAsP strained-layer superlattice injection lasers operating at 4.0 μm grown by metal-organic chemical vapor deposition

    Page(s): 3438 - 3440
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    We report high power mid-infrared electrical injection operation of laser diodes based on InAsSb/InAsP strained-layer superlattices grown on InAs substrate by metal-organic chemical vapor deposition. The broad-area laser diodes with 100 μm aperture and 1800 μm cavity length demonstrate peak output powers of 546 and 94 mW in pulsed and cw operation respectively at 100 K with a threshold current density as low as 100 A/cm2. © 1999 American Institute of Physics. View full abstract»

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  • A vertical cavity light emitting InGaN quantum well heterostructure

    Page(s): 3441 - 3443
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    A method is described for fabricating a vertical cavity light emitting structure for nitride semiconductors. The process involves the separation of a InGaN/GaN/AlGaN quantum well heterostructure from its sapphire substrate an its enclosure by a pair of high reflectivity, low loss dielectric mirrors to define the optical resonator. We have demonstrated a cavity Q factor exceeding 600 in initial experiments, suggesting that the approach can be useful for blue and near ultraviolet resonant cavity light emitting diodes and vertical cavity lasers. © 1999 American Institute of Physics. View full abstract»

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  • Indium tin oxide thin films for organic light-emitting devices

    Page(s): 3444 - 3446
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    High-quality indium tin oxide (ITO) thin films (150–200 nm) were grown on glass substrates by pulsed laser deposition (PLD) without postdeposition annealing. The electrical, optical, and structural properties of these films were investigated as a function of substrate temperature, oxygen pressure, and film thickness. PLD provides very uniform ITO films with high transparency (≥85% in 400–700 nm spectrum) and low electrical resistivity (2–4×10-4 Ω cm). The Hall mobility and carrier density for a 170-nm-thick film deposited at 300 °C are 29 cm2/V s and 1.45×1021cm-3, respectively. Atomic force microscopy measurements of the ITO films indicated that their root-mean-square surface roughness (∼5 Å) is superior to that (∼40 Å) of commercially available ITO films deposited by sputtering. ITO films grown at room temperature by PLD were used to study the electroluminescence (EL) performance of organic light-emitting devices. The EL performance was comparable to that measured with commercial ITO anodes. © 1999 American Institute of Physics. View full abstract»

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  • Response of 1.6 μm Er:Y3Al5O12 fiber-optic temperature sensor up to 1520 K

    Page(s): 3447 - 3449
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    Fiber-optic temperature sensors based on fluorescence decay of the 1.6 μm transition in Er:Y3Al5O12 (Er:YAG) have been operated up to 1520 K. The probes are of a monolithic construction consisting of a single-crystal YAG lead fiber and an Er:YAG tip. The temperature-dependent fluorescence decay data show the dominance of the phonon mode at 220 cm-1 in mediating multiphonon relaxation in YAG at high temperatures. Such a sensor was used in the direct measurement of temperature in the interior of molten aluminum. © 1999 American Institute of Physics. View full abstract»

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  • Measurements of the THz absorption and dispersion of ZnTe and their relevance to the electro-optic detection of THz radiation

    Page(s): 3450 - 3452
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    Via THz time-domain spectroscopy, we have measured the absorption and index of refraction of single-crystal 〈110〉 ZnTe from 0.3 to 4.5 THz. We find that the absorption is dominated by two lower-frequency phonon lines at 1.6 and 3.7 THz and not by the transverse-optical (TO) -phonon line at 5.3 THz as previously assumed. However, the index of refraction is determined mainly by the TO-phonon line. Using these data, we discuss a frequency-domain picture of electro-optic detection of THz radiation below the TO-phonon resonance and compare with the photoconductive THz receiver over the same frequency range. © 1999 American Institute of Physics. View full abstract»

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  • Investigation of nanolocal fluorescence resonance energy transfer for scanning probe microscopy

    Page(s): 3453 - 3455
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    Fluorescence resonance energy transfer (FRET) has been observed between donor dye molecules deposited onto the sample surface and acceptor dye molecules deposited onto the scanning near-field optical microscope (SNOM) or atomic force microscope tip. FRET was observed only when the tip acquired a contact with the sample and took place in a region of few tens of square nanometers in size when thousands (hundreds) of molecules are involved. In view of the obtained results, the perspectives for the construction of a one-atom FRET SNOM are described. © 1999 American Institute of Physics. View full abstract»

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  • Nanocrystalline titanium dioxide-dispersed semiconducting polymer photodetectors

    Page(s): 3456 - 3458
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    Photodetection properties of nanocrystalline titanium dioxide, TiO2, dispersed in poly-2-methoxy-5-(2-ethyl-hexoxy)-1,4 paraphenylenevinylene MEHPPV are studied. Responsivity as high as 50 mA/W is observed in the single-layered composite device. The spectral response is sensitive to the magnitude of the bias in the low-voltage range and the crossover from a symbatic to antibatic response is closely followed. At higher reverse bias, the response is relatively uniform throughout the entire spectral range. Differences in the switching response in the forward bias and reverse bias are observed with a pronounced effect of the persistence photocurrent in the forward bias. © 1999 American Institute of Physics. View full abstract»

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  • Photorefractive Bragg gratings in nematic liquid crystals aligned by a magnetic field

    Page(s): 3459 - 3461
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    Photorefractive Bragg gratings are observed in low-molar-mass nematic liquid crystals doped with electron donor and acceptor molecules. This is accomplished by alignment of the nematic liquid crystals in a 0.3 T magnetic field, which produces thicker homeotropic aligned samples than traditional surfactant techniques. Grating fringe spacings as low as 3.7 μm are achieved with 176-μm-thick samples, producing grating Q values of 33. Up to this point, low molar mass nematic liquid crystals have exhibited photorefractive gratings with Q≤1. Asymmetric two-beam coupling and photoconductivity experiments are performed to verify the photorefractive origin of the gratings. © 1999 American Institute of Physics. View full abstract»

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  • Bias-enhanced nucleation and growth of the aligned carbon nanotubes with open ends under microwave plasma synthesis

    Page(s): 3462 - 3464
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    Aligned carbon nanotubes with open ends have been fabricated on silicon wafer in one step using a microwave plasma enhanced chemical vapor deposition system with a mixture of methane and hydrogen as precursors. High concentration hydrogen plasma and high negative bias voltage to the substrate induce anisotropic etching of carbon nanotubes and can effectively reduce the randomly oriented carbon nanotubes. The mechanism of aligned carbon nanotubes with open ends is proposed in this letter. © 1999 American Institute of Physics. View full abstract»

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  • Study of ground-state titanium ion velocity distributions in laser-produced plasma plumes

    Page(s): 3465 - 3467
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    The velocity distribution of ground-state titanium ions within a low-temperature plasma resulting from the laser ablation of a titanium target has been investigated. A KrF excimer laser was focused onto the target at moderate fluences (≪10 Jcm-2) in vacuum (∼2×10-5Torr). Time-of-flight distributions were determined as functions of distance from target and laser fluence using absorption spectroscopy. The results were found to be described consistently by a Maxwell–Boltzmann distribution with zero flow velocity. The most probable velocity was found to scale with the square root of the incident laser fluence. © 1999 American Institute of Physics. View full abstract»

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  • Guiding radio frequency waves on metallic foils

    Page(s): 3468 - 3470
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    The propagation of electromagnetic surface waves along thin metallic strips was investigated. Efficient guidance of surface waves over distances of many kilometers can now be realized since: (1) low attenuation of the electromagnetic waves can be achieved by increasing the width of the strip, (2) losses by scattering are small because of the large reduction in the radial extension of the electric field, and (3) thin foils are lightweight. Other means (e.g., coaxial line or waveguides) of transporting electromagnetic waves produce orders of magnitude increase in weight, cost, and attenuation. © 1999 American Institute of Physics. View full abstract»

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  • Patterning of cubic and hexagonal GaN by Cl2/N2-based reactive ion etching

    Page(s): 3471 - 3473
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    Chlorine-based dry etching of hexagonal and cubic GaN epilayers grown by dc plasma-assisted molecular beam epitaxy is investigated using a conventional parallel electrode reactor. It is found that the addition of nitrogen results in a shallow maximum for etch rates at 37% N2 content in a low-pressure plasma and a monotonically decreasing etch rate in higher-pressure plasmas. Etching with a low-pressure plasma produces smooth surfaces and almost vertical sidewalls at sufficiently high etch rates. © 1999 American Institute of Physics.   View full abstract»

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  • Flow dynamics of sheared liquids explored by inelastic neutron scattering

    Page(s): 3474 - 3476
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    We have applied high resolution neutron spectroscopy to elucidate the dynamics of sheared liquids. At room temperature, the macroscopic flow of the lubricant yields a peak of the scattered intensity at roughly half the velocity of the driving disk demonstrating a nonclassical flow, whereas at higher temperature the expected linear velocity profile establishes. The data also give information on a modification of local diffusion modes for a liquid in a shear field. © 1999 American Institute of Physics. View full abstract»

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  • Threshold behavior analysis of in-plane switching mode liquid-crystal cells with asymmetrical surface condition

    Page(s): 3477 - 3479
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    The threshold behavior of the in-plane switching (IPS) mode liquid-crystal cells with different (asymmetric) anchoring strength at two liquid-crystal/substrate interfaces was investigated by linear stability analysis. Similarity in stability characteristics between the IPS mode and the surface stabilized ferroelectric mode was clarified. The analysis showed that, with parallel rubbing of the two substrate surfaces, only the (symmetric) switching initialized from the center of the liquid-crystal layer will occur even with the asymmetric surface condition. This means that the basic switching process of the IPS mode does not change with the asymmetricities of the surface conditions. © 1999 American Institute of Physics. View full abstract»

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  • Infrared absorption of Li acceptors and shallow donors in ZnSe

    Page(s): 3480 - 3482
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    Using Fourier transform infrared spectroscopy, we have observed the absorption spectra of holes bound to acceptors in bulk ZnSe below 100 K. The absorption is assigned to hole transition of Li acceptors from the 1S3/2 ground state to the 2P3/2 excited state. The obtained transition energy of 72.9±0.1 meV is one order more precise than that obtained by photoluminescence measurements. In addition, absorption lines due to shallow donors are observed below 30 K, and the intensity is enhanced by excitation with a blue light emitting diode. The 1s–2p transition energies of three kinds of donors Al, Cl, and In are estimated at 18.96, 19.64, and 21.67 meV, respectively. © 1999 American Institute of Physics.   View full abstract»

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  • Revival of interband crystalline reflectance from nanocrystallites in porous silicon by immersion plating

    Page(s): 3483 - 3485
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    We prepared porous silicon for which the UV reflectance (3.3–6 eV) is nearly eliminated, and exhibits no features at the Si interband bulk transitions 3.3, 4.3, and 5.5 eV. Plating with a thin layer of copper is found to cause recovery of the UV bulk-like crystalline reflectance and interband resonances. This provides evidence that the loss of crystalline absorption is reversible and is not due to a permanent loss in the crystalline structure. This may relate to a recent model in which the optical activity of ultra small nanocrystallites is produced by a new Si–Si crystalline configuration (or phase), distinct from but interconnected to the diamond-like configuration by a potential barrier. © 1999 American Institute of Physics. View full abstract»

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  • Photoluminescence study of ZnS/ZnMgS single quantum wells

    Page(s): 3486 - 3488
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    We report a photoluminescence (PL) study of ZnS/ZnMgS strained-layer single quantum wells. The main PL peak from ZnS is attributed to light-hole free excitons. Quantum confinement causes it to shift from 3.76 eV to higher energy, 3.84 eV, with decreasing well width. Hydrostatic and shear deformation potentials are determined from energies of light- and heavy-hole exciton emission, to be a=-6.4 eV and b=-1.0 eV, respectively. © 1999 American Institute of Physics. View full abstract»

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  • Improvements in electrical properties of (Ba,Sr)TiO3 capacitor with chemical vapor deposited Pt top electrode using Pt hexafluoroacetylacetonate

    Page(s): 3489 - 3491
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    Electrical properties of (Bs,Sr)TiO3 (BST) thin films are characterized with sputtered and metal organic chemical vapor deposited (MOCVD) Pt top electrodes. BST films with MOCVD Pt top electrodes, which were deposited using Pt(CF3COCHCOCF3)2 (Pt-HFA) as a precursor, showed less leakage current without bulged curves and a higher dielectric constant than those with sputtered Pt top electrodes. The improvement of electrical properties seems to result from the reduction of interface trap sites with the incorporation of fluorine atoms from HFA ligands. © 1999 American Institute of Physics. View full abstract»

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  • Plasma-assisted pulsed laser deposition of SrBi2Ta2O9 thin films of improved ferroelectric and crystalline properties

    Page(s): 3492 - 3494
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    Significant effect of the introduction of O2-plasma discharge during pulsed laser ablative deposition of SrBi2Ta2O9 (SBT) films on improving the crystallite orientation and ferroelectric properties has been described. O2-plasma assists in the formation of highly crystalline films at a low 700 °C temperature over (111) oriented Pt films coated Si(100) single crystal substrates at a nominal pressure of 200 mTorr. Plasma excitation potential, applied at an auxiliary ring electrode placed near the substrate, has a profound effect on surface morphology, crystallite orientation, and remnant polarization, Pr values. At -350 V, SBT growth at 700 °C with predominant (a-b) orientation showing high Pr∼6.5 μC/cm2 in the as-deposited state has been obtained. In comparison, SBT films deposited identically but without the plasma show a low Pr of ∼1.7 μC/cm2. Ionized cationic species along with ionic and atomic oxygen present in the plasma improve thermodynamic stability of the film growth through enhanced chemical reactivity and thus eliminates the need for any severe postgrowth crystallization anneal step in the synthesis of SBT films. Impingement of energetic O2 ions and atomic oxygen helps lower the nucleation barrier for the growth of (a-b) crystallites and changes the c-axis orientation from normal to near parallel to the film plane. Quality of the film declines with the plasma excitation potential as enhanced kinetic - - energy of impinging O2 ions introduce defects and reduce nucleation density by resputtering from the substrate. © 1999 American Institute of Physics. View full abstract»

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  • High conduction-band offset of AlInAsSb/InGaAs multiple quantum wells grown by metalorganic vapor phase epitaxy

    Page(s): 3495 - 3497
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    Unstrained Al0.66In0.34As0.85Sb0.15/In0.53Ga0.47As multiple-quantum-well (MQW) structures have been grown by metalorganic vapor phase epitaxy. Low-temperature photoluminescence was performed for these MQW structures. We compared the experimental data with the theoretical calculations. The conduction-band offset ratio of AlInAsSb/InGaAs heterojunction was set as an adjustable parameter in the theoretical model. We estimated the conduction-band offset ratio to be 0.90±0.05 for the Al0.66In0.34As0.85Sb0.15/In0.53Ga0.47As heterojunction. © 1999 American Institute of Physics. 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