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Applied Physics Letters

Issue 8 • Date Aug 1998

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Displaying Results 1 - 25 of 52
  • 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
  • Stress-induced lateral confinement of light in epitaxial BaTiO3 films grown by radio-frequency magnetron sputtering

    Page(s): 1017 - 1019
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    We report channel waveguides formed in epitaxial BaTiO3 films that were grown on MgO single-crystal substrates using rf magnetron sputtering. In the channel waveguides developed, the lateral confinement of light is achieved via the photoelastic and piezoelectric/electro-optic effects in BaTiO3 induced by thin-film stress. Numerical analyses were also carried out on the stress and piezoelectric field distributions in the channel structure, assuming bulk materials properties. The refractive index changes were then calculated taking into account both the photoelastic and electro-optic effects of BaTiO3. The simulation result suggests that the electro-optic effect (caused by the stress-induced piezoelectric field) accounts for a significant portion (∼10%) of the refractive index change in the channel region. © 1998 American Institute of Physics. View full abstract»

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  • Waveguide laser film in erbium-doped KTiOPO4 by pulsed laser deposition

    Page(s): 1020 - 1022
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    Erbium doping into potassium titanyl phosphate (KTiOPO4 or KTP) was performed by pulsed laser deposition. Waveguide laser film in Er-doped KTiOPO4 was formed using both KTiOPO4 and erbium as targets and optically polished KTiOPO4 as a substrate. Rutherford backscattering, photoluminescence spectrometry, x-ray diffraction, and prism coupling method are used to investigate the properties of Er-doped KTiOPO4. The results show that (1) Er-doped KTiOPO4 emits the characteristic photoluminescence of Er3+ around 1.54 μm corresponding to transition between the 4I13/2 and 4I15/2 manifolds of the Er3+ ions in KTiOPO4 host. (2) two bright modes in Er-doped KTiOPO4 were observed. This approach may be useful for direct fabrication of thin film waveguide laser for other optoelectrical materials. © 1998 American Institute of Physics. View full abstract»

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  • Correlation between in situ optical emission spectroscopy in a reactive Ar/O2 rf magnetron sputtering discharge and Pb(ZrxTi1-x)O3 thin film composition

    Page(s): 1023 - 1025
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    Lead zirconate titanate Pb(ZrxTi1-x)O3 (PZT) thin films have been deposited by rf magnetron sputtering on Si substrates from a metallic target of nominal composition Pb1.1(Zr0.4Ti0.6) in a reactive argon/oxygen gas mixture. During plasma deposition, in situ optical emission spectroscopy measurements show clearly a correlation between the evolution of characteristic atomic emission line intensities Zr—386.4 nm, Ti—399.9 nm, Pb—405.8 nm, and O—777.2 nm and the thin-film composition determined by a simultaneous use of Rutherford backscattering spectroscopy and nuclear reaction analysis. © 1998 American Institute of Physics. View full abstract»

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  • Determination of frontier orbital alignment and band bending at an organic semiconductor heterointerface by combined x-ray and ultraviolet photoemission measurements

    Page(s): 1026 - 1028
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    The alignment of the highest occupied molecular orbitals (HOMO) at the tris (8-hydroxy quinoline) aluminum (Alq3)/N,N-di-(3-methylphenyl)-N,Ndiphenyl-4,4-diaminobiphenyl (TPD) heterojunction, used in organic light-emitting diodes (OLED), was determined by growing a TPD layer in several steps on a thick Alq3 substrate layer. After each growth step the sample was characterized in situ by x-ray and ultraviolet photoemission spectroscopy. The offset of the HOMO maxima at the interface was determined to be -0.13 eV from Alq3 to TPD. By including the known HOMO–lowest occupied molecular orbital (LUMO) gaps for both molecules into the evaluation, the offset of the LUMO minima was determined to be -0.33 eV from Alq3 to TPD. These values are consistent with previous assumptions that this interface represents a higher barrier for electron injection from Alq3 to TPD than for hole injection from TPD to Alq3. © 1998 American Institute of Physics. View full abstract»

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  • Sonoluminescence initiated by laser irradiation of carbon suspensions

    Page(s): 1029 - 1031
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    We report observation of sonoluminescence following irradiation of suspensions of carbon in water with a high power, pulsed laser. The mechanism for generation of a gas bubble is chemical in origin: the heating of the carbon particles by absorption of laser radiation causes the production of high pressure H2 and CO through reaction of carbon with the water surrounding the particles. Expansion of the bubble past its equilibrium diameter results in oscillation of the bubble diameter which, several hundred μs after the initial formation of the bubble, results in emission of optical and acoustic radiation. The effects of laser power, the concentration of carbon in the suspension, dissolved Ar, and temperature on the sonoluminescent intensity are reported. © 1998 American Institute of Physics. View full abstract»

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  • Cotton–Mouton effect measurement with the Fabry–Perot eigenstates

    Page(s): 1032 - 1034
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    We show that, using the eigenstates of a high-finesse Fabry–Perot cavity, we can measure the small Cotton–Mouton birefringence of gases with a simple tabletop apparatus. It requires only modest magnetic fields (B≪1 T) and uses an ultrastable Zerodur high-finesse optical cavity. The method is validated by the measurement of the Cotton–Mouton constant of air and a sensitivity of 2.5×10-9rad is obtained for the single pass birefringence. © 1998 American Institute of Physics. View full abstract»

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  • Near-field optical imaging of light propagation in semiconductor waveguide structures

    Page(s): 1035 - 1037
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    We have investigated light propagation in optical devices by near-field scanning optical microscopy (NSOM) at the telecommunication wavelength of 1.55 μm. NSOM images obtained on the top of channel waveguides measure the mode profile perpendicular to the propagation direction and show a modulation of intensity along this direction. This modulation demonstrates the periodic variation of the mode size predicted for the propagation in small guides and marks the direction of propagation. We show that NSOM analysis can completely assess complex optical devices with subwavelength resolution: determination of the optical path, variation of the light intensity along this path, and measurement of local radiative losses. © 1998 American Institute of Physics. View full abstract»

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  • High temperature excitonic stimulated emission from ZnO epitaxial layers

    Page(s): 1038 - 1040
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    The emission spectrum of high quality ZnO epilayers is studied from room temperature up to 550 K. At room temperature and low excitation power a single emission peak is observed which may be identified with the free exciton from its peak energy and dependence on temperature. However, when excitation intensities exceed 400 kW cm-2 a sharp peak emerges at lower energy which we attribute to exciton-exciton scattering. At higher excitation intensities (≫800 kW cm-2) a second stimulated emission peak emerges at even lower energies: we attribute this peak to be stimulated emission of an electron hole plasma. Similar features are observed for all temperatures up to 550 K. © 1998 American Institute of Physics. View full abstract»

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  • Laser-based ultrasound detection using photorefractive quantum wells

    Page(s): 1041 - 1043
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    We demonstrate a laser-based adaptive ultrasonic homodyne receiver using dynamic holography in AlGaAs/GaAs photorefractive multiple quantum wells. The dynamic hologram acts as an adaptive beamsplitter that compensates wavefront distortions in the presence of speckle and requires no path-length stabilization. The photorefractive quantum wells have the unique ability to achieve maximum linear homodyne detection regardless of the value of the photorefractive phase shift by tuning the excitonic spectral phase. We achieve a root mean square noise-equivalent surface displacement of 6.7×10-7 Å(W/Hz)1/2. © 1998 American Institute of Physics. View full abstract»

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  • Evidence of Si presence in self-assembled Ge islands deposited on a Si(001) substrate

    Page(s): 1044 - 1046
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    Nominal Ge islands were grown by a molecular beam epitaxy technique on a Si(001) substrate. Island positions and shapes were measured by atomic force microscopy. Two types of islands with different sizes and shapes are present. The Si concentration distribution inside the islands was measured by Raman imaging technique with a 0.4 μm resolution, and was found to vary between 10% and 30% in large islands and be 10% in smaller islands. © 1998 American Institute of Physics. View full abstract»

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  • The large magnetoresistance property of La0.5Sr0.5CoO3-x thin films prepared by pulsed laser deposition

    Page(s): 1047 - 1049
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    High-quality (001) thin film La0.5Sr0.5CoO3-x (LSCO) has been prepared on (001) SrTiO3 substrates by pulsed laser deposition under different oxygen pressures with and without postannealing. C-axis expansion of the LSCO with reducing oxygen pressure was revealed. The electrical resistivity increased over five orders of magnitude when oxygen pressure varied from 1.0 mbar (plus postannealing) to 10-3 mbar. The negative magnetoresistance (n-MR) property as a function of temperature and oxygen pressure was investigated. Linear dependence of the n-MR ratio on magnetic field and temperature was found and significant effect of oxygen stoichiometry on the n-MR was demonstrated. The film prepared at 650 °C and 0.1 mbar oxygen shows a n-MR ratio of -16% at 81 K under a field of only 0.2 T. © 1998 American Institute of Physics. View full abstract»

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  • Chemical vapor deposition of diamond growth using a chemical precursor

    Page(s): 1050 - 1052
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    A nucleation method to form diamond on chemically pretreated silicon (111) surfaces is reported. The nucleation consisted of binding covalently 2,2-divinyladamantane molecules on the silicon substrate. Subsequently, low pressure diamond growth was performed via microwave plasma chemical vapor deposition in a tubular deposition system. The resulting diamond layers presented a good crystallinity and the Raman spectra showed a very sharp peak at 1331 cm-1. © 1998 American Institute of Physics. View full abstract»

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  • Si adatom surface migration biasing by elastic strain gradients during capping of Ge or Si1-xGex hut islands

    Page(s): 1053 - 1055
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    Hut cluster formation during Ge or Si1-xGex solid source molecular beam epitaxial growth on Si(001) is a well-known kinetic pathway for partial strain relief. It results in undulated morphologies with {105} facets allowing a|| lattice parameter relaxation on the island apexes. Here, we show how subsequent Si coverages, grown at 500 °C, avoid being tensile strained and impede further increase of stored elastic strain energy. Dominant inhomogeneous Si surface diffusions take place as proven by a Ge marker technique able to provide transmission electron microscopy or high-resolution transmission electron microscopy images of the initial Si morphology stages and by reflection high-energy electron diffraction examinations. This mechanism prevails for high enough Si growth rates, able to quench lateral Ge diffusion and limit chemical strain relief. Mediated by stress variations on the noncapped island curvatures, Si is depleted from the top of the islands and accumulates in the troughs of the ripples where it accommodates mostly unstrained. By this selective Si coverage, the surface undergoes a rapid smoothing and a|| recovery toward the Si bulk value. When the Ge containing islands are completely buried, their strain, dictated by the Si buffer and cap layers, ends by being mainly along the growth direction or tetragonal (Δa||=0). © 1998 American Institute of Physics. View full abstract»

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  • Cooling by adiabatic pressure application in Pr1-xLaxNiO3

    Page(s): 1056 - 1058
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    A novel principle for cooling by adiabatic pressure application in the mixed crystalline compound Pr1-xLaxNiO3 is described and experimentally verified. Cooling occurs in the vicinity of the structural phase transition where the electronic ground state of the Pr3+ ions changes from a singlet to a doublet state. By properly choosing the La concentration x, the cooling effect can be achieved down to some 100 mK. Furthermore, Pr1-xLaxNiO3 can be used for second and third stage cooling down to the μK region by classical paramagnetic and nuclear demagnetization techniques, respectively. © 1998 American Institute of Physics. View full abstract»

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  • Preparation of atomically flat Co(110) films on Cu(110)

    Page(s): 1059 - 1061
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    It is shown that the growth mode of cobalt on the Cu(110) surface at 350 K can be changed from three-dimensional to extended layer-by-layer growth by pre- and co-adsorption of oxygen. The shape and the intensity of the growth oscillations observed in thermal energy helium atom scattering experiments depends sensitively on the total oxygen coverage. Helium diffraction reveals that different oxygen induced surface reconstructions of the top-most Co layer are responsible for the presence or absence of layer-by-layer growth in an extended coverage range. © 1998 American Institute of Physics. View full abstract»

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  • Reflective homeotropic mode in a twisted nematic liquid crystal

    Page(s): 1062 - 1064
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    This letter reports on a novel liquid crystal (LC) display device capable of achromatic reflection in a twisted homeotropic configuration using a chiral nematic LC with negative dielectric anisotropy. Using the elastic continuum formalism, we arrived at simulated values for each parameter of interest, including external twist, cell gap, molecular chirality for the chiral pitch, and the surface anchoring energy. The experimental results correspond well with the calculated expectations, exhibiting EO properties that demonstrate excellent achromatic reflection, extinction, and a high contrast ratio. © 1998 American Institute of Physics. View full abstract»

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  • Infrared analysis of deuterated carbon–nitrogen films obtained by dual-ion-beam-assisted-deposition

    Page(s): 1065 - 1067
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    The isotopic effect on the infrared spectra is used to determine the existence of nitrogen–hydrogen bonds in amorphous carbon–nitrogen alloys (a-CNx) prepared by dual-ion-beam-assisted deposition. The deuteration experiments and the evolution of the infrared spectra upon atmospheric exposure show that hydroxyls are incorporated from atmospheric moisture. © 1998 American Institute of Physics. View full abstract»

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  • Characterization of dislocations in germanium substrates induced by mechanical stress

    Page(s): 1068 - 1070
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    Dislocations are observed in germanium crystals (9° off axis toward the [011] direction) that have undergone plastic deformation. Optical microscopy reveals that the substrates exhibit a crosshatch pattern, consisting of ridges and trenches that extend in the [011] and [011¯] directions. Further characterization of these features with scanning tunneling microscopy shows that they consist of bands of steps. These bands are created when a group of dislocations emerge onto the crystal surface from the bulk. The dislocations are determined to be type (a/2)<011>. © 1998 American Institute of Physics. View full abstract»

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  • Coulomb blockade in Sb nanocrystals formed in thin, thermally grown SiO2 layers by low-energy ion implantation

    Page(s): 1071 - 1073
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    Sb nanocrystals were formed in thin, thermally grown SiO2 layers using low-energy ion implantation followed by thermal annealing. These Sb nanocrystals have good size and position uniformity. Both the narrow as-implanted profile and the compressive strain that exists near the SiO2/Si interface supposedly contribute to the uniformity. The I–V characteristics of the diode structure show a Coulomb blockade region around 0 V and a Coulomb staircase at 4.2 K. The Coulomb blockade region was observed up to a temperature of 100 K. The technique offers the possibility of developing practical Si-based single-electron devices. © 1998 American Institute of Physics. View full abstract»

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  • Anisotropic misfit dislocation nucleation in two-dimensional grown InAs/GaAs(001) heterostructures

    Page(s): 1074 - 1076
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    We report on structural investigations of the plastic strain relief in the highly mismatched InAs/GaAs(001) system grown in the layer-by-layer growth mode. The misfit dislocation generation mechanism is observed to be anisotropic in the two perpendicular 〈110〉 directions. We explain this result by the interplay between the chemically inequivalent dislocation types present in compound semiconductors and the applied growth condition. © 1998 American Institute of Physics. View full abstract»

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  • Stress-related interdiffusion in dc sputtered TiN/B–C–N multilayers

    Page(s): 1077 - 1079
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    The diffusion in TiN/B–C–N multilayers during vacuum annealing at temperatures up to 1000 °C and/or 300 keV argon irradiation is studied. Changes in composition, stress field, bilayer repeat length, and interface quality are reported. The effect of stress on diffusion is proved by performing the same annealing or the same irradiation on a multilayer with and without compressive stress. During thermal annealing, demixing or phase separation is observed. On the contrary, during irradiation, mixing occurs. Both phenomena are enhanced in the presence of the stress field. © 1998 American Institute of Physics. View full abstract»

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  • Properties of Ba(Mg1/3Ta2/3)O3 thin films prepared by metalorganic solution deposition technique for microwave applications

    Page(s): 1080 - 1082
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    We report on the properties of Ba(Mg1/3Ta2/3)O3 thin films prepared by the metalorganic solution deposition technique. Bulk Ba(Mg1/3Ta2/3)O3 ceramics have shown excellent dielectric properties at microwave frequencies; however, the high sintering temperature of bulk material is the major obstacle in their use as dielectric resonators to miniaturize microwave circuits. It was possible to obtain an ordered-perovskite phase of 0.3-μm-thick Ba(Mg1/3Ta2/3)O3 films with trigonal symmetry at an annealing temperature of 700 °C, which is much lower than the bulk sintering temperatures. The electrical measurements were conducted on Pt/Ba(Mg1/3Ta2/3)O3/Pt capacitors. The typical measured small signal dielectric constant and dissipation factor at 100 kHz were 22.2 and 0.009, respectively. The dielectric constant of thin films was comparable to the typical values r∼23.5–25) reported for bulk ceramics. The temperature coefficient of capacitance was -145 ppm/°C in the measured temperature range of 25–125 °C. The leakage current density was lower than 10-7A/cm2 at an applied electric field of 0.5 MV/cm. The high dielectric constant, which is comparable to bulk, low dielectric loss, and good temperature and bias stability suggest - - the suitability of Ba(Mg1/3Ta2/3)O3 thin films for microwave communications and integrated capacitor applications. © 1998 American Institute of Physics. View full abstract»

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  • Temperature dependence of electromigration dynamics in Al interconnects by real-time microscopy

    Page(s): 1083 - 1085
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    Real-time transmission electron microscopy (TEM) was used to directly examine the temperature dependence of electromigration-induced void and failure dynamics over the range 200–350 °C. The studies were done using submicron Al interconnects and a special sample stage, which allowed TEM observations to be recorded while heating and passing current through the sample. A novel sample design dramatically minimized any Joule heating in the runners. Our experiments directly reveal that the mechanism responsible for void and failure dynamics at temperatures ≪250 °C is distinctly different from that at higher temperatures. These results have implications regarding methods used for predicting electromigration reliability at use conditions from accelerated test data. © 1998 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