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3 Apr 2000

Volume 76, Issue 14, pp. 1795-1957

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Thermal imaging through ordered bundles of infrared-transmitting silver-halide fibers

E. Rave, D. Shemesh, and A. Katzir

Appl. Phys. Lett. 76, 1795 (2000); http://dx.doi.org/10.1063/1.126168 (3 pages) | Cited 7 times

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Ordered bundles of infrared-transmitting silver-halide (AgClxBr1−x) fibers were fabricated by extrusion. Bundles of total area 5–20 mm2 and lengths 5–50 cm included 100–2500 individual fibers and the packing fraction was 0.2–0.3. Each of the individual fibers was transparent in the spectral range 3–30 μm, and therefore, the whole bundle was suitable for thermal imaging. The modulation transfer function was studied using the “bar chart” and the “knife-edge” methods. The resolution was found to be 4–5 lines/mm for a 900 fiber bundle. Thermal images of objects at room temperature were transmitted from the entrance ends to the exit ends of the bundles. © 2000 American Institute of Physics.
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42.79.Pw Imaging detectors and sensors
42.81.Bm Fabrication, cladding, and splicing
42.81.Pa Sensors, gyros
07.60.Vg Fiber-optic instruments
42.30.Lr Modulation and optical transfer functions

Polarization of 129Xe with high power external-cavity laser diode arrays

J. N. Zerger, M. J. Lim, K. P. Coulter, and T. E. Chupp

Appl. Phys. Lett. 76, 1798 (2000); http://dx.doi.org/10.1063/1.126169 (3 pages) | Cited 13 times

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We demonstrate narrowing of a 2 W, broad area laser diode array and present calculations of the resulting improvement of 129Xe polarization by spin exchange with laser optically pumped Rb vapor. This improvement significantly impacts both medical imaging with laser polarized noble gas and spin-exchange pumped noble gas maser research. © 2000 American Institute of Physics.
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32.80.Xx Level crossing and optical pumping
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Phase-modulated beams technique for thin photorefractive films characterization

Yu. O. Barmenkov, A. V. Kir’yanov, A. N. Starodumov, N. M. Kozhevnikov, and H. Lemmetyinen

Appl. Phys. Lett. 76, 1801 (2000); http://dx.doi.org/10.1063/1.126170 (3 pages) | Cited 5 times

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The phase-modulated beams technique is developed for nonlinear thin photorefractive films characterization. In the Raman–Nath diffraction approximation, the formulas are deduced, allowing us to measure the amplitude of phase grating recorded in a film and its nonlinear refractive index n2. The method is applied for studying Langmuir–Blodgett multilayer thin ( ∼ 0.6 μm) films of Bacteriorhodopsin at wavelength 633 nm. © 2000 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ln Holographic recording materials; optical storage media
78.66.Qn Polymers; organic compounds
42.40.Kw Holographic interferometry; other holographic techniques
42.70.Jk Polymers and organics
42.79.Wc Optical coatings
68.18.-g Langmuir-Blodgett films on liquids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.40.Eq Holographic optical elements; holographic gratings

Improved characteristics of InGaN multiple-quantum-well light-emitting diode by GaN/AlGaN distributed Bragg reflector grown on sapphire

N. Nakada, M. Nakaji, H. Ishikawa, T. Egawa, M. Umeno, and T. Jimbo

Appl. Phys. Lett. 76, 1804 (2000); http://dx.doi.org/10.1063/1.126171 (3 pages) | Cited 34 times

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An InGaN multiple-quantum-well light-emitting diode (LED) containing a GaN/AlGaN distributed Bragg reflector has been grown on a sapphire substrate by metalorganic chemical vapor deposition. Comparing with the conventional LED, the output power has been improved from 79 to 120 μW under 20 mA direct current biasing condition and the external quantum efficiency has been also improved from 0.16% to 0.23% under 10 mA dc current. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.79.Bh Lenses, prisms and mirrors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Fd III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

4.8 μm vertical emitting PbTe quantum-well lasers based on high-finesse EuTe/Pb1−xEuxTe microcavities

G. Springholz, T. Schwarzl, M. Aigle, H. Pascher, and W. Heiss

Appl. Phys. Lett. 76, 1807 (2000); http://dx.doi.org/10.1063/1.126172 (3 pages) | Cited 18 times

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Vertical laser emission at 4.8 μm from PbTe quantum wells in high-finesse Pb0.95Eu0.05Te/EuTe microcavity structures at temperatures between 35 and 85 K is reported. The vertical-cavity laser structure was grown by molecular-beam epitaxy on BaF2(111) substrates, and consisted of a 2λ cavity with four 20 nm quantum wells at the cavity antinodes. Laser emission was excited by optical pumping with a pulsed Nd:YVO4 laser. The comparison of the cavity mode positions with envelope function calculations of the quantum-well energy levels indicates that, in this temperature range, lasing is due to transitions between the ground level of the oblique valleys in the conduction and valence bands. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Sa Microcavity and microdisk lasers

Control of color and efficiency of light-emitting diodes based on polyfluorenes blended with hole-transporting molecules

D. Sainova, T. Miteva, H. G. Nothofer, U. Scherf, I. Glowacki, J. Ulanski, H. Fujikawa, and D. Neher

Appl. Phys. Lett. 76, 1810 (2000); http://dx.doi.org/10.1063/1.126173 (3 pages) | Cited 90 times

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Adding low-molecular-weight hole-transporting molecules (HTM) with different oxidation potentials to the polyfluorene emission layer of single-layer light-emitting diodes causes significant changes in the device properties. The pronounced increase in luminance efficiency combined with a decrease in current is attributed to significant hole trapping, as further suggested by thermoluminescence experiments. Using a oligo-triphenylamine HTM with an ionization potential of ∼ 4.9 eV, light-emitting diodes with stable blue emission, a brightness of 800 cd/m2 and an efficiency of 0.87 cd/A were realized. Further, the red-emitting contribution to the spectra as observed in the pure polymer devices could be fully suppressed. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
78.60.Kn Thermoluminescence

High-performance blue light-emitting diode based on a binaphthyl-containing polyfluorene

Xuezhong Jiang, Sen Liu, Hong Ma, and Alex K.-Y. Jen

Appl. Phys. Lett. 76, 1813 (2000); http://dx.doi.org/10.1063/1.126174 (3 pages) | Cited 37 times

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We report efficient blue electroluminescence (EL) from multilayer polymer light-emitting diodes using a binaphthyl-containing polyfluorene as the emitting layer and a series of thermally polymerized triphenylamine/tetraphenyldiaminobiphenyl-containing polymers as the hole transport layer. The polymer possesses a high photoluminescence quantum efficiency of 44%. The polymer light-emitting diodes exhibit EL emission peak at 420 or 446 nm, depending on the hole transporting materials. The EL reaches maximum brightness and external quantum efficiency of 3070 cd/m2 and 0.82%, respectively. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials

Observation of Bragg reflection in photonic crystals synthesized from air spheres in a titania matrix

A. Richel, N. P. Johnson, and D. W. McComb

Appl. Phys. Lett. 76, 1816 (2000); http://dx.doi.org/10.1063/1.126175 (3 pages) | Cited 67 times

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Three-dimensional photonic crystals made of close-packed air spheres in an interconnected titania matrix have been fabricated using a self-organized template of polystyrene microspheres of 400 nm diameter. The matrix was obtained by vacuum-assisted infiltration of a precursor, with subsequent removal of the microspheres by calcination. Electron microscopy has confirmed the ordering of the structure and the presence of features likely to enlarge the photonic band gap. The reflection spectra of the crystal measured at different angles of incidence are consistent with Bragg’s law and with theoretical calculations, confirming the photonic nature of the material. © 2000 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics
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Enhancement of soft x-ray emission from a cryogenically cooled Ar gas jet irradiated by 25 fs laser pulse

T. Mocek, C. M. Kim, H. J. Shin, D. G. Lee, Y. H. Cha, K. H. Hong, and C. H. Nam

Appl. Phys. Lett. 76, 1819 (2000); http://dx.doi.org/10.1063/1.126176 (3 pages) | Cited 21 times

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Soft x-ray spectra (40–180 Å) produced by the interaction of 25 fs laser pulses at an intensity of ∼ 7×1016 W/cm2 with a cryogenically cooled Ar gas jet have been measured. New spectral lines from Ar8+ and Ar9+ charge states appeared with decreasing gas temperature. Nonlinear increase of x-ray line emission from Ar7+, Ar8+, and Ar9+ was observed with cooling, which saturated below certain temperature. The drastic change in the spectrum is attributed to efficient collisional heating and collisional ionization of growing (102–103 atoms) Ar clusters from the cooled jet. © 2000 American Institute of Physics.
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32.30.Rj X-ray spectra
32.80.Fb Photoionization of atoms and ions
36.40.Gk Plasma and collective effects in clusters
36.40.Mr Spectroscopy and geometrical structure of clusters

Enhancement of ion extraction from a cold plasma with radio-frequency plasma heating

Akira Ohzu, Yoji Suzuki, Yoichiro Maruyama, and Takashi Arisawa

Appl. Phys. Lett. 76, 1822 (2000); http://dx.doi.org/10.1063/1.126177 (3 pages)

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Ion extraction from a cold plasma produced by laser multiphoton ionization has been enhanced by using radio-frequency (140 MHz) dielectric plasma heating. When 10 W in heating power is applied to a plasma of ion density around 3×1010 cm−3, it is observed that the peak ion flux extracted with an electrostatic voltage of 20 V increases by a factor of more than 2. The time for extracting all the ions becomes short by a factor of 3 without any production of radio-frequency discharged plasma. It is considered that these results are due to the increase in the electron temperature of the plasma. This method will be very useful for the process of ion extraction in atomic vapor laser isotope separation. © 2000 American Institute of Physics.
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52.50.Gj Plasma heating by particle beams
52.80.Pi High-frequency and RF discharges
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Defect-enhanced solid-state amorphization in Zr100−xAlx/Ni thin-film diffusion couples

M. Gimbel, S. Schneider, E. Spiecker, and M. Seibt

Appl. Phys. Lett. 76, 1825 (2000); http://dx.doi.org/10.1063/1.126178 (3 pages)

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The interdiffusion reaction between supersaturated nanocrystalline Zr100−xAlx and crystalline Ni films leads to the formation of a planar amorphous Zr–Al–Ni interlayer. This solid-state amorphization reaction has been investigated by in situ measurement of electrical conductance and by transmission electron microscopy. With increasing defect density in the Zr100−xAlx layers, the diffusivity of Ni in the amorphous interlayer increases and the activation energy decreases. These results are discussed with respect to Stephenson’s analysis of interdiffusion and stress formation in systems with components of differing mobilities. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
61.43.Dq Amorphous semiconductors, metals, and alloys
73.61.At Metal and metallic alloys
72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys

Optically detected magnetic-resonance mapping on the yellow luminescence in GaN

F. K. Koschnick, K. Michael, J.-M. Spaeth, B. Beaumont, and P. Gibart

Appl. Phys. Lett. 76, 1828 (2000); http://dx.doi.org/10.1063/1.126179 (3 pages) | Cited 5 times

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A mapping investigation was performed with photoluminescence-detected electron paramagnetic resonance (PL-EPR) via the yellow luminescence on nominally undoped, metal–organic vapor-phase epitaxy-grown GaN on sapphire. From the results, it is concluded that the PL-EPR signals observed in these samples represent different recombination channels which contribute to the yellow luminescence. Therefore, our results do not support the model of Glaser et al. [Phys. Rev. B 51, 13326 (1995)] for the mechanism of the yellow luminescence proposed recently. © 2000 American Institute of Physics.
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76.70.Hb Optically detected magnetic resonance (ODMR)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Influence of molybdenum on the formation of C54 TiSi2: Template phenomenon versus grain-size effect

S.-L. Zhang and F. M. d’Heurle

Appl. Phys. Lett. 76, 1831 (2000); http://dx.doi.org/10.1063/1.126180 (3 pages) | Cited 14 times

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Experimental results are presented for the formation of TiSi2 in the presence of an ultrathin Mo layer deposited either at the interface between Ti and Si or on top of Ti/Si. The formation of C54 TiSi2 is clearly shown to be enhanced with a surface Mo layer, although the effect is less pronounced as compared to the use of an interposed Mo layer. The results can be accounted for with a template mechanism where the formation of C40 (Mo, Ti)Si2 is crucial for the epitaxial growth of C54 TiSi2 atop. Possible grain-size effects on the formation of C54 TiSi2 are also discussed. © 2000 American Institute of Physics.
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81.15.Np Solid phase epitaxy; growth from solid phases
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Enhancement of silicon oxidation rate due to tensile mechanical stress

Jui-Yuan Yen and Jenn-Gwo Hwu

Appl. Phys. Lett. 76, 1834 (2000); http://dx.doi.org/10.1063/1.126181 (2 pages) | Cited 11 times

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Oxidation of silicon wafers under external mechanical stress was studied in this work. From the oxide thickness profile measured by an automatic ellipsometer, it was found that the oxidation kinetics of silicon was affected by the mechanical stress. The tensile stress strongly enhances the oxidation rate of silicon. A concept was proposed to explain this phenomenon by using a well-known physical Si–SiO2 lattice model. The tensile stress in the silicon will enlarge the atom spacing of silicon and make the oxidation to be easier and faster. A simulated deformation of silicon substrate under tensile stress was also given to support this concept. This work is a direct evidence of the effect of mechanical stress on silicon oxidation. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
62.20.F- Deformation and plasticity

Waveguide ultrasonic force microscopy at 60 MHz

K. Inagaki, O. V. Kolosov, G. A. D. Briggs, and O. B. Wright

Appl. Phys. Lett. 76, 1836 (2000); http://dx.doi.org/10.1063/1.126184 (3 pages) | Cited 17 times

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We present measurements using ultrasonic force microscopy at ∼ 60 MHz, operating in a “waveguide” mode in which the cantilever base is vibrated and flexural ultrasonic vibrations are launched down the cantilever without exciting any particular cantilever resonance. The nonlinearity of the tip-sample force-distance curve allows the conversion of a modulated ultrasonic frequency into a low frequency vibration of the cantilever, detected in a conventional atomic force microscope. Images of Ge quantum dots on a Si substrate show contrast related to elasticity and adhesion differences, and this is interpreted with the Johnson–Kendall–Roberts model of the force-distance curve. © 2000 American Institute of Physics.
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43.58.Ls Acoustical lenses and microscopes
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
07.79.Lh Atomic force microscopes
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
62.20.D- Elasticity

Defect annihilation in AlN thin films by ultrahigh temperature processing

Z. Y. Fan, G. Rong, N. Newman, and David J. Smith

Appl. Phys. Lett. 76, 1839 (2000); http://dx.doi.org/10.1063/1.126185 (3 pages) | Cited 10 times

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Postgrowth thermal processing in the range of 1200–1400 °C is shown to improve markedly the quality of thin (∼200 nm) AlN films grown by molecular beam epitaxy on SiC substrates. Comparison of both on-axis (0002) and off-axis (10math2) x-ray diffraction peaks documents this improvement. Cross-sectional transmission electron micrographs confirm the reduction in dislocations and grain boundaries, while plan-view micrographs demonstrate that threading defect densities can be reduced to ∼ 3×108/cm2 after annealing. The thermal treatment is particularly effective because of the unusually large temperature window between the onset of a near-zero reactant sticking coefficient at ∼1200 °C and AlN thermal decomposition at ∼1400 °C. The Al sticking coefficient and the AlN decomposition rate are also reported. © 2000 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.72.Mm Grain and twin boundaries
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Selective growth of high quality GaN on Si(111) substrates

M. Seon, T. Prokofyeva, M. Holtz, S. A. Nikishin, N. N. Faleev, and H. Temkin

Appl. Phys. Lett. 76, 1842 (2000); http://dx.doi.org/10.1063/1.126186 (3 pages) | Cited 19 times

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We demonstrate selective growth of high-quality GaN by gas-source molecular beam epitaxy on Si(111) wafers patterned with SiO2. GaN was grown on wafers having two different buffer layers. The first buffer layer contains two AlGaN/GaN superlattices, separated by GaN spacer, grown on AlN, with a total thickness of 400 nm. The second is a thin AlN (1.5 nm) buffer layer. X-ray diffraction confirms (0001) growth orientation, smooth interfaces, and coherence lengths comparable to the layer thickness in both samples. In the case of the thin AlN buffer layer, the tensile stress measured by the E2 Raman line shift is attributed to the mismatch in the thermal expansion coefficients of GaN and Si. However, when the AlGaN/GaN superlattice buffer layer is grown first, a reduced stress is measured. High carrier concentrations (≈1018 cm−3) are seen in the GaN grown on the thin AlN buffer layer, which we attribute to the incorporation of silicon from the substrate during the growth process. The superlattice buffer layer is seen to inhibit this diffusion, resulting in a carrier concentration of <1017 cm−3 in the GaN. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.60.Bs Mechanical and acoustical properties

Highly ordered films of quaterthiophene grown by seeded supersonic beams

S. Iannotta, T. Toccoli, F. Biasioli, A. Boschetti, and M. Ferrari

Appl. Phys. Lett. 76, 1845 (2000); http://dx.doi.org/10.1063/1.126187 (3 pages) | Cited 16 times

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Seeded supersonic beams of oligothiophenes have been developed and used to grow very high quality films on CaF2 and SiO2. Optical characterizations show features previously observed only on single crystals and very thin films. In particular, the vibronic progression of the 0–0 transition is well resolved at 10 K. Highly supersonic beams give best results. High quality films are produced over a range of thicknesses ≥ 500 nm. The correlation between properties of the films and beam parameters are discussed. The energy state of oligomers is envisaged to play a key role in the growth. © 2000 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
63.20.-e Phonons in crystal lattices
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds

Second-harmonic generation from realistic film–substrate interfaces: The effects of strain

I. L. Lyubchanskii, N. N. Dadoenkova, M. I. Lyubchanskii, Th. Rasing, Jae-Woo Jeong, and Sung-Chul Shin

Appl. Phys. Lett. 76, 1848 (2000); http://dx.doi.org/10.1063/1.126188 (3 pages) | Cited 10 times

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The optical second-harmonic generation from a thin crystalline film on a substrate is theoretically investigated for both s and p polarized incident light. The contributions of lattice misfit strain as well as of misfit dislocation strain to the second-order nonlinear optical susceptibility are described using a nonlinear photoelastic tensor and can be separated by a polarization analysis of the scattered light at the second harmonic frequency. For the s(ω)→s(2ω) and p(ω)→s(2ω) scattering geometries, the nonlinear optical signal will be determined by dislocation strain only, whereas for the s(ω)→p(2ω) and p(ω)→p(2ω) geometries both lattice misfit strain and misfit dislocation strain will contribute. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
68.60.Bs Mechanical and acoustical properties
78.66.-w Optical properties of specific thin films
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
42.65.An Optical susceptibility, hyperpolarizability
61.72.Bb Theories and models of crystal defects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Dynamic photoluminescence change of porous Si upon exposure to thermoelectrons/D atoms and D2O

T. Wadayama, T. Arigane, K. Hayamizu, T. Shibahara, D. Hino, and A. Hatta

Appl. Phys. Lett. 76, 1851 (2000); http://dx.doi.org/10.1063/1.126189 (3 pages) | Cited 3 times

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In situ photoluminescence (PL) and transmission IR spectral measurements have been carried out for porous Si (PS) after exposure to thermoelectrons and subsequent exposure to D atoms or D2O. Upon exposure to thermoelectrons the PL band (765 nm) of the PS almost diminished accompanied by the intensity reduction of the IR bands due to Si-Hx (x = 1–3) species. A subsequent D atom exposure resulted in a recovery of the PL band with the formation of Si-Dx bonds. In contrast, D2O exposure gave rise to a new PL band at 650 nm in addition to a 745 nm band accompanied by the emergence of IR bands due to Si-OD and Si-D bonds: the integrated PL intensity after the D2O exposure is 1.2 times larger than the PL intensity of the as-anodized PS. These results suggest that the PL of the PS contains an important contribution from the surface Si-O bonds. © 2000 American Institute of Physics.
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78.55.Mb Porous materials
61.43.Gt Powders, porous materials
79.20.Kz Other electron-impact emission phenomena
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.55.Ap Elemental semiconductors
78.30.Am Elemental semiconductors and insulators

Dielectric function of aggregates of small metallic particles embedded in host insulating matrix

Leonid G. Grechko, Vitaly N. Pustovit, and Keith W. Whites

Appl. Phys. Lett. 76, 1854 (2000); http://dx.doi.org/10.1063/1.126190 (3 pages) | Cited 10 times

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The optical properties of clusters with metallic spherical particles embedded in an insulating matrix are studied. A theoretical approach is proposed for the calculation of the macroscopic dielectric response for a collection of spheres at random positions embedded in a homogeneous medium. While accounting for the dipole–dipole interaction between particles, we have considered the frequency dependence behavior of the imaginary part of the effective dielectric constant in this system with two kinds of particles of different sizes. © 2000 American Institute of Physics.
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78.66.Sq Composite materials
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Detection of luminescent single ultrasmall silicon nanoparticles using fluctuation correlation spectroscopy

O. Akcakir, J. Therrien, G. Belomoin, N. Barry, J. D. Muller, E. Gratton, and M. Nayfeh

Appl. Phys. Lett. 76, 1857 (2000); http://dx.doi.org/10.1063/1.126191 (3 pages) | Cited 68 times

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We dispersed electrochemical etched Si into a colloid of ultrasmall blue luminescent nanoparticles, observable with the naked eye, in room light. We use two-photon near-infrared femtosecond excitation at 780 nm to record the fluctuating time series of the luminescence, and determine the number density, brightness, and size of diffusing fluorescent particles. The luminescence efficiency of particles is high enough such that we are able to detect a single particle, in a focal volume, of 1 pcm3. The measurements yield a particle size of 1 nm, consistent with direct imaging by transmission electron microscopy. They also yield an excitation efficiency under two-photon excitation two to threefold larger than that of fluorescein. Detection of single particles paves the way for their use as labels in biosensing applications. © 2000 American Institute of Physics.
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78.66.Vs Fine-particle systems
78.55.Ap Elemental semiconductors
07.60.Rd Visible and ultraviolet spectrometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
87.85.J- Biomaterials

Interface structure of hydride vapor phase epitaxial GaN grown with high-temperature reactively sputtered AlN buffer

E. Valcheva, T. Paskova, S. Tungasmita, P. O. Å. Persson, J. Birch, E. B. Svedberg, L. Hultman, and B. Monemar

Appl. Phys. Lett. 76, 1860 (2000); http://dx.doi.org/10.1063/1.126192 (3 pages) | Cited 15 times

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Thick hydride vapor phase epitaxy GaN layers have been grown on a-plane sapphire using high-temperature ion-assisted reactively sputtered AlN as a buffer layer. Transmission electron microscopy and atomic force microscopy were carried out to study the formation of the two interfaces sapphire/AlN and AlN/GaN, and their influence on the microstructure of both the buffer layer and the main GaN layer. It was demonstrated that the high-temperature reactively sputtered buffer layer provides a good alternative for hydride vapor phase epitaxy growth of GaN layers. In particular, the buffer promotes a specific interface ordering mechanism different from that observed on low-temperature buffers. © 2000 American Institute of Physics.
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68.35.Ct Interface structure and roughness
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Cd Deposition by sputtering

Resonant x-ray scattering at the Se edge in liquid crystal free-standing films and devices

L. S. Matkin, H. F. Gleeson, P. Mach, C. C. Huang, R. Pindak, G. Srajer, J. Pollmann, J. W. Goodby, M. Hird, and A. Seed

Appl. Phys. Lett. 76, 1863 (2000); http://dx.doi.org/10.1063/1.126193 (3 pages) | Cited 21 times

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Resonant x-ray diffraction was carried out at the Se K edge in thick free-standing films of a selenophene liquid crystalline material, revealing detail of the structure of the ferro-, ferri-, and antiferroelectric phases. The ferrielectric phase was shown to have a three-layer superlattice. Moreover, the structure of a lower temperature hexatic phase was established. For the antiferroelectric phase, investigations were also carried out in a planar device configuration. The device allowed resonant scattering experiments to be carried out with and without the application of an electric field and resonant data are compared with electro-optic measurements carried out on the same device. © 2000 American Institute of Physics.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
42.79.Kr Display devices, liquid-crystal devices
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
64.70.M- Transitions in liquid crystals
77.80.B- Phase transitions and Curie point
61.05.cf X-ray scattering (including small-angle scattering)
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Carrier transport in GaAs/AlAs type-II superlattices under electric field: Switch from X–X to Γ–Γ transfer

M. Hosoda, N. Ohtani, K. Kuroyanagi, and C. Domoto

Appl. Phys. Lett. 76, 1866 (2000); http://dx.doi.org/10.1063/1.126194 (3 pages)

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A switch in carrier transport from X–X to Γ–X–Γ is found in a GaAs/AlAs type-II superlattice under an electric field. This phenomenon is caused by an X–Γ transfer, as demonstrated by the photoluminescence, photocurrent response, and current–voltage characteristics. Under a high electric field, most of the electrons flow through the Γ path even in type-II superlattices. © 2000 American Institute of Physics.
Show PACS
73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.50.Fq High-field and nonlinear effects
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