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7 Jun 2004

Volume 84, Issue 23, pp. 4599-4816

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4650 (2004); http://dx.doi.org/10.1063/1.1759390 (3 pages)

David I. Woodward, Ian M. Reaney, Gaiying Y. Yang, Elizabeth C. Dickey, and Clive A. Randall
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Dipolar interaction effects on the thermally activated magnetic relaxation of two-dimensional nanoparticle ensembles

S. I. Denisov, T. V. Lyutyy, and K. N. Trohidou

Appl. Phys. Lett. 84, 4672 (2004); http://dx.doi.org/10.1063/1.1759782 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2004

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The thermally activated magnetic relaxation in two-dimensional lattices of dipolar interacting nanoparticles with large uniaxial perpendicular anisotropy is studied by a numerical method and within the mean-field approximation for comparison. The role that the correlation effects play in magnetic relaxation and the influence of lattice structure and bias magnetic field on the relaxation process are revealed. The correlations of the nanoparticle magnetic moments enhance relaxation on small times, delay it on large times, and reduce the steady-state absolute magnetization at nonzero bias fields. In a hexagonal lattice, magnetic relaxation on small times occurs faster and the steady-state absolute magnetization has the larger magnitude than in a square lattice with the same lattice spacing. © 2004 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
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Ultrafast valence intersubband hole relaxation in InGaN multiple-quantum-well laser diodes

Kian-Giap Gan, Chi-Kuang Sun, Steven P. DenBaars, and John E. Bowers

Appl. Phys. Lett. 84, 4675 (2004); http://dx.doi.org/10.1063/1.1760211 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2004

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The ultrafast carrier dynamics in InGaN multiple-quantum-well (MQW) laser diodes were investigated using a time-resolved bias-lead monitoring technique. From the optical selection rules of TE and TM polarized light, one can selectively excite and probe different valence-subband-to-conduction-subband transitions in the MQW structure with different polarized pump and probe light. The subband structure of the MQW structure of the laser diode was calculated and is verified by electroluminescence measurement. Using this technique, ultrafast valence intersubband hole relaxation processes (τ<0.35 ps) were found to dominate the observed carrier dynamics. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.47.-p Spectroscopy of solid state dynamics
78.67.De Quantum wells

Femtosecond optical pulse propagation in subwavelength metallic slits

A. Dechant and A. Y. Elezzabi

Appl. Phys. Lett. 84, 4678 (2004); http://dx.doi.org/10.1063/1.1760215 (3 pages) | Cited 20 times

Online Publication Date: 19 May 2004

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Subwavelength slit arrays embedded in thin silver films demonstrate a marked ability to modify an incident optical pulse’s temporal profile. Ultrashort pulse propagation through these arrays is accompanied by both an increased initial transmission, as well as a subsequent pulse train re-radiation. The role of impulsively excited surface plasmons is investigated as a mechanism for this enhanced transmission and re-radiation. By simply changing the geometrical parameters of the array, pulse reshaping is easily achieved, and in some cases superluminal light flow is observed. © 2004 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Kc Metals, semimetals, and alloys
78.30.Er Solid metals and alloys
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Persistence of (In,Ga)As quantum-dot chains under index deviation from GaAs(100)

Z. M. Wang, Yu. I. Mazur, G. J. Salamo, P. M. Lytvin, V. V. Strelchuk, and M. Ya. Valakh

Appl. Phys. Lett. 84, 4681 (2004); http://dx.doi.org/10.1063/1.1760219 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2004

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Utilizing the naturally curved surface contours provided by oval defects on a GaAs(100) surface, we demonstrate that alignment of quantum-dot chains formed during the growth of (In,Ga)As multilayers is unyielding to a modest deviation of surface orientation from (100) of about 0.7° along [01-1] and 8° along [011]. This finding suggests that the strain-driven kinetic anisotropy responsible for the formation of the quantum dot chains dominates over selective island formation at steps due to surface misorientation. The robustness of the quantum dot chain adds to its potential for its future application. © 2004 American Institute of Physics.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.65.Ac Multilayers
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Observation of resonant energy transfer in Au:CdS nanocomposite

G. H. Ma, J. He, K. Rajiv, S. H. Tang, Y. Yang, and M. Nogami

Appl. Phys. Lett. 84, 4684 (2004); http://dx.doi.org/10.1063/1.1760220 (3 pages) | Cited 15 times

Online Publication Date: 19 May 2004

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Au:CdS nanocomposite film was investigated using femtosecond pump–probe measurement at 800 nm. Time dependence of transmittance shows a two-photon absorption followed by a saturable absorption and recovery process, which clearly demonstrates that resonant energy transfer between CdS and Au nanocomposite systems occur with excitation at 800 nm. In addition, enhancement of the two-photon absorption coefficient in Au:CdS nanocomposite with a factor of more than 6 was observed compared to that of bulk CdS. © 2004 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Arbitrary angle waveguiding applications of two-dimensional curvilinear-lattice photonic crystals

Javad Zarbakhsh, Frank Hagmann, Sergei F. Mingaleev, Kurt Busch, and Kurt Hingerl

Appl. Phys. Lett. 84, 4687 (2004); http://dx.doi.org/10.1063/1.1760222 (3 pages) | Cited 24 times

Online Publication Date: 19 May 2004

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We introduce a fresh class of photonic band-gap materials, curvilinear-lattice photonic crystals, whose distinctive feature is that their individual scatterers are arranged in a curvilinear lattice. We show that adhering to some restrictions in the acceptable lattice transformations, one can achieve omnidirectional photonic band gaps for an entire subclass of such structures. We demonstrate, designing an efficient arbitrary-angle waveguide bend, that curvilinear-lattice photonic crystals can be employed for creation of original types of nanophotonic devices. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Time-domain measurement of picosecond light-pulse propagation in a two-dimensional photonic crystal-slab waveguide

Takashi Asano, Kazuaki Kiyota, Daisuke Kumamoto, Bong-Shik Song, and Susumu Noda

Appl. Phys. Lett. 84, 4690 (2004); http://dx.doi.org/10.1063/1.1760224 (3 pages) | Cited 30 times

Online Publication Date: 19 May 2004

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The optical properties of line-defect waveguides in two-dimensional photonic crystal slabs are investigated using picosecond light pulses. Time-domain waveforms of the light pulse propagating through the waveguide are successfully observed using an autocorrelation method. The group velocity of the waveguide is directly determined from the group delay time for light pulses reflected back and forth along the waveguide. A small group velocity of one-twentieth the speed of light in vacuum is observed at a frequency near the edge of the waveguide mode. The frequency dependence of the group velocity is also measured, and the group-velocity dispersion is found to be larger than that of normal single-mode optical fibers by a factor of 104–105. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Deep blue widely tunable organic solid-state laser based on a spirobifluorene derivative

D. Schneider, T. Rabe, T. Riedl, T. Dobbertin, O. Werner, M. Kröger, E. Becker, H.-H. Johannes, W. Kowalsky, T. Weimann, J. Wang, P. Hinze, A. Gerhard, P. Stössel, and H. Vestweber

Appl. Phys. Lett. 84, 4693 (2004); http://dx.doi.org/10.1063/1.1760227 (3 pages) | Cited 22 times

Online Publication Date: 19 May 2004

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We report on amplified spontaneous emission and optically pumped deep blue lasing in the organic spirobifluorene derivative 2,7-bis(biphenyl-4-yl)-2′,7′-di-tert-butyl-9,9′-spirobifluorene. Solid-state lasing is observed in thin films of this material deposited on a distributed-feedback (DFB) grating substrate. The laser wavelength can be tuned from 401.5 to 434.2 nm depending on the grating period of the Bragg reflector. The blue edge of this interval at 401.5 nm makes this laser an extremely short wavelength organic DFB laser. When pumping with a pulsed nitrogen laser at 337 nm, we observe a laser threshold energy density of 83 μJ/cm2. These results render this spiro compound an excellent candidate for blue-emitting diode lasers. © 2004 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
85.60.Jb Light-emitting devices

Electroluminescence from self-organized “microdomes”

Olaf Karthaus, Chihaya Adachi, Shigeya Kurimura, and Takahito Oyamada

Appl. Phys. Lett. 84, 4696 (2004); http://dx.doi.org/10.1063/1.1760592 (3 pages) | Cited 15 times

Online Publication Date: 19 May 2004

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The preparation of a self-organized, microstructured organic electroluminescent device is reported. A dewetting process is used to form (sub)micrometer-sized dewetted patches (“domes”) of a hole transport material (tolyl-phenyl-diaminobiphenyl, TPD) on an indium-tin-oxide electrode. The domes are regular in size and spacing. Evaporation of an electron transport material (tris-8-hydroxyquinoline aluminum, Alq3) and an Mg/Ag top electrode leads to a device with electroluminescing spots of micrometer dimensions and a spacing of a few micrometers. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.-a Thin film structure and morphology

Light coupling with multimode photonic crystal waveguides

Zhi-Yuan Li, Lan-Lan Lin, and Kai-Ming Ho

Appl. Phys. Lett. 84, 4699 (2004); http://dx.doi.org/10.1063/1.1760596 (3 pages) | Cited 17 times

Online Publication Date: 19 May 2004

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We use a transfer-matrix method (TMM) to investigate light coupling into and out of single-end multimode photonic crystal waveguides. Without multiple-reflection complexity, this approach allows for unambiguous quantitative determination of the coupling efficiency of external light into each guided mode and transition among various guided modes. The TMM can provide a powerful analytical tool to understand and design complex multimode photonic crystal waveguides. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
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Origin of low-friction behavior in graphite investigated by surface x-ray diffraction

Bing K. Yen, Birgit E. Schwickert, and Michael F. Toney

Appl. Phys. Lett. 84, 4702 (2004); http://dx.doi.org/10.1063/1.1760597 (3 pages) | Cited 13 times

Online Publication Date: 19 May 2004

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Contrary to popular belief, the slipperiness of graphite is not an intrinsic property. The presence of vapors, such as water, is required for graphite to lubricate; in vacuum or dry environments, the friction and wear rate of graphite are high. A widely accepted explanation involves weakening of the binding force between basal planes near the surface, thereby allowing these planes to shear easily. This weakening results from proposed chemisorption or intercalation of vapor molecules near the surface, leading to an increase in the interlayer spacing between near-surface basal planes. Here we use x-ray diffraction from a synchrotron source to show that the basal plane spacing at the surface is the same in vacuum, ambient air, or water vapor saturated air. These results refute this long-held view that the low friction behavior of graphite is due to shearing of weakened basal planes. © 2004 American Institute of Physics.
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81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
68.43.Mn Adsorption kinetics
68.35.Af Atomic scale friction
83.85.Hf X-ray and neutron scattering
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The influence of the annealing sequence on p+/n junctions observed by scanning capacitance microscopy

M. N. Chang, C. Y. Chen, W. W. Wan, and J. H. Liang

Appl. Phys. Lett. 84, 4705 (2004); http://dx.doi.org/10.1063/1.1762692 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2004

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This letter reports on the investigation of p+–n junction variation produced by various annealing sequences. With well-controlled photoperturbation, we have employed scanning capacitance microscopy to directly observe the junction narrowing induced by post-spike furnace annealing. For p+–n junctions, it is revealed that post-spike furnace annealing may degrade the electrical activation of boron atoms, leading to junction narrowing without significant boron diffusion. The mechanism and the stability of electrical junctions formed by spike annealing are also discussed. The experimental results also clearly show that furnace annealing followed by spike annealing can result in junction broadening with a more concentrated boron profile. © 2004 American Institute of Physics.
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81.40.Gh Other heat and thermomechanical treatments
66.30.H- Self-diffusion and ionic conduction in nonmetals
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Fabrication of vertically aligned carbon nanowalls using capacitively coupled plasma-enhanced chemical vapor deposition assisted by hydrogen radical injection

M. Hiramatsu, K. Shiji, H. Amano, and M. Hori

Appl. Phys. Lett. 84, 4708 (2004); http://dx.doi.org/10.1063/1.1762702 (3 pages) | Cited 103 times

Online Publication Date: 19 May 2004

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Two-dimensional carbon nanostructures (carbon nanowalls) were fabricated using capacitively coupled radio-frequency plasma-enhanced chemical vapor deposition assisted by H radical injection. Carbon nanowalls were grown on Si, SiO2, and sapphire substrates without catalyst, and independent of substrate materials. Correlation between carbon nanowall growth and fabrication conditions, such as carbon source gases was investigated. In the case using C2F6/H2 system, aligned carbon nanowalls were grown vertically on the substrate, while carbon nanowalls grown using CH4/H2 system were waved and thin (<10 nm). In the case of the deposition without H radical injection, on the other hand, carbon nanowalls were not fabricated. © 2004 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
61.46.-w Structure of nanoscale materials
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Growth and pyroelectric property of 0.2 mol % Fe-doped Pb(Mg1/3Nb2/3)O3-0.38PbTiO3 single crystals measured by a dynamic technique

Xinming Wan, Xingui Tang, Jie Wang, H. L. W. Chan, C. L. Choy, and Haosu Luo

Appl. Phys. Lett. 84, 4711 (2004); http://dx.doi.org/10.1063/1.1762982 (3 pages) | Cited 10 times

Online Publication Date: 19 May 2004

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To develop a high-performance pyroelectric infrared detector, large-size and high-quality 0.2 mol % Fe-doped Pb(Mg1/3Nb2/3)O3-0.38PbTiO3 single crystals have been grown by a modified Bridgman technique with a seed crystal. At 50 Hz, the doped single crystal showed a lower dielectric constant of 310 compared with the pure one. A low dielectric loss of 0.0067 was also obtained by doping with small concentration of iron ions. Piezoelectric coefficient (d33) of 〈001〉 oriented sample was ∼260 pC/N. The pyroelectric properties and their temperature dependence were measured by the dynamic technique. At room temperature, the pyroelectric coefficient and calculated detectivity figure of merit FD are 568 μC/m2 K and 53 μPa−1/2, respectively. The values of current response figure of merit Fi and voltage response figure of merit Fv are 227.2 pm/V and 0.083 m2/C, respectively. These excellent pyroelectric properties as well as being able to produce large-size and high-quality single crystals make this kind of single crystal very promising for high-performance infrared detectors and other pyroelectric applications. © 2004 American Institute of Physics.
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81.10.Fq Growth from melts; zone melting and refining
77.22.Ch Permittivity (dielectric function)
77.70.+a Pyroelectric and electrocaloric effects
85.60.Gz Photodetectors (including infrared and CCD detectors)
77.22.Gm Dielectric loss and relaxation
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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End-bonding multiwalled carbon nanotubes in alumina templates: Superconducting proximity effect

J. Haruyama, A. Tokita, N. Kobayashi, M. Nomura, S. Miyadai, K. Takazawa, A. Takeda, and Y. Kanda

Appl. Phys. Lett. 84, 4714 (2004); http://dx.doi.org/10.1063/1.1755416 (3 pages)

Online Publication Date: 20 May 2004

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We cut off the top parts of multiwalled carbon nanotubes (MWNTs), which are synthesized in the nanopores of an alumina template and grown over the template surface from the pores, by utilizing ultrasonic cleaning. This leads to highly regularly aligned MWNTs with open top ends and tubes of the same length in the template. These open top ends can be end-bonded by evaporating gold/niobium electrodes and performing optimal annealing. We find that these niobium/MWNTs junctions result in highly transparent interfaces. As evidence, proximity-induced superconductivity and supercurrents are shown in the MWNTs. © 2004 American Institute of Physics.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
61.46.-w Structure of nanoscale materials
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Optical and electrical properties of (1-101)GaN grown on a 7° off-axis (001)Si substrate

T. Hikosaka, T. Narita, Y. Honda, M. Yamaguchi, and N. Sawaki

Appl. Phys. Lett. 84, 4717 (2004); http://dx.doi.org/10.1063/1.1758300 (3 pages) | Cited 21 times

Online Publication Date: 20 May 2004

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Uniform growth of (1-101)GaN was performed on coalesced stripes of GaN which had been prepared by selective metalorganic vapor phase epitaxy on a 7° off-axis (001)Si substrate via an AlN intermediate layer. The cathodoluminescence spectra at 4 K exhibited a donor bound excitonic emission at 358 nm followed by defect-related emission peaks at 363, 371, and 376 nm. The 363 and 376 emission bands are observed upon the coalescence region. The Hall measurements exhibited p-type conduction at 80–300 K (the hole carrier density 6.3×1012 cm−2 and hole mobility 278 cm2/V s at 100 K). The activation energy of the acceptor was estimated to be 60 meV. The possible origin of the p-type conduction is discussed in relation to the unintentionally doped carbon. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.35.-y Excitons and related phenomena

Transport properties of [2,2]-paracyclophane thin films

Wenping Hu, Bruno Gompf, Jens Pflaum, Dieter Schweitzer, and Martin Dressel

Appl. Phys. Lett. 84, 4720 (2004); http://dx.doi.org/10.1063/1.1758773 (3 pages) | Cited 19 times

Online Publication Date: 20 May 2004

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The transport properties of [2,2]-paracyclophane thin films prepared by molecular beam epitaxy were studied by space-charge-limited current measurements. This organic semiconductor, which has a three-dimensional π-system comparable to that of C60, is an interesting material for molecular electronic applications due to its remarkably high mobility and its insensitivity against photo-oxidation. The current–voltage characteristics were recorded using a coplanar electrode geometry which has the advantage, that after deposition no further processing of the organic semiconducting layer is necessary. In polycrystalline films hole mobilities up to 10−2 cm2 V−1 s−1 were observed at room temperature. © 2004 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Ee Mobility edges; hopping transport
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Stacking of InAs/InP(001) quantum wires studied by in situ stress measurements: Role of inhomogeneous stress fields

David Fuster, María Ujué González, Luisa González, Yolanda González, Teresa Ben, Arturo Ponce, and Sergio I. Molina

Appl. Phys. Lett. 84, 4723 (2004); http://dx.doi.org/10.1063/1.1759374 (3 pages) | Cited 15 times

Online Publication Date: 20 May 2004

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Size and spatial distribution homogeneity of nanostructures is greatly improved by making stacks of nanostructures separated by thin spacers. In this work, we present in situ and in real time stress measurements and reflection high-energy electron diffraction observations and ex situ transmission electron microscopy (TEM) characterization of stacked layers of InAs quantum wires (QWRs) separated by InP spacer layers, d(InP), of thickness between 3 and 20 nm. For d(InP)<20 nm, the amount of InAs involved in the created QWR from the second stack layer on, exceeds that provided by the In cell. Our results suggest that in those cases InAs three dimensional islands formation starts at the P/As switching and lasts during further InAs deposition. We propose an explanation for this process that is strongly supported on TEM observations. The results obtained in this work imply that concepts like the existence of a critical thickness for two- to three-dimensional growth mode transition should be revised in correlated QWR stacks of layers. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
68.65.Ac Multilayers
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Electromagnetic study of the quality factor of pillar microcavities in the small diameter limit

Ph. Lalanne, J. P. Hugonin, and J. M. Gérard

Appl. Phys. Lett. 84, 4726 (2004); http://dx.doi.org/10.1063/1.1759375 (3 pages) | Cited 24 times

Online Publication Date: 20 May 2004

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A thorough electromagnetic study of pillar microcavities reveals a surprising behavior for their Q factors in the strong confinement limit. Q displays a fast oscillatory variation as a function of the pillar diameter, and reaches values well in excess of the quality factor of the reference planar cavity. This behavior is explained by the hybrid character of the cavity mode in the small diameter limit, which results mainly from the electromagnetic coupling of the HE11 (i.e., fundamental) and EH11 guided modes of the cavity spacer through the associated Bloch modes in the Bragg mirrors. © 2004 American Institute of Physics.
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42.79.-e Optical elements, devices, and systems
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Planar Hall effect sensor for magnetic micro- and nanobead detection

L. Ejsing, M. F. Hansen, A. K. Menon, H. A. Ferreira, D. L. Graham, and P. P. Freitas

Appl. Phys. Lett. 84, 4729 (2004); http://dx.doi.org/10.1063/1.1759380 (3 pages) | Cited 60 times

Online Publication Date: 20 May 2004

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Magnetic bead sensors based on the planar Hall effect in thin films of exchange-biased permalloy have been fabricated and characterized. Typical sensitivities are 3 μV/Oe mA. The sensor response to an applied magnetic field has been measured without and with coatings of commercially available 2 μm and 250 nm magnetic beads used for bioapplications (Micromer-M and Nanomag-D, Micromod, Germany). Detection of both types of beads and single bead detection of 2 μm beads is demonstrated, i.e., the technique is feasible for magnetic biosensors. Single 2 μm beads yield 300 nV signals at 10 mA and 15 Oe applied field. © 2004 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
85.75.Nn Hybrid Hall devices
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Subwavelength emitters in the near-infrared based on mercury telluride nanocrystals

P. Olk, B. C. Buchler, V. Sandoghdar, N. Gaponik, A. Eychmüller, and A. L. Rogach

Appl. Phys. Lett. 84, 4732 (2004); http://dx.doi.org/10.1063/1.1759386 (3 pages) | Cited 17 times

Online Publication Date: 20 May 2004

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The optical properties of near-infrared-emitting mercury telluride (HgTe) nanocrystals are investigated using fluorescence confocal microscopy. The HgTe quantum dots were coated with a “layer-by-layer” process on latex spheres with diameters down to 150 nm and number of layers varying from 1 to 3. The individual spheres act as bright subwavelength light sources. Measurements of the fluorescence decay show that the lifetime varies with the number of nanocrystal layers. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources

Ignition studies of Al/Fe2O3 energetic nanocomposites

L. Menon, S. Patibandla, K. Bhargava Ram, S. I. Shkuratov, D. Aurongzeb, M. Holtz, J. Berg, J. Yun, and H. Temkin

Appl. Phys. Lett. 84, 4735 (2004); http://dx.doi.org/10.1063/1.1759387 (3 pages) | Cited 20 times

Online Publication Date: 20 May 2004

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We prepare energetic nanocomposites, which undergo an exothermic reaction when ignited at moderate temperature. The nanocomposites are a mixture of Al fuel and Fe2O3 oxidizer where Fe2O3 is in the form of an array of nanowires embedded in the thin Al film. We achieve a very high packing density of the nanocomposites, precise control of oxidizer–fuel sizes at the nanoscale level, and direct contact between oxidizer and fuel. We find that the flame temperature does not depend on ignition temperature. © 2004 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.16.Pr Micro- and nano-oxidation
82.33.-z Reactions in various media
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Material modifications induced by laser annealing in two-dimensional structures

Antonino La Magna, Paola Alippi, Vittorio Privitera, Silvia Scalese, Salvatore Pannitteri, Guglielmo Fortunato, Luigi Mariucci, and Marco Camalleri

Appl. Phys. Lett. 84, 4738 (2004); http://dx.doi.org/10.1063/1.1759772 (3 pages) | Cited 6 times

Online Publication Date: 20 May 2004

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The effects of the laser irradiation on metal-oxide-semiconductor structures are investigated by means of a phase-field methodology. We numerically solved the model equations in one- and two-dimensional structures also containing SiO2/amorphous-Si/crystalline-Si stacks. The simulated laser annealing processes are discussed in detail, pointing out the influence of the geometrical constraints on the irradiation effects in the samples. The simulation results are compared with the experimental two-dimensional delineation of dopant profiles. These comparisons show the importance of the joint theoretical and experimental investigations in order to fully understand the phenomena occurring in submicron sized laser irradiated structures. © 2004 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.-d Radiation effects on specific materials
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La0.7Pr0.3MnO3 ceramic: An electron-doped colossal magnetoresistive manganite

Ping Duan, Zhenghao Chen, Shouyu Dai, Yueliang Zhou, Huibin Lu, Kuijuan Jin, and Bolin Cheng

Appl. Phys. Lett. 84, 4741 (2004); http://dx.doi.org/10.1063/1.1759775 (3 pages) | Cited 8 times

Online Publication Date: 20 May 2004

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We report a study on the synthesis, electrical transport, and magnetic properties of Pr-doped LaMnO3 ceramic material. We have found that La1−xPrxMnO3+δ (x = 0.3) synthesized using solid-state reaction shows semiconductor behavior, and no colossal magnetoresistance (CMR) effect; while it shows CMR behavior when it is annealed in a flowing argon at certain temperature (about 873 K), which suggests that La0.7Pr0.3MnO3+δ has been transferred to La0.7Pr0.3MnO3. The x-ray photoemission spectroscopy reveals that Pr ions are in a mixed-valence state of Pr4+ and Pr3+ in this compound. Therefore, La1−xPrxMnO3 (x = 0.3) could be an electron-doped CMR manganite. © 2004 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
72.60.+g Mixed conductivity and conductivity transitions
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Double focusing of hard x rays using combined multilayer and Bragg–Fresnel optics

M. Yasa, Y. Li, C. B. Mammen, J. Als-Nielsen, J. Hoszowska, C. Mocuta, and A. Freund

Appl. Phys. Lett. 84, 4744 (2004); http://dx.doi.org/10.1063/1.1759779 (3 pages) | Cited 3 times

Online Publication Date: 20 May 2004

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A multilayer Bragg–Fresnel x-ray lens (MBFL) structure that combines diffraction and geometric focusing on a single device is presented. With the MBFL, the linear BFL focuses the x-ray beam vertically while the bent multilayer focuses x rays horizontally. This combination eliminates the need for a second mirror in the conventional Kirkpatrick–Baez-based microprobe, which will be advantageous in x-ray fluorescence microscopy as well as microdiffraction applications. The characterization of the MBFL was carried out at the European Synchrotron Radiation Facility and a 1.6 μm (vertical)×12 μm (horizontal) focus was obtained from a 250 μm (V)×200 μm (H) incident beam. With a binary Fresnel lens efficiency of about 35% this yields a gain of almost three orders of magnitude compared to obtaining the same spot size by a raw aperture. © 2004 American Institute of Physics.
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41.50.+h X-ray beams and x-ray optics
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