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8 Mar 2004

Volume 84, Issue 10, pp. 1623-1807

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1798 (2004); http://dx.doi.org/10.1063/1.1664019 (3 pages)

Bartosz A. Grzybowski, Michal Radkowski, Christopher J. Campbell, Jessamine Ng Lee, and George M. Whitesides
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Fabrication of planar optical waveguides by electrical microcontact printing

Daniel B. Wolfe, J. Christopher Love, Byron D. Gates, George M. Whitesides, Richard S. Conroy, and Mara Prentiss

Appl. Phys. Lett. 84, 1623 (2004); http://dx.doi.org/10.1063/1.1651329 (3 pages) | Cited 20 times

Online Publication Date: 2 March 2004

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This letter describes the fabrication by electrical microcontact printing (E-μCP) of planar, optical waveguides, and splitters made of poly(4-vinylphenol) doped with phloxine B. This soft-lithographic technique uses a poly(dimethylsiloxane) (PDMS) stamp coated with a thin gold film to pattern the flow of current through the film of doped polymer. The current bleaches the phloxine B, and thus creates regions of high (unbleached; waveguide core) and low (bleached; waveguide cladding) refractive index. The maximum exposure time to obtain Δn = 0.025 was 90 s. This system is useful for guiding light having λ = 600–1310 nm. These polymer waveguides preserve polarization, and are able to guide light around 90° corners with a minimum radius of curvature of 1.6 mm. E-μCP patterned a 1×4 optical power splitter in 10 s. This technique is potentially useful for rapid prototyping of planar and multilevel optical devices. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Recording of polarization holograms in photodarkened amorphous chalcogenide films

K. E. Asatryan, S. Frédérick, T. Galstian, and R. Vallée

Appl. Phys. Lett. 84, 1626 (2004); http://dx.doi.org/10.1063/1.1666999 (3 pages) | Cited 8 times

Online Publication Date: 2 March 2004

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Polarization gratings were recorded in amorphous As2S3 chalcogenide thin films in three orthogonal recording configurations. The analysis of polarization discrimination properties of such vector gratings revealed a poor performance. It was shown that the main reason for this is the presence of nondesired scalar modulation of the same period. An exception is (s+p) recording configuration, where a pure polarization grating may be obtained even for relatively high photoexposures. © 2004 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.40.Ht Hologram recording and readout methods
42.70.Gi Light-sensitive materials
61.43.Fs Glasses
78.66.Jg Amorphous semiconductors; glasses

Multiple channeled phenomena in heterostructures with defects mode

Zhanshan Wang, Li Wang, Yonggang Wu, Lingyan Chen, Xiaoshuang Chen, and Wei Lu

Appl. Phys. Lett. 84, 1629 (2004); http://dx.doi.org/10.1063/1.1651650 (3 pages) | Cited 47 times

Online Publication Date: 2 March 2004

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Transmission studies for multiple heterostructures inserted with defects are presented. The results show that the enlargement of the forbidden band and the realization of multiple channeled filtering can be reached simultaneously with these configurations. The frequency, frequency interval, and number of channels can be tuned by adjusting geometric and physical parameters of the defects. Sidebands of the forbidden band can be substantially restricted as compared with that of periodic structures. Experimental fabrication of the designed configurations is carried out with the heterostructures containing TiO2/SiO2 multilayer defects, and the results agree with the calculation very well. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials

Two-photon lasing of dye-doped photonic crystal lasers

Koichiro Shirota, Hong-Bo Sun, and Satoshi Kawata

Appl. Phys. Lett. 84, 1632 (2004); http://dx.doi.org/10.1063/1.1666996 (3 pages) | Cited 10 times

Online Publication Date: 2 March 2004

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We report two-photon pump lasing action of a photonic crystal laser, which comprises fluorescent dye-doped chiral nematic liquid crystals. The dye absorbs light peaking at 466 nm, while the pumping was conducted at 1000 nm wavelength. Due to redistribution of density of states by a stopping band, a strong single-mode stimulated emission was observed at the band edge wavelength of 608 nm with 1 nm detection-limited linewidth. A comparative study shows that under an identical pumping geometry, the two-photon lasing threshold is only 120 times larger than that for the single-photon excitation, a ratio lower than those generally reported for up-conversion lasing. © 2004 American Institute of Physics.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Mv Dye lasers
42.70.Qs Photonic bandgap materials
78.45.+h Stimulated emission
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
78.55.Bq Liquids

A monochromatic and high-power terahertz source tunable in the ranges of 2.7–38.4 and 58.2–3540 μm for variety of potential applications

Wei Shi and Yujie J. Ding

Appl. Phys. Lett. 84, 1635 (2004); http://dx.doi.org/10.1063/1.1649802 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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Based on phase-matched collinear difference-frequency generation in a single GaSe crystal, continuously tunable and coherent radiation in the extremely wide ranges of 2.7–38.4 and 58.2–3540 μm has been achieved. This unique source has the additional advantages of high coherence (narrow linewidth) and simple alignment. The peak output power for the terahertz radiation reaches 209 W at the wavelength of 196 μm (1.53 THz), which corresponds to a power conversion efficiency of 0.055%. Moreover, the terahertz transmission spectra on DNA macromolecules and protein were directly measured, demonstrating some potential and important applications of this terahertz source. © 2004 American Institute of Physics.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
42.72.Ai Infrared sources
87.14.E- Proteins
87.14.G- Nucleic acids
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
87.80.-y Biophysical techniques (research methods)

Temperature-insensitive Ge–B–SiO2 planar lightwave circuits by inductively coupled plasma-enhanced chemical vapor deposition

Q. Y. Zhang, K. Pita, L. P. Zuo, and S. Takahashi

Appl. Phys. Lett. 84, 1638 (2004); http://dx.doi.org/10.1063/1.1664011 (3 pages) | Cited 3 times

Online Publication Date: 2 March 2004

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Low-propagation-loss Ge–B–SiO2 planar waveguides have been achieved by inductively coupled plasma-enhanced chemical vapor deposition. The significant effects due to annealing temperature, hydrogen loading, and KrF excimer ultraviolet laser irradiation on the optical properties of Ge–B–SiO2 films have been investigated. A temperature-insensitive Mach–Zehnder interferometer-like optical filter has been demonstrated by means of a double-core fabrication method using 10GeO2–90SiO2 (10G90S) and 8GeO2–5B2O3–87SiO2 (8G5B87S) as two different waveguide cores. We have achieved less than 0.5 pm/°C temperature dependence of the central wavelength of the filter at 1550 nm while varying the temperature from −20 to 80 °C. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments

Thermal decomposition of a thin AgOx layer generating optical near-field

A. V. Kolobov, A. Rogalev, F. Wilhelm, N. Jaouen, T. Shima, and J. Tominaga

Appl. Phys. Lett. 84, 1641 (2004); http://dx.doi.org/10.1063/1.1667003 (3 pages) | Cited 16 times

Online Publication Date: 2 March 2004

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Thermal decomposition of AgOx thin layers generating optical near field have been studied by Ag LIII edge x-ray absorption near-edge structure. We found that, different from previous assumptions, the starting layer is a mixture of AgO (∼40%) and Ag2O (∼60%). We further observed that thermal decomposition starts at a temperature as low as 50 °C. The decomposition process exhibits three stages and the oxide layer at intermediate stages consists of a mixture of AgO, Ag2O, and metallic Ag with different fractions of each phase. Activation energies of the decomposition of the thin oxide layer have been determined for different decomposition stages, the obtained values being different from that for powder oxides. © 2004 American Institute of Physics.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.70.Dm X-ray absorption spectra

Extended phase matching of second-harmonic generation in periodically poled KTiOPO4 with zero group-velocity mismatch

Friedrich König and Franco N. C. Wong

Appl. Phys. Lett. 84, 1644 (2004); http://dx.doi.org/10.1063/1.1668320 (3 pages) | Cited 16 times

Online Publication Date: 2 March 2004

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Under extended phase-matching conditions, the first frequency derivative of the wave-vector mismatch is zero and the phase-matching bandwidth is greatly increased. We present extensive three-wave mixing measurements of the wave-vector mismatch and obtain improved Sellmeier equations for KTiOPO4. We observed a type-II extended phase-matching bandwidth of 100 nm for second-harmonic generation in periodically poled KTiOPO4, centered at the fundamental wavelength of 1584 nm. Applications in quantum entanglement and frequency metrology are discussed. © 2004 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
06.30.Ft Time and frequency
42.50.-p Quantum optics

Application of strontium silicate yellow phosphor for white light-emitting diodes

Joung Kyu Park, Chang Hae Kim, Seung Hyok Park, Hee Dong Park, and Se Young Choi

Appl. Phys. Lett. 84, 1647 (2004); http://dx.doi.org/10.1063/1.1667620 (3 pages) | Cited 147 times

Online Publication Date: 2 March 2004

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In order to develop a yellow phosphor that emits efficiently under the 450–470 nm excitation range, we have synthesized a Eu2+-activated Sr3SiO5 yellow phosphor and attempted to develop white light-emitting diodes (LEDs) by combining them with a InGaN blue LED chip (460 nm). Two distinct emission bands from the InGaN-based LED and the Sr3SiO5:Eu phosphor are clearly observed at 460 nm and at 570 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that InGaN (460 nm chip)-based Sr3SiO5:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460 nm chip)-based YAG:Ce. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.55.Hx Other solid inorganic materials

Dynamic filamentation and beam quality of quantum-dot lasers

E. Gehrig, O. Hess, C. Ribbat, R. L. Sellin, and D. Bimberg

Appl. Phys. Lett. 84, 1650 (2004); http://dx.doi.org/10.1063/1.1668330 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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We present a comparative study of numerical simulations and experiments on the spatiotemporal dynamics and emission characteristics of quantum-well and quantum-dot lasers of identical structure. They show that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude–phase coupling enable a significant improvement of beam quality compared to quantum-well lasers of identical geometry. Near-field profiles and beam quality (M2) parameters calculated on the basis of time-dependent effective Maxwell–Bloch equations into which the physical properties of the active media are included via space-dependent material parameters, effective time constants, and matrix elements are fully confirmed by experimental measurements. Together they indicate that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude–phase coupling enable a significant improvement of beam quality compared with quantum-well lasers of identical geometry. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics
85.30.De Semiconductor-device characterization, design, and modeling

Fluorene-based low band-gap copolymers for high performance photovoltaic devices

Qingmei Zhou, Qiong Hou, Liping Zheng, Xianyu Deng, Gang Yu, and Yong Cao

Appl. Phys. Lett. 84, 1653 (2004); http://dx.doi.org/10.1063/1.1667614 (3 pages) | Cited 87 times

Online Publication Date: 2 March 2004

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Low band-gap, soluble conjugated copolymers were synthesized from 9,9-dioctylfluorene and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (PFO-DBT) and different composition ratios were used for the donor material in bulk heterojunction polymer photovoltaic cells (PVCs). In PVCs made with PFO-DBT:PCBM (methano-fullerene [6,6]-phenyl C61-butyric acid methyl ester) blends, the spectral response is extended up to 650 nm and the open-circuit voltage (Voc) is improved to 0.95 V. The energy conversion efficiency (ηe) in devices with optimized composition reaches 2.24% under an AM1.5 solar simulator (78.2 mW/cm2). In contrast to organic PVCs previously published, these PVCs retain high energy conversion efficiency at illumination up to 5 suns of AM1.5 spectral illumination. This feature allows high efficiency polymer PVC modules made in combination with a light concentrator. © 2004 American Institute of Physics.
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82.35.Jk Copolymers, phase transitions, structure
61.41.+e Polymers, elastomers, and plastics
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
68.55.-a Thin film structure and morphology
78.40.Pg Disordered solids
78.30.Jw Organic compounds, polymers
42.70.Jk Polymers and organics

Tunable and white light-emitting diodes of monolayer fluorinated benzoxazole graft copolymers

S. J. Bai, C. C. Wu, T. D. Dang, F. E. Arnold, and B. Sakaran

Appl. Phys. Lett. 84, 1656 (2004); http://dx.doi.org/10.1063/1.1667262 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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Coil-like graft copolymers of poly(Am-co-B(1−m)) containing identical heterocyclic aromatic benzoxazole with trifluoromethyl-ethyl as the backbone and pendants of monohydroxl (Am) and/or bidecyloxyl (B(1−m)) on their phenylene ring were studied for luminescence properties. The copolymers were synthesized with molar fraction m ranging from 0, 0.25, 0.5, 0.75, to 1, and then dissolved and spun onto a Spectrosil® quartz slide or an indium-tin-oxide (ITO) substrate. The fluorescence properties of copolymers were investigated by ultraviolet–visible absorption covering 185 nm to 800 nm and photoluminescence (PL) emission excited at 363 nm. The PL results exhibited an excellent chromatic tuning, ranging from green to white emission as m decreased. Aluminum electron injectors were evaporated onto the copolymer/ITO unit making it into monolayer light-emitting diodes for current–voltage and electroluminescence (EL) responses. An emission threshold voltage of 6 V was achieved for all the monolayer copolymer devices. The Commission Internationale de l’Eclairage coordinates of the EL emission were from (0.25, 0.53) to (0.24,0.31) covering a wide visible range including white light emission. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
42.70.Jk Polymers and organics
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.41.+e Polymers, elastomers, and plastics
78.66.Qn Polymers; organic compounds
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Broadband tuning of external cavity bound-to-continuum quantum-cascade lasers

Richard Maulini, Mattias Beck, Jérôme Faist, and Emilio Gini

Appl. Phys. Lett. 84, 1659 (2004); http://dx.doi.org/10.1063/1.1667609 (3 pages) | Cited 51 times

Online Publication Date: 2 March 2004

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A quantum-cascade structure based on a bound-to-continuum design exhibiting a broad gain curve is presented. The full width at half maximum of the measured luminescence spectrum is 297 cm−1 at room temperature. Grating-coupled external cavity lasers using this active region could be tuned over 150 cm−1 (1.45 μm), which is equal to 15% of the free running wavelength (λ ≅ 10 μm), in pulsed mode at room temperature. Time resolved spectra showed a single-mode operation with a 30 dB side mode suppression ratio after the first 12 ns of the pulse. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.60.Fi Electroluminescence
78.47.-p Spectroscopy of solid state dynamics
78.67.De Quantum wells

Periodically poled near-stoichiometric lithium tantalate for optical parametric oscillation

Nan Ei Yu, Sunao Kurimura, Yoshiyuki Nomura, Masaru Nakamura, Kenji Kitamura, Jun Sakuma, Yoshio Otani, and Akira Shiratori

Appl. Phys. Lett. 84, 1662 (2004); http://dx.doi.org/10.1063/1.1667616 (3 pages) | Cited 18 times

Online Publication Date: 2 March 2004

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A 35-mm-long periodically poled device was fabricated from a near-stoichiometric lithium tantalate, and optical parametric oscillation was demonstrated with a low oscillation threshold (106 mW). The emitted signal and idler wavelengths were 1.53–1.63 and 3.06–3.49 μm, respectively, and the highest slope conversion efficiency was 65% with a maximum output power of 628 mW at 1.1 W pumping. The influence of Curie temperature inhomogeneity on fabrication of the device was investigated to improve poling quality in long devices. © 2004 American Institute of Physics.
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42.65.Yj Optical parametric oscillators and amplifiers
77.22.Ej Polarization and depolarization
61.66.Bi Elemental solids
61.66.Dk Alloys

Single dye molecules in an oxygen-depleted environment as photostable organic triggered single-photon sources

Y. Lill and B. Hecht

Appl. Phys. Lett. 84, 1665 (2004); http://dx.doi.org/10.1063/1.1667591 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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We demonstrate, that under nitrogen atmosphere, 20% of single DiIC18(3) (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) molecules in poly(methylmethacrylate) show an extremely low photobleaching quantum yield of (4.66±0.07)×10−8 together with a reasonably short triplet lifetime. We exploit these properties to demonstrate that the system can be used to produce a triggered single-photon source based exclusively on organic materials. © 2004 American Institute of Physics.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
78.55.Kz Solid organic materials
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Atmospheric pressure microplasmas for modifying sealed microfluidic devices

Jon K. Evju, Peter B. Howell, Laurie E. Locascio, Michael J. Tarlov, and James J. Hickman

Appl. Phys. Lett. 84, 1668 (2004); http://dx.doi.org/10.1063/1.1668327 (3 pages) | Cited 27 times

Online Publication Date: 2 March 2004

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A dc microdischarge technique for the chemical modification of microchannel walls is reported. In this method, an atmospheric pressure plasma is ignited directly in the channels of assembled microfluidic devices. Our results show that strongly hydrophilic or hydrophobic properties are imparted to the walls of polystyrene microchannels by the appropriate selection of a plasma gas. This localized tuning of the surface and wetting properties is expected to be useful in the manufacture of microfluidic channels in a variety of substrates. Small area x-ray photoelectron spectroscopy was used to identify oxygen and fluorine on polystyrene surfaces resulting from the plasma treatments. © 2004 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.77.-j Plasma applications
81.65.-b Surface treatments
82.40.Np Temporal and spatial patterns in surface reactions
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Properties of InN layers grown on 6H–SiC(0001) by plasma-assisted molecular beam epitaxy

Tommy Ive, Oliver Brandt, Manfred Ramsteiner, Manfred Giehler, Helmar Kostial, and Klaus H. Ploog

Appl. Phys. Lett. 84, 1671 (2004); http://dx.doi.org/10.1063/1.1668318 (3 pages) | Cited 26 times

Online Publication Date: 2 March 2004

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We study the impact of different buffer layers and growth conditions on the properties of InN layers grown on 6H–SiC(0001) by plasma-assisted molecular beam epitaxy. Both GaN and AlN buffer layers result in a significant improvement of the structural quality compared to InN layers grown directly on the SiC substrate. However, to obtain layers exhibiting a high structural integrity, smooth surface morphology, high mobility and strong band-to-band photoluminescence, contradicting growth conditions are found to be required. Furthermore, since InN(0001) dissociates already at temperatures below the onset of In desorption, it is difficult to avoid In accumulation and inclusions of crystalline In in the layer under In-rich conditions. © 2004 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.43.Mn Adsorption kinetics
61.72.Qq Microscopic defects (voids, inclusions, etc.)

On the criteria for the formation of nanoquasicrystalline phase

B. S. Murty and K. Hono

Appl. Phys. Lett. 84, 1674 (2004); http://dx.doi.org/10.1063/1.1667265 (3 pages) | Cited 11 times

Online Publication Date: 2 March 2004

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The formation of nanoquasicrystalline phase is reported directly from the liquid on melt spinning over a wide range of wheel velocities of 10–30 m/s in Zr–Pd system at the eutectic composition (Zr75Pd25 alloy). The earlier studies in the Zr–Pd system (Zr70Pd30 and Zr65Pd35 alloys) showed nanoquasicrystallization on annealing of the amorphous phase obtained by melt spinning. Based on the existing results in various systems, a large negative enthalpy of mixing and/or existence of Frank–Kasper-type phases appear to be the crucial criteria for the formation of nanoquasicrystalline phase in any system. © 2004 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
64.70.D- Solid-liquid transitions
61.43.Dq Amorphous semiconductors, metals, and alloys
65.40.G- Other thermodynamical quantities

Correlation of thermal stability with structural properties of ultrathin single-walled carbon nanotubes

Changyong Xiao, Hardy Sze On Chan, Guo Qin Xu, Kwuan Tzee Lim, and Jianyi Lin

Appl. Phys. Lett. 84, 1677 (2004); http://dx.doi.org/10.1063/1.1664016 (3 pages) | Cited 2 times

Online Publication Date: 2 March 2004

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Based on quantum chemical calculations, we have established the relationship between the thermal stability and structural properties of ultrathin single-walled carbon nanotubes (SWCNTs). Our results on the heat of formation as a function of tube diameter predict a lower limit of 0.341 nm in diameter for experimentally observable SWCNTs. The absence of any distinctive minimum points on the heat of formation curve implies the experimental difficulties in obtaining uniform tubes. A detailed correlation between their curvature and chemical bonding properties was obtained for both the zigzag and armchair conformations. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
82.60.Cx Enthalpies of combustion, reaction, and formation
61.50.Lt Crystal binding; cohesive energy
65.90.+i Other topics in thermal properties of condensed matter (restricted to new topics in section 65)

On the angular dependence of focused laser ablation by nanosecond pulses in solgel and polymer materials

D. S. George, A. Onischenko, and A. S. Holmes

Appl. Phys. Lett. 84, 1680 (2004); http://dx.doi.org/10.1063/1.1655702 (3 pages) | Cited 2 times

Online Publication Date: 2 March 2004

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Focused laser ablation by single laser pulses at varying angles of incidence is studied in two materials of interest: a solgel (Ormocer 4) and a polymer (SU8). For a range of angles (up to 70° from normal), and for low-energy (<20 μJ), 40 ns pulses at 266 nm wavelength, the ablation depth along the direction of the incident laser beam is found to be independent of the angle of incidence. This allows the crater profiles at oblique incidence to be generated directly from the crater profiles at normal incidence by a simple coordinate transformation. This result is of use in the development of simulation tools for direct-write laser ablation. A simple model based on the moving ablation front approach is shown to be consistent with the observed behavior. © 2004 American Institute of Physics.
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52.38.Mf Laser ablation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.65.-b Surface treatments

Optically active erbium–oxygen complexes in GaAs

J. Coutinho, R. Jones, M. J. Shaw, P. R. Briddon, and S. Öberg

Appl. Phys. Lett. 84, 1683 (2004); http://dx.doi.org/10.1063/1.1668323 (3 pages) | Cited 7 times

Online Publication Date: 2 March 2004

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Density functional modeling of Er and Er–O complexes in GaAs show that Er impurities at the Ga site are not efficient channels for exciton recombination, but decorative O atoms play crucial roles in inhibiting Er precipitation and in creating the necessary conditions for electron-hole capture. Among the defects studied, the ErGaOAs and ErGa(OAs)2 models have the symmetry and carrier trap location close to the defect responsible for the strong 1.54 μm photoluminescence band in Er, O codoped GaAs. © 2004 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.35.-y Excitons and related phenomena

Nonlinear optical properties of neodymium-doped bismuth titanate thin films using Z-scan technique

Y. H. Wang, B. Gu, G. D. Xu, and Y. Y. Zhu

Appl. Phys. Lett. 84, 1686 (2004); http://dx.doi.org/10.1063/1.1667618 (3 pages) | Cited 13 times

Online Publication Date: 2 March 2004

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Bi3.75Nd0.25Ti3O12 (BNT0.25) thin film with good surface morphology and layered perovskite structure was fabricated by a metalorganic solution deposition process. Their fundamental optical constants (the band gap, linear refractive index, and absorption coefficient) were obtained through optical transmittance measurements. The nonlinear optical properties of the film were investigated by using a top-hat Z-scan method. Large positive nonlinear refractive index n2 and two-photon absorption coefficient β were determined to be 4.52×10−7 esu and 5.24×10−7 m/W, respectively. All of the results show that the BNT0.25 thin film is promising for applications in nonlinear optical devices. © 2004 American Institute of Physics.
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78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.55.-g Dielectric thin films
42.65.-k Nonlinear optics
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology

Coupling in a twin-core microstructured polymer optical fiber

W. E. P. Padden, M. A. van Eijkelenborg, A. Argyros, and N. A. Issa

Appl. Phys. Lett. 84, 1689 (2004); http://dx.doi.org/10.1063/1.1651651 (3 pages) | Cited 15 times

Online Publication Date: 2 March 2004

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Theoretical calculations and experimental results are reported for a microstructured polymer optical fiber twin-core coupler. Beat lengths are calculated using a fully vectorial, Fourier decomposition method, which show that the beat length is extremely sensitive to any core asymmetry. Reasonably good agreement between theory and experiment is obtained. © 2004 American Institute of Physics.
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42.81.Qb Fiber waveguides, couplers, and arrays
42.70.Jk Polymers and organics

Compressive shock wave response of a Zr-based bulk amorphous alloy

Stefan J. Turneaure, J. M. Winey, and Y. M. Gupta

Appl. Phys. Lett. 84, 1692 (2004); http://dx.doi.org/10.1063/1.1667261 (3 pages) | Cited 17 times

Online Publication Date: 2 March 2004

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Plane shock wave experiments were performed at peak stresses up to 13 GPa on Zr-based bulk amorphous alloy (BAA) samples. A velocity interferometer was used to measure the particle velocity history either at the impact surface or at the rear surface of the BAA samples. From the measured particle velocity histories, the Hugoniot elastic limit (HEL) was determined to be 7.1±0.3 GPa, corresponding to an elastic strain of approximately 4%. For experiments in which the peak stress exceeded the HEL, a clear two-wave structure consisting of an elastic precursor followed by a plastic wave was observed. Measurements of the transmitted wave profiles, along with direct determination of the longitudinal stress and particle velocity at the impact surface, suggest that the shear strength of the Zr-based BAA is reduced as it is shocked above the elastic limit. © 2004 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
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Reduction of positional errors in a four-point probe resistance measurement

D. C. Worledge

Appl. Phys. Lett. 84, 1695 (2004); http://dx.doi.org/10.1063/1.1655697 (3 pages) | Cited 4 times

Online Publication Date: 2 March 2004

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A method for reducing resistance errors due to inaccuracy in the positions of the probes in a collinear four-point probe resistance measurement of a thin film is presented. By using a linear combination of two measurements which differ by interchange of the I− and V− leads, positional errors can be eliminated to first order. Experimental data measured using microprobes show a substantial reduction in absolute error from 3.4% down to 0.01%–0.1%, and an improvement in precision by a factor of 2–4. The application of this technique to the current-in-plane tunneling method to measure electrical properties of unpatterned magnetic tunnel junction wafers is discussed. © 2004 American Institute of Physics.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.68.+m Photography, photographic instruments; xerography
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