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25 Oct 2004

Volume 85, Issue 17, pp. 3657-3939

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3851 (2004); http://dx.doi.org/10.1063/1.1808886 (3 pages)

P. Guha, S. Kar, and S. Chaudhuri
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Ultraviolet photonic crystal laser

X. Wu, A. Yamilov, X. Liu, S. Li, V. P. Dravid, R. P. H. Chang, and H. Cao

Appl. Phys. Lett. 85, 3657 (2004); http://dx.doi.org/10.1063/1.1808888 (3 pages) | Cited 52 times

Online Publication Date: 29 October 2004

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We fabricated two-dimensional photonic crystal structures in zinc oxide films with focused-ion-beam etching. Lasing is realized in the near-ultraviolet frequency at room temperature under optical pumping. From the measurement of lasing frequency and spatial profile of the lasing modes, as well as the photonic band structure calculation, we conclude that lasing occurs in the strongly localized defect modes near the edges of photonic band gap. These defect modes originate from the structure disorder unintentionally introduced during the fabrication process.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Px Semiconductor lasers; laser diodes
42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning

Terahertz emission from electrically pumped gallium doped silicon devices

P.-C. Lv, R. T. Troeger, S. Kim, S. K. Ray, K. W. Goossen, J. Kolodzey, I. N. Yassievich, M. A. Odnoblyudov, and M. S. Kagan

Appl. Phys. Lett. 85, 3660 (2004); http://dx.doi.org/10.1063/1.1808878 (3 pages) | Cited 15 times

Online Publication Date: 29 October 2004

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Current pumped terahertz (THz) emitting devices have been fabricated from gallium doped silicon. The time resolved peak power was 12 μW per facet at a peak pumping current of 400 mA, and the emission was observed up to temperatures near 30 K. The spectra occurred in two distinct series at 7.9–8.5 THz, and at 13.2–13.8 THz. The emission was attributed to the radiative transitions of holes from the split sublevels of the 1Γ8 excited state to the sublevels of the 1Γ8+ ground state and the 1Γ7+ ground state, yielding an energy separation of 22±0.07 meV between the two ground states. These results indicated that emitters based on Ga impurity transitions open up a range of THz frequencies, and the properties of their spectra can improve the understanding of impurity level physics.
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85.30.-z Semiconductor devices
71.55.Cn Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
84.40.-x Radiowave and microwave (including millimeter wave) technology
72.20.Ht High-field and nonlinear effects

Fabrication and performance of efficient blue light emitting III-nitride photonic crystals

Lu Chen and Arto V. Nurmikko

Appl. Phys. Lett. 85, 3663 (2004); http://dx.doi.org/10.1063/1.1808881 (3 pages) | Cited 17 times

Online Publication Date: 29 October 2004

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We have fabricated and characterized a light emitting photonic crystal slab in the blue near 460 nm, based on InGaN quantum well active material. A multilayer nanopattern transfer technique was developed to fabricate these optical structures. The dependence of the photoluminescence enhancement on specific pattern dimension, coupled with distinct polarization characteristics of emission, was found to be in good agreement with theoretical simulations, thereby supporting the existence of photonic crystal band gap. The results suggest that practical fabrication of photonic crystal slabtype light emitting diodes for enhanced external quantum efficiency in the blue and ultraviolet is feasible.
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42.70.Qs Photonic bandgap materials
81.07.St Quantum wells
78.55.Cr III-V semiconductors
78.67.De Quantum wells
68.65.Fg Quantum wells
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography

Detection of chemical species using ultraviolet microdisk lasers

W. Fang, D. B. Buchholz, R. C. Bailey, J. T. Hupp, R. P. H. Chang, and H. Cao

Appl. Phys. Lett. 85, 3666 (2004); http://dx.doi.org/10.1063/1.1807967 (3 pages) | Cited 16 times

Online Publication Date: 29 October 2004

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We have utilized hybrid zinc oxide∕silica microdisk lasers to sense volatile organic compounds, such as toluene and nitrobenzene. Nonspecific adsorption of these organic molecules onto the microdisk surface causes an increase in the disk refractive index, ultimately resulting in a redshift of the observed lasing wavelengths. The monitoring of these shifts provides the sensing modality. Microdisk lasers were found to respond rapidly and reversibly to the investigated chemicals demonstrating, in principal, the chemical and biological sensing capabilities of such devices.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.43.Mn Adsorption kinetics

Vertically emitting annular Bragg lasers using polymer epitaxial transfer

William M. J. Green, Jacob Scheuer, Guy DeRose, and Amnon Yariv

Appl. Phys. Lett. 85, 3669 (2004); http://dx.doi.org/10.1063/1.1807970 (3 pages) | Cited 5 times

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Fabrication of a planar semiconductor microcavity, composed of cylindrical Bragg reflectors surrounding a radial defect, is demonstrated. A versatile polymer bonding process is used to transfer active InGaAsP resonators to a low-index transfer substrate. Vertical emission of in-plane modes lasing at telecom wavelengths is observed under pulsed optical excitation with a submilliwatt threshold.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Sa Microcavity and microdisk lasers
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.40.Hp Lithography, masks and pattern transfer
78.55.Cr III-V semiconductors

Strong charge carrier confinement in purely strain induced GaAs∕InAlAs single quantum wires

R. Schuster, H. Hajak, M. Reinwald, W. Wegscheider, D. Schuh, M. Bichler, and G. Abstreiter

Appl. Phys. Lett. 85, 3672 (2004); http://dx.doi.org/10.1063/1.1807948 (3 pages) | Cited 1 time

Online Publication Date: 29 October 2004

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We report on micro-photoluminescence studies of single quantum wires which were grown by molecular beam epitaxy. Employing the cleaved edge overgrowth technique, quantum wires located in an overgrown (011) oriented GaAs quantum well originate purely from the tensile strain field of InAlAs layers grown along the [100] direction. These stressor layers are separated by 1-μm-wide AlGaAs barriers so that the photoluminescence signals of different quantum wires can be resolved individually. Their confinement energy varies systematically with the widths of the stressor and overgrown layers, reaching values as high as 51.5 meV. The quantum wire signals are characterized by a smooth line shape even for the lowest excitation powers, indicating the absence of pronounced exciton localization.
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81.07.Vb Quantum wires
73.21.Hb Quantum wires
81.05.Ea III-V semiconductors
78.67.Lt Quantum wires
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Room temperature operation of InGaAs∕InGaAsP∕InP quantum dot lasers

J. W. Jang, S. H. Pyun, S. H. Lee, I. C. Lee, Weon G. Jeong, R. Stevenson, P. Daniel Dapkus, N. J. Kim, M. S. Hwang, and D. Lee

Appl. Phys. Lett. 85, 3675 (2004); http://dx.doi.org/10.1063/1.1812365 (3 pages) | Cited 22 times

Online Publication Date: 29 October 2004

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The growth conditions for InGaAs∕InGaAsP∕InP quantum dots (QDs) have been optimized and QDs of high luminescence efficiency and the room temperature operation of QD lasers emitting at ∼1.5 μm have been demonstrated. Lattice-matched InGaAsP (λg=1.0–1.1 μm) was used as a barrier layer for the InGaAs QDs and the emission wavelength was controlled by the QD composition. High-density InGaAs QDs with an areal density as high as 1.13×1011 cm−2 have been grown. The integrated and peak intensity of the photoluminescence (PL) spectra at room temperature are as high as 25% and 10% of those at 10 K, respectively. The room temperature PL peak intensity is about 50% that of a high-quality InGaAs∕InP quantum well. Room temperature, pulsed operation at ∼1.5 μm has been achieved from broad area lasers with a 1 mm cavity length. Threshold current density per QD stack of ∼430 A∕cm2 is measured for the five-, seven-, and ten-stack QD lasers.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
42.55.Px Semiconductor lasers; laser diodes
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.63.Kv Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Femtosecond time-resolved dispersion relation of complex nonlinear refractive index in a semiconductor quantum well

Fumikazu Inuzuka, Kazuhiko Misawa, Kenichi Nishi, and Roy Lang

Appl. Phys. Lett. 85, 3678 (2004); http://dx.doi.org/10.1063/1.1808225 (3 pages)

Online Publication Date: 29 October 2004

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We present simultaneous measurement of femtosecond time-resolved nonlinear phase and amplitude changes around the excitonic resonance of the AlGaAs∕GaAs quantum well using polarization-division Sagnac interferometer. The nonlinear complex refractive index of the semiconductor material for all-optical devices is successfully determined from directly measured nonlinear phase and amplitude changes.
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68.65.Fg Quantum wells
78.67.De Quantum wells
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.An Optical susceptibility, hyperpolarizability
78.47.-p Spectroscopy of solid state dynamics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Fabrication of a three-dimensional terahertz photonic crystal using monosized spherical particles

Kenta Takagi, Kazunori Seno, and Akira Kawasaki

Appl. Phys. Lett. 85, 3681 (2004); http://dx.doi.org/10.1063/1.1812375 (3 pages) | Cited 18 times

Online Publication Date: 29 October 2004

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Three-dimensional artificial crystals with periodicity corresponding to terahertz wave lengths were fabricated by self-assembling monosized metal spherical particles. The metal crystals were weakly sintered to utilize them as templates. The metal templates were inverted to air spheres crystal embedded in dielectric resin though infiltration and etching. The resulting resin inverted crystals clearly presented the photonic stop gaps within terahertz wave region and the frequencies of the gaps were confirmed to agree well with calculation by plane wave expansion method.
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42.70.Qs Photonic bandgap materials
78.70.Gq Microwave and radio-frequency interactions
81.65.Cf Surface cleaning, etching, patterning
78.20.-e Optical properties of bulk materials and thin films
42.86.+b Optical workshop techniques

Tunable laser using micromachined grating with continuous wavelength tuning

A. Q. Liu, X. M. Zhang, D. Y. Tang, and C. Lu

Appl. Phys. Lett. 85, 3684 (2004); http://dx.doi.org/10.1063/1.1812595 (3 pages) | Cited 13 times

Online Publication Date: 29 October 2004

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This letter develops a method that is able to optimize the grating pivot position to obtain maximum continuous tuning range for a Littrow laser, and also verifies the method by implementation of a single-chip integrated laser using the microelectromechanical systems (MEMS) technology. The laser consists of a semiconductor gain chip, a microlens, and a MEMS blazed grating arranged in the Littrow configuration. The laser is integrated onto a single silicon chip while maintaining the ability of continuous tuning in a large range. It has a compact size of 2.0 mm×1.5 mm×0.6 mm, and has obtained a tuning range of 30.3 nm with a resolution of 0.03 nm∕V2, a maximum power of 0.4 dBm and a side mode suppression ratio of 26 dB. Other merits include fast tuning speed, improved mechanical/wavelength stability, batch fabrication, and low cost.
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42.55.Sa Microcavity and microdisk lasers
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings
42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
85.60.-q Optoelectronic devices

Giant optical nonlinearity of a Bi2Nd2Ti3O12 ferroelectric thin film

Bing Gu, Yue-Hua Wang, Xian-Chu Peng, Jian-Ping Ding, Jing-Liang He, and Hui-Tian Wang

Appl. Phys. Lett. 85, 3687 (2004); http://dx.doi.org/10.1063/1.1810626 (3 pages) | Cited 22 times

Online Publication Date: 29 October 2004

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We investigate the optical nonlinearity of a Bi2Nd2Ti3O4 ferroelectric thin film using the top-hat Z scan technique at a wavelength of 532 nm with 35 ps duration pulses. The film exhibits the fast and giant optical nonlinearities having the two-photon absorption coefficient of 3.1×104 cm∕GW and the nonlinear refraction coefficient of 0.7 cm2∕GW, respectively. The mechanism of the optical nonlinearity is discussed in detail. In particular, we also give two important formulas for the top-hat Z scan, which are very valuable and helpful for estimating the nonlinear optical coefficients when the material possesses the simultaneous nonlinear absorption and nonlinear refraction.
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77.55.-g Dielectric thin films
78.66.Nk Insulators
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.-k Nonlinear optics
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Self-phase modulation of submicrojoule femtosecond pulses in a hollow-core photonic-crystal fiber

S. O. Konorov, D. A. Sidorov-Biryukov, A. M. Zheltikov, I. Bugar, D. Chorvat, D. Chorvat, V. I. Beloglazov, N. B. Skibina, M. J. Bloemer, and M. Scalora

Appl. Phys. Lett. 85, 3690 (2004); http://dx.doi.org/10.1063/1.1806278 (3 pages) | Cited 11 times

Online Publication Date: 29 October 2004

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Hollow-core photonic-crystal fibers (PCFs) capable of transporting sub-100-fs pulses of Ti:sapphire laser radiation in one of their transmission peaks centered around 800 nm have been designed and demonstrated. These fibers are shown to enhance self-phase modulation of submicrojoule 100-fs Ti:sapphire laser pulses, allowing a spectral bandwidth of 35 nm to be achieved with an 8-cm PCF sample.
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42.81.Bm Fabrication, cladding, and splicing
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.60.Rn Relaxation oscillations and long pulse operation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Rayleigh scattering, mode coupling, and optical loss in silicon microdisks

Matthew Borselli, Kartik Srinivasan, Paul E. Barclay, and Oskar Painter

Appl. Phys. Lett. 85, 3693 (2004); http://dx.doi.org/10.1063/1.1811378 (3 pages) | Cited 38 times

Online Publication Date: 29 October 2004

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High refractive index contrast optical microdisk resonators fabricated from silicon-on-insulator wafers are studied using an external silica fiber taper waveguide as a wafer-scale optical probe. Measurements performed in the 1500 nm wavelength band show that these silicon microdisks can support whispering-gallery modes with quality factors as high as 5.2×105, limited by Rayleigh scattering from fabrication induced surface roughness. Microdisks with radii as small as 2.5 μm are studied, with measured quality factors as high as 4.7×105 for an optical mode volume of 5.3 (λ∕n)3.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
68.35.B- Structure of clean surfaces (and surface reconstruction)

White-light generation through ultraviolet-emitting diode and white-emitting phosphor

Jong Su Kim, Pyung Eun Jeon, Yun Hyung Park, Jun Chul Choi, Hong Lee Park, Gwang Chul Kim, and Tae Whan Kim

Appl. Phys. Lett. 85, 3696 (2004); http://dx.doi.org/10.1063/1.1808501 (3 pages) | Cited 133 times

Online Publication Date: 29 October 2004

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White-light-emitting diodes are fabricated by using 375 nm emitting InGaN chip with Sr3MgSi2O8:Eu2+ (blue and yellow) or Sr3MgSi2O8:Eu2+, Mn2+ (blue, yellow, and red). At a color temperature of 5892 K, the color coordinates are x=0.32, y=0.33, and the color rendering index is 84%; at a color temperature of 4494 K, the color coordinates are x=0.35, y=0.33, and the color rendering index is 92%. The blue (470 nm) and yellow (570 nm) emission bands are originated from Eu2+ ions, while the red (680) emission band is originated from Mn2+ ions in Sr3MgSi2O8 host. The energy transfer among three bands occurs due to the spectral overlap between emission and absorption bands. It is confirmed by the faster decay time of the energy donor. Our white-light-emitting diodes show higher color reproducibility, higher color stability on forward-bias current, and excellent color rendering index in comparison with a commercial YAG:Ce3+-based white-light-emitting diode.
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85.60.Jb Light-emitting devices
78.55.Hx Other solid inorganic materials

Structural and interface properties of an AlN diamond ultraviolet light emitting diode

C. R. Miskys, J. A. Garrido, M. Hermann, M. Eickhoff, C. E. Nebel, M. Stutzmann, and G. Vogg

Appl. Phys. Lett. 85, 3699 (2004); http://dx.doi.org/10.1063/1.1811382 (3 pages) | Cited 6 times

Online Publication Date: 29 October 2004

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Two practically fully relaxed AlN domains were identified by x-ray diffractometry for AlN grown on (100) diamond. The epitaxial orientation relationships (0001)[10math0] AlNI∥(100)[011] diamond for the predominant AlN domain (type I) and (0001)[math2math0] AlNII∥(100)[011] diamond for the second domain (type II) are obtained. Surface morphology measurements corroborate the good structural quality of the AlN film. In addition, the intrinsic built-in voltage of a n‐AlN∕p-diamond diode was determined as 1.15 V. By spectrally resolved photocurrent measurements, the ultraviolet electroluminescence emission was confirmed to originate at the heterojunction interface, and is most probably due to a defect center.
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85.60.Jb Light-emitting devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.60.Fi Electroluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Surface acoustic wave ultraviolet photodetectors using epitaxial ZnO multilayers grown on r-plane sapphire

Nuri W. Emanetoglu, Jun Zhu, Ying Chen, Jian Zhong, Yimin Chen, and Yicheng Lu

Appl. Phys. Lett. 85, 3702 (2004); http://dx.doi.org/10.1063/1.1811383 (3 pages) | Cited 53 times

Online Publication Date: 29 October 2004

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A surface acoustic wave (SAW) ultraviolet (UV) photodetector is made of a zinc oxide (ZnO) based epitaxial multilayer structure on an r-plane sapphire (r-Al2O3) substrate. Piezoelectric and semiconducting ZnO layers are used for SAW excitation and photodetection, respectively. A thin Mg0.2Zn0.8O layer grown between the two ZnO layers isolates the semiconducting layer from the piezoelectric one. In contrast to previously reported SAW UV detectors on GaN and LiNbO3, the Sezawa SAW mode in the ZnO∕r-Al2O3 system is used for its high acoustic velocity and large maximum effective piezoelectric coupling constant. The interaction of the SAW with the photogenerated carriers in the semiconducting ZnO layer results in a phase shift and an insertion loss change, as functions of light wavelength and power. The ZnO SAW UV detector can be used as a passive zero-power remote wireless UV sensor.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
77.65.Bn Piezoelectric and electrostrictive constants

High-order corrected fields of ultrashort, tightly focused laser pulses

J. F. Hua, Y. K. Ho, Y. Z. Lin, Z. Chen, Y. J. Xie, S. Y. Zhang, Z. Yan, and J. J. Xu

Appl. Phys. Lett. 85, 3705 (2004); http://dx.doi.org/10.1063/1.1811384 (3 pages) | Cited 15 times

Online Publication Date: 29 October 2004

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High-order correction to the fields of ultrashort, tightly focused laser pulses expressed in power series of ε=1∕(ω0t0) and s=1∕(k0w00) (ω0=ck0 the central oscillatory frequency, t0 the pulse duration for half period, w00 the beam waist radius at the central frequency ω0), are derived. These expressions can be used to describe accurately the fields of laser pulses, and are suitable for practical calculations. The first-order correction terms to the fields based on paraxial approximation are explicitly given. They are applied to a simulation study of electron dynamics in laser pulse field with special attention given to the vacuum laser acceleration scheme. We found that as long as ω0t0>20, the zeroth-order approximation (long pulse approximation) is adequate for describing the interaction. For ω0t0<20, higher-order corrections have to be taken into account.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.55.Ah General laser theory
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Shape precompensation in two-photon laser nanowriting of photonic lattices

Hong-Bo Sun, Tooru Suwa, Kenji Takada, Remo Proietti Zaccaria, Moon-Soo Kim, Kwang-Sup Lee, and Satoshi Kawata

Appl. Phys. Lett. 85, 3708 (2004); http://dx.doi.org/10.1063/1.1807019 (3 pages) | Cited 27 times

Online Publication Date: 29 October 2004

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We first analyze why most of the photonic crystals produced by two-photon photopolymerization technique exhibit no photonic band gap effect. And then subdiffraction-limited resolution-enabled finely quantified pixel writing, a scheme that has been used in micromachine fabrication, is adopted as the solution. As a result, higher accuracy in depicting and better reproducibility in both fabrication and photonic band gap effect observation are obtained. More important, the method allows for precise precompensation of the structure shrinkage induced by photochemical reactions of polymerization, which may pave the way to high-fidelity fabrication of polymer photonic and optoelectronic devices that require strictly the structural parameters.
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42.70.Qs Photonic bandgap materials
82.50.Pt Multiphoton processes
81.16.Rf Micro- and nanoscale pattern formation
42.70.Jk Polymers and organics
42.62.-b Laser applications
82.35.-x Polymers: properties; reactions; polymerization

Bistable bend-splay liquid crystal display

X. J. Yu and H. S. Kwok

Appl. Phys. Lett. 85, 3711 (2004); http://dx.doi.org/10.1063/1.1810215 (3 pages) | Cited 24 times

Online Publication Date: 29 October 2004

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A bistable liquid crystal display based on the bend and splay configurations has been demonstrated. This display can be switched between the bend and splay deformation in a three-electrode configuration and has infinite bistable lifetime. It also has wide viewing angles, excellent contrast ratios, and very fast selection. Selection electric pulse duration of 50 μs can be used to switch this display, implying the possibility of a high information content applications.
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42.79.Kr Display devices, liquid-crystal devices
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Theoretical optimization of the self-organized growth of nanoscale arrays through a figure of merit

E. Vasco

Appl. Phys. Lett. 85, 3714 (2004); http://dx.doi.org/10.1063/1.1807032 (3 pages) | Cited 2 times

Online Publication Date: 29 October 2004

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A figure of merit is proposed in order to optimize the self-organized growth of nanoscale elements into one-/two-dimensional arrays via a fine selection of the deposition/annealing conditions. This figure of merit has been designed to account for the most significant defects inherent in such arrays. Its versatility has been studied by kinetic Monte Carlo simulations of self-organized growth of metal clusters on the 7×7 reconstructed Si(111) surface. The optimization relationships between deposition/annealing conditions and characteristics of the metal-on-Si(111)7×7 systems are obtained and analyzed within the framework of competition between thermodynamical tendencies and kinetic limitations.
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81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters
61.46.-w Structure of nanoscale materials

Composition profiling of InAs∕GaAs quantum dots

A. Lemaître, G. Patriarche, and F. Glas

Appl. Phys. Lett. 85, 3717 (2004); http://dx.doi.org/10.1063/1.1811796 (3 pages) | Cited 35 times

Online Publication Date: 29 October 2004

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We propose a simple and straightforward technique to measure the composition distribution of In(Ga)As∕GaAs quantum dots (QDs). This method is based on the quantitative analysis of 002 dark field image contrast in cross-sectional transmission electron microscopy. InAs∕GaAs QDs show strong InGaAs alloying resulting in the formation, prior to capping, of an inverted indium composition gradient, with higher In concentration at the top. Such a mechanism implies a large Ga mass transport from the substrate. The capping process is also investigated. It strongly affects the QD shape by dissolving the apex via surface migration of indium atoms away from the dot.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
68.35.Fx Diffusion; interface formation
68.37.Lp Transmission electron microscopy (TEM)

Abnormal reduction of Eu ions and luminescence in CaB2O4: Eu thin films

J. H. Hao and J. Gao

Appl. Phys. Lett. 85, 3720 (2004); http://dx.doi.org/10.1063/1.1808876 (3 pages) | Cited 16 times

Online Publication Date: 29 October 2004

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Thin films of CaB2O4: Eu were deposited on glass substrates by spray pyrolysis. The abnormal reduction of Eu3+ to Eu2+ in as-grown thin films was found at the growth temperatures from 300 to 500 °C. Blue cathodoluminescence was observed by annealing films in air, correlating with further abnormal reduction of Eu ions and crystallization of compounds. These phenomena were explained by an electron transfer mechanism. The chromaticity coordinates were x=0.193 and y=0.089 with a dominant wavelength of 455 nm. Our results indicate calcium borate doped with Eu is a blue phosphor at temperatures suitable for the use of glass substrates in flat panel applications.
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68.55.A- Nucleation and growth
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.66.Nk Insulators
81.15.Rs Spray coating techniques
81.40.Gh Other heat and thermomechanical treatments
78.60.Hk Cathodoluminescence, ionoluminescence
64.70.K- Solid-solid transitions

Observation of negative thermo-optical coefficient in cubic MgZnO thin films

H. P. Zhou, W. Z. Shen, N. B. Chen, and H. Z. Wu

Appl. Phys. Lett. 85, 3723 (2004); http://dx.doi.org/10.1063/1.1808882 (3 pages) | Cited 4 times

Online Publication Date: 29 October 2004

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We report on the investigation of thermo-optical coefficient (dn∕dT) in cubic MgZnO thin films through temperature-dependent (10–295 K) optical transmission measurements. As a result of potential fluctuation, we observe an anomalous thermal behavior of the band gap in the ternary MgZnO alloy, which limits the observation of negative dn∕dT up to 200 K. The negative dn∕dT is evidenced by the phase shift from the prominent Fabry-Pérot interference fringes and modeled by taking into account the thermal and electronic background contribution, as well as the Wannier exciton effect. It is found that the large thermal expansion in cubic MgZnO plays a key role in the observed negative dn∕dT.
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81.05.Dz II-VI semiconductors
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors
65.40.De Thermal expansion; thermomechanical effects
71.35.-y Excitons and related phenomena

The generation of highly monodisperse droplets through the breakup of hydrodynamically focused microthread in a microfluidic device

Qingyi Xu and Mitsutoshi Nakajima

Appl. Phys. Lett. 85, 3726 (2004); http://dx.doi.org/10.1063/1.1812380 (3 pages) | Cited 72 times

Online Publication Date: 29 October 2004

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We used a controllable three-stream laminar flow system to hydrodynamically focus a viscous stream, flowing between two inviscid streams, to cause instability and eventual breakup. The characteristics of the focusing and breakup of the viscous stream are presented here. Breakup occurred as the viscous stream was focused to a characteristic width of several micrometers. Highly monodisperse droplets with diameters smaller than the width of the junction of the three inlet channels were formed through the rapid periodic breakup of the focused microthread. Size, production rate, and patterning can be precisely controlled with this approach.
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47.15.Fe Stability of laminar flows
47.55.D- Drops and bubbles
47.85.Dh Hydrodynamics, hydraulics, hydrostatics
47.20.Cq Inviscid instability
47.85.Np Fluidics

Blue emission from CaS:Cu,F thin-film electroluminescent device fabricated on Si substrate

Shintaro Hakamata, Mami Ehara, Haruki Fukada, Hiroko Kominami, Yoichiro Nakanishi, and Yoshinori Hatanaka

Appl. Phys. Lett. 85, 3729 (2004); http://dx.doi.org/10.1063/1.1812381 (2 pages)

Online Publication Date: 29 October 2004

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Thin-film electroluminescent (TFEL) devices were fabricated on Si substrates by using SiO2 and Y2O3 films as insulator layers, and ZnS films as buffer layers. The device annealed at 850 °C for 10 min in Ar showed a purple EL with a peak at 425 nm. Commission Internationale de l’Eclairage (CIE) color coordinates of x=0.217, y=0.223 under driving at 220 V0−p of 1 kHz trapezoidal wave. The purple EL from CaS:Cu TFEL device could be achieved, although luminance was weak, and a little longer wavelength component was included.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing
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