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4 Dec 2000

Volume 77, Issue 23, pp. 3683-3863

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High-speed light modulation using complex refractive-index changes of electro-optic polymers

Kenji Harada, Katsuhiro Munakata, Masahide Itoh, Toyohiko Yatagai, Yutaka Honda, and Shinsuke Umegaki

Appl. Phys. Lett. 77, 3683 (2000); http://dx.doi.org/10.1063/1.1329857 (3 pages) | Cited 8 times

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We propose a promising type of light modulator using complex refractive-index changes of electro-optic polymers in the wavelength region of absorption. The material used in this study is a high-glass-transition-temperature active-polyimide thin film. The wavelength dependence of electrically induced complex refractive-index changes and the modulation efficiency are evaluated. A modulation efficiency of 33.8% has been realized with 141 V rms applied potential at a wavelength of 633 nm. Very fast modulation at over 25 MHz has been demonstrated. © 2000 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
42.79.Hp Optical processors, correlators, and modulators
42.70.Jk Polymers and organics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.25.Gy Edge and boundary effects; reflection and refraction
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Modal competition in implant-apertured index-guided vertical-cavity surface-emitting lasers

Jean-François P. Seurin, Guobin Liu, Shun Lien Chuang, Leo M. F. Chirovsky, W. S. Hobson, and J. Lopata

Appl. Phys. Lett. 77, 3686 (2000); http://dx.doi.org/10.1063/1.1329859 (3 pages) | Cited 4 times

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We present a detailed theoretical study on the optical and L–I characteristics of implant-apertured index-guided vertical-cavity surface-emitting lasers. Our theory is based on a beam propagation method combined with thermal, gain, and rate-equation models. Spatial hole burning and modal competition are taken into account. Our results are in excellent agreement with the experimental data and show the effect of the current aperture size (determined by the ion implant) on the modal performance of these devices. In particular, the current-aperture size can be fixed independently from the index-guide size to obtain minimum threshold, single-mode operation. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift

Quasilinear electro-optical response in a polymer-dispersed nematic liquid crystal

F. P. Nicoletta, D. Cupelli, G. De Filpo, M. Macchione, and G. Chidichimo

Appl. Phys. Lett. 77, 3689 (2000); http://dx.doi.org/10.1063/1.1330223 (3 pages) | Cited 3 times

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Polymer-dispersed nematic liquid crystals are known to exhibit a quadratic electro-optic response. For practical applications, a linear dependence on the applied electric field is often required. In this letter, polymer-dispersed nematic liquid crystal films with a built-in dc electric field are shown to be good electro-optical devices with a linear response. The built-in electric field is obtained by energizing films with an external dc field. The electro-optical response dependence on the strength and frequency of the driving field is discussed. © 2000 American Institute of Physics.
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78.20.Jq Electro-optical effects
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Adaptive femtosecond optical pulse combining

R. Jones, D. D. Nolte, and M. R. Melloch

Appl. Phys. Lett. 77, 3692 (2000); http://dx.doi.org/10.1063/1.1329866 (3 pages) | Cited 3 times

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We combine two nominal 100 fs pulses into a pulse train using an adaptive holographic quantum-well film as an adaptive pulse combiner in a two-wave mixing geometry. The two pulses in the combined pulse train are phase-locked and are immune to drifting optical path differences or delay times between the two input pulses. The phase is controlled by the choice of center wavelength. The spectrum of the pulse train is equivalent to the spectral interferogram between two ultrafast pulses. © 2000 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
07.60.Ly Interferometers
42.40.Kw Holographic interferometry; other holographic techniques

Near-field fluorescence imaging with 32 nm resolution based on microfabricated cantilevered probes

Rolf Eckert, J. Moritz Freyland, Henkjan Gersen, Harry Heinzelmann, Gregor Schürmann, Wilfried Noell, Urs Staufer, and Nico F. de Rooij

Appl. Phys. Lett. 77, 3695 (2000); http://dx.doi.org/10.1063/1.1330571 (3 pages) | Cited 38 times

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High-resolution near-field optical imaging with microfabricated probes is demonstrated. The probes are made from solid quartz tips fabricated at the end of silicon cantilevers and covered with a 60-nm-thick aluminum film. Transmission electron micrographs indicate a continuous aluminum layer at the tip apex. A specially designed instrument combines the advantages of near-field optical and beam-deflection force microscopy. Near-field optical data of latex bead projection patterns in transmission and of single fluorophores have been obtained in constant-height imaging mode. An artifact-free optical resolution of 31.7±3.6 nm has been deduced from full width at half maximum values of single molecule images. © 2000 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
87.64.mt Near-field scanning
42.30.Va Image forming and processing

Photonic quantum-well structures: Multiple channeled filtering phenomena

Feng Qiao, Chun Zhang, Jun Wan, and Jian Zi

Appl. Phys. Lett. 77, 3698 (2000); http://dx.doi.org/10.1063/1.1330570 (3 pages) | Cited 61 times

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One can construct photonic quantum-well structures by stacking different photonic crystals in a way similar to semiconductor quantum wells, provided that the photonic band gaps of the constituent photonic crystals are properly aligned. If the photonic band of the photonic crystal in the well region is just located into the photonic band gap of the photonic crystal in the barrier region, quantized confined photonic states will appear owing to the photonic confinement effects. It is found that the number of the confined states can be tuned by adjusting the number of period of the well region, leading to the phenomena of multiple channeled filtering. A huge amplification of the field intensity is found in the well region for the confined photonic states. © 2000 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.50.Ct Quantum description of interaction of light and matter; related experiments
78.66.-w Optical properties of specific thin films

Photoinduced processes in Sn-doped silica fiber preforms

N. Chiodini, S. Ghidini, A. Paleari, G. Brambilla, and V. Pruneri

Appl. Phys. Lett. 77, 3701 (2000); http://dx.doi.org/10.1063/1.1330749 (3 pages) | Cited 8 times

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Effects induced by KrF ultraviolet excimer laser on Sn-doped silica fiber performs were analyzed by means of optical and electron paramagnetic resonance (EPR) techniques. Bond breaking in substitutional Sn sites was evidenced by the Sn–E′ EPR signal due to sp3 unpaired electrons in threefold coordinated Sn sites. Red photoluminescence excited at 633 nm, due to nonbridging-oxygen sites, was also observed after laser exposure. The intensity of this emission did not follow the Sn concentration profile, being observed at the core–cladding interface and in the core center. Birefringence data showed that these effects are accompanied by stress relief in the Sn-doped region. Different structural features of core and cladding were evidenced by micro-Raman measurements and related to the observed photosensitivity. © 2000 American Institute of Physics.
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42.81.Gs Birefringence, polarization
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Hx Other solid inorganic materials
76.30.Mi Color centers and other defects
61.82.Ms Insulators
78.20.Fm Birefringence
42.70.Gi Light-sensitive materials

Erbium emission from porous silicon one-dimensional photonic band gap structures

Herman A. Lopez and Philippe M. Fauchet

Appl. Phys. Lett. 77, 3704 (2000); http://dx.doi.org/10.1063/1.1331082 (3 pages) | Cited 23 times

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We report tunable, narrow, directional, and enhanced erbium emission from one-dimensional photonic band gap structures. The structures are prepared by anodic etching of crystalline silicon and consist of two highly reflecting porous silicon Bragg reflectors sandwiching an active layer. The cavities are doped by cathodic electromigration of the erbium ions into the porous silicon matrix, followed by high temperature oxidation. By controlling the oxidation temperature of the structure, the position of the erbium emission near 1.5 μm is tuned to regions where the natural erbium spectrum is very weak. The erbium emission from the cavity is narrowed to a full width at half maximum of 12 nm with a quality factor Q of 130, highly directional with a 20° emission cone around the normal axis, and enhanced by more than one order of magnitude. © 2000 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.55.Mb Porous materials
81.05.Rm Porous materials; granular materials
78.66.Db Elemental semiconductors and insulators
81.65.Cf Surface cleaning, etching, patterning
78.55.Ap Elemental semiconductors
66.30.Qa Electromigration

Highly efficient 2% Nd:yttrium aluminum garnet ceramic laser

Jianren Lu, Mahendra Prabhu, Jianqiu Xu, Ken-ichi Ueda, Hideki Yagi, Takakimi Yanagitani, and Alexander A. Kaminskii

Appl. Phys. Lett. 77, 3707 (2000); http://dx.doi.org/10.1063/1.1331091 (3 pages) | Cited 70 times

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A highly efficient diode-laser end-pumped polycrystalline 2% Nd:yttrium aluminum garnet (YAG) ceramics laser that is comparable in efficiency with Nd:YAG single crystal laser has been developed. With 883 mW pumping, 465-mW-cw laser output at 1064 nm has been obtained corresponding to an optical-to-optical efficiency of 52.7%. The laser threshold is only 30 mW with R = 97% output coupler. © 2000 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.55.Hx Other solid inorganic materials

Near-field aperture fabricated by solid–solid diffusion

Yoshimasa Suzuki, Hiroshi Fuji, Junji Tominaga, Takashi Nakano, and Nobufumi Atoda

Appl. Phys. Lett. 77, 3710 (2000); http://dx.doi.org/10.1063/1.1331345 (3 pages) | Cited 2 times

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It is well known that some metals (such as Ag) can diffuse into chalcogenides (such as Te) to produce alloys at room temperature. Using this solid–solid diffusion, we propose a technique to fabricate a near-field probe. Some basic experiments were carried out by this technique, and we obtained images on both the atomic-force microscope and scanning near-field optical microscope at the same time. Furthermore, it was found that the shading of Te is superior to that of other metals such as Ag and Al. © 2000 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
66.30.Ny Chemical interdiffusion; diffusion barriers
07.79.Fc Near-field scanning optical microscopes
07.79.Lh Atomic force microscopes
68.35.Fx Diffusion; interface formation

Optical parametric amplification in composite polymer/ion exchanged planar waveguide

M. Alshikh Khalil, G. Vitrant, P. Raimond, P. A. Chollet, and F. Kajzar

Appl. Phys. Lett. 77, 3713 (2000); http://dx.doi.org/10.1063/1.1331352 (3 pages) | Cited 2 times

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A simple hybrid polymer/ion exchanged planar optical waveguiding structure has been fabricated which allows us to realize phase matching between different guided modes without any corrugation or modulation of the structure. A nonlinear polymer is deposited on top of glass substrate with a waveguide realized by the ion-exchange technique. Efficient optical parametric amplification is demonstrated for a pump at 532 nm and a signal at 814 nm. A 1 dB internal optical gain is achieved after propagation on 5 mm, with a pump power of 15 kW/mm. © 2000 American Institute of Physics.
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42.65.Yj Optical parametric oscillators and amplifiers
42.82.Et Waveguides, couplers, and arrays
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics
42.82.Fv Hybrid systems

Three-terminal bistable twisted nematic liquid crystal displays

Jian-Xin Guo, Zhi-Guo Meng, Man Wong, and Hoi-Sing Kwok

Appl. Phys. Lett. 77, 3716 (2000); http://dx.doi.org/10.1063/1.1328363 (3 pages) | Cited 35 times

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A three-terminal bistable twisted nematic liquid crystal display has been demonstrated. This display makes use of a combination of strong in-plane electric fields and vertical electric field for switching between the ϕ and the ϕ+π twist states. The lifetimes of the two bistable twist states are infinite, which is a significant improvement over conventional bistable twisted nematic displays. © 2000 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Electro-optic effect of periodically poled optical superlattice LiNbO3 and its applications

Yan-Qing Lu, Zhi-Liang Wan, Quan Wang, Yuan-Xin Xi, and Nai-Ben Ming

Appl. Phys. Lett. 77, 3719 (2000); http://dx.doi.org/10.1063/1.1329325 (3 pages) | Cited 51 times

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The electro-optic effect of periodically poled optical superlattice LiNbO3 (PPLN) was studied. Because of the periodic electro-optic (EO) coefficient, the reciprocal vector of the periodic structure can be used to compensate for the phase mismatch between the ordinary and extraordinary waves, which is similar to the nonlinear optical frequency conversion process. If the quasi-phase-matching condition is satisfied, polarization of a light propagated in PPLN can rotate linearly with the applied electric field, which shows that PPLN may be used as a precise spectral filter or an EO switch. © 2000 American Institute of Physics.
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78.20.Jq Electro-optical effects
42.70.Mp Nonlinear optical crystals
78.66.Nk Insulators
42.79.Ci Filters, zone plates, and polarizers
42.79.Hp Optical processors, correlators, and modulators

Intersubband absorption at λ ∼ 1.55 μm in well- and modulation-doped GaN/AlGaN multiple quantum wells with superlattice barriers

Claire Gmachl, Hock M. Ng, S.-N. George Chu, and Alfred Y. Cho

Appl. Phys. Lett. 77, 3722 (2000); http://dx.doi.org/10.1063/1.1332108 (3 pages) | Cited 151 times

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Intersubband optical absorption around 1.55 μm has been measured in GaN/AlGaN multiple quantum wells (MQWs) grown by molecular-beam epitaxy. First, peak absorption wavelengths as short as 1.41 μm are reported for ultranarrow, ⩾11 Å wide, well-doped MQWs with high, 85%, AlN mole-fraction barriers. Second, in order to enable modulation doping as well as the use of lower AlN mole-fraction barriers, we designed and fabricated QWs embedded in barriers consisting of a short period superlattice of narrow GaN QWs and only 65% AlN mole-fraction barriers. The resulting electron Bragg confinement allows peak absorption wavelengths as short as 1.52 μm. Furthermore, the structures can now be modulation doped through doping of the narrow superlattice wells and subsequent charge transfer into the active well. We observe a reduction of the absorption linewidth, from ∼200 to ∼130 meV, for these structures. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
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Radio-frequency plasma cleaning for mitigation of high-power microwave-pulse shortening in a coaxial gyrotron

William E. Cohen, Ronald M. Gilgenbach, Reginald L. Jaynes, Christopher W. Peters, Mike R. Lopez, Y. Y. Lau, Scott A. Anderson, Mary L. Brake, and Thomas A. Spencer

Appl. Phys. Lett. 77, 3725 (2000); http://dx.doi.org/10.1063/1.1329862 (3 pages) | Cited 3 times

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Results are reported demonstrating that radio-frequency (rf) plasma cleaning is an effective technique for mitigating microwave-pulse shortening (i.e., lengthening the pulse) in a multimegawatt, large-orbit, coaxial gyrotron. Cleaning plasmas were generated by 50 W of rf power at 13.56 MHz in nitrogen fill gas in the pressure range 15–25 mTorr. Improvements in the averaged microwave energy output of this high-power-microwave device ranged from 15% to 245% for different initial conditions and cleaning protocols. The mechanism for this improvement is believed to be rf plasma sputtering of excess water vapor from the cavity/waveguide and subsequent removal of the contaminant by cryogenic vacuum pumps. © 2000 American Institute of Physics.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
84.40.Az Waveguides, transmission lines, striplines

Thermal and nonthermal ion emission during high-fluence femtosecond laser ablation of metallic targets

S. Amoruso, X. Wang, C. Altucci, C. de Lisio, M. Armenante, R. Bruzzese, and R. Velotta

Appl. Phys. Lett. 77, 3728 (2000); http://dx.doi.org/10.1063/1.1329869 (3 pages) | Cited 26 times

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We have investigated the emission of positive ions from metallic targets irradiated with intense, ultrashort laser pulses (≈120 fs) at 780 nm, in both S and P polarized states. The measured energy spectra show the presence of a nonthermal, high-energy (several keV) ion component accompanying low-energy ions (tens of eV) produced by a thermal mechanism. The yield of the high-energy component shows a strong dependence on both laser fluence and light polarization. For the low-energy component a higher ablation efficiency was observed for P polarization, and ascribed to a more effective absorption mechanism active during the laser–target interaction. © 2000 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
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Growth of large-scale GaN nanowires and tubes by direct reaction of Ga with NH3

Maoqi He, Indira Minus, Piezhen Zhou, S. Noor Mohammed, Joshua B. Halpern, Randy Jacobs, Wendy L. Sarney, Lourdes Salamanca-Riba, and R. D. Vispute

Appl. Phys. Lett. 77, 3731 (2000); http://dx.doi.org/10.1063/1.1329863 (3 pages) | Cited 98 times

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Large-scale wurtzite GaN nanowires and nanotubes were grown by direct reaction of metal gallium vapor with flowing ammonia in an 850–900 °C horizontal oven. The cylindrical structures were as long as 500 μm with diameters between 26 and ∼100 nm. Transmission electron microscopy, scanning electron microscopy, and x-ray diffraction were used to measure the size and structures of the samples. Preliminary results show that the size of the nanowires depends on the temperature and the NH3 flow rate. The growth mechanism is discussed briefly. The simple method presented here demonstrates that GaN nanowires can be grown without the use of a template or catalyst, as reported elsewhere. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Ea III-V semiconductors
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Elastic constants of Pd39Ni10Cu30P21 bulk metallic glass under high pressure

Li Min Wang, L. L. Sun, W. H. Wang, R. J. Wang, Z. J. Zhan, D. Y. Dai, and W. K. Wang

Appl. Phys. Lett. 77, 3734 (2000); http://dx.doi.org/10.1063/1.1330560 (3 pages) | Cited 24 times

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The pressure-dependent acoustic velocities of a Pd39Ni10Cu30P21 bulk metallic glass (BMG) have been measured up to 0.5 GPa by using an ultrasonic technique with the pulse echo overlap method. The elastic constants, the Debye temperature, and their pressure dependence are obtained. The isothermal equation of state (EOS) of the BMG is established in terms of the Murnaghan form. The atomic configurations of the BMG are discussed by comparing the elastic constants and the EOS with those of its metallic component and of other amorphous materials. © 2000 American Institute of Physics.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.05.Kf Glasses (including metallic glasses)
62.65.+k Acoustical properties of solids
62.50.-p High-pressure effects in solids and liquids
62.20.D- Elasticity
61.43.Fs Glasses
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
64.30.-t Equations of state of specific substances

Atomic scale characterization of oxygen vacancy segregation at SrTiO3 grain boundaries

R. F. Klie and N. D. Browning

Appl. Phys. Lett. 77, 3737 (2000); http://dx.doi.org/10.1063/1.1330572 (3 pages) | Cited 28 times

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We have examined the atomic structure, composition, and bonding at a nominally undoped 58° [001] tilt grain boundary in SrTiO3 in order to develop an understanding of the control that the grain boundary plane exerts over the bulk properties. Room temperature and in situ heating experiments show that there is a segregation of oxygen vacancies to the grain boundary that is increased at elevated temperatures and is independent of the cation arrangement. These measurements provide direct support for recent experimental and theoretical predictions that nonstoichiometry, and in particular oxygen vacancies, are responsible for the widely observed grain boundary properties. © 2000 American Institute of Physics.
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61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
61.72.J- Point defects and defect clusters
61.66.Bi Elemental solids
61.66.Dk Alloys

Development of cross-hatch morphology during growth of lattice mismatched layers

A. M. Andrews, A. E. Romanov, J. S. Speck, M. Bobeth, and W. Pompe

Appl. Phys. Lett. 77, 3740 (2000); http://dx.doi.org/10.1063/1.1330567 (3 pages) | Cited 13 times

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An approach for understanding the cross-hatch morphology in lattice mismatched heteroepitaxial film growth is developed. It is argued that both strain relaxation associated with misfit dislocation formation and lateral surface step flow are required for the appearance of mesoscopic scale surface undulations during layer growth. The results of Monte Carlo simulations for dislocation assisted strain relaxation and consequent film growth predict the development of cross-hatch patterns with a characteristic surface undulation magnitude ∼50 Å in an approximately 70% relaxed In0.25Ga0.75As layers. This is supported by atomic force microscopy observations of cross-hatch morphology in the same composition samples grown well beyond the critical thickness for misfit dislocation formation. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Characteristics of free-standing hydride-vapor-phase-epitaxy-grown GaN with very low defect concentration

P. Visconti, K. M. Jones, M. A. Reshchikov, F. Yun, R. Cingolani, H. Morkoç, S. S. Park, and K. Y. Lee

Appl. Phys. Lett. 77, 3743 (2000); http://dx.doi.org/10.1063/1.1330563 (3 pages) | Cited 23 times

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A free-standing 300-μm-thick GaN template grown by hydride vapor phase epitaxy has been characterized for its structural and optical properties using x-ray diffraction, defect delineation etch followed by imaging with atomic force microscopy, and variable temperature photoluminescence. The Ga face and the N face of the c-plane GaN exhibited a wide variation in terms of the defect density. The defect concentrations on Ga and N faces were about 5×105 cm−2 for the former and about 1×107 cm−2 for the latter. The full width at half maximum of the symmetric (0002) x-ray diffraction peak was 69 and 160 arc sec for the Ga and N faces, respectively. That for the asymmetric (10–14) peak was 103 and 140 arc sec for Ga and N faces, respectively. The donor bound exciton linewidth as measured on the Ga and N faces (after a chemical etching to remove the damage) is about 1 meV each at 10 K. Instead of the commonly observed yellow band, this sample displayed a green band, which is centered at about 2.44 eV. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Resonant Raman scattering in self-organized InAs/GaAs quantum dots

R. Heitz, H. Born, A. Hoffmann, D. Bimberg, I. Mukhametzhanov, and A. Madhukar

Appl. Phys. Lett. 77, 3746 (2000); http://dx.doi.org/10.1063/1.1329321 (3 pages) | Cited 19 times

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The exciton-phonon coupling in self-organized InAs/GaAs quantum dots (QDs) is investigated under resonant excitation of the ground-state transition. First- and second-order phonon sidebands of the TO (30.3 meV) and LO (33.2 meV) modes of the strained InAs QDs as well as an interface (35.9 meV) mode are resolved. Huang–Rhys factors of 0.012, 0.026, and 0.006, respectively, indicate enhanced polar exciton-phonon coupling in such strained low-symmetry QDs. Time-resolved measurements support the local character of the phonon modes. © 2000 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.Gg Exciton-mediated interactions
78.47.-p Spectroscopy of solid state dynamics

Transmission electron microscopy observation of deformation microstructure under spherical indentation in silicon

J. E. Bradby, J. S. Williams, J. Wong-Leung, M. V. Swain, and P. Munroe

Appl. Phys. Lett. 77, 3749 (2000); http://dx.doi.org/10.1063/1.1332110 (3 pages) | Cited 92 times

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Spherical indentation of crystalline silicon has been studied using cross-sectional transmission electron microscopy (XTEM). Indentation loads were chosen below and above the yield point for silicon to investigate the modes of plastic deformation. Slip planes are visible in the XTEM micrographs in both indentation loads studied. A thin layer of polycrystalline material has been identified (indexed as Si-XII from diffraction patterns) on the low-load indentation. The higher-load indentation revealed a large region of amorphous silicon. The sequence of structural deformation by indentation in silicon has been observed with the initial deformation mechanism being slip until phase transformations can take place. © 2000 American Institute of Physics.
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62.20.F- Deformation and plasticity
61.43.Dq Amorphous semiconductors, metals, and alloys
64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Yarn ball polymer microstructures: A structural transition phenomenon induced by an electric field

Pavel A. Kossyrev and Gregory P. Crawford

Appl. Phys. Lett. 77, 3752 (2000); http://dx.doi.org/10.1063/1.1330753 (3 pages) | Cited 4 times

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We report on an unusual polymer “yarn ball” microstructure that is created through a template-based synthetic process involving reactive mesogens. We present experimental results of a unique structural transition of the yarn ball when subjected to an electric field, and describe this transition with a modified elastic theory. We model the interactions of the mesogenic thread segments that comprise the yarn ball in terms of mean-field theory by introducing an intersegment potential. © 2000 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
64.70.K- Solid-solid transitions

Excitonic properties of MgS/ZnSe quantum wells

B. Urbaszek, A. Balocchi, C. Bradford, C. Morhain, C. B. O’Donnell, K. A. Prior, and B. C. Cavenett

Appl. Phys. Lett. 77, 3755 (2000); http://dx.doi.org/10.1063/1.1331095 (3 pages) | Cited 8 times

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Magnetic field and temperature dependent measurements are used to study the excitonic properties of high quality ZnSe quantum wells in MgS barriers grown by molecular beam epitaxy. The small inhomogeneous broadening of the samples allows the observation of higher excited exciton states. Due to the large difference in band gap between ZnSe and MgS a value of 43.9 meV was measured for the exciton binding energy which is the largest reported for this material system. The full width at half maximum of the heavy hole transitions is measured as a function of temperature and the broadening of the excitonic transitions in narrow quantum wells is reduced compared to the ZnSe bulk value due to the expected reduction in the LO-phonon scattering. © 2000 American Institute of Physics.
Show PACS
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Ji Excitons in magnetic fields; magnetoexcitons
71.15.Nc Total energy and cohesive energy calculations
71.35.Gg Exciton-mediated interactions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
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