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12 Feb 2007

Volume 90, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 079903 (2007); http://dx.doi.org/10.1063/1.2692435 (3 pages)

Dong-Yol Yang, Sang Hu Park, Tae Woo Lim, Hong-Jin Kong, Shin Wook Yi, Hyun Kwan Yang, and Kwang-Sup Lee
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Diode-pumped 188 fs mode-locked Yb3+:Y2O3 ceramic laser

Masaki Tokurakawa, Kazunori Takaichi, Akira Shirakawa, Ken-ichi Ueda, Hideki Yagi, Takagimi Yanagitani, and Alexander A. Kaminskii

Appl. Phys. Lett. 90, 071101 (2007); http://dx.doi.org/10.1063/1.2476385 (3 pages) | Cited 11 times

Online Publication Date: 12 February 2007

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The authors have demonstrated a diode-pumped passively mode-locked Yb3+:Y2O3 ceramic laser by use of a semiconductor saturable absorber mirror. 188 fs pulses at a center wavelength of 1038 nm are obtained. The maximum output power is 220 mW at an absorbed pump power of 2.4 W with a diffraction-limited beam quality (M2<1.1). This is the shortest pulse generation from Yb-doped sesquioxide lasers and ceramic lasers ever reported.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Bh Lenses, prisms and mirrors
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Fabrication of high-Q chalcogenide photonic crystal resonators by e-beam lithography

Yinlan Ruan, Myung-Ki Kim, Yong-He Lee, Barry Luther-Davies, and Andrei Rode

Appl. Phys. Lett. 90, 071102 (2007); http://dx.doi.org/10.1063/1.2476416 (3 pages) | Cited 20 times

Online Publication Date: 12 February 2007

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The authors report design, fabrication, and characterization of photonic crystal nanocavities in nonlinear chalcogenide glass using e-beam lithography and chemically assisted ion beam etching. The design indicated that three-hole missing cavities with simultaneously modified side hole position and radii showed the maximum quality factor of 14 000, which was insensitive to the fabrication error of side holes. The fabricated cavities presented coupling dips of −2.6 dB at the wavelength of 1550 nm and quality factors up to 10 000 when excited with the evanescent field from a tapered optical fiber.
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42.82.Gw Other integrated-optical elements and systems
42.86.+b Optical workshop techniques
42.15.Eq Optical system design
42.81.Wg Other fiber-optical devices

Diode pumped passive Q switching of Yb3+-doped GdAl3(BO3)4 nonlinear laser crystal

Alain Brenier, Chaoyang Tu, Zhaojie Zhu, and Jianfu Li

Appl. Phys. Lett. 90, 071103 (2007); http://dx.doi.org/10.1063/1.2460394 (3 pages) | Cited 10 times

Online Publication Date: 12 February 2007

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The authors report the passive Q switching of a diode pumped Yb:GdAl3(BO3)4 (Yb:GAB) laser. The slopes of the average output power are 25% and 39.5% under different experimental conditions. The repetition rates occur in the 1–4.5 kHz range and pulse energies of 125 and 165 μJ with about 30 ns duration are obtained. An experimental comparison with passively Q-switched Nd:GAB laser is provided. A theoretical analysis is performed. It is in reasonable agreement with the experimental data and it is shown to be a useful tool for predicting the optimization of the cavity parameters.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Hj Laser materials
42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Whispering gallery modes in highly hexagonal symmetric structures of SBA-1 mesoporous silica

C. W. Chen and Y. F. Chen

Appl. Phys. Lett. 90, 071104 (2007); http://dx.doi.org/10.1063/1.2472798 (3 pages) | Cited 1 time

Online Publication Date: 12 February 2007

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An interesting optical resonant mode, called whispering gallery mode (WGM), has been discovered inside the highly hexagonal three dimensional symmetry of SBA-1 mesoporous silica. The hexagonal structure provides a suitable environment for the light wave to circulate around due to multiple total internal reflections at the resonator’s boundary and generates the resonant states. Based on the hexagonal total internal reflecting model, the observed eigenmodes can be explained quite well. The authors also discovered that under the condition of WGMs, the absorption of CO2 and H2O molecules can be greatly enhanced.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
61.43.Gt Powders, porous materials

High speed silicon photonic crystal waveguide modulator for low voltage operation

Lanlan Gu, Wei Jiang, Xiaonan Chen, Li Wang, and Ray T. Chen

Appl. Phys. Lett. 90, 071105 (2007); http://dx.doi.org/10.1063/1.2475580 (3 pages) | Cited 46 times

Online Publication Date: 12 February 2007

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A high speed compact silicon modulator is experimentally demonstrated to work at a low driving voltage desirable for on-chip applications. As carrier injection is the only practical option for optical modulation in silicon, a lower limit of current density ( ∼ 104 A/cm2) exists for achieving gigahertz modulation in the p-i-n diode configuration. Exploiting the slow group velocity of light in photonic crystal waveguides, the interaction length of this Mach-Zehnder interferometer-type silicon modulator is reduced significantly compared to conventional modulators. The required high current density is achieved with a low voltage (2 V) by scaling down the interaction length to 80 μm.
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42.79.Hp Optical processors, correlators, and modulators
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.60.Ly Interferometers

Reduction in feature size of two-photon polymerization using SCR500

Dengfeng Tan, Yan Li, Fengjie Qi, Hong Yang, Qihuang Gong, Xianzi Dong, and Xuanming Duan

Appl. Phys. Lett. 90, 071106 (2007); http://dx.doi.org/10.1063/1.2535504 (3 pages) | Cited 54 times

Online Publication Date: 13 February 2007

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Fabricated by femtosecond laser pulses at wavelength λ of 780 nm, the feature size of two-photon polymerization using SCR500 was reduced to λ/50. Lines with sub-25-nm width were produced by controlling the incident laser power and the laser focus scan speed up to 700 μm/s. Based on repolymerization between two structures close to each other, the feature size was further reduced to ∼ 15 nm, which demonstrated the potential for three-dimensional nanofabrication with high spatial resolution.
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42.62.-b Laser applications
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
81.16.Mk Laser-assisted deposition

Optical tuning and switching of photonic defect modes in cholestericliquid crystals

Hiroyuki Yoshida, Chee Heng Lee, Yusuke Miura, Akihiko Fujii, and Masanori Ozaki

Appl. Phys. Lett. 90, 071107 (2007); http://dx.doi.org/10.1063/1.2560805 (3 pages) | Cited 14 times

Online Publication Date: 15 February 2007

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Optical tuning of photonic defect modes in cholesteric liquid crystals is demonstrated based on a contrast in the pitch length. Two-photon laser lithography was performed in a cholesteric helix to leave an unpolymerized region in the center to act as a structural defect. The unpolymerized region was then substituted by an azobenzene dye-doped cholesteric liquid crystal which exhibits a pitch shortening upon ultraviolet exposure. Reversible shifting or on-off switching of the defect mode was realized as a result of selectively inducing a pitch shortening of the cholesteric liquid crystal at the defect and changing the contrast in the pitch length between the bulk and defect.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.70.Df Liquid crystals

Resonant energy transfer within a colloidal nanocrystal polymer host system

Stefan Kaufmann, Thilo Stöferle, Nikolaj Moll, Rainer F. Mahrt, Ulli Scherf, Argiri Tsami, Dmitri V. Talapin, and Christopher B. Murray

Appl. Phys. Lett. 90, 071108 (2007); http://dx.doi.org/10.1063/1.2645592 (3 pages) | Cited 8 times

Online Publication Date: 15 February 2007

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The authors report on resonant energy transfer of nonequilibrium excitons in an amorphous polyfluorene donor CdSe/ZnS core-shell nanocrystal acceptor system. By time-resolved photoluminescence (PL) spectroscopy, they have investigated the PL decay behavior of the primarily excited polyfluorene in dependence of the concentration of the nanocrystals. The authors are able to demonstrate that the finite rise time of the PL transient monitored at the spectral position of the acceptor PL directly reflects the PL decay of the donor.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics

Role of buffer in organic solar cells using C60 as an acceptor

Q. L. Song, C. M. Li, M. L. Wang, X. Y. Sun, and X. Y. Hou

Appl. Phys. Lett. 90, 071109 (2007); http://dx.doi.org/10.1063/1.2695733 (3 pages) | Cited 31 times

Online Publication Date: 15 February 2007

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A thin buffer layer is indispensable for a high power conversion efficiency in an organic solar cell with fullerene (C60) as the acceptor. In present work, the authors proposed that the role of the buffer layer in an organic solar cell is to prohibit the electron transfer from metal to C60, and thus a desired built-in electric field can promote the free carrier collection. The built-in electric field in different organic solar cells with and without the thin C60 layer was studied by the transient photovoltage technique. The experimental results supported our proposal and indicated that the exciton blocking effect reported in the literature might not be the role of the buffer layer.
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84.60.Jt Photoelectric conversion

Pressure tuning the optical transmission properties of photonic band gap composites

Yurong Ying, Jiqiang Xia, and Stephen H. Foulger

Appl. Phys. Lett. 90, 071110 (2007); http://dx.doi.org/10.1063/1.2454656 (3 pages) | Cited 6 times

Online Publication Date: 16 February 2007

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A pressure cell was configured to allow the dynamic tuning of the transmission characteristics of a mechanochromic colloidally based photonic crystal. The rejection wavelength exhibited a 212 nm shift from 645 to 433 nm with an applied pressure of 20 kPa. At pressures greater than 5 kPa, the rejection wavelength shifted ∼ −8 nm for every incremental 1 kPa rise in pressure.
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42.70.Qs Photonic bandgap materials

Influences of resonant wavelengths on performances of microcavity organic light-emitting devices

Chun-Liang Lin, Han-Chieh Chang, Kun-Cheng Tien, and Chung-Chih Wu

Appl. Phys. Lett. 90, 071111 (2007); http://dx.doi.org/10.1063/1.2472541 (3 pages) | Cited 25 times

Online Publication Date: 16 February 2007

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In this letter, we investigate theoretically and experimentally the influences of resonant wavelengths on performances of microcavity organic light-emitting devices. Results show that by setting the normal-direction resonant wavelength around the peak wavelength of the intrinsic emission, one obtains the highest luminance enhancement along the normal direction and hardly detectable color shift with viewing angles, yet accompanied by highly directed emission. On the other hand, the highest enhancement ( ∼ 1.4 times) in external quantum efficiencies and the most uniform brightness distribution are obtained by setting the normal-direction resonant wavelength of 20–40 nm longer than the peak wavelength of the intrinsic emission, yet with noticeable color shift over viewing angles. Due to the trade-offs between different emission characteristics in choosing the resonant wavelength, the exact design of microcavity devices would depend on actual applications.
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85.60.Jb Light-emitting devices

Examination of the spatial and temporal field distributions of single-cycle terahertz pulses at a beam focus

Andreas Bitzer, Markus Walther, Andreas Kern, Stefan Gorenflo, and Hanspeter Helm

Appl. Phys. Lett. 90, 071112 (2007); http://dx.doi.org/10.1063/1.2472717 (3 pages) | Cited 4 times

Online Publication Date: 16 February 2007

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Measurements of spatially resolved beam profiles of single-cycle terahertz pulses are presented. In the approach here the terahertz beam is scanned over the stationary electro-optic detector using a gimbal-mounted mirror. A detailed study of the temporal- and frequency-dependent field in the region of the terahertz focus reveals field patterns which are dominated by diffraction and absorption. The observed field distribution is reproduced in model calculations. The exceptionally high signal to noise ratio and the high frequency and spatial resolution of the experiment here facilitate the observation of minute field distortions caused by the anomalous dispersion of absorbers in the beam path from the spatially resolved field pattern.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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Period multiplication and chaotic phenomena in atmospheric dielectric-barrier glow discharges

Y. H. Wang, Y. T. Zhang, D. Z. Wang, and M. G. Kong

Appl. Phys. Lett. 90, 071501 (2007); http://dx.doi.org/10.1063/1.2475831 (3 pages) | Cited 17 times

Online Publication Date: 12 February 2007

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In this letter, evidence of temporal plasma nonlinearity in which atmospheric dielectric-barrier discharges undergo period multiplication and chaos using a one-dimensional fluid model is reported. Under the conditions conducive for chaotic states, several frequency windows are identified in which period multiplication and secondary bifurcations are observed. Such time-domain nonlinearity is important for controlling instabilities in atmospheric glow discharges.
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52.80.Hc Glow; corona
52.25.Gj Fluctuation and chaos phenomena
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
05.45.Pq Numerical simulations of chaotic systems

Generation of high-power arbitrary-wave-form modulated inductively coupled plasmas for materials processing

Yasunori Tanaka, Yu Morishita, Shunsuke Fushie, Kyota Okunaga, and Yoshihiko Uesugi

Appl. Phys. Lett. 90, 071502 (2007); http://dx.doi.org/10.1063/1.2696885 (3 pages) | Cited 5 times

Online Publication Date: 15 February 2007

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An arbitrary-wave-form modulated induction thermal plasma (AMITP) system was developed using a high-power semiconductor high-frequency power supply. The modulated high-power plasma is a breakthrough technique for controlling the temperature and the radical density in high-density plasmas. The arbitrary-wave-form modulation of the coil current enables more detailed control of the temperature of the high-density plasmas than the pulse-amplitude modulation that has already been developed. The Ar AMITP with intentionally modulated coil current could be generated at a power of 10–15 kW. Results showed that the Ar excitation temperature between the specified excitation levels was changed intentionally according to the modulation control signal.
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52.50.Dg Plasma sources
52.77.Dq Plasma-based ion implantation and deposition
52.25.Fi Transport properties
52.75.Hn Plasma torches
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Effect of intense chirped pulses on the coherent phonon generation in Te

O. V. Misochko, T. Dekorsy, S. V. Andreev, V. O. Kompanets, Yu. A. Matveets, A. G. Stepanov, and S. V. Chekalin

Appl. Phys. Lett. 90, 071901 (2007); http://dx.doi.org/10.1063/1.2476306 (3 pages) | Cited 2 times

Online Publication Date: 12 February 2007

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The authors have studied the influence of chirped laser pulses on the coherent phonon generation in single crystal Te. They have shown that the pulse chirp affects the amplitude of coherent phonons with A1 symmetry in the case of intense excitation only. By varying the chirp of an intense exciting pulse, the authors demonstrated that negatively chirped pulses are almost twice more effective in the creation of lattice coherence than positively chirped pulses.
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78.47.-p Spectroscopy of solid state dynamics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
63.20.-e Phonons in crystal lattices

Emission of unidentified energy from growing ice crystals

XiaoFeng Shen

Appl. Phys. Lett. 90, 071902 (2007); http://dx.doi.org/10.1063/1.2472536 (3 pages)

Online Publication Date: 12 February 2007

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Power-compensated differential scanning calorimeter (DSC) was used to quantitatively measure the thermodynamic and kinetic course in the phase transition of water and gallium. When the media between the samples and the temperature sensor were changed, the ratio of the thermal energy given off by freezing water to that absorbed by melting ice was different. A type of unidentified energy was emitted from the growing ice crystals in supercooled water. The emission came off with greater part of latent energy released from the freezing water. Kinetic analysis of the DSC data further confirmed the above conclusion.
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65.40.G- Other thermodynamical quantities
64.70.D- Solid-liquid transitions
82.60.Cx Enthalpies of combustion, reaction, and formation

Room temperature green light emission from nonpolar cubic InGaN/GaN multi-quantum-wells

Shunfeng Li, Jörg Schörmann, Donat J. As, and Klaus Lischka

Appl. Phys. Lett. 90, 071903 (2007); http://dx.doi.org/10.1063/1.2475564 (3 pages) | Cited 12 times

Online Publication Date: 12 February 2007

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Cubic InGaN/GaN multi-quantum-wells (MQWs) with high structural and optical quality are achieved by utilizing freestanding 3C-SiC (001) substrates and optimizing InGaN quantum well growth. Superlattice peaks up to fifth order are clearly resolved in x-ray diffraction. Bright green room temperature photoluminescence (PL) from c-InxGa1−xN/GaN MQWs (x = 0.16) is observed. The full width at half maximum of the PL emission is about 240 meV at 300 K. The PL intensity increases with well thickness, prooving that polarization fields which can limit the performance of the wurtzite III-nitride based devices are absent. The diffusion length of excess carriers is about 17 nm.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Hs Quantum wells

Manipulation of strain relaxation in metamorphic heterostructures

I. Tångring, S. M. Wang, X. R. Zhu, A. Larsson, Z. H. Lai, and M. Sadeghi

Appl. Phys. Lett. 90, 071904 (2007); http://dx.doi.org/10.1063/1.2435609 (3 pages) | Cited 3 times

Online Publication Date: 12 February 2007

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The authors have discovered that high doping densities in an alloy graded InGaAs buffer have dramatic effects on strain relaxation dynamics and consequently surface and optical qualities in metamorphic heterostructures. Compared with undoped graded buffers, the use of Be doping significantly improves structural, surface, and optical qualities while the use of Si doping deteriorates all these properties. This discovery is significant for the realization of metamorphic optoelectronic devices.
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81.05.Ea III-V semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.S- Impurities in crystals
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Phase diagrams for growing ordered heteroepitaxial quantum dots and quantum rings by surface prepatterning

P. Liu, Y. W. Zhang, and C. Lu

Appl. Phys. Lett. 90, 071905 (2007); http://dx.doi.org/10.1063/1.2560981 (3 pages) | Cited 4 times

Online Publication Date: 13 February 2007

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Three-dimensional computer simulations are performed to obtain the phase diagrams for heteroepitaxially grown ordered quantum dots and quantum rings by surface prepatterning. Concave patterning in a squared array may lead to the formation of ordered dots, whereas convex patterning in a squared array may initially lead to the formation of ordered quantum rings, then a transition into quantum dots with further growth. The evolution of the surface chemical potential during growth explains the formation of the ordered surface structures.
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81.30.Dz Phase diagrams of other materials
68.65.Hb Quantum dots (patterned in quantum wells)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Fabrication of deeply undercut GaN-based microdisk structures on silicon platforms

S. Vicknesh, S. Tripathy, Vivian K. X. Lin, L. S. Wang, and S. J. Chua

Appl. Phys. Lett. 90, 071906 (2007); http://dx.doi.org/10.1063/1.2472558 (3 pages) | Cited 5 times

Online Publication Date: 13 February 2007

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The authors demonstrate the use of a dry releasing technique to achieve deeply undercut GaN-based microdisk structures supported by silicon platforms. Varying dimensions of microdisk structures on silicon posts with large air gaps are fabricated by a XeF2-based dry etching of the underlying silicon material. The residual stress variation in these microdisks is studied by high spectral resolution micro-Raman mapping. Such a fabrication technique may effectively improve the light extraction efficiency from GaN-based microdisk light emitting diodes on silicon substrates.
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81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.30.Fs III-V and II-VI semiconductors
62.20.-x Mechanical properties of solids

Exciton spin splitting in ultrathin InAs layers

Zheng Sun, Z. Y. Xu, Yang Ji, B. Q. Sun, B. R. Wang, S. S. Huang, and H. Q. Ni

Appl. Phys. Lett. 90, 071907 (2007); http://dx.doi.org/10.1063/1.2539600 (3 pages) | Cited 4 times

Online Publication Date: 14 February 2007

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Unique spin splitting behaviors in ultrathin InAs layers, which show very different spin splitting characteristics between the InAs monolayer (ML) and submonolayer (SML) have been observed. While distinct spin splitting is observed in an InAs ML, no visible spin splitting is found in a 1/3 ML InAs SML. In addition, the spin relaxation time in the 1/3 ML InAs is found to be much longer than that in the 1 ML sample. These results are in good agreement with the theoretical prediction that the interexcitonic exchange interaction plays a dominant role in energy splitting, while the intraexciton exchange interaction controls the spin relaxation.
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71.35.-y Excitons and related phenomena
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.70.Gm Exchange interactions
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Mechanism for strong yellow emission of Y3Al5O12:Ce3+ phosphor under electron irradiation for the application to field emission backlight units

Ho Seong Jang, Jong Hyuk Kang, Yu-Ho Won, Sora Lee, and Duk Young Jeon

Appl. Phys. Lett. 90, 071908 (2007); http://dx.doi.org/10.1063/1.2643064 (3 pages) | Cited 7 times

Online Publication Date: 14 February 2007

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This letter reports a strong yellow emission of Y3Al5O12:Ce3+ (YAG:Ce) mixed with ZnS:Ag,Cl under electron excitation. The penetration depths of electron of 1 keV and photon of 2.7 eV in YAG:Ce were estimated to be approximately 1450 Å and 4.65 mm, respectively. Deeper penetration of blue light from ZnS:Ag,Cl helps to excite a larger number of Ce3+ in a mixture (ZnS:Ag,Cl+YAG:Ce), and YAG:Ce showed strong yellow emission via both cathodoluminescence and photoluminescence. The mixture showed the brightness of 120.5% compared to R,G,B phosphor mixture. This mixture of two phosphors was applied to a carbon nanotube field emission backlight unit.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.55.-m Photoluminescence, properties and materials
79.70.+q Field emission, ionization, evaporation, and desorption

Cooling-rate induced softening in a Zr50Cu50 bulk metallic glass

Y. Liu, H. Bei, C. T. Liu, and E. P. George

Appl. Phys. Lett. 90, 071909 (2007); http://dx.doi.org/10.1063/1.2678909 (3 pages) | Cited 23 times

Online Publication Date: 15 February 2007

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Contrary to the cooling-rate induced hardening observed in crystalline metals, the authors report here an unexpected surface softening in rapidly solidified Zr50Cu50 bulk metallic glass. A soft layer ∼ 500 μm thick was detected near the surface with both hardness and elastic modulus increasing from the surface to the interior. To understand the reason for this, a correlation between cooling rate and defect concentration was derived. Defect concentration was found to increase as the cooling rate increased, suggesting that surface softening may be the result of freezing-in of excess defects, induced by a faster cooling rate near the surface compared to the interior.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness
62.20.D- Elasticity
68.35.Gy Mechanical properties; surface strains
81.30.Fb Solidification

Intersubband absorption in CdSe/ZnxCdyMg1−x−ySe self-assembled quantum dot multilayers

A. Shen, H. Lu, W. Charles, I. Yokomizo, M. C. Tamargo, K. J. Franz, C. Gmachl, S. K. Zhang, X. Zhou, R. R. Alfano, and H. C. Liu

Appl. Phys. Lett. 90, 071910 (2007); http://dx.doi.org/10.1063/1.2679783 (3 pages) | Cited 4 times

Online Publication Date: 15 February 2007

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The authors report the observation of intersubband absorption in multilayers of CdSe/ZnxCdyMg1−x−ySe self-assembled quantum dots. The samples were grown by molecular beam epitaxy on InP substrates. For samples with the CdSe dot layers doped with Cl and with the deposited CdSe equivalent layer thickness between 5.2 and 6.9 ML, peak absorption between 2.5 and 3.5 μm was observed. These materials are promising for intersubband devices operating in the mid- and near-infrared ranges.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.30.-j Infrared and Raman spectra
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Shock compression response of nanoiron powder compact

Chengda Dai, Daniel Eakins, Naresh Thadhani, and J. Ping Liu

Appl. Phys. Lett. 90, 071911 (2007); http://dx.doi.org/10.1063/1.2695522 (3 pages) | Cited 6 times

Online Publication Date: 15 February 2007

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The shock compression response of nano-Fe powder ( ∼ 25 nm) pressed to ∼ 35% theoretical maximum density was determined based on shock stress and wave velocity measurements using piezoelectric stress gauges. The obtained data show a discontinuity in shock wave velocity plotted against particle velocity and an inflexion in specific volume from compression to expansion with increasing shock stress. It is found that the Hugoniot of 25 nm Fe powder cannot be fully described using analytical models that are otherwise capable of predicting the Hugoniot of micron-sized powder or highly porous materials.
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62.50.-p High-pressure effects in solids and liquids
64.30.-t Equations of state of specific substances
62.25.-g Mechanical properties of nanoscale systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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