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25 Feb 2008

Volume 92, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 081101 (2008); http://dx.doi.org/10.1063/1.2883874 (3 pages)

Marcel W. Pruessner, Todd H. Stievater, and William S. Rabinovich
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In-plane microelectromechanical resonator with integrated Fabry–Pérot cavity

Marcel W. Pruessner, Todd H. Stievater, and William S. Rabinovich

Appl. Phys. Lett. 92, 081101 (2008); http://dx.doi.org/10.1063/1.2883874 (3 pages) | Cited 12 times

Online Publication Date: 25 February 2008

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A silicon-on-insulator in-plane microelectromechanical resonator coupled to a high-Q (Q ≈ 4,200), high finesse (FMax = 265) optical Fabry–Pérot microcavity is presented. The cavity utilizes high reflectance dry-etched silicon/air distributed Bragg reflectors. By suspending one of the Bragg mirrors to a microbridge resonator, the mirror can be displaced and the cavity is tuned. Using electrostatic actuation, bidirectional cavity tuning from −12.1 to +17.0 nm (29.1 nm total range) is demonstrated near 1601 nm wavelength. The device also enables measurement of thermal-mechanical noise with sensitivity better than 10 fm/Hz1/2 and may find application in high resolution sensors.
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07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.82.Et Waveguides, couplers, and arrays
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.79.Bh Lenses, prisms and mirrors
42.79.Ci Filters, zone plates, and polarizers

Temperature dependence of the gain profile for terahertz quantum cascade lasers

Rikard Nelander and Andreas Wacker

Appl. Phys. Lett. 92, 081102 (2008); http://dx.doi.org/10.1063/1.2884686 (3 pages) | Cited 30 times

Online Publication Date: 25 February 2008

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We study the rapid decrease of peak gain in resonant-phonon terahertz quantum cascade lasers with increasing temperature. The effect of various microscopic scattering processes on the gain profile as a function of temperature is discussed. We argue that increased broadening, primarily due to increased impurity scattering, and not diminishing population inversion, is the main reason for the reduction of peak gain.
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42.55.Px Semiconductor lasers; laser diodes
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Near-infrared waveguide-based nickel silicide Schottky-barrier photodetector for optical communications

Shiyang Zhu, M. B. Yu, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 92, 081103 (2008); http://dx.doi.org/10.1063/1.2885089 (3 pages) | Cited 20 times

Online Publication Date: 25 February 2008

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Integrated silicon-on-insulator waveguide-based silicide Schottky-barrier photodetectors were fabricated using low-cost standard Si complementary metal-oxide-semiconductor processing technology. The thin epitaxial NiSi2 layer formed by solid-state Ti-interlayer mediated epitaxy on the top of Si-waveguide absorbs light propagating through the waveguide effectively and exhibits excellent rectifying property on both p-Si and n-Si. NiSi2/p-Si detectors with tapered geometry demonstrate dark current of ∼ 3.0 nA at room temperature, responsivity of ∼ 4.6 mA/W at wavelengths ranging from 1520 to 1620 nm, and 3 dB bandwidth of ∼ 2.0 GHz. The approaches for further improvement in responsivity are addressed.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.30.Tv Field effect devices

Eu2+–Mn2+ phosphor saturation in 5 mm light emitting diode lamps

A. A. Setlur, J. J. Shiang, and U. Happek

Appl. Phys. Lett. 92, 081104 (2008); http://dx.doi.org/10.1063/1.2885093 (3 pages) | Cited 27 times

Online Publication Date: 25 February 2008

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This letter reports on phosphor quenching by saturation, a sublinear phosphor response with excitation intensity, in light emitting diode (LED) packages using 405 nm LEDs and Ca5(PO4)3Cl:Eu2+,Mn2+ phosphors. This saturation is due to the high light flux incident on the phosphors in these LED packages and the slow radiative relaxation rate of Mn2+. Apart from known saturation processes of Mn2+ ground state depletion and energy transfer between excited Mn2+ ions, an additional quenching pathway, Eu2+→Mn2+ (excited) energy transfer, is taken into account to quantitatively fit both the efficiency under pulsed operation and the time-resolved luminescence of Ca5(PO4)3Cl:Eu2+,Mn2+.
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85.60.Jb Light-emitting devices

Raman gain from waveguides inscribed in KGd(WO4)2 by high repetition rate femtosecond laser

S. M. Eaton, C. A. Merchant, R. Iyer, A. J. Zilkie, A. S. Helmy, J. S. Aitchison, P. R. Herman, D. Kraemer, R. J. D. Miller, C. Hnatovsky, and R. S. Taylor

Appl. Phys. Lett. 92, 081105 (2008); http://dx.doi.org/10.1063/1.2884188 (3 pages) | Cited 14 times

Online Publication Date: 26 February 2008

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We report the formation of waveguides in Raman-active KGd(WO4)2 with a focused, high repetition rate femtosecond laser. Parallel guiding regions, formed to either side of the laser-induced damage track, supported TE and TM modes that coupled efficiently to optical fiber at telecom wavelengths. Micro-Raman spectroscopy of the guiding regions revealed the preservation of the characteristic 768 and 901 cm−1 Raman mode intensities. Raman gain with 6% efficiency was demonstrated for the 768 cm−1 Raman line by pumping the waveguide with an infrared 80 ps source, the first time Raman gain has been reported in laser formed waveguides.
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42.62.-b Laser applications
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques

Investigation of Pr3+ as a sensitizer in quantum-cutting fluoride phosphors

Te-Ju Lee, Li-Yang Luo, Bing-Ming Cheng, Wei-Guang Diau, and Teng-Ming Chen

Appl. Phys. Lett. 92, 081106 (2008); http://dx.doi.org/10.1063/1.2884690 (3 pages) | Cited 13 times

Online Publication Date: 26 February 2008

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A quantum-cutting (QC) phosphor K2GdF5:Eu3+ shows poor optical absorption and a theoretical quantum efficiency (QE) of 107% in the ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectral ranges. Pr3+ was codoped as a sensitizer in K2GdF5:Eu3+, thus increasing the absorption in the UV and VUV spectral regions; the theoretical QE of K2GdF5:Eu3+,Pr3+ was increased to 138%. The spectra indicate that the possible mechanisms of QC and energy transfer differ from those of phosphors containing the Gd3+–Eu3+ couple. Temporally resolved measurements of fluorescence decay confirm the proposed QC mechanism for the phosphor containing the Gd3+–Eu3+,Pr3+ system.
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78.55.Hx Other solid inorganic materials
78.40.Ha Other nonmetallic inorganics

Monolithic InGaN-based white light-emitting diodes with blue, green, and amber emissions

Sung-Nam Lee, H. S. Paek, H. Kim, T. Jang, and Y. Park

Appl. Phys. Lett. 92, 081107 (2008); http://dx.doi.org/10.1063/1.2887884 (3 pages) | Cited 4 times

Online Publication Date: 27 February 2008

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We demonstrated a monolithic white light-emitting diodes (LEDs) epitaxial structure with blue, green, and amber emissions by introducing the blue InGaN/GaN five quantum wells (QWs) and InGaN/GaN single quantum well (SQW) with In-phase separated green/amber emissions as an active layer. Three wavelength emissions were developed by increasing the thickness of InGaN SQW grown on blue InGaN five QWs. From high resolution transmission electron microscope, In-phase separation was clearly observed in a 3.5-nm-thick InGaN SQW. In-phase separation would be generated by the spinodal decomposition which was promoted by the composition pulling effect related to the increment of well thickness. Therefore, white lighting LEDs with three wavelengths for blue emission from InGaN/GaN five QWs and green/amber emissions were achieved by the In-phase separation in InGaN SQW.
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85.60.Jb Light-emitting devices

Near-field optical trapping with an ultrashort pulsed laser beam

Smitha Kuriakose, Dru Morrish, Xiaosong Gan, James W. M. Chon, Kishan Dholakia, and Min Gu

Appl. Phys. Lett. 92, 081108 (2008); http://dx.doi.org/10.1063/1.2888771 (3 pages) | Cited 5 times

Online Publication Date: 28 February 2008

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We report the focused evanescent optical trapping of nonfluorescent and fluorescent dielectric microspheres using a femtosecond laser. The experiment confirms that the trapping efficiency increases with the size of the particles. As a result, a pulsed laser has been used to trap particles in the Mie regime and to excite whispering gallery modes in them. The excitation of whispering gallery modes in a near-field femtosecond trap shows a significant suppression of the two-photon fluorescence background with an improvement of the photon storage factor by 46%, as compared to far-field two-photon excitation.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift

Terahertz wave generation from a dc-biased multimode laser

Sylwester Latkowski, Frederic Surre, and Pascal Landais

Appl. Phys. Lett. 92, 081109 (2008); http://dx.doi.org/10.1063/1.2884525 (3 pages) | Cited 4 times

Online Publication Date: 28 February 2008

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We present results achieved in the generation of terahertz wave by a semiconductor laser. It is a Fabry–Pérot based device with shallow grooves implemented on its p-side to engineer the longitudinal mode spectrum. The laser is dc-biased and temperature controlled at 298 K. The main two modes are separated by 3 nm at 1550 nm with a side-mode-suppression ratio of 25 dB. Using a frequency resolved optical gating, evidence of mode beating at 373 GHz is observed. With a bolometer interfaced to a Fourier transform interferometer, the second harmonic signal is measured at 690 GHz.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Dispersive gain and loss in midinfrared quantum cascade laser

D. G. Revin, M. R. Soulby, J. W. Cockburn, Q. Yang, C. Manz, and J. Wagner

Appl. Phys. Lett. 92, 081110 (2008); http://dx.doi.org/10.1063/1.2884699 (3 pages) | Cited 11 times

Online Publication Date: 28 February 2008

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We report the measurements of dispersive gain (simultaneous coexistence of gain and losses on a single intersubband transition) in a quantum cascade laser. Broadband transmission spectra through the waveguide of a λ ∼ 4.7 μm In0.53Ga0.47As/AlAs0.56Sb0.44/InP quantum cascade laser have been studied at a bias below laser threshold and at different temperatures. For a certain range of current, and at temperatures higher than about 150 K, the transmission spectra show clear dispersive gain/loss behavior with the possibility for intersubband gain to be observed even without global population inversion between laser levels.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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Laser-induced breakdown spectroscopy in reactive flows of hydrocarbon-air mixtures

Amalia Michalakou, Polychronis Stavropoulos, and Stelios Couris

Appl. Phys. Lett. 92, 081501 (2008); http://dx.doi.org/10.1063/1.2839378 (3 pages) | Cited 7 times

Online Publication Date: 25 February 2008

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Laser-induced breakdown spectroscopy is used for the determination of the local equivalence ratio (i.e., the ratio of the actual fuel-to-oxidizer mass over the ratio of the fuel-to-oxidizer mass at stoichiometry) in different methane-, ethylene-, and propane-air mixtures. In particular, it is shown that the ratio of the intensities of the atomic spectral lines of H, C, and O, emitted from a laser-induced spark in the gaseous mixture, can be used for the rapid and accurate determination of the local equivalence ratio.
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47.70.-n Reactive and radiative flows
51.70.+f Optical and dielectric properties

An 11 cm long atmospheric pressure cold plasma plume for applications of plasma medicine

XinPei Lu, ZhongHe Jiang, Qing Xiong, ZhiYuan Tang, XiWei Hu, and Yuan Pan

Appl. Phys. Lett. 92, 081502 (2008); http://dx.doi.org/10.1063/1.2883945 (2 pages) | Cited 50 times

Online Publication Date: 26 February 2008

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In this letter, a room temperature atmospheric pressure plasma jet device is reported. The high voltage electrode of the device is covered by a quartz tube with one end closed. The device, which is driven by a kilohertz ac power supply, is capable of generating a plasma plume up to 11 cm long in the surrounding room air. The rotational and vibrational temperatures of the plasma plume are 300 and 2300 K, respectively. A simple electrical model shows that, when the plasma plume is contacted with a human, the voltage drop on the human is less than 66 V for applied voltage of 5 kV (rms).
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87.80.-y Biophysical techniques (research methods)
52.77.-j Plasma applications
52.75.-d Plasma devices

Nonequilibrium atmospheric pressure plasma with ultrahigh electron density and high performance for glass surface cleaning

Masahiro Iwasaki, Hirotoshi Inui, Yuto Matsudaira, Hiroyuki Kano, Naofumi Yoshida, Masafumi Ito, and Masaru Hori

Appl. Phys. Lett. 92, 081503 (2008); http://dx.doi.org/10.1063/1.2885084 (3 pages) | Cited 17 times

Online Publication Date: 26 February 2008

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We produced a nonequilibrium atmospheric pressure plasma by applying an alternative current between two electrodes. The gas temperature and electron density were evaluated using optical emission spectroscopy. It was found that the plasma had gas temperatures from 1800 to 2150 K and ultrahigh electron densities in the order of 1016 cm−3. A remarkably high oxygen radical concentration of 1.6×1015 cm−3 was obtained at a 1% O2/Ar gas flow rate of 15 slm (standard liters per minute). Contact angles below 10° were obtained in the process of glass cleaning with a plasma exposure time of 23 ms.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)

A concept of ferroelectric microparticle propulsion thruster

D. Yarmolich, V. Vekselman, and Ya. E. Krasik

Appl. Phys. Lett. 92, 081504 (2008); http://dx.doi.org/10.1063/1.2888955 (3 pages) | Cited 5 times

Online Publication Date: 28 February 2008

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A space propulsion concept using charged ferroelectric microparticles as a propellant is suggested. The measured ferroelectric plasma source thrust, produced mainly by microparticles emission, reaches ∼ 9×10−4 N. The obtained trajectories of microparticles demonstrate that the majority of the microparticles are positively charged, which permits further improvement of the thruster.
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52.75.Di Ion and plasma propulsion
52.50.Dg Plasma sources

Acceleration gradient of a plasma wakefield accelerator

Han S. Uhm

Appl. Phys. Lett. 92, 081505 (2008); http://dx.doi.org/10.1063/1.2887877 (3 pages) | Cited 3 times

Online Publication Date: 28 February 2008

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The phase velocity of the wakefield waves is identical to the electron beam velocity. A theoretical analysis indicates that the acceleration gradient of the wakefield accelerator normalized by the wave breaking amplitude is K0(ξ)/K1(ξ), where K0(ξ) and K1(ξ) are the modified Bessel functions of the second kind of order zero and one, respectively and ξ is the beam parameter representing the beam intensity. It is also shown that the beam density must be considerably higher than the diffuse plasma density for the large radial velocity of plasma electrons that are required for a high acceleration gradient.
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41.75.Jv Laser-driven acceleration
29.20.Ej Linear accelerators
52.38.Kd Laser-plasma acceleration of electrons and ions
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Application of quantum cascade lasers in studies of low-pressure plasmas: Characterization of rapid passage effects on density and temperature measurements

J. H. van Helden, S. J. Horrocks, and G. A. D. Ritchie

Appl. Phys. Lett. 92, 081506 (2008); http://dx.doi.org/10.1063/1.2885725 (3 pages) | Cited 9 times

Online Publication Date: 29 February 2008

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The application of quantum cascade lasers in the intrapulse operation mode for low-pressure plasma spectroscopy is hampered by the observation of rapid passage effects, leading to lower quantitative accuracy. We demonstrate that accurate densities and rotational temperatures of CH4 within a CH4 plasma can be obtained by characterizing the rapid passage effects in gas phase conditions prior to carrying out the plasma measurements. Furthermore, we show that the ratios of the integrated absorption of two transitions are not affected by the rapid passage effect and, thus, rotational temperatures of species can be obtained.
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52.25.-b Plasma properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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First-principles calculations of elastic properties of Cu3Sn superstructure

Jiunn Chen, Yi-Shao Lai, Chung-Yuan Ren, and Di-Jing Huang

Appl. Phys. Lett. 92, 081901 (2008); http://dx.doi.org/10.1063/1.2884685 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2008

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We report the elastic properties of Cu3Sn superstructure based on first-principles calculations. Polycrystalline Young’s modulus and Poisson’s ratio are deduced from the calculated elastic stiffness. The calculations of electronic structures with the principal strains along different directions unravel the electronic nature of anisotropic elasticity of Cu3Sn. Weak Sn–Cu bonding in Cu3Sn suggests that Sn atoms are the dominant diffusion species, revealing the mechanism of vacancy formation within the Cu3Sn superstructure.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
71.15.-m Methods of electronic structure calculations
71.20.Be Transition metals and alloys
61.72.jd Vacancies
66.30.-h Diffusion in solids

Nonlinear optical absorption and reflection of single wall carbon nanotube thin films by Z-scan technique

Daisuke Shimamoto, Takaaki Sakurai, Minoru Itoh, Yoong Ahm Kim, Takuya Hayashi, Morinobu Endo, and Mauricio Terrones

Appl. Phys. Lett. 92, 081902 (2008); http://dx.doi.org/10.1063/1.2884695 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2008

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Both the nonlinear optical transmission and reflection characteristics of HiPco-based single wall carbon nanotube (SWNT) thin films are studied by using the Z-scan method with femtosecond laser pulses at a wavelength of 1.46 μm. The nonlinear absorption coefficient and nonlinear refractive index are obtained as (5.4±2.0)×10−7 cm/W and (1.1±0.5)×10−11 cm2/W, respectively, which are considerably greater than those of other optical materials. This large optical nonlinearity is ascribed to (a) homogeneously deposited thin nanotube film on optically transparent barium fluoride, (b) just-resonant excitation condition, and (c) intrinsic saturable absorption feature of SWNTs.
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78.66.Tr Fullerenes and related materials
78.67.Ch Nanotubes
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Wc Optical coatings
81.16.Mk Laser-assisted deposition

Tougher ultrafine grain Cu via high-angle grain boundaries and low dislocation density

Y. H. Zhao, J. F. Bingert, Y. T. Zhu, X. Z. Liao, R. Z. Valiev, Z. Horita, T. G. Langdon, Y. Z. Zhou, and E. J. Lavernia

Appl. Phys. Lett. 92, 081903 (2008); http://dx.doi.org/10.1063/1.2870014 (3 pages) | Cited 47 times

Online Publication Date: 25 February 2008

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Although there are a few isolated examples of excellent strength and ductility in single-phase metals with ultrafine grained (UFG) structures, the precise role of different microstructural features responsible for these results is not fully understood. Here, we demonstrate that a large fraction of high-angle grain boundaries and a low dislocation density may significantly improve the toughness and uniform elongation of UFG Cu by increasing its strain-hardening rate without any concomitant sacrifice in its yield strength. Our study provides a strategy for synthesizing tough UFG materials.
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61.72.Mm Grain and twin boundaries
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.fk Ductility, malleability
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
62.20.fg Shape-memory effect; yield stress; superelasticity

Composition dependence of dielectric function in ferroelectric BaCoxTi1−xO3 films grown on quartz substrates by transmittance spectra

Z. G. Hu, Y. W. Li, M. Zhu, Z. Q. Zhu, and J. H. Chu

Appl. Phys. Lett. 92, 081904 (2008); http://dx.doi.org/10.1063/1.2870094 (3 pages) | Cited 11 times

Online Publication Date: 25 February 2008

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Near-infrared-ultraviolet optical properties of BaCoxTi1−xO3 (BCT) (x from 1.0% to 10%) films have been investigated by the transmittance spectra. The dispersion functions in the photon energy range of 1.24–6.2 eV have been extracted by fitting the experimental data with Adachi’s model. It was found that the oscillator and dispersion energies linearly increase with the Co composition and the maximum optical transition occurs near the energy range of 4.3–5.0 eV for the BCT materials. The absorption coefficient at the visible region linearly increases with the composition due to grain boundaries and disorder induced band tail into the forbidden gap.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.66.Nk Insulators

Misfit dislocation blocking by dilute nitride intermediate layers

J. Schöne, E. Spiecker, F. Dimroth, A. W. Bett, and W. Jäger

Appl. Phys. Lett. 92, 081905 (2008); http://dx.doi.org/10.1063/1.2888750 (3 pages) | Cited 2 times

Online Publication Date: 26 February 2008

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Defect formation and strain relaxation in step-graded GaAs1−xNx and GaAs1−yPy buffer structures grown by metal-organic vapor phase epitaxy on GaAs(001) substrates have been investigated by transmission electron microscopy and high-resolution x-ray diffractometry. From the comparison of different buffer concepts, it is shown that, by introducing intermediate GaAs1−xNx layers with N concentrations x ≥ 2% into a GaAs1−xPx buffer structure, dislocation formation and strain relaxation are effectively suppressed during subsequent growth of layers with tensile strains. It is argued that a similar concept, however, modified by using layers of differing alloy composition, can be used for layer systems with compressive strains. Appropriately alloyed intermediate dilute nitride layers appear to offer a powerful concept for engineering defect distributions and layer strain in semiconductor technology.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.60.Bs Mechanical and acoustical properties

Single-photon emission from single quantum dots in a hybrid pillar microcavity

Takao Yamaguchi, Takehiko Tawara, Hidehiko Kamada, Hideki Gotoh, Hiroshi Okamoto, Hidetoshi Nakano, and Osamu Mikami

Appl. Phys. Lett. 92, 081906 (2008); http://dx.doi.org/10.1063/1.2840711 (3 pages) | Cited 4 times

Online Publication Date: 26 February 2008

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We demonstrate 1240 nm single-photon emissions from InAs quantum dots (QDs) embedded in a hybrid pillar microcavity consisting of dielectric and semiconductor distributed Bragg reflectors. The QDs are grown by metal organic chemical vapor deposition. Discrete emission lines corresponding to isolated QDs in the hybrid pillar are observed with a spontaneous emission rate enhanced by a factor of 2. Single-photon emissions are confirmed by antibunching in a second-order photon correlation function.
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42.79.Dj Gratings
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Magnetic properties of carbon nanotube terminally connecting metal molecular complexes

M. S. Si and D. S. Xue

Appl. Phys. Lett. 92, 081907 (2008); http://dx.doi.org/10.1063/1.2883964 (3 pages) | Cited 1 time

Online Publication Date: 26 February 2008

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Carbon nanotubes are good candidates to promote communication between paramagnetic centers at large distances through a highly delocalized π system. Our research uses ab initio methods to predict the equilibrium configuration and magnetic properties of dinuclear iron metal molecular complexes connected by carbon nanotubes. The results show that the presence of surprisingly strong exchange coupling at very large distances for this kind of system and the coupling is ferromagnetic.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
71.70.Gm Exchange interactions
75.50.Xx Molecular magnets
71.15.-m Methods of electronic structure calculations
75.30.Et Exchange and superexchange interactions

Saturation of surface roughening instabilities by plastic deformation

Michael Andersen, Nasr Ghoniem, and Akiyuki Takahashi

Appl. Phys. Lett. 92, 081908 (2008); http://dx.doi.org/10.1063/1.2842412 (3 pages)

Online Publication Date: 26 February 2008

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Surface roughening instabilities driven by a competition between elastic and surface energy contributions are shown to be saturated by plastic energy dissipation. It is shown that these morphological instabilities do not experience unbounded growth as predicted by consideration of elastic energy alone and that their growth is limited by dislocation emission from higher curvature grooves.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Lm Deformation, plasticity, and creep
68.35.Md Surface thermodynamics, surface energies
62.20.F- Deformation and plasticity

Composition dependence of the phonon strain shift coefficients of SiGe alloys revisited

J. S. Reparaz, A. Bernardi, A. R. Goñi, M. I. Alonso, and M. Garriga

Appl. Phys. Lett. 92, 081909 (2008); http://dx.doi.org/10.1063/1.2884526 (3 pages) | Cited 17 times

Online Publication Date: 26 February 2008

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By combining Raman scattering from the cleaved edge and under hydrostatic pressure, we have accurately determined the tetragonal phonon deformation potentials of strained Si1−xGex alloys in the entire compositional range for the Ge-like, Si-like, and mixed Si–Ge optical modes. A known biaxial strain is induced on thin alloy layers by pseudomorphic epitaxial growth on silicon and subsequent capping. We also determine the strain shift coefficient of the three modes, which are essentially independent of Ge content between 0.4 and 1. This is key information for an effective use of Raman scattering as strain-characterization tool in SiGe nanostructures.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.50.Gh Disordered crystalline alloys
62.50.-p High-pressure effects in solids and liquids
78.30.Am Elemental semiconductors and insulators
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