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25 Feb 2008

Volume 92, Issue 8, Articles (08xxxx)

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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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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

Nonlinear relaxation of zero-dimension-trapped microcavity polaritons

Ounsi El Daif, Gaël Nardin, Taofiq K. Paraïso, Augustin Baas, Maxime Richard, J.-P. Brantut, Thierry Guillet, Francois Morier-Genoud, and Benoit Deveaud-Plédran

Appl. Phys. Lett. 92, 081910 (2008); http://dx.doi.org/10.1063/1.2885018 (3 pages) | Cited 5 times

Online Publication Date: 26 February 2008

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We study the emission properties of confined polariton states in shallow zero-dimensional traps under nonresonant excitation. We evidence several relaxation regimes. For slightly negative photon-exciton detuning, we observe a nonlinear increase of the emission intensity, characteristic of carrier-carrier scattering assisted relaxation under strong-coupling regime. This demonstrates the efficient relaxation toward a confined state of the system. For slightly positive detuning, we observe the transition from strong to weak coupling regime and then to single-mode lasing.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors

Impact of annealing on morphology and ferromagnetism of ZnO nanorods

Zijie Yan, Yanwei Ma, Dongliang Wang, Junhong Wang, Zhaoshun Gao, Lei Wang, Peng Yu, and Tao Song

Appl. Phys. Lett. 92, 081911 (2008); http://dx.doi.org/10.1063/1.2887906 (3 pages) | Cited 30 times

Online Publication Date: 27 February 2008

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Room temperature ferromagnetism has been observed in ZnO nanorods prepared by hydrothermal method. Saturation magnetization of ∼ 0.004 emu/g was measured in the nanorods with diameters of ∼ 10 nm and lengths of below 100 nm, and the magnetization reduced with the increase of the size. Annealing of the samples at 900 °C in air completely transformed the nanorods into twinning structures and weakened the magnetizations. The mechanism of morphology transformation was discussed. Analysis indicates that the interstitial zinc at the surface may contribute to the ferromagnetism in ZnO nanorods.
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75.75.-c Magnetic properties of nanostructures
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Nt Magnetic annealing and temperature-hysteresis effects
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Measuring the interface stress of nanocrystalline iron

Patrik Zimmer and Rainer Birringer

Appl. Phys. Lett. 92, 081912 (2008); http://dx.doi.org/10.1063/1.2888751 (3 pages) | Cited 5 times

Online Publication Date: 27 February 2008

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With the ongoing miniaturization of structures and devices down to the nanometer scale, we notice concomitant escalation of atoms located at surfaces or interfaces. Presence of surfaces and interfaces generates stresses in nanoscale structures that can easily exceed 1 GPa. We developed and applied a method for measuring the absolute value of grain-boundary stress. Since investigation of grain-boundary stress as well as phase-boundary stress of body-centered-cubic materials has not been addressed so far, we aimed at determining the grain-boundary stress f of nanocrystalline Fe. By means of x-ray diffraction measurements of average grain size and residual-strain-free lattice spacings, we deduced a value of f = 1.1±0.2 N/m.
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61.46.Hk Nanocrystals
61.72.Mm Grain and twin boundaries
68.35.Gy Mechanical properties; surface strains

Highly coherent thermal emission obtained by plasmonic bandgap structures

Gabriel Biener, Nir Dahan, Avi Niv, Vladimir Kleiner, and Erez Hasman

Appl. Phys. Lett. 92, 081913 (2008); http://dx.doi.org/10.1063/1.2883948 (3 pages) | Cited 10 times

Online Publication Date: 27 February 2008

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We demonstrate an extraordinary quasimonochromatic thermal emission with high spatial coherence length (lc>2400λ) and a quality factor Q = 2320 at radiation frequencies that are much smaller than the plasma frequency of metal (ω≪ωp). This emission is achieved by forming a plasmonic bandgap, which is obtained by a periodic structure on a metallic surface. Such a structure modifies the dynamics of the surface wave and results in a van Hove singularity [ Van Hove, Phys. Rev. 89, 1189 (1953) ] in the spectral density of states while maintaining a large coherence length.
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79.40.+z Thermionic emission
78.68.+m Optical properties of surfaces
42.72.Ai Infrared sources
42.25.Kb Coherence

Nanograin nucleation initiated by intergrain sliding and/or lattice slip in nanomaterials

S. V. Bobylev and I. A. Ovid’ko

Appl. Phys. Lett. 92, 081914 (2008); http://dx.doi.org/10.1063/1.2885069 (3 pages) | Cited 6 times

Online Publication Date: 27 February 2008

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Stress-induced nucleation of nanoscale grains (nanograins) in deformed nanocrystalline metals and ceramics is theoretically described as a process initiated by intergrain sliding and/or lattice slip. The nanograin nucleation occurs through splitting and migration of grain boundaries containing disclination dipoles produced by intergrain sliding and/or lattice slip. It is shown that the nanograin nucleation is energetically favorable in mechanically loaded nanocrystalline Al and α-Al2O3 in certain ranges of their parameters and the external stress level.
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61.72.Mm Grain and twin boundaries
66.30.-h Diffusion in solids
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
61.72.Bb Theories and models of crystal defects

Phosphorescence characteristics of ruthenium complex as an optical transducer for biosensors

Sean B. Pieper, Santano P. Mestas, Kevin L. Lear, Zhong Zhong, and Kenneth F. Reardon

Appl. Phys. Lett. 92, 081915 (2008); http://dx.doi.org/10.1063/1.2885082 (3 pages) | Cited 4 times

Online Publication Date: 27 February 2008

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The saturation intensity, photobleaching, and decay lifetime of tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) chloride [Ru(dpp)3] are investigated. The saturation point was estimated to be 11.8 W/cm2 and subsequently measured to be 11.5 W/cm2. Photobleaching of this dye at a peak absorbance equivalence of 6.6 W/cm2 is observed over 2 days resulting in a 14% decrease in intensity within 20 min and 47% decrease over two days yielding an unacceptably short operational lifetime under saturated conditions. Lower optical excitation levels in the application of oxygen sensitive fluorescence type fiber optic enzymatic biosensor systems are required and yield acceptable photobleaching rates.
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87.85.fk Biosensors
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.81.Pa Sensors, gyros
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