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12 Jan 2009

Volume 94, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 022101 (2009); http://dx.doi.org/10.1063/1.3065067 (3 pages)

Hong Li and Qing Zhang
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Annealing effects on faceting of InAs/GaAs(001) quantum dots

E. Placidi, A. Della Pia, and F. Arciprete

Appl. Phys. Lett. 94, 021901 (2009); http://dx.doi.org/10.1063/1.3056654 (3 pages) | Cited 12 times

Online Publication Date: 12 January 2009

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The aspect ratio and faceting evolution of quantum dots grown at 500 °C were studied as a function of postgrowth annealing temperature. We show that faceting and aspect ratio strictly depend on growth conditions. The evolution toward {136} and {137} facets is kinetically limited and occurs under different experimental conditions. Furthermore long annealing procedures lead to the occurrence of low aspect ratio domes different from those forming at higher growth temperatures.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.72.Cc Kinetics of defect formation and annealing
81.05.Ea III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments

Nonlinear optical properties of graphene oxide in nanosecond and picosecond regimes

Zhibo Liu, Yan Wang, Xiaoliang Zhang, Yanfei Xu, Yongsheng Chen, and Jianguo Tian

Appl. Phys. Lett. 94, 021902 (2009); http://dx.doi.org/10.1063/1.3068498 (3 pages) | Cited 35 times

Online Publication Date: 12 January 2009

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The nonlinear optical properties of graphene oxide (GO) were investigated at 532 nm in nanosecond and picosecond regimes. Results show that two-photon absorption dominates nonlinear absorption process of GO in the case of picosecond pulses, while excited state nonlinearities play an important role in the case of nanosecond pulses. Additionally, we compared nonlinear optical properties of three different dimensional carbon-based materials (two-dimensional graphene, one-dimensional carbon nanotube, and zero-dimensional fullerene) in nanosecond and picosecond regimes, respectively. The nonlinear mechanism of GO is distinctly different from nonlinear scattering of carbon nanotube and excited state nonlinearity of fullerene.
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42.65.-k Nonlinear optics
81.05.ub Fullerenes and related materials

Dynamics of gold nanoparticles in a polymer melt

Christopher A. Grabowski, Bijoy Adhikary, and Ashis Mukhopadhyay

Appl. Phys. Lett. 94, 021903 (2009); http://dx.doi.org/10.1063/1.3070533 (3 pages) | Cited 9 times

Online Publication Date: 12 January 2009

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Gold nanoparticles are used as a luminescent contrast agent to study size-dependent dynamics in polymer matrix. The experiments measured the diffusion coefficient of particles in poly(butyl methacrylate) melt by tracking their motion within a diffraction-limited focus of a laser with 150 fs pulses at 800 nm. Our results indicate that for unentangled polymers, when the particle radius (R) is greater than the gyration radius (Rg) of the chain, the Stokes–Einstein relation can accurately predict particle dynamics. For longer chains, if the entanglement mesh length is larger than R, the particle diffuses ∼ 250 times faster than predicted by the Stokes–Einstein relation.
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66.10.C- Diffusion and thermal diffusion
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Investigation of interfacial interaction and structural transition for epoxy/nanotube composites by positron annihilation lifetime spectroscopy

Wei Zhou, Junjun Wang, Zhenli Gong, Jing Gong, Ning Qi, and Bo Wang

Appl. Phys. Lett. 94, 021904 (2009); http://dx.doi.org/10.1063/1.3067873 (3 pages) | Cited 6 times

Online Publication Date: 14 January 2009

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Positron annihilation lifetime spectroscopy was employed to study the effect of amine modification on interfacial interaction and structural transition for epoxy/multiwalled carbon nanotube (MWNT) composites. Temperature dependence of orthopositronium lifetimes suggests that sample with amine-modified MWNTs possesses the highest glass transition temperature compared with unmodified samples and neat epoxy resin, which indicates that stronger interfacial interactions exist between epoxy matrix and amine-modified MWNTs, as a result of the covalent bonds and other weak forces. This is testified by interaction parameter β calculated in terms of the positron annihilation parameter.
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64.70.K- Solid-solid transitions
78.70.Bj Positron annihilation

Anomalous nonlinearity parameters of solids at low acoustic drive amplitudes

William T. Yost and John H. Cantrell

Appl. Phys. Lett. 94, 021905 (2009); http://dx.doi.org/10.1063/1.3068490 (3 pages) | Cited 4 times

Online Publication Date: 14 January 2009

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Measurements of the nonlinearity parameter β as a function of acoustic drive amplitude are reported for polycrystalline aluminum alloy 2024, IN100 nickel-base superalloy, and monocrystalline Al[110]. The measurements show that the variations in β reported by [ Barnard, Appl. Phys. Lett. 74, 2447 (1999) ] result from the influence of the Peierls barrier on dislocation motion in the material. The dislocation motion is responsible not only for the hooklike behavior at the low drive amplitudes reported by Barnard but also for an oscillatory dependence of β at larger drive amplitudes not previously reported.
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62.65.+k Acoustical properties of solids
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

The energetics of dislocations accelerating and decelerating through the shear-wave speed barrier

Xanthippi Markenscoff and Surong Huang

Appl. Phys. Lett. 94, 021906 (2009); http://dx.doi.org/10.1063/1.3072351 (3 pages) | Cited 2 times

Online Publication Date: 14 January 2009

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The question of whether a dislocation can accelerate through the shear-wave speed “barrier” is addressed by analyzing the transient motion at the instant when the velocity equals the shear-wave speed in the presence of acceleration. The stresses carried by the forming Mach wave fronts depend on the acceleration at this instant, and the energy required to push the dislocation through the shear-wave speed barrier is determined by means of the “contour-independent” dynamic J integral, which defines the self-force on a moving defect, and is obtained as a function of the acceleration as it crosses the barrier. For decelerating motion through the shear-wave speed barrier this energy is released as dissipation.
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62.30.+d Mechanical and elastic waves; vibrations
61.72.Bb Theories and models of crystal defects

Paradoxical phenomena between the homogeneous and inhomogeneous deformations of metallic glasses

Kyoung-Won Park, Chang-Myeon Lee, Mi-Rim Lee, Eric Fleury, Michael L. Falk, and Jae-Chul Lee

Appl. Phys. Lett. 94, 021907 (2009); http://dx.doi.org/10.1063/1.3064920 (3 pages) | Cited 3 times

Online Publication Date: 15 January 2009

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Experiments in binary alloys demonstrate that metallic glasses exhibiting more plastic strain during homogeneous deformation tend to show lower global plasticity during inhomogeneous deformation. Testing of Cu–Zr binary alloys supports the hypothesis that the formation energy of a shear transformation zone, as extracted from the experimental data, is related to the homogeneous flow rate. We also report the microstructural aspects that control the global plasticity of metallic glasses in the light of structural disordering, softening, and shear localization.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Size-dependent photoelastic effect in ZnO nanorods

H. Y. Shih, T. T. Chen, Y. C. Chen, T. H. Lin, L. W. Chang, and Y. F. Chen

Appl. Phys. Lett. 94, 021908 (2009); http://dx.doi.org/10.1063/1.3072350 (3 pages) | Cited 3 times

Online Publication Date: 15 January 2009

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Manipulation of internal strain by an external light beam called photoelastic effect has been firmly established in ZnO nanorods. The underlying mechanism of this interesting phenomenon arises from the combination of the screening of internal electric field and converse piezoelectric effect. We demonstrate that the photoelastic effect is more pronounced in thinner nanorods due to a larger surface to volume ratio. In addition to giving a good evidence for the existence of photoelastic effect in semiconductor nanorods, our finding also provides an excellent possibility for the development of nanoscale optical modulators.
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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)
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
77.65.-j Piezoelectricity and electromechanical effects

Atomic-scale in situ observation of lattice dislocations passing through twin boundaries

Y. B. Wang and M. L. Sui

Appl. Phys. Lett. 94, 021909 (2009); http://dx.doi.org/10.1063/1.3072801 (3 pages) | Cited 15 times

Online Publication Date: 15 January 2009

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In situ transmission electron microscopy tensile experiments were carried out to investigate lattice dislocation and twin boundary (TB) interaction in Cu with nanoscale growth twins. Results show that extended dislocations form inside thick twin lamellas and slip toward TBs. The extended dislocations shrink, combine, and redissociate when they pass through TBs, leaving behind detwinning partial dislocations at the TBs. The mechanism of the observed dislocation/TB interactions and the effect of the mechanism on mechanical properties are discussed.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries

Stabilizing nanostructured materials by coherent nanotwins and their grain boundary triple junction drag

C. Saldana, T. G. Murthy, M. R. Shankar, E. A. Stach, and S. Chandrasekar

Appl. Phys. Lett. 94, 021910 (2009); http://dx.doi.org/10.1063/1.3072595 (3 pages) | Cited 11 times

Online Publication Date: 16 January 2009

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The role of nanotwin lamellae in enhancing thermal stability of nanostructured materials is examined. Nanostructured copper with varying densities of twins was generated by controlling the deformation strain rate during severe plastic deformation at cryogenic temperatures. While the nanostructured materials produced under cryogenic conditions are characteristically unstable even at room temperatures, their stability is markedly improved when a dense dispersion of nanotwins is introduced. Observations of the role of nanotwins in pinning grain and subgrain structures suggest an interfacial engineering approach to enhancing the stability of nanostructured alloys.
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61.72.Mm Grain and twin boundaries
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.40.Lm Deformation, plasticity, and creep

Growth dynamics of C60 thin films: Effect of molecular structure

S. Yim and T. S. Jones

Appl. Phys. Lett. 94, 021911 (2009); http://dx.doi.org/10.1063/1.3072805 (3 pages) | Cited 5 times

Online Publication Date: 16 January 2009

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The surface morphology and growth behavior of fullerene thin films have been studied by atomic force microscopy and height difference correlation function analysis. In contrast to the large growth exponents (β) previously reported for other organic semiconductor thin-film materials, a relatively small β value of 0.39±0.10 was determined. Simulations of (1+1)-dimensional surface lateral diffusion models indicate that the evolution of deep grain boundaries leads to a rapid increase in β. We suggest that the commonly observed large β values for organic thin films are due to their intrinsically anisotropic molecular structures and hence different stacking directions between crystallite domains.
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68.55.ap Fullerenes
68.37.Ps Atomic force microscopy (AFM)
61.72.Mm Grain and twin boundaries
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