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17 Nov 2008

Volume 93, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 93, 201101 (2008); http://dx.doi.org/10.1063/1.3025818 (3 pages)

W. Dai and C. M. Soukoulis
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Polymer stabilized liquid crystal films reflecting both right- and left-circularly polarized light

Jinbao Guo, Hui Cao, Jie Wei, Duowei Zhang, Fang Liu, Guohui Pan, Dongyu Zhao, Wanli He, and Huai Yang

Appl. Phys. Lett. 93, 201901 (2008); http://dx.doi.org/10.1063/1.3003869 (3 pages) | Cited 15 times

Online Publication Date: 17 November 2008

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A single-layer polymer stabilized liquid crystal (PSLC) film reflecting both right- and left-circularly polarized light has been developed by a wash-out/refill method. The PSLC film was achieved by prefabricating the polymer network with a left-handed helical structure and then refilling a cholesteric liquid crystal with a right-handed helical structure into the network. The reflection intensity of the PSLC film is close to 100% when the pitch lengths of the two opposite helical structures are the same. It was demonstrated that the memory effect of the polymer network is an important mechanism for the resulting film properties.
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68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics

A Dnv point group structure possessing complete band gap based on gradual heterostructure and self-simulating sphere

Tianrui Zhai, Zhaona Wang, Rongkuo Zhao, Jing Zhou, Dahe Liu, and Xiangdong Zhang

Appl. Phys. Lett. 93, 201902 (2008); http://dx.doi.org/10.1063/1.3031671 (3 pages) | Cited 4 times

Online Publication Date: 17 November 2008

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A structure with Dnv point group was fabricated by compounding a gradual heterostructure and a self-simulating sphere. The gradual heterostructure has two-dimensional omnidirectional band gap and the self-simulating sphere makes it possess a complete band gap. The experimental results were explained by theoretical analysis. This kind of structure can be implemented using low refractive index materials.
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42.70.Qs Photonic bandgap materials
79.60.Jv Interfaces; heterostructures; nanostructures
71.20.Tx Fullerenes and related materials; intercalation compounds

Ab initio investigation on oxygen defect clusters in UO2+x

Hua Y. Geng, Ying Chen, Yasunori Kaneta, and Motoyasu Kinoshita

Appl. Phys. Lett. 93, 201903 (2008); http://dx.doi.org/10.1063/1.3035846 (3 pages) | Cited 8 times

Online Publication Date: 19 November 2008

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Oxygen defect clustering in uranium dioxide had been indicated in powder neutron diffraction measurements, and an empirical clustering mechanism had been proposed to explain the data. However, using first-principles LSDA+U calculations, we find that this empirical model, in fact, cannot work. A more physically reasonable model is proposed based on a thermodynamical competition between point defects and cuboctahedral clusters. This mechanism interprets the puzzled origin of the observed asymmetric interstitial O′ and O″ naturally. It also gives a good and consistent agreement with all available experimental data, except the high occupation of the O″ site.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.jj Interstitials
71.20.Ps Other inorganic compounds

Directional enhanced acoustic radiation caused by a point cavity in a finite-size two-dimensional phononic crystal

Feng-Chia Hsu, Tsung-Tsong Wu, Jin-Chen Hsu, and Jia-Hong Sun

Appl. Phys. Lett. 93, 201904 (2008); http://dx.doi.org/10.1063/1.3033220 (3 pages) | Cited 6 times

Online Publication Date: 19 November 2008

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In this letter, we present results of a study on the directional enhanced radiation generated by a point resonant cavity operating at the band-gap frequency of a two-dimensional finite-size phononic crystal. We find that the directive radiation for operating frequency within the band gap comes from the direction-dependent transmittance property of the square-lattice phononic crystal. The directive-radiation characteristic can be capitalized on enhancing the emission from the phononic crystals by coupling the source with point-defect modes, and the enhanced directive radiation patterns with main lobe width less than 12.9° are demonstrated.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
62.65.+k Acoustical properties of solids
63.20.kp Phonon-defect interactions
61.72.J- Point defects and defect clusters

Segregation of tungsten at γ′(L12)/γ(fcc) interfaces in a Ni-based superalloy: An atom-probe tomographic and first-principles study

Yaron Amouyal, Zugang Mao, and David N. Seidman

Appl. Phys. Lett. 93, 201905 (2008); http://dx.doi.org/10.1063/1.3026745 (3 pages) | Cited 9 times

Online Publication Date: 20 November 2008

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γ(fcc)/γ′(L12) heterophase interfaces in a Ni-based superalloy are investigated using atom-probe tomography and first-principles calculations. Flat {100} interfaces exhibit a confined (nonmonotonic) Gibbsian interfacial excess of tungsten, ΓW = 1.2±0.2 nm−2, corresponding to a 5 mJ m−2 decrease in interfacial free energy. Conversely, no measurable segregation of W is detected at curved interfaces. First-principles calculations for a Ni–Al–W system having a {100} interface indicate a decrease in the interfacial energy of 5 mJ m−2 due to W segregation. Similar calculations for {110} and {111} interfaces predict an increase of 1 and 9 mJ m−2 in their energies, respectively, and therefore no heterophase segregation.
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64.75.Op Phase separation and segregation in alloying
68.35.Md Surface thermodynamics, surface energies

Influence of a bimodal eutectic structure on the plasticity of a (Ti70.5Fe29.5)91Sn9 ultrafine composite

J. H. Han, K. B. Kim, S. Yi, J. M. Park, D. H. Kim, S. Pauly, and J. Eckert

Appl. Phys. Lett. 93, 201906 (2008); http://dx.doi.org/10.1063/1.3029745 (3 pages) | Cited 21 times

Online Publication Date: 20 November 2008

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Systematic investigations on the microstructural evolution of a bimodal eutectic (Ti70.5Fe29.5)91Sn9 ultrafine composite containing Ti3Sn dendrites upon compression reveal that local deformation of the dendrites dominates the early stage of deformation with a plastic strain of εp = 5.8%. After further deformation (εp = 10.2%), a wavy propagation of shear bands indicative of dissipation of the shear stress is caused by a rotation of the coarse eutectic structure along the interfaces of the bimodal eutectic structure.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
68.35.Gy Mechanical properties; surface strains

Nanomechanical thermal analysis of electrospun polymer fibers

Wei Wang, Andrew J. Bushby, and Asa H. Barber

Appl. Phys. Lett. 93, 201907 (2008); http://dx.doi.org/10.1063/1.3033222 (3 pages) | Cited 9 times

Online Publication Date: 20 November 2008

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Thermomechanical properties of individual electrospun semicrystalline polyethylene oxide (PEO) fibers were measured using atomic force microscopy based indentation. Fibers showed a higher elastic modulus than corresponding films despite a lower crystallinity, indicating significant molecular alignment along the principle fiber axis. Heating of the fibers gave a progressive loss in elastic modulus highlighting a dominant amorphous thermomechanical response. This is in contrast to softening of an amorphous phase and melting of a crystalline phase in semicrystalline bulk PEO films.
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81.40.Gh Other heat and thermomechanical treatments
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.60.Bs Mechanical and acoustical properties
62.20.de Elastic moduli
62.20.Qp Friction, tribology, and hardness

Polarity driven formation of InAs/GaAs hierarchical nanowire heterostructures

Mohanchand Paladugu, Jin Zou, Ya-Nan Guo, Xin Zhang, Hannah J. Joyce, Qiang Gao, H. Hoe Tan, C. Jagadish, and Yong Kim

Appl. Phys. Lett. 93, 201908 (2008); http://dx.doi.org/10.1063/1.3033551 (3 pages) | Cited 16 times

Online Publication Date: 20 November 2008

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The structural and morphological characteristics of InAs/GaAs radial nanowire heterostructures were investigated using transmission electron microscopy. It has been found that the radial growth of InAs was preferentially initiated on the {112}A sidewalls of GaAs nanowires. This preferential deposition leads to extraordinarily asymmetric InAs/GaAs radial nanowire heterostructures. Such formation of radial nanowire heterostructures provides an opportunity to engineer hierarchical nanostructures, which further widens the potential applications of semiconductor nanostructures.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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)
62.23.Hj Nanowires
68.37.Lp Transmission electron microscopy (TEM)

Why so strong for the lotus leaf?

Zhiguang Guo, Weimin Liu, and Bao-Lian Su

Appl. Phys. Lett. 93, 201909 (2008); http://dx.doi.org/10.1063/1.3036535 (3 pages) | Cited 10 times

Online Publication Date: 21 November 2008

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The authors discussed the potential reasons why the lotus leaf is so strong by means of scanning electron microscopy (SEM). The results showed that the good mechanical properties of lotus leaf should be attributed to its architecture, such as paralleled microtubes structure, umbrellalike structure, and hierarchically layered hexagon structure. The important observation from this work is that the surface of the rear face of the lotus leaf seems to be constituted by the layers of hexagons whose hierarchical pilling up of size decreases as we go deeper from surface. This is a typical fractal-like phenomenon.
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87.17.Rt Cell adhesion and cell mechanics

Characterizing the global dispersion of carbon nanotubes in ceramic matrix nanocomposites

Orsolya Koszor, Levente Tapasztó, Márton Markó, and Csaba Balázsi

Appl. Phys. Lett. 93, 201910 (2008); http://dx.doi.org/10.1063/1.3029746 (3 pages) | Cited 3 times

Online Publication Date: 21 November 2008

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The dispersion of single-walled carbon nanotubes in silicon nitride ceramic matrices has been investigated by small angle neutron scattering experiments. In contrast to electron microscopy investigations of fracture surfaces, neutron scattering measurements provide information on the bulk dispersion of nanotubes within the matrix. The scattering intensities reveal a decay exponent characteristic to surface fractals, which indicates that the predominant part of nanotubes can be found in loose networks surrounding the grains of the polycrystalline matrix.
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81.05.Mh Cermets, ceramic and refractory composites
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.25.Mn Fracture/brittleness
61.46.-w Structure of nanoscale materials
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