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20 Aug 2012

Volume 101, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 101, 081102 (2012); http://dx.doi.org/10.1063/1.4745791 (3 pages)

M. K. Wu, M. Feng, and N. Holonyak, Jr.
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Ultrafast electron diffraction with radio-frequency compressed electron pulses

Robert P. Chatelain, Vance R. Morrison, Chris Godbout, and Bradley J. Siwick

Appl. Phys. Lett. 101, 081901 (2012); http://dx.doi.org/10.1063/1.4747155 (4 pages) | Cited 4 times

Online Publication Date: 20 August 2012

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We report on the complete characterization of time resolution in an ultrafast electron diffraction (UED) instrument based on radio-frequency electron pulse compression. The temporal impulse response function of the instrument was determined directly in pump-probe geometry by performing electron-laser pulse cross-correlation measurements using the ponderomotive interaction. With optimal settings, a stable impulse response of 334±10 fs was measured at a bunch charge of 0.1 pC (6.24 × 105 electrons/pulse); a dramatic improvement compared to performance without pulse compression. Phase stability currently limits the impulse response of the UED diffractometer to the range of 334–500 fs, for bunch charges ranging between 0.1 and 0.6 pC.
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07.77.Ka Charged-particle beam sources and detectors
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Visible luminescence from hydrogenated amorphous silicon modified by femtosecond laser radiation

Andrey V. Emelyanov, Andrey G. Kazanskii, Mark V. Khenkin, Pavel A. Forsh, Pavel K. Kashkarov, Mindaugas Gecevicius, Martynas Beresna, and Peter G. Kazansky

Appl. Phys. Lett. 101, 081902 (2012); http://dx.doi.org/10.1063/1.4747207 (3 pages)

Online Publication Date: 21 August 2012

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Visible luminescence is observed from the composite of SiO2 with embedded silicon nanocrystallites produced by femtosecond laser irradiation of hydrogenated amorphous silicon (a-Si:H) film in air. The photoluminescence originates from the defect states at the interface between silicon crystallites and SiO2 matrix. The method could be used for fabrication of luminescent layers to increase energy conversion of a-Si:H solar cells.
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78.67.Sc Nanoaggregates; nanocomposites
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
78.47.J- Ultrafast spectroscopy (<1 psec)

Enhanced Raman scattering and photoluminescence of Bi3.25La0.75Ti3O12 nanotube arrays for optical and ferroelectric multifunctional applications

J. Z. Zhang (张金中), M. J. Han (韩美杰), Y. W. Li (李亚巍), Z. G. Hu (胡志高), and J. H. Chu (褚君浩)

Appl. Phys. Lett. 101, 081903 (2012); http://dx.doi.org/10.1063/1.4747218 (5 pages)

Online Publication Date: 21 August 2012

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Raman scattering enhancement has been observed from highly ordered ferroelectric Bi3.25La0.75Ti3O12 nanotube (BLT-NT) arrays prepared by a template-assisted method. Scattering enhancement factor which is the ratio of average Raman intensity per molecule for nanostructure and film is evaluated to be about 92, 257, and 623 corresponding to the outer diameters of 50, 100, and 200 nm, respectively. The phenomena can be attributed to unique surface, microstructure, grain size, and tensile stress in the curved nanotube walls. These results indicate that BLT-NT arrays are suitable for fabricating multifunctional devices due to remaining good ferroelectricity.
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78.67.Ch Nanotubes
61.46.Fg Nanotubes
77.80.-e Ferroelectricity and antiferroelectricity
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
78.66.Nk Insulators

Back focal plane imaging spectroscopy of photonic crystals

Rebecca Wagner, Lars Heerklotz, Nikolai Kortenbruck, and Frank Cichos

Appl. Phys. Lett. 101, 081904 (2012); http://dx.doi.org/10.1063/1.4746251 (4 pages)

Online Publication Date: 21 August 2012

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Back focal plane imaging spectroscopy is introduced to record angle resolved emission spectra of 3-dimensional colloidal photonic crystals. The auto-fluorescence of the colloids is used to quickly map the photonic band structure up to 72 % of the solid angle of a semisphere with the help of a high numerical aperture objective. Local excitation provides spatially resolved information on the photonic crystal’s optical properties. The obtained fractional density of states allows direct conclusions on the crystal’s stacking faults or defects.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
82.70.Dd Colloids
61.72.Nn Stacking faults and other planar or extended defects
78.55.-m Photoluminescence, properties and materials

Surface plasmon resonances of Ga nanoparticle arrays

M. Kang, T. W. Saucer, M. V. Warren, J. H. Wu, H. Sun, V. Sih, and R. S. Goldman

Appl. Phys. Lett. 101, 081905 (2012); http://dx.doi.org/10.1063/1.4742328 (4 pages) | Cited 2 times

Online Publication Date: 21 August 2012

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We have examined the influence of particle and chain diameter on surface plasmon resonance (SPR) energy of 2D and 1D Ga nanoparticle (NP) arrays fabricated using focused-ion-beam irradiation of GaN surfaces. Maxima in the extinction spectra suggest the presence of SPR at visible and near-infrared wavelengths. The SPR energies increase with decreasing NP or chain diameter, due to particle diameter-dependent dipole interactions within the metallic NPs. The SPR quality factors are comparable to those reported from Ag and Au NPs, suggesting Ga NPs as a promising alternative plasmonic material.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.40.Kc Metals, semimetals, and alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.68.+m Optical properties of surfaces
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

On the role of hierarchical twins for achieving maximum yield strength in nanotwinned metals

Linli Zhu, Hongning Kou, and Jian Lu

Appl. Phys. Lett. 101, 081906 (2012); http://dx.doi.org/10.1063/1.4747333 (4 pages) | Cited 2 times

Online Publication Date: 22 August 2012

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The dependence of the strength of polycrystalline metals with hierarchical nanotwins on twin spacing and grain size is theoretically studied with a dislocation-based theoretical model, which describes the twin spacing-dependent flow stress. The analysis indicates that the flow stress first decreases with the decrease of twin spacing in primary twin lamellae, and then rises up to an ultimate value, while it is reinforced directly when reducing the size of the secondary twin lamellae. It is found that there exist optimal twin spacings in primary and secondary twin lamellae, as the function of the grain size, which yields a maximal strength in this hierarchical nanostructure. The present results provide a new perspective to design the microstructures for reinforcing the mechanical properties in nanostructural materials.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
62.20.fq Plasticity and superplasticity
61.46.-w Structure of nanoscale materials
61.72.Mm Grain and twin boundaries

Resolving quandaries surrounding NiTi

Jifeng Wang and Huseyin Sehitoglu

Appl. Phys. Lett. 101, 081907 (2012); http://dx.doi.org/10.1063/1.4747488 (3 pages)

Online Publication Date: 22 August 2012

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We address a quandary associated with the phase stability of NiTi. The B19′ (monoclinic lattice) has been experimentally observed while B33 (base-centered orthorhombic lattice) has been proposed on theoretical grounds to have a lower energy. With high-resolution shearing steps, we show unequivocally that a significant energy barrier exists between the martensitic B19′ and B33 which is dependent on pressure. The transition state designated as B19′1 has an energy level 25 meV/atom higher compared to B19′. We note that the formation of B33 can be suppressed because of the presence of the B19′1 high energy barrier which increases considerably under tensile hydrostatic stress.
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81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
61.66.Dk Alloys

Significantly enhanced thermoelectric figure of merit through Cu, Sb co-substitutions for Te in Ga2Te3

Jiaolin Cui, Yulan Gao, Hong Zhou, Yapeng Li, Qingsen Meng, and Jiangfeng Yang

Appl. Phys. Lett. 101, 081908 (2012); http://dx.doi.org/10.1063/1.4747621 (4 pages)

Online Publication Date: 22 August 2012

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Here, we used two elements Cu and Sb as the substitutes for Te in Ga2Te3 and observed a giant enhancement in thermoelectric figure of merit (ZT). This potential substituted Ga2Cu0.05SbxTe2.95−x (x = 0.2) gives the maximum ZT value of 0.5 at 700 K, more than 3 times as high as that of intrinsic Ga2Te3. The enhancement in ZT is attributed to the significantly reduced thermal conductivity caused mainly by the presence of Cu at Ga vacancy planes, and remarkably improved electrical conductivity by the occupation of Sb at Te sites, which increases the carrier concentration and conserves the high mobility.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Mechanical properties of graphynes under tension: A molecular dynamics study

Y. Y. Zhang, Q. X. Pei, and C. M. Wang

Appl. Phys. Lett. 101, 081909 (2012); http://dx.doi.org/10.1063/1.4747719 (4 pages) | Cited 3 times

Online Publication Date: 22 August 2012

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Graphyne is the allotrope of graphene. In this letter, four different graphynes (α, β, γ, and 6,6,12-graphenes) are investigated by molecular dynamics simulations to explore their mechanical properties and failure mechanisms. It is found that the presence of the acetylenic linkages in graphynes leads to a significant reduction in fracture stress and Young’s modulus with the degree of reduction being proportional to the percentage of the linkages. This deterioration in mechanical properties stems from the low atom density in graphynes and weak single bonds in the acetylenic linkages where the facture is initiated.
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81.05.ue Graphene
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
62.20.de Elastic moduli
61.48.Gh Structure of graphene

Mechanical and electrical characterization of semiconducting ZnO nanorings by direct nano-manipulation

Wenjie Mai, Long Zhang, Yudong Gu, Shiqing Huang, Zongfu Zhang, Changshi Lao, Peihua Yang, Pengfei Qiang, and Zhongwei Chen

Appl. Phys. Lett. 101, 081910 (2012); http://dx.doi.org/10.1063/1.4747807 (4 pages)

Online Publication Date: 23 August 2012

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With assistance from a nano-manipulator system inside a scanning electron microscope chamber, mechanical and electrical properties of ZnO nanorings were investigated. The change of a fractured nanoring to nearly straight nanobelts was strong evidence to support the previously proposed electrostatic-force-induced self-coiling model, and our computational simulation results indicated the fracture force was 25–30 μN. The contact between a tungsten tip of the manipulator and a ZnO nanoring was confirmed as the Schottky type; therefore, the change of I–V curves of the nanoring under compression was attributed to the Schottky barrier height changes.
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81.05.Dz II-VI semiconductors
61.46.Np Structure of nanotubes (hollow nanowires)
81.16.Ta Atom manipulation
71.20.Nr Semiconductor compounds
61.46.-w Structure of nanoscale materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.16.-c Methods of micro- and nanofabrication and processing

Planar arrays of magnetic nanocrystals embedded in GaN

A. Navarro-Quezada, T. Devillers, Tian Li, and A. Bonanni

Appl. Phys. Lett. 101, 081911 (2012); http://dx.doi.org/10.1063/1.4747809 (4 pages) | Cited 1 time

Online Publication Date: 23 August 2012

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Single planar arrays of GaxFe4−xN magnetic nanocrystals embedded in GaN have been fabricated in an epitaxial process. The phase of the nanocrystals and their epitaxial relationship with the host matrix are studied via high-resolution transmission electron microscopy and high-resolution x-ray diffraction. By changing the growth parameters and mode, the crystallographic phase and chemical composition of the nanocrystals can be varied on demand. In view of the different magnetic properties of the various phases, applications in room-temperature ferromagnetic as well as antiferromagnetic spintronic devices are envisaged.
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75.75.-c Magnetic properties of nanostructures
81.05.Ea III-V semiconductors
71.20.Nr Semiconductor compounds
75.47.-m Magnetotransport phenomena; materials for magnetotransport

Experimental demonstration of surface morphology independent electromagnetic chiral edge states originated from magnetic plasmon resonance

Yin Poo, Rui-xin Wu, Shiyang Liu, Yan Yang, Zhifang Lin, and S. T. Chui

Appl. Phys. Lett. 101, 081912 (2012); http://dx.doi.org/10.1063/1.4747810 (5 pages)

Online Publication Date: 23 August 2012

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It is experimentally demonstrated that within the photonic band gap induced by magnetic surface plasmon (MSP) resonance in a honeycomb magnetic photonic crystal, there can exist self-guiding electromagnetic chiral edge states whose dispersion curves are insensitive to the surface morphology when the system is truncated. The unique characteristic of the MSP induced edge states enables flexible design of robust unidirectional subwavelength waveguides that contain bends at various angles, providing an alternative way for manipulating electromagnetic waves at subwavelength scales.
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42.70.Qs Photonic bandgap materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
41.20.Jb Electromagnetic wave propagation; radiowave propagation
42.82.Et Waveguides, couplers, and arrays

Discontinuous design of negative index metamaterials based on mode hybridization

Nian-Hai Shen, Lei Zhang, Thomas Koschny, Babak Dastmalchi, Maria Kafesaki, and Costas M. Soukoulis

Appl. Phys. Lett. 101, 081913 (2012); http://dx.doi.org/10.1063/1.4748361 (3 pages)

Online Publication Date: 24 August 2012

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An electric inductor-capacitor (ELC) resonator provides a series of electrical resonances and a pair of ELC resonators leads to the split of each resonance into two modes, i.e., magnetic and electric modes, corresponding to antisymmetric and symmetric current distributions. With the meticulous design of the ELC resonator, we can achieve a negative index metamaterial through mode hybridization by overlapping the first electric resonance mode and the second magnetic resonance mode. Such non-connected designs may offer opportunities to achieve three-dimensional negative index metamaterials.
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42.70.-a Optical materials
84.40.-x Radiowave and microwave (including millimeter wave) technology
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