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19 Nov 2007

Volume 91, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 212501 (2007); http://dx.doi.org/10.1063/1.2813047 (3 pages)

M. V. Milošević, G. R. Berdiyorov, and F. M. Peeters
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Influence of aspect ratio of carbon nanotube on percolation threshold in ferroelectric polymer nanocomposite

Sheng-Hong Yao, Zhi-Min Dang, Mei-Juan Jiang, Hai-Ping Xu, and Jinbo Bai

Appl. Phys. Lett. 91, 212901 (2007); http://dx.doi.org/10.1063/1.2817746 (3 pages) | Cited 35 times

Online Publication Date: 20 November 2007

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Multiwall carbon nanotube (MWNT) with different aspect ratio (AR) was dispersed into ferroelectric polyvinylidene fluoride (PVDF) to fabricate the MWNT/PVDF nanocomposites. An increase of dielectric constant with increasing the AR value was observed in the MWNT/PVDF composites. Meanwhile, the result showed that the change of percolation threshold displayed the same rule with that of critical exponent, and both of them increased with increase of AR in some extent, which provides an effective and simple way to describe the dielectric transition of practical composites in the neighborhood of percolation threshold with the scaling theory.
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81.07.De Nanotubes
77.84.Lf Composite materials
77.84.Jd Polymers; organic compounds
77.22.Ch Permittivity (dielectric function)

Nanostructured barium titanate composites for embedded radio frequency applications

A. Biswas, I. S. Bayer, P. C. Karulkar, A. Tripathi, D. K. Avasthi, M. G. Norton, and J. B. Szczech

Appl. Phys. Lett. 91, 212902 (2007); http://dx.doi.org/10.1063/1.2811714 (3 pages) | Cited 3 times

Online Publication Date: 20 November 2007

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We describe a vapor-phase codeposition method to fabricate a ceramic-in-polymer composite system comprising ferroelectric barium titanate nanoparticles in a highly polarizable polyaniline-polyurethane copolymer host. As-deposited composites exhibited a capacitance density of 15 nF/cm2 and a resonance frequency close to 100 MHz with a loss tangent of 0.8. Annealing nanocomposites at 135 °C resulted in slightly reduced but frequency-independent capacitance density ( ∼ 10 nF/cm2) with a loss tangent of 0.1 and resonance frequency at 200 MHz. The interplay of polarization modes is discussed in relation to capacitor performance. The fabricated capacitors have potential for applications in embedded technology in the radio frequency.
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81.05.Qk Reinforced polymers and polymer-based composites
81.07.Bc Nanocrystalline materials
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Magnetodielectric coupling in core/shell BaTiO3/γ-Fe2O3 nanoparticles

Y. S. Koo, T. Bonaedy, K. D. Sung, J. H. Jung, J. B. Yoon, Y. H. Jo, M. H. Jung, H. J. Lee, T. Y. Koo, and Y. H. Jeong

Appl. Phys. Lett. 91, 212903 (2007); http://dx.doi.org/10.1063/1.2817940 (3 pages) | Cited 16 times

Online Publication Date: 20 November 2007

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We report an intriguing magnetodielectric coupling in BaTiO3/γ-Fe2O3 dielectric core/ferrimagnetic shell nanoparticles. The dielectric constant steeply increases with magnetic field, and the frequency dependent magnetodielectric curve shows a resonancelike peak at high temperatures, while it decreases smoothly with field and no peak appears in the frequency dependent magnetodielectric curve at low temperatures. We attribute the observed magnetodielectric coupling to the Maxwell-Wagner effect combined with magnetoresistance at high temperatures and to possible spin-lattice coupling and its modification near interfaces at low temperatures.
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75.80.+q Magnetomechanical effects, magnetostriction
77.22.Ch Permittivity (dielectric function)
72.20.My Galvanomagnetic and other magnetotransport effects

Effect of molecular weight on the dielectric breakdown strength of ferroelectric poly(vinylidene fluoride-chlorotrifluoroethylene)s

Jason Claude, Yingying Lu, and Qing Wang

Appl. Phys. Lett. 91, 212904 (2007); http://dx.doi.org/10.1063/1.2816327 (3 pages) | Cited 11 times

Online Publication Date: 21 November 2007

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The dielectric strengths of poly(vinylidene fluoride-chlorotrifluoroethylene) copolymers have been investigated as a function of molecular weights (MW) at different temperatures. We have shown that the electrical breakdown strength increases with increasing MW and decreasing temperature. Experimental measurements of the electrical breakdown field at 25 °C agree fairly well with an electromechanical breakdown model. The dielectric breakdown at lower temperatures near and below the glass transition is attributed to the existence of thermal breakdown process, which is supported by numerical calculations and experimental measurements.
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77.22.Jp Dielectric breakdown and space-charge effects
77.84.Jd Polymers; organic compounds

Double hysteresis loop in (Pb0.90La0.10)Ti0.975O3/Pb(Zr0.20Ti0.80)O3 bilayer thin films

Jiagang Wu, Jiliang Zhu, Dingquan Xiao, and Jianguo Zhu

Appl. Phys. Lett. 91, 212905 (2007); http://dx.doi.org/10.1063/1.2817745 (3 pages) | Cited 10 times

Online Publication Date: 21 November 2007

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(Pb0.90La0.10)Ti0.975O3/Pb(Zr0.20Ti0.80)O3 bilayer thin films were fabricated using radio frequency magnetron sputtering with a PbOx buffer layer. The x-ray diffraction patterns show that the bilayers possess highly (100) orientation. Polarization hysteresis and capacitance-voltage characteristics of the bilayers show clear antiferroelectric (AFE) characteristics. The related mechanism for double hysteresis loop was also discussed. The competition among the intrinsic ferroelectric coupling at the interface between bilayers gives rise to an AFE polarization behavior.
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77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
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Pi-shape gate polycrystalline silicon thin-film transistor for nonvolatile memory applications

Shih-Ching Chen, Ting-Chang Chang, Po-Tsun Liu, Yung-Chun Wu, Chin-Cheng Ko, Sidney Yang, Li-Wei Feng, S. M. Sze, Chun-Yen Chang, and Chen-Hsin Lien

Appl. Phys. Lett. 91, 213101 (2007); http://dx.doi.org/10.1063/1.2813621 (3 pages) | Cited 5 times

Online Publication Date: 19 November 2007

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In this work, we studied a pi-shape gate polycrystalline silicon thin-film transistor (poly-Si TFT) with silicon-oxide-nitride-oxide-silicon (SONOS) layers and nanowire channels for the application of electric driver and nonvolatile memory. The proposed pi-gate TFT-SONOS has superior transfer characteristics and its output characteristic also exhibits the high driving current and the suppression of the kink effect. For memory application, the device can provide high program/erase efficiency and large threshold voltage shift under adequate bias operation. The enhanced performance for the pi-gate TFT-SONOS is attributed to the larger effective channel width and the number of channel corners.
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85.30.Tv Field effect devices

In situ investigation of the liquid/solid interface of a block copolymer solution under shear stress using microbeam grazing-incidence small-angle x-ray scattering

Andreas Timmann, Stephan Volkher Roth, Steffen Fischer, and Stephan Förster

Appl. Phys. Lett. 91, 213102 (2007); http://dx.doi.org/10.1063/1.2815929 (3 pages) | Cited 2 times

Online Publication Date: 19 November 2007

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An aqueous solution of poly(isoprene55-block-ethylene oxide170) was investigated at different temperatures combining rheometry in plate/plate-geometry and microbeam grazing incidence small-angle x-ray scattering. In the vicinity of the rotator plate, we were able to separate the bulk scattering of the solution from the grazing incident signal stemming of the interface and to determine a thickness of an interface layer at the liquid-solid interface. We followed the thickness of the interface layer in situ as a function of shear rate. This kind of measurements can be important to decide if the first micellar layer sicks or slips at the surface under shear.
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82.70.Dd Colloids
62.10.+s Mechanical properties of liquids
68.08.De Liquid-solid interface structure: measurements and simulations
78.70.Ck X-ray scattering

Single-electron quantum dot in Si/SiGe with integrated charge sensing

C. B. Simmons, Madhu Thalakulam, Nakul Shaji, Levente J. Klein, Hua Qin, R. H. Blick, D. E. Savage, M. G. Lagally, S. N. Coppersmith, and M. A. Eriksson

Appl. Phys. Lett. 91, 213103 (2007); http://dx.doi.org/10.1063/1.2816331 (3 pages) | Cited 33 times

Online Publication Date: 20 November 2007

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Single-electron occupation is an essential component to the measurement and manipulation of spin in quantum dots, capabilities that are important for quantum information processing. Si/SiGe is of interest for semiconductor spin qubits, but single-electron quantum dots have not yet been achieved in this system. We report the fabrication and measurement of a top-gated quantum dot occupied by a single electron in a Si/SiGe heterostructure. Transport through the quantum dot is directly correlated with charge sensing from an integrated quantum point contact, and this charge sensing is used to confirm single-electron occupancy in the quantum dot.
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73.63.Kv Quantum dots
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Coupling between surface plasmons via thermal emission of a dielectric layer sandwiched between two metal periodic layers

Ming-Wei Tsai, Chia-Yi Chen, Yu-Wei Jiang, Yi-Han Ye, Hsu-Yu Chang, Tzu-Hung Chuang, and Si-Chen Lee

Appl. Phys. Lett. 91, 213104 (2007); http://dx.doi.org/10.1063/1.2779964 (3 pages) | Cited 3 times

Online Publication Date: 20 November 2007

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Metal/SiO2/metal trilayer thermally generated infrared emitters with different top and bottom periodic metal arrangements were fabricated and their emission spectra were measured. The coupling mechanisms of surface plasmon polaritons at top and bottom periodic metal structures were characterized. It is found that the top surface plasmon converted to light radiation directly, whereas the bottom surface plasmon can radiate out when its emission peak position matches that of the top surface plasmon. This opens the way to fabricate the high temperature operated, narrow bandwidth, and multiwavelength infrared light source.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Anisotropic polarizability of isolated semiconducting single-wall carbon nanotubes in alternating electric fields

J. A. Fagan, V. Bajpai, B. J. Bauer, and E. K. Hobbie

Appl. Phys. Lett. 91, 213105 (2007); http://dx.doi.org/10.1063/1.2807850 (3 pages) | Cited 4 times

Online Publication Date: 21 November 2007

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We measure the linear dichroism for aqueous suspensions of isolated semiconducting single-wall carbon nanotubes (SWCNTs) in alternating electric fields. The field-induced alignment of length-purified SWCNTs is determined from the anisotropy of the first and second interband optical transitions for the (6,5) semiconducting species. At 3 kHz, the effective anisotropic polarizability of the DNA-wrapped SWCNTs is of order 10−28 F m2, comparable to that of a high-aspect-ratio conducting rod, but a factor of 5 larger than that of gold colloidal rods and an order of magnitude larger than that of tobacco mosaic virus.
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78.67.Ch Nanotubes
78.20.Fm Birefringence
82.70.Kj Emulsions and suspensions
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Enhanced circular dichroism via slow light in dispersive structured media

Jesper Pedersen and Niels Asger Mortensen

Appl. Phys. Lett. 91, 213501 (2007); http://dx.doi.org/10.1063/1.2814937 (3 pages) | Cited 4 times

Online Publication Date: 19 November 2007

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Circular dichroism (CD) is in widespread use as a means of determining enantiomeric excess. We show how slow-light phenomena in dispersive structured media allow for a reduction in the required optical path length of an order of magnitude. The same ideas may be used to enhance the sensitivity of CD measurements while maintaining the same optical path length through the sample. Finally, the sensitivity may be enhanced in frequency regimes where CD data are typically not accessible due to a modest chiral response of the enantiomers.
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78.20.Fm Birefringence

Efficient white-light-emitting diodes based on polyfluorene doped with fluorescent chromophores

Suqin Fan, Mingliang Sun, Jian Wang, Wei Yang, and Yong Cao

Appl. Phys. Lett. 91, 213502 (2007); http://dx.doi.org/10.1063/1.2812569 (3 pages) | Cited 11 times

Online Publication Date: 21 November 2007

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Orange-red emitting small molecule chromorephores, 4,7-di-2-thienyl-2,1,3-benzothiadiazole, 4,7-(2′-diselenophenyl)-2,1,3-benzothiadiazole, and 4,7-bis(N-methylpyrrol-2-yl)-2,1,3-benzo-thiadiazole were synthesized and used for fabrication of fluorescent white-emitting device with polyfluorene (PFO) as host by solution processing. By careful controlling of dopant concentration, balanced narrow band-gap (NGB) electroluminescence (EL) emission can be obtained by solution processing due to the incomplete energy transfer from PFO to narrow band gap molecules. EL spectra of the obtained devices were very stable at a wide range of operating voltage. The best white-emitting device reached luminous efficiency of 7.54 cd/A with the CIE coordinates (0.33, 0.34) at luminance over 1000 cd/m2.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling
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Application of nonlinear dynamics to monitoring progressive fatigue damage in human cortical bone

T. J. Ulrich, Paul A. Johnson, Marie Müller, David Mitton, Maryline Talmant, and Pascal Laugier

Appl. Phys. Lett. 91, 213901 (2007); http://dx.doi.org/10.1063/1.2809565 (3 pages) | Cited 9 times

Online Publication Date: 19 November 2007

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In this work, the results of applying nonlinear dynamics to study progressive material fatigue in human bone are described. Material nonlinear dynamical response has been shown to be associated with mechanical damage. The progressive mechanical damage experiments were conducted in cortical bone extracted from a human femur. After each damage step, the material dynamical nonlinear response was measured by applying wave modulation and extracting a nonlinear parameter proportional to the sideband amplitude. The nonlinear parameter increases rapidly with damage step, indicating increased damage after the initial cycling procedure, while the quasistatic stiffness taken from the cycling experiments shows little change.
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43.25.-x Nonlinear acoustics
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Structural and magnetic properties of nanocrystalline RuCo alloys

S. B. Qadri, T. M. Keller, M. Laskoski, C. A. Little, M. S. Osofsky, and H. R. Khan

Appl. Phys. Lett. 91, 214101 (2007); http://dx.doi.org/10.1063/1.2814061 (3 pages) | Cited 1 time

Online Publication Date: 20 November 2007

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Nanoparticles of Ru1−xCox (0 ⩽ x ⩽ 1) in the carbon matrix were synthesized over the entire compositional range using organometallic precursors. For Co concentrations with x ⩽ 0.75, a hexagonal close packed phase was formed, whereas a face centered cubic phase was observed for x>0.75. The crystallite sizes varied between 5 and 10 nm. In addition, multiwalled carbon nanotubes formed during the pyrolysis of the precursors. Increasing ferromagnetic order was observed with increasing Co concentration.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.16.Be Chemical synthesis methods
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Experimental verification of backward wave propagation at photonic crystal surfaces

S. Foteinopoulou, G. Kenanakis, N. Katsarakis, I. Tsiapa, M. Kafesaki, E. N. Economou, and C. M. Soukoulis

Appl. Phys. Lett. 91, 214102 (2007); http://dx.doi.org/10.1063/1.2814154 (3 pages) | Cited 5 times

Online Publication Date: 20 November 2007

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Backward wave propagation is the true manifestation of left-handed electromagnetism and not negative refraction which occurs also at the interface of right-handed systems. Here we experimentally demonstrate in a direct fashion the backward wave propagation phenomenon, which takes place at the surface of a properly designed photonic crystal. Our microwave experiment could open other venues for the verification of left-handed behavior in optical metamaterials.
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42.70.Qs Photonic bandgap materials
78.68.+m Optical properties of surfaces

Tensile deformation accommodation in microscopic metallic glasses via subnanocluster reconstructions

Ch. E. Lekka, A. Ibenskas, A. R. Yavari, and G. A. Evangelakis

Appl. Phys. Lett. 91, 214103 (2007); http://dx.doi.org/10.1063/1.2816912 (3 pages) | Cited 37 times

Online Publication Date: 21 November 2007

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We present results on the structure and the atomistic mechanisms for tensile deformation accommodation of the Cu46Zr54 microscopic metallic glass. At equilibrium, 23% of the atoms belong to tiny Cu-centered icosahedral clusters (Cu-ICO) and approximately 41% Zr centered slightly larger ICO-like clusters. Under deformation, the number of Cu-ICOs remains dynamically constant until yielding through a continuous cluster destruction-recreation process. Plastic deformation occurs homogeneously and is locally accommodated through the formation of rhombic dodecahedral clusters with significant ( ∼ 2%) atomic density drop. These findings explain very recent experimental results demonstrating the fundamental differences of plastic deformation mechanisms between bulk metallic and microscopic glasses.
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81.40.Lm Deformation, plasticity, and creep
61.43.Fs Glasses
61.44.Br Quasicrystals
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Comment on “Optical and magneto-optical properties of AuMnSn” [ Appl. Phys. Lett. 88, 121909 (2006) ]

P. Ravindran, Laila Offernes, and A. Kjekshus

Appl. Phys. Lett. 91, 216101 (2007); http://dx.doi.org/10.1063/1.2804560 (3 pages)

Online Publication Date: 19 November 2007

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Abstract Unavailable
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78.20.Ls Magneto-optical effects
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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