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24 Dec 2012

Volume 101, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 263501 (2012); http://dx.doi.org/10.1063/1.4772532 (4 pages)

Youngki Yoon and Sayeef Salahuddin
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Direct observation of substitutional Ga after ion implantation in Ge by means of extended x-ray absorption fine structure

S. Decoster, B. Johannessen, C. J. Glover, S. Cottenier, T. Bierschenk, H. Salama, F. Kremer, K. Temst, A. Vantomme, and M. C. Ridgway

Appl. Phys. Lett. 101, 261904 (2012); http://dx.doi.org/10.1063/1.4773185 (4 pages)

Online Publication Date: 27 December 2012

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We present an experimental lattice location study of Ga atoms in Ge after ion implantation at elevated temperature (250°C). Using extended x-ray absorption fine structure (EXAFS) experiments and a dedicated sample preparation method, we have studied the lattice location of Ga atoms in Ge with a concentration ranging from 0.5 at. % down to 0.005 at. %. At Ga concentrations ≤ 0.05 at.%, all Ga dopants are substitutional directly after ion implantation, without the need for post-implantation thermal annealing. At higher Ga concentrations, a reduction in the EXAFS amplitude is observed, indicating that a fraction of the Ga atoms is located in a defective environment. The local strain induced by the Ga atoms in the Ge matrix is independent of the Ga concentration and extends only to the first nearest neighbor Ge shell, where a 1% contraction in bond length has been measured, in agreement with density functional theory calculations.
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61.72.uf Ge and Si
61.50.Lt Crystal binding; cohesive energy
78.70.Dm X-ray absorption spectra

Efficient focalization of antisymmetric Lamb waves in gradient-index phononic crystal plates

Jinfeng Zhao, Rémi Marchal, Bernard Bonello, and Olga Boyko

Appl. Phys. Lett. 101, 261905 (2012); http://dx.doi.org/10.1063/1.4773369 (4 pages)

Online Publication Date: 27 December 2012

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The focalization of elastic waves within a two dimensional gradient-index phononic crystal (GRIN PC) is numerically and experimentally investigated. The structure is formed by a square lattice of air holes in a silicon plate with transverse variation of holes’ diameters. The geometry and efficiency of focalization are computed with a finite element method. A non-contact laser-ultrasonic technique is used both to excite flexural Lamb waves and to monitor in situ the displacements field within the GRIN PC. The efficient subwavelength focusing is achieved and analyzed; furthermore, we describe the oscillatory behavior of focusing and show the relationship between the responses of waves in GRIN PC and the source intensity.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
42.79.Ry Gradient-index (GRIN) devices

Nanoscale study of the current transport through transrotational NiSi/n-Si contacts by conductive atomic force microscopy

Alessandra Alberti and Filippo Giannazzo

Appl. Phys. Lett. 101, 261906 (2012); http://dx.doi.org/10.1063/1.4773488 (4 pages)

Online Publication Date: 28 December 2012

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The average electrical behaviour of transrotational NiSi layers used as contacts in diode structures on n-type Si was correlated to the local structure and conduction paths inside each domain by using conductive-atomic force microscopy. It was found that, independently of the domain orientation, the central portion of the domain (core ∼ 20 nm) possesses a Schottky barrier lower than in the rest of the structure. This was ascribed to an effect of the structural coupling between the NiSi lattice and the silicon substrate as realised at the interface in virtue of the pseudoepitaxial relationship established since the early stages of the reaction.
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85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Hi Surface barrier, boundary, and point contact devices
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Anisotropy of effective masses in CuInSe2

M. V. Yakushev, F. Luckert, A. V. Rodina, C. Faugeras, A. V. Karotki, A. V. Mudryi, and R. W. Martin

Appl. Phys. Lett. 101, 262101 (2012); http://dx.doi.org/10.1063/1.4773480 (5 pages)

Online Publication Date: 26 December 2012

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Anisotropy of the valence band is experimentally demonstrated in CuInSe2, a key component of the absorber layer in one of the leading thin-film solar cell technology. By changing the orientation of applied magnetic fields with respect to the crystal lattice, we measure considerable differences in the diamagnetic shifts and effective g-factors for the A and B free excitons. The resulting free exciton reduced masses are combined with a perturbation model for non-degenerate independent excitons and theoretical dielectric constants to provide the anisotropic effective hole masses, revealing anisotropies of 5.5 (4.2) for the A (B) valence bands.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
71.35.-y Excitons and related phenomena
75.20.Ck Nonmetals
77.22.Ch Permittivity (dielectric function)

Effect of dislocations on electron mobility in AlGaN/GaN and AlGaN/AlN/GaN heterostructures

Stephen W. Kaun, Peter G. Burke, Man Hoi Wong, Erin C. H. Kyle, Umesh K. Mishra, and James S. Speck

Appl. Phys. Lett. 101, 262102 (2012); http://dx.doi.org/10.1063/1.4773510 (4 pages) | Cited 2 times

Online Publication Date: 26 December 2012

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AlxGa1−xN/GaN (x = 0.06, 0.12, 0.24) and AlGaN/AlN/GaN heterostructures were grown on 6 H-SiC, GaN-on-sapphire, and free-standing GaN, resulting in heterostructures with threading dislocation densities of ∼2 × 1010, ∼5 × 108, and ∼5 × 107 cm−2, respectively. All growths were performed under Ga-rich conditions by plasma-assisted molecular beam epitaxy. Dominant scattering mechanisms with variations in threading dislocation density and sheet concentration were indicated through temperature-dependent Hall measurements. The inclusion of an AlN interlayer was also considered. Dislocation scattering contributed to reduced mobility in these heterostructures, especially when sheet concentration was low or when an AlN interlayer was present.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.20.Ee Mobility edges; hopping transport

Performance and stability of solution-based cadmium sulfide thin film transistors: Role of CdS cluster size and film composition

A. L. Salas-Villasenor, I. Mejia, M. Sotelo-Lerma, B. E Gnade, and M. A. Quevedo-Lopez

Appl. Phys. Lett. 101, 262103 (2012); http://dx.doi.org/10.1063/1.4773184 (5 pages)

Online Publication Date: 27 December 2012

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Improved carrier mobility and threshold voltage (VT) stability in cadmium sulfide (CdS) thin film transistors (TFTs) were studied and attributed to larger grain clusters in thicker CdS films rather than individual crystallite size. Non-zero VT shifts (∼200 mV) in thicker films are attributed to the presence of cadmium hydroxide [Cd(OH)2] at the dielectric/CdS interface resulting from the chemical bath deposition process used to deposit the CdS films. VT and mobility analyses indicate that clusters of CdS grains have a larger impact on TFT performance and stability than the presence of impurities in the bulk of the CdS. TFTs using this fabrication method achieved mobilities of ∼22 cm2/Vs with VT of 7 V and ΔVT of <200 mV after testing. The maximum processing temperature is 100 °C which makes this process compatible with flexible substrates.
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85.30.Tv Field effect devices
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Role of Al and Ti for ohmic contact formation in AlGaN/GaN heterostructures

Hirokuni Tokuda, Toshikazu Kojima, and Masaaki Kuzuhara

Appl. Phys. Lett. 101, 262104 (2012); http://dx.doi.org/10.1063/1.4773511 (4 pages)

Online Publication Date: 27 December 2012

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A mechanism for ohmic contact formation using Ti/Al based metals on AlGaN/GaN heterostructures has been investigated by measuring temperature dependence of sheet electron density (ns) and mobility (μ). It was found that both ns and μ at room temperature for Ti/Al deposited sample were increased by annealing in vacuum, while not for Al/Ti deposited one. The results, especially increase in μ, cannot be understood by the conventional ohmic formation model, including Ti-N (nitrogen) complex formation or N vacancy formation. As the most probable mechanism for the increase in ns and μ, we have proposed a model, in which tensile strain is induced by the reaction of Ti/Al and AlGaN after annealing.
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73.40.Ns Metal-nonmetal contacts
61.72.jd Vacancies
68.55.at Other materials
61.72.Cc Kinetics of defect formation and annealing
72.20.Fr Low-field transport and mobility; piezoresistance

Microscopic four-point-probe resistivity measurements of shallow, high density doping layers in silicon

Craig M. Polley, Warrick R. Clarke, Jill A. Miwa, Michelle Y. Simmons, and Justin W. Wells

Appl. Phys. Lett. 101, 262105 (2012); http://dx.doi.org/10.1063/1.4773485 (4 pages) | Cited 1 time

Online Publication Date: 28 December 2012

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We present room temperature resistivity measurements of shallow, monolayer doped phosphorus in silicon, a material system of interest for both conventional microelectronic manufacturing, and future quantum electronic devices. Using an in-situ variable spacing microscopic four-probe system, we demonstrate the ability to separate the conductivity of the substrate and the doping layer. We show that the obtained sensitivity to the dopant layer derives from a combination of the nanoscale contacting areas and the conductivity difference between the highly doped 2D layer and the substrate. At an encapsulation depth of only 4 nm, we demonstrate a room temperature resistivity of 1.4 kΩ/◻.
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72.20.-i Conductivity phenomena in semiconductors and insulators
72.80.Cw Elemental semiconductors
61.72.uf Ge and Si

Acceptors in ZnO nanocrystals: A reinterpretation

W. Gehlhoff and A. Hoffmann

Appl. Phys. Lett. 101, 262106 (2012); http://dx.doi.org/10.1063/1.4773524 (4 pages)

Online Publication Date: 28 December 2012

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In a recent article, Teklemichael et al. reported on the identification of an uncompensated acceptor in ZnO nanocrystals using infrared spectroscopy and electron paramagnetic resonance (EPR) in the dark and under illumination. Most of their conclusions, interpretations, and suggestions turned out to be erroneous. The observed EPR signals were interpreted to originate from axial and nonaxial VZn-H defects. We show that the given interpretation of the EPR results is based on misinterpretations of EPR spectra arising from defects in nanocrystals. The explanation of the infrared absorption lines is in conflict with recent results of valence band ordering and valence band splitting.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
76.30.Mi Color centers and other defects
78.30.Fs III-V and II-VI semiconductors
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Thermally assisted spin-transfer torque magnetization reversal in uniaxial nanomagnets

D. Pinna, Aditi Mitra, D. L. Stein, and A. D. Kent

Appl. Phys. Lett. 101, 262401 (2012); http://dx.doi.org/10.1063/1.4773053 (4 pages) | Cited 1 time

Online Publication Date: 26 December 2012

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We simulate the stochastic Landau-Lifshitz-Gilbert dynamics of a uniaxial nanomagnet out to sub-millisecond timescales using a graphical processing unit based micromagnetic code and determine the effect of geometrical tilts between the spin-current and uniaxial anisotropy axes on the thermally assisted reversal dynamics. The asymptotic behavior of the switching time (I→0, 〈τ〉∝exp(−ξ(1−I)2)) is approached gradually, indicating a broad crossover regime between the ballistic and thermally assisted spin transfer reversal. Interestingly, the functional form of the mean switching time is shown to be independent of the angle between the spin current and magnet's uniaxial axes. These results have important implications for modeling the energetics of thermally assisted magnetization reversal of spin transfer magnetic random access memory bit cells.
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75.60.Jk Magnetization reversal mechanisms
75.75.-c Magnetic properties of nanostructures
75.78.-n Magnetization dynamics
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials

Yoke-shaped MgO-barrier magnetic tunnel junction sensors

J. Y. Chen, N. Carroll, J. F. Feng, and J. M. D. Coey

Appl. Phys. Lett. 101, 262402 (2012); http://dx.doi.org/10.1063/1.4773180 (4 pages)

Online Publication Date: 26 December 2012

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Yoke-shaped sensors based on MgO-barrier magnetic tunnel junctions have been designed, fabricated, and studied; they show a good linear tunneling magnetoresistance (TMR) response. A nearly-perpendicular configuration of two ferromagnetic electrodes was set by two-step annealing together with shape anisotropy. The low-frequency noise characterization shows these yoke-shaped TMR sensors have relatively low magnetic 1/f noise. The field sensitivity is up to 27%/mT, while the field detectivity reaches 4.6 nT/math at 10 Hz and 460 pT/math at 1 kHz. These TMR sensors may be useful for applications such as biomagnetic detection.
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85.75.Ss Magnetic field sensors using spin polarized transport
07.55.-w Magnetic instruments and components
75.47.Lx Magnetic oxides
81.40.Gh Other heat and thermomechanical treatments

Magnetoresistive effect of a topological-insulator waveguide in the presence of a magnetic field

Yuan Li, Mansoor B. A. Jalil, Seng Ghee Tan, Guanghui Zhou, and Zhenghong Qian

Appl. Phys. Lett. 101, 262403 (2012); http://dx.doi.org/10.1063/1.4773489 (4 pages)

Online Publication Date: 26 December 2012

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We investigate the transport properties of a topological insulator (TI) waveguide in the presence of an external magnetic field. We demonstrate that the magnetic field can modulate the energy gap induced by the transverse confinement and may even result in the closure of the band gap. The dependence of the magnetic field and the temperature on the magnetoresistance (MR) is also analyzed. The MR ratio increases linearly and exhibits a nonsaturation behaviour at high fields. The MR behavior also exhibits weak temperature dependence such that a high MR is maintained over a broad temperature range. The robustness of the MR up to room temperature can be exploited for magneto-electronic device applications.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.20.At Surface states, band structure, electron density of states

Stochastic switching asymmetry in magnetoresistive stacks due to adjacent nanowire stray field

M. T. Bryan, N. A. Porter, J. S. Claydon, M. A. Bashir, G. Burnell, C. H. Marrows, T. Schrefl, and D. A. Allwood

Appl. Phys. Lett. 101, 262404 (2012); http://dx.doi.org/10.1063/1.4773370 (4 pages)

Online Publication Date: 27 December 2012

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Giant-magnetoresistance was used to measure the switching of patterned multilayer stacks either close to or removed from a ferromagnetic nanowire. Stray fields from the nanowire greatly changed the stack's free layer hysteresis characteristics. Four distinct switching modes were observed when the applied field opposed the pinned layer magnetization, but reproducible switching occurred otherwise. Micromagnetic modeling suggested that the asymmetry was due to interlayer stray field interactions and the Oersted field from the measuring current, while the switching modes were due to transverse components from the nanowire stray field. The results demonstrate the feasibility of remote electrical detection of nanowire magnetization.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Alternating domains with uniaxial and biaxial magnetic anisotropy in epitaxial Fe films on BaTiO3

Tuomas H. E. Lahtinen, Yasuhiro Shirahata, Lide Yao, Kévin J. A. Franke, Gorige Venkataiah, Tomoyasu Taniyama, and Sebastiaan van Dijken

Appl. Phys. Lett. 101, 262405 (2012); http://dx.doi.org/10.1063/1.4773482 (4 pages) | Cited 2 times

Online Publication Date: 27 December 2012

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We report on domain formation and magnetization reversal in epitaxial Fe films on ferroelectric BaTiO3 substrates with ferroelastic a–c stripe domains. The Fe films exhibit biaxial magnetic anisotropy on top of c domains with out-of-plane polarization, whereas the in-plane lattice elongation of a domains induces uniaxial magnetoelastic anisotropy via inverse magnetostriction. The strong modulation of magnetic anisotropy symmetry results in full imprinting of the a–c domain pattern in the Fe films. Exchange and magnetostatic interactions between neighboring magnetic stripes further influence magnetization reversal and pattern formation within the a and c domains.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
62.20.D- Elasticity
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

Spin precession modulation in a magnetic bilayer

A. Stupakiewicz, M. Pashkevich, A. Maziewski, A. Stognij, and N. Novitskii

Appl. Phys. Lett. 101, 262406 (2012); http://dx.doi.org/10.1063/1.4773508 (4 pages)

Online Publication Date: 27 December 2012

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We report on modulation of the spin precession in a Co/garnet bilayer by femtosecond laser excitation using time-resolved magneto-optical tools. Damped oscillations in the Faraday rotation transients representing precessional motion of the magnetization vector are observed in both the 2 nm Co layer and 1.8 μm garnet of the bilayer with distinct frequencies differing by about a factor of two. The excitation efficiency of these precessions strongly depends on the out-of-plane magnetic field. The modulation effect with the coupling in a magnetic bilayer can be useful for non-thermally controlling the magnetization of nanomagnets and ultrafast switching in magnetic nanodevices.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Investigation of induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers

Stephan Geprägs, Sibylle Meyer, Stephan Altmannshofer, Matthias Opel, Fabrice Wilhelm, Andrei Rogalev, Rudolf Gross, and Sebastian T. B. Goennenwein

Appl. Phys. Lett. 101, 262407 (2012); http://dx.doi.org/10.1063/1.4773509 (4 pages) | Cited 2 times

Online Publication Date: 28 December 2012

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Using X-ray magnetic circular dichroism (XMCD) measurements, we explore the possible existence of induced magnetic moments in thin Pt films deposited onto the ferrimagnetic insulator yttrium iron garnet (Y3Fe5O12). Such a magnetic proximity effect is well established for Pt/ferromagnetic metal heterostructures. Indeed, we observe a clear XMCD signal at the Pt L3 edge in Pt/Fe bilayers, while no such signal can be discerned in XMCD traces of Pt/Y3Fe5O12 bilayers. Integrating the XMCD signals allows to estimate an upper limit for the induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
81.15.Dj E-beam and hot filament evaporation deposition
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
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Superconducting nanowire single photon detectors on-fiber

Gil Bachar, Ilya Baskin, Oleg Shtempluck, and Eyal Buks

Appl. Phys. Lett. 101, 262601 (2012); http://dx.doi.org/10.1063/1.4773305 (3 pages)

Online Publication Date: 26 December 2012

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We present a design of a superconducting nanowire single photon detector fabricated on a core of a single mode optical fiber. The proposed design allows high overlap between the fiber light mode and the detector, and consequently, our fabricated devices can remain small in dimension and maintain speed of operation, without sacrificing the detection efficiency. The on-fiber fabrication method is detailed, together with experimental results. The proposed method can be exploited in the future for the fabrication of other fiber coupled devices.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.60.Vg Fiber-optic instruments
42.15.Eq Optical system design
42.81.Bm Fabrication, cladding, and splicing
42.81.Pa Sensors, gyros
85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
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Dielectric and enhanced pyroelectric properties of (Pb0.325Sr0.675)TiO3 ceramics under direct current bias field

Xiuyun Lei, Xianlin Dong, Chaoliang Mao, Ying Chen, Fei Cao, and Genshui Wang

Appl. Phys. Lett. 101, 262901 (2012); http://dx.doi.org/10.1063/1.4773219 (3 pages) | Cited 1 time

Online Publication Date: 26 December 2012

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(Pb0.325Sr0.675)TiO3 (PST) ceramics were prepared by a traditional solid-state reaction technique. The dielectric and enhanced pyroelectric properties of PST ceramics were investigated under a DC bias field. The dielectric permittivity and dielectric loss of PST ceramics at Curie temperature were 2.97 × 10−4 and 0.006 without DC bias field, respectively. With a DC electric field of 0–500 V/mm, the maximum pyroelectric coefficient and the largest figure of merit (Fd) of PST ceramics were obtained, about 60 × 10−8 C cm−2 K−1 and 26 × 10−5 Pa−1/2, respectively. PST ceramics with such superior electric field enhanced pyroelectric properties have the potential for uncooled focal plane array detectors application.
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77.70.+a Pyroelectric and electrocaloric effects
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Electrically modulated photoluminescence in ferroelectric liquid crystal

Prasun Ganguly, T. Joshi, S. Singh, D. Haranath, and A. M. Biradar

Appl. Phys. Lett. 101, 262902 (2012); http://dx.doi.org/10.1063/1.4773366 (3 pages)

Online Publication Date: 27 December 2012

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multimedia

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Electrical modulation and switching of photoluminescence (PL) have been demonstrated in pure deformed helix ferroelectric liquid crystal (DHFLC) material. The PL intensity increases and peak position shifts towards lower wavelength above a threshold voltage which continues up to a saturation voltage. This is attributed to the helix unwinding phenomenon in the DHFLC on the application of an electric field. Moreover, the PL intensity could be switched between high intensity (field-on) and low intensity (field-off) positions. These studies would add a new dimension to ferroelectric liquid crystal's application in the area of optical devices.
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61.30.-v Liquid crystals
77.80.Fm Switching phenomena
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
78.55.Bq Liquids
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Ultrahigh conductivity of large area suspended few layer graphene films

Nima Rouhi, Yung Yu Wang, and Peter J. Burke

Appl. Phys. Lett. 101, 263101 (2012); http://dx.doi.org/10.1063/1.4772797 (3 pages)

Online Publication Date: 26 December 2012

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Room-temperature (atmospheric-pressure) electrical conductivity measurements of wafer-scale, large-area suspended (few layer) graphene membranes with areas up to 1000 μm2 (30 μm × 30 μm) are presented. Multiple devices on one wafer can be fabricated with high yield from the same chemical vapor deposition grown graphene sheet, transferred from a nickel growth substrate to large opening in a suspended silicon nitride support membrane. This represents areas two to orders of magnitude larger than prior transport studies on any suspended graphene device (single or few layer). We find a sheet conductivity of ∼2500 e2/h (or about 10 Ω/sq) of the suspended graphene, which is an order of magnitude higher than any previously reported sheet conductance of few layer graphene.
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73.61.Wp Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.48.Gh Structure of graphene
68.65.Pq Graphene films
81.05.ue Graphene
72.80.Rj Fullerenes and related materials

Study of radiation effects on the cell structure and evaluation of the dose delivered by x-ray and α-particles microscopy

Ewelina Kosior, Peter Cloetens, Guillaume Devès, Richard Ortega, and Sylvain Bohic

Appl. Phys. Lett. 101, 263102 (2012); http://dx.doi.org/10.1063/1.4773181 (4 pages) | Cited 1 time

Online Publication Date: 26 December 2012

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Hard X-ray fluorescence microscopy and magnified phase contrast imaging are combined to study radiation effects on cells. Experiments were performed on freeze-dried cells at the nano-imaging station ID22NI of the European synchrotron radiation facility. Quantitative phase contrast imaging provides maps of the projected mass and is used to evaluate the structural changes due to irradiation during X-ray fluorescence experiments. Complementary to phase contrast imaging, scanning transmission ion microscopy is performed and doses of all the experiments are compared. We demonstrate the sensitivity of the proposed approach to study radiation-induced damage at the sub-cellular level.
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87.53.Bn Dosimetry/exposure assessment
87.64.M- Optical microscopy
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.85.Tt X-ray microscopes
87.17.-d Cell processes

Raman spectrum method for characterization of pull-in voltages of graphene capacitive shunt switches

Peng Li, Zheng You, and Tianhong Cui

Appl. Phys. Lett. 101, 263103 (2012); http://dx.doi.org/10.1063/1.4773183 (5 pages) | Cited 1 time

Online Publication Date: 27 December 2012

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An approach using Raman spectrum method is reported to measure pull-in voltages of graphene capacitive shunt switches. When the bias excesses the pull-in voltage, the Raman spectrum's intensity largely decreases. Two factors that contribute to the intensity reduction are investigated. Moreover, by monitoring the frequency shift of G peak and 2D band, we are able to detect the pull-in voltage and measure the strain change in graphene beams during switching.
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84.32.Dd Connectors, relays, and switches
85.65.+h Molecular electronic devices

Real time x-ray studies during nanostructure formation on silicon via low energy ion beam irradiation using ultrathin iron films

Osman El-Atwani, Anastassiya Suslova, Alexander DeMasi, Sean Gonderman, Justin Fowler, Mohamad El-Atwani, Karl Ludwig, and Jean Paul Allain

Appl. Phys. Lett. 101, 263104 (2012); http://dx.doi.org/10.1063/1.4773202 (4 pages) | Cited 1 time

Online Publication Date: 27 December 2012

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Real time grazing incidence small angle x-ray scattering and x-ray fluorescence (XRF) are used to elucidate nanodot formation on silicon surfaces during low energy ion beam irradiation of ultrathin iron-coated silicon substrates. Four surface modification stages were identified: (1) surface roughening due to film erosion, (2) surface smoothing and silicon-iron mixing, (3) structure formation, and (4) structure smoothing. The results conclude that 2.5 × 1015 iron atoms in a 50 nm depth triggers surface nanopatterning with a correlated nanodots distance of 25 nm. Moreover, there is a wide window in time where the surface can have correlated nanostructures even after the removal of all the iron atoms from the sample as confirmed by XRF and ex-situ x-ray photoelectron spectroscopy (XPS). In addition, in-situ XPS results indicated silicide formation, which plays a role in the structure formation mechanism.
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81.16.Rf Micro- and nanoscale pattern formation
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.80.Jh Ion radiation effects
61.82.Rx Nanocrystalline materials
78.70.Ck X-ray scattering

The impact of oxygen on the morphology of gas-phase prepared Au nanoparticles

D. Pohl, A. Surrey, L. Schultz, and B. Rellinghaus

Appl. Phys. Lett. 101, 263105 (2012); http://dx.doi.org/10.1063/1.4773203 (5 pages)

Online Publication Date: 27 December 2012

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We present an easy procedure for the synthesis of single crystalline gold nanoparticles with a mean diameter of 4 nm using a DC-sputtering in an argon-oxygen gas mixture. Morphology population statistics have been determined to quantify the influence of oxygen. It is found that the particles undergo a structural transition from predominantly icosahedral to single crystalline particles with increasing amount of oxygen. Aberration-corrected high-resolution transmission electron microscopy investigation proves that likewise prepared single crystalline nanoparticles are defect and oxygen free. In contrast, the icosahedral particles prepared with pure argon show the presence of edge dislocations pointing to an energetic disfavoring already at these relatively small particle sizes. This morphology control of clean and uncovered Au nanoparticles provides a high application potential, e.g., for studying the influence of the particle morphology on plasmonic and catalytic properties.
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81.07.Bc Nanocrystalline materials
81.15.Cd Deposition by sputtering
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.Nd Structural transitions in nanoscale materials

Effects of Be doping on InP nanowire growth mechanisms

R. J. Yee, S. J. Gibson, V. G. Dubrovskii, and R. R. LaPierre

Appl. Phys. Lett. 101, 263106 (2012); http://dx.doi.org/10.1063/1.4773206 (5 pages) | Cited 1 time

Online Publication Date: 27 December 2012

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Be-doped InP nanowires were grown by the gold-assisted vapour-liquid-solid mechanism in a gas source molecular beam epitaxy system. The InP nanowire length versus diameter [L(D)] dependence revealed an unexpected transition with increasing Be dopant concentration. At Be dopant concentration below ∼1018 cm−3, nanowires exhibited the usual inverse L(D) relationship, indicating a diffusion-limited growth regime. However, as dopant concentration increased, the nanowire growth rate was suppressed for small diameters, resulting in an unusual L(D) dependence that increased before saturating in height at about 400 nm. The cause of this may be a change in the droplet chemical potential, introducing a barrier to island nucleation. We propose a model accounting for the limitations of diffusion length and monolayer nucleation to explain this behaviour.
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61.72.uj III-V and II-VI semiconductors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.-c Methods of micro- and nanofabrication and processing
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)
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