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2 Jan 2012

Volume 100, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 013101 (2012); http://dx.doi.org/10.1063/1.3673334 (3 pages)

Patrice Genevet, Nanfang Yu, Francesco Aieta, Jiao Lin, Mikhail A. Kats, Romain Blanchard, Marlan O. Scully, Zeno Gaburro, and Federico Capasso
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Fundamental limits on optical transparency of transparent conducting oxides: Free-carrier absorption in SnO2

H. Peelaers, E. Kioupakis, and C. G. Van de Walle

Appl. Phys. Lett. 100, 011914 (2012); http://dx.doi.org/10.1063/1.3671162 (3 pages) | Cited 7 times

Online Publication Date: 6 January 2012

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Transparent conducting oxides combine high electrical conductivity with transparency to visible light. However, the large concentration of free electrons introduces a source of absorption that limits the transparency. Here, we evaluate the importance of phonon-assisted free-carrier absorption in SnO2 completely from first principles. Our results show that absorption is modest in the visible and much stronger in the UV and infrared. We also provide insight into the mechanisms that govern absorption in different wavelength regimes.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics
72.80.Jc Other crystalline inorganic semiconductors
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Electric-field-induced current-voltage characteristics in electronic conducting perovskite thin films

Jennifer L. M. Rupp, Patrick Reinhard, Daniele Pergolesi, Thomas Ryll, Rene Tölke, and Enrico Traversa

Appl. Phys. Lett. 100, 012101 (2012); http://dx.doi.org/10.1063/1.3663529 (3 pages) | Cited 3 times

Online Publication Date: 3 January 2012

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Mixed ionic-electronic conductors (MIECs) such as the (La,Sr)(Co,Fe)O3−d perovskite family are well described in their charge transport through their high temperature applications, i.e., as solid-oxide fuel cell electrodes (600–1000 °C). In this study, the current-voltage (I-V) profiles of these well-known MIEC perovskites are studied between room temperature and 150 °C under bias of ±15 V for potential applications in resistance random access memories. The impact of the metal-oxide interface on the I-V characteristics ranging from ohmic to non-linear hysteretic is discussed for metals of varying work functions and redox potentials, as well as changes in metal electrode distances and areas.
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82.47.Ed Solid-oxide fuel cells (SOFC)
88.30.pn Solid oxide fuel cells
68.55.-a Thin film structure and morphology
72.60.+g Mixed conductivity and conductivity transitions
73.40.Cg Contact resistance, contact potential
82.45.Fk Electrodes

Resonant carrier scattering by core-shell nanoparticles for thermoelectric power factor enhancement

Je-Hyeong Bahk, Parthiban Santhanam, Zhixi Bian, Rajeev Ram, and Ali Shakouri

Appl. Phys. Lett. 100, 012102 (2012); http://dx.doi.org/10.1063/1.3673615 (4 pages) | Cited 3 times

Online Publication Date: 3 January 2012

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We theoretically investigate the use of energetically sharp resonances of core-shell nanoparticles embedded in semiconductors to selectively scatter carriers and thereby enhance the thermoelectric power factor and figure of merit. Appropriate selection of materials for the core-shell band structure can lead to the formation of quasi-bound states inside the nanoparticles, which strongly scatter carriers near these energy levels, making sharp features in the energy-dependent electron relaxation time. We find that the power factor of PbTe at 80 K is enhanced by more than 80% when core-shell nanoparticles of 3 nm core diameter and 1.5 nm shell width are introduced with density 1 × 1018 cm−3.
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81.07.Bc Nanocrystalline materials
73.63.Bd Nanocrystalline materials
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Pa Thermoelectric and thermomagnetic effects

Relaxation dynamics and residual strain in metamorphic AlSb on GaAs

J. M. Ripalda, A. M. Sanchez, A. G. Taboada, A. Rivera, B. Alén, Y. González, L. González, F. Briones, T. J. Rotter, and G. Balakrishnan

Appl. Phys. Lett. 100, 012103 (2012); http://dx.doi.org/10.1063/1.3674986 (4 pages)

Online Publication Date: 3 January 2012

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We have observed the evolution of the accumulated stress during heteroepitaxial growth of highly lattice mismatched AlSb on GaAs by measuring the deformation of the substrate as a function of time. High resolution transmission electron microscopy images show almost all of the plastic relaxation is accommodated by an array of 90° misfit dislocations at the interface. The in-plane lattice parameter of the resulting metamorphic AlSb is slightly smaller (0.3%) than the bulk value and perfectly matches the lattice parameter of bulk GaSb. It is, therefore, possible to grow nearly stress-free GaSb on GaAs using a metamorphic AlSb buffer layer.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.fq Plasticity and superplasticity
81.40.Lm Deformation, plasticity, and creep
68.60.Bs Mechanical and acoustical properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Optical pumping and reversal of hole spin in InAs/GaAs quantum dots

F. Fras, B. Eble, F. Bernardot, C. Testelin, M. Chamarro, A. Miard, and A. Lemaître

Appl. Phys. Lett. 100, 012104 (2012); http://dx.doi.org/10.1063/1.3673828 (4 pages) | Cited 3 times

Online Publication Date: 4 January 2012

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We have obtained the optical pumping of hole spins, in p-doped InAs/GaAs quantum dots, via the generation of an intermediate trion state by a train of circularly polarized pulses. We show that we can optically control the orientation of the initialized hole spin, independently of the orientation of the intermediate trion state, by choosing the excitation energy of the circularly polarized light. This brings a supplementary degree of freedom for hole-spin manipulations in quantum dots.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
71.35.Pq Charged excitons (trions)
78.67.Hc Quantum dots

Band offsets in HfO2/InGaZnO4 heterojunctions

Hyun Cho, E. A. Douglas, B. P. Gila, V. Craciun, E. S. Lambers, Fan Ren, and S. J. Pearton

Appl. Phys. Lett. 100, 012105 (2012); http://dx.doi.org/10.1063/1.3673905 (3 pages) | Cited 4 times

Online Publication Date: 4 January 2012

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The valence band discontinuity (ΔEV) of sputter deposited HfO2/InZnGaO4 (IGZO) heterostructures was obtained from x-ray photoelectron spectroscopy measurements. The HfO2 exhibited a bandgap of 6.07 eV from absorption measurements. A value of ΔEV = 0.48 ± 0.025 eV was obtained by using the Ga 2p3/2, Zn 2p3/2, and In 3d5/2 energy levels as references. This implies a conduction band offset ΔEC of 2.39 eV in HfO2/InGaZnO4 heterostructures and a nested interface band alignment.
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73.20.At Surface states, band structure, electron density of states
81.15.Cd Deposition by sputtering
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Motion detection of a micromechanical cantilever through magneto-piezovoltage in two-dimensional electron systems

H. Yamaguchi, H. Okamoto, S. Ishihara, and Y. Hirayama

Appl. Phys. Lett. 100, 012106 (2012); http://dx.doi.org/10.1063/1.3674288 (3 pages)

Online Publication Date: 4 January 2012

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We study the strain-induced voltage generation, i.e., piezovoltage, in a two-dimensional electron system under a magnetic field at low temperature. We find its strong magnetic-field dependence, where the voltage increases up to several microvolts at the boundaries between localized and extended electronic states. The order of magnitude of the generated electrical power is comparable to that of the energy dissipation in mechanical vibration, indicating high-efficiency mechanical-to-electrical energy transduction.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Proton-irradiated InAlN/GaN high electron mobility transistors at 5, 10, and 15 MeV energies

H.-Y. Kim, C. F. Lo, L. Liu, F. Ren, J. Kim, and S. J. Pearton

Appl. Phys. Lett. 100, 012107 (2012); http://dx.doi.org/10.1063/1.3673906 (3 pages) | Cited 3 times

Online Publication Date: 5 January 2012

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InAlN/GaN high electron mobility transistors (HEMTs) grown on SiC substrates were subjected to 5-15 MeV high energy protons with a fixed 5 × 1015 cm−2 fluence. The saturation currents and gate leakage currents of all the proton-irradiated InAlN/GaN HEMTs were degraded. Proton irradiation at lower energy was found to degrade the direct current (DC) current-voltage (I-V) characteristics more severely than higher-energy irradiation, because the energy loss component of the lower energy protons was larger than those of higher-energy protons in the vicinity of the 2-dimensional electron gas conducting channel. Our experimental results were consistent with stopping and range of ions in matter simulation results of the energy deposition profile by the protons.
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85.30.Tv Field effect devices

Carbon-mediated growth of thin, fully relaxed germanium films on silicon

D. Tetzlaff, T. F. Wietler, E. Bugiel, and H. J. Osten

Appl. Phys. Lett. 100, 012108 (2012); http://dx.doi.org/10.1063/1.3675450 (3 pages) | Cited 1 time

Online Publication Date: 6 January 2012

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Smooth, fully relaxed Ge layers (thickness below 100 nm) were grown directly on Si(001) in a cyclic process flow. Each cycle consists of a low temperature epitaxy step followed by the deposition of less than a monolayer of carbon and subsequent thermal annealing. Full strain relaxation was achieved for 65 nm thin Ge films. Carbon, which is not incorporated homogenously into the Ge layer, prevents the formation of islands during thermal annealing. The lattice mismatch is accommodated via a regular dislocation array of complete edge dislocations localized at the Si/Ge interface.
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68.55.ag Semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.60.Bs Mechanical and acoustical properties
81.05.Cy Elemental semiconductors
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Tunneling magnetoresistance oscillations due to charging effects in MgO double barrier magnetic tunnel junctions

Ruisheng Liu, See-Hun Yang, Xin Jiang, Teya Topuria, Philip M. Rice, Charles Rettner, and Stuart Parkin

Appl. Phys. Lett. 100, 012401 (2012); http://dx.doi.org/10.1063/1.3673557 (3 pages) | Cited 2 times

Online Publication Date: 3 January 2012

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We observe single-electron tunneling effect and tunneling magnetoresistance (TMR) oscillations in MgO double barrier magnetic tunnel junctions patterned with electron beam lithography and argon ion milling. The TMR oscillations are induced by the interplay of single charge effect and spin-dependent tunneling. The oscillations and its period can be well-controlled by properly engineering the thickness of MgO tunnel barriers and the size of the tunnel junctions.
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75.47.Pq Other materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces

Spin transfer torque programming dipole coupled nanomagnet arrays

Andrew Lyle, Jonathan Harms, Todd Klein, August Lentsch, Daniel Martens, Angeline Klemm, and Jian-Ping Wang

Appl. Phys. Lett. 100, 012402 (2012); http://dx.doi.org/10.1063/1.3673618 (3 pages)

Online Publication Date: 3 January 2012

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We experimentally demonstrated spin transfer torque (STT) programming of dipole coupled nanomagnets using magnetic tunnel junctions. The STT write operations were performed in conjunction with a clock field used in magnetic quantum cellular automata (MQCA) operations. The spacing and number of nanomagnets in the transmission line strongly affected the STT programming of the individual pillars. These MQCA transmission lines ranged in length from 2 elements to 20 elements, while device sizes ranged between 50 nm × 80 nm and 70 nm × 100 nm with spacing between 10 nm and 15 nm. With the application of the clock field, currents of 100-200 μA are sufficient to STT program the device. The demonstration of STT programming of individual nanomagnets in a dipole coupled array marks a significant step forward for applications such as MQCA logic device.
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84.30.Sk Pulse and digital circuits

Engineering magnetic domains in manganite thin films by laser interference

S. R. Bakaul, W. Lin, and T. Wu

Appl. Phys. Lett. 100, 012403 (2012); http://dx.doi.org/10.1063/1.3673870 (4 pages) | Cited 2 times

Online Publication Date: 4 January 2012

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We report on the laser interference (LI) aided conversion from maze-like to stripe-like magnetic domains in La1−xSrxMnO3 (x ∼ 0.3) thin films grown on LaAlO3 substrates. This conversion is attributed to the periodic, local, and rapid heating by LI which facilitates the reconfiguration of magnetic domains without damaging the film structures. By annealing the sample, the stripe-like domains can be converted back to the maze-like state. Our result represents a non-magnetic scheme for reversible magnetic domain engineering in ferromagnetic thin films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
81.40.Gh Other heat and thermomechanical treatments

Reversal and excitations of a nanoscale magnetic domain by sustained pure spin currents

Han Zou, Shuhan Chen, and Yi Ji

Appl. Phys. Lett. 100, 012404 (2012); http://dx.doi.org/10.1063/1.3673855 (3 pages) | Cited 1 time

Online Publication Date: 5 January 2012

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Spin-transfer effects induced by pure spin currents are explored in nonlocal spin valves by using sustained injection currents. Compared to pulsed injection currents used in previous experiments, this approach provides persistent spin-transfer torques and preserves the history of the reversal process. A nanoscale domain in a magnetic wire can be switched reversibly by the sustained pure spin currents. In addition, dips in nonlocal spin signal curves are observed at high magnetic fields for only one polarity of the injection currents. This indicates stable-state magnetization precession around the external field driven by the sustained pure spin currents.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
75.75.Fk Domain structures in nanoparticles
75.78.Fg Dynamics of domain structures

Local electrical characterization of resonant magnetization motion in a single ferromagnetic sub-micrometer particle in lateral geometry

A. Slobodskyy and B. J. van Wees

Appl. Phys. Lett. 100, 012405 (2012); http://dx.doi.org/10.1063/1.3673908 (3 pages)

Online Publication Date: 5 January 2012

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In this article, a detailed characterization of a magnetization motion in a single sub-micrometer and multi-terminal ferromagnetic structure in lateral geometry is performed in a GHz regime using direct DC characterization technique. We have shown applicability of the Stoner-Wohlfarth model [E. C. Stoner and E. P. Wohlfarth, Philos. Trans. R. Soc. London, Ser. A 240, 599 (1948)] to the long (large length to width ratio) magnetic nano-structure. Applying the model to experimental data, we are able to extract relevant magnetization motion parameters and show a correlation between high frequency inductive currents and local magnetization. DC voltage generated over the structure at the resonance, with external magnetic field under an angle to the shape anisotropy axis, is explained.
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75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.75.-c Magnetic properties of nanostructures
75.50.Bb Fe and its alloys

Hysteretic anomalous Hall effect in a ferromagnetic, Mn-rich Ge:Mn nanonet

Danilo Bürger, Shengqiang Zhou, Marcel Höwler, Xin Ou, György J. Kovacs, Helfried Reuther, Arndt Mücklich, Wolfgang Skorupa, Manfred Helm, and Heidemarie Schmidt

Appl. Phys. Lett. 100, 012406 (2012); http://dx.doi.org/10.1063/1.3674981 (4 pages) | Cited 4 times

Online Publication Date: 6 January 2012

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Ferromagnetic Ge:Mn has been fabricated by Mn implantation in intrinsic Ge wafers and by pulsed laser annealing with a pulse duration of 300 ns. Due to a segregation instability during laser annealing, Mn segregates at the liquid-solid interface and an approximately 40 nm thick Ge:Mn surface layer is strongly enriched with Mn. Plan-view images reveal a percolating Mn-rich nanonet. Hysteretic anomalous Hall effect has been observed up to 30 K, but it vanishes after etching away the 40 nm thick Mn-rich Ge:Mn surface layer. The nanonet seems to support the correlation between magnetization and hysteretic Hall resistance. Intrinsic scattering in the threads or vertices of this nanonet may lead to the observed anomalous Hall effect.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Cw Elemental semiconductors
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.ag Semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
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Reducing vortex losses in superconducting microwave resonators with microsphere patterned antidot arrays

D. Bothner, C. Clauss, E. Koroknay, M. Kemmler, T. Gaber, M. Jetter, M. Scheffler, P. Michler, M. Dressel, D. Koelle, and R. Kleiner

Appl. Phys. Lett. 100, 012601 (2012); http://dx.doi.org/10.1063/1.3673869 (3 pages) | Cited 5 times

Online Publication Date: 4 January 2012

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We experimentally investigate the vortex induced energy losses in niobium coplanar waveguide resonators with and without quasihexagonal arrays of nanoholes (antidots), where large-area antidot patterns have been fabricated using self-assembling microsphere lithography. We perform transmission spectroscopy experiments around 6.25 GHz in magnetic field cooling and zero field cooling procedures with perpendicular magnetic fields up to B = 27 mT at a temperature T = 4.2 K. We find that the introduction of antidot arrays into resonators reduces vortex induced losses by more than one order of magnitude.
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85.25.Am Superconducting device characterization, design, and modeling
84.40.Az Waveguides, transmission lines, striplines

Structural and transport characterization of ultra thin Ba0.05Sr0.95TiO3 layers grown over Nb electrodes for the development of Josephson junctions

M. Sirena, L. Avilés Félix, G. A. Carvacho Vera, H. L. Navarro Fernández, L. B. Steren, R. Bernard, J. Briático, N. Bergeal, J. Lesueur, and G. Faini

Appl. Phys. Lett. 100, 012602 (2012); http://dx.doi.org/10.1063/1.3675332 (4 pages) | Cited 1 time

Online Publication Date: 5 January 2012

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A phenomenological approach was used to obtain critical information about the structure and electrical properties of ultra thin Ba0.05Sr0.95TiO3 (BSTO) layers over Nb electrodes. The method allows, in a simple way, to study and to optimize the growth of the barrier in order to improve the performance and application of Josephson junctions. A very good control of the layer thickness with a low roughness was achieved during the deposition process. The BSTO layers present an energy barrier of 0.6 eV and an attenuation length of 0.4 nm, indicating its good insulating properties for the development of Josephson junctions with improved performance.
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74.50.+r Tunneling phenomena; Josephson effects
73.40.Gk Tunneling
74.81.Fa Josephson junction arrays and wire networks
85.25.Cp Josephson devices
85.75.Mm Spin polarized resonant tunnel junctions
74.78.Fk Multilayers, superlattices, heterostructures
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Role of coexisting tetragonal regions in the rhombohedral phase of Na0.5Bi0.5TiO3-xat.%BaTiO3 crystals on enhanced piezoelectric properties on approaching the morphotropic phase boundary

Jianjun Yao, Niven Monsegue, Mitsuhiro Murayama, Weinan Leng, William T. Reynolds, Qinhui Zhang, Haosu Luo, Jiefang Li, Wenwei Ge, and D. Viehland

Appl. Phys. Lett. 100, 012901 (2012); http://dx.doi.org/10.1063/1.3673832 (4 pages) | Cited 10 times

Online Publication Date: 3 January 2012

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The ferroelectric domain and local structures of Na0.5Bi0.5TiO3-xat.%BaTiO3 (NBT-x%BT) crystals for x = 0, 4.5, and 5.5 have been investigated by transmission electron microscopy. The results show that the size of polar nano-regions was refined with increasing xat. %BT. The tetragonal phase volume fraction, as identified by in-phase octahedral tilting, was found to be increased with BT. The findings indicate that the large electric field induced strains in morphotropic phase boundary compositions of NBT-x%BT originate not only from polarization rotation but also polarization extension.
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77.65.Ly Strain-induced piezoelectric fields
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
61.66.Fn Inorganic compounds
81.16.-c Methods of micro- and nanofabrication and processing

Relaxor ferroelectric characteristics of Ba5LaTi3Nb7O30 tungsten bronze ceramics

Kun Li, Xiao Li Zhu, Xiao Qiang Liu, and Xiang Ming Chen

Appl. Phys. Lett. 100, 012902 (2012); http://dx.doi.org/10.1063/1.3673913 (4 pages) | Cited 6 times

Online Publication Date: 3 January 2012

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Ba5LaTi3Nb7O30 tungsten-bronze ferroelectric ceramics were synthesized and characterized. The tetragonal tungsten bronze structure in space group P4/mbm was confirmed, and a broad permittivity peak with strong frequency dispersion was observed around 250 K where the peak points well fitted the Vogel-Fulcher relationship [H. Vogel, Phys. Zeit. 22, 645 (1921); G. S. Fulcher, J. Am. Ceram. Soc. 8, 339 (1925)]. The temperature dependence of the ferroelectric hysteresis indicated the paraelectric to ferroelectric phase transition in the temperature range between 153 and 273 K. The high temperature permittivity curve deviated from the Curie-Weiss law in quite a narrow temperature region above Tmax, which reflected the weak correlations between the polar nanoregions. The Curie-Weiss constant (C) was 1.218 × 105 K, which was consistent with that for the displacive type ferroelectric. No DSC peak was detected over the temperature region investigated here. Moreover, the Curie-Weiss constant below Tmax (C′) was just two times of C, and the second order phase transition was confirmed for Ba5LaTi3Nb7O30.
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77.80.Jk Relaxor ferroelectrics
61.66.Fn Inorganic compounds
77.84.Ek Niobates and tantalates
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis

Size-dependent low-frequency dielectric properties in the BaTiO3/poly(vinylidene fluoride) nanocomposite films

Ben-Hui Fan, Jun-Wei Zha, Dongrui Wang, Jun Zhao, and Zhi-Min Dang

Appl. Phys. Lett. 100, 012903 (2012); http://dx.doi.org/10.1063/1.3673555 (4 pages) | Cited 7 times

Online Publication Date: 4 January 2012

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Effects of inorganic nanoparticles size and thermal agitation on dielectric properties of BaTiO3/poly(vinylidene fluoride) (BT/PVDF) nanocomposite films at low frequency were studied. The dielectric properties of the BT/PVDF nanocomposite films with three kinds of diameters of BT nanoparticles loading at 50 vol. % were studied in a wide frequency range from 10−2 Hz to 107 Hz by two measured processes. A significant low-frequency dielectric permittivity increase and the difference in dielectric properties between two measured processes were discussed. Interfacial polarization, crystal phase effect, and thermal agitation are considered to analyze the significant increase and difference in dielectric behaviors.
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77.22.Ch Permittivity (dielectric function)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
77.22.Ej Polarization and depolarization
77.22.Gm Dielectric loss and relaxation
81.05.Qk Reinforced polymers and polymer-based composites

Biocompatible ferroelectric (Na,K)NbO3 nanofibers

A. Jalalian and A. M. Grishin

Appl. Phys. Lett. 100, 012904 (2012); http://dx.doi.org/10.1063/1.3673282 (4 pages)

Online Publication Date: 5 January 2012

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Dense homogeneous textile composed from continuous bead-free sodium potassium niobate (NKN) nanofibers 100 μm long and 50-200 nm in diameter was sintered by sol-gel calcination assisted electrospinning. High resolution electron microscopy and x-ray diffraction revealed preferential cube-on-cube growth of fibers in [001] direction. Raman spectrum of NKN fibers contains all the features characteristic to electrically poled orthorhombic phase. In contrast to polycrystalline ceramics, it shows relative enhancement of the Raman cross section of isotropic A1g(ν1) mode compared with polar axis defined F2g(ν5) and Eg(ν2) vibrations. We interpret this as an evidence for superparaelectric state of NKN nanofibers. Spontaneous polarization inside highly crystalline nanofiber exists at room temperature though big distance between fibers prevents the settling of a net macroscopic polarization.
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77.80.-e Ferroelectricity and antiferroelectricity
78.30.Hv Other nonmetallic inorganics
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
77.22.Ej Polarization and depolarization
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Ultra-thin plasmonic optical vortex plate based on phase discontinuities

Patrice Genevet, Nanfang Yu, Francesco Aieta, Jiao Lin, Mikhail A. Kats, Romain Blanchard, Marlan O. Scully, Zeno Gaburro, and Federico Capasso

Appl. Phys. Lett. 100, 013101 (2012); http://dx.doi.org/10.1063/1.3673334 (3 pages) | Cited 20 times

Online Publication Date: 3 January 2012

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A flat optical device that generates optical vortices with a variety of topological charges is demonstrated. This device spatially modulates light beams over a distance much smaller than the wavelength in the direction of propagation by means of an array of V-shaped plasmonic antennas with sub-wavelength separation. Optical vortices are shown to develop after a sub-wavelength propagation distance from the array, a feature that has major potential implications for integrated optics.
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42.79.Hp Optical processors, correlators, and modulators
84.40.Ba Antennas: theory, components and accessories

High field-gradient dysprosium tips for magnetic resonance force microscopy

H. J. Mamin, C. T. Rettner, M. H. Sherwood, L. Gao, and D. Rugar

Appl. Phys. Lett. 100, 013102 (2012); http://dx.doi.org/10.1063/1.3673910 (4 pages) | Cited 4 times

Online Publication Date: 3 January 2012

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Magnetic resonance force microscopy (MRFM) is based on measuring the attonewton-scale force between nuclear or electronic spins and a magnetic tip. The force is directly proportional to the magnetic field gradient generated by the tip, making a high moment nanoscale magnet desirable. Dysprosium, with a bulk magnetization 70% higher than iron, is a suitable candidate for such a tip. We have performed MRFM to quantitatively characterize two Dy nanomagnets. We find that magnetic field gradients as high as 6 MT/m (60 G/nm) can be generated, a 40% enhancement compared to our previous FeCo tips.
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75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Observation of nonlinear absorption and visible photoluminescence emission in chemically synthesized Cu2+ doped ZnS nanoparticles

A. K. Kole, P. Kumbhakar, and U. Chatterjee

Appl. Phys. Lett. 100, 013103 (2012); http://dx.doi.org/10.1063/1.3674307 (3 pages) | Cited 3 times

Online Publication Date: 3 January 2012

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Nonlinear optical properties of chemically synthesized ZnS and Cu2+ doped ZnS nanoparticles of average sizes ∼2.5 nm are reported by using open aperture z-scan technique with the Nd:YAG laser second harmonic radiation at 532 nm. Tunable photoluminescence emissions in the visible region due to the increase in concentration of Cu2+ doping in ZnS are observed at room temperature. By analyzing the experimental z-scan data, it is found that three photon absorptions (3PA) are taking place in all the samples. The extracted values of 3PA coefficients of the samples are ∼109 times higher than that of bulk ZnS.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.Be Chemical synthesis methods
78.40.Fy Semiconductors
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors

Predicting shape and stability of air–water interface on superhydrophobic surfaces comprised of pores with arbitrary shapes and depths

B. Emami, H. Vahedi Tafreshi, M. Gad-el-Hak, and G. C. Tepper

Appl. Phys. Lett. 100, 013104 (2012); http://dx.doi.org/10.1063/1.3673619 (4 pages) | Cited 6 times

Online Publication Date: 4 January 2012

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An integro-differential equation for the three dimensional shape of air–water interface on superhydrophobic surfaces comprised of pores with arbitrary shapes and depths is developed and used to predict the static critical pressure under which such surfaces depart from the non-wetting state. Our equation balances the capillary forces with the pressure of the air entrapped in the pores and that of the water over the interface. Stability of shallow and deep circular, elliptical, and polygonal pores is compared with one another and a general conclusion is drawn for designing pore shapes for superhydrophobic surfaces with maximum stability.
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68.03.Cd Surface tension and related phenomena
68.08.Bc Wetting
02.60.Lj Ordinary and partial differential equations; boundary value problems
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