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30 May 2011

Volume 98, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 223101 (2011); http://dx.doi.org/10.1063/1.3595266 (3 pages)

Takahiro Ohori, Yasuhide Ohno, Kenzo Maehashi, Koichi Inoue, Yutaka Hayashi, and Kazuhiko Matsumoto
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Theoretical insight of adsorption cooling

Anutosh Chakraborty, Kai Choong Leong, Kyaw Thu, Bidyut Baran Saha, and Kim Choon Ng

Appl. Phys. Lett. 98, 221910 (2011); http://dx.doi.org/10.1063/1.3592260 (3 pages) | Cited 4 times

Online Publication Date: 3 June 2011

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This letter proposes and presents a thermodynamic formulation to calculate the energetic performances of an adsorption cooler as a function of pore widths and volumes of solid adsorbents. The simulated results in terms of the coefficient of performance are validated with experimental data. It is found from the present analysis that the performance of an adsorption cooling device is influenced mainly by the physical characteristics of solid adsorbents, and the characteristics energy between the adsorbent-adsorbate systems. The present study confirms that there exists a special type of silica gel having optimal physical characteristics that allows us to obtain the best performance.
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68.43.Mn Adsorption kinetics
82.70.Gg Gels and sols
68.35.Md Surface thermodynamics, surface energies
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Multilayer graphene under vertical electric field

S. Bala Kumar and Jing Guo

Appl. Phys. Lett. 98, 222101 (2011); http://dx.doi.org/10.1063/1.3595335 (3 pages) | Cited 7 times

Online Publication Date: 31 May 2011

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We study the effect of vertical electric field (E-field) on the electronic properties of multilayer graphene. We show that the effective mass, electron velocity, and density-of-state of a bilayer graphene are modified under the E-field. We also study the transformation of the band structure of multilayer graphenes. E-field induces finite (zero) band gap in the even (odd)-layer ABA-stacking graphene. On the other hand, finite band gap is induced in all ABC-stacking graphene. We also identify the optimum E-field to obtain the maximum band gap in the multilayer graphenes. Finally, we compare our results with the experimental results of a field-effect-transistor.
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73.22.Pr Electronic structure of graphene
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.21.Ac Multilayers
61.48.Gh Structure of graphene

Effective passivation of Si surfaces by plasma deposited SiOx/a-SiNx:H stacks

G. Dingemans, M. M. Mandoc, S. Bordihn, M. C. M. van de Sanden, and W. M. M. Kessels

Appl. Phys. Lett. 98, 222102 (2011); http://dx.doi.org/10.1063/1.3595940 (3 pages) | Cited 7 times

Online Publication Date: 31 May 2011

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Very low surface recombination velocities <6 and <11 cm/s were obtained for SiOx/a-SiNx:H stacks synthesized by plasma-enhanced chemical vapor deposition on low resistivity n- and p-type c-Si, respectively. The stacks induced a constant effective lifetime under low illumination, comparable to Al2O3 on p-type Si. Compared to single layer a-SiNx:H, a lower positive fixed charge density was revealed by second-harmonic generation measurements, while field-effect passivation was absent for a reference stack comprising thermally grown SiO2. The results indicate that hydrogenation of interface states played a key role in the passivation and remained effective up to annealing temperatures >800 °C.
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81.65.Rv Passivation
61.43.-j Disordered solids
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Two-dimensional electron gas transport anisotropy in N-polar GaN/AlGaN heterostructures

G. A. Umana-Membreno, T. B. Fehlberg, S. Kolluri, D. F. Brown, S. Keller, U. K. Mishra, B. D. Nener, L. Faraone, and G. Parish

Appl. Phys. Lett. 98, 222103 (2011); http://dx.doi.org/10.1063/1.3595341 (3 pages) | Cited 2 times

Online Publication Date: 1 June 2011

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Magnetic-field dependent Hall-effect measurements and mobility spectrum analysis were employed to study anisotropic transport in N-polar GaN/Al0.3Ga0.7N heterostructures grown on vicinal sapphire substrates. The significant anisotropy in the mobility in the parallel and perpendicular directions to the miscut direction was accompanied by a slight anisotropy in charge density. A single electron species was found in the direction parallel to the steps resulting from growth on the vicinal substrates; while in the perpendicular direction two distinct electrons peaks were evident at T ≤ 150 K. The lower average mobility in the perpendicular direction is attributed to interface roughness scattering.
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81.05.Ea III-V semiconductors
68.35.Ct Interface structure and roughness
72.20.Fr Low-field transport and mobility; piezoresistance
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Accuracy evaluation of single-electron shuttle transfer in Si nanowire metal-oxide-semiconductor field-effect transistors

Gento Yamahata, Katsuhiko Nishiguchi, and Akira Fujiwara

Appl. Phys. Lett. 98, 222104 (2011); http://dx.doi.org/10.1063/1.3595683 (3 pages) | Cited 1 time

Online Publication Date: 2 June 2011

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We report on evaluation of transfer accuracy in a single-electron turnstile using silicon nanowire metal-oxide-semiconductor field-effect transistors at 17 K. Single-electron shuttle transfer and single-shot detection of a single electron are used to detect errors of the transfer. Errors for the transfer through an electrostatically formed island are ascribed to thermal processes. We also observed single-electron transfer mediated by a trap level, which exhibits a wide current plateau and a low error rate.
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81.05.Cy Elemental semiconductors
85.30.Tv Field effect devices
81.07.Gf Nanowires

Effect of SiC wafer miscut angle on the morphology and Hall mobility of epitaxially grown graphene

Christos Dimitrakopoulos, Alfred Grill, Timothy J. McArdle, Zihong Liu, Robert Wisnieff, and Dimitri A. Antoniadis

Appl. Phys. Lett. 98, 222105 (2011); http://dx.doi.org/10.1063/1.3595945 (3 pages) | Cited 3 times

Online Publication Date: 2 June 2011

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We show that the surface morphology and electrical properties of graphene grown on SiC(0001) wafers depend strongly on miscut angle, even for nominally “on-axis” wafers. Graphene grown on pit-free surfaces with narrow terraces (miscut above 0.28°) shows substantially lower Hall mobility than graphene on surfaces with miscut angles below 0.1° that have wider terraces with some pits. The effect of pits on mobility is not detrimental if flat, pit-free areas with dimensions larger than the carrier mean free path remain between pits. Using these results, we optimized the growth process, achieving room-temperature mobility up to 3015 cm2/V s at N = 2.0×1012 cm−2.
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72.80.Vp Electronic transport in graphene
68.47.-b Solid-gas/vacuum interfaces: types of surfaces
72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
61.48.Gh Structure of graphene

An observation of charge trapping phenomena in GaN/AlGaN/Gd2O3/Ni–Au structure

Liann Be Chang, Atanu Das, Ray Ming Lin, Siddheswar Maikap, Ming Jer Jeng, and Shu Tsun Chou

Appl. Phys. Lett. 98, 222106 (2011); http://dx.doi.org/10.1063/1.3596382 (3 pages) | Cited 3 times

Online Publication Date: 2 June 2011

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Charge trapping, especially electron trapping phenomena in GaN/AlGaN/Gd2O3/Ni–Au metal-oxide-semiconductor structure have been investigated. Owing to crystallization of Gd2O3 film after annealing at 900 °C in ambient air for 30 s, a significant memory window of 1.6 V is observed under 5 V@100 ms programming pulse compared with that of as-deposited sample. The fabricated structure exhibits no erase phenomena under large negative bias of −20 V. Only time dependent natural charge loss is occurred. Even so, 0.9 V of memory window is still remained after 21 h of retention. Good endurance of 103 cycles with 2.0 V memory window is also obtained.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Observation of the memory steps in graphene at elevated temperatures

Sergey L. Rumyantsev, Guanxiong Liu, Michael S. Shur, and Alexander A. Balandin

Appl. Phys. Lett. 98, 222107 (2011); http://dx.doi.org/10.1063/1.3596441 (3 pages) | Cited 2 times

Online Publication Date: 2 June 2011

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We found that the current-voltage characteristics of graphene transistors exhibit an intriguing feature—an abrupt change in the current near zero gate bias at temperatures above 500 K. The strength of this effect, which we refer to as the memory step by analogy with the memory dips—known phenomenon in electron glasses, depends on the rate of the gate voltage sweep. The slower the sweep, the more pronounced is the step in the current. Despite differences in examined graphene transistors, the memory step always appears at Vg ≈ 0 V. The observed memory steps are likely related to the slow relaxation processes in graphene. This new phenomenon in graphene can be used for applications in sensors and switches.
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85.35.Gv Single electron devices
85.65.+h Molecular electronic devices

Electron hopping interactions in amorphous ZnO films probed by x-ray absorption near edge structure analysis

Deok-Yong Cho, Jeong Hwan Kim, and Cheol Seong Hwang

Appl. Phys. Lett. 98, 222108 (2011); http://dx.doi.org/10.1063/1.3596701 (3 pages)

Online Publication Date: 3 June 2011

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The x-ray absorption near edge structures of amorphous ZnO (a-ZnO) films were examined. The near-edge structure, which reflects the virtual electron hopping interactions in the photoabsorption final states, increased in intensity compared to crystalline ZnO. Theoretical path-by-path analyses revealed that this reflects the extinction of the multiple hopping processes found in paths such as Zn→O→O′→Zn or Zn→O→Zn′→Zn while the Zn–(O or Zn) hopping interactions remain. This suggests that the structural disorders in a-ZnO can induce the localization of the conduction band through the limited hopping interactions.
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73.61.Ga II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors
78.70.Dm X-ray absorption spectra

Effects of substrate orientation on the structural and electronic properties of epitaxial graphene on SiC(0001)

Joshua A. Robinson, Kathleen A. Trumbull, Michael LaBella, III, Randall Cavalero, Matthew J. Hollander, Michael Zhu, Maxwell T. Wetherington, Mark Fanton, and David W. Snyder

Appl. Phys. Lett. 98, 222109 (2011); http://dx.doi.org/10.1063/1.3597356 (3 pages) | Cited 4 times

Online Publication Date: 3 June 2011

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We investigate graphene transport and structural properties as a function of silicon carbide (SiC) wafer orientation. Terrace step edge density is found to increase with wafer misorientation from SiC(0001). This results in a monotonic increase in average graphene thickness, as well as a 30% increase in carrier density and 40% decrease in mobility up to 0.45° miscut toward (1math00). Beyond 0.45°, average thickness and carrier density continues to increase; however, carrier mobility is similar to low-miscut angles, suggesting that the interaction between graphene and SiC(0001) may be fundamentally different that of graphene/SiC(1math0n).
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72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Wp Fullerenes and related materials
61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene

Rare earth chalcogenide Ce3Te4 as high efficiency high temperature thermoelectric material

Xiaochun Wang, Ronggui Yang, Yong Zhang, Peihong Zhang, and Yu Xue

Appl. Phys. Lett. 98, 222110 (2011); http://dx.doi.org/10.1063/1.3597409 (3 pages) | Cited 1 time

Online Publication Date: 3 June 2011

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The electronic band structures of Ce3Te4 have been studied using the first-principles density-functional theory calculations. It is found that the density of states of Ce3Te4 has a very high delta-shaped peak appearing 0.21 eV above the Fermi level, which mainly comes from the f orbital electrons of the rare-earth element Ce. Using the simple theory proposed by Mahan and Sofo, [Proc. Natl. Acad. Sci. U.S.A. 93, 7436 (1996)] , we obtain an ideal value of zT = 13.5 for Ce3Te4 at T = 1200 K, suggesting that the rare-earth chalcogenide Ce3Te4 could be a promising high efficiency high temperature thermoelectric material.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds

Analysis of surface morphology at leakage current sources of 4H–SiC Schottky barrier diodes

Takashi Katsuno, Yukihiko Watanabe, Hirokazu Fujiwara, Masaki Konishi, Hideki Naruoka, Jun Morimoto, Tomoo Morino, and Takeshi Endo

Appl. Phys. Lett. 98, 222111 (2011); http://dx.doi.org/10.1063/1.3597413 (3 pages) | Cited 2 times

Online Publication Date: 3 June 2011

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The surface morphologies of leakage current sources of 4H–SiC Schottky barrier diode were analyzed using atomic force microscopy (AFM). Nanosized circular cone shaped pits (nanopits) were observed at the leakage current sources. Leakage currents were generated due to the concentration of electric fields at the nanopits during measurements of the reverse bias characteristics. The positions of the nanopits correspond to the positions of threading dislocations (TDs), which were identified from molten potassium hydroxide (KOH) etching. The most important factor of leakage current generation was determined to be the surface morphology of the TDs rather than the presence of TDs.
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85.30.Kk Junction diodes

Replacement of oxide glass with metallic glass for Ag screen printing metallization on Si emitter

Se Yun Kim, Sang Soo Jee, Ka Ram Lim, Won Tae Kim, Do Hyang Kim, Eun-Sung Lee, Young Hwan Kim, Sang Mock Lee, Jun Ho Lee, and Jürgen Eckert

Appl. Phys. Lett. 98, 222112 (2011); http://dx.doi.org/10.1063/1.3596469 (3 pages) | Cited 6 times

Online Publication Date: 3 June 2011

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Cu–Zr-based metallic glass (MG) has been applied as a binding agent of Ag paste for front contact formation in Si solar cell by screen printing process. Use of electroconductive MG binder significantly improves the quality of the contact by the formation of highly dense 10–50 nm size Ag crystallites and the noncorrugation of the emitter surface with a very shallow Ag crystallite penetration depth of 10–30 nm. Nanoscale Ag crystallites form on the emitter surface by local Si–Cu–Ag eutectic melting, leading to the formation of pyramidal pits on the Si emitter surface, followed by precipitation of Ag crystallites during cooling.
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88.40.jj Silicon solar cells
85.40.Ls Metallization, contacts, interconnects; device isolation
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FePt L10/A1 graded media with a rough interphase boundary

Jehyun Lee, Vasilis Alexandrakis, Markus Fuger, Barbara Dymerska, Dieter Suess, Dimitris Niarchos, and Josef Fidler

Appl. Phys. Lett. 98, 222501 (2011); http://dx.doi.org/10.1063/1.3595307 (3 pages) | Cited 4 times

Online Publication Date: 31 May 2011

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A graded media consisting of FePt L10(hard) and A1(soft) phases separated by a rough wedge-shaped interphase boundary, the “phase graded media” is suggested. The rough interface helps domain wall propagation from the soft to the hard phase, owing to the easily reversed wedge tips of the hard phase. The reversed domain expands in the hard phase with a small additional field. As a result, the switching field of the phase graded media was reduced to 13 kOe which is 16% of FePt L10 single phase (79 kOe), the reduction is comparable with the stacked graded media.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure

From positive to negative magnetoresistance in graphene with increasing disorder

Yang-Bo Zhou, Bing-Hong Han, Zhi-Min Liao, Han-Chun Wu, and Da-Peng Yu

Appl. Phys. Lett. 98, 222502 (2011); http://dx.doi.org/10.1063/1.3595681 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2011

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Artificial disorder was introduced gradually into monolayer graphene by controlling Ga+ ion irradiation and the corresponding electronic transport properties regulated by gate voltage, source-drain voltage, temperature, and magnetic field were studied experimentally. An unsaturated positive magnetoresistance (MR) up to 100% at ∼ 5 T was observed in as-fabricated graphene, while there is significant negative MR in disordered graphene. This phenomenon was attributed to the monocrystalline breaking and crystallite-boundary scattering in disordered graphene.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Wp Fullerenes and related materials
75.70.Ak Magnetic properties of monolayers and thin films
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Robust surface electronic properties of topological insulators: Bi2Te3 films grown by molecular beam epitaxy

L. Plucinski, G. Mussler, J. Krumrain, A. Herdt, S. Suga, D. Grützmacher, and C. M. Schneider

Appl. Phys. Lett. 98, 222503 (2011); http://dx.doi.org/10.1063/1.3595309 (3 pages) | Cited 5 times

Online Publication Date: 1 June 2011

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The surface electronic properties of the important topological insulator Bi2Te3 are shown to be robust under an extended surface preparation procedure, which includes exposure to atmosphere and subsequent cleaning and recrystallization by an optimized in situ sputter-anneal procedure under ultrahigh vacuum conditions. Clear Dirac-cone features are displayed in high-resolution angle-resolved photoemission spectra from the resulting samples, indicating remarkable insensitivity of the topological surface state to cleaning-induced surface roughness.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.65.Cf Surface cleaning, etching, patterning
68.55.aj Insulators

Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1−xKxFe2As2 superconductors

Lei Wang, Yanwei Ma, Qingxiao Wang, Kun Li, Xixiang Zhang, Yanpeng Qi, Zhaoshun Gao, Xianping Zhang, Dongliang Wang, Chao Yao, and Chunlei Wang

Appl. Phys. Lett. 98, 222504 (2011); http://dx.doi.org/10.1063/1.3592580 (3 pages) | Cited 11 times

Online Publication Date: 1 June 2011

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We report here an atomic resolution study of the structure and composition of the grain boundaries in polycrystalline Sr0.6K0.4Fe2As2 superconductor. A large fraction of grain boundaries contain amorphous layers larger than the coherence length, while some others contain nanometer-scale crystallites sandwiched in between amorphous layers. We also find that there is significant oxygen enrichment at the grain boundaries. Such results explain the relatively low transport critical current density (Jc) of polycrystalline samples with respect to that of bicrystal films.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
74.70.Xa Pnictides and chalcogenides
61.72.Mm Grain and twin boundaries
74.25.F- Transport properties
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
74.25.Sv Critical currents

Hybridization-induced oscillatory magnetic polarization of C60 orbitals at the C60/Fe(001) interface

T. L. A. Tran, P. K. J. Wong, M. P. de Jong, W. G. van der Wiel, Y. Q. Zhan, and M. Fahlman

Appl. Phys. Lett. 98, 222505 (2011); http://dx.doi.org/10.1063/1.3595269 (3 pages) | Cited 7 times

Online Publication Date: 2 June 2011

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We have studied the electronic and magnetic properties of the interface between C60 molecules and a Fe(001) surface. X-ray absorption spectroscopy and x-ray magnetic circular dichroism studies of C60 monolayers on Fe(001) surfaces show that hybridization between the frontier orbitals of C60 and continuum states of Fe leads to a significant magnetic polarization of C60 π∗-derived orbitals. The magnitude and also the sign of this polarization were found to depend markedly on the excitation energy. These observations underline the importance of tailoring the interfacial spin polarization at the Fermi level of ferromagnet/organic semiconductor interfaces for applications in organic spintronics.
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73.20.At Surface states, band structure, electron density of states
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra

Three-dimensional ferromagnetic architectures with multiple metastable states

F. Nasirpouri, M. A. Engbarth, S. J. Bending, L. M. Peter, A. Knittel, H. Fangohr, and M. V. Milošević

Appl. Phys. Lett. 98, 222506 (2011); http://dx.doi.org/10.1063/1.3595339 (3 pages) | Cited 1 time

Online Publication Date: 2 June 2011

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We demonstrate controllable dual-bath electrodeposition of nickel on architecture-tunable three-dimensional (3D) silver microcrystals. Magnetic hysteresis loops of individual highly faceted Ag-Ni core-shell elements reveal magnetization reversal that comprises multiple sharp steps corresponding to different stable magnetic states. Finite-element micromagnetic simulations on smaller systems show several jumps during magnetization reversal which correspond to transitions between different magnetic vortex states. Structures of this type could be realizations of an advanced magnetic data storage architecture whereby each element represents one multibit, storing a combination of several conventional bits depending on the overall number of possible magnetic states associated with the 3D core-shell shape.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
81.15.Pq Electrodeposition, electroplating
75.78.Cd Micromagnetic simulations
75.50.Cc Other ferromagnetic metals and alloys

Nanocomposite exchange-spring magnet synthesized by gas phase method: From isotropic to anisotropic

Xiaoqi Liu, Shihai He, Jiao-Ming Qiu, and Jian-Ping Wang

Appl. Phys. Lett. 98, 222507 (2011); http://dx.doi.org/10.1063/1.3597225 (3 pages) | Cited 6 times

Online Publication Date: 3 June 2011

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The fabrication of anisotropic nanocomposite exchange-spring magnets is demonstrated experimentally by using a gas-phase nanoparticle deposition technique. High resolution transmission electron microscopy images prove the experimental easy-axis definition of embedded hard magnetic nanoparticles in soft magnetic matrix. Exchange coupling between the hard and soft phases is confirmed by measuring recoil loops and δ M-H curve of the anisotropic FePt/Fe0.8Ni0.2 nanocomposite. The magnetic energy product for the anisotropic exchange-spring magnet is 224% higher than the isotropic case.
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75.75.Cd Fabrication of magnetic nanostructures
75.30.Et Exchange and superexchange interactions
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials

Rise and fall of defect induced ferromagnetism in SiC single crystals

Lin Li, S. Prucnal, S. D. Yao, K. Potzger, W. Anwand, A. Wagner, and Shengqiang Zhou

Appl. Phys. Lett. 98, 222508 (2011); http://dx.doi.org/10.1063/1.3597629 (3 pages) | Cited 7 times

Online Publication Date: 3 June 2011

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6H–SiC (silicon carbide) single crystals containing VSi–VC divacancies are investigated with respect to magnetic and structural properties. We found that an initial increase in structural disorder leads to pronounced ferromagnetic properties at room temperature. Further introduction of disorder lowers the saturation magnetization and is accompanied with the onset of lattice amorphization. Close to the threshold of full amorphization, also divacancy clusters are formed and the saturation magnetization nearly drops to zero.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.jd Vacancies
61.66.Fn Inorganic compounds

Electric field modulation of magnetoresistance in multiferroic heterostructures for ultralow power electronics

Ming Liu, Shandong Li, Ogheneyunume Obi, Jing Lou, Scott Rand, and Nian X. Sun

Appl. Phys. Lett. 98, 222509 (2011); http://dx.doi.org/10.1063/1.3597796 (3 pages) | Cited 12 times

Online Publication Date: 3 June 2011

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An energy-efficiency technique for electrically modulating magnetoresistance was demonstrated in multiferroic anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR) heterostructures. A giant electric field (E-field) induced magnetic anisotropy caused by a strong magnetoelectric coupling was utilized to control the orientation of magnetization and thus dynamically manipulate magnetoresistance in AMR and GMR devices. A multiband tunable AMR field sensor was designed and developed to dramatically enhance the measurement range by 15 times. In addition, two types of E-field determination of GMR in spin-valve structures are studied. The results indicate an energy efficiency approach to controlling magnetoresistance by E-field rather than magnetic field, which shows great potential for novel low power electronic and spintronic devices.
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75.85.+t Magnetoelectric effects, multiferroics
07.55.-w Magnetic instruments and components
75.30.Gw Magnetic anisotropy
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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Energy harvesting by nonlinear capacitance variation for a relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer

H. Zhu, S. Pruvost, P. J. Cottinet, and D. Guyomar

Appl. Phys. Lett. 98, 222901 (2011); http://dx.doi.org/10.1063/1.3595325 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2011

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The present letter describes the investigation of the electrostatic energy harvesting through nonlinear capacitance variation caused by changes in temperature for a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer. Owing to the electric tunability of the terpolymer, the harvested energy can-using an Ericsson cycle-be simulated from permittivity under a dc electric field. When going from 25 to 0 °C, it was found, from simulation, that the harvested energy increased up to 240 mJ/cm3 when raising the electric field at 80 kV/mm. Experimental measurement was also carried out, thus confirming the feasibility of electrostatic energy harvesting through low temperature Ericsson cycle.
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77.84.Jd Polymers; organic compounds
84.60.-h Direct energy conversion and storage
77.80.Jk Relaxor ferroelectrics
77.22.Ch Permittivity (dielectric function)

Electrodes controlling phase diagrams of symmetric ferroelectric tunneling junctions or capacitors

W. J. Chen, Yue Zheng, and Biao Wang

Appl. Phys. Lett. 98, 222902 (2011); http://dx.doi.org/10.1063/1.3591163 (3 pages)

Online Publication Date: 2 June 2011

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Electrodes controlling the “misfit strain-temperature” phase diagrams of symmetric ferroelectric tunneling junctions or capacitors have been investigated. Taking into account effect of the imperfect charge screening in electrodes, it is found that the phase diagrams can be significantly shifted with changing coefficients of electrodes. Results about the dielectric constants also indicate promising controllability of other properties for ferroelectric tunnel junction or capacitor by adjusting electrodes.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

High Q-factor sapphire whispering gallery mode microwave resonator at single photon energies and millikelvin temperatures

Daniel L. Creedon, Yarema Reshitnyk, Warrick Farr, John M. Martinis, Timothy L. Duty, and Michael E. Tobar

Appl. Phys. Lett. 98, 222903 (2011); http://dx.doi.org/10.1063/1.3595942 (3 pages) | Cited 1 time

Online Publication Date: 3 June 2011

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The microwave properties of a crystalline sapphire dielectric whispering gallery mode resonator have been measured at very low excitation strength (E/ℏω ≈ 1) and low temperatures (T ≈ 30 mK). The measurements were sensitive enough to observe saturation due to a highly detuned electron spin resonance, which limited the loss tangent of the material to about 2×10−8 measured at 13.868 and 13.259 GHz. Small power dependent frequency shifts were also measured which correspond to an added magnetic susceptibility of order 10−9. This work shows that quantum limited microwave resonators with Q-factors >108 are possible with the implementation of a sapphire whispering gallery mode system.
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84.40.Az Waveguides, transmission lines, striplines
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