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25 Apr 2011

Volume 98, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 171102 (2011); http://dx.doi.org/10.1063/1.3582035 (3 pages)

Shigeru Nakayama, Satomi Ishida, Satoshi Iwamoto, and Yasuhiko Arakawa
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A topological point defect regulates the evolution of extended defects in irradiated silicon

Hyoungki Park and John W. Wilkins

Appl. Phys. Lett. 98, 171915 (2011); http://dx.doi.org/10.1063/1.3585656 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2011

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Clustering and annihilation of atomic-scale bond defects dominate nucleation and evolution of submicron-scale extended interstitial defects in irradiated silicon. Molecular dynamics simulations reveal the role of the bond defect in the thermal evolution of extended defects and identify the atomistic evolution paths. Accurate density functional theory calculations establish formation energies, activation barriers, and electronic structures of the bond defect and its clusters, and extended interstitial defects.
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61.72.jj Interstitials
71.20.Mq Elemental semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
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Depletion of the In2O3(001) and (111) surface electron accumulation by an oxygen plasma surface treatment

Oliver Bierwagen, James S. Speck, Takahiro Nagata, Toyohiro Chikyow, Yoshiyuki Yamashita, Hideki Yoshikawa, and Keisuke Kobayashi

Appl. Phys. Lett. 98, 172101 (2011); http://dx.doi.org/10.1063/1.3583446 (3 pages) | Cited 6 times

Online Publication Date: 25 April 2011

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Using x-ray photoemission spectroscopy (XPS) and current-voltage (I-V) measurements of Hg contacts we show that the surface electron accumulation layer of In2O3 can be removed by an oxygen plasma treatment. For the untreated sample, XPS measured a downward band bending toward the surface and a conduction band peak, and the I-V curve was linear which indicated the presence of a surface accumulation layer. After the treatment an upward bending, the absence of the conduction band peak, and a nonlinear I-V curve indicated the absence of the surface accumulation layer. The sheet resistance of the surface accumulation layer of >45 kΩ was deduced from the increase of the total sheet resistance upon the treatment. The removal of the surface electron accumulation layer opens up the possibility to use Schottky contacts for electrical characterization and device applications of semiconducting In2O3.
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73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.20.Nr Semiconductor compounds
72.80.Jc Other crystalline inorganic semiconductors
73.40.Ns Metal-nonmetal contacts

Tuning Fano-type resonances in coupled quantum point contacts by applying asymmetric voltages

Rubén C. Villarreal, Francisco Mireles, Ernesto E. Marinero, and Bruce A. Gurney

Appl. Phys. Lett. 98, 172102 (2011); http://dx.doi.org/10.1063/1.3579538 (3 pages)

Online Publication Date: 26 April 2011

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We study the ballistic magnetotransport in a double quantum point contact (QPC) device consisting of a quasi-one-dimensional quantum wire with an embedded islandlike impurity-etched nanohole as in a recently published experiment { J. C. Chen et al., [Appl. Phys. Lett. 94, 012105 (2009)] }. We reproduce the zero field quantized conductance, the interference phenomenon induced by the coupled QPCs, as well as the Ramsauer-like resonances observed in the experiments. At finite magnetic fields Fano-type resonances arises in the conductance due to the formation of localized states at the impurity periphery and to an interedge state resonant coupling effect. It is predicted that the Fano-type resonances can be controlled by an asymmetric confinement of the QPCs.
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85.35.Ds Quantum interference devices
73.23.Ad Ballistic transport
73.63.Rt Nanoscale contacts

Effects of interwall interaction on the electrical conductance at the junction between a double-walled carbon nanotube and copper electrodes

Feng Gao, Jianmin Qu, and Matthew Yao

Appl. Phys. Lett. 98, 172103 (2011); http://dx.doi.org/10.1063/1.3582242 (3 pages) | Cited 1 time

Online Publication Date: 27 April 2011

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Considered in this letter are the effects of interwall interaction on the electrical conductance at the junction of a double-walled carbon nanotube (DWCNT) between two copper electrodes. In the end-contact configuration, the effect of interwall interaction on the electrical conductance is rather weak, and both walls of DWCNT contribute to the electronic transport almost as if they are parallel connectors. In the side-contact configuration, not only the inner tube does not contribute to the overall electrical conductance, its presence hinders the electronic transport of the outer wall by causing significant localization of density of states near the Fermi level.
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73.63.Fg Nanotubes
73.20.At Surface states, band structure, electron density of states
61.46.Fg Nanotubes

High-temperature thermoelectric properties of Cu2Ga4Te7 with defect zinc-blende structure

Theerayuth Plirdpring, Ken Kurosaki, Atsuko Kosuga, Manabu Ishimaru, Adul Harnwunggmoung, Tohru Sugahara, Yuji Ohishi, Hiroaki Muta, and Shinsuke Yamanaka

Appl. Phys. Lett. 98, 172104 (2011); http://dx.doi.org/10.1063/1.3583662 (3 pages) | Cited 7 times

Online Publication Date: 27 April 2011

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Here we show the high-temperature thermoelectric (TE) properties of Cu2Ga4Te7 with the defect zinc-blende structure in which one-seventh of the cation sites are structural vacancies. Cu2Ga4Te7 exhibited relatively low electrical resistivity (ρ) and thermal conductivity (κ) and moderate positive Seebeck coefficient (S) at high temperatures, making this compound a promising high-performance p-type TE material. At 940 K, the S, ρ, and κ were +215 μV K−1, 10.1×10−5 Ω m, and 0.67 Wm−1 K−1, respectively, which resulted in the maximum dimensionless figure of merit ZT ( = S2T/ρ/κ, where T is the absolute temperature) of 0.64.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.jd Vacancies
72.80.Sk Insulators

Quantum magnetoresistance of the PrFeAsO oxypnictide

D. Bhoi, P. Mandal, P. Choudhury, S. Pandya, and V. Ganesan

Appl. Phys. Lett. 98, 172105 (2011); http://dx.doi.org/10.1063/1.3584023 (3 pages) | Cited 2 times

Online Publication Date: 28 April 2011

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We report the observation of an unusual B dependence of transverse magnetoresistance (MR) in the PrFeAsO, one of the parent compound of pnictide superconductors. Below the spin density wave transition, MR is large, positive and increases with decreasing temperature. At low temperatures, MR increases linearly with B up to 14 T. For T ≥ 40 K, MR versus B curve develops a weak curvature in the low-field region which indicates a crossover from B linear to B2 dependence as B→0. The B linear MR originates from the Dirac cone states and has been explained by the quantum mechanical model proposed by Abrikosov.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Xa Pnictides and chalcogenides
75.30.Ds Spin waves
75.47.Lx Magnetic oxides

Schottky barrier height reduction for metal/n-GaSb contact by inserting TiO2 interfacial layer with low tunneling resistance

Ze Yuan, Aneesh Nainani, Yun Sun, J.-Y. Jason Lin, Piero Pianetta, and Krishna C. Saraswat

Appl. Phys. Lett. 98, 172106 (2011); http://dx.doi.org/10.1063/1.3584862 (3 pages) | Cited 8 times

Online Publication Date: 29 April 2011

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Fermi level pinning near GaSb valence band edge leads to high Schottky barrier height for metal/n-type GaSb contacts. However, this effect can be alleviated by depinning of the Fermi level with the introduction of thin interfacial dielectric. In this paper, the use of TiO2 allows depinning of the Fermi level without introducing excessive tunneling resistance due to the low conduction band offset, estimated by synchrotron radiation photoemission spectroscopy. It is shown the insertion of TiO2 results in reduction in Schottky barrier height and greater than four orders of magnitude increase in current density for metal contacts on n-type GaSb.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
71.20.Nr Semiconductor compounds

Rectifying behavior in La2/3Sr1/3MnO3/MgO/SrRuO3 magnetic tunnel junctions

Hongguang Cheng, Zuli Liu, and Kailun Yao

Appl. Phys. Lett. 98, 172107 (2011); http://dx.doi.org/10.1063/1.3586242 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2011

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We report first principles calculations of transport properties of the all-oxide La2/3Sr1/3MnO3/MgO/SrRuO3 magnetic tunnel junctions. A sizeable rectifying behavior which can be enhanced by increasing the MgO barrier thickness is predicted theoretically. For the device with 13 layers of MgO barrier, the positive current is about two orders of magnitude larger than the reverse leakage current. The rectifying behavior arises from the symmetry-filtering properties of the MgO barrier. This rectifying effect which is totally dominated by quantum tunneling could be used to design faster quantum devices such as tunnel diode and tunnel transistor.
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73.40.Ei Rectification
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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Room-temperature spin-dependent tunneling through molecules

S. Wang, F. J. Yue, J. Shi, Y. J. Shi, A. Hu, Y. W. Du, and D. Wu

Appl. Phys. Lett. 98, 172501 (2011); http://dx.doi.org/10.1063/1.3583585 (3 pages) | Cited 3 times

Online Publication Date: 25 April 2011

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We have fabricated assemblies of molecular junctions comprised of superparamagnetic Fe3O4 nanoparticles self-assembled with alkane molecules of different lengths as the spacer. The electrical resistance increases exponentially over nearly two decades as the molecular length varies from 0.7 to 2.5 nm, indicating that electrons tunnel through the molecules that are chemically bonded with Fe3O4 nanoparticles. Up to ∼ 21% room-temperature magnetoresistance is observed. Remarkably, the tunneling magnetoresistance ratio stays nearly independent of molecular length, which entails room-temperature spin-conserving transport in organic molecules.
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85.75.Mm Spin polarized resonant tunnel junctions
75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.Lx Magnetic oxides
72.25.-b Spin polarized transport

[Co/Pd]–NiFe exchange springs with tunable magnetization tilt angle

T. N. Anh Nguyen, Y. Fang, V. Fallahi, N. Benatmane, S. M. Mohseni, R. K. Dumas, and Johan Åkerman

Appl. Phys. Lett. 98, 172502 (2011); http://dx.doi.org/10.1063/1.3580612 (3 pages) | Cited 7 times

Online Publication Date: 26 April 2011

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We investigate exchange coupled [Co/Pd]5–NiFe thin films. Due to competition between the in-plane shape anisotropy of the NiFe and strong perpendicular magnetic anisotropy of the [Co/Pd]5 multilayer, unique magnetic configurations are achievable. In particular, we explore the out-of-plane magnetization tilt angle of the NiFe layer. Experimental results, based on conventional magnetometry, ferromagnetic resonance, and magnetic force microscopy, agree well with one-dimensional micromagnetic simulations. We find that the tilt angle is highly tunable (0°–60°) over a small range of NiFe thicknesses (4.8–8 nm). Potential applications for high power, zero-field operation spin torque oscillators are discussed.
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75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Bb Fe and its alloys

Ferrimagnetic stripe domain formation in antiferromagnetically-coupled Co/Pt–Co/Ni–Co/Pt multilayers studied via soft x-ray techniques

O. Hellwig, C. M. Günther, F. Radu, A. Menzel, W. F. Schlotter, J. Lüning, and S. Eisebitt

Appl. Phys. Lett. 98, 172503 (2011); http://dx.doi.org/10.1063/1.3583454 (3 pages)

Online Publication Date: 27 April 2011

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We investigate the macroscopic and microscopic magnetic reversal in perpendicular anisotropy antiferromagnetically (AF) coupled [Co/Pt]N−1/Co–Ru–[Co/Ni]M−1/Co–Ru–[Co/Pt]N−1/Co multilayers (ML) using soft x-ray spectroholography and local, as well as area-integrated, soft x-ray hysteresis loop techniques. For N = 25⪢M = 3 we find ferrimagnetic stripe domains in remanence due to the combination of strong dipolar fields from the thick Co/Pt MLs with a strong AF-interlayer exchange coupling of the thin Co/Ni ML in the center, which reverses its polarity three times during a magnetic field reversal. Furthermore, local hysteresis loops reveal distinct random spin-flip avalanches, thus indicating the existence of local magnetic pinning sites due to the insertion of the center Co/Ni stack.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
78.70.-g Interactions of particles and radiation with matter
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Optimized design of a low-resistance electrical conductor for the multimegahertz range

André Kurs, Morris Kesler, and Steven G. Johnson

Appl. Phys. Lett. 98, 172504 (2011); http://dx.doi.org/10.1063/1.3569141 (3 pages) | Cited 1 time

Online Publication Date: 28 April 2011

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We propose a design for a conductive wire composed of several mutually insulated coaxial conducting shells. With the help of numerical optimization, it is possible to obtain electrical resistances significantly lower than those of a heavy-gauge copper wire or litz wire in the 2–20 MHz range. Moreover, much of the reduction in resistance can be achieved for just a few shells; in contrast, litz wire would need to contain ∼ 104 strands to perform comparably in this frequency range.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
02.60.Pn Numerical optimization

Tuning magnetocaloric effect with nanocrystallite size

S. P. Mathew and S. N. Kaul

Appl. Phys. Lett. 98, 172505 (2011); http://dx.doi.org/10.1063/1.3584018 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2011

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We demonstrate that the average nanocrystallite size and size distribution can be used as control parameters to respectively tune the peak value and the width-at-half-maximum of the isothermal magnetic entropy change or the adiabatic temperature change during the magnetization process (magnetocaloric effect) such that a reasonably large relative cooling power, conducive to magnetic refrigeration, is achieved.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Influence of ion irradiation on switching field and switching field distribution in arrays of Co/Pd-based bit pattern media

T. Hauet, O. Hellwig, S.-H. Park, C. Beigné, E. Dobisz, B. D. Terris, and D. Ravelosona

Appl. Phys. Lett. 98, 172506 (2011); http://dx.doi.org/10.1063/1.3581896 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2011

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We have used ion irradiation to tune switching field and switching field distribution (SFD) in polycrystalline Co/Pd multilayer-based bit pattern media. Light He+ ion irradiation strongly decreases perpendicular magnetic anisotropy amplitude due to Co/Pd interface intermixing, while the granular structure, i.e., the crystalline anisotropy, remains unchanged. In dot arrays, the anisotropy reduction leads to a decrease in coercivity (HC) but also to a strong broadening of the normalized SFD/HC (in percentage), since the relative impact of misaligned grains is enhanced. Our experiment thus confirms the major role of misorientated grains in SFD of nanodevice arrays.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.80.Jh Ion radiation effects

Electric-field control of phase separation and memory effect in Pr0.6Ca0.4MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures

Q. P. Chen, J. J. Yang, Y. G. Zhao, S. Zhang, J. W. Wang, M. H. Zhu, Y. Yu, X. Z. Zhang, Zhu Wang, Bin Yang, D. Xie, and T. L. Ren

Appl. Phys. Lett. 98, 172507 (2011); http://dx.doi.org/10.1063/1.3584025 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2011

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Heterostructures were fabricated by growing Pr0.6Ca0.4MnO3 (PCMO) films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates. It was shown that the magnetizations of the samples can be tuned dramatically by electric fields via piezostrain and the effect is dominated by the change in phase separation. More interestingly, the electric-field control of magnetization is nonvolatile, manifesting a memory effect of strain. The results were discussed by considering the effect of electric-field-induced strain on the energy landscape of PCMO and the resultant change in phase separation. This work is helpful for exploring the evolution of phase separation with well-controlled strains and the magnetoelectric coupling effect.
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77.55.Nv Multiferroic/magnetoelectric films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.85.+t Magnetoelectric effects, multiferroics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Observation of spin wave modes depending on a tunable periodic magnetic field

Lihui Bai, Makoto Kohda, and Junsaku Nitta

Appl. Phys. Lett. 98, 172508 (2011); http://dx.doi.org/10.1063/1.3584032 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2011

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Excited spin waves in Ni0.8Fe0.2 strips are studied by detecting electrical signals with the use of a spin rectification effect. Through a meander control line, a periodic magnetic field is applied on the strips. Spin wave modes strongly depends on the periodic magnetic field. In a short period sample, we find spin wave coupling effect controlled by the periodic magnetic field, which can be used as a tunable spin wave filter.
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75.76.+j Spin transport effects
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Giant reversible anisotropic magnetocaloric effect in an antiferromagnetic EuFe2As2 single crystal

M. S. Kim, N. H. Sung, Yoonkook Son, M. S. Ko, and B. K. Cho

Appl. Phys. Lett. 98, 172509 (2011); http://dx.doi.org/10.1063/1.3579254 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2011

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Here, we report the characterization of a giant reversible anisotropic magnetocaloric effect in a EuFe2As2 single crystal. The magnetic properties of EuFe2As2 single crystals are quite interesting; they display a small magnetic hysteresis, anisotropy, and a first-order magnetic phase transition. The maximum magnetic entropy change in in-plane magnetic-field direction was 14.6 J/kg K around 20 K and out-of-plane was 10.3 J/kg K around 20 K as a result of changing the magnetic field from 0 to 5 T. These results suggest the possibility of using EuFe2As2 single crystals in magnetic refrigeration applications.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Single crystal silicon capacitors with low microwave loss in the single photon regime

S. J. Weber, K. W. Murch, D. H. Slichter, R. Vijay, and I. Siddiqi

Appl. Phys. Lett. 98, 172510 (2011); http://dx.doi.org/10.1063/1.3583449 (3 pages) | Cited 7 times

Online Publication Date: 29 April 2011

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We have fabricated superconducting microwave resonators in a lumped element geometry using single crystal silicon dielectric parallel plate capacitors with C>2 pF. Aluminum devices with resonant frequencies between 4.0 and 6.5 GHz exhibited an average internal quality factor Qi of 2×105 in the single photon excitation regime at T = 20 mK. Attributing the observed loss solely to the capacitive element, our measurements place an upper bound on the loss tangent of the silicon dielectric layer of tan δi = 5×10−6. This level of loss is an order of magnitude lower than is currently observed in structures incorporating amorphous dielectric materials, thus making single crystal silicon capacitors an attractive, robust route for realizing long-lived quantum circuits.
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85.25.Am Superconducting device characterization, design, and modeling
84.40.Az Waveguides, transmission lines, striplines
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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Electronic and structural properties of the oxygen vacancy in BaTiO3

Minseok Choi, Fumiyasu Oba, and Isao Tanaka

Appl. Phys. Lett. 98, 172901 (2011); http://dx.doi.org/10.1063/1.3583460 (3 pages) | Cited 5 times

Online Publication Date: 26 April 2011

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The electronic and structural properties of the oxygen vacancy (VO) in cubic BaTiO3 are studied using first-principles calculations based on a hybrid Hartree–Fock density functional approach. Our calculations identify the double shallow donor behavior of VO, indicating its contribution to the n-type conductivity. In addition, a metastable configuration is found, which shows an off-symmetric atomic structure around VO in conjunction with deep localized electronic states in the band gap. Based on the identified characteristics of VO, the previous experimental and theoretical findings are explained.
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61.72.jd Vacancies
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Impact of ultrathin Al2O3 diffusion barriers on defects in high-k LaLuO3 on Si

S. Shen, Y. Liu, R. G. Gordon, and L. J. Brillson

Appl. Phys. Lett. 98, 172902 (2011); http://dx.doi.org/10.1063/1.3583462 (3 pages) | Cited 3 times

Online Publication Date: 27 April 2011

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We used depth-resolved cathodoluminescence spectroscopy (DRCLS) to measure trap energies and relative densities in metal/high-κ dielectric LaLuO3/Si stacks, defects produced by LaLuO3–Si interdiffusion, and suppression of these defects by monolayer-thick Al2O3 interlayers. DRCLS reveals deep levels at 3.8, 4.2, and 4.7 eV above the valence band, consistent with LaLuO3 oxygen vacancies predicted by theory and a 5.5 eV band gap. Oxygen annealing produces LaLuO3/Si interdiffusion that increases 3.8 eV defect density and which a 0.4 nm Al2O3 completely removes. Transmission electron microscopy and current leakage results shows that Al2O3 prevent LaLuO3/Si silicate layer formation and dramatically lower defects with oxygen annealing.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.jd Vacancies
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation

Nanometer scale study of HfO2 trap states using single electron tunneling force spectroscopy

D. W. Winslow, J. P. Johnson, and C. C. Williams

Appl. Phys. Lett. 98, 172903 (2011); http://dx.doi.org/10.1063/1.3580767 (3 pages) | Cited 1 time

Online Publication Date: 27 April 2011

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Standard methods to characterize trap states in dielectric films typically provide spatially averaged measurements. The development of single electron tunneling force spectroscopy has provided for the measurement of the energy of single trap states with atomic scale spatial resolution. In this letter, data taken on HfO2 films using this method is presented and discussed. Analysis of individual spectra shows that there is spatial variation in the density of trap states in these films. The spectra found by averaging data obtained from forty different locations shows good agreement with data taken via standard methods and with theoretical predictions.
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71.55.Ht Other nonmetals
77.55.-g Dielectric thin films
73.40.Gk Tunneling
71.20.Ps Other inorganic compounds
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Li-doped B2C graphene as potential hydrogen storage medium

Hui An, Chun-sheng Liu, Zhi Zeng, Chao Fan, and Xin Ju

Appl. Phys. Lett. 98, 173101 (2011); http://dx.doi.org/10.1063/1.3583465 (3 pages) | Cited 5 times

Online Publication Date: 25 April 2011

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Based on first-principles density functional theory, we show that Li-doped B2C graphene can serve as a high-capacity hydrogen storage medium with the gravimetric density of 7.54 wt %. The present results indicate that the strong binding of Li onto the substrate comes from the hybridizations of B 2p and C 2p orbitals with the partial occupancy of Li 2p orbitals. Both the polarization mechanism and the orbital hybridizations contribute to the adsorption of H2 molecules and the resulting adsorption energy is in the range of 0.12–0.22 eV/H2. The system reported here is favorable for the reversible hydrogen adsorption/desorption at the room temperature.
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88.30.rd Inorganic metal hydrides
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.43.Mn Adsorption kinetics
84.60.Ve Energy storage systems, including capacitor banks
68.43.Nr Desorption kinetics
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Graphyne- and graphdiyne-based nanoribbons: Density functional theory calculations of electronic structures

L. D. Pan, L. Z. Zhang, B. Q. Song, S. X. Du, and H.-J. Gao

Appl. Phys. Lett. 98, 173102 (2011); http://dx.doi.org/10.1063/1.3583507 (3 pages) | Cited 20 times

Online Publication Date: 25 April 2011

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We report on the configurations and electronic properties of graphyne and graphdiyne nanoribbons with armchair and zigzag edges investigated with first principles calculations. Our results show that all the nanoribbons are semiconductors with suitable band gaps similar to silicon. And their band gaps decrease as widths of nanoribbons increase. We also find that the band gap is at the Γ point for all graphdiyne ribbons and it is at the X point for all graphyne ribbons. Of particular interest, the band gap of zigzag graphyne nanoribbons show a unique “step effect” as the width increases. This property is good for tuning of the energy band gap, as in a certain range of the ribbon width, the energy gap remains constant and in reality the edge cannot be as neat as that in a theoretic model.
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81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Effect of surface passivation on dopant distribution in Si quantum dots: The case of B and P doping

Jie Ma, Su-Huai Wei, Nathan R. Neale, and Arthur J. Nozik

Appl. Phys. Lett. 98, 173103 (2011); http://dx.doi.org/10.1063/1.3583663 (3 pages) | Cited 4 times

Online Publication Date: 25 April 2011

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Despite many efforts, the doping behavior in Si quantum dots (QDs) is still not well understood. Theoretical work shows that boron as an acceptor prefers to stay near the surface and phosphorous as a donor may stay close to the center in a perfectly hydrogen passivated QD. However, experiment studies seem suggesting an opposite trend. Using first-principle methods, we show that the discrepancy could be explained by the imperfectness of surface passivation of the QD. We find that, in QDs with hydrogen deficient or oxygen rich surfaces, phosphorous prefers the surface sites and boron may stay inside, consistent with experiment observations.
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61.72.uf Ge and Si
71.55.Cn Elemental semiconductors
81.65.Rv Passivation
71.15.-m Methods of electronic structure calculations

Strong coupling between a photonic crystal nanobeam cavity and a single quantum dot

Ryuichi Ohta, Yasutomo Ota, Masahiro Nomura, Naoto Kumagai, Satomi Ishida, Satoshi Iwamoto, and Yasuhiko Arakawa

Appl. Phys. Lett. 98, 173104 (2011); http://dx.doi.org/10.1063/1.3579535 (3 pages) | Cited 8 times

Online Publication Date: 26 April 2011

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Show Abstract
We demonstrated the strong coupling between a one-dimensional photonic crystal nanobeam cavity and a single quantum dot (QD). Thanks to a high quality factor ( ∼ 25 000) with small mode volume [0.38×(n/λ)3] of the nanobeam cavity, an anticrossing behavior with a vacuum Rabi splitting of 226 μeV was observed. The ratio of the QD-cavity coupling strength to the cavity decay rate, which is a figure of merit of quantum optical applications, is estimated to 2.1. This is the highest value among any QD-based cavity quantum electrodynamics systems reported so far.
Show PACS
42.50.Pq Cavity quantum electrodynamics; micromasers
42.70.Qs Photonic bandgap materials
42.79.-e Optical elements, devices, and systems
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