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27 Feb 2012

Volume 100, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 093101 (2012); http://dx.doi.org/10.1063/1.3687190 (4 pages)

Jinhai Mao, Li Huang, Yi Pan, Min Gao, Junfeng He, Haitao Zhou, Haiming Guo, Yuan Tian, Qiang Zou, Lizhi Zhang, Haigang Zhang, Yeliang Wang, Shixuan Du, Xingjiang Zhou, A. H. Castro Neto, et al.
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High 5.2 peak-to-valley current ratio in Si/SiGe resonant interband tunnel diodes grown by chemical vapor deposition

Anisha Ramesh, Paul R. Berger, and Roger Loo

Appl. Phys. Lett. 100, 092104 (2012); http://dx.doi.org/10.1063/1.3684834 (4 pages) | Cited 1 time

Online Publication Date: 28 February 2012

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Si/SiGe resonant interband tunnel diodes were fabricated using chemical vapor deposition (CVD) on 200-mm diameter p-doped silicon wafers. The resonant interband tunnel diode structure consists of a p+-i-n+ diode that incorporates vapor phase doped δ-doping to enhance quantum mechanical tunneling probability. The tunneling barrier thickness is varied from 2 nm to 8 nm, and a record peak-to-valley current ratio of 5.2 for a CVD process is reported for a 6 nm barrier thickness with a room temperature peak tunneling current of 20 A/cm2. The current density increases exponentially with spacer thickness reduction with a maximum value of 280 A/cm2 for a 2 nm barrier.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Kk Junction diodes

AlGaN/GaN high electron mobility transistors with nickel oxide based gates formed by high temperature oxidation

T. Lalinský, G. Vanko, M. Vallo, E. Dobročka, I. Rýger, and A. Vincze

Appl. Phys. Lett. 100, 092105 (2012); http://dx.doi.org/10.1063/1.3690047 (3 pages) | Cited 1 time

Online Publication Date: 29 February 2012

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We report on the design of gates of AlGaN/GaN high electron mobility transistors (HEMTs) to be predetermined for high temperature applications. In this design, nickel oxide (NiO) gate interfacial layer is formed by high temperature oxidation (T = 500–800 °C, for 1 min) of 15 nm thick Ni gate contact layer to provide a high temperature stable gate interface. AlGaN/GaN HEMTs with thermic NiO gate contact layer show excellent dc performance with higher peak transconductance, larger gate voltage swing, higher linearity, and thermal stability as compared to the reference device based on Ni gate contact layer.
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85.30.Tv Field effect devices

Excitonic diffusion dynamics in ZnO

H. Jeong, K. Min, S. Byun, C. J. Stanton, D. H. Reitze, J. K. Yoo, G. C. Yi, and Y. D. Jho

Appl. Phys. Lett. 100, 092106 (2012); http://dx.doi.org/10.1063/1.3690055 (3 pages) | Cited 1 time

Online Publication Date: 29 February 2012

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We investigate excitonic carrier diffusion in both bulk ZnO and nanorods (NRs). Using time-resolved differential reflectivity spectroscopy, we observe a fast decaying component together with a longer exponential relaxation. In bulk ZnO, we find that the fast decay term (∼1 ps) originates from excitonic diffusion along the growth direction. By probing at both the A and B excitons, we find different diffusion coefficients for each. In ZnO nanorods, the diffusion contribution is missing. We attribute this to two effects: (1) defects in the nanorods substantially slow the diffusion process and (2) excitons in nanorods are generated more uniformly than in bulk.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
66.30.hp Molecular crystals
78.47.jg Time resolved reflection spectroscopy
78.67.Qa Nanorods

High room-temperature optical gain in Ga(NAsP)/Si heterostructures

N. Koukourakis, C. Bückers, D. A. Funke, N. C. Gerhardt, S. Liebich, S. Chatterjee, C. Lange, M. Zimprich, K. Volz, W. Stolz, B. Kunert, S. W. Koch, and M. R. Hofmann

Appl. Phys. Lett. 100, 092107 (2012); http://dx.doi.org/10.1063/1.3690886 (3 pages) | Cited 1 time

Online Publication Date: 29 February 2012

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We analyze the modal gain of Ga(NAsP) multi quantum-well heterostructures pseudomorphically grown on (001) silicon substrate by metal-organic vapor-phase epitaxy. Using the variable stripe length method, we obtain high modal gain values up to 78 cm−1 at room temperature that are comparable to the values of common high quality III-V laser material. We find good agreement between experimental results and theoretically calculated gain spectra obtained using a microscopic model. The results underline the high potential of Ga(NAsP) as an active material for directly electrically pumped lasers on silicon substrate.
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78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Hard x-ray photoelectron spectroscopy of chalcopyrite solar cell components

A. Gloskovskii, C. A. Jenkins, S. Ouardi, B. Balke, G. H. Fecher, X.-F. Dai, T. Gruhn, B. Johnson, I. Lauermann, R. Caballero, C. A. Kaufmann, and C. Felser

Appl. Phys. Lett. 100, 092108 (2012); http://dx.doi.org/10.1063/1.3687197 (3 pages)

Online Publication Date: 29 February 2012

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Hard x-ray photoelectron spectroscopy is used to examine the partial density of states of Cu(In,Ga)Se2 (CIGSe), a semiconducting component of solar cells. The investigated, thin Cu(In,Ga)Se2 films were produced by multi-stage co-evaporation. Details of the measured core level and valence band spectra are compared to the calculated density of states. The semiconducting type electronic structure of Cu(In,Ga)Se2 is clearly resolved in the hard x-ray photoelectron spectra.
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88.40.H- Solar cells (photovoltaics)

Bi-induced p-type conductivity in nominally undoped Ga(AsBi)

G. Pettinari, A. Patanè, A. Polimeni, M. Capizzi, Xianfeng Lu, and T. Tiedje

Appl. Phys. Lett. 100, 092109 (2012); http://dx.doi.org/10.1063/1.3690901 (4 pages) | Cited 4 times

Online Publication Date: 1 March 2012

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We report p-type conductivity in nominally undoped GaAs1–xBix epilayers for a wide range of Bi-concentrations (0.6% ≤ x ≤ 10.6%). The counterintuitive increase of the conductivity with increasing x is paralleled by an increase in the density of free holes by more than three orders of magnitude in the investigated Bi-concentration range. The p-type conductivity results from holes thermally excited from Bi-induced acceptor levels lying at 26.8 meV above the valence band edge of GaAs1−xBix with concentration up to 2.4 × 1017 cm−3 at x = 10.6%.
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73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors

Formation of the yttrium/germanium interface: Fermi-level pinning and intermixing at room temperature

Z. Q. Liu, W. K. Chim, S. Y. Chiam, J. S. Pan, and C. M. Ng

Appl. Phys. Lett. 100, 092110 (2012); http://dx.doi.org/10.1063/1.3690941 (4 pages)

Online Publication Date: 1 March 2012

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Understanding interfacial phenomena is crucial for precise control in the growth of materials for advanced semiconductor devices. A systematic in situ coverage dependent study is conducted to study the Schottky barrier evolution and chemical reactions at the yttrium/germanium interface. Adatom-induced band bending is present in the early growth stages while metal-induced gap states resulted in strong Fermi level pinning at larger yttrium (Y) thicknesses. Furthermore, significant intermixing occurs at 3 Å thickness of Y and saturates at 17 Å of Y. The underlying mechanism behind this self-limiting intermixing is well-described by a combination of chemical bond and metal-induced weakening theories. The implications of our findings on device performance are discussed.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states

Nano-lithography free formation of high density Ge-on-insulator network for epitaxial template

Hiroyuki Yokoyama, Kaoru Toko, Taizoh Sadoh, and Masanobu Miyao

Appl. Phys. Lett. 100, 092111 (2012); http://dx.doi.org/10.1063/1.3691258 (4 pages) | Cited 1 time

Online Publication Date: 1 March 2012

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High-quality Ge-on-insulator (GOI) structures are essential for integrating multi-functional devices onto the Si-platform. We develop the nano-lithography free method for single-crystalline GOI networks by combining partial Ge evaporation and rapid-melting growth techniques. This realizes chip size GOI with high Ge coverage fractions (>75%), which is crisscrossed with nano-spacing (∼100 nm width). Over-epitaxy of Ge on the GOI network is also examined, which achieves single-crystalline GOI uniform-plane by covering the nano-spacing. This proves the validity of high-density GOI networks as the epitaxial template. This method will facilitate the heterogeneous integration of Ge, III-V semiconductors, and magnetic materials on the Si-platform.
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81.16.Nd Micro- and nanolithography
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Back-action-induced non-equilibrium effect in electron charge counting statistics

HaiOu Li, Ming Xiao, Gang Cao, Cheng Zhou, RuNan Shang, Tao Tu, GuangCan Guo, HongWen Jiang, and GuoPing Guo

Appl. Phys. Lett. 100, 092112 (2012); http://dx.doi.org/10.1063/1.3691255 (4 pages) | Cited 1 time

Online Publication Date: 2 March 2012

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We study real-time charge-counting statistics measured by a quantum point contact (QPC) coupled to a single quantum dot (QD) subject to different back-action strengths. By tuning the QD-QPC coupling or the QPC bias, we control the QPC back-action, which drives the QD electrons out of thermal equilibrium. The random telegraph signal (RTS) statistics show strong and tunable non-thermal-equilibrium saturation effect, which can be quantitatively characterized as a back-action-induced tunneling-out rate. We find that the QD-QPC coupling and QPC bias voltage play different roles in determining the back-action strength and the cut-off energy.
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73.40.Gk Tunneling
73.63.Kv Quantum dots

Correlated conductivity and work function changes in epitaxial graphene

Md. W. K. Nomani, V. Shields, G. Tompa, N. Sbrockey, M. G. Spencer, R. A. Webb, and G. Koley

Appl. Phys. Lett. 100, 092113 (2012); http://dx.doi.org/10.1063/1.3691628 (4 pages) | Cited 2 times

Online Publication Date: 2 March 2012

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Correlation between conductance and surface work function (SWF) changes caused by molecular adsorption on epitaxial graphene on both faces of 6 H-SiC has been investigated. The SWF and conductance changes, explained on the basis of graphene band diagram, indicate C-face multilayer and Si-face few layer graphene behave as p and n-type sensing layers, respectively. A quantitative model correlating conductance and SWF changes has been proposed within the framework of Boltzmann transport theory. Our results further indicate that for epitaxial graphene, the charge interaction by the adsorbed molecules and related work function changes can be strongly influenced by the SiC substrate.
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73.61.Wp Fullerenes and related materials
68.43.Mn Adsorption kinetics
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Exciton spin relaxation in In0.53Ga0.47As/AlAs0.56Sb0.44 quantum wells

K. Sasayama, S. Nakanishi, R. Yamaguchi, Y. Oyanagi, T. Ushimi, S. Gozu, T. Mozume, and A. Tackeuchi

Appl. Phys. Lett. 100, 092401 (2012); http://dx.doi.org/10.1063/1.3690833 (3 pages)

Online Publication Date: 29 February 2012

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The spin relaxation process of In0.53Ga0.47As/AlAs0.56Sb0.44 quantum wells is investigated by spin-dependent pump and probe reflectance measurements with a high time resolution of 200 fs. The observed spin relaxation time of 17.5 ps at 20 K indicates high potential for applications to high-speed optical devices. A positive temperature dependence of the spin relaxation time due to the unique band structure is observed at 30–100 K. The spin relaxation is found to be mainly governed by the Bir-Aronov-Pikus process [Sov. Phys. JETP 42, 705 (1976)] below 100 K and by the D’yakonov-Perel’ process above 100 K.
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71.35.-y Excitons and related phenomena
73.20.At Surface states, band structure, electron density of states
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.De Quantum wells
71.20.Nr Semiconductor compounds

In situ multifrequency ferromagnetic resonance and x-ray magnetic circular dichroism investigations on Fe/GaAs(110): Enhanced g-factor

F. M. Römer, M. Möller, K. Wagner, L. Gathmann, R. Narkowicz, H. Zähres, B. R. Salles, P. Torelli, R. Meckenstock, J. Lindner, and M. Farle

Appl. Phys. Lett. 100, 092402 (2012); http://dx.doi.org/10.1063/1.3687726 (4 pages)

Online Publication Date: 1 March 2012

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We determined the magnetic anisotropy energy and g-factor of an uncapped 10 nm thick Fe/GaAs(110) film using a setup that allows frequency (1.5–26.5 GHz) as well as angular dependent ferromagnetic resonance measurements under ultrahigh vacuum conditions. The g-factor g = 2.61±0.1 is unusually high at room temperature and can be interpreted as the result of an increased orbital moment due to strain. This interpretation is supported by more surface sensitive x-ray magnetic circular dichroism measurements which yield g = 2.21±0.02 measured at remanence. The difference in g may be the result of magnetic field dependent magnetostriction which influences the orbital moment.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
72.30.+q High-frequency effects; plasma effects
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects
78.66.-w Optical properties of specific thin films
75.80.+q Magnetomechanical effects, magnetostriction

Enhanced spin pumping at yttrium iron garnet/Au interfaces

C. Burrowes, B. Heinrich, B. Kardasz, E. A. Montoya, E. Girt, Yiyan Sun, Young-Yeal Song, and Mingzhong Wu

Appl. Phys. Lett. 100, 092403 (2012); http://dx.doi.org/10.1063/1.3690918 (4 pages) | Cited 11 times

Online Publication Date: 1 March 2012

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Spin injection across the ferrimagnetic insulator yttrium iron garnet (YIG)/normal metal Au interface was studied using ferromagnetic resonance. The spin mixing conductance was determined by comparing the Gilbert damping parameter α in YIG/Au and YIG/Au/Fe heterostructures. The main purpose of this study was to correlate the spin pumping efficiency with chemical modifications of the YIG film surface using in situ etching and deposition techniques. By means of Ar+ ion beam etching, one is able to increase the spin mixing conductance at the YIG/Au interface by a factor of 5 compared to the untreated YIG/Au interface.
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72.25.Mk Spin transport through interfaces
73.40.Ns Metal-nonmetal contacts
75.50.Dd Nonmetallic ferromagnetic materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Room-temperature anomalous Hall effect in amorphous Si-based magnetic semiconductor

Jia-Hsien Yao, Hsiu-Hau Lin, Yun-Liang Soo, Tai-Sing Wu, Jai-Lin Tsai, Ming-Der Lan, and Tsung-Shune Chin

Appl. Phys. Lett. 100, 092404 (2012); http://dx.doi.org/10.1063/1.3691173 (4 pages) | Cited 1 time

Online Publication Date: 1 March 2012

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Here, we show that Mn-doped amorphous hydrogenated Si reveals room-temperature ferromagnetism. Various characterization techniques rule out the formation of magnetic clusters. In particular, anomalous Hall-effect is found even at 300 K in annealed Si89.5Mn10.5 samples. The observed anomalous Hall-effect provides direct evidence that the ferromagnetic order is coupled to the itinerant carriers, making these samples workable magnetic semiconductors. This work demonstrates the great potential for Si-based semiconductor spintronics at room temperature, which is readily integrated with the current information technology.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Cw Elemental semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
61.72.Cc Kinetics of defect formation and annealing

Nonuniform current and spin accumulation in a 1 μm thick n-GaAs channel

B. Endres, M. Ciorga, R. Wagner, S. Ringer, M. Utz, D. Bougeard, D. Weiss, C. H. Back, and G. Bayreuther

Appl. Phys. Lett. 100, 092405 (2012); http://dx.doi.org/10.1063/1.3691175 (4 pages)

Online Publication Date: 1 March 2012

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The spin accumulation in a n-GaAs channel produced by spin extraction into a (Ga,Mn)As contact is measured by cross-sectional imaging of the spin polarization in GaAs. The spin polarization is observed in a 1 μm thick n-GaAs channel with the maximum polarization near the contact edge opposite to the maximum current density. The one-dimensional model of electron drift and spin diffusion, frequently used, cannot explain this observation. It also leads to incorrect spin lifetimes from Hanle curves with a strong bias and distance dependence. Numerical simulations based on a two-dimensional drift-diffusion model, however, reproduce the observed spin distribution quite well and lead to realistic spin lifetimes.
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72.25.Dc Spin polarized transport in semiconductors
75.30.Ds Spin waves
75.30.Wx Spin crossover
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Pp Magnetic semiconductors
75.78.Cd Micromagnetic simulations

Physical limits of pure superparamagnetic Fe3O4 nanoparticles for a local hyperthermia agent in nanomedicine

Minhong Jeun, Sanghoon Lee, Jae Kyeong Kang, Asahi Tomitaka, Keon Wook Kang, Young Il Kim, Yasushi Takemura, Kyung-Won Chung, Jiyeon Kwak, and Seongtae Bae

Appl. Phys. Lett. 100, 092406 (2012); http://dx.doi.org/10.1063/1.3689751 (4 pages) | Cited 2 times

Online Publication Date: 1 March 2012

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Magnetic and AC magnetically induced heating characteristics of Fe3O4 nanoparticles (IONs) with different mean diameters, d, systematically controlled from 4.2 to 22.5 nm were investigated to explore the physical relationship between magnetic phase and specific loss power (SLP) for hyperthermia agent applications. It was experimentally confirmed that the IONs had three magnetic phases and correspondingly different SLP characteristics depending on the particle sizes. Furthermore, it was demonstrated that pure superparamagnetic phase IONs (d < 9.8 nm) showed insufficient SLPs critically limiting for hyperthermia applications due to smaller AC hysteresis loss power (Néel relaxation loss power) originated from lower out-of-phase magnetic susceptibility.
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87.85.Rs Nanotechnologies-applications
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
87.19.Pp Biothermics and thermal processes in biology
87.85.J- Biomaterials

Half-metallic p-electron ferromagnetism in alkaline earth doped AlAs: A first-principles calculation

Yong-Hong Zhao, Yong-Feng Li, and Yong Liu

Appl. Phys. Lett. 100, 092407 (2012); http://dx.doi.org/10.1063/1.3692591 (3 pages) | Cited 1 time

Online Publication Date: 2 March 2012

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We investigated the p-electron ferromagnetism in alkaline earth doped AlAs by using first-principles calculations. The modified Becke and Johnson potential is used to give a much more reasonable semiconductor gap. Our results demonstrate that ferromagnetic phase is always energetically favorable than the antiferromagnetic and nonmagnetic ones for all considered compounds. Magnetic moments are mainly attributed to the partly filled anionic p states. Especially, half-metallic ferromagnetism has been obtained for Ca- and Sr-doped AlAs, which may be promising for spintronic applications. The calculated results are also useful for understanding of the origin of ferromagnetism in diluted magnetic semiconductors.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Pp Magnetic semiconductors
75.50.Ee Antiferromagnetics
71.55.Eq III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
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Deposition of epitaxial BiFeO3/CoFe2O4 nanocomposites on (001) SrTiO3 by combinatorial pulsed laser deposition

Nicolas M. Aimon, Dong Hun Kim, Hong Kyoon Choi, and C. A. Ross

Appl. Phys. Lett. 100, 092901 (2012); http://dx.doi.org/10.1063/1.3690957 (4 pages) | Cited 10 times

Online Publication Date: 28 February 2012

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BiFeO3/CoFe2O4 (BFO/CFO) nanocomposites were grown on SrTiO3 by pulsed laser deposition using a combinatorial method in which Bi1.2FeO3 and CoFe2O4 targets are alternately ablated. The films had the same vertically nanostructured morphology as thin films prepared by ablation of a single target, consisting of epitaxial CoFe2O4 pillars in a BiFeO3 matrix. In a series of samples synthesized with a compositional spread, the out-of-plane magnetic anisotropy and the out-of-plane compressive strain of the CoFe2O4 pillars increased with decreasing volume fraction, and the anisotropy agreed with the value predicted from the strain state and magnetoelastic coefficients of CoFe2O4. These results show the dominant effect of magnetoelastic anisotropy in determining the magnetic hysteresis of the nanocomposite.
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81.15.Fg Pulsed laser ablation deposition
81.40.Lm Deformation, plasticity, and creep
68.55.at Other materials
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction

Magnetoelectric manipulation of domain wall configuration in thin film Ni/[Pb(Mn1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (001) heterostructure

Chin-Jui Hsu (許晉睿), Joshua L. Hockel, and Gregory P. Carman

Appl. Phys. Lett. 100, 092902 (2012); http://dx.doi.org/10.1063/1.3690953 (4 pages) | Cited 6 times

Online Publication Date: 29 February 2012

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This paper reports experimental observations of partial and reversible out-of-plane magnetization change in a thin film Ni/[Pb(Mn1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (001) heterostructure. Electric-field-induced isotropic in-plane compressive strain (∼1000 ppm) eliminates the stripe domain pattern in a 60-nm-thick Ni thin film. When the electric field is removed, the stripe domains are returned to their original configurations with some domain wall pinning perturbations due to ferroelectric domain texturing. The observed domain structure change is attributed to the transition from Bloch wall to Néel wall and the broadening of the Bloch wall. This out-of-plane magnetization change does not occur in thicker (100-nm-thick) Ni thin film.
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75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Kw Domain structure (including magnetic bubbles and vortices)
77.80.Dj Domain structure; hysteresis

Experimental study and theoretical prediction of dielectric permittivity in BaTiO3/polyimide nanocomposite films

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

Appl. Phys. Lett. 100, 092903 (2012); http://dx.doi.org/10.1063/1.3691198 (4 pages) | Cited 4 times

Online Publication Date: 29 February 2012

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Theoretical models were used to predict dielectric permittivities of the thermosetting polyimide (PI) matrix nanocomposite films loading with BaTiO3 (BT) nanoparticles prepared by the alkoxide route. The observed dielectric permittivities are in good agreement with calculated values using Jayasundere equation and effective medium theory when the interactions of nanoparticle-nanoparticle and nanoparticle-polymer are considered. Additionally, temperature dependence of dielectric permittivity of the BT/PI nanocomposite films at 103 Hz was also studied for both heating from −50 to 150 °C and cooling from 150 to −50 °C. The transformation in crystal phase of BT and changes of free volume in PI were considered to be the main factors influencing the dielectric permittivities of the BT/PI nanocomposite films.
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81.05.Qk Reinforced polymers and polymer-based composites
81.40.Rs Electrical and magnetic properties related to treatment conditions
77.55.-g Dielectric thin films
73.61.-r Electrical properties of specific thin films
77.22.Ch Permittivity (dielectric function)

Theoretical model for artificial structure modulation of HfO2/SiOx/Si interface by deposition of a dopant material

Naoto Umezawa and Kenji Shiraishi

Appl. Phys. Lett. 100, 092904 (2012); http://dx.doi.org/10.1063/1.3689968 (4 pages)

Online Publication Date: 29 February 2012

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Realization of an abrupt HfO2/Si interface without unintentional oxidation of the silicon substrate is a crucial task for the development of modern field-effect transistors. Here, we present a theoretical model which suggests that deposition of a dopant material on the HfO2 layer turns it into an oxygen absorber, suppressing the formation of SiOx at the interface. Tantalum is predicted as an effective dopant in HfO2 for this purpose.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology

Dipole spring ferroelectrics in superlattice SrTiO3/BaTiO3 thin films exhibiting constricted hysteresis loops

Pingping Wu, Xingqiao Ma, Yulan Li, Venkatraman Gopalan, and Long-Qing Chen

Appl. Phys. Lett. 100, 092905 (2012); http://dx.doi.org/10.1063/1.3691172 (4 pages) | Cited 1 time

Online Publication Date: 1 March 2012

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Ferroelectric superlattice heterostructures have recently been explored for potential applications in electronic devices. In this letter, we employed the phase-field approach to simulate the domain structure and switching of a (BaTiO3)8/(SrTiO3)3 superlattice film constrained by a GdScO3 substrate. A constricted ferroelectric hysteresis loop was observed with a high saturation polarization but a small coercive field. The shape of the hysteresis loop is understood by analyzing the ferroelectric polarization distributions during switching. It is demonstrated that the multilayers stack behaves as dipole spring ferroelectric, named in analogy to exchange spring magnets in magnetic multilayers that show similar loops.
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77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
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Silicon layer intercalation of centimeter-scale, epitaxially grown monolayer graphene on Ru(0001)

Jinhai Mao, Li Huang, Yi Pan, Min Gao, Junfeng He, Haitao Zhou, Haiming Guo, Yuan Tian, Qiang Zou, Lizhi Zhang, Haigang Zhang, Yeliang Wang, Shixuan Du, Xingjiang Zhou, A. H. Castro Neto, et al.

Appl. Phys. Lett. 100, 093101 (2012); http://dx.doi.org/10.1063/1.3687190 (4 pages) | Cited 16 times

Online Publication Date: 27 February 2012

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We develop a strategy for graphene growth on Ru(0001) followed by silicon-layer intercalation that not only weakens the interaction of graphene with the metal substrate but also retains its superlative properties. This G/Si/Ru architecture, produced by silicon-layer intercalation approach (SIA), was characterized by scanning tunneling microscopy/spectroscopy and angle resolved electron photoemission spectroscopy. These experiments show high structural and electronic qualities of this new composite. The SIA allows for an atomic control of the distance between the graphene and the metal substrate that can be used as a top gate. Our results show potential for the next generation of graphene-based materials with tailored properties.
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68.55.ap Fullerenes
71.20.Tx Fullerenes and related materials; intercalation compounds
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Vacancy analysis in a Ni-Nb-Zr-H glassy alloy by positron annihilation spectroscopy

Mikio Fukuhara

Appl. Phys. Lett. 100, 093102 (2012); http://dx.doi.org/10.1063/1.3688303 (3 pages) | Cited 2 times

Online Publication Date: 27 February 2012

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The positron lifetimes of Ni36Nb24Zr40 and (Ni0.36Nb0.24Zr0.40)90H10 glassy alloys are almost the same but longer than those of pure Zr, Nb, and Ni crystals, indicating that they have higher density of vacancies with smaller size than in crystals. The coincidence Doppler broadening spectrum for both specimens shows that the contribution of Ni around the vacancies is lower than that of Zr and Nb, suggesting that hydrogen atoms favour to exist between Ni atoms comprising neighboring distorted icosahedral Zr5Ni5Nb3 clusters. Thus, these results provide a substitute model of quantum dot tunneling along Ni–H–Ni atomic bond arrays among the clusters.
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61.72.jd Vacancies
78.67.Hc Quantum dots
78.70.Bj Positron annihilation
61.43.Dq Amorphous semiconductors, metals, and alloys
61.43.Fs Glasses

In-situ x-ray characterization of wurtzite formation in GaAs nanowires

Peter Krogstrup, Morten Hannibal Madsen, Wen Hu, Miwa Kozu, Yuka Nakata, Jesper Nygård, Masamitu Takahasi, and Robert Feidenhans’l

Appl. Phys. Lett. 100, 093103 (2012); http://dx.doi.org/10.1063/1.3688489 (4 pages) | Cited 7 times

Online Publication Date: 27 February 2012

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In-situ monitoring of the crystal structure formation during Ga-assisted GaAs nanowire growth on Si(111) substrates has been performed in a combined molecular beam epitaxy growth and x-ray characterization experiment. Under Ga rich conditions, we show that an increase in the V/III ratio increases the formation rate of the wurtzite structure. Moreover, the response time for changes in the structural phase formation to changes in the beam fluxes is observed to be much longer than predicted time scales of adatom kinetics and liquid diffusion. This suggests that the morphology of the growth interface plays the key role for the relative growth structure formation rates.
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81.07.Gf Nanowires
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.05.Ea III-V semiconductors
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