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28 May 2012

Volume 100, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 222402 (2012); http://dx.doi.org/10.1063/1.3700809 (4 pages)

Felix Balhorn, Simon Jeni, Wolfgang Hansen, Detlef Heitmann, and Stefan Mendach
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Ferromagnetism carried by highly delocalized hybrid states in Sc-doped ZnO thin films

Mohammed Benali Kanoun, Souraya Goumri-Said, Aurélien Manchon, and Udo Schwingenschlögl

Appl. Phys. Lett. 100, 222406 (2012); http://dx.doi.org/10.1063/1.4721807 (4 pages) | Cited 1 time

Online Publication Date: 29 May 2012

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We present first-principles results for Sc-doped ZnO thin films. Neighboring Sc atoms in the surface and/or subsurface layers are found to be coupled ferromagnetically, where only two of the possible configurations induce spin polarization. In the first configuration, the polarization is carried by the Sc d states as expected for transition metal doping. However, there is a second configuration which is energetically favorable. It is governed by polarized hybrid states of the Zn s, O p, and Sc d orbitals. Such highly delocalized states can be an important ingredient for understanding the magnetism of doped ZnO thin films.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.15.-m Methods of electronic structure calculations
72.25.-b Spin polarized transport
75.50.Pp Magnetic semiconductors

Transport and magnetic properties of the Co2MnSi/Al/Co2MnSi trilayer

H. L. Yu, H. B. Zhang, X. F. Jiang, Y. Zheng, and G. W. Yang

Appl. Phys. Lett. 100, 222407 (2012); http://dx.doi.org/10.1063/1.4725513 (4 pages)

Online Publication Date: 30 May 2012

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Using density functional theory and non-equilibrium Green’s function analysis, we studied the interface structure, interface stability, and magnetic and transport properties of the Co2MnSi/Al/Co2MnSi trilayer. It was found that only the CoCo/Al architecture is thermodynamically stable among four interfacial architectures, CoCo/Al, MnSi/Al, MnMn/Al, and SiSi/Al, and the other interface architectures are not accessible within the limits set under thermodynamic equilibrium with other phases. Calculations of the transmission spectrum, conductance, and resistance-area product showed that the Co2MnSi/Al/Co2MnSi trilayer is a promising candidate for the next-generation of recording sensors in ultrahigh-density hard disks.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.35.Ct Interface structure and roughness
72.80.Sk Insulators
71.20.Gj Other metals and alloys

Carrier localization and out of plane anisotropic magnetoresistance in Nd0.55−xSmxSr0.45MnO3 thin films

M. K. Srivastava, A. Kaur, and H. K. Singh

Appl. Phys. Lett. 100, 222408 (2012); http://dx.doi.org/10.1063/1.4722815 (4 pages) | Cited 2 times

Online Publication Date: 30 May 2012

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The impact of carrier localization on the anisotropic magnetoresistance (AMR) has been investigated in Nd0.55−xSmxSr0.45MnO3 (x = 0.00–0.45) thin films. The substitution of smaller Sm3+ cations for larger Nd3+ reduces the average radius of the A-site of the perovskite lattice and enhances size disorder. This quenched disorder results in (1) enhanced Jahn-Teller (J-T) distortion as suggested by decrease in the out of plane lattice constant, (2) stronger carrier localization as evidenced by enhancement in the activation energy of small polaron hopping, (3) decrease in the ferromagnetic (FM) and insulator-metal transition (IMT) temperatures (TC/TIM), (4) sharpening of the IMT, (5) increase in the low field MR, and (6) large enhancement in the AMR. The AMR-T curves of all the films show a maximum just below TIM. The peak AMR measured at small magnetic field of 4.2 kOe increases from −5% for x = 0.00 to −60% for x = 0.45. The enhancement in AMR has been explained in terms of the unquenching of the orbital angular momentum of t2g3 and eg1 configuration and spin fluctuations due to stronger J-T distortion at higher values of x.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Ns Metal-nonmetal contacts
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
81.40.Gh Other heat and thermomechanical treatments
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Charge-carrier mediated ferromagnetism in Mo-doped In2O3 films

Chang-Yup Park, Chun-Yeol You, Kun-Rok Jeon, and Sung-Chul Shin

Appl. Phys. Lett. 100, 222409 (2012); http://dx.doi.org/10.1063/1.4722928 (4 pages) | Cited 2 times

Online Publication Date: 30 May 2012

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We investigated the correlation between the ferromagnetism and electric resistivity of Mo-doped (3–10 at. %) In2O3 films. We find that the saturation magnetization increases with the Mo concentration until it reaches its maximum at 7 at. % Mo doping (7.1 emu/cm3), after which it rapidly decreases upon higher doping concentration. Interestingly, the resistivity reveals opposite behavior with the Mo concentration, showing a minimum value at 7 at. % Mo doping. According to the temperature-dependent resistivity and the Hall effect measurements, we find that the samples with higher magnetization show metallic behavior with higher electron concentration. Notably, the samples show a linear relationship between the carrier concentration and the degree of magnetization. We believe the ferromagnetism in Mo-doped In2O3 is ascribed to the indirect exchange interaction mediated by the charge carriers.
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73.61.Le Other inorganic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
61.72.up Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors

Thickness dependence of magneto-optical effects in (Ga,Mn)As epitaxial layers

B. Al-Qadi, N. Nishizawa, K. Nishibayashi, M. Kaneko, and H. Munekata

Appl. Phys. Lett. 100, 222410 (2012); http://dx.doi.org/10.1063/1.4724215 (4 pages) | Cited 2 times

Online Publication Date: 31 May 2012

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Rotation angle (θMO) of a linearly polarized light reflected from in-plane, ferromagnetic (Ga,Mn)As layers was measured precisely using a magneto-optical microscope. The θMO value varies non-linearly as a function of (Ga,Mn)As layer thickness d, showing a maximum at d = 50–60 nm. The thickness dependent θMO was analyzed quantitatively with a model based on an interference effect incorporating birefringence and dichroism, and it has been concluded that the contribution of magnetization-vector dependent refractive index, a magnetic birefringence, is responsible for the observed magneto-optical effect. The magnitude of magnetic birefringence appears to be comparable to those of uniaxial birefringence crystals.
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78.20.Ls Magneto-optical effects
78.20.Fm Birefringence
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators
75.70.Ak Magnetic properties of monolayers and thin films

Suppression of the precessional motion of magnetization in a nanostructured synthetic ferrimagnet

Jong Min Lee and Sang Ho Lim

Appl. Phys. Lett. 100, 222411 (2012); http://dx.doi.org/10.1063/1.4724209 (4 pages) | Cited 1 time

Online Publication Date: 1 June 2012

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The suppression of the precessional oscillation of magnetization is investigated in a nanostructured synthetic ferrimagnet. Both the duration and magnitude of an applied magnetic field pulse play an important role in suppressing the precessional motion. This is in contrast to a single magnetic layer, where efficient suppression can be done by controlling the pulse duration only. The reason for this is that the precessional motion of the two magnetizations in the synthetic ferrimagnet is strongly coupled and, at the conditions of current interest, the coupled precessional motion occurs in the optic mode, where the two magnetizations oscillate in opposite directions.
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75.75.-c Magnetic properties of nanostructures
75.78.Cd Micromagnetic simulations
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
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Ferromagnetic Josephson switching device with high characteristic voltage

Timofei I. Larkin, Vitaly V. Bol’ginov, Vasily S. Stolyarov, Valery V. Ryazanov, Igor V. Vernik, Sergey K. Tolpygo, and Oleg A. Mukhanov

Appl. Phys. Lett. 100, 222601 (2012); http://dx.doi.org/10.1063/1.4723576 (5 pages) | Cited 3 times

Online Publication Date: 30 May 2012

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We develop a fast magnetic Josephson junction (MJJ)—a superconducting ferromagnetic device for a scalable high-density cryogenic memory compatible in speed and fabrication with energy-efficient single flux quantum (SFQ) circuits. We present experimental results for superconductor-insulator-ferromagnet-superconductor (SIFS) MJJs with high characteristic voltage IcRn of >700 μV proving their applicability for superconducting circuits. By applying magnetic field pulses, the device can be switched between MJJ logic states. The MJJ IcRn product is only ∼30% lower than that of conventional junction co-produced in the same process, allowing for integration of MJJ-based and SIS-based ultra-fast digital SFQ circuits operating at tens of gigahertz.
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85.25.Cp Josephson devices
84.30.Sk Pulse and digital circuits
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits

Superconducting fluctuations and anomalous phonon renormalization much above superconducting transition temperature in Ca4Al2O5.7Fe2As2

Pradeep Kumar, A. Bera, D. V. S Muthu, P. M. Shirage, A. Iyo, and A. K. Sood

Appl. Phys. Lett. 100, 222602 (2012); http://dx.doi.org/10.1063/1.4724206 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2012

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Raman studies on Ca4Al2O5.7Fe2As2 superconductor in the temperature range of 5 K to 300 K, covering the superconducting transition temperature Tc = 28.3 K, reveal that the Raman mode at ∼230 cm−1 shows a sharp jump in frequency by ∼2% and linewidth increases by ∼175% at To ∼ 60 K. Below To, anomalous softening of the mode frequency and a large decrease by ∼10 cm−1 in the linewidth are observed. These precursor effects at T0 (∼2Tc) are attributed to significant superconducting fluctuations, possibly enhanced due to reduced dimensionality arising from weak coupling between the well separated (∼15 Å) Fe-As layers in the unit cell. A large blue-shift of the mode frequency between 300 K and 60 K (∼7%) indicates strong spin-phonon coupling in this superconductor.
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74.40.-n Fluctuation phenomena
74.25.Gz Optical properties
74.62.-c Transition temperature variations, phase diagrams
74.10.+v Occurrence, potential candidates
74.25.Kc Phonons
74.70.Xa Pnictides and chalcogenides
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The asymmetrical degradation behavior on drain bias stress under illumination for InGaZnO thin film transistors

Sheng-Yao Huang, Ting-Chang Chang, Li-Wei Lin, Man-Chun Yang, Min-Chen Chen, Jhe-Ciou Jhu, and Fu-Yen Jian

Appl. Phys. Lett. 100, 222901 (2012); http://dx.doi.org/10.1063/1.4722787 (4 pages) | Cited 2 times

Online Publication Date: 29 May 2012

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This paper investigates behavior of drain bias stress and gate-drain bias stress under illumination for InGaZnO thin film transistors as the current-driver operated. Properties exhibit two-stage degradation behavior during drain bias stress. The photo-excited hole non-uniform trapping from illumination induces drain side barrier lowering and causes an apparent hump phenomenon of the subthreshold swing. However, the positive threshold voltage shift without a hump phenomenon after gate-drain bias stress is different degradation behaviors. It is reliant on whether or not an inversion layer exists in the channel. This work also employs capacitance-voltage measurement to further clarify the mechanism of degradation behaviors.
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85.30.Tv Field effect devices

Enhanced electrocaloric effect in poly(vinylidene fluoride-trifluoroethylene)-based terpolymer/copolymer blends

Xiang-zhong Chen, Xiao-shi Qian, Xinyu Li, S. G. Lu, Hai-ming Gu, Minren Lin, Qun-dong Shen, and Q. M. Zhang

Appl. Phys. Lett. 100, 222902 (2012); http://dx.doi.org/10.1063/1.4722932 (4 pages) | Cited 8 times

Online Publication Date: 29 May 2012

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The electrocaloric effect in the blends of poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF-TrFE-CFE)) with small amount of poly(vinylidene fluoride–trifluoroethylene) (P(VDF-TrFE)) is investigated. It was found that small amount of P(VDF-TrFE) (∼10 wt. %) can cause a more than 10% increase in the crystallinity in the blends. Although the two polymers form separate crystalline phases, the interfacial couplings to the random defects in the terpolymer convert the normal ferroelectric P(VDF-TrFE) into a relaxor ferroelectric. As a result, the blends with 10 wt. % of P(VDF-TrFE) exhibit a 30% increase in the adiabatic temperature change over the entire experimental temperature range (20 °C–60 °C).
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77.70.+a Pyroelectric and electrocaloric effects
77.80.Jk Relaxor ferroelectrics
77.84.Jd Polymers; organic compounds

A model for the frequency dispersion of the high-k metal-oxide-semiconductor capacitance in accumulation

B. Yao, Z. B. Fang, Y. Y. Zhu, T. Ji, and G. He

Appl. Phys. Lett. 100, 222903 (2012); http://dx.doi.org/10.1063/1.4722934 (4 pages)

Online Publication Date: 30 May 2012

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High-frequency capacitance-voltage measurements have been made on metal-oxide-semiconductor capacitors by using single crystalline Er2O3 high-k gate dielectrics. Based on our analysis, it has been found that frequency dispersion of Er2O3 capacitance in accumulation decreases consistently with the increase of the frequency. A correction model is proposed to explain these frequency dispersion phenomena and the capacitance-frequency equations are obtained from the impedance expression of the equivalent circuit. Based on the simulated capacitance-frequency, it can be concluded that frequency dispersion of Er2O3 capacitance in accumulation originates from the existence of the parasitic resistances, the series resistances, and the formed SiOx interfacial layer.
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84.32.Tt Capacitors

Origin of thickness dependent dc electrical breakdown in dielectrics

George Chen, Junwei Zhao, Shengtao Li, and Lisheng Zhong

Appl. Phys. Lett. 100, 222904 (2012); http://dx.doi.org/10.1063/1.4721809 (4 pages) | Cited 4 times

Online Publication Date: 31 May 2012

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A model based on space charge dynamics under high dc electric field has been proposed to explain commonly observed thickness dependent breakdown of polymeric material. The formation and dynamics of space charge will result in local electric field enhancement that has a direct impact on dielectric breakdown. The simulation results show that the breakdown depends on the sample thickness with a power index of 0.143, indicating the space charge and its dynamics are responsible for thickness dependent breakdown. The model also predicts the effect of voltage ramping rate on the electrical breakdown strength.
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77.22.Jp Dielectric breakdown and space-charge effects

How to generate high twin densities in nano-ferroics: Thermal quench and low temperature shear

E. K. H. Salje, X. Ding, Z. Zhao, and T. Lookman

Appl. Phys. Lett. 100, 222905 (2012); http://dx.doi.org/10.1063/1.4724192 (3 pages) | Cited 4 times

Online Publication Date: 31 May 2012

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High domain boundary densities in ferroic nano materials are generated in computer simulation studies by (1) fast quench from a para-elastic into a ferroelastic phase and (2) by shear of small samples at low temperatures inside the stability field of the ferroelastic phase. Quenched samples evolve from tweed to junctions to stripe pattern. In driven systems, no tweed exists and the mesoscopic structure ‘nucleates’ rapidly when a yield stress is surpassed. The nucleated domain patterns are long-lived and change towards the single domain state only when the external strain is further increased.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
81.40.Gh Other heat and thermomechanical treatments
75.85.+t Magnetoelectric effects, multiferroics

Nano-domain engineering in ultrashort-period ferroelectric superlattices

Taekjib Choi, Bae Ho Park, Hyunjung Shin, and Jaichan Lee

Appl. Phys. Lett. 100, 222906 (2012); http://dx.doi.org/10.1063/1.4722791 (4 pages)

Online Publication Date: 1 June 2012

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Ultrashort-period PbZrO3/PbTiO3 (PTO/PZO) ferroelectric/antiferroelectric superlattices are proposed for nano-domain engineering. They behaved like single ferroelectric metamaterials with monodomain excluding a 90° domain boundary, irrespective of their total thicknesses. Further, nanosized 180° domains, as small as ∼12 nm, were achieved by applying a short pulse voltage. Such domain structures of superlattices result from the lowering of the symmetry of supercell by specific atomic stacking in superlattices, contrary to the domain structures of ferroelectric thin films developed by the strain-induced ferroelectric instability. We suggest that ferroelectric superlattices with an ultrashort-period have a clear advantage for nano-domain engineering with greatly enhanced long term stability of the domains.
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77.80.Dj Domain structure; hysteresis
61.46.-w Structure of nanoscale materials

B-site ordering induced suppression of magnetic cluster glass and dielectric anomaly in La2−xBixCoMnO6

Yijia Bai, Xiaojuan Liu, Yanjie Xia, Hongping Li, Xiaolong Deng, Lin Han, Qingshuang Liang, Xiaojie Wu, Zhongchang Wang, and Jian Meng

Appl. Phys. Lett. 100, 222907 (2012); http://dx.doi.org/10.1063/1.4722936 (4 pages)

Online Publication Date: 1 June 2012

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We report the heat, magnetic, and dielectric properties of La2−xBixCoMnO6 with a series of Bi doping concentrations, focusing especially on the impact of A-site doping on B-site ordering. We demonstrate that the B-site ordering is enhanced via the Bi doping, resulting in a suppressed cluster-glass behavior, larger dielectric constant, and smaller tangent loss. Surprisingly, a pronounced step-like dielectric anomaly turns up near the spin-freezing temperature in the Bi-free oxide, which is suppressed significantly after Bi doping. We attribute the suppression of anomaly to the lessened amount of antisite defects at the B sites and the associated strengthened electronic localization.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.J- Point defects and defect clusters
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
65.40.Ba Heat capacity

Third-order electric-field-induced dipolar resonances from patterned barium-strontium-titanate thin-films

Ryan C. Toonen and M. W. Cole

Appl. Phys. Lett. 100, 222908 (2012); http://dx.doi.org/10.1063/1.4723692 (5 pages) | Cited 1 time

Online Publication Date: 1 June 2012

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Using microwave reflection spectroscopy, the complex permittivities of etch defined, 240 nm thick, (Ba0.6Sr0.4)TiO3, thin films have been measured over the frequency range of (1 to 4) GHz. Anomalous electric-field-induced electro-acoustic resonances were observed and characterized as a function of extrinsic electric field magnitude, ambient temperature, and sample diameter. The real and imaginary parts of the measured permittivities were fit to frequency-dependent functions derived from the Lorentz oscillator model. From these functions, extracted static dielectric constants were found to display excellent agreement with a closed-form expression derived by calculating third-order nonlinear susceptibility from the Landau-Devonshire-Ginzberg model.
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77.84.Cg PZT ceramics and other titanates
78.70.Gq Microwave and radio-frequency interactions
77.22.Ch Permittivity (dielectric function)
73.50.Rb Acoustoelectric and magnetoacoustic effects

Electrocaloric properties of epitaxial strontium titanate films

J. Zhang, I. B. Misirlioglu, S. P. Alpay, and G. A. Rossetti, Jr.

Appl. Phys. Lett. 100, 222909 (2012); http://dx.doi.org/10.1063/1.4721668 (4 pages) | Cited 1 time

Online Publication Date: 1 June 2012

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The electrocaloric (EC) response of strontium titanate thin films is computed as a function of misfit strain, temperature, electric field strength, and electrode configuration using a nonlinear thermodynamic theory. For films in a capacitor configuration on compressive substrates, the transition between paraelectric and strain-induced ferroelectric tetragonal phases produces a large adiabatic temperature change, ΔT = 5 K, at room temperature for electric field changes ΔE = 1200 kV/cm. For films on tensile substrates, the transition between the paraelectric and strain-induced ferroelectric orthorhombic phases can also be accessed using inter-digitated electrodes (IDEs). The maximum EC response occurs for IDEs with a [110] orientation.
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77.70.+a Pyroelectric and electrocaloric effects
77.80.-e Ferroelectricity and antiferroelectricity
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
77.55.Kt Pyroelectric films
77.55.Px Epitaxial and superlattice films
68.55.-a Thin film structure and morphology

Triple-point-type morphotropic phase boundary based large piezoelectric Pb-free material—Ba(Ti0.8Hf0.2)O3-(Ba0.7Ca0.3)TiO3

Chao Zhou, Wenfeng Liu, Dezhen Xue, Xiaobing Ren, Huixin Bao, Jinghui Gao, and Lixue Zhang

Appl. Phys. Lett. 100, 222910 (2012); http://dx.doi.org/10.1063/1.4724216 (5 pages) | Cited 3 times

Online Publication Date: 1 June 2012

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We report a large piezoelectric Pb-free system—Ba(Ti0.8Hf0.2)O3-(Ba0.7Ca0.3)TiO3, designed upon a triple-point morphotropic phase boundary (TMPB) idea. The system shows anomalies of both ac (dielectric and piezoelectric) and dc (P-E hysteresis) properties around TMPB, especially the d33 achieving ∼550 pC/N at room temperature. Moreover, the detected non-zero thermal hysteresis around triple point shows a first order transition nature and non-isotropic polarization state, as well as verified by our theoretical Landau-type deduction, thus being considered as an important factor to influence the piezoelectricity along TMPB. Our work may stimulate the study on triple-point-related critical phenomena in other ferroic systems.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
77.80.B- Phase transitions and Curie point
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Transparent SiO2-Ag core-satellite nanoparticle assembled layer for plasmonic-based chemical sensors

Tsung-Han Chen, Ren-Der Jean, Kuo-Chuang Chiu, Chun-Hua Chen, and Dean-Mo Liu

Appl. Phys. Lett. 100, 223101 (2012); http://dx.doi.org/10.1063/1.4722583 (4 pages)

Online Publication Date: 29 May 2012

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We discovered a promising sensing capability of SiO2@Ag core-satellite nanoparticles with respect to organic melamine when they were consolidated into a solid-type thin-film entity. A series of theoretical models were proposed which provided calculation outcomes superior to those of existing models for the localized surface plasmon resonance spectra of the solid-state assemblies. We envisioned not only that such a SiO2@Ag film is a potential candidate for a transparent solid-state optical nanosensor for the detection of organic molecules but also that the resulting plasmonic resonance model facilitates a better understanding of such a solid-state nanosensor used for a number of sensory applications.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys

Intrinsic characteristics of transmission line of graphenes at microwave frequencies

Hee-Jo Lee, Eunho Kim, Jong-Gwan Yook, and Jongwan Jung

Appl. Phys. Lett. 100, 223102 (2012); http://dx.doi.org/10.1063/1.4722585 (3 pages) | Cited 1 time

Online Publication Date: 29 May 2012

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In this paper, we have quantitatively evaluated the effective surface conductivity of chemical vapor deposition-grown graphene through a full-wave electromagnetic method and also investigated the intrinsic characteristics of the transmission line (TL) of the graphene at frequency ranging from 0.5 to 40 GHz. According to the simulated data based on the measured S-parameters, the effective conductivity of single- and multi-layer graphene (MLG) was about 4.3 × 106 S/m and 1.2 × 106 S/m, respectively. Furthermore, we confirm that multi-layer graphene is more suitable for use in transmission lines compared to single-layer graphene in the observed frequency region.
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73.25.+i Surface conductivity and carrier phenomena
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Excitonic origin of enhanced luminescence quantum efficiency in MgZnO/ZnO coaxial nanowire heterostructures

Jinkyoung Yoo, Bonghwan Chon, Wei Tang, Taiha Joo, Le Si Dang, and Gyu-Chul Yi

Appl. Phys. Lett. 100, 223103 (2012); http://dx.doi.org/10.1063/1.4721519 (4 pages)

Online Publication Date: 29 May 2012

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The effect of exciton transport on luminescence efficiency was investigated by time-resolved photoluminescence and spatially resolved cathodoluminescence spectroscopy. The internal quantum efficiency of ZnO nanowire (NW) increased from 45% to 56% due to formation of a MgZnO/ZnO coaxial NW heterostructure. MgZnO shell layer formation induced a decrease in the exciton diffusion length and diffusion coefficient from 150 to 120 nm and 9.8 to 6.4 cm2/s, respectively. The change in exciton transport characteristics indicated that exciton transport, in addition to the surface passivation effect, was an important factor determining the luminescence efficiency in the coaxial NW heterostructure.
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71.35.-y Excitons and related phenomena
78.55.Et II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Dz II-VI semiconductors
81.65.Rv Passivation
78.47.jd Time resolved luminescence

High potential sensitivity in heterodyne amplitude-modulation Kelvin probe force microscopy

Yasuhiro Sugawara, Lili Kou, Zongmin Ma, Takeshi Kamijo, Yoshitaka Naitoh, and Yan Jun Li

Appl. Phys. Lett. 100, 223104 (2012); http://dx.doi.org/10.1063/1.4723697 (4 pages) | Cited 1 time

Online Publication Date: 29 May 2012

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A surface potential measurement method using amplitude-modulation and heterodyne techniques is proposed. The effect of the stray capacitance between a cantilever and a sample in Kelvin probe force microscopy and the electrostatic force spectroscopy measurements are almost completely removed, because the distance (z) dependence of the modulated electrostatic force increases from 1/z to1/z2. This method improves the sensitivity of short range forces and reduces the surface potential measurement crosstalk that is induced by topographic feedback. This method has the advantage of high potential sensitivity due to the high cantilever Q value under vacuum. Quantitative surface potential measurements are demonstrated.
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07.79.Lh Atomic force microscopes

Programmable synthesis of shape-, structure-, and composition-modulated one-dimensional heterostructures by galvanic displacement reaction

Hyunsung Jung, Hoyoung Suh, Carlos M. Hangarter, Jae Hong Lim, Young-In Lee, Yong-Ho Choa, Kimin Hong, and Nosang V. Myung

Appl. Phys. Lett. 100, 223105 (2012); http://dx.doi.org/10.1063/1.4722919 (4 pages) | Cited 1 time

Online Publication Date: 30 May 2012

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One-dimensional heterostructures consisting of periodically modulated bismuth telluride tube/wire were synthesized by galvanic displacement reaction of Co/Ni multi-segmented sacrificial nanowires. Utilizing the difference in redox potential and corrosion behavior of Co and Ni, segments, dimension, composition, and structure of the individual segments were also precisely engineered. The programmable ability to synthesize heterostructures with simultaneously modulation of various dimensions in ambient conditions may lead to an effective route to synthesize high performance nanodevices including nanoelectronics, optoelectronics, sensors, and thermoelectrics.
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81.07.Bc Nanocrystalline materials
73.40.Ns Metal-nonmetal contacts

Probing buried layers by photoelectron spectromicroscopy with hard x-ray excitation

C. Wiemann, M. Patt, S. Cramm, M. Escher, M. Merkel, A. Gloskovskii, S. Thiess, W. Drube, and C. M. Schneider

Appl. Phys. Lett. 100, 223106 (2012); http://dx.doi.org/10.1063/1.4722940 (3 pages) | Cited 1 time

Online Publication Date: 30 May 2012

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We report about a proof-of-principle experiment which explores the perspectives of performing hard x-ray photoemission spectromicroscopy with high lateral resolution. Our results obtained with an energy-filtered photoemission microscope at the PETRA III storage ring facility using hard x-ray excitation up to 6.5 keV photon energy demonstrate that it is possible to obtain selected-area x-ray photoemission spectra from regions less than 500 nm in diameter.
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79.60.Jv Interfaces; heterostructures; nanostructures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Atomistic simulations of heat transport in real-scale silicon nanowire devices

Ivan Duchemin and Davide Donadio

Appl. Phys. Lett. 100, 223107 (2012); http://dx.doi.org/10.1063/1.4723632 (4 pages) | Cited 1 time

Online Publication Date: 30 May 2012

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Utilizing atomistic lattice dynamics and scattering theory, we study thermal transport in nanodevices made of 10 nm thick silicon nanowires, from 10 to 100 nm long, sandwiched between two bulk reservoirs. We find that thermal transport in devices differs significantly from that of suspended extended nanowires, due to phonon scattering at the contact interfaces. We show that thermal conductance and the phonon transport regime can be tuned from ballistic to diffusive by varying the surface roughness of the nanowires and their length. In devices containing short crystalline wires, phonon tunneling occurs and enhances the conductance beyond that of single contacts.
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85.30.De Semiconductor-device characterization, design, and modeling
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