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5 Dec 2011

Volume 99, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 233701 (2011); http://dx.doi.org/10.1063/1.3651756 (3 pages)

Melis Hazar, Robert L. Steward, Jr., Chia-Jung Chang, Cynthia J. Orndoff, Yukai Zeng, Mon-Shu Ho, Philip R. LeDuc, and Chao-Min Cheng
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Electrical detection of nonlinear ferromagnetic resonance in single elliptical permalloy thin film using a magnetic tunnel junction

Chong Bi, Xin Fan, Liqing Pan, Xiaoming Kou, Jun Wu, Qinghui Yang, Huaiwu Zhang, and John Q. Xiao

Appl. Phys. Lett. 99, 232506 (2011); http://dx.doi.org/10.1063/1.3670302 (3 pages)

Online Publication Date: 9 December 2011

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A quantitative method to detect ferromagnetic resonance using magnetic tunnel junction structure has been developed. Experimental results reveal three distinct regions for single elliptical permalloy film of micrometer lateral size. Above the spin wave instability threshold, the experimental results show a linear response of the longitudinal magnetization component to the microwave field amplitude over a large range rather than a lock-up phenomenon appeared in macroscopic permalloy films and then a phase limiting behavior. The linear behavior can be described by the theoretical model describing subsidiary resonance.
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75.70.Ak Magnetic properties of monolayers and thin films
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Finite size versus surface effects on magnetic properties of antiferromagnetic particles

Suman Mandal, Krishnakumar S. R. Menon, S. K. Mahatha, and S. Banerjee

Appl. Phys. Lett. 99, 232507 (2011); http://dx.doi.org/10.1063/1.3668091 (4 pages) | Cited 4 times

Online Publication Date: 9 December 2011

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The observation of finite magnetic moment in antiferromagnetic materials is quite unusual and has been immensely investigated in nanoparticle systems. Here, the structural and magnetic properties of NiO particles are explored by x-ray diffraction, extended x-ray absorption fine structure, and magnetization measurements. Using similar-sized particles with different surface defect structure, we show that the observed magnetic enhancement, which is present even beyond finite-size limit, is due to the surface effects. However, the well known spin glass freezing is found to occur only in nano-regime.
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75.75.-c Magnetic properties of nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.70.Dm X-ray absorption spectra
75.50.Lk Spin glasses and other random magnets
75.50.Ee Antiferromagnetics
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Piezoresponse force microscopy of domains and walls in multiferroic HoMnO3

Edward B. Lochocki, S. Park, Nara Lee, S.-W. Cheong, and Weida Wu

Appl. Phys. Lett. 99, 232901 (2011); http://dx.doi.org/10.1063/1.3665255 (3 pages) | Cited 6 times

Online Publication Date: 5 December 2011

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We report ambient piezoresponse force microscopy (PFM) studies of the multiferroic hexagonal manganite HoMnO3 performed on the cleaved (110) surface of a single-crystal specimen. By changing the sample orientation with respect to the cantilever, we observed an unexpected out-of-plane PFM signal at domain walls, which depends on domain wall orientation, in addition to the expected in-plane PFM signal in domains. Further studies confirmed that the domain wall PFM signal results from an out-of-plane displacement, which can be explained by a simple model of local elastic response with the conservation of unit cell volume at head-on domain walls.
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77.80.Dj Domain structure; hysteresis
81.40.Jj Elasticity and anelasticity, stress-strain relations
77.65.-j Piezoelectricity and electromechanical effects

Titania/alumina bilayer gate insulators for InGaAs metal-oxide-semiconductor devices

Jaesoo Ahn, Irina Geppert, Marika Gunji, Martin Holland, Iain Thayne, Moshe Eizenberg, and Paul C. McIntyre

Appl. Phys. Lett. 99, 232902 (2011); http://dx.doi.org/10.1063/1.3662966 (3 pages) | Cited 3 times

Online Publication Date: 5 December 2011

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We describe the electrical properties of atomic layer deposited TiO2/Al2O3 bilayer gate oxides which simultaneously achieve high gate capacitance density and low gate leakage current density. Crystallization of the initially amorphous TiO2 film contributes to a significant accumulation capacitance increase (∼33%) observed after a forming gas anneal at 400 °C. The bilayer dielectrics reduce gate leakage current density by approximately one order of magnitude at flatband compared to Al2O3 single layer of comparable capacitance equivalent thickness. The conduction band offset of TiO2 relative to InGaAs is 0.6 eV, contributing to the ability of the stacked dielectric to suppress gate leakage conduction.
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85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing

X-ray nanodiffraction of tilted domains in a poled epitaxial BiFeO3 thin film

S. O. Hruszkewycz, C. M. Folkman, M. J. Highland, M. V. Holt, S. H. Baek, S. K. Streiffer, P. Baldo, C. B. Eom, and P. H. Fuoss

Appl. Phys. Lett. 99, 232903 (2011); http://dx.doi.org/10.1063/1.3665627 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2011

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We present measurements of crystallographic domain tilts in a (001) BiFeO3 thin film using focused beam x-ray nanodiffraction. Films were ferroelectrically pre-poled with an electric field orthogonal and parallel to as-grown tilt domain stripes. The tilt domains, associated with higher energy (010) vertical twin walls, displayed different nanostructural responses based on the poling orientation. Specifically, an electric field applied perpendicular to the as-grown domain stripe allowed the domain tilts and associated vertical twin walls to persist. The result demonstrates that thin film ferroelectric devices can be designed to maintain unexpected domain morphologies in working poled environments.
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77.80.Dj Domain structure; hysteresis
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.35.bt Other materials
77.55.Nv Multiferroic/magnetoelectric films
77.55.Px Epitaxial and superlattice films
77.22.Ej Polarization and depolarization

Study of slow oxide trap creating random telegraph noise within a gate edge overlap region in inversion mode

Heung-Jae Cho, Younghwan Son, Seunghyun Jang, and Hyungcheol Shin

Appl. Phys. Lett. 99, 232904 (2011); http://dx.doi.org/10.1063/1.3665628 (3 pages)

Online Publication Date: 6 December 2011

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We investigated a slow oxide trap causing a random telegraph noise (RTN) within a gate edge overlap region in an inversion mode at metal/high-k dielectric nMOSFETs. The oxide trap was observed to generate RTN only in gate leakage current (Ig RTN) without in drain current (Id RTN) in the inversion mode. Through the analysis of the RTN dependence on drain, source, and body bias, we found that the oxide trap in the dielectric exists not within the channel area but within the gate edge overlap region, resulting in the absence of Id RTN.
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85.30.Tv Field effect devices

Suppression of vacancy defects in epitaxial La-doped SrTiO3 films

D. J. Keeble, B. Jalan, L. Ravelli, W. Egger, G. Kanda, and S. Stemmer

Appl. Phys. Lett. 99, 232905 (2011); http://dx.doi.org/10.1063/1.3664398 (3 pages) | Cited 5 times

Online Publication Date: 6 December 2011

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Variable energy positron annihilation lifetime spectroscopy of high-mobility La-doped SrTiO3 grown by molecular beam epitaxy found that the films contained sufficiently low concentrations of Sr vacancies and vacancy cluster defects to allow the observation of positron annihilation events from the perfect lattice. This enabled the concentrations of charged cation vacancies to be estimated, and these were found to be at least an order of magnitude below the La-dopant concentrations.
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68.55.aj Insulators
61.72.jd Vacancies
78.70.Bj Positron annihilation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Antiferroelectric–ferroelectric phase boundary enhances polarization extension in rhombohedral Pb(Zr,Ti)O3

Anirban Ghosh and Dragan Damjanovic

Appl. Phys. Lett. 99, 232906 (2011); http://dx.doi.org/10.1063/1.3666233 (3 pages)

Online Publication Date: 7 December 2011

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The main mechanism of properties enhancement in the morphotropic phase boundary region separating tetragonal and rhombohedral phases of Pb(Zr1-xTix)O3 (PZT) is related to polarization rotation. It is shown here that in proximity of the morphotropic phase boundary separating antiferroelectric and rhombohedral phases (near x = 0.1) and at elevated temperatures the properties are dominated by polarization extension. These results may provide a guideline for developing alternative piezoelectric materials to PZT.
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77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
61.66.Fn Inorganic compounds
81.30.Dz Phase diagrams of other materials

Influence of lattice parameters on the dielectric constant of tetragonal ZrO2 and La-doped ZrO2 crystals in thin films deposited by atomic layer deposition on Ge(001)

C. Wiemer, A. Debernardi, A. Lamperti, A. Molle, O. Salicio, L. Lamagna, and M. Fanciulli

Appl. Phys. Lett. 99, 232907 (2011); http://dx.doi.org/10.1063/1.3666237 (3 pages) | Cited 1 time

Online Publication Date: 7 December 2011

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In ZrO2 crystals, the highest dielectric constant (k) is ascribed to the tetragonal phase. By the use of density functional theory and synchrotron radiation x-ray diffraction, we show how the a and c lattice parameters of the tetragonal phase influence the resulting k. Highest k values are obtained at increasing both a and c, while k is reduced for compressive strained cells. The determination of a and c on La-doped ZrO2 and ZrO2 thin films deposited by atomic layer deposition on Ge (001) allowed us to elucidate the influence of La doping and Ge diffusion on the k value.
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77.22.Ch Permittivity (dielectric function)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.up Other materials
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.aj Insulators

Decoupling electrocaloric effect from Joule heating in a solid state cooling device

M. Quintero, L. Ghivelder, F. Gomez-Marlasca, and F. Parisi

Appl. Phys. Lett. 99, 232908 (2011); http://dx.doi.org/10.1063/1.3665949 (3 pages) | Cited 1 time

Online Publication Date: 7 December 2011

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We report a heat dynamics analysis of the electrocaloric effect (ECE) in commercial multilayer capacitors based on BaTiO3 dielectric, a promising candidate for applications as a solid state cooling device. Direct measurements of the time evolution of the sample’s temperature changes under different applied voltages allow us to decouple the contributions from Joule heating and from the ECE. Heat balance equations were used to model the thermal coupling between different parts of the system. Fingerprints of Joule heating and the ECE could be resolved at different time scales. We argue that Joule heating and the thermal coupling of the device to the environment must be carefully taken in to account in future developments of refrigeration technologies employing the ECE.
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84.32.Tt Capacitors

Threshold shift observed in resistive switching in metal-oxide-semiconductor transistors and the effect of forming gas anneal

W. H. Liu, K. L. Pey, X. Wu, N. Raghavan, A. Padovani, L. Larcher, L. Vandelli, M. Bosman, and T. Kauerauf

Appl. Phys. Lett. 99, 232909 (2011); http://dx.doi.org/10.1063/1.3669525 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2011

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The resistive switching mechanism, which is crucial for the operations of resistive random access memory (RRAM) devices, is investigated using HfO2 based MOSFETs. After the SET operation, MOSFETs exhibit a threshold voltage (VT) shift that is found to be closely related to the formation of conductive filaments in the gate oxide. The RESET operation performed through a forming gas anneal treatment is found to have the same effect of applying a reverse polarity gate voltage sweep, as usually done in bipolar switching RRAM devices. After RESET, the gate current and VT measured shift back to their pristine levels, indicating the passivation of oxygen vacancies (forming the conductive path) as the most likely physical mechanism responsible for RRAMs RESET operation. Transmission electron microscopy analysis and physical simulations support these conclusions.
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85.30.Tv Field effect devices

Defects control for improved electrical properties in (Ba0.8Sr0.2)(Zr0.2Ti0.8)O3 films by Co acceptor doping

Jun Miao, Khian Hooi Chew, and Yong Jiang

Appl. Phys. Lett. 99, 232910 (2011); http://dx.doi.org/10.1063/1.3666021 (3 pages) | Cited 4 times

Online Publication Date: 8 December 2011

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(Ba0.8Sr0.2)(Zr0.2Ti0.8)O3 (BSZT) films were grown on La0.5Sr0.5CoO3 buffered (001) SrTiO3 substrates by pulsed laser deposition. Effects of Co doping on electrical properties of the films were investigated to establish material design through defects control. The doping led to a significant improvement in the electrical properties with reduction in leakage current and dielectric loss. In addition, the dielectric tunability and figure of merit were enhanced, implying that Co-doped BSZT films are promising materials for tunable microware applications. Our detail studies suggest that the improved electrical properties of Co-doped BSZT films are closely related to defect concentrations in the films.
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73.61.Ng Insulators
77.22.Gm Dielectric loss and relaxation
81.15.Fg Pulsed laser ablation deposition
61.72.sd Impurity concentration
68.55.at Other materials
77.55.-g Dielectric thin films
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Thermal conductance modulator based on folded graphene nanoribbons

Tao Ouyang, Yuanping Chen, Yuee Xie, G. M. Stocks, and Jianxin Zhong

Appl. Phys. Lett. 99, 233101 (2011); http://dx.doi.org/10.1063/1.3665184 (4 pages) | Cited 3 times

Online Publication Date: 5 December 2011

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Based on folded graphene nanoribbons, we report a thermal conductance modulator which performs analogous operations as the rheostat in electronic circuits. This fundamental device can controllably and reversibly modulate the thermal conductance by varying the geometric structures and its tuning range can be up to 40% of the conductance of unfolded nanoribbons (∼1 nm wide and 7–15 nm long). Under this modulation, the conductance shows a linearly dependence on the folded angle, while undergoes a transition with the variation of the inter-layer distance. This primary thermal device may have great potential applications for phononic circuits and nanoscale thermal management.
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65.80.Ck Thermal properties of graphene
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
81.05.ue Graphene

Local contact potential difference of molecular self-assemblies investigated by Kelvin probe force microscopy

Evan J. Spadafora, Mathieu Linares, Wan Zaireen Nisa Yahya, Frédéric Lincker, Renaud Demadrille, and Benjamin Grevin

Appl. Phys. Lett. 99, 233102 (2011); http://dx.doi.org/10.1063/1.3662850 (3 pages) | Cited 1 time

Online Publication Date: 5 December 2011

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Self-assembled pi-conjugated oligomer nanowires have been investigated by frequency modulation atomic force microscopy and amplitude modulation Kelvin probe force microscopy under ultra high vacuum. The distance dependence of the contact potential difference (CPD) has been analyzed by combining high resolution imaging with distance-spectroscopy measurements. It is shown that the apparition of a damping contrast characterizes the onset of short range electrostatic (SRE) forces, which are responsible for the occurrence of local CPD (LCPD) modulations correlated with the molecular lattice. By working at the onset of the damping contrast, the tip-surface separation can be adjusted to minimize the contribution of SRE forces to the measured CPD.
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81.16.Dn Self-assembly
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)
73.40.Cg Contact resistance, contact potential

Surface enhanced Raman scattering of aged graphene: Effects of annealing in vacuum

Yingying Wang, Zhenhua Ni, Aizhi Li, Zainab Zafar, Yan Zhang, Zhonghua Ni, Shiliang Qu, Teng Qiu, Ting Yu, and Ze Xiang Shen

Appl. Phys. Lett. 99, 233103 (2011); http://dx.doi.org/10.1063/1.3665624 (3 pages) | Cited 2 times

Online Publication Date: 5 December 2011

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In this paper, we report a simple method to recover the surface enhanced Raman scattering activity of aged graphene. The Raman signals of Rhodamine molecules absorbed on aged graphene are dramatically increased after vacuum annealing and comparable to those on fresh graphene. Atomic force microscopy measurements indicate that residues on aged graphene surface can efficiently be removed by vacuum annealing, which makes target molecule closely contact with graphene. We also find that the hole doping in graphene will facilitate charge transfer between graphene and molecule. These results confirm the strong Raman enhancement of target molecule absorbed on graphene is due to the charge transfer mechanism.
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78.30.Na Fullerenes and related materials
78.68.+m Optical properties of surfaces
81.40.Gh Other heat and thermomechanical treatments
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
61.48.Gh Structure of graphene
78.67.Wj Optical properties of graphene

Optically switchable molecular device using microsphere based junctions

V. Faramarzi, C. Raimondo, F. Reinders, M. Mayor, P. Samorì, and B. Doudin

Appl. Phys. Lett. 99, 233104 (2011); http://dx.doi.org/10.1063/1.3665940 (3 pages) | Cited 1 time

Online Publication Date: 5 December 2011

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Metallic planar electrodes are bridged using microspheres coated with chemisorbed azobenzene self-assembled monolayers. The circuit exhibits light-induced switching, with reproducibility over 90%, as statistically determined and compared to junctions incorporating photo-insensitive alkanethiol layers. Microsphere interconnects provide direct access to molecular transport properties, with reliability and stability, making multifunctional molecular electronics devices possible.
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85.65.+h Molecular electronic devices

Ballistic thermal conductance in graphene nanoribbon with double-cavity structure

Xiao-Fang Peng, Xin-Jun Wang, Zhi-Qiang Gong, and Ke-Qiu Chen

Appl. Phys. Lett. 99, 233105 (2011); http://dx.doi.org/10.1063/1.3666221 (3 pages) | Cited 4 times

Online Publication Date: 6 December 2011

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We investigate phonon transport and thermal conductance in a Graphene Nanoribbon modulated with a double-cavity quantum structure at low temperatures. Two methods are compared: the force-constant and elastic wave continuum models. Calculations show that both the models show the similar thermal conductance property at low temperatures despite the excited theory of the discrete phonon modes in quantum structure being not the same. However, in the higher temperature region, the thermal conductance in the force-constant model is bigger than that in the elastic wave continuum model. The difference originates from the inequable cutoff frequencies of the phonon modes. A brief analysis of these results is given.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
63.22.Rc Phonons in graphene
62.30.+d Mechanical and elastic waves; vibrations

Surface effects in a semiconductor photonic nanowire and spectral stability of an embedded single quantum dot

Inah Yeo, Nitin S. Malik, Mathieu Munsch, Emmanuel Dupuy, Joël Bleuse, Yann-Michel Niquet, Jean-Michel Gérard, Julien Claudon, Édouard Wagner, Signe Seidelin, Alexia Auffèves, Jean-Philippe Poizat, and Gilles Nogues

Appl. Phys. Lett. 99, 233106 (2011); http://dx.doi.org/10.1063/1.3665629 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2011

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We evidence the influence of surface effects for InAs quantum dots embedded into GaAs photonic nanowires used as efficient single photon sources. We observe a continuous temporal drift of the emission energy that is an obstacle to resonant quantum optics experiments at the single photon level. We attribute the drift to the sticking of oxygen molecules onto the wire, which modifies the surface charge and hence the electric field seen by the quantum dot. The influence of temperature and excitation laser power on this phenomenon is studied. Most importantly, we demonstrate a proper treatment of the nanowire surface to suppress the drift.
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78.67.Hc Quantum dots
78.67.Uh Nanowires
73.40.-c Electronic transport in interface structures

Audio mixing in a tri-port nano-electro-mechanical device

M. Defoort, K. Lulla, J.-S. Heron, O. Bourgeois, E. Collin, and F. Pistolesi

Appl. Phys. Lett. 99, 233107 (2011); http://dx.doi.org/10.1063/1.3665958 (3 pages) | Cited 2 times

Online Publication Date: 7 December 2011

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We report on experiments performed on a cantilever-based tri-port nano-electro-mechanical (NEMS) device. Two ports are used for actuation and detection through the magnetomotive scheme, while the third port is a capacitively coupled gate electrode. By applying a low frequency voltage signal on the gate, we demonstrate mixing in the mechanical response of the device, even for low magnetomotive drives without resorting to conduction measurements through the NEMS. The technique can thus be used, in particular, in the linear regime as an alternative to nonlinear mixing for normal conducting devices. An analytic theory is presented reproducing the data without free parameters.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors

Tunable singlet-triplet splitting in a few-electron Si/SiGe quantum dot

Zhan Shi, C. B. Simmons, J. R. Prance, John King Gamble, Mark Friesen, D. E. Savage, M. G. Lagally, S. N. Coppersmith, and M. A. Eriksson

Appl. Phys. Lett. 99, 233108 (2011); http://dx.doi.org/10.1063/1.3666232 (3 pages) | Cited 8 times

Online Publication Date: 8 December 2011

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We measure the excited-state spectrum of a Si/SiGe quantum dot as a function of in-plane magnetic field and identify the spin of the lowest three eigenstates in an effective two-electron regime. We extract the singlet-triplet splitting, an essential parameter for spin qubits, from the data. We find it to be tunable by lateral displacement of the dot, which is realized by changing two gate voltages on opposite sides of the device. We present calculations showing the data are consistent with a spectrum in which the first excited state of the dot is a valley-orbit state.
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73.21.La Quantum dots
81.07.Ta Quantum dots
71.20.Mq Elemental semiconductors
71.35.-y Excitons and related phenomena

Ab-initio multiplet calculation of oxygen vacancy effect on Ti-L2,3 electron energy loss near edge structures of BaTiO3

S. Ootsuki, H. Ikeno, Y. Umeda, H. Moriwake, A. Kuwabara, O. Kido, S. Ueda, I. Tanaka, Y. Fujikawa, and T. Mizoguchi

Appl. Phys. Lett. 99, 233109 (2011); http://dx.doi.org/10.1063/1.3663543 (3 pages)

Online Publication Date: 8 December 2011

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The effect of oxygen vacancy on Ti-L2,3 electron energy-loss near-edge structures (ELNES) of BaTiO3 was theoretically investigated through ab initio multiplet calculation. The presence of an oxygen vacancy influences spectral features not only at the nearest neighbor Ti site but also at Ti sites further from the oxygen vacancy. The effects of different oxygen vacancy concentrations were also investigated. Based on this study, it was concluded that the detection limit for oxygen vacancy with Ti-L2,3 ELNES is approximately 1%.
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79.20.Uv Electron energy loss spectroscopy
61.72.jd Vacancies

Unintentional doping induced splitting of G peak in bilayer graphene

S. S. Lin, B. G. Chen, C. T. Pan, S. Hu, P. Tian, and L. M. Tong

Appl. Phys. Lett. 99, 233110 (2011); http://dx.doi.org/10.1063/1.3666821 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2011

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Raman characterizations show the G peak of an unintentional doped single crystal bilayer graphene (BLG) splits into two peaks: S and AS peaks. From the relative shift between S and AS peaks, the doping concentration is estimated to be from 8.8 × 1012 cm−2 to 2 × 1013 cm−2, as in the same order of that in monolayer graphene prepared under the same condition. The dopants distribute relatively homogeneously in a 0.7 mm× 0.3 mm large BLG judged through the G peak splitting. The 2D peak of heavy doped BLG can only be deconvoluted into three peaks, corresponding to 2D1B, 2D1A, and 2D2A peaks.
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61.72.up Other materials
78.30.Na Fullerenes and related materials
78.67.Wj Optical properties of graphene
63.20.kd Phonon-electron interactions
63.22.Rc Phonons in graphene

Mismatched alloy nanowires for electronic structure tuning

Joanne W. L. Yim, Costas P. Grigoropoulos, and Junqiao Wu

Appl. Phys. Lett. 99, 233111 (2011); http://dx.doi.org/10.1063/1.3666223 (3 pages)

Online Publication Date: 9 December 2011

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Electronic structure engineering is essential for producing materials suited for efficient solid-state devices. Mismatched semiconductors offer wide tunability of electronic structure with only a small change in composition. Here, we report a combined compound-elemental source vapor transport method for synthesis of mismatched alloy nanowires (NWs) of ZnSe1−xTex across the composition range. The alloy composition can be continuously tuned by varying the growth temperature from ZnSe (x = 0) at higher temperature to ZnTe (x = 1) at lower temperature. The nanowires have structure and bandgaps consistent with their compositions, with lattice parameters varying with Vegard’s law and emissions following predicted extreme bandgap bowing.
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81.07.Gf Nanowires
71.20.Nr Semiconductor compounds
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)
81.16.-c Methods of micro- and nanofabrication and processing
81.05.Dz II-VI semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems

Band-gap-dependent emissions from conjugated polymers coupled silver nanocap array

Fan Kong, Xueqin Zhang, Xianzhong Lang, Baoping Lin, Yimin Yang, and Teng Qiu

Appl. Phys. Lett. 99, 233112 (2011); http://dx.doi.org/10.1063/1.3667195 (3 pages) | Cited 1 time

Online Publication Date: 9 December 2011

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The optical properties of poly(2,5-dioctyloxy-p-phenylene) (PPP) and poly[3-(2,5,8-trioxanonyl) thiophene] (P3TT) coupled silver nanocap array have been investigated. The absorption spectrum of P3TT and the emission spectrum of PPP match the absorption of the silver nanocap array. Plasmon energy transfer occurs from the silver nanocap array to P3TT or from PPP to the silver nanocap array, resulting in the largely increased or decreased photoluminescence (PL), respectively. The PL enhancement of the P3TT coupled silver nanocap array is more than 9-fold; whereas the PL intensity of the PPP coupled silver nanocap array is less than one-tenth of the PPP film.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.55.-m Photoluminescence, properties and materials
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.30.-j Infrared and Raman spectra
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Doping profile of InP nanowires directly imaged by photoemission electron microscopy

M. Hjort, J. Wallentin, R. Timm, A. A. Zakharov, J. N. Andersen, L. Samuelson, M. T. Borgström, and A. Mikkelsen

Appl. Phys. Lett. 99, 233113 (2011); http://dx.doi.org/10.1063/1.3662933 (3 pages) | Cited 3 times

Online Publication Date: 9 December 2011

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InP nanowires (NWs) with differently doped segments were studied with nanoscale resolution using synchrotron based photoemission electron microscopy. We clearly resolved axially stacked n-type and undoped segments of the NWs without the need of additional processing or contacting. The lengths and relative doping levels of different NW segments as well as space charge regions were determined indicating memory effects of sulfur during growth. The surface chemistry of the nanowires was monitored simultaneously, showing that in the present case, the doping contrast was independent of the presence or absence of a native oxide.
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61.72.uj III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures
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