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20 Sep 2010

Volume 97, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 97, 123101 (2010); http://dx.doi.org/10.1063/1.3490637 (3 pages)

Mark W. Licurse and Peter K. Davies
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Nanocheckerboard modulations in (NaNd)(MgW)O6

Mark W. Licurse and Peter K. Davies

Appl. Phys. Lett. 97, 123101 (2010); http://dx.doi.org/10.1063/1.3490637 (3 pages) | Cited 1 time

Online Publication Date: 20 September 2010

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Data is presented for a complex structural and compositional modulation in the perovskite (NaNd)(MgW)O6. This modulation creates a large 14ap×14ap×2ap supercell (ap ≈ 3.9 Å is the lattice parameter of the cubic perovskite aristotype) containing ordered regions with doubled (110) d-spacings in the a-b plane separated by two-dimensional periodic antiphase boundaries and accompanied by a nanocheckerboard pattern. Faint periodic modulations in Z-contrast images suggest an associated periodic variation in composition. The presence of a sodium rich impurity implies the composition of the stable perovskite is nonstoichiometric.
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61.66.Fn Inorganic compounds
61.66.Bi Elemental solids
61.66.Dk Alloys

Resistance switching at the interface of LaAlO3/SrTiO3

Y. Z. Chen, J. L. Zhao, J. R. Sun, N. Pryds, and B. G. Shen

Appl. Phys. Lett. 97, 123102 (2010); http://dx.doi.org/10.1063/1.3490646 (3 pages) | Cited 8 times

Online Publication Date: 20 September 2010

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At the interface of LaAlO3/SrTiO3 with film thickness of 3 unit cells or greater, a reproducible electric-field-induced bipolar resistance switching of the interfacial conduction is observed on nanometer scale by a biased conducting atomic force microscopy under vacuum environment. The switching behavior is suggested to be an intrinsic feature of the SrTiO3 single crystal substrates, which mainly originates from the modulation of oxygen ion transfer in SrTiO3 surface by external electric field in the vicinity of interface, whereas the LaAlO3 film acts as a barrier layer.
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73.40.-c Electronic transport in interface structures
68.37.Ps Atomic force microscopy (AFM)
68.55.-a Thin film structure and morphology

Theoretical investigation of Möbius strips formed from graphene

Xianlong Wang, Xiaohong Zheng, Meiyan Ni, Liangjian Zou, and Zhi Zeng

Appl. Phys. Lett. 97, 123103 (2010); http://dx.doi.org/10.1063/1.3489982 (3 pages) | Cited 2 times

Online Publication Date: 23 September 2010

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First-principle calculations are performed on the formation of graphene Möbius strips and their shape evolution as a function of the strip width. Results show that Möbius strips formed from graphene nanoribbons with fixed length and different widths are stable. With the increase in the width, one planar triangular region appears, and finally, the strip evolves into three equilateral triangles stacked together. Physical properties such as deformation energy density, strain effects, and edge magnetism are discussed. As a result from the special topology, unlike zigzag-edged graphene nanoribbons, Möbius strips are ferromagnets with nonzero total magnetic moments observed at the edge.
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61.48.Gh Structure of graphene
81.05.ue Graphene
61.46.-w Structure of nanoscale materials
62.20.F- Deformation and plasticity

A theoretical framework to obtain interface’s shapes during the high-temperature annealing of high-aspect-ratio gratings

Marcos F. Castez, Roberto C. Salvarezza, Jun Nakamura, and Koichi Sudoh

Appl. Phys. Lett. 97, 123104 (2010); http://dx.doi.org/10.1063/1.3492442 (3 pages) | Cited 2 times

Online Publication Date: 23 September 2010

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High-temperature annealing applied to solid samples produces important morphological modifications on their surfaces, particularly in high-aspect-ratio gratings. We show, how by means of a framework based in a nonlinear analysis of the Mullins’ equation [ J. Appl. Phys. 28, 333 (1957)] , we can mathematically reproduce surface’s shapes just by measuring a few characteristic features of the interfaces (essentially pattern’s amplitudes and wavelengths). We compared our results with experimental data on silicon samples, finding a close agreement between experimental shapes and those theoretically predicted. The introduced framework could be particularly useful in those situations where no cross-sectional information were available.
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68.35.Fx Diffusion; interface formation
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing

Dielectric thickness dependence of carrier mobility in graphene with HfO2 top dielectric

Babak Fallahazad, Seyoung Kim, Luigi Colombo, and Emanuel Tutuc

Appl. Phys. Lett. 97, 123105 (2010); http://dx.doi.org/10.1063/1.3492843 (3 pages) | Cited 13 times

Online Publication Date: 23 September 2010

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We investigate the carrier mobility in monolayer and bilayer graphene with a top HfO2 dielectric, as a function of the HfO2 film thickness and temperature. The results show that the carrier mobility decreases during the deposition of the first 2–4 nm of top dielectric and remains constant for thicker layers. The carrier mobility shows a relatively weak dependence on temperature indicating that phonon scattering does not play a dominant role in controlling the carrier mobility. The data strongly suggest that fixed charged impurities located in close proximity to the graphene are responsible for the mobility degradation.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
77.55.dj For nonsilicon electronics (Ge, III-V, II-VI, organic electronics)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Structural morphology of acoustically levitated and heated nanosilica droplet

Ranganathan Kumar, Erick Tijerino, Abhishek Saha, and Saptarshi Basu

Appl. Phys. Lett. 97, 123106 (2010); http://dx.doi.org/10.1063/1.3493178 (3 pages) | Cited 3 times

Online Publication Date: 23 September 2010

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We study the vaporization and precipitation dynamics of a nanosilica encapsulated water droplet by levitating it acoustically and heating it with a CO2 laser. For all concentrations, we observe three phases: solvent evaporation, surface agglomeration, and precipitation leading to bowl or ring shaped structures. At higher concentrations, ring reorientation and rotation are seen consistently. The surface temperature from an infrared camera is seen to be dependent on the final geometrical shape of the droplet and its rotation induced by the acoustic field of the levitator. With nonuniform particle distribution, these structures can experience rupture which modifies the droplet rotational speed.
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68.03.Cd Surface tension and related phenomena
62.60.+v Acoustical properties of liquids
47.55.dr Interactions with surfaces
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.03.Fg Evaporation and condensation of liquids
47.85.Np Fluidics

CdSe quantum dot-sensitized solar cell employing TiO2 nanotube working-electrode and Cu2S counter-electrode

Qing Shen, Akari Yamada, Satoru Tamura, and Taro Toyoda

Appl. Phys. Lett. 97, 123107 (2010); http://dx.doi.org/10.1063/1.3491245 (3 pages) | Cited 22 times

Online Publication Date: 23 September 2010

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We proposed a CdSe quantum dot (QD)-sensitized solar cell (QDSSC), which is constructed with a CdSe QD adsorbed TiO2 nanotube working electrode on a Ti substrate, a ring shaped Cu2S counter electrode, prepared on a brass substrate having a glass window, and polysulfide electrolyte. The light was incident from the counter electrode. An incident photon to current conversion efficiency as high as 65% and a photovoltaic conversion efficiency as high as 1.8% under one sun have been achieved. We have demonstrated less costly QDSSC, without the requirement for both a transparent conductive electrode or a platinum film.
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88.40.jm Thin film III-V and II-VI based solar cells

Interrelation of transport and optical properties in gold nanoclusters

G. W. Shu, T. Y. Chen, J. L. Shen, C. A. J. Lin, W. H. Chang, W. H. Chan, H. H. Wang, H. I. Yeh, and W. C. Chou

Appl. Phys. Lett. 97, 123108 (2010); http://dx.doi.org/10.1063/1.3491288 (3 pages) | Cited 2 times

Online Publication Date: 23 September 2010

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Temperature dependence of the electrical conductivity and photoluminescence (PL) in Au nanoclusters (NCs) is investigated. The correlation of the conductivity and PL in Au NCs at different temperatures is evident: (i) for T<50 K, both the conductivity and PL intensity decrease with temperature, which suggests thermal structural fluctuations; (ii) for 50 K<T<90 K, conductivity and PL are explained by variable range hopping; (iii) for 90 K<T<170 K, simple thermal activated hopping dominates in conductivity, with a rate-equation model proposed to analyze the carrier transfer in PL.
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78.66.Bz Metals and metallic alloys
78.55.Hx Other solid inorganic materials
73.61.At Metal and metallic alloys
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Anharmonic modal coupling in a bulk micromechanical resonator

Tyler Dunn, Josef-Stefan Wenzler, and Pritiraj Mohanty

Appl. Phys. Lett. 97, 123109 (2010); http://dx.doi.org/10.1063/1.3489423 (3 pages) | Cited 3 times

Online Publication Date: 23 September 2010

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We present measurements of nonlinear coupling between various acoustic modes of a micromechanical resonator. Piezoelectric transduction allows measurement of both flexural and bulk longitudinal modes up to microwave frequencies, and we find that all modes of the device couple, regardless of type. This coupling thus provides a means of mechanical nonlinear signal processing across a wide range of frequencies. Through controlled simultaneous excitation, we quantify coupling strength by measuring the frequency shift in a detector mode in response to the known energy of a driven mode.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Electronic states of InAs/GaAs quantum dots by scanning tunneling spectroscopy

S. Gaan, Guowei He, R. M. Feenstra, J. Walker, and E. Towe

Appl. Phys. Lett. 97, 123110 (2010); http://dx.doi.org/10.1063/1.3491551 (3 pages) | Cited 4 times

Online Publication Date: 23 September 2010

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InAs/GaAs quantum-dot (QD) heterostructures grown by molecular-beam epitaxy are studied using cross-sectional scanning tunneling microscopy and spectroscopy. Individual InAs QDs are resolved in the images. Tunneling spectra acquired 3–4 nm from the QDs show a peak located in the upper part of the GaAs band gap originating from the lowest electron confined state, together with a tail extending out from the valence band from hole confined states. A line-shape analysis is used to deduce the binding energies of the electron and hole QD states.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
73.21.La Quantum dots
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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