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26 Mar 2012

Volume 100, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 133701 (2012); http://dx.doi.org/10.1063/1.3696019 (3 pages)

Hewei Liu, Feng Chen, Qing Yang, Pubo Qu, Shengguan He, Xianhua Wang, Jinhai Si, and Xun Hou
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Carrier dynamics and conductivity of SnO2 nanowires investigated by time-resolved terahertz spectroscopy

Demetra Tsokkou, Andreas Othonos, and Matthew Zervos

Appl. Phys. Lett. 100, 133101 (2012); http://dx.doi.org/10.1063/1.3698097 (4 pages) | Cited 2 times

Online Publication Date: 26 March 2012

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THz spectroscopy has been applied to investigate the photo-induced and intrinsic conductivity in SnO2 nanowires using the Drude-Smith model. The refractive index of the nanowires was found to decrease from 2.4 to 2.1 with increasing THz frequency and the dc mobility of the non-excited nanowires was determined to be 72 ± 10 cm2/Vs. Measurements reveal that scattering times are carrier density dependent, while a strong suppression of long transport is evident. Intensity-dependent measurements provided an estimate of the Auger coefficient found to be γ = (7.2 ± 2.0) × 10−31 cm6/s.
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73.63.Bd Nanocrystalline materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.70.Gq Microwave and radio-frequency interactions
79.20.Fv Electron impact: Auger emission
78.47.jg Time resolved reflection spectroscopy
78.67.Uh Nanowires
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance

First-principles simulation of oxygen diffusion in HfOx: Role in the resistive switching mechanism

S. Clima, Y. Y. Chen, R. Degraeve, M. Mees, K. Sankaran, B. Govoreanu, M. Jurczak, S. De Gendt, and G. Pourtois

Appl. Phys. Lett. 100, 133102 (2012); http://dx.doi.org/10.1063/1.3697690 (4 pages) | Cited 8 times

Online Publication Date: 26 March 2012

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Transition metal oxide-based resistor random access memory (RRAM) takes advantage of oxygen-related defects in its principle of operation. Since the change in resistivity of the material is controlled by the oxygen deficiency level, it is of major importance to quantify the kinetics of the oxygen diffusion, key factor for oxide stoichiometry. Ab initio accelerated molecular dynamics techniques are employed to investigate the oxygen diffusivity in amorphous hafnia (HfOx, x = 1.97, 1.0, 0.5). The computed kinetics is in agreement with experimental measurements.
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66.30.J- Diffusion of impurities
61.66.Bi Elemental solids
61.66.Dk Alloys

Probing crossover from analogous weak antilocalization to localization by an Aharonov-Bohm interferometer on topological insulator surface

Zhen-Guo Fu, Ping Zhang, and Shu-Shen Li

Appl. Phys. Lett. 100, 133103 (2012); http://dx.doi.org/10.1063/1.3697993 (5 pages)

Online Publication Date: 27 March 2012

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We propose a scanning tunneling microscopy Aharonov-Bohm (AB) interferometer on the surface of a topological insulator (TI) to probe the crossover from analogous weak antilocalization to weak localization phenomenon via the AB oscillations in spin-resolved local density of states (LDOS). Based on our analytical and numerical results, we show that with increasing the energy gap of TI surface states, the Φ0/2 = hc/2e periodic AB oscillations in spin-resolved LDOS gradually transit into the Φ0 periodic oscillations.
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73.20.Fz Weak or Anderson localization
71.20.Ps Other inorganic compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.20.At Surface states, band structure, electron density of states

Highly versatile concept for precise tailoring of nanogranular composites with a gas aggregation cluster source

B. Gojdka, V. Zaporojtchenko, V. Hrkac, J. Xiong, L. Kienle, T. Strunskus, and F. Faupel

Appl. Phys. Lett. 100, 133104 (2012); http://dx.doi.org/10.1063/1.3696640 (3 pages) | Cited 2 times

Online Publication Date: 27 March 2012

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A concept for the precise tailoring of a wide variety of nanogranular composites with a gas aggregation cluster source and a magnetron is presented. Electrical charging of the preformed clusters and the substrate in a plasma is discussed as a fundamental physical hindrance for conventional co-sputtering with a cluster source. The proposed concept overcomes this hindrance and is experimentally demonstrated for the deposition of a dielectric aluminum nitride matrix with embedded magnetic cobalt clusters. Chemical, magnetic, and structural analyses of the composite confirm the feasibility of the proposed concept as a versatile route for the preparation of nanocomposites.
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75.75.Cd Fabrication of magnetic nanostructures
81.07.-b Nanoscale materials and structures: fabrication and characterization
77.84.Lf Composite materials
75.50.Tt Fine-particle systems; nanocrystalline materials

Acoustically induced current flow in graphene

V. Miseikis, J. E. Cunningham, K. Saeed, R. O’Rorke, and A. G. Davies

Appl. Phys. Lett. 100, 133105 (2012); http://dx.doi.org/10.1063/1.3697403 (4 pages)

Online Publication Date: 27 March 2012

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We demonstrate the directed control of charge carriers in graphene using the electric field that accompanies the propagation of surface acoustic waves (SAWs) on a piezoelectric surface. Graphene grown by chemical vapor deposition was transferred to the surface of lithium niobate, allowing its direct integration with interdigital transducers used for SAW generation and detection. Radio frequency (RF) signal applied to the transducers at their resonant frequency was found to generate a direct current flow by the transport of p-type charge carriers. The acoustically induced current scales linearly with the applied RF power and can be observed even in presence of a counter-flow current induced by an applied bias.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.80.Vp Electronic transport in graphene
73.61.Wp Fullerenes and related materials

Investigation of micro/nanoring formation by protein solution evaporation inside confined microwells

Kuo-Feng Lo and Yi-Je Juang

Appl. Phys. Lett. 100, 133106 (2012); http://dx.doi.org/10.1063/1.3697828 (4 pages) | Cited 1 time

Online Publication Date: 27 March 2012

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In this study, fabrication of the micro/nanoring-like structures was accomplished via solution evaporation inside the microwells. A phenomenological mechanism for the evaporation process inside the microconfinement was proposed, which is different from that for evaporation of a droplet on a substrate in the ambient condition where either the coffee-ring effect or the Marangoni effect is observed. Moreover, reasoning about how the solvent evaporates from the microwells was also provided. It was found that the normalized height of the deposited structure was approximately proportional to the solution concentration.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
64.70.F- Liquid-vapor transitions
61.46.-w Structure of nanoscale materials

Effect of in-situ oxygen on the electronic properties of graphene grown by carbon molecular beam epitaxy

Jeongho Park, W. C. Mitchel, Said Elhamri, and Tyson C. Back

Appl. Phys. Lett. 100, 133107 (2012); http://dx.doi.org/10.1063/1.3697830 (4 pages)

Online Publication Date: 27 March 2012

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We report that graphene grown by molecular beam epitaxy from solid carbon (CMBE) on (0001) SiC in the presence of unintentional oxygen exhibits a small bandgap on the order of tens of meV. The presence of bandgaps is confirmed by temperature dependent Hall effect and resistivity measurements. X-ray photoelectron spectroscopy (XPS) measurements suggest that oxygen incorporates into the SiC substrate in the form of O-Si-C and not into the graphene as graphene oxide or some other species. The effect is independent of the carrier type of the graphene. Temperature dependent transport measurements show the presence of hopping conduction in the resistivity and a concurrent disappearance of the Hall voltage. Interactions between the graphene layers and the oxidized substrate are believed to be responsible for the bandgap.
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73.22.Pr Electronic structure of graphene
72.20.My Galvanomagnetic and other magnetotransport effects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.ag Semiconductors

Absolute absorption cross sections of ligand-free colloidal germanium nanocrystals

Zachary C. Holman and Uwe R. Kortshagen

Appl. Phys. Lett. 100, 133108 (2012); http://dx.doi.org/10.1063/1.3698091 (4 pages) | Cited 3 times

Online Publication Date: 28 March 2012

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Extinction spectra of colloidal germanium nanocrystals suspended in benzonitrile without the use of ligands were measured, and absolute absorption cross sections are reported. Comparison to cross sections calculated using the Mie solution to Maxwell’s equations reveals that, as the mean nanocrystal size is reduced from 11 to 4 nm, the absorption features below 3.5 eV blueshift because of quantum confinement effects. The shifts are not, however, sufficiently large for the nanocrystal cores to produce the blue photoluminescence commonly observed from germanium nanocrystals. At energies greater than 3.5 eV the Mie and measured cross sections overlap, indicating a bulk-like band structure.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
78.55.Ap Elemental semiconductors
82.70.Dd Colloids

Second and higher harmonics generation with memristive systems

Guy Z. Cohen, Yuriy V. Pershin, and Massimiliano Di Ventra

Appl. Phys. Lett. 100, 133109 (2012); http://dx.doi.org/10.1063/1.3698153 (3 pages)

Online Publication Date: 28 March 2012

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We show that memristive systems can be used very efficiently to generate passively both double and higher frequency harmonics. A technique for maximizing the power conversion efficiency into any given harmonic is developed and applied to a single memristive system and memristive bridge circuits. We find much higher rates of power conversion compared to the standard diode bridge, with the memristive bridge more efficient for second and higher harmonics generation compared to the single memristive system. The memristive bridge circuit optimized for second harmonic generation behaves as a two-quarter-wave rectifier.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
84.30.Jc Power electronics; power supply circuits

Atomistic elucidation of the effect of surface roughness on curvature-dependent surface energy, surface stress, and elasticity

P. Mohammadi and P. Sharma

Appl. Phys. Lett. 100, 133110 (2012); http://dx.doi.org/10.1063/1.3695069 (4 pages) | Cited 3 times

Online Publication Date: 28 March 2012

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It is well known that surface energy and the associated properties such as surface stress and surface elasticity have a significant effect on the physical behavior of nanostructures. In this letter, using a combination of atomistic simulations and a simple continuum model, we elucidate the role of surface roughness on the renormalization of surface stress, surface elastic constants, as well as the (generally ignored) term that represents the curvature dependence of surface energy (crystalline Tolman’s length). We find, consistent with a recent theoretical prediction and in sharp contrast to few others, that the surface stress is negligibly impacted by roughness. However, even moderate roughness is seen to dramatically alter the surface elasticity modulus as well as the crystalline Tolman’s length. We illustrate a simple application on the impact of roughness on nanosensors.
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65.40.gp Surface energy
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
64.60.ae Renormalization-group theory
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants

Structural investigations of interfaces in Fe90Sc10 nanoglasses using high-energy x-ray diffraction

M. Ghafari, S. Kohara, H. Hahn, H. Gleiter, T. Feng, R. Witte, and S. Kamali

Appl. Phys. Lett. 100, 133111 (2012); http://dx.doi.org/10.1063/1.3699228 (4 pages) | Cited 3 times

Online Publication Date: 28 March 2012

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High-resolution diffraction experiments of Fe90Sc10 nanoglasses and rapidly quenched metallic glasses as reference materials have been performed using high-energy x-rays with a wavelength of 0.21 Å from a synchrotron radiation source. Nanoglasses are amorphous alloys with a significant fraction of interfaces on the nanometer scale. The short- and intermediate-range orders of a nanoglass are different from the well known amorphous materials produced by rapid quenching from the melt. These structural modifications have significant influence on the physical properties. In this paper, the short- and intermediate-range orders of the nanoglass Fe90Sc10 and the reference metallic glass Fe90Sc10 alloy prepared by rapid quenching are discussed.
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61.43.Fs Glasses
61.46.-w Structure of nanoscale materials
81.05.Kf Glasses (including metallic glasses)
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Gh Other heat and thermomechanical treatments

Hexagonal and pentagonal shapes of self-catalyzed one-dimensional GaAs nanostructures: Shape dependence of the phase evolutions

Young Heon Kim, Dong Woo Park, Sang Jun Lee, KwangMoo Kim, and Yun Chang Park

Appl. Phys. Lett. 100, 133112 (2012); http://dx.doi.org/10.1063/1.3698468 (4 pages)

Online Publication Date: 29 March 2012

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Hexagonal and pentagonal shapes of one-dimensional (1-D) nanostructures were observed at the growth of GaAs by molecular beam epitaxy method without catalyst aid. We report on the phase evolution dependence on the shapes of 1-D GaAs nanostructures. The hexagonal-shaped nanostructures showed a transition region composed of twin boundaries and stacking faults during the phase transition from a zinc-blende (ZB) structure to a wurtzite (WZ) structure. On the other hand, the pentagonal-shaped nanostructures appeared to have an abrupt transition from a ZB structure to a WZ structure and to be elongated along 〈11math〉 directions of a ZB structure.
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61.46.-w Structure of nanoscale materials
61.72.Nn Stacking faults and other planar or extended defects
64.70.Nd Structural transitions in nanoscale materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.-c Methods of micro- and nanofabrication and processing
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors

Low-cost shrink lithography with sub-22 nm resolution

Bo Zhang, Min Zhang, and Tianhong Cui

Appl. Phys. Lett. 100, 133113 (2012); http://dx.doi.org/10.1063/1.3697836 (4 pages) | Cited 1 time

Online Publication Date: 30 March 2012

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A low-cost shrink lithogragphy technique with 21 nm resolution is presented in this paper. The shrink lithography uses embossing approach to pattern the heat-shrink polymer film, and thermally shrink the film as a shadow mask subsequently. Metal patterns with diffferent feature sizes were achieved from a single mold by shrink lithography through controlling the shrink contidions including temperature and force. A biosensor based on a suspended graphene nanoribbon is fabricated with the shrink lithography, demonstrating the potential application of this process to the fabrication of nanodevices and integrated circuits.
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85.40.Hp Lithography, masks and pattern transfer
68.55.am Polymers and organics
81.16.Nd Micro- and nanolithography
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