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24 Dec 2012

Volume 101, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 101, 263501 (2012); http://dx.doi.org/10.1063/1.4772532 (4 pages)

Youngki Yoon and Sayeef Salahuddin
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Ultrahigh conductivity of large area suspended few layer graphene films

Nima Rouhi, Yung Yu Wang, and Peter J. Burke

Appl. Phys. Lett. 101, 263101 (2012); http://dx.doi.org/10.1063/1.4772797 (3 pages)

Online Publication Date: 26 December 2012

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Room-temperature (atmospheric-pressure) electrical conductivity measurements of wafer-scale, large-area suspended (few layer) graphene membranes with areas up to 1000 μm2 (30 μm × 30 μm) are presented. Multiple devices on one wafer can be fabricated with high yield from the same chemical vapor deposition grown graphene sheet, transferred from a nickel growth substrate to large opening in a suspended silicon nitride support membrane. This represents areas two to orders of magnitude larger than prior transport studies on any suspended graphene device (single or few layer). We find a sheet conductivity of ∼2500 e2/h (or about 10 Ω/sq) of the suspended graphene, which is an order of magnitude higher than any previously reported sheet conductance of few layer graphene.
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73.61.Wp Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.48.Gh Structure of graphene
68.65.Pq Graphene films
81.05.ue Graphene
72.80.Rj Fullerenes and related materials

Study of radiation effects on the cell structure and evaluation of the dose delivered by x-ray and α-particles microscopy

Ewelina Kosior, Peter Cloetens, Guillaume Devès, Richard Ortega, and Sylvain Bohic

Appl. Phys. Lett. 101, 263102 (2012); http://dx.doi.org/10.1063/1.4773181 (4 pages) | Cited 1 time

Online Publication Date: 26 December 2012

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Hard X-ray fluorescence microscopy and magnified phase contrast imaging are combined to study radiation effects on cells. Experiments were performed on freeze-dried cells at the nano-imaging station ID22NI of the European synchrotron radiation facility. Quantitative phase contrast imaging provides maps of the projected mass and is used to evaluate the structural changes due to irradiation during X-ray fluorescence experiments. Complementary to phase contrast imaging, scanning transmission ion microscopy is performed and doses of all the experiments are compared. We demonstrate the sensitivity of the proposed approach to study radiation-induced damage at the sub-cellular level.
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87.53.Bn Dosimetry/exposure assessment
87.64.M- Optical microscopy
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.85.Tt X-ray microscopes
87.17.-d Cell processes

Raman spectrum method for characterization of pull-in voltages of graphene capacitive shunt switches

Peng Li, Zheng You, and Tianhong Cui

Appl. Phys. Lett. 101, 263103 (2012); http://dx.doi.org/10.1063/1.4773183 (5 pages) | Cited 1 time

Online Publication Date: 27 December 2012

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An approach using Raman spectrum method is reported to measure pull-in voltages of graphene capacitive shunt switches. When the bias excesses the pull-in voltage, the Raman spectrum's intensity largely decreases. Two factors that contribute to the intensity reduction are investigated. Moreover, by monitoring the frequency shift of G peak and 2D band, we are able to detect the pull-in voltage and measure the strain change in graphene beams during switching.
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84.32.Dd Connectors, relays, and switches
85.65.+h Molecular electronic devices

Real time x-ray studies during nanostructure formation on silicon via low energy ion beam irradiation using ultrathin iron films

Osman El-Atwani, Anastassiya Suslova, Alexander DeMasi, Sean Gonderman, Justin Fowler, Mohamad El-Atwani, Karl Ludwig, and Jean Paul Allain

Appl. Phys. Lett. 101, 263104 (2012); http://dx.doi.org/10.1063/1.4773202 (4 pages) | Cited 1 time

Online Publication Date: 27 December 2012

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Real time grazing incidence small angle x-ray scattering and x-ray fluorescence (XRF) are used to elucidate nanodot formation on silicon surfaces during low energy ion beam irradiation of ultrathin iron-coated silicon substrates. Four surface modification stages were identified: (1) surface roughening due to film erosion, (2) surface smoothing and silicon-iron mixing, (3) structure formation, and (4) structure smoothing. The results conclude that 2.5 × 1015 iron atoms in a 50 nm depth triggers surface nanopatterning with a correlated nanodots distance of 25 nm. Moreover, there is a wide window in time where the surface can have correlated nanostructures even after the removal of all the iron atoms from the sample as confirmed by XRF and ex-situ x-ray photoelectron spectroscopy (XPS). In addition, in-situ XPS results indicated silicide formation, which plays a role in the structure formation mechanism.
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81.16.Rf Micro- and nanoscale pattern formation
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.80.Jh Ion radiation effects
61.82.Rx Nanocrystalline materials
78.70.Ck X-ray scattering

The impact of oxygen on the morphology of gas-phase prepared Au nanoparticles

D. Pohl, A. Surrey, L. Schultz, and B. Rellinghaus

Appl. Phys. Lett. 101, 263105 (2012); http://dx.doi.org/10.1063/1.4773203 (5 pages)

Online Publication Date: 27 December 2012

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We present an easy procedure for the synthesis of single crystalline gold nanoparticles with a mean diameter of 4 nm using a DC-sputtering in an argon-oxygen gas mixture. Morphology population statistics have been determined to quantify the influence of oxygen. It is found that the particles undergo a structural transition from predominantly icosahedral to single crystalline particles with increasing amount of oxygen. Aberration-corrected high-resolution transmission electron microscopy investigation proves that likewise prepared single crystalline nanoparticles are defect and oxygen free. In contrast, the icosahedral particles prepared with pure argon show the presence of edge dislocations pointing to an energetic disfavoring already at these relatively small particle sizes. This morphology control of clean and uncovered Au nanoparticles provides a high application potential, e.g., for studying the influence of the particle morphology on plasmonic and catalytic properties.
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81.07.Bc Nanocrystalline materials
81.15.Cd Deposition by sputtering
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.Nd Structural transitions in nanoscale materials

Effects of Be doping on InP nanowire growth mechanisms

R. J. Yee, S. J. Gibson, V. G. Dubrovskii, and R. R. LaPierre

Appl. Phys. Lett. 101, 263106 (2012); http://dx.doi.org/10.1063/1.4773206 (5 pages) | Cited 1 time

Online Publication Date: 27 December 2012

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Be-doped InP nanowires were grown by the gold-assisted vapour-liquid-solid mechanism in a gas source molecular beam epitaxy system. The InP nanowire length versus diameter [L(D)] dependence revealed an unexpected transition with increasing Be dopant concentration. At Be dopant concentration below ∼1018 cm−3, nanowires exhibited the usual inverse L(D) relationship, indicating a diffusion-limited growth regime. However, as dopant concentration increased, the nanowire growth rate was suppressed for small diameters, resulting in an unusual L(D) dependence that increased before saturating in height at about 400 nm. The cause of this may be a change in the droplet chemical potential, introducing a barrier to island nucleation. We propose a model accounting for the limitations of diffusion length and monolayer nucleation to explain this behaviour.
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61.72.uj III-V and II-VI semiconductors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.-c Methods of micro- and nanofabrication and processing
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)

Impact of wavelength dependent thermo-elastic laser ablation mechanism on the generation of nanoparticles from thin gold films

N. Haustrup and G. M. O'Connor

Appl. Phys. Lett. 101, 263107 (2012); http://dx.doi.org/10.1063/1.4773301 (5 pages)

Online Publication Date: 28 December 2012

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This experimental study provides an insight into the wavelength dependence of femtosecond ablation mechanisms of thin gold films. A wavelength dependent, linear relationship was identified between the volume of the grain microstructure of 20 nm thick films and the volume of the nanoparticles generated during laser ablation. Laser ablation at 343 nm and 515 nm wavelengths resulted in the same linear relationship between the grain volume and the nanoparticle volume. However, no relationship at all was observed when ablated at 1030 nm. The wavelength dependence of these results was attributed to differing absorption mechanisms that ultimately lead to differing ablation mechanisms and nanoparticle formation.
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42.62.-b Laser applications
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.-a Thin film structure and morphology
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Jj Elasticity and anelasticity, stress-strain relations

Spin blockade with spin singlet electrons

Y. C. Sun, S. Amaha, S. M. Huang, J. J. Lin, K. Kono, and K. Ono

Appl. Phys. Lett. 101, 263108 (2012); http://dx.doi.org/10.1063/1.4773304 (3 pages)

Online Publication Date: 28 December 2012

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We observe a singlet spin blockade (SSB) in two-electron vertical double quantum dots where the single-electron transport is blocked for spin singlet electrons. In contrast to the conventional Pauli spin blockade with spin triplet electrons, this singlet spin blockade is observed under high magnetic field, where the doubly occupied states in one of the dots go beyond the singlet-triplet ground-state transition. The SSB region in Coulomb diamond measurements is in agreement with the two-electron excitation spectrum. A leakage current of 10 pA order is observed in SSB, consistent with the spin singlet lifetime due to random nuclear spin fluctuations.
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73.21.La Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)

Step like surface potential on few layered graphene oxide

M. Jaafar, G. López-Polín, C. Gómez-Navarro, and J. Gómez-Herrero

Appl. Phys. Lett. 101, 263109 (2012); http://dx.doi.org/10.1063/1.4773357 (4 pages)

Online Publication Date: 28 December 2012

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We report surface potential maps of few layered graphene oxide films on different substrates. Kelvin probe force microscopy images reveal that the surface potential decreases in steps with increasing number of layers on the substrate until five layers are reached, where it saturates to a constant value. This intrinsic behavior is smeared out in the presence of ambient humidity where the surface potential is shielded by the presence of a thin water layer on the surface. This effect can be exploited to quickly determine the number of layers of graphene oxide on a substrate.
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68.65.Pq Graphene films
68.08.Bc Wetting
68.35.bd Metals and alloys
68.35.bg Semiconductors

Porous silicon micro- and nanoparticles for printed humidity sensors

Tero Jalkanen, Ermei Mäkilä, Anni Määttänen, Jaani Tuura, Martti Kaasalainen, Vesa-Pekka Lehto, Petri Ihalainen, Jouko Peltonen, and Jarno Salonen

Appl. Phys. Lett. 101, 263110 (2012); http://dx.doi.org/10.1063/1.4773361 (4 pages)

Online Publication Date: 28 December 2012

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In this work, the feasibility of porous silicon particles for producing printed humidity sensors is examined. A proof of concept is provided by producing fully functional humidity sensors on a glass substrate by drop casting a particle solution on top of inkjet printed silver electrodes. Sensor sensitivity towards changes in relative humidity is examined. The results show that the sensors provide good sensitivity and reproducible results throughout the entire relative humidity range. In addition, negligibly small hysteresis accompanied by relatively fast response and recovery times is also demonstrated.
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07.07.Vx Hygrometers; hygrometry
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Tuning metal-insulator transition by one dimensional alignment of giant electronic domains in artificially size-controlled epitaxial VO2 wires

Hidefumi Takami, Kenichi Kawatani, Hiroki Ueda, Kohei Fujiwara, Teruo Kanki, and Hidekazu Tanaka

Appl. Phys. Lett. 101, 263111 (2012); http://dx.doi.org/10.1063/1.4773371 (4 pages) | Cited 1 time

Online Publication Date: 28 December 2012

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We demonstrate control of spatial dimensionality of disordered configurations of giant electronic domains in systematically size-changed VO2 wires on TiO2 (001) substrates. One-dimensional alignment of the domains appears in wires narrower than 15 μm width, while two-dimensional configurations were observed for larger ones. The rearrangement of domains from two to one dimension causes modification of electronic properties.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions

Two dimensional crystal tunneling devices for THz operation

B. D. Kong, C. Zeng, D. K. Gaskill, K. L. Wang, and K. W. Kim

Appl. Phys. Lett. 101, 263112 (2012); http://dx.doi.org/10.1063/1.4773514 (5 pages) | Cited 1 time

Online Publication Date: 28 December 2012

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Two dimensional crystal heterostructures are shown to possess a unique opportunity for nonlinear THz devices. In contrast to the oxide tunneling barrier, the uniformity of layered crystal insulators provides an ideal condition for tunneling barriers in the atomic scale. Numerical calculations based on a first-principles method clearly indicate the feasibility of diode operation with barriers as thin as two monolayers when placed between graphene-metal asymmetric electrodes. Further analysis predicts cut-off frequencies over 10 THz while maintaining strong nonlinearity for zero-bias rectification. Application to hot electron transistors is also examined, illustrating potentially superior performance in the frequency range inaccessible thus far.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Tv Field effect devices
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