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15 Oct 2012

Volume 101, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 161105 (2012); http://dx.doi.org/10.1063/1.4744947 (4 pages)

Nan Niu, Tsung-Li Liu, Igor Aharonovich, Kasey J. Russell, Alexander Woolf, Thomas C. Sadler, Haitham A. R. El-Ella, Menno J. Kappers, Rachel A. Oliver, and Evelyn L. Hu
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Diamondoid coating enables disruptive approach for chemical and magnetic imaging with 10 nm spatial resolution

Hitoshi Ishiwata, Yves Acremann, Andreas Scholl, Eli Rotenberg, Olav Hellwig, Elizabeth Dobisz, Andrew Doran, Boryslav A. Tkachenko, Andrey A. Fokin, Peter R. Schreiner, Jeremy E. P. Dahl, Robert M. K. Carlson, Nick Melosh, Zhi-Xun Shen, and Hendrik Ohldag

Appl. Phys. Lett. 101, 163101 (2012); http://dx.doi.org/10.1063/1.4756893 (5 pages)

Online Publication Date: 15 October 2012

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Diamondoids are unique molecular nano-materials with diamond structure and fascinating properties such as negative electron affinity and short electron mean free paths. A thin layer of diamondoids deposited on a cathode is able to act as an electron monochromator, reducing the energy spread of photo-emitted electrons from a surface. This property can be applied effectively to improve the spatial resolution in x-ray photoemission electron microscopy (X-PEEM), which is limited by chromatic aberration of the electron optics. In this paper, we present X-PEEM measurements reaching the technological relevant spatial resolution of 10 nm without the need of expensive and complex corrective optics. Our results provide a simple approach to image surface chemical and magnetic information at nanometer scales by employing diamondoids.
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81.16.Dn Self-assembly
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ng Insulators
78.70.Dm X-ray absorption spectra
79.60.Jv Interfaces; heterostructures; nanostructures

Inclined-incidence quasi-Fresnel lens for prefocusing of synchrotron radiation x-ray beams

Yasushi Kagoshima, Hidekazu Takano, and Shingo Takeda

Appl. Phys. Lett. 101, 163102 (2012); http://dx.doi.org/10.1063/1.4759150 (4 pages)

Online Publication Date: 16 October 2012

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An inclined-incidence quasi-Fresnel lens made of acrylic resin has been developed for prefocusing in synchrotron radiation x-ray beamlines. By inclining the lens, the grating aspect ratio is large enough for x-ray use. As it operates in transmission mode with negligible beam deflection and offset, little additional equipment is needed to introduce it into existing beamlines. It is fabricated by sheet-press forming, enabling inexpensive mass production. The prototype was able to focus a 730-μm-wide beam to a width of 80 μm with a photon flux density gain of 5.6 at an x-ray energy of 10 keV.
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07.85.Qe Synchrotron radiation instrumentation

Size-dependent radiative decay processes in graphene quantum dots

Sung Kim, Dong Hee Shin, Chang Oh Kim, Soo Seok Kang, Jong Min Kim, Suk-Ho Choi, Li-Hua Jin, Yong-Hoon Cho, Sung Won Hwang, and Cheolsoo Sone

Appl. Phys. Lett. 101, 163103 (2012); http://dx.doi.org/10.1063/1.4760269 (4 pages) | Cited 2 times

Online Publication Date: 16 October 2012

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Radiative decay processes have been studied in graphene quantum dots (GQDs) by varying their size. The photoluminescence (PL) decay traces are well fitted to a biexponential function with lifetimes of τ1 and τ2, indicating their fast and slow components, respectively. The τ1 is almost constant, irrespective of the average GQD size (da) for two excitation wavelengths of 305 and 356 nm. In contrast, the τ2 decreases as da increases for da ≤ ∼17 nm, but da > ∼17 nm, it increases with increasing da for both the excitation wavelengths, similar to the size-dependent behaviors of the time-integrated PL peak energy. We propose that the τ1 and τ2 originate from size-independent fast band-to-band transition and size-dependent slow transition resulting from the edge-state variation at the periphery of GQDs, respectively.
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78.67.Hc Quantum dots
61.48.Gh Structure of graphene
78.67.Wj Optical properties of graphene
78.55.Hx Other solid inorganic materials
68.65.Hb Quantum dots (patterned in quantum wells)

Controlling the current flux in magnetic-barrier induced graphene waveguide

Cesar E. P. Villegas and Marcos R. S. Tavares

Appl. Phys. Lett. 101, 163104 (2012); http://dx.doi.org/10.1063/1.4759267 (4 pages)

Online Publication Date: 17 October 2012

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We theoretically propose a simple model to control the charge-density flux in graphene waveguides produced by either magnetic or electrostatic barriers. We carefully study the lowest energy guided mode and find unexpected extended states for small reflected angles contributing to flux that might be related to the superposition of surface and bound states. We also show possible manipulation of the charge carrier density, and so of the current flux, by simply changing the magnetization intensity or the waveguide width. Our results indicate how to reassess previous current flux by changing the magnetization parameter only.
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73.61.Wp Fullerenes and related materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effect of radical fluorination on mono- and bi-layer graphene in Ar/F2 plasma

K. Tahara, T. Iwasaki, A. Matsutani, and M. Hatano

Appl. Phys. Lett. 101, 163105 (2012); http://dx.doi.org/10.1063/1.4760268 (4 pages)

Online Publication Date: 17 October 2012

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Fluorinated graphene has the possibility to achieve unique properties and functions in graphene. We propose a highly controlled fluorination method utilizing fluorine radicals in Ar/F2 plasma. To suppress ion bombardments and improve the reaction with fluorine radicals on graphene, the substrate was placed “face down” in the plasma chamber. Although monolayer graphene was more reactive than bilayer, fluorination of bilayer reached the level of ID/IG ∼ 0.5 in Raman D peak intensity at 532 nm excitation. Annealing fluorinated samples proved reversibility of radical fluorination for both mono- and bi-layer graphenes. X-ray photoelectron spectroscopy showed the existence of carbon-fluorine bonding.
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81.05.ue Graphene
81.40.Gh Other heat and thermomechanical treatments
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Dp Adsorbed layers and thin films
78.67.Wj Optical properties of graphene
78.30.Na Fullerenes and related materials

Mechanism for radiative recombination and defect properties of GaP/GaNP core/shell nanowires

A. Dobrovolsky, J. E. Stehr, S. L. Chen, Y. J. Kuang, S. Sukrittanon, C. W. Tu, W. M. Chen, and I. A. Buyanova

Appl. Phys. Lett. 101, 163106 (2012); http://dx.doi.org/10.1063/1.4760273 (4 pages) | Cited 1 time

Online Publication Date: 17 October 2012

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Recombination processes in GaP/GaNP core/shell nanowires (NWs) grown on a Si substrate by molecular beam epitaxy are examined using a variety of optical characterization techniques, including cw- and time-resolved photoluminescence and optically detected magnetic resonance (ODMR). Superior optical quality of the structures is demonstrated based on the observation of intense emission from a single NW at room temperature. This emission is shown to originate from radiative transitions within N-related localized states. From ODMR, growth of GaP/GaNP NWs is also found to facilitate formation of complex defects containing a P atom at its core that act as centers of competing non-radiative recombination.
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68.65.La Quantum wires (patterned in quantum wells)
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)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.-y Defects and impurities in crystals; microstructure
78.55.Cr III-V semiconductors

Near-infrared enhanced carbon nanodots by thermally assisted growth

Xiaoming Wen, Pyng Yu, Yon-Rui Toh, Yu-Chieh Lee, An-Chia Hsu, and Jau Tang

Appl. Phys. Lett. 101, 163107 (2012); http://dx.doi.org/10.1063/1.4760275 (4 pages) | Cited 2 times

Online Publication Date: 18 October 2012

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The near-infrared emission, matching the biological window, is conducive to biological applications. To date, most of the reported carbon nanodots emit the blue to green fluorescence and few of carbon nanodots emit the near-infrared with relatively lower efficiency. Here, we report an approach to generate or to enhance the near-infrared luminescence from the green luminescent carbon nanodots. Experiments reveal that the near-infrared emission is significantly enhanced by thermally assisted growth in vacuum, which is attributed to the formation of the larger nano-domains from the small carbon clusters at elevated temperatures.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.16.-c Methods of micro- and nanofabrication and processing
78.55.Hx Other solid inorganic materials
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Liquid-like instabilities in gold nanowires fabricated by focused ion beam lithography

J. P. Naik, K. Das, P. D. Prewett, A. K. Raychaudhuri, and Yifang Chen

Appl. Phys. Lett. 101, 163108 (2012); http://dx.doi.org/10.1063/1.4761249 (4 pages)

Online Publication Date: 18 October 2012

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Observation of liquid-like instabilities is reported in Au nanowires formed by nanopatterning of Au films using focused ion beam (FIB) on different types of Si substrates including those passivated with SiO2 or Si3N4 surfaces. The onset of the instability, which can ultimately lead to break up of the FIB patterned nanowires into gold islands, occurs when the diameter of the nanowire is below a critical range, which depends on the conductivity of the substrate and the extent of native oxide present on it. We also observe the formation of Taylor cones on very narrow nanowires grown on insulating substrates at the onset of instabilities. This effect is further strong evidence of liquid behaviour and is the result of charging of the wires during FIB nanofabrication.
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81.16.Nd Micro- and nanolithography
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)
73.25.+i Surface conductivity and carrier phenomena
81.16.Rf Micro- and nanoscale pattern formation

Graphene layer growth on silicon substrates with nickel film by pulse arc plasma deposition

K. Fujita, K. Banno, H. R. Aryal, and T. Egawa

Appl. Phys. Lett. 101, 163109 (2012); http://dx.doi.org/10.1063/1.4761474 (3 pages)

Online Publication Date: 18 October 2012

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Carbon layer has been grown on a Ni/SiO2/Si(111) substrate under high vacuum pressure by pulse arc plasma deposition. From the results of Raman spectroscopy for the sample, it is found that graphene was formed by ex-situ annealing of sample grown at room temperature. Furthermore, for the sample grown at high temperature, graphene formation was shown and optimum temperature was around 1000 °C. Transmission electron microscopy observation of the sample suggests that the graphene was grown from step site caused by grain of Ni film. The results show that the pulse arc plasma technique has the possibility for acquiring homogenous graphene layer with controlled layer thickness.
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78.66.Tr Fullerenes and related materials
68.65.Pq Graphene films
52.77.Dq Plasma-based ion implantation and deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
78.30.Na Fullerenes and related materials
81.40.Gh Other heat and thermomechanical treatments
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