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17 Jan 2011

Volume 98, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 98, 031101 (2011); http://dx.doi.org/10.1063/1.3529469 (3 pages)

Sinan Balci, Askin Kocabas, Coskun Kocabas, and Atilla Aydinli
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Epitaxial growth and structural property of graphene on Pt(111)

M. Gao, Y. Pan, L. Huang, H. Hu, L. Z. Zhang, H. M. Guo, S. X. Du, and H.-J. Gao

Appl. Phys. Lett. 98, 033101 (2011); http://dx.doi.org/10.1063/1.3543624 (3 pages) | Cited 3 times

Online Publication Date: 18 January 2011

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We report on epitaxial growth of graphene on Pt(111) surface. It was found out that the proportion of different rotational domains varies with growth temperature and the graphene quality can be improved by adjusting both the growth temperature and ethylene exposure. Rippled and unrippled domains of high quality graphene are observed. The adhesive energy and electronic structure of two models, representing rippled and unrippled graphene, are obtained with density functional theory calculation, which shows that the interaction between graphene and Pt(111) surface is very weak and the electronic structure is nearly the same as that of a free standing graphene.
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61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
81.05.ue Graphene
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Highly selective spectral response with enhanced responsivity of n-ZnO/p-Si radial heterojunction nanowire photodiodes

Han-Don Um, Syed Abdul Moiz, Kwang-Tae Park, Jin-Young Jung, Sang-Won Jee, Cheol Hyoun Ahn, Dong Chan Kim, Hyung Koun Cho, Dong-Wook Kim, and Jung-Ho Lee

Appl. Phys. Lett. 98, 033102 (2011); http://dx.doi.org/10.1063/1.3543845 (3 pages) | Cited 7 times

Online Publication Date: 18 January 2011

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A radial heterojunction nanowire diode (RND) array consisting of a ZnO (shell)/Si (core) structure was fabricated using conformal coating of a n-type ZnO layer that surrounded a p-type Si nanowire. In both ultraviolet (UV) and visible ranges, the photoresponsivity of the RND was larger than that of a planar thin film diode (PD) owing to the efficient carrier collection with improved light absorption. Compared to a PD, in the forward bias, a 6 μm long RND resulted in a ∼ 2.7 times enhancement of the UV responsivity at λ = 365 nm, which could be explained based on the oxygen-related hole-trap mechanism. Under a reverse bias, UV-blind visible detection was observed while the UV response was suppressed.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Behind the change of the photoluminescence property of metal-coated ZnO nanowire arrays

Y. J. Fang, J. Sha, Z. L. Wang, Y. T. Wan, W. W. Xia, and Y. W. Wang

Appl. Phys. Lett. 98, 033103 (2011); http://dx.doi.org/10.1063/1.3543902 (3 pages) | Cited 3 times

Online Publication Date: 18 January 2011

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The effect of metal coating on the photoluminescence (PL) properties of ZnO nanowire arrays has been investigated in detail in this letter. The Zn coating induces remarkable enhancement of the ultraviolet and green emissions of the nanowires, while the deposition of Ag leads to notable decrement of them. A model considering the type of contacts formed between metals and ZnO is proposed to interpret the change of the PL spectra. Also, this model is strongly supported by the PL variation of the nanowires after coating with other kinds of metals.
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78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
73.40.Ns Metal-nonmetal contacts
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)
78.67.Uh Nanowires
73.21.Hb Quantum wires

Energy and matter-efficient size-selective growth of thin quantum wires in a plasma

K. Ostrikov and H. Mehdipour

Appl. Phys. Lett. 98, 033104 (2011); http://dx.doi.org/10.1063/1.3540645 (3 pages) | Cited 1 time

Online Publication Date: 18 January 2011

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It is shown that plasmas can minimize the adverse Gibbs-Thompson effect in thin quantum wire growth. The model of Si nanowire nucleation includes the unprecedented combination of the plasma sheath, ion- and radical-induced species creation and heating effects on the surface and within an Au catalyst nanoparticle. Compared to neutral gas thermal processes, much thinner, size-selective wires can nucleate at the same temperature and pressure while much lower energy and matter budget is needed to grow same-size wires. This explains the experimental observations and may lead to energy- and matter-efficient synthesis of a broader range of one-dimensional quantum structures.
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68.65.La Quantum wires (patterned in quantum wells)
52.40.Kh Plasma sheaths
73.21.Hb Quantum wires
73.63.Nm Quantum wires
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)

Air-gap heterostructures

Ch. Heyn, M. Schmidt, S. Schwaiger, A. Stemmann, S. Mendach, and W. Hansen

Appl. Phys. Lett. 98, 033105 (2011); http://dx.doi.org/10.1063/1.3544047 (3 pages)

Online Publication Date: 19 January 2011

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We demonstrate the fabrication of thin GaAs layers which quasi hover above the underlying GaAs substrate. The hovering layers have a perfect epitaxial relationship to the substrate crystal lattice and are connected to the substrate surface only by lattice matched nanopillars of low density. These air-gap heterostructures are created by combining in situ molecular beam epitaxy compatible self-assembled droplet-etching and ex situ selective wet-chemical etching.
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81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning

Direct image of a molecular orientation of a liquid crystal using directional polymerization of photoreactive mesogen

You-Jin Lee, Chang-Jae Yu, Young-Ki Kim, Soo In Jo, and Jae-Hoon Kim

Appl. Phys. Lett. 98, 033106 (2011); http://dx.doi.org/10.1063/1.3537959 (3 pages)

Online Publication Date: 19 January 2011

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We present a method for visualizing the geometrical distribution of a liquid crystal (LC) arrangement using the replication of the molecular orientation by a mixture of alignment layers. We found that the anisotropic diffusion of the reactive mesogen (RM) monomers, mixed with an alignment layer, in contact with the LC was governed by the LC director through application of external voltage and allowed the directional polymerization under ultraviolet light illumination. The directional polymerization of a RM transferred and visualized the LC arrangement even at optically indistinct LC distributions.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
82.35.-x Polymers: properties; reactions; polymerization
66.10.-x Diffusion and ionic conduction in liquids

Influence of hydrogen functionalization on thermal conductivity of graphene: Nonequilibrium molecular dynamics simulations

Shih-Kai Chien, Yue-Tzu Yang, and Cha’o-Kuang Chen

Appl. Phys. Lett. 98, 033107 (2011); http://dx.doi.org/10.1063/1.3543622 (3 pages) | Cited 6 times

Online Publication Date: 20 January 2011

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The influence of hydrogen coverage on the thermal conductivity of typical armchair hydrogen functionalized graphene is investigated using a nonequilibrium molecular dynamics simulation. We also study the effects of easy-rotation of unsupported sp3 bonds. We find that the system exhibits a rapid drop in thermal conductivity with hydrogen coverage, where hydrogen coverage down to as little as 2.5% of the graphene carbon atoms reduces the thermal conductivity by about 40%. The simulation results indicate that the effect is due to a reduction in the phonon mean free path.
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65.80.Ck Thermal properties of graphene
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.Rc Phonons in graphene

Growth and electrical properties of Al-catalyzed Si nanowires

Seok-Youl Choi (최석열), Wayne Y. Fung, and Wei Lu

Appl. Phys. Lett. 98, 033108 (2011); http://dx.doi.org/10.1063/1.3544933 (3 pages) | Cited 1 time

Online Publication Date: 20 January 2011

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We report the growth and electrical characterization of small-diameter, Al-catalyzed silicon nanowires. Large quantities of Si nanowires can be grown with a fast growth rate at a low temperature of 520 °C via a vapor-liquid-solid process using Al as catalyst. The use of high H2 partial pressure was found to effectively mitigate the Al catalyst oxidation problem, and higher SiH4 partial pressure was found to produce smaller diameter nanowires. Electrical measurements show that small diameter (d< ∼ 25 nm) Al-catalyzed nanowires behave as p-type semiconductors with good gate response, while larger diameter Al-catalyzed nanowires behave as degenerately Al-doped semiconductors.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.61.Cw Elemental semiconductors
81.07.Gf Nanowires
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