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25 May 2009

Volume 94, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 94, 213101 (2009); http://dx.doi.org/10.1063/1.3139865 (3 pages)

Chul-Ho Lee, Jinkyoung Yoo, Young Joon Hong, Jeonghui Cho, Yong-Jin Kim, Seong-Ran Jeon, Jong Hyeob Baek, and Gyu-Chul Yi
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GaN/In1−xGaxN/GaN/ZnO nanoarchitecture light emitting diode microarrays

Chul-Ho Lee, Jinkyoung Yoo, Young Joon Hong, Jeonghui Cho, Yong-Jin Kim, Seong-Ran Jeon, Jong Hyeob Baek, and Gyu-Chul Yi

Appl. Phys. Lett. 94, 213101 (2009); http://dx.doi.org/10.1063/1.3139865 (3 pages) | Cited 19 times

Online Publication Date: 26 May 2009

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We studied the fabrication and electroluminescent (EL) characteristics of GaN/In1−xGaxN/GaN/ZnO nanoarchitecture light emitting diode (LED) microarrays consisting of position-controlled GaN/ZnO coaxial nanotube heterostructures. For the fabrication of nanoarchitecture LED arrays, n-GaN, GaN/In0.24Ga0.76N multiquantum well (MQW) structures and p-GaN layers were deposited coaxially over the entire surface of position-controlled ZnO nanotube arrays grown vertically on c-plane sapphire substrates. The nanoarchitecture LEDs exhibited strong green and blue emission from the GaN/GaN/In0.24Ga0.76N MQWs at room temperature. Furthermore, the origins of dominant EL peaks are also discussed.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling

Photon management by metallic nanodiscs in thin film solar cells

Carsten Rockstuhl and Falk Lederer

Appl. Phys. Lett. 94, 213102 (2009); http://dx.doi.org/10.1063/1.3141402 (3 pages) | Cited 30 times

Online Publication Date: 26 May 2009

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We investigate the absorption enhancement by metallic nanodiscs in thin-film amorphous silicon solar cells. The effect is quantitatively evaluated by rigorously solving Maxwell’s equations. We show that 50% more photons can be absorbed using geometries accessible for current nanofabrication technologies. Moreover, the thinner the solar cell, the larger the absorption enhancement. Detailed investigations prove that the enhancement can be related to the excitation of localized plasmon polaritons. The simultaneous enhancement in both the near-field amplitude and the scattering cross section at resonance as the leading physical mechanism is discussed in detail.
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84.60.Jt Photoelectric conversion
81.16.-c Methods of micro- and nanofabrication and processing
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Nonlocal bias spectroscopy of the self-consistent bound state in quantum point contacts near pinch off

Y. Yoon, M.-G. Kang, P. Ivanushkin, L. Mourokh, T. Morimoto (森本崇弘), N. Aoki (青木伸之), J. L. Reno, Y. Ochiai (落合勇一), and J. P. Bird

Appl. Phys. Lett. 94, 213103 (2009); http://dx.doi.org/10.1063/1.3142418 (3 pages) | Cited 7 times

Online Publication Date: 26 May 2009

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We perform nonlocal bias spectroscopy of the self-consistent bound state (BS) in quantum point contacts (QPCs), determining the lever arm (γ) that governs the gate-voltage induced shift in its energy. The value of γ allows us to infer an enhanced g factor, and large remnant spin splitting, for the BS. Our results show many similarities with bias spectroscopy of quantum dots and are reproduced by calculations that assume a discrete BS coupled to a reservoir. This study therefore provides independent evidence in support of the notion of BS formation in QPCs.
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73.21.La Quantum dots

High angular tolerant color filter using subwavelength grating

Byoung-Ho Cheong, O. N. Prudnikov, Eunhyoung Cho, Hae-Sung Kim, Jaeho Yu, Young-Sang Cho, Hwan-Young Choi, and Sung Tae Shin

Appl. Phys. Lett. 94, 213104 (2009); http://dx.doi.org/10.1063/1.3139058 (3 pages) | Cited 10 times

Online Publication Date: 26 May 2009

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A reflective color filter based on a two-dimensional subwavelength grating is proposed. The filter has been designed by performing numerical simulations and has been fabricated on 5×5 mm2 quartz glass using electron beam lithography. The grating color filter shows reflectance of 74% and spectral width of about 80 nm. Furthermore, it has good angular tolerance, up to ±45°, for unpolarized incident light. By analyzing the reflectance spectral distributions in the band diagram, we found that high angular tolerance is achieved due to the high refractive index contrast of grating structures.
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42.79.Ci Filters, zone plates, and polarizers

Real-time in situ spectroscopic ellipsometry of GaSb nanostructures during sputtering

I. S. Nerbø, S. Le Roy, M. Kildemo, and E. Søndergård

Appl. Phys. Lett. 94, 213105 (2009); http://dx.doi.org/10.1063/1.3133350 (3 pages) | Cited 6 times

Online Publication Date: 27 May 2009

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We demonstrate that real-time in situ spectroscopic ellipsometry can be used to measure the height evolution of nanostructures during low energy ion sputtering of GaSb. A graded anisotropic effective medium approximation is used to extract the height from the optical measurements. Two different growth regimes have been observed, first exponential then followed by a linear regime. The linear regime is not expected from the traditional sputtering theories. The in situ results correspond well to ex situ atomic force microscopy measurements.
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81.65.Cf Surface cleaning, etching, patterning
61.46.-w Structure of nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing
81.07.Bc Nanocrystalline materials

Behavior of a chemically doped graphene junction

Damon B. Farmer, Yu-Ming Lin, Ali Afzali-Ardakani, and Phaedon Avouris

Appl. Phys. Lett. 94, 213106 (2009); http://dx.doi.org/10.1063/1.3142865 (3 pages) | Cited 36 times

Online Publication Date: 28 May 2009

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Polyethylene imine and diazonium salts are used as complementary molecular dopants to engineer a doping profile in a graphene transistor. Electronic transport in this device reveals the presence of two distinct resistance maxima, alluding to neutrality point separation and subsequent formation of a spatially abrupt junction. Carrier mobility in this device is not significantly affected by molecular doping or junction formation, and carrier transmission is found to scale inversely with the effective channel length of the device. Chemical dilutions are used to modify the dopant concentration and, in effect, alter the properties of the junction.
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85.30.-z Semiconductor devices
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Le Polymers; organic compounds (including organic semiconductors)

Growth of Si0.75Ge0.25 alloy nanowires in a separated H-field by microwave processing

Charu Lata Dube, Subhash C. Kashyap, D. C. Dube, and D. K. Agarwal

Appl. Phys. Lett. 94, 213107 (2009); http://dx.doi.org/10.1063/1.3143232 (3 pages) | Cited 7 times

Online Publication Date: 28 May 2009

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This paper presents a rapid and novel technique of growing nanowires of Si0.75Ge0.25 alloy at 900 °C in less than 10 min by processing the constituents in a TE011 single mode cylindrical resonant cavity, operated at 2.45 GHz and ∼ 300 W. The microstructural, crystal structural, and x-ray photoelectron spectroscopic studies of the nanowires have been carried out to establish their dimensions, crystallographic structure, and composition, respectively. It is proposed that the growth of nanowires is due to electromagnetic field assisted morphological transformation.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.-b Nanoscale materials and structures: fabrication and characterization
79.60.Bm Clean metal, semiconductor, and insulator surfaces
64.70.kg Semiconductors
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)

Thermoelectric performance of silicon nanowires

Gang Zhang, Qingxin Zhang, Cong-Tinh Bui, Guo-Qiang Lo, and Baowen Li

Appl. Phys. Lett. 94, 213108 (2009); http://dx.doi.org/10.1063/1.3143616 (3 pages) | Cited 20 times

Online Publication Date: 28 May 2009

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With finite element simulation and analytic modeling, the thermoelectric performance of silicon nanowires (SiNWs) is studied. Large cooling temperature is observed which increases remarkably as thermal conductivity of SiNW decreases. Moreover, high cooling power density of 6.6×103 W/cm2 is achieved which is about 600 times larger than that of commercial thermoelectric modules. Moreover, SiNW cooler can reach the coefficient as high as 61%. All these features make SiNW a very promising material in application of on-chip temperature controlling and heat dissipating for hot spots inside integrated circuits.
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72.20.Pa Thermoelectric and thermomagnetic effects
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)
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
73.63.-b Electronic transport in nanoscale materials and structures

Geometric effect on surface enhanced Raman scattering of nanoporous gold: Improving Raman scattering by tailoring ligament and nanopore ratios

X. Y. Lang, L. Y. Chen, P. F. Guan, T. Fujita, and M. W. Chen

Appl. Phys. Lett. 94, 213109 (2009); http://dx.doi.org/10.1063/1.3143628 (3 pages) | Cited 17 times

Online Publication Date: 28 May 2009

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We have synthesized nanoporous gold (NPG) films with a nanostructure consisting of small nanopores and large gold ligaments by the combination of chemical dealloying and electroless plating. The NPG films exhibit dramatic improvement in surface enhanced Raman scattering (SERS) in comparison with the conventional NPG. The superior SERS effect of the NPG films results from the confluence effect of enhanced local surface plasmon fields and electromagnetic coupling between ligaments, as well as the weak plasmon damping with increasing gold ligament sizes.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Bx Metals, semimetals, and alloys
78.66.Bz Metals and metallic alloys
78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.30.Er Solid metals and alloys

Self-assembled nanoparticle spirals from two-dimensional compositional banding in thin films

Dinesh K. Venkatachalam, Neville H. Fletcher, Dinesh K. Sood, and Robert G. Elliman

Appl. Phys. Lett. 94, 213110 (2009); http://dx.doi.org/10.1063/1.3143666 (3 pages) | Cited 1 time

Online Publication Date: 28 May 2009

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A self-assembly process is reported in which spiral patterns of gold nanoparticles form on silicon surfaces during the epitaxial crystallization of thin gold-silicon alloy layers. This behavior is observed only for gold concentrations above a critical value and is shown to result from two-dimensional compositional banding of a liquid alloy layer during the crystallization process. The compositional banding consists of alternate gold-rich and silicon-rich alloy bands, which are shown to be a direct consequence of free energy minimization, the band spacing being that which gives the maximum diffusive composition-separation rate. Gold nanoparticles subsequently form by Ostwald ripening on the surface of the gold-rich bands to give rise to the observed spiral patterns.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly
65.40.G- Other thermodynamical quantities
64.70.dg Crystallization of specific substances
68.55.-a Thin film structure and morphology
73.22.-f Electronic structure of nanoscale materials and related systems

Resident electron spin dynamics of II-VI quantum dots

V. Gapon, J. Puls, and F. Henneberger

Appl. Phys. Lett. 94, 213111 (2009); http://dx.doi.org/10.1063/1.3139755 (3 pages) | Cited 2 times

Online Publication Date: 28 May 2009

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The spin dynamics of single electrons resident to charged CdSe/ZnSe quantum dots is studied. The spin-orbit mediated spin lifetime is uncovered. It follows a magnetic-field dependence of τso = 190 ms T4/B4. Below about B = 2 T, the electron-nuclear hyperfine coupling takes over and the electron spin lifetime shortens. We analyze the temperature dependence of the spin transfer via hyperfine interaction and find that the efficiency for the formation of a nuclear dynamical polarization increases up to 100 K.
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71.70.Jp Nuclear states and interactions
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.63.Kv Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization

Order-disorder transition and Curie transition in Ni70Fe30 nanoalloy

P. Y. Li, H. M. Lu, Z. H. Cao, S. C. Tang, X. K. Meng, X. S. Li, and Z. H. Jiang

Appl. Phys. Lett. 94, 213112 (2009); http://dx.doi.org/10.1063/1.3143610 (3 pages) | Cited 7 times

Online Publication Date: 29 May 2009

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This letter addresses the issue of the order-disorder and Curie transitions in Ni70Fe30 nanoalloy. The ordered phase is observed at room temperature while the disordered phase appears when the nanoalloy is heated up to 773 K. By means of mechanical spectroscopy, x-ray diffraction, and vibrating sample magnetometer measurements, the order-disorder and Curie transition temperatures of 20 nm Ni70Fe30 nanoalloy are determined to be 636 and 728 K, both lower than the corresponding values in the coarse-grained form. Moreover, the reduction in these two critical temperatures is consistent with the predictions of a thermodynamic analytical model.
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81.07.Bc Nanocrystalline materials
64.60.Cn Order-disorder transformations
64.70.K- Solid-solid transitions
77.80.B- Phase transitions and Curie point
75.50.Bb Fe and its alloys

Enhanced ultraviolet emission from hybrid structures of single-walled carbon nanotubes/ZnO films

Sung Kim, Dong Hee Shin, Chang Oh Kim, Sung Won Hwang, Suk-Ho Choi, Seungmuk Ji, and Ja-Yong Koo

Appl. Phys. Lett. 94, 213113 (2009); http://dx.doi.org/10.1063/1.3148646 (3 pages) | Cited 6 times

Online Publication Date: 29 May 2009

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We report interesting observation of strong enhancement of ultraviolet luminescence from hybrid structures of single-walled carbon nanotubes (SWNTs)/ZnO. SWNTs of 3–120 nm thickness (t) were deposited on top of 100 nm ZnO films/n-type Si (100) wafer by spin coating and vacuum filtration to form the hybrid structures. Photoluminescence (PL) intensity of the hybrid structures increases with increasing t up to 10 nm, becomes almost ten times larger at t = 10 nm than that of the bare ZnO film and decreases with increasing t above 10 nm. This strong PL enhancement is also confirmed by PL mapping. These findings are discussed based on the surface-plasmon-mediated emission mechanism.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.55.-m Photoluminescence, properties and materials
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