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4 Apr 2011

Volume 98, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 141903 (2011); http://dx.doi.org/10.1063/1.3548546 (3 pages)

H. Hattab, A. T. N’Diaye, D. Wall, G. Jnawali, J. Coraux, C. Busse, R. van Gastel, B. Poelsema, T. Michely, F.-J. Meyer zu Heringdorf, and M. Horn-von Hoegen
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UV nanoimprint lithography for the realization of large-area ordered SiGe/Si(001) island arrays

E. Lausecker, M. Brehm, M. Grydlik, F. Hackl, I. Bergmair, M. Mühlberger, T. Fromherz, F. Schäffler, and G. Bauer

Appl. Phys. Lett. 98, 143101 (2011); http://dx.doi.org/10.1063/1.3575554 (3 pages) | Cited 6 times

Online Publication Date: 4 April 2011

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We use UV nanoimprint lithography for the pit-patterning of silicon substrates. Ordered silicon-germanium islands are grown inside these pits by molecular-beam epitaxy on arrays of 3×3 mm2 and characterized by atomic force microscopy (AFM) and photoluminescence (PL) measurements. AFM-based statistics reveals an extremely uniform size distribution of the islands in the patterned areas. These results are confirmed by very narrow and uniform PL peaks recorded at various positions across the patterned arrays.
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81.16.Nd Micro- and nanolithography
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Hx Other solid inorganic materials

Photocurrent spectroscopy of single CdS nanosheets: Valence band structure and two photon absorption

P. Kumar, A. Wade, L. M. Smith, H. E. Jackson, J. M. Yarrison-Rice, Y.-J. Choi, and J.-G. Park

Appl. Phys. Lett. 98, 143102 (2011); http://dx.doi.org/10.1063/1.3573859 (3 pages) | Cited 1 time

Online Publication Date: 4 April 2011

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Photocurrent spectroscopy has been carried out on single CdS nanosheet devices in the metal-semiconductor-metal configuration with both Schottky and Ohmic contacts. Spatial imaging of the photocurrent shows that the photosensitive regions are localized at the reverse biased contact for Schottky type contacts and uniformly distributed throughout the nanosheet for Ohmic contacts. Photocurrent spectra show excitonic resonances at low temperatures corresponding to the A, B, C hole bands. Subband gap pulsed laser excitation reveals two-photon absorption dominated photocurrents consistent with a nonlinear coefficient of β = 2 cm/GW for these nanosheet devices.
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79.60.Jv Interfaces; heterostructures; nanostructures
71.20.Nr Semiconductor compounds
72.40.+w Photoconduction and photovoltaic effects
73.22.-f Electronic structure of nanoscale materials and related systems
73.63.Bd Nanocrystalline materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Mn-doped thiolated Au25 nanoclusters: Atomic configuration, magnetic properties, and a possible high-performance spin filter

M. Zhou, Y. Q. Cai, M. G. Zeng, C. Zhang, and Y. P. Feng

Appl. Phys. Lett. 98, 143103 (2011); http://dx.doi.org/10.1063/1.3575203 (3 pages) | Cited 2 times

Online Publication Date: 5 April 2011

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We report an ab inito investigation on the ground-state atomic configuration, electronic structures, magnetic, and spin-dependent transport properties of Mn-doped Au25 nanoclusters protected by thiolate. It is found that the most stable dopant sites are near surfaces, rather than the center position of the nanoparticles. Transport calculations show that high- performance spin filters can be achieved by sandwiching these doped clusters between two nonmagnetic Au electrodes. The nearly perfect spin filtering originates from localized magnetic moments of these clusters that are well protected by ligands from the presence of electrodes.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
75.30.Ds Spin waves
75.30.Cr Saturation moments and magnetic susceptibilities
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
72.25.-b Spin polarized transport
71.15.-m Methods of electronic structure calculations

Improved light-emitting diode performance by conformal overgrowth of multiple quantum wells and fully coalesced p-type GaN on GaN nanowires

P. Frajtag, A. M. Hosalli, G. K. Bradshaw, N. Nepal, N. A. El-Masry, and S. M. Bedair

Appl. Phys. Lett. 98, 143104 (2011); http://dx.doi.org/10.1063/1.3572032 (3 pages) | Cited 1 time

Online Publication Date: 6 April 2011

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We demonstrate a light-emitting diode (LED) structure with multiple quantum wells (MQWs) conformally grown on semipolar and nonpolar plane facets of n-GaN nanowires (NWs), followed by deposition of fully coalesced p-GaN on these nanowires. Overgrowth on the nanowires’ tips results in inclusion of high density voids, about one micron in height, in the GaN film. The light output intensity of NWs LEDs is more than three times higher than corresponding c-plane LEDs grown simultaneously. We believe this results from a reduced defect density, increased effective area of conformally grown MQWs, absence of polar plane orientation, and improved light extraction.
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85.60.Jb Light-emitting devices

Nanograting transfer for light extraction in organic light-emitting devices

Ziyao Wang, Julian Hauss, Christoph Vannahme, Uwe Bog, Sönke Klinkhammer, Dong Zhao, Martina Gerken, Timo Mappes, and Uli Lemmer

Appl. Phys. Lett. 98, 143105 (2011); http://dx.doi.org/10.1063/1.3572336 (3 pages) | Cited 1 time

Online Publication Date: 6 April 2011

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Damage-free transfer of nanogratings as waveguide mode extraction elements onto the top of top-emission organic light-emitting devices (OLEDs) was realized with the assistance of cyclic olefin copolymer molds. Photoluminescence and electroluminescence measurements together with transfer matrix calculations were used to identify the extracted waveguide modes. The presented one-step, wet-free, and etchless nanotransfer approach can avoid damage on the top-emission OLED structure and does not adversely affect the OLED performance. It offers the possibility for the independent optimization of OLED fabrication and nanofabrication, and has potential applications in organic optoelectronic devices, especially top-emission OLEDs.
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85.60.Jb Light-emitting devices
42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Statistical property of the effect of Au nanoparticle decoration on the carbon nanotube network

Sung Min Seo, Tae June Kang, Jun Ho Cheon, Jaeheung Lim, In Young Chung, Yong Hyup Kim, and Young June Park

Appl. Phys. Lett. 98, 143106 (2011); http://dx.doi.org/10.1063/1.3561736 (3 pages)

Online Publication Date: 7 April 2011

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Statistical analysis of the change in electrical characteristic of single-walled carbon nanotube (swCNT) network after the decoration of Au nanoparticles (NPs) is presented. We have fabricated 100 unitary swCNT network devices on a single chip employing a concentric electrode array by swCNT dip-coating and thermal evaporation of Au. The experimental results show that the decoration of Au-NP on the swCNT network can decrease not only its resistance but also variation in the resistance distribution. Remarkably, we have found that the change in electrical characteristic is correlated with the resistance value of the bare swCNT network.
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81.07.De Nanotubes
73.61.Wp Fullerenes and related materials
02.50.-r Probability theory, stochastic processes, and statistics
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Bandgap opening in boron nitride confined armchair graphene nanoribbon

Gyungseon Seol and Jing Guo

Appl. Phys. Lett. 98, 143107 (2011); http://dx.doi.org/10.1063/1.3571282 (3 pages) | Cited 5 times

Online Publication Date: 8 April 2011

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Graphene nanoribbons (GNRs) have seized strong interest. Recent studies show that domains of graphene in monolayer hexagonal boron nitride (h-BN) can be synthesized. Using the first principle calculations we have studied the electronic properties of armchair GNRs (AGNRs) confined by BN nanoribbons (BNNRs). While, H-terminated AGNRs have a close to zero bandgap with the width index of 3p+2, AGNRs confined by BNNRs exhibit a considerable bandgap. The bandgap opening is primarily due to perturbation to the on-site potentials of atoms at AGNR edges. A tight binding model is parameterized to confirm this mechanism and enable future device studies.
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71.20.Nr Semiconductor compounds
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.35.Ct Interface structure and roughness

Electrode-contact enhancement in silicon nanowire-array-textured solar cells

Chen Chen, Rui Jia, Haofeng Li, Yanlong Meng, Xinyu Liu, Tianchun Ye, Seiya Kasai, Hashizume Tamotsu, Nanjian Wu, Shanli Wang, and Junhao Chu

Appl. Phys. Lett. 98, 143108 (2011); http://dx.doi.org/10.1063/1.3576924 (3 pages) | Cited 2 times

Online Publication Date: 8 April 2011

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In the case of the silicon (Si) nanowire (NW)-array-textured solar cells, the electrode-contact enhancement has been achieved using a simple and convenient double-step diffusion process to form a highly doped N+ region at the tips of a Si-NW array. The series resistance can be effectively reduced, leading to an increase in the short-circuit current density in the cell. We have studied the physical mechanism of the impact of an increase in doping level at the tips of a Si-NW array on the electrode-contact property, which would benefit in realizing an improvement in cell performance in such a nanostructure solar cell.
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88.40.H- Solar cells (photovoltaics)

Optimization of the current pulse for spin-torque switches

Tom Dunn and Alex Kamenev

Appl. Phys. Lett. 98, 143109 (2011); http://dx.doi.org/10.1063/1.3576929 (3 pages) | Cited 3 times

Online Publication Date: 8 April 2011

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We address optimization of the spin current intensity profile needed to achieve spin torque switching of a nanomagnet. For systems with Ohmic dissipation we prove that the optimal current drives the magnetization along the trajectory, which is exact time-reversed replica of the relaxation trajectory toward the equilibrium. In practice it means that the optimal current is very nearly twice the minimal critical current needed to switch the magnet. Pulse duration of such an optimal current is a slow logarithmic function of temperature and the required probability of switching.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
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