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23 May 2011

Volume 98, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 98, 212504 (2011); http://dx.doi.org/10.1063/1.3593371 (3 pages)

K. Okumura, T. Ishikura, M. Soda, T. Asaka, H. Nakamura, Y. Wakabayashi, and T. Kimura
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Large spectral tunability of narrow geometric resonances of periodic arrays of metallic nanoparticles in a nematic liquid crystal

Jia Li, Yi Ma, Ying Gu, Iam-Choon Khoo, and Qihuang Gong

Appl. Phys. Lett. 98, 213101 (2011); http://dx.doi.org/10.1063/1.3592756 (3 pages) | Cited 9 times

Online Publication Date: 23 May 2011

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We investigated the geometric resonances of periodic arrays of gold nanoparticles embedded in a nematic liquid crystal using a semi-analytical method. By changing the liquid crystal’s refractive index seen by the scattered light propagating along the array axis, the geometric resonance can be modulated according to an analytical law. The spectral tunability is proportional to the index difference (ne−no) of the liquid crystal and the interparticle distance i.e., Δλ = (ne−no)d, which is as large as 100 nm. The large and easily controlled tunability of this compound structure makes it desirable for design of plasmon-based sensors and switches.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
78.68.+m Optical properties of surfaces

Visible electroluminescence from hybrid colloidal silicon quantum dot-organic light-emitting diodes

Chang-Ching Tu, Liang Tang, Jiangdong Huang, Apostolos Voutsas, and Lih Y. Lin

Appl. Phys. Lett. 98, 213102 (2011); http://dx.doi.org/10.1063/1.3593382 (3 pages) | Cited 3 times

Online Publication Date: 23 May 2011

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We demonstrate hybrid colloidal silicon quantum dot (SiQD)-organic light-emitting diodes with electroluminescence (EL) in the visible wavelengths. The device using blue photoluminescence (PL) SiQDs as emitters shows multiple EL peaks which are attributed to carrier recombination in the core quantum confinement states, the hole-transport-layer and the surface trap states, respectively. However, the red PL SiQD device shows a single EL peak consistent with the PL peak. These findings are in agreement with the previous report that large Stokes shift were observed for oxidized blue emission SiQDs due to oxide states while red emission SiQDs show negligible PL shift after oxidation.
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85.60.Jb Light-emitting devices
78.55.-m Photoluminescence, properties and materials
73.21.La Quantum dots
81.07.Ta Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence

Single-molecule refrigerators: Substitution and gate effects

Yu-Shen Liu and Yu-Chang Chen

Appl. Phys. Lett. 98, 213103 (2011); http://dx.doi.org/10.1063/1.3593379 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2011

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Using a first-principles approach, we investigate the quantum cooling effects in single-molecule junctions. In comparison with the unsubstituted butanethiol single-molecule junction as a refrigerator, the amino-substituted butanethiol single-molecule junction shows significant enhancement in the coefficient of performance (COP). The enhancement is attributed to the appearance of new states in the neighborhood of chemical potentials due to amino substitution. The COP of butanethiol refrigerator can be improved further by the gate voltages.
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85.65.+h Molecular electronic devices

Ultralow-voltage design of graphene PN junction quantum reflective switch transistor

Thibault Sohier and Bin Yu

Appl. Phys. Lett. 98, 213104 (2011); http://dx.doi.org/10.1063/1.3593956 (3 pages)

Online Publication Date: 24 May 2011

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We propose the concept of a graphene-based quantum reflective switch (QRS) for low-power logic application. With the unique electronic properties of graphene, a tilted PN junction is used to implement logic switch function with 103 ON/OFF ratio. Carriers are reflected on an electrostatically induced potential step with strong incidence-angle-dependency due to the widening of classically forbidden energies. Optimized design of the device for ultralow-voltage operating has been conducted. The device is constantly ON with a turning-off gate voltage around 180 mV using thin HfO2 as the gate dielectric. The results suggest a class of logic switch devices operating with micropower dissipation.
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84.32.Dd Connectors, relays, and switches
84.30.Sk Pulse and digital circuits

In(Ga)As/GaAs(001) quantum dot molecules probed by nanofocus high resolution x-ray diffraction with 100 nm resolution

M. Dubslaff, M. Hanke, M. Burghammer, S. Schöder, R. Hoppe, C. G. Schroer, Yu. I. Mazur, Zh. M. Wang, J. H. Lee, and G. J. Salamo

Appl. Phys. Lett. 98, 213105 (2011); http://dx.doi.org/10.1063/1.3593960 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2011

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In(Ga)As quantum dots, which laterally self-assemble into quantum dot molecules, have been studied by scanning x-ray nanodiffraction, finite element calculations and subsequent kinematical diffraction simulations. X-ray beam sizes of 100 nm enable small scattering volumes comparable to the object size at extremely high local flux densities ( ≈ 104 photons nm−2 s−1). By that bulk contributions to the scattering are effectively reduced. Area maps of various individual quantum dot molecules have been measured, whereas the diffraction patterns therein reveal spatially resolved information about the inter quantum dot position correlation function.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
02.70.Dh Finite-element and Galerkin methods
81.16.Dn Self-assembly
78.70.Ck X-ray scattering

A simple in situ method to detect graphene formation at SiC surfaces

S. Oida, J. B. Hannon, R. M. Tromp, F. R. McFeely, and J. Yurkas

Appl. Phys. Lett. 98, 213106 (2011); http://dx.doi.org/10.1063/1.3593483 (3 pages)

Online Publication Date: 25 May 2011

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We describe a simple method to detect the formation of graphene during Si sublimation from SiC surfaces at elevated temperature. The method exploits differences in the thermionic emission current density between graphene and SiC. When graphene forms, the thermionic current from the sample increases by a factor of about 20. The increase in thermionic emission can be detected in situ using a biased plate located near the sample. The ability to detect when graphene forms during processing is useful in optimizing graphene synthesis processes.
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81.05.ue Graphene
79.40.+z Thermionic emission

Hydrogenated grain boundaries in graphene

W. H. Brito, R. Kagimura, and R. H. Miwa

Appl. Phys. Lett. 98, 213107 (2011); http://dx.doi.org/10.1063/1.3592578 (3 pages) | Cited 1 time

Online Publication Date: 26 May 2011

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We have investigated by means of ab initio calculations the structural and electronic properties of hydrogenated graphene structures with distinct grain boundary defects. Our total energy results reveal that the adsorption of a single H is more stable at defect. Further total energy calculations indicate that the adsorption of two H on two neighbor carbons, forming a basic unit of graphane, is more stable at the defect region. Therefore, we expect that these extended defects would work as a nucleation region for the formation of a narrow graphane strip embedded in graphene region.
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61.72.Mm Grain and twin boundaries
61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
71.15.Nc Total energy and cohesive energy calculations
68.43.Mn Adsorption kinetics
61.72.Nn Stacking faults and other planar or extended defects
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