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19 Oct 2009

Volume 95, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 95, 162501 (2009); http://dx.doi.org/10.1063/1.3248257 (3 pages)

W. W. Lei, D. Liu, P. W. Zhu, X. H. Chen, Q. Zhao, G. H. Wen, Q. L. Cui, and G. T. Zou
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Bright three-band white light generated from CdSe/ZnSe quantum dot-assisted Sr3SiO5:Ce3+,Li+-based white light-emitting diode with high color rendering index

Ho Seong Jang, Byoung-Hwa Kwon, Heesun Yang, and Duk Young Jeon

Appl. Phys. Lett. 95, 161901 (2009); http://dx.doi.org/10.1063/1.3246800 (3 pages) | Cited 15 times

Online Publication Date: 19 October 2009

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In this study, bright three-band white light was generated from the CdSe/ZnSe quantum dot (QD)-assisted Sr3SiO5:Ce3+,Li+-based white light-emitting diode (WLED). The CdSe/ZnSe core/shell structure was confirmed by energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. The CdSe/ZnSe QDs showed high quantum efficiency (79%) and contributed to the high luminous efficiency (ηL) of the fabricated WLED. The WLED showed bright natural white with excellent color rendering property (ηL = 26.8 lm/W, color temperature = 6140 K, and color rendering index = 85) and high stability against the increase in forward bias currents from 20 to 70 mA.
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85.60.Jb Light-emitting devices
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.21.La Quantum dots
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Origin of reduction in phonon thermal conductivity of microporous solids

Patrick E. Hopkins, Peter T. Rakich, Roy H. Olsson, Ihab F. El-kady, and Leslie M. Phinney

Appl. Phys. Lett. 95, 161902 (2009); http://dx.doi.org/10.1063/1.3250166 (3 pages) | Cited 11 times

Online Publication Date: 20 October 2009

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Porous structures have strong tunable size effects due to increased surface area. Size effects on phonon thermal conductivity have been observed in porous materials with periodic voids on the order of microns. This letter explores the origin of this size effect on phonon thermal conductivity observed in periodic microporous membranes. Pore-edge boundary scattering of low frequency phonons explains the temperature trends in the thermal conductivity; further reduction in thermal conductivity is explained by the porosity.
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63.20.-e Phonons in crystal lattices
61.43.Gt Powders, porous materials
72.30.+q High-frequency effects; plasma effects
66.70.Df Metals, alloys, and semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Highly ordered, half-metallic Co2FeSi single crystals

C. G. F. Blum, C. A. Jenkins, J. Barth, C. Felser, S. Wurmehl, G. Friemel, C. Hess, G. Behr, B. Büchner, A. Reller, S. Riegg, S. G. Ebbinghaus, T. Ellis, P. J. Jacobs, J. T. Kohlhepp, et al.

Appl. Phys. Lett. 95, 161903 (2009); http://dx.doi.org/10.1063/1.3242370 (3 pages) | Cited 7 times

Online Publication Date: 20 October 2009

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A wide variety of properties such as half-metallicity is found among Heusler compounds. In order to separate intrinsic and extrinsic properties, high quality single crystals are required. Here, we report on differently grown crystals of the half-metallic ferromagnet Co2FeSi. All crystals show excellent ordering, resulting in outstanding electrical behavior with low residual resistivity and high residual-resistivity-ratio. All Co2FeSi crystals show a plateau in the resistivity below 50 K, which might point to half-metallic ferromagnetism. The cross-over from this unusual to more conventional transport (T2 dependence) around 50 K indicates the onset of spin flip scattering and thus is indispensable for understanding the strong temperature dependence of Co2FeSi tunneling magnetoresistance-devices.
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75.47.Pq Other materials
72.25.-b Spin polarized transport

Stimulated emission at 340 nm from AlGaN multiple quantum well grown using high temperature AlN buffer technologies on sapphire

Q. Wang, Y. P. Gong, J. F. Zhang, J. Bai, F. Ranalli, and T. Wang

Appl. Phys. Lett. 95, 161904 (2009); http://dx.doi.org/10.1063/1.3253416 (3 pages) | Cited 7 times

Online Publication Date: 20 October 2009

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It is necessary to further improve crystal quality of AlGaN multiple quantum well (MQW) structures on sapphire in order to achieve ultraviolet (UV) laser diodes. Two buffer technologies have been introduced based on our high temperature AlN buffer technology: modified “GaN interlayer” and “multiple porous AlN buffer.” The Al0.16Ga0.84N/Al0.05Ga0.95N MQWs have been grown on top of the two kinds of buffers on sapphire. High resolution x-ray diffraction measurements have confirmed that the crystal quality has been massively improved. As a result, an UV stimulated emission at 340 nm has been observed via optical pumping with a low threshold power of ∼ 6.6 kW/cm2 at room temperature. The developed approaches potentially provide a simple way for achieving electrical injection UV (including deep UV) laser.
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78.67.De Quantum wells
68.55.-a Thin film structure and morphology
61.43.Gt Powders, porous materials
78.45.+h Stimulated emission
78.66.Fd III-V semiconductors

Glass-forming ability enhanced by proper additions of oxygen in a Fe-based bulk metallic glass

H. X. Li, J. E. Gao, Z. B. Jiao, Y. Wu, and Z. P. Lu

Appl. Phys. Lett. 95, 161905 (2009); http://dx.doi.org/10.1063/1.3248186 (3 pages) | Cited 9 times

Online Publication Date: 20 October 2009

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Effects of oxygen on glass formation in the Fe73Mo3.0C7.0Si3.3B5.0P8.7 bulk metallic glass were studied in detail. Surprisingly, it was found that a critical level of oxygen is effective in enhancing the glass-forming ability of the current Fe-based bulk metallic glass due to the facts that (i) oxygen can increase the crystallization resistance via suppressing the precipitation of the competitive primary phase and (ii) oxygen can stabilize the glass-forming liquid as manifested by the decrease in the liquidus temperature. However, excess oxygen additions will destabilize the liquid and induce the formation of more stable oxygen-containing crystalline phase, thus deteriorating the glass-forming ability.
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64.70.pe Metallic glasses
61.43.Fs Glasses
64.70.dg Crystallization of specific substances

Crossover in thermal transport properties of natural, perovskite-structured superlattices

Aleksandr Chernatynskiy, Robin W. Grimes, Mark A. Zurbuchen, David R. Clarke, and Simon R. Phillpot

Appl. Phys. Lett. 95, 161906 (2009); http://dx.doi.org/10.1063/1.3253421 (3 pages) | Cited 5 times

Online Publication Date: 20 October 2009

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Atomic-level simulations are used to analyze the thermal-transport properties of a naturally layered material: the Ruddlesden–Popper phase, formed by interleaving perovskite layers of strontium titanate with strontium oxide rocksalt layers. The thermal conductivity parallel to the plane of structural layering is found to be systematically greater than that perpendicular to the layering. With decreasing number of perovskite blocks in the structure, a transition is seen from the thermal-transport properties of a bulk solid containing interfaces to that of an anisotropic monolithic material. The exact transition point should be temperature dependent and might enable tuning of the thermal conductance properties of the material.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
68.65.Cd Superlattices

Vapor generation in a nanoparticle liquid suspension using a focused, continuous laser

Robert A. Taylor, Patrick E. Phelan, Todd Otanicar, Ronald J. Adrian, and Ravi S. Prasher

Appl. Phys. Lett. 95, 161907 (2009); http://dx.doi.org/10.1063/1.3250174 (3 pages) | Cited 6 times

Online Publication Date: 21 October 2009

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This letter discusses experimentation with optically induced phase change in nanoparticle liquid suspensions—commonly termed nanofluids. Four different types of nanofluids at five concentrations were exposed to a ∼ 120 mW, 532 nm laser beam to determine the minimum laser flux needed to create vapor. Laser irradiance was varied between 0–770 W cm−2. While the experiments were simple, they involved many complex, interrelated physical phenomena, including: subcooled boiling, thermal driven particle/bubble motion, nanoparticle radiative absorption/scattering, and nanoparticle clumping. Such phenomena could enable novel solar collectors in which the working fluid directly absorbs energy and undergoes phase change in a single step.
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47.85.Np Fluidics
47.57.E- Suspensions
82.70.Kj Emulsions and suspensions
47.55.D- Drops and bubbles
47.55.dp Cavitation and boiling

Strain effects on the intersubband transitions in GaN/AlN multiple quantum wells grown by low-temperature metal organic vapor phase epitaxy with AlGaN interlayer

Hassanet Sodabanlu, Jung-Seung Yang, Masakazu Sugiyama, Yukihiro Shimogaki, and Yoshiaki Nakano

Appl. Phys. Lett. 95, 161908 (2009); http://dx.doi.org/10.1063/1.3253715 (3 pages) | Cited 5 times

Online Publication Date: 22 October 2009

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The strain in low-temperature-grown GaN/AlN multiple quantum wells (MQWs) have been tailored by inserting an AlGaN interlayer between an AlN template and the MQWs, for the purpose of intersubband transition (ISBT) at shorter wavelength (1.52 μm) with smaller full-width at half-maximum (FWHM) (113 meV). The strain in GaN wells, ISBT wavelength and its FWHM were dependent on Al-content in the AlGaN interlayer. The compressive strain in GaN wells shifted ISBT to shorter wavelengths and narrowed absorption peaks. The interlayer with an appropriate Al-content has been proved to be mandatory for achieving strong and short-wavelength ISBT by metal organic vapor phase epitaxy-grown GaN/AlN MQWs.
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62.25.-g Mechanical properties of nanoscale systems
68.65.Fg Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Phase partitioning and site-preference of hafnium in the γ′(L12)/γ(fcc) system in Ni-based superalloys: An atom-probe tomographic and first-principles study

Yaron Amouyal, Zugang Mao, and David N. Seidman

Appl. Phys. Lett. 95, 161909 (2009); http://dx.doi.org/10.1063/1.3248146 (3 pages) | Cited 5 times

Online Publication Date: 22 October 2009

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Atom-probe tomography (APT) and first-principles calculations are employed to investigate the partitioning of Hf in the γ′(L12)/γ(fcc) phases in two multicomponent Ni-based superalloys. APT results indicate strong partitioning of Hf atoms to the γ(fcc)-phase. We perform first-principles calculations of the substitutional formation energy of Hf for a model γ(Ni)/γ′(Ni3Al) system indicating Hf partitioning to the γ′-phase. Additional calculations of the Hf–Cr binding energy suggest, however, that Cr atoms, which partition to the γ-phase, have a strong attractive binding energy with Hf atoms, thus predicting a reversal of the Hf partitioning in favor of the γ-phase due to alloying with Cr.
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81.30.Bx Phase diagrams of metals, alloys, and oxides
61.50.Lt Crystal binding; cohesive energy
89.20.Kk Engineering

Thermal contact resistance between graphene and silicon dioxide

Z. Chen, W. Jang, W. Bao, C. N. Lau, and C. Dames

Appl. Phys. Lett. 95, 161910 (2009); http://dx.doi.org/10.1063/1.3245315 (3 pages) | Cited 33 times

Online Publication Date: 23 October 2009

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The thermal contact resistance between graphene and silicon dioxide was measured using a differential 3ω method. The sample thicknesses were 1.2 (single-layer graphene), 1.5, 2.8, and 3.0 nm, as determined by atomic force microscopy. All samples exhibited approximately the same temperature trend from 42 to 310 K, with no clear thickness dependence. The contact resistance at room temperature ranges from 5.6×10−9 to 1.2×10−8 m2 K/W, which is significantly lower than previous measurements involving related carbon materials. These results underscore graphene’s potential for applications in microelectronics and thermal management structures.
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73.40.Cg Contact resistance, contact potential
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
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