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19 Oct 2009

Volume 95, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

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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A multispectral and polarization-selective surface-plasmon resonant midinfrared detector

Jessie Rosenberg, Rajeev V. Shenoi, Thomas E. Vandervelde, Sanjay Krishna, and Oskar Painter

Appl. Phys. Lett. 95, 161101 (2009); http://dx.doi.org/10.1063/1.3244204 (3 pages) | Cited 13 times

Online Publication Date: 19 October 2009

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We demonstrate a multispectral polarization sensitive midinfrared dots-in-a-well photodetector utilizing surface-plasmonic resonant elements, with tailorable frequency response and polarization selectivity. The resonant responsivity of the surface-plasmon detector shows an enhancement of up to five times that of an unpatterned control detector. As the plasmonic resonator involves only surface patterning of the top metal contact, this method is independent of light-absorbing material and can easily be integrated with current focal plane array processing for imaging applications.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Wide-band continuous-wave terahertz source with a vertically integrated photomixer

E. Peytavit, J-F. Lampin, F. Hindle, C. Yang, and G. Mouret

Appl. Phys. Lett. 95, 161102 (2009); http://dx.doi.org/10.1063/1.3251071 (3 pages) | Cited 3 times

Online Publication Date: 20 October 2009

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A transverse electromagnetic horn antenna is monolithically integrated with a low temperature grown GaAs vertical photodetector on a silicon substrate forming a vertically integrated photomixer. Continuous-wave terahertz radiation is generated at frequencies up to 3.5 THz with a power level reaching 20 nW around 3 THz. Microwave and material concepts allow both qualitative and quantitative explanations of the experimental results. The thin film microstrip line topology has been adapted for active devices by an Au–Au thermocompression layer transfer technique and seems to be a promising generic tool for a new generation of efficient terahertz devices.
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84.40.Ba Antennas: theory, components and accessories
85.60.Gz Photodetectors (including infrared and CCD detectors)

Ultrabroadband supercontinuum generation from ultraviolet to 6.28 μm in a fluoride fiber

Guanshi Qin, Xin Yan, Chihiro Kito, Meisong Liao, Chitrarekha Chaudhari, Takenobu Suzuki, and Yasutake Ohishi

Appl. Phys. Lett. 95, 161103 (2009); http://dx.doi.org/10.1063/1.3254214 (3 pages) | Cited 24 times

Online Publication Date: 21 October 2009

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Ultrabroadband supercontinuum light expanding from ultraviolet to 6.28 μm is generated in a centimeter-long fluoride fiber pumped by a 1450 nm femtosecond laser. The spectral broadening in the fluoride fiber is caused by self-phase modulation, Raman scattering and four-wave mixing. The experimental and simulated results show that fluoride fiber is a promising candidate for generating the midinfrared supercontinuum light up to 8 μm.
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42.81.Dp Propagation, scattering, and losses; solitons
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Variable liquid crystal pretilt angles generated by photoalignment in homeotropically aligned azo dye-doped liquid crystals

Andy Ying-Guey Fuh, Cheng-Kai Liu, Ko-Ting Cheng, Chi-Lung Ting, Che-Chang Chen, Paul Chang-Po Chao, and Hsu-Kuan Hsu

Appl. Phys. Lett. 95, 161104 (2009); http://dx.doi.org/10.1063/1.3253413 (3 pages) | Cited 9 times

Online Publication Date: 21 October 2009

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This letter demonstrates the feasibility of producing variable liquid crystal (LC) pretilt angles using light-induced ripple structures (LIRSs) in homeotropically aligned azo dye-doped liquid crystals (ADDLCs). Illuminating homeotropically aligned ADDLCs with a linearly polarized light for a suitable period yields the LIRSs which provide LCs an anisotropic homogeneous anchoring force. Experimentally, the effective alignment force produced by the homeotropic alignment layer and the LIRSs determines the LC pretilt angle (24° to 63.5°), defined from the normal to the substrate. A no-bias pi cell for liquid crystal displays is demonstrated using this approach.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions
85.60.Pg Display systems

Nonlinear laser-driven electron resonance acceleration in an inhomogeneous magnetic field

Jun Li, Bai-Song Xie, Hai-Bo Sang, Xue-Ren Hong, Shan Zhang, and M. Y. Yu

Appl. Phys. Lett. 95, 161105 (2009); http://dx.doi.org/10.1063/1.3253415 (3 pages) | Cited 1 time

Online Publication Date: 21 October 2009

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Electron resonance acceleration by an intense laser pulse in an inhomogeneous external magnetic field is investigated. The acceleration mechanism makes use of electron cyclotron resonance to increase the electron energy. By appropriately tailoring the radial gradient of the magnetic field, an electron in the rising front part of laser pulse will be attracted toward the cyclotron-resonance radius and be trapped there, so that it can gain much energy. It is shown that the electron net energy gain can be up to the GeV level.
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41.75.Jv Laser-driven acceleration
52.38.Kd Laser-plasma acceleration of electrons and ions

Effect of uniaxial-strain on Ge p-i-n photodiodes integrated on Si

Hyun-Yong Yu, Donghyun Kim, Shen Ren, Masaharu Kobayashi, David A. B. Miller, Yoshio Nishi, and Krishna C. Saraswat

Appl. Phys. Lett. 95, 161106 (2009); http://dx.doi.org/10.1063/1.3254181 (3 pages) | Cited 3 times

Online Publication Date: 22 October 2009

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We demonstrate the effect of uniaxial tensile and compressive strain in Ge p-i-n photodiode integrated on Si using four-point bending structures. Responsivity at 1550 nm is increased from 0.67 to 0.75 A/W by tensile strain in the 〈110〉 direction while for compressive strain it decreases from 0.67 to 0.477 A/W. These uniaxial tensile and compressive strains also effectively result in shifts of the absorption spectra toward longer and shorter wavelength as they reduce or increase the direct bandgap energy of the Ge layer, respectively.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling

Ultraviolet and solar-blind spectral imaging with subwavelength transmission gratings

S. H. Lim and E. T. Yu

Appl. Phys. Lett. 95, 161107 (2009); http://dx.doi.org/10.1063/1.3257365 (3 pages) | Cited 2 times

Online Publication Date: 23 October 2009

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Aluminum gratings with subwavelength slit widths were designed and analyzed for spectral filtering of ultraviolet (UV) light. Although schemes for optical wavelength filtering have been thoroughly studied, options for UV wavelength filtering are far more limited. We analyze the unique requirements for UV based imaging and evaluate the suitability of our structures by electromagnetic simulations and experimental measurements. Rayleigh–Wood anomalies are shown to lead to sharp drops in transmission at resonance wavelengths, producing a high finesse band reject filter. Finally, we show that the structures are effective for both TE and TM polarizations and easily integrated onto semiconductor photodetectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Ci Filters, zone plates, and polarizers
FREE

Multi-beam multi-wavelength semiconductor lasers

Nanfang Yu, Mikhail A. Kats, Christian Pflügl, Markus Geiser, Qi Jie Wang, Mikhail A. Belkin, Federico Capasso, Milan Fischer, Andreas Wittmann, Jérôme Faist, Tadataka Edamura, Shinichi Furuta, Masamichi Yamanishi, and Hirofumi Kan

Appl. Phys. Lett. 95, 161108 (2009); http://dx.doi.org/10.1063/1.3253713 (3 pages) | Cited 9 times

Online Publication Date: 23 October 2009

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Multibeam emission and spatial wavelength demultiplexing in semiconductor lasers by patterning their facets with plasmonic structures is reported. Specifically, a single-wavelength laser was made to emit beams in two directions by defining on its facet two metallic gratings with different periods. The output of a dual-color laser was spatially separated according to wavelength by using a single metallic grating. The designs can be integrated with a broad range of active or passive optical components for applications such as interferometry and demultiplexing.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.82.-m Integrated optics
42.79.Dj Gratings

Influence of nanocrystal size on dielectric functions of Si nanocrystals embedded in SiO2 matrix

Rong-Jun Zhang, Yi-Ming Chen, Wei-Jie Lu, Qing-Yuan Cai, Yu-Xiang Zheng, and Liang-Yao Chen

Appl. Phys. Lett. 95, 161109 (2009); http://dx.doi.org/10.1063/1.3254183 (3 pages) | Cited 6 times

Online Publication Date: 23 October 2009

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The complex dielectric functions of Si-nanocrystals (nc-Si) with different sizes embedded in SiO2 matrix synthesized by SiOx/SiO2 superlattice approach is obtained by spectroscopic ellipsometry. The Maxwell–Garnett effective medium approximation and the Lorentz oscillator model are employed in the spectra fitting. The dependence of the dielectric functions on the nc-Si size is observed. A significant suppression in amplitude of the dielectric functions with respect to bulk crystalline silicon, and a large influence of the nc-Si size on the E1 and E2 critical points are observed and discussed.
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81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.05.Cy Elemental semiconductors
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
81.16.-c Methods of micro- and nanofabrication and processing
77.22.Ch Permittivity (dielectric function)

Efficient hole transport in asymmetric coupled InGaN multiple quantum wells

Jiang-Yong Zhang, Li-E Cai, Bao-Ping Zhang, Xiao-Long Hu, Fang Jiang, Jin-Zhong Yu, and Qi-Ming Wang

Appl. Phys. Lett. 95, 161110 (2009); http://dx.doi.org/10.1063/1.3254232 (3 pages) | Cited 9 times

Online Publication Date: 23 October 2009

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InGaN based light emitting devices (LEDs) with asymmetric coupled quantum wells (AS-QWs) and conventional symmetric coupled quantum wells (CS-QWs) active structures were grown by metal-organic chemical vapor deposition technique. The LEDs with AS-QWs active region show improved light emission intensity and reduced forward voltage compared with LEDs with CS-QWs active region. Based on the electroluminescence measurements and the devices structure analysis, it can be concluded that these improvements are mainly attributed to the efficient hole tunneling through barriers and consequently the uniform distribution of carriers in the AS-QWs.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

All-optical signal gating using ytterbium-doped fiber and a pair of thermally expanded core fibers

Linh Viet Nguyen and Youngjoo Chung

Appl. Phys. Lett. 95, 161111 (2009); http://dx.doi.org/10.1063/1.3233971 (3 pages) | Cited 1 time

Online Publication Date: 23 October 2009

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We report all-optical signal gating using ytterbium-doped fiber (YDF) and a pair of thermally expanded core fibers (TECFs). Splicing the YDF with two TECFs at their expanded-core ends, we obtained an interference pattern in the transmission spectrum of the device. When pumped by a laser diode at 980 nm, the interference fringes shift to longer wavelength due mainly to the resonantly enhanced nonlinearity of the YDF. Consequently, signals within the interference pattern can be gated or blocked all optically. Full gating of cw signals at 1564.21 and 1564.54 nm were obtained using a pump power of about 38.44 mW.
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42.82.Gw Other integrated-optical elements and systems
42.81.Bm Fabrication, cladding, and splicing
42.82.Cr Fabrication techniques; lithography, pattern transfer
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Real time monitoring of the interaction of Si (100) with atomic hydrogen: The “H-insertion/Si-etching” kinetic model explaining Si surface modifications

Giuseppe V. Bianco, Maria Losurdo, Maria M. Giangregorio, Pio Capezzuto, and Giovanni Bruno

Appl. Phys. Lett. 95, 161501 (2009); http://dx.doi.org/10.1063/1.3245312 (3 pages) | Cited 4 times

Online Publication Date: 20 October 2009

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The interaction of p- and n-type crystalline silicon [c-Si (100)], with atomic hydrogen produced by a remote radiofrequency (13.56 MHz) H2 plasma has been investigated in real time using in situ spectroscopic ellipsometry. The effects of substrate doping, temperature and time on the c-Si surface modifications are discussed. A thicker hydrogenated surface layer forms for n-type Si. This hydrogenated layer is subsequently etched by further exposure to hydrogen. A kinetic model based on the competition between hydrogen insertion and silicon etching is proposed to explain modifications of c-Si, and the rate constants of the hydrogen insertion and silicon etching processes are determined.
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81.65.Cf Surface cleaning, etching, patterning
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Nr Association, addition, insertion, cluster formation
68.47.Fg Semiconductor surfaces

Linear arrays of stable atmospheric pressure microplasmas

Zhi-Bo Zhang and Jeffrey Hopwood

Appl. Phys. Lett. 95, 161502 (2009); http://dx.doi.org/10.1063/1.3251793 (3 pages) | Cited 2 times

Online Publication Date: 20 October 2009

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Microdischarges produce cold atmospheric plasma when the discharge current is limited by the quenching of a microwave resonator. A quarter-wavelength microstripline resonator is shown to support stable atmospheric microplasma in pure argon. Electrical characterization of the microplasma shows that its impedance is resistive and capacitive (Zp = 500−j900 Ω). An array of these linear resonators generates a stable, line-shaped microplasma operating from a single power source due to close-coupling among adjacent resonators. Both simulations and experiments confirm that coupled-mode theory describes the collective behavior of linear microplasma arrays.
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52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges
52.25.Fi Transport properties
84.40.Az Waveguides, transmission lines, striplines
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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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Correlating dopant distributions and electrical properties of boron-doped silicon nanowires

Ruth A. Schlitz, Daniel E. Perea, Jessica L. Lensch-Falk, Eric R. Hemesath, and Lincoln J. Lauhon

Appl. Phys. Lett. 95, 162101 (2009); http://dx.doi.org/10.1063/1.3250431 (3 pages) | Cited 19 times

Online Publication Date: 19 October 2009

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Quantitative nonuniform radial doping profiles in vapor liquid solid grown boron-doped silicon nanowires are correlated with axial variations in electrical properties. Boron concentrations measured by atom probe tomography are lower for the core material grown from a gold catalyst than for material deposited on the nanowire surface. Transistors fabricated along a single nanowire exhibit a transition from nonlinear contact-dominated behavior to linear behavior with increasing thickness of the dopant-enriched surface layer. Simple models confirm that the surface is doped to a level that enables the contact resistance to become comparable to the channel resistance, suggesting that unintentional surface doping may play a role in lowering contact resistances in some nanowire devices.
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61.72.uf Ge and Si
85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
73.63.-b Electronic transport in nanoscale materials and structures
81.16.-c Methods of micro- and nanofabrication and processing
73.40.Cg Contact resistance, contact potential

n-type β-FeSi2/intrinsic-Si/p-type Si heterojunction photodiodes for near-infrared light detection at room temperature

Mahmoud Shaban, Shota Izumi, Keita Nomoto, and Tsuyoshi Yoshitake

Appl. Phys. Lett. 95, 162102 (2009); http://dx.doi.org/10.1063/1.3250171 (3 pages) | Cited 8 times

Online Publication Date: 20 October 2009

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n-Type β-FeSi2/intrinsic-Si/p-type Si heterojunctions, prepared by facing-targets direct-current sputtering, were evaluated as near-infrared photodetectors. The built-in potential was estimated to be approximately 1 V from capacitance-voltage characteristics. Diodes with a junction area of 0.03 mm2 exhibited a junction capacitance of 4.4 pF at zero bias. At room temperature, the devices exhibited responsivity of 140 mA/W and external quantum efficiency of 13% at a bias voltage of −5 V. The detectivity at zero bias was estimated to be 2.8×109 cm√Hz/W at the wavelength of 1.31 μm. These results indicate their high application potential as near-infrared photodiodes integrated with Si.
Show PACS
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.60.Dw Photodiodes; phototransistors; photoresistors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
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