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24 Aug 2009

Volume 95, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 082507 (2009); http://dx.doi.org/10.1063/1.3186782 (3 pages)

Sang-Koog Kim, Ki-Suk Lee, and Dong-Soo Han
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A ultraviolet-visible-near infrared photodetector using nanocrystalline Si superlattice

Zhenrui Yu and Mariano Aceves-Mijares

Appl. Phys. Lett. 95, 081101 (2009); http://dx.doi.org/10.1063/1.3210784 (2 pages) | Cited 4 times

Online Publication Date: 24 August 2009

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We report a simple silicon/Si nanocrystal superlattice/indium tin oxide structure as a photodetector, which shows a very high photosensitivity in a wide wavelength range from ultraviolet (UV) to near infrared. The fabrication of this photodetector structure is easily integrated into a standard process of Si microelectronics. The light and dark current versus voltage characteristics and photoluminescence of the photodetector show that the optical down-conversion of UV light by the superlattice layer is the main reason of the enhanced UV response.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Optical contrast and clarity of graphene on an arbitrary substrate

Xuefeng Wang, Ming Zhao, and David D. Nolte

Appl. Phys. Lett. 95, 081102 (2009); http://dx.doi.org/10.1063/1.3212735 (3 pages) | Cited 13 times

Online Publication Date: 24 August 2009

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A molecularly thin dielectric film on a multilayer substrate can be treated as an additive perturbation of the substrate reflection coefficient r, for which the perturbation depends only on r and the optical properties of the film. This general result is applied to the problem of graphene on arbitrary substrates that seek to maximize the film contrast. We define clarity to describe the graphene image quality in the presence of charge-coupled device noise. A substrate with r = 1 produces the highest graphene clarity in most practical situations.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
77.55.-g Dielectric thin films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Overcoming gain-bandwidth product constraint in slow light Raman amplification with the use of light-stopping schemes

Sunil Sandhu, Michelle L. Povinelli, and Shanhui Fan

Appl. Phys. Lett. 95, 081103 (2009); http://dx.doi.org/10.1063/1.3211126 (3 pages) | Cited 1 time

Online Publication Date: 25 August 2009

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We show that a light-stopping system with Raman amplification can overcome the gain-bandwidth constraint of slow light Raman amplification systems. The gain scales linearly with the time the pulse spends in the stopped state and is thus much larger than the gain experienced in a slow light system of the same length and operating bandwidth. We present a theoretical analysis of Raman amplification in such a light-stopping system and verify the results using numerical simulations.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.-e Optical elements, devices, and systems

A step forward toward smart white lighting: Combination of glass phosphor and light emitting diodes

L. H. C. Andrade, S. M. Lima, A. Novatski, A. Steimacher, J. H. Rohling, A. N. Medina, A. C. Bento, M. L. Baesso, Y. Guyot, and G. Boulon

Appl. Phys. Lett. 95, 081104 (2009); http://dx.doi.org/10.1063/1.3186784 (3 pages) | Cited 19 times

Online Publication Date: 25 August 2009

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We present our recent achievements of a glass able to produce smart white light combining a glass phosphor with light emitting diodes (LEDs). The combined emissions of Ce3+-doped calcium aluminosilicate glass and the 405 nm LED using the Commission Internationale de l’Éclairage 1931 chromatic diagram showed that this system presents an emission close to the ideal white light and allows tunability. In addition, the glass blue emission overlaps with the spectral range of the retinal photoreceptors involved in circadian responses. This glass combined with UV LED emission is suitable for circadian lights and therefore may contribute to improve environmental lighting and human well being.
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85.60.Jb Light-emitting devices
78.55.Hx Other solid inorganic materials

The correlation between electron density and anchoring strength in the inorganic vertical alignment layer

Byoung Har Hwang, Young Bum Yoo, Jin Young Oh, Soo Sang Chae, Hong Koo Baik, Se Jong Lee, and Kie Moon Song

Appl. Phys. Lett. 95, 081105 (2009); http://dx.doi.org/10.1063/1.3211117 (3 pages)

Online Publication Date: 26 August 2009

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The relationship between the liquid crystal (LC) alignment and the density of the silicon oxide alignment layer was studied by theoretical and experimental approaches. The thin films were deposited by various methods and conditions, and then their densities were analyzed by x-ray reflectivity measurement. The alignment of LC was highly dependent on their densities, which we found to be closely related to the number of interacting dipoles. Ultimately, a-SiOx thin film with lower density gives rise to the uniform vertical alignment of liquid crystal.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
68.15.+e Liquid thin films
61.20.-p Structure of liquids
81.15.Cd Deposition by sputtering

Double walled carbon nanotubes as ultrafast optical switches

N. Kamaraju, Sunil Kumar, Y. A. Kim, T. Hayashi, H. Muramatsu, M. Endo, and A. K. Sood

Appl. Phys. Lett. 95, 081106 (2009); http://dx.doi.org/10.1063/1.3213396 (3 pages) | Cited 4 times

Online Publication Date: 26 August 2009

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Pristine and molybdenum filled double walled carbon nanotubes (DWNTs) suspended in D2O show excellent ultrafast optical switching properties investigated through femtosecond Z-scan and degenerate pump-probe method using 50 fs pulses with central photon energy of 1.57 eV. For pristine-DWNT, the two photon absorption coefficient, β and nonlinear refraction coefficient, n2 are 4.9×10−8 cm/W, and 9.5×10−11 cm2/W, respectively, which yield one photon figure of merit, W = 133 and two photon figure of merit, T = 0.4. The degenerate pump-probe measurements show strong photoinduced bleaching with biexponential decay with time constants ∼ 150 and 600 fs.
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78.67.Ch Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Broadband blue superluminescent light-emitting diodes based on GaN

E. Feltin, A. Castiglia, G. Cosendey, L. Sulmoni, J.-F. Carlin, N. Grandjean, M. Rossetti, J. Dorsaz, V. Laino, M. Duelk, and C. Velez

Appl. Phys. Lett. 95, 081107 (2009); http://dx.doi.org/10.1063/1.3202786 (3 pages) | Cited 7 times

Online Publication Date: 26 August 2009

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We report on the achievement of III-nitride blue superluminescent light-emitting diodes on GaN substrates. The epitaxial structure includes an active region made of In0.12Ga0.88N quantum wells in a GaN/AlGaN waveguide. Superluminescence under cw operation is observed at room temperature for a current of 130 mA and a current density of 8 kA/cm2. The central emission wavelength is 420 nm and the emission bandwidth is ∼ 5 nm in the superluminescence regime. A peak optical output power of 100 mW is obtained at 630 mA under pulsed operation and an average power of 10 mW is achieved at a duty cycle of 20%.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Excitation-induced energy shifts in the optical gain spectra of InN quantum dots

M. Lorke, J. Seebeck, P. Gartner, F. Jahnke, and S. Schulz

Appl. Phys. Lett. 95, 081108 (2009); http://dx.doi.org/10.1063/1.3213543 (3 pages) | Cited 2 times

Online Publication Date: 27 August 2009

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A microscopic theory for the optical absorption and gain spectra of InN quantum-dot systems is used to study the combined influence of material properties and interaction-induced effects. Atomistic tight-binding calculations for the single-particle properties of the self-assembled quantum-dot and wetting-layer system are used in conjunction with a many-body description of Coulomb interaction and carrier phonon interaction. We analyze the carrier-density and temperature dependence of strong excitation-induced energy shifts of the dipole-allowed quantum-dot transitions.
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78.67.Hc Quantum dots
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.21.La Quantum dots
73.63.Kv Quantum dots
78.40.Fy Semiconductors

Single source coherent anti-Stokes Raman microspectroscopy using spectral focusing

Wolfgang Langbein, Israel Rocha-Mendoza, and Paola Borri

Appl. Phys. Lett. 95, 081109 (2009); http://dx.doi.org/10.1063/1.3216073 (3 pages) | Cited 10 times

Online Publication Date: 27 August 2009

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We demonstrate coherent anti-Stokes Raman scattering (CARS) microspectroscopy using a single Ti:sapphire laser oscillator and simple passive optical elements. Spectral selection by dichroic mirrors and linear chirping by glass elements creates a vibrational excitation tuneable over a large spectral range ( ∼ 800–2200 cm−1) with adjustable spectral resolution ( ∼ 10–100 cm−1). We furthermore demonstrate the applicability of differential CARS, enhancing the chemical selectivity, with the proposed single-laser configuration.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.79.Bh Lenses, prisms and mirrors

m-plane pure blue laser diodes with p-GaN/n-AlGaN-based asymmetric cladding and InGaN-based wave-guiding layers

You-Da Lin, Chia-Yen Huang, Matthew T. Hardy, Po Shan Hsu, Kenji Fujito, Arpan Chakraborty, Hiroaki Ohta, James S. Speck, Steven P. DenBaars, and Shuji Nakamura

Appl. Phys. Lett. 95, 081110 (2009); http://dx.doi.org/10.1063/1.3212146 (3 pages) | Cited 7 times

Online Publication Date: 27 August 2009

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Asymmetric p-GaN/n-AlGaN-cladded InGaN-based pure blue (440–460 nm) laser diodes were fabricated based on the nonpolar m-plane GaN technology. Simulation results showed high indium content (5%–10%) InGaN wave-guiding layers mainly contributed to the optical confinement, so that n-AlGan layer can be used to control of the peak position of the optical mode to achieve high optical confinement factor and low internal loss. By using this laser structure, lasing wavelengths of 443 and 465 nm with threshold current densities 14 and 19 kA/cm2, respectively, were demonstrated without facet coating.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Gn Optical waveguides and couplers

Efficient picosecond optical parametric oscillator based on periodically poled lithium tantalate

Kalyan V. Bhupathiraju, Joseph D. Rowley, and Feruz Ganikhanov

Appl. Phys. Lett. 95, 081111 (2009); http://dx.doi.org/10.1063/1.3216588 (3 pages) | Cited 2 times

Online Publication Date: 27 August 2009

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Generation of transform limited picosecond pulses continuously tunable across wavelengths in the near-infrared (995–1340 nm) and midinfrared (2.1–3.6 μm) range is demonstrated in an optical parametric oscillator (OPO) based on a periodically poled stoichiometric lithium tantalate crystal. The OPO, which is synchronously pumped by a mode-locked Ti:sapphire laser, delivers about 1 W in combined average power at a repetition rate of 74 MHz, which represents close to 45% extraction efficiency in output power. With wavelength and bandwidth controlled via an intracavity diffraction grating, about 2.7 ps pulses with 3.8–10.9 cm−1 bandwidth (full width at half maximum) were generated across the tuning range in the near-infrared thus making the OPO an optimal source for use in various nonlinear spectroscopy and microscopy applications that require high spectral resolution.
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42.65.Lm Parametric down conversion and production of entangled photons
42.79.Dj Gratings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Record pulsed power demonstration of a 2 μm GaSb-based optically pumped semiconductor laser grown lattice-mismatched on an AlAs/GaAs Bragg mirror and substrate

J. M. Yarborough, Yi-Ying Lai (賴奕穎), Yushi Kaneda (金田有史), Jörg Hader, Jerome V. Moloney, T. J. Rotter, G. Balakrishnan, C. Hains, D. Huffaker, S. W. Koch, and R. Bedford

Appl. Phys. Lett. 95, 081112 (2009); http://dx.doi.org/10.1063/1.3212891 (3 pages) | Cited 3 times

Online Publication Date: 27 August 2009

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An optically pumped semiconductor laser resonant periodic gain structure, grown lattice-mismatched on an AlAs/GaAs Bragg mirror, exhibits a peak pulsed power of 70 W when pumped with a pulsed 1064 nm neodymium doped yttrium aluminum garnet laser.
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42.55.Px Semiconductor lasers; laser diodes
42.82.-m Integrated optics
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings

Practical B and P doping via SixSnyGe1−x−y−zMz quaternaries lattice matched to Ge: Structural, electrical, and strain behavior

Y.-Y. Fang, J. Tolle, A. V. G. Chizmeshya, J. Kouvetakis, V. R. D’Costa, and J. Menendez

Appl. Phys. Lett. 95, 081113 (2009); http://dx.doi.org/10.1063/1.3204456 (3 pages)

Online Publication Date: 28 August 2009

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We describe the fabrication of B and P doped SiGeSn ternaries, lattice-matched to Ge, with compositions adjusted to independently tune the band gap. These are deposited at 320–350 °C with superior crystallinity and morphology via in situ reactions of diborane (p-type) and designer P(SiH3)3 and P(GeH3)3 precursors (n-type). Device-level carrier concentrations in the 1019–1020/cm3 range are produced yielding film resistivities and carrier mobilities comparable to those of Ge indicating negligible alloy scattering. High boron levels induce a significant and systematic contraction of the host lattice, which is compensated by an adjustment of the Sn/Si ratio in accord with a simple model based on Vegard’s law, the mismatch of covalent radii of the constituents, and the absolute hydrostatic deformation potentials for the band edges.
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61.72.up Other materials
73.61.Le Other inorganic semiconductors
71.20.Nr Semiconductor compounds
72.20.Fr Low-field transport and mobility; piezoresistance
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Rate equation analysis of efficiency droop in InGaN light-emitting diodes

Han-Youl Ryu, Hyun-Sung Kim, and Jong-In Shim

Appl. Phys. Lett. 95, 081114 (2009); http://dx.doi.org/10.1063/1.3216578 (3 pages) | Cited 38 times

Online Publication Date: 28 August 2009

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Efficiency droop in InGaN light-emitting diodes (LEDs) is analyzed based on the rate equation model. By using the peak point of the efficiency versus current-density relation as the parameters of the rate equation analysis, internal quantum efficiency and each recombination current at arbitrary current density can be unambiguously determined without any knowledge of A, B, and C coefficients. The theoretical analysis is compared with measured efficiency of a LED sample and good agreement between the model and experiment is found. The investigation of recombination coefficients shows that Auger recombination alone is not sufficient to explain the efficiency droop of InGaN LEDs.
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85.60.Jb Light-emitting devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Flow shaping using three-dimensional microscale gas discharge

Chin-Cheng Wang and Subrata Roy

Appl. Phys. Lett. 95, 081501 (2009); http://dx.doi.org/10.1063/1.3216046 (3 pages) | Cited 2 times

Online Publication Date: 28 August 2009

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We introduce a flow shaping mechanism using surface compliant microscale gas discharge. A three-dimensional finite element-based multiscale ionized gas flow code is utilized to analyze charge separation, potential distribution, and flow inducement mechanism. For the case of quiescent flow, a horseshoe-shaped plasma generator is introduced. Due to its unusual shape, the three-dimensional electric force excites a pinching effect on the fluid inside selectively powered electrode arc. Such effect is capable of tripping the flow-ejecting fluid normal to the plane of the actuator and thus can be very useful for many applications.
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52.30.-q Plasma dynamics and flow
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.50.Nr Plasma heating by DC fields; ohmic heating, arcs
52.58.Lq Z-pinches, plasma focus, and other pinch devices
02.70.Dh Finite-element and Galerkin methods
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Prediction of ordering and spontaneous rotation of epitaxial habits in substrate-coherent InGaN and GaAsSb

Jefferson Zhe Liu, Giancarlo Trimarchi, and Alex Zunger

Appl. Phys. Lett. 95, 081901 (2009); http://dx.doi.org/10.1063/1.3200234 (3 pages)

Online Publication Date: 24 August 2009

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Coherently strained In0.5Ga0.5N on GaN and CaO substrates are theoretically predicted to show stable ordering in the chalcopyrite structure, as is Ga2AsSb on GaAs and InP substrates. Depending on the substrate and the film concentration, we predict a spontaneous rotation of the stablest chalcopyrite film axis from perpendicular to parallel to the (001) substrate.
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68.55.ag Semiconductors
68.35.bg Semiconductors
81.65.-b Surface treatments

Flexoelectric studies on mixtures of compounds made of rodlike and bent-core molecules

Brindaban Kundu, Arun Roy, R. Pratibha, and N. V. Madhusudana

Appl. Phys. Lett. 95, 081902 (2009); http://dx.doi.org/10.1063/1.3213544 (3 pages) | Cited 5 times

Online Publication Date: 24 August 2009

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We report measurements of the temperature variations of the flexoelastic ratio (e1−e3)/K of octadecyl cyanobiphenyl and a mixture of this compound with another one with bent-core (BC) molecules, using hybrid aligned nematic cells. Addition of 5 mol % of the BC compound doubles the flexoelastic ratio, implying that the BC compound has ∼ 20 times larger value compared to that of the compound with calamitic molecules. Mixtures with >11 mol % of the BC compound exhibit only a homeotropic alignment. We develop a simple model to account for this result which arises because of a large positive self-energy due to flexoelectric polarization.
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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

Transmission electron microscopy investigation of microtwins and double positioning domains in (111) 3C-SiC in relation with the carbonization conditions

S. Roy, M. Portail, T. Chassagne, J. M. Chauveau, P. Vennéguès, and M. Zielinski

Appl. Phys. Lett. 95, 081903 (2009); http://dx.doi.org/10.1063/1.3202783 (3 pages) | Cited 6 times

Online Publication Date: 24 August 2009

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In this work, transmission electron microscopy is used to investigate the influence of the carbonization conditions on the formation of crystal defects in 3C-SiC layers deposited on (111) silicon. We focus on two kinds of defects; (1) the stacking faults and microtwins lying in the (mathmath1) planes, and (2) the double positioning domains. While the density of the stacking faults and microtwins is found independent on the carbonization conditions, the size of the double positioning domains is strongly influenced by the propane flow rate and can be related to the substrate sealing at the early stage of carbonization.
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71.55.Ht Other nonmetals
61.72.Mm Grain and twin boundaries
68.37.Og High-resolution transmission electron microscopy (HRTEM)
61.72.Nn Stacking faults and other planar or extended defects

Highly dense amorphous Nb2O5 films with closed nanosized pores

M. Vinnichenko, A. Rogozin, D. Grambole, F. Munnik, A. Kolitsch, W. Möller, O. Stenzel, S. Wilbrandt, A. Chuvilin, and U. Kaiser

Appl. Phys. Lett. 95, 081904 (2009); http://dx.doi.org/10.1063/1.3212731 (3 pages) | Cited 1 time

Online Publication Date: 24 August 2009

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This study is focused on tailoring the porosity of Nb2O5 films during reactive pulsed magnetron sputtering. Dense amorphous films containing nanopores only in deeper regions have been grown at a high rate using substrate temperatures below 60 °C. The films exhibit a high refractive index, n400 = 2.54, a low extinction coefficient, k400 ∼ 6×10−4, a low mechanical stress (−90 MPa), and a negligible thermal shift. The specific depth distribution of the nanopores is believed to be the reason for the optimum trade-off between a high refractive index and low mechanical stress.
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68.55.-a Thin film structure and morphology
61.43.Gt Powders, porous materials
62.25.-g Mechanical properties of nanoscale systems
81.15.Cd Deposition by sputtering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Jg Amorphous semiconductors; glasses
61.46.-w Structure of nanoscale materials

Investigation on the role of nitrogen in crystallization of Sb-rich phase change materials

Jihoon Choi, Hyun Seok Lee, Taek Sung Lee, Suyoun Lee, Won Mok Kim, Donghwan Kim, and Byung-ki Cheong

Appl. Phys. Lett. 95, 081905 (2009); http://dx.doi.org/10.1063/1.3211871 (3 pages) | Cited 5 times

Online Publication Date: 26 August 2009

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To better understand the role of nitrogen (N) during crystallization of Sb-rich phase change materials, a study was conducted using Sb and Sb70Te30 as host materials of N. Crystallization of the as-sputtered Sb–N films of varying N content was examined to reveal that Sb–N bonds are formed in the as-sputtered states, enhancing amorphous phase stability increasingly with N content. Crystallization appeared to proceed with irreversible dissociation of these bonds to form N2 molecules that may then exist stably during the subsequent memory operations. N2 molecules are considered to play as growth-retarding agents as demonstrated with memory operations of N-doped Sb70Te30.
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64.70.dg Crystallization of specific substances
42.70.-a Optical materials
61.43.Er Other amorphous solids
61.72.up Other materials
68.55.aj Insulators
81.15.Cd Deposition by sputtering

Strain balanced InAs/InAsSb superlattice structures with optical emission to 10 μm

D. Lackner, O. J. Pitts, M. Steger, A. Yang, M. L. W. Thewalt, and S. P. Watkins

Appl. Phys. Lett. 95, 081906 (2009); http://dx.doi.org/10.1063/1.3216041 (3 pages) | Cited 8 times

Online Publication Date: 26 August 2009

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We report the growth and optical characterization of InAsSb/InAs strain balanced superlattice structures on GaSb substrates for potential application in midinfrared photodetectors. Photoluminescence (PL) emission was observed in the range 5 μm ≤ λ ≤ 10 μm at 4 K for Sb compositions 0.14 ≤ xSb ≤ 0.27. The PL energy was found to depend approximately linearly on antimony, consistent with a type II band lineup. The dependence of the emission energies on the Sb mole fraction is in agreement with trends predicted by various theoretical works. The data suggest that this transition reaches zero energy for a composition of xSb = 0.37.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Toward an ideal Schottky barrier on 3C-SiC

Jens Eriksson, Ming Hung Weng, Fabrizio Roccaforte, Filippo Giannazzo, Stefano Leone, and Vito Raineri

Appl. Phys. Lett. 95, 081907 (2009); http://dx.doi.org/10.1063/1.3211965 (3 pages) | Cited 9 times

Online Publication Date: 27 August 2009

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The electrical characteristics of Au/3C-SiC Schottky diodes were studied as a function of contact area. While the larger diodes were characterized by conventional current-voltage measurements, conductive atomic force microscopy was used to perform current-voltage measurements on diodes of contact radius down to 5 μm. The results show that the Schottky barrier height increases upon reducing the contact area, and for the smallest diodes the value approaches the ideal barrier height of the system. The results were correlated with defects in the 3C-SiC and an analytical expression was derived to describe the dependence of the barrier height on the defect density.
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85.30.Kk Junction diodes
73.40.Ns Metal-nonmetal contacts
85.30.De Semiconductor-device characterization, design, and modeling
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Hi Surface barrier, boundary, and point contact devices

Enhanced plasticity in a Zr-based bulk metallic glass composite with in situ formed intermetallic phases

G. Chen, H. Bei, Y. Cao, A. Gali, C. T. Liu, and E. P. George

Appl. Phys. Lett. 95, 081908 (2009); http://dx.doi.org/10.1063/1.3211912 (3 pages) | Cited 8 times

Online Publication Date: 28 August 2009

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An in situ formed intermetallic phase/bulk metallic glass composite with high strength and good plasticity was fabricated by casting Zr55.0Cu29.0Ni8.0Al8.0 melts. In situ formed tetragonal structured (Zr,Ni,Al)2(Cu,Ni,Al) intermetallic particles with a hardness of 9.6±0.3 GPa improve the fracture strength of the composite. Micrographs of the fractured samples reveal that the shear band spacing is smaller than the intermetallic particles, indicating that they can effectively block shear band propagation before catastrophic fracture.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
61.43.Fs Glasses
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
81.20.-n Methods of materials synthesis and materials processing
81.05.Pj Glass-based composites, vitroceramics
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Threshold field of phase change memory materials measured using phase change bridge devices

Daniel Krebs, Simone Raoux, Charles T. Rettner, Geoffrey W. Burr, Martin Salinga, and Matthias Wuttig

Appl. Phys. Lett. 95, 082101 (2009); http://dx.doi.org/10.1063/1.3210792 (3 pages) | Cited 26 times

Online Publication Date: 24 August 2009

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The threshold switching effect of phase change memory devices is typically parameterized by the threshold voltage at which this breakdown occurs. Using phase change memory bridge devices of variable length, we prove unambiguously that the important parameter for threshold switching is a critical electrical field and not a threshold voltage. By switching phase change bridge devices from the amorphous-as-deposited state, we obtain threshold fields for Ge15Sb85, Ag- and In-doped Sb2Te, Ge2Sb2Te5, and 4 nm thick Sb devices of 8.1, 19, 56, and 94 V/μm, respectively.
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81.90.+c Other topics in materials science (restricted to new topics in section 81)
42.70.-a Optical materials

Softening of the tunneling gap in modulation-doped GaAs/AlGaAs asymmetric coupled double quantum wells in magnetic fields

Y. H. Shin, Y. H. Park, C. H. Perry, J. A. Simmons, T. Takamasu, and Yongmin Kim

Appl. Phys. Lett. 95, 082102 (2009); http://dx.doi.org/10.1063/1.3213352 (3 pages)

Online Publication Date: 24 August 2009

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Magnetophotoluminescence emissions were measured from modulation doped GaAs/AlGaAs asymmetric double quantum wells, wherein a thin barrier (25 Å) was sandwiched between a single quantum well (SQW) and a single heterojuction (SHJ). In the SQW, Landau level mixing is observed at the quantum Hall states. At ν<2, the lowest Landau level transition undergoes an exciton transition. For the SHJ region, the free carrier transitions become excitonic at the crossing point of the GaAs free exciton and the tunneling band gap shows a marked softening. An exciton-exciton interaction is shown to be responsible for the behavior of the subband energy levels in magnetic fields.
Show PACS
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
81.07.St Quantum wells
78.67.De Quantum wells
78.20.Ls Magneto-optical effects
71.35.-y Excitons and related phenomena
73.21.Fg Quantum wells
73.43.Jn Tunneling
71.70.Di Landau levels
73.40.Gk Tunneling
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