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19 Jun 2006

Volume 88, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 251907 (2006); http://dx.doi.org/10.1063/1.2216885 (3 pages)

Martin Maldovan and Edwin L. Thomas
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Silver-halide segmented cladding fibers for the middle infrared

Arnon Millo, Itay Naeh, Yaron Lavi, and Abraham Katzir

Appl. Phys. Lett. 88, 251101 (2006); http://dx.doi.org/10.1063/1.2213958 (3 pages) | Cited 10 times

Online Publication Date: 19 June 2006

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There is a wide interest in single-mode optical fibers for the middle infrared range of 3–30 μm. These fibers will be useful for a variety of applications such as spatial filtering and interferometry. However, many technical and theoretical problems hindered the development of such fibers. Segmented cladding fibers may make it possible to combine an extremely large core area and single mode operation over a large spectral range. The design parameters may accurately control the optical properties of such fibers. We report here the design and fabrication of segmented cladding fibers made of crystalline silver halides, which are highly transparent in the middle infrared.
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42.81.Bm Fabrication, cladding, and splicing
42.15.Eq Optical system design

Improving crystal quality of InGaAs/GaAs quantum dots by inductively coupled Ar plasma

D. Nie, T. Mei, H. S. Djie, B. S. Ooi, and X. H. Zhang

Appl. Phys. Lett. 88, 251102 (2006); http://dx.doi.org/10.1063/1.2215602 (3 pages) | Cited 1 time

Online Publication Date: 19 June 2006

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The crystal quality of InGaAs/GaAs quantum dots (QDs) is substantially improved without redistribution of composition using inductively coupled Ar plasma exposure. After plasma exposure, the QDs exhibit an increase in photoluminescence intensity by a factor of 1.7 while keeping the peak wavelength unshifted, and the band gap blueshift after rapid thermal annealing is suppressed, denoting an improvement in thermal stability. The time-resolved photoluminescence shows an increase in carrier lifetime from 735 to 1140 ps by plasma exposure, indicating the mechanism of grown-in defects reduction in the QD regions.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
52.77.-j Plasma applications
61.72.Cc Kinetics of defect formation and annealing

Enhanced electron field emission from oriented columnar AlN and mechanism

A. P. Huang, Paul K. Chu, and X. L. Wu

Appl. Phys. Lett. 88, 251103 (2006); http://dx.doi.org/10.1063/1.2216353 (3 pages) | Cited 4 times

Online Publication Date: 19 June 2006

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(002) oriented AlN thin films with a columnar microstructure fabricated by vapor phase deposition with a sample bias exhibit excellent field emission properties. The field emission current density increases with smaller film thickness, and at a thickness of 400 nm, the current density reaches 9.9 μA/cm2 and the turn-on field is close to 5 V/μm. Atomic force microscopy discloses nanoscale protrusions on the surface that greatly expand the emission area and efficiency. The Fowler-Nordheim plot reveals a linear dependence under low electric field (<17 V/μm), suggesting that the emission current originates from the quantum tunneling effect.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.Ey III-V semiconductors
73.40.Gk Tunneling
68.47.Fg Semiconductor surfaces

Fabrication of two-dimensional metallodielectric quasicrystals by single-beam holography

Yi Yang, Suhuai Zhang, and Guo Ping Wang

Appl. Phys. Lett. 88, 251104 (2006); http://dx.doi.org/10.1063/1.2216871 (3 pages) | Cited 11 times

Online Publication Date: 20 June 2006

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We experimentally demonstrate a single-beam holography for creating Ag nanoparticle-embedded eight-fold quasicrystals. By adjusting the phase relation of interference beams through an optical mask, we obtain eight-fold symmetry structures with three different profiles. The structure of quasicrystals is confirmed through scanning electron microscopy and optical diffraction pattern, respectively. Furthermore, we also numerically demonstrate that the method can encode even higher symmetric structures such as the most complex 14- and 18-fold quasicrystals as well by computer simulations.
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42.40.Kw Holographic interferometry; other holographic techniques
42.70.-a Optical materials
42.86.+b Optical workshop techniques

Si nanocrystals in a distributed feedback laser cavity

K. Dohnalová, I. Pelant, P. Gilliot, O. Crégut, and B. Hönerlage

Appl. Phys. Lett. 88, 251105 (2006); http://dx.doi.org/10.1063/1.2216888 (3 pages) | Cited 6 times

Online Publication Date: 20 June 2006

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We investigate an optically induced distributed-feedback cavity, containing a densely packed luminescent silicon nanocrystal layer in a SiO2 based matrix as active medium. In the presence of optical feedback, we have observed a nonlinear increase in the spectrally resolved emission intensity on the blue emission wing, which consists of two main contributions: (i) a broad amplified region around 550 nm, showing fast photoluminescence decay around 100 ns, depending on the excitation intensity, and (ii) a narrower peak located at about 580 nm. The latter exhibits a spectral shift, which varies with the cavity tuning.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking

Strong circular Bragg phenomena in self-ordered porous helical nanorod arrays of Alq3

Peter C. P. Hrudey, Bryan Szeto, and Michael J. Brett

Appl. Phys. Lett. 88, 251106 (2006); http://dx.doi.org/10.1063/1.2216903 (3 pages) | Cited 18 times

Online Publication Date: 20 June 2006

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Porous chiral thin films composed of a nearly hexagonal-close-packed array of helical nanorods of tris-(8-hydroxyquinoline) aluminum (Alq3) are fabricated using glancing angle deposition and exhibit a one-dimensional polarization-dependent photonic stop band. These chiral thin films transmit only one handedness of circularly polarized light and emit highly circularly polarized photoluminescence. The strong circular Bragg phenomena exhibited by these films suggest potential for use of these films in low-threshold mirrorless lasing and circularly polarized emission applications, while the porosity of the films allows for infiltration by dyes or liquid crystals to enable the formation of unique hybrid materials.
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78.66.Qn Polymers; organic compounds
78.55.Mb Porous materials
78.20.Ek Optical activity
42.70.Jk Polymers and organics
42.70.Qs Photonic bandgap materials

Origin of detection wavelength tuning in quantum dots-in-a-well infrared photodetectors

Nenad Vukmirović, Dragan Indjin, Zoran Ikonić, and Paul Harrison

Appl. Phys. Lett. 88, 251107 (2006); http://dx.doi.org/10.1063/1.2216920 (3 pages) | Cited 14 times

Online Publication Date: 20 June 2006

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A theoretical investigation is performed in order to understand the origin of change of the operating wavelength of quantum dots-in-a-well photodetectors when the well width is varied. The energy levels and wave functions were found using the eight-band strain dependent k∙p model and the intraband optical absorption spectrum was calculated in the dipole approximation within the framework of first order perturbation theory. It was found that the pure effect of changes of well width cannot be responsible for the shifts of the peaks observed in experiment [ Raghavan et al., J. Appl. Phys. 96, 1036 (2004) ], which are therefore ascribed to unintentional changes in dot dimensions.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Electro-optical sampling at near-zero optical bias

Yuelin Li

Appl. Phys. Lett. 88, 251108 (2006); http://dx.doi.org/10.1063/1.2214143 (3 pages) | Cited 1 time

Online Publication Date: 20 June 2006

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We report a detailed study of distortion effects in electro-optical sampling measurement at near-zero optical bias. It is found that when the induced optical retardation has a dynamic range larger than the optical bias, a false polarity change of the field can be observed merely due to the amplitude change of the field under investigation. The distortion cannot be corrected in general. However, when the optical bias is known, this phenomenon can be exploited to derive the absolute field amplitude under study.
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07.60.-j Optical instruments and equipment

Dependence of saturation effects on electron confinement and injector doping in GaAs/Al0.45Ga0.55As quantum-cascade lasers

S. Höfling, V. D. Jovanović, D. Indjin, J. P. Reithmaier, A. Forchel, Z. Ikonić, N. Vukmirović, P. Harrison, A. Mirčetić, and V. Milanović

Appl. Phys. Lett. 88, 251109 (2006); http://dx.doi.org/10.1063/1.2214128 (3 pages) | Cited 3 times

Online Publication Date: 21 June 2006

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We report on a detailed experimental and theoretical analysis of the role of injector doping density on both the threshold current density (Jth) and the saturation current density (Jsat), determining the dynamic range of the quantum cascade lasers. The experimental results were obtained from two growth series of λ ≈ 9 μm GaAs/Al0.45Ga0.55As quantum-cascade lasers based on single and double phonon resonance depopulation mechanisms. We derive a quasilinear dependence of Jth on the injector doping density of both designs for doping range as wide as (4–10)×1011 cm−2. Despite threshold current increase the faster rise of saturation current with doping results in an enhanced dynamic range for injector doping up to ∼ 8×1011 cm−2. For higher doping levels, Jsat itself saturates. Furthermore, our investigations yield that single phonon resonance devices exhibit clear current saturation simultaneously with a decrease of the optical power, whereas two phonon resonance devices show only power saturation, which we attribute to increased leakage currents. These deteriorate the laser performance of the latter design at higher operational temperatures.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
61.72.uj III-V and II-VI semiconductors

Efficient white-light-emitting diodes based on poly(N-vinylcarbazole) doped with blue fluorescent and orange phosphorescent materials

Ping-I Shih, Ching-Fong Shu, Yung-Liang Tung, and Yun Chi

Appl. Phys. Lett. 88, 251110 (2006); http://dx.doi.org/10.1063/1.2214141 (3 pages) | Cited 85 times

Online Publication Date: 21 June 2006

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We have fabricated polymer white-light-emitting devices possessing a single emitting layer containing a hole-transporting host polymer, poly(N-vinylcarbazole), and an electron-transporting auxiliary, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, doped with a blue-light-emitting amino-substituted distyrylarylene fluorescent dye and an orange-light-emitting osmium phosphor. The doubly doped device exhibited an intense white emission having Commission Internationale de l’Eclairage coordinates of (0.33, 0.34), a high external quantum efficiency of 6.12% (13.2 cd/A), and a maximum brightness of 11 306 cd/m2. The color coordinates remained unchanged over a range of operating voltages, even at luminance as high as 1×104 cd/m2.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics

Zinc oxide nanodonut prepared by vapor-phase transport process

Liang-Chiun Chao, Ping-Chang Chiang, Shih-Hsuan Yang, Jian-Wei Huang, Chung-Chi Liau, Jyh-Shin Chen, and Chien-Ying Su

Appl. Phys. Lett. 88, 251111 (2006); http://dx.doi.org/10.1063/1.2214146 (3 pages) | Cited 3 times

Online Publication Date: 21 June 2006

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Zinc oxide nanodonuts have been synthesized using vapor-phase transport method. Zinc oxide powder, graphite powder, and erbium oxide powder were mixed with a molar ratio of 1:1:0.2 and heated at 1050 °C in a flowing argon environment. Perfectly donut-shaped nanostructures with outer diameters ranging from 450 to 850 nm were observed. The inner diameter of the zinc oxide donut varies from 75 to 95 nm and the vertical distance from the highest point to the lowest point vary from 85 to 130 nm. The composition of the nanodonut was analyzed using Auger electron spectroscopy and was found to be mainly of zinc oxide. Diffusion of silicon into the zinc oxide layer was confirmed by secondary ion mass spectroscopy.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Dz II-VI semiconductors
81.16.Hc Catalytic methods
61.46.-w Structure of nanoscale materials
66.30.Pa Diffusion in nanoscale solids
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Laser noise reduction in air

Pierre Béjot, Jérôme Kasparian, Estelle Salmon, Roland Ackermann, Nicolas Gisin, and Jean-Pierre Wolf

Appl. Phys. Lett. 88, 251112 (2006); http://dx.doi.org/10.1063/1.2216402 (3 pages) | Cited 4 times

Online Publication Date: 21 June 2006

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Fluctuations of the white-light supercontinuum produced by ultrashort laser pulses in self-guided filaments (spatiotemporal solitons) in air are investigated. We demonstrate that correlations exist within the white-light supercontinuum, and that they can be used to significantly reduce the laser intensity noise by filtering the spectrum. More precisely, the fundamental wavelength is anticorrelated with the wings of the continuum, while conjugated wavelength pairs on both sides of the continuum are strongly correlated. Spectral filtering of the continuum reduces the laser intensity noise by 1.2 dB, showing that fluctuations are rejected to the edges of the spectrum.
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42.65.Tg Optical solitons; nonlinear guided waves
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
42.50.Lc Quantum fluctuations, quantum noise, and quantum jumps

Stable polarization gratings recorded in azo-dye-doped liquid crystals

Suraj P. Gorkhali, Sylvain G. Cloutier, Gregory P. Crawford, and Robert A. Pelcovits

Appl. Phys. Lett. 88, 251113 (2006); http://dx.doi.org/10.1063/1.2214176 (3 pages) | Cited 19 times

Online Publication Date: 22 June 2006

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We report on the design, fabrication, electro-optical performance, and stability of switchable polarization gratings formed in azo-dye-doped nematic liquid crystals. Stable gratings are demonstrated even after applying saturating electric fields (8 V/μm) and after heating to extreme temperatures (T = 190 °C). A simple phenomenological model is presented to show that the Freedericksz threshold voltage depends on surface and volume contributions. The observed thresholdless behavior indicates that the grating stability is consistent with a surface-stabilizing effect.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
61.30.-v Liquid crystals

Strong enhancement of Er3+ emission at room temperature in silicon-on-insulator photonic crystal waveguides

M. Galli, A. Politi, M. Belotti, D. Gerace, M. Liscidini, M. Patrini, L. C. Andreani, M. Miritello, A. Irrera, F. Priolo, and Y. Chen

Appl. Phys. Lett. 88, 251114 (2006); http://dx.doi.org/10.1063/1.2214180 (3 pages) | Cited 13 times

Online Publication Date: 22 June 2006

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We have realized silicon-on-insulator photonic crystal (PhC) waveguides with intense 1.54 μm emission at room temperature. The slabs contain a thin layer of SiO2 with Er3+ doped silicon nanoclusters embedded at the center of the Si core and are patterned with a triangular lattice of holes. An enhancement by more than two orders of magnitude of the Er3+ near-normal emission is observed when the transition is in resonance with an appropriate mode of the PhC slab. The results are in very good agreement with calculated photonic bands and emission spectra. These findings are important for the realization of Si-compatible efficient light emitters at telecom wavelengths.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
78.55.Hx Other solid inorganic materials

Guided-mode resonance Brewster filters with multiple channels

Zhanshan Wang, Tian Sang, Li Wang, Jingtao Zhu, Yonggang Wu, and Lingyan Chen

Appl. Phys. Lett. 88, 251115 (2006); http://dx.doi.org/10.1063/1.2215610 (3 pages) | Cited 20 times

Online Publication Date: 22 June 2006

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In this letter, a type of guided-mode resonance (GMR) reflection filter incorporating multimode resonance and the Brewster effect is presented. Long-range, low sidebands, and multiple channels are found to be obtainable for a single-layer GMR reflection filter with a TM-polarized plane wave incident at the Brewster angle. Detailed characteristics are calculated using rigorous coupled-wave analysis. In our calculation, for TM-polarized incident wave, we find it sufficiently accurate to calculate the effect index by using the zero-order permittivity ε0,TM of the effective media theory, and narrowband multichannel reflectance can be achieved at the Brewster angle by tuning the grating depth.
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42.79.Ci Filters, zone plates, and polarizers
42.15.Eq Optical system design

Low resistivity p-ZnO films fabricated by sol-gel spin coating

Yongge Cao, Lei Miao, Sakae Tanemura, Masaki Tanemura, Yohei Kuno, and Yasuhiko Hayashi

Appl. Phys. Lett. 88, 251116 (2006); http://dx.doi.org/10.1063/1.2215618 (3 pages) | Cited 39 times

Online Publication Date: 22 June 2006

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N-doped and In-N-codoped ZnO films were fabricated on quartz glass substrate by sol-gel spin coating. Their p-type conductivities were characterized by the Hall measurements, revealing low resistivities of the order of 10−1 Ω cm. Thin-film junctions comprising an undoped ZnO layer and a N-doped ZnO layer displayed the typical rectifying characteristics, suggesting formation of p-n homojunctions at the interfaces.
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73.61.Ga II-VI semiconductors
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Ei Rectification
61.72.uj III-V and II-VI semiconductors

Tunable watt-level blue-green vertical-external-cavity surface-emitting lasers by intracavity frequency doubling

Li Fan, Ta-Chen Hsu, Mahmoud Fallahi, James T. Murray, Robert Bedford, Yushi Kaneda, Jörg Hader, Aramais R. Zakharian, Jerome V. Moloney, Stephan W. Koch, and Wolfgang Stolz

Appl. Phys. Lett. 88, 251117 (2006); http://dx.doi.org/10.1063/1.2215635 (3 pages) | Cited 23 times

Online Publication Date: 23 June 2006

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We report on the development and the demonstration of a tunable, watt-level, blue-green, linearly polarized vertical-external-cavity surface-emitting lasers operating around 488 nm by intracavity second-harmonic generation. By using lithium triborate crystal, we have achieved over 1.3 W continuous wave blue-green power at 488 nm with a 5 nm tunability.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Temperature dependent characteristics of λ ∼ 3.8 μm room-temperature continuous-wave quantum-cascade lasers

J. S. Yu, A. Evans, S. Slivken, S. R. Darvish, and M. Razeghi

Appl. Phys. Lett. 88, 251118 (2006); http://dx.doi.org/10.1063/1.2216024 (3 pages) | Cited 53 times

Online Publication Date: 23 June 2006

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Temperature dependent characteristics of λ ∼ 3.8 μm quantum-cascade lasers (QCLs) operating up to 318 K in continuous-wave (cw) mode are reported. A high-reflectivity coated 11.5-μm-wide and 4-mm-long epilayer-down bonded QCL using a diamond submount shows a considerable improved cw operation with an output power of 143 mW and a threshold current density of 1.51 kA/cm2 at 298 K. The temperature dependence on optical and electrical performances of the QCLs with respect to the output power, slope efficiency, threshold current/voltage, turn-on voltage, differential series resistance, and emission wavelength are investigated systematically above liquid nitrogen temperature.
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42.55.Px Semiconductor lasers; laser diodes

Enhanced terahertz detection via ErAs:GaAs nanoisland superlattices

John F. O’Hara, J. M. O. Zide, A. C. Gossard, A. J. Taylor, and R. D. Averitt

Appl. Phys. Lett. 88, 251119 (2006); http://dx.doi.org/10.1063/1.2216026 (3 pages) | Cited 16 times

Online Publication Date: 23 June 2006

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We demonstrate enhanced terahertz detection using photoconductive antennas based on self-assembled ErAs:GaAs nanoisland superlattices. Three detectors are compared; one each fabricated on low-temperature grown GaAs, radiation-damaged silicon-on-sapphire, and an ErAs:GaAs superlattice. The ErAs:GaAs based detector shows a strong enhancement in terahertz detection efficiency with respect to incident optical power, though optical saturation occurs more rapidly. Detected terahertz bandwidth and signal-to-noise ratios are simultaneously maintained or improved.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Terahertz pulse propagation using plasmon-polariton-like surface modes on structured conductive surfaces

Stefan A. Maier and Steve R. Andrews

Appl. Phys. Lett. 88, 251120 (2006); http://dx.doi.org/10.1063/1.2216105 (3 pages) | Cited 26 times

Online Publication Date: 23 June 2006

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The dispersion relation and confinement of plasmon-polariton-like terahertz surface modes sustained by a perfectly conducting planar surface patterned with a regular lattice of holes are studied using full-field three-dimensional numerical simulations. Edge coupling and subsequent surface guiding with subwavelength vertical confinement of the frequency components below the band edge of the surface mode is demonstrated for a broadband pulse with 0.5 THz ⩽ f ⩽ 2 THz. Additionally, the constraints imposed by lattice constant and hole size on the creation of defect waveguides offering lateral confinement are discussed.
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78.68.+m Optical properties of surfaces
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
41.20.Jb Electromagnetic wave propagation; radiowave propagation
42.79.Gn Optical waveguides and couplers
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Breakdown voltages for discharges initiated from plasma pulses produced by high-frequency excimer lasers

Michiteru Yamaura

Appl. Phys. Lett. 88, 251501 (2006); http://dx.doi.org/10.1063/1.2216896 (3 pages) | Cited 2 times

Online Publication Date: 20 June 2006

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The triggering ability under the different electric field was investigated using a KrF excimer laser with a high repetition rate of kilohertz order. Measurements were made of the magnitude of impulse voltages that were required to initiate a discharge from plasmas produced by a high-frequency excimer laser. Breakdown voltages were found to be reduced by 50% through the production of plasmas in the discharge gap by a high-frequency excimer laser. However, under direct-current electric field, triggering ability decreased drastically due to low plasma density. It is considered that such laser operation applied for laser-triggered lightning due to the produced location of plasma channel is formed under the impulse electric field since an electric field of the location drastically reduces temporary when the downward leader from thunderclouds propagates to the plasma channel.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.Jm Ionization of plasmas
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
92.60.Pw Atmospheric electricity, lightning
92.60.Nv Cloud physics and chemistry

Plasma acceleration from radio-frequency discharge in dielectric capillary

A. Dunaevsky, Y. Raitses, and N. J. Fisch

Appl. Phys. Lett. 88, 251502 (2006); http://dx.doi.org/10.1063/1.2214127 (3 pages) | Cited 16 times

Online Publication Date: 22 June 2006

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A capacitive rf discharge was demonstrated in a dielectric capillary for generation of quasineutral plasma flow with energies of several tens of eV. A potential gradient at the open end of the capillary and high-temperature electrons in the capillary discharge promote the ion acceleration. The plasma flow was generated from a ceramic capillary with inner diameter of ∼ 0.8 mm and a length of ∼ 10 mm, at a gas flow rate of 2–10 SCCM (SCCM denotes cubic centimeter per minute at STP) and input power of 15–20 W. The ion energy spectrum consists of high-energy accelerated ions and a low-energy tail formed due to ionization in the acceleration region. The relatively wide plume angle of ∼ 65° indicates that the acceleration region is placed outside the capillary and has a convex shape. Estimated total efficiency at 2 SCCM Xe flow rate and 15 W input power reaches 2%–3%. This approach may be attractive for micropropulsion applications due to its simplicity, low weight and small dimensions of the source, and the absence of a cathode neutralizer.
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52.75.Di Ion and plasma propulsion
52.80.Pi High-frequency and RF discharges
52.30.-q Plasma dynamics and flow
52.25.Jm Ionization of plasmas
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Microscopic structures of MgO barrier layers in single-crystal Fe/MgO/Fe magnetic tunnel junctions showing giant tunneling magnetoresistance

M. Mizuguchi, Y. Suzuki, T. Nagahama, and S. Yuasa

Appl. Phys. Lett. 88, 251901 (2006); http://dx.doi.org/10.1063/1.2213953 (3 pages) | Cited 5 times

Online Publication Date: 19 June 2006

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The microscopic structures of MgO(001) barrier layers in magnetic tunnel junctions showing giant tunneling magnetoresistance were characterized by in situ scanning tunneling microscopy. The MgO thin films formed exceedingly flat surfaces, and their terraces were made even flatter by annealing after deposition. This flattening of MgO surfaces apparently promotes coherent transport of electrons, which should enhance the tunneling magnetoresistance ratio. Local tunneling spectroscopy revealed that an annealed MgO layer has a critical thickness between 3 and 5 ML (monolayer), and a continuous film without pinholes can be formed over the thickness.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Rw Metal-insulator-metal structures
75.47.Lx Magnetic oxides
75.47.De Giant magnetoresistance

Influence of thermal conductivity on the glass-forming ability of Ni-based and Cu-based alloys

Dmitri V. Louzguine-Luzgin, Albertus Deny Setyawan, Hidemi Kato, and Akihisa Inoue

Appl. Phys. Lett. 88, 251902 (2006); http://dx.doi.org/10.1063/1.2213967 (2 pages) | Cited 8 times

Online Publication Date: 19 June 2006

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In the present letter we compare the thermal conductivities of Cu- and Ni-based alloys in relation with their cooling rates and glass-forming abilities. The cooling rates obtained for Cu- and Ni-based bulk glass-forming alloys are found to scale with the thermal conductivities of the base elements. Relatively low thermal conductivity of Ni-based alloy compared to the Cu-based one explains its lower glass-forming ability. The results also indicate that the thermal conductivity of the molten alloy should be also used as an indicator of the glass-forming ability among the other factors.
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72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Surface roughness and strain effects on ZnO nanorod growth

S.-H. Park, S.-Y. Seo, S.-H. Kim, and S.-W. Han

Appl. Phys. Lett. 88, 251903 (2006); http://dx.doi.org/10.1063/1.2215631 (3 pages) | Cited 10 times

Online Publication Date: 19 June 2006

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Vertically aligned ZnO nanorods were fabricated on Al2O3(001) substrates with various GaN interlayers by a catalyst-free metal-organic chemical vapor deposition. We observed that the shape and quality of ZnO nanorods grown on the GaN interlayers were considerably sensitive to the surface roughness of the interlayers. We also investigated orientation-dependent residual strain in the ZnO nanorods grown on Al2O3 substrates using polarized x-ray absorption fine structure (XAFS) measurements at Zn K edge. The XAFS revealed that the residual strain relaxation of Zn–O pairs in ab plane played a key role in the ZnO nanorod growth.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.70.Dm X-ray absorption spectra
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
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