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9 Jul 2012

Volume 101, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 023101 (2012); http://dx.doi.org/10.1063/1.4731792 (4 pages)

Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, and Qi-Huo Wei
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Ultrafast all-optical gated amplifier based on ZnO nanowire lasing

Marijn A. M. Versteegh, Peter J. S. van Capel, and Jaap I. Dijkhuis

Appl. Phys. Lett. 101, 021101 (2012); http://dx.doi.org/10.1063/1.4733972 (3 pages)

Online Publication Date: 9 July 2012

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We present an ultrafast all-optical gated amplifier, or transistor, consisting of a forest of ZnO nanowire lasers. A gate light pulse creates a dense electron-hole plasma and excites laser action inside the nanowires. Source light traversing the nanolaser forest is amplified, partly as it is guided through the nanowires, and partly as it propagates diffusively through the forest. We have measured transmission increases at the drain up to a factor 34 for 385-nm light. Time-resolved amplification measurements show that the lasing is rapidly self-quenching, yielding pulse responses as short as 1.2 ps.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Frequency tunable x-ray/γ-ray source via Thomson backscattering on flying mirror from laser foil interaction

Meng Wen (温猛), Luling Jin (金璐玲), Yuanrong Lu (陆元荣), Jiaer Chen (陈佳洱), and Xueqing Yan (颜学庆)

Appl. Phys. Lett. 101, 021102 (2012); http://dx.doi.org/10.1063/1.4734503 (4 pages) | Cited 1 time

Online Publication Date: 9 July 2012

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A scheme to generate a frequency tunable x-ray/γ-ray source via Thomson backscattering is proposed. In this model, a few-cycle drive pulse with relativistic intensity interacts with a target (combined with a thin and a thick foil) to produce a flying mirror, and a counter propagating probe pulse is applied to generate a high frequency pulse on it. By adjusting the separation between these two foils, the frequency of the Thomson backscattering light generated from the flying mirror can be tuned in a range from ωL to >106ωL, i.e., x-ray or γ-ray with tunable frequency is obtained. The energy dispersion of the flying mirror, as well as the spectrum width of the Thomson backscattering are studied.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.27.Ny Relativistic plasmas
52.38.Ph X-ray, γ-ray, and particle generation

Fully automatized quantum cascade laser design by genetic optimization

A. Bismuto, R. Terazzi, B. Hinkov, M. Beck, and J. Faist

Appl. Phys. Lett. 101, 021103 (2012); http://dx.doi.org/10.1063/1.4734389 (4 pages) | Cited 1 time

Online Publication Date: 10 July 2012

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Using a transport model based on the density matrix formalism, a fully automatized technique to design quantum cascade structures in the mid-infrared is presented that implements a genetic algorithm where the wallplug efficiency has been used as merit factor. Starting from a reference design, the model converges after few generations on an optimized design that presents a better carrier injection in the upper lasing state. Both the designs have been fabricated using buried heterostructure process and the optimized design shows a pronounced increase in the laser operation range and higher output powers. In good agreement with the simulations, the laser efficiency increases from 5% to 12%.
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42.60.By Design of specific laser systems
02.60.Pn Numerical optimization
42.55.Px Semiconductor lasers; laser diodes

Negative refraction and partial focusing with a crossed wire mesh: Physical insights and experimental verification

Tiago A. Morgado, João S. Marcos, Stanislav I. Maslovski, and Mário G. Silveirinha

Appl. Phys. Lett. 101, 021104 (2012); http://dx.doi.org/10.1063/1.4734510 (4 pages) | Cited 2 times

Online Publication Date: 10 July 2012

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We experimentally verify that a flat metamaterial lens formed by nonconnected crossed metallic wires enables the partial focusing of electromagnetic waves, as a consequence of the phenomenon of all-angle broadband negative refraction in such media. We prove that the strength of the negative refraction effect can be controlled by adjusting the angle between the crossed wires.
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42.79.Bh Lenses, prisms and mirrors
42.70.-a Optical materials

Efficient and broadband polarization rotator using horizontal slot waveguide for silicon photonics

Huijuan Zhang, Suchandrima Das, Jing Zhang, Ying Huang, Chao Li, Shiyi Chen, Haifeng Zhou, Mingbin Yu, Patrick Guo-Qiang Lo, and John T. L. Thong

Appl. Phys. Lett. 101, 021105 (2012); http://dx.doi.org/10.1063/1.4734640 (4 pages) | Cited 5 times

Online Publication Date: 10 July 2012

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We report an efficient and low-loss polarization rotator based on mode evolution using horizontal slot waveguide. The device is fabricated using complementary metal–oxide–semiconductor compatible processes, which allows monolithic integration with active drive electronics and other photonic components. A rotator fabricated with 100 μm transition length provides a high extinction ratio >14 dB for both transverse-magnetic (TM)-transverse-electric (TE) and TE-TM rotation. The excess loss of the device is <1 dB for both rotations as etching of the bottom Si waveguide is prevented. The device also exhibits a uniform rotation response over C+L band wavelength range of 1530-1600 nm.
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42.82.Et Waveguides, couplers, and arrays
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
42.82.Cr Fabrication techniques; lithography, pattern transfer

High operating temperature interband cascade midwave infrared detector based on type-II InAs/GaSb strained layer superlattice

Nutan Gautam, S. Myers, A. V. Barve, Brianna Klein, E. P. Smith, D. R. Rhiger, L. R. Dawson, and S. Krishna

Appl. Phys. Lett. 101, 021106 (2012); http://dx.doi.org/10.1063/1.4733660 (4 pages) | Cited 2 times

Online Publication Date: 10 July 2012

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We report on an interband cascade mid-wave infrared (MWIR) detector based on type-II InAs/GaSb/AlSb strained layer superlattices (T2SL). The reported device has a seven-stage cascade region, each segment containing a MWIR absorber region, a graded T2SL transport region, and an interband tunneling region. Above room temperature spectral response was observed, with a cutoff wavelength of 7 μm at 420 K. Detailed radiometric measurements yielded a Johnson noise limited detectivity of 3.0 × 1011 cmHz1/2W−1 (8.9 × 108 cmHz1/2W−1) and a dark current density of 3.6 × 10−7 A/cm−2 (7.3 × 10−3 A/cm−2) near zero bias with a 100% cutoff wavelength of 5.2 μm and 6.2 μm at 77 K (295 K), respectively, with an estimated 36.2% QE.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Terahertz intracavity generation from output coupler consisting of stacked GaP plates

Pu Zhao, Srinivasa Ragam, Yujie J. Ding, and Ioulia B. Zotova

Appl. Phys. Lett. 101, 021107 (2012); http://dx.doi.org/10.1063/1.4734511 (3 pages)

Online Publication Date: 11 July 2012

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We demonstrate intracavity terahertz generation from an output coupler of a compact dual-frequency solid state laser. The output coupler consisting of unbonded and stacked GaP plates is used as a second-order nonlinear medium where the difference-frequency generation takes place. When quasi-phase matching is achieved within the alternatively rotated GaP plates, terahertz output power is significantly enhanced compared with that for the corresponding external-cavity configuration.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Gn Optical waveguides and couplers
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

A magnifying fiber element with an array of sub-wavelength Ge/ZnSe pixel waveguides for infrared imaging

Mahesh Krishnamurthi, Eftihia Barnes, Justin R. Sparks, Rongrui He, Neil F. Baril, Pier J. A. Sazio, John V. Badding, and Venkatraman Gopalan

Appl. Phys. Lett. 101, 021108 (2012); http://dx.doi.org/10.1063/1.4734787 (5 pages) | Cited 2 times

Online Publication Date: 11 July 2012

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We demonstrate an array of tapered Ge-core/ZnSe-cladding waveguides in a silica fiber matrix for infrared image transfer and a pixel magnification of 3.5× at 3.39 μm and 10.64 μm wavelengths. The structure was synthesized by a high-pressure chemical vapor deposition technique to deposit the semiconductor waveguides within the holes of a silica based microstructured optical fiber. The core/cladding structure reduces the optical propagation loss through the waveguides, and good isolation between the pixels is demonstrated. With further material improvements, these structures could be useful for applications such as infrared endoscopic imaging.
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42.79.Pw Imaging detectors and sensors
42.81.-i Fiber optics
42.79.Gn Optical waveguides and couplers

Near field enhancement in silver nanoantenna-superlens systems

Zhengtong Liu (刘政通), Erping Li (李尔平), Vladimir M. Shalaev, and Alexander V. Kildishev

Appl. Phys. Lett. 101, 021109 (2012); http://dx.doi.org/10.1063/1.4732793 (3 pages)

Online Publication Date: 12 July 2012

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We demonstrate near field enhancement generation in silver nanoantenna-superlens systems via numerical modeling. Using near-field interference and global optimization algorithms, we can design nanoantenna-superlens systems with mismatched permittivities, whose performance can match those with matched permittivities. The systems studied here may find broad applications in the fields of sensing, such as field-enhanced fluorescence and surface-enhanced Raman scattering, and the methodology used here can be applied to the designing and optimization of other devices, such as two-dimensional near field focusing lens.
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42.79.-e Optical elements, devices, and systems
02.60.Pn Numerical optimization
42.15.Eq Optical system design

Asymmetric Fano resonance in eye-like microring system

Chen Qiu, Ping Yu, Ting Hu, Fan Wang, Xiaoqing Jiang, and Jianyi Yang

Appl. Phys. Lett. 101, 021110 (2012); http://dx.doi.org/10.1063/1.4735258 (4 pages) | Cited 1 time

Online Publication Date: 12 July 2012

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In this paper, the Fano resonance in the “eye-like” microring resonator system (EMRS) is theoretically and experimentally investigated. The asymmetric Fano-resonance line shape of EMRS is generated by adding a microring inside and coupling with the outer ring to produce a nonlinear phase shift. The EMRS was fabricated on silicon-on-insulator wafer by the complementary metal-oxide-semiconductor compatible process. Compared to the conventional single-stage microring add-drop filter structure, the maximum sharpness of the transmission of the drop port is enhanced 3 times, and the drop port extinction ratio is increased by about 20 dB. The experimental results are in good agreement with the theoretical analysis.
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42.79.Ci Filters, zone plates, and polarizers
42.82.-m Integrated optics

Performance improvement in nanoparticle-assisted stimulated-emission-depletion nanoscopy

Yonatan Sivan

Appl. Phys. Lett. 101, 021111 (2012); http://dx.doi.org/10.1063/1.4735319 (4 pages) | Cited 2 times

Online Publication Date: 12 July 2012

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We revisit stimulated-emission-depletion (STED) nanoscopy theory for the case when metal nanoparticles are used to improve the nanoscope’s performance. We show that the improved performance can be estimated in a simple way with no need for heavy computations. We then systematically study the dependence of the improved performance on the field and decay rate enhancements, as well as on the STED pulse and time-gating durations.
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78.45.+h Stimulated emission

First-order light-induced orientation transition in nematic liquid crystal in the presence of low-frequency electric field

I. A. Budagovsky, D. S. Pavlov, S. A. Shvetsov, M. P. Smayev, A. S. Zolot’ko, N. I. Boiko, and M. I. Barnik

Appl. Phys. Lett. 101, 021112 (2012); http://dx.doi.org/10.1063/1.4736409 (3 pages)

Online Publication Date: 12 July 2012

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Director deformation in a planar nematic liquid crystal (NLC) with negative optical nonlinearity (director rotates away from the light field) has been studied. First-order orientation transition and a wide hysteresis loop were observed at changing the light intensity in the presence of an ac field that is non-perpendicular to the undistorted director of liquid crystal due to pretilt. The theory of light beam interaction with NLC under ac field was constructed.
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64.70.mf Theory and modeling of specific liquid crystal transitions, including computer simulation
42.65.-k Nonlinear optics
61.30.-v Liquid crystals

Electrical measurement of internal quantum efficiency and extraction efficiency of III-N light-emitting diodes

Pyry Kivisaari, Lauri Riuttanen, Jani Oksanen, Sami Suihkonen, Muhammad Ali, Harri Lipsanen, and Jukka Tulkki

Appl. Phys. Lett. 101, 021113 (2012); http://dx.doi.org/10.1063/1.4736565 (4 pages) | Cited 3 times

Online Publication Date: 13 July 2012

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We propose a direct electrical measurement method for determining the extraction efficiency (EXE) and internal quantum efficiency (IQE) of III-Nitride light-emitting diodes (LEDs). The method is based on measuring the optical output power as a function of injection current at current densities near the external quantum efficiency (EQE) maximum and extracting IQE and EXE from the measurement data. In contrast to conventional methods, our method requires no low temperature measurements or prior knowledge of the device structure. The method is far more convenient than commonly used methods because it enables measuring the EXE and IQE of different LED structures at room temperature directly in a repeatable and consistent way. This enables convenient comparison of LED structures. We apply the method to determine the IQE and EXE of one commercial LED and selected self-grown planar LED chips to compare the effects of different LED structure designs. Our results are in line with published experimental results and also give more insight to our earlier findings regarding the effects of growth parameters on the quantum efficiency. In addition, our measurement method allows estimating the Shockley-Read-Hall and radiative recombination parameters if the Auger parameter is known.
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85.60.Jb Light-emitting devices

Enhancing the locality of optical interrogation with photonic-crystal fibers

Lyubov V. Doronina-Amitonova, Il’ya V. Fedotov, Olga I. Ivashkina, Marina A. Zots, Andrei B. Fedotov, Konstantin V. Anokhin, and Aleksei M. Zheltikov

Appl. Phys. Lett. 101, 021114 (2012); http://dx.doi.org/10.1063/1.4727901 (4 pages) | Cited 1 time

Online Publication Date: 13 July 2012

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Small-core photonic-crystal fibers (PCFs) are shown to enhance the locality of optical interrogation in fiber-probe-based imaging. We demonstrate that, in a typical fluorescence imaging experiment, the longitudinal dimension of the interrogated region closely follows the amtan−1θd scaling with the effective mode radius am and the beam-divergence angle θd. The confinement of optical interrogation provided by small-core, high-index-step PCF probes is high enough to enable interrogation of individual neurons in a typical brain imaging experiment.
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87.19.lh Optical imaging of neuronal activity
42.70.Qs Photonic bandgap materials
42.81.Wg Other fiber-optical devices
87.85.Pq Biomedical imaging

Nanostructure Ag dots for improving thermal stability of Ag reflector for GaN-based light-emitting diodes

Joon-Woo Jeon, Woong-Sun Yum, Semi Oh, Kyoung-Kook Kim, and Tae-Yeon Seong

Appl. Phys. Lett. 101, 021115 (2012); http://dx.doi.org/10.1063/1.4737015 (4 pages)

Online Publication Date: 13 July 2012

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We report the improved thermal stability of Ag reflectors for GaN-based light-emitting diodes (LEDs) using Ag nano-dots (∼65–∼190 nm in size). The nano-dot Ag samples show much higher reflectance than the Ag only samples. The annealed nano-dot Ag samples exhibit a smoother surface, where the grains contain numerous micro-twins. 〈111〉 texture becomes more dominantly evolved in the nano-dot Ag samples than in the Ag only samples after annealing. LEDs with the 300 °C-annealed nano-dot Ag reflectors exhibit 15%–36% higher output power (at 20 mA) than LEDs with the 300 and 400 °C-annealed Ag only reflectors.
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85.60.Jb Light-emitting devices

Directional whispering gallery mode emission from Limaçon-shaped electrically pumped quantum dot micropillar lasers

F. Albert, C. Hopfmann, A. Eberspächer, F. Arnold, M. Emmerling, C. Schneider, S. Höfling, A. Forchel, M. Kamp, J. Wiersig, and S. Reitzenstein

Appl. Phys. Lett. 101, 021116 (2012); http://dx.doi.org/10.1063/1.4733726 (4 pages) | Cited 2 times

Online Publication Date: 13 July 2012

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We experimentally demonstrate directional far field emission from whispering gallery modes (WGMs) in electrically driven quantum dot micropillar lasers. In-plane directionality of whispering gallery mode emission is obtained by patterning micropillars with Limaçon-shaped cross-section and an upper air-bridge contact for current injection. The micropillar lasers with radii R0 down to 4.5 μm show Q-factors of 40 000 and threshold currents of 40 μA at low temperature. We achieved a far field divergence of about 30° and a directionality of 1.67 ± 0.15 for an optimal Limaçon deformation factor ɛ ≈ 0.5. Parameter dependent studies of the directional emission as a function of ɛ reveal good qualitative agreement with theoretical predictions.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.By Design of specific laser systems
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High-quality surface passivation of silicon using native oxide and silicon nitride layers

Zahidur R. Chowdhury, Kevin Cho, and Nazir P. Kherani

Appl. Phys. Lett. 101, 021601 (2012); http://dx.doi.org/10.1063/1.4733336 (4 pages) | Cited 1 time

Online Publication Date: 9 July 2012

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We report on the attainment of high quality surface passivation of crystalline silicon using facile native oxide and plasma enhanced chemical vapour deposition SiNx. Using systematic measurements of excess carrier density dependent minority carrier lifetime, it is observed that the inferred interface defect density decreases with increasing native oxide thickness while the interface charge density remains unchanged with thickness, which ranges from 0.2 Å to 10 Å. A surface recombination velocity of 8 cm/s is attained corresponding to a native oxide layer thickness of ∼10 Å. Similar chemically grown oxide layer followed by SiNx deposition is shown to yield comparable passivation, indicating practical viability of the passivation scheme.
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81.65.Rv Passivation
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Thickness effects on the magnetic and electrical transport properties of highly epitaxial LaBaCo2O5.5+δ thin films on MgO substrates

Chunrui Ma, Ming Liu, Gregory Collins, Jian Liu, Yamei Zhang, Chonglin Chen, Jie He, Jiechao Jiang, and Efstathios I. Meletis

Appl. Phys. Lett. 101, 021602 (2012); http://dx.doi.org/10.1063/1.4734386 (4 pages) | Cited 2 times

Online Publication Date: 10 July 2012

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The transport properties of double perovskite LaBaCo2O5.5+δ thin films with different thicknesses were systemically studied. A thin (7 nm in thickness), disordered LaBaCo2O5.5+δ layer was formed at the interface between the film and substrate. The films had a typical semiconductor behavior with antiferromagnetic and ferromagnetic behavior coexisting at low temperature. Although the Curie temperature was independent of the film thickness, the coercive fields and magnetizations increase with increasing the film thickness. An ultra large magnetoresistance effect value of about 44% was obtained at 60 K for the film of 82 nm.
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68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
77.80.-e Ferroelectricity and antiferroelectricity

Epitaxial graphene on single domain 3C-SiC(100) thin films grown on off-axis Si(100)

A. Ouerghi, A. Balan, C. Castelli, M. Picher, R. Belkhou, M. Eddrief, M. G. Silly, M. Marangolo, A. Shukla, and F. Sirotti

Appl. Phys. Lett. 101, 021603 (2012); http://dx.doi.org/10.1063/1.4734396 (5 pages) | Cited 2 times

Online Publication Date: 11 July 2012

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The current process of growing graphene by thermal decomposition of 3C-SiC(100) on silicon is technologically attractive. Here, we study epitaxial graphene on single domain 3C-SiC films on off-axis Si(100). The structural and electronic properties of such graphene layers are explored by atomic force microscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy. Using low energy electron diffraction, we show that graphene exhibits single planar domains. Near-edge x-ray absorption fine structure is used to characterize the sample, which confirms that the graphene layers present sp2 hybridization and are homogeneously parallel to the substrate surface.
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68.55.ap Fullerenes
68.55.J- Morphology of films
61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
78.67.Wj Optical properties of graphene
78.30.Na Fullerenes and related materials
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Ultrafast carrier phonon dynamics in NaOH-reacted graphite oxide film

Dongwook Lee, Xingquan Zou, Xi Zhu, J. W. Seo, Jacqueline M. Cole, Federica Bondino, Elena Magnano, Saritha K. Nair, and Haibin Su

Appl. Phys. Lett. 101, 021604 (2012); http://dx.doi.org/10.1063/1.4736572 (5 pages)

Online Publication Date: 12 July 2012

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NaOH-reacted graphite oxide film was prepared by decomposing epoxy groups in graphite oxide into hydroxyl and -ONa groups with NaOH solution. Ultrafast carrier dynamics of the sample were studied by time-resolved transient differential reflection (ΔR/R). The data show two exponential relaxation processes. The slow relaxation process ( ∼ 2ps) is ascribed to low energy acoustic phonon mediated scattering. The electron-phonon coupling and first-principles calculation results demonstrate that -OH and -ONa groups in the sample are strongly coupled. Thus, we attribute the fast relaxation process ( ∼ 0.17ps) to the coupling of hydroxyl and -ONa groups in the sample.
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63.20.kd Phonon-electron interactions
68.55.aj Insulators
78.47.jg Time resolved reflection spectroscopy
62.65.+k Acoustical properties of solids
71.38.-k Polarons and electron-phonon interactions
78.66.Tr Fullerenes and related materials

Adsorption of silicon on Au(110): An ordered two dimensional surface alloy

Hanna Enriquez, Andrew Mayne, Abdelkader Kara, Sébastien Vizzini, Silvan Roth, Boubekeur Lalmi, Ari P Seitsonen, Bernard Aufray, Thomas Greber, Rachid Belkhou, Gérald Dujardin, and Hamid Oughaddou

Appl. Phys. Lett. 101, 021605 (2012); http://dx.doi.org/10.1063/1.4735310 (5 pages) | Cited 1 time

Online Publication Date: 13 July 2012

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We report on experimental evidence for the formation of a two dimensional Si/Au(110) surface alloy. In this study, we have used a combination of scanning tunneling microscopy, low energy electron diffraction, Auger electron spectroscopy, and ab initio calculations based on density functional theory. A highly ordered and stable Si-Au surface alloy is observed subsequent to growth of a sub-monolayer of silicon on an Au(110) substrate kept above the eutectic temperature.
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68.43.Mn Adsorption kinetics
79.20.Fv Electron impact: Auger emission
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Epitaxial growth of Ti3SiC2 thin films with basal planes parallel or orthogonal to the surface on α-SiC

A. Drevin-Bazin, J. F. Barbot, M. Alkazaz, T. Cabioch, and M. F. Beaufort

Appl. Phys. Lett. 101, 021606 (2012); http://dx.doi.org/10.1063/1.4737018 (3 pages) | Cited 1 time

Online Publication Date: 13 July 2012

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The growth of Ti3SiC2 thin films were studied onto α-SiC substrates differently oriented by thermal annealing of TiAl layers deposited by magnetron sputtering. For any substrate’s orientation, transmission electron microscopy coupled with x-ray diffraction showed the coherent epitaxial growth of Ti3SiC2 films along basal planes of SiC. Specifically for the (11math0) 4H-SiC, Ti3SiC2 basal planes are found to be orthogonal to the surface. The continuous or textured nature of Ti3SiC2 films does not depend of the SiC stacking sequence and is explained by a step-flow mechanism of growth mode. The ohmic character of the contact was confirmed by current-voltage measurements.
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81.15.Cd Deposition by sputtering
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments
68.55.jm Texture
73.40.Ns Metal-nonmetal contacts
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Femtosecond laser-induced asymmetric large scale waves on gold surfaces

Taek Yong Hwang and Chunlei Guo

Appl. Phys. Lett. 101, 021901 (2012); http://dx.doi.org/10.1063/1.4733968 (4 pages) | Cited 1 time

Online Publication Date: 9 July 2012

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multimedia

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With femtosecond (fs) pulse irradiation, we investigate the morphological evolution of a unique type of fs laser-induced periodic surface structure, called nanostructure-covered large scale waves (NC-LSWs), covered by iterating stripe patterns of nanostructures and microstructures with a period of tens of microns. By monitoring the morphological profile of NC-LSWs following fs laser heating of Au, we show that the NC-LSWs are highly asymmetrically formed and propagate on a gold surface. We believe that the selective laser ablation of Au surface and the subsequent mass transfer of liquid Au following nonuniform energy deposition result in the asymmetric NC-LSW propagation on metals.
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81.05.Bx Metals, semimetals, and alloys
81.65.-b Surface treatments
79.20.Eb Laser ablation
68.35.bd Metals and alloys
61.82.Bg Metals and alloys
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Atomic and electronic structures of Zr-(Co,Ni,Cu)-Al metallic glasses

C. C. Yuan, X. Shen, J. Cui, L. Gu, R. C. Yu, and X. K. Xi

Appl. Phys. Lett. 101, 021902 (2012); http://dx.doi.org/10.1063/1.4734390 (4 pages)

Online Publication Date: 10 July 2012

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The atomic and electronic structures of transition metal-metalloid based Zr60Co(Ni,Cu)28Al12 bulk metallic glasses (MGs) are probed by 27Al nuclear magnetic resonance (NMR) spectroscopy. The magnitude and evolution of 27Al isotropic shifts indicate that the Fermi level moves toward a minimum upon transition metal 3d sub-band filling and provides experimental evidence for pd hybridization bonding mechanism, which is further supported by the observation of Co L23 edges, and the prepeaks near Al L23 and K edges in electron energy loss spectroscopy. This investigation provides insight into the bonding mechanisms in MGs, which are relevant for understanding of their mechanical behaviors.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
76.60.Cq Chemical and Knight shifts
79.20.Uv Electron energy loss spectroscopy
61.43.Fs Glasses
62.20.-x Mechanical properties of solids

A structural viscosity model for magnetorheology

Claudio L. A. Berli and Juan de Vicente

Appl. Phys. Lett. 101, 021903 (2012); http://dx.doi.org/10.1063/1.4734504 (4 pages) | Cited 4 times

Online Publication Date: 11 July 2012

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A structural viscosity model is proposed, which describes the shear viscosity from the balance between build up (magnetic field-induced clustering) and breakdown (shear-induced breakup) of particle aggregates. The model accounts for typical deviations from Bingham model predictions that are extensively reported in the MR literature. More precisely, the model (i) provides a physical ground for the observed Casson-like shear flow behaviour, (ii) predicts the existence of a low shear plateau in weak MR fluids, and (iii) asymptotically recovers the typical Bingham-like behavior that is observed in (strong) conventional MR fluids at experimentally accessible times.
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47.65.Cb Magnetic fluids and ferrofluids
47.50.Cd Modeling
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