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17 Sep 2012

Volume 101, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 123901 (2012); http://dx.doi.org/10.1063/1.4751469 (4 pages)

Chin-An Lin, K. P. Huang, S. T. Ho, Mei-Wen Huang, and Jr-Hau He
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Octagonal silica toroidal microcavity for controlled optical coupling

Takumi Kato, Wataru Yoshiki, Ryo Suzuki, and Takasumi Tanabe

Appl. Phys. Lett. 101, 121101 (2012); http://dx.doi.org/10.1063/1.4752746 (4 pages)

Online Publication Date: 17 September 2012

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We fabricated polygonal silica toroidal microcavities to achieve stable mechanical coupling with an evanescent coupler such as a tapered fiber. The octagonal cavity was fabricated by using a combination of isotropic etching, anisotropic etching, and laser reflow. It offers both high and low coupling efficiencies with the cavity mode even when the coupler is in contact with the cavity, which makes the device more practically because of easy alignment. A numerical simulation showed that an octagonal silica toroidal microcavity had an optical quality factor of 8.8 × 106.
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42.81.Qb Fiber waveguides, couplers, and arrays
42.81.Bm Fabrication, cladding, and splicing
42.62.-b Laser applications

Impact of spectral broadening on plasmonic enhancement with metallic gratings

Xue Feng, Kaiyu Cui, Fang Liu, and Yidong Huang

Appl. Phys. Lett. 101, 121102 (2012); http://dx.doi.org/10.1063/1.4753806 (4 pages) | Cited 1 time

Online Publication Date: 17 September 2012

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The Purcell factor (PF) of the propagating surface plasmon polariton (SPP) mode on metallic grating is evaluated with full integration formula of Fermi's golden rule, while both spontaneous emission linewidth of single quantum dot and the spectrum broadening of photonic density of state (DOS) due to the propagation loss of SPP mode are involved. It is found that the PF would be degraded by taking account of the emission linewidth. For emitters with narrow linewidth, the DOS broadening is dominant while it would be helpful to some degree for wide-linewidth emitters.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Dj Gratings
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Longitudinal computer-generated holograms for digital frequency control in electronically tunable terahertz lasers

Subhasish Chakraborty, Owen P. Marshall, Md. Khairuzzaman, Chen-Wei Hsin, Harvey E. Beere, and David A. Ritchie

Appl. Phys. Lett. 101, 121103 (2012); http://dx.doi.org/10.1063/1.4753814 (5 pages) | Cited 4 times

Online Publication Date: 17 September 2012

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Longitudinal computer-generated holograms (LCGHs) can be used for the inverse design of aperiodic photonic lattices for customizable frequency control of light propagation. A one-dimensional binary LCGH, designed to harness the coarse gain tuning of a terahertz (THz) quantum cascade laser (QCL) operating at around 2.9 THz, is patterned directly by ion milling into the surface plasmon-based waveguides of pre-characterized QCLs. The initial multi-mode emission is suppressed in favour of electronically controlled, discretely tunable single-mode lasing spanning over 160 GHz. Side-mode suppression ratios of over 20 dB are also demonstrated in these tunable THz LCGH-QCLs.
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42.40.Jv Computer-generated holograms
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers

Ordered ZnO nanorods-based heterojunction light-emitting diodes with graphene current spreading layer

S. G. Zhang, X. W. Zhang, F. T. Si, J. J. Dong, J. X. Wang, X. Liu, Z. G. Yin, and H. L. Gao

Appl. Phys. Lett. 101, 121104 (2012); http://dx.doi.org/10.1063/1.4753926 (4 pages)

Online Publication Date: 18 September 2012

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Ordered ZnO nanorods-based heterojunction light-emitting diodes (LEDs) have been fabricated by adopting few-layer graphene as a current spreading layer. The strong emission at low currents infers the high interfacial quality between GaN and ordered ZnO nanorods, and the current spreading effect resulting from graphene. The improved electroluminescence performance was achieved compared to the ZnO nanorods-based LED with a conventional indium-tin-oxide electrode, which can be attributed to the stable, reliable, and low resistance ohmic-contacts between graphene and ZnO nanorods, as well as the high transmittance of graphene. These results demonstrate feasibility of using graphene as electrodes for high-efficiency ZnO nanorods-based LEDs.
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85.60.Jb Light-emitting devices
84.32.Dd Connectors, relays, and switches
85.30.Kk Junction diodes

Silicon waveguides and devices for the mid-infrared

Milan M. Milošević, Milos Nedeljkovic, Taha M. Ben Masaud, Ehsan Jaberansary, Harold M. H. Chong, Neil G. Emerson, Graham T. Reed, and Goran Z. Mashanovich

Appl. Phys. Lett. 101, 121105 (2012); http://dx.doi.org/10.1063/1.4753948 (4 pages) | Cited 3 times

Online Publication Date: 18 September 2012

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We report on the design, fabrication, and characterization of silicon-on-insulator rib and strip waveguides at wavelengths longer than 3.7 μm. Propagation losses of 1.5 ± 0.2 dB/cm at 3.73 μm and 1.8 ± 0.2 dB/cm at 3.8 μm have been measured for rib waveguides, whilst submicron strip waveguides exhibited propagation losses of 4.6 ± 1.1 dB/cm at the wavelength of 3.74 μm. A 1×2 multimode interference (MMI) splitter and racetrack resonators based on submicron strip waveguides are also examined. Optical losses of 3.6 ± 0.2 dB/MMI and a racetrack resonator Q-value of 8.2 k are obtained at 3.74 μm.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
42.15.Eq Optical system design

Performance and polarization effects in (11math2) long wavelength light emitting diodes grown on stress relaxed InGaN buffer layers

Ingrid L. Koslow, Matthew T. Hardy, Po Shan Hsu, Po-Yuan Dang, Feng Wu, Alexey Romanov, Yuh-Renn Wu, Erin C. Young, Shuji Nakamura, James S. Speck, and Steven P. DenBaars

Appl. Phys. Lett. 101, 121106 (2012); http://dx.doi.org/10.1063/1.4753949 (4 pages) | Cited 1 time

Online Publication Date: 18 September 2012

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Long wavelength (525–575 nm) (11math2) light emitting diodes were grown pseudomorphically on stress relaxed InGaN buffer layers. Basal plane dislocation glide led to the formation of misfit dislocations confined to the bottom of the InGaN buffer layer. This provided one-dimensional plastic relaxation in the film interior, including the device active region. The change of the stress state of the quantum well due to one-dimensional plastic relaxation altered the valence band structure, which produced a significant shift in polarization of emitted light. Devices grown on relaxed buffers demonstrated equivalent output power compared to those for control samples without relaxation.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Broad wavelength tunability from external cavity quantum-dot mode-locked laser

D. I. Nikitichev, K. A. Fedorova, Y. Ding, A. Alhazime, A. Able, W. Kaenders, I. Krestnikov, D. Livshits, and E. U. Rafailov

Appl. Phys. Lett. 101, 121107 (2012); http://dx.doi.org/10.1063/1.4751034 (4 pages)

Online Publication Date: 18 September 2012

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Broadband wavelength tunability over 136 nm (between 1182.5 nm and 1319 nm) of picosecond pulses in passive mode-locked regime is demonstrated in a multi-section quantum-dot laser in external cavity configuration at room temperature. The maximum peak power of 870 mW with 15 ps pulse duration was achieved at 1226 nm wavelength.
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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
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Accurate photoconductive antenna characterization using a thin film polarizer

H. Park, E. P. J. Parrott, Z. Huang, H. P. Chan, and E. Pickwell-MacPherson

Appl. Phys. Lett. 101, 121108 (2012); http://dx.doi.org/10.1063/1.4753795 (4 pages)

Online Publication Date: 19 September 2012

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The horizontal and vertical polarizations of the terahertz radiation emitted from a small-gap dipole photo-conductive antenna are characterised using a single detector and a homemade thin-film wire grid polarizer. The two polarizations are seen to be temporally distinct. In addition, the dependence of the position of the excitation spot on the dipole with the polarity of the horizontal polarization is studied where a reversal in the horizontal polarization is observed between the two edges of the antenna anode.
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84.40.Ba Antennas: theory, components and accessories

On the mechanism of electrochemical modulation of plasmonic resonances

L.-H. Shao, M. Ruther, S. Linden, M. Wegener, and J. Weissmüller

Appl. Phys. Lett. 101, 121109 (2012); http://dx.doi.org/10.1063/1.4753805 (5 pages)

Online Publication Date: 19 September 2012

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Recent electrochemical experiments on gold-based photonic metamaterials have shown a sizable reversible tuning and modulation of plasmonic resonances. Here, we study the mechanism of the electrochemical modulation by measuring the change of the resonance transmittance and resonance frequency during underpotential deposition of Pb, Cu, and electrosorption of OH. The electric resistance change of the resonators is identified as decisive for the resonance transmittance change, while the space-charge layer at the metal surface shifts the resonance frequency.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
77.22.Jp Dielectric breakdown and space-charge effects
78.66.Bz Metals and metallic alloys

High-power tunable two-wavelength generation in a two chip co-linear T-cavity vertical external-cavity surface-emitting laser

Chris Hessenius, Michal Lukowski, and Mahmoud Fallahi

Appl. Phys. Lett. 101, 121110 (2012); http://dx.doi.org/10.1063/1.4754295 (3 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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We report the design and experimental results of a two chip co-linear T-cavity vertical external cavity surface emitting laser (VECSEL) capable of generating two continuously tunable orthogonally polarized lasing wavelengths. A polarizing beamsplitter is used to overlap two VECSEL cavities thus generating high-power intra-cavity two-wavelength generation ideal for type-II nonlinear frequency conversion. Nearly equal power at each wavelength with a combined dual-wavelength CW output power in excess of 13 W was observed. In a high Q cavity, the wavelength separation was tuned from 35 nm to 52 nm by using birefringent filters in regions where each wavelength lases independently of the other.
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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
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Fm Reflectors, beam splitters, and deflectors

Cylindrical, periodic surface lattice—Theory, dispersion analysis, and experiment

I. V. Konoplev, A. J. MacLachlan, C. W. Robertson, A. W. Cross, and A. D. R. Phelps

Appl. Phys. Lett. 101, 121111 (2012); http://dx.doi.org/10.1063/1.4754572 (5 pages) | Cited 1 time

Online Publication Date: 20 September 2012

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A two-dimensional surface lattice of cylindrical topology obtained via perturbing the inner surface of a cylinder is considered. Periodic perturbations of the surface lead to observation of high-impedance, dielectric-like media and resonant coupling of surface and non-propagating volume fields. This allows synthesis of tailored-for-purpose “coating” material with dispersion suitable, for instance, to mediate a Cherenkov type interaction. An analytical model of the lattice is discussed and coupled-wave equations are derived. Variations of the lattice dispersive properties with variation of parameters are shown, illustrating the tailoring of the structure's electromagnetic properties. Experimental results are presented showing agreement with the theoretical model.
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61.90.+d Other topics in structure of solids and liquids; crystallography (restricted to new topics in section 61)
41.60.Bq Cherenkov radiation

Surface plasmon coupling efficiency from nanoslit apertures to metal-insulator-metal waveguides

Haifeng Hu, Xie Zeng, Lina Wang, Yun Xu, Guofeng Song, and Qiaoqiang Gan

Appl. Phys. Lett. 101, 121112 (2012); http://dx.doi.org/10.1063/1.4754137 (5 pages) | Cited 2 times

Online Publication Date: 20 September 2012

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Coupling is a critical issue for most plasmonic nanostructures. However, the coupling efficiency for many nanoplasmonic architectures is relatively weak due to the lack of theoretical optimization approaches. Consequently, it is essential to address the understanding of the mechanism and improvement of the coupling efficiency through nanoplasmonic structures. In this letter, we provide a theoretical analysis to quantitatively predict the coupling efficiency from infinite-length and finite-length nanoslits to planar metal-insulator-metal (MIM) waveguide structures, both analytically and numerically. This design principle will be useful for the development of MIM plasmonic networks to bridge the gap between photonics, optoelectronics, and nanoelectronics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.40.Rw Metal-insulator-metal structures

Field-effect active plasmonics for ultracompact electro-optic switching

Arif E. Çetin, Ahmet A. Yanik, Alket Mertiri, Shyamsunder Erramilli, Özgür E. Müstecaplıoğlu, and Hatice Altug

Appl. Phys. Lett. 101, 121113 (2012); http://dx.doi.org/10.1063/1.4754139 (4 pages) | Cited 3 times

Online Publication Date: 20 September 2012

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Merging of electronics and photonics at subwavelength dimensions could potentially allow development of ultracompact electro-optic modulators and active optical interconnects. Here, we introduce a field-effect active plasmonic modulator where the metallic ring serves as both a photonic resonator and a field electrode. By exploiting the simultaneous electronic and photonic functionalities of our plasmonic device, we show devices offering significantly improved modulation depths (as high as ∼10.85 dB) compared to active dielectric micro-ring resonators. Device concepts introduced in this work are applicable in realization of various integrated components and could play an important role in development of active plasmonic circuits.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.82.-m Integrated optics

Angular degrees of freedom in twin-beam parametric down-conversion

Martin Levenius, Valdas Pasiskevicius, and Katia Gallo

Appl. Phys. Lett. 101, 121114 (2012); http://dx.doi.org/10.1063/1.4754148 (4 pages)

Online Publication Date: 20 September 2012

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We investigate the effect of angular tuning on coherently coupled optical parametric generation (OPG) in two-dimensional purely nonlinear lattices and demonstrate how it allows accessing both shared signal and shared idler regimes, resulting in twin-beam outputs in the mid- and near infrared, respectively. Furthermore, we present the results of a systematic spectral and angular mapping of the twin-beam OPG response in the near-infrared as a function of the pump incidence angle.
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42.65.Lm Parametric down conversion and production of entangled photons
42.65.Yj Optical parametric oscillators and amplifiers
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Athermal and tunable operations of 850 nm vertical cavity surface emitting lasers with thermally actuated T-shape membrane structure

Hayato Sano, Norihiko Nakata, Masanori Nakahama, Akihiro Matsutani, and Fumio Koyama

Appl. Phys. Lett. 101, 121115 (2012); http://dx.doi.org/10.1063/1.4753807 (4 pages)

Online Publication Date: 21 September 2012

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We demonstrate the athermal operation and the wavelength tuning of 850 nm GaAs-based vertical cavity surface emitting lasers with a thermally actuated cantilever structure. The thermal actuation of a top distributed Bragg reflector mirror enables us to compensate the temperature drift of lasing wavelengths. The temperature dependence of lasing wavelengths could be controlled from −0.011 nm/K to −0.18 nm/K by changing the cantilever length. In addition, a T-shape membrane structure was introduced for efficient electro-thermal tuning. A small temperature dependence of −0.011 nm/K and wavelength tuning of 4 nm were obtained.
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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
42.79.Bh Lenses, prisms and mirrors
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Ozone-exposure and annealing effects on graphene-on-SiO2 transistors

E. X. Zhang, A. K. M. Newaz, B. Wang, C. X. Zhang, D. M. Fleetwood, K. I. Bolotin, R. D. Schrimpf, S. T. Pantelides, and M. L. Alles

Appl. Phys. Lett. 101, 121601 (2012); http://dx.doi.org/10.1063/1.4753817 (3 pages) | Cited 1 time

Online Publication Date: 17 September 2012

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We employ resistance measurements and Raman spectroscopy to investigate the effects of UV ozone (UVO) exposure and Ar annealing on graphene-on-SiO2 transistors. Shorter UVO exposures lead to oxygen adsorption and doping; longer exposures lead to significant defect generation and then to etching. Elevated-temperature Ar annealing following UVO exposure leads to local defect healing, as shown by the evolution of the characteristic Raman D- and G-peaks. In striking contrast, the overall graphene transistor resistance increases significantly due to void formation. Density functional calculations show that carbon-oxygen reactions lead to efficient consumption and release of C atoms (as CO or CO2) under conditions of high surface oxygen concentration.
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85.30.De Semiconductor-device characterization, design, and modeling

In situ control of As dimer orientation on Ge(100) surfaces

Sebastian Brückner, Oliver Supplie, Enrique Barrigón, Johannes Luczak, Peter Kleinschmidt, Ignacio Rey-Stolle, Henning Döscher, and Thomas Hannappel

Appl. Phys. Lett. 101, 121602 (2012); http://dx.doi.org/10.1063/1.4754122 (4 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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We investigated the preparation of single domain Ge(100):As surfaces in a metal-organic vapor phase epitaxy reactor. In situ reflection anisotropy spectra (RAS) of vicinal substrates change when arsenic is supplied either by tertiarybutylarsine or by background As4 during annealing. Low energy electron diffraction shows mutually perpendicular orientations of dimers, scanning tunneling microscopy reveals distinct differences in the step structure, and x-ray photoelectron spectroscopy confirms differences in the As coverage of the Ge(100):As samples. Their RAS signals consist of contributions related to As dimer orientation and to step structure, enabling precise in situ control over preparation of single domain Ge(100):As surfaces.
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68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.47.Fg Semiconductor surfaces
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Robust hydrophobic Fe-based amorphous coating by thermal spraying

C. Zhang, Y. Wu, and L. Liu

Appl. Phys. Lett. 101, 121603 (2012); http://dx.doi.org/10.1063/1.4754140 (4 pages)

Online Publication Date: 20 September 2012

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Metallic surface is intrinsically hydrophilic due to its high surface energy. In this work, we present a different picture that highly hydrophobic metallic coatings could be directly fabricated by thermal spraying of Fe-based amorphous powders through the surface roughness control. These hydrophobic coatings are amorphous, exhibiting super-high hardness and excellent corrosion resistance. With low surface energy modification, the coatings become superhydrophobic and exhibit clearly self-cleaning effect. The present work opens a window for the applications of the amorphous coatings.
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81.65.Cf Surface cleaning, etching, patterning
61.43.Fs Glasses
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains
68.35.Md Surface thermodynamics, surface energies
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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Screw-rotation twinning through helical movement of triple-partials

Pan Liu, Kui Du, Jianxin Zhang, Lihua Wang, Yonghai Yue, Evan Ma, Yuefei Zhang, Ze Zhang, Mingwei Chen, and Xiaodong Han

Appl. Phys. Lett. 101, 121901 (2012); http://dx.doi.org/10.1063/1.4752747 (5 pages)

Online Publication Date: 17 September 2012

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By in situ uniaxial-tensile tests with dynamic and atomic scale observation, we report the quantitative investigation of strain-induced deformation-twinning process through incoherent twin boundary propagation in nanocrystalline Au. The consecutive and quantitative strain maps revealed that a strong compressive strain, up to 5.8%, was formed. A screw-rotation twinning mechanism by consecutive and collective screw-rotations of triple-partials along a [111] screw-axis is proposed. This twin generates a macro-strain of 0.707, same as the conventional shear twins, but in a helical manner.
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61.72.Mm Grain and twin boundaries
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Polarized and diameter-dependent Raman scattering from individual aluminum nitride nanowires: The antenna and cavity effects

Hsu-Cheng Hsu, Geng-Ming Hsu, Yu-shiung Lai, Zhe Chuan Feng, Shuo-Yen Tseng, Anders Lundskog, Urban Forsberg, Erik Janzén, Kuei-Hsien Chen, and Li-Chyong Chen

Appl. Phys. Lett. 101, 121902 (2012); http://dx.doi.org/10.1063/1.4753798 (5 pages)

Online Publication Date: 17 September 2012

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Raman scattering of individual aluminum nitride (AlN) nanowires is investigated systematically. The axial direction of single nanowire can be rapidly verified by polarized Raman scattering. The angular dependencies of E2(high) mode show strongly anisotropic behavior in smaller nanowires, which results from optical antenna effect. Raman enhancement (RE) per unit volume of E2(high) increases with decreasing diameter of nanowires. Compared to the thin film, ∼200-fold increase of RE is observed in AlN nanowires having diameter less than 50 nm, which is far beyond the quantum confinement regime. Such a large RE can be attributed to the effects of resonant cavity and stimulated Raman scattering.
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81.05.Ea III-V semiconductors
78.67.Uh Nanowires
81.07.Gf Nanowires
78.30.Fs III-V and II-VI semiconductors

Control of growth and the processes of energy transfer from CdSe quantum dots for Nd3+ ions in a vitreous system: Thermal annealing time

N. O. Dantas, E. O. Serqueira, V. Anjos, and M. J. V. Bell

Appl. Phys. Lett. 101, 121903 (2012); http://dx.doi.org/10.1063/1.4753800 (4 pages)

Online Publication Date: 17 September 2012

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The authors report clear evidence of radiative and nonradiative energy transfer from CdSe quantum dots to Nd3+ ions in a glass system synthesized by melting method. An efficient control of energy transfer can be obtained by controlling the mean radius of the CdSe quantum dots. Increase of about 100% of the near infrared Nd3+ emission (4F3/2 → 4I9/2) was observed as a function of thermal annealing time.
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78.55.-m Photoluminescence, properties and materials
78.67.Hc Quantum dots
81.05.Kf Glasses (including metallic glasses)
81.07.Ta Quantum dots
81.40.Gh Other heat and thermomechanical treatments

Photoluminescence dynamics in solid formulations of colloidal PbSe quantum dots: Three-dimensional versus two-dimensional films

Rafael Quintero-Torres, Charles A. Foell, Jothirmayanantham Pichaandi, Frank C. J. M. van Veggel, and Jeff F. Young

Appl. Phys. Lett. 101, 121904 (2012); http://dx.doi.org/10.1063/1.4752737 (4 pages)

Online Publication Date: 18 September 2012

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Time-resolved photoluminescence spectroscopy is used to compare decay dynamics of colloidal PbSe quantum dots as (i) dilute dispersions in hexanes, (ii) thick, dense, emulsive films, and (iii) sub-monolayer films on silicon surfaces. Accounting for the effect of each dielectric environment on exciton radiative decay rates, we deduce the non-radiative decay rate of excitons increases going from solution to thick films by ≈6 fold and to sub-monolayer films by ≈7–16 fold. This is attributed to surface passivation degradation due to a lack of mobile ligands when the particles are taken out of solution.
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78.55.Hx Other solid inorganic materials
82.70.Dd Colloids
82.70.Kj Emulsions and suspensions
68.18.-g Langmuir-Blodgett films on liquids
73.21.La Quantum dots
71.35.-y Excitons and related phenomena

Intense upconversion luminescence and origin study in Tm3+/Yb3+ codoped calcium scandate

Jing Li, Jiahua Zhang, Zhendong Hao, Xia Zhang, Jihong Zhao, and Yongshi Luo

Appl. Phys. Lett. 101, 121905 (2012); http://dx.doi.org/10.1063/1.4753802 (4 pages) | Cited 1 time

Online Publication Date: 18 September 2012

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Doping concentration optimized CaSc2O4:0.004Tm3+/0.1Yb3+ shows stronger upconversion luminescence (UCL) than doping concentration also optimized typical oxide upconverting phosphor Y2O3:0.004Tm3+/0.1Yb3+ upon 980 nm laser diode pump. The two-step up converted 3H4 → 3H6 near infrared emission peaked around 800 nm and the three-step up converted 1G4 → 3H6 blue emission around 480 nm of Tm3+ is enhanced by a factor of 3.5 and 2.2, respectively. On analyzing the 2F5/2 → 2F7/2 emission intensities and decay curves of Yb3+ in the two hosts, we reveal that Yb3+ in CaSc2O4 exhibits both a larger absorption cross section at 980 nm and Yb3+ → Tm3+ first step energy transfer coefficient (9.29 × 10−17 cm3 s−1) than that (2.87 × 10−17 cm3 s−1) in Y2O3, indicating that CaSc2O4 is an excellent host for achieving very intense UCL in Tm3+/Yb3+ codoped oxide upconverting materials.
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78.55.Hx Other solid inorganic materials
61.72.sd Impurity concentration

Signature of viscous flow units in apparent elastic regime of metallic glasses

Z. Wang, P. Wen, L. S. Huo, H. Y. Bai, and W. H. Wang

Appl. Phys. Lett. 101, 121906 (2012); http://dx.doi.org/10.1063/1.4753813 (4 pages) | Cited 1 time

Online Publication Date: 18 September 2012

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We characterize and identify the flow units in two typical metallic glasses (MGs), which have markedly different β-relaxation behaviors and mechanical properties. The viscoelastic hysteresis loops are found in the cyclic deformation in the nominal elastic regime of the metallic glasses. We show that the hysteresis loops are related to the activation of the flow units in metallic glasses, and a model is proposed to describe the flow units. We demonstrate that the flow units are both the deformation units of the anelastic and plastic deformation behaviors and the structural origin of the β-relaxation in metallic glasses.
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81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.fq Plasticity and superplasticity
61.43.Fs Glasses
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations

Simulating the interface morphology of silver thick film contacts on n-type Si-(100) and Si-(111)

Stefan Kontermann, Alexander Ruf, Ralf Preu, and Gerhard Willeke

Appl. Phys. Lett. 101, 121907 (2012); http://dx.doi.org/10.1063/1.4752228 (4 pages)

Online Publication Date: 18 September 2012

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Silver crystals at the interface of silver thick film contacts carry the current across such contacts and therefore govern the contact resistance. The crystals grow nearly exclusively in pits in the silicon surface, which form during contact formation before the crystals and hence determine the amount and size of crystals. We simulate the mechanism of pit formation at such contact interfaces by using a model based on the removal probability of silicon surface atoms. The model leads to good agreement between experimentally observed and simulated pits. The results enable the prediction of pit formation in dependence of contact processing parameters.
Show PACS
68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
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