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15 Jun 2009

Volume 94, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 241101 (2009); http://dx.doi.org/10.1063/1.3153146 (3 pages)

G. Walter, C. H. Wu, H. W. Then, M. Feng, and N. Holonyak, Jr.
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4.3 GHz optical bandwidth light emitting transistor

G. Walter, C. H. Wu, H. W. Then, M. Feng, and N. Holonyak, Jr.

Appl. Phys. Lett. 94, 241101 (2009); http://dx.doi.org/10.1063/1.3153146 (3 pages) | Cited 11 times

Online Publication Date: 15 June 2009

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We demonstrate a quantum-well base heterojunction bipolar light emitting transistor (HBLET) operating in the common collector configuration with a 3 dB optical response bandwidth f3 dB of 4.3 GHz. The HBLET has a current gain, β ( = |ΔIC/ΔIB|) as high as 30, and can be operated as a three-port device to provide simultaneously an optical and electrical output with gain. The f3 dB of 4.3 GHz corresponds to an effective carrier recombination lifetime of 37 ps, and shows that “fast” spontaneous recombination can be harnessed for high-speed modulation.
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85.60.Jb Light-emitting devices

Diagnostic of laser contrast using target reflectivity

A. S. Pirozhkov, I. W. Choi, J. H. Sung, S. K. Lee, T. J. Yu, T. M. Jeong, I J. Kim, N. Hafz, C. M. Kim, K. H. Pae, Y.-C. Noh, D.-K. Ko, J. Lee, A. P. L. Robinson, P. Foster, et al.

Appl. Phys. Lett. 94, 241102 (2009); http://dx.doi.org/10.1063/1.3148330 (3 pages) | Cited 4 times

Online Publication Date: 15 June 2009

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Using three different laser systems, we demonstrate a convenient and simple plasma based diagnostic of the contrast of high-power short-pulse lasers. The technique is based on measuring the specular reflectivity from a solid target. The reflectivity remains high even at relativistic intensities above 1019 W/cm2 in the case of a high-contrast prepulse-free laser. On the contrary, the specular reflectivity drops with increasing intensities in the case of systems with insufficient contrast due to beam breakup and increased absorption caused by preplasma.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.25.-p Wave optics

Ultrafast photodetection in an all-silicon chip enabled by two-photon absorption

J. Bravo-Abad, E. P. Ippen, and M. Soljačić

Appl. Phys. Lett. 94, 241103 (2009); http://dx.doi.org/10.1063/1.3155135 (3 pages) | Cited 13 times

Online Publication Date: 15 June 2009

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In this letter we theoretically demonstrate that by dramatically enhancing two-photon absorption, all-silicon optical microresonators can act as efficient photodetectors for light at telecom wavelengths. We illustrate this approach with two specific designs based on a ring resonator and a photonic crystal cavity. The proposed scheme is fully compatible with standard silicon complementary metal-oxide-semiconductor processing technology, and thus, could contribute to the development of chip-scale integrated photodetectors based exclusively on silicon.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Coupled microsphere clusters for detecting molecule’s dipole moment orientation

Dmitry V. Guzatov and Ulrike Woggon

Appl. Phys. Lett. 94, 241104 (2009); http://dx.doi.org/10.1063/1.3155188 (3 pages) | Cited 2 times

Online Publication Date: 16 June 2009

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A three-sphere microsphere cluster is proposed as sensor of the dipole moment orientation of molecules or nanocrystals. A single dipole source of electromagnetic radiation adsorbed on the surface of one of the microspheres excites the whole, weakly coupled microsphere cluster and creates a field in all neighboring spheres. Since the maximal values of the relative intensity of the field modes and the spatial field distribution depends on the orientation of the radiation source, a second microsphere of the cluster can be used as a sensing sphere to measure in situ almost background-free the molecule’s optical dipole moment orientation.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
36.40.-c Atomic and molecular clusters

Resonant enhancement of second order sideband generation for intraexcitonic transitions in GaAs/AlGaAs multiple quantum wells

M. Wagner, H. Schneider, S. Winnerl, M. Helm, T. Roch, A. M. Andrews, S. Schartner, and G. Strasser

Appl. Phys. Lett. 94, 241105 (2009); http://dx.doi.org/10.1063/1.3155189 (3 pages) | Cited 7 times

Online Publication Date: 16 June 2009

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We present an experimental study on efficient second order sideband generation in symmetric undoped GaAs/AlGaAs multiple quantum wells. A near-infrared laser tuned to excitonic interband transitions is mixed with an in-plane polarized terahertz beam from a free-electron laser. The terahertz beam is tuned either to the intraexcitonic heavy-hole 1s-2p transition or to the interexcitonic heavy-hole light-hole transition. We find strong evidence that the intraexcitonic transition is of paramount influence on n = ±2 sideband generation, leading to an order-of-magnitude resonant enhancement of the conversion efficiency up to 0.1% at low temperature. At room temperature, the efficiency drops only by a factor of 7 for low terahertz powers.
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78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors
78.70.Gq Microwave and radio-frequency interactions
71.35.-y Excitons and related phenomena

Amplified spontaneous emission in the spiropyran-biopolymer based system

Jaroslaw Mysliwiec, Lech Sznitko, Stanislaw Bartkiewicz, Andrzej Miniewicz, Zacaria Essaidi, Francois Kajzar, and Bouchta Sahraoui

Appl. Phys. Lett. 94, 241106 (2009); http://dx.doi.org/10.1063/1.3155203 (3 pages) | Cited 13 times

Online Publication Date: 16 June 2009

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Amplified spontaneous emission (ASE) phenomenon in the 6-nitro-1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indolin] organic dye dispersed in a solid matrix has been observed. The biopolymer system deoxyribonucleic acid blended with cationic surfactant molecule cetyltrimethyl-ammonium chloride served as a matrix. ASE appeared under sample excitation by UV light pulses (λ = 355 nm) coming from nanosecond or picosecond neodymium doped yttrium aluminum garnet lasers and has been reinforced with green (λ = 532 nm) light excitation followed UV light pulse. The ASE characteristics in function of different excitation pulse energies as well as signal gain were measured.
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42.55.Mv Dye lasers
78.55.Kz Solid organic materials
78.47.-p Spectroscopy of solid state dynamics

Electro-optic modulation in slotted resonant photonic crystal heterostructures

Jan Hendrik Wülbern, Jan Hampe, Alexander Petrov, Manfred Eich, Jingdong Luo, Alex K.-Y. Jen, Andrea Di Falco, Thomas F. Krauss, and Jürgen Bruns

Appl. Phys. Lett. 94, 241107 (2009); http://dx.doi.org/10.1063/1.3156033 (3 pages) | Cited 15 times

Online Publication Date: 17 June 2009

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Two dimensional photonic crystal waveguides in high index materials enable integrated optical devices with an extremely small geometrical footprint on the scale of micrometers. Slotted waveguides are based on the guiding of light in low refractive index materials and a field enhancement in this particular region of the device. In this letter we experimentally demonstrate electro-optic modulation in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with nonlinear optical polymers. A photonic crystal heterostructure is used to create a cavity, while simultaneously serving as an electrical connection from the slot to the metal electrodes that carry the modulation signal.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials

Near-infrared silicon quantum dots metal-oxide-semiconductor field-effect transistor photodetector

Jia-Min Shieh, Wen-Chien Yu, Jung Y. Huang, Chao-Kei Wang, Bau-Tong Dai, Huang-Yan Jhan, Chih-Wei Hsu, Hao-Chung Kuo, Fu-Liang Yang, and Ci-Ling Pan

Appl. Phys. Lett. 94, 241108 (2009); http://dx.doi.org/10.1063/1.3156806 (3 pages) | Cited 7 times

Online Publication Date: 17 June 2009

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A fully silicon-based metal-oxide-semiconductor field-effect transistor is demonstrated for the detection of near-infrared light. Si nanocrystals (nc-Si) are synthesized in the nanopore channels of mesoporous silica (MS) inserted between two oxide layers to form a complete gate structure of polycrystalline Si/SiO2/nc-Si-in-MS/SiO2 with a polycrystalline Si electrode. Illuminating the gate with near-infrared light, a photoresponsivity as high as 2.8 A/W at 1.55 μm can be achieved. The improved photoresponsivity is attributed to from optical transitions via interface states and a current amplification mechanism of the device.
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85.30.Tv Field effect devices
85.60.Gz Photodetectors (including infrared and CCD detectors)
81.16.-c Methods of micro- and nanofabrication and processing
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Single mode coupled optofluidic ring resonator dye lasers

Xiang Wu, Yuze Sun, Jonathan D. Suter, and Xudong Fan

Appl. Phys. Lett. 94, 241109 (2009); http://dx.doi.org/10.1063/1.3156861 (3 pages) | Cited 6 times

Online Publication Date: 17 June 2009

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The authors demonstrate the single mode dye laser from a coupled optofluidic ring resonator that consists of a cylindrical ring resonator fused onto the inner surface of a thin-walled capillary ring resonator. The whispering gallery modes in each ring resonator interact strongly and utilize the Vernier effect to generate single mode laser emission. The lasing threshold is 3.0 μJ/mm2. The light can be coupled out through an optical taper in contact with the capillary.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.79.Gn Optical waveguides and couplers

A pillar-array based two-dimensional photonic crystal microcavity

Tao Xu, Ning Zhu, Michelle Y.-C. Xu, Lech Wosinski, J. Stewart Aitchison, and H. E. Ruda

Appl. Phys. Lett. 94, 241110 (2009); http://dx.doi.org/10.1063/1.3152245 (3 pages) | Cited 6 times

Online Publication Date: 17 June 2009

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Experimental results are presented for a high quality factor cavity based on pillar arrays. The cavity is formed from a square lattice of silicon pillars of finite height. The quality factor of the fundamental mode is about 7300 when the cavity is in air and 7800 when it is immersed in water. Since a pillar array has a large percent of connected void space and confines TM modes effectively, it has great promise for use in numerous areas including biochemical sensing and quantum cascade lasers.
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42.70.Qs Photonic bandgap materials

Controlling the outcoupled power in a dual wavelength optically pumped semiconductor laser

Andrew P. Ongstad, Ron Kaspi, Anna Tauke-Pedretti, Joseph C. Chavez, Michael L. Tilton, and Gregory C. Dente

Appl. Phys. Lett. 94, 241111 (2009); http://dx.doi.org/10.1063/1.3155427 (3 pages) | Cited 2 times

Online Publication Date: 17 June 2009

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We present a study of a dual wavelength optically pumped midinfrared semiconductor laser. In order to control the outcoupled power of each wavelength, the modal overlap between the adjacent gain regions was minimized while the pump absorbance for each gain region was balanced. The nominal power expectation, based solely on the absorbed power per gain region, was observed to be generally in good agreement with measurement. Improved power accounting can be accomplished if the waveguide loss and internal efficiency at each operational wavelength is known.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Photon energy and carrier density dependence of spin dynamics in bulk CdTe crystal at room temperature

Hong Ma, Zuanming Jin, Guohong Ma, Weiming Liu, and Sing Hai Tang

Appl. Phys. Lett. 94, 241112 (2009); http://dx.doi.org/10.1063/1.3155428 (3 pages) | Cited 9 times

Online Publication Date: 17 June 2009

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Excitation photon energy and carrier density dependence of spin dynamics in bulk CdTe crystal was studied by time resolved pump-probe reflectivity technique at room temperature. The results show that spin relaxation time decreases monotonously. While with increasing excitation carrier density, the time constants increases initially then decreases after reaching a maximum value. Our experimental results reveal that both D’yakonov–Perel’ [ M. I. D’yakonov and V. I. Perel’, Sov. Phys. JETP 38, 177 (1974) ] and Elliot–Yafet [ R. J. Elliott, Phys. Rev. 96, 266 (1954) ; Y. Yafet, Solid State Phys. 14, 1 (1963) ] mechanisms dominate the spin relaxation process in CdTe crystal.
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72.25.-b Spin polarized transport
78.47.D- Time resolved spectroscopy (>1 psec)
78.47.J- Ultrafast spectroscopy (<1 psec)
72.20.Fr Low-field transport and mobility; piezoresistance

Orientation dependent emission properties of columnar quantum dash laser structures

S. Hein, P. Podemski, G. Sęk, J. Misiewicz, P. Ridha, A. Fiore, G. Patriarche, S. Höfling, and A. Forchel

Appl. Phys. Lett. 94, 241113 (2009); http://dx.doi.org/10.1063/1.3156029 (3 pages)

Online Publication Date: 18 June 2009

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InAs columnar quantum dash (CQDash) structures on (100) InP have been realized by gas source molecular beam epitaxy for stacking numbers of up to 24. Laser devices show low threshold current densities between 0.73 and 3.5 kA/cm2, dependent on the CQDash orientation within the cavity. Photoluminescence and electroluminescence measurements confirm a strong relationship between the polarization degree of the emission and the orientation of the CQDashes. Eventually, the polarization of the CQDash emission could be changed from predominantly transverse electric to transverse magnetic by simply altering the dash alignment relative to the light propagation axis.
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42.55.Px Semiconductor lasers; laser diodes
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems

Hole size dependence of forward emission from organic dyes coated with two-dimensional metallic arrays

J. Li, J. B. Xu, and H. C. Ong

Appl. Phys. Lett. 94, 241114 (2009); http://dx.doi.org/10.1063/1.3157133 (3 pages) | Cited 7 times

Online Publication Date: 18 June 2009

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The effects of hole size on the forward emission from organic dyes coated with two-dimensional Au hole arrays have been studied by angle-dependent reflectivity and photoluminescence. It is found that when the hole radius increases from 73 to 116 nm, the emission intensity and bandwidth are enhanced by 2.5 and 2 times, respectively. By correlating the photoluminescence and reflectivity mappings, we have attributed the enhancement of emission primarily to the increase in radiation coupling efficiency to surface plasmons and surface plasmon radiative decay rate.
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78.55.Kz Solid organic materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Observation of temperature-independent internal Er3+ relaxation efficiency in Si-rich SiO2 films

Oleksandr Savchyn, Ravi M. Todi, Kevin R. Coffey, and Pieter G. Kik

Appl. Phys. Lett. 94, 241115 (2009); http://dx.doi.org/10.1063/1.3157135 (3 pages) | Cited 6 times

Online Publication Date: 18 June 2009

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Time-dependent photoluminescence measurements of low-temperature-annealed Er-doped Si-rich SiO2 were conducted at sample temperatures 15–300 K. The erbium internal relaxation efficiency from the second (4I11/2) to the first (4I13/2) excited state upon luminescence-center-mediated Er3+ excitation is investigated. Despite the observation of temperature-dependent relaxation rates, the erbium internal relaxation efficiency is found to be remarkably temperature independent, which suggests that the internal relaxation efficiency is near unity. Internal relaxation is shown to account for 50%–55% of the 4I13/2 excitation events in the entire temperature range. These results demonstrate that high pump efficiency and stable operation of devices based on this material will be possible under varying thermal conditions.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
61.72.up Other materials
81.40.Gh Other heat and thermomechanical treatments

Tip-enhanced single molecule fluorescence near-field microscopy in aqueous environment

Heinrich G. Frey, Jan Paskarbeit, and Dario Anselmetti

Appl. Phys. Lett. 94, 241116 (2009); http://dx.doi.org/10.1063/1.3155190 (3 pages) | Cited 1 time

Online Publication Date: 18 June 2009

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For nanobiophysical applications, scanning near-field optical microscopy must combine high optical resolution and single fluorescent molecule sensitivity with the ability to operate in aqueous solution. These requirements can be achieved using the electric field enhancement at the tip of illuminated silicon probes for atomic force miscroscopy (AFM), whereby single ATTO-740 dye molecules could be imaged at an optical resolution down to 20 nm under ambient conditions as well as in aqueous solution. Two illumination modes have been tested: (a) bottom illumination in a total internal reflection microscopy setup and (b) direct top illumination, both with dedicated phase-sensitive single photon counting technology in dynamic AFM mode of operation.
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07.79.Fc Near-field scanning optical microscopes
07.79.Lh Atomic force microscopes
87.64.Dz Scanning tunneling and atomic force microscopy
87.64.mt Near-field scanning
87.64.kv Fluorescence
87.80.Nj Single-molecule techniques

Net motion of an ensemble of many Brownian particles captured with a self-mixing laser

Kenju Otsuka, Takayuki Ohtomo, Hironori Makino, Seiichi Sudo, and Jing-Yuan Ko

Appl. Phys. Lett. 94, 241117 (2009); http://dx.doi.org/10.1063/1.3156826 (3 pages) | Cited 1 time

Online Publication Date: 19 June 2009

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The overall dynamics of Brownian particles suspended in water were captured with high time resolution by using a self-mixing thin-slice solid-state laser. The net motion of an ensemble of many particles moving in the small imaging field observed at given time intervals was found to be represented by Brownian motions of an effective medium obeying the Ornstein–Uhlenbeck process, whose physical parameters have scaling relations with those of a real turbid medium. An approach toward measuring particle diffusion constants is described.
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42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
05.40.Jc Brownian motion
82.70.Kj Emulsions and suspensions
42.55.Rz Doped-insulator lasers and other solid state lasers

Dynamic optically induced planar terahertz quasioptics

D. G. Cooke and P. Uhd Jepsen

Appl. Phys. Lett. 94, 241118 (2009); http://dx.doi.org/10.1063/1.3153988 (3 pages) | Cited 2 times

Online Publication Date: 19 June 2009

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Optical control of the propagation direction of a terahertz pulse inside an optically transparent parallel plate waveguide is demonstrated by patterned charge carrier photoexcitation of a silicon slab embedded within the waveguide. It is shown experimentally and through finite element simulations that photoexcitations with sufficient conductivity can induce a partial reflection, capable of steering the pulse inside the two-dimensional waveguide. A beamsplitter is demonstrated as proof of principle and is used to delay the arrival of the reflected terahertz pulse at the detector by several picoseconds by moving the excitation in the plane.
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42.82.-m Integrated optics
42.79.Fm Reflectors, beam splitters, and deflectors

Ultrafast rerouting of light via slow modes in a nanophotonic directional coupler

T. Kampfrath, D. M. Beggs, T. P. White, M. Burresi, D. van Oosten, T. F. Krauss, and L. Kuipers

Appl. Phys. Lett. 94, 241119 (2009); http://dx.doi.org/10.1063/1.3153989 (3 pages) | Cited 14 times

Online Publication Date: 19 June 2009

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We demonstrate that two coupled photonic-crystal waveguides can route two subsequently arriving light pulses to different output ports even though the pulses are only 3 ps apart. This rerouting of light is due to an ultrafast shift in the transmittance spectrum triggered by the generation of electrons and holes in the Si base material by a femtosecond laser pulse. The use of slow-light modes allows for a coupler length of only 5.2 μm. Since these modes are not directly involved, the 3 ps dead time is solely determined by the duration of the input pulse rather than its transit time through the device.
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42.82.Et Waveguides, couplers, and arrays
42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Exciton-related electroluminescence from ZnO nanowire light-emitting diodes

Mariano A. Zimmler, Tobias Voss, Carsten Ronning, and Federico Capasso

Appl. Phys. Lett. 94, 241120 (2009); http://dx.doi.org/10.1063/1.3157274 (3 pages) | Cited 21 times

Online Publication Date: 19 June 2009

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The authors study the microscopic origin of the electroluminescence from zinc oxide (ZnO) nanowire light-emitting diodes (LEDs) fabricated on a heavily doped p-type silicon (p-Si) substrate. By comparing the low-temperature photoluminescence and electroluminescence of a single nanowire LED, bound- and free-exciton related recombination processes, together with their longitudinal-optical phonon replicas, can be identified as the origin of both electroluminescence and photoluminescence.
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85.60.Jb Light-emitting devices

Ultraviolet coherent random lasing in randomly assembled SnO2 nanowires

H. Y. Yang, S. F. Yu, S. P. Lau, S. H. Tsang, G. Z. Xing, and T. Wu

Appl. Phys. Lett. 94, 241121 (2009); http://dx.doi.org/10.1063/1.3157842 (3 pages) | Cited 17 times

Online Publication Date: 19 June 2009

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Although nanostructured SnO2 exhibited ultraviolet stimulated emission at room temperature, the low emission intensities and occurrence of gain saturation restricted them to be considered as luminescent materials for semiconductor lasers. In this letter, we find that a large ultraviolet excitonic gain can be obtained from SnO2 nanowires coated with an amorphous layer. Under effective pumping, ultraviolet coherent random lasing can be realized from randomly assembled SnO2 nanowires at room temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Increasing diffraction efficiency by heating phase gratings formed by femtosecond laser irradiation in poly(methyl methacrylate)

Satoshi Hirono, Makoto Kasuya, Katsumi Matsuda, Yasuyuki Ozeki, Kazuyoshi Itoh, Hiroyuki Mochizuki, and Wataru Watanabe

Appl. Phys. Lett. 94, 241122 (2009); http://dx.doi.org/10.1063/1.3155506 (3 pages) | Cited 12 times

Online Publication Date: 19 June 2009

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The diffraction efficiency of phase gratings formed by femtosecond laser irradiation in poly(methyl methacrylate) was increased by more than an order of magnitude by subsequent heating below the glass transition temperature (Tg). The first-order Bragg diffraction efficiency of a 10 μm period grating was 1.9% without heating, whereas it increased to 72% when heated at 70 °C for 500 h. This is because the induced refractive index changes (Δn) were increased by heating. From the Lorentz–Lorenz equation, one of the reasons why Δn increases by heating could be a slight volume contraction in the irradiated area.
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42.70.Jk Polymers and organics
42.79.Dj Gratings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
64.70.P- Glass transitions of specific systems
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Low temperature hydrogen desorption in MgAl thin films achieved by using a nanoscale Ta/Pd bilayer catalyst

Helmut Fritzsche, Colin Ophus, Chris T. Harrower, Erik Luber, and David Mitlin

Appl. Phys. Lett. 94, 241901 (2009); http://dx.doi.org/10.1063/1.3154550 (3 pages) | Cited 10 times

Online Publication Date: 15 June 2009

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We used a nanoscale (5 nm Ta/5 nm Pd) bilayer catalyst to achieve remarkable desorption kinetics for thin films. Full hydrogen desorption occurred at 100 °C with a noticeable desorption even at room temperature. This is a significant improvement relative to the 175 °C needed to fully desorb an identical film with a single Pd layer acting as the catalyst. Neutron reflectometry confirmed that the Ta/Pd bilayer remained intact both after hydrogen absorption and following the hydrogen desorption. We used x-ray diffraction analysis to gather complementary information regarding the crystal structure of the as-synthesized, sorbed and desorbed film.
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68.43.Nr Desorption kinetics
68.65.Ac Multilayers
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.-a Thin film structure and morphology

Negative thermal expansion of ReO3 in the extended temperature range

Tapan Chatterji, Thomas C. Hansen, Michela Brunelli, and Paul F. Henry

Appl. Phys. Lett. 94, 241902 (2009); http://dx.doi.org/10.1063/1.3155191 (3 pages) | Cited 6 times

Online Publication Date: 15 June 2009

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We reported previously [ T. Chatterji et al., Phys. Rev. B 78, 134105 (2008) ] negative thermal expansion (NTE) in ReO3 in the limited temperature range from 2 to 220 K. Here we discovered NTE in ReO3 at higher-temperature region from 600 to 680 K. We determined the temperature variation in the lattice parameter and the unit cell volume of ReO3 by neutron diffraction. The temperature variation in the lattice parameter and the unit cell volume show two regions of NTE and two minima. We attribute the NTE of ReO3 to be the result of anharmonicity and anomalous softening of M3 phonon mode.
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65.40.De Thermal expansion; thermomechanical effects
61.66.Fn Inorganic compounds
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Cascade emissions of an erbium-ytterbium doped silica-zirconia nanostructured optical fiber under supercontinuum irradiation

Gurvan Brasse, Christine Restoin, Jean-Louis Auguste, and Jean-Marc Blondy

Appl. Phys. Lett. 94, 241903 (2009); http://dx.doi.org/10.1063/1.3155193 (3 pages) | Cited 1 time

Online Publication Date: 15 June 2009

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An erbium-ytterbium doped silica-zirconia nanostructured optical fiber is elaborated by using the chemical sol-gel method and its waveguiding properties are studied. A supercontinuum irradiation of the so-fabricated fiber leads to an exotic cascade emission of photons at 515 and 640 nm, as well as a wide emission band between 530 and 590 nm. Upconversion mechanisms and downconversion mechanisms are finally highlighted to explain these phenomena.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
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