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29 Dec 2008

Volume 93, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 261101 (2008); http://dx.doi.org/10.1063/1.3053074 (3 pages)

Takashi Fujikura, Osamu Matsuda, Dieter M. Profunser, Oliver B. Wright, Jeremy Masson, and Sylvain Ballandras
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Real-time imaging of acoustic waves on a bulk acoustic resonator

Takashi Fujikura, Osamu Matsuda, Dieter M. Profunser, Oliver B. Wright, Jeremy Masson, and Sylvain Ballandras

Appl. Phys. Lett. 93, 261101 (2008); http://dx.doi.org/10.1063/1.3053074 (3 pages) | Cited 8 times

Online Publication Date: 29 December 2008

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Time resolved images of acoustic waves in the 100 MHz–2.2 GHz range are obtained for an electrically excited thin-film bulk acoustic wave resonator by means of an ultrafast optical technique. Electrical pulses, synchronized to ultrashort laser pulses, piezoelectrically excite the device, and synchronous near-infrared laser pulses interferometrically detect surface motion. The frequency dispersion is extracted using spatiotemporal Fourier transforms, revealing both longitudinal and surface acoustic modes.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.58.Fm Sound level meters, level recorders, sound pressure, particle velocity, and sound intensity measurements, meters, and controllers
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators

Partial confinement photonic crystal waveguides

S. Saini, C.-Y. Hong, N. Pfaff, L. C. Kimerling, and J. Michel

Appl. Phys. Lett. 93, 261102 (2008); http://dx.doi.org/10.1063/1.3059553 (3 pages) | Cited 2 times

Online Publication Date: 29 December 2008

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One-dimensional photonic crystal waveguides with an incomplete photonic band gap are modeled and proposed for an integration application that exploits their property of partial angular confinement. Planar apodized photonic crystal structures are deposited by plasma enhanced chemical vapor deposition and characterized by reflectivity as a function of angle and polarization, validating a partial confinement design for light at 850 nm wavelength. Partial confinement identifies an approach for tailoring waveguide properties by the exploitation of conformal film deposition over a substrate with angularly dependent topology. An application for an optoelectronic transceiver is demonstrated.
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42.82.Et Waveguides, couplers, and arrays
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Bq Design and performance testing of integrated-optical systems

Optical far-field and near-field observations of the strong angular dispersion in a lithium niobate photonic crystal superprism designed for double (passive and active) demultiplexer applications

Séverine Diziain, Julien Amet, Fadi I. Baida, and Maria-Pilar Bernal

Appl. Phys. Lett. 93, 261103 (2008); http://dx.doi.org/10.1063/1.3059558 (3 pages) | Cited 11 times

Online Publication Date: 29 December 2008

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We report on a lithium niobate photonic crystal (PC) superprism device designed for double demultiplexer applications. In fact, the strong angular beam steering cannot only be reached by passively tuning the wavelength but it can also be actively controlled by the Pockels effect enhanced due to the slow light phenomenon. The performance of the passive device is demonstrated by measuring its transmission properties. Optical far field and near-field experiments, corroborated by two-dimensional finite difference time domain (2D-FDTD) calculations, exhibit an angular dispersion of 1.5°/nm. A value as high as 4.3°/nm is expected by improving the PC design as supported by 2D-FDTD simulation.
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42.79.-e Optical elements, devices, and systems
02.70.Bf Finite-difference methods
42.70.Qs Photonic bandgap materials
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
78.20.Jq Electro-optical effects

Terahertz Si:B blocked-impurity-band detectors defined by nonepitaxial methods

P. Rauter, T. Fromherz, S. Winnerl, M. Zier, A. Kolitsch, M. Helm, and G. Bauer

Appl. Phys. Lett. 93, 261104 (2008); http://dx.doi.org/10.1063/1.3059559 (3 pages) | Cited 2 times

Online Publication Date: 29 December 2008

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The molecular beam epitaxial (MBE) fabrication of blocked-impurity-band detectors (BIB) has been a technologically complex and delicate matter ever since its demonstration in silicon, and has not been adapted for other material systems offering detection onsets at lower terahertz frequencies. We report the fabrication and characterization of a vertical Si:B BIB, circumventing the intrinsically troublesome MBE growth of an ultrapure blocking layer by employing ion implantation. We present a thorough characterization of our device, which exhibits highly competitive figures of merits. Our results not only increase the accessibility of BIB fabrication tools for ultrasensitive terahertz detection but also open a road to other material systems.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
61.72.U- Doping and impurity implantation
85.60.Gz Photodetectors (including infrared and CCD detectors)

Intracavity terahertz generation inside a high-energy ultrafast soliton fiber laser

Gabor Matthäus, Bülend Ortaç, Jens Limpert, Stefan Nolte, Rico Hohmuth, Martin Voitsch, Wolfgang Richter, Boris Pradarutti, and Andreas Tünnermann

Appl. Phys. Lett. 93, 261105 (2008); http://dx.doi.org/10.1063/1.3056118 (3 pages) | Cited 4 times

Online Publication Date: 29 December 2008

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Intracavity terahertz emission inside a high-energy ultrafast Yb-doped fiber laser is presented. The terahertz radiation is generated by a transient photocurrent induced at the surface of a saturable InGaAs multiquantum well grown by molecular beam epitaxy on top of a semiconductor Bragg reflector. This device simultaneously works as the saturable absorber mirror for initiating and managing the passive mode locking required for the ultrashort pulse operation of the laser system. The maximum terahertz average power achieved is 4.2 μW, which reveals a net conversion efficiency of 3.1×10−5.
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42.55.Wd Fiber lasers
73.25.+i Surface conductivity and carrier phenomena
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.82.Gw Other integrated-optical elements and systems
72.40.+w Photoconduction and photovoltaic effects
42.60.Fc Modulation, tuning, and mode locking

Systematic study of broadband terahertz gas sensor

Xiaofei Lu, Nicholas Karpowicz, Yunqing Chen, and X.-C. Zhang

Appl. Phys. Lett. 93, 261106 (2008); http://dx.doi.org/10.1063/1.3056119 (3 pages) | Cited 10 times

Online Publication Date: 29 December 2008

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Broadband terahertz wave detection through field-induced second harmonic generation was systematically investigated using selected gases. The dependences of the detected second harmonic intensity on probe pulse energy, bias field strength, gas pressure, and third order nonlinear susceptibility are systematically investigated with xenon, nitrogen, SF6, and alkanes. Experiment results reveal that the detected second harmonic intensity quadratically depends on the third order nonlinear susceptibility of the gas. Two orders of magnitude enhancement in the dynamic range of broadband terahertz wave detection are observed with alkane gas (C4H10) sensor.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

The observation of comblike transmission spectrum from a tapered single mode fiber tip

Y. Li and X. Bao

Appl. Phys. Lett. 93, 261107 (2008); http://dx.doi.org/10.1063/1.3059574 (3 pages) | Cited 5 times

Online Publication Date: 29 December 2008

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Tapered fiber tips are fabricated by the fast stretching of a heated single mode fiber until it breaks. As the fiber tip diameter decreases, the propagation mode converts from the single core mode to a few cladding modes. The cladding modes are then emitted from the fiber tip and interfere with each other in the near field. Along the propagation direction, the optical field is found to be modulated due to multibeam interferences. Interestingly, broadband transmission spectrums show equidistant comblike peaks. A tunable spatial filter based on a fiber tip is realized to reshape a broadband light source.
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42.81.-i Fiber optics
42.79.Ci Filters, zone plates, and polarizers

High-quality InGaN/GaN heterojunctions and their photovoltaic effects

Xinhe Zheng, Ray-Hua Horng, Dong-Sing Wuu, Mu-Tao Chu, Wen-Yih Liao, Ming-Hsien Wu, Ray-Ming Lin, and Yuan-Chieh Lu

Appl. Phys. Lett. 93, 261108 (2008); http://dx.doi.org/10.1063/1.3056628 (3 pages) | Cited 34 times

Online Publication Date: 29 December 2008

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High-quality p-GaN/i-In0.1Ga0.9N/n-GaN heterojunctional epilayers are grown on (0001)-oriented sapphire substrates by metal organic chemical vapor deposition. The Pendellösung fringes around the InGaN peak in high-resolution x-ray diffraction (HRXRD) confirm a sharp interface between InGaN and GaN films. The corresponding HRXRD and photoluminescence measurements demonstrate that there is no observable phase separation. The improvement in crystal quality yields high-performance photovoltaic cells with open-circuit voltage of around 2.1 eV and fill factor up to 81% under standard AM 1.5 condition. The dark current-voltage measurements show very large shunt resistance, implying an insignificant leakage current in the devices and therefore achieving the high fill factor in the illuminated case.
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72.40.+w Photoconduction and photovoltaic effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Geometrical effects in the energy transfer mechanism for silicon nanocrystals and Er3+

K. Choy, F. Lenz, X. X. Liang, F. Marsiglio, and A. Meldrum

Appl. Phys. Lett. 93, 261109 (2008); http://dx.doi.org/10.1063/1.3058440 (3 pages) | Cited 12 times

Online Publication Date: 29 December 2008

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Silicon nanoclusters (NCs) strongly sensitize the luminescence of Er3+ ions. Attempts to calculate the interaction distance have assumed that the Förster [Ann. Phys. 437, 55 (1948) ] and Dexter [J. Chem. Phys. 21, 836 (1953) ] relationships for point-to-point energy transfer can be applied to experiments based on multilayered thin-film specimens. Here, the effective finite plane-to-plane relationships are derived for both interaction mechanisms. These relationships show that energy transfer can result from the Förster interaction despite the fact that the measured luminescence intensity varies much more weakly with NC-Er3+ separation than predicted by theory for point dipoles. An effective energy transfer distance is found for the NC-Er3+ system.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
61.46.Hk Nanocrystals
78.55.Ap Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Experimental quality factor determination of guided-mode resonances in photonic crystal slabs

Yousef Nazirizadeh, Uli Lemmer, and Martina Gerken

Appl. Phys. Lett. 93, 261110 (2008); http://dx.doi.org/10.1063/1.3058682 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2008

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We report on a method how quality factors of guided-mode resonances in photonic crystal slabs (PCSs) can be determined in the reciprocal space. Transmission measurements through PCSs are performed using crossed polarization filters before and after the PCS. Consequently the unwanted illumination source is suppressed and only the guided-mode resonances are revealed. This method allows for a spatially resolved quality factor determination in the reciprocal space. As an example we scan a two-dimensional PCS and visualize its inhomogeneities. Although the resonance wavelength variations were only ≈3 nm, the quality factor varies from 100 to 350.
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42.70.Qs Photonic bandgap materials
42.25.Bs Wave propagation, transmission and absorption
42.25.Ja Polarization

Low-loss nonselectively oxidized AlxGa1−xAs heterostructure waveguides

Y. Lou and D. C. Hall

Appl. Phys. Lett. 93, 261111 (2008); http://dx.doi.org/10.1063/1.3058709 (3 pages)

Online Publication Date: 29 December 2008

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The use of nonselective AlGaAs oxidation (i.e., via the use of controlled, dilute O2 addition during wet thermal oxidation) enables a significant propagation loss reduction in fully oxidized Al0.3Ga0.7As/Al0.85Ga0.15As planar oxide single heterostructure waveguides. Prism coupling measurements are utilized to characterize the oxidized waveguide cladding and core layer thicknesses, refractive indices, and propagation loss. At a wavelength of 633 nm, above the Al0.3Ga0.7As core’s bandgap energy, the strongly absorbing semiconductor heterostructure waveguide is converted by nonselective oxidation to a transparent oxide heterostructure waveguide with a propagation loss of only 5.0 dB/cm (1.15 cm−1). A low loss of 3.6 dB/cm (0.83 cm−1) is obtained at 1.3 μm.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Temperature compensated overdrive in vertically aligned liquid crystal displays

Pieter J. M. Vanbrabant, Nathalie Velthoven-Dessaud, Jan F. Strömer, and Kristiaan Neyts

Appl. Phys. Lett. 93, 261112 (2008); http://dx.doi.org/10.1063/1.3058714 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2008

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The occurrence of backflow in vertically aligned liquid crystal displays (VA-LCDs) inhibits application of conventional overdrive techniques to achieve faster switching. This (hydro)dynamic behavior is simulated accurately by using the Leslie–Ericksen theory in a one-dimensional model. Taking the limitations due to backflow into account from these simulations, we designed overdrive schemes for VA-LCDs. The temperature sensitivity of a fixed overdrive table was eliminated by adapting the scheme to the simulated temperature variations in the dynamic behavior. Experimental verification in the 25–75 °C range shows that the resulting temperature compensated overdrive leads to faster switching, which is expected to be artifact free.
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85.60.Pg Display systems

Multilayer stacking technique for holographic polymer dispersed liquid crystals

Sameet K. Shriyan, Kashma K. Rai, Alyssa Bellingham, and Adam K. Fontecchio

Appl. Phys. Lett. 93, 261113 (2008); http://dx.doi.org/10.1063/1.3058763 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2008

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We demonstrate an alternate method of stacking holographic polymer dispersed liquid crystal (HPDLC) reflection gratings on substrates coated with indium tin oxide on both sides allowing independent switching of each grating in the stack. Successive layers of the stack are formed by switching existing layers, while exposing the subsequent layer to an interference pattern. Wavefront analysis based on wavefront propagation through HPDLC with electric field on and off is used to substantiate the improvement in the reflection efficiency of the layers in the stack. Results show an optical path length reduction due to elimination of substrate layers at each grating.
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42.40.Eq Holographic optical elements; holographic gratings
42.79.Wc Optical coatings
42.70.Df Liquid crystals

Time and spectrally resolved enhanced fluorescence using silver nanoparticle impregnated polycarbonate substrates

Laura Lagonigro, Anna C. Peacock, Stefan Rohrmoser, Tom Hasell, Steven M. Howdle, Pier J. A. Sazio, and Pavlos G. Lagoudakis

Appl. Phys. Lett. 93, 261114 (2008); http://dx.doi.org/10.1063/1.3059567 (3 pages) | Cited 1 time

Online Publication Date: 31 December 2008

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Silver nanoparticle impregnated polycarbonate strips have been investigated as substrates for metal-enhanced photoluminescence of a blue emitting dye molecule (coumarin 102). By considering simultaneous time and spectrally resolved photoluminescence we observed fluorescence enhancement resulting from plasmon coupling with an increase in the emission by a factor of ∼8.5 with an associated reduction in the photon lifetime. We relate the fast and slow components of the observed emission decay to the presence of both monomers and aggregates in the films and we discuss their different responses to the plasmon coupling.
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78.47.jd Time resolved luminescence
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds

Enhancing and tuning absorption properties of microwave absorbing materials using metamaterials

Yanhong Zou, Leyong Jiang, Shuangchun Wen, Weixing Shu, Yongjun Qing, Zhixiang Tang, Hailu Luo, and Dianyuan Fan

Appl. Phys. Lett. 93, 261115 (2008); http://dx.doi.org/10.1063/1.3062854 (3 pages) | Cited 7 times

Online Publication Date: 31 December 2008

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We proposed and demonstrated a scheme to enhance and tune absorption properties of conventional microwave absorbing materials (MAMs) by metamaterials (MMs). By covering a MAM, say, carbonyl iron powder coating, with MMs composed of split ring resonators (SRRs) and wires, we show both by experiments and by simulations that the maximum reflection loss (RL) is increased significantly and the frequency region for absorption is shifted to lower frequency. The frequency region in which the maximum RL is less than −10 dB shifts from 5–7 to 4.2–6.2 GHz for perpendicular polarization electromagnetic waves and to 4–9 GHz for parallel polarization waves. Simulation results reveal that the magnetic resonance obtained by SRRs and the electric resonance obtained by copper wires are the main factors in enhancing and tuning microwave absorption properties.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Tunability of notch angles in quantum cascade microlasers with highly deformed spiral resonators

Dongxia Qu, Richard Cendejas, Zhijun Liu, Claire Gmachl, and Fred Towner

Appl. Phys. Lett. 93, 261116 (2008); http://dx.doi.org/10.1063/1.3058679 (3 pages) | Cited 3 times

Online Publication Date: 31 December 2008

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We study the mode spectra and lasing thresholds of spiral-shaped quantum cascade lasers with a deformation in the range of 10%–45% with respect to the radius and with various notch angles. We observe that the initial lasing wavelength and the threshold of a laser are correlated with each other, and they can be jointly tuned by both the deformation coefficient and notch angle. The dependence of the cavity loss on the deformation coefficient is analyzed via the measured lasing thresholds and frequency dependent gain coefficients. Moreover, we achieve single mode emission by tuning the notch angle and deformation coefficients.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Sa Microcavity and microdisk lasers

Luminescent properties in the strain adjusted phosphor-free GaN based white light-emitting diode

H. Fang, L. W. Sang, L. B. Zhao, S. L. Qi, Y. Z. Zhang, X. L. Yang, Z. J. Yang, and G. Y. Zhang

Appl. Phys. Lett. 93, 261117 (2008); http://dx.doi.org/10.1063/1.3063044 (3 pages) | Cited 6 times

Online Publication Date: 31 December 2008

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A kind of phosphor-free GaN based white light-emitting diode was fabricated with a strain adjusting InGaN interlayer. The origin of the strain adjusted white luminescent properties was studied with cathodoluminescence, asymmetrically reciprocal space mapping with high resolution x-ray diffraction, and scanning electron microscopy. The yellow and blue components of the electroluminescence spectrum were attributed to the high indium core and the adjacent indium depleted region in the inverted pyramidal pits on the device surface, respectively. These pits existed at the end of the dislocations induced by the strain relaxation process of the InGaN interlayer.
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85.60.Jb Light-emitting devices
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A continuous kilohertz Cu Kα source produced by submillijoule femtosecond laser pulses for phase contrast imaging

J. A. Chakera, A. Ali, Y. Y. Tsui, and R. Fedosejevs

Appl. Phys. Lett. 93, 261501 (2008); http://dx.doi.org/10.1063/1.3046727 (3 pages) | Cited 5 times

Online Publication Date: 29 December 2008

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We report a continuously operated Cu Kα x-ray source produced by a commercial kilohertz submillijoule femtosecond laser system. The source has an x-ray conversion of ∼ 4×10−5 into Kα line emission at 8.05 keV. The microplasma x-ray source has a size of 8 μm (full width at half maximum) produced by focusing 260 μJ laser pulses on a moving Cu-wire target. An average photon flux of ∼ 1.1×109 photons/sr/s is obtained using the above laser pulses. The source has been used to record phase contrast images of test samples. This compact x-ray source can serve as a low cost operating system for phase contrast imaging in clinical applications.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.50.Dg Plasma sources
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Diagnostics of ballistic electrons in a dc/rf hybrid capacitively coupled discharge

Lin Xu, Lee Chen, Merritt Funk, Alok Ranjan, Mike Hummel, Ron Bravenec, Radha Sundararajan, Demetre J. Economou, and Vincent M. Donnelly

Appl. Phys. Lett. 93, 261502 (2008); http://dx.doi.org/10.1063/1.3062853 (3 pages) | Cited 10 times

Online Publication Date: 31 December 2008

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The energy distribution of ballistic electrons in a dc/rf hybrid parallel-plate capacitively coupled plasma reactor was measured. Ballistic electrons originated as secondaries produced by ion and electron bombardment of the electrodes. The energy distribution of ballistic electrons peaked at the value of the negative bias applied to the dc electrode. As that bias became more negative, the ballistic electron current on the rf substrate electrode increased dramatically. The ion current on the dc electrode also increased.
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52.70.Ds Electric and magnetic measurements
73.23.Ad Ballistic transport
61.80.Fe Electron and positron radiation effects
61.80.Jh Ion radiation effects
52.80.Pi High-frequency and RF discharges

Electron heating in radio-frequency capacitively coupled atmospheric-pressure plasmas

D. W. Liu, F. Iza, and M. G. Kong

Appl. Phys. Lett. 93, 261503 (2008); http://dx.doi.org/10.1063/1.3058686 (3 pages) | Cited 20 times

Online Publication Date: 31 December 2008

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In atmospheric-pressure plasmas the main electron heating mechanism is Ohmic heating, which has distinct spatial and temporal evolutions in the α and γ modes. In γ discharges, ionizing avalanches in the sheaths are initiated not only by secondary electrons but also by metastable pooling reactions. In α discharges, heating takes place at the sheath edges and in contrast with low-pressure plasmas, close to 50% of the power absorbed by the electrons is absorbed at the edge of the retreating sheaths. This heating is due to a field enhancement caused by the large collisionality in atmospheric-pressure discharges.
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52.50.Nr Plasma heating by DC fields; ohmic heating, arcs
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.80.-s Electric discharges
52.40.Kh Plasma sheaths

Plasma-controlled adatom delivery and (re)distribution: Enabling uninterrupted, low-temperature growth of ultralong vertically aligned single walled carbon nanotubes

Eugene Tam and Kostya (Ken) Ostrikov

Appl. Phys. Lett. 93, 261504 (2008); http://dx.doi.org/10.1063/1.3058766 (3 pages) | Cited 7 times

Online Publication Date: 31 December 2008

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Large-scale ( ∼ 109 atoms) numerical simulations reveal that plasma-controlled dynamic delivery and redistribution of carbon atoms between the substrate and nanotube surfaces enable the growth of ultralong single walled carbon nanotubes (SWCNTs) and explain the common experimental observation of slower growth at advanced stages. It is shown that the plasma-based processes feature up to two orders of magnitude higher growth rates than equivalent neutral-gas systems and are better suited for the SWCNT synthesis at low nanodevice friendly temperatures.
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81.07.De Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.15.Jj Ion and electron beam-assisted deposition; ion plating
52.77.Dq Plasma-based ion implantation and deposition
81.16.-c Methods of micro- and nanofabrication and processing
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Subnanosecond time-resolved x-ray measurements using an organic-inorganic perovskite scintillator

S. Kishimoto, K. Shibuya, F. Nishikido, M. Koshimizu, R. Haruki, and Y. Yoda

Appl. Phys. Lett. 93, 261901 (2008); http://dx.doi.org/10.1063/1.3059562 (3 pages) | Cited 2 times

Online Publication Date: 29 December 2008

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We have developed a fast x-ray detector using an organic-inorganic perovskite scintillator of phenethylamine lead bromide (PhE-PbBr4). The scintillator had a dominant light emission with a fast decay time of 9.9 ns. An x-ray detector equipped with a 0.9-mm-thick PhE-PbBr4 crystal was used to detect nuclear resonant scattering in 61Ni (the first excited level: 67.41 keV; lifetime: 7.6 ns) by using synchrotron radiation. With this detector, we could successfully record the decaying gamma rays emitted from 61Ni with a time resolution of 0.7 ns (full width at half maximum) and a relatively high detection efficiency of 24%.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
29.40.Mc Scintillation detectors

Dynamic delamination of patterned thin films

Soma S. V. Kandula, Phuong Tran, Philippe H. Geubelle, and Nancy R. Sottos

Appl. Phys. Lett. 93, 261902 (2008); http://dx.doi.org/10.1063/1.3056639 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2008

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We investigate laser-induced dynamic delamination of a patterned thin film on a substrate. Controlled delamination results from our insertion of a weak adhesion region beneath the film. The inertial forces acting on the weakly bonded portion of the film lead to stable propagation of a crack along the film/substrate interface. Through a simple energy balance, we extract the critical energy for interfacial failure, a quantity that is difficult and sometimes impossible to characterize by more conventional methods for many thin film/substrate combinations.
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68.60.Bs Mechanical and acoustical properties
68.55.J- Morphology of films
62.20.mt Cracks
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

TixSi1−xO2 optical coatings with tunable index and their response to intense subpicosecond laser pulse irradiation

D. Nguyen, L. A. Emmert, I. V. Cravetchi, M. Mero, W. Rudolph, M. Jupe, M. Lappschies, K. Starke, and D. Ristau

Appl. Phys. Lett. 93, 261903 (2008); http://dx.doi.org/10.1063/1.3050536 (3 pages) | Cited 8 times

Online Publication Date: 29 December 2008

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Ion-beam sputtered TixSi1−xO2 binary-oxide films of high optical quality with tunable bandgap and refractive index were produced using zone targets. The suitability of the films for high-power subpicosecond laser applications is explored by laser breakdown measurements. The observed scaling laws of the single-pulse breakdown threshold—a power law with respect to pulse duration and a linear law with respect to bandgap energy—are similar to results obtained with high-quality simple oxides. The single- and multiple-pulse breakdown behaviors of these binary films indicate only slightly larger defect densities than found in simple oxides.
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78.66.Nk Insulators
42.79.Wc Optical coatings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Photoluminescence dynamics of exciton-exciton scattering in a lightly alloyed InGaN thin film

M. Nakayama and K. Sakaguchi

Appl. Phys. Lett. 93, 261904 (2008); http://dx.doi.org/10.1063/1.3054166 (3 pages)

Online Publication Date: 30 December 2008

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We have investigated the photoluminescence (PL) dynamics of a lightly alloyed In0.02Ga0.98N thin film under intense excitation conditions at 10 K. In the In0.02Ga0.98N thin film, a PL band due to exciton-exciton scattering, the so-called P band, appears with a thresholdlike nature in the excitation-power region higher than ∼ 3 μJ/cm2. Under the condition that the exciton-exciton scattering occurs, the PL-decay profile consists of a fast decay component of the P band (of the order of 10 ps) and a slow decay component of a localized exciton band. The decay time of the P band gradually shortens with increasing excitation power. The change in the decay time can be explained qualitatively by the photon-like characteristics of the lower polariton branch that is the final state of the P emission. Furthermore, we have clearly observed the temporal change in the peak energy of the P band, which reflects an effective temperature of the excitonic system. The energy shift of the P band suggests that the P emission process reaches equilibrium with the lattice temperature after ∼ 100 ps.
Show PACS
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.-y Excitons and related phenomena
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