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28 Nov 2005

Volume 87, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 221108 (2005); http://dx.doi.org/10.1063/1.2137458 (3 pages)

V. Barna, S. Ferjani, A. De Luca, R. Caputo, N. Scaramuzza, C. Versace, and G. Strangi
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Optical properties of tetrapod-shaped CdTe nanocrystals

Davide Tarì, Milena De Giorgi, Fabio Della Sala, Luigi Carbone, Roman Krahne, Liberato Manna, Roberto Cingolani, Stefan Kudera, and Wolfgang J. Parak

Appl. Phys. Lett. 87, 224101 (2005); http://dx.doi.org/10.1063/1.2130727 (3 pages) | Cited 22 times

Online Publication Date: 21 November 2005

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We studied the carrier confinement in tetrapod-shaped colloidal CdTe nanocrystals by means of absorption, photoluminescence, and photoluminescence excitation spectroscopy at room and cryogenic temperatures. The spectra show features characteristic of the tetrapod shape together with a clear dependence on the dominant confinement parameter, i.e., the diameter of the tetrapod arm. Theoretical calculations based on an envelope-function approximation and using the exact tetrapod shape have been performed to assign the observed spectral features. Oscillator strength and size dependence of the transitions energy have been calculated showing a direct correlation between the oscillator strength and the nanocrystal shape.
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78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Coulomb explosion potential sputtering induced by slow highly charged ion impact

Masahide Tona, Satoshi Takahashi, Kazuo Nagata, Nobuo Yoshiyasu, Chikashi Yamada, Nobuyuki Nakamura, Shunsuke Ohtani, and Makoto Sakurai

Appl. Phys. Lett. 87, 224102 (2005); http://dx.doi.org/10.1063/1.2136361 (3 pages) | Cited 7 times

Online Publication Date: 21 November 2005

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We have observed secondary ion emission from a hydrogen-terminated Si(111) 1×1 surface and a native SiO2 thin film on the Si substrate (SiO2/Si) irradiated with slow (vion<vBohr) iodine highly charged ions (HCIs) in a wide range of charge state q from q = 15 up to 50. The yields of secondary ions evaluated from time-of-flight mass spectra showed rapid increases with q of the projectile. The relation of the yields to the potential energy of HCIs is discussed in terms of the Coulomb explosion model. It was found that the simultaneous emission of multiple Si+ ions occurs in an event of a single high-q HCI impact onto the SiO2/Si.
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68.47.Fg Semiconductor surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.82.Ms Insulators

Microwave-cut silicon layer transfer

D. C. Thompson, T. L. Alford, J. W. Mayer, T. Hochbauer, M. Nastasi, S. S. Lau, N. David Theodore, K. Henttinen, llkka Suni, and Paul K. Chu

Appl. Phys. Lett. 87, 224103 (2005); http://dx.doi.org/10.1063/1.2135395 (3 pages) | Cited 6 times

Online Publication Date: 22 November 2005

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Microwave heating is used to initiate exfoliation of silicon layers in conjunction with the ion-cut process for transfer of silicon layers onto insulator or heterogeneous layered substrates. Samples were processed inside a 2.45 GHz, 1300 W cavity applicator microwave system for time durations as low as 12 s. This is a significant decrease in exfoliation incubation times. Sample temperatures measured by pyrometry were within previous published ranges. Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy were used to determine layer thickness and crystallinity. Surface quality was measured by using atomic force microscopy. Hall measurements were used to characterize electrical properties as a function of postcut anneal time and temperature.
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81.05.Cy Elemental semiconductors
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
72.20.My Galvanomagnetic and other magnetotransport effects

Maser oscillation in a whispering-gallery-mode microwave resonator

P.-Y. Bourgeois, N. Bazin, Y. Kersalé, V. Giordano, M. E. Tobar, and M. Oxborrow

Appl. Phys. Lett. 87, 224104 (2005); http://dx.doi.org/10.1063/1.2137452 (3 pages) | Cited 9 times

Online Publication Date: 23 November 2005

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We report the observation of above-threshold maser oscillation in a whispering-gallery (WG)-mode resonator, whose quasitransverse-magnetic, 17th-azimuthal-order WG mode, at a frequency of approximately 12.038 GHz, with a loaded Q of several hundred million, is supported on a cylinder of monocrystalline sapphire. An electron spin resonance associated with Fe3+ ions, that are substitutively included within the sapphire at an effective concentration of a few parts per billion, coincides in frequency with that of the (considerably narrower) WG mode. By applying a cw “pump” to the resonator at a frequency of approximately 31.34 GHz, with no applied dc magnetic field, the WG (“signal”) mode is energized through a three-level maser scheme. Preliminary measurements demonstrate a frequency stability (Allan deviation) of a few times 10−14 for sampling intervals up to 100 s.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)

Surface-detached V-shaped yoke of obliquely bonded magnetostrictive strips for high transduction of ultrasonic torsional waves

Chan Il Park, Woochul Kim, Seung Hyun Cho, and Yoon Young Kim

Appl. Phys. Lett. 87, 224105 (2005); http://dx.doi.org/10.1063/1.2133927 (3 pages) | Cited 11 times

Online Publication Date: 23 November 2005

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When slender magnetostrictive strips that are obliquely bonded on the surface of a pipe are subjected to a time-varying magnetic field, the strips deform mechanically because of the magnetostrictive effect and in turn, ultrasonic torsional waves are generated in the pipe. If the magnetic flux density in the strips can be increased by simply modifying the magnetic path, the sensitivity of the generated wave signal with respect to the applied magnetic field strength can be considerably enhanced even without increasing the magnetic field strength. Sensitivity has been one of the most important factors in sensors. To achieve this objective, yokes can be used, but improper yoke configurations can generate unwanted additional wave modes with no sensitivity improvement. Consequently, the problem of an optimal yoke configuration to increase the sensitivity was formulated as a topology optimization problem, and an interesting V-shaped yoke was found to be the optimal configuration. When the designed yokes were employed in actual experiments, the sensitivity of the measured wave signal was increased by as much as 7.5 times without needing to increase the magnetic strength.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
89.20.Kk Engineering
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
43.38.Ct
02.60.Pn Numerical optimization

Controlled nonuniformity in macroporous silicon pore growth

Sven Matthias, Frank Müller, and Ulrich Gösele

Appl. Phys. Lett. 87, 224106 (2005); http://dx.doi.org/10.1063/1.2137688 (3 pages) | Cited 3 times

Online Publication Date: 23 November 2005

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Photoelectrochemical etching of uniform prestructured silicon wafers in hydrofluoric acid containing solutions yields periodic structures that can be applied to two- and three-dimensional photonic crystals or microfluidics. Here we demonstrate experimentally macroporous silicon etching initiated by a nonuniform predefined lattice. For conveniently chosen parameters we observe a stable growth of pores whose geometrical appearance depends strongly on the spatially different nucleation conditions. Moreover, we show preliminary results on three-dimensionally shaped pores. This material can be used to realize hybrid photonic crystal structures and incorporate waveguides in three-dimensional photonic crystals.
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81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials
81.65.Cf Surface cleaning, etching, patterning
61.43.Gt Powders, porous materials

Absolute determination of inelastic mean-free paths and surface excitation parameters by absolute reflection electron energy loss spectrum analysis

T. Nagatomi and K. Goto

Appl. Phys. Lett. 87, 224107 (2005); http://dx.doi.org/10.1063/1.2135211 (3 pages) | Cited 6 times

Online Publication Date: 23 November 2005

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An analytical approach was proposed for simultaneously determining an inelastic mean-free path (IMFP) and a surface excitation parameter (SEP) with absolute units by the analysis of an absolute experimental reflection electron energy loss spectrum. The IMFPs and SEPs in Ni were deduced for electrons of 300 to 3000 eV. The obtained IMFPs were in good agreement with those calculated using the TPP-2M equation. The Chen-type empirical formula was proposed for determining the SEP. The results confirmed the applicability of the present approach for determining the IMFP and SEP for medium-energy electrons.
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79.20.-m Impact phenomena (including electron spectra and sputtering)
68.49.Jk Electron scattering from surfaces
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