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10 May 2004

Volume 84, Issue 19, pp. 3723-3937

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 3933 (2004); http://dx.doi.org/10.1063/1.1745103 (3 pages)

A. Cassinese, G. M. De Luca, A. Prigiobbo, M. Salluzzo, and R. Vaglio
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Imaging phonons in a fcc Pu–Ga alloy by thermal diffuse x-ray scattering

Joe Wong, M. Wall, A. J. Schwartz, R. Xu, M. Holt, Hawoong Hong, P. Zschack, and T.-C. Chiang

Appl. Phys. Lett. 84, 3747 (2004); http://dx.doi.org/10.1063/1.1737482 (3 pages) | Cited 10 times

Online Publication Date: 29 April 2004

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X-ray thermal diffuse scattering intensity patterns from phonons in a fcc δ-Pu–Ga alloy have been recorded using an 18 keV undulator x-ray beam with a beam diameter of 25 μm. The results are consistent with patterns calculated using the Born–von Karman force constant model of lattice dynamics, and support the pronounced softening of the transverse acoustic branch along the [111] direction observed from inelastic x-ray scattering measurements. This work demonstrates the feasibility of using a “large-grain, small beam” approach to study lattice properties, such as phonon dispersion curves, of materials not readily available in the form of large single crystals. © 2004 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.70.Ck X-ray scattering

Two-dimensional computational model for electrochemical micromachining with ultrashort voltage pulses

Jason A. Kenney, Gyeong S. Hwang, and Woonsup Shin

Appl. Phys. Lett. 84, 3774 (2004); http://dx.doi.org/10.1063/1.1738937 (3 pages) | Cited 14 times

Online Publication Date: 29 April 2004

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We have developed a computational model to simulate electrochemical micromachining of conducting substrates with ultrashort voltage pulses. This theoretical approach integrates (i) a circuit model to describe charging and discharging of electrochemical double layers and electric field variation in electrolytes and (ii) the level set method to simulate feature profile evolution during electrochemical etching. Our simulation results of transient current responses and etch profile evolution are qualitatively in agreement with experimental observations. From our simulations, we find that the resolution of etched features is a strong function of the substrate double layer capacity which may be controlled by electrolyte concentration and pulse duration. © 2004 American Institute of Physics.
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82.45.Fk Electrodes
82.45.Aa Electrochemical synthesis
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
82.45.Gj Electrolytes
82.20.Wt Computational modeling; simulation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Microwave radiation force and torque on a disk resonator excited by a circularly polarized plane wave

S. Makarov and S. Kulkarni

Appl. Phys. Lett. 84, 3795 (2004); http://dx.doi.org/10.1063/1.1739517 (3 pages)

Online Publication Date: 29 April 2004

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A numerical simulation method [S. Makarov and S. Kulkarni, Appl. Phys. Lett. 84, 1600 (2004)] is used in order to determine the radiation force and radiation torque on a parallel-plate disk resonator, whose size is comparable to wavelength. The method is based on the MOM solution of the electric-field integral equation, accurate calculation of the near field, and removal of the self-interaction terms responsible for the pinch effect. The local force/torque distribution at the normal incidence of a circularly polarized plane wave is found. It is observed that, at the resonance, the individual disks are subject to unexpectedly large local force densities, despite the fact that the net radiation force on the resonator remains very small. On the other hand, the total axial torque on the disk resonator also increases at the resonance. © 2004 American Institute of Physics.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Phonon–boundary scattering in ultrathin single-crystal silicon layers

W. Liu and M. Asheghi

Appl. Phys. Lett. 84, 3819 (2004); http://dx.doi.org/10.1063/1.1741039 (3 pages) | Cited 51 times

Online Publication Date: 29 April 2004

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Thermal engineering of many nanoscale sensors, actuators, and high-density thermomechanical data storage devices, as well as the self-heating in deep submicron transistors, are largely influenced by thermal conduction in ultrathin silicon layers. The present study measures the lateral thermal conductivity of single-crystal silicon layers of thicknesses 20 and 100 nm at temperatures between 20 and 300 K, using Joule heating and electrical–resistance thermometry in suspended microfabricated structures. The thermal conductivity of the 20 nm thick silicon layer is ∼22 W m−1 K−1, which is nearly an order of magnitude smaller than the bulk value at room temperature. In general, a large reduction in thermal conductivity resulting from phonon–boundary scattering, particularly at low temperatures, is observed. It appears that the classical thermal conductivity theory that accounts for the reduced phonon mean-free paths based on a solution of the Boltzmann transport equation along a layer is able to capture the ballistic, or nonlocal, phonon transport in ultrathin silicon films. © 2004 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.20.K- Phonon interactions

Large effects due to electron–phonon-impurity interference in the resistivity of Pt/C-Ga composite nanowires

J.-F. Lin, J. P. Bird, L. Rotkina, A. Sergeev, and V. Mitin

Appl. Phys. Lett. 84, 3828 (2004); http://dx.doi.org/10.1063/1.1745108 (3 pages) | Cited 18 times

Online Publication Date: 29 April 2004

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The temperature-dependent resistivity of highly disordered Pt/C-Ga composite nanowires is shown to be well described by the interference of electron–phonon scattering and elastic electron scattering from boundaries and defects. The strongly disordered nature of these wires, combined with a high value of their Debye temperature, are responsible for the pronounced nature of the interference effects in their resistivity. © 2004 American Institute of Physics.
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73.63.Nm Quantum wires
63.20.K- Phonon interactions
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Evaluation of manganite films on silicon for uncooled bolometric applications

R. J. Choudhary, Anjali S. Ogale, S. R. Shinde, S. Hullavarad, S. B. Ogale, T. Venkatesan, R. N. Bathe, S. I. Patil, and Ravi Kumar

Appl. Phys. Lett. 84, 3846 (2004); http://dx.doi.org/10.1063/1.1748837 (3 pages) | Cited 23 times

Online Publication Date: 29 April 2004

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Pulsed-laser-deposited polycrystalline/amorphous films of mixed-valent manganites [La0.7Ca0.3MnO3 (LCMO), La0.5Sr0.5MnO3 (LSMO), La0.5Ba0.5MnO3 (LBMO), and (La0.6Pr0.4)0.67Ca0.33MnO3 (LPCMO)] grown at low temperature (450 °C) on single crystal (001) silicon substrate are evaluated for uncooled bolometric applications. It is shown that the temperature coefficient of resistance (TCR) and electrical noise (Sv) depend on the chemical composition. The optimum performance is found for LCMO with TCR of ∼7% K−1 and spectral noise ∼ 8.9×10−13 V2/Hz. In LBMO and LSMO the noise is much lower, but so is the TCR (1.5%–2% K−1). In LPCMO the TCR is high ( ∼ 10% K−1) and the noise is as well. © 2004 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.61.Ng Insulators
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

A prototype microthermophotovoltaic power generator

W. M. Yang, S. K. Chou, C. Shu, Z. W. Li, and H. Xue

Appl. Phys. Lett. 84, 3864 (2004); http://dx.doi.org/10.1063/1.1751614 (3 pages) | Cited 17 times

Online Publication Date: 29 April 2004

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A prototype microthermophotovoltaic (micro-TPV) power generator is described in this letter. The system is made of a SiC (silicon carbide) emitter, a simple nine-layer dielectric filter, and a GaSb (gallium antimony) photovoltaic cell array. In a microcombustor of 0.113 cm3 in volume, when the flow rate of hydrogen is 4.20 g/h, the micro-TPV system is able to deliver an electrical power output of 1.02 W, corresponding to an open-circuit electrical voltage of 2.28 V and a short-circuit current of 0.59 A. The prototype of the micro-TPV system will make it possible for us to substitute batteries with micropower generators in micromechanical devices in the near future. © 2004 American Institute of Physics.
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84.60.Jt Photoelectric conversion
85.80.-b Thermoelectromagnetic and other devices

Time reversal kaleidoscope: A smart transducer for three-dimensional ultrasonic imaging

Gabriel Montaldo, Delphine Palacio, Mickael Tanter, and Mathias Fink

Appl. Phys. Lett. 84, 3879 (2004); http://dx.doi.org/10.1063/1.1738186 (3 pages) | Cited 10 times

Online Publication Date: 29 April 2004

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The design of two dimensional (2D) arrays for three dimensional (3D) ultrasonic imaging is a major challenge in medical and nondestructive applications. Thousands of transducers are typically needed for beam focusing and steering in 3D volumes. Here, we report a promising approach for producing 3D images with a small number of transducers using the combined concepts of time reversal mirrors and chaotic reverberating cavities. Due to multiple reverberations inside the cavity, a “kaleidoscopic” transducer array is created with thousands of virtual transducers equivalent to 2D matrices. Beyond the scope of 3D medical imaging, this work leads to the concept of “smart” transducer. © 2004 American Institute of Physics.
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43.38.Hz Transducer arrays, acoustic interaction effects in arrays
43.80.Vj Acoustical medical instrumentation and measurement techniques
43.35.Wa Biological effects of ultrasound, ultrasonic tomography
43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction
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