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30 Jul 2007

Volume 91, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 052901 (2007); http://dx.doi.org/10.1063/1.2767146 (3 pages)

Wei-Feng Rao and Yu U. Wang
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Measurement approach of Brownian motion force by an abrupt tapered fiber optic tweezers

Libo Yuan, Zhihai Liu, and Jun Yang

Appl. Phys. Lett. 91, 054101 (2007); http://dx.doi.org/10.1063/1.2760179 (3 pages) | Cited 2 times

Online Publication Date: 30 July 2007

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A Brownian motion force measurement fiber optic probe is fabricated and demonstrated. The specially designed abrupt tapered fiber tip can be used to trap small particles. By way of comparing the value of Brownian motion random force with the trapping force exerted on the same particle at the ambient temperature T, the Brownian motion force can be measured.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.81.Pa Sensors, gyros
05.40.Jc Brownian motion
07.10.Pz Instruments for strain, force, and torque

Solute transport in porous media: Dispersion tensor of periodic networks

Guillermo H. Goldsztein

Appl. Phys. Lett. 91, 054102 (2007); http://dx.doi.org/10.1063/1.2760180 (3 pages)

Online Publication Date: 30 July 2007

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The authors study solute transport in periodic networks of channels. They identify the parameter regime where a local physical mechanism that occurs at the intersections of channels is the dominant cause of dispersion and obtain the macroscopic transport equation that the concentration of solute satisfies.
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47.56.+r Flows through porous media
81.05.Rm Porous materials; granular materials
61.43.Gt Powders, porous materials

Fe-rich and Mn-rich nanodomains in Li1.2Mn0.4Fe0.4O2 positive electrode materials for lithium-ion batteries

J. Kikkawa, T. Akita, M. Tabuchi, M. Shikano, K. Tatsumi, and M. Kohyama

Appl. Phys. Lett. 91, 054103 (2007); http://dx.doi.org/10.1063/1.2757587 (3 pages) | Cited 16 times

Online Publication Date: 30 July 2007

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The authors investigated the distribution and local valence states of transition metal ions in a positive electrode material for lithium-ion batteries, Li1.2Mn0.4Fe0.4O2 nanoparticles, by electron energy-loss spectroscopy combined with scanning transmission electron microscopy. The experiments clarified the coexistence of Mn-rich and Fe-rich nanodomains in each single particle, and it is found that Fe-rich nanodomains contain Mn3+ ions which should be active in a redox reaction in spite of previous views of inactive Mn4+ ions in this material. The authors discuss a redox mechanism associated with the nanodomains.
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82.47.Aa Lithium-ion batteries
82.45.Fk Electrodes

Reduction of speckles in retinal reflection

Vassilios Albanis, Erez N. Ribak, and Yuval Carmon

Appl. Phys. Lett. 91, 054104 (2007); http://dx.doi.org/10.1063/1.2761835 (3 pages) | Cited 3 times

Online Publication Date: 31 July 2007

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Speckle noise can deteriorate the quality of wave-front sensors measuring ocular aberrations. To counter that, a narrow laser beam was acoustically modulated before entering the eye and creating a spot on the retina. Light was scattered back through the aberrations into the sensor. The increased spot size, wider angular spread, and temporal modulation of the incoming beam averaged out the speckles, producing a more uniform response of the wave-front sensor. The method applies also to retinal imagers and to nonbiological speckle.
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42.15.Fr Aberrations
42.30.Ms Speckle and moiré patterns
42.79.-e Optical elements, devices, and systems

Fringe-shifting interferometric laser lithography with optical nonlinearity for micro- and nanofabrications

Jun Amako, Daisuke Sawaki, and Makoto Kato

Appl. Phys. Lett. 91, 054105 (2007); http://dx.doi.org/10.1063/1.2767233 (3 pages)

Online Publication Date: 31 July 2007

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The authors demonstrate an interferometric laser lithography process armed with a fringe-shifting technique, which utilizes nonlinear light-matter interaction. With this method, multiphoton-sensitive materials are ablated using ultrashort pulse interference fringes, enabling the ablated regions to be spaced by a fraction of the fringe pitch. For concept-proving experiments, confocal optics equipped with a diffractive beam splitter and a phase shifter are built to perform a fringe shift. This creates a phase difference between split beams that interfere with each other, producing high-contrast fringes. Precise control of beam intensity and beam phase is essential.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Nd Micro- and nanolithography
42.62.-b Laser applications

Optical and magnetic behavior of erbium-doped GaN epilayers grown by metal-organic chemical vapor deposition

J. M. Zavada, N. Nepal, C. Ugolini, J. Y. Lin, H. X. Jiang, R. Davies, J. Hite, C. R. Abernathy, S. J. Pearton, E. E. Brown, and U. Hömmerich

Appl. Phys. Lett. 91, 054106 (2007); http://dx.doi.org/10.1063/1.2767992 (3 pages) | Cited 14 times

Online Publication Date: 1 August 2007

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The authors report on the optical and magnetic properties of GaN epilayers, grown by metal-organic chemical vapor deposition, with in situ Er doping at concentrations up to ∼ 1021 cm−3. Using ultraviolet laser excitation, all samples exhibited photoluminescence near 1540 nm with the integrated intensity approximately proportional to the Er concentration. Data from superconducting quantum interference device measurements indicated room temperature ferromagnetic ordering in all Er-doped GaN epilayers. The saturation magnetization in these samples also followed a nearly linear fit to the Er concentration. X-ray diffraction spectra did not reveal evidence of any second phases over this range of Er concentrations.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors

Correlations between structure and random walk dynamics in directed complex networks

Luciano da Fontoura Costa, Olaf Sporns, Lucas Antiqueira, Maria das Graças Volpe Nunes, and Osvaldo N. Oliveira

Appl. Phys. Lett. 91, 054107 (2007); http://dx.doi.org/10.1063/1.2766683 (3 pages) | Cited 10 times

Online Publication Date: 1 August 2007

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In this letter the authors discuss the relationship between structure and random walk dynamics in directed complex networks, with an emphasis on identifying whether a topological hub is also a dynamical hub. They establish the necessary conditions for networks to be topologically and dynamically fully correlated (e.g., word adjacency and airport networks), and show that in this case Zipf’s law is a consequence of the match between structure and dynamics. They also show that real-world neuronal networks and the world wide web are not fully correlated, implying that their more intensely connected nodes are not necessarily highly active.
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89.75.Fb Structures and organization in complex systems

Resonant x-ray emission spectroscopy of multiferroic TbMnO3

J. M. Chen, C. K. Chen, T. L. Chou, I. Jarrige, H. Ishii, K. T. Lu, Y. Q. Cai, K. S. Liang, J. M. Lee, S. W. Huang, T. J. Yang, C. C. Shen, R. S. Liu, J. Y. Lin, H. T. Jeng, et al.

Appl. Phys. Lett. 91, 054108 (2007); http://dx.doi.org/10.1063/1.2762288 (3 pages) | Cited 4 times

Online Publication Date: 1 August 2007

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The Mn 3d valence states in single-crystalline TbMnO3 were probed using x-ray absorption spectroscopy and resonant x-ray emission spectroscopy (RXES). The polarized Mn K-edge x-ray absorption spectra show a strong polarization dependence, particularly for the white line region, indicating the strong anisotropic Mn–O bonding within the ab plane in TbMnO3. The RXES data obtained at the Mn K edge clearly reveal that unoccupied Mn 3d states exhibit a relatively delocalized character, stemming from hybridization of the Mn 3d states with the neighboring Mn 4p orbitals. The authors demonstrated that resonant x-ray emission spectroscopy is able to characterize the degree of localization of the unoccupied states or hole carriers in manganites.
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78.70.En X-ray emission spectra and fluorescence
78.70.Dm X-ray absorption spectra
75.50.Ee Antiferromagnetics
77.80.-e Ferroelectricity and antiferroelectricity

IR imaging using a cantilever-based focal plane array fabricated by deep reactive ion etching technique

Xin Wang, Shenglin Ma, Xiaomei Yu, Ming Liu, Xiaohua Liu, and Yuejin Zhao

Appl. Phys. Lett. 91, 054109 (2007); http://dx.doi.org/10.1063/1.2768024 (3 pages) | Cited 3 times

Online Publication Date: 2 August 2007

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The authors report on a novel substrate-free cantilever-based focal plane array (FPA) fabricated by a deep reactive ion etching technique and discuss its performance as an uncooled infrared imager. A visible optical readout was designed to simultaneously measure the deflections of all the cantilevers in the FPA. The noise equivalent temperature difference (NETD) of our FPA can be reduced by 60% compared to the one fabricated by sacrificial layer technique and some cantilevers exhibited NETD of 375 mK, approaching the theoretical prediction of 89.7 mK. The FPA has a bending response to temperature of 86 nm/K and a response time of 21 ms.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)
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