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17 May 2010

Volume 96, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 96, 203102 (2010); http://dx.doi.org/10.1063/1.3429125 (3 pages)

Qimin Quan, Parag B. Deotare, and Marko Loncar
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90° polarization rotator using a bilayered chiral metamaterial with giant optical activity

Yuqian Ye and Sailing He

Appl. Phys. Lett. 96, 203501 (2010); http://dx.doi.org/10.1063/1.3429683 (3 pages) | Cited 25 times

Online Publication Date: 17 May 2010

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A bilayered chiral metamaterial is proposed to realize a 90° polarization rotator, whose giant optical activity is due to the transverse magnetic dipole coupling among the metallic wire pairs of enantiomeric patterns. By transmission through this thin bilayered structure of less than λ/30 thick, a linearly polarized wave is converted to its cross polarization with a resonant polarization conversion efficiency of over 90%. It is demonstrated that the chirality in the propagation direction makes this efficient cross-polarization conversion possible.
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42.70.-a Optical materials
42.25.Ja Polarization

Giant resonance frequency tunable magnetoelectric effect in a device of Pb(Zr0.52Ti0.48)O3 drum transducer, NdFeB magnet, and Fe-core solenoid

Min Zeng, Siu Wing Or, and Helen Lai Wa Chan

Appl. Phys. Lett. 96, 203502 (2010); http://dx.doi.org/10.1063/1.3428429 (3 pages) | Cited 8 times

Online Publication Date: 17 May 2010

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Magnetoelectric (ME) effect has been studied in a device of Pb(Zr0.52Ti0.48)O3 (PZT) drum transducer, NdFeB magnet, and Fe-core solenoid. A unique ME effect is found to originate from the magnetic force-induced effectively amplified piezoelectric effect. Under the application of a magnet with dimensions of ϕ22×7.6 mm2, a giant ME coefficient of 13.2 V/cm Oe and a power density of 16.4 μW/Oe across a 14 kΩ resistor were obtained at the first order radial resonance frequency of 650 Hz. Importantly, with increasing magnet mass, the resonance frequency decreases, while the resonance ME effect first increases and then decreases, which means a tunable resonance ME effect.
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43.38.Fx Piezoelectric and ferroelectric transducers
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Hh Inductors and coils; wiring
75.85.+t Magnetoelectric effects, multiferroics

Surface acoustic wave devices based on AlN/sapphire structure for high temperature applications

Thierry Aubert, Omar Elmazria, Badreddine Assouar, Laurent Bouvot, and Mourad Oudich

Appl. Phys. Lett. 96, 203503 (2010); http://dx.doi.org/10.1063/1.3430042 (3 pages) | Cited 8 times

Online Publication Date: 18 May 2010

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AlN/sapphire layered structure has been investigated as a potential substrate for surface acoustic wave (SAW) devices operating at high temperatures up to 950 °C under air atmosphere. Frequency characterizations of the SAW delay lines based on this structure indicate a slight increase of 2 dB in the insertion losses after annealing for 30 min at 900 °C. Scanning electron and atomic force microscopy as well as x-ray diffraction measurements suggest that theses losses are due to the deterioration of the Pt/Ta electrodes and to a slight oxidation of the AlN film.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
68.37.Ps Atomic force microscopy (AFM)

Performance improvement of phase change memory cell by using a cerium dioxide buffer layer

Fei Shang, Jiwei Zhai, Sannian Song, Zhitang Song, and Changzhou Wang

Appl. Phys. Lett. 96, 203504 (2010); http://dx.doi.org/10.1063/1.3428578 (3 pages) | Cited 5 times

Online Publication Date: 18 May 2010

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The performance of phase change memory (PCM) cell, based on Ge2Sb2Te5, was significantly improved by using a CeO2 buffer layer. The presence of a buffer layer remarkably reduced the reset voltage of the PCM cell. Even at voltage pulse width of 10 ns, the buffered PCM cell could accomplish reset operation. Theoretical thermal simulation of reset process was conducted. It is concluded that the improved performance of the PCM cell with a CeO2 buffer layer can be attributed to the fact that the buffer layer not only acted as heating layer but also reduced efficiently the cell dissipated power.
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84.30.Sk Pulse and digital circuits
68.55.-a Thin film structure and morphology

Frequency-dependent stability of parallel-plate electrostatic actuators in conductive fluids

T. L. Sounart, H. V. Panchawagh, and R. L. Mahajan

Appl. Phys. Lett. 96, 203505 (2010); http://dx.doi.org/10.1063/1.3389491 (3 pages) | Cited 3 times

Online Publication Date: 19 May 2010

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We present an electromechanical stability analysis of passivated parallel-plate electrostatic actuators in conductive dielectric media and show that the pull-in instability can be eliminated by tuning the applied frequency below a design-dependent stability limit. A partial instability region is also obtained, where the actuator jumps from the pull-in displacement to another stable position within the gap. The results predict that the stability limit is always greater than the critical actuation frequency, and therefore any device that is feasible to actuate in a conductive fluid can be operated with stability over the full range of motion.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
07.07.Tw Servo and control equipment; robots

Improved microwave and noise performance of InAlAs/InGaAs metamorphic high-electron-mobility transistor with a liquid phase oxidized InGaAs gate without gate recess

Kuan-Wei Lee, Hsien-Cheng Lin, Fang-Ming Lee, Hou-Kuei Huang, and Yeong-Her Wang

Appl. Phys. Lett. 96, 203506 (2010); http://dx.doi.org/10.1063/1.3430569 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2010

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The metal-oxide-semiconductor metamorphic high-electron-mobility transistor (MOS-MHEMT) with an oxide grown by liquid phase oxidation on the InGaAs capping layer without a gate recess exhibits a lower leakage current density with suppressed impact ionization, better microwave characteristics, and improved high frequency noise performance compared to the conventional MHEMT with a recessed gate. The improved high frequency performance is due to the lower gate-source and gate-drain capacitances of the InAlAs/InGaAs MOS-MHEMT. Reduced surface recombination and impact ionization may also contribute to the improved frequency response, noise performance, and associated gain.
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85.30.Tv Field effect devices

Fabrication of InAs/GaAs quantum dot solar cells with enhanced photocurrent and without degradation of open circuit voltage

Denis Guimard, Ryo Morihara, Damien Bordel, Katsuaki Tanabe, Yuki Wakayama, Masao Nishioka, and Yasuhiko Arakawa

Appl. Phys. Lett. 96, 203507 (2010); http://dx.doi.org/10.1063/1.3427392 (3 pages) | Cited 42 times

Online Publication Date: 21 May 2010

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We report the fabrication of InAs/GaAs quantum dot solar cells (QDSCs) with enhanced photocurrent and no degradation in open circuit voltage (VOC) compared to a solar cell grown without QDs and composed solely of wetting layers. Notably, the achievement of such high VOC does not require electronic coupling. We report QDSCs with a light absorption range extended up to 1.3 μm and evidence a trade-off between VOC and QD ground-state energy. These results are of major significance to the design of high efficiency QDSCs.
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81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
88.40.jp Multijunction solar cells

Removal of near-interface traps at SiO2/4H–SiC (0001) interfaces by phosphorus incorporation

Dai Okamoto, Hiroshi Yano, Tomoaki Hatayama, and Takashi Fuyuki

Appl. Phys. Lett. 96, 203508 (2010); http://dx.doi.org/10.1063/1.3432404 (3 pages) | Cited 10 times

Online Publication Date: 21 May 2010

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Effective removal of near-interface traps (NITs) in SiO2/4H–SiC (0001) structures through phosphorus incorporation is demonstrated in this paper. Low-temperature capacitance-voltage and thermal dielectric relaxation current measurements were employed to investigate NITs in oxides prepared by dry oxidation, NO annealing, and POCl3 annealing. Both the measurements revealed that the density of electrons trapped in NITs in POCl3-annealed oxide is smaller than that in dry and NO-annealed oxides. The drastic elimination of NITs lowers the interface state density and increases the channel mobility in 4H–SiC metal-oxide-semiconductor field-effect transistors.
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73.20.At Surface states, band structure, electron density of states
77.22.Gm Dielectric loss and relaxation
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Microfluidic sorting with high-speed single-layer membrane valves

Adam R. Abate, Jeremy J. Agresti, and David A. Weitz

Appl. Phys. Lett. 96, 203509 (2010); http://dx.doi.org/10.1063/1.3431281 (3 pages) | Cited 12 times

Online Publication Date: 21 May 2010

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Sorting is one of the most important applications of microfluidic devices; however, current sorters place specific requirements on the density, size, and electrical properties of the objects to be sorted, limiting applicability. We present widely applicable microfluidic sorting. We use high-speed single-layer membrane valves to control flows in a bifurcating channel junction, to direct the paths of objects. This allows sorting at hundreds of hertz. Moreover, since the sorting action is mechanical, it is very widely applicable—to drops, particles, and even living cells.
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47.85.Np Fluidics
89.20.Kk Engineering
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.85.L- Flow control
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