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23 Jan 2012

Volume 100, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 041101 (2012); http://dx.doi.org/10.1063/1.3675885 (4 pages)

Seung Ho Choi and Young L. Kim
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Electric resonance-rectifier circuit for renewable energy conversion

C. Boström, B. Ekergård, and M. Leijon

Appl. Phys. Lett. 100, 043511 (2012); http://dx.doi.org/10.1063/1.3680097 (3 pages) | Cited 1 time

Online Publication Date: 27 January 2012

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Variable speed generators are used more frequently for converting the energy from renewable energy sources to electric energy. The power production form a variable speed generator is dependent on the electrical damping of the generator. In this paper, a resonance circuit connected to a direct driven linear generator used for wave energy utilization is investigated. At resonance, the electrical damping in the generator increases which results in an increased power production. The results show that resonance can be achieved with the suggested circuit.
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84.30.Jc Power electronics; power supply circuits

Improved photoresponse of InAs/GaAs quantum dot infrared photodetectors by using GaAs1−xSbx strain reducing layer

Chia-Tze Huang, Yu-Cheng Chen, and Si-Chen Lee

Appl. Phys. Lett. 100, 043512 (2012); http://dx.doi.org/10.1063/1.3679132 (4 pages) | Cited 2 times

Online Publication Date: 27 January 2012

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The effect of a GaAs1−xSbx strain reducing layer on the performance of InAs/GaAs quantum-dot infrared photodetectors was investigated. The results suggest that increasing Sb composition x from 0 to 0.2 leads to an enhanced peak response and a pronounced narrowing of the band width of the spectral response from 3.3 to 1.5 μm. For a photodetector with GaAs0.8Sb0.2 strain reducing layer, the best responsivity obtained is 533 mA/W, which is 380 times higher than that without strain reducing layer. In addition, the operating temperature increases from 50 to 90 K when increasing Sb composition from 0 to 0.2.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.-z Semiconductor devices

Numerical analysis on the effects of bandgap energy and polarization of electron blocking layer in near-ultraviolet light-emitting diodes

Yen-Kuang Kuo (郭艷光), Yu-Han Chen (陳鈺涵), Jih-Yuan Chang (張誌原), and Miao-Chan Tsai (蔡妙嬋)

Appl. Phys. Lett. 100, 043513 (2012); http://dx.doi.org/10.1063/1.3679180 (3 pages) | Cited 1 time

Online Publication Date: 27 January 2012

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The influences of bandgap energy and polarization of the electron blocking layer (EBL) in near-ultraviolet light-emitting diodes (NUV LEDs) are systematically investigated. Design curves for the output power of NUV LEDs as a function of bandgap energy and polarization of EBL are provided. The simulation results show that, when the bandgap of the EBL increases, the polarization and polarization-induced charge increase accordingly. Both mechanisms have opposite effects for the EBL in confining electrons. The NUV LEDs with an EBL of large bandgap or small polarization have improved performance due to the enhanced efficiency of electron confining and hole injection.
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85.60.Jb Light-emitting devices
02.60.-x Numerical approximation and analysis
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Optical planar waveguide for cell counting

John LeBlanc, Andrew J. Mueller, Adrian Prinz, and Manish J. Butte

Appl. Phys. Lett. 100, 043701 (2012); http://dx.doi.org/10.1063/1.3678339 (5 pages) | Cited 1 time

Online Publication Date: 23 January 2012

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Low cost counting of cells has medical applications in screening, military medicine, disaster medicine, and rural healthcare. In this report, we present a shallow, buried, planar waveguide fabricated by potassium ion exchange in glass that enables low-cost and rapid counting of metal-tagged objects that lie in the evanescent field of the waveguide. Laser light transmitted through the waveguide was attenuated proportionately to the presence of metal-coated microstructures fabricated from photoresist. This technology enables the low-cost enumeration of cells from blood, urine, or other biofluids.
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87.85.-d Biomedical engineering
42.79.Gn Optical waveguides and couplers

Evidence of ferroelectricity and phase transition in pressed diphenylalanine peptide nanotubes

Igor Bdikin, Vladimir Bystrov, Svitlana Kopyl, Rui P. G. Lopes, Ivonne Delgadillo, José Gracio, Elena Mishina, Alexander Sigov, and Andrei L. Kholkin

Appl. Phys. Lett. 100, 043702 (2012); http://dx.doi.org/10.1063/1.3676417 (4 pages) | Cited 7 times

Online Publication Date: 24 January 2012

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Self-assembled peptide nanotubes (PNT) are unique nanoscale objects having a great potential for a multitude of applications. Strong piezoactivity and polar properties in aromatic dipeptides were recently observed in stand-alone nanotubes using piezoresponse force microscopy and 2nd harmonic generation. In this work, we report macroscopic dielectric and polarization vs. field measurements on pressed PNTs before and after annealing at 150 °C. The results corroborate nanoscale study and present a clear evidence of ferroelectric-like behaviour and phase transition in this technologically important material. The dielectric constant of PNT pellets obeys apparent Curie-Weiss (CW) law with the CW constant C ≈ 230 °C and transition temperature at T ≈ 142 °C.
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77.80.B- Phase transitions and Curie point
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
81.16.Dn Self-assembly
81.40.Gh Other heat and thermomechanical treatments

Intravascular ultrasound chirp imaging

D. Maresca, K. Jansen, G. Renaud, G. van Soest, X. Li, Q. Zhou, N. de Jong, K. K. Shung, and A. F. W. van der Steen

Appl. Phys. Lett. 100, 043703 (2012); http://dx.doi.org/10.1063/1.3679375 (3 pages) | Cited 2 times

Online Publication Date: 25 January 2012

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We demonstrate the feasibility of intravascular ultrasound (IVUS) chirp imaging as well as chirp reversal ultrasound contrast imaging at intravascular ultrasound frequency. Chirp excitations were emitted with a 34 MHz single crystal intravascular transducer and compared to conventional Gaussian-shaped pulses of equal acoustic pressure. The signal to noise ratio of the chirp images was increased by up to 9 dB relative to the conventional images. Imaging of contrast microbubbles was implemented by chirp reversal, achieving a contrast to tissue ratio of 12 dB. The method shows potential for intravascular imaging of structures in and beyond coronary atherosclerotic plaques including vasa vasorum.
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87.63.dh Ultrasonographic imaging
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
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Experimental studies of complex hydride YMn2H6 on formation kinetics and x-ray absorption fine structure analyses

Motoaki Matsuo, Daiju Matsumura, Yasuo Nishihata, Guanqiao Li, Nao Hiyama, Satoshi Semboshi, and Shin-ichi Orimo

Appl. Phys. Lett. 100, 044101 (2012); http://dx.doi.org/10.1063/1.3678032 (3 pages) | Cited 2 times

Online Publication Date: 24 January 2012

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Formation kinetics of a complex hydride YMn2H6 with [MnH6]5− complex anion from a metal hydride YMn2H4.5 was investigated in the temperature range between 373 K and 448 K under 25 MPa H2. The time dependent of the YMn2H6 formation fraction suggested that the formation kinetics are controlled by random nucleation and growth with the activation energy of 113 kJ/mol H2. Local structure of YMn2H6 synthesized was also studied by x-ray absorption fine structure analysis. Mn–H covalent bonding nature in [MnH6]5− complex anion was successfully detected and the Mn–H distance was determined to be 1.67 ± 0.05 Å.
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78.70.Dm X-ray absorption spectra
82.40.-g Chemical kinetics and reactions: special regimes and techniques

Electron energy distribution function and plasma parameters across magnetic filters

A. Aanesland, J. Bredin, P. Chabert, and V. Godyak

Appl. Phys. Lett. 100, 044102 (2012); http://dx.doi.org/10.1063/1.3680088 (3 pages) | Cited 3 times

Online Publication Date: 24 January 2012

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The electron energy distribution function (EEDF) is measured across a magnetic filter in inductively coupled plasmas. The measured EEDFs are found to be Maxwellian in the elastic energy range with the corresponding electron temperature monotonously decreasing along the positive gradient of the magnetic field. At the maximum of the magnetic field, the electron temperature reaches its minimum and remains nearly constant in the area of the negative gradient of the field, where the plasma density distribution exhibits a local minimum.
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52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements

Efficient second harmonic generation in a metamaterial with two resonant modes coupled through two varactor diodes

Toshihiro Nakanishi, Yasuhiro Tamayama, and Masao Kitano

Appl. Phys. Lett. 100, 044103 (2012); http://dx.doi.org/10.1063/1.3679652 (3 pages) | Cited 1 time

Online Publication Date: 26 January 2012

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We present an effective method to generate second harmonic (SH) waves using nonlinear metamaterial composed of coupled split ring resonators (CSRRs) with varactor (variable capacitance) diodes. The CSRR structure has two resonant modes: a symmetric mode that resonates at the fundamental frequency and an anti-symmetric mode that resonates at the SH frequency. Resonant fundamental waves in the symmetric mode generate resonant SH waves in the anti-symmetric mode. The double resonance contributes to effective SH radiation. In the experiment, we observe 19.6 dB enhancement in the SH radiation in comparison with the nonlinear metamaterial that resonates only for the fundamental waves.
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43.25.-x Nonlinear acoustics
84.32.Tt Capacitors
41.20.-q Applied classical electromagnetism
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.-a Optical materials

Negative differential thermal conductance through vacuum

Linxiao Zhu, Clayton R. Otey, and Shanhui Fan

Appl. Phys. Lett. 100, 044104 (2012); http://dx.doi.org/10.1063/1.3679694 (3 pages) | Cited 6 times

Online Publication Date: 26 January 2012

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We propose a scheme for achieving negative differential thermal conductance in near-field electromagnetic thermal transfer. As an example, we show that the scheme can be implemented with two slabs of silicon carbide brought in close proximity to each other. We also describe how a bistable thermal switch can be constructed in this manner.
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66.70.Df Metals, alloys, and semiconductors

Decreasing high ion energy during transition in pulsed inductively coupled plasmas

Ankur Agarwal, Phillip J. Stout, Samer Banna, Shahid Rauf, and Ken Collins

Appl. Phys. Lett. 100, 044105 (2012); http://dx.doi.org/10.1063/1.3679075 (4 pages) | Cited 3 times

Online Publication Date: 27 January 2012

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Pulsed RF plasmas sustained in electronegative gas mixtures are increasingly being employed for plasma etching at future technological nodes. During the plasma transition from the afterglow to the active-glow, ion energies at the wafer can substantially increase due to the high voltage required to deposit bias power into few electrons. These high energy ions, albeit few, increase the possibility of ion bombardment damage and are, therefore, detrimental to the etching process. Strategies to decrease the high ion energies during transition are investigated using a two-dimensional computational plasma model. Results for poly-Si etch in an Ar/Cl2 gas mixture indicate that the high ion energies can be reduced by offsetting the bias pulse from the source pulse with minimal impact on the etch depth rates.
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52.77.Bn Etching and cleaning
52.80.Hc Glow; corona
81.65.Cf Surface cleaning, etching, patterning
52.25.Fi Transport properties
52.50.Dg Plasma sources
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Comment on “The electromagnetic property of chemically reduced graphene oxide and its application as microwave absorbing material” [Appl. Phys. Lett. 98, 072906 (2011)]

F. Qin and C. Brosseau

Appl. Phys. Lett. 100, 046101 (2012); http://dx.doi.org/10.1063/1.3678192 (2 pages) | Cited 1 time

Online Publication Date: 25 January 2012

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Abstract Unavailable
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
82.30.-b Specific chemical reactions; reaction mechanisms
61.48.Gh Structure of graphene
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Response to “Comment on ‘The electromagnetic property of chemically reduced graphene oxide and its application as microwave absorbing material’” [Appl. Phys. Lett. 100, 046101 (2012)]

Chao Wang, Xijiang Han, Ping Xu, Xiaolin Zhang, Yunchen Du, Surong Hu, Jingyu Wang, and Xiaohong Wang

Appl. Phys. Lett. 100, 046102 (2012); http://dx.doi.org/10.1063/1.3678193 (1 page)

Online Publication Date: 25 January 2012

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Abstract Unavailable
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73.61.Wp Fullerenes and related materials
77.22.Ch Permittivity (dielectric function)
78.70.Gq Microwave and radio-frequency interactions
82.30.-b Specific chemical reactions; reaction mechanisms
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Publisher’s Note: “Role of correlation effects in the superconducting material: InV6S8” [Appl. Phys. Lett. 99, 221904 (2011)]

M. Ramzan and R. Ahuja

Appl. Phys. Lett. 100, 049901 (2012); http://dx.doi.org/10.1063/1.3679545 (1 page)

Online Publication Date: 25 January 2012

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Abstract Unavailable
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99.10.Fg Publisher's note
74.70.-b Superconducting materials other than cuprates
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Publisher’s Note: “Fluxgate based detection of magnetic nanoparticle dynamics in a rotating magnetic field” [Appl. Phys. Lett. 99, 112501 (2011)]

Jan Dieckhoff, Meinhard Schilling, and Frank Ludwig

Appl. Phys. Lett. 100, 049902 (2012); http://dx.doi.org/10.1063/1.3676626 (1 page)

Online Publication Date: 25 January 2012

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Abstract Unavailable
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99.10.Fg Publisher's note
75.75.-c Magnetic properties of nanostructures
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