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16 May 2011

Volume 98, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 201101 (2011); http://dx.doi.org/10.1063/1.3590716 (3 pages)

Martynas Beresna, Mindaugas Gecevičius, Peter G. Kazansky, and Titas Gertus
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Radially polarized optical vortex converter created by femtosecond laser nanostructuring of glass

Martynas Beresna, Mindaugas Gecevičius, Peter G. Kazansky, and Titas Gertus

Appl. Phys. Lett. 98, 201101 (2011); http://dx.doi.org/10.1063/1.3590716 (3 pages) | Cited 4 times

Online Publication Date: 16 May 2011

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We demonstrate the generation of optical vortices with radial or azimuthal polarization using a space variant polarization converter, fabricated by femtosecond laser writing of self-assembled nanostructures in silica glass. Manipulation of the induced form birefringence is achieved by controlling writing parameters, in particular, the polarization azimuth of the writing beam. The fabricated converter allows switching from radial to azimuthal polarization by controlling the handedness of incident circular polarization.
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42.79.Ci Filters, zone plates, and polarizers
42.62.-b Laser applications
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Ce Glasses, quartz
81.16.Dn Self-assembly

High gain 1.55 μm diode lasers based on InAs quantum dot like active regions

C. Gilfert, V. Ivanov, N. Oehl, M. Yacob, and J. P. Reithmaier

Appl. Phys. Lett. 98, 201102 (2011); http://dx.doi.org/10.1063/1.3590727 (3 pages)

Online Publication Date: 16 May 2011

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InP diode lasers with InAs quantum dot (QD) like active regions emitting at 1.55 μm have been fabricated. The QDs were grown in an As2 mode, which reduces the degree of elongation of the nanospecies yielding nearly circular shapes. Lasers with four to six dot layers show low absorption αi<10 cm−1 and high modal gain Γg0 of 10 cm−1 per QD layer (QDL) and above. The high gain values are compatible with an inhomogeneous linewidth that is much narrower than in quantum dash material, which is the common nanoscale gain material in the InP system.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Power efficiency estimation of silicon nanocrystals based light emitting devices in alternating current regime

A. Marconi, A. Anopchenko, G. Pucker, and L. Pavesi

Appl. Phys. Lett. 98, 201103 (2011); http://dx.doi.org/10.1063/1.3592566 (3 pages) | Cited 1 time

Online Publication Date: 17 May 2011

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The power efficiency of silicon nanocrystal light-emitting devices is studied in alternating current (ac) regime. An experimental method based on impedance spectroscopy is proposed. The power efficiency in ac regime is higher than the one measured in direct current before a threshold frequency and decreases significantly for higher frequencies. This decrease is attributed to an increase in electrical power injected at high frequencies and it is directly related to the disordered microscopic structure of the active material. The proposed method can be applied for any kind of device for which it is possible to measure the impedance characteristic.
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85.60.Jb Light-emitting devices
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

High-performance metamorphic InGaAs resonant cavity enhanced photodetector grown on GaAs substrate

S. Q. Liu, Q. Han, B. Zhu, X. H. Yang, H. Q. Ni, J. F. He, X. Wang, M. F. Li, Y. Zhu, J. Wang, X. P. Wang, and Z. C. Niu

Appl. Phys. Lett. 98, 201104 (2011); http://dx.doi.org/10.1063/1.3592569 (3 pages)

Online Publication Date: 17 May 2011

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In this letter, we demonstrated a top illuminated 1.55 μm metamorphic InGaAs resonant-cavity-enhanced p-i-n photodetector grown on GaAs substrate. The photodetectors were grown by a solid-source molecular beam epitaxy system. The high quality linearly graded InxAl0.4Ga1−x−0.4As metamorphic buffer layer enabled photodiodes to achieve ultralow dark current densities of 2.3×10−6 A/cm2 at 0 V and 4.2×10−5 A/cm2 at a reverse bias of 5 V. A high quantum efficiency of 84.4% at resonant wavelength of 1542 nm, a full width at half maximum about 14 nm, and a −3 dB bandwidth up to 13 GHz were also obtained.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
84.40.Az Waveguides, transmission lines, striplines

Semiconductor nanoring lasers

Min W. Kim and P.-C. Ku

Appl. Phys. Lett. 98, 201105 (2011); http://dx.doi.org/10.1063/1.3592739 (3 pages) | Cited 2 times

Online Publication Date: 18 May 2011

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Lasing in a subwavelength metal-clad nanoring resonator has been demonstrated with a tunable emission wavelength, controlled by the width of the ring. The emission wavelength is shown to be tunable within a 10 nm wavelength range by changing the ring width between 240 and 340 nm. This property is expected to mitigate a common nanolaser problem of fine-tuning the emission wavelength without significantly changing the laser dimensions.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking

Room-temperature emission at telecom wavelengths from silicon photonic crystal nanocavities

R. Lo Savio, S. L. Portalupi, D. Gerace, A. Shakoor, T. F. Krauss, L. O’Faolain, L. C. Andreani, and M. Galli

Appl. Phys. Lett. 98, 201106 (2011); http://dx.doi.org/10.1063/1.3591174 (3 pages)

Online Publication Date: 18 May 2011

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Strongly enhanced light emission at wavelengths between 1.3 and 1.6 μm is reported at room temperature in silicon photonic crystal (PhC) nanocavities with optimized out-coupling efficiency. Sharp peaks corresponding to the resonant modes of PhC nanocavities dominate the broad sub-bandgap emission from optically active defects in the crystalline Si membrane. We measure a 300-fold enhancement of the emission from the PhC nanocavity due to a combination of far-field enhancement and the Purcell effect. The cavity enhanced emission has a very weak temperature dependence, namely less than a factor of 2 reduction between 10 K and room temperature, which makes this approach suitable for the realization of efficient light sources as well as providing a quick and easy tool for the broadband optical characterization of silicon-on-insulator nanostructures.
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42.70.Qs Photonic bandgap materials

High quantum efficiency InGaN/GaN multiple quantum well solar cells with spectral response extending out to 520 nm

R. M. Farrell, C. J. Neufeld, S. C. Cruz, J. R. Lang, M. Iza, S. Keller, S. Nakamura, S. P. DenBaars, U. K. Mishra, and J. S. Speck

Appl. Phys. Lett. 98, 201107 (2011); http://dx.doi.org/10.1063/1.3591976 (3 pages) | Cited 4 times

Online Publication Date: 18 May 2011

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We demonstrate high quantum efficiency InGaN/GaN multiple quantum well (QW) solar cells with spectral response extending out to 520 nm. Increasing the number of QWs in the active region did not reduce the carrier collection efficiency for devices with 10, 20, and 30 QWs. Solar cells with 30 QWs and an intentionally roughened p-GaN surface exhibited a peak external quantum efficiency (EQE) of 70.9% at 390 nm, an EQE of 39.0% at 450 nm, an open circuit voltage of 1.93 V, and a short circuit current density of 2.53 mA/cm2 under 1.2 suns AM1.5G equivalent illumination.
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88.40.hj Efficiency and performance of solar cells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.40.Fy Semiconductors
78.30.Fs III-V and II-VI semiconductors

Exploiting long-ranged order in quasiperiodic structures for broadband plasmonic excitation

B. le Feber, J. Cesario, H. Zeijlemaker, N. Rotenberg, and L. Kuipers

Appl. Phys. Lett. 98, 201108 (2011); http://dx.doi.org/10.1063/1.3592847 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2011

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A comparison of transmission spectra from periodic, quasiperiodic, and randomly spaced slit arrays in thick gold films reveals resonant plasmonic excitations that arise solely due to the long-range order of the quasiperiodic structures. Specifically, first-order plasmonic resonances at the air-gold interface of the quasiperiodic arrays are identified at a broader range of wavelengths than those observed from periodic structures with the same average slit distance. Thus, a quasiperiodic plasmonic coupler that couples both visible and near-infrared light to surface plasmon polaritons is designed and demonstrated.
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42.79.Gn Optical waveguides and couplers
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Lasing in Thue–Morse structures with optimized aperiodicity

Heeso Noh, Jin-Kyu Yang, Svetlana V. Boriskina, Michael J. Rooks, Glenn S. Solomon, Luca Dal Negro, and Hui Cao

Appl. Phys. Lett. 98, 201109 (2011); http://dx.doi.org/10.1063/1.3592850 (3 pages)

Online Publication Date: 19 May 2011

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We demonstrate lasing in two-dimensional Thue–Morse structures fabricated in a semiconductor membrane. By changing the relative size of two scatterers that correspond to the building blocks A and B, we gradually vary structural aperiodicity and find an optimal degree of aperiodicity where light confinement is maximal and lasing is the strongest. At various degrees of aperiodicity, different types of modes acquire the highest quality factors and may be selected for lasing. This work opens a way of controlling lasing characteristic via structural aperiodicity.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Highly efficient blue phosphorescent polymer light-emitting diodes by using interfacial modification

Lu Li, Jun Liu, Zhibin Yu, and Qibing Pei

Appl. Phys. Lett. 98, 201110 (2011); http://dx.doi.org/10.1063/1.3593380 (3 pages)

Online Publication Date: 19 May 2011

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Solution processed highly efficient blue electrophosphorescent polymer light-emitting diodes have been fabricated containing an oligo(ethylene oxide) (PEO-DME) additive to enhance the electroluminescence efficiency. The addition of PEO-DME at 5–10 wt % effectively lowers both the electron and hole injection barriers. The maximum current efficiency obtained was 26.5 cd/A at an emission brightness of 2500 cd/m2. The high performance is due to (i) improved charge carrier injection at the interface resulting from specific interfacial interactions between PEO-DME and aluminum and (ii) improved charge carrier transporting ability and high electric field resulting from PEO-DME doping.
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85.60.Jb Light-emitting devices

Photoinduced transparency of effective three-photon absorption coefficient for femtosecond laser pulses in Ge16As29Se55 thin films

A. R. Barik, K. V. Adarsh, Ramakanta Naik, C. S. Suchand Sandeep, Reji Philip, Donghui Zhao, and Himanshu Jain

Appl. Phys. Lett. 98, 201111 (2011); http://dx.doi.org/10.1063/1.3591978 (3 pages)

Online Publication Date: 19 May 2011

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We report a dramatic change in effective three-photon absorption coefficient of amorphous Ge16As29Se55 thin films, when its optical band gap decreases by 10 meV with 532 nm light illumination. This large change provides valuable information on the higher excited states, which are otherwise inaccessible via normal optical absorption. The results also indicate that photodarkening in chalcogenide glasses can serve as an effective tool to tune the multiphoton absorption in a rather simple way.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Jg Amorphous semiconductors; glasses
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
78.47.J- Ultrafast spectroscopy (<1 psec)

Cleaved-facet violet laser diodes with lattice-matched Al0.82In0.18N/GaN multilayers as n-cladding

R. Charash, H. Kim-Chauveau, J-M. Lamy, M. Akther, P. P. Maaskant, E. Frayssinet, P. de Mierry, A. D. Dräger, J-Y. Duboz, A. Hangleiter, and B. Corbett

Appl. Phys. Lett. 98, 201112 (2011); http://dx.doi.org/10.1063/1.3589974 (3 pages)

Online Publication Date: 19 May 2011

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Electrically injected, edge-emitting cleaved-facet violet laser diodes were realized using a 480 nm thick lattice matched Si doped Al0.82In0.18N/GaN multilayer as the cladding on the n-side of the waveguide. Far-field measurements verify strong mode confinement to the waveguide. An extra voltage is measured and investigated using separate mesa structures with a single AlInN insertion. This showed that the electron current has a small thermally activated shunt resistance with a barrier of 0.135 eV and a current which scales according to Vn, where n ∼ 3 at current densities appropriate to laser operation.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Interference of surface plasmon polaritons from a “point” source

Xifeng Ren, Aiping Liu, Changling Zou, Lulu Wang, Yongjing Cai, Fangwen Sun, Guangcan Guo, and Guoping Guo

Appl. Phys. Lett. 98, 201113 (2011); http://dx.doi.org/10.1063/1.3592757 (3 pages)

Online Publication Date: 20 May 2011

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The interference patterns of the surface plasmon polaritons (SPPs) on the metal surface from a “point” source are observed. Innovation to the previous works, a point SPPs source with diameter of 100 nm is generated at the freely chosen positions on Au/air interface using near field excitation method. Such a point source provides good enough coherence to generate obvious interference phenomenon. This point SPPs source may be useful in the investigation of plasmonics for its high coherence, deterministic position, and minimum requirement for the initial light source.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.68.+m Optical properties of surfaces
78.66.Bz Metals and metallic alloys

Liquid-core low-refractive-index-contrast Bragg fiber sensor

Hang Qu and Maksim Skorobogatiy

Appl. Phys. Lett. 98, 201114 (2011); http://dx.doi.org/10.1063/1.3592758 (3 pages)

Online Publication Date: 20 May 2011

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We propose and experimentally demonstrate a low-refractive-index-contrast hollow-core Bragg fiber sensor for liquid analyte refractive index detection. The sensor operates using a resonant sensing principle—when the refractive index of a liquid analyte in the fiber core changes, the resonant confinement of the fiber guided mode will also change, leading to both the spectral shifts and intensity changes in fiber transmission. As a demonstration, we characterize the Bragg fiber sensor using a set of NaCl solutions with different concentrations. Strong spectral shifts are obtained with the sensor experimental sensitivity found to be ∼ 1400 nm/refractive index unit, which is comparable to that of a surface plasmon resonance sensor. Besides using theoretical modeling we show that low-refractive-index-contrast Bragg fibers are more suitable for liquid-analyte sensing applications than their high-refractive-index-contrast counterparts.
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42.81.Pa Sensors, gyros
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.81.Dp Propagation, scattering, and losses; solitons

Measurement of dwell times of spin polarized rubidium atoms on octadecyltrichlorosilane- and paraffin-coated surfaces

Emily Ulanski and Zhen Wu

Appl. Phys. Lett. 98, 201115 (2011); http://dx.doi.org/10.1063/1.3591172 (3 pages)

Online Publication Date: 20 May 2011

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We report the measurement of dwell times of spin polarized Rb atoms on octadecyltrichlorosilane (OTS)- and paraffin-coated surfaces. We find that at a cell temperature of 72 °C the dwell times for OTS- and paraffin-coated surfaces are 0.9±0.1 μs and 1.8±0.2 μs, respectively. Since the relaxation probability on paraffin is almost one order of magnitude smaller than that on OTS, the longer dwell time for paraffin indicates that the average strength of the interactions experienced by Rb atoms while they are inside paraffin is much weaker than while they are inside OTS.
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37.10.Gh Atom traps and guides
34.35.+a Interactions of atoms and molecules with surfaces

Spatial dependence of output pulse delay in a niobium nitride nanowire superconducting single-photon detector

J. A. O’Connor, M. G. Tanner, C. M. Natarajan, G. S. Buller, R. J. Warburton, S. Miki, Z. Wang, S. W. Nam, and R. H. Hadfield

Appl. Phys. Lett. 98, 201116 (2011); http://dx.doi.org/10.1063/1.3581054 (3 pages) | Cited 1 time

Online Publication Date: 20 May 2011

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We report on the position-dependent variation in output pulse timing across a superconducting single-photon detector. Our device consists of a single niobium nitride nanowire meander (100 nm width, 4 nm film thickness, 2 mm length). We use a confocal microscope configuration (full width at half maximum-spot size 1.3 μm at 1550 nm wavelength) and a femtosecond laser to study local variations in detection efficiency and output pulse timing. Pulse delays of up to 50 ps across the device correlate to local detection efficiency and resistance variations. This study indicates an underlying mechanism for timing jitter in superconducting nanowire devices.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
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Dynamics of laser-produced Sn microplasma for a high-brightness extreme ultraviolet light source

S. Yuspeh, Y. Tao, R. A. Burdt, M. S. Tillack, Y. Ueno, and F. Najmabadi

Appl. Phys. Lett. 98, 201501 (2011); http://dx.doi.org/10.1063/1.3589359 (3 pages) | Cited 2 times

Online Publication Date: 18 May 2011

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The effect of laser focal spot diameters of 26 and 150 μm on 13.5 nm extreme ultraviolet (EUV) radiation is investigated. Simulations show that the smaller spot size has a shorter electron plasma density scale length and deeper and denser laser energy deposition region. This results in additional time required for plasma expansion and radiation transport to efficiently emit EUV light. This is experimentally observed as an increase in the delay between the EUV emission and the laser pulse. The shorter scale length plasma reabsorbs less EUV light, resulting in a higher conversion efficiency, smaller and slightly brighter light source.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Dg Plasma sources
52.25.Fi Transport properties
42.72.Bj Visible and ultraviolet sources
52.38.Kd Laser-plasma acceleration of electrons and ions
52.65.-y Plasma simulation
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Polymorphic transformation mechanism of η and η′ in single crystalline Cu6Sn5

M. Y. Li, Z. H. Zhang, and J. M. Kim

Appl. Phys. Lett. 98, 201901 (2011); http://dx.doi.org/10.1063/1.3590715 (3 pages)

Online Publication Date: 16 May 2011

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Polymorphic transformation mechanism of η and η′ in single crystalline Cu6Sn5 has been investigated in this study. η phase exists at room temperature in the quenched specimens and transforms to η′ phase under aging at 150 °C for 40 d. The nucleation and growth of η′ phase is observed by field emission scanning electron microscope and surface reconstruction of polymorphic transformation is confirmed by both x-ray diffractometer and differential scanning calorimetry analysis. The results show that the volumetric strain energy is the dominant reason for occurring polymorphic transformation rather than order-disorder transition of η and η′ phases.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
68.35.B- Structure of clean surfaces (and surface reconstruction)
64.60.qj Studies of nucleation in specific substances
81.40.Gh Other heat and thermomechanical treatments

Fractal nature of multiple shear bands in severely deformed metallic glass

B. A. Sun and W. H. Wang

Appl. Phys. Lett. 98, 201902 (2011); http://dx.doi.org/10.1063/1.3592249 (3 pages)

Online Publication Date: 16 May 2011

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We present an analysis of fractal geometry of extensive and complex shear band patterns in a severely deformed metallic glass. We show that the shear band patterns have fractal characteristics, and the fractal dimensions are determined by the stress noise induced by the interaction between shear bands. A theoretical model of the spatial evolution of multiple shear bands is proposed in which the collective shear bands slide is considered as a stochastic process far from thermodynamic equilibrium.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.05.Kf Glasses (including metallic glasses)
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
05.45.Df Fractals

Electronic structure, chemical bonding features, and electron charge density of the double-cubane single crystal [Sb7S8Br2](AlCl4)3

Ali H. Reshak, H. Kamarudin, S. Auluck, B. Minofar, and I. V. Kityk

Appl. Phys. Lett. 98, 201903 (2011); http://dx.doi.org/10.1063/1.3583674 (3 pages)

Online Publication Date: 16 May 2011

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The present calculations were performed using all-electron full potential linearized augmented plane wave method based on the density functional theory. We have optimized the structure of the double-cubane single crystal [Sb7S8Br2](AlCl4)3, starting with the x-ray diffraction data Zhang et al., [J. Am. Chem. Soc. 131, 9896 (2009)] , by minimization of the forces (1 mRy/au) acting on the atoms, keeping the lattice parameters fixed at the experimental values. Our calculations show that [Sb7S8Br2](AlCl4)3 possesses a wide indirect energy band gap of about 1.6 eV (2.03 eV) using local density approximation (Engel–Vosko generalized gradient approximation) exchange correlation potentials. To describe the bonding properties we have evaluated the electronic charge space density contour in four planes-namely (001), (110), (100), and (010) which show that this compound possesses a considerable anisotropy. The contour plot shows partial ionic and strong covalent bonding between S–Sb, Al–Cl, S–Br, S–S, Cl–Cl, and Sb–Br atoms.
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71.20.Ps Other inorganic compounds
61.66.Fn Inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.50.Lt Crystal binding; cohesive energy
73.20.At Surface states, band structure, electron density of states

Controlling polarization anisotropy of site-controlled InAs/InP (100) quantum dots

Jiayue Yuan, Hao Wang, René P. J. van Veldhoven, Jia Wang, Tjibbe de Vries, Barry Smalbrugge, C. Y. Jin, Peter Nouwens, Erik Jan Geluk, Andrei Yu. Silov, and Richard Nötzel

Appl. Phys. Lett. 98, 201904 (2011); http://dx.doi.org/10.1063/1.3591155 (3 pages)

Online Publication Date: 17 May 2011

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We report on the shape and polarization control of site-controlled multiple and single InAs quantum dots (QDs) on InP pyramids grown by selective-area metal-organic vapor phase epitaxy. With increasing growth temperature the QDs elongate causing strong linear polarization of the photoluminescence. With reduced pyramid base/pyramid top area/QD number, the degree of polarization decreases, attributed to the symmetric pyramid top, reaching zero for single QDs grown at lower temperature. This control of linear polarization is important for entangled photon sources operating in the 1.55 μm wavelength region.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors

Direct identification of interstitial Mn in heavily p-type doped GaAs and evidence of its high thermal stability

L. M. C. Pereira, U. Wahl, S. Decoster, J. G. Correia, M. R. da Silva, A. Vantomme, and J. P. Araújo

Appl. Phys. Lett. 98, 201905 (2011); http://dx.doi.org/10.1063/1.3592568 (3 pages) | Cited 1 time

Online Publication Date: 18 May 2011

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We report on the lattice location of Mn in heavily p-type doped GaAs by means of β− emission channeling from the decay of 56Mn. The majority of the Mn atoms substitute for Ga and up to 31% occupy the tetrahedral interstitial site with As nearest neighbors. Contrary to the general belief, we find that interstitial Mn is immobile up to 400 °C, with an activation energy for diffusion of 1.7–2.3 eV. Such high thermal stability of interstitial Mn has significant implications on the strategies and prospects for achieving room temperature ferromagnetism in Ga1−xMnxAs.
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61.72.jj Interstitials
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
66.30.Lw Diffusion of other defects
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Analysis of frequency band structure in one-dimensional sonic crystal using Webster horn equation

A. Gupta, K. M. Lim, and C. H. Chew

Appl. Phys. Lett. 98, 201906 (2011); http://dx.doi.org/10.1063/1.3592570 (3 pages)

Online Publication Date: 18 May 2011

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Sound propagation through periodic arrangement of scatterers lead to formation of bands of frequencies, known as band gaps, where sound cannot propagate though the structure. We propose a method based on Webster horn equation, along with Floquet theorem, to predict the band gap of a one-dimensional periodic structure made of hard sound-scatterers. The method is further modified to obtain the complex wave numbers, which give the decay constants. The decay constant is used to predict the sound attenuation of the evanescent wave in the finite sonic crystal. The theoretical prediction is verified with experimental measurements.
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62.65.+k Acoustical properties of solids
71.20.-b Electron density of states and band structure of crystalline solids

Far-infrared study of substrate-effect on large scale graphene

Joo Youn Kim, Chul Lee, Sukang Bae, Keun Soo Kim, Byung Hee Hong, and E. J. Choi

Appl. Phys. Lett. 98, 201907 (2011); http://dx.doi.org/10.1063/1.3590773 (3 pages) | Cited 3 times

Online Publication Date: 19 May 2011

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From far-IR Drude absorption measurement we determine carrier density (N) and carrier scattering rate (Γ) of graphene deposited on buffer-layer/SiO2 composite substrate. Two types of buffer-layers, (1) polar dielectric oxide ZnO and SrTiO3 (2) organic thin film hexamethyldisilazane and polymethyl methacrylate (PMMA) were studied. N varies widely over 0.12–11.8(×1012 cm−2) range depending on the buffer-layer. In contrast Γ remains almost constant, ∼ 100 cm−1, irrespective of the buffer-layers. This indicates that carrier mobility (μ) of graphene depends on substrate through N, but not by Γ as commonly believed.
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78.67.Wj Optical properties of graphene
78.30.Na Fullerenes and related materials
72.20.Fr Low-field transport and mobility; piezoresistance

Anneal treatment to reduce the creation rate of light-induced metastable defects in device-quality hydrogenated amorphous silicon

David C. Bobela, Howard M. Branz, and Paul Stradins

Appl. Phys. Lett. 98, 201908 (2011); http://dx.doi.org/10.1063/1.3592264 (3 pages)

Online Publication Date: 19 May 2011

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We observe a dramatic reduction in the Staebler–Wronski metastable defect creation efficiency in device-quality films of hydrogenated amorphous silicon after they undergo a 20 min anneal treatment at 350 to 400 °C. After several hours of rapid degradation with a high intensity pulsed laser, there are about half as many total dangling bond defects in the annealed samples as in unannealed control samples. This reduction is observed in both 1.02-μm- and 0.22-μm-thick films, indicating it is not a surface-related artifact. The improved stability is likely caused by H motion, which restructures the Si–Si network and H-related nanovoids.
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61.72.Cc Kinetics of defect formation and annealing
72.40.+w Photoconduction and photovoltaic effects
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
71.55.Cn Elemental semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)
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  1. Magnetism and carrier modulation in (Ga,Mn)As/organic-dye hybrid devices
  2. In-plane manipulation of quantum dots in high quality laterally contacted micropillar cavities
  3. Nano-sized light emitting diodes by near field laser exposure
  4. First-principles time-dependent simulation of laser assisted desorption of hydrogen atoms from H–Si(111) surface
  5. Anisotropy induced wave birefringence in bounded supercritical plasma confined in a multicusp magnetic field
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