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8 Sep 2008

Volume 93, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 101905 (2008); http://dx.doi.org/10.1063/1.2977760 (3 pages)

Mei Wang, Yinwei Li, Tian Cui, Yanming Ma, and Guangtian Zou
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Evanescent wave magnetometers with ultrathin ( ∼ 100 μm) cells

K. F. Zhao and Z. Wu

Appl. Phys. Lett. 93, 101101 (2008); http://dx.doi.org/10.1063/1.2966153 (3 pages)

Online Publication Date: 8 September 2008

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We studied the performance of an evanescent wave magnetometer with a coated cell of adjustable length. The cell length varies from a few millimeters to less than 100 μm. Two kinds of antirelaxation coatings are used: octadecyltrichlorosilane (OTS) and dichlorooctamethyltetrasiloxane (Surfasil). Sub-kilohertz linewidth can be achieved for a 100 μm thick OTS-coated cell. Magnetometers with coated ultrathin cells have superior performance in inhomogeneous magnetic fields, and can achieve a spatial resolution of better than 25 μm.
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07.55.Ge Magnetometers for magnetic field measurements
75.70.Ak Magnetic properties of monolayers and thin films

Terahertz emission from a large-area GaInAsN emitter

Falk Peter, Stephan Winnerl, Harald Schneider, Manfred Helm, and Klaus Köhler

Appl. Phys. Lett. 93, 101102 (2008); http://dx.doi.org/10.1063/1.2978398 (3 pages) | Cited 5 times

Online Publication Date: 8 September 2008

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A large-area interdigitated terahertz emitter based on molecular-beam epitaxy grown GaInAsN with an additional AlGaAs heterostructure is investigated as a terahertz source for excitation wavelengths between 1.1 and 1.5 μm. The optical and electrical properties of the emitter material exhibit absorption up to a wavelength of 1.5 μm and have a resistivity of 550 kΩ cm. Terahertz waves were detected by electro-optical sampling with a bandwidth exceeding 2 THz. Best performance is found for excitation wavelengths below 1.35 μm. Furthermore the emission properties for several excitation powers are investigated, showing a linear increase in terahertz emission.
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85.30.Kk Junction diodes
84.40.-x Radiowave and microwave (including millimeter wave) technology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Spectral bandwidth and phase effects of resonantly excited ultrafast surface plasmon pulses

S. E. Yalcin, Y. Wang, and M. Achermann

Appl. Phys. Lett. 93, 101103 (2008); http://dx.doi.org/10.1063/1.2978399 (3 pages) | Cited 4 times

Online Publication Date: 8 September 2008

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We report on the detailed analysis of femtosecond surface plasmon polariton (SPP) pulse generation under resonant excitation. Using prism coupling technique we excite femtosecond SPP pulses at a gold/air interface with ultrafast laser pulses. We show that the photon-SPP coupling is a resonant process with a finite spectral bandwidth that causes a spectral phase shift and a narrowing of the SPP pulse spectrum. Both effects result in a temporal pulse broadening and, therefore, set a lower limit on the duration of ultrafast SPP pulses with consequences for ultrafast SPP applications.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

High-intensity nanosecond-pulsed laser-induced plasma in air, water, and vacuum: A comparative study of the early-stage evolution using a physics-based predictive model

Benxin Wu

Appl. Phys. Lett. 93, 101104 (2008); http://dx.doi.org/10.1063/1.2979704 (3 pages) | Cited 8 times

Online Publication Date: 8 September 2008

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A comparative study has been performed for properties (temperature, density, and electron Coulomb coupling constant) of plasma induced by high-intensity ( ∼ GW/cm2) nanosecond laser-metal interactions in air, water, and vacuum. The study is for early-stage (t≲30 ns) plasma evolution, where the above plasma properties are very difficult to measure experimentally and hence a comparative property study has been rarely reported in literature. In this paper a physics-based predictive model is used as the investigation tool. The model was verified based on experimental measurements for the early-stage plasma pressure and front propagation and the late-stage (t≳30 ns) plasma temperature and electron number density, which are relatively easy to measure. Therefore, the experimentally verified model can provide reasonably accurate information on the difficult-to-measure plasma temperature and density in the early-stage at least in the semiquantitative sense, and the information will be very useful for the fundamental laser plasma study and relevant laser applications. It has been found that plasma with very different temperatures and densities can be created in different media.
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52.25.-b Plasma properties
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

A crystalline-orientation self-selected linearly polarized Yb:Y3Al5O12 microchip laser

Jun Dong, Akira Shirakawa, and Ken-ichi Ueda

Appl. Phys. Lett. 93, 101105 (2008); http://dx.doi.org/10.1063/1.2980423 (3 pages) | Cited 4 times

Online Publication Date: 9 September 2008

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Crystalline-orientation and pump dependent polarization states of Yb:Y3Al5O12 microchip lasers were observed experimentally. Linear polarization was observed at six crystalline orientations in the (111) plane relative to the beam propagation direction along the [111] crystalline axis of Yb:Y3Al5O12 crystal. The extinction ratio of the linear polarization decreases and the laser tends to oscillate at random polarization state at high pump power levels. Linear polarization states of Yb:Y3Al5O12 microchip laser was selected by the anisotropic spectroscopic properties of the Yb3+-ion in cubic Y3Al5O12 crystal. The random polarization oscillation at high pump power was caused by the strong thermal-induced birefringence and depolarization.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Sa Microcavity and microdisk lasers
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.70.Hj Laser materials

Phase diagram of lossy negative index metamaterials

Rui-xin Wu and Da-yong Zou

Appl. Phys. Lett. 93, 101106 (2008); http://dx.doi.org/10.1063/1.2980401 (3 pages) | Cited 4 times

Online Publication Date: 10 September 2008

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For lossy metamaterials, there exist the negative index of refraction regimes that may originate from double negative or single negative of the real parts of complex permittivity and permeability. To represent the regimes of negative index, a material quality factor space is proposed. Within the space the different negative index regimes are found located in the different regions. The contour map of the complex index of refraction in the space show that the negative index can be always possible to realize in three ways, and the loss of single negative metamaterials is greater than that of double negative metamaterials.
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42.70.-a Optical materials
42.25.Bs Wave propagation, transmission and absorption
42.25.Gy Edge and boundary effects; reflection and refraction

Single-photon-emitting diode at liquid nitrogen temperature

X. M. Dou, X. Y. Chang, B. Q. Sun, Y. H. Xiong, Z. C. Niu, S. S. Huang, H. Q. Ni, Y. Du, and J. B. Xia

Appl. Phys. Lett. 93, 101107 (2008); http://dx.doi.org/10.1063/1.2980517 (3 pages) | Cited 6 times

Online Publication Date: 10 September 2008

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We report on the study of a single-photon-emitting diode at 77 K. The device is composed of InAs/GaAs quantum dots embedded in the i-region of a p-i-n diode structure. The high signal to noise ratio of the electroluminescence, as well as the small second order correlation function at zero-delay g(2)(0), implies that the device has a low multiphoton emission probability. By comparing the device performances under different excitation conditions, we have, in detail, discussed the basic parameters, such as signal to noise ratio and g(2)(0), and provided some useful information for the future application.
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85.60.Jb Light-emitting devices

Temperature dependence and physical properties of Ga(NAsP)/GaP semiconductor lasers

J. Chamings, A. R. Adams, S. J. Sweeney, B. Kunert, K. Volz, and W. Stolz

Appl. Phys. Lett. 93, 101108 (2008); http://dx.doi.org/10.1063/1.2975845 (3 pages) | Cited 7 times

Online Publication Date: 11 September 2008

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We report on the properties of GaNAsP/GaP lasers which offer a potential route to producing lasers monolithically on silicon. Lasing has been observed over a wide temperature range with pulsed threshold current density of 2.5 kA/cm2 at 80 K (λ = 890 nm). Temperature dependence measurements show that the radiative component of the threshold is relatively temperature stable while the overall threshold current is temperature sensitive. A sublinear variation of spontaneous emission versus current coupled with a decrease in external quantum efficiency with increasing temperature and an increase in threshold current with hydrostatic pressure implies that a carrier leakage path is the dominant carrier recombination mechanism.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.82.Bq Design and performance testing of integrated-optical systems

Demonstration of a ZnO/MgZnO-based one-dimensional photonic crystal multiquantum well laser

Daniel Hofstetter, Ricardo Théron, Abdel-Hamid El-Shaer, Andrey Bakin, and Andreas Waag

Appl. Phys. Lett. 93, 101109 (2008); http://dx.doi.org/10.1063/1.2978203 (3 pages) | Cited 4 times

Online Publication Date: 11 September 2008

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A ZnO/MgZnO-based one-dimensional photonic crystal multiquantum well laser operating at an emission wavelength of 360.7 nm is demonstrated. The photonic crystal providing optical feedback was fabricated in the form of parallel grooves with a period of 277.3 nm and a depth of 100 nm in a Si3N4 layer deposited directly on the epitaxial material. At a temperature of 11 K, 16 mW peak power is emitted from the laser surface, and the threshold intensity amounts to 0.33 MW/cm2. From temperature-dependent output power versus pump intensity curves, we deduced a T0 of 60 K and a maximal operating temperature of 135 K.
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42.55.Px Semiconductor lasers; laser diodes
42.70.Qs Photonic bandgap materials
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
42.82.Cr Fabrication techniques; lithography, pattern transfer

Evanescent field response to immunoassay layer thickness on planar waveguides

Rongjin Yan, Guangwei Yuan, Matthew D. Stephens, Xinya He, Charles S. Henry, David S. Dandy, and Kevin L. Lear

Appl. Phys. Lett. 93, 101110 (2008); http://dx.doi.org/10.1063/1.2981212 (3 pages) | Cited 7 times

Online Publication Date: 11 September 2008

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The response of a compact photonic immunoassay biosensor based on a planar waveguide to variation in antigen (C-reactive protein) concentration as well as waveguide ridge height has been investigated. Near-field scanning optical microscope measurements indicate 1.7%/nm and 3.3%/nm top surface optical intensity modulation due to changes in effective adlayer thickness on waveguides with 16.5 and 10 nm ridge heights, respectively. Beam propagation method simulations are in good agreement with the experimental sensitivities as well as the observation of leaky mode interference both within and after the adlayer region.
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87.80.-y Biophysical techniques (research methods)
42.79.Gn Optical waveguides and couplers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Evanescent coupling in arrays of type II femtosecond laser-written waveguides in bulk x-cut lithium niobate

Matthias Heinrich, Alexander Szameit, Felix Dreisow, Sven Döring, Jens Thomas, Stefan Nolte, Andreas Tünnermann, and Antonio Ancona

Appl. Phys. Lett. 93, 101111 (2008); http://dx.doi.org/10.1063/1.2981801 (3 pages) | Cited 6 times

Online Publication Date: 11 September 2008

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We report on the first fabrication of evanescently coupled planar arrays of type II waveguides in x-cut lithium niobate (LiNbO3) by femtosecond laser inscription. A particular choice of writing parameters allows the evanescent field of the individual waveguide modes to extend significantly beyond the damage lines into the neighboring guides, thus realizing a coupling constant of 2.2 cm−1 at a wavelength of 633 nm.
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42.79.Gn Optical waveguides and couplers
42.70.-a Optical materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.62.-b Laser applications

The effect of the last quantum barrier on the internal quantum efficiency of InGaN-light emitting diode

Eun-Hyun Park, Jin Jang, Shalini Gupta, Ian Ferguson, Soo-Kun Jeon, Jae-Gu Lim, Jun-Serk Lee, Cheol-Hoi Kim, and Joong-Seo Park

Appl. Phys. Lett. 93, 101112 (2008); http://dx.doi.org/10.1063/1.2981640 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2008

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The effect of the last quantum barrier (LQB) on the internal quantum efficiency of GaN-light emitting diode (LED) was systematically investigated using a dual-wavelength GaN-LED design. Compared with a conventional GaN-LQB, a high indium contained In0.03Ga0.97N-LQB efficiently reduced the unintentional Mg impurity in the last quantum well and improved its photoluminescence and electroluminescence intensity up to 72% and 15%, respectively.
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85.60.Jb Light-emitting devices

Enhanced optical transmission: Role of the localized surface plasmon

Shan Wu, Qian-jin Wang, Xiao-gang Yin, Jia-qi Li, Ding Zhu, Shi-qiang Liu, and Yong-yuan Zhu

Appl. Phys. Lett. 93, 101113 (2008); http://dx.doi.org/10.1063/1.2977488 (3 pages) | Cited 13 times

Online Publication Date: 12 September 2008

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We report the observation of enhanced optical transmission through the metal subwavelength hole arrays with nanoparticle inside the hole, and demonstrate the transmission enhancement and the suppression due to the excitation of the localized surface plasmon (LSP). We interpret this phenomenon with the Fano theory considering the real and imaginary parts of the polarizability of the LSP.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Er Solid metals and alloys
72.25.Ba Spin polarized transport in metals

Room-temperature midinfrared two-photon photodetector

H. Schneider, H. C. Liu, S. Winnerl, O. Drachenko, M. Helm, and J. Faist

Appl. Phys. Lett. 93, 101114 (2008); http://dx.doi.org/10.1063/1.2977864 (3 pages) | Cited 5 times

Online Publication Date: 12 September 2008

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We report on a two-photon detector based on resonantly enhanced nonlinear absorption between subbands in InGaAs/InAlAs quantum wells and demonstrate its use as a quadratic autocorrelator for midinfrared pulses. Modified device design allows for device operation at room temperature, which is crucial for applications in practical systems.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
68.65.Fg Quantum wells
81.07.St Quantum wells
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Investigation of spectral gain narrowing in quantum cascade lasers using terahertz time domain spectroscopy

N. Jukam, S. S. Dhillon, D. Oustinov, Z.-Y. Zhao, S. Hameau, J. Tignon, S. Barbieri, A. Vasanelli, P. Filloux, C. Sirtori, and X. Marcadet

Appl. Phys. Lett. 93, 101115 (2008); http://dx.doi.org/10.1063/1.2979682 (3 pages) | Cited 17 times

Online Publication Date: 12 September 2008

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The spectral gain of bound-to-continuum terahertz quantum cascade lasers (QCLs) is measured as a function of current density using terahertz time-domain spectroscopy. During lasing action the full width at half maximum (FWHM) of the gain is found to monotonically decrease with increasing current density until lasing action stops at which point the FWHM reaches a minimum (0.22 THz for a laser operating at 2.1 THz). Band structure calculations show that the spectral gain narrowing is due to the alignment and misalignment of the injector with the active region as a function of the applied bias field.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.By Design of specific laser systems
78.70.Gq Microwave and radio-frequency interactions

Spatial modulation instability driven by light-enhanced nonlinearities in semiconductor CdZnTe:V crystals

Sharon Shwartz, Mordechai Segev, Emil Zolotoyabko, and Uri El-Hanany

Appl. Phys. Lett. 93, 101116 (2008); http://dx.doi.org/10.1063/1.2982084 (3 pages) | Cited 2 times

Online Publication Date: 12 September 2008

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We present the experimental observation of spatial modulation instability in photorefractive semiconductor crystals (CdZnTe:V), where the optical nonlinear effects are enhanced by light. We find that the total refractive index change can be expressed as sum of a uniform index change, which can exceed the value of 0.003, and a local index change which is limited to ≈ 1.6×10−4. However, only the later, arising from the intensity-enhanced photorefractive effect, contributes to the formation of the modulation instability. Finally, we find that the refractive index change experiences large temporal fluctuations induced by the combination of uniform cw illumination and applied electric field.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Monolithic white light emitting diodes using a (Ga,In)N/GaN multiple quantum well light converter

B. Damilano, A. Dussaigne, J. Brault, T. Huault, F. Natali, P. Demolon, P. De Mierry, S. Chenot, and J. Massies

Appl. Phys. Lett. 93, 101117 (2008); http://dx.doi.org/10.1063/1.2982097 (3 pages) | Cited 6 times

Online Publication Date: 12 September 2008

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A monolithic white light emitting diode using a (Ga,In)N/GaN multiple quantum well (MQW) light converter is demonstrated. Blue photons emitted under electrical injection by (Ga,In)N/GaN QWs located inside a GaN p-n junction are partly absorbed by another (Ga,In)N/GaN MQW situated outside the junction which emits yellow-green light. The combination of the blue and yellow-green components results in white light emission.
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85.60.Jb Light-emitting devices
68.65.Fg Quantum wells
81.07.St Quantum wells
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Order of magnitude enhancement in neutron emission with deuterium-krypton admixture operation in miniature plasma focus device

Rishi Verma, P. Lee, S. Lee, S. V. Springham, T. L. Tan, R. S. Rawat, and M. Krishnan

Appl. Phys. Lett. 93, 101501 (2008); http://dx.doi.org/10.1063/1.2979683 (3 pages) | Cited 10 times

Online Publication Date: 8 September 2008

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The effect of varied concentrations of deuterium-krypton (D2–Kr) admixture on the neutron emission of a fast miniature plasma focus device was investigated. It was found that a judicious concentration of Kr in D2 can significantly enhance the neutron yield. The maximum average neutron yield of (1±0.27)×104 n/shot for pure D2 filling at 3 mbars was enhanced to (3.14±0.4)×105 n/shot with D2+2% Kr admixture operation, which represents a >30-fold increase. More than an order of magnitude enhancement in the average neutron yield was observed over the broader operating range of 1–4 mbars for D2+2% Kr and D2+5% Kr admixtures.
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52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.59.Hq Dense plasma focus
29.25.Dz Neutron sources

Reversed scheme of thin foil acceleration

S. Borodziuk, A. Kasperczuk, T. Pisarczyk, J. Ullschmied, E. Krousky, K. Masek, M. Pfeifer, K. Rohlena, J. Skala, and P. Pisarczyk

Appl. Phys. Lett. 93, 101502 (2008); http://dx.doi.org/10.1063/1.2979700 (3 pages) | Cited 3 times

Online Publication Date: 8 September 2008

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An alternative concept for accelerating thin foils to high velocity has been proposed and tested. The thin (10 μm) Al foil has been accelerated by the ablative plasma generated by means of the third harmonic (λ = 0.438 μm, τ = 250 ps) of the iodine laser pulse of the energies of 75 and 190 J irradiating a massive Cu target. Two separation distances of the foil from the massive target of 100 and 500 μm were used. It has been shown that this method of an indirect, two-step acceleration, named as the reversed acceleration scheme, can be more effective than the classic, direct-drive approach. The Al flyer foil has reached a velocity of ∼ 1.3×107 cm/s, i.e., significantly higher than that in the comparable “classic” ablative acceleration experiment.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
79.20.Ds Laser-beam impact phenomena

Gas-temperature-dependent generation of cryoplasma jet under atmospheric pressure

Yuri Noma, Jai Hyuk Choi, Takaaki Tomai, and Kazuo Terashima

Appl. Phys. Lett. 93, 101503 (2008); http://dx.doi.org/10.1063/1.2980436 (3 pages) | Cited 9 times

Online Publication Date: 12 September 2008

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Plasma with a gas temperature below room temperature is not yet fully understood although it is expected to be an attractive tool for applications to material processing. In the present work, gas-temperature-dependent generation of a cryoplasma jet was studied. So far, we have generated a helium cryoplasma jet (296–5 K) under atmospheric pressure. At gas temperatures below 20 K, the helium excimer, He2, was observed clearly from by optical emission spectroscopy.
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52.50.-b Plasma production and heating
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Optical properties of GaN/AlGaN quantum wells grown on nonpolar substrates

T. J. Badcock, P. Dawson, M. J. Kappers, C. McAleese, J. L. Hollander, C. F. Johnston, D. V. Sridhara Rao, A. M. Sanchez, and C. J. Humphreys

Appl. Phys. Lett. 93, 101901 (2008); http://dx.doi.org/10.1063/1.2971205 (3 pages) | Cited 16 times

Online Publication Date: 8 September 2008

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In this paper we report on the optical properties of a series of GaN/AlGaN multiple quantum well structures grown on a-plane (11math0) GaN, which had been deposited on r-plane (1math02) sapphire substrates, compared to a reference GaN template of the same orientation. The low temperature photoluminescence spectrum of the template layer is dominated by two emission bands, which we attribute to recombination involving excitons in the bulk of the layer and electrons and holes trapped at basal-plane stacking faults, designated X1 and X2, respectively. The photoluminescence spectra from the quantum well structures show similar emission bands except that both X1 and X2 shift to higher energy with decreasing quantum well thickness. The shift to higher energy is due to the effects of quantum confinement on carriers trapped at the stacking faults that intersect the quantum wells, as well as those excitons that are localized within the quantum wells. This assignment is based partly on excitation spectroscopy that reveals exciton transitions associated with electrons from the n = 1 and n = 2 quantum well confined states.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena

On electromechanical stability of dielectric elastomers

R. Díaz-Calleja, E. Riande, and M. J. Sanchis

Appl. Phys. Lett. 93, 101902 (2008); http://dx.doi.org/10.1063/1.2972124 (3 pages) | Cited 32 times

Online Publication Date: 8 September 2008

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This paper studies the competition between electric and mechanical force fields simultaneously applied to a polar elastomer that can lead to electric breakdown. The analysis of the system, performed assuming that the free energy of the elastomer is simply the addition of polarizing and stretching energies leads to the classical “thermodynamic” (in this case “electromechanical”) stability.
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77.22.Jp Dielectric breakdown and space-charge effects
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Enhanced nonradiative Auger recombination in p-type modulation doped InAs/GaAs quantum dots

Y. D. Jang, T. J. Badcock, D. J. Mowbray, M. S. Skolnick, J. Park, D. Lee, H. Y. Liu, M. Hopkinson, R. A. Hogg, and A. D. Andreev

Appl. Phys. Lett. 93, 101903 (2008); http://dx.doi.org/10.1063/1.2975961 (3 pages) | Cited 5 times

Online Publication Date: 8 September 2008

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The photoluminescence efficiency and carrier recombination time of p-type modulation doped InAs/GaAs quantum dots (QDs) have been measured as a function of doping density. At 10 K the carrier lifetime decreases from 1200 to 350 ps over the doping range of 0 and 30 acceptors/QD. This behavior is attributed to an enhancement of the Auger-type recombination due to the presence of extrinsic holes in the QDs. The hole density dependence of the Auger process is found to be weaker than in bulk semiconductors and quantum wells (QWs).
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73.63.Kv Quantum dots
73.63.Hs Quantum wells
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
79.20.Fv Electron impact: Auger emission
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Vacancy formation during oxidation of silicon crystal surface

M. Suezawa, Y. Yamamoto, M. Suemitsu, N. Usami, and I. Yonenaga

Appl. Phys. Lett. 93, 101904 (2008); http://dx.doi.org/10.1063/1.2979708 (3 pages)

Online Publication Date: 8 September 2008

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To study the formation of interstitials and vacancies during oxidation of silicon crystals, we applied a quenching method, namely, oxidation at high temperatures in mixed gases of water vapor and H2 followed by the quenching into water. Contrary to our expectation, the vacancy concentration was higher than that of the thermal equilibrium during the short duration of oxidation.
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61.72.jd Vacancies
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments

Origin of hardness in WB4 and its implications for ReB4, TaB4, MoB4, TcB4, and OsB4

Mei Wang, Yinwei Li, Tian Cui, Yanming Ma, and Guangtian Zou

Appl. Phys. Lett. 93, 101905 (2008); http://dx.doi.org/10.1063/1.2977760 (3 pages) | Cited 40 times

Online Publication Date: 9 September 2008

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First-principles calculations were performed on the superhard material, WB4 (Vicker hardness exceeding 46 GPa), to reveal the origin of its high hardness. Our simulated lattice parameters, bulk modulus, and hardness are in excellent agreement with the experimental data. A three-dimensional B network with a peculiar B2 dimer along the z-axis and a xy planar honeycomb B sublattice is uncovered to be mainly responsible for the high hardness. We further predicted that five other transition metal B compounds (TMB4, TM = Re, Mo, Ta, Os, and Tc) within the WB4 structure are potential superhard materials.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness
62.20.de Elastic moduli
61.66.Fn Inorganic compounds
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