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16 Jun 2008

Volume 92, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 243101 (2008); http://dx.doi.org/10.1063/1.2943414 (3 pages)

Yufeng Guo, Wanlin Guo, and Changfeng Chen
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Dynamic heterodyne near field scattering

D. Magatti, M. D. Alaimo, M. A. C. Potenza, and F. Ferri

Appl. Phys. Lett. 92, 241101 (2008); http://dx.doi.org/10.1063/1.2937841 (3 pages) | Cited 11 times

Online Publication Date: 16 June 2008

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The technique heterodyne near field scattering (HNFS), originally developed for low-angle static light scattering, has also been implemented for carrying out dynamic light scattering. While the classical dynamic light scattering method measures the intensity-intensity correlation function, dynamic HNFS gives directly the field-field correlation function, without any assumption on the statistical properties of the sample, as the ones required by the Siegert relation. The technique has been tested with calibrated Brownian particles and its performances compared to those of the classical dynamic light scattering method.
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42.25.Fx Diffraction and scattering
05.40.Jc Brownian motion

Whispering gallery mode lasing in zinc oxide microwires

Christian Czekalla, Chris Sturm, Rüdiger Schmidt-Grund, Bingqiang Cao, Michael Lorenz, and Marius Grundmann

Appl. Phys. Lett. 92, 241102 (2008); http://dx.doi.org/10.1063/1.2946660 (3 pages) | Cited 52 times

Online Publication Date: 17 June 2008

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Lasing on whispering gallery modes was excited by optical pumping in single zinc oxide microwires fabricated by a simple carbothermal evaporation process. The experimentally observed laser modes agree precisely with the predicted energetic positions obtained from a plane wave model. Systematic diameter dependent measurements have been carried out for diameters of the microwires between 3 and 12 μm. The investigated microlasers are found to have a lasing threshold of about 170 kW/cm2 at 10 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Sa Microcavity and microdisk lasers

Performance enhancement of GaN ultraviolet avalanche photodiodes with p-type δ-doping

C. Bayram, J. L. Pau, R. McClintock, and M. Razeghi

Appl. Phys. Lett. 92, 241103 (2008); http://dx.doi.org/10.1063/1.2948857 (3 pages) | Cited 12 times

Online Publication Date: 17 June 2008

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High quality δ-doped p-GaN is used as a means of improving the performance of back-illuminated GaN avalanche photodiodes (APDs). Devices with δ-doped p-GaN show consistently lower leakage current and lower breakdown voltage than those with bulk p-GaN. APDs with δ-doped p-GaN also achieve a maximum multiplication gain of 5.1×104, more than 50 times higher than that obtained in devices with bulk p-GaN. The better device performance of APDs with δ-doped p-GaN is attributed to the higher structural quality of the p-GaN layer achieved via δ-doping.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Kk Junction diodes

Efficiency and reliability enhancement of silicon nanocrystal field-effect luminescence from nitride-oxide gate stacks

M. Perálvarez, Josep Carreras, J. Barreto, A. Morales, C. Domínguez, and B. Garrido

Appl. Phys. Lett. 92, 241104 (2008); http://dx.doi.org/10.1063/1.2939562 (3 pages) | Cited 13 times

Online Publication Date: 17 June 2008

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We report on a field-effect light emitting device based on silicon nanocrystals in silicon oxide deposited by plasma-enhanced chemical vapor deposition. The device shows high power efficiency and long lifetime. The power efficiency is enhanced up to ∼ 0.1% by the presence of a silicon nitride control layer. The leakage current reduction induced by this nitride buffer effectively increases the power efficiency two orders of magnitude with regard to similarly processed devices with solely oxide. In addition, the nitride cools down the electrons that reach the polycrystalline silicon gate lowering the formation of defects, which significantly reduces the device degradation.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling
85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
85.40.Sz Deposition technology

Strong light-matter coupling in ultrathin double dielectric mirror GaN microcavities

K. Bejtka, F. Réveret, R. W. Martin, P. R. Edwards, A. Vasson, J. Leymarie, I. R. Sellers, J. Y. Duboz, M. Leroux, and F. Semond

Appl. Phys. Lett. 92, 241105 (2008); http://dx.doi.org/10.1063/1.2944263 (3 pages) | Cited 4 times

Online Publication Date: 17 June 2008

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Strong light-matter coupling is demonstrated at low temperature in an ultrathin GaN microcavity fabricated using two silica/zirconia Bragg mirrors, in addition to a three-period epitaxial (Al,Ga)N mirror serving as an etch stop and assuring good quality of the overgrown GaN. The λ/2 cavity is grown by molecular beam epitaxy on a Si substrate. Analysis of angle-resolved data reveal key features of the strong coupling regime in both reflectivity and transmission spectra at 5 K: anticrossing with a normal mode splitting of 43±2 meV and 56±2 meV for reflectivity and transmission, respectively, and narrowing of the lower polariton linewidth near resonance.
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42.86.+b Optical workshop techniques
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.79.Wc Optical coatings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Enhanced terahertz radiation from high stacking fault density nonpolar GaN

Grace D. Metcalfe, Hongen Shen, Michael Wraback, Asako Hirai, Feng Wu, and James S. Speck

Appl. Phys. Lett. 92, 241106 (2008); http://dx.doi.org/10.1063/1.2937911 (3 pages) | Cited 12 times

Online Publication Date: 17 June 2008

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Terahertz emission from high stacking fault density m-GaN has been observed using ultrafast pulse excitation. The terahertz signal exhibits a 360° periodicity with sample rotation and a polarity flip at 180°, characteristic of real carrier transport in an in-plane electric field parallel to the c axis induced by stacking fault (SF)-terminated internal polarization at wurtzite domain boundaries. The terahertz emission can be enhanced by several times relative to that from a SF-free m-GaN sample, for which the terahertz signal emanates from surface surge currents and diffusion-driven carrier transport normal to the surface and is independent of the c-axis orientation.
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78.47.D- Time resolved spectroscopy (>1 psec)
61.72.Nn Stacking faults and other planar or extended defects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Photoemission study of Cs–NF3 activated GaAs(100) negative electron affinity photocathodes

Zhi Liu, Yun Sun, Samuel Peterson, and Piero Pianetta

Appl. Phys. Lett. 92, 241107 (2008); http://dx.doi.org/10.1063/1.2945276 (3 pages) | Cited 17 times

Online Publication Date: 17 June 2008

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GaAs based negative electron affinity photocathodes activated with Cs and NF3 are used as polarized electron sources for linear accelerators. It is generally believed that the activation layer consists of CsF. The activation layers of Cs–NF3 on GaAs photocathodes are herein investigated using synchrotron radiation photoelectron spectroscopy. F1s, N1s, and other core levels are recorded at photon energies ranging from 70 to 820 eV. Surprisingly, a significant amount of nitrogen is observed in the activation layers. Two distinct species of nitrogen are observed, one of which decreases along with the fluorine signal as the yield of the photocathode decays with time.
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85.60.Ha Photomultipliers; phototubes and photocathodes
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Negative refraction with high transmission at visible and near-infrared wavelengths

Changchun Yan, Yiping Cui, Qiong Wang, Shichuang Zhuo, and Jianxin Li

Appl. Phys. Lett. 92, 241108 (2008); http://dx.doi.org/10.1063/1.2938413 (3 pages) | Cited 4 times

Online Publication Date: 17 June 2008

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A left-handed material, a metal waveguide with arrays of metal rods within it, is investigated in this letter. The simulation results have shown that the refractive indices are negative between 512 and 898 nm, while the negative-index band with high transmission ranges roughly from 672 to 798 nm. This is an effective method to the realization of negative refraction at visible frequencies. The mechanism of resonance has been revealed by simulating the distributions of induced current in a unit cell. A wedge-shaped structure has also been designed to provide direct evidence for the negative refraction behavior.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Green light emitting diodes on a-plane GaN bulk substrates

Theeradetch Detchprohm, Mingwei Zhu, Yufeng Li, Yong Xia, Christian Wetzel, Edward A. Preble, Lianghong Liu, Tanya Paskova, and Drew Hanser

Appl. Phys. Lett. 92, 241109 (2008); http://dx.doi.org/10.1063/1.2945664 (3 pages) | Cited 22 times

Online Publication Date: 17 June 2008

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We report the development of 520–540 nm green light emitting diodes (LEDs) grown along the nonpolar a axis of GaN. GaInN/GaN-based quantum well structures were grown in homoepitaxy on both, a-plane bulk GaN and a-plane GaN on r-plane sapphire. LEDs on GaN show higher, virtually dislocation-free crystalline quality and three times higher light output power when compared to those on r-plane sapphire. Both structures show a much smaller wavelength blue shift for increasing current density (<10 nm for 0.1 to 12.7 A/cm2) than conventional LEDs grown along the polar c axis.
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85.60.Jb Light-emitting devices

Time dependent degradation of photovoltaic modules by ultraviolet light

Claus G. Zimmermann

Appl. Phys. Lett. 92, 241110 (2008); http://dx.doi.org/10.1063/1.2947589 (3 pages) | Cited 5 times

Online Publication Date: 18 June 2008

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For high efficiency silicone encapsulated solar modules for concentrator photovoltaic systems or space applications, the question of performance degradation due to long term exposure to ultraviolet (UV) light is addressed. The transparent silicones DC93-500 and Elastosil S690 and S695 were subjected to a time and wavelength resolved UV test with a total accumulated dose of 10 000 equivalent sun hours. Based on a model for the kinetics of photodegradation, it is shown that the measured decrease in transmittance translates into a universal logarithmic time dependence for the module short circuit current. The UV related performance impact over 15 years under the AM0 spectrum in space and the terrestrial AM1.5 spectrum with 500× concentration is quantified.
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84.60.Jt Photoelectric conversion

Fluorescence lifetime of Mn-doped ZnSe quantum dots with size dependence

Chenli Gan, Yanpeng Zhang, David Battaglia, Xiaogang Peng, and Min Xiao

Appl. Phys. Lett. 92, 241111 (2008); http://dx.doi.org/10.1063/1.2945274 (3 pages) | Cited 10 times

Online Publication Date: 18 June 2008

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Radiative lifetimes of high quality Mn:ZnSe nanocrystals synthesized by nucleation-doping method are experimentally measured at wavelength near 580 nm. The slow decay rate in millisecond time scale is identified as the radiative decay from the 4T1 metastable excited state of Mn2+ ions embedded in the ZnSe nanocrystals. Also, two fast decay components are measured at this wavelength with much lower intensities, which can be attributed to the emission tails from the host ZnSe nanocrystals and from the surface-trap states or the self-activated luminescence due to Mn ion pairs, respectively. Size dependences of the radiative decay rates for the Mn:ZnSe samples are measured.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
73.21.La Quantum dots
61.72.U- Doping and impurity implantation
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Ultrafast reset time of superconducting single photon detectors

M. Tarkhov, J. Claudon, J. Ph. Poizat, A. Korneev, A. Divochiy, O. Minaeva, V. Seleznev, N. Kaurova, B. Voronov, A. V. Semenov, and G. Gol’tsman

Appl. Phys. Lett. 92, 241112 (2008); http://dx.doi.org/10.1063/1.2945277 (3 pages) | Cited 20 times

Online Publication Date: 18 June 2008

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We have measured the ultrafast reset time of NbN superconducting single photon detectors (SSPDs) based on a design consisting of N parallel superconducting stripes. Compared to a standard SSPD of identical active area, the parallel SSPD displays a similar detection efficiency and a kinetic inductance, which is divided by N2. For N = 12, the duration of the voltage detection pulse is reduced by nearly two orders of magnitude down to 200 ps. The timing jitter associated with the rising front is only 16 ps. These results open a way to efficient detectors with ultrahigh counting rate exceeding 1 GHz.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Surface plasmon enhanced transmission and directivity through subwavelength slit in X-band microwaves

Liang Wang, Jin-Xiang Cao, Lei Liu, You Lv, and Shi-Jian Zheng

Appl. Phys. Lett. 92, 241113 (2008); http://dx.doi.org/10.1063/1.2944136 (3 pages) | Cited 3 times

Online Publication Date: 19 June 2008

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In this letter, we experimentally investigated the transmission of microwaves through a single subwavelength slit surrounded by periodic grooves in metallic aluminum plates. Significant transmission enhancement (16.2-fold) and angular confinement (±18°) were observed at X-band microwave frequencies (8–12 GHz). We demonstrated that the coupled surface plasmons were involved in the interesting transmission process. The little angular divergence was attributed to the periodic structures of the exit surface. The experimental results show good agreement with theory and are of relevance not only for further understanding the underlying science but also for enlarging applications based on this phenomenon.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces

Strong orange/red electroluminescence from hydrogenated polymorphous silicon carbon light-emitting devices

I. Stenger, A. Abramov, C. Barthou, Th. Nguyen-Tran, A. Frigout, and P. Roca i Cabarrocas

Appl. Phys. Lett. 92, 241114 (2008); http://dx.doi.org/10.1063/1.2948852 (3 pages) | Cited 7 times

Online Publication Date: 19 June 2008

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We report on electroluminescent P-I-N diodes containing silicon nanocrystals embedded in an amorphous silicon carbon matrix as emitting material. The as-deposited devices mostly contain amorphous Si nanoparticles and emit weakly in the IR. After a forming process consisting of the application of a high current density to the structure, the intensity of the electroluminescence increases by a factor of 30 and shifts to the red. The forming process is characterized by electroluminescence measurements and the induced crystallization of the nanoparticles is evidenced by Raman scattering spectroscopy measurements. These results are interpreted as a metal induced crystallization.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

Gain and continuous-wave laser power enhancement with a multiple discharge electric oxygen-iodine laser

J. W. Zimmerman, B. S. Woodard, G. F. Benavides, D. L. Carroll, J. T. Verdeyen, A. D. Palla, and W. C. Solomon

Appl. Phys. Lett. 92, 241115 (2008); http://dx.doi.org/10.1063/1.2948860 (3 pages) | Cited 5 times

Online Publication Date: 19 June 2008

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Herein the authors report on the demonstration of a 70% enhancement in gain and 98% enhancement in continuous-wave laser power on the 1315 nm transition of atomic iodine via an increase in flow rates and pressure using multiple discharges in an electric oxygen-iodine laser. O2(a 1Δ) is produced by two parallel radio-frequency-excited electric discharges sustained in an O2–He–NO gas mixture, a secondary discharge predissociated the molecular iodine, and I(2P1/2) is then pumped using energy transferred from O2(a 1Δ). A gain of 0.17% cm−1 was obtained and the total laser output power was 12.3 W.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems

Multibands of negative refractive indexes in the left-handed metamaterials with multiple dendritic structures

Weiren Zhu, Xiaopeng Zhao, and Jiquan Guo

Appl. Phys. Lett. 92, 241116 (2008); http://dx.doi.org/10.1063/1.2949552 (3 pages) | Cited 26 times

Online Publication Date: 19 June 2008

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We demonstrate that the multibands of negative refraction indexes in the left-handed metamaterials may be appeared based on multiple dendritic structures cells. Employing microwave transmission experiment, the medium exhibits simultaneous negative refraction at the frequencies of 9.50, 10.24, and 10.78 GHz for the electromagnetic wave parallel incidence, and at the frequencies of 9.24, 9.98, and 10.78 GHz for normal incidence. The multiple dendritic metamaterials here open a way to prepare the cloak suitable for multifrequencies, especially for the cloak of infrared or visible frequency.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials

Three dimensional photoelasticity with equilibrium constraint

Kenji Oguni, M. L. L. Wijerathne, and Muneo Hori

Appl. Phys. Lett. 92, 241117 (2008); http://dx.doi.org/10.1063/1.2949683 (3 pages)

Online Publication Date: 19 June 2008

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A method for stress field tomography based on three dimensional photoelasticity has been developed. The proper treatment of the nonlinearity and the ill-posedness is the key to the robust tomographic method. In the proposed method, the nonlinearity has been addressed by the load incremental approach which divides the nonlinear solution space into segments with unique solutions. Also, the ill-posedness has been suppressed by introducing constraints from the equilibrium of the stress field. Validating both numerically and experimentally, the proposed method is shown to be robust enough and applicable to experimental stress measurements.
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81.70.Fy Nondestructive testing: optical methods
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Efficient GaN slab vertical light-emitting diode covered with a patterned high-index layer

Sun-Kyung Kim, Hyun Kyong Cho, Duk Kyu Bae, Jeong Soo Lee, Hong-Gyu Park, and Yong-Hee Lee

Appl. Phys. Lett. 92, 241118 (2008); http://dx.doi.org/10.1063/1.2945892 (3 pages) | Cited 18 times

Online Publication Date: 19 June 2008

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We demonstrate the enhancement of light extraction from a wide-area (500×500 μm2) GaN slab light-emitting diode (LED) that results from covering it with a TiO2-patterned layer. To fabricate this device, a Cu supporter is electroplated onto the p-GaN face followed by detaching the sapphire substrate with a laser lift-off process. At the standard current of 60 mA, the wall-plug efficiency of the TiO2-patterned LED is ∼ 14.8%, i.e., the efficiency is enhanced by a factor of ∼ 1.8 over that of nonpatterned LEDs. Our three-dimensional finite-difference time-domain computations confirm that this output increases with the index of the patterned layer.
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85.60.Jb Light-emitting devices

Liquid microlens with tunable focal length and light transmission

Gui-Rong Xiong, Yong-Hao Han, Cheng Sun, Li-Guo Sun, Guo-Zhi Han, and Zhong-Ze Gu

Appl. Phys. Lett. 92, 241119 (2008); http://dx.doi.org/10.1063/1.2944265 (3 pages) | Cited 3 times

Online Publication Date: 20 June 2008

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A microfluidic design was created to allow liquid microlens to control focal length and light transmission. The focal length of the microlens was controlled by varying the volume of liquid infused into the liquid cell. The cell extruded a polydimethylsiloxane film and produced a changeable curvature. The imaging ability of the microlens was tuned by taking advantage of the phase transition of poly-N-isopropylacrylamide in the liquid. The phase transition temperature was controlled in the range of 25.6–34.5 °C by changing the ion concentration.
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47.85.Np Fluidics
78.66.Qn Polymers; organic compounds

Contact photolithographic micropatterning for bistable nematic liquid crystal displays

Jun-ichi Niitsuma, Makoto Yoneya, and Hiroshi Yokoyama

Appl. Phys. Lett. 92, 241120 (2008); http://dx.doi.org/10.1063/1.2945631 (3 pages) | Cited 7 times

Online Publication Date: 20 June 2008

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Orthogonal alignment patterns of 2×2 μm2 size that induce nematic bistability were fabricated over 4×4 cm2 by a double exposure process employing a rewritable photoalignment material. Bistable liquid crystal cells with patterned surfaces were fabricated, and reproducible switching between the bistable states driven by orthogonal in-plane electric fields at 8.2 and 3.9 V/μm was confirmed.
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42.79.Kr Display devices, liquid-crystal devices
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.82.Cr Fabrication techniques; lithography, pattern transfer
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Cold atmospheric pressure air plasma jet for medical applications

J. F. Kolb, A.-A H. Mohamed, R. O. Price, R. J. Swanson, A. Bowman, R. L. Chiavarini, M. Stacey, and K. H. Schoenbach

Appl. Phys. Lett. 92, 241501 (2008); http://dx.doi.org/10.1063/1.2940325 (3 pages) | Cited 98 times

Online Publication Date: 17 June 2008

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By flowing atmospheric pressure air through a direct current powered microhollow cathode discharge, we were able to generate a 2 cm long plasma jet. With increasing flow rate, the flow becomes turbulent and temperatures of the jet are reduced to values close to room temperature. Utilizing the jet, yeast grown on agar can be eradicated with a treatment of only a few seconds. Conversely, animal studies show no skin damage even with exposures ten times longer than needed for pathogen extermination. This cold plasma jet provides an effective mode of treatment for yeast infections of the skin.
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87.80.-y Biophysical techniques (research methods)
52.75.-d Plasma devices
52.25.-b Plasma properties
52.80.-s Electric discharges
87.19.xg Fungal diseases

Pure-tin microdroplets irradiated with double laser pulses for efficient and minimum-mass extreme-ultraviolet light source production

Shinsuke Fujioka, Masashi Shimomura, Yoshinori Shimada, Shinsuke Maeda, Hirokazu Sakaguchi, Yuki Nakai, Tatsuya Aota, Hiroaki Nishimura, Norimasa Ozaki, Atsushi Sunahara, Katsunobu Nishihara, Noriaki Miyanaga, Yasukazu Izawa, and Kunioki Mima

Appl. Phys. Lett. 92, 241502 (2008); http://dx.doi.org/10.1063/1.2948874 (3 pages) | Cited 18 times

Online Publication Date: 18 June 2008

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Laser-driven expansion of pure-tin microdroplets was demonstrated to produce an efficient and low-debris extreme-ultraviolet (EUV) light source. The pre-expansion is indispensable for resolving the considerable mismatch between the optimal laser spot diameter ( ∼ 300 μm) and the diameter ( ∼ 20 μm) of microdroplets containing the minimum-mass Sn fuel for generating the required EUV radiant energy ( ∼ 10 mJ/pulse). Explosive expansion of microdroplets was attained by using a laser prepulse, whose intensity was at least 3×1011 W/cm2. The expanded microdroplet was irradiated with a CO2 laser pulse to generate EUV light. A combination of low density and long-scale length of the expanded microdroplet leads to a higher EUV energy conversion efficiency (4%) than that (2.5%) obtained from planar Sn targets irradiated by a single CO2 laser pulse. This scheme can be used to produce a practical EUV light source system.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.72.Bj Visible and ultraviolet sources

Cold microplasma plume produced by a compact and flexible generator at atmospheric pressure

T. L. Ni, F. Ding, X. D. Zhu, X. H. Wen, and H. Y. Zhou

Appl. Phys. Lett. 92, 241503 (2008); http://dx.doi.org/10.1063/1.2945888 (3 pages) | Cited 9 times

Online Publication Date: 18 June 2008

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In this letter, we report a cold microplasma generator at atmospheric pressure excited at 1 kHz in a pin to hole-electrode configuration by using soft materials partly. A nitrogen plasma plume with a length of more than 5 cm can be produced at low electrical power of 0.7 W without high feed gas pressure. The generator exhibits a compact structure with flexible property, which is suitable for treating thermally sensitive materials and biomedical materials, especially for delicate objects in an irregular confined space. Optical emission spectroscopy is used to spatially identify excited species in plasma plume.
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52.50.Dg Plasma sources
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.77.-j Plasma applications

High Kα x-ray conversion efficiency from extended source gas jet targets irradiated by ultra short laser pulses

N. L. Kugland, C. G. Constantin, P. Neumayer, H.-K. Chung, A. Collette, E. L. Dewald, D. H. Froula, S. H. Glenzer, A. Kemp, A. L. Kritcher, J. S. Ross, and C. Niemann

Appl. Phys. Lett. 92, 241504 (2008); http://dx.doi.org/10.1063/1.2945795 (3 pages) | Cited 15 times

Online Publication Date: 20 June 2008

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The absolute laser conversion efficiency to Kα-like inner shell x-rays (integrated from Kα to Kβ) is observed to be an order of magnitude higher in argon gas jets than in solid targets due to enhanced emission from higher ionization stages following ultrashort pulse laser irradiation. Particle-in-cell and spectral simulations indicate that these observations are consistent with Kα emission from a warm Ar plasma subject to hot electron inner-shell ionization. These results demonstrate that gas jet targets are bright, high conversion efficiency, high repetition rate, debris-free multi-keV x-ray sources for spectrally resolved scattering and backlighting of rapidly evolving dense matter.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.75.-d Plasma devices
52.80.-s Electric discharges
52.65.Rr Particle-in-cell method
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Pressure-induced incompressibility of ReC and effect of metallic bonding on its hardness

Huiyang Gou, Li Hou, Jingwu Zhang, and Faming Gao

Appl. Phys. Lett. 92, 241901 (2008); http://dx.doi.org/10.1063/1.2938031 (3 pages) | Cited 26 times

Online Publication Date: 16 June 2008

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The compressible behaviors of the selected 5d transition metal carbides MC (M = W,Re,Os,Ir) with hexagonal tungsten carbide-type structure were studied by first-principles calculations. Results indicate that the incompressibility of ReC exceeds that of diamond under higher pressure. The calculated method for hardness of crystals with partial metallic bonding is suggested and the calculated results indicate that hexagonal ReC crystal possesses excellent mechanical properties.
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81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.F- Deformation and plasticity
62.20.Qp Friction, tribology, and hardness
63.20.dk First-principles theory
65.40.G- Other thermodynamical quantities
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