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1 Apr 2012

Volume 111, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 071101 (2012); http://dx.doi.org/10.1063/1.3694674 (23 pages)

Shunfeng Li and Andreas Waag
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GaN based nanorods for solid state lighting

Shunfeng Li and Andreas Waag

J. Appl. Phys. 111, 071101 (2012); http://dx.doi.org/10.1063/1.3694674 (23 pages)

Online Publication Date: 2 April 2012

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In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.07.Bc Nanocrystalline materials
85.60.Jb Light-emitting devices
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back to top Lasers, Optics, and Optoelectronics

Manipulation of electromagnetically-induced transparency in planar metamaterials based on phase coupling

Xing-Ri Jin, Yuehui Lu, Jinwoo Park, Haiyu Zheng, Feng Gao, YoungPak Lee, Joo Yull Rhee, Ki Won Kim, H. Cheong, and Won Ho Jang

J. Appl. Phys. 111, 073101 (2012); http://dx.doi.org/10.1063/1.3699197 (4 pages)

Online Publication Date: 3 April 2012

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We experimentally demonstrated a controllable electromagnetically induced transparency (EIT)-like spectral response at microwave frequencies in a planar metamaterial consisting of two identical split-ring resonators (SRRs) with side-by-side symmetry. In our scheme, phase coupling between the two SRRs (serving as the bright mode), which were excited strongly by the incident wave, was employed, and it was found that the EIT-like spectral response could be controlled by simply adjusting the incident angle. Thus, our scheme may be used for electromagnetic-wave switching. A high group index for slow-light application and a high quality factor could be obtained by simply controlling the incident angle.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.70.Gq Microwave and radio-frequency interactions

Optical and electrical characteristics of asymmetric nanowire solar cells

Myung-Dong Ko, Chang-Ki Baek, Taiuk Rim, Sooyoung Park, and Yoon-Ha Jeong

J. Appl. Phys. 111, 073102 (2012); http://dx.doi.org/10.1063/1.3699212 (5 pages)

Online Publication Date: 4 April 2012

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We propose an asymmetric radial structure developed via simulation that improves the optical and electrical characteristics of silicon nanowire (SiNW) solar cells. This nanostructure is designed by shrinking the bottom core diameter and holding the top core diameter fixed in the SiNW, which results in a total reflection of the incident light in the outer wall of the shell due to the difference in the refractive index. The reflection enhances light trapping and concentration, which results in a 10 times higher optical generation rate and greater optical absorption in the high energy regime as compared with the fundamental symmetric radial structure. Further, we found that the efficiency is increased by over 10% when the bottom core diameter is decreased. The proposed structure has great potential to effectively improve the efficiency in concert with optimizing the design parameters.
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88.40.jj Silicon solar cells

Optical dielectric behaviors of copper zinc alloy thin films

Guang Yang (杨广), Jingbo Sun (孙竞博), and Ji Zhou (周济)

J. Appl. Phys. 111, 073103 (2012); http://dx.doi.org/10.1063/1.3700347 (8 pages)

Online Publication Date: 5 April 2012

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Variable angle spectroscopic ellipsometry (VASE) was employed to investigate the dielectric behaviors of Cu-Zn alloy films on silicon substrate prepared using direct current (DC) magnetron sputtering. The influence of the thickness and alloy composition on the dielectric properties of Cu-Zn alloys was studied. A dielectric function model combining with a surface effective medium theory (EMA) layer and a thin Lorentz-Drude layer was established to all alloy films to determine the dielectric functions. It shows that the dispersion behaviors of the alloy films are sensitive to the film thickness and the composition of the alloys.
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68.55.-a Thin film structure and morphology
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
81.15.Cd Deposition by sputtering

Isotope separation of 17O by photodissociation of ozone with near-infrared laser irradiation

Shigeru Hayashida, Takashi Kambe, Tetsuya Sato, Takehiro Igarashi, and Hiroaki Kuze

J. Appl. Phys. 111, 073104 (2012); http://dx.doi.org/10.1063/1.3702565 (5 pages)

Online Publication Date: 10 April 2012

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Oxygen-17 is a stable oxygen isotope useful for various diagnostics in both engineering and medical applications. Enrichment of 17O, however, has been very costly due to the lack of appropriate methods that enable efficient production of 17O on an industrial level. In this paper, we report the first 17O-selective photodissociation of ozone at a relatively high pressure, which has been achieved by irradiating a gas mixture of 10 vol% O3-90 vol% CF4 with narrowband laser. The experiment was conducted on a pilot-plant scale. A total laser power of 1.6 W was generated by external-cavity diode lasers with all the laser wavelengths fixed at the peak of an absorption line of 16O16O17O around 1 μm. The beams were introduced into a 25 -m long photoreaction cell under the sealed-off condition with a total pressure of 20 kPa. Lower cell temperature reduced the background decomposition of ozone, and at the temperature of 158 K, an 17O enrichment factor of 2.2 was attained.
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82.50.Bc Processes caused by infrared radiation
32.10.Bi Atomic masses, mass spectra, abundances, and isotopes
33.80.Gj Diffuse spectra; predissociation, photodissociation
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Equifrequency curve dispersion in dielectric-loaded plasmonic crystals

C. J. Regan, L. Grave de Peralta, and A. A. Bernussi

J. Appl. Phys. 111, 073105 (2012); http://dx.doi.org/10.1063/1.3702790 (5 pages)

Online Publication Date: 10 April 2012

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We present a quantitative description of the momentum-space dispersion and directivity of light propagation in dielectric-loaded plasmonic crystals. In our analysis the three-dimensional lossy plasmonic crystals are modeled by two-dimensional lossless dielectric crystals with real effective refractive indexes. Simulated equifrequency curves are in excellent agreement with measured Fourier plane images obtained from dye-doped dielectric-loaded plasmonic crystals with different lattice geometries and parameters. Our results provide fundamental information about the origin of the directional bandgaps in these structures.
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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)
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Determination of the absolute internal quantum efficiency of photoluminescence in GaN co-doped with Si and Zn

M. A. Reshchikov, M. Foussekis, J. D. McNamara, A. Behrends, A. Bakin, and A. Waag

J. Appl. Phys. 111, 073106 (2012); http://dx.doi.org/10.1063/1.3699312 (12 pages)

Online Publication Date: 10 April 2012

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The optical properties of high-quality GaN co-doped with silicon and zinc are investigated by using temperature-dependent continuous-wave and time-resolved photoluminescence measurements. The blue luminescence band is related to the ZnGa acceptor in GaN:Si,Zn, which exhibits an exceptionally high absolute internal quantum efficiency (IQE). An IQE above 90% was calculated for several samples having different concentrations of Zn. Accurate and reliable values of the IQE were obtained by using several approaches based on rate equations. The concentrations of the ZnGa acceptors and free electrons were also estimated from the photoluminescence measurements.
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78.55.Hx Other solid inorganic materials

Design and modeling of InAs/GaSb type II superlattice based dual-band infrared detectors

Gamini Ariyawansa, Matt Grupen, Joshua M. Duran, John E. Scheihing, Thomas R. Nelson, and Michael T. Eismann

J. Appl. Phys. 111, 073107 (2012); http://dx.doi.org/10.1063/1.3702581 (10 pages)

Online Publication Date: 11 April 2012

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The objective of this paper is to provide a credible analysis for predicting the spectral responsivity of InAs/GaSb/AlSb type-II superlattice (T2SL) based dual-band infrared photodetectors. An overview of the T2SL based design criteria is given and new dual-band detector architecture with a model dual-band detector structure designed to detect light in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) ranges is presented. The absorption coefficient is modeled empirically and the quantum efficiency spectra are calculated using a numerical model and Hovel’s analytical expressions. The spectral cross-talk due to the response of the LWIR channel to residual MWIR light is also investigated. It is shown that the significance of this cross-talk primarily depends on the temperature of the target (scene) being detected. For MWIR/MWIR (two bands in the MWIR range) dual-band detectors, the spectral cross-talk becomes significant irrespective of the target temperature. Eliminating the spectral cross-talk in T2SL dual-band detectors presently remains a challenge.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.21.Cd Superlattices

Analysis of dielectric loaded surface plasmon waveguide structures: Transfer matrix method for plasmonic devices

Xiao Yong He, Qi Jie Wang, and Siu Fung Yu

J. Appl. Phys. 111, 073108 (2012); http://dx.doi.org/10.1063/1.3703468 (6 pages)

Online Publication Date: 11 April 2012

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The propagation properties of dielectric loaded surface plasmon polariton (DLSPP) waveguide structures have been investigated by using the transfer matrix method (TMM), which is simple and has a fast calculation speed. The results obtained from the TMM agree well with those from the finite element method. As a demonstration, we investigate the waveguide properties of DLSPP structures in the terahertz and near-infrared regimes. The TMM is potentially a powerful and effective tool for studying various plasmonic waveguide structures, which may find important applications in integrated photonic devices and sensors.
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42.79.Gn Optical waveguides and couplers
84.40.Az Waveguides, transmission lines, striplines
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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)

A method to extract absorption coefficient of thin films from transmission spectra of the films on thick substrates

Sean W. King and Milan Milosevic

J. Appl. Phys. 111, 073109 (2012); http://dx.doi.org/10.1063/1.3700178 (9 pages)

Online Publication Date: 11 April 2012

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In this paper we present a method that allows extraction of the absorption coefficient of a thin film from transmittance spectrum of the film on a silicon substrate. The method essentially removes all “optical effects,” such as interference fringes, reflectance losses, substrate absorption, etc. The method requires that the refractive index of the film is known at one wavelength and that the thickness of the film is approximately known, both of which are generally available from ellipsometric measurements. As a by-product of the procedure, the method also extracts optical constants of the film over the entire spectral range of interest and provides improved values of thickness and refractive index over those provided by ellipsometry.
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78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Am Elemental semiconductors and insulators

Electronic states and intraband terahertz optical transitions in InGaAs quantum rods

Nikola Prodanović, Nenad Vukmirović, Dragan Indjin, Zoran Ikonić, and Paul Harrison

J. Appl. Phys. 111, 073110 (2012); http://dx.doi.org/10.1063/1.3692069 (6 pages)

Online Publication Date: 11 April 2012

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Strain-dependent eight-band k·p method is used to analyze the electronic structure and intraband optical transitions in self-assembled InGaAs quantum rods in the terahertz range. The calculation of absorption spectra for the growth- and in-plane-polarized radiation shows some similarities to those of quantum well and single quantum dot structures, augmented with contribution from transitions between the dot and quantum well states. The influence of rod height on the electronic structure and the intraband absorption spectra is also investigated. It is found that the energy of maximal terahertz absorption can be tailored by the rod height for both in-plane and in-growth polarized radiation.
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73.21.La Quantum dots
71.15.-m Methods of electronic structure calculations
71.20.Nr Semiconductor compounds
78.67.Hc Quantum dots
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

A phonon scattering assisted injection and extraction based terahertz quantum cascade laser

E. Dupont, S. Fathololoumi, Z. R. Wasilewski, G. Aers, S. R. Laframboise, M. Lindskog, S. G. Razavipour, A. Wacker, D. Ban, and H. C. Liu

J. Appl. Phys. 111, 073111 (2012); http://dx.doi.org/10.1063/1.3702571 (10 pages)

Online Publication Date: 12 April 2012

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A lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the GaAs/Al0.25Ga0.75As material system that maximizes the product of population inversion and oscillator strength at 150 K. The fabricated devices using Au double-metal waveguides show lasing at 3.2 THz up to 138 K. The electrical characteristics display no sign of differential resistance drop at lasing threshold, which, in conjunction with the low optical power of the device, suggest—thanks to the rate equation model—a slow depopulation rate of the lower lasing state, a hypothesis confirmed by non-equilibrium Green’s function calculations.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
02.60.Pn Numerical optimization

Temperature and composition dependence of photoluminescence dynamics in CdSxSe1−x (0 ≤ x ≤ 1) nanobelts

H. W. Liu, J. P. Lu, H. M. Fan, C. H. Sow, S. H. Tang, and X. H. Zhang

J. Appl. Phys. 111, 073112 (2012); http://dx.doi.org/10.1063/1.3702889 (6 pages)

Online Publication Date: 12 April 2012

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CdSxSe1−x nanobelts with uniform and controllable composition are successfully fabricated by a one-step vapor-liquid-solid process. Temperature-dependent steady and time-resolved transient photoluminescence (PL) are studied for the obtained CdSxSe1−x nanobelts as well as pure CdS and CdSe nanobelts prepared in same method. For all samples, both band edge and surface state emission are found to contribute to the observed PL spectra. However, the emission originated from surface state is quite weak for CdSxSe1−x nanobelts as compared to CdS and CdSe. The reduced surface state emission in CdSxSe1−x nanobelts is ascribed to exciton localization due to random potential fluctuations. This attribution is further confirmed by the time-decay PL profiles where a very fast process of exciton transfer from interior to surface of nanobelts, observed in CdS and CdSe nanobelts, is absent for CdSxSe1−x nanobelts. These observations reveal that the surface effect of CdSxSe1−x nanobelts is less significant than that in CdS and CdSe nanobelts, which consequently leads to enhanced band-edge emission in CdSxSe1−x nanobelts.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.35.-y Excitons and related phenomena
78.55.Et II-VI semiconductors

Confinement effects on valence-subband character and polarization anisotropy in (11math2) semipolar InGaN/GaN quantum wells

Christopher Roberts, Qimin Yan, Mao-Sheng Miao, and Chris G. Van de Walle

J. Appl. Phys. 111, 073113 (2012); http://dx.doi.org/10.1063/1.3702798 (4 pages)

Online Publication Date: 13 April 2012

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We perform self-consistent Schrödinger-Poisson simulations on (11math2) In-GaN/GaN quantum wells (QW). By solving the 6 × 6 k·p Hamiltonian, including strain and polarization fields, we study the separation, ordering, and wavefunction character of the topmost valence bands in the QW and their dependence on In composition and QW width. Our results show that quantum confinement has only slight effects on the ordering and the character of the valence states and therefore cannot be the cause of the experimentally observed optical polarization switching. Instead, the switching may be due to the inhomogeneous strain distribution in (11math2) InGaN films with high In composition.
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73.21.Fg Quantum wells
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds
back to top Plasmas and Electrical Discharges

Photonic band structures of two-dimensional magnetized plasma photonic crystals

L. Qi

J. Appl. Phys. 111, 073301 (2012); http://dx.doi.org/10.1063/1.3699213 (8 pages)

Online Publication Date: 4 April 2012

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By using modified plane wave method, photonic band structures of the transverse electric polarization for two types of two-dimensional magnetized plasma photonic crystals are obtained, and influences of the external magnetic field, plasma density, and dielectric materials on the dispersion curves are studied, respectively. Results show that two areas of flat bands appear in the dispersion curves due to the role of external magnetic field, and the higher frequencies of the up and down flat bands are corresponding to the right-circled and left-circled cutoff frequencies, respectively. Adjusting external magnetic field and plasma density can not only control positions of the flat bands, but also can control the location and width of the local gap; increasing relative dielectric constant of the dielectric materials makes omni-direction gaps appear.
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42.70.Qs Photonic bandgap materials
52.25.-b Plasma properties
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Optical breakdown threshold investigation of 1064 nm laser induced air plasmas

Magesh Thiyagarajan and Shane Thompson

J. Appl. Phys. 111, 073302 (2012); http://dx.doi.org/10.1063/1.3699368 (8 pages)

Online Publication Date: 6 April 2012

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We present the theoretical and experimental measurements and analysis of the optical breakdown threshold for dry air by 1064 nm infrared laser radiation and the significance of the multiphoton and collisional cascade ionization process on the breakdown threshold measurements over pressures range from 10 to 2000 Torr. Theoretical estimates of the breakdown threshold laser intensities and electric fields are obtained using two distinct theories namely multiphoton and collisional cascade ionization theories. The theoretical estimates are validated by experimental measurements and analysis of laser induced breakdown processes in dry air at a wavelength of 1064 nm by focusing 450 mJ max, 6 ns, 75 MW max high-power 1064 nm IR laser radiation onto a 20 μm radius spot size that produces laser intensities up to 3 – 6 TW/cm2, sufficient for air ionization over the pressures of interest ranging from 10 to 2000 Torr. Analysis of the measured breakdown threshold laser intensities and electric fields are carried out in relation with classical and quantum theoretical ionization processes, operating pressures. Comparative analysis of the laser air breakdown results at 1064 nm with corresponding results of a shorter laser wavelength (193 nm) [M. Thiyagarajan and J. E. Scharer, IEEE Trans. Plasma Sci. 36, 2512 (2008)] and a longer microwave wavelength (108 nm) [A. D. MacDonald, Microwave Breakdown in Gases (Wiley, New York, 1966)]. A universal scaling analysis of the breakdown threshold measurements provided a direct comparison of breakdown threshold values over a wide range of frequencies ranging from microwave to ultraviolet frequencies. Comparison of 1064 nm laser induced effective field intensities for air breakdown measurements with data calculated based on the collisional cascade and multiphoton breakdown theories is used successfully to determine the scaled collisional microwave portion. The measured breakdown threshold of 1064 nm laser intensities are then scaled to classical microwave breakdown theory after correcting for the multiphoton ionization process for different pressures and good agreement, regarding both pressure dependence and breakdown threshold electric fields, is obtained. The effect of the presence of submicron particles on the 1064 nm breakdown threshold was also investigated. The measurements show that higher breakdown field is required, especially at lower pressures, and in close agreement with classical microwave breakdown theory and measurements in air.
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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.)
52.70.Gw Radio-frequency and microwave measurements
52.80.Pi High-frequency and RF discharges
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Jm Ionization of plasmas

Multiple scattering of ultra-high frequency electromagnetic waves by two plasma cylinders

Wu Xiao-po, Shi Jia-ming, Wang Jia-chun, Yuan Zhong-cai, Xu Bo, Zhao Da-peng, Chen Zong-sheng, and Lin Zhi-dan

J. Appl. Phys. 111, 073303 (2012); http://dx.doi.org/10.1063/1.3702406 (6 pages)

Online Publication Date: 9 April 2012

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Multiple scattering of ultrahigh frequency (UHF) electromagnetic waves by two argon plasma cylinders is investigated, rigorously applying the boundary value method. The results are verified and validated with the method of moments. Approximate expressions for the far field, taking into account the interaction between the plasma cylinders, are derived briefly after some mathematical manipulations. Numerical results are presented for the case of E-polarized UHF incidence with varied striking angles and different separation distances between the cylinders; comparisons of the scattering distributions are given in detail as well. It is found that the interaction between the plasma cylinders plays a non-negligible role in scattered energy redistributing, which is useful in the future research of intelligent plasma antennas.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
02.60.-x Numerical approximation and analysis

Atmospheric pressure dielectric barrier microplasmas inside hollow-core optical fibers

Longfei Ji, Dongping Liu, Ying Song, and Jinhai Niu

J. Appl. Phys. 111, 073304 (2012); http://dx.doi.org/10.1063/1.3702818 (6 pages)

Online Publication Date: 12 April 2012

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An atmospheric glow microplasma is generated in the hollow core of microns-thick optical fibers (>1 m long) when the sinusoidal voltage with a peak voltage of 5 kV and a frequency of 5.0 kHz is applied to these microelectrodes along the outside of optical fibers. Measurements show that the atmospheric glow microdischarge consists of current pulses with amplitudes of tens of amperes and pulse widths of several microseconds. Atmospheric surface barrier discharges are formed along the inner surface of hollow optical fibers between adjacent microelectrodes, which results in the pulsed glow microdischarges. By flowing octafluorocyclobutane (c-C4F8)/helium (He) mixtures through the hollow-core optical fiber, fluorocarbon polymer (FCP) coatings are deposited on the inner surface of the > 1 m long optical fiber. Analysis indicates that the glow microdischarge contributes to the uniform deposition of FCP coatings on the inner surface of hollow fibers. The in situ optical emission measurements show that various carbon-containing species, such as CF2, CN, and C2 are generated in the visually uniform microplasmas. The discharge mechanism is discussed based on the I-V and optical emission measurements and FCP coating characterizations.
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42.79.-e Optical elements, devices, and systems
42.81.-i Fiber optics

Stability of very-high pressure arc discharges against perturbations of the electron temperature

M. S. Benilov and U. Hechtfischer

J. Appl. Phys. 111, 073305 (2012); http://dx.doi.org/10.1063/1.3702469 (8 pages)

Online Publication Date: 13 April 2012

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See Also: Publisher's Note

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We study the stability of the energy balance of the electron gas in very high–pressure plasmas against longitudinal perturbations, using a local dispersion analysis. After deriving a dispersion equation, we apply the model to a very high–pressure (100 bar) xenon plasma and find instability for electron temperatures, Te, in a window between 2400 K and 5500-7000 K, depending on the current density (106–108 A/m2). The instability can be traced back to the Joule heating of the electron gas being a growing function of Te, which is due to a rising dependence of the electron-atom collision frequency on Te. We then analyze the Te range occurring in very high–pressure xenon lamps and conclude that only the near-anode region exhibits Te sufficiently low for this instability to occur. Indeed, previous experiments have revealed that such lamps develop, under certain conditions, voltage oscillations accompanied by electromagnetic interference, and this instability has been pinned down to the plasma-anode interaction. A relation between the mechanisms of the considered instability and multiple anodic attachments of high-pressure arcs is discussed.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Ultrafast laser-induced changes in optical properties of semiconductors

C. C. Chirila, Freda C. H. Lim, and M. G. Gavaza

J. Appl. Phys. 111, 073501 (2012); http://dx.doi.org/10.1063/1.3698300 (10 pages)

Online Publication Date: 2 April 2012

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We study the effect of laser radiation on optical properties of semiconductors of industrial interest. The material is pumped with a laser of chosen central frequency, for which the absorption is maximal, thus inducing electron dynamics, which modifies the optical properties. By using an improved theoretical model, we study ultrafast dynamic changes in the refraction index and reflectivity corresponding to a wide frequency-interval of probing radiation and identify that interval where these optical changes are most significant.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.J- Ultrafast spectroscopy (<1 psec)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Titanium and magnesium Co-alloyed hematite thin films for photoelectrochemical water splitting

Houwen Tang, Wan-Jian Yin, M. A. Matin, Heli Wang, Todd Deutsch, Mowafak M. Al-Jassim, John A. Turner, and Yanfa Yan

J. Appl. Phys. 111, 073502 (2012); http://dx.doi.org/10.1063/1.3699016 (8 pages)

Online Publication Date: 2 April 2012

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Using a combination of density functional theory calculation and materials synthesis and characterization we examine the properties of charge-compensated Ti and Mg co-alloyed hematite thin films for the application of photoelectrochemical (PEC) water splitting. We find that the charge-compensated co-alloying results in the following effects: (1) It enhances the solubility of Mg and Ti, which leads to reduced electron effective mass and therefore increased electron mobility; (2) It tunes the carrier density and therefore allows the optimization of electrical conductivity; and (3) It reduces the density of charged defects and therefore reduces carrier recombination. As a result, the Ti and Mg co-alloyed hematite thin films exhibit improved water oxidation photocurrent magnitudes as compared to pure hematite thin films. Our results suggest that charge-compensated co-alloying is a plausible approach for engineering hematite for the application of PEC water splitting.
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73.61.At Metal and metallic alloys
68.55.aj Insulators
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.20.Ee Mobility edges; hopping transport

Fluorescence properties and energy transfer study of Er3+/Nd3+ doped fluorophosphate glass pumped at 800 and 980 nm for mid-infrared laser applications

Ying Tian, Rongrong Xu, Lili Hu, and Junjie Zhang

J. Appl. Phys. 111, 073503 (2012); http://dx.doi.org/10.1063/1.3699059 (6 pages)

Online Publication Date: 2 April 2012

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The fluorescence properties of 2.7 μm emission as well as near infrared emissions in Er3+/Nd3+ doped fluorophosphate glasses are investigated under 800 and 980 nm excitation. The fluorescence dynamics and energy transfer processes between Er and Nd ions in different pumping schemes are reported. Three Judd-Ofelt intensity parameters, energy transfer microparameters, and efficiency have been determined using the Judd-Ofelt and Förster-Dexter theories. The calculated energy transfer efficiency of the Er3+:4I13/2 level to the Nd3+:4I15/2 level is as high as 83.91%. The results indicate that Nd3+ may be an efficient sensitizer for Er3+ to obtain mid-infrared emission and the more suitable pumping scheme of 2.7 μm laser applications for Er3+/Nd3+ doped fluorophosphate glass is 980 nm excitation.
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78.55.Hx Other solid inorganic materials

Capability of photoluminescence for characterization of multi-crystalline silicon

T. Mchedlidze, W. Seifert, M. Kittler, A. T. Blumenau, B. Birkmann, T. Mono, and M. Müller

J. Appl. Phys. 111, 073504 (2012); http://dx.doi.org/10.1063/1.3699275 (11 pages)

Online Publication Date: 2 April 2012

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Application of various characterization methods for the investigation of photovoltaic materials allows fast progress in perfection of their quality. However, capabilities of the methods should be clearly understood and the methods should be applied in the correct manner to avoid false and/or unreliable interpretation of the results. We applied photoluminescence (PL) for characterization of multi-crystalline silicon (mc-Si) samples and compared the obtained results with carrier lifetime measurement data for the same samples. The analyses revealed strong influence of surface recombination and optical shadowing from grain boundaries on the interpretation of the PL results. Proper surface passivation allows application of defect-related luminescence for the characterization of mc-Si along with traditionally used band-to-band luminescence.
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78.55.Ap Elemental semiconductors
81.65.Rv Passivation
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
72.80.Cw Elemental semiconductors
73.25.+i Surface conductivity and carrier phenomena

Defect-induced solid state amorphization of molecular crystals

Lei Lei, Teresa Carvajal, and Marisol Koslowski

J. Appl. Phys. 111, 073505 (2012); http://dx.doi.org/10.1063/1.3698500 (8 pages)

Online Publication Date: 3 April 2012

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We investigate the process of mechanically induced amorphization in small molecule organic crystals under extensive deformation. In this work, we develop a model that describes the amorphization of molecular crystals, in which the plastic response is calculated with a phase field dislocation dynamics theory in four materials: acetaminophen, sucrose, γ-indomethacin, and aspirin. The model is able to predict the fraction of amorphous material generated in single crystals for a given applied stress. Our results show that γ-indomethacin and sucrose demonstrate large volume fractions of amorphous material after sufficient plastic deformation, while smaller amorphous volume fractions are predicted in acetaminophen and aspirin, in agreement with experimental observation.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

One-photon band gap engineering of borate glass doped with ZnO for photonics applications

Manal Abdel-Baki, Fathy A. Abdel-Wahab, and Fouad El-Diasty

J. Appl. Phys. 111, 073506 (2012); http://dx.doi.org/10.1063/1.3698623 (10 pages)

Online Publication Date: 3 April 2012

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Lithium tungsten borate glass of the composition (0.56-x)B2O3–0.4Li2O–xZnO–0.04WO3 (0 ≤ x ≤ 0.1 mol. %) is prepared for photonics applications. The glass is doped with ZnO to tune the glass absorption characteristics in a wide spectrum range (200–2500 nm). Chemical bond approach, including chemical structure, electronegativity, bond ionicity, nearest-neighbor coordination, and other chemical bonding aspect, is used to analyze and to explain the obtained glass properties such as: transmittance, absorption, electronic structure parameters (bandgap, Fermi level, and Urbach exciton-phonon coupling), Wannier free excitons excitation (applying Elliott’s model), and two-photon absorption coefficient as a result of replacement of B2O3 by ZnO.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.35.-y Excitons and related phenomena
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.40.Pg Disordered solids
81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses
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