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1 Nov 2009

Volume 106, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 106, 091301 (2009); http://dx.doi.org/10.1063/1.3218758 (14 pages)

N. K. Bourne, G. T. Gray, III, and J. C. F. Millett
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On the shock response of cubic metals

N. K. Bourne, G. T. Gray, III, and J. C. F. Millett

J. Appl. Phys. 106, 091301 (2009); http://dx.doi.org/10.1063/1.3218758 (14 pages) | Cited 10 times

Online Publication Date: 6 November 2009

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The response of four cubic metals to shock loading is reviewed in order to understand the effects of microstructure on continuum response. Experiments are described that link defect generation and storage mechanisms at the mesoscale to observations in the bulk. Four materials were reviewed; these were fcc nickel, the ordered fcc intermetallic Ni3Al, the bcc metal tantalum, and two alloys based on the intermetallic phase TiAl; Ti–46.5Al–2Cr–2Nb and Ti–48Al–2Cr–2Nb–1B. The experiments described are in two groups: first, equation of state and shear strength measurements using Manganin stress gauges and, second, postshock microstructural examinations and measurement of changes in mechanical properties. The behaviors described are linked through the description of time dependent plasticity mechanisms to the final states achieved. Recovered targets displayed dislocation microstructures illustrating processes active during the shock-loading process. Reloading of previously shock-prestrained samples illustrated shock strengthening for the fcc metals Ni and Ni3Al while showing no such effect for bcc Ta and for the intermetallic TiAl. This difference in effective shock hardening has been related, on the one hand, to the fact that bcc metals have fewer available slip systems that can operate than fcc crystals and to the observation that the lower symmetry materials (Ta and TiAl) both possess high Peierls stress and thus have higher resistances to defect motion in the lattice under shock-loading conditions. These behaviors, compared between these four materials, illustrate the role of defect generation, transport, storage, and interaction in determining the response of materials to shock prestraining.
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81.40.Lm Deformation, plasticity, and creep
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
62.50.Ef Shock wave effects in solids and liquids
62.20.fq Plasticity and superplasticity
61.72.Lk Linear defects: dislocations, disclinations
64.30.-t Equations of state of specific substances
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
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Broadband mid-infrared generation by difference-frequency generation in strongly dispersive Bragg reflection waveguides

Ritwick Das and K. Thyagarajan

J. Appl. Phys. 106, 093101 (2009); http://dx.doi.org/10.1063/1.3247072 (6 pages)

Online Publication Date: 2 November 2009

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We present a novel scheme for generation of broadband mid-infrared (mid-IR) radiation using a quasiphase-matched difference-frequency-generation (DFG) process in a planar high index core symmetric Bragg reflection waveguide (BRW) geometry based on GaN/AlxGa1−xN system. By suitably tailoring the dispersion properties of the BRW so as to maintain the phase-matching condition over a broad range of pump wavelengths, we show that the pump acceptance bandwidth could be enhanced by nine to ten times for a DFG process. This manifests into a broadband mid-IR difference-frequency idler with greater than 280 nm bandwidth close to 4.35 μm wavelength. Since the design presented here exploits the dispersive features of the BRW; we can shift the broadband characteristics to any desired region of the mid-IR spectrum within the constraints imposed by transparency and nonlinearity of the constituent materials. The design also facilitates pumping by standard high-power solid-state laser sources.
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42.65.Wi Nonlinear waveguides
42.72.Ai Infrared sources
42.79.Gn Optical waveguides and couplers

Linear and nonlinear optical properties of ZnO/PMMA nanocomposite films

B. Kulyk, B. Sahraoui, O. Krupka, V. Kapustianyk, V. Rudyk, E. Berdowska, S. Tkaczyk, and I. Kityk

J. Appl. Phys. 106, 093102 (2009); http://dx.doi.org/10.1063/1.3253745 (6 pages) | Cited 7 times

Online Publication Date: 3 November 2009

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The nanoscale crystals (NCs) of ZnO were embedded into polymethylmethacrylate (PMMA) polymeric matrix and nanocomposite films were prepared by modified spin coating method. The surface of the ZnO/PMMA nanocomposite films has been investigated using atomic force and scanning electron microscopy. The prepared films are highly transparent, the ultraviolet-visible spectra show their high optical quality. The second and third harmonic generation (SHG and THG) studies of ZnO/PMMA nanocomposite films with different concentrations of ZnO NCs were carried out at λ = 1.064 μm and the effective values of the second and third order nonlinear susceptibilities were estimated to be higher than that of ZnO bulk for the films at low concentration of ZnO NCs. This could indicate that surface effects in ZnO/PMMA nanocomposite films have a dominant role over bulk effects for the SHG and THG processes.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
81.05.Qk Reinforced polymers and polymer-based composites
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.40.-q Absorption and reflection spectra: visible and ultraviolet
81.05.Dz II-VI semiconductors
68.55.ag Semiconductors
42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
81.16.Ta Atom manipulation
68.55.am Polymers and organics

Diffracted magneto-optical Kerr effect of a Ni magnetic grating

J. B. Kim, Y. H. Lu, M. H. Cho, Y. P. Lee, J. Y. Rhee, J.-H. Lee, and K.-M. Ho

J. Appl. Phys. 106, 093103 (2009); http://dx.doi.org/10.1063/1.3247972 (3 pages) | Cited 2 times

Online Publication Date: 3 November 2009

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We report the results of a joint experimental and theoretical investigation focused on the magneto-optical (MO) properties of one-dimensional magnetic grating structure made of Ni. It was found that the longitudinal Kerr rotation of the second-order diffracted beam is nearly three times larger than that of the zeroth-order beam. The calculational results further confirmed the experimental ones, and almost perfectly reproduced the measured hysteresis loops of the longitudinal MO Kerr rotation, elucidating the origin of the enhanced MO rotation.
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78.20.Ls Magneto-optical effects
42.25.Fx Diffraction and scattering
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
42.79.Dj Gratings
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Spectroscopic determination of the doping and mobility of terahertz quantum cascade structures

J. Lloyd-Hughes, Y. L. Delley, G. Scalari, M. Fischer, V. Liverini, M. Beck, and J. Faist

J. Appl. Phys. 106, 093104 (2009); http://dx.doi.org/10.1063/1.3247973 (4 pages) | Cited 3 times

Online Publication Date: 5 November 2009

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Terahertz time-domain spectroscopy is shown to provide a convenient and rapid means to measure the conductivity of individual layers in semiconductor heterostructures such as terahertz quantum cascade lasers. By modeling the complex transmission at terahertz frequencies, the electron density and the in-plane momentum scattering time of the active regions and doped contact layers were determined for both GaAs/AlGaAs and InGaAs/InAlAs epilayers. The measured temperature dependence of the electron scattering rate revealed the significance of impurity and LO phonon scattering. The implications for laser operation at room temperature are discussed by considering the changes in absorption and resonant tunneling current with temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Investigation of doped calcium aluminosilicate glass: A coupling between thermal-expansion and thermal-diffusion models for assessment of nonradiative relaxation time and characteristic diffusion time

N. E. Souza Filho, A. C. Nogueira, J. H. Rohling, M. L. Baesso, A. N. Medina, A. P. L. Siqueira, J. A. Sampaio, H. Vargas, and A. C. Bento

J. Appl. Phys. 106, 093105 (2009); http://dx.doi.org/10.1063/1.3253580 (9 pages) | Cited 1 time

Online Publication Date: 6 November 2009

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This paper discusses the use of photoacoustic models to obtain the nonradiative relaxation time (τ) and characteristic diffusion time (τβ) for a sample showing visible absorption bands from fluorescent ion-doped low-silica calcium aluminosilicate glass. Two models allowing phase shift analyses, the thermal-expansion and thermal-diffusion models, are briefly reviewed. These models have limitations when the photoacoustic signal depends on both factors, in a coupling mechanism. An alternative model is proposed to take both thermal expansion and thermal diffusion into account with a single temperature solution for the heat-coupled differential equation. This model is simulated for absorbing samples near the thermally thick region. The model is applied to Eu–V codoped glass showing intermediate signal dependence from ω−1.0 to ω−3/2. The nonradiative time and characteristic diffusion time are derived with 33<τ(ms)<39, and τβ(ms) ∼ 70 ms for the Eu-ion and 340<τβ(ms)<710 for the V-ion. Four absorption bands were analyzed (280, 350, 420, and 600 nm), which showed a signal dependence from ω−1.1 to ω−1.52. Absorption coefficients were derived from τβ in the range of 15<β(cm−1)<51, which agreed fairly well with spectrophotometer data for the same ions.
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78.55.Qr Amorphous materials; glasses and other disordered solids
65.40.De Thermal expansion; thermomechanical effects
66.70.Hk Glasses and polymers
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Numerical model and study of cascaded third harmonic generation in two-sectioned a periodically poled Mg-doped LiTaO3 structure

Oleg A. Louchev and Satoshi Wada

J. Appl. Phys. 106, 093106 (2009); http://dx.doi.org/10.1063/1.3253749 (5 pages) | Cited 1 time

Online Publication Date: 6 November 2009

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The feasibility of cascaded second harmonic generation (SHG) and third harmonic generation (THG) in a monolithic two-sectioned periodically poled lithium tantalate crystal is analyzed. Simulation using a computational nonlinear optical model rigorously coupled with a thermal model suggests that 25%–30% THG efficiency can be achieved for a 3 W 20 ns pulsed 1.064 μm laser operating at 10 kHz if the crystal is composed of two sections: (i) ≈ 8.0 μm period first-order SHG structure and (ii) ≈ 6.6 μm period third-order THG structure. Significant inhibition of THG efficiency arises due to absorption of SH and TH, the heat release along the crystal, and associated thermal dephasing and lensing which can be effectively compensated by decreasing the temperature of the operating crystal below the quasiphase matching temperature. Corrections for the energy exchange lengths for optimal SHG and THG section design are suggested.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.72.up Other materials

Optically active Er3+ ions in SiO2 codoped with Si nanoclusters

D. Navarro-Urrios, Y. Lebour, O. Jambois, B. Garrido, A. Pitanti, N. Daldosso, L. Pavesi, J. Cardin, K. Hijazi, L. Khomenkova, F. Gourbilleau, and R. Rizk

J. Appl. Phys. 106, 093107 (2009); http://dx.doi.org/10.1063/1.3253753 (5 pages) | Cited 9 times

Online Publication Date: 6 November 2009

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Optical properties of directly excited erbium (Er3+) ions have been studied in silicon rich silicon oxide materials codoped with Er3+. The spectral dependence of the direct excitation cross section (σdir) of the Er3+ atomic 4I15/2→4I11/2 transition (around 0.98 μm) has been measured by time resolved μ-photoluminescence measurements. We have determined that σdir is 9.0±1.5×10−21 cm2 at 983 nm, at least twice larger than the value determined on a stoichiometric SiO2 matrix. This result, in combination with a measurement of the population of excited Er3+ as a function of the pumping flux, has allowed quantifying accurately the amount of optically active Er3+. This concentration is, in the best of the cases, 26% of the total Er population measured by secondary ion mass spectrometry, which means that only this percentage could provide optical gain in an eventual optical amplifier based on this material.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.66.Bi Elemental solids
61.66.Dk Alloys
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.07.Bc Nanocrystalline materials
78.47.jd Time resolved luminescence
61.72.up Other materials

Multiple enhanced transmission bands through compound periodic array of rectangular holes

Jian-Qiang Liu, Xing-Bing Chao, Jian-Ning Wei, Meng-Dong He, Ling-Ling Wang, Qing Wan, and Yu Wang

J. Appl. Phys. 106, 093108 (2009); http://dx.doi.org/10.1063/1.3254248 (5 pages) | Cited 5 times

Online Publication Date: 10 November 2009

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Based on the finite-difference time-domain method, we demonstrate multiple enhanced transmission bands through subwavelength compound periodic array of rectangular holes by adjusting the cutoff wavelength of each hole. The results show that the transmission spectrum of this structure is almost a compound of that of the corresponding periodic hole arrays with simple cell, when the holes are arranged appropriately. It is also found that the surface plasmon resonance peak and the localized resonance peak exhibit different behaviors as the symmetry of compound periodic structure varies. The proposed method provides an effective way to achieve enhanced transmission simultaneously at different selected wavelengths in the visible and infrared regions.
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78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Theoretical analysis of thermally tunable microring resonator filters made of dielectric-loaded plasmonic waveguides

Odysseas Tsilipakos, Traianos V. Yioultsis, and Emmanouil E. Kriezis

J. Appl. Phys. 106, 093109 (2009); http://dx.doi.org/10.1063/1.3256139 (8 pages) | Cited 13 times

Online Publication Date: 10 November 2009

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Microring resonator filters, which are made of dielectric-loaded surface plasmon polariton waveguides and operate in the telecom spectral range, are thoroughly analyzed by means of vectorial three dimensional (3D) finite element method (FEM) simulations. The filters’ functional characteristics, such as the resonant frequencies where the transmission minima occur, the free spectral range, the extinction ratio, and the minima linewidth associated with the quality factor of the resonances, are investigated for different values of the key structural parameters, namely, the ring radius and the gap separating the bus waveguide from the ring. The rigorous 3D-FEM simulations are qualitatively complemented by a simplified model. Apart from the harmonic propagation simulations, the uncoupled microring is treated as an eigenvalue problem, and the frequencies of the resonances are compared with those of the transmission minima. Furthermore, the possibility of exploiting the thermally tuned microring resonator filter as a switching element is explored. The shift in the transmission minima is quantified when the ring’s refractive index is altered by virtue of Ohmic heating, and in addition to that, the temporal response is assessed by solving the transient problem.
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42.79.Ci Filters, zone plates, and polarizers
42.82.Et Waveguides, couplers, and arrays
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Gn Optical waveguides and couplers

Reliability assessment and degradation analysis of 1.3 μm GaInNAs lasers

W. Lu, S. Bull, J. J. Lim, R. MacKenzie, S. Sujecki, A. V. Andrianov, M. Sadeghi, S. M. Wang, A. Larsson, P. Melanen, P. Sipilä, P. Uusimaa, C. T. Foxon, and E. C. Larkins

J. Appl. Phys. 106, 093110 (2009); http://dx.doi.org/10.1063/1.3256156 (7 pages) | Cited 1 time

Online Publication Date: 12 November 2009

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The degradation of 1.3 μm GaInNAs lasers was investigated using accelerated aging tests. This was followed by comprehensive characterization, including standard light-current-voltage (L-I-V) characterization, capacitance measurements, photoluminescence microscopy (PLM), on-axis amplified spontaneous emission (ASE) spectra measurements, and photocurrent (PC) and electroluminescence (EL) spectroscopies. The slope efficiency of the device dropped by 50% with a 300% increase in the threshold current after the accelerated aging test. The ideality factors of the aged devices are higher than those of the unaged devices. PLM images showed no evidence of catastrophic optical mirror damage. The measured capacitances of the aged devices are all similar to those of the unaged devices, indicating that there was no significant dopant diffusion in the junction region. Fourier transforms of the ASE spectra showed that no intracavity defects were present in the aged lasers, suggesting that intracavity defects are not responsible for the rapid degradation of the aged devices. Although the PC measurements showed defects at 0.88–0.95 eV and at ∼ 0.76 eV, these defect signatures did not increase with aging. On the other hand, EL measurements revealed that radiative deep level defects were generated during the aging tests, which may be related to the degradation of the devices. Based on the above measurement results, we identify the generation of radiative deep level defects as the main causes of degradation of these devices.
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42.55.Px Semiconductor lasers; laser diodes
42.87.-d Optical testing techniques
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.By Design of specific laser systems

Influence of nanoparticle height on plasmonic resonance wavelength and electromagnetic field enhancement in two-dimensional arrays

John Henson, Jeff DiMaria, and Roberto Paiella

J. Appl. Phys. 106, 093111 (2009); http://dx.doi.org/10.1063/1.3255979 (6 pages) | Cited 7 times

Online Publication Date: 13 November 2009

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A detailed experimental and theoretical study of the plasmonic properties of silver nanoparticle arrays as a function of nanoparticle height is presented. Specifically, several square periodic arrays have been fabricated by electron beam lithography and characterized via transmission spectroscopy measurements. The same arrays have also been numerically investigated via finite-difference time-domain calculations of their scattering and absorption cross sections and steady-state field intensity distributions. The results of this study show that the collective plasmonic resonances of these arrays can be effectively blueshifted by increasing the nanoparticle height, while at the same time maximizing the average field enhancement in the substrate and maintaining small absorption losses. This approach can therefore be used to extend the spectral reach of lithographically defined metallic nanoparticle arrays for practical applications such as light-emission efficiency enhancement.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.16.Nd Micro- and nanolithography
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Bc Nanocrystalline materials

Mid-infrared emission from InAs quantum dots, wells, and dots on well nanostructures grown on InP (100) by metal organic vapor phase epitaxy

Junji Kotani, Peter J. van Veldhoven, and Richard Nötzel

J. Appl. Phys. 106, 093112 (2009); http://dx.doi.org/10.1063/1.3257243 (5 pages) | Cited 4 times

Online Publication Date: 13 November 2009

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A detailed analysis to extend the emission wavelength of InAs/InP nanostructures is presented employing InAs quantum dots (QDs), InAs quantum wells (QWs), and a combination of InAs QDs and QWs grown on InGaAsP/InP (100) by metal organic vapor phase epitaxy. First the optimized growth conditions of InAs QDs are established and an emission wavelength of 2.16 μm is achieved by capping with strain reducing InGaAs layers. Second, InAs QWs are grown under metal-stable conditions with the longest emission wavelength of 2.26 μm for a 4 nm QW. Finally, a combined InAs QDs on QW structure is realized. The InAs QD density is drastically increased on the QW and the longest emission wavelength of 2.46 μm is obtained at 6 K from sparse huge QDs. These findings open routes to extend the emission wavelength in the InAs/InP materials system beyond 2.4 μm using InAs QDs on QW structures.
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78.67.De Quantum wells
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
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Characteristics of a micro dielectric barrier discharge ignited by a cold cathode with high ion-induced secondary electron emission for plasma display panel

Giichiro Uchida, Satoshi Uchida, Hiroshi Kajiyama, and Tsutae Shinoda

J. Appl. Phys. 106, 093301 (2009); http://dx.doi.org/10.1063/1.3253723 (6 pages) | Cited 3 times

Online Publication Date: 2 November 2009

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We present here measurements of plasma display panel (PDP) ignited by SrO and SrCaO cold cathodes with high yield of ion-induced secondary electron emission (high γi). SrO- and SrCaO-cathode PDPs attain high luminous efficacy at low applied voltage, where the breakdown voltage is 30% lower than that of ordinary MgO-cathode PDP. Current and emission measurement clearly demonstrates that SrO- and SrCaO-cathode PDPs operated at low voltage realize a discharge with smaller current flow and lower electron energy, which are considerably appropriate for high luminous efficacy of PDP. Simulation analysis shows the effect of the high-γi cathode on the luminous efficacy of PDP. A discharge ignited by the high-γi cathode realizes high electron heating efficiency due to the abundant seed electrons from the high-γi cathode, resulting in high luminous efficacy of PDP.
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52.75.-d Plasma devices
52.80.-s Electric discharges

Modeling the flux of high energy negative ions during reactive magnetron sputtering

S. Mahieu, W. P. Leroy, K. Van Aeken, and D. Depla

J. Appl. Phys. 106, 093302 (2009); http://dx.doi.org/10.1063/1.3247545 (7 pages) | Cited 12 times

Online Publication Date: 4 November 2009

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The negative ion flux during reactive sputtering from planar and rotating cylindrical magnetrons has been studied. Energy resolved mass spectrometry was used to measure the energy and mass distribution of the negative ions. Also the angular distribution of the high energy ions was characterized for planar as well as for rotating cylindrical magnetrons. Besides these measurements, a binary collision Monte Carlo simulation code, SiMTRA, was adapted in order to simulate the energy, mass, and angular distribution of the high energy negative ions. All simulated distributions, for both planar and rotating cylindrical magnetrons, were in excellent correspondence with the experimental observations. Also a model for the amount of high energy negative O− ions was proposed. Indeed, the logarithm of the amount of high energy negative O− ions is shown to be related to the secondary electron emission yield of the oxide target, and these two parameters are known to be related to the work function. The SiMTRA simulations, in combination with knowledge of the work function or secondary electron emission yield of the target, allow modeling the flux of high energy negative ions during reactive magnetron sputtering.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Hx Electron impact: secondary emission
73.30.+y Surface double layers, Schottky barriers, and work functions

Polarimetry and Schlieren diagnostics of underwater exploding wires

A. V. Fedotov-Gefen and Ya. E. Krasik

J. Appl. Phys. 106, 093303 (2009); http://dx.doi.org/10.1063/1.3255825 (8 pages) | Cited 1 time

Online Publication Date: 9 November 2009

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Nondisturbing laser-probing polarimetry (based on the Faraday and Kerr effects) and Schlieren diagnostics were used in the investigation of underwater electrical wire explosion. Measuring the polarization plane rotation angle of a probing laser beam due to the Faraday effect allows one to determine an axially resolved current flowing through the exploding wire, unlike commonly used current probes. This optical method of measuring current yields results that match those obtained using a current viewing resistor within an accuracy of 10%. The same optical setup allows simultaneous space-resolved measurement of the electric field using the Kerr effect. It was shown that the maximal amplitude of the electric field in the vicinity of the high-voltage electrode is ∼ 80 kV/cm and that the radial electric field is <1 MV/cm during the wire explosion. Finally, it was shown that the use of Schlieren diagnostics allows one to obtain qualitatively the density distribution behind the shock wave front, which is important for the determination of the energy transfer from the discharge channel to the generated water flow.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
52.80.-s Electric discharges
52.35.Tc Shock waves and discontinuities
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Structural and optical properties of Zn0.9Mn0.1O/ZnO core-shell nanowires designed by pulsed laser deposition

V. E. Kaydashev, E. M. Kaidashev, M. Peres, T. Monteiro, M. R. Correia, N. A. Sobolev, L. C. Alves, N. Franco, and E. Alves

J. Appl. Phys. 106, 093501 (2009); http://dx.doi.org/10.1063/1.3253572 (4 pages) | Cited 4 times

Online Publication Date: 3 November 2009

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Core-shell ZnO/ZnMnO nanowires on a-Al2O3 and GaN (buffer layer)/Si (111) substrates were fabricated by pulsed laser deposition using a Au catalyst. Two ZnO targets with a Mn content of 10% were sintered at 1150 and 550 °C in order to achieve the domination in them of paramagnetic MnO2 and ferromagnetic Mn2O3 phases, respectively. Cluster mechanism of laser ablation as a source of possible incorporation of secondary phases to the wire shell is discussed. Raman spectroscopy under excitation by an Ar+ laser revealed a broad peak related to the Mn-induced disorder and a redshift in the A1-LO phonon. Resonant Raman measurements revealed an increase in the multiphonon scattering caused by disorder in ZnO upon doping by Mn. Besides the UV emission, a vibronic green emission band assisted by a ∼ 71 meV LO phonon is also observed in the photoluminescence spectra. Core-shell structures with smooth shells show a high exciton to green band intensity ratio ( ∼ 10) even at room temperature.
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81.16.Mk Laser-assisted deposition
78.67.Lt Quantum wires
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Sintering and crystallization behavior of CaMgSi2O6–NaFeSi2O6 based glass-ceramics

Ashutosh Goel, Anna Maria Ferrari, Ishu Kansal, Maria J. Pascual, Luisa Barbieri, Federica Bondioli, Isabella Lancellotti, Manuel J. Ribeiro, and José M. F. Ferreira

J. Appl. Phys. 106, 093502 (2009); http://dx.doi.org/10.1063/1.3239852 (7 pages) | Cited 1 time

Online Publication Date: 4 November 2009

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We report on the synthesis, sintering, and crystallization behaviors of a glass with a composition corresponding to 90 mol % CaMgSi2O6−10 mol % NaFeSi2O6. The investigated glass composition crystallized superficially immediately after casting of the melt and needs a high cooling rate (rapid quenching) in order to produce an amorphous glass. Differential thermal analysis and hot-stage microscopy were employed to investigate the glass forming ability, sintering behavior, relative nucleation rate, and crystallization behavior of the glass composition. The crystalline phase assemblage in the glass-ceramics was studied under nonisothermal heating conditions in the temperature range of 850–950 °C in both air and N2 atmosphere. X-ray diffraction studies adjoined with the Rietveld–reference intensity ratio method were employed to quantify the amount of crystalline phases, while electron microscopy was used to shed some light on the microstructure of the resultant glass-ceramics. Well sintered glass-ceramics with diopside as the primary crystalline phase were obtained where the amount of diopside varied with the heating conditions.
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81.05.Pj Glass-based composites, vitroceramics
64.70.kj Glasses

Study of the oxidation state and the structural aspects of the V-doped TiO2

K. Bhattacharyya, S. Varma, A. K. Tripathi, D. Bhattacharyya, O. Mathon, and A. K. Tyagi

J. Appl. Phys. 106, 093503 (2009); http://dx.doi.org/10.1063/1.3253761 (7 pages) | Cited 1 time

Online Publication Date: 5 November 2009

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A modified sol-gel method for synthesizing vanadium doped titania is being reported. These materials were thoroughly characterized for their oxidation states by electron paramagnetic resonance and x-ray absorption near edge structure and the local environment of the V-atom were investigated by the x-ray absorption fine structure. V-doped titania was found to be more active than nanotitania for photo-oxidation of methane in air under ambient conditions using UV-visible irradiation. The vanadium doping in the crystal lattice of titania leads to a mixture of oxidation states of 4+ and 5+ in the crystal lattice sites of the TiO2, which is crucial for its catalytic activity.
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82.50.Hp Processes caused by visible and UV light
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
78.70.Dm X-ray absorption spectra
61.72.U- Doping and impurity implantation

Surface modification of magnetic recording media by filtered cathodic vacuum arc

H.-S. Zhang and K. Komvopoulos

J. Appl. Phys. 106, 093504 (2009); http://dx.doi.org/10.1063/1.3245399 (7 pages) | Cited 26 times

Online Publication Date: 5 November 2009

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Surface modification of a magnetic recording medium was accomplished by filtered cathodic vacuum arc (FCVA). The carbon overcoat of thin-film disks was removed by Ar+ ion sputter etching in vacuum to prevent oxidation of the exposed magnetic medium, which was then modified by FCVA carbon plasma under conditions of zero and −100 V pulsed substrate bias. Monte Carlo simulations performed with the T-DYN code, x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and surface force microscopy (SFM) provided insight into carbon implantation profiles, surface chemical composition, roughness, and nanomechanical properties of the surface-treated magnetic medium. The dependence of surface modification on the FCVA treatment conditions is discussed in the context of T-DYN, XPS, AFM, and SFM results. The findings of this study demonstrate the potential of FCVA to provide overcoat-free magnetic recording media exhibiting oxidation resistance and enhanced nanomechanical properties.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
81.05.Bx Metals, semimetals, and alloys
52.77.Bn Etching and cleaning
68.35.Gy Mechanical properties; surface strains
75.50.Ss Magnetic recording materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Reactive Ni/Ti nanolaminates

D. P. Adams, M. A. Rodriguez, J. P. McDonald, M. M. Bai, E. Jones, Jr., L. Brewer, and J. J. Moore

J. Appl. Phys. 106, 093505 (2009); http://dx.doi.org/10.1063/1.3253591 (8 pages) | Cited 6 times

Online Publication Date: 6 November 2009

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Nickel/titanium nanolaminates fabricated by sputter deposition exhibited rapid, high-temperature synthesis. When heated locally, self-sustained reactions were produced in freestanding Ni/Ti multilayer foils characterized by average propagation speeds between ∼ 0.1 and 1.4 m/s. The speed of a propagating reaction front was affected by total foil thickness and bilayer thickness (layer periodicity). In contrast to previous work with compacted Ni–Ti powders, no preheating of Ni/Ti foils was required to maintain self-propagating reactions. High-temperature synthesis was also stimulated by rapid global heating demonstrating low ignition temperatures (Tig) ∼ 300–400 °C for nanolaminates. Ignition temperature was influenced by bilayer thickness with more coarse laminate designs exhibiting increased Tig. Foils reacted in a vacuum apparatus developed either as single-phase B2 cubic NiTi (austenite) or as a mixed-phase structure that was composed of monoclinic B19′ NiTi (martensite), hexagonal NiTi2, and B2 NiTi. Single-phase, cubic B2 NiTi generally formed when the initial bilayer thickness was made small.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
68.65.Ac Multilayers
81.15.Cd Deposition by sputtering
81.07.-b Nanoscale materials and structures: fabrication and characterization

Effect of ultraviolet irradiation on luminescence properties of undoped ZnS and ZnS:Ag nanoparticles

Hua Qu, Lixin Cao, Ge Su, Wei Liu, Yuanguang Sun, and Bohua Dong

J. Appl. Phys. 106, 093506 (2009); http://dx.doi.org/10.1063/1.3253756 (6 pages) | Cited 3 times

Online Publication Date: 6 November 2009

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Undoped ZnS and ZnS:Ag nanoparticles have been prepared through hydrothemal synthesis. The changes of luminescence properties induced by ultraviolet irradiation have been investigated. For both samples, the initial slight increase in luminescence is ascribed to the fast electron filling, while the succedent decrease is supposed to be caused by nonradiative pathways originating from some unknown photochemical products. The more remarkable decrease in ZnS:Ag is put down to the segregation of Ag on the surfaces of ZnS:Ag nanoparticles. Multipeaks Gaussian fitting is applied to the emission spectra. The fitting peaks around 490 nm in both samples are related with the surface states emission and the fitting peaks around 456 nm in ZnS nanoparticles and 443 nm in ZnS:Ag nanoparticles are attributed to the type of donor-acceptor pair luminescence, which corresponds to the transition between different donor levels and acceptor levels in different samples. A model of stretched exponential function is used to fit the fluorescence decay spectra. Result shows that the introduction of Ag+ ions causes a spectacular lifetime shortening of ZnS. Experiment result also verifies the model as that the lifetimes of both samples are notably shortened after irradiation for 2 h.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.82.Rx Nanocrystalline materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Et II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing

Reaction pathway analysis for dislocation nucleation from a Ni surface step

Shotaro Hara, Satoshi Izumi, and Shinsuke Sakai

J. Appl. Phys. 106, 093507 (2009); http://dx.doi.org/10.1063/1.3254178 (4 pages) | Cited 3 times

Online Publication Date: 6 November 2009

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Threshold strain required for a thermally activated dislocation nucleation from a Ni surface step has been measured using an atomistic-based reaction pathway analysis. We show that the saddle-point configuration and the stress-dependent activation energy are strongly influenced by the presence of a surface step. Our results provide insight into the previous experimental findings concerning the mechanism on a coherency loss at the Ni/Cu(001) interface. We conclude that the coherency strain caused by a lattice mismatch between Ni and Cu does not yield a sufficient driving force for the dislocation nucleation.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.Gy Mechanical properties; surface strains
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Mechanism of Na-doped p-type ZnO films: Suppressing Na interstitials by codoping with H and Na of appropriate concentrations

S. S. Lin, H. P. He, Y. F. Lu, and Z. Z. Ye

J. Appl. Phys. 106, 093508 (2009); http://dx.doi.org/10.1063/1.3254221 (5 pages) | Cited 9 times

Online Publication Date: 6 November 2009

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Hydrogen is codoped with sodium into ZnO films. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy indicate that the Na concentration decreases as the substrate temperature increases. Hall-effect tests reveal a transition from n-type to p-type conduction when the growth temperature increases, which is explained by the suppression of Na interstitials by codoping with H and Na of appropriate concentrations. An insulating intended Na–H codoped sample shows reduced resistivity and p-type conductivity after annealing at 550 °C, which may be due to dissociation of NaZn–H complexes. The realization of p-type ZnO by Na–H codoping may explain the discrepancies in behavior of Na in ZnO and suggests the potential of Na–H codoping method [ E.-C. Lee and K. J. Chang, Phys. Rev. B 70, 115210 (2004) ].
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61.72.uj III-V and II-VI semiconductors
61.72.sd Impurity concentration
79.60.Dp Adsorbed layers and thin films
61.72.jj Interstitials
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
73.61.Ga II-VI semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Nanoindentation-induced phase transformation in relaxed and unrelaxed ion-implanted amorphous germanium

D. J. Oliver, J. E. Bradby, S. Ruffell, J. S. Williams, and P. Munroe

J. Appl. Phys. 106, 093509 (2009); http://dx.doi.org/10.1063/1.3255999 (6 pages) | Cited 2 times

Online Publication Date: 6 November 2009

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We have investigated nanoindentation-induced plastic deformation in amorphous germanium (a-Ge) prepared by high-energy self-ion implantation. Using cross-sectional transmission electron microscopy, micro-Raman spectroscopy, and force-displacement curve analysis, we find strong evidence for a pressure-induced metallic phase transformation during indentation. Crystalline diamond-cubic Ge-I is observed in residual indents. Relaxed and unrelaxed structural states of a-Ge exhibit similar behavior on loading, but transform at different pressures on unloading. Both forms are markedly softer mechanically than crystalline Ge. These results assist in furthering the understanding of the intriguing phenomenon known as “explosive crystallization.”
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62.20.fq Plasticity and superplasticity
81.40.Lm Deformation, plasticity, and creep
78.30.Am Elemental semiconductors and insulators
61.72.uf Ge and Si
64.70.dg Crystallization of specific substances
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