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15 Dec 2011

Volume 110, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 110, 121301 (2011); http://dx.doi.org/10.1063/1.3665219 (29 pages)

T. Fujita, M. B. A. Jalil, S. G. Tan, and S. Murakami
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Gauge fields in spintronics

T. Fujita, M. B. A. Jalil, S. G. Tan, and S. Murakami

J. Appl. Phys. 110, 121301 (2011); http://dx.doi.org/10.1063/1.3665219 (29 pages)

Online Publication Date: 22 December 2011

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We present an overview of gauge fields in spintronics, focusing on their origin and physical consequences. Important topics, such as the Berry gauge field associated with adiabatic quantum evolution as well as gauge fields arising from other non-adiabatic considerations, are discussed. We examine the appearance and effects of gauge fields across three spaces, namely real-space, momentum-space, and time, taking on a largely semiclassical approach. We seize the opportunity to study other “spin-like” systems, including graphene, topological insulators, magnonics, and photonics, which emphasize the ubiquity and importance of gauge fields. We aim to provide an intuitive and pedagogical insight into the role played by gauge fields in spin transport.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
72.25.-b Spin polarized transport
73.20.-r Electron states at surfaces and interfaces
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back to top Lasers, Optics, and Optoelectronics

Vertical cavity surface emitting lasers with the active layer position detuned from standing wave antinode for picosecond pulse generation by gain switching

Boris S. Ryvkin, Eugene A. Avrutin, and Juha T. Kostamovaara

J. Appl. Phys. 110, 123101 (2011); http://dx.doi.org/10.1063/1.3668321 (5 pages)

Online Publication Date: 19 December 2011

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A vertical cavity surface emitting laser with the active layer position detuned from the standing wave antinode is proposed for the purpose of high energy picosecond pulse generation by gain switching and analysed using numerical simulations and a fully analytical model. An optimum value of the confinement factor for high-energy pulse generation is predicted and its origins discussed.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking

Study of 375 nm ultraviolet InGaN/AlGaN light-emitting diodes with heavily Si-doped GaN transition layer in growth mode, internal quantum efficiency, and device performance

Shih-Cheng Huang, Kun-Ching Shen, Dong-Sing Wuu, Po-Min Tu, Hao-Chung Kuo, Chia-Cheng Tu, and Ray-Hua Horng

J. Appl. Phys. 110, 123102 (2011); http://dx.doi.org/10.1063/1.3669377 (5 pages)

Online Publication Date: 20 December 2011

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High performance 375 nm ultraviolet (UV) InGaN/AlGaN light-emitting diodes (LEDs) were demonstrated with inserting a heavy Si-doped GaN transition layer by metal-organic chemical vapor deposition. From transmission electron microcopy (TEM) image, the dislocation densities were significantly reduced due to the existence of the heavily Si-doping growth mode transition layer (GMTL), which results in residual stress relaxation and 3D growth. The internal quantum efficiency (IQE) of the LEDs with GMTL was measured by power-dependent photoluminescence (PL) to be 40.6% higher than ones without GMTL. The GMTL leads to the superior IQE performance of LEDs not only in decreasing carrier consumption at nonradiative recombination centers but also in partially mitigating the efficiency droop tendency. When the vertical-type LED chips (size: 1 mm × 1 mm) was driven with a 350 mA injection current, the output powers of the LEDs with and without GMTL were measured to be 286.7 and 204.2 mW, respectively. A 40.4% enhancement of light output power was achieved. Therefore, using the GMTL to reduce dislocations would be a promising prospective for InGaN/AlGaN UV-LEDs to achieve high IQE.
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85.60.Jb Light-emitting devices

Blueshift of bandgap energy and reduction of non-radiative defect density due to precise control of InAs-on-GaSb interface in type-II InAs/GaSb superlattice

A. Jasik, I. Sankowska, D. Pierścińska, K. Regiński, K. Pierściński, and J. Kubacka-Traczyk

J. Appl. Phys. 110, 123103 (2011); http://dx.doi.org/10.1063/1.3671024 (5 pages)

Online Publication Date: 22 December 2011

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We have investigated the influence of As-soak parameters at InAs-on-GaSb interfaces on the structural and optical parameters of InAs/GaSb superlattices (SLs). The lattice-matched SLs were obtained for two sets of technological parameters. For a long As-soak time of 12.0 s and high V/III ratio of 10, the photoluminescence (PL) analysis indicates the presence of a non-radiative recombination channel. For a shorter time of 2.8 s and a reduced V/III ratio of 5.6, the PL excitation power dependence is close to that relevant for a clear excitonic recombination. The spectral blueshift of the bandgap energy of 23 meV was observed for SLs with GaAs-like interface thicknesses of 0.4 ML and 1.0 ML and other fixed parameters.
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73.21.Cd Superlattices
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
68.55.ag Semiconductors
78.66.Fd III-V semiconductors

A semi-analytical model for semiconductor solar cells

D. Ding, S. R. Johnson, S.-Q. Yu, S.-N. Wu, and Y.-H. Zhang

J. Appl. Phys. 110, 123104 (2011); http://dx.doi.org/10.1063/1.3671061 (17 pages) | Cited 2 times

Online Publication Date: 23 December 2011

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A semi-analytical model is constructed for single- and multi-junction solar cells. This model incorporates the key performance aspects of practical devices, including nonradiative recombination, photon recycling within a given junction, spontaneous emission coupling between junctions, and non-step-like absorptance and emittance with below-bandgap tail absorption. Four typical planar structures with the combinations of a smooth/textured top surface and an absorbing/reflecting substrate (or backside surface) are investigated, through which the extracted power and four types of fundamental loss mechanisms, transmission, thermalization, spatial-relaxation, and recombination loss are analyzed for both single- and multi-junction solar cells. The below-bandgap tail absorption increases the short-circuit current but decreases the output and open-circuit voltage. Using a straightforward formulism this model provides the initial design parameters and the achievable efficiencies for both single- and multiple-junction solar cells over a wide range of material quality. The achievable efficiency limits calculated using the best reported materials and AM1.5 G one sun for GaAs and Si single-junction solar cells are, respectively, 27.4 and 21.1% for semiconductor slabs with a flat surface and a non-reflecting index-matched absorbing substrate, and 30.8 and 26.4% for semiconductor slabs with a textured surface and an ideal 100% reflecting backside surface. Two important design rules for both single- and multi-junction solar cells are established: i) the optimal junction thickness decreases and the optimal bandgap energy increases when nonradiative recombination increases; and ii) the optimal junction thickness increases and the optimal bandgap energy decreases for higher solar concentrations.
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88.40.jj Silicon solar cells
88.40.jp Multijunction solar cells

Infrared surface plasmons on heavily doped silicon

Monas Shahzad, Gautam Medhi, Robert E. Peale, Walter R. Buchwald, Justin W. Cleary, Richard Soref, Glenn D. Boreman, and Oliver Edwards

J. Appl. Phys. 110, 123105 (2011); http://dx.doi.org/10.1063/1.3672738 (6 pages) | Cited 3 times

Online Publication Date: 27 December 2011

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Conductors with infrared plasma frequencies are potentially useful hosts of surface plasmon polaritons (SPP) with sub-wavelength mode confinement for sensing applications. A challenge is to identify such a conductor that also has sharp SPP excitation resonances and the capability to be functionalized for biosensor applications. In this paper we present experimental and theoretical investigations of IR SPPs on doped silicon and their excitation resonances on doped-silicon gratings. The measured complex permittivity spectra for p-type silicon with carrier concentration 6×1019 and 1×1020 cm−3 show that these materials should support SPPs beyond 11 and 6 μm wavelengths, respectively. The permittivity spectra were used to calculate SPP mode heights above the silicon surface and SPP propagation lengths. Reasonable merit criteria applied to these quantities suggest that only the heaviest doped material has sensor potential, and then mainly within the wavelength range 6 to 10 μm. Photon-to-plasmon coupling resonances, a necessary condition for sensing, were demonstrated near 10 μm wavelength for this material. The shape and position of these resonances agree well with simple analytic calculations based on the theory of Hessel and Oliner (1965).
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.30.Am Elemental semiconductors and insulators
77.22.Ch Permittivity (dielectric function)

Direct measurement of plasmon propagation lengths on lithographically defined metallic waveguides on GaAs

G. Bracher, K. Schraml, C. Jakubeit, M. Kaniber, and J. J. Finley

J. Appl. Phys. 110, 123106 (2011); http://dx.doi.org/10.1063/1.3671641 (4 pages) | Cited 1 time

Online Publication Date: 27 December 2011

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We present optical investigations of rectangular surface plasmon polariton (SPP) waveguides (WGs) lithographically defined on GaAs substrates. The plasmon propagation length is directly determined using a confocal microscope, with independent polarization control in both excitation and detection channels. Surface plasmon polaritons are launched along the waveguide using a lithographically defined defect at one end. At the remote end of the waveguide, they scatter into the far-field, where they are imaged using a CCD camera. By monitoring the length dependence of the intensity of scattered light from the waveguide end, we directly extract the propagation length, obtaining values ranging from LSPP = 10 to 40 μm depending on the waveguide width (ωWG = 2–5 μm) and excitation wavelength (760–920 nm). Results are in good accord with theoretical expectations demonstrating the high quality of the lithographically defined structures. The results obtained are of strong relevance for the development of future semiconductor based integrated plasmonic technologies.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys

Measurement of second hyperpolarizability components of a conjugated polymer

Haibin Yu, Xiaoxu Deng, Xiaohui Zhu, Honggen Li, Xianfeng Chen, Wei Wei, and Feng Liu

J. Appl. Phys. 110, 123107 (2011); http://dx.doi.org/10.1063/1.3672440 (5 pages)

Online Publication Date: 28 December 2011

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A method has been proposed to determine the components of the second hyperpolarizability γ(-ω4;ω3,ω2,ω1) of a conjugated polymer in the off-resonant region based on the attenuated- total-reflection technique. By doing a least-square fit to the experimental data of γ(-ω;0,0,ω) for the quadratic electro-optic effect, the frequency-independent term of the components of γ(-ω4;ω3,ω2,ω1) is obtained, from which the components of γ(-ω4;ω3,ω2,ω1) are determined .
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78.20.Jq Electro-optical effects

Reduction of internal polarization fields in InGaN quantum wells by InGaN/AlGaN ultra-thin superlattice barriers with different indium composition

Young-Kyun Noh, Moon-Deock Kim, and Jae-Eung Oh

J. Appl. Phys. 110, 123108 (2011); http://dx.doi.org/10.1063/1.3666060 (5 pages)

Online Publication Date: 29 December 2011

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The internal well polarization field in InGaN quantum wells (QWs), surrounded by strain-compensated (InxGa1−xN)/(Al0.065Ga0.935N) ultra-thin superlattice (SC-SL) barriers with different indium composition, is investigated. The indium composition of InGaN constituent of superlattice barriers has been varied in the range from 0.04 to 0.18. It is observed that the increase of indium composition of InGaN into the barrier results in a strong blue-shift of the peak wavelength of the room-temperature photoluminescence (RT-PL) and the significant increase in the intensity of the luminescence emission until too much indium is added into InGaN layers of superlattice barriers. From the bias-dependent photoluminescence measurements, it is determined that the blue-shift and intensity increase of the emission are caused by the decrease of well polarization field as the indium composition in InGaN of SC-SL barrier increases. In case of In0.16Ga0.84N containing SC-SL barriers, the well internal polarization field is greatly reduced to −0.33 MV/cm from −1.5 MV/cm with respect to typical GaN barriers, indicating that the internal field reduction similar to that obtained in semi-polar InGaN/GaN quantum wells can be obtained by applying the strain-compensating barrier to polar substrates.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Thermal dependence of the optical gain and threshold current density of GaInNAs/GaAs/AlGaAs quantum well lasers

Shudong Wu and Li Wan

J. Appl. Phys. 110, 123109 (2011); http://dx.doi.org/10.1063/1.3672819 (4 pages) | Cited 2 times

Online Publication Date: 30 December 2011

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The thermal dependence of the optical gain and threshold current density of GaInNAs/GaAs/AlGaAs quantum well (QW) lasers with the emission wavelength of 1.3 μm have been theoretically investigated. The optical gain is found to decrease with the increase of the temperature due to the hole leakage in the separate confinement heterostructure (SCH) region. The distribution of unconfined electrons in the SCH region is negligible while the distribution of unconfined holes in the SCH region plays an important role in the leakage process, reflecting the smaller bandgap discontinuity in the valence band than in the conduction band. The threshold current density increases with the increase of temperature, which is dominated by the monomolecular recombination process. Our calculated threshold current densities with temperatures are in agreement with the available experimental results.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Thickness independent magneto-optical coupling constant of nickel films in the visible spectral range

K. Mok, C. Scarlat, G. J. Kovács, L. Li, V. Zviagin, J. McCord, M. Helm, and H. Schmidt

J. Appl. Phys. 110, 123110 (2011); http://dx.doi.org/10.1063/1.3672834 (4 pages) | Cited 1 time

Online Publication Date: 30 December 2011

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Magneto-optical properties of nominally 10, 20, and 30 nm thick ferromagnetic Ni films have been investigated at room temperature by vector-magneto-optical generalized ellipsometry under saturated magnetization conditions in the sample surface plane. The magneto-optical dielectric tensor of Ni has been determined by reflection Mueller matrix ellipsometry in the spectral range from 300 to 1100 nm. Different sets of magnetic field induced Mueller matrix elements enable us to identify the magnetization directions in the sample. The extracted magnetic field and thickness independent magneto-optical coupling constant is useful for modeling the Mueller matrix and complex Kerr angle of magnetized Ni thin films in layered sample systems in dependence of the incident angle of light, wavelength, and magnetization.
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78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Cc Other ferromagnetic metals and alloys
78.40.Kc Metals, semimetals, and alloys
78.66.Bz Metals and metallic alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Transverse thermoelectric response in tilted orientation La1−xSrxCoO3 (0.05 ≤ x ≤ 0.4) thin films

Y. Wang, L. Yu, B. Jiang, and P. X. Zhang

J. Appl. Phys. 110, 123111 (2011); http://dx.doi.org/10.1063/1.3673552 (5 pages)

Online Publication Date: 30 December 2011

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La1−xSrxCoO3 (0.05 ≤ x ≤ 0.4) thin films with tilted c-axis have been grown on vicinal cut LaAlO3 (100) substrates by pulse laser deposition. The single phase and the epitaxial growth of these thin films have been checked by x-ray diffraction analysis. Transverse thermoelectric voltage response in these films has been studied at room temperature by using a pulse laser as the thermal source. The maximum voltage response has been observed in La0.7Sr0.3CoO3 films in this series of oxides, with the responsivity of 1.23 V/mJ in 10° tilted film. The resistivity and the thermal diffusivity have been reckoned as the main physical parameters to determine the time response of establishment and decay processes of transverse thermoelectric voltage, respectively. Smaller resistivity leads to fast response speed to establish the voltage, while larger thermal diffusivity results in the fast decay of voltage.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.61.Ng Insulators
81.15.Fg Pulsed laser ablation deposition
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
68.55.aj Insulators
back to top Plasmas and Electrical Discharges

Chemical bond modification in porous SiOCH films by H2 and H2/N2 plasmas investigated by in situ infrared reflection absorption spectroscopy

Hiroshi Yamamoto, Kohei Asano, Kenji Ishikawa, Makoto Sekine, Hisataka Hayashi, Itsuko Sakai, Tokuhisa Ohiwa, Keigo Takeda, Hiroki Kondo, and Masaru Hori

J. Appl. Phys. 110, 123301 (2011); http://dx.doi.org/10.1063/1.3671547 (8 pages) | Cited 4 times

Online Publication Date: 28 December 2011

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The modification of porous low-dielectric (low-k) SiOCH films by ashing plasma irradiation and subsequent exposure to air was investigated by in situ characterizations. Porous blanket SiOCH film surfaces were treated by a H2 or H2/N2 plasma in a 100-MHz capacitively coupled plasma reactor. The individual or combined effects of light, radicals, and ions generated by the plasmas on the chemical bonds in the porous SiOCH films were characterized using an in situ evaluation and by in situ Fourier-transform infrared reflection absorption spectroscopy (IR-RAS). In situ IR-RAS analysis revealed that the number of Si-OH, Si-H, and Si-NH2 bonds increased while the number of Si-CH3 bonds decreased during exposure to a H2 or H2/N2 plasma. Subsequent air exposure increased the number of Si-OH bonds by modifying Si-O-Si structures. The experimental results indicate that light emitted from a H2 or H2/N2 plasma can break Si-CH3 and Si-O-Si bonds and thereby generate dangling bonds. Radicals (e.g., NxHy and H radicals) can break Si-CH3 and Si-O-Si bonds and Si-NH2, Si–H, and Si-OH bonds could be formed. Si-NH2, Si-H, and dangling bonds react with moisture in the air cause the formation of Si-OH bonds. The dehydroxylation reaction on Si-OH was found to be the origin of Si-O-Si network structures. The mechanism of the degradation of porous low-k SiOCH films induced by a H2 or H2/N2 plasma is discussed based on the in situ characterization results.
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68.35.Fx Diffusion; interface formation
78.30.Hv Other nonmetallic inorganics
81.65.Cf Surface cleaning, etching, patterning
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.55.df For silicon electronics

Estimation of electron temperature and density of the decay plasma in a laser-assisted discharge plasma extreme ultraviolet source by using a modified Stark broadening method

Qiushi Zhu, Takahiro Muto, Junzaburo Yamada, Nozomu Kishi, Masato Watanabe, Akitoshi Okino, Kazuhiko Horioka, and Eiki Hotta

J. Appl. Phys. 110, 123302 (2011); http://dx.doi.org/10.1063/1.3672816 (8 pages)

Online Publication Date: 30 December 2011

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In order to investigate the plasma expansion behaviors and the electrical recovery process after the maximum implosion in our tin fueled laser-assisted discharge plasma (LDP) 13.5 nm EUV source, we developed and evaluated a cost-efficient spectroscopic method to determine the electron temperature Te and density ne simultaneously, by using Stark broadenings of two Sn II isolated lines (5s24f2F°5/2 – 5s25d2D3/2 558.9 nm and 5s26d2D5/2 – 5s26p2P°3/2 556.2 nm) spontaneously emitted from the plasma. The spatial-resolved evolutions of Te and ne of the expansion plasma over 50 to 900 ns after the maximum implosion were obtained using this modified Stark broadening method. According to the different ne decay characteristics along the Z-pinch axis, the expansion velocity of the electrons was estimated as ∼1.2 × 104 ms− 1 from the plasma shell between the electrodes towards the cathode and the anode. The decay time constant of ne was measured as 183 ± 24 ns. Based on the theories of plasma adiabatic expansion and electron-impact ionization, the minimum time-span that electrical recovery between the electrodes needs in order to guarantee the next succeeding regular EUV-emitting discharge was estimated to be 70.5 μs. Therefore, the maximum repetition rate of our LDP EUV source is ∼14 kHz, which enables the output to reach 125 W/(2πsr).
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Qj Explosions; exploding wires
52.50.Dg Plasma sources
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.Fi Transport properties
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Invariant x-ray elastic constants and their use in determining hydrostatic stress

Conal E. Murray

J. Appl. Phys. 110, 123501 (2011); http://dx.doi.org/10.1063/1.3667294 (8 pages) | Cited 1 time

Online Publication Date: 16 December 2011

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The measurement of stress using x-ray diffraction requires knowledge of the constitutive equation linking strain and stress for the sample under investigation. With the exception of single-crystal materials, a unique constitutive relation does not exist requiring an average over the diffracting ensemble. Such averaging techniques provide bounds to the range of x-ray elastic constants, whose values depend on the elastic anisotropy of the material, the mechanical response of the crystallites and often the x-ray reflection chosen. In fact, for materials possessing cubic symmetry, the general x-ray stress equation can be reduced to a form that relates the measured strain to the hydrostatic stress and the bulk modulus, quantities that are invariant with respect to crystal orientation. These orientations do not correspond to stress-free values but rather to lattice parameters that are independent of the x-ray reflection used. Examples include the application of this technique to a test case of an isotropic, biaxially stressed film, and determining the triaxial stress states in capped features. The validity of these orientations, which are developed for specific stress states, relies on the assumption that the polycrystalline aggregate behaves as a quasi-isotropic ensemble.
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68.60.Bs Mechanical and acoustical properties
62.20.de Elastic moduli
62.20.dq Other elastic constants
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.55.-a Thin film structure and morphology

Diversity of electronic transitions and photoluminescence properties in nanocrystalline Mn/Fe-doped tin dioxide semiconductor films: An effect from oxygen pressure

W. L. Yu (余温雷), W. W. Li (李文武), J. D. Wu (吴嘉达), J. Sun (孙剑), Z. G. Hu (胡志高), and J. H. Chu (褚君浩)

J. Appl. Phys. 110, 123502 (2011); http://dx.doi.org/10.1063/1.3669374 (10 pages)

Online Publication Date: 19 December 2011

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Transition metal (TM: Mn or Fe) doped tin dioxide (SnO2) films with the compositions of 5% (Sn0.95TM0.05O2) have been deposited on sapphire substrates by pulsed laser deposition under oxygen pressure (Po) varied from 10−4 to 1 Pa. The x-ray diffraction, scanning electron microscopy, and infrared spectra analysis show that different TM dopants can affect the variations of crystallization and lattice distortion. Moreover, x-ray photoelectron spectroscopies indicate that the effective Po during the growth does not change the valence state of Sn4+ in the Sn0.95TM0.05O2 films. The spectral behaviors of the films have been investigated in the photon energy range of 0.47-6.5 eV (2650-190 nm). From transmittance spectra, the shoulder structures become more prominent for the Sn0.95Fe0.05O2 film than those for the Sn0.95Mn0.05O2 film due to the Fe repelling effect of a stronger p-d hybridization. The refractive index values for the Sn0.95Mn0.05O2 film are found to be larger than those for the Sn0.95Fe0.05O2 film at the photon energy of 0.47 eV. The main peaks at about 1.9 and 2.2 eV in photoluminescence (PL) emission spectra for both Sn0.95Mn0.05O2 and Sn0.95Fe0.05O2 films can be observed, and it could be explained by the fact that the electrons in the conduction band of SnO2 relax to defect states and then radiatively recombine with the holes. From direct comparison of PL and transmittance results for the films, the electronic transition energies, the emission peaks’ intensities and positions are shown to present the Po dependent behavior. The distinct trends indicate that the incorporation of Mn and Fe elements can provide a significant difference in the crystalline and electronic band structure. It can be concluded that the oxygen pressure and dopant contributions are responsible for the adjustment of electronic band structures and result in different optical response behaviors for the Sn0.95TM0.05O2 films.
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71.20.Nr Semiconductor compounds
71.55.Ht Other nonmetals
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors

Thermal tuning of Lamb wave band structure in a two-dimensional phononic crystal plate

Yuanwei Yao, Fugen Wu, Xin Zhang, and Zhilin Hou

J. Appl. Phys. 110, 123503 (2011); http://dx.doi.org/10.1063/1.3669391 (4 pages)

Online Publication Date: 19 December 2011

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Using supercell-plane-wave-expansion method, we have made a theoretical study of the temperature effects on the band structure of Lamb wave in a two-dimensional phononic crystal plate. The numerical results show that the Lamb wave bandgap is very sensitive to temperature. For the case of Ba0.7Sr0.3TiO3/epoxy phononic crystal, the width of bandgap becomes narrower in a hexagonal lattice system as the temperature increases, but it becomes wider in a phononic crystal plate with square lattice. On the other hand, for the case of air/Ba0.7Sr0.3TiO3 plate with square lattice, wider and higher complete bandgap can be created in a higher temperature. These results are quite different from that in the infinite phononic crystal and one-dimensional phononic crystal plate.
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68.35.Iv Acoustical properties
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
77.80.-e Ferroelectricity and antiferroelectricity

Effects of cryogenic temperature on dynamic fragmentation of laser shock-loaded metal foils

T. de Rességuier, E. Lescoute, D. Loison, J. M. Chevalier, and F. Ducasse

J. Appl. Phys. 110, 123504 (2011); http://dx.doi.org/10.1063/1.3670005 (8 pages) | Cited 1 time

Online Publication Date: 19 December 2011

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Although shock-induced fracture and fragmentation of materials at low temperatures are issues of considerable interest for many applications, such as the protection from hypervelocity impacts in outer space or the ongoing development of high energy laser facilities aiming at inertial confinement fusion, little data can be found on the subject yet. In this paper, laser driven shock experiments are performed on gold and aluminum samples at both ambient and cryogenic (down to about 30 K) temperatures. Complementary techniques including transverse optical shadowgraphy, time-resolved velocity measurements, and post-recovery analyses are combined to assess the effects of target temperature upon the processes of microjetting, spallation, and dynamic punching, which are expected to govern fragments generation and ejection. The results indicate that cryogenic temperature tends to reduce the resistance to tensile and shear stresses, promotes brittle fracture, and leads to slightly higher fragments ejection velocities.
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62.50.Ef Shock wave effects in solids and liquids
68.55.aj Insulators
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture

High pressure structural stability of BaLiF3

A. K. Mishra, Nandini Garg, K. V. Shanavas, S. N. Achary, A. K. Tyagi, and Surinder M. Sharma

J. Appl. Phys. 110, 123505 (2011); http://dx.doi.org/10.1063/1.3670036 (6 pages)

Online Publication Date: 20 December 2011

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High pressure x-ray diffraction studies on inverse-perovskite BaLiF3 show that this compound is structurally stable up to ∼50 GPa. The bulk modulus of BaLiF3 is determined to be 75.9 GPa which is in close agreement with that determined from a semi-empirical formulation. Our ab initio calculations show that among the three alkaline earth fluoro perovskites (ALiF3, A = Ba, Ca, and Sr) which crystallize in the inverse-perovskite structure, BaLiF3 is the least brittle at ambient conditions and also that the degree of brittleness decreases at high pressures. The behavior of the elastic constants at high pressure accompanied by a reduction in the bandgap indicates a decrease in the directional nature of the bonding.
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61.66.Fn Inorganic compounds
62.50.-p High-pressure effects in solids and liquids
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mj Brittleness
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Paramagnetic defects in electron-irradiated yttria-stabilized zirconia: Effect of yttria content

Jean-Marc Costantini, François Beuneu, Sarah Morrison-Smith, Ram Devanathan, and William J. Weber

J. Appl. Phys. 110, 123506 (2011); http://dx.doi.org/10.1063/1.3666062 (9 pages)

Online Publication Date: 20 December 2011

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We have studied the effect of the yttria content on the paramagnetic centers in electron-irradiated yttria-stabilized zirconia (ZrO2: Y3+) or YSZ. Single crystals with 9.5 mol % or 18 mol % Y2O3 were irradiated with electrons of 1.0, 1.5, 2.0, and 2.5 MeV. The paramagnetic center production was studied by X-band electron paramagnetic resonance (EPR) spectroscopy. The same paramagnetic centers were identified for both chemical compositions, namely two electron centers, i.e., (i) F+-type centers (involving singly ionized oxygen vacancies), and (ii) so-called T centers (Zr3+ in a trigonal symmetry site), as well as hole-centers. A strong effect is observed on the production of hole-centers that is strongly enhanced when doubling the yttria content. However, no striking effect is found on the electron centers (except the enhancement of an extra line associated with the F+-type centers). It is concluded that hole-centers are produced by inelastic interactions, whereas F+-type centers are produced by elastic collisions with no effect of the yttria content on the defect production rate. In the latter case, the threshold displacement energy (Ed) of oxygen is estimated from the electron-energy dependence of the F+-type center production rate, with no significant effect of the yttria content on Ed. An Ed value larger than 120 eV is found. This is supported by classical molecular dynamics (MD) simulations with a Buckingham-type potential that show Ed values for Y and O are likely to be in excess of 200 eV. Due to the difficulty in displacing O or Y atoms, the radiation-induced defects may alternatively be a result of Zr atom displacements for Ed = 80 ± 1 eV with subsequent defect rearrangement.
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71.55.Ht Other nonmetals
76.30.He Platinum and palladium group (4d and 5d) ions and impurities (Zr-Ag and Hf-Au)
76.30.Mi Color centers and other defects
61.72.jn Color centers
61.72.up Other materials
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Experimental and theoretical studies on the enhanced photoluminescence activity of zinc sulfide with a capping agent

Yuri V. B. de Santana, Cristiane W. Raubach, Mateus M. Ferrer, Felipe La Porta, Julio R. Sambrano, Valéria M. Longo, Edson R. Leite, and Elson Longo

J. Appl. Phys. 110, 123507 (2011); http://dx.doi.org/10.1063/1.3666070 (7 pages)

Online Publication Date: 20 December 2011

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The photoluminescence (PL) emission from zinc sulfide (ZnS) synthesized by the microwave-assisted solvothermal method in the presence/absence of a capping agent was examined to understand the key role of its PL activity. In addition, we also investigated the electronic structure using a first-principle calculation based on density functional theory (DFT) applied to periodic models at B·LYP level. Two models were selected to simulate the effects of structural deformation on the electronic structure; the ordered o-ZnS model and the disordered d-ZnS model, dislocating the Zn atom, 0.1 Å, in the z-direction. The PLemission in the visible region showed different peak positions and intensities in capped and uncapped ZnS. The PL emission was linked to distinct distortions in lattices and the emission of two colors, green in the capped and blue in the uncapped, was also examined in the light of favorable structural and electronic conditions. The computational simulations indicate that the electronic behavior can be associated with the new electronic levels above the valence band.
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81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
78.40.Fy Semiconductors
71.20.Nr Semiconductor compounds

Atomic-scale structural evolution from disorder to order in an amorphous metal

F. Li, X. J. Liu, H. Y. Hou, G. Chen, and G. L. Chen

J. Appl. Phys. 110, 123508 (2011); http://dx.doi.org/10.1063/1.3669450 (6 pages)

Online Publication Date: 21 December 2011

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In this paper, we performed molecular dynamics simulations to study the atomic-scale structural evolution from disorder to order during the isothermal annealing of an amorphous Ni. Three plateaus in the time dependent potential energy and mean square displacement (MSD) curves were observed, indicating that the atomic ordering process from amorphous to nanocrystalline Ni undergoes three distinct stages. The structural analyses reveal that the atomic structural evolution is associated with these three stages: Disordered atoms adjust their relative positions to form a one-dimensional (1D) periodic structure at the first stage, then form a 2D periodic structure at the second stage, and finally form a 3D periodic nanocrystal. Further analyses of potential energy and MSD difference and dynamics demonstrate that the structural change from the 2D to 3D structure is more difficult than that from the 1D to 2D structure, because both the 1D and 2D quasi-ordered structures belong to transition states and have similar structural features in nature. Our findings may provide new insights into the nanocrystallization of amorphous alloys and implications for producing nanostructured materials.
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61.50.Ks Crystallographic aspects of phase transformations; pressure effects
64.60.Cn Order-disorder transformations
64.70.Nd Structural transitions in nanoscale materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
64.70.kd Metals and alloys
61.43.Bn Structural modeling: serial-addition models, computer simulation

Effects of composition and compositional distribution on the electronic structure of ZnSe1−xTex ternary quantum dots

Sumeet C. Pandey and Dimitrios Maroudas

J. Appl. Phys. 110, 123509 (2011); http://dx.doi.org/10.1063/1.3670039 (6 pages) | Cited 1 time

Online Publication Date: 21 December 2011

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We report results of first-principles density functional theory (DFT) calculations for the electronic structure of ZnSe1−xTex ternary quantum dots (TQDs) and the effects of composition and compositional distribution on the electron density distribution, electronic density of states, and band gap. We analyze the electronic structure of five types of nanocrystal configurations, namely, pristine ZnSe and ZnTe quantum dots, as well as ZnSe/ZnTe core/shell, ZnTe/ZnSe reverse core/shell, and randomly alloyed ZnSe1−xTex TQDs. We find that the band gaps for ZnSe/ZnTe core/shell TQDs are nonlinearly dependent on the number of Te atoms in the shell, whereas presence of Te in the core of alloyed ZnSe1−xTex TQDs modifies the electronic energy levels abruptly and significantly in the limits of x → 0 and x → 1. Our results imply that distribution of Te atoms in the TQD in the form of a ZnSe/ZnTe core/shell configuration allows for optimum tunability of the band gap and wave function confinement in TQDs.
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73.21.La Quantum dots
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Structural and electrical characterization of silicided Ni/Au contacts formed at low temperature (<300 °C) on p-type [001] silicon

A. Alberti, P. Badalà, G. Pellegrino, and A. Santangelo

J. Appl. Phys. 110, 123510 (2011); http://dx.doi.org/10.1063/1.3670995 (6 pages) | Cited 2 times

Online Publication Date: 21 December 2011

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Silicided Ni/Au contacts with very low contact resistance were realized on p-type [001] silicon at low temperature by ex-situ or, alternatively, by in situ annealing processes. During the ex-situ annealing, performed at 200  °C for 10 s, a uniformly thin (14 nm) Ni2Si layer was formed having an extremely flat interface with silicon thanks to the trans-rotational structure of the silicide. During the in situ annealing, promoted by a sputter etch processing (T < 300  °C), a 44 nm-thick silicide layer was formed as a mixture of trans-rotational NiSi and epitaxial NiSi2, domains. In both cases, using a low thermal budget has guaranteed a limited consumption of silicon during the reaction process and a good adhesion with the substrate avoiding gold contaminations. As a consequence of the presence of trans-rotational domains, wherein a pseudo-epitaxial relationship between the silicide and the silicon lattices is established, an ohmic behavior was observed in a wide range of substrate doping (3.5 × 1018 ÷ 3 × 1019 B/cm3) for both annealing processes (in situ and ex-situ). On the other hand, conventional TiNiAu and CrNiAu contacts showed, in the same range of B doping concentration, a rectifying behavior with systematically higher specific contact resistance values (Rc) compared to those of the Ni silicided contacts.
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73.40.Ns Metal-nonmetal contacts
68.35.Ct Interface structure and roughness
81.40.Gh Other heat and thermomechanical treatments
73.40.Cg Contact resistance, contact potential
73.40.Ei Rectification

Synthesis and characterization of titanium-alloyed hematite thin films for photoelectrochemical water splitting

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

J. Appl. Phys. 110, 123511 (2011); http://dx.doi.org/10.1063/1.3671414 (7 pages) | Cited 2 times

Online Publication Date: 22 December 2011

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We have synthesized pure and Ti-alloyed hematite thin films on F doped SnO2 coated glass substrates by radio frequency magnetron co-sputtering of iron oxide and titanium targets in mixed Ar/O2 and mixed N2/O2 ambient. We found that the hematite films deposited in the N2/O2 ambient exhibit much poorer crystallinity than the films deposited in the Ar/O2 ambient. We determined that Ti alloying leads to increased electron carrier concentration and crystallinity, and reduced bandgaps. Moreover, Ti-alloyed hematite thin films exhibited improved photoelectrochemical performance as compared with the pure hematite films: The photocurrents were enhanced and the photocurrent onset shifted to less positive potentials.
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81.15.Cd Deposition by sputtering
82.45.-h Electrochemistry and electrophoresis
82.50.-m Photochemistry
71.20.Ps Other inorganic compounds
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ng Insulators
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