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28 May 2013

Volume 113, Issue 20 (partial)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 204101 (2013); http://dx.doi.org/10.1063/1.4801881 (6 pages)

Methee Promsawat, Anucha Watcharapasorn, Hamel N. Tailor, Sukanda Jiansirisomboon, and Zuo-Guang Ye
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back to top Plasmas and Electrical Discharges

Hydrodynamics of the molten metal in a vacuum arc cathode spot at near-threshold currents

G. A. Mesyats and N. M. Zubarev

J. Appl. Phys. 113, 203301 (2013); http://dx.doi.org/10.1063/1.4807303 (4 pages)

Online Publication Date: 22 May 2013

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The extrusion of the molten metal from a microcrater formed on a metal cathode during the operation of a vacuum arc is considered. The problem is thought to be similar to the classical hydrodynamic problem of a liquid drop impact on a solid surface. Based on this analogy, the conditions are analyzed under which the liquid will change its regular behavior (spreading over the cathode surface) into a singular behavior (formation of microjets and droplets). It is shown that the conditions realized in vacuum arc cathode spots at near-threshold currents are close to the threshold conditions for splashing of the molten metal. This points to a considerable contribution of hydrodynamic processes to the self-sustained operation of a vacuum arc and, in particular, gives grounds to relate the existence of a threshold arc current to the existence of a splashing threshold for liquid metal.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Wq Discharge in liquids and solids
52.75.-d Plasma devices
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Effects of pressure, temperature, and hydrogen during graphene growth on SiC(0001) using propane-hydrogen chemical vapor deposition

A. Michon, S. Vézian, E. Roudon, D. Lefebvre, M. Zielinski, T. Chassagne, and M. Portail

J. Appl. Phys. 113, 203501 (2013); http://dx.doi.org/10.1063/1.4806998 (8 pages)

Online Publication Date: 22 May 2013

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Graphene growth from a propane flow in a hydrogen environment (propane-hydrogen chemical vapor deposition (CVD)) on SiC differentiates from other growth methods in that it offers the possibility to obtain various graphene structures on the Si-face depending on growth conditions. The different structures include the (6√3 × 6√3)-R30° reconstruction of the graphene/SiC interface, which is commonly observed on the Si-face, but also the rotational disorder which is generally observed on the C-face. In this work, growth mechanisms leading to the formation of the different structures are studied and discussed. For that purpose, we have grown graphene on SiC(0001) (Si-face) using propane-hydrogen CVD at various pressure and temperature and studied these samples extensively by means of low energy electron diffraction and atomic force microscopy. Pressure and temperature conditions leading to the formation of the different structures are identified and plotted in a pressure-temperature diagram. This diagram, together with other characterizations (X-ray photoemission and scanning tunneling microscopy), is the basis of further discussions on the carbon supply mechanisms and on the kinetics effects. The entire work underlines the important role of hydrogen during growth and its effects on the final graphene structure.
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81.05.ue Graphene
68.35.bp Fullerenes
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Ct Interface structure and roughness
61.48.Gh Structure of graphene

Anisotropic optical and thermoelectric properties of In4Se3 and In4Te3

Xingfu Li, Bin Xu, Gongqi Yu, Li Xue, and Lin Yi

J. Appl. Phys. 113, 203502 (2013); http://dx.doi.org/10.1063/1.4807312 (6 pages)

Online Publication Date: 22 May 2013

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The anisotropic optical and thermoelectric properties of In4Se3 and In4Te3 are studied by the first-principles calculation using the full-potential linearized augmented plane-wave method and the semiclassical Boltzmann theory. The optical properties show highly anisotropic in the energy range between 0.0 and 12.0 eV for In4Se3 and between 0.0 and 10.0 eV for In4Te3 while it is isotropic in the higher energy range for In4Se3. In contrast to S, the anisotropies of the electrical conductivities and power factors are great affected by the change of the temperature. Their anisotropies become larger along three directions with the growth of the temperature. S2σ/τ along the y direction is much higher than that along the x and z directions for In4Se3, which shows that the thermoelectric thin films with excellent performance can be obtained along the (010) surface. By studying the anisotropy of transport properties, we find that the transport properties of In4Se3 are better than that of In4Te3, which mainly comes from the small band gap of In4Se3. The anisotropy of S2σ/τ for In4Se3 is larger than that for In4Te3, and the anisotropy of S2σ/τ is mainly due to the anisotropy of σ/τ.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
73.50.Lw Thermoelectric effects
78.30.Hv Other nonmetallic inorganics
71.15.-m Methods of electronic structure calculations
back to top Electronic Structure and Transport

Effect of growth oxygen pressure on anisotropic-strain-induced phase separation in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films

Bowen Zhi, Guanyin Gao, Zhen Huang, Lingfei Wang, Xuelian Tan, Pingfan Chen, and Wenbin Wu

J. Appl. Phys. 113, 203701 (2013); http://dx.doi.org/10.1063/1.4807293 (5 pages)

Online Publication Date: 22 May 2013

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The effect of deposition oxygen pressure (PO) on phase separation (PS) induced in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films was investigated. Fully oxygenated films grown at high PO are anisotropically strained. They exhibit PS over a wide temperature range, because of the large orthorhombicity of NdGaO3 substrates. The paramagnetic insulator-to-ferromagnetic metal (FM) and FM-to-antiferromagnetic insulator (AFI) transitions gradually shift to lower temperatures with decreasing PO. The AFI state is initially weakened (PO ≥ 30 Pa), but then becomes more robust against the magnetic field (PO < 30 Pa). The out-of-plane film lattice parameter increases with decreasing PO. For films grown at PO ≥ 30 Pa, the slight oxygen deficiency may enlarge the lattice unit cell, reduce the anisotropic strain, and suppress the AFI state. Films deposited at PO < 30 Pa instead experience an average compressive strain. The enhanced compressive strain and structural defects in the films may lead to the robust AFI state. These results aid our understanding of PS in manganite films.
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68.55.A- Nucleation and growth
68.60.-p Physical properties of thin films, nonelectronic
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
62.50.-p High-pressure effects in solids and liquids
back to top Magnetism and Superconductivity

Nanorods of Co/Pd multilayers fabricated by glancing angle deposition for advanced media

Hao Su, Anusha Natarajarathinam, and Subhadra Gupta

J. Appl. Phys. 113, 203901 (2013); http://dx.doi.org/10.1063/1.4807168 (4 pages)

Online Publication Date: 22 May 2013

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Perpendicular anisotropy magnetic nanorods composed of Co/Pd multilayers have been successfully fabricated by glancing angle deposition (GLAD) in a planetary sputtering system. Co and Pd layer thickness, ratio, and bilayer number were optimized for both normal and GLAD depositions. Scanning electron micrographs estimated the nanorods to be about 12 nm in diameter. M-H loops showed that the coercivity for the GLAD nanorods increased from 1.3 kOe for the normally deposited continuous films to 2.9 kOe for the GLAD nanorod array, a 123% increase.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
75.75.Cd Fabrication of magnetic nanostructures
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Expanding the longitudinal magnetoimpedance sensor range by direct bias current

M. Ipatov, V. Zhukova, A. Zhukov, and J. Gonzalez

J. Appl. Phys. 113, 203902 (2013); http://dx.doi.org/10.1063/1.4807296 (6 pages)

Online Publication Date: 22 May 2013

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We investigated the effects of induced helical anisotropy and application of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwires both separately and together. We demonstrated that when both parameters are present, i.e., a dc bias current IB is applied to the microwire with induced helical anisotropy, the longitudinal MI sensor range can be considerably extended up to the fields considerably higher than its anisotropy field as the slope of MI curve dZ/dHE remains rather high. A highly asymmetric longitudinal MI dependence with a rather high slope at the zero-field point was obtained. Reversing the bias current IB causes reversal of the bias field direction and results in a mirroring of the MI dependence. This gives a possibility to determine both the sign and the magnitude of the external magnetic field. The obtained results can be used in development of the longitudinal MI sensors with increased sensitivity and/or range.
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07.55.-w Magnetic instruments and components
back to top Dielectrics and Ferroelectricity

Enhanced dielectric, ferroelectric, and electrostrictive properties of Pb(Mg1/3Nb2/3)0.9Ti0.1O3 ceramics by ZnO modification

Methee Promsawat, Anucha Watcharapasorn, Hamel N. Tailor, Sukanda Jiansirisomboon, and Zuo-Guang Ye

J. Appl. Phys. 113, 204101 (2013); http://dx.doi.org/10.1063/1.4801881 (6 pages)

Online Publication Date: 22 May 2013

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The effects of ZnO modification on the dielectric, ferroelectric, and electrostrictive properties of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (PMNT) ceramics are systematically studied in this work. The PMNT/xZnO (with x = 0, 0.4, 2.0, 4.0, and 11.0 mol. %) ceramics of complex perovskite structure were prepared by solid state reaction and sintering process. It is found that the maximum value of the dielectric constant decreases with increasing ZnO amount up to x = 4.0 mol. %, and then significantly increases with x = 11.0 mol. %. The temperature of maximum dielectric constant tends to increase, while the diffuseness of the dielectric peak is reduced, with increasing ZnO content. The remanent polarization and the coercive field increase with increasing ZnO concentration. The induced strain and the electrostrictive coefficient reach the maximum values of 0.10% (at E = 10 kV/cm) and 12.94 × 10−16 m2/V2, respectively, with x = 2.0 mol. % ZnO. The ceramic doped with a high ZnO content (11.0 mol. %) exhibits a macroscopically polar phase with a well-developed ferroelectric hysteresis loop and butterfly-shaped bipolar piezoelectric response. This enhanced long-range polarization and the resulting properties are attributed to the effects of the partial substitution of Zn2+ for Mg2+, which favors a higher degree of polar order and a lower degree of relaxor behavior.
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77.80.Dj Domain structure; hysteresis
77.80.Jk Relaxor ferroelectrics
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects

Kelvin force microscopy characterization of charging effect in thin a-SiOxNy:H layers deposited in pulsed plasma enhanced chemical vapor deposition process by tuning the Silicon-environment

C. Villeneuve-Faure, K. Makasheva, C. Bonafos, B. Despax, L. Boudou, P. Pons, and G. Teyssedre

J. Appl. Phys. 113, 204102 (2013); http://dx.doi.org/10.1063/1.4805026 (10 pages)

Online Publication Date: 22 May 2013

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Results from a study on the charging effect of a-SiOxNy:H thin layers are presented in this paper. Issues related to structural and electrical characterization of these layers are discussed. Spectroscopic ellipsometry was used to determine accurately the layer thickness and their optical properties, while the Kelvin Force Microscopy (KFM) was applied to characterize the local electrical properties of the layers. Obtained results reveal that by tuning the Si-environment in a-SiOxNy:H thin dielectric layers, deposited in plasma assisted process, a strong modification of the surface and volume charge conduction can be achieved. Particularly, increasing Si-content in the a-SiOxNy:H layers rises the volume conduction and charges retention. Thus, local electrical properties of thin dielectric layers can be engineered in order to meet specific requirements.
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68.55.at Other materials
73.61.Ng Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Effect of nanoparticle polarization on relative permittivity of transformer oil-based nanofluids

Jin Miao, Ming Dong, Ming Ren, Xuezhou Wu, Liangping Shen, and Hao Wang

J. Appl. Phys. 113, 204103 (2013); http://dx.doi.org/10.1063/1.4807297 (5 pages)

Online Publication Date: 22 May 2013

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Our experiments on a transformer oil-based nanofluid (NF) with ZnO nanoparticles reveal a higher relative permittivity than that of pure transformer oil. Meanwhile, the relative permittivity of ZnO NF presents a linear increase with nanoparticle volumetric concentration and a linear decrease with ambient temperature. A model based on nanoparticle polarization is proposed to investigate the mechanisms of NF relative permittivity. Analysis of the presented polarization model suggests that the value of the NF relative permittivity is dominantly determined by transformer oil, while the higher relative permittivity of NFs compared with that of pure oil is mainly caused by nanoparticle inner polarization.
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77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
back to top Nanoscale Science and Design

Bottom-up modeling of Al/Ni multilayer combustion: Effect of intermixing and role of vacancy defects on the ignition process

A. Hemeryck, J.-M. Ducéré, C. Lanthony, A. Estève, C. Rossi, M. Djafari-Rouhani, and D. Estève

J. Appl. Phys. 113, 204301 (2013); http://dx.doi.org/10.1063/1.4807164 (11 pages)

Online Publication Date: 22 May 2013

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Vapor deposited multilayered aluminum/oxide and bimetallics are promising materials for Micro Electro Mechanical System technologies as energy carriers, for instance, microinitiators or heat microsources in biological or chemical applications. Among these materials, the Al/Ni couple has received much attention both experimentally and theoretically. However, the detailed relation between the chemical composition of the intermixed interfacial regions and its impact on the ignition capabilities remains elusive. In this contribution, we propose a two-fold strategy combining atomistic density functional theory (DFT) calculations and a macroscopic 1D model of chemical kinetics. The DFT calculations allow the description of the elementary chemical processes (involving Al, Ni atoms and vacancies basic ingredients) and to parameterize the macroscopic model, in which the system is described as a stack of infinite layers. This gives the temporal evolution of the system composition and temperature. We demonstrate that the amount of vacancies, originating from the deposition process and the Al and Ni lattice mismatch, plays a critical role on both the ignition time and the temperature. The presence of vacancies enhances the migration of atoms between layers and so dramatically speeds up the atomic mixing at low temperatures far below ignition temperature, also pointing to the relation between experimental deposition procedures and ageing of the nanolaminates.
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64.75.Ef Mixing
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
82.20.Pm Rate constants, reaction cross sections, and activation energies
61.72.jd Vacancies
back to top Device Physics

Influence of anneal atmosphere on ZnO-nanorod photoluminescent and morphological properties with self-powered photodetector performance

S. M. Hatch, J. Briscoe, A. Sapelkin, W. P. Gillin, J. B. Gilchrist, M. P. Ryan, S. Heutz, and S. Dunn

J. Appl. Phys. 113, 204501 (2013); http://dx.doi.org/10.1063/1.4805349 (9 pages)

Online Publication Date: 22 May 2013

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ZnO nanorods synthesised using an aqueous pH 11 solution are shown to exhibit surface-sensitive morphology post-annealing in oxygen, air, and nitrogen as shown by scanning electron microscopy and transmission electron microscopy analysis. Raman analysis confirms the nanorods were nitrogen-doped and that nitrogen incorporation takes place during the synthesis procedure in the form of N-Hx. A strong green photoluminescence is observed post-annealing for all samples, the intensity of which is dependent on the atmosphere of anneal. This luminescence is linked to zinc vacancies as recent reports have indicated that these defects are energetically favoured with the annealing conditions used herein. ZnO-nanorod/CuSCN diodes are fabricated to examine the effect of material properties on photodetector device performance. The devices exhibit a photocurrent at zero bias, creating a self-powered photodetector. A photocurrent response of 30 μA (at 6 mW cm−2 irradiance) is measured, with a rise time of ∼25 ns, and sensitivity to both UV and visible light (475–525 nm).
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81.16.-c Methods of micro- and nanofabrication and processing
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing
78.55.Cr III-V semiconductors
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
85.60.Gz Photodetectors (including infrared and CCD detectors)

Nano-particle based scattering layers for optical efficiency enhancement of organic light-emitting diodes and organic solar cells

Hong-Wei Chang, Jonghee Lee, Simone Hofmann, Yong Hyun Kim, Lars Müller-Meskamp, Björn Lüssem, Chung-Chih Wu, Karl Leo, and Malte C. Gather

J. Appl. Phys. 113, 204502 (2013); http://dx.doi.org/10.1063/1.4807000 (8 pages)

Online Publication Date: 22 May 2013

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The performance of both organic light-emitting diodes (OLEDs) and organic solar cells (OSC) depends on efficient coupling between optical far field modes and the emitting/absorbing region of the device. Current approaches towards OLEDs with efficient light-extraction often are limited to single-color emission or require expensive, non-standard substrates or top-down structuring, which reduces compatibility with large-area light sources. Here, we report on integrating solution-processed nano-particle based light-scattering films close to the active region of organic semiconductor devices. In OLEDs, these films efficiently extract light that would otherwise remain trapped in the device. Without additional external outcoupling structures, translucent white OLEDs containing these scattering films achieve luminous efficacies of 46 lm W−1 and external quantum efficiencies of 33% (both at 1000 cd m−2). These are by far the highest numbers ever reported for translucent white OLEDs and the best values in the open literature for any white device on a conventional substrate. By applying additional light-extraction structures, 62 lm W−1 and 46% EQE are reached. Besides universally enhancing light-extraction in various OLED configurations, including flexible, translucent, single-color, and white OLEDs, the nano-particle scattering film boosts the short-circuit current density in translucent organic solar cells by up to 70%.
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88.40.H- Solar cells (photovoltaics)
88.40.J- Types of solar cells
85.60.Jb Light-emitting devices
back to top Interdisciplinary and General Physics

The effect of Na+ and K+ doping on the properties of sol-gel deposited 2-hydroxy-1,4-naphthoquinone thin films

Mahmoud Al-Omari, Kivanc Sel, Anja Mueller, Axel Mellinger, and Tolga Kaya

J. Appl. Phys. 113, 204901 (2013); http://dx.doi.org/10.1063/1.4805359 (6 pages)

Online Publication Date: 22 May 2013

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We describe the use of 2-hydroxy-1,4-naphthoquinone (HNQ) thin films as a potential water vapor and electrolyte sensing material towards the goal of non-invasive relative humidity and sweat detection. We have successfully made HNQ sol-gel thin films and studied the effects of sodium and potassium ions on their optical and electrical characteristics. Ultraviolet-visible absorbance and Fourier transform infrared spectroscopy measurements along with scanning electron microscopy demonstrated that we were able to dope HNQ thin films with Na+ and K+ ions, which are the main electrolyte contents in sweat. While the conductivity of thin films increased by at least an order of magnitude, energy band gaps decreased by doping HNQ with Na+ and K+ ions. Relative humidity test results showed that HNQ-based thin-films can be used as a sensing material for water vapor. Room temperature current-voltage measurements were also performed to determine the surface conductivity.
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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)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.am Polymers and organics
78.30.Jw Organic compounds, polymers
78.40.Me Organic compounds and polymers
73.61.Ph Polymers; organic compounds
73.25.+i Surface conductivity and carrier phenomena

Study of dopant activation in biaxially compressively strained SiGe layers using excimer laser annealing

G. V. Luong, S. Wirths, S. Stefanov, B. Holländer, J. Schubert, J. C. Conde, T. Stoica, U. Breuer, S. Chiussi, M. Goryll, D. Buca, and S. Mantl

J. Appl. Phys. 113, 204902 (2013); http://dx.doi.org/10.1063/1.4807001 (9 pages)

Online Publication Date: 22 May 2013

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Excimer Laser Annealing (ELA) with a wavelength of 248 nm is used to study doping of biaxialy compressively strained Si1−xGex/Si heterostructures. The challenge is to achieve a high activation of As in SiGe, while conserving the elastic strain and suppressing dopant diffusion. Doping of 20 nm Si0.64Ge0.36 layers by ion implantation of 1 × 1015 As+/cm2 and subsequent laser annealing using single 20 ns pulse with an energy density of 0.6 J/cm2 leads to an As activation of about 20% and a sheet resistance of 650 Ω/sq. At this laser energy density, the entire SiGe layer melts and the subsequent fast recrystallization on a nanosecond time scale allows high As incorporation into the lattice. Moreover, using these annealing parameters, the SiGe layer exhibits epitaxial regrowth with negligible strain relaxation. ELA at energy densities greater than 0.6 J/cm2 resembles Pulsed Lased Induced Epitaxy, leading to an intermixing of the SiGe layer with the Si substrate, thus to thicker single-crystalline strained SiGe layers with sheet resistance down to 62 Ω/sq. Effects of energy densities on composition, crystal quality, activation of As and co-doping with B are discussed and related to the spatial and temporal evolution of the temperature in the irradiated zone, as simulated by Finite Element Methods.
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61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si

Simulation and experiment of substrate aluminum grain orientation dependent self-ordering in anodic porous alumina

Chuan Cheng, K. Y. Ng, N. R. Aluru, and A. H. W. Ngan

J. Appl. Phys. 113, 204903 (2013); http://dx.doi.org/10.1063/1.4807295 (9 pages)

Online Publication Date: 22 May 2013

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Recent experiments have indicated a strong influence of the substrate grain orientation on the self-ordering in anodic porous alumina. Anodic porous alumina with straight pore channels grown in a stable, self-ordered manner is formed on (001) oriented Al grain, while disordered porous pattern is formed on (101) oriented Al grain with tilted pore channels growing in an unstable manner. In this work, numerical simulation of the pore growth process is carried out to understand this phenomenon. The rate-determining step of the oxide growth is assumed to be the Cabrera-Mott barrier at the oxide/electrolyte (o/e) interface, while the substrate is assumed to determine the ratio β between the ionization and oxidation reactions at the metal/oxide (m/o) interface. By numerically solving the electric field inside a growing porous alumina during anodization, the migration rates of the ions and hence the evolution of the o/e and m/o interfaces are computed. The simulated results show that pore growth is more stable when β is higher. A higher β corresponds to more Al ionized and migrating away from the m/o interface rather than being oxidized, and hence a higher retained O:Al ratio in the oxide. Experimentally measured oxygen content in the self-ordered porous alumina on (001) Al is indeed found to be about 3% higher than that in the disordered alumina on (101) Al, in agreement with the theoretical prediction. The results, therefore, suggest that ionization on (001) Al substrate is relatively easier than on (101) Al, and this leads to the more stable growth of the pore channels on (001) Al.
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61.72.Mm Grain and twin boundaries
81.65.Mq Oxidation
82.45.Gj Electrolytes
61.43.Gt Powders, porous materials
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