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23 Mar 2009

Volume 94, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 94, 122502 (2009); http://dx.doi.org/10.1063/1.3100783 (3 pages)

Junhua Wang, Yisheng Shi, Juexian Cao, and Ruqian Wu
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An acoustic emission study of the effect of a magnetic field on the martensitic transition in Ni2MnGa

Benno Ludwig, Christian Strothkaemper, Uwe Klemradt, Xavier Moya, Lluís Mañosa, Eduard Vives, and Antoni Planes

Appl. Phys. Lett. 94, 121901 (2009); http://dx.doi.org/10.1063/1.3103289 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2009

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Acoustic emission measurements during the martensitic transition of a Ni–Mn–Ga magnetic shape-memory alloy reveal the intermittent and jerky character of the transition. The distribution of the amplitude of the acoustic emission events shows power law behavior, which reflects the absence of characteristic scales in the process. In this paper we show that the distribution is affected by an applied magnetic field, which proves that the transition dynamics is strongly influenced by magnetostructural coupling taking place at multiple length scales. The martensitic start temperature and the power law exponent of the amplitude distribution are measured in dependence of the applied field.
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62.65.+k Acoustical properties of solids
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions

Pulsed metal-organic chemical vapor deposition of high-quality AlN/GaN superlattices for near-infrared intersubband transitions

C. Bayram, N. Péré-laperne, R. McClintock, B. Fain, and M. Razeghi

Appl. Phys. Lett. 94, 121902 (2009); http://dx.doi.org/10.1063/1.3104857 (3 pages) | Cited 15 times

Online Publication Date: 23 March 2009

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A pulsed metal-organic chemical vapor deposition technique is developed for the growth of high-quality AlN/GaN superlattices (SLs) with intersubband (ISB) transitions at optical communications wavelengths. Tunability of the AlN and GaN layers is demonstrated. Indium is shown to improve SL surface and structural quality. Capping thickness is shown to be crucial for ISB transition characteristics. Effects of barrier- and well-doping on the ISB absorption are reported.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.Cd Superlattices
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

On the anisotropic shear resistance of hard transition metal nitrides TMN (TM = Ti, Zr, Hf)

R. F. Zhang, S. H. Sheng, and S. Veprek

Appl. Phys. Lett. 94, 121903 (2009); http://dx.doi.org/10.1063/1.3105990 (3 pages) | Cited 9 times

Online Publication Date: 23 March 2009

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The anisotropic shear moduli and strengths of hard fcc-TMN (TM = Ti, Zr, Hf) have been calculated by ab initio density functional theory in order to better understand their shear resistance. TiN shows the largest shear strength among the three nitrides, being consistent with the known facts that TiN is harder than HfN which is harder than ZrN. The electronic origin is further addressed. Based on the smooth shapes of the stress-strain curves and on the variation of electronic structure during shear deformations, the abrupt lattice instability mode reported previously for TiN (110)〈1math0〉 shear deformation is not supported by our data.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Correlations between elastic moduli and molar volume in metallic glasses

J. Q. Wang, W. H. Wang, H. B. Yu, and H. Y. Bai

Appl. Phys. Lett. 94, 121904 (2009); http://dx.doi.org/10.1063/1.3106110 (3 pages) | Cited 7 times

Online Publication Date: 23 March 2009

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We report clear correlations between bulk modulus (K) and average molar volume Vm, and between Poisson’s ratio ν and Vm for various bulk metallic glasses. The origin for the correlations between elastic moduli and Vm are discussed. The established correlation, associated with Poisson’s ratio ν, and since the ν correlates with plasticity of metallic glasses, indicates that the average molar volume is important factor to be considered for plastic metallic glasses searching. The found correlations also suggest a close relation between the mechanical properties and the short-range atomic bonding, and assist in understanding deformation behavior in metallic glasses.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Conditions to cancel the laser polarization dependence of a subwavelength tip

J. Houard, A. Vella, F. Vurpillot, and B. Deconihout

Appl. Phys. Lett. 94, 121905 (2009); http://dx.doi.org/10.1063/1.3095829 (3 pages) | Cited 6 times

Online Publication Date: 23 March 2009

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Using laser assisted atom probe tomography, we investigate the polarization dependence of the absorption coefficient of a subwavelength Al tip illuminated by an ultrashort laser pulse. In practice, we find an equilibrium condition as a function of the incident wavelength for which the atom evaporation rate becomes independent of the wave polarization. It is experimentally shown that this condition only depends on the ratio between the tip radius and the laser wavelength. Furthermore, our calculations demonstrate that a transverse local plasmon polariton mode can be resonantly excited at the tip apex.
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07.60.Pb Conventional optical microscopes
07.79.Cz Scanning tunneling microscopes
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.22.Lp Collective excitations
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Lateral epitaxial overgrowth of (0001) AlN on patterned sapphire using hydride vapor phase epitaxy

Scott A. Newman, Derrick S. Kamber, Troy J. Baker, Yuan Wu, Feng Wu, Zhen Chen, Shuji Namakura, James S. Speck, and Steven P. DenBaars

Appl. Phys. Lett. 94, 121906 (2009); http://dx.doi.org/10.1063/1.3089253 (3 pages) | Cited 3 times

Online Publication Date: 24 March 2009

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Coalesced, crack-free (0001) AlN films were grown on stripe patterned sapphire substrates without AlN seed layers using hydride vapor phase epitaxy. Using templates with stripes oriented in the 〈11math0〉sapphire direction, lateral epitaxial overgrowth AlN films were coalesced over trench regions as wide as 10 μm despite parasitic sidewall and trench growth. Using transmission electron microscopy, a reduction in the dislocation density from 1.6×109 cm−2 in the seed region to less than 1.0×108 cm−2 in the wing region was demonstrated. Atomic force microscopy and cathodoluminescence measurements were also performed to assess the material quality.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Lk Linear defects: dislocations, disclinations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Ea III-V semiconductors

Growth of deformation twins in room-temperature rolled nanocrystalline nickel

X. Y. Zhang, X. L. Wu, and A. W. Zhu

Appl. Phys. Lett. 94, 121907 (2009); http://dx.doi.org/10.1063/1.3104858 (3 pages) | Cited 6 times

Online Publication Date: 24 March 2009

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Deformation twinning has been observed in room-temperature rolled nanocrystalline Ni. The growth of the deformation twins via the emission of partial dislocations from a grain boundary has been examined in detail. Partial dislocations on neighboring slip planes may migrate for different distances and then remain in the grain interior, leading to the formation of a steplike twin boundary (TB). With continued twin growth, the TBs become gradually distorted and lose their coherent character due to accumulated high stresses. Moreover, we propose that microtwins may form near such TBs due to the emission of partial dislocations from the TB.
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61.72.Mm Grain and twin boundaries
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
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Introduction of molecular scale porosity into semicrystalline polymer thin films using supercritical carbon dioxide

Peter Gin, Mitsunori Asada, Maya K. Endoh, Cynthia Gedelian, Toh-Ming Lu, and Tadanori Koga

Appl. Phys. Lett. 94, 121908 (2009); http://dx.doi.org/10.1063/1.3104851 (3 pages) | Cited 3 times

Online Publication Date: 26 March 2009

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We report supercritical carbon dioxide (scCO2) technology used for forming a large degree of molecular scale porosity in semicrystalline polymer thin films. The following three steps were integrated: (i) pre-exposure to an organic solvent which melted crystalline structures but did not cause a decrease in thickness, (ii) scCO2 exposure under the unique conditions where the anomalous absorption of CO2 occurred, and (iii) subsequent quick evaporation of CO2 to preserve the swollen structures. This unified process resulted in homogenous low-density polyphenylene vinylene films (a 15% reduction in density) with the sustained structure for at least 6 months at room temperature.
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61.43.Gt Powders, porous materials
64.70.F- Liquid-vapor transitions
61.41.+e Polymers, elastomers, and plastics
68.55.am Polymers and organics

Polarization field mapping of Al0.85In0.15N/AlN/GaN heterostructure

Lin Zhou, David A. Cullen, David J. Smith, Martha R. McCartney, Anas Mouti, M. Gonschorek, E. Feltin, J. F. Carlin, and N. Grandjean

Appl. Phys. Lett. 94, 121909 (2009); http://dx.doi.org/10.1063/1.3108084 (3 pages) | Cited 9 times

Online Publication Date: 27 March 2009

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Off-axis electron holography has been used to measure the built-in potential profile across an Al0.85In0.15N/AlN/GaN high electron mobility transistor heterostructure. Profile measurements indicated a polarization-induced electric field of 6.9 MV/cm within the AlN layer. A two-dimensional electron gas with a density of ∼ 2.1×1013 cm−2 was located in the GaN layer at ∼ 0.8 nm away from the AlN/GaN interface in reasonable agreement with the reported simulations. Electron microscopy confirmed that the Al0.85In0.15N layer was uniform and that Al0.85In0.15N/AlN and AlN/GaN interfaces were abrupt and well defined.
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85.30.Tv Field effect devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Formation energies of antisite defects in Y3Al5O12: A first-principles study

Bo Liu, Mu Gu, Xiaolin Liu, Shiming Huang, and Chen Ni

Appl. Phys. Lett. 94, 121910 (2009); http://dx.doi.org/10.1063/1.3109799 (3 pages) | Cited 6 times

Online Publication Date: 27 March 2009

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We perform the first-principles calculations for the formation energies of cation antisite defects in Y3Al5O12. This method provides precise values of formation energy and thus allows us to estimate the defect concentration. The calculations show that YAl,16a is the most predominant antisite defects at high temperature for the single crystal growth and its concentration significantly decreases at low temperature for the single-crystalline film preparation. The calculated defect concentrations are quantitatively accord with the experimental estimation. AlY has high formation energy even with excess Al2O3, which indicates AlY is energetically unfavorable and the defect process is not intrinsic but nonstoichiometry.
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61.72.J- Point defects and defect clusters
61.72.Bb Theories and models of crystal defects
71.55.Ht Other nonmetals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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