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3 Dec 2012

Volume 101, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 233101 (2012); http://dx.doi.org/10.1063/1.4749281 (3 pages)

S. A. Studenikin, J. Thorgrimson, G. C. Aers, A. Kam, P. Zawadzki, Z. R. Wasilewski, A. Bogan, and A. S. Sachrajda
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Lattice strains and polarized luminescence in homoepitaxial growth of a-plane ZnO

Hiroaki Matsui and Hitoshi Tabata

Appl. Phys. Lett. 101, 231901 (2012); http://dx.doi.org/10.1063/1.4769036 (4 pages)

Online Publication Date: 3 December 2012

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In-plane lattice strains in a-plane zinc oxide (ZnO) homoepitaxial layers were selectively introduced by changing substrate type and growth conditions. Strain-free layers were observed when using a Crystec ZnO substrate, which resulted in atomically flat surfaces with nano-facets consisting of the m-plane (10-10) at atomic scale. In contrast, ZnO layers on Goodwill ZnO substrates possessed in-plane lattice strains due to generation of basal-plane stacking faults. The degree of lattice strains was systematically changed by the oxygen pressure, which clarified the close correlation between photoluminescence (PL) polarization and lattice strains. The polarization ratio of PL enhanced with the lattice strains.
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78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors

Nanosecond pulsed laser blackening of copper

Guang Tang, Andrew C. Hourd, and Amin Abdolvand

Appl. Phys. Lett. 101, 231902 (2012); http://dx.doi.org/10.1063/1.4769215 (4 pages) | Cited 1 time

Online Publication Date: 4 December 2012

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Nanosecond (12 ns) pulsed laser processing of copper at 532 nm resulted in the formation of homogenously distributed, highly organized microstructures. This led to the fabrication of large area black copper substrates with absorbance of over 97% in the spectral range from 250 nm to 750 nm, and a broadband absorbance of over 80% between 750 nm and 2500 nm. Optical and chemical analyses of the fabricated black metal are presented and discussed. The employed laser is an industrially adaptable source and the presented technique for fabrication of black copper could find applications in broadband thermal radiation sources, solar energy absorbers, irradiative heat transfer devices, and thermophotovoltaics.
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81.65.-b Surface treatments
78.47.J- Ultrafast spectroscopy (<1 psec)
42.62.Cf Industrial applications

Applied stress controls the production of nano-twins in coarse-grained metals

Y. Cao, Y. B. Wang, X. Z. Liao, M. Kawasaki, S. P. Ringer, T. G. Langdon, and Y. T. Zhu

Appl. Phys. Lett. 101, 231903 (2012); http://dx.doi.org/10.1063/1.4769216 (5 pages) | Cited 2 times

Online Publication Date: 4 December 2012

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We present evidence that the level of the applied stress plays a critical role in deformation twinning in face-centred cubic alloys. While conventional cold rolling of a face-centred cubic structure produces a microstructure with a high-density of extended dislocations, increasing the applied stress using high-pressure torsion gives a nano-twinned coarse-grained structure. This suggests the existence of a critical stress for deformation twinning which thereby delineates an approach for the production of nano-twinned microstructures in coarse-grained materials with superior mechanical properties.
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61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
62.50.-p High-pressure effects in solids and liquids

Competing nonlinearities with metamaterials

Polina V. Kapitanova, Alexey P. Slobozhnanyuk, Ilya V. Shadrivov, Pavel A. Belov, and Yuri S. Kivshar

Appl. Phys. Lett. 101, 231904 (2012); http://dx.doi.org/10.1063/1.4768945 (4 pages)

Online Publication Date: 4 December 2012

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We suggest an approach for creating metamaterials with sign-varying nonlinear response. We demonstrate that microwave metamaterials with such competing nonlinearities can be created by loading split-ring resonators (“meta-atoms” of the structure) with pairs of varactor diodes and photodiodes exhibiting nonmonotonic resonance frequency shift with changing incident microwave power. Additionally, the nonlinear response of such metamaterials can be controlled by illuminating the meta-atoms by light.
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42.70.-a Optical materials
42.65.-k Nonlinear optics

Inverse melting in stressed fused silica

Philippe Bouchut

Appl. Phys. Lett. 101, 231905 (2012); http://dx.doi.org/10.1063/1.4769357 (4 pages)

Online Publication Date: 5 December 2012

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The emissive properties of proton implanted fused silica surfaces have been studied by laser beam annealing. When submitted to a high thermal step from a focused CO2 laser, an intense near infra-red thermoluminescence peak rises at a heating rate threshold. The in plane tensile stress relaxes and silica melts. We show that in the irreversible inverse melting of stressed fused silica, the protons exo-diffuse through internal modes coupling. The heat and mass transfer is one entropy flux whose dynamics are regulated by the mass transport. Inverse melting is the thermodynamic process that initiates the glass transition when heating.
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64.70.dj Melting of specific substances
61.72.Cc Kinetics of defect formation and annealing
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
65.40.De Thermal expansion; thermomechanical effects
78.60.Kn Thermoluminescence

Mitigating residual stress in Cu metallization

Conal E. Murray, Jean Jordan-Sweet, E. Todd Ryan, and Michael F. Toney

Appl. Phys. Lett. 101, 231906 (2012); http://dx.doi.org/10.1063/1.4769366 (4 pages)

Online Publication Date: 5 December 2012

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The application of a cryogenic thermal excursion to passivated copper films has been demonstrated to dramatically reduce the magnitude of residual stress and to induce compressive, in-plane stress at room temperature. In-situ x-ray diffraction measurements reveal the evolution of in-plane stress within SiCxNyHz and TaN capped Cu films, which undergo significant plastic behavior on cooling and as the film approaches room temperature during heating. The resulting compressive stress represents a more favorable condition to mitigate voiding within the metallization. In-situ and ex-situ measurements of SiCxNyHz capped Cu films reveal that the final stress state is independent of cooling rate.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Microstructure and martensitic transformation in the Fe-Mn-Al-Ni shape memory alloy with B2-type coherent fine particles

T. Omori, M. Nagasako, M. Okano, K. Endo, and R. Kainuma

Appl. Phys. Lett. 101, 231907 (2012); http://dx.doi.org/10.1063/1.4769375 (4 pages)

Online Publication Date: 5 December 2012

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Microstructure and martensitic transformation yielding a magnetic change were investigated for Fe43.5Mn34Al15Ni7.5 alloy with B2-type fine precipitates. Thermoelastic martensitic transformation from the ferromagnetic parent phase to the weak magnetic martensite with a nano-twinned fcc structure was confirmed. High-angle annular dark-field scanning transmission electron microscopic observation revealed that a β particle of about 10 nm maintains coherency with the matrix martensite phase, even though distorted due to the martensitic transformation. The martensitic transformation temperatures decreased about 75 K by application of a magnetic field of 70 kOe and magnetic field-induced reverse martensitic transformation was confirmed.
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81.30.Kf Martensitic transformations
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
61.72.Mm Grain and twin boundaries
75.50.Bb Fe and its alloys

Thermal conductivity of nano-grained SrTiO3 thin films

Brian M. Foley, Harlan J. Brown-Shaklee, John C. Duda, Ramez Cheaito, Brady J. Gibbons, Doug Medlin, Jon F. Ihlefeld, and Patrick E. Hopkins

Appl. Phys. Lett. 101, 231908 (2012); http://dx.doi.org/10.1063/1.4769448 (4 pages) | Cited 2 times

Online Publication Date: 6 December 2012

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We measure the thermal conductivities of nano-grained strontium titanate (ng-SrTiO3) films deposited on sapphire substrates via time-domain thermoreflectance. The 170 nm thick oxide films of varying grain-size were prepared from a chemical solution deposition process. We find that the thermal conductivity of ng-SrTiO3 decreases with decreasing average grain size and attribute this to increased phonon scattering at grain boundaries. Our data are well described by a model that accounts for the spectral nature of anharmonic Umklapp scattering along with grain boundary scattering and scattering due to the film thickness.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
78.20.N- Thermo-optic effects
61.46.-w Structure of nanoscale materials
63.20.Ry Anharmonic lattice modes
63.20.kd Phonon-electron interactions
63.20.kg Phonon-phonon interactions

Evaluation on residual stress in Bi3.15(Eu0.7Nd0.15)Ti3O12 polycrystalline ferroelectric thin film by using the orientation average method

Y. Wei, H. B. Cheng, X. Y. Wang, and X. J. Zheng

Appl. Phys. Lett. 101, 231909 (2012); http://dx.doi.org/10.1063/1.4769811 (4 pages)

Online Publication Date: 6 December 2012

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We propose an orientation average method to evaluate residual stresses in polycrystalline thin films. Bi3.15(Eu0.7Nd0.15)Ti3O12 was used to verify our approach, with films prepared by metal organic decomposition at various annealing temperatures. The mechanical properties and microstructure were characterized by nanoindentation and X-ray diffraction. The thin film annealed at 600 °C has the largest residual compressive stress of 771 MPa among all thin films. The residual stresses are evaluated by the proposed method and traditional sin2ψ method, and the maximum distinction is less than 6.43%, demonstrating that the proposed method is reliable and convenient to evaluate residual stress in polycrystalline thin films.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.55.A- Nucleation and growth
77.55.fp Other ferroelectric films
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.40.Gh Other heat and thermomechanical treatments

Growth analysis of (Ag,Cu)InSe2 thin films via real time spectroscopic ellipsometry

S. A. Little, V. Ranjan, R. W. Collins, and S. Marsillac

Appl. Phys. Lett. 101, 231910 (2012); http://dx.doi.org/10.1063/1.4769902 (4 pages)

Online Publication Date: 7 December 2012

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In situ and ex situ characterization methods have been applied to investigate the properties of (Ag,Cu)InSe2 (ACIS) thin films. Data acquired from real time spectroscopic ellipsometry (RTSE) experiments were analyzed to extract the evolution of the nucleating, bulk, and surface roughness layer thicknesses. The evolution of these layer thicknesses suggests a transition from Volmer-Weber to Stranski-Krastanov type behavior when Cu is replaced by Ag. The complex dielectric functions of ACIS at both deposition and room temperature as a function of film composition were also extracted from the RTSE data, enabling parameterization of the alloy optical properties.
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68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Li Other semiconductors
81.05.Hd Other semiconductors
81.15.Cd Deposition by sputtering
68.35.bg Semiconductors

A visualization of threading dislocations formation and dynamics in mosaic growth of GaN-based light emitting diode epitaxial layers on (0001) sapphire

P. Ravadgar, R. H. Horng, and S. L. Ou

Appl. Phys. Lett. 101, 231911 (2012); http://dx.doi.org/10.1063/1.4769905 (5 pages)

Online Publication Date: 7 December 2012

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A clear visualization of the origin and characteristics of threading dislocations (TDs) of GaN-based light emitting diode epitaxial layers on (0001) sapphire substrates have been carried out. Special experimental set up and chemical etchant along with field emission scanning electron microscopy are employed to study the dynamics of GaN TDs at different growth stages. Cross-sectional transmission electron microscopy analysis visualized the formation of edge TDs is arising from extension of coalescences at boundaries of different tilting-twining nucleation grains “mosaic growth.” Etch pits as representatives of edge TDs are in agreement with previous theoretical models and analyses of TDs core position and characteristics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries
78.66.Fd III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
85.60.Jb Light-emitting devices
68.55.ag Semiconductors
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