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17 Aug 2009

Volume 95, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 073703 (2009); http://dx.doi.org/10.1063/1.3152768 (3 pages)

Mohammud R. Noor, Swati Goyal, Shawn M. Christensen, and Samir M. Iqbal
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Carbon nanotube induced enhancement of electroluminescence of phosphor

Min Jong Bae, Shang Hyeun Park, Tae Won Jeong, Jeong Hee Lee, In Taek Han, Yong Wan Jin, Jong Min Kim, Jin-Young Kim, Ji Beom Yoo, and Se Gi Yu

Appl. Phys. Lett. 95, 071901 (2009); http://dx.doi.org/10.1063/1.3196430 (3 pages) | Cited 7 times

Online Publication Date: 17 August 2009

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Electroluminescence (EL) was observed on conventional cathodoluminescent (CL) phosphor with the incorporation of carbon nanotube (CNT) at ambient air. The role of CNT can be understood as enhancing the local electrical field, which allows electron injection to the active center of phosphor at relatively low operating voltages. In this EL device, the brightness of CL phosphor was significantly improved from no light emission in the case of no addition of CNT to 35 cd/m2 with 1 wt % CNT at 10 kHz of ac 300 V.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
78.60.Fi Electroluminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Fg Nanotubes
78.67.Ch Nanotubes
78.60.Hk Cathodoluminescence, ionoluminescence

Tailoring UV cure depth profiles for optimal mechanical properties of organosilicate thin films

Taek-Soo Kim, Dmytro Chumakov, Ehrenfried Zschech, and Reinhold H. Dauskardt

Appl. Phys. Lett. 95, 071902 (2009); http://dx.doi.org/10.1063/1.3190198 (3 pages) | Cited 2 times

Online Publication Date: 18 August 2009

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The adhesive and cohesive properties of organosilicate thin films are remarkably insensitive to UV curing. We demonstrate how to maximize these properties with UV standing waves together with an optical spacer underlying layer. Using a simulation of the UV cure profile through the film thickness, we demonstrate how a UV transparent SiN optical spacer layer can be selected to maximize curing at both sides of the organosilicate film with marked increases in interfacial fracture energy. On the contrary, a UV absorbing SiCN underlying layer resulted in significantly reduced UV intensities and small improvements of the interfacial fracture energies.
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68.60.Wm Other nonelectronic physical properties
68.55.am Polymers and organics
82.50.-m Photochemistry
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.25.Mn Fracture/brittleness
62.20.mm Fracture

Quasifree Mg–H thin films

A. Baldi, V. Palmisano, M. Gonzalez-Silveira, Y. Pivak, M. Slaman, H. Schreuders, B. Dam, and R. Griessen

Appl. Phys. Lett. 95, 071903 (2009); http://dx.doi.org/10.1063/1.3210791 (3 pages) | Cited 15 times

Online Publication Date: 19 August 2009

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The thermodynamics of hydrogen absorption in Pd-capped Mg films are strongly dependent on the magnesium thickness. In the present work, we suppress such dependency by inserting a thin Ti layer between Mg and Pd. By means of optical measurements, we show that the surface energy contribution to the destabilization of MgH2 is negligible. The inserted Ti layer prevents Mg–Pd alloy formation at the Mg/Pd interface, leading to quasifree Mg films and enhancing the kinetics of hydrogen desorption. Our observations are important for the development of thin film devices.
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68.55.jd Thickness
68.43.Nr Desorption kinetics
65.40.gp Surface energy

Nucleation tendency and crystallizing phase in silicate glasses: A structural aspect

Yoshihiro Takahashi, Hirokazu Masai, and Takumi Fujiwara

Appl. Phys. Lett. 95, 071904 (2009); http://dx.doi.org/10.1063/1.3206931 (3 pages) | Cited 6 times

Online Publication Date: 19 August 2009

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We consider the relationship of nucleation tendency with crystallizing-phase structures in silicate glasses using glassy sanbornite (1BaO–2SiO2) that shows homogeneous nucleation resulting crystallization of Ba5Si8O21 and β-BaSi2O5 phases with a layered structure of a network modifier and a network former. This trend is also confirmed in other silicate glasses with homogeneous nucleation tendency, which has been assessed by Zanotto and other researchers. It is suggested that the structural dimension of the crystallizing phase governs the nucleation tendency in silicate glasses.
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61.43.Fs Glasses
64.60.qj Studies of nucleation in specific substances
64.70.kj Glasses

Indium migration paths in V-defects of InAlN grown by metal-organic vapor phase epitaxy

Th. Kehagias, G. P. Dimitrakopulos, J. Kioseoglou, H. Kirmse, C. Giesen, M. Heuken, A. Georgakilas, W. Neumann, Th. Karakostas, and Ph. Komninou

Appl. Phys. Lett. 95, 071905 (2009); http://dx.doi.org/10.1063/1.3204454 (3 pages) | Cited 25 times

Online Publication Date: 20 August 2009

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InAlN thin films grown on GaN/Al2O3 (0001) templates by metal-organic vapor phase epitaxy were studied by transmission electron microscopy techniques. V-defects in the form of hexagonal inverted pyramids with {10math1} sidewalls were observed on the films’ surfaces linked to the termination of threading dislocations. Their origin is explained by the different surface atom mobility of In and Al and the built-in strain relaxation. Indium segregation in the films is influenced by the formation of V-defects, the edges and the apexes of which function as paths of migrating indium atoms diffusing along nanopipes formed at the open-core threading dislocations.
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66.30.Lw Diffusion of other defects
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
68.35.Dv Composition, segregation; defects and impurities
71.55.Eq III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Enhancing plasticity of Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass by precompression

J. L. Zhang, H. B. Yu, J. X. Lu, H. Y. Bai, and C. H. Shek

Appl. Phys. Lett. 95, 071906 (2009); http://dx.doi.org/10.1063/1.3211112 (3 pages) | Cited 10 times

Online Publication Date: 21 August 2009

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Precompression treatments on Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass rods with tapered ends induced controllable stress distributions and resulted in residual stress accompanied with a few tiny shear bands after unloading. The built-in stress state increased macroscopic plasticity dramatically and produced predictable distributions of shear bands in the cylindrical samples cut from the taper-ended samples. The macroscopic plasticity was interpreted in terms of the competition among different types of shear bands.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
46.35.+z Viscoelasticity, plasticity, viscoplasticity
81.05.Kf Glasses (including metallic glasses)
46.70.Hg Membranes, rods, and strings

Strong and ductile nanostructured Cu-carbon nanotube composite

Hongqi Li, Amit Misra, Zenji Horita, Carl C. Koch, Nathan A. Mara, Patricia O. Dickerson, and Yuntian Zhu

Appl. Phys. Lett. 95, 071907 (2009); http://dx.doi.org/10.1063/1.3211921 (3 pages) | Cited 13 times

Online Publication Date: 21 August 2009

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Nanocrystalline carbon nanotube (CNT)—reinforced Cu composite (grain size <25 nm) with high strength and good ductility was developed. Pillar testing reveals that its strength and plastic strain could be as large as 1700 MPa and 29%, respectively. Compared with its counterpart made under the same condition, an addition of 1 wt % CNTs leads to a dramatic increase in strength, stiffness and toughness without a sacrifice in ductility. Microstructural analysis discloses that in the Cu matrix, CNTs could be distributed either at grain boundaries or inside grains and could inhibit dislocation nucleation and motion, resulting in an increase in the strength.
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62.23.Pq Composites (nanosystems embedded in a larger structure)
61.46.-w Structure of nanoscale materials
81.40.Lm Deformation, plasticity, and creep
62.20.fk Ductility, malleability
62.20.fq Plasticity and superplasticity
61.72.Mm Grain and twin boundaries
61.46.Fg Nanotubes
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.25.-g Mechanical properties of nanoscale systems

Intermediate-band material based on GaAs quantum rings for solar cells

Jiang Wu, Dali Shao, Zhenhua Li, M. O. Manasreh, Vasyl P. Kunets, Zhiming M. Wang, and G. J. Salamo

Appl. Phys. Lett. 95, 071908 (2009); http://dx.doi.org/10.1063/1.3211971 (3 pages) | Cited 13 times

Online Publication Date: 21 August 2009

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The intermediate-band concept is invoked to explain the photoresponse spectra obtained for unbiased devices fabricated from GaAs quantum rings grown by a droplet epitaxy technique on lattice-matched Al0.3Ga0.7As barriers. The photoresponse spectra where measured at room temperature in the visible-near-infrared spectral range. The presence of the intermediate band in the device active region is confirmed by measuring the mid-infrared photoresponse, which is attributed to the intersubband transitions in the conduction band. The photocurrent was measured at room temperature and found to be about four orders of magnitude larger than the dark current in the voltage range of ± 4.0 V.
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84.60.Jt Photoelectric conversion
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.63.Bd Nanocrystalline materials
73.63.Kv Quantum dots
78.30.Fs III-V and II-VI semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
72.40.+w Photoconduction and photovoltaic effects
78.67.Hc Quantum dots
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Precursive stage of nanocrystallization in niobium oxide-containing glass

Yoshihiro Takahashi, Hirokazu Masai, Minoru Osada, and Takumi Fujiwara

Appl. Phys. Lett. 95, 071909 (2009); http://dx.doi.org/10.1063/1.3211989 (3 pages) | Cited 9 times

Online Publication Date: 21 August 2009

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In situ observation of inelastic light scattering in Raman and Boson regions was performed in a niobiogermanate glass with a high nucleation ability during heating in order to examine its nanocrystallization dynamics. The relation of structural heterogeneity to the precursive stage of crystallization is also discussed. It is suggested that evolution of nuclei occurs in a nanometric niobate-rich region due to density fluctuation in the supercooled liquid phase prior to nanocrystallization.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
64.60.Q- Nucleation
64.70.ph Nonmetallic glasses (silicates, oxides, selenides, etc.)
42.65.-k Nonlinear optics
42.70.Ce Glasses, quartz
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Crystallization times of Ge–Te phase change materials as a function of composition

S. Raoux, H.-Y. Cheng, M. A. Caldwell, and H.-S. P. Wong

Appl. Phys. Lett. 95, 071910 (2009); http://dx.doi.org/10.1063/1.3212732 (3 pages) | Cited 28 times

Online Publication Date: 21 August 2009

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The crystallization times of Ge–Te phase change materials with variable Ge concentrations (29.5–72.4 at. %) were studied. A very strong dependence of the crystallization time on the composition for as-deposited, amorphous films was confirmed, with a minimum for the stoichiometric composition GeTe. The dependence is weaker for melt-quenched, amorphous material and crystallization times are between one to almost four orders of magnitude shorter than for as-deposited materials. This is promising for applications because recrystallization from the melt-quenched phase is the relevant process for optical and solid state memory, and fast crystallization and weak dependence on compositional variations are desirable.
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64.70.kg Semiconductors
42.70.Gi Light-sensitive materials
68.60.-p Physical properties of thin films, nonelectronic
61.66.Bi Elemental solids
61.66.Dk Alloys
81.40.Gh Other heat and thermomechanical treatments

Grain boundary complexions: The interplay of premelting, prewetting, and multilayer adsorption

Jian Luo

Appl. Phys. Lett. 95, 071911 (2009); http://dx.doi.org/10.1063/1.3212733 (3 pages) | Cited 8 times

Online Publication Date: 21 August 2009

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A thermodynamic model for coupled adsorption and disordering transitions at grain boundaries is developed by combining diffuse-interface and lattice-gas models and incorporating colloidal type interfacial forces. This model produces a systematical spectrum of interfacial phenomena for grain boundaries, including first-order and continuous coupled prewetting and premelting transitions, critical points, multilayer adsorption, layering and roughening, and complete wetting and drying, and it produces a series of grain boundary “phases” (complexions) with character similar to those observed by [ Dillon et al., Acta Mater. 55, 6208 (2007) ]. The presence of dispersion and electrostatic forces in ceramic materials can appreciably change grain boundary transitions.
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61.72.Mm Grain and twin boundaries
64.70.K- Solid-solid transitions
64.60.Cn Order-disorder transformations
68.43.Mn Adsorption kinetics
68.08.Bc Wetting
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