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14 Aug 2006

Volume 89, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 073501 (2006); http://dx.doi.org/10.1063/1.2335838 (3 pages)

Ingrid Graz, Martin Kaltenbrunner, Christoph Keplinger, Reinhard Schwödiauer, Siegfried Bauer, Stéphanie P. Lacour, and Sigurd Wagner
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Self-driven formation and structure of single crystal platelets of Zn3As2

N. Kouklin, S. Sen, and M. Gajdardziska-Josifovska

Appl. Phys. Lett. 89, 071901 (2006); http://dx.doi.org/10.1063/1.2335682 (3 pages) | Cited 3 times

Online Publication Date: 14 August 2006

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In this work the authors introduce and provide details on the stoichiometrically controlled self-driven formation of freestanding single crystal platelets in Zn3As2 by a direct self-catalytic vapor-solid growth mechanism. The platelets feature dimensions of up to ∼ 1 cm and mirrorlike microscopically flat top surfaces. A coherent formation of pyramids and wires has been further observed on some of the platelet top surfaces, the growth mechanism of which is discussed. This study might open pathways for facile engineering of high-performance semiconductor via a direct vapor-solid conversion of polycrystalline semiconductor powders into single crystal substrates on a large scale and with low cost.
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81.05.Hd Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Optimization of the surface and structural quality of N-face InN grown by molecular beam epitaxy

G. Koblmüller, C. S. Gallinat, S. Bernardis, J. S. Speck, G. D. Chern, E. D. Readinger, H. Shen, and M. Wraback

Appl. Phys. Lett. 89, 071902 (2006); http://dx.doi.org/10.1063/1.2335685 (3 pages) | Cited 54 times

Online Publication Date: 14 August 2006

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The authors demonstrate the impact of growth kinetics on the surface and structural properties of N-face InN grown by molecular beam epitaxy. Superior surface morphology with step-flow growth features is achieved consistently under In-rich conditions in a low-temperature region of 500–540 °C. Remarkably, off-axis x-ray rocking curve (ω scans) widths are found to be independent of the growth conditions. The band gap determined from optical absorption measurements of optimized InN is 0.651 eV, while photoluminescence peak emission occurs at even lower energies of ∼ 0.626 eV. Hall measurements show room temperature peak electron mobilities as high as 2370 cm2/V s at a carrier concentration in the low 1017 cm−3 region. Analysis of the thickness dependence of the carrier concentration demonstrates a n-type surface accumulation layer with a sheet carrier concentration of ∼ 3×1013 cm−2.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
71.20.Nr Semiconductor compounds

On the solute coupling at the moving solid/liquid interface during equiaxed solidification

X. Yao

Appl. Phys. Lett. 89, 071903 (2006); http://dx.doi.org/10.1063/1.2336079 (3 pages)

Online Publication Date: 14 August 2006

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Integral mass conservation was widely accepted for the solute coupling to solve solute redistribution during equiaxed solidification so far. The present study revealed that the integral form was invalid for moving boundary problems as it could not represent the mass balance at the moving interface. Accordingly, differential mass conservation at the solid/liquid interface was used to solve solute diffusion for spherical geometry. The model was applied for hydrogen diffusion in solidification to validate that the hydrogen enrichment was significant and depended on the growth rate.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
64.70.D- Solid-liquid transitions

Shear-strain induced decomposition of 1,1-diamino-2,2-dinitroethylene

M. M. Kuklja, S. N. Rashkeev, and F. J. Zerilli

Appl. Phys. Lett. 89, 071904 (2006); http://dx.doi.org/10.1063/1.2335680 (3 pages) | Cited 8 times

Online Publication Date: 15 August 2006

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The structural and electronic features of shear strains in the molecular crystal 1,1-diamino-2,2-dinitroethylene and their effect on decomposition of the material are investigated. The authors demonstrate that shear strains lower the decomposition barrier and narrow the band gap of the solid and thus facilitate thermal chemistry in molecular materials. The appearance of defect-related electronic states in the band gap is consistent with previous results for dislocation modeling in molecular solids and with experiments on energetic materials. The dynamic behavior of the band gap contains a rich variety of information about the details of the decomposition processes at the initiation stage.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
64.75.-g Phase equilibria
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.66.Hq Organic compounds

Influence of N incorporation on In content in GaInNAs/GaNAs quantum wells grown by plasma-assisted molecular beam epitaxy

H. F. Liu, N. Xiang, and S. J. Chua

Appl. Phys. Lett. 89, 071905 (2006); http://dx.doi.org/10.1063/1.2335804 (3 pages) | Cited 7 times

Online Publication Date: 15 August 2006

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The authors investigated the synthesis of GaIn(N)As/Ga(N)As multiple quantum wells by molecular beam epitaxy. Introducing N into the GaInAs appears to suppress the incorporation of In as indicated by reflective high-energy electron diffraction (RHEED). This effect is mainly due to the N-induced enhancement of In surface segregation at the growth front and is evidenced by the increasing damping rate of RHEED oscillations with N incorporation. The N-induced enhancement of In segregation in the GaInNAs quantum wells is confirmed by secondary-ion-mass spectroscopy and high-resolution x-ray diffractions, and its origin is discussed.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Dv Composition, segregation; defects and impurities
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

High hydrogen content complex hydrides: A density-functional study

P. Vajeeston, P. Ravindran, A. Kjekshus, and H. Fjellvåg

Appl. Phys. Lett. 89, 071906 (2006); http://dx.doi.org/10.1063/1.2217159 (3 pages) | Cited 26 times

Online Publication Date: 15 August 2006

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Density-functional-theory calculations within the generalized-gradient approximation are used to establish the ground-state structure, optimized geometry, and electronic structure for Mg(AlH4)2 and Mg(BH4)2. Among 28 structural arrangements used as inputs for structural optimization calculations, the experimentally known framework is reproduced for Mg(AlH4)2 (space group Pmathm1) with positional and unit-cell parameters in good agreement with the experimental findings. The crystal structure of Mg(BH4)2 is predicted, the ground-state framework being orthorhombic (space group Pmc21; Pearson symbol oP22 with a fascinating two-dimensional arrangement of Mg2+ ions and [BH4]2− tetrahedra. The formation energy for the predicted Mg(BH4)2 phase is investigated along different reaction pathways. The electronic structures reveal that Mg(AlH4)2 and Mg(AlH4)2 are insulators with calculated band gaps of around 4.5 and 6.2 eV, respectively.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
61.66.Fn Inorganic compounds
84.60.-h Direct energy conversion and storage

Thickness of shear bands in metallic glasses

Y. Zhang and A. L. Greer

Appl. Phys. Lett. 89, 071907 (2006); http://dx.doi.org/10.1063/1.2336598 (3 pages) | Cited 88 times

Online Publication Date: 15 August 2006

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A review of measurements and atomistic modeling shows that shear bands in metallic glasses have a characteristic thickness of ∼ 10 nm. Such extreme localization of plastic deformation, within a thicker liquidlike layer implied by fracture-surface morphology, cannot have a thermal origin. By analogy with granular materials, the thickness is linked to the local structural rearrangements required to generate dilatation. This analysis suggests that first-coordination-shell clusters may be significant structural units in metallic glasses.
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61.43.Fs Glasses
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.M- Structural failure of materials
61.43.Bn Structural modeling: serial-addition models, computer simulation

Work hardening ability of ductile Ti45Cu40Ni7.5Zr5Sn2.5 and Cu47.5Zr47.5Al5 bulk metallic glasses

K. B. Kim, J. Das, S. Venkataraman, S. Yi, and J. Eckert

Appl. Phys. Lett. 89, 071908 (2006); http://dx.doi.org/10.1063/1.2337534 (3 pages) | Cited 24 times

Online Publication Date: 16 August 2006

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Ductile Ti45Cu40Ni7.5Zr5Sn2.5 and Cu47.5Zr47.5Al5 bulk metallic glasses (BMGs) present different work hardening abilities under compression. Microstructural investigations reveal that nanoscale chemical heterogeneities occur throughout the samples. The morphology of the chemically heterogeneous domains in the as-cast Ti45Cu40Ni7.5Zr5Sn2.5 BMG is irregular and significantly interconnected. In contrast, the as-cast Cu47.5Zr47.5Al5 BMG exhibits a spherical morphology of the chemically heterogeneous regions. Furthermore, the distribution of the nanoscale chemical heterogeneity is macroscopically inhomogeneous throughout the material. These findings suggest that the different work hardening abilities of the Ti45Cu40Ni7.5Zr5Sn2.5 and Cu47.5Zr47.5Al5 BMGs possibly originate from the different morphologies and distributions of the chemically heterogeneous regions.
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61.43.Fs Glasses
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.F- Deformation and plasticity

Melt dispersion mechanism for fast reaction of nanothermites

Valery I. Levitas, Blaine W. Asay, Steven F. Son, and Michelle Pantoya

Appl. Phys. Lett. 89, 071909 (2006); http://dx.doi.org/10.1063/1.2335362 (3 pages) | Cited 38 times

Online Publication Date: 16 August 2006

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An unexpected mechanism for fast oxidation of Al nanoparticles covered by a thin oxide shell (OS) is proposed. The volume change due to melting of Al induces pressures of 0.1–4 GPa and causes spallation of the OS. A subsequent unloading wave creates high tensile pressures resulting in dispersion of liquid Al clusters, oxidation of which is not limited by diffusion (in contrast to traditional mechanisms). Physical parameters controlling this process are determined. Methods to promote this melt dispersion mechanism, and consequently, improve efficiency of energetic nanothermites are discussed.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
82.40.Fp Shock wave initiated reactions, high-pressure chemistry
82.60.Qr Thermodynamics of nanoparticles
82.70.-y Disperse systems; complex fluids

Binary eutectic clusters and glass formation in ideal glass-forming liquids

Z. P. Lu, J. Shen, D. W. Xing, J. F. Sun, and C. T. Liu

Appl. Phys. Lett. 89, 071910 (2006); http://dx.doi.org/10.1063/1.2336597 (3 pages) | Cited 27 times

Online Publication Date: 16 August 2006

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In this letter, a physical concept of binary eutectic clusters in “ideal” glass-forming liquids is proposed based on the characteristics of most well-known bulk metallic glasses (BMGs). The authors approach also includes the treatment of binary eutectic clusters as basic units, which leads to the development of a simple but reliable method for designing BMGs more efficiently and effectively in these unique glass-forming liquids. As an example, bulk glass formers with superior glass-forming ability in the Zr–Ni–Cu–Al and Zr–Fe–Cu–Al systems were identified with the use of the strategy.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses
61.25.Mv Liquid metals and alloys
81.05.Kf Glasses (including metallic glasses)

Hexagonal diamond synthesis on h-GaN strained films

Abha Misra, Pawan K. Tyagi, Brajesh S. Yadav, P. Rai, D. S. Misra, Vivek Pancholi, and I. D. Samajdar

Appl. Phys. Lett. 89, 071911 (2006); http://dx.doi.org/10.1063/1.2218043 (3 pages) | Cited 7 times

Online Publication Date: 17 August 2006

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Chemical vapor deposited diamond films grown on strained gallium nitride-coated quartz substrate are found to display a dominantly hexagonal diamond phase. The phase identification is done using Raman spectroscopy and orientation imaging microscopy (OIM). The presence of a 1324.4 cm−1 band in the Raman spectra is attributed to a hexagonal diamond symmetry, but the unambiguous signature of the hexagonal phase is confirmed by OIM. A phase map of the sample clearly shows that 88% of the scanned sample area is hexagonal diamond.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Am Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Buckling of C60 whiskers

Koji Asaka, Ryoei Kato, Kun’ichi Miyazawa, and Tokushi Kizuka

Appl. Phys. Lett. 89, 071912 (2006); http://dx.doi.org/10.1063/1.2336590 (3 pages) | Cited 12 times

Online Publication Date: 17 August 2006

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The authors demonstrated the mechanics of materials for crystalline whiskers composed of C60 molecules; compressive deformation of the whiskers was observed by in situ transmission electron microscopy with simultaneous force measurement by means of an optical cantilever method, as used in atomic force microscopy. In response to compression along the long axis, the whiskers bent first elastically, then buckled. A whisker with 160 nm diameter fractured brittlely at a strain of 0.08. According to Euler’s formula, Young’s modulus of the whisker was estimated to be 32–54 GPa, which is 160%–650% of that of C60 bulk crystals.
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81.05.ub Fullerenes and related materials
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.F- Deformation and plasticity

Low compressible noble metal carbides with rocksalt structure: Ab initio total energy calculations of the elastic stability

Chang-Zeng Fan, Song-Yan Zeng, Zai-Ji Zhan, Ri-Ping Liu, Wen-Kui Wang, Ping Zhang, and Yu-Gui Yao

Appl. Phys. Lett. 89, 071913 (2006); http://dx.doi.org/10.1063/1.2335571 (3 pages) | Cited 23 times

Online Publication Date: 17 August 2006

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The authors have systematically studied the mechanical stability of all noble metal carbides with a rocksalt structure by calculating their elastic constants within the density function theory scheme. It was found that only four carbides (RuC, PdC, AgC, and PtC) are mechanically stable. In particular, the authors have shown that RuC, PdC, and PtC have very high bulk modulus, which has been remarkably observed by the most recent experiment for the case of PtC. From the calculated density of states, it can be concluded that these compounds are metallic, like the conventional group IV and group V transition metal carbides.
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62.20.D- Elasticity
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Room temperature gas sensitivity of ultrathin SnO2 films prepared from Langmuir-Blodgett film precursors

Sipra Choudhury, C. A. Betty, K. G. Girija, and S. K. Kulshreshtha

Appl. Phys. Lett. 89, 071914 (2006); http://dx.doi.org/10.1063/1.2336725 (3 pages) | Cited 10 times

Online Publication Date: 17 August 2006

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The authors report the room temperature gas sensitivity of ultrathin SnO2 films prepared by thermal decomposition of multilayer Langmuir-Blodgett (LB) films. The SnO2 films, which are characterized by various spectroscopic techniques and electrical measurements, have been shown to sense ammonia gas at room temperature with fast response and recovery. The presence of a large number of surface states in the ultrathin SnO2 film is responsible for the room temperature gas sensitivity. Present results demonstrate the potential of LB technique to fabricate high quality ultrathin oxide films useful for sensor applications.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.Le Other inorganic semiconductors
81.05.Hd Other semiconductors
73.20.At Surface states, band structure, electron density of states

Groups III and V impurity solubilities in silicon due to laser, flash, and solid-phase-epitaxial-regrowth anneals

R. Duffy, T. Dao, Y. Tamminga, K. van der Tak, F. Roozeboom, and E. Augendre

Appl. Phys. Lett. 89, 071915 (2006); http://dx.doi.org/10.1063/1.2337081 (3 pages) | Cited 15 times

Online Publication Date: 17 August 2006

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In this work the authors studied impurity solubilities of groups III and V elements in silicon resulting from laser anneal, flash anneal, and solid-phase-epitaxial regrowth. Rutherford backscattering channeling analysis was used to determine substitutional impurity depth profiles generated from the difference between the random and aligned spectra. Despite the large difference in peak temperatures and times, the anneals produce similar results with maximum solubilities beating the maximum equilibrium values by one to two orders of magnitude depending on the impurity. The correlation between the metastable solubility and the equilibrium distribution coefficient allows a prediction of values for other impurities not extracted experimentally.
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64.75.-g Phase equilibria
61.72.S- Impurities in crystals
61.72.uf Ge and Si
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.15.Np Solid phase epitaxy; growth from solid phases
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Migration and redistribution of oxygen vacancy in barium titanate ceramics

L. Chen, X. M. Xiong, H. Meng, P. Lv, and J. X. Zhang

Appl. Phys. Lett. 89, 071916 (2006); http://dx.doi.org/10.1063/1.2337097 (3 pages) | Cited 15 times

Online Publication Date: 17 August 2006

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Degradation of barium titanate based multilayer capacitor mainly results from migration and redistribution of oxygen vacancy. For barium titanate ceramics, the authors observe an internal friction relaxation peak around 70 °C due to oxygen vacancy, and its relaxation strength differs greatly for specimen aged at 85 °C for 120 h and at 150 °C for 5 h. Two possible explanations are proposed, one based on symmetry-conforming short-range order while the other on the interaction between oxygen vacancy and domain wall during aging process. In any case, relaxation thermodynamics is a powerful tool to investigate the migration and redistribution of oxygen vacancy in barium titanate ceramics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging

Conformational flexibility and its effect on the vibrationally resolved absorption and fluorescence spectra of oligofluorenes

Jian Song, Wan Zhen Liang, Yi Zhao, and Jinlong Yang

Appl. Phys. Lett. 89, 071917 (2006); http://dx.doi.org/10.1063/1.2337530 (3 pages) | Cited 7 times

Online Publication Date: 18 August 2006

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The authors present a first-principles density-functional theory study on the electronic excitation of oligofluorenes. Their results indicate that the strong electron-nuclear coupling results in a dynamic structural distortion in the S1 state, which extends over eight monomers in the center of the long chain and contributes a relaxation energy of ∼ 0.23 eV. The field-induced density matrices evidence that the excitons localize in the regions where the structural alternations occur. The asymmetry of absorption and fluorescence spectra of oligofluorenes is significantly pronounced. The experimentally observed spectroscopic features are reasonably reproduced by properly taking into account the anharmonic torsional potentials without any adjustable parameters.
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42.70.Jk Polymers and organics
78.30.Jw Organic compounds, polymers
33.20.Ea Infrared spectra
33.50.Dq Fluorescence and phosphorescence spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

Surface morphologies of homoepitaxial ZnO on Zn- and O-polar substrates by plasma assisted molecular beam epitaxy

Huaizhe Xu, K. Ohtani, M. Yamao, and H. Ohno

Appl. Phys. Lett. 89, 071918 (2006); http://dx.doi.org/10.1063/1.2337541 (3 pages) | Cited 21 times

Online Publication Date: 18 August 2006

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Homoepitaxial ZnO layers are grown on Zn-polar (0001) and O-polar (000math) surfaces of single crystal ZnO substrates by plasma assisted molecular beam epitaxy. It is found that the growth conditions to obtain smooth surfaces are significantly different for the two surface polarities. For growth on Zn-polar surface, moderate temperature (650 °C) and highly O-rich condition (low Zn/O2) are required, while high temperature (1000–1050 °C) and Zn-rich condition (high Zn/O2 ratio) are essential for growth on O-polar surfaces.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.A- Nucleation and growth
68.47.Fg Semiconductor surfaces
52.77.-j Plasma applications

Local epitaxial growth of aluminum nitride and molybdenum thin films in fiber texture using aluminum nitride interlayer

Toshihiro Kamohara, Morito Akiyama, Naohiro Ueno, Kazuhiro Nonaka, and Noriyuki Kuwano

Appl. Phys. Lett. 89, 071919 (2006); http://dx.doi.org/10.1063/1.2337558 (3 pages) | Cited 5 times

Online Publication Date: 18 August 2006

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The authors have found the local epitaxial growth of aluminum nitride (AlN) and molybdenum (Mo) films in fiber texture, although the interface between the AlN and Mo films has different crystal symmetries. The local heteroepitaxial relationship is (0001)AlN[2mathmath0]‖(110)Mo[math11]‖(0001)AlN[2mathmath0]. The AlN films changes from nonequiaxed microstructures to equiaxed columnar structures. The authors think that the AlN interlayer is effective in decreasing the crystallization energy of the Mo electrode due to the coherent heteroepitaxial nucleation. It is interesting that the local heteroepitaxial relationship does not satisfy the criteria for heteroepitaxial growth.
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81.05.Ea III-V semiconductors
81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth

Observation of secondary relaxation in a fragile Pd40Ni10Cu30P20 bulk metallic glass

Zuo Feng Zhao, Ping Wen, Wei Hua Wang, and C. H. Shek

Appl. Phys. Lett. 89, 071920 (2006); http://dx.doi.org/10.1063/1.2337876 (3 pages) | Cited 12 times

Online Publication Date: 18 August 2006

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The dynamic elastic moduli in the temperature domain of a Pd40Ni10Cu30P20 bulk metallic glass were measured with dynamic mechanical spectroscopy at frequencies less than 100 Hz. The primary relaxation is characterized by a single loss modulus peak and a rapid drop of storage modulus in the metallic supercooled liquid region. Below the conventional glass transition temperature, a pronounced shoulder in the loss modulus curves appears and the corresponding storage modulus decreases with increasing temperature. The phenomenon is common to glass formers of all types. The observations present the evidence of the existence of the slow β relaxation and affirm the universality of the separation of the primary and secondary relaxations in the supercooled liquid.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses

Red-light-emitting diodes fabricated by near-ultraviolet InGaN chips with molybdate phosphors

Zhengliang Wang, Hongbin Liang, Jing Wang, Menglian Gong, and Qiang Su

Appl. Phys. Lett. 89, 071921 (2006); http://dx.doi.org/10.1063/1.2335579 (3 pages) | Cited 42 times

Online Publication Date: 18 August 2006

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Phosphors Na5La(MoO4)4:xEu3+ and NaEu(MoO4)2 were prepared with a solid-state reaction technique. Their photoluminescent properties were investigated at room temperature. Bright red-light-emitting diodes were fabricated by coating the phosphors onto near-ultraviolet/violet-emitting InGaN chips, respectively. The diodes prepared with phosphor Na5Eu(MoO4)4 show appropriate CIE chromaticity coordinates (x = 0.65,y = 0.34) and exhibit more intensive red emission than that prepared with NaEu(MoO4)2, indicating that Na5Eu(MoO4)4 may be applied as an excellent red component for near-ultraviolet InGaN-based white diodes.
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85.60.Jb Light-emitting devices
78.55.Hx Other solid inorganic materials

Photoluminescence and multiphonon resonant Raman scattering in low-temperature grown ZnO nanostructures

Bhupendra Kumar, Hao Gong, Shue Yin Chow, Sudhiranjan Tripathy, and Younan Hua

Appl. Phys. Lett. 89, 071922 (2006); http://dx.doi.org/10.1063/1.2336997 (3 pages) | Cited 30 times

Online Publication Date: 18 August 2006

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The authors report on the optical properties of nanocrystalline ZnO grown at 200 °C by radio-frequency magnetron sputtering. The nanocrystalline nature of the films was confirmed by cross-sectional transmission electron microscopy. In these films, ZnO nanocrystals with an average size of about 3–5 nm were embedded in an amorphous matrix. The photoluminescence spectra from such nanostructured thin films show the near-band-edge emissions around 3.3 eV. A redshift of about 8–11 cm−1 is observed in the case of first-order longitudinal-optical (LO) phonon of ZnO in such nanostructures when compared to the LO phonon peak of bulk ZnO. The ultraviolet resonant Raman excitation at 77 K shows multiphonon LO modes up to eighth order.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
68.55.A- Nucleation and growth
61.46.-w Structure of nanoscale materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Optical determination of three-dimensional nanotrack profiles generated by single swift-heavy ion impacts in lithium niobate

J. Olivares, A. García-Navarro, G. García, A. Mýndez, and F. Agulló-López

Appl. Phys. Lett. 89, 071923 (2006); http://dx.doi.org/10.1063/1.2236221 (3 pages) | Cited 13 times

Online Publication Date: 18 August 2006

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Three-dimensional (3D) profiles of single nanotracks generated by a low impact density of Cl ions at 46 MeV have been determined by optical methods, using an effective-medium approach. The buried location of the maximum stopping power induces a surface optical waveguiding layer even at ultralow fluences (1011–1013 at./cm2) that allows to obtain the effective refractive index profiles (from dark-mode measurements). Combining the optical information with Rutherford backscattering spectroscopy/channeling experiments, the existence of a surrounding defective halo around the amorphous track core has been ascertained. The 3D profile of the halo has also been determined.
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81.16.-c Methods of micro- and nanofabrication and processing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
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