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5 Mar 2007

Volume 90, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 90, 101901 (2007); http://dx.doi.org/10.1063/1.2712772 (3 pages)

S. N. Yi, Jong H. Na, Kwan H. Lee, Anas F. Jarjour, Robert A. Taylor, Y. S. Park, T. W. Kang, S. Kim, D. H. Ha, G. Andrew, and D. Briggs
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Photoluminescence properties of a single GaN nanorod with GaN/AlGaN multilayer quantum disks

S. N. Yi, Jong H. Na, Kwan H. Lee, Anas F. Jarjour, Robert A. Taylor, Y. S. Park, T. W. Kang, S. Kim, D. H. Ha, G. Andrew, and D. Briggs

Appl. Phys. Lett. 90, 101901 (2007); http://dx.doi.org/10.1063/1.2712772 (3 pages) | Cited 14 times

Online Publication Date: 5 March 2007

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Photoluminescence (PL) properties of a single nanorod containing multiple GaN quantum disks separated by AlGaN potential barriers are investigated using micro-PL spectroscopy. Previous studies reported ensemble spectra from many nanorods. The PL spectra show different features depending on the region of the nanorod excited by the laser, including a sharp feature originating from the quantum disk region. The distinct differences between the PL from the different regions are discussed. The results imply that excitons are strongly confined in the quantum disks, and the authors suggest that small quantum disks can be regarded as quantum dots having a discrete density of states.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena

Study of the defect elimination mechanisms in aspect ratio trapping Ge growth

J. Bai, J.-S. Park, Z. Cheng, M. Curtin, B. Adekore, M. Carroll, A. Lochtefeld, and M. Dudley

Appl. Phys. Lett. 90, 101902 (2007); http://dx.doi.org/10.1063/1.2711276 (3 pages) | Cited 21 times

Online Publication Date: 5 March 2007

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Recent research has demonstrated the effectiveness of the “aspect ratio trapping” technique for eliminating threading dislocations in Ge grown selectively in submicron trenches on Si substrates. In this letter, analysis of the mechanisms by which dislocation elimination is achieved has been carried out. Detailed transmission electron microscopy studies reveal that facets, when formed early in the growth process, play a dominant role in determining the configurations of threading dislocations in the films. These dislocations are shown to behave as “growth dislocations,” which are replicated during growth approximately along the facet normal and so are deflected out from the center of the selective epitaxial regions.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.A- Nucleation and growth
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Epitaxial growth and magnetic properties of La0.7Sr0.3MnO3 films on (0001) sapphire

V. Bhosle and J. Narayan

Appl. Phys. Lett. 90, 101903 (2007); http://dx.doi.org/10.1063/1.2472537 (3 pages) | Cited 5 times

Online Publication Date: 5 March 2007

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In this letter the authors report the growth of (110) oriented La0.7Sr0.3MnO3 films on (0001) single-crystal sapphire substrate. Growth of La0.7Sr0.3MnO3 (LSMO) films with a fixed orientation was achieved by carefully controlling the deposition conditions, specifically the substrate temperature. The fixed orientation relationship between the film and the sapphire substrate ((110)f‖(0002)s, (math10)f‖(0math10)s, (002)f‖(math110)s), has been explained via domain matching epitaxy, where there is perfect matching in one direction and 19% planar misfit in the perpendicular direction. LSMO films showed interesting magnetic anisotropy along the two mutually perpendicular in-plane directions, corresponding to [002]f as strong and [math10]f as weak magnetization directions.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials

Synchrotron x-ray study of polycrystalline wurtzite Zn1−xMgxO (0 ⩽ x ⩽ 0.15): Evolution of crystal structure and polarization

Young-Il Kim, Katharine Page, and Ram Seshadri

Appl. Phys. Lett. 90, 101904 (2007); http://dx.doi.org/10.1063/1.2711289 (3 pages) | Cited 18 times

Online Publication Date: 6 March 2007

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The effect of Mg substitution on the crystal structure of wurtzite ZnO is presented based on synchrotron x-ray diffraction studies of polycrystalline Zn1−xMgxO ( ⩽ x ⩽ 0.15). Increase in Mg concentration results in pronounced c-axis compression of the hexagonal lattice, and in diminution of the off-center cation displacement within each tetrahedral ZnO4 unit. Going from ZnO to Zn0.85Mg0.15O, significant changes in the ionic polarization are observed (−5.6 to −4.8 μC/cm2), despite only subtle increments in the cell volume ( ∼ 0.03%) and the ab-area dimension ( ∼ 0.1%).
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61.66.Fn Inorganic compounds
71.55.Gs II-VI semiconductors

Alloying induced degradation of the absorption edge of InAsxSb1−x

Bhavtosh Bansal, V. K. Dixit, V. Venkataraman, and H. L. Bhat

Appl. Phys. Lett. 90, 101905 (2007); http://dx.doi.org/10.1063/1.2711388 (3 pages) | Cited 4 times

Online Publication Date: 6 March 2007

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InAsxSb1−x alloys show a strong bowing in the energy gap, the energy gap of the alloy can be less than the gap of the two parent compounds. The authors demonstrate that a consequence of this alloying is a systematic degradation in the sharpness of the absorption edge. The alloy disorder induced band-tail (Urbach tail) characteristics are quantitatively studied for InAs0.05Sb0.95.
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71.20.Nr Semiconductor compounds

Diffusion on (110) surface of molecular crystal pentaerythritol tetranitrate

Jian Wang, Ted Golfinopoulos, Richard H. Gee, and Hanchen Huang

Appl. Phys. Lett. 90, 101906 (2007); http://dx.doi.org/10.1063/1.2709955 (3 pages) | Cited 1 time

Online Publication Date: 6 March 2007

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Using classical molecular dynamics simulations, the authors investigate the diffusion mechanisms of admolecules on the (110) surface of molecular crystal pentaerythritol tetranitrate. The results show that admolecules (1) are stable at off-lattice sites, (2) diffuse along close-packed [1math1] and [math11] directions, and (3) detach from the surface at 350 K and above. Based on the number of diffusion jumps as a function of temperature, The authors estimate the jump frequency to be v = 1.14×1012 e−0.08eV/kT/s.
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68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation

Martensite nucleation on dislocations in Cu–Al–Ni shape memory alloys

A. Ibarra, D. Caillard, J. San Juan, and M. L. Nó

Appl. Phys. Lett. 90, 101907 (2007); http://dx.doi.org/10.1063/1.2710076 (3 pages) | Cited 14 times

Online Publication Date: 6 March 2007

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In the present work, the martensite nucleation on dislocations has been observed. Cu–Al–Ni shape memory alloys have been superelastic cycled inside the transmission electron microscope. The in situ experiences show that the dislocations in β phase can be a nucleation site for γ3′ and β3′ martensites, which at the same time have been characterized by electron diffraction. The martensite plates can nucleate on the dislocations when the stress is applied and retransform to the βL21 phase when the sample is unloaded. The results are discussed in terms of the atomic configuration of the dislocation core, which facilitates the martensite nucleation.
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81.40.Lm Deformation, plasticity, and creep
81.30.Kf Martensitic transformations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Technique for azimuthal anchoring measurement of nematic liquid crystals using magnetic field induced deformation

Jong-Hyun Kim and Hyunchul Choi

Appl. Phys. Lett. 90, 101908 (2007); http://dx.doi.org/10.1063/1.2711662 (3 pages) | Cited 1 time

Online Publication Date: 6 March 2007

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The authors devised a technique for measuring the azimuthal anchoring coefficient of nematic liquid crystals. The coefficient was estimated calculating the varying ratio of magnetic coherence length to extrapolation length using light transmission to magnetic field. The paralleled control of the directors on the entrance surface, polarizer axis and magnetic field enables the transmission to sensitively reflect the anchoring. The extrapolation length was 0.48 μm for polyimide rubbed surface, 0.56 μm for rubbed poly-vinyl alcohol and 5.6 μm for photo-aligned polyimide. This technique has advantages such as insensitiveness to sample adjustment, covering wide range of anchoring and independence on the cell gap, electrodes and impurity.
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61.30.Vx Polymer liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Jf Defects in liquid crystals

First-principles elastic constants of α- and θ-Al2O3

Shunli Shang, Yi Wang, and Zi-Kui Liu

Appl. Phys. Lett. 90, 101909 (2007); http://dx.doi.org/10.1063/1.2711762 (3 pages) | Cited 33 times

Online Publication Date: 7 March 2007

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Using an efficient strain-stress method, the first-principles elastic constants cij’s of α-Al2O3 and θ-Al2O3 have been predicted within the local density approximation and the generalized gradient approximation. It is indicated that more accurate calculations of cij’s can be accomplished by the local density approximation. The predicted cij’s of θ-Al2O3 provide helpful guidance for future measurements, especially the predicted negative c15. The present results make the stress estimation in thermally grown oxides containing of α- and θ-Al2O3 possible, which in turn provide helpful insights for preventing the failure of thermal barrier coatings on components in gas-turbine engines.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Synthesis and photoluminescence of Mn-doped zinc sulfide nanoparticles

Dongyeon Son, Dae-Ryong Jung, Jongmin Kim, Taeho Moon, Chunjoong Kim, and Byungwoo Park

Appl. Phys. Lett. 90, 101910 (2007); http://dx.doi.org/10.1063/1.2711709 (3 pages) | Cited 27 times

Online Publication Date: 8 March 2007

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Mn-doped zinc sulfide nanoparticles were synthesized using a liquid-solid-solution method, as a simple synthetic route for preparing nearly monodispersed nanocrystals with a diameter of 7.3±0.7 nm. The influence of doping concentration for optimum luminescence properties was studied with the nonuniform distribution of local strain and the capping effect. The improved photoluminescence properties of the 450 °C-annealed samples with 1.0 at. % Mn doping are attributed to both the removal of water/organics and the enhanced crystallinity (reduced local strain).
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81.05.Dz II-VI semiconductors
81.10.Dn Growth from solutions
78.55.Et II-VI semiconductors
61.72.up Other materials
61.66.Fn Inorganic compounds
61.72.Cc Kinetics of defect formation and annealing

Transformation-induced plasticity in an ultrafine-grained steel: An in situ neutron diffraction study

Kaixiang Tao, Hahn Choo, Hongqi Li, Bjørn Clausen, Jae-Eun Jin, and Young-Kook Lee

Appl. Phys. Lett. 90, 101911 (2007); http://dx.doi.org/10.1063/1.2711758 (3 pages) | Cited 25 times

Online Publication Date: 8 March 2007

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An ultrafine-grained steel with an average grain size of about 350 nm was developed. The tensile testing at ambient temperature shows a threefold increase in the yield strength compared to its coarse-grained counterpart. Moreover, the increase in the strength was achieved without the sacrifice of the ductility due to strain-induced martensitic transformation. The evolution of lattice strains and phase fractions of the austenite and martensite phases during the deformation was investigated using in situ neutron diffraction to provide a micromechanical understanding of the transformation-induced plasticity responsible for the combination of high strength and ductility.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
64.70.K- Solid-solid transitions

Superhard nanocomposite of dense polymorphs of boron nitride: Noncarbon material has reached diamond hardness

Natalia Dubrovinskaia, Vladimir L. Solozhenko, Nobuyoshi Miyajima, Vladimir Dmitriev, Oleksandr O. Kurakevych, and Leonid Dubrovinsky

Appl. Phys. Lett. 90, 101912 (2007); http://dx.doi.org/10.1063/1.2711277 (3 pages) | Cited 33 times

Online Publication Date: 8 March 2007

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The authors report a synthesis of unique superhard aggregated boron nitride nanocomposites (ABNNCs) showing the enhancement of hardness up to 100% in comparison with single crystal c-BN. Such a great hardness increase is due to the combination of the Hall-Petch and the quantum confinement effects. The decrease of the grain size down to 14 nm and the simultaneous formation of the two dense BN phases with hexagonal and cubic structures within the grains at nano- and subnanolevel result in enormous mechanical property enhancement with maximum hardness of 85(5) GPa. Thus, ABNNC is the first non-carbon-based bulk material with the value of hard-ness approaching that of single crystal and polycrystalline diamond and aggregated diamond nanorods. ABNNC also has an unusually high fracture toughness for superhard materials (K1C = 15 MPa m0.5) and wear resistance (WH = 11; compare, for industrial polycrystalline diamond, WH = 3–4), in combination with high thermal stability (above 1600 K in air), making it an exceptional superabrasive.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
61.46.Hk Nanocrystals
81.07.Bc Nanocrystalline materials

Temperature dependence of the photoluminescence emission from thiol-capped PbS quantum dots

L. Turyanska, A. Patanè, M. Henini, B. Hennequin, and N. R. Thomas

Appl. Phys. Lett. 90, 101913 (2007); http://dx.doi.org/10.1063/1.2711529 (3 pages) | Cited 26 times

Online Publication Date: 8 March 2007

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The authors report the temperature dependence of the near-infrared photoluminescence (PL) emission from thiol-capped PbS quantum dots. The high thermal stability of the PL allows the authors to study the thermal broadening of the dot emission over an extended temperature range (4–300 K). The authors show that the linewidth of the dot PL emission is strongly enhanced at temperatures above 150 K. This behavior is attributed to dephasing of the quantum electronic states by carrier interaction with longitudinal optical phonons. The authors’ data also indicate that the strength of the carrier-phonon coupling is larger in smaller dots.
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78.67.Hc Quantum dots
78.55.Hx Other solid inorganic materials
73.21.La Quantum dots
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.-e Phonons in crystal lattices

Kinetically constraint zero- and one-dimensional heteroepitaxial island growth

Zhipeng Li, Manish Kumar Singh, Eng Soon Tok, Joyce Pei Ying Tan, Ming Lin, and Yong-Lim Foo

Appl. Phys. Lett. 90, 101914 (2007); http://dx.doi.org/10.1063/1.2711402 (3 pages) | Cited 6 times

Online Publication Date: 8 March 2007

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Direct observation of the dynamics, formation, and selective growth of low dimensional epitaxial Fe13Ge8 structures [zero-dimensional (0D) compact islands or one-dimensional (1D) wires of different aspect ratios] was conducted in real time using in situ ultra high vacuum transmission electron microscopy at 350, 430, 480, and 510 °C. Both types of island (0D/1D) share the same epitaxial relation to the underlying Ge substrate. The compact islands are formed preferentially at lower deposition temperature while wires, which are kinetically constrained, at higher temperature. The effective Ea for growth along two orthogonal azimuths of an Fe13Ge8 island are 0.17 and 0.95 eV. The temperature dependence in morphological evolution is due to anisotropy in corner barriers and ledge diffusion on orthogonal azimuths during growth.
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81.07.Vb Quantum wires
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.65.La Quantum wires (patterned in quantum wells)
66.30.-h Diffusion in solids

Observation of strain and temperature induced changes in the band structure of thin La0.8MnO3−δ films

T. A. Tyson, Q. Qian, M. A. DeLeon, C. Dubourdieu, L. Fratila, Y. Q. Cai, and K. H. Ahn

Appl. Phys. Lett. 90, 101915 (2007); http://dx.doi.org/10.1063/1.2711779 (3 pages)

Online Publication Date: 9 March 2007

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Mn K-edge resonant inelastic x-ray scattering measurements were performed on films of La0.8MnO3−δ. The measurements reveal that strain causes large shifts of the bands above the Fermi level. The Mn 3d band switches from a narrow upshifted peak at high temperature to a broad bulklike band at low temperature in ultrathin films. The strain induced switching behavior opens the possibility of tuning the transition to higher temperatures for device applications in this class of manganite materials.
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71.20.Ps Other inorganic compounds
68.60.Bs Mechanical and acoustical properties
78.70.Ck X-ray scattering

Evidence for “superfilling” of submicrometer trenches with electroless copper deposit

Madoka Hasegawa, Noriyuki Yamachika, Yosi Shacham-Diamand, Yutaka Okinaka, and Tetsuya Osaka

Appl. Phys. Lett. 90, 101916 (2007); http://dx.doi.org/10.1063/1.2712505 (3 pages) | Cited 14 times

Online Publication Date: 9 March 2007

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Void-free copper filling of trenches for ultralarge scale integrated interconnect structure was demonstrated by electroless deposition technique using polyethylene glycol as an inhibiting bath additive. With this electroless plating bath, the authors succeeded in demonstrating superfilling. Of particular interest is that the deposition at trench opening was nil during the filling process, while that at the bottom was very fast. This letter presents a demonstration and a proof of superfilling of trenches by electroless copper deposition.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Sz Deposition technology

Direct evidence on magnetic-field-induced phase transition in a NiCoMnIn ferromagnetic shape memory alloy under a stress field

Y. D. Wang, Yang Ren, E. W. Huang, Z. H. Nie, G. Wang, Y. D. Liu, J. N. Deng, L. Zuo, H. Choo, P. K. Liaw, and D. E. Brown

Appl. Phys. Lett. 90, 101917 (2007); http://dx.doi.org/10.1063/1.2712509 (3 pages) | Cited 15 times

Online Publication Date: 9 March 2007

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The magnetoelasticity and magnetoplasticity behaviors of a Ni–Co–Mn–In ferromagnetic shape memory alloy (FSMA) induced by the reverse phase transformation interplayed under multiple (temperature, magnetic, and stress) fields were captured directly by high-energy synchrotron x-ray diffraction technique. The experiments showed the direct experimental evidence of that a stress ( ∼ 50 MPa) applied to this material made a complete recovery of the original orientations of the martensite variants, showing a full shape memory effect. This finding offers the in-depth understanding the fundamental properties and applications of the Ni–Co–Mn–In FSMA with the magnetic-field-induced reverse transformation.
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81.05.Bx Metals, semimetals, and alloys
81.30.Kf Martensitic transformations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Self-assembled formation of ZnO hexagonal micropyramids with high luminescence efficiency

DaeGwi Kim, Shuji Wakaiki, Shingo Komura, Masaaki Nakayama, Yukimasa Mori, and Kazuyo Suzuki

Appl. Phys. Lett. 90, 101918 (2007); http://dx.doi.org/10.1063/1.2713123 (3 pages) | Cited 8 times

Online Publication Date: 9 March 2007

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The authors have found the self-assembled formation of ZnO hexagonal micropyramids after the growth of a sufficiently thick ZnO layer on a (0001) Al2O3 substrate by rf-magnetron sputtering deposition. It was confirmed by scanning electron microscopy that the orientations of the micropyramids are well arranged. The reflection and photoluminescence spectra at 10 K demonstrate that optical properties of the total growth layer are of high quality. The noticeable discovery with the use of cathodoluminescence spectroscopy is that the luminescence intensity of the micropyramids is 30 times stronger than that of the underlying layer; namely, strong enhancement of luminescence is realized in the self-assembled micropyramids.
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81.16.Dn Self-assembly
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
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