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22 Aug 2011

Volume 99, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 083104 (2011); http://dx.doi.org/10.1063/1.3625926 (3 pages)

E. Detsi, Z. G. Chen, W. P. Vellinga, P. R. Onck, and J. T. M. De Hosson
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Analysis of thermal band gap variations of PbS quantum dots by Fourier transform transmission and emission spectroscopy

B. Ullrich, J. S. Wang, and G. J. Brown

Appl. Phys. Lett. 99, 081901 (2011); http://dx.doi.org/10.1063/1.3623486 (3 pages) | Cited 8 times

Online Publication Date: 22 August 2011

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Fourier transmission and emission spectroscopy was employed in the range from 5 to 300 K to measure the thermal band gap shift of 4.7 nm PbS quantum dots. The analytical comparison of fits carried out with the expressions of Varshni and Fan revealed limited accuracy of the Varshni fitting parameters. Evidence is presented that transmission spectroscopy in conjunction with the Fan model concurs with the microscopic material features, resulting in a tool to determine intrinsic properties of quantum dots.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
71.20.Nr Semiconductor compounds
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials

Two-photon-pumped stimulated emission from ZnO single crystal

T. C. He, R. Chen, W. W. Lin, F. Huang, and H. D. Sun

Appl. Phys. Lett. 99, 081902 (2011); http://dx.doi.org/10.1063/1.3628329 (3 pages) | Cited 6 times

Online Publication Date: 22 August 2011

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We report on two-photon-pumped stimulated emission (SE) from ZnO single crystal at low temperature. Under nanosecond pulse excitation, two-photon absorption induced SE with a threshold of 2.8 MW/cm2 is observed, which is ascribed to the inelastic exciton-exciton scattering. The mechanism of the SE is further confirmed by temperature dependent photoluminescence spectra. However, it is interesting to find that under one photon pumping with the same power density, no SE is observed from the sample. Such unusual phenomenon is explained by the nonradiative surface recombination induced carriers depletion under single photon excitation.
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78.55.Et II-VI semiconductors
78.47.J- Ultrafast spectroscopy (<1 psec)

THz dielectric anisotropy of metal slanted columnar thin films

T. Hofmann, D. Schmidt, A. Boosalis, P. Kühne, R. Skomski, C. M. Herzinger, J. A. Woollam, M. Schubert, and E. Schubert

Appl. Phys. Lett. 99, 081903 (2011); http://dx.doi.org/10.1063/1.3626846 (3 pages) | Cited 6 times

Online Publication Date: 23 August 2011

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The anisotropic optical dielectric functions of a metal (cobalt) slanted columnar thin film deposited by electron-beam glancing angle deposition are reported for the terahertz (THz) frequency domain using generalized spectroscopic ellipsometry. We employ a simple effective medium dielectric function homogenization approach to describe the observed optical response. The approach describes isolated, electrically conductive columns which render the thin film biaxial (orthorhombic). Our findings suggest controlled variability of dielectric polarizability and anisotropy in the THz spectral range by choice of geometry, material, and structure.
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75.30.Gw Magnetic anisotropy
73.61.At Metal and metallic alloys
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Large area quasi-free standing monolayer graphene on 3C-SiC(111)

C. Coletti, K. V. Emtsev, A. A. Zakharov, T. Ouisse, D. Chaussende, and U. Starke

Appl. Phys. Lett. 99, 081904 (2011); http://dx.doi.org/10.1063/1.3618674 (3 pages) | Cited 11 times

Online Publication Date: 23 August 2011

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Large scale, homogeneous quasi-free standing monolayer graphene is obtained on cubic silicon carbide, i.e., the 3C-SiC(111) surface, which represents an appealing and cost effective platform for graphene growth. The quasi-free monolayer is produced by intercalation of hydrogen under the interfacial, (6math×6math)R30 °-reconstructed carbon layer. After intercalation, angle resolved photoemission spectroscopy reveals sharp linear π-bands. The decoupling of graphene from the substrate is identified by x-ray photoemission spectroscopy and low energy electron diffraction. Atomic force microscopy and low energy electron microscopy demonstrate that homogeneous monolayer domains extend over areas of hundreds of square-micrometers.
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61.48.Gh Structure of graphene
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Periodic variation of stress in sputter deposited Si/WSi2 multilayers

Kimberly MacArthur, Bing Shi, Ray Conley, and Albert T. Macrander

Appl. Phys. Lett. 99, 081905 (2011); http://dx.doi.org/10.1063/1.3628242 (3 pages) | Cited 1 time

Online Publication Date: 23 August 2011

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A tension increment after sputter deposition of 1 nm of WSi2 onto sputtered Si was observed at low Ar gas pressures. Wafer curvature data on multilayers were found to have a periodic variation corresponding to the multilayer period, and this permitted statistical analyses to improve the sensitivity to small stresses. The observation of tension instead of compression in the initial stage of growth is reported, and a model invoking surface rearrangement is invoked. The data also bear on an unusual surface smoothing phenomena for sputtered Si surfaces caused by the sputter deposition of WSi2. We furthermore report that for low Ar pressures the Si layers are the predominant source of built-up stress.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.65.Ac Multilayers
81.15.Cd Deposition by sputtering

A study of spin isomer conversion kinetics in supercritical fluid hydrogen for cryogenic fuel storage technologies

Manyalibo J. Matthews, Guillaume Petitpas, and Salvador M. Aceves

Appl. Phys. Lett. 99, 081906 (2011); http://dx.doi.org/10.1063/1.3628453 (3 pages) | Cited 1 time

Online Publication Date: 23 August 2011

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A detailed kinetic study of para-ortho hydrogen conversion under supercritical conditions using rotational Raman scattering is presented. Isochoric measurements of initially low ortho concentrations over temperatures 32 < T < 280 K and densities 0.014 < ρ < 0.060 g/cm3 were used to derive kinetic rate constants k(ρ, T) by solving an autocatalytic kinetic rate equation. At low ortho concentrations and T < 100 K, k is found to be ∼2× higher than previous results based on thermal conductivity measurements, decreasing weakly with temperature, similar to Wigner’s original paramagnetic theory. Accurate modeling of k(ρ, T) is critical in predicting cryogenic hydrogen fuel tank dormancy performance for hydrogen-power vehicles.
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88.30.R- Hydrogen storage
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Controlled cation stoichiometry in pulsed laser deposition-grown BaTiO3 epitaxial thin films with laser fluence

Daisuke Kan and Yuichi Shimakawa

Appl. Phys. Lett. 99, 081907 (2011); http://dx.doi.org/10.1063/1.3628461 (3 pages) | Cited 4 times

Online Publication Date: 23 August 2011

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We investigated effects of the laser fluence on structural and ferroelectric properties in BaTiO3 epitaxial thin films grown by pulsed laser deposition. We find that the low laser fluence causes the cation non-stoichiometry in the films. X-ray diffraction and ferroelectric hysteresis loop measurements reveal the strong impacts of the fluence-dependent cation non-stoichiometry on the structural and ferroelectric properties of the films. The ferroelectricity is observed for the films grown with the fluence larger than 1.3 J/cm2, where the cation ratio is kept close to stoichiometric. These results demonstrate that the cation stoichiometry controlled with the laser fluence plays an important role in determining the structural and ferroelectric properties in the BaTiO3 films.
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77.80.Dj Domain structure; hysteresis
61.66.Bi Elemental solids
61.66.Dk Alloys
81.15.Fg Pulsed laser ablation deposition
77.55.fe BaTiO3-based films
68.55.A- Nucleation and growth

Phase-change control of ferromagnetism in GeTe-based phase change magnetic thin-films by pulsed laser deposition

F. Tong, J. H. Hao, Z. P. Chen, G. Y. Gao, and X. S. Miao

Appl. Phys. Lett. 99, 081908 (2011); http://dx.doi.org/10.1063/1.3628660 (3 pages) | Cited 6 times

Online Publication Date: 23 August 2011

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Phase change control of ferromagnetism in Ge0.98Fe0.02Te thin film prepared by pulsed laser deposition is investigated. The magnetic property of Fe doped phase change material GeTe is found to vary with phase change between amorphous and crystalline states corresponding to the variation of conductance during phase change. The results indicate that a fast control of ferromagnetism by phase change can be realized. The measurement of temperature dependent magnetization shows a long range ferromagnetic interaction in ordered crystalline phase and a short range ferromagnetic interaction in frustrated amorphous phase, which is consistent with phase change.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Et Exchange and superexchange interactions
75.50.Pp Magnetic semiconductors
81.05.Gc Amorphous semiconductors
81.15.Fg Pulsed laser ablation deposition
75.50.Dd Nonmetallic ferromagnetic materials

Enhancement of electric field and Raman scattering by Ag coated Ni nanotips

Dexian Ye, Stephen Mutisya, and Massimo Bertino

Appl. Phys. Lett. 99, 081909 (2011); http://dx.doi.org/10.1063/1.3627164 (3 pages) | Cited 4 times

Online Publication Date: 24 August 2011

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Localization and enhancement of electric field by Ag-coated vertical Ni nanotip arrays were studied by using finite-different time domain calculations. With the 30 nm thick Ag coating, the nanotips can localize and enhance the electric field to more than 103 times under the excitation of TE-polarized light with a 532 nm wavelength. Nanotip-enhanced Raman scattering of cytochrome-c protein was demonstrated in a confocal Raman microscope. Significant enhancement of Raman spectrum was achieved at 1 × 10−9 mol/l concentration of the proteins.
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87.15.M- Spectra of biomolecules
02.70.Bf Finite-difference methods
78.30.Jw Organic compounds, polymers
87.14.E- Proteins

Void formation in melt-grown silicon studied by molecular dynamics simulations: From grown-in faulted dislocation loops to vacancy clusters

Johan Pohl and Karsten Albe

Appl. Phys. Lett. 99, 081910 (2011); http://dx.doi.org/10.1063/1.3630028 (3 pages)

Online Publication Date: 24 August 2011

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Molecular dynamics simulations of a dislocation based mechanism for void formation in silicon are presented. By studying a moving solid-liquid interface in Si, we observe the formation of dislocation loops on (111) facets consisting of coherency and anticoherency dislocations, which disband within nanoseconds into vacancy clusters of 10 or more vacancies. These vacancy clusters can act as nucleation seeds for the experimentally observed octahedral single and double voids.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.jd Vacancies
61.72.Bb Theories and models of crystal defects

Anomalous complete opaqueness in a sparse array of gold nanoparticle chains

Benfeng Bai, Xiaowei Li, Ismo Vartiainen, Anni Lehmuskero, Guoguo Kang, Jari Turunen, Markku Kuittinen, and Pasi Vahimaa

Appl. Phys. Lett. 99, 081911 (2011); http://dx.doi.org/10.1063/1.3631671 (3 pages)

Online Publication Date: 24 August 2011

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We report on an anomalous polarization-switching extinction effect in a sparse array of gold nanoparticle chains: under normal incidence of light, the array is almost transparent for one polarization; whereas it is fully opaque (with nearly zero transmittance) for the orthogonal polarization within a narrow band, even though the nanoparticles cover only a tiny fraction (say, 3.5%) of the transparent substrate surface. We reveal that the strong polarization-dependent short-range dipolar coupling and long-range radiative coupling of gold nanoparticles in this highly asymmetric array is responsible for this extraordinary effect.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.05.Bx Metals, semimetals, and alloys
81.07.Wx Nanopowders
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Misfit dislocation formation via pre-existing threading dislocation glide in (11math2) semipolar heteroepitaxy

Po Shan Hsu, Erin C. Young, Alexey E. Romanov, Kenji Fujito, Steven P. DenBaars, Shuji Nakamura, and James S. Speck

Appl. Phys. Lett. 99, 081912 (2011); http://dx.doi.org/10.1063/1.3628459 (3 pages) | Cited 17 times

Online Publication Date: 24 August 2011

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Cathodoluminescence (CL) was used to study the onset of mechanical stress relaxation in low indium composition semipolar (11math2) InxGa1−xN lattice-mismatched layers grown on bulk GaN substrates. Monochromatic CL of short interfacial misfit dislocation (MD) segments showed a single threading dislocation (TD) associated with each MD segment—demonstrating that the initial stage of MD formation in semipolar III-nitride heterostructures proceeded by the bending and glide of pre-existing TDs on the (0001) slip plane. The state of coherency as determined by panchromatic CL is also compared to that determined by x-ray diffraction analysis based on crystallographic epilayer tilt and Matthew-Blakeslee’s critical thickness calculations.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations

Fabrication of thin, luminescent, single-crystal diamond membranes

Andrew P. Magyar, Jonathan C. Lee, Andi M. Limarga, Igor Aharonovich, Fabian Rol, David R. Clarke, Mengbing Huang, and Evelyn L. Hu

Appl. Phys. Lett. 99, 081913 (2011); http://dx.doi.org/10.1063/1.3628463 (3 pages) | Cited 7 times

Online Publication Date: 24 August 2011

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The formation of single-crystal diamond membranes is an important prerequisite for the fabrication of high-quality optical cavities in this material. Diamond membranes fabricated using lift-off processes involving the creation of a damaged layer through ion implantation often suffer from residual ion damage, which severely limits their usefulness for photonic structures. The current work demonstrates that strategic etch removal of the most highly defective material yields thin, single-crystal diamond membranes with strong photoluminescence and a Raman signature approaching that of single-crystal bulk diamond. These optically active membranes can form the starting point for fabrication of high-quality optical resonators.
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81.05.ug Diamond
61.72.U- Doping and impurity implantation
81.65.Cf Surface cleaning, etching, patterning
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials

InP-based InAs/InGaAs quantum wells with type-I emission beyond 3 μm

Y. Gu, Y. G. Zhang, K. Wang, X. Fang, C. Li, Y. Y. Cao, A. Z. Li, and Y. Y. Li

Appl. Phys. Lett. 99, 081914 (2011); http://dx.doi.org/10.1063/1.3629999 (3 pages) | Cited 6 times

Online Publication Date: 25 August 2011

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This work reports on InAs/In0.53Ga0.47As strain compensated quantum well structures on InP-based metamorphic buffer to generate the type-I emission of beyond 3 μm. The metamorphic buffer is composed of InxAl1−xAs graded layer and In0.8Ga0.2As virtual substrate layer. Atomic force microscope, transmission electron microscope and x-ray diffraction measurements show the moderate surface and structural properties. A photoluminescence signal up to 3.05 μm has been achieved at 300 K, which is one of the longest wavelengths from the interband emission of InP-based antimony-free structure. It is promising to employ this quantum well structure on metamorphic buffer for the laser demonstration with emission around 3 μm.
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78.67.De Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors

Energetics and electronic structure of La/Sr disorder at the interface of SrTiO3/LaTiO3 heterostructure

J. J. Pulikkotil, S. Auluck, Pramod Kumar, Anjana Dogra, and R. C. Budhani

Appl. Phys. Lett. 99, 081915 (2011); http://dx.doi.org/10.1063/1.3629786 (3 pages)

Online Publication Date: 26 August 2011

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In the artificially tailored heterostructures of certain materials, a polar discontinuity across the interface introduces a large energy cost. The total energy of such systems may be reduced either by electronic reconstruction leading to the interface phases or by simple atomic reconstruction by inter-site cation mixing. While most of the experiments and theoretical calculations assume an abrupt interface, in this work, we consider the La/Sr inter-site disorder across the interface of SrTiO3/LaTiO3 heterostructures and study its energetics and electronic structure properties. The calculations find that inter-site mixing of La/Sr atoms across the interface also reduces the total energy. However, the extent of such disorder is found to be dramatically minimized by allowing the interfacial atoms to relax fully and that for such systems, the changes in the electronic structure are negligible.
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73.20.-r Electron states at surfaces and interfaces
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
71.15.Nc Total energy and cohesive energy calculations

Effect of epitaxial strain on the cation distribution in spinel ferrites CoFe2O4 and NiFe2O4: A density functional theory study

Daniel Fritsch and Claude Ederer

Appl. Phys. Lett. 99, 081916 (2011); http://dx.doi.org/10.1063/1.3631676 (3 pages) | Cited 11 times

Online Publication Date: 26 August 2011

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The effect of epitaxial strain on the cation distribution in spinel ferrites CoFe2O4 and NiFe2O4 is investigated by GGA+U total energy calculations. We obtain a very strong (moderate) tendency for cation inversion in NiFe2O4 (CoFe2O4), in agreement with experimental bulk studies. This preference for the inverse spinel structure is reduced by tensile epitaxial strain, which can lead to strong sensitivity of the cation distribution on specific growth conditions in thin films. Furthermore, we obtain significant energy differences between different cation arrangements with the same degree of inversion, providing further evidence for recently proposed short range B site order in NiFe2O4.
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68.60.Bs Mechanical and acoustical properties
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations
71.20.Ps Other inorganic compounds
75.50.Gg Ferrimagnetics
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