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13 Oct 2008

Volume 93, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 93, 151101 (2008); http://dx.doi.org/10.1063/1.2996271 (3 pages)

Xuefeng Zeng and Hongrui Jiang
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Time-resolved cathodoluminescence of Mg-doped GaN

A. M. Fischer, S. Srinivasan, F. A. Ponce, B. Monemar, F. Bertram, and J. Christen

Appl. Phys. Lett. 93, 151901 (2008); http://dx.doi.org/10.1063/1.3000383 (3 pages)

Online Publication Date: 13 October 2008

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The optical properties of GaN films doped with magnesium concentrations of the order of 1018 and 1019 cm−3 have been analyzed by picosecond time-resolved cathodoluminescence spectroscopy. Two luminescence bands in the vicinity of ∼ 3.45 and ∼ 3.27 eV are observed to increase in intensity with Mg concentration. They have been identified as related to acceptor-bound exciton and donor-acceptor pair (DAP) transitions, respectively. Time-resolved cathodoluminescence spectra, taken at low temperatures ( ∼ 4 K), show that the lifetime of the DAP peak (3.27 eV) and of what appears to be its first longitudinal-optical phonon replica at ∼ 3.19 eV decrease with increasing Mg concentration. These peaks differ in their recombination kinetics, strongly suggesting the existence of an underlying broad emission band which may be related to Mg.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Super-radiance of excitons in a single ZnO nanostructure

C. R. Ding, W. Lin, B. C. Chen, F. L. Zhao, J. W. Dong, M. Shi, H. Z. Wang, Y. F. Hsu, and A. B. Djurišić

Appl. Phys. Lett. 93, 151902 (2008); http://dx.doi.org/10.1063/1.3000612 (3 pages) | Cited 6 times

Online Publication Date: 13 October 2008

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Super-radiance of excitons in a single ZnO tetrapod nanostructure has been observed. The emitted pulses exhibited very short duration, and the emission peak intensity exhibited exponential increase with the increased pump density. Multiple narrow emission peaks with short peak spacing have been observed in the emission spectra of a single ZnO tetrapod nanostructure.
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71.35.-y Excitons and related phenomena
78.45.+h Stimulated emission
78.60.Hk Cathodoluminescence, ionoluminescence
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Buried melting in germanium implanted silicon by millisecond flash lamp annealing

Matthias Voelskow, Rossen Yankov, Wolfgang Skorupa, Jörg Pezoldt, and Thomas Kups

Appl. Phys. Lett. 93, 151903 (2008); http://dx.doi.org/10.1063/1.2993332 (3 pages) | Cited 1 time

Online Publication Date: 13 October 2008

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Flash lamp annealing in the millisecond range has been used to induce buried melting in silicon. For this purpose high dose high-energy germanium implantation has been employed to lower the melting temperature of silicon in a predetermined depth region. Subsequent flash lamp treatment at high energy densities leads to local melting of the germanium rich layer. The thickness of the molten layer has been found to depend on the irradiation energy density. During the cool-down period, epitaxial crystallization takes place resulting in a largely defect-free layer.
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
64.70.dj Melting of specific substances
61.72.Cc Kinetics of defect formation and annealing
64.70.dg Crystallization of specific substances

In situ characterization of strontium surface segregation in epitaxial La0.7Sr0.3MnO3 thin films as a function of oxygen partial pressure

Tim T. Fister, Dillon D. Fong, Jeffrey A. Eastman, Peter M. Baldo, Matthew J. Highland, Paul H. Fuoss, Kavaipatti R. Balasubramaniam, Joanna C. Meador, and Paul A. Salvador

Appl. Phys. Lett. 93, 151904 (2008); http://dx.doi.org/10.1063/1.2987731 (3 pages) | Cited 26 times

Online Publication Date: 13 October 2008

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Using in situ synchrotron measurements of total reflection x-ray fluorescence, we find evidence of strontium surface segregation in (001)-oriented La0.7Sr0.3MnO3 thin films over a wide range of temperatures (25–900 °C) and oxygen partial pressures (pO2 = 0.15–150 Torr). The strontium surface concentration is observed to increase with decreasing pO2, suggesting that the surface oxygen vacancy concentration plays a significant role in controlling the degree of segregation. Interestingly, the enthalpy of segregation becomes less exothermic with increasing pO2, varying from −9.5 to −2.0 kJ/mol. In contrast, the La0.7Sr0.3MnO3 film thickness and epitaxial strain state have little impact on segregation behavior.
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68.35.Dv Composition, segregation; defects and impurities
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
75.70.Ak Magnetic properties of monolayers and thin films
61.72.jd Vacancies
82.60.-s Chemical thermodynamics

Correlated reduction in micropipe cross sections in SiC growth

M. Yu. Gutkin, A. G. Sheinerman, M. A. Smirnov, V. G. Kohn, T. S. Argunova, J. H. Je, and J. W. Jung

Appl. Phys. Lett. 93, 151905 (2008); http://dx.doi.org/10.1063/1.2998572 (3 pages) | Cited 6 times

Online Publication Date: 13 October 2008

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We reveal a correlated reduction in the cross sections of two neighboring micropipes (MPs) in the crystal growth of silicon carbide using computer simulation of phase contrast images. The correlated reduction is explained by the exchange of full-core dislocations in a contact-free reaction between two parallel MPs. We develop a theoretical model that describes the energetics of this process.
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81.05.Hd Other semiconductors
81.10.Bk Growth from vapor
61.72.Lk Linear defects: dislocations, disclinations

Intrinsic generation of OH groups in dry silicon dioxide upon thermal treatments

Laura Nuccio, Simonpietro Agnello, and Roberto Boscaino

Appl. Phys. Lett. 93, 151906 (2008); http://dx.doi.org/10.1063/1.2998581 (3 pages) | Cited 6 times

Online Publication Date: 13 October 2008

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We show the existence of an intrinsic generation mechanism of OH groups in synthetic dry silica upon thermal treatments. Samples are treated for ∼ 160 h at 390 °C in He at 2.7 or 180 bar, and the growth of the OH IR absorption band at 3670 cm−1 is observed. An OH concentration of ∼ 1018 cm−3 is estimated. Possible contributions of reactions with molecules absorbed from the atmosphere are excluded. Reactions with H2O already contained in the samples are rejected by IR measurements. The observed OH generation is attributed to the reaction of network sites with H2 already present in the material. Possible reaction paths are examined.
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81.40.Gh Other heat and thermomechanical treatments
78.30.Hv Other nonmetallic inorganics

Mg composition dependent strain analysis in nonpolar a-plane MgxZn1−xO films

G. Saraf, Y. Lu, and T. Siegrist

Appl. Phys. Lett. 93, 151907 (2008); http://dx.doi.org/10.1063/1.3000636 (3 pages) | Cited 5 times

Online Publication Date: 14 October 2008

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Nonpolar a-plane (11math0) MgxZn1−xO (a-MgxZn1−xO) films are deposited on (01math2) r-sapphire substrates using metalorganic chemical vapor deposition with varying Mg composition (x from 0 to 0.25). Unit cell parameters with Mg composition are determined by high-resolution triple-axis x-ray diffraction. In-plane strain along the c-axis [0001] and m-axis [1math00] in the films is anisotropic and increases with increasing Mg composition. The in-plane strain anisotropy changes with Mg composition in a-MgxZn1−xO. Calculations are carried out to determine the influence of Mg content on the residual interfacial strain.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
68.55.Nq Composition and phase identification
68.60.Bs Mechanical and acoustical properties
61.05.cp X-ray diffraction

Improved characteristics and issues of m-plane InGaN films grown on low defect density m-plane freestanding GaN substrates by metalorganic vapor phase epitaxy

S. F. Chichibu, H. Yamaguchi, L. Zhao, M. Kubota, T. Onuma, K. Okamoto, and H. Ohta

Appl. Phys. Lett. 93, 151908 (2008); http://dx.doi.org/10.1063/1.2998580 (3 pages) | Cited 12 times

Online Publication Date: 14 October 2008

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Improved quantum efficiency and short radiative lifetime were demonstrated for the near-band-edge emission of nearly stacking-fault-free, 200–250-nm-thick, m-plane pseudomorphic InxGa1−xN (0<x ≤ 0.14) films grown by metalorganic vapor phase epitaxy on the low threading dislocation density (<5×106 cm−2) freestanding (FS) GaN substrates. Values of full width at half maximum of x-ray ω-rocking curves of the InxGa1−xN films remain unchanged as the substrate values being 80 and 60 arcsec for the (10math0) diffraction with 〈0001〉 and 〈11math0〉 azimuths, respectively, and 80 arcsec for the (10math2) diffraction. As the surface flatness was improved, the incorporation efficiency of In was lower than the cases for c-plane growth and m-plane growth on a defective GaN substrate, according to nonidentical surface kinetics and absence of inclined/tilted planes, respectively.
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68.47.Fg Semiconductor surfaces
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.35.bg Semiconductors

Atomic-scale structure and composition of tungsten carbide reinforced diamondlike carbon films

T. W. Scharf, M. C. Romanes, K. C. Mahdak, J. Y. Hwang, R. Banerjee, R. D. Evans, and G. L. Doll

Appl. Phys. Lett. 93, 151909 (2008); http://dx.doi.org/10.1063/1.2995860 (3 pages) | Cited 8 times

Online Publication Date: 14 October 2008

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This study presents the true atomic-scale structure and composition of hard/lubricious nanocomposite diamondlike carbon (DLC) films. Nanocrystalline tungsten carbide ( ∼ 2–4 nm precipitates) in mixed sp3/sp2 amorphous C–H matrices was characterized using the combination of three-dimensional atom probe (3DAP) tomography and transmission electron microscopy. Excellent correspondence in structural and chemical layering was observed (alternating ∼ 25 nm thick carbon-rich and tungsten-rich layers) with 3DAP also revealing C32+ and C2H4+ species in the carbon-rich layers and W2+, WC2+, C+, and C2+ species in the tungsten-rich layers. 3D morphology and chemical partitioning of the WC nanoprecipitates in the tungsten-rich layers are also discussed.
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68.55.-a Thin film structure and morphology
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
81.30.Mh Solid-phase precipitation

Thermal emittance changes at the charge ordering transition of (Sm0.35Ca0.65)MnO3

P. Laffez, C. Napierala, M. Zaghrioui, V. Ta Phuoc, A. Hassini, and M. R. Ammar

Appl. Phys. Lett. 93, 151910 (2008); http://dx.doi.org/10.1063/1.2999372 (3 pages) | Cited 6 times

Online Publication Date: 14 October 2008

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The reversible charge ordering transition of (Sm1−x,Cax)MnO3 is associated with strong changes in electrical, magnetic, and infrared properties. In this work, normal spectral emissivity is calculated from infrared reflectance of bulk polished ceramics. Emissivity versus temperature shows a sharp variation at the charge ordering transition near room temperature. By comparing the apparent temperature of the sample with the absolute temperature, we show that Sm0.35Ca0.65MnO3 is a good candidate for infrared furtivity around room temperature.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
72.80.Sk Insulators
75.80.+q Magnetomechanical effects, magnetostriction
71.30.+h Metal-insulator transitions and other electronic transitions

Stress-induced α″ martensitic (110) twinning in β-Ti alloys

D. H. Ping, Y. Yamabe-Mitarai, C. Y. Cui, F. X. Yin, and M. A. Choudhry

Appl. Phys. Lett. 93, 151911 (2008); http://dx.doi.org/10.1063/1.3002295 (3 pages) | Cited 4 times

Online Publication Date: 15 October 2008

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A fully transformed α″ martensite with stress-induced nanoscale {110}, {021}-type compound twin or a 90° rotation twin has been experimentally explored and unambiguously characterized in traditional β-type Ti alloys, which usually undergo a partial martensitic transformation [a β grain partially transformed into α″ with internal (111) twin] by quenching. This newly observed twinning, which matches with the predication based on the deformation twinning theory of Bilby and Crocker [Proc. R. Soc. 288, 241 (1965) ], can help to explain the deformation mechanism and aid future development of advanced materials.
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81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
64.70.K- Solid-solid transitions
61.72.Mm Grain and twin boundaries
62.20.F- Deformation and plasticity

Scattering-based hole burning through volume speckles in a random medium with tunable diffusion constant

Shunsuke Murai, Koji Fujita, Takayuki Hirao, Kazuki Nakanishi, Kazuyuki Hirao, and Katsuhisa Tanaka

Appl. Phys. Lett. 93, 151912 (2008); http://dx.doi.org/10.1063/1.2955830 (3 pages) | Cited 1 time

Online Publication Date: 15 October 2008

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A photoreactive random medium with tunable diffusion constant D is fabricated by infiltrating Sm2+-doped macroporous aluminosilicate glass with liquid crystal (LC). Time-resolved transmission experiment reveals that D in the LC-infiltrated sample changes abruptly at around 35 °C due to the phase transition of LC between nematic and isotropic. The hole burning effect based on the interference of multiply scattered light is investigated with a particular motivation of controlling hole burning properties externally via temperature. We demonstrate that the holes are separately registered in each LC phase and can be detected selectively depending on the temperature.
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78.47.nd Hole burning spectroscopy
61.43.Fs Glasses
61.30.-v Liquid crystals
64.70.M- Transitions in liquid crystals

On the growth mechanism of plasma deposited amorphous silicon thin films

Sumeet C. Pandey, Tejinder Singh, and Dimitrios Maroudas

Appl. Phys. Lett. 93, 151913 (2008); http://dx.doi.org/10.1063/1.2990641 (3 pages) | Cited 3 times

Online Publication Date: 16 October 2008

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We propose a comprehensive mechanism of amorphous silicon thin film growth by plasma deposition based on results of kinetic Monte Carlo simulations according to a database constructed by first-principles density functional theory calculations. The growth mechanism consists of various surface kinetic events including radical-surface and adsorbed radical-radical interactions, radical-surface diffusion, and surface hydride dissociation reactions. Of particular importance is the radical dissociative adsorption mediated by Si over-coordination defects along the reaction pathway. The proposed mechanism explains fully the experimentally measured surface composition of plasma deposited films under conditions that make the silyl radical the dominant deposition precursor.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.ag Semiconductors
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
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The time reversed elastic nonlinearity diagnostic applied to evaluation of diffusion bonds

T. J. Ulrich, Alexander M. Sutin, Thomas Claytor, Pallas Papin, Pierre-Yves Le Bas, and James A. TenCate

Appl. Phys. Lett. 93, 151914 (2008); http://dx.doi.org/10.1063/1.2998408 (3 pages) | Cited 10 times

Online Publication Date: 16 October 2008

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With the recent application of time reversed acoustics and nonlinear elasticity to imaging mechanical damage, the development of time reversal based nondestructive evaluation techniques has begun. Here, diffusion bonded metal disks containing intentionally disbonded regions are analyzed using the time reversed elastic nonlinearity diagnostic. The nonlinear results are compared with linear ultrasonic imaging (C scan). Scanning electron microscopy is shown to illustrate the differences between the features seen by the linear and nonlinear methods.
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81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
66.30.Ny Chemical interdiffusion; diffusion barriers
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Physical factors controlling the ductility of bulk metallic glasses

Y. Liu, H. Wu, C. T. Liu, Z. Zhang, and V. Keppens

Appl. Phys. Lett. 93, 151915 (2008); http://dx.doi.org/10.1063/1.2998410 (3 pages) | Cited 6 times

Online Publication Date: 16 October 2008

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In order to identify key physical factor controlling the deformation and fracture behavior of bulk metallic glasses (BMGs), we compiled and analyzed the elastic moduli and compressive ductility for BMGs. In addition, new modulus data were generated in the critical ranges in order to facilitate the analysis. We have found that the intrinsic ductility of BMGs can be correlated with the bulk-to-shear modulus ratio B/G according to Pugh’s [Philos. Mag. 45, 823 (1954) ] rule. In some individual BMG systems, for example, Fe based, the relationship seems to be very clear. The physical meaning of this correlation is discussed in terms of atomic bonding and connectivity.
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81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.20.mm Fracture
62.20.fk Ductility, malleability
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Reversible growth-mode transition in SrRuO3 epitaxy

R. Bachelet, F. Sánchez, J. Santiso, and J. Fontcuberta

Appl. Phys. Lett. 93, 151916 (2008); http://dx.doi.org/10.1063/1.3001932 (3 pages) | Cited 7 times

Online Publication Date: 16 October 2008

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It is known that a transition from layer-by-layer (LbL) to step-flow (SF) can occur at the earliest stages of SrRuO3 growth on SrTiO3(001). We report here the observation of a reversible transition between these two-dimensional growth modes that can occur at any SrRuO3 thickness, tuned by short growth interruption. We show that under SF mode, growth interruption allows step-edge straightening, thus resulting in enhanced island nucleation on locally wider terraces and reduced adatom incorporation at step edges. As a result, the LbL mode is recovered. This reversible transition critically influences the growing-layer morphology and is of crucial interest in epitaxial-heterostructure fabrication.
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68.55.A- Nucleation and growth
68.55.J- Morphology of films

Realization of defect-free epitaxial core-shell GaAs/AlGaAs nanowire heterostructures

Michael J. Tambe, Sung Keun Lim, Matthew J. Smith, Lawrence F. Allard, and Silvija Gradečak

Appl. Phys. Lett. 93, 151917 (2008); http://dx.doi.org/10.1063/1.3002299 (3 pages) | Cited 15 times

Online Publication Date: 17 October 2008

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We report the controlled growth of vertically aligned GaAs/AlGaAs core-shell nanowires. By optimizing the shell deposition temperature and catalyst density we maintain high temperature stability and achieve defect-free epitaxial AlGaAs shell deposition with high aluminum incorporation. Energy dispersive x-ray analysis determines the shell composition to be Al0.9Ga0.1As and measures the uniformity of the shell thickness. Lattice-resolved high-angle annular dark-field scanning transmission electron microscopy images confirm the core-shell interface to be defect-free, epitaxial, and atomically sharp. The ability to realize GaAs/AlGaAs core-shell nanowires with precise control over the morphology and composition is essential to the development of nanowire-based high mobility electronics.
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81.07.Bc Nanocrystalline materials
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
68.65.La Quantum wires (patterned in quantum wells)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Formation and decomposition of AlH3 in the aluminum-hydrogen system

H. Saitoh, A. Machida, Y. Katayama, and K. Aoki

Appl. Phys. Lett. 93, 151918 (2008); http://dx.doi.org/10.1063/1.3002374 (3 pages) | Cited 28 times

Online Publication Date: 17 October 2008

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The pressure-temperature diagram of hydrogen-aluminum system was determined for a pressure range of 0–10 GPa and a temperature range of 27–800 °C by in situ x-ray diffraction measurements. Pristine aluminum was hydrogenated to trihydride at 8.9 GPa and 600 °C. The cyclic formation and decomposition of the hydride resulted in lowering of the hydrogenation conditions down to 4.9 GPa and 330 °C. Transparent single crystals were recovered at ambient conditions.
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84.60.-h Direct energy conversion and storage
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Uniformly dimerized C60 film prepared by deposition under in situ photoirradiation

H. Tanimoto, K. Yamada, H. Mizubayashi, Y. Matsumoto, H. Naramaoto, and S. Sakai

Appl. Phys. Lett. 93, 151919 (2008); http://dx.doi.org/10.1063/1.3003866 (3 pages) | Cited 2 times

Online Publication Date: 17 October 2008

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C60 films with thicknesses of 100–480 nm were deposited on Si reed substrates under in situ photoirradiation. In anelasticity measurements, no internal friction peaks associated with rotational motions of the C60 molecules were observed, and Young’s modulus was 1.5 times larger than that of a pristine C60 material. X-ray diffraction patterns suggested that the face-centered cubic lattice was contracted by about 3% and locally distorted from the pristine C60 material. Raman spectra very similar to those reported for dimerized C60 were also obtained. These characteristics recovered to those of the pristine C60 materials after annealing the C60 films at 523 K. These results indicate uniform dimerization in C60 films deposited under in situ photoirradiation.
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68.60.Bs Mechanical and acoustical properties
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.de Elastic moduli
78.30.Na Fullerenes and related materials
81.40.Gh Other heat and thermomechanical treatments
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