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17 Jul 2006

Volume 89, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 031107 (2006); http://dx.doi.org/10.1063/1.2222329 (3 pages)

Jiaguang Han, Zhiyuan Zhu, Sanith Ray, Abul K. Azad, Weili Zhang, Mingxia He, Shihong Li, and Yiping Zhao
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Second harmonic scattered light from a transparent glass-ceramic containing sodium niobate nanocrystals

Ernesto Valdez, Cid B. de Araújo, and A. A. Lipovskii

Appl. Phys. Lett. 89, 031901 (2006); http://dx.doi.org/10.1063/1.2221879 (3 pages) | Cited 5 times

Online Publication Date: 17 July 2006

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A study of the incoherent second harmonic radiation generated in a transparent glass-ceramic which consists of sodium niobate nanocrystals embedded in a silica-niobate glass is reported. A nanosecond laser operating at 1064 nm was used, and measurements were performed for samples with nanocrystal filling fractions up to 37%. The results allow the measurements of the first hyperpolarizability per nanocrystal, β = 166×10−30 esu.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Anti-Stokes photoluminescence in ZnO microcrystal

Weitao Cao, Weimin Du, Fuhai Su, and Guohua Li

Appl. Phys. Lett. 89, 031902 (2006); http://dx.doi.org/10.1063/1.2222257 (3 pages) | Cited 3 times

Online Publication Date: 17 July 2006

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Low temperature (10 K) strong anti-Stokes photoluminescence (ASPL) of ZnO microcrystal excited by low power cw 532 nm laser is reported here. Energy upconversion of 1.1 eV is obtained in our experiment with no conventional nonlinear effect. Through the study of the normal photoluminescence and temperature dependence of ASPL we conclude that the green band luminescence in ZnO is related to deep donor to valance band transition. Using the two-step two-photon absorption model, we provide a plausible mechanism leading to the ASPL phenomenon in our experiment.
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78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors

Kinetic details of the nucleation in supercooled liquid metals

J. Liu, J. Z. Zhao, and Z. Q. Hu

Appl. Phys. Lett. 89, 031903 (2006); http://dx.doi.org/10.1063/1.2222335 (3 pages) | Cited 8 times

Online Publication Date: 17 July 2006

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The kinetic details of the nucleation in a supercooled Ni6Cu4 melt are investigated using molecular dynamics simulation method. It is indicated that the nucleus is a random mixture of a large number of fcc structures and a small number of hcp structures. The growth rate of the nucleus increases linearly with undercooling (ΔT). The results show the microstructure evolution in the supercooled liquid of Ni6Cu4 clearly.
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64.60.Q- Nucleation
61.25.Mv Liquid metals and alloys
61.20.Ja Computer simulation of liquid structure

Size-induced strain and stiffness of nanocrystals

G. Ouyang, X. L. Li, X. Tan, and G. W. Yang

Appl. Phys. Lett. 89, 031904 (2006); http://dx.doi.org/10.1063/1.2221897 (3 pages) | Cited 23 times

Online Publication Date: 18 July 2006

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An analytical model has been developed for the size-induced strain and stiffness of a nanocrystal from the perspective of thermodynamics and continuum medium mechanics. A core-shell structure with surface skin shell of an atomic diameter has been considered for the nanocrystal structure. Contribution from chemical and structural effects to the surface energy has also been considered. It has been found that the elastic modulus increases with the inverse of crystal size and the vibration frequency is higher than that of the bulk. The theoretical predictions are consistent with experimental observations.
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81.07.Bc Nanocrystalline materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.25.-g Mechanical properties of nanoscale systems
61.46.Hk Nanocrystals
68.35.Md Surface thermodynamics, surface energies

Strain relaxation in buried SrRuO3 layer in (Ca1−xSrx)(Zr1−xRux)O3/SrRuO3/SrTiO3 system

Soo Gil Kim, Yudi Wang, and I-Wei Chen

Appl. Phys. Lett. 89, 031905 (2006); http://dx.doi.org/10.1063/1.2221900 (3 pages) | Cited 4 times

Online Publication Date: 18 July 2006

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A novel relaxation phenomenon occurs in buried SrRuO3 layers in strained (Ca1−xSrx)(Zr1−xRux)O3/SrRuO3/SrTiO3 (001) thin film system. The lightly strained SrRuO3 buried layer is initially clamped by the SrTiO3 substrate. After a heavily strained (Ca1−xSrx)(Zr1−xRux)O3 overlayer is deposited, localized strain relaxation develops in the buried layer. This is manifested by a crosshatch pattern of ⟨100⟩ corrugations on the surface, due to the slip of ⟨110⟩ {110} threading dislocations. The phenomenon can be controlled by tuning the growth kinetics and strain energy of the overlayer.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Deformation-induced nanostructuring in a Ti–Nb–Ta–In β alloy

W. Xu, K. B. Kim, J. Das, M. Calin, B. Rellinghaus, and J. Eckert

Appl. Phys. Lett. 89, 031906 (2006); http://dx.doi.org/10.1063/1.2222239 (3 pages) | Cited 20 times

Online Publication Date: 18 July 2006

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Easy deformation-induced nanostructuring was found in a Ti–Nb–Ta–In β alloy with low stability against α″ martensitic transformation. Upon severe plastic deformation at the sample center, the reversible β→α″ martensitic transformation plays a significant role for grain refinement. A possible mechanism is proposed, in which the formation of fine martensite, the interaction among slip dislocations, martensite and twins, and the reversible transition from α″ back to β phase are considered as the main causes leading to pronounced grain refinement to the nanoscale.
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64.70.Nd Structural transitions in nanoscale materials
61.46.-w Structure of nanoscale materials
81.40.Lm Deformation, plasticity, and creep
81.30.Kf Martensitic transformations
62.25.-g Mechanical properties of nanoscale systems
62.20.F- Deformation and plasticity
64.70.K- Solid-solid transitions

Nitrogen incorporation in GaNAs layers grown by molecular beam epitaxy

Q. X. Zhao, S. M. Wang, M. Sadeghi, A. Larsson, M. Friesel, and M. Willander

Appl. Phys. Lett. 89, 031907 (2006); http://dx.doi.org/10.1063/1.2219133 (3 pages) | Cited 7 times

Online Publication Date: 18 July 2006

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GaNAs/GaAs quantum wells with high N concentrations, grown by molecular beam epitaxy, have been investigated by secondary-ion mass spectrometry (SIMS), high resolution x-ray diffraction (XRD), and photoluminescence (PL) measurements. The substitutional N concentration in an 18 nm thick strained GaNAs layer varies from 1.4% to 5.9% when the growth rate is reduced from 1 to 0.2 μm/h. By further reducing the growth rate, more N can be incorporated but relaxation occurs. Both the total N concentration, deduced from SIMS measurements, and the substitutional N concentration, deduced from XRD measurements, increase with reduced growth rate. By comparing the SIMS and XRD results, we found that a large amount of N was not in substitutional position when the substitutional N concentration is high (>4%). The experimental results also show that there is no detectable change of total and substitutional N concentrations, within the instrument resolutions, after rapid thermal annealing at 700 °C for 30 s. However, PL measurements show a strong blueshift of the emission wavelength after annealing and the PL intensity increases by more than one order of magnitude.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
78.67.De Quantum wells

Photoreflectance-probed excited states in InAs/InGaAlAs quantum dashes grown on InP substrate

W. Rudno-Rudziński, R. Kudrawiec, P. Podemski, G. Sęk, J. Misiewicz, A. Somers, R. Schwertberger, J. P. Reithmaier, and A. Forchel

Appl. Phys. Lett. 89, 031908 (2006); http://dx.doi.org/10.1063/1.2226503 (3 pages) | Cited 12 times

Online Publication Date: 18 July 2006

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Photoreflectance (PR) measurements have been performed on InAs/In0.53Ga0.23Al0.24As quantum dashes (QDashes) molecular-beam epitaxy grown on InP substrate. The PR features related to all relevant parts of the structure have been detected, including the ground and excited state optical transitions in QDashes. QDash ground state transition shifts from 1.5 to almost 2 μm with the increase in the thickness of InAs layer, corresponding to the increase in the average size of the dashes. Excited state transitions have been clearly observed at the energy of about 150 meV above the ground state transition energy.
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78.67.Lt Quantum wires
78.55.Cr III-V semiconductors
73.21.Hb Quantum wires

Photoluminescence and optical gain due to exciton-electron scattering in a high quality GaN thin film

M. Nakayama, H. Tanaka, M. Ando, and T. Uemura

Appl. Phys. Lett. 89, 031909 (2006); http://dx.doi.org/10.1063/1.2226992 (3 pages) | Cited 1 time

Online Publication Date: 18 July 2006

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We have investigated photoluminescence (PL) properties of a high quality GaN thin film grown by metal organic vapor phase epitaxy under intense excitation conditions in a high temperature regime from 120 K to room temperature. It is found that a PL band peculiar to intense excitation conditions appears with a threshold-like behavior. The energy spacing between the PL band at the threshold excitation power and the A exciton is proportional to temperature. The extrapolation of the linear dependence results in zero value of the energy spacing at absolute zero temperature. These PL profiles are specific to an emission process originating from exciton-electron scattering. Furthermore, we have demonstrated that the exciton-electron scattering process produces optical gain at room temperature from measurements of PL with a variable stripe-length method.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Photoinduced fluorescence enhancement in CdSe/ZnS quantum dot monolayers: Influence of substrate

Takafumi Uematsu, Shinya Maenosono, and Yukio Yamaguchi

Appl. Phys. Lett. 89, 031910 (2006); http://dx.doi.org/10.1063/1.2227053 (3 pages) | Cited 8 times

Online Publication Date: 18 July 2006

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Photoinduced fluorescence enhancement (PFE) of CdSe/ZnS core/shell quantum dot (QD) films on SiOx substrates was investigated. The fluorescence intensity of the QD film on SiO1.9 was greatly enhanced by continuous irradiation in vacuum, while the same QD film on SiO0.6 showed a small enhancement of the fluorescence intensity. After irradiation, the rate of fluorescence decay of the QD film on SiO0.6 was smaller than that of the QD film on SiO1.9. Our results suggest that the origin of PFE derives from the photoejection of electrons into the substrate, and that the oxygen-excess-related defects work as trap sites for the electrons.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.66.Hf II-VI semiconductors

Hydrogen-plasma-induced thermal donors in high resistivity n-type magnetic Czochralski-grown silicon

Y. L. Huang, E. Simoen, C. Claeys, J. M. Rafí, P. Clauws, R. Job, and W. R. Fahrner

Appl. Phys. Lett. 89, 031911 (2006); http://dx.doi.org/10.1063/1.2227076 (3 pages) | Cited 4 times

Online Publication Date: 18 July 2006

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In this work, the formation of donors in n-type high resistivity magnetic Czochralski-grown silicon wafers, directly exposed to a hydrogen plasma, is investigated by a combination of capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements. C-V analysis demonstrates diffusionlike concentration profiles close to the surface, pointing to the formation of hydrogen-related shallow donors in silicon during the hydrogenation. In addition, oxygen thermal donors are created during a subsequent annealing (20 min) performed at 350–450 °C, as demonstrated by DLTS. It is shown that the hydrogen-related shallow donors are the dominant donors in as-hydrogenated samples, while hydrogen acts as a catalyst during the formation of oxygen thermal donors in the temperature range of 350–450 °C. It is finally shown that the formation of both kinds of donors is Fermi-level dependent.
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71.55.Cn Elemental semiconductors
72.80.Cw Elemental semiconductors
75.50.Pp Magnetic semiconductors
52.77.Dq Plasma-based ion implantation and deposition
61.72.Cc Kinetics of defect formation and annealing
71.20.Mq Elemental semiconductors

Formation of nanovoids in high-dose hydrogen implanted GaN

I. Radu, R. Singh, R. Scholz, U. Gösele, S. Christiansen, G. Brüderl, C. Eichler, and V. Härle

Appl. Phys. Lett. 89, 031912 (2006); http://dx.doi.org/10.1063/1.2221526 (2 pages) | Cited 12 times

Online Publication Date: 18 July 2006

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The formation of nanovoids upon high-dose hydrogen implantation and subsequent annealing in GaN is investigated by transmission electron microscopy. The epitaxial GaN layers on sapphire were implanted at room temperature with H2+ ions at 100 keV with a dose of 13×1016 cm−2. Cross section transmission electron microscopy investigations revealed that nanovoids about 2 nm in diameter had formed during hydrogen implantation at room temperature while large microcracks ( ∼ 150–200 nm long) occurred upon annealing (1 h at 700 °C) leading to surface blistering. The nanovoids serve as precursors to the microcrack formation and are essential for the blistering process.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.37.Lp Transmission electron microscopy (TEM)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Bidirectional thermal expansion measurement for evaluating Poisson’s ratio of thin films

Jiping Ye, Satoshi Shimizu, Shigeo Sato, Nobuo Kojima, and Junnji Noro

Appl. Phys. Lett. 89, 031913 (2006); http://dx.doi.org/10.1063/1.2227524 (3 pages) | Cited 3 times

Online Publication Date: 18 July 2006

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An original and practical method is demonstrated for determining Poisson’s ratio of thin films by detecting thermal expansion in two directions perpendicular to each other. In the direction within the film, the temperature gradient of the biaxial thermal stress Δσf/ΔT was obtained by substrate curvature measurements; in the direction perpendicular to the film, the temperature gradient of the whole thermal expansion strain Δd/dΔT along the film thickness d was measured by x-ray reflectivity. It was found that Poisson’s ratio of thin films with a thickness of several hundred nanometers can be determined from Δσf/ΔT, Δd/dΔT, reduced modulus Er of the film, and from the thermal expansion coefficient αs of the substrate.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
65.40.De Thermal expansion; thermomechanical effects

Room temperature bonding of silicon and lithium niobate

M. M. R. Howlader, T. Suga, and M. J. Kim

Appl. Phys. Lett. 89, 031914 (2006); http://dx.doi.org/10.1063/1.2229262 (3 pages) | Cited 4 times

Online Publication Date: 19 July 2006

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The feasibility of wafer-level bonding was examined for silicon (Si)/lithium niobate (LiNbO3) wafers by using a modified surface activated bonding process at room temperature. A low energy argon ion source of 80 eV energy with 3 A current was used, which was capable of sputter cleaning and depositing Fe nanolayers on the surfaces. Visual inspection showed that almost all of the 4 in. Si/LiNbO3 wafers were bonded. The measured bond strengths were as high as 37 MPa but were inhomogeneous. This is due to the lack of uniform application of force over the surfaces (which are not parallel to the jigs) and the pulling angles during the pulling test. A 5 nm thick amorphous layer was observed across the Si/LiNbO3 interface. Electron energy loss spectroscopy analysis confirmed the presence of Fe in the interfacial amorphous layer. This Fe-containing interfacial layer appears to be responsible for the high bonding strength observed between Si/LiNbO3 at room temperature.
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81.20.Vj Joining; welding
81.65.Cf Surface cleaning, etching, patterning
61.80.Jh Ion radiation effects
61.82.-d Radiation effects on specific materials

Ca test of Al2O3 gas diffusion barriers grown by atomic layer deposition on polymers

P. F. Carcia, R. S. McLean, M. H. Reilly, M. D. Groner, and S. M. George

Appl. Phys. Lett. 89, 031915 (2006); http://dx.doi.org/10.1063/1.2221912 (3 pages) | Cited 78 times

Online Publication Date: 19 July 2006

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Quantitative Ca tests were used to determine the water vapor transmission rate (WVTR) through 25 nm thick Al2O3 gas diffusion barriers grown on plastic by atomic layer deposition (ALD). The measured WVTRs were 1.7×10−5 g/m2 day at 38 °C and 6.5×10−5 g/m2 day at 60 °C. Based on the apparent activation energy, the WVTR at 23 °C is estimated to be only 6×10−6 g/m2 day. The WVTR values for the Al2O3 ALD film are very similar to the WVTR value for the glass control. These Ca tests indicate that Al2O3 ALD gas diffusion barriers should enable display and lighting applications of highly moisture sensitive organic light-emitting diodes on plastic.
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81.05.Bx Metals, semimetals, and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth

Investigation of the initial stage of GaN epitaxial growth on 6H-SiC (0001) at room temperature

M. H. Kim, M. Oshima, H. Kinoshita, Y. Shirakura, K. Miyamura, J. Ohta, A. Kobayashi, and H. Fujioka

Appl. Phys. Lett. 89, 031916 (2006); http://dx.doi.org/10.1063/1.2227616 (3 pages) | Cited 22 times

Online Publication Date: 19 July 2006

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We have investigated the initial stage of GaN epitaxial growth on 6H-SiC (0001) at low substrate temperatures by pulsed laser deposition (PLD). We found that GaN grows epitaxially even at room temperature (RT) on atomically flat 6H-SiC (0001) surfaces, which can be explained by the enhanced surface migration of film precursors due to the use of PLD and atomically flat substrates. In situ reflection high-energy election diffraction observations have revealed that GaN films grown at above 300 °C proceed in a three-dimensional mode, while those at RT proceed in a layer-by-layer growth mode with atomically flat terraces and steps. The step height turned out to be 1.5 nm, which is the same height as the steps on the SiC substrates. This result indicates that the step height on the SiC surface is retained as the GaN grows.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition

Effect of the initial structure of silicon surface on the generation of multiple structural phases by cyclic microindentation

P. S. Pizani, R. G. Jasinevicius, and A. R. Zanatta

Appl. Phys. Lett. 89, 031917 (2006); http://dx.doi.org/10.1063/1.2227644 (3 pages) | Cited 7 times

Online Publication Date: 19 July 2006

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Raman scattering technique was used to investigate the structural phase transformations and multiple phase generation of silicon induced by cyclic microindentations. Indentation cycles were performed on three different samples: monocrystalline, amorphous film, and on partially amorphous silicon generated by single point diamond turning. The results indicated that the formation of some pressure induced structural phases may be dependent upon the initial structural state of the materials surface: Several different structural phases were only observed in crystalline and partially amorphous Si after microindentation cycles. For completely amorphous Si, no phase formation was evidenced even after several cyclic indentations.
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68.35.Gy Mechanical properties; surface strains
68.55.-a Thin film structure and morphology
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
78.30.Am Elemental semiconductors and insulators
64.70.K- Solid-solid transitions
68.47.Fg Semiconductor surfaces

Growth and epitaxial structure of LaVOx films

Y. Hotta, Y. Mukunoki, T. Susaki, H. Y. Hwang, L. Fitting, and D. A. Muller

Appl. Phys. Lett. 89, 031918 (2006); http://dx.doi.org/10.1063/1.2227786 (3 pages) | Cited 9 times

Online Publication Date: 20 July 2006

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We have studied the phase diagram of LaVOx films grown on (001) SrTiO3 substrates by pulsed laser deposition. With increasing oxygen partial pressure, the growth phase diagram varies between epitaxial perovskite LaV3+O3 single crystal films and polycrystalline monoclinic LaV5+O4. An interesting feature is the lack of an accessible phase corresponding to V4+, resulting in an extended region of phase coexistence of LaVO3 and LaVO4. Atomically flat LaVO3 could be grown in both layer-by-layer and step-flow growth modes, making this a promising candidate for incorporating strongly correlated electrons in atomic-scale perovskite heterostructures.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
81.30.Dz Phase diagrams of other materials
71.27.+a Strongly correlated electron systems; heavy fermions

Effect of two-step growth on the heteroepitaxial growth of InSb thin film on Si (001) substrate: A transmission electron microscopy study

Y. H. Kim, J. Y. Lee, Y. G. Noh, M. D. Kim, Y. J. Kwon, J. E. Oh, and R. Gronsky

Appl. Phys. Lett. 89, 031919 (2006); http://dx.doi.org/10.1063/1.2228028 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2006

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InSb thin films were grown on Si (001) substrate via both conventional one-step growth and two-step growth methods by molecular beam epitaxy. The effect of two-step growth was investigated by transmission electron microscopy. A lot of planar defects and surface steps were observed in the InSb thin film directly grown on buffer layer. The crystalline quality of the InSb thin film was improved when it was grown via two-step growth. The low-temperature InSb initiation layer of two-step growth relieved a misfit strain by generating 90° misfit dislocations and obstructed the propagation of defects by trapping at the interface.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Fluid dielectric loading on leaky Lamb wave of a piezoelectric plate

Yung-Chun Lee and Shi Hoa Kuo

Appl. Phys. Lett. 89, 031920 (2006); http://dx.doi.org/10.1063/1.2234286 (3 pages) | Cited 1 time

Online Publication Date: 20 July 2006

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This letter reports a high-precision wave measurement system for accurately determining the velocity of leaky Lamb wave. For an X-cut LiNbO3 plate, the change in leaky Lamb wave velocity induced by fluid’s dielectric loading effect has been measured. The measured correlation between fluid’s permittivity and induced wave velocity variation has been compared with theoretical results obtained form partial wave theory. Good agreements are observed. Potential applications of this wave measurement system are addressed.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
68.35.Iv Acoustical properties
77.22.Ch Permittivity (dielectric function)

Complex quantum ring structures formed by droplet epitaxy

Shesong Huang, Zhichuan Niu, Zhidan Fang, Haiqiao Ni, Zheng Gong, and Jianbai Xia

Appl. Phys. Lett. 89, 031921 (2006); http://dx.doi.org/10.1063/1.2234564 (3 pages) | Cited 26 times

Online Publication Date: 20 July 2006

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Well-defined complex quantum ring structures formed by droplet epitaxy are demonstrated. By varying the temperature of the crystallizing Ga droplets and changing the As flux, GaAs/AlGaAs quantum single rings and concentric quantum double rings are fabricated, and double-ring complexes are observed. The growth mechanism of these quantum ring complexes is addressed.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.65.Hb Quantum dots (patterned in quantum wells)

Partial-dislocation-mediated processes in nanocrystalline Ni with nonequilibrium grain boundaries

X. L. Wu and Y. T Zhu

Appl. Phys. Lett. 89, 031922 (2006); http://dx.doi.org/10.1063/1.2227639 (3 pages) | Cited 26 times

Online Publication Date: 20 July 2006

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The partial-dislocation-mediated processes have so far eluded high-resolution transmission electron microscopy studies in nanocrystalline (nc) Ni with nonequilibrium grain boundaries. It is revealed that the nc Ni deformed largely by twinning instead of extended partials. The underlying mechanisms including dissociated dislocations, high residual stresses, and stress concentrations near stacking faults are demonstrated and discussed.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.46.Hk Nanocrystals
61.72.Mm Grain and twin boundaries
68.37.Lp Transmission electron microscopy (TEM)
61.72.Nn Stacking faults and other planar or extended defects

Initial stage of the overgrowth of InP on InAs/InP(001) quantum dots: Formation of InP terraces driven by preferential nucleation on quantum dot edges

G. Saint-Girons, G. Patriarche, A. Michon, G. Beaudoin, I. Sagnes, K. Smaali, and M. Troyon

Appl. Phys. Lett. 89, 031923 (2006); http://dx.doi.org/10.1063/1.2233554 (3 pages) | Cited 7 times

Online Publication Date: 21 July 2006

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This letter reports on the growth mechanism of the InP cap layer over InAs/InP quantum dots (QDs) fabricated by metal organic vapor phase epitaxy (MOVPE). QD edges are shown to act as preferential nucleation sites for the InP cap layer, leading to the formation of InP domains around the nanostructures. As/P exchange reactions are at the origin of the planarization of the top of the QDs under P-rich ambient, thus leading to a final QD height equal to the local thickness of the InP cap layer. The possibility to use As/P exchange reactions to homogenize the height distribution of MOVPE grown InAs/InP QDs is discussed on the basis of these observations.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
64.60.Q- Nucleation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

On the existence of Einstein oscillators and thermal conductivity in bulk metallic glass

Zhenhua Zhou, Ctirad Uher, Donghua Xu, W. L. Johnson, W. Gannon, and M. C. Aronson

Appl. Phys. Lett. 89, 031924 (2006); http://dx.doi.org/10.1063/1.2234281 (3 pages) | Cited 8 times

Online Publication Date: 21 July 2006

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Low-temperature specific heat and thermal conductivity of bulk metallic glasses are measured to identify the primary vibrational modes associated with their unique structures. An Einstein-type localized vibrational mode with an Einstein temperature of 112 K is found in bulk metallic glass Ni59.5Nb33.6Sn6.9. This localized vibrational mode causes resonant scattering of phonons and results in the localization of phonons which leaves the phonon hopping conduction the limiting mechanism of thermal transport in bulk metallic glass Ni59.5Nb33.6Sn6.9 at high temperature.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.50.-x Vibrational states in disordered systems
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
61.43.Fs Glasses

Elastic modulus of polystyrene film from near surface to bulk measured by nanoindentation using atomic force microscopy

Koji Miyake, Noriaki Satomi, and Shinya Sasaki

Appl. Phys. Lett. 89, 031925 (2006); http://dx.doi.org/10.1063/1.2234648 (3 pages) | Cited 25 times

Online Publication Date: 21 July 2006

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Using atomic force microscopy with a spherical indenter, we evaluated the surface and bulk elastic modulus of thick and thin polystyrene films. The elastic modulus of the thick films at penetration depths of more than 10 nm was equivalent to that of bulk measured by a tensile test. In the thin films, the estimated values were greatly affected by the substrate material at penetration depths of more than 7 nm. When the penetration depth was less than 5 nm, however, the elastic modulus of both thin and thick films was slightly smaller than that of the bulk values.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.60.Bs Mechanical and acoustical properties
68.35.Gy Mechanical properties; surface strains
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