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1 Oct 2010

Volume 108, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 108, 071301 (2010); http://dx.doi.org/10.1063/1.3460809 (38 pages)

Y. H. Wu, T. Yu, and Z. X. Shen
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back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Spectroscopic analysis of Eu3+ -and Eu3+:Yb3+-doped yttrium silicate crystalline powders prepared by combustion synthesis

Nikifor Rakov, Dayanne F. Amaral, Renato B. Guimarães, and Glauco S. Maciel

J. Appl. Phys. 108, 073501 (2010); http://dx.doi.org/10.1063/1.3489992 (6 pages) | Cited 8 times

Online Publication Date: 4 October 2010

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Yttrium silicate powders doped with Eu3+ and codoped with Eu3+ and Yb3+ were prepared by combustion synthesis. The x-ray powder diffraction data showed the presence of Y2SiO5 and Y2Si2O7 crystalline phases. Singly doped (1 wt %) sample illuminated with ultraviolet light (λ = 256 nm) showed the characteristic red luminescence corresponding to 5D0→7FJ transitions of Eu3+. The Judd–Ofelt intensity parameters were calculated from experimental data and the radiative and nonradiative relaxation rates were estimated. The results showed that the nonradiative relaxation rate is smaller in yttrium silicate compared to yttrium oxide powder, a reference material, prepared under similar conditions. Codoped samples were exposed to near-infrared laser excitation (λ = 975 nm) and the red luminescence of Eu3+ was also observed. In this case, the luminescence is achieved due to a cooperative upconversion (CUC) process involving energy transfer (ET) from pairs of ytterbium ions to europium ions. The ET rate was estimated by fitting a rate equation model with the dynamics of CUC red emission.
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78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Hx Other solid inorganic materials
81.05.Cy Elemental semiconductors
61.43.Gt Powders, porous materials

The role of aging on the mechanical and microstructural response of aluminum 6061 to one-dimensional shock loading

J. C. F. Millett, N. K. Bourne, M. Q. Chu, I. P. Jones, G. T. Gray, III, and G. Appleby-Thomas

J. Appl. Phys. 108, 073502 (2010); http://dx.doi.org/10.1063/1.3490135 (9 pages) | Cited 2 times

Online Publication Date: 4 October 2010

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The shock response of the aluminum alloy 6061, and its variation according to heat treatment have been monitored via the placement of stress gauges in such orientations so as to be sensitive to the lateral component of stress, and hence the shear strength. To complement these measurements, the postshock microstructure and mechanical response have also been determined via full one-dimensional recovery techniques. Results have shown that the solution treated (T0) state, as a largely single phase material displays a fast rising shock pulse with a significant degree of hardening behind the shock front. This indicates that a high degree of dislocation generation is expected. Postshock analysis of recovered samples has confirmed this hypothesis, with dislocation cells being observed and a notable increase in the yield strength in comparison to the as-received material. In contrast, the aged (T6) experiments showed a much longer rise time with a lower degree of hardening behind the shock front. Microstructural analysis postshock shows a more randomized dislocation distribution, with little or no postshock hardening occurring once the shock induced strain has been accounted for. This has been attributed to the presence of fine Mg2Si precipitates inhibiting the motion and generation of dislocations. These measurements are in agreement with work previously carried out on this material. Comparison of the shear strengths of the two heat treatments also shows that although the T6 condition is a little higher than T0, the differences are somewhat lower than expected.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
61.72.Lk Linear defects: dislocations, disclinations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Gh Other heat and thermomechanical treatments
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging

Inverse Hall–Petch relationship in the nanostructured TiO2: Skin-depth energy pinning versus surface preferential melting

X. J. Liu, L. W. Yang, Z. F. Zhou, Paul K. Chu, and Chang Q. Sun

J. Appl. Phys. 108, 073503 (2010); http://dx.doi.org/10.1063/1.3471818 (5 pages) | Cited 1 time

Online Publication Date: 5 October 2010

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The functional dependence of stress, elastic modulus, melting point, and their interdependence on the identities (bond order, nature, length, and strength) of a representative bond of the specimen has been established for deeper insight into the transition from the conventional Hall–Petch relationship (HPR) to the inverse HPR (IHPR) for nanostructured TiO2. Theoretical reproduction of the observed inverse HPR suggests that the intrinsic competition between the energy-density gain (elastic modulus enhancement) and the cohesive-energy remnant (melting point depression) in the grain boundaries originates and the extrinsic competition between the activation and the inhibition of atomic dislocations activates the IHPR.
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61.46.-w Structure of nanoscale materials
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
64.70.dj Melting of specific substances
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.23.-c Structural classes of nanoscale systems

Optical characteristics of a-plane ZnO/Zn0.8Mg0.2O multiple quantum wells grown by pulsed laser deposition

T. S. Ko, T. C. Lu, L. F. Zhuo, W. L. Wang, M. H. Liang, H. C. Kuo, S. C. Wang, Li Chang, and D. Y. Lin

J. Appl. Phys. 108, 073504 (2010); http://dx.doi.org/10.1063/1.3488898 (5 pages) | Cited 7 times

Online Publication Date: 5 October 2010

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We reported optical properties of a-plane ZnO/ZnMgO multiple quantum wells (MQWs) structure grown by the pulse laser deposition system. The emission peak energy of a-plane ZnO/ZnMgO MQWs kept invariant in the power-dependent photoluminescence (PL) measurement, indicating the nonpolar characteristics due to the lack of built-in electric fields. Large exciton binding energy of 68 meV was deduced and no apparent S-curve appeared in temperature-dependent PL results, demonstrating less carrier localization effect in a-plane ZnO/ZnMgO MQWs. Large difference in electronic transition levels of 45 meV due to the valence band splitting was observed in the polarization dependent absorption spectrum. Furthermore, the high degree of polarization of 92% and 56% at 20 and 300 K in PL emission of a-plane ZnO/ZnMgO MQWs were obtained.
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78.67.De Quantum wells
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition

Short and intermediate range order of Ge20Se80−xTex glasses

A. H. Moharram, M. A. Hefni, and A. M. Abdel-Baset

J. Appl. Phys. 108, 073505 (2010); http://dx.doi.org/10.1063/1.3488907 (5 pages)

Online Publication Date: 5 October 2010

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The total structure factor, S(K), have been obtained for the chalcogenide Ge20Se80−xTex (where x = 0, 10, 20, and 30 at. %) glasses using x-ray diffraction in the wave vector interval 0.28 ≤ K ≤ 6.87 Å−1. The appearance of the first sharp diffraction peak in the structure factor indicates the presence of the intermediate range order. The radii of the first- and second-coordination shells (r1,r2) are increased linearly with Te addition. The large covalent radius of Te atom in compare with that of Se atom was behind the above linear increase. The first coordination number shows insignificant changes with Te content. The obtained values of r1/r2 ratio and the corresponding bond angle (Θ) indicate that the structural units inside the present alloys are Ge(Se1/2)4 tetrahedra connected by chains of the chalcogen atoms. Raman spectra confirm the above conclusion and in the same time exclude the existence of Ge(Te1/2)4 tetrahedra. Based on the chemical ordered network mode, Te–Te bonds are responsible for the different behavior of Te-rich (30 at. %) glass from others.
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61.43.Fs Glasses
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Chemical potentials for Au-assisted vapor-liquid-solid growth of III-V nanowires

Frank Glas

J. Appl. Phys. 108, 073506 (2010); http://dx.doi.org/10.1063/1.3488908 (6 pages) | Cited 6 times

Online Publication Date: 5 October 2010

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For use in quantitatively modeling the growth of gold-seeded semiconductor nanowires in the vapor-liquid-solid mode, we calculate the difference of chemical potential between a liquid melt formed of group III and group V atoms dissolved in gold and the corresponding solid III-V binary compound. Fits to our results are provided for seven compounds as simple polynomials of the concentrations in the III-V-Au liquid and temperature. We find that the difference of chemical potential increases with the group III and group V concentrations, decreases with increasing temperature, and can easily reach several hundreds of meV per III-V pair. We discuss these values and variations in the light of published experimental results, in particular as regards the crystalline structure adopted by the nanowires during growth.
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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)
81.07.Gf Nanowires
81.10.Fq Growth from melts; zone melting and refining

Photoluminescence in electronic ferroelectric Er1−xYbxFe2O4

R. Wang, H. X. Yang, Y. B. Qin, B. Dong, J. Q. Li, and Jimin Zhao

J. Appl. Phys. 108, 073507 (2010); http://dx.doi.org/10.1063/1.3490212 (5 pages)

Online Publication Date: 5 October 2010

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Strong Stark splitting, which is nearly independent of the R-ions replacement, has been observed through the photoluminescence investigation of electronic ferroelectric Er1−xYbxFe2O4 (x = 0, 0.8, 0.9, and 0.95). Initially multiple radiative decay channels have been investigated, especially the visible transition 4F9/2→4I15/2, of which a quenching effect has been observed. A series of small non-Raman peaks have been observed superimposed on a broadband photoluminescence spectrum, of which we tentatively assign Stark splitting to be the cause. The splitting of the 4F9/2 and 4I15/2 levels is found to be 54 meV and 66 meV, respectively. This unusually large Stark splitting at visible range indicates the existence of strong local field originated from the W-layer in the charge-frustrated ErFe2O4.
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78.55.Hx Other solid inorganic materials
77.80.-e Ferroelectricity and antiferroelectricity
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Jq Electro-optical effects

Near band edge anisotropic optical transitions in wide band gap semiconductor Cu2ZnSiS4

S. Levcenco, D. Dumcenco, Y. S. Huang, E. Arushanov, V. Tezlevan, K. K. Tiong, and C. H. Du

J. Appl. Phys. 108, 073508 (2010); http://dx.doi.org/10.1063/1.3490219 (5 pages) | Cited 5 times

Online Publication Date: 6 October 2010

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In this study, anisotropic near band edge transitions of Cu2ZnSiS4 single crystals grown by chemical vapor transport were characterized by using polarization-dependent absorption, piezoreflectance (PzR) and surface photovoltage (SPV) spectroscopy techniques at room temperature. The measurements were carried out on the as grown basal plane with the normal along [2 1 0] and the axis c parallel to the long edge of the crystal platelet. Analysis of absorption and SPV spectra reveal indirect allowed transitions for the absorption edge of Cu2ZnSiS4. The estimated values of indirect band gap are 2.97 eV and 3.07 eV, respectively, for E⊥c and E∥c polarization configurations. The polarization-dependent PzR and SPV spectra in the vicinity of the direct band gap of Cu2ZnSiS4 reveal features E⊥ex and E∥ex at around 3.32 eV and 3.41 eV for E⊥c and E∥c polarizations, respectively. Both features E⊥ex and E∥ex are associated with the interband excitonic transitions at point Γ and can be explained by crystal-field splitting of valence band. Based on the experimental observations, a plausible band structure near band edge of Cu2ZnSiS4 is proposed.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
81.10.Bk Growth from vapor
72.40.+w Photoconduction and photovoltaic effects

Atomic force microscopy of orb-spider-web-silks to measure surface nanostructuring and evaluate silk fibers per strand

D. M. Kane, N. Naidoo, and G. R. Staib

J. Appl. Phys. 108, 073509 (2010); http://dx.doi.org/10.1063/1.3490220 (5 pages) | Cited 3 times

Online Publication Date: 6 October 2010

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Atomic force microscopy (AFM) study is used to measure the surface topology and roughness of radial and capture spider silks on the micro- and nanoscale. This is done for silks of the orb weaver spider Argiope keyserlingi. Capture silk has a surface roughness that is five times less than that for radial silk. The capture silk has an equivalent flatness of λ/100 (5–6 nm deep surface features) as an optical surface. This is equivalent to a very highly polished optical surface. AFM does show the number of silk fibers that make up a silk thread but geometric distortion occurs during sample preparation. This prevented AFM from accurately measuring the silk topology on the microscale in this study.
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68.35.bm Polymers, organics
61.46.-w Structure of nanoscale materials
68.37.Ps Atomic force microscopy (AFM)

Reversible room temperature ferromagnetism in undoped zinc oxide: Correlation between defects and physical properties

Siddhartha Mal, Sudhakar Nori, Chunming Jin, J. Narayan, S. Nellutla, A. I. Smirnov, and J. T. Prater

J. Appl. Phys. 108, 073510 (2010); http://dx.doi.org/10.1063/1.3491037 (10 pages) | Cited 14 times

Online Publication Date: 6 October 2010

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We report a systematic study of the structural, chemical, electrical, optical, and magnetic properties of undoped ZnO thin films grown under different conditions as well as the films that were annealed in various environments. Oxygen-annealed films displayed a sequential transition from ferromagnetism to diamagnetism as a function of the annealing temperature. An increase in the green band intensity has been observed in oxygen-annealed ZnO films. Reversible switching of room-temperature ferromagnetism and n-type conductivity have been demonstrated by oxygen and vacuum annealing. Electron paramagnetic resonance data were found to be in agreement with the results of magnetization and conductivity measurements. Possibility of external ferromagnetic impurity as the origin of the unconventional room temperature ferromagnetism in these films has been ruled out by secondary ion mass spectrometer and electron energy loss spectroscopy studies. Correlation between structural, electrical, optical, and magnetic properties has been established in terms of defects and defect complexes. Taken together, our data indicate that the ferromagnetic order in ZnO matrix might be defect-mediated.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

A continuum framework for grain boundary diffusion in thin film/substrate systems

Can Ayas and Erik van der Giessen

J. Appl. Phys. 108, 073511 (2010); http://dx.doi.org/10.1063/1.3488897 (10 pages)

Online Publication Date: 6 October 2010

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A two-dimensional continuum model is developed for stress relaxation in thin films through grain boundary (GB) diffusion. When a thin film with columnar grains is subjected to thermal stress, stress gradients along the GBs are relaxed by diffusion of material from the film surface into the GBs. The transported material constitutes a wedge and becomes the source of stress inside the adjacent elastic grains that are perfectly bonded to the substrate. In the model, the coupling between diffusion and elasticity is obtained by numerically solving the governing equations in a staggered manner. A finite difference scheme is used to solve the diffusion equations, modified in order to implement realistic boundary conditions, while the elasticity problem is solved with the finite element method. The solutions reveal the existence of a universal power law scaling between the unrelaxed fraction of stress and the grain aspect ratio. For slender grains, the GB wedge attains a more uniform shape and relaxation is more effective. The kinetics of the process depends not only on the grain aspect ratio but also strongly on the thickness of the film. In case there is no adhesion between film and substrate, complete stress relaxation is attained albeit at a slightly slower rate.
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61.72.Mm Grain and twin boundaries
66.30.-h Diffusion in solids
68.55.-a Thin film structure and morphology
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Formation trends of ordered self-assembled nanoislands on stepped substrates

S. Liang, H. L. Zhu, D. H. Kong, and W. Wang

J. Appl. Phys. 108, 073512 (2010); http://dx.doi.org/10.1063/1.3490184 (5 pages) | Cited 1 time

Online Publication Date: 6 October 2010

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The growth of ordered self-assembled nanoislands on stepped substrates is studied systematically by kinetic Monte Carlo simulations. As the terrace width is small, the formation of nanoislands is confined in the steps and nanoislands ordered in lines or nanowires can be obtained. The Schwoebel barrier at the step edges has a great influence on the evolution of both the size and space distributions of the islands. When the terrace width is relatively large, self-ordering of nanoislands in the center regions of the terraces happens. An unexpected trend of the nanoisland self-ordering is found as the deposition thickness is larger than 0.2 ML, which can be related to the attractive migrations between nearby islands.
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81.16.Dn Self-assembly
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)
61.43.Bn Structural modeling: serial-addition models, computer simulation

Hydrogen storage and phase transformations in Mg–Pd nanoparticles

E. Callini, L. Pasquini, L. H. Rude, T. K. Nielsen, T. R. Jensen, and E. Bonetti

J. Appl. Phys. 108, 073513 (2010); http://dx.doi.org/10.1063/1.3490206 (7 pages) | Cited 5 times

Online Publication Date: 6 October 2010

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Microstructure refinement and synergic coupling among different phases are currently explored strategies to improve the hydrogen storage properties of traditional materials. In this work, we apply a combination of these methods and synthesize Mg–Pd composite nanoparticles by inert gas condensation of Mg vapors followed by vacuum evaporation of Pd clusters. Irreversible formation of the Mg6Pd intermetallic phase takes place upon vacuum annealing, resulting in Mg/Mg6Pd composite nanoparticles. Their hydrogen storage properties are investigated and connected to the undergoing phase transformations by gas-volumetric techniques and in situ synchrotron radiation powder x-ray diffraction. Mg6Pd transforms reversibly into different Mg–Pd intermetallic compounds upon hydrogen absorption, depending on temperature and pressure. In particular, at 573 K and 1 MPa hydrogen pressure, the metal-hydride transition leads to the formation of Mg3Pd and Mg5Pd2 phases. By increasing the pressure to 5 MPa, the Pd-richer MgPd intermetallic is obtained. Upon hydrogen desorption, the Mg6Pd phase is reversibly recovered. These phase transformations result in a specific hydrogen storage capacity associated with Mg–Pd intermetallics, which attain the maximum value of 3.96 wt % for MgPd and influence both the thermodynamics and kinetics of hydrogen sorption in the composite nanoparticles.
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88.30.R- Hydrogen storage
68.43.Nr Desorption kinetics
81.07.Bc Nanocrystalline materials
65.40.G- Other thermodynamical quantities
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments
64.70.fm Thermodynamics studies of evaporation and condensation
68.43.Mn Adsorption kinetics

Interaction of dopant atoms with stacking faults in silicon crystals

Y. Ohno, T. Taishi, Y. Tokumoto, and I. Yonenaga

J. Appl. Phys. 108, 073514 (2010); http://dx.doi.org/10.1063/1.3490753 (4 pages) | Cited 2 times

Online Publication Date: 7 October 2010

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Variation in stacking fault energy with annealing at 1173 K were identified in Czochralski-grown silicon crystals heavily doped with n- or p-type dopant atoms. In n-type crystals, the energy decreased with increasing annealing time. The higher the concentration of dopant atoms, the larger the degree of the decrease. On the other hand, the energy was unchanged during annealing in p-type and nondoped crystals. These results imply that n-type dopant atoms segregate nearby a stacking fault, via their thermal migration, under an electronic interaction leading to a reduction in the stacking fault energy.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Nn Stacking faults and other planar or extended defects
61.72.sd Impurity concentration
61.72.Cc Kinetics of defect formation and annealing

Role of dispersion on phononic thermal boundary conductance

John C. Duda, Thomas E. Beechem, Justin L. Smoyer, Pamela M. Norris, and Patrick E. Hopkins

J. Appl. Phys. 108, 073515 (2010); http://dx.doi.org/10.1063/1.3483943 (10 pages) | Cited 17 times

Online Publication Date: 7 October 2010

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The diffuse mismatch model (DMM) is one of the most widely implemented models for predicting thermal boundary conductance at interfaces where phonons dominate interfacial thermal transport. In the original presentation of the DMM, the materials comprising the interface were described as Debye solids. Such a treatment, while accurate in the low temperature regime for which the model was originally intended, is less accurate at higher temperatures. Here, the DMM is reformulated such that, in place of Debye dispersion, the materials on either side of the interface are described by an isotropic dispersion obtained from exact phonon dispersion diagrams in the [100] crystallographic direction. This reformulated model is applied to three interfaces of interest: Cr–Si, Cu–Ge, and Ge–Si. It is found that Debye dispersion leads to substantially higher predictions of thermal boundary conductance. Additionally, it is shown that optical phonons play a significant role in interfacial thermal transport, a notion not previously explored. Lastly, the role of the assumed dispersion is more broadly explored for Cu–Ge interfaces. The prediction of thermal boundary conductance via the DMM with the assumed isotropic [100] dispersion relationships is compared to predictions with isotropic [111] and exact three-dimensional phonon dispersion relationships. It is found that regardless of the chosen crystallographic direction, the predictions of thermal boundary conductance using isotropic phonon dispersion relationships are within a factor of two of those predictions using an exact three-dimensional phonon dispersion.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Mechanism of amorphous state formation, crystalline structure, and hyperfine interactions in DyMn6−xGe6Fex (0 ≤ x ≤ 6) alloys

Z. Śniadecki, B. Mielniczuk, B. Idzikowski, J.-M. Greneche, and U. K. Rößler

J. Appl. Phys. 108, 073516 (2010); http://dx.doi.org/10.1063/1.3490246 (6 pages)

Online Publication Date: 7 October 2010

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Metallic glass formation is observed in rapidly quenched quaternary DyMn6−xGe6Fex (0 ≤ x ≤ 6) alloys. The easy formation of amorphous states competes with the nucleation of ternary 1:6:6 rare earth-transition metal-metal compounds DyMn6Ge6 and DyFe6Ge6. The ribbon shaped samples were quenched and investigated by x-ray diffraction, differential scanning calorimetry, and 57Fe Mössbauer spectrometry. Melt-spun alloys from the series of DyMn6−xGe6Fex with x = 0, 2 ≤ x ≤ 3, and x = 6 do not display an amorphous state but a crystalline chemically disordered structure similar to that of TbCu7- or TbFe6Sn6-type (space group P6/mmm). Amorphous samples exhibit two crystallization steps but there is no clear evidence for a glass transition effect in the calorimetric data. The Kissinger analysis was performed to calculate the effective activation energy Ea, which is equal to 345±20 kJ/mol for amorphous DyMn5.5Ge6Fe0.5 alloy. Mössbauer spectra at 77 and 300 K consist of either magnetic sextets or quadrupolar doublets for high and low Fe content, respectively. The features reflect the dilution of Fe on crystallographic sites and the subsequent increase in topological and chemical disorder when the Mn content increases. The Miedema's semiempirical model was used to calculate the formation enthalpies of amorphous alloys (ΔHform). The calculated values are consistent with experimental results. The present model allows thus to explain the better glass forming ability for the compositions with high Mn content, where ΔHform is the most negative.
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64.70.kj Glasses
64.70.pe Metallic glasses
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.60.qj Studies of nucleation in specific substances
61.66.Dk Alloys
71.70.Jp Nuclear states and interactions

Fracture of electrodes in lithium-ion batteries caused by fast charging

Kejie Zhao, Matt Pharr, Joost J. Vlassak, and Zhigang Suo

J. Appl. Phys. 108, 073517 (2010); http://dx.doi.org/10.1063/1.3492617 (6 pages) | Cited 24 times

Online Publication Date: 8 October 2010

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During charging or discharging of a lithium-ion battery, lithium is extracted from one electrode and inserted into the other. This extraction-insertion reaction causes the electrodes to deform. An electrode is often composed of small active particles in a matrix. If the battery is charged at a rate faster than lithium can homogenize in an active particle by diffusion, the inhomogeneous distribution of lithium results in stresses that may cause the particle to fracture. The distributions of lithium and stress in a LiCoO2 particle are calculated. The energy release rates are then calculated for the particle containing preexisting cracks. These calculations predict the critical rate of charging and size of the particle, below which fracture is averted.
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88.80.ff Batteries
46.50.+a Fracture mechanics, fatigue and cracks

High-pressure x-ray diffraction study of bulk and nanocrystalline PbMoO4

D. Errandonea, D. Santamaria-Perez, V. Grover, S. N. Achary, and A. K. Tyagi

J. Appl. Phys. 108, 073518 (2010); http://dx.doi.org/10.1063/1.3493048 (5 pages) | Cited 6 times

Online Publication Date: 8 October 2010

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We studied the effects of high-pressure on the crystalline structure of bulk and nanocrystalline scheelite-type PbMoO4. We found that in both cases the compressibility of the materials is highly nonisotropic, being the c-axis the most compressible one. We also observed that the volume compressibility of nanocrystals becomes higher that the bulk one at 5 GPa. In addition, at 10.7(8) GPa we observed the onset of an structural phase transition in bulk PbMoO4. The high-pressure phase has a monoclinic structure similar to M-fergusonite. The transition is reversible and not volume change is detected between the low-pressure and high-pressure phases. No additional structural changes or evidence of decomposition are found up to 21.1 GPa. In contrast nanocrystalline PbMoO4 remains in the scheelite structure at least up to 16.1 GPa. Finally, the equation of state for bulk and nanocrystalline PbMoO4 are also determined.
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62.50.-p High-pressure effects in solids and liquids
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
64.70.K- Solid-solid transitions
81.40.Lm Deformation, plasticity, and creep
61.66.-f Structure of specific crystalline solids

Mechanisms leading to fast relaxation of liquid crystal cells aligned with conductive polymers

Gaetano Nicastro, Nicola Scaramuzza, Roberto Bartolino, Anca-Luiza Alexe-Ionescu, and Andrei Th. Ionescu

J. Appl. Phys. 108, 073519 (2010); http://dx.doi.org/10.1063/1.3477326 (6 pages) | Cited 2 times

Online Publication Date: 8 October 2010

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Using nematic liquid crystal cells aligned by conductive polymers, like polyaniline or doped polypyrrole, a very fast electro-optic response is observed. We show that when a switch that interrupts the voltage across the cell is placed between the cell and the ground, the largest voltage drop is on the switch in its open position. The voltage distribution among the nematic cell and the switch is evaluated. The role played in this very fast electro-optic response of the ionic charges built on the interfaces together with the redox processes among the free charges in the polymer-liquid crystal interface is also described. For an asymmetric cell (only one side covered with a conductive polymer) a rectifying effect appears. In this case a circuital model is used to mimic the steplike behavior of the transmitted light during the relaxation of the system.
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61.30.Vx Polymer liquid crystals
78.20.Jq Electro-optical effects

Thermal conduction in thin films measured by optical surface thermal lensing

Jean-Philippe Bourgoin, Guy-Germain Allogho, and Alain Haché

J. Appl. Phys. 108, 073520 (2010); http://dx.doi.org/10.1063/1.3490185 (6 pages) | Cited 9 times

Online Publication Date: 8 October 2010

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Thermal conduction across thin films is measured optically by using the surface thermal lensing effect. Pump-probe laser measurements combined with numerical modeling are used to study thermal conduction in a variety of materials as thin as 10 nm. The method is relatively simple, robust, rapid, and offers an alternative to current techniques. Thermal conductivity in gold films is found to drop from 300 to 100 W/Km when the film thickness is reduced from 2000 to 100 nm. Results for silver, tin and aluminum films are also presented and compared with results from other studies.
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68.60.Dv Thermal stability; thermal effects
78.20.nb Photothermal effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Dynamic phase transformation of crystalline silicon under the dry and wet impact studied by molecular dynamics simulation

Ruling Chen, Jianbin Luo, Dan Guo, and Hong Lei

J. Appl. Phys. 108, 073521 (2010); http://dx.doi.org/10.1063/1.3490757 (6 pages) | Cited 4 times

Online Publication Date: 8 October 2010

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Molecular dynamics simulation is applied in analyzing quantitatively the dynamic phase transformation of crystalline silicon under the dry and wet impact, respectively. At the impact loading stage, the phase transformation between fourfold silicon atoms and fivefold or threefold silicon atoms is affected only by the local pressure. The influence of the local temperature or the contact area on the phase transformation will emerge from the impact unloading stage. And the dynamic process of phase transformation between fourfold atoms and fivefold or threefold atoms will obey the Boltzmann distribution law by stages. The variance of the number of fivefold or fourfold atoms at impact loading stage is almost the same as the impact unloading stage. Furthermore, the dynamic residence time of fivefold or threefold atoms formed during the impact process will be about 250 fs. The half-life of these atoms is about 50 fs.
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64.70.kg Semiconductors
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Strain effects in GaN epilayers grown on different substrates by metal organic vapor phase epitaxy

L. Zhang (张丽旸), K. Cheng, S. Degroote, M. Leys, M. Germain, and G. Borghs

J. Appl. Phys. 108, 073522 (2010); http://dx.doi.org/10.1063/1.3493115 (6 pages) | Cited 4 times

Online Publication Date: 11 October 2010

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For practical applications, it is important to control strain by carefully tuning growth conditions for stress modification. Strain can have a pronounced impact on device behavior and is caused by extrinsic thermal stress and a tunable intrinsic growth stress. The impact of strain on GaN epilayers was investigated by photoluminescence and high resolution x-ray diffraction (XRD). The GaN samples were grown by metal organic vapor phase epitaxy, on sapphire, 4H–SiC, freestanding GaN and Si (111) substrates. Both free and bound exciton transitions were observed at low temperature, and their energy shift was analyzed with respect to the strain values derived from XRD. We also characterized the valence band split and the GaN bandgap as a function of the strain at 4 K.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Angular effects of nanostructure-covered femtosecond laser induced periodic surface structures on metals

Taek Yong Hwang and Chunlei Guo

J. Appl. Phys. 108, 073523 (2010); http://dx.doi.org/10.1063/1.3487934 (4 pages) | Cited 6 times

Online Publication Date: 11 October 2010

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In this paper, we study nanostructure-covered laser induced periodic surface structures (NC-LIPSSs) on metals produced by femtosecond laser pulses incident at various angles. For the first time, we show that the dependence of NC-LIPSS period on the incident beam angle deviates significantly from that of regular LIPSSs studied previously using longer laser pulses. Our study shows that this deviation is due to the nanostructures on LIPSSs that can be explained by the Maxwell–Garnett theory of effective media.
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81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
68.35.bd Metals and alloys
42.62.-b Laser applications

Spectral properties and 1.55 μm laser operation of Ce3+:Yb3+:Er3+:NaLa(WO4)2 crystal

Xinghong Gong, Yujin Chen, Yanfu Lin, Jianhua Huang, Zundu Luo, and Yidong Huang

J. Appl. Phys. 108, 073524 (2010); http://dx.doi.org/10.1063/1.3488895 (7 pages) | Cited 2 times

Online Publication Date: 11 October 2010

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A series of x at. %Ce3+:10 at. %Yb3+:1 at. %Er3+:NaLa(WO4)2 (x = 0,10,…,50) crystal powders were prepared by high temperature solid phase reaction. The effect of Ce3+ concentration on the 4I11/2→4I13/2 transition of Er3+ ions was analyzed. A single crystal of 48 at. %Ce3+:10.4 at. %Yb3+:1.6 at. %Er3+:NaLa(WO4)2 was grown by the Czochralski method. 1.2 W quasicontinuous-wave laser around 1.55 μm was realized when a 2.61 mm thick c-cut slice of the crystal was pumped by a diode laser at 970 nm. The achieved highest slope efficiency was 12.3% and the threshold was 3.8 W.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Xi Diode-pumped lasers
81.10.Fq Growth from melts; zone melting and refining

Nonlinear optical studies on nanocolloidal Ga–Sb–Ge–Se chalcogenide glass

R. Tintu, V. P. N. Nampoori, P. Radhakrishnan, and Sheenu Thomas

J. Appl. Phys. 108, 073525 (2010); http://dx.doi.org/10.1063/1.3481097 (5 pages) | Cited 5 times

Online Publication Date: 11 October 2010

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In this paper we report the preparation and the optical studies on nanocolloidal solutions of Ga5Sb10Ge25Se60 for the first time. The optical band gap of the material is found to be tunable depending on the cluster size. The cluster formation and the dependence of the cluster size with concentration were confirmed by the scanning electron microscope analysis. Nonlinear optical characterization of these solutions were studied by the Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz).The studies show that the material is highly nonlinear. The solutions show reverse saturable absorption, which makes it useful for optical limiting applications.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.47.jh Coherent nonlinear optical spectroscopy
82.70.Dd Colloids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
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