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10 Sep 2007

Volume 91, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 91, 112501 (2007); http://dx.doi.org/10.1063/1.2780107 (3 pages)

Y. Liu, S. Gliga, R. Hertel, and C. M. Schneider
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Local structure characterization in quasicrystal-forming Zr80Pt20 binary amorphous alloy

Junji Saida, Takashi Sanada, Shigeo Sato, Muneyuki Imafuku, and Akihisa Inoue

Appl. Phys. Lett. 91, 111901 (2007); http://dx.doi.org/10.1063/1.2778750 (3 pages) | Cited 4 times

Online Publication Date: 11 September 2007

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The local structure of melt-spun Zr80Pt20 alloy was investigated in the amorphous and icosahedral quasicrystal (QC)-formed states by x-ray diffraction and extended x-ray absorption fine structure measurements. While the local environment around the Zr atom in the amorphous state is considerably different from that in the QC-formed state, it remains during the quasicrystallization around the Pt atom. It is suggested that the stable icosahedral local structure is mainly formed in the center of the Pt atom in the amorphous state.
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61.44.Br Quasicrystals
78.70.Dm X-ray absorption spectra

Thermodynamic formalism of minimum heat source temperature for driving advanced adsorption cooling device

Bidyut Baran Saha, Anutosh Chakraborty, Shigeru Koyama, Kandadai Srinivasan, Kim Choon Ng, Takao Kashiwagi, and Pradip Dutta

Appl. Phys. Lett. 91, 111902 (2007); http://dx.doi.org/10.1063/1.2780117 (3 pages) | Cited 10 times

Online Publication Date: 11 September 2007

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This letter presents a thermodynamic formulation to calculate the minimum driving heat source temperature of an advanced solid sorption cooling device, and it is validated with experimental data. This formalism has been developed from the rigor of the Boltzmann distribution function and the condensation approximation of adsorptive molecules. An interesting and useful finding has been established from this formalism that it is possible to construct a solid sorption refrigeration device that operates in a cycle transferring heat from a low temperature source to a heat sink with a driving heat source at a temperature close to but above ambient.
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44.10.+i Heat conduction
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Resonant Raman scattering in hydrogen and nitrogen doped ZnO

F. Friedrich and N. H. Nickel

Appl. Phys. Lett. 91, 111903 (2007); http://dx.doi.org/10.1063/1.2783222 (3 pages) | Cited 24 times

Online Publication Date: 11 September 2007

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Raman backscattering measurements were performed on single crystal ZnO for different excitation wavelengths before and after ion implantation with hydrogen and nitrogen. In addition to the formation of H- and N-related defects due to implantation, anomalous Raman modes were observed. Recently, the anomalous Raman modes have been attributed to the disorder-induced activation of silent modes. However, we will show that part of the observed modes are due to the resonantly enhanced longitudinal optical phonons.
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78.30.Fs III-V and II-VI semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Thickness and stoichiometry dependence of the thermal conductivity of GeSbTe films

John P. Reifenberg, Matthew A. Panzer, SangBum Kim, Aaron M. Gibby, Yuan Zhang, Simon Wong, H.-S. Philip Wong, Eric Pop, and Kenneth E. Goodson

Appl. Phys. Lett. 91, 111904 (2007); http://dx.doi.org/10.1063/1.2784169 (3 pages) | Cited 27 times

Online Publication Date: 11 September 2007

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Thermal conduction in GeSbTe films strongly influences the writing energy and time for phase change memory (PCM) technology. This study measures the thermal conductivity of Ge2Sb2Te5 between 25 and 340 °C for layers with thicknesses near 60, 120, and 350 nm. A strong thickness dependence of the thermal conductivity is attributed to a combination of thermal boundary resistance (TBR) and microstructural imperfections. Stoichiometric variations significantly alter the phase transition temperatures but do not strongly impact the thermal conductivity at a given temperature. This work makes progress on extracting the TBR for Ge2Sb2Te5 films, which is a critical unknown parameter for PCM simulations.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys
61.66.Bi Elemental solids
61.66.Dk Alloys
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Effect of measured distance and angle tuning on transmission properties of split-ring resonators

Chuang Li, Huiqing Fan, and Nanjing Li

Appl. Phys. Lett. 91, 111905 (2007); http://dx.doi.org/10.1063/1.2785117 (3 pages)

Online Publication Date: 11 September 2007

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Transmission properties of a layer of split-ring resonators (SRRs) are investigated experimentally in free space with the propagation direction of the electromagnetic field perpendicular to the SRR-patterned substrate. It is shown that the response frequency of SRRs is independent of the measured distance. In addition, the qualitative change from electric resonance of SRRs to magnetic resonance with the variation of angle between electric field and the symmetric axis of SRR is presented. The results suggest a simple way of obtaining magnetic resonance of SRRs, even left-handed behavior.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials

Low temperature LO-phonon dynamics of MgZnO nanoalloys

Jesse Huso, John L. Morrison, Heather Hoeck, Erin Casey, Leah Bergman, T. D. Pounds, and M. G. Norton

Appl. Phys. Lett. 91, 111906 (2007); http://dx.doi.org/10.1063/1.2784189 (3 pages) | Cited 10 times

Online Publication Date: 12 September 2007

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In this paper, the authors present research on the low temperature resonant Raman scattering of the LO modes of Mg0.2Zn0.8O nanocrystals. They found that in the LO spectral range, two coupled modes appear: the main LO mode of the alloy and a low frequency mode redshifted by ∼ 27 cm−1 relative to the main one. The low frequency mode was analyzed in terms of three mechanisms applicable to Raman scattering of an alloy system that might result in its activation: phase segregation due to the low solubility limit of the MgO–ZnO alloy system, a convolution of the A1(LO) with the E1(LO) mode, and an order-disorder state. Their analyses indicate that the principle mechanism that activates the low frequency mode is scattering due to the disordered state of the nanoalloys.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Fs III-V and II-VI semiconductors
64.75.-g Phase equilibria

Acoustic and optical phonon assisted formation of biexcitons

Ching-Ju Pan, Kuo-Feng Lin, and Wen-Feng Hsieh

Appl. Phys. Lett. 91, 111907 (2007); http://dx.doi.org/10.1063/1.2784180 (3 pages) | Cited 10 times

Online Publication Date: 13 September 2007

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Efficient exciton relaxation is required for bounding two cooled excitons to form biexciton. Acoustic and optical phonon scatterings playing key roles in exciton relaxation are responsible for formation of biexcitons at various temperatures. Using ZnO powders, the authors observed a sublinear dependence on excitation power at low temperature, in which the relaxation process involves only emission of acoustic phonons due to the excitons having kinetic energy lower than those of the optical phonons. However, the exponent comes near theoretical value of 2 for participation of optical phonons when the exciton kinetic energy approaches to the energy of the lowest optical phonon.
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71.35.-y Excitons and related phenomena
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.55.Et II-VI semiconductors

Study of structural transition from metastable zinc blende to rocksalt crystal in molecular beam epitaxy MgS/ZnSe/GaAs multilayer system

L. Nasi, C. Bocchi, A. Catellani, F. Germini, J. K. Morrod, K. A. Prior, and G. Calestani

Appl. Phys. Lett. 91, 111908 (2007); http://dx.doi.org/10.1063/1.2784182 (3 pages) | Cited 3 times

Online Publication Date: 13 September 2007

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The stable crystal structure of magnesium sulfide (MgS) is rocksalt. However, the metastable zinc-blende structure is obtained when MgS is deposited by molecular beam epitaxy (MBE) on (001) zinc-blende substrates with a relatively small misfit. In the present work, the zinc blende to rocksalt phase transition is analyzed in MgS/ZnSe/GaAs multilayer samples grown by MBE with different MgS layer thicknesses. By x-ray diffraction and transmission electron microscopy methods, a partial nucleation of MgS rocksalt is evidenced and correlated to the presence of stacking faults at the bottom interface. The unexpected coexistence of both rocksalt and zinc-blende MgS structural phases is discussed.
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64.70.K- Solid-solid transitions
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification

Slow electromagnetic propagation with low group velocity dispersion in an all-metamaterial-based waveguide

J. W. Dong and H. Z. Wang

Appl. Phys. Lett. 91, 111909 (2007); http://dx.doi.org/10.1063/1.2784201 (3 pages) | Cited 10 times

Online Publication Date: 13 September 2007

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The authors found that zero group velocity exists in a two-dimensional planar waveguide consisting of a left-handed metamaterial core and two identical claddings with negative permittivity. The mechanism is realized in a waveguide guiding a vortex mode, which results in the cancellation of the power flows between the core and the claddings. Moreover, by varying the waveguide thickness, the authors can manipulate the pulse velocity in the slow-light regime while simultaneously minimizing the pulse distortion. In addition, issues associated with energy loss are discussed.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Chemical phase transitions of a Si oxide film on SiC by MeV electron beam irradiation

C. Jeon, J. H. Nam, W. Song, C.-Y. Park, J. R. Ahn, M.-C. Jung, H. J. Shin, Y. H. Han, and B. C. Lee

Appl. Phys. Lett. 91, 111910 (2007); http://dx.doi.org/10.1063/1.2783483 (3 pages) | Cited 2 times

Online Publication Date: 13 September 2007

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An ultrathin Si oxide film grown on a 6H-SiC(0001) wafer was irradiated with 1 MeV electron beam to examine its effect on the chemical species of a Si oxide/SiC wafer, where the Si oxide film was composed of SiO2, Si suboxides (Si3+, Si2+, and Si1+), and Si oxycarbides (Si–C–O). Scanning photoelectron microscopy and Si 2p core-level spectroscopy show that e-beam irradiation induces chemical phase transitions from the Si suboxides and Si oxycarbides to SiO2. This suggests that e-beam irradiation is an efficient and simple method of producing a chemically uniform SiO2 film on SiC without thermal and chemical treatments.
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61.80.Fe Electron and positron radiation effects
61.82.Ms Insulators
82.30.-b Specific chemical reactions; reaction mechanisms

Load induced stresses and plastic deformation in 450 mm silicon wafers

A. Fischer and G. Kissinger

Appl. Phys. Lett. 91, 111911 (2007); http://dx.doi.org/10.1063/1.2784964 (3 pages) | Cited 4 times

Online Publication Date: 13 September 2007

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The authors present the physical basis for estimation of gravitational constraints in 450 mm silicon wafers subjected to high temperature processes. They have identified and quantified the relevant phenomena to predict the mechanical behavior of very large silicon wafers horizontally stacked and ring- or pointlike supported in a vertical-type furnace. It is shown that load induced stress at the supports increases directly proportional with increasing wafer diameter, although the weight of the wafer increases with the square of diameter. The results allow the optimization for a defect-free high temperature treatment of 450 mm wafer used for leading edge device fabrication in future.
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81.05.Cy Elemental semiconductors
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Gh Other heat and thermomechanical treatments
62.20.F- Deformation and plasticity
62.20.D- Elasticity

Self-written gradient double claddlike optical guiding channels of high stability

Armen Zohrabyan, Amir Tork, Rouslan Birabassov, and Tigran Galstian

Appl. Phys. Lett. 91, 111912 (2007); http://dx.doi.org/10.1063/1.2770775 (3 pages) | Cited 7 times

Online Publication Date: 14 September 2007

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Composite photopolymerizable material and self-writing method are developed, allowing the creation of very stable (in time) gradient double-clad optical waveguides with W form of refractive index profile. The guide is formed by the mutual counter diffusion of reactive and nonreactive molecules followed by photopolymerization. After the guide formation by a Gaussian intensity shaped beam, the mixture is simply fixed by uniform irradiation without additional processing. More than 2 cm length permanent self-guiding channels are created. The obtained results could be useful for “optical bonding” of dissimilar optical devices.
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42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.62.-b Laser applications

The role of hydrostatic stress in determining the bandgap of InN epilayers

Abdul Kadir, Tapas Ganguli, Ravi Kumar, M. R. Gokhale, A. P. Shah, Sandip Ghosh, B. M. Arora, and Arnab Bhattacharya

Appl. Phys. Lett. 91, 111913 (2007); http://dx.doi.org/10.1063/1.2784199 (3 pages) | Cited 10 times

Online Publication Date: 14 September 2007

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This letter establishes a correlation between the internal stress in InN epilayers and their optical properties such as the measured absorption band edge and photoluminescence emission wavelength. By a careful evaluation of the lattice constants of InN epilayers grown on c-plane sapphire substrates under various conditions by metalorganic vapor phase epitaxy, the authors find that the films are under primarily hydrostatic strain. The corresponding stress results in a shift in the band edge to higher energy. The effect is significant and may be responsible for some of the variations in InN bandgap reported in the literature.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Slip transfer through a general high angle grain boundary in nanocrystalline aluminum

C. Brandl, E. Bitzek, P. M. Derlet, and H. Van Swygenhoven

Appl. Phys. Lett. 91, 111914 (2007); http://dx.doi.org/10.1063/1.2784939 (3 pages) | Cited 8 times

Online Publication Date: 14 September 2007

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The atomistic details of a slip transfer through a general high angle grain boundary in three dimensional nanocrystalline Al are reported and discussed in terms of possible implications for mesoscopic simulation models.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.Mm Grain and twin boundaries
61.46.Hk Nanocrystals
62.20.F- Deformation and plasticity

Effects of focused ion beam milling on the nanomechanical behavior of a molybdenum-alloy single crystal

H. Bei, S. Shim, M. K. Miller, G. M. Pharr, and E. P. George

Appl. Phys. Lett. 91, 111915 (2007); http://dx.doi.org/10.1063/1.2784948 (3 pages) | Cited 5 times

Online Publication Date: 14 September 2007

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Nanoindentation was performed on a Mo-alloy single crystal to investigate effects of focused ion beam (FIB) milling on mechanical behavior. On a non-FIB-milled surface, pop-ins were observed on all load-displacement curves corresponding to a transition from elastic to plastic deformation. Similar pop-ins were not detected on surfaces subjected to FIB milling. This difference indicates that FIB milling introduces damage that obviates the need for dislocation nucleation during subsequent deformation. A second effect of FIB milling is that it increased the surface hardness. Together, these effects could be the source of the size effects reported in the literature on micropillar tests.
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81.05.Bx Metals, semimetals, and alloys
61.80.Jh Ion radiation effects
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.Gy Mechanical properties; surface strains
64.60.Q- Nucleation

Characteristic optical properties of transparent color conversion film prepared from YAG:Ce3+ nanoparticles

R. Kasuya, A. Kawano, T. Isobe, H. Kuma, and J. Katano

Appl. Phys. Lett. 91, 111916 (2007); http://dx.doi.org/10.1063/1.2785131 (3 pages) | Cited 36 times

Online Publication Date: 14 September 2007

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The authors produced the transparent color conversion thick film which is composed of a high concentration of YAG:Ce3+ nanoparticles prepared by glycothermal method, and characterized its optical properties. The transmittance of the 200 μm thick film with the nanoparticle content 70.7 wt % was 82% at 525 nm corresponding to the emission peak of YAG:Ce3+. The intensity of photoluminescence due to the 5d→4f transition of Ce3+ in YAG:Ce3+ nanoparticles was doubled by placing a reflection mirror at the back of the transparent film. Judging from this result, the transparent film of YAG:Ce3+ nanoparticles has markedly low scattering loss.
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78.66.Nk Insulators
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
75.50.Gg Ferrimagnetics

Experimental and theoretical studies of lattice dynamics of Mg-doped InN

V. Yu. Davydov, A. A. Klochikhin, M. B. Smirnov, A. N. Smirnov, I. N. Goncharuk, D. A. Kurdyukov, Hai Lu, William J. Schaff, H.-M. Lee, H.-W. Lin, and S. Gwo

Appl. Phys. Lett. 91, 111917 (2007); http://dx.doi.org/10.1063/1.2785137 (3 pages) | Cited 6 times

Online Publication Date: 14 September 2007

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Raman studies of Mg-doped InN films with a Mg content from NMg = 3.3×1019 to 5.5×1021 cm−3 are reported. Raman and secondary ion mass spectroscopy data on the Mg content have been found to correlate well. Lattice dynamics of hexagonal InN with substitutional impurities and vacancies has been investigated in the framework of the cluster approach. Energy positions of local vibrational modes in InN have been calculated and compared with experimental findings. It is concluded that Raman spectroscopy is a good tool for quantitative characterization of Mg-doped InN.
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63.20.-e Phonons in crystal lattices
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.J- Point defects and defect clusters

Spectral characterization of transparent (Nd0.01Y0.94La0.05)2O3 laser ceramics

Qiuhong Yang, C. G. Dou, J. Ding, X. M. Hu, and J. Xu

Appl. Phys. Lett. 91, 111918 (2007); http://dx.doi.org/10.1063/1.2785151 (2 pages) | Cited 10 times

Online Publication Date: 14 September 2007

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The spectrum properties of transparent (Nd0.01Y0.94La0.05)2O3 ceramics were investigated. It was found that all absorption bands of (Nd0.01Y0.94La0.05)2O3 ceramics are broadened, of which the full width at half maximum of the peak centered at 804 nm is 8 nm and its absorption cross section is 1.02×10−20 cm2. The emission cross section of (Nd0.01Y0.94La0.05)2O3 ceramics located at 1078 nm is 5.71×10−20 cm2 and its fluorescent lifetime is 0.214 ms, which are similar to those of 1.0 at. %Nd:Y2O3 ceramics. These indicate that (Nd0.01Y0.94La0.05)2O3 transparent ceramics has excellent spectroscopic properties.
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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
78.55.Hx Other solid inorganic materials
42.70.Hj Laser materials

Yield stress of monocrystalline rhenium nanowires

L. Philippe, I. Peyrot, J. Michler, A. W. Hassel, and S. Milenkovic

Appl. Phys. Lett. 91, 111919 (2007); http://dx.doi.org/10.1063/1.2785153 (3 pages) | Cited 10 times

Online Publication Date: 14 September 2007

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The yield stress of monocrystalline Rhenium nanowires grown by directional solidification was measured by nanobending testing. The average yield stress calculated from the deflection was between 10 and 60 GPa, which represents roughly 10% of the rhenium Young modulus along the nanowire’s direction. Analytical results are compared to the ones obtained with a more complex finite element simulation. Origins of the experimental observed yield stress values variations are discussed in terms of experimental measurement errors, elastic anisotropy, and the presence of an oxide layer on the nanowire surface.
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81.07.Bc Nanocrystalline materials
81.40.Lm Deformation, plasticity, and creep
81.30.Fb Solidification
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
61.46.Hk Nanocrystals
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