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Patriarca L.,Polytechnic of Milan | Abuzaid W.,University of Illinois at Urbana - Champaign | Sehitoglu H.,University of Illinois at Urbana - Champaign | Maier H.J.,University of Paderborn | Chumlyakov Y.,Siberian Physical and Technical Institute
Materials Characterization | Year: 2012

Tension and compression experiments were conducted on body-centered cubic Fe -47.8 at pct. Cr single crystals. The critical resolved shear stress (CRSS) magnitudes for slip nucleation, twin nucleation and twin migration were established. We show that the nucleation of slip occurs at a CRSS of about 88. MPa, while twinning nucleates at a CRSS of about 191. MPa with an associated load drop. Following twin nucleation, twin migration proceeds at a CRSS that is lower than the initiation stress (≈. 114-153. MPa). The experimental results of the nucleation stresses indicate that the Schmid law holds to a first approximation for the slip and twin nucleation cases, but to a lesser extent for twin migration particularly when considerable slip strains preceded twinning. The CRSSs were determined experimentally using digital image correlation (DIC) in conjunction with electron back scattering diffraction (EBSD). The DIC measurements enabled pinpointing the precise stress on the stress-strain curves where twins or slip were activated. The crystal orientations were obtained using EBSD and used to determine the activated twin and slip systems through trace analysis. © 2012 Elsevier Inc.

Geints Y.E.,Zuev Institute of Atmospheric Optics | Panamarev N.S.,Siberian Physical and Technical Institute | Zemlyanov A.A.,Siberian Physical and Technical Institute
Journal of Optics | Year: 2011

We report on the experimental observation of the temporal dynamics of diffraction pattern formation when a low-power Gaussian laser beam passes through a cell with nanoparticles suspended in a liquid. As it turned out, the stable far-field picture on the screen is formed in the interval of a few seconds after laser radiation passage. These diffraction patterns consist of several coaxial bright and dark rings, whose diameter and number vary, depending on the type and concentration of the colloidal solution, as well as on the optical depth of the colloid and laser power. The observed behavior of the diffraction pattern dynamics are interpreted theoretically based on the Fresnel-Kirchhoff integral and the analytical solution of the heat transfer equation. © 2011 IOP Publishing Ltd.

Geints Y.E.,Zuev Institute of Atmospheric Optics | Panamarev N.S.,Siberian Physical and Technical Institute | Zemlyanov A.A.,Siberian Physical and Technical Institute
Progress in Electromagnetics Research Symposium | Year: 2011

We report on the results of our systematic experimental investigations of the diffraction pattern (DP) formed due to CW low-power laser beam propagation through a cell with metal nanocolloids (NC). We have used different types of metal NC and for the first time have studied thoroughly the temporal dynamics and structural characteristics of far-field DP. The experimental data has shown that in the observation plane the dynamic diffraction structure was formed. It consists of several coaxial light and dark rings, whose diameters and number increased with time and varied depending on the type and concentration of the colloidal solution. The stable diffraction pattern with the fixed number of fringes is formed at the screen for periods of several seconds from the beginning of the exposure to laser radiation. The number of formed rings is inversely proportional to the optical thickness of the colloid and to the laser power also. The experimental results have been interpreted theoretically from the viewpoint of thermal self-action of laser radiation in the absorbing medium. Colloidal silver nanoparticles serve as centers which efficiently absorb laser radiation and transfer the heat to the host liquid due to the thermal conductivity, thus giving rise to the temperature gradient across the laser beam. Since the thermooptical nonlinearity of the liquid leads to the decrease in the refractive index of the medium at the places, where the medium temperature is higher, the nonlinear negative phase shift appears in the zone of the beam action. This phase shift acts on the radiation as a defocusing aberration lens and leads to the formation of fringes observed in the far-field diffraction zone. Based on the analytical solution to the heat transfer equation of a homogeneous medium with a thermal source caused by the linear absorption of laser radiation, we have calculated the spatiotemporal profiles of temperature increments of silver nanocolloids. To determine the structure of the far field, we used the Fresnel-Kirchhoff integral in Fraunhofer approximation. This allowed us to derive formulae, which related the number of bright rings in the observation plane and the angular size of the entire diffraction pattern to thermophysical characteristics of the liquid solvent, volume fraction of the metal sol, and parameters of the laser beam.

Atuchin V.V.,Tomsk State University | Bereznaya S.A.,Siberian Physical and Technical Institute | Beisel N.F.,Novosibirsk State University | Korotchenko Z.V.,Siberian Physical and Technical Institute | And 4 more authors.
Materials Chemistry and Physics | Year: 2014

The Cr-doped GaSe crystals have been grown by Bridgman method, and Cr effective segregation coefficient has been estimated as Keff = 0.027 ± 0.002. The upper limit of chromium content achieved in GaSe:Cr crystal is as low as Cs = 0.006 mass% as determined using atomic absorption spectroscopy (AAS). Optical transparency range and dispersive optical constants of GaSe:Cr are similar to those in pure GaSe as obtained with optical spectrometry and spectroscopic ellipsometry (SE). The GaSe:Cr is a highly compensated p-type semiconductor with hole concentration p = 1 × 10 15 cm-3 and carrier mobility μ = 15-30 cm2 V-1 s-1 at 300 K. © 2014 Elsevier B.V. All rights reserved.

Huang X.,Yale University | Chumlyakov Y.I.,Siberian Physical and Technical Institute | Ramirez A.G.,Yale University
Nanotechnology | Year: 2012

One-dimensional single crystal nanostructures have garnered much attention, from their low-dimensional physics to their technological uses, due to their unique properties and potential applications, from sensors to interconnects. There is an increasing interest in metallic titanium nanowires, yet their single crystal form has not been actualized. Vaporliquidsolid (VLS) and template-assisted top-down methods are common means for nanowire synthesis; however, each has limitations with respect to nanowire composition and crystallinity. Here we show a simple electrochemical method to generate single crystal titanium nanowires on monocrystalline NiTi substrates. This work is a significant advance in addressing the challenge of growing single crystal titanium nanowires, which had been precluded by titaniums reactivity. Nanowires grew non-parallel to the surface and in a periodic arrangement along specific substrate directions; this behavior is attributed to a defect-driven mechanism. This synthesis technique ushers in new and rapid routes for single crystal metallic nanostructures, which have considerable implications for nanoscale electronics. © 2012 IOP Publishing Ltd.

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