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  • 1
    Electronic Resource
    Electronic Resource
    Picosecond dynamics of surface electron transfer processes: Surface restricted transient grating studies of the n-TiO2/H2O interface (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1253-1269 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The surface restricted transient grating is demonstrated as a sensitive probe of ultrafast surface reaction dynamics. Studies of doped single crystal n-TiO2 (001) surfaces in air demonstrate linear trapping processes, assigned to crystal defects within the surface deformation layer, that limit carrier lifetimes to 5 ns. Direct in situ grating studies at photochemically active n-TiO2/H2O interfaces demonstrate that the dominant mechanism of interfacial electron transfer in this system involves thermalized hole carriers at the atomic surface. The dynamics are consistent with adsorbed OH− as the initial hole acceptor. In addition, optical generation of coherent surface acoustic modes is demonstrated. A detailed theory is presented for the grating excitation of the surface acoustics. Acoustic propagation in the H2O half-space of the TiO2/H2O liquid interface gives evidence for a phase change of the water layer at the polar TiO2 (001) surface to a solid phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456130
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    Paper (German National Licenses)
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  • 2
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    The exploration of the effect of microstructure on crackling noise systems (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-08-18
    Description: A wide variety of physical systems respond to changing external conditions through discrete impulsive events called jerks, typically leading to collective “crackling noise” behaviour. Statistical distributions of jerky events often exhibit a universal scale-invariant power law, regardless of the specific mechanisms that are responsible for crackling noise processes and microstructural features that affect them. Here, we analyse uniaxial compression loading curves of two different physical systems that exhibit jerky behaviour: a martensitic NiMnGa single crystal and a stack of corrugated fiberboards. The jerky response is attributed to a non-uniform twin boundary motion along the NiMnGa crystal and to a local buckling of individual fiberboard layers. In both cases, our analysis reveals that different variables exhibit different statistical distributions. While the velocity of temporal processes within jerky events exhibits scale invariant distribution, the irreversible displacements induced throughout complete events are distributed around a characteristic value. In the case of NiMnGa, the displacement of a twin boundary is directly related to the length-scale of the internal magneto-mechanical microstructure. Similarly, the displacement of the fiberboard stack corresponds to the thickness of individual board layers. These observations reveal the effect of the internal microstructure on crackling noise systems and demonstrate an analysis approach for uncovering the details of the jerk mechanism.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    The effects of temperature on the lattice barrier for twin wall motion (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-07-30
    Description: The sideways motion of twin walls in ferroic materials requires overcoming an intrinsic energy barrier that originates from the periodicity of the crystal structure. Here, we measure the temperature dependence of the lattice barrier in a ferromagnetic Ni-Mn-Ga crystal using the pulsed magnetic field method. Our results reveal a monotonic decrease in the lattice barrier with increasing temperature. Yet, the barrier does not vanish as the temperature approaches the temperature of the martensite to austenite transformation. These findings enable the formulation of an analytical expression that correlates the lattice barrier to the physical properties of the twin wall, such as its thickness and the associated transformation strain. The derived relation provides a good quantitative description of the data measured in Ni-Mn-Ga.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    The effects of magnetic and mechanical microstructures on the twinning stress in Ni-Mn-Ga (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-01-01
    Description: The ferromagnetic 10M Ni-Mn-Ga alloy exhibits complex magnetic and mechanical microstructures, which are expected to form barriers for motion of macro twin boundaries. Here, the contributions of both microstructures to the magnitude of the twinning stress property are investigated experimentally. A series of uniaxial loading-unloading curves are taken under different orientation angles of a constant magnetic field. The different 180 ° magnetic domains microstructures that are formed across the twin boundary in each case are visualised using a magneto optical film. Analysis of the different loading curves and the corresponding magnetic microstructures show that the latter does not contribute to the barriers for twin boundary motion. In accordance, the internal resisting stress for twin boundary motion under any magnetic field can be taken as the twinning stress measured in the absence of an external field. In addition, a statistical analysis of the fine features in the loading profiles reveals that the barrier for twinning is associated with a μ m sized characteristic length scale. This length scale corresponds to the typical thickness of micro-twinning laminates that constitute a mechanical microstructure. These findings indicate that the magnitude of the twinning stress in 10M Ni-Mn-Ga is determined by the characteristic fine twinned mechanical microstructure of this alloy.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    The effects of microstructure on crackling noise during martensitic transformation in Cu-Al-Ni (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-10-27
    Description: Martensitic phase transformations often exhibit crackling noise response of the emitted energy. This type of behavior implies that the phase transformation proceeds through numerous events that do not exhibit any characteristic scale. On the other hand, the twinned microstructure along the phase boundary exhibits a characteristic size that is expected to affect the propagation of the phase boundary. Here, we present a statistical analysis of jerky events during martensitic transformation, induced by uniaxial compression of a single crystal Cu-Al-Ni. The results indicate that the characteristic length scale of the internal twinned microstructure dictates μ m -scale displacement events of the phase boundary. At the same time, each of these μ m -scale events proceeds through a multitude of smaller events that span several orders of magnitude and follow a scale-invariant power law distribution. The smaller events are associated with the local nucleation and propagation of twinning interfaces close to the phase boundary.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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