6,230 research outputs found
Substrate surface engineering for tailoring properties of functional ceramic thin films
Using oxide substrates for functional ceramic thin film deposition beyond
their usual application as chemical inert, lattice-matched support for the
films represents a novel concept in ceramic thin film research. The substrates
are applied as a functional element in order to controllably modify the atom
arrangement and the growth mode of ceramic prototype materials such as cuprate
superconductors and colossal magnetoresistance manganites. One example is the
use of epitaxial strain to adjust the relative positions of cations and anions
in the film and thus modify their physical properties. The other makes use of
vicinal cut SrTiO3 which enables the fabrication of regular nanoscale step and
terrace structures. In YBa2Cu3O7-x thin films grown on vicinal cut SrTiO3
single crystals a regular array of antiphase boundaries is generated causing an
anisotropic enhancement of flux-line pinning. In the case of La-Ca-Mn-O thin
films grown on vicinal cut substrates it could be demonstrated that magnetic
in-plane anisotropy is achieved.Comment: 6 page
Impact of intrinsic localized modes of atomic motion on materials properties
Recent neutron and x-ray scattering measurements show intrinsic localized
modes (ILMs) in metallic uranium and ionic sodium iodide. Here, the role ILMs
play in the behavior of these materials is examined. With the thermal
activation of ILMs, thermal expansion is enhanced, made more anisotropic, and,
at a microscopic level, becomes inhomogeneous. Interstitial diffusion, ionic
conductivity, the annealing rate of radiation damage, and void growth are all
influenced by ILMs. The lattice thermal conductivity is suppressed above the
ILM activation temperature while no impact is observed in the electrical
conductivity. This complement of transport properties suggests that ILMs could
improve thermoelectric performance. Ramifications also include thermal
ratcheting, a transition from brittle to ductile fracture, and possibly a phase
transformation in uranium.Comment: 34 pages, 11 figure
The magnetoelectrochemical switch
In the field of spintronics, the archetype solid-state two-terminal device is the spin valve, where the resistance is controlled by the magnetization configuration. We show here how this concept of spin-dependent switch can be extended to magnetic electrodes in solution, by magnetic control of their chemical environment. Appropriate nanoscale design allows a huge enhancement of the magnetic force field experienced by paramagnetic molecular species in solutions, which changes between repulsive and attractive on changing the electrodes' magnetic orientations. Specifically, the field gradient force created within a sub-100-nm-sized nanogap separating two magnetic electrodes can be reversed by changing the orientation of the electrodes' magnetization relative to the current flowing between the electrodes. This can result in a breaking or making of an electric nanocontact, with a change of resistance by a factor of up to 103. The results reveal how an external field can impact chemical equilibrium in the vicinity of nanoscale magnetic circuits
Field-control, phase-transitions, and life's emergence
Instances of critical-like characteristics in living systems at each
organizational level as well as the spontaneous emergence of computation
(Langton), indicate the relevance of self-organized criticality (SOC). But
extrapolating complex bio-systems to life's origins, brings up a paradox: how
could simple organics--lacking the 'soft matter' response properties of today's
bio-molecules--have dissipated energy from primordial reactions in a controlled
manner for their 'ordering'? Nevertheless, a causal link of life's macroscopic
irreversible dynamics to the microscopic reversible laws of statistical
mechanics is indicated via the 'functional-takeover' of a soft magnetic
scaffold by organics (c.f. Cairns-Smith's 'crystal-scaffold'). A
field-controlled structure offers a mechanism for bootstrapping--bottom-up
assembly with top-down control: its super-paramagnetic components obey
reversible dynamics, but its dissipation of H-field energy for aggregation
breaks time-reversal symmetry. The responsive adjustments of the controlled
(host) mineral system to environmental changes would bring about mutual
coupling between random organic sets supported by it; here the generation of
long-range correlations within organic (guest) networks could include SOC-like
mechanisms. And, such cooperative adjustments enable the selection of the
functional configuration by altering the inorganic network's capacity to assist
a spontaneous process. A non-equilibrium dynamics could now drive the
kinetically-oriented system towards a series of phase-transitions with
appropriate organic replacements 'taking-over' its functions.Comment: 54 pages, pdf fil
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