Search results for "Length scale"
showing 10 items of 75 documents
Heterogeneity at the glass transition: what do we know?
2002
We critically discuss the information that can be obtained from experiments with respect to the existence, the life time, and the length scale of dynamical heterogeneity in glass-forming liquids. The ability to select a dynamically distinguishable subensemble and observe its return to the full equilibrium ensemble is illustrated by examples from multi-dimensional NMR. We also discuss non-resonant hole burning spectroscopy as an example for which two separate time scales are involved.
Tip-induced mobilization upon cooling of Ni monolayers on Re(0001)
2021
Usually, cooling a metal sample down to cryogenic temperatures leads to immobilization of the surface atoms. In this study, we demonstrate a movement of Ni adatoms at $4.6\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ on Ni films grown on a Re(0001) single crystal, while the surface is rigid at room temperature. The mobility is observed from 2 to 20 atomic-layer-thick films. Measurements at intermediate temperatures reveal an increasing mobility with decreasing temperature. The observed velocity of advancing steps is consistent with a model considering a sudden release of material, eventually triggered by the tip, followed by free diffusion. According to the model, an increasing length scale for t…
Anomalous tracer diffusion in film forming colloidal dispersions
2000
Film forming colloidal dispersions can be conceived as a material composed of interpenetrating hydrophobic (polymer) and hydrophilic (partially broken interfaces) phases where the transport properties of one phase are influenced by the geometric confinement effect imposed by the other. We studied the transport properties of film forming colloidal dispersions by introducing hydrophobic dye molecules into the colloidal particles and determining their motion with forced Rayleigh Scattering as a function of length scale (grating distance A) and water content. At water contents between 18 and 3 weight percent we find signatures of anomalous tracer diffusion, namely stretched exponential decay cu…
Orientation of polybutadiene chains in a thermoplastic elastomer
1996
The orientation of polybutadiene chains in thermoplastic elastomers based on hydrogen bonding complexes is investigated under uniaxial deformation by two-dimensional small-angle neutron scattering (SANS), deuteron magnetic resonance spectroscopy (2H-NMR), optical birefringence and infrared dichroism spectroscopy (FTIR-D). While SANS probes orientation on the length scale of the radius of gyration,2H-NMR, birefringence and FTIR-D monitor orientation on a segmental scale. The deformation of the elastomer chains appears to be affine on the different length scales.
Charge Mobility and Dynamics in Spin-Crossover Nanoparticles Studied by Time-Resolved Microwave Conductivity
2018
We use the electrode-less time-resolved microwave conductivity (TRMC) technique to characterize spin-crossover (SCO) nanoparticles. We show that TRMC is a simple and accurate mean for simultaneously as-sessing the magnetic state of SCO compounds and charge transport information on the nanometre length scale. In the low-spin state from liquid nitrogen temperature up to 360 K the TRMC measurements present two well-defined regimes in the mobility and in the half-life times, possessing similar transition tempera-tures TR near 225 K. Below TR, an activation-less regime associated with short lifetimes of the charge carri-ers points at the presence of shallow-trap states. Above TR, these states ar…
Atomic-scale magnetic domain walls in quasi-one-dimensional Fe nanostripes.
2001
Fe nanostripes on W(110) are investigated by Kerr magnetometry and spin-polarized scanning tunneling microscopy (SP-STM). An Arrhenius law is observed for the temperature dependent magnetic susceptibility indicating a one-dimensional magnetic behavior. The activation energy for creating antiparallel spin blocks indicates extremely narrow domain walls with a width on a length scale of the lattice constant. This is confirmed by imaging the domain wall by SP-STM. This information allows the quantification of the exchange stiffness and the anisotropy constant.
Nanoscale heterogeneity if glass-forming liquids: experimental advances
1998
Abstract Recent evidence indicates that in supercooled liquids the cooperativity of molecular motion extends over certain temporal and spatial ranges. A key advance is the experimental and theoretical exploration of higher-order correlation functions that can track the molecular coordinates for more than just two points in time or space. Uncontested experimental determinations of the heterogeneity length scale at the glass transition remain a major goal.
Spectroscopic Signature of the Superparamagnetic Transition and Surface Spin Disorder in CoFe2O4 Nanoparticles
2012
Phonons are exquisitely sensitive to finite length scale effects in a wide variety of materials. To investigate confinement in combination with strong magnetoelastic interactions, we measured the infrared vibrational properties of CoFe(2)O(4) nanoparticles and compared our results to trends in the coercivity over the same size range and to the response of the bulk material. Remarkably, the spectroscopic response is sensitive to the size-induced crossover to the superparamagnetic state, which occurs between 7 and 10 nm. A spin-phonon coupling analysis supports the core-shell model. Moreover, it provides an estimate of the magnetically disordered shell thickness, which increases from 0.4 nm i…
Length Scale of the Spin Seebeck Effect
2015
We investigate the origin of the spin Seebeck effect in yttrium iron garnet (YIG) samples for film thicknesses from 20 nm to 50 μm at room temperature and 50 K. Our results reveal a characteristic increase of the longitudinal spin Seebeck effect amplitude with the thickness of the insulating ferrimagnetic YIG, which levels off at a critical thickness that increases with decreasing temperature. The observed behavior cannot be explained as an interface effect or by variations of the material parameters. Comparison to numerical simulations of thermal magnonic spin currents yields qualitative agreement for the thickness dependence resulting from the finite magnon propagation length. This allow…
Two-Length-Scale Structure in Some Computer-Generated Aggregates Grown by Diffusion-Limited Aggregation
1994
AbstractThe properties of some aggregates “grown” on a computer by diffusion-limited aggregation have been investigated. Calculations showed that the intensity of the small-angle x-ray and neutron scattering from the aggregates was proportional to q−D for qL ≫ 1, where D > 0, L is a length that characterizes the large-scale structure of the aggregate, q = 4πλ−1 sin(θ/2), γ is the wavelength, and θ is the scattering angle. The magnitude of the exponent D was appreciably smaller than the fractal dimensions that many simulations have shown to be typical of the mass fractal aggregates grown by diffusion-limited aggregation. The calculations suggest that the aggregates have structure on two d…