78 research outputs found
Structural order in plasmonic superlattices
The assembly of plasmonic nanoparticles into ordered 2D- and 3D-superlattices could pave the way towards new tailored materials for plasmonic sensing, photocatalysis and manipulation of light on the nanoscale. The properties of such materials strongly depend on their geometry, and accordingly straightforward protocols to obtain precise plasmonic superlattices are highly desirable. Here, we synthesize large areas of crystalline mono-, bi- and multilayers of gold nanoparticles >20nm with a small number of defects. The superlattices can be described as hexagonal crystals with standard deviations of the lattice parameter below 1%. The periodic arrangement within the superlattices leads to new well-defined collective plasmon-polariton modes. The general level of achieved superlattice quality will be of benefit for a broad range of applications, ranging from fundamental studies of light-matter interaction to optical metamaterials and substrates for surface-enhanced spectroscopies. Superlattices of nanoparticles promise new properties emerging from the periodic order. Here, the authors describe the synthesis of superlattices of plasmonic gold nanoparticles with high crystallinity and demonstrate how new plasmon-polariton modes appear in the structures
Disentangling structural and kinetic components of the {\alpha}-relaxation in supercooled metallic liquids
The particle motion associated to the {\alpha}-relaxation in supercooled
liquids is still challenging scientists due to its difficulty to be probed
experimentally. By combining synchrotron techniques, we found the existence of
microscopic structure-dynamics relationships in Pt42.5Cu27Ni9.5P21 and
Pd42.5Cu27Ni9.5P21 liquids which allows us to disentangle structural and
kinetic contributions to the {\alpha}-process. While the two alloys show
similar kinetic fragilities, their structural fragilities differ and correlate
with the temperature dependence of the stretching parameter describing the
decay of the density fluctuations. This implies that the evolution of dynamical
heterogeneities in supercooled alloys is determined by the rigidity of the melt
structure. We find also that the atomic motion not only reflects the
topological order but also the chemical short-range order, which can lead to a
surprising slowdown of the {\alpha}-process at the mesoscopic length scale.
These results will contribute to the comprehension of the glass transition,
which is still missing
Disentangling structural and kinetic components of the α-relaxation in supercooled metallic liquids
The particle motion associated to the α-relaxation in supercooled liquids is still challenging
scientists due to its difficulty to be probed experimentally. By combining synchrotron techniques, we report the existence of microscopic structure-dynamics relationships in
Pt42.5Cu27Ni9.5P21 and Pd42.5Cu27Ni9.5P21 liquids which allows us to disentangle structural and
kinetic contributions to the α-process. While the two alloys show similar kinetic fragilities,
their structural fragilities differ and correlate with the temperature dependence of the
stretching parameter describing the decay of the density fluctuations. This implies that the
evolution of dynamical heterogeneities in supercooled alloys is determined by the rigidity of
the melt structure. We find also that the atomic motion not only reflects the topological order
but also the chemical short-range order, which can lead to a surprising slowdown of the αprocess at the mesoscopic length scale. These results will contribute to the comprehension of
the glass transition, which is still missing
Coherent X-ray Scattering Reveals Nanoscale Fluctuations in Hydrated Proteins
Hydrated proteins undergo a transition in the deeply supercooled regime,
which is attributed to rapid changes in hydration water and protein structural
dynamics. Here, we investigate the nanoscale stress relaxation in hydrated
lysozyme proteins stimulated and probed by X-ray Photon Correlation
Spectroscopy (XPCS). This approach allows us to access the nanoscale dynamic
response in the deeply supercooled regime (T = 180 K) which is typically not
accessible through equilibrium methods. The relaxation time constants exhibit
Arrhenius temperature dependence upon cooling with a minimum in the
Kohlrausch-Williams-Watts exponent at T = 227 K. The observed minimum is
attributed to an increase in dynamical heterogeneity, which coincides with
enhanced fluctuations observed in the two-time correlation functions and a
maximum in the dynamic susceptibility quantified by the normalised variance
. Our study provides new insights into X-ray stimulated stress
relaxation and the underlying mechanisms behind spatio-temporal fluctuations in
biological granular materials
Brownian and advective dynamics in microflow studied by coherent X-ray scattering experiments
Combining microfluidics with coherent X-ray illumination offers the possibility to not only measure the structure but also the dynamics of flowing samples in a single-scattering experiment. Here, the power of this combination is demonstrated by studying the advective and Brownian dynamics of colloidal suspensions in microflow of different geometries. Using an experimental setup with a fast two-dimensional detector and performing X-ray correlation spectroscopy by calculating two-dimensional maps of the intensity auto-correlation functions, it was possible to evaluate the sample structure and furthermore to characterize the detailed flow behavior, including flow geometry, main flow directions, advective flow velocities and diffusive dynamics. By scanning a microfocused X-ray beam over a microfluidic device, the anisotropic auto-correlation functions of driven colloidal suspensions in straight, curved and constricted microchannels were mapped with the spatial resolution of the X-ray beam. This method has not only a huge potential for studying flow patterns in complex fluids but also to generally characterize anisotropic dynamics in materials
Influence of the threshold settings of photon counting detectors on the observed speckle contrast in coherent scattering experiments
Speckle-based experiments, in particular X-ray Photon Correlation Spectroscopy (XPCS), are among the ones that benefit most from the development of next generation light sources. The key quantity that determines whether or not it will be possible to perform an XPCS experiment is the speckle contrast β, which measures the visibility of the speckle pattern. The speckle contrast is influenced by geometrical conditions and light-source properties [1], and recently it has been noticed that artifacts in photon-counting detectors strongly interfere with the determination of the real value of β when the number of detected photons per frame is extremely low [2]. Here we report how the threshold setting of a photon counting detector, an EIGER X 4M, affects the detected contrast even at non extreme illumination conditions (0.01-0.05 photons/pixel/second). We found that by increasing the threshold value, not only leads to the expected drop in detected intensity, but also to a significant increase in the value of β. Additionally we will present an in-operando situation in which the higher threshold helps critically to increase the signal-to-noise ratio of the measured scattering pattern resulting in a five-fold increment of the speckle contrast
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