Karol Vegso

Towards strain gauges based on a self-assembled nanoparticle monolayer--SAXS study.

An in situ small-angle x-ray scattering study of the nanoparticle displacement in a self-assembled monolayer as a function of a supporting membrane strain is presented. The average nanoparticle spacing is 6.7 nm in the unstrained state and increases in the applied force direction, following linearly the membrane strain which reaches the maximum value of 11%. The experimental results suggest a continuous mutual shift of the nanoparticles and their gradual separation with the growing stress rather than nanoparticle islands formation. No measurable shift of the nanoparticles was observed in the direction perpendicular to the applied stress.

Modified Langmuir-Blodgett deposition of nanoparticles - measurement of 2D to 3D ordered arrays

Modified Langmuir-Blodgett deposition of nanoparticles - measurement of 2D to 3D ordered arrays The ordered nanoparticle monolayers and multilayers over macroscopic areas were prepared by the modified Langmuir-Blodgett method. Using this approach, the nanoparticle monolayer is formed on the water surface by compression and subsequently it is transferred onto the substrate by a controlled removal of the water subphase. The ordering and homogeneity of the prepared mono- and multilayers was studied by scanning electron microscope (SEM), grazing-incidence small-angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR) techniques. From the results it follows that an ordered nanoparticle monolayer was formed over a large area. For the multilayer, the layering and lateral ordering of each layer was confirmed by XRR and SEM performed after the deposition of each nanoparticle layer.

Nonequilibrium Phases of Nanoparticle Langmuir Films

We report on an in-situ observation of the colloidal silver nanoparticle self-assembly into a close-packed monolayer at the air/water interface followed by a 2D to 3D transition. Using the fast tracking GISAXS technique, we were able to observe the immediate response to the compression of the self-assembled nanoparticle layer at the air/water interface and to identify all relevant intermediate stages including those far from the equilibrium. In particular, a new nonequilibrium phase before the monolayer collapse via the 2D to 3D transition was found that is inaccessible by the competing direct space imaging techniques such as the scanning and transmission electron microscopies due to the high water vapor pressure and surface tension.

Kinetics of nanoparticle reassembly mediated by UV-photolysis of surfactant.

Real-time reassembly of an ordered nanoparticle monolayer due to UV-photolysis of the surfactant shell of nanoparticles was observed. The technique of grazing-incidence small-angle X-ray scattering provided the possibility to track in situ the nanoparticle pair correlation function of the sample processed in a UV-ozone reactor. The analysis revealed a total shift of approximately 1 nm of the nanoparticle nearest-neighbor distance. The temporal evolution of the interparticle distance proved to be the first-order process governed by the UV-photolysis and described by a single-exponential decay function. The nanoparticles tend to agglomerate into a labyrinth-like structure with a typical length scale of some 30 nm.

Measurement of nanopatterned surfaces by real and reciprocal space techniques

Measurement of nanopatterned surfaces by real and reciprocal space techniques A newly developed laboratory grazing-incidence small-angle X-ray scattering GISAXS system capable of statistical measurements of surface morphology at the nanometer scale was developed. The potential of the GISAXS system is compared to the AFM technique for a nanopatterned silicon surface produced by ion-beam erosion. The characteristic period of the ion-beam induced ripples and their lateral correlation length were estimated from AFM. Using GISAXS the reciprocal space map of surface morphology was measured and analyzed. The two microfocus X-ray sources emitting radiation at the Cu-Kα and Cr-Kα were used. The lateral periods of ripples obtained by the reciprocal space mapping techniques match the results of real space techniques. The setup has the potential to monitor and control the deposition process and formation of nanostructures with sufficient temporal and spatial resolution.

GISAXS analysis of 3D nanoparticle assemblies?effect of vertical nanoparticle ordering

We report on grazing-incidence small-angle x-ray scattering (GISAXS) study of 3D nanoparticle arrays prepared by two different methods from colloidal solutions-layer-by-layer Langmuir-Schaefer deposition and spontaneous self-assembling during the solvent evaporation. GISAXS results are evaluated within the distorted wave Born approximation (DWBA) considering the multiple scattering effects and employing a simplified multilayer model to reduce the computing time. In the model, particular layers are represented by nanoparticle chains where the positions of individual nanoparticles are generated following a model of cumulative disorder. The nanoparticle size dispersion is considered as well. Three model cases are distinguished-no shift between the neighboring chains (AA stacking), a shift equal to half of the mean interparticle distance (AB stacking) and random shift between the chains. The first two cases correspond to vertically correlated nanoparticle positions across different chains. A comparison of the experimental GISAXS patterns with the model cases enabled us to distinguish important differences between the 3D arrays prepared by the two methods. In particular, laterally ordered layers without vertical correlation of the nanoparticle positions were found in the nanoparticle multilayers prepared by the Langmuir-Schaefer method. On the other hand, the solvent evaporation under particular conditions produced highly ordered 3D nanoparticle assemblies where both laterally and vertically correlated nanoparticle positions were found.

Potential use of V-channel Ge(220) monochromators in X-ray metrology and imaging

Several ways of tuning a higher asymmetry factor (>10) in V-channel X-ray monochromators, for metrological and imaging applications, were analysed. A more than sixfold intensity increase for compositionally and thermally tuned cases was achieved.

Extreme X-ray beam compression for a high-resolution table-top grazing-incidence small-angle X-ray scattering setup

The application of V-shaped channel-cut GeSi(220) and Ge(220) monochro-mators for one-dimensional extreme X-ray beam compression was tested on atable-top setup for grazing-incidence small-angle X-ray scattering (GISAXS)with a microfocus source. A lattice constant gradient and different asymmetryangles of the diffractors were employed to enhance the compression factorto 21and 15, respectively. It was demonstrated that the output beam parameters interms of the size, divergence, photon flux and spectral bandwidth surpass thoseof the slit collimators used traditionally in GISAXS. A beam size far below100 mm allows a high-resolution spatial GISAXS mapping, while the reciprocalspace resolution of 500 nmapproaches the level ofsynchrotron measurementsand allows a fast one-shot detection of high-resolution GISAXS patterns. Anoversamplingshiftsthedetectionlimitupto 1 mm.Theveryshortdesignofthecompact high-resolution table-top GISAXS setup is another advantage of theextremebeamcompression.BenefitsofV-shapedmonochromatorsformedium-resolution X-ray diffraction experiments as a bonus application are demon-strated by a comparison with parallel channel-cut monochromators combinedwith a slit.1. IntroductionIncreasing demand for dedicated structural characterizationfacilities triggered by progress in materials science, nano-technologies and other fields has stimulated new develop-ments in X-ray instrumentation. Microfocus X-ray sourceswithbuilt-inreflectiveopticsareatypicalexampleofadvancesthat have allowed some experiments to be moved fromsynchrotron to laboratory and that have enhanced throughputof laboratory measurements. In particular, grazing-incidencesmall-angle X-ray scattering (GISAXS) is a unique techniquefor nondestructive characterization of nanostructures and insitu probing of processes at the nanoscale, which is applicablein diverse fields of science (Renaud et al., 2003, 2009; Mu¨ller-Buschbaum et al., 2007). Commercial table-top SAXS andGISAXS setups with a microfocus X-ray source are availablenowadays. Here, traditional schemes for shaping a narrowcollimated beam such as a slit collimator or a modified Kratkycamera cannot provide effective collection of the sourceintensity and cause a considerable intensity loss. While this isnot so much an issue for synchrotron measurements, it iscrucial for laboratory setups. New solutions for beam condi-tioning are urgently needed to fully utilize the potential of thelaboratory microfocus X-ray sources.Asymmetric X-ray diffraction offers the possibility of beamfootprint control (compression or expansion) depending onthe asymmetry angle and the Bragg angle

Preparation of sterically stabilized gold nanoparticles for plasmonic applications

Plasmonic nanoparticles such as those of gold or silver have been recently investigated as a possible way to improve light absorption in thin film solar cells. Here, a simple method for the preparation of spherical plasmonic gold nanoparticles in the form of a colloidal solution is presented. The nanoparticle diameter is controlled in the range from several nm to tens of nm depending on the synthesis parameters with the size dispersion down to 14 %. The synthesis is based on thermal decomposition and reduction of the chloroauric acid in the presence of a stabilizing capping agent (surfactant) that is very slowly injected into the hot solvent. The surfactant prevents uncontrolled nanoparticle aggregation during the growth process. The nanoparticle size and shape depend on the type of the stabilizing agent. Surfactants with different lengths of the hydrocarbon chains such as Z-octa-9-decenylamine (oleylamine) with AgNO3 and polyvinylpyrrolidone with AgNO3 were used for the steric stabilization. Hydrodynamic diameter of the gold nanoparticles in the colloidal solution was determined by dynamic light scattering while the size of the nanoparticle metallic core was found by small-angle X-ray scattering. The UV-VIS-NIR spectrophotometer measurements revealed a plasmon resonance absorption in the 500–600 nm range. Self-assembled nanoparticle arrays on a silicon substrate were prepared by drop casting followed by spontaneous evaporation of the solvent and by a modified Langmuir-Blodgett deposition. The degree of perfection of the self-assembled arrays was analyzed by scanning electron microscopy and grazing-incidence small-angle X-ray scattering. Homogeneous close-packed hexagonal ordering of the nanoparticles stretching over large areas was evidenced. These results document the viability of the proposed nanoparticle synthesis for the preparation of high-quality plasmonic templates for thin film solar cells with enhanced power conversion efficiency, surface enhanced Raman scattering, and other applications.

Morphological and Electrical Properties of Stretched Nanoparticle Layers

To examine perspectives of nanoparticle films in the role of active elements in strain sensors, morphological and electrical properties of self-assembled Au nanoparticle monolayer prepared by modified Langmuir-Schaefer technique onto supporting Mylar foil were studied under elongation. Along the probing of electrical response (characterized by the gauge factor of about 60), the small-angle x-ray scattering (SAXS) characterization assessed an average interparticle distance change, which was shown to vary proportionally to the substrate elongation. The approach allowed to unambiguously address the mechanism of the deformation-resistivity transduction.