Grazing-incidence Small-angle X-ray Scattering Technique Research Articles

In-Situ GISAXS Study of Supramolecular Nanofibers having Ultrafast Humidity Sensitivity

Self assembled nanofibers derived from donor-acceptor (D-A) pair of dodecyl methyl viologen (DMV) and potassium salt of coronene tetracarboxylate (CS) is an excellent material for the development of organic electronic devices particularly for ultrafast response to relative humidity (RH). Here we have presented the results of in-situ grazing incidence small angle x-ray scattering (GISAXS) measurements to understand aridity dependent self reorganization of the nanofibers. The instantaneous changes in the organization of the nanofibers was monitored with different equilibrium RH conditions. Additionally formation of nanofibers during drying was studied by GISAXS technique – the results show two distinct stages of structural arrangements, first the formation of a lamellar mesophase and then, the evolution of a distorted hexagonal lattice. The RH dependent GISAXS results revealed a high degree of swelling in the lattice of the micelles and reduction in the distortion of the hexagonal structure with increase in RH. In high RH condition, the nanofibers show elliptical distortion but could not break into lamellar phase as observed during formation through drying. This observed structural deformation gives insight into nanoscopic structural changes of the micelles with change in RH around it and in turn explains ultrafast sensitivity in its conductivity for RH variation.

Probing the surface microstructure of layer-by-layer self-assembly chitosan/poly(l-glutamic acid) multilayers: A grazing-incidence small-angle X-ray scattering study.

This study characterized the surface structure of layer-by-layer self-assembly chitosan/poly(L-glutamic acid) multilayers through grazing-incidence small-angle X-ray scattering (GISAXS), X-ray reflectivity (XRR), and atomic force microscopy (AFM). A weakly long-period ordered structure along the in-plane direction was firstly observed in the polyelectrolyte multilayer by the GISAXS technique. This structure can be attributed to the specific domains on the film surface. In the domain, nanodroplets that were formed by polyelectrolyte molecules were orderly arranged along the free surface of the films. This ordered structure gradually disappeared with the increasing bilayer number because of the complex merging behavior of nanodroplets into large islands. Furthermore, resonant diffuse scattering became evident in the GISAXS patterns as the number of bilayers in the polyelectrolyte multilayer was increased. Notably, the lateral cutoff length of resonant diffuse scattering for these polyelectrolyte films was comparable with the long-period value of the ordered nanodroplets in the polyelectrolyte multilayer. Therefore, the nanodroplets could be considered as a basic transmission unit for structure propagation from the inner interface to the film surface. It suggests that the surface structure with length scale larger than the size of nanodroplets was partially complicated from the interface structure near the substrate, but surface structure smaller than the cutoff length was mainly depended on the conformation of nanodroplets.

Silver Nanoparticle Monolayer-to-Bilayer Transition at the Air/Water Interface as Studied by the GISAXS Technique: Application of a New Paracrystal Model

An original diffraction model for the analysis of grazing-incidence small-angle X-ray scattering (GISAXS) from the nanoparticle Langmuir films was developed. This model relies on the concept of the 2D hexagonal paracrystal and employs the distorted-wave Born approximation that is relevant for GISAXS measurements at the air/water interface when the angle of incidence is close to the critical value. The model comprises the cases of the close-packed nanoparticle monolayer and bilayer with the AB-type layer stacking. In this way, both the lateral (along the interface) and vertical (normal to the interface) correlations of the nanoparticle positions can be analyzed. The model was applied to an in situ GISAXS study of the formation of a silver nanoparticle Langmuir film during compression at the air/water interface in the Langmuir-Blodgett trough. Spherical nanoparticles of 5.8 ± 0.6 nm diameter were employed. Different compression stages starting from the submonolayer up to the monolayer collapse via bilayer formation were analyzed in terms of the mean lateral interparticle distance, degree of paracrystal disorder, interlayer distance, vertical disorder, and layer-stacking type in the bilayer as well as the ratio between the monolayer and bilayer coverage in the final film. The model developed is applicable to any nanoparticle Langmuir film formed at the air/liquid interface to extract structural parameters on the nanoscale. The particular results obtained have direct implications on the preparation of silver plasmonic templates with "hot spots" for surface-enhanced Raman scattering.

A GISAXS study of the angular dependence of carbon nanotubes grown on a plain substrate by the dc HF CCVD process

We report on a quantitative Grazing Incidence Small Angle X-ray Scattering (GISAXS) study of the angular dependence of oriented carbon nanotubes (CNTs) grown by a catalytically activated, plasma direct current or plasma enhanced and hot filaments-assisted catalytic chemical vapour deposition (dc HF CCVD or PE HF CCVD) process. To synthesize these CNTs, some transition metal (TM) particles were used as a catalyst and dispersed on plain SiO2 (thickness 5 nm)/Si(100) substrates prior to the growth of CNTs. Some morphological (diameter, height) and disorder parameters have been determined using the GISAXS technique in the framework of Effective Layer Born Approximation (ELBA) and Distorted-Wave Born Approximation (DWBA) on noncorrelated multilayer systems. The GISAXS patterns, although dominated by envelope features of disordered islands, provide important complementary quantitative information about CNT films. The results are compared to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. Furthermore, the GISAXS patterns could only be acceptably reproduced by considering an inter-mixing C–Co contribution and the metallic cobalt let on top of the CNT. While monitoring the incidence angle, we found that the disorder parameter decreases with increasing incidence angle, showing that the in-plane system order increases from the surface to the inner layers.

Application of Grazing-Incidence Small-Angle X-Ray Scattering Technique to Semiconducting Composite Materials

Grazing-incidence small-angle scattering (GI-SAXS) technique was applied to self-assembled Ge islands capped with Si. GI-SAXS has a merit over TEM and AFM that the structure of islands buried in a cap layer for stabilization can be evaluated nondestructively. By analyzing the scattering patterns, the size of Ge islands was estimated to be about 5 nm in height and 26 nm in diameter, with the islands density of 4.2×1014/m2. From the best fitting of two-dimensional model intensity to the experiments, the shape of the islands was deduced