ABSTRACT
We show experimentally that a resolution far beyond that of conventional far-field optical profilometers can be reached with optical diffraction tomography. This result is obtained in the presence of multiple scattering when using an adapted inverse scattering algorithm for profile reconstruction. This new profilometry technique, whose resolution can be compared to that of atomic microscopes, also gives access to the permittivity of the surface.
ABSTRACT
We present a marker-free microscope that records the phase, amplitude, and polarization state of the field diffracted by the sample for different illumination directions. The data are processed with an appropriate inversion method to yield the sample permittivity map. We observe that the full-polarized information ameliorates significantly the three-dimensional image of weakly scattering subdiffraction objects. A resolution about one-fourth of the illumination wavelength is experimentally demonstrated on complex samples.
ABSTRACT
Specular x-ray reflectivity has been used to study the changes in the thermal fluctuation behavior of eight layer freely suspended N-(4-n-butoxybenzilidene)-4-n-octylaniline (4O.8) films during the process of successive layer-by-layer crystallizations. Each of these steps is preceded by the formation of an intermediate layer structure with in-plane hexatic ordering. We find an unusually large reduction of the fluctuations after the emergence of only the first hexatic toplayer. The fluctuation profiles over the film are in all cases quenched at the surfaces though less so after each crystallization step. This behavior supports theoretical arguments that hexatic order is reduced by out-of-plane smectic layer fluctuations.
ABSTRACT
We present a theory developed to describe the diffuse double layer of electrolytic soap films. The hydrophobic nature of the soap molecules is modeled, in an effective field theory for the system, by the introduction of a free energetic potential favoring the presence of the soap molecules at the film surface. This potential can take various forms, depending on how accurately we wish to model the geometry of the system. The resulting theory is analyzed and leads to the estimation of the electrostatic interactions at the mean field level. A whole range of physical observables is predicted including the electrostatic component of the disjoining pressure isotherm and the Gibbs adsorption isotherm of the system. We compare the theory with accurate disjoining pressure measurements (using X-ray specular reflectivity) carried out on systems composed of sodium dodecyl sulphate (SDS) with two different monovalent electrolytes on a wide range of salinity. The theory appears to account particularly well for the experimental data. A comparison with the DLVO theory is given. Finally, we discuss the limitations of the theory and its modification due to the inclusion of dispersion forces. Copyright 1997 Academic Press. Copyright 1997Academic Press
