We investigated a gradient of nanometer-sized, self-assembled gold clusters on top of a thin polymer film. Using an advanced characterization method for gradient surfaces and thin films, the characteristic change in cluster height is detected. Our unprecedented approach combining a powerful thin-film characterization method with a micrometer-sized x-ray beam enhances the spatial resolution used thus far by two orders of magnitude. We show that this advanced concept allows for a nondestructive and contact-free reconstruction of the three-dimensional structure and morphology of the nanocluster gradient layer. Despite its change in thickness, the individual clusters’ in-plane shape and distance remains constant.

We show that a position-sensitive sample surface information of multiple-scaled polymer films is successfully addressed with micro-focus grazing-incidence small-angle X-ray scattering (µ-GISAXS). From the analysis of the diffuse scattering without further model assumptions the length scale of the heterogeneous structures is determinable. The method is illustrated by an example of two-step dewetted polystyrene (PS) films exhibiting droplets on a nano scale in coexistence with mesoscopic drops. The results are compared to scanning force microscopy measurements. As compared to the conventional transmission geometry using the same micro-focus optics the resolvable length scale is increased by one order of magnitude.

No abstract

The characteristic in-plane length scales of ultrathin films of regenerated cellulose are measured using noncontact atomic force microscopy (NC-AFM) and grazing incidence small-angle x-ray scattering (GISAXS) in ambient atmosphere and under various humidity conditions. The aim is to elucidate the structural basis for the excellent compatibility of cellulose supports to planar lipid membranes. Films are deposited on silicon wafers by Langmuir-Blodgett (LB) transfer and spin coating. NC-AFM height profiles and the resulting calculated power spectral density functions indicate that both kinds of cellulose films have almost identical root-mean-square roughness values (0.7–0.8 nm) and very similar characteristic length scales (32 nm), respectively. GISAXS measurements, both above and below the critical angle of total external reflection, show that the dominant length scales in the bulk and near the surface of the films are comparable (∼50 nm). The origin of these length scales can be attributed to the bundle of rodlike molecules of cellulose that result during the regeneration process (i.e., as a consequence of the cleavage of the silyl side chains of trimethylsilylcellulose). Exposure of the cellulose samples to various humidities shows that above a relative humidity of 97% a significant swelling of the films occurs, which is consistent with our previous findings. The swelling of films with more than 30 LB monolayers of cellulose induces a remarkable out-of-plane rearrangement of the cellulose bundles, due to a reduced influence of the solid substrate compared to thinner films with only eight to ten LB monolayers.

X-ray scattering based on synchrotron radiation enables the detection of polymeric structures at interfaces despite the weak contrast between adjacent polymers build-up from different monomeric units. Variable types of polymeric structures result from typical pattern directing mechanisms, such as dewetting in case of homopolymer films, phase separation in polymer blend films, micro-phase separation in diblock copolymer films and surface enrichment in statistical copolymer films. The pattern directing mechanisms introduce structures ordered perpendicular and parallel to the polymeric surface. Consequently, specular and off-specular X-ray scattering is applied as demonstrated within examples. From scattering the characteristic structures which are not accessible by means of other techniques are determined. Limitations with respect to isolated objects such as holes are discussed.