Influence of van der Waals Interactions on Morphology and Dynamics in Ultrathin Liquid Films at Silicon Oxide Interfaces

Abstract

Single molecule tracer diffusion studies of evaporating (thinning) ultrathin tetrakis-2-ethylhexoxysilane (TEHOS) films on silicon with 100 nm thermal oxide reveal a considerable slowdown of the molecular mobility within less than 4 nm above the substrate (corresponding to a few molecular TEHOS layers). This is related to restricted mobility and structure formation of the liquid in this region, in agreement with information obtained from a long-time ellipsometric study of thinning TEHOS films on silicon substrates with 100 nm thermal or 2 nm native oxide. Both show evidence for the formation of up to four layers. Additionally, on thermal oxide, a lateral flow of the liquid is observed, while the film on the native oxide forms an almost flat surface and shows negligible flow. Thus, on the 2 nm native oxide the liquid mobility is even more restricted in close vicinity to the substrate as compared to the 100 nm thermal oxide. In addition, we found a significantly smaller initial film thickness in case of the native oxide under similar dipcoating conditions. We ascribe these differences to van der Waals interactions with the underlying silicon in case of the native oxide, whereas the thermal oxide suffices to shield those interactions.

Wettability alteration of oil-wet carbonate by silica nanofluid

“…Significant silicon concentrations were detected on five points on the sample surface after nanomodification (Table 4), which indicates that nanoparticles were rather homogeneously distributed on the surface, consistent with previous studies on glass and silicon substrates [7,63]. The slight variation of silica concentration is related to small perturbations in the nanofluid's homogeneity and the surface roughness of the substrate [40,64].…”

Optical investigation of diffusion of single Ag markers in confined water films

“…The solid-liquid systems are stable at least for days. We suggest that the structure formation in ultrathin water films controls the diffusion of Ag clusters in an analogous way as has been reported for diffusing dye molecules in ultrathin viscous liquids (Schuster et al 2004;Täuber et al 2013) and liquid crystal films (Schulz et al 2011(Schulz et al , 2012.…”

“…Due to their small size and surface sensitivity, single-quantum objects are ideal probes to investigate the structure and the related dynamics of nanomaterials such as pores (Hellriegel et al 2004), ultrathin films (Schuster et al 2004;Täuber et al 2013), or liquid crystal films (Schulz et al 2011(Schulz et al , 2012.…”

Single Molecule Studies on Dynamics in Liquid Crystals

“…Schulz et al . additionally analyzed their SMT experiments via probability distributions of diffusivities, which are scaled square displacements of detected tracers at a fixed time time lang (scaled single steps) [26,35,36]. Within these probability distributions of diffusivities, deviations from homogeneous diffusion can be easily seen as deviations from a mono-exponential decay.…”