22.10.2021 Our article Wafer-Scale Electroactive Nanoporous Silicon: Large and Fully Reversible Electrochemo-Mechanical Actuation in Aqueous Electrolytes has been published in Advanced Materials.
We present experiments and computer simulations on the wetting behaviour of water on molecularly thin, self-assembled alkane carpets of dotriacontane (n-C32H66 or C32) physisorbed on the hydrophilic native oxide layer of silicon surfaces during dip-coating from a binary alkane solution. By changing the dip-coating velocity we control the initial C32 surface coverage and achieve distinct film morphologies, encompassing homogeneous coatings with self-organised nanopatterns that range from dendritic nano-islands to stripes. These patterns exhibit a good water wettability even though the carpets are initially prepared with a high coverage of hydrophobic alkane molecules. Using in-liquid atomic force microscopy, along with molecular dynamics simulations, we trace this to a rearrangement of the alkane layers upon contact with water. Water molecules displace to a large extent the first adsorbed alkane monolayer and thereby reduce the hydrophobic C32 surface coverage. Thus, our experiments evidence that water molecules can very effectively hydrophilize initially hydrophobic surfaces that consist of weakly bound hydrocarbon carpets.
14.06.2021 Nanostructuring of materials leads to completely new, often surprising properties; this makes them highly interesting for new fields of application and technologies. However, whether these materials can be processed into robust components and thus find their way into applications depends very much on their mechanical properties. These are usually particularly difficult to determine without changing them through the measuring process or even destroying the materials. Within a German-French research team we have now developed a non-contact and non-destructive measurement method using laser ultrasound in such a way that the elastic properties of nanostructured materials can be characterised in detail. The results are reported in an article entitled "Laser-excited elastic guided waves reveal the complex mechanics of nanoporous silicon" in the journal Nature Communications (see also the DESY/TUHH press release: German/English).