Prof. Dr. Claudia Backes from University Kassel.

Making nanomaterial inks from insoluble rocks

Liquid exfoliation has become an important production technique to give access to large quantities of two-dimensional nanosheets in colloidal dispersion. Importantly, this is a highly versatile technique that can be applied to numerous layered materials beyond graphene. While this was clear over 10 years ago, some major obstacles on the fundamental level of exfoliation, size selection and characterisation had to be overcome. In this talk, I will review the most important steps that allowed us to arrive at a point, where it is possible to produce samples suitable for (device) applications. This will include the following aspects:

• Elaborating reliable deposition and analysis protocols to quantify lateral size and layer number by AFM
• Size selection through centrifugation using band sedimentation and liquid cascade centrifugation including a novel quantitative description with an equation of motion accounting for dimensionality
• Crucial insights in the exfoliation mechanism that is based on simultaneous nanosheet delamination and tearing with an equipartition of energy
• The realisation that size and thickness information is encoded in optical absorption and extinction spectra that allows to derive metrics for nanosheet size through a correlation with microscopy statistics
• Exfoliation under inert gas which enables the analysis of degradation kinetics and thermodynamics (i.e. activation energy) revealing that many types of nanosheets are less stable in ambient conditions than expected
• Controlled deposition into tiled networks of well-aligned nanosheets with dense coverage suitable for raindrop triboelectric generators

Strategies for achieving basal plane and edge functionalisation of transition metal dichalcogenide nanosheets in the liquid phase