High pressure scanning tunnelling microscopy (HP-STM) significantly contributed to bridging the ‘pressure gap’ between surface science and real-life conditions. However, this is a pure imaging technique and does not contain any chemical information. Spectroscopy techniques like APXPS and PM-IRRAS that are applicable at ambient pressures provide chemical information but are macroscopic techniques. In view of this, the following major hurdles need to be overcome in order to advance this field of science further:
- None of our techniques can probe insulating materials efficiently, an important drawback as more than 90% of real catalysts are supported on oxides.
- Spectroscopy techniques cannot probe surfaces at all length scales, especially at the lower nanometre scale, i.e., with ~10 nm resolution. Current methods also do not provide access to material-specific physical properties (e.g., work function, permittivity, etc.) at the lower nanometre scale. Real catalysts are typically composed of metallic nanoparticles (NPs) dispersed on oxides. These NPs are inherently heterogeneous in their shape and size. Moreover, various surface sites clearly exist within a single particle, so reactivity variations will exist even at the single nanoparticle level.
Our solution is using a high-pressure atomic force microscopy (HP-AFM) in the presence of gases up to atmospheric pressure. AFM is not limited to electrically conducting materials and it can operate at ambient pressures. Moreover, it is multi-functional, namely, it can be used to map the topography while probing a material-specific property. The material-specific property we are after depends on the polarisability of the material and therefore is different for metals and oxides, and can eventually be used as a chemical fingerprint.