Non-contact Atomic Force Microscopy of Ordered Porous Materials

Ordered porous materials (OPMs) are of scientific and technological
interest because of their ability to selectively interact with atoms and
molecules throughout the bulk of the material, resulting in
molecule-specific sorption and filtering. The properties of internal
pore surfaces are extensively studied. However, the OPM external
surface, which controls access to these pores, is not. Our research
employs a non-contact atomic force microscope in ultrahigh vacuum to
probe the surfaces of OPMs on a molecular level. Our goals are to
understand the natural configuration of the external surface and its
interaction with water and acid-gas molecules, both of which tend to
degrade organic OPMs such as metal-organic frameworks (MOFs). AFM
images of CuBDC nanosheets (a quasi-2D MOF) indicate that internal pores
may be obstructed due to rotations between the topmost layers of the
material. Results from other OPMs will be presented, as well as a
discussion of techniques and challenges.