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.