Electron microscopy of organic-inorganic interfaces: advantages of low voltage

Low voltage electron microscopy has been applied to many types of materials in the last several decades with great success. The extremely strong interaction of the low voltage electrons with the sample gives high scattering contrast, however it can also result in significant damage of the specimen. Irreparable damage to several types of organic materials results from their large cross section for ionization, or radiolysis, at low voltage. Knock-on damage, which is significant at high voltages for many ceramics, semiconductors, minerals and ordered carbonaceous material such as graphene, is often reduced at low voltages. For organics which damage by radiolysis, measured beam stability increases at higher voltages, but the mass-thickness contrast is also reduced. An increased defocus can be used to generate phase contrast at higher voltages, although it comes at the expense of resolution, as the first zero in the contrast transfer function moves toward larger length scales with increasing defocus. Several examples of low and high voltage (5kV up to 300kV) experimental TEM images of organic-inorganic interfaces are used to demonstrate these phenomena.