High resolution UHV-AFM surface analysis on polymeric materials: Baltic Amber

In this paper we present, for the first time, the results from Atomic Force Microscopy (AFM) surface studies from freshly fractured Baltic Amber samples, carried out under ultrahigh vacuum (UHV) conditions from micrometer to nanometer resolution. The micrometric AFM images provide a structural clue to the birefringent behavior occasionally observed with amber samples. Two-dimensional pair-distance distributions of the nanometric AFM images prove the completely amorphous structure of the material. This, together with the detection of individual motifs such as aromatic rings, supports the notion of amber being an amorphous polymeric organic network, consistent with the accompanying X-Ray Photoelectron spectroscopy (XPS) data. No nanocrystalline inclusions could be found. The results also show that it is possible to obtain atomically resolved AFM images from amorphous dielectric surfaces.

Research Highlights
► The similarity of all AFM images indicates homogeneity of the material throughout.
► The observed regular patterns could explain the amber’s anomalous birefringence.
► The lack of any macro- order in the samples indicates the amorphous nature of amber.
► Highly resolved images reveal an amorphous structure on the atomic scale.
► First time “direct” proofs confirm that the amber structure is a polymeric network.