Scanning electron-stimulated desorption microscopy of model-biological surfaces.

Abstract

Electron-stimulated desorption (ESD) of ions and neutrals from surfaces has been used to study chemisorption in many simple gas–solid systems1,2, but there has been much less effort devoted to ESD studies with significant spatial resolution3–7. ESD contrasts with scanning electron microscopy because ESD signals depend sensitively on the coverage and binding of an adsorbed species1. Applying scanning ESD to biological surfaces permits the surface chemical variations to be mapped using simple low mass adsorbates8 in comparison with conventional electron microscopy of biological matters which relies on heavy-metal stain technology9. We show here how scanning ESD can complement scanning Auger electron microscopy in mapping the surface chemistry of biological substrates. A model biological substrate constructed from a deposited synthetic polypeptide monolayer (polymethyl-glutamate) is used as the controlled sample surface. Micrographs display a spatial variation in H+ desorption with a resolution of 10−4 cm. We also discuss limitations to resolution as dictated by signal-to-noise considerations. The contrast mechanism would be useful for studying the important biological surface problems such as membrane morphology, cell-interfacial composition, and cell-to-cell adhesion.