Limits of elemental contrast by low energy electron point source holography

作者：Livadaru Lucian^*; Mutus Josh; Wolkow Robert A

来源：Journal of Applied Physics, 2011, 110(9): 094305.

DOI：10.1063/1.3658250

Motivated by the need for less destructive imaging of nanostructures, we pursue point-source in-line holography (also known as point projection microscopy, or PPM) with very low energy electrons (similar to 100 eV). This technique exploits the recent creation of ultrasharp and robust nanotips, which can field emit electrons from a single atom at their apex, thus creating a path to an extremely coherent source of electrons for holography. Our method has the potential to achieve atom resolved images of nanostructures including biological molecules. We demonstrate a further advantage of PPM emerging from the fact that the very low energy electrons employed experience a large elastic scattering cross section relative to many-kV electrons. Moreover, the variation of scattering factors as a function of atom type allows for enhanced elemental contrast. The idea that one can obtain chemical information about a sample whereas imaging it by PPM is worth pursuing in more detail, and here we undertake simulations of this scheme to assess its feasibility to first order. Model results for small molecules and adatoms on graphene substrates, where very small damage is expected, indicate that a phase contrast is obtainable between elements with significantly different Z-numbers. For example, for typical setup parameters, atoms such as C and P are discernible, whereas C and N are not.

• 出版日期2011-11-1