Mapping of the local density of states with very slow electrons in SEM

Abstract

The local density of electron states is important characteristics of solids, which can be utilized in materials science when distinguishing between different crystal orientations in a polycrystalline matter, mapping the local density of dopants in semiconductors, etc. Non-imaging application of the reflection of slow electrons (VLEED — very low energy electron diffraction) knows so called energy band structure region on the intensity vs. energy curve for the specularly reflected (00) spot, which appears below the threshold where the first nonspecular diffracted beam appears [1]. The incoming electron wave impinging on the sample surface has to “convert” into electron waves of the crystal periodicity, i.e. into Bloch states. This condition makes penetration of incident electrons proportional to the local density of states coupled to the incident wave. Electron reflection becomes then inversely proportional to the local density of states and the reflected flux can measure the density. Crucial condition is sufficiently low absorption of injected hot electrons, which is available below about 20 to 30 eV above the Fermi level.