In situ microscopy is a well-established investigation technique for many areas of material science . Especially in situ heating experiments have become an important tool for the analysis of phase transitions and material behavior at high temperatures. For instance, the phenomenon of solid-state dewetting has been elucidated by in situ heating experiments using the various techniques provided by transmission electron microscopy (TEM) . However, some questions related to such phenomena cannot be analyzed purely by TEM due to the limited field of view and lack of topographic contrast. Additionally, the high beam energies usually associated with TEM are non-optimal or even detrimental to the investigation of light element-materials, like Carbon Nanotubes and Graphene because of low contrast and knock-on damage. Scanning Electron Microscopy (SEM) could alleviate these problems, however in situ heating combined with transmission diffraction so far is not possible for this technique.
In this work we introduce a novel heating and diffraction setup in the SEM enabling the simultaneous acquisition of real space and reciprocal space information in situ. Low Energy Nano Diffraction (LEND) in transmission is based on the combination of a fluorescent screen positioned below the sample with a dedicated CMOS camera. The technique has been implemented and successfully tested on graphene and polycrystalline gold. For graphene a hexagonal spot like diffraction pattern can be obtained due to the small convergence angle (hence nano diffraction) typically encountered in SEM. For gold the same is possible for very thin films. With increasing film thickness the contribution of dynamical scattering becomes more prevalent, resulting in familiar transmission Kikuchi diffraction (TKD) patterns. With our setup we could successfully demonstrate LEND down to an energy of 0.5 keV (hence low energy).
A custom-built heating stage for DENS Solution Wildfire Nano-Chips in combination with the LEND setup offers combined in situ heating, imaging and transmission diffraction in SEM. To showcase the power of this technique solid state dewetting experiments on metal thin films will be shown, where the simultaneous acquisition of real- and reciprocal space information in situ is needed to elucidate phenomena such as grain rotation.
In the future in situ heating and diffraction experiments combined with mechanical and electrical stimuli are planned.