Combining SEM with AFM for in situ Correlative Microscopy

Abstract

With the large amount of current research and development focused on nano wires, carbon nano tubes, and other nano scale materials, imaging these materials has become a large part of the challenges involved. The two most prominent methods for imaging at the nano scale are Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). These complimentary methods utilize fundamentally different principles for generating imagery ‐ SEM exploits the interaction of electrons with matter, while AFM is based on physical interaction of a sharp tip with the sample surface. Both approaches have strengths and weaknesses. The SEM's strength is to quickly generate images with a large range of magnifications, making it easy to locate the area of interest. Additionally, the SEM beam can be used to characterize materials beyond mere imaging (e.g. EDX elemental mapping, etc.). Beyond that, the use of Focussed Ion Beams (FIB) enhances the ability for modification or preparation of samples. However, scanning beams do not yield 3D information, e.g. “invisible” contamination layers or the precise surface structure of novel materials such as solar cells. The AFM's main advantage lies in its ability to obtain 3D information, the downsides are that it is hard to find the target area and image generation is slow. Combining these two tools into one setup ‐ putting an AFM inside an SEM ‐ gives quick access to a more complete data set. Additionally, FIB‐milled or FIB‐deposited structures can be characterized using this combination of tools in a FIB/SEM system. The utility of this combination of tools is demonstrated with several examples where locating the area of interest purely by AFM or light microscopy would have been highly impractical.