Low-energy electron microscopy as a tool for analysis of self-assembled molecular layers on surfaces

Low-energy electron microscopy (LEEM) is a surface science method that works primarily in the ultrahigh vacuum environment. It provides information complementary to the other established techniques: it extends the limited view of scanning probe microscopies from nanometers to micrometers and measurement time down to tens of milliseconds, enabling to visualize the changes during sample treatment, e.g., annealing, deposition, and gas or light exposure. From the point of structural analysis, it allows the measurement of diffraction patterns from an area of diameter below 200 nm and imaging of phase distribution on the surfaces either through dark-field imaging or LEEM-I(V) fingerprinting. The advanced modes provide local angle-resolved photoelectron spectra and surface potential distribution. In this review, we aim to describe the utilization of LEEM to study self-assembled molecular structures on solid surfaces. We present the LEEM instrumentation and analysis of measured data in a tutorial way to provide the necessary background knowledge to enter the field. In the second part, we summarize the knowledge obtained by LEEM for several selected systems, which points to the strength of LEEM in understanding the self-assembled molecular systems and its synergy with other surface science techniques.