The description and function characterization of a flange-on type low energy electron mi- croscope are given. In this microscope a magnetic beam separator with 10° deflection angle is used in order to facilitate compacting the instrument on a single 10 in. flange. Mean- while some correcting elements in the electron optical system are simplified to reduce the complexities of construction and operation. The sample is set close to ground potential, so that all the electrostatic lenses are easily to float at high voltages. The performance of the microscope in typical low energy electron microscopy, low energy electron diffraction and photoemission electron microscopy modes is demonstrated through several experiments. A lateral resolution of 51 nm is estimated for low energy electron microscopy imaging. With femtosecond laser as light source, the consequent nonlinear photoemission makes this micro-scope also suitable for the observation of optical near field phenomena and a lateral resolution of 110 nm is obtained.
