In-situ PEEM techniques, water and aqueous solution can be observed by PEEM. The resolution of PEEM is limited to about 10 nm, which results from a spread of the photoelectron emission angle. Angle resolved photoemission spectroscopy (ARPES) is a powerful tool for structure analysis. However, it may be difficult to make angle-resolved and energy-selective PEEM measurements because of a lack of intensity. The availability of synchrotron-radiation light sources can offer exciting possibilities in this regard. Comparison from other techniques Transmission electron microscopy (TEM) and scanning electron microscopy (SEM): PEEM differs from these two microscopies by using an electric accelerating field at the surface of specimen. The specimen is part of the electron-optical system. Low-energy electron microscopy (LEEM) and mirror electron microscopy (MEM): these two electron emission microscopy use electron gun supply beams which are directed toward the specimen, decelerated and backscattered from the specimen or reflected just before reaching the specimen. In photoemission electron microscopy (PEEM) the same specimen geometry and immersion lens are used, but the electron guns are omitted. New PEEM technologies Time resolved photoemission electron microscopy (TR-PEEM) is well suited for real-time observation of fast processes on surfaces equipped with pulsed synchrotron radiation for illumination. Time-of-flight Photoemission electron microscopy (TOF-PEEM): TOF-PEEM is PEEM using an ultrafast gated CCD camera or a time-and space-resolving counting detector for observing fast processes on surfaces. Multiphoton Photoemission electron microscopy: Multiphoton PEEM can be employed for the study of localized surface plasmon excitations in nanoclusters or for direct spatial observation of the hot-electron lifetime in structured films using femtosecond lasers. PEEM in liquids and dense gases: The development of microfabricated thin liquid cells in late 1990s enabled wide field-of-view transmission X-ray microscopy of liquid and gaseous samples confined between two SiN membranes. In such a configuration, the vacuum side of the second membrane was coated with the photoemitting material and PEEM was used to record the spatial variations of the transmitted light. True PEEM imaging of liquid interfaces in photoelectrons has been realized through ultrathin electron transparent membranes such as graphene. Further development of the UHV compatible graphene liquid cells enabled studies of electrochemical and electrified liquid-solid interfaces with standard PEEM setups without the use of the differential pumping. Notes References James A. Samson, David L. Ederer (1998). Vacuum Ultraviolet Spectroscopy. Academic Press Andrzej Wieckowski, Elena R. Savinova, Constantinos G. Vayenas (2003). Catalysis and Electrocatalysis at Nanoparticle Surfaces. CRC Press Harm Hinrich