photo emission electron microscope, PEEM

A "PEEM (photo emission electron microscope)" is a microscope to form a surface image of a specimen using photoelectrons generated from a specimen illuminated with ultraviolet rays or vacuum ultraviolet rays. The generated photoelectrons are accelerated by an acceleration electric field (acting as an immersion lens) just above the specimen. This electric field also acts as an objective lens. The imaging lens system is placed after the objective-lens field. An enlarged image is observed with a screen or a CCD camera. Since the intensity of the photo-electron image depends on the work function and the wavelength of the excitation light, selecting an appropriate excitation wavelength enables us to acquire an image sensitive to electronic structures of atoms on the specimen surface, and also to view a contrast formed by surface structures. To obtain information on a clean surface, the specimen area is kept at ultrahigh vacuum. PEEM can be further equipped with an imaging filter for energy selection of photo electrons to obtain detailed information on electronic structures. The function of PEEM is often added to LEEM (low energy electron microscope) which has the same imaging system as that of PEEM.

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