Photoemission electron microscopy

[citation needed] The excitation is usually produced by ultraviolet light, synchrotron radiation or X-ray sources.

In 1965, G. Burroughs at the Night Vision Laboratory, Fort Belvoir, Virginia built the bakeable electrostatic lenses and metal-sealed valves for PEEM.

During the 1960s, in the PEEM, as well as TEM, the specimens were grounded and could be transferred in the UHV environment to several positions for photocathode formation, processing and observation.

The first commercially available PEEM was designed and tested by Engel during the 1960s for his thesis work under E. Ruska and developed it into a marketable product, called the "Metioskop KE3", by Balzers in 1971.

It creates at any given moment a complete picture of the photoelectron distribution emitted from the imaged surface region.

The viewed area of the specimen must be illuminated homogeneously with appropriate radiation (ranging from UV to hard x-rays).

UV light is the most common radiation used in PEEM because very bright sources are available, such as mercury lamps.

The faster electrons, leaving the surface exactly along the center line of the PEEM, will also negatively influence the resolution due to the chromatic aberration of the cathode lens.

So resolution r is approximately: In the equation, d is the distance between the specimen and the objective, ΔE is the distribution width of the initial electron energies and U is the accelerating voltage.

The main task of this lens combination is the deceleration of the fast 20 keV electrons to energies for which the channelplate has its highest sensitivity.

Using such instrument, one can acquire elemental images with chemical state sensibility or work function maps.

Compared to many other electron microscopy techniques, time-resolved PEEM offers a very high temporal resolution of only a few femtoseconds with prospects of advancing it to the attosecond regime.

By repeating this experiment with a series of waiting times between pump and probe pulse, a movie of the dynamics on a sample can be recorded.

In recent years, pulses with shorter wavelengths have been used to achieve a more direct access to the instantaneous electron excitation in the material.

By employing additional time-of-flight or high-pass energy recording in the PEEM, information about the instantaneous electronic distribution in a nanostructure can be extracted with high spatial and temporal resolution.

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.