Low energy electron microscopy (LEEM) is a surface imaging technique in which the surface is illuminated by an approximately parallel electron beam at near normal incidence. The image is formed with those electrons which are elas- tically backscattered into a small angular region around the surface normal. The limitation to a small angular region is necessary because of the large aberrations of the objective lens which produces the primary image. This lens is a so-called cathode lens which not only has imaging properties but at the same time decelerates the fast electrons of the illuminating beam to the desired low energy at the specimen and re-accelerates the backscattered electrons to high energies again. In order to achieve this, the specimen is at a high negative potential which differs from the potential of the emitter of the electron gun of the illumination system by V 0 = E 0/e, where E 0 is the energy of the electrons at the specimen. Typical energy values are E = eV = 15−20 keV for the fast electrons and 0 < E 0 < 50 eV at the specimen. There are three fundamental quantities which are important in LEEM: resolution, intensity and contrast. These will be discussed in Sect. 12.1. Section 12.1 also describes how LEEM can be combined with other surface characterization techniques, such as low energy electron diffraction (LEED), photoemission electron microscopy (PEEM) and other emission microscopies. Section 12.2 illustrates the applications of LEEM and of the associated techniques to the study of clean surfaces, while Sect. 12.3 presents examples of the power of LEEM in the study of surface layers. Section 12.4 gives an outlook for possible future developments. A brief summary (Sect. 12.5) concludes this chapter.

https://iopscience.iop.org/article/10.1088/0034-4885/57/9/002/pdf

Low energy electron microscopy

Transformations on clean Si(111) stepped surface during sublimation

The equilibrium shape of silicon

Surface faceting and the equilibrium crystal shape

Scanning Low-Energy Electron Microscopy

UHV-SEM observations of cleaning process and step formation on silicon (111) surfaces by annealing

Low energy scanning electron microscopy combined with low energy electron diffraction

Surface analyses by low energy SEM in ultra high vacuum

Formation of domains on reconstructed structure in Si(110) vicinal surfaces

An ultra high vacuum SEM of low energy (UHV-LE-SEM) has been developed for surface analysis combined with electron energy spectroscopy and reflection electron diffraction. The most sensitive primary electron energy of SEM image to the surface analysis was experimentally measured as a function of the primary electron energy Ep in a range of 100 eV to 3 keV and was several hundred eV for an absorption electron image on Si from the observations of the contrast change due to the surface adsorption and desorption less than one monolayer. The secondary or absorption electron image has a very high sensitivity to the surface and detects the surface change of 10-2 to 10-3 monolayer in coverage. The sensitivity is 102 to 103 times higher than that of the Auger electron image. The point analysis by the low energy electron spectroscopy has been performed at the same time in a spatial resolution of 0.1 ?m. Some examples of surface microanalysis by UHV-LE-SEM for cleaning process of Si(lll) surface and surface segregation of SUS-304 L stainless steel by heat treatment are shown. Furthermore, some experimentals of the angular resolved secondary electron and the angular resolved electron loss spectroscopies are demonstrated as a new technique of the surface analysis and it is found that those spectra change distinctly by the effect of the electron diffraction with respect to the incident and diffracted beams for single crystal specimens.

Y. Ishikawa

Papers

UHV-SEM observations of cleaning process and step formation on silicon (111) surfaces by annealing

Low energy scanning electron microscopy combined with low energy electron diffraction

Surface analyses by low energy SEM in ultra high vacuum

Formation of domains on reconstructed structure in Si(110) vicinal surfaces

Analytical scanning electron microscopy in uhv for solid surface