Electron beams

Unlike X-rays and gamma rays, electrons are rapidly attenuated. The maximum range of a 1-million-volt electron is about 4 m in air and about 5 cm in water. In 

FIGURE 28. Structural model of the evaporated film. (Reprinted from Ref. 30.) 

The first step (Fig. 29a) is the evaporation of the polysilane material and recrystallization on the substrate. The film is then irradiated by the electron beam (Fig. 29b). In the irradiated area of the film, C-O-C, Si-O-C, and Si-O-Si bonds are formed between nearest-neighbor polysilane chains. Thus the 

FIGURE 29. Process for the fabrication of the submicron pattern. (Reprinted from Ref. 130.) 

---

Application of ceramics allows using stainless steel as vacuum envelope. No surface charges ean deflect the electron beam. Mechanical elements and functions can be easily integrated into the envelope due to its stability. 

XES, Soft x-ray emission An x-ray or electron beam Energy levels and chemical... 

ESD Electron-stimulated (impact) desorption [148, 149] An electron beam (100-200) eV) ejects ions from a surface Surface sites and adsorbed species... 

Figure Al.7.12 shows the scattered electron kinetic energy distribution produced when a monoenergetic electron beam is incident on an A1 surface. Some of the electrons are elastically backscattered with essentially...

Figure Al.7.12. Secondary electron kinetic energy distribution, obtained by measuring the scadered electrons produced by bombardment of Al(lOO) with a 170 eV electron beam. The spectrum shows the elastic peak, loss features due to the excitation of plasmons, a signal due to the emission of Al LMM Auger electrons and the inelastic tail. The exact position of the cutoff at 0 eV depends on die surface work fimction.

A popular electron-based teclmique is Auger electron spectroscopy (AES), which is described in section Bl.25.2.2. In AES, a 3-5 keV electron beam is used to knock out iimer-shell, or core, electrons from atoms in the near-surface region of the material. Core holes are unstable, and are soon filled by either fluorescence or Auger decay. In the Auger... 

Figure Al.7.13. ESDIAD patterns showing the angular distributions of F emitted from PF adsorbed on Ru (0001) under electron bombardment, (a) 0.25 ML coverage, (b) the same surface following electron beam damage.

Marrian C R K, Perkins F K, Brandow S L, Koloski T S, Dobisz E A and Calvert J M 1994 Low voltage electron beam lithography in self-assembled ultrathin films with the scanning tunneling microscope Appi. Rhys. Lett. 64 390... 

Madey T E ef a/1993 Structure and kinetics of electron beam damage in a chemisorbed monolayer PFjOn Ru(OOOI) Desorption Induced by Electronic Transitions DIET V vol 31, ed A R Burns, E B Stechel and D R Jennison (Berlin Springer)... 

The above Cl reactions will occur if they are exothennic. In order for these reactions to occur with high efficiency, the pressure in the ion source must be raised to the milliTorr level. Also, the reagent species are often introduced in large excess so that they are preferentially ionized by the electron beam. 

Szule]ko J E and McMahon T B 1991 A pulsed electron beam, variable temperature, high pressure mass... 

The history of EM (for an overview see table Bl.17,1) can be interpreted as the development of two concepts the electron beam either illuminates a large area of tire sample ( flood-beam illumination , as in the typical transmission electron microscope (TEM) imaging using a spread-out beam) or just one point, i.e. focused to the smallest spot possible, which is then scaimed across the sample (scaiming transmission electron microscopy (STEM) or scaiming electron microscopy (SEM)). In both situations the electron beam is considered as a matter wave interacting with the sample and microscopy simply studies the interaction of the scattered electrons. 

Busch focuses an electron beam with a magnetic lens 1931 Ruska and colleagues build the first TEM protoype... 

Cambridge Instruments builds the first commercial SEM 1968 Crewe and colleagues introduce the PEG as electron beam source 1968 Crewe and colleagues build the first STEM prototype 1995 Zach proves the concept of a corrected LVSEM... 

Modem EMs use electromagnetic lenses, shift devices and spectrometers. However, electrostatic devices have always been used as electron beam accelerators and are increasingly being used for other tasks, e.g. as the objective lens (LVSEM, [10]). 

EM instmments can be distinguished by the way the infonnation, i.e. the interacting electrons, is detected. Figure Bl.17.2 shows the typical situations for TEM, STEM, and SEM. For TEM the transmitted electron beam of the brightfield illumination is imaged simply as in an light microscope, using the objective and... 

Figure Bl.17.2. Typical electron beam path diagrams for TEM (a), STEM (b) and SEM (c). These schematic diagrams illustrate the way the different signals can be detected m the different instmments.

Except for the phase-contrast detector in STEM [9], STEM and SEM detectors do not track the position of the recorded electron. The spatial information of an image is fonned instead by assigning the measured electron current to the known position of the scaimed incident electron beam. This infomiation is then mapped into a 2D pixel array, which is depicted either on a TV screen or digitalized in a computer. 

Specimens for (S)TEM have to be transparent to the electron beam. In order to get good contrast and resolution, they have to be thin enough to minimize inelastic scattering. The required thin sections of organic materials can be obtained by ultramicrotomy eitlier after embedding into suitable resms (mostly epoxy- or methacrylate resins [H]) or directly at low temperatures by cryo-ultramicrotomy [12]. 

The infonuation that can be extracted from inorganic samples depends mainly on tlie electron beam/specimen interaction and instrumental parameters [1], in contrast to organic and biological materials, where it depends strongly on specimen preparation. 

---