Electromagnetic guns

THERMOELECTRICALLY MODULATEDE/NANOSCALE MULTILAYERED GRADIENT MATERIALS FOR APPLICATION IN THE ELECTROMAGNETIC GUN SYSTEMS... 

Figure 79 Electromagnetic gun for cold adhesives (by courtesy of Robatech...

An electron gun produces and accelerates the electron beam, which is reduced in diameter (demagnified) by one or more electromagnetic electron lenses. Electromagnetic scanning coils move this small electron probe (i.e., the beam) across the specimen in a raster. Electron detectors beyond the specimen collect a signal that is used to modulate the intensity on a cathode-ray tube that is scanned in synchronism with the beam on the specimen. A schematic of the essential components in a dedicated STEM system is shown in Figure 2. 

As the beam travels down the column, a number of electromagnetic lenses are used to guide the beam to the sample [44], The condenser lenses are part of the illumination system and are used to deliver electrons from the electron gun crossover to the sample. The condenser lenses determine the beam current reaching the sample. The objective, or final, lens determines the final spot size of the beam. A set of scanning coils are also present in the instrument column to scan the beam in a raster pattern over an area of the sample. At each point, data is collected and the points are combined to form the image. More detail on the data collection is given in the image formation section. 

In a SEM equipment, the electrons which result from the emission from a filament located in the electron gun are accelerated, with the help of a voltage ranging from 1 to 30keV (see Figure 4.10) [8,52], The electron emission event takes place in a vacuum milieu ranging from 10-4 to 10-10 Torr. Then, the accelerated electrons are directed to the specimen by a series of electromagnetic lenses in the electron column (see Figure 4.10) [8,52],... 

There are six ways to heat materials in the lab open flame, steam, thermal radiation, electromagnetic bombardment (microwave ovens) passive electrical resistance (such as hot air guns), and direct electrical resistance (such as hot plates). All of these heating methods (except thermal radiation) use conduction to heat the container holding the material to make the material hot. 

The principles ofTEM and HRTEM have been discussed in several textbooks [6, 7]. A TEM column can be described using a ray diagram as shown in Figure 10.1, which is very similar to that for an optical microscope. The most important components in an electron microscope are the electron source (normally called the electron gun) and a group of electromagnetic lenses. 

The basic construction of a modern transmission electron microscope is shown schematically in Figure 2.2. It consists of an electron gun and an assembly of electromagnetic lenses, all within a column which is evacuated to about 10 Torr (= 2.7 x 10 Pa). The beam of electrons produced by the electron gun is accelerated by a high voltage and then focused onto... 

Utilizes the effects of electromagnetic fields to control the trajectory of isolated ions and thereby measures their mass to charge (m/z) ratio. In this work the formation of ions are accomplished by bombardment of polymer sample with a xenon gun. The samples are prepared by blending 1 pi of 1 wt% water solution of PEQ with 0.5 pi of glycerol on the tip of a stainless steel probe. The xenon atoms striking the sample surface generate quasimolecular ions [M-t-H] resulting In a series of peaks, 44 units apart. 

The spatial resolution of the composition maps mainly depend on the diameter of the beam. Auger imaging is a well developed technique because focusing the electron beam is readily achieved by the use of an electromagnetic lens. The diameter of the electron beam can be as small as about 10 nm when a field emission gun is used. Focusing the X-ray beam in XPS is difficult because the X-rays are electrically neutral and cannot be focused with an electromagnetic field. For modern XPS instruments, a monochromatic X-ray beam can be focused down to a diameter of about 10 /rm using a special X-ray gun and a special crystal monochromator. 

A simplified diagram of a SEM is shown in Figure 1. An electron gun emits electrons (by thermionic or field emission) which are accelerated down the column by a large potential energy (typically 1-30 keV). Electromagnetic lenses and mechanical apertures are used to demagnify and focus the electrons to form an electron probe of small diameter and high current density. 

As is shown in Fig. 54 the electrons emitted from a hidden hot filament and accelerated in the electrical field are deflected by, say, 270° magnetically with this type of gun and thus focused to the evaporation material. Small amounts of evaporated material from the hot filament cannot contaminate the films. A high voltage in the range between 6 - 10 kV accelerates the electrons in the direction to the anode that is the crucible. The size of the focal spot can be varied by variation of the Wehnelt potential and in addition there is an electromagnetic X-Y sweep. The first is particularly important when metals and dielectric materials have to be evaporated in the same charge. Since the power densities of some 10 kW cm 2 required for metals would destroy most of the dielectrics, a wobble modulation of the focused beam is inadequate, and dielectric materials must be evaporated by a soft evidently defocused electron beam. The required power density is about 1 - 2 kW cm 2. 

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