Rastered electron beam

All samples were analyzed with a Physical Electronics Industries SIMS-3500 spectrometer using a 5 KeV Ar+ primary ion beam and a 5 KeV rastered electron beam to reduce charging of the insulating glass surface. 

When the video chip receives the signal from the pen, it latches (stores) the current position of the raster (electron beam) in a set of registers (memory locations within the chip). The stored value can then be read, and the position where the pen is touching the screen can be calculated. In 128 mode, the 128 s BASIC 7.0 provides the functions PEN(O) and PEN(l), which return the x- and y-coordinates, respectively, of the light pen s position on the screen. 

EDS/WDS — characteristic x-rays which are emitted as a result of a static or rastered electron beam impinging on a sample. The analysis of this radiation by EDS (simultaneous analysis for fluorine to uranium) or WDS (sequential analysis for beryllium to uranium) yields compositional, element specific, information of... 

The vacuum fluorescence (VF) tube is a modification of the CRT in which the rastered electron beam is replaced by a hot cathode addressable for each pixel. It has proved to be the most useful of the flat CRTs, a bright, rugged, inexpensive display preferred for automobile applications. The cold-cathode version of the VF display is called t it field emission display (FED). Prototype models have been recently shown at Display Works 98. The glass used in these flat displays is similar to that used in conventional CRTs (Table 7.2). 

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. 

The results shown in Figure 6 above are an example of this mode of analysis, but include additional information on the chemical states of the Si. The third most frequently used mode of analysis is the Auger mapping mode, in which an Auger peak of a particular element is monitored while the primary electron beam is raster scanned over an area. This mode determines the spatial distribution, across the surface, of the element of interest, rather than in depth, as depth profiling does. Of course, the second and third modes can be combined to produce a three-dimensional spatial distribution of the element. The fourth operational mode is just a subset of the third mode a line scan of the primary beam is done across a region of interest, instead of rastering over an area. 

If an incident electron beam of sufficient energy for AES is rastered over a surface in a manner similar to that in a scanning electron microscope (SEM), and if the analyzer is set to accept electrons of Auger energies characteristic of a particular element, then an elemental map or image is again obtained, similar to XPS for the Quantum 2000 (Sect. 2.1.2.5). 

As opposed to XPS, AES signals typically exhibit complex structure, and sometimes require elaborate data treatment. Also, AES does not easily provide information on oxidation states, as XPS does. On the other hand, AES is often acquired by using easy-to-focus electron beams as the excitation source, and can therefore be used in a rastering mode for the microanalysis of nanosized spots... 

Secondary ion mass spectra were measured using a Perkin-Elmer+PHI 3500 instrument. Experiments were carried out with 4 kV Ar ions at beam currents of 3 and 300 nanoamps. Spectra were measured to at least 500 daltons (d). Samples were prepared in the manner used for the XPS studies. For measurements on the pure complexes, sample charging occurred, as evidenced by the inability to record secondary ion mass spectra. To reduce charging, a low energy electron beam (50-400 eV) was rastered across the sample during SIMS analysis. Positive and negative ion SIMS spectra were recorded however, only positive ion spectra are of interest for this discussion. In the spectra only unipositive ions were detected, so that the mass numbers detected correspond to combinations of the various isotopes of the elements in the ion. Thus an ion at m/z 17 d is assigned to... 

Figure 40. Operating modes for electron beam systems left — raster scan coupled with continuous table motion right — vector scan, step and repeat.

To avoid any flicker in the image, the electron beam is scanned across and down the screen, many times per second, following a predetermined set of parallel lines, the method being known as raster scanning. The phosphor dots are the picture elements or pixels and light up as the beam scans across each one. In colour televisions and monitors additive mixing of the three colours of red, green and blue produces the... 

In scanning electron microscopy (SEM), a finely focussed electron beam probe moves from one point on the specimen to the next to form a raster pattern, just as in television imaging. The intensity of scattered or secondary electrons is continuously... 

Electron Microprobe. Since the electron beam diameter is only 1 /xm, it is unlikely that the volume sampled represents the bulk composition. To obtain as representative analyses as possible, the focal spot is electronically scanned over a square area of 300 /xm X 300 /xm. In some cases, where one dimension of the section was < 300 /xm, the area scanned was necessarily reduced to 100 /xm X 100 /xm. Assuming a penetration depth of 1 /xm (5), the standard 300 /xm square raster samples a volume of <— 9 X 104 /xm3 = 1 /xgram. 

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