The source is mounted to the monochromator via a three axis mechanical aligner. This aligner provides the precision motions necessary to optically position the anode with respect to the monochromator crystal set.
THEORY OF OPERATION
This x-ray source is the "Secondary" source. it is mounted on the 10-420 X-ray monochromator (see figure), and it generates Al K_alpha x-rays, which are diffracted and focused by the monochromator.
- Filament selection. When the FILAMENT ENERGIZE push button on the 32-096 X-ray Source Control is pushed, the source functions in the focused mode. Likewise, when the second button is selected, the source functions in the diffuse mode. CAUTION: NEVER SELECT BOTH FILAMENTS SIMULTANEOUSLY!
Source Aligner Operation. The source aligner provides three orthogonal axes of alignment. The procedure for aligning the 10-610 X-ray Source to the monochromator crystal set is found in the Model 10-420 Monochromator manual.
X-RAY SOURCE SELECTION
The PHI 5600 has a dual anode, non-monochromatic x-ray source and a monochromatic Al Kα x-ray source.
The monochromatic x-ray source should be used for the following reasons:
- The 10-610 x-ray source generates x-rays very efficiently and provides good sensitivity.
- A monochromator filters out undesired high energy x-rays, x-ray satellites, and narrows the Al Kα lines, greatly reducing x-ray-induced sample damage.
- The filtered Al Kα beam eliminates x-ray satellites, eliminating some peak overlaps and, in general, simplifies the spectra and peak identification.
- The filtered Al Kα beam provides a narrower x-ray energy distribution, increasing the energy resolution and chemical sensitivity of the instrument.
- There may be situations where a peak overlap exists between a photoelectron peak and an Auger peak, changing the x-ray energy can eliminate this overlap; this would be the most common reason to use the non-monochromatic x-ray source.
The monochromatic x-ray source has two filaments: a 2 mm filament and a 7 mm filament. Physical Electronics recommends using the 2 mm filament, because this will provide the highest sensitivity. Note: the charge neutralization system will effectively neutralize insulating samples under these conditions.
SELECTING THE SIZE OF THE ANALYSIS AREA
The x-ray sources flood a relatively large area of the sample with x-rays, and the size of the analysis area is determined by the energy analyzer input lens. The user has control of two variables that effect the size of the analysis area. The first is the size of the aperture in the analyzer input lens. A rotary motion located on the side of the analyzer input lens is turned to select one of five apertures. Aperture 1 is the smallest and 5 is the largest. The aperture also must be selected in the Analyzer/Detector menu to apply the correct lens voltage for the selected analysis area. The second variable is the relative magnification of the input lens. Three magnifications are available: large (1 X), small (1/3 X) and minimum (1/5 X)
SELECTING A PASS ENERGY
The pass energy determines the energy that detected photoelectrons will have as they pass through the hemispherical analyzer. The lower this energy is, the better the energy-resolving capability of the analyzer is. However, as pass energy is lowered to improve energy resolution, the intensity of the detected photoelectron peaks is reduced. This relationship is nearly linear (when the pass energy is reduced by a factor of two, so is the detected count rate). When elemental information is of primary interest, such as in survey spectra, a high pass energy and a large data step size should be used. When detailed chemical information is being sought, a lower pass energy and smaller data step sizes should be used. By selecting a pass energy that is no lower that necessary to resolve the ESCA peaks of interest, you will maintain as high a count rate as possible and improve the efficiency of your experiments.
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