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How to Scan

 

How scanning is specified by means of the graphical user interface (GUI) is described in Chapter 5. In this chapter it is only referred to the actual input files which are read by SESAME during program execution.

The electron beam can be either scanned over the sample surface or kept on one spot at the surface. This may be specified in the input file by the variable SCAN (logical) in the &EBEAM namelist (see Chapter 9.3). The default value for SCAN is false.

  
Table 6.2: Variables needed for the specification of scanning

 

If scanning is chosen in the input deck then the scanning area is defined by the two variables XESPOT, the lateral electron impact position, and XRANGE, the lateral scanning area, both in the &MSETUP namelist (see Chapter 9.6). The lateral center position of your simulation geometry is the default value for XESPOT, both for scanning and non-scanning. The scanning range is always XRANGE/2 on both sides of XESPOT. The maximum extension is adjusted by SESAME so that XRANGE/2 is not greater than the distance from XESPOT to the nearest vertical boundary of the simulation geometry, i.e. XRANGE can never be larger then the lateral expansion of the geometry. If neither XESPOT nor XRANGE is specified in the input file then the beam is scanned over the whole geometry (default for SCAN=T).

The angle between the x-axis (the lateral expansion of the simulation geometry) and the scan direction may be specified by the SCANANG variable in the &MSETUP namelist (see Chapter 9.6). The default value for SCANANG is 0.

If the beam is not scanned then XESPOT defines the lateral position of the electron beam at the sample's surface. XRANGE and SCANANG have no effect in this case. For a better understanding of the previously outlined situation see figure 6.4.

If the electron beam is scanned then the number of electron beam impact positions is determined either by NLSCP, the number of lateral scan positions, which can be specified in the input file (see Chapter 9.7), or by the magnification MAGNI (see Chapter 9.6) in conjunction with the pixel distance on the CRT, XPCRT, which may be defined in the &INSTR namelist (see Chapter 9.7).

The default value for XPCRT is 0.25 mm, for MAGNI it is 10000 (10kX), and for NLSCP it is one (means: no scanning). If both MAGNI and NLSCP are explicitly specified in the input file then NLSCP is ignored and the number of electron impact positions is calculated according to the values of MAGNI and XPCRT.



next up previous contents
Next: How to Specify Up: How to Specify Previous: How to Describe



Horst Wagner
Tue Mar 19 10:24:55 MET 1996