How the electron detector 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.
In this manual the term electron detector refers to both the electron detector (e.g. electron multiplier) itself as well as to an optional energy analyzer. For each simulation you can specify up to five different electron detectors enumerated from #1 to #5. In simulation the electron detector is applied to all output acronyms which start with the letters 'D' or 'A' (e.g. DEY,AEE,...) (see Chapter 9.9).
Table 6.4: Variables needed for the specification of the electron detector
In the current release of SESAME the electron detector (analyzer entrance) is assumed to be annular. You can specify minimal and maximal acceptance angle (see Figure 6.6) using the variables EDTHMN and EDTHMX . Only electrons which leave the sample in a direction within this solid angle are counted. Furthermore, in case an energy dependent transmission curve is specified, only a fractional part of this electron is considered to be detected, i.e. the probability that this electron would have been detected.
The default electron detector is a detector with ideal (100 % )
transmission positioned exactly over the sample surface.
The default detector is always available as detector #0.
Using default values you will achieve the same results for example in the case of 'DEE' and 'BEE' (see Chapter 9.9) because every backscattered electron will reach the detector and will be detected.
Following variables are used to specify the electron detector :
The polar angle spread of acceptance of your detectors are specified with the variables EDTHMN and EDTHMX in the record &DETECT. The form is EDTHMN = min# 1,min# 2,... and EDTHMX = max# 1,max# 2,... You can also position each electron detector arbitrarily by specifying a polar and an azimuthal angle (see Fig. 6.6). These angles are defined with the variables EDTHET ( detector) and EDPHI ( detector) in the record &MSETUP.
Figure 6.6: Angles needed for description of the electron detector size and position.
To define an energy dependent transmission curve you have to specify
a data file in the variable FEDTRN containing the transmission
of your detector.
This ASCII file must have the following format:
Where is the transmission of the detector/analyzer at the energy
given in eV.
Values for transmission between given energy points are obtained by
linear interpolation.
Notice:
Example: You want to compare results for two different CMAs.
This can be done in one single simulation by specifying two detectors. The correct specification for this example is:
EDTHMX = 48,45
FEDTRN(1) = CMA.TRN
FEDTRN(2) = CMA.TRN
& MODEL EDTHET(1) = 30
EDTHET(2) = 30
& DETECT EDTHMN = 36,39
The contents of the file CMA.TRN could for example be:
0 0
10000 1
which means that the transmission would linearly increase with electron energy up to 100
The corresponding transmission can be seen in fig..
Figure 6.7: Detector transmission for above example file