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How to Describe the Composition of Your Target

 

How the target composition 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.

To describe the sample under investigation, you have to specify the following two things:

  1. The geometry of your sample (the geometry specification is explained in Chapter 6.6). The geometry defines the shape of the sample and is stored in the geometry file. This file must be specified in the input file by means of the CGFILE variable of the &TARGET namelist (see Chapter 9.4).
  2. The composition of your sample, i.e. which region contains which elements. The description of the target composition specification will follow now.

The composition of your target is specified in your input deck by means of the &TARGET namelist (Chapter 9.4). A typical example of such a specification is the &TARGET namelist of the geometry shown in Figure 6.8 (see Chapter 6.6).

 &TARGET
        NREG=3
        ATMAT='SI3,N4','SI','SI,O2'
        DENS=3.1,2.33,2.2
        CGFILE='TEST.GEO'
 &END

The variable NREG represents the number of regions of the geometry. This number is also specified in the geometry file CGFILE. If the number of regions specified in CGFILE and in NREG are different SESAME will stop (This is a security check. It is a simple test, checking whether the geometry will correspond to the target description or not).

The string array ATMAT contains the chemical abbreviations of all elements of the target and their relative fractions according to the different regions. The chemical abbreviations in one region as well as the strings describing different regions must be separated by commas ( Note: strings must be enclosed by single quotes!). Relative fractions of elements in one region must, if necessary at all, be specified right after the corresponding chemical abbreviation without a blank, comma or any other character inbetween. In this particular example, for instance, the first region is composed of three parts Silicon and four parts Nitrogen, which is equivalent to Silicon-nitride, the second region is pure Silicon, and the third region consists of one part Silicon and 2 parts Oxygen, which is equivalent to Silicondioxide. The relative fractions in each region will be automatically normalized to unity. This means 'Si,O2' and Si0.33,W0.77 will give the same result.

The variable DENS determines the density of each region in . In this case it is: DENS=3.1,2.33,2.2. The first value in density corresponds to the first region. The first region consists of , which has a density of 3.1 . The second value is the density of pure Si in the second region (2.33 ) and the third value represents the density of (the third region), namely 2.2 .

The last input needed in the &TARGET namelist is the name of the geometry file specified by the CGFILE variable. Further information about the geometry file can be found in Chapter 6.6.

Now, for demonstration purposes, we change the composition in the second region from pure Si to . Four elements can be found in the target now. Then the modified &TARGET namelist looks like:

 &TARGET
        NREG=3
        ATMAT='SI3,N4','AL2,O3','SI,O2'
        DENS=3.1,2.5,2.2
        CGFILE='TEST.GEO'
 &END

NREG remains unchanged, of course, because the sample still consists of three different regions. ATMAT has been updated to represent in the second region instead of pure Si. The density of the second region has been changed to 2.5 which is the density of . No changes to the geometry file are necessary since only the composition has been modified - the geometry is the same.

All variables needed for the specification of the target composition are summarized in Table 6.5.

  
Table 6.5: Variables needed for the specification of the target composition



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



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