Manipulating Spectra
Materials are described within DTSA-II by their
composition and density. Te composition can be defined on an element-by-element basis in terms of weight fraction or atomic fraction. Te editor allows you to enter compositions using either format and to transform between the two composition formats. Stoichiometric materials. For stoichiometric compounds,
the quickest way to enter materials is to enter a chemical formula into the “name” field and then press the button with the magnifying glass icon. Te formula will be parsed and the correct composition automatically entered. For example, entering “Al2O3” will produce a material (Al2O3 / alumina) with 47.07 percent by weight Al and 52.93 percent by weight O. For the parser to work, the element abbreviations must be capitalized correctly, and the formula must be unambiguous. Te parser can handle complex formulas like “Ca5(PO4)3F” for fluorapatite where the PO4 term is taken three times for a total of 5 Ca atoms, 3 P atoms, 12 O atoms, and 1 F atom per unit cell. Non-stoichiometric materials. If the material is not
Figure 2: The spectrum properties dialog. This dialog permits editing the properties of one or more spectra.
If multiple spectra are selected simultaneously, then the
behavior of the spectrum property panel changes. Te panel only displays the subset of properties that all the selected spectra share in common. For example, the “beam energy” property will display if all the selected spectra were collected at the same beam energy. Tis behavior permits you to review the properties common to multiple spectra. Modifying spectrum properties. Many of the spectrum
properties can be modified on a spectrum-by-spectrum basis or in batch mode. Select one or more spectra that you wish to modify in the spectrum list panel. Ten select the “tools → edit spectrum properties” menu item. Te spectrum properties dialog will display. Trough this dialog you can associate the spectra with different detectors or edit the beam energy, probe current (both before and aſter acquisition), live time, working distance, and other descriptive properties. Only those values that you actively modify will be updated when you select “ok” to close the dialog. Te same modifications will be made simultaneously to all selected spectra. Please note that only the in-memory copy of the spectrum is changed. To record the changes, you must save the spectrum to disk.
The Material Editor Specifying materials. Spectra from materials of known
composition are oſten used to quantify spectra from unknown materials. Te user must specify a description of the known material with the spectrum. Tis can be accomplished by selecting one or more spectra in the spectrum list then selecting the “tools → assign material” menu item. Te material editor dialog is used in many different contexts and, despite its simple appearance (see Figure 3), is really quite sophisticated.
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Figure 3: The material editor dialog. This dialog allows you to specify the composition and density of the material from which a spectrum was collected. The dialog is backed by a database, which remembers the definition of the materials indexed by their name for recall later.
stoichiometric (for example, glasses or alloys), it is possible to enter the composition element-by-element using the “element” and “quantity” edit boxes and the “add” button. If the editor contains incorrect information, you can use the “clear” button to eliminate it all or the “delete” button to remove individual elements. Te format for the quantity data depends on whether the “mode” is “weight fraction” or “atomic proportion.” If the mode is weight fraction, enter the amount of each element as a percentage by weight of the total mass. If the mode is atomic proportion, enter for each element the number of atoms per unit cell. Regardless of how you enter the composition, each material
can be assigned a user-friendly name like “Fluorapatite” and a density in grams per cubic centimeter. Not all uses of
the material property
require a density, but it is oſten a good idea to enter the correct density when available. Rather than forcing
the user to enter material data
afresh each time,
the material editor dialog is backed by a database. Te material database is indexed by material name. If the database contains a material, then you can enter the name into the dialog’s name edit window and press the tab button or the magnifying glass button. Te dialog will search the database for a material name that matches (exact,
www.microscopy-today.com • 2011 May
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