5. Transfer function

The transfer function menu item Drawing-Transfer function (Alt-D + Ctrl-T) opens the window shown on figure 5.1 when a crystal structure is not yet defined. In that case the toolbox offers 3 tools for printing the drawing, , saving the drawing in .gif format, , or selecting a microscope with the microscope dialogue,. The window contains 4 boxes that controls the drawing parameters and options:

the Options box to draw envelopes, the Transfer function box to plot either the amplitude, phase, intensity or envelopes of the transfer function, the envelopes box that permits the drawing of either the coherent transfer function or this function damped by the spatial or temporal envelope ot their product. The Controls box allow to change the drawing parameters, i.e. accelerating voltage, beam convergence, defocus, defocus spread, objective aperture size, spherical aberration coefficient, specimen drift and vibration.

Figure 5.1 (Transfer function window, crystal not yet defined)

Once a crystal is defined or loaded, the transfer function window offers the possibility to modify the specimen settings, (figure 5.2).

Figure 5.2 (the transfer function dialogue after loading or defining a crystal structure)

With a crystal defined, the transfer function window can be used to identify the spatial frequencies that the microscope transmits for a given set of adjustment parameters. The Options box offers 2 new check buttons (+(hkl) lines and ZOLZ) that plots all reflections with their amplitude within the interval [0, 20 nm-1] or only the reflections of the Zero Order Laue Zone. A predefined set of extended defocuses (positive for under focus as the Oz direction points to the electron gun) is offered on the defocus panel.

Figure 5.3 (The amplitude and position of the reflections are plotted)

All the other controls are pretty obvious. Figure 5.3 shows the Coherent Transfer Function, the spatial, temporal envelopes and their product, the objective aperture and the (h,k,l) reflections of the ZOLZ for a [2,1,0] direction.

Figure 5.4 (Transfer function with TiO2 reflections, [1,2,1] zone axis)