software to fit optical spectra - Quantum Materials Group

3. Tutorial
This chapter shows how to solve typical problems using RefFIT. Each section is devoted
to a particular task. I suggest you to go through the sections sequentially, since the last parts do
not repeat the detailed explanations, given in the beginning. It is especially important to read
the first section (3.1), which deals with the most basic RefFIT objects.
Of course, before the going through this tutorial, you should install RefFIT on your
computer. This simple procedure is explained in section 4.2.
3.1. Drude-Lorentz fitting of a reflectivity spectrum
As I already mentioned, RefFIT was created as a reflectivity fitting routine with the
Drude-Lorentz dielectric function (Equation 2-18). The normal-incidence reflectivity R (ω)
is
expressed via the dielectric function ε (ω)
according to Fresnel formula:
2
1−
ε
R = .
1+
ε
It is one the most common data analysis that solid-state infrared spectroscopists do. So why
don’t we try it first?
In order to do it in RefFIT, one should first open a model window by choosing “Model”
from the “Window” menu (Figure 3-1). It contains a particular DL model that can be used later
on for plotting graphs, fitting data and so on. In this window we can add or delete the Lorenzian
terms and manually edit parameters. The “Einf” field stands for ε ∞ ; “Wo”, “Wp” and “G”
designate the transverse frequency ω 0i
, the plasma frequency ω pi and the scattering rate γ i
respectively, measured in inverse centimeters 10 (cm -1 ). By the way, 1 eV is about 8000 cm -1 .
Let us keep for a while the initial values (Figure 3-1).
10
Inverse centimeters are apparently invented by the infrared spectroscopists to make the life of normal people
more difficult ☺.
Guide to RefFIT Page 25