software to fit optical spectra - Quantum Materials Group

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extra model type 2, etc. In this case “Einf” is not treated as a parameter but just as model type identifier and the text labels in the Model window do not have original meanings anymore. Particular meaning of parameters in the “Lorenzian” section depends on the model type. I must apologize for such an ‘awkward’ convention, which was temporarily chosen to avoid the major changes in the program’s user interface. In future RefFIT versions a more elegant way to distinguish model types will surely be found. Each model has a set of output quantities, which depends on the model type. Different quantities are designated by abbreviations. For instance, reflectivity is referred to as “R”, the real part of conductivity – “S1”, penetration depth – “PD” etc. These abbreviations are meaningful only for the Dielectric Function model. For other types the meaning of the output quantities is different, although the same abbreviations are used. The next sections describe different model types. 4.6. “Dielectric function” model In the “Dielectric Function” model the complex dielectric function ε = ε1 + iε 2 is calculated as a sum (linear superposition) of different terms, e.g., Drude, Lorentz, or others, using the parameters residing in the “Model” window. The dielectric function has only one component, thus this model is applicable either to the isotropic sample or to the special experiment geometry, when only one component of the dielectric tensor is involved 18 . All the output optical quantities are derived from the dielectric function. In some cases extra parameters are used from the “Experimental parameters” set. For example, the transmission of a thin sample depends on sample thickness. Table 4-2 lists all output quantities of the “Dielectric Function” model. The formulas in this table refer to the complex refraction index N = n1 + in2 = ε , complex reflectivity 1− N ωε r = r1 + ir2 = and complex optical conductivity σ = σ 1 + iσ 2 = . 1+ N 4πi Quantity abbreviation “R” Normalincidence reflectivity of semi-infinite Description Calculation formula(s) Units Experimental parameters sample “T” Normalincidence transmission of a finitethickness sample, 2 α R | r | - Scaling factor T T α average , where 18 Some special models can combine several isotropic dielectric function to form a tensor. of R ( α R ) - sample thickness ( d ), thickness spread ( s d ), scaling factor Guide to RefFIT Page 56
considering multiple (Fabri- Perot) internal reflections and a possible thickness spread “TT” Normalincidence transmission of a finitethickness sample, ignoring multiple (Fabri- Perot) internal reflections but considering a possible thickness spread “Rp” Grazingincidence reflectivity (ppolarization) T N ∑ wi average = i= 0 N ∑ i= 1 T ( d ) Guide to RefFIT Page 57 w 1 ⎛ i − N / 2 ⎞ wi = , d i = d⎜1 + sd ⎟ , N + 1 ⎝ N ⎠ ( N = 10 ), 2 ( 1− r ) t( d) T ( d) = , 2 1− r t( d) ⎛ ω ⎞ t( d) = exp⎜i ε d ⎟ ⎝ c ⎠ T T α T average , where N ∑ i = average i = 0 N ∑ i = 1 w i i i 2 wT ( d ) 1 ⎛ i − N / 2 ⎞ wi = , d i = d⎜1 + sd ⎟ , N + 1 ⎝ N ⎠ ( N = 10 ), 2 T ( d) = ( 1− r ) t( d) , ⎛ ω ⎞ t( d) = exp⎜i ε d ⎟ ⎝ c ⎠ α R R p R p average i 2 , where N ∑ wi average = i= 0 N ∑ i= 1 R p w i , , (θ ) 1 ⎛ i − N / 2 ⎞ wi = , θ i = θ⎜1 + sd ⎟ , N + 1 ⎝ N ⎠ ( N = 10 ), 2 R p ( θ ) = rp ( θ ) , r p ε cosθ − ( θ ) = ε cosθ + i ε − sin , ε − sin 2 2 θ θ of T ( α T ) - sample thickness (d), thickness spread (sd), scaling factor of T (αT) - angle of incidence (θ ), angle spread ( s θ ), scaling factor of R ( α R )
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Last updated: 20.04.2004 Guide to R
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Page 23 and 24: In these cases the fitting of the d
Page 25 and 26: 3. Tutorial This chapter shows how
Page 27 and 28: Figure 3-3 Graph contents window is
Page 29 and 30: Figure 3-7 Click the button and in
Page 31 and 32: If you are still far from this fitt
Page 33 and 34: Figure 3-15 The model and experimen
Page 35 and 36: Figure 3-18 The “Graph properties
Page 37 and 38: Figure 3-20 Loading the reflectivit
Page 39 and 40: Figure 3-22 The general RefFIT view
Page 41 and 42: Figure 3-25 The general RefFIT view
Page 43 and 44: MainWindow(XPos = 0, YPos = 0, Widt
Page 45 and 46: emarkable ‘anomaly’, related to
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Page 49 and 50: # restores the original application
Page 51 and 52: 4. Reference 4.1. System requiremen
Page 53 and 54: Figure 4-2 The “Parameter control
Page 55: The model file stores information a
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Page 65 and 66: Iinc Itrans ε ε ( 1) ( 2) … (n)
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Page 91 and 92: XMin Double Minimal X (frequency) v
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