Chemistry Reference
In-Depth Information
Fig. 37 Experimental RAS spectra of porphyrin thin films of (a) 0.2 nm, (b) 1 nm, and (c)5nm
thickness, with the corresponding AFM images collected over 3
m
2
-wide regions. The best fit
curve obtained for the RAS spectra are reported as
dashed lines
. The best fit curve of the RAS
spectrum in
panel
b is a linear superposition of two Voigt curves: the one centered at 430 nm
(
continuous line
) as a contribute of the 0.2-nm layer, which shows the RAS spectrum maximum
centered at 430 nm, and the other one (
dotted line
), positioned at 439 nm, as a shifted contribute of
the 5-nm layer, whose RAS spectrum maximum is at 444 nm (From Bussetti et al. [
73
]. Reprinted
with permission. Copyright 2014. American Chemical Society.)
3-
ʼ
profile used in spectroscopy, which convolves a Lorentzian line shape with a
Gaussian broadening) associated to the different phases (2D and 3D) shown by
AFM. Both the 0.2-nm-thick film (which behaves as a slightly modified 2D phase,
with a negligible 3D contribution) and the 5-nm-thick sample (where the 3D phase
is definitely dominant) are fitted just by using a single Voigt curve, while the
1-nm-thick sample (intermediate between the other two cases) has been interpreted
in terms of the contemporary presence of the 2D and the 3D phases, by using two
Voigt curves that are linearly superimposed with different relative weight for
different film thickness. The fits (dashed lines) are compared with the RAS spectra,
validating an excellent agreement with the experimental data.
The demonstrated sensitivity of RAS spectra to the coexistence of the 2D and 3D
phases, and more generally to the presence of an additional layer (or part of it)
grown over the very first, offers the possibility to conclude that the “supposed”
