Optical Anisotropy of Thin and Ultrathin Porphyrin Layers - Applications of Porphyrinoids - page 92

Fig. 30 RAS spectra as a function of the amount of deposited H 2 TPP ( panel a) and STM images
( panels b-e) recorded at the corresponding values of the coverage. The inset in panel a reports the
molecular structure (From Scarselli et al. [ 69 ])
indication of a change in the porphyrin alignment during the formation of additional
top layers: in particular, the tilt angle modifies, as a consequence of the interaction
of the molecules with the substrate, progressively screened by the underlying
layers [ 59 , 67 ].
STM images recorded at this coverage on different sample areas show that
extended regions of the graphite substrate are covered by an ordered molecular
adlayer, extending over hundreds of square nanometers. In panel b of Fig. 30 ,a
detail of the ordered layer is highlighted, where bright structures, mostly circular in
shape, are arranged in a quasi-hexagonal packing. Although it is reminiscent of the