262
E.F. Sheka
Fig. 15.2 Effectively unpaired electrons of the pentacene molecule. (a) Calculated N DA image,
UBS HF singlet state. (b) AFM imaging of pentacene on Cu(111) using a CO-at-Au tip [49].
(c) Extracted vertical force along the molecule long axis [49]
AFM with unprecedented high resolution [49] (see Fig. 15.2b). The molecule image was obtained by using the short-range chemical forces of noncontact AFM. The
forces profiles are shown in Fig. 15.2c. As seen in the figure, the least forces and,
consequently, the weakest interaction are observed at the molecule ends (the brightest area in Fig. 15.2b) while the strongest interaction (the darkest area in Fig. 15.2b)
is characteristic for the molecule central area. Since the interaction of the CO apex
of the AFM tip is obviously proportional to the electron density on the atoms above
which the tip is located, thus recorded AFM molecule image should be inverted
by color with respect to the N DA image map in Fig. 15.2a. This has actually been
observed exhibiting the first evidence of the distribution of the effectively unpaired
electrons in the sp 2 molecules. The next example concerns a similar imaging of the
olympicene molecule that has been synthesized on the eve of the London Olympic
E.F. Sheka
Fig. 15.2 Effectively unpaired electrons of the pentacene molecule. (a) Calculated N DA image,
UBS HF singlet state. (b) AFM imaging of pentacene on Cu(111) using a CO-at-Au tip [49].
(c) Extracted vertical force along the molecule long axis [49]
AFM with unprecedented high resolution [49] (see Fig. 15.2b). The molecule image was obtained by using the short-range chemical forces of noncontact AFM. The
forces profiles are shown in Fig. 15.2c. As seen in the figure, the least forces and,
consequently, the weakest interaction are observed at the molecule ends (the brightest area in Fig. 15.2b) while the strongest interaction (the darkest area in Fig. 15.2b)
is characteristic for the molecule central area. Since the interaction of the CO apex
of the AFM tip is obviously proportional to the electron density on the atoms above
which the tip is located, thus recorded AFM molecule image should be inverted
by color with respect to the N DA image map in Fig. 15.2a. This has actually been
observed exhibiting the first evidence of the distribution of the effectively unpaired
electrons in the sp 2 molecules. The next example concerns a similar imaging of the
olympicene molecule that has been synthesized on the eve of the London Olympic