Ion Irradiation of Solid Carbons - Polyynes: Synthesis, Properties, and Applications - page 267

FIGURE 13.2 Raman spectra of a cluster assembled carbon thin film obtained in situ
(i.e. with the sample obtained still within the vacuum chamber) at 77K and at room
temperature, and that taken after exposure to air (about 15min). Spectra have been
vertically shifted for clarity.
1000-2000 cm 1 region of the Raman spectrum of a carbon system is dra-
matically dependent on the exciting wavelength. This has ruled out all the
speculations on the possibility of obtaining information on the sp 2 /sp 3
bonding ratio from a single spectrum obtained with a single excitation
wavelength. Indeed, a visible excitation wavelength definitely gives signals
prevalently due to the graphitic component of the investigated system. The
situation changes if ultraviolet excitation is employed, because cross section
considerations give the possibility to observe a typical sp 3 signal (T line)
located at around 1050-1100 cm 1 , although a resonance study is desirable
even in these cases.
Signals considered to be representative of linear carbons (sp hybridiza-
tion) are located at about 2000-2100 cm 1 . In this case the broad band
found in our samples can be composed by a convolution of cumulene and
polyyne-like structures [14].