Doping induced absorption

Figure 7-25. Doping induced absorption of u-6T at low (solid line) and high (dolled line) doping concentrations.

Figure 8-5. Transmission difference spectra of m-LPPP films at 7=77 K excited at 3.2 eV for various pump-probe delays. The inset zooms out the low energy region for 0 ps (solid line) and 400 ps (dashed line) delay. Doping induced absorption (D1A) data are also shown for comparison (from Ref. (251 with permission).

Fig. 1.17. Comparison of doping-induced absorption for P30T over an extended energy range. Doping was achieved (i) chemically via exposure to iodine vapour for three different exposure times, (ii) by (pump-probe) photoexcitation, (iii) electro-chemically for two current exposure times...

The doping-induced absorption (DIA) spectrum of -6T doped by FeCh in CH2CI2 solution is shown at light and heavy dopant concentrations in Figure... 

Fig.5. Chlorine-doping-induced absorption spectra of [Pt(en)2][Pt(en)2Cl2] (0104)4 for the polarization parallel to the chain axis at room temperature. The numbers are the reaction time in hours with the chlorine gas of 1 atom. 

Nevertheless, even for polyacetylene, the electronic structure is not that of a simple metal in which the bond-alternation and the tc-tc gap have gone to zero there are infrared active vibrational modes (IRAV) and a pseudo-gap. This is indicated by the spectra in Figure 2 which demonstrate the remarkable similarity between the doping-induced absorption found with heavily doped trans-(CH)x, and the photoinduced absorption spectrum observed in the pristine semiconductor containing a very few photoexcitations. Not only are the same IRAV mode spectral features observed, they have almost identical frequencies. 

In Fig. 22.10a we show the PM spectrum of a-6T in the energy range of 0.7-2.1 eV at 10 K and pump modulation frequency of =200 Hz [75]. The spectrum exhibits three main features the two bands marked P and Pz at 0.80 and 1.54 eV, respectively, and the band BPi at 1.1 eV. As can be seen in Fig. 22.10b, the BP band almost completely disappears in the out-of-phase spectrum, proving that the photoexcitations responsible for it have much shorter lifetimes than those responsible for Pi and Pz-Furthermore, P and Pz have a different temperature dependence than BP. Each of these three peaks is accompanied by a phonon replica at 0.97, 1.27, and 1.63 eV, respectively. We note that each of the main PA peaks in the PM spectrum, namely P, Pz, and BPi, corresponds to the respective band in the doping-induced absorption mentioned above [30,75]. We therefore tentatively identify Pi and Pz at 0.8 and 1.54 eV,... 

There is another spectral feature in the spin 1/2 A-ADMR spectrum, however, that is absent in doping-induced absorption. This is the 5A/ < 0 band peaking at... 

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