| Popis: |
Electronic transport of photoinjected holes in high molecular weight linear polymers with silicon and germanium backbone displays a familiar pattern of electric field and temperature dependence similar to behavior already reported in a very diverse collection of glassy molecular solids. At fixed electric fields, during both rate and step heating, the mobility activation energy e in all these polymers changes abruptly and reversibly at a temperature Tc, which is specific for each polymer, without concurrent abrupt changes in mobilities. These temperatures coincide with the respective glass transition temperatures Tg. In all cases, the below-Tg activation is higher than above Tg. In polymers with aliphatic side groups, e(t > t g) is extremely low, practically approaching zero. The change of activation near Tg is similar to that observed in amorphous charge-transporting polymers and other glasses including selenium and its alloys. Polymers such as poly(di-n-hexylsilylene) (PDHS) which undergo conformational transitions at temperatures TTr due to side chain crystallization and melting, also experience a change in mobility and its activation energy at TTr. The change in the transport behavior and the association with the bathochromic shift in the uv spectra is demonstrated. |
