Higher Transitions - Extended States

In the case of 6T little efforts have been done towards a band like description of the excitonic or the charge carriers, because in most cases disorder dominated the experimental data [30] (see below) and hence a band like description did not seem applicable. However, Siegrist et al. [103] applied an extended Hilckel theory to 

In summary the experimental observations do not allow up to now to draw a clear picture about the conduction band levels for ohgothiophenes. The various experimental investigations on organic moleciflar crystals [109], and the recent experiments on ultrapure FETs of 6T [11,126,127] showed that it seems necessary to improve the sample quality in terms of order and cleanliness to study the influence of the inter-molecular coupling on the motion of charges and hence on the conduction levels. 

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Assuming that Hi = p, 021 = tt32 = 043 = 054 = R, thus, a 2 = 023 = CC34 = 045 = 1 + R where the rest values of a are zero. Considering the above, yields the following transition probability matrix which can be easily extended to a higher number of states ... 

The transition into the oriented state is accompanied by the formation of a neck , a sharp and abrupt local constriction of the sample, in which the extent of orientation and the degree of extension are mudh higher than in the rest of the polymer. After the neck has been formed, further orientation of the sample occurs by spreading of the neck to the entire length of the polymer. When the sample is extended after passing into the oriented state, it undergoes further deformation and at some critical extension it breaks. 

First of all the term stress-induced crystallization includes crystallization occuring at any extensions or deformations both large and small (in the latter case, ECC are not formed and an ordinary oriented sample is obtained). In contrast, orientational crystallization is a crystallization that occurs at melt extensions corresponding to fi > when chains are considerably extended prior to crystallization and the formation of an intermediate oriented phase is followed by crystallization from the preoriented state. Hence, orientational crystallization proceeds in two steps the first step is the transition of the isotropic melt into the nematic phase (first-order transition of the order-disorder type) and the second involves crystallization with the formation of ECC from the nematic phase (second- or higher-order transition not related to the change in the symmetry elements of the system). 

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