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3.5 p3ht/zno interface: low deposition rate 37surface. For the low density case a better matching can beobtained. For this reason, in order to favor the order at theinterface, we generate our atomistic model by using s-foilswith interdigitation distance 15.8 Å.The s-foil is let to relax on the surface under the attractiveinteraction with the ZnO substrate. We find that theinitial interdigitation distance is affected during the formationof the interface. The initial value is preserved only forthe first P3HT layers and the polymer disorder increaseswith the distance from ZnO (see Figure 3.4 and Figure 3.5).Figure 3.5.: Final configuration of the LDR system at low temperature.The above visual analysis is confirmed quantitatively bycalculating the structure factor of the polymer in the threex, y and z direction. In particular the peak in y and x directionare lowered with respect to the ideal s-crystal (compareFigure 3.6 left and middle with Figure 2.10 top andmiddle). The lowering of S z in top-right panel of Figure 3.6and its broadening, indicates an increasing disorder in theπ − π direction.The interface has been also studied at room temperature(annealing at 300 K by Nosé-Hoover thermostat). Itis found that the first polymer layer remains fixed to thesurface because of the strong ZnO-polymer interaction butthe disorder induced by thermal fluctuations affects subsequentlayers (see Figure 3.7). This is indicated by thelowering of S y in the bottom-middle panel of Figure 3.6.Moreover, the S z peak shift to lower q values indicates anincrease of the interplanar distance (from 4 to 4.5 Å) inducedby temperature.