ИСТИНА

Crystalline organic semiconducting monolayers have high potential for flexible ultrathin electronics. The electrical behavior of devices based on highly crystalline thin films is essentially anisotropic. However, the local monolayer crystalline structure has practically not been studied. To probe the monolayer domain structure Raman microscopy can serve as a useful tool. Due to the Raman anisotropy effect,i one can distinguish differently oriented domains. In this work, we report Raman study of semiconducting Hex-TTPTT-Hex monolayer prepared by solution cast-assembly technique.(Fig 1.a) As the monolayers give a very weak Raman signal, to amplify it, we apply surface-enhanced Raman spectroscopy (SERS). For this, we prepared a Si-substrate covered with thin gold film using thermal evaporation. Then a monolayer film was deposited. We succeeded in obtaining Raman map for Hex-TTPTT-Hex. (Fig 1.b) Analyzing this map in accordance with polarized optical(C-DIC) and atomic force microscopies, we found that Hex-TTPTT-Hex film has a domain structure. Furthermore, Raman mapping allowed us to detect the presence of the monolayer molecules between the domains. The spectrum of molecules between the domains differs from the crystalline one, indicating great difference in orientation of molecules in these areas. We suppose that the substance between the domains is amorphous. Using theoretical quantum chemistry modelling in GAMESSii allowed us to calculate dependence of Raman spectrum on the orientation of the Hex-TTPTT-Hex molecule. With these data, we developed a model relating the experimental spectra and orientation of molecules in different crystalline domains. These results enable us to control 2-D orientation of the crystals and thus electrical conductivity charge transport of the device. iSushchinskii M.M. Raman spectra of molecules and crystals (1969). iiM.W.Schmidt, K.K.Baldridge, et al. J. Comput. Chem., 14, 1347-1363(1993).