15:45 〜 16:00
▲ [11p-M112-9] Raman spectroscopic investigation of Dinaphthothienothiophene in a transistor device
キーワード：DNTT, Raman spectroscopy
Dinaphthothienothiophene (DNTT, C22H12S2) is a promising organic semiconductor material for organic field-effect transistors (OFETs) due to its high charge-carrier mobility and thermal stability. The charge-carrier mobility depends upon their structural properties, such as the molecular density distribution and molecular orientations of DNTT molecules in OFET devices. Therefore, investigating these properties would be important for further improvement in the device performance. Raman spectroscopy, a powerful and simple technique, can be utilized to investigate these structural properties with a high spatial resolution of a few hundreds of nanometers.
In this study, we report Raman spectroscopic investigations of DNTT molecule on an actual transistor device. We measured the Raman spectrum of DNTT molecules that shows multiple vibrational modes as shown in Fig. 1(a). The Raman image, constructed from the intensity of the vibrational mode at peak 1, shows the density distribution of DNTT molecules in the device as shown in Fig. 1(b). Further, the observed vibrational modes were identified by the density functional theory calculation. The calculation result indicated that the vibrational mode marked as peak 2 was dominated by the atomic displacements along the perpendicular direction of the long molecular axis of DNTT molecule. Since, DNTT molecules stand vertically on the substrate in the active layer of the device, the polarization dependence of this mode can be used to identify the twist of DNTT molecule along its molecular axis. A Raman image constructed by the intensity ratio of peak 2 obtained by two mutually-perpendicular polarizations of incident light reveals the molecular twist of DNTT molecules as shown in Fig. 1 (c). Hence, our study shows that the orientations of DNTT molecules were not uniform and this information would be important for optimizing fabrication process of the device for better performance.
In this study, we report Raman spectroscopic investigations of DNTT molecule on an actual transistor device. We measured the Raman spectrum of DNTT molecules that shows multiple vibrational modes as shown in Fig. 1(a). The Raman image, constructed from the intensity of the vibrational mode at peak 1, shows the density distribution of DNTT molecules in the device as shown in Fig. 1(b). Further, the observed vibrational modes were identified by the density functional theory calculation. The calculation result indicated that the vibrational mode marked as peak 2 was dominated by the atomic displacements along the perpendicular direction of the long molecular axis of DNTT molecule. Since, DNTT molecules stand vertically on the substrate in the active layer of the device, the polarization dependence of this mode can be used to identify the twist of DNTT molecule along its molecular axis. A Raman image constructed by the intensity ratio of peak 2 obtained by two mutually-perpendicular polarizations of incident light reveals the molecular twist of DNTT molecules as shown in Fig. 1 (c). Hence, our study shows that the orientations of DNTT molecules were not uniform and this information would be important for optimizing fabrication process of the device for better performance.