Phase Control of Fullerene Materials through Chemical Synthesis and Field Effect Doping

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Organic thin film transistors (TFTs) are attracting a great deal of attention due to the relatively high field-effect mobility in several organic materials. In these organic semiconductors, however, researchers have not established a reliable method of doping in a very low density level, although this has been crucial for technology development of inorganic semiconductors. Here we discuss a new technique that enables us to control the charge density at the channel by employing organosilane self-assembled monolayers (SAMs) on SIO_2 gate insulators. SAMs with fluorine and amino groups have been shown to accumulate holes and electrons, respectively, in the transistor channel : These properties are understood in terms of the effects of electric dipoles of the SAMs molecules and weak charge transfer between organic films and SAMs.In-situ high pressure x-ray diffraction experiments and the first-principle local density functional calculations revealed that a transformation from the two-dimensional (2D) tetragonal C60 polymer to a three-dimensional (3D) polymer takes place via. a highly anisotropic compression of C60 molecules along the c-axis, as an irreversible first-order order transformation above 20 GPa. In the 3D polymer phase, the 2+2 bonds remains in the 2D plane, while neighboring layers are connected by the 3+3 bonds. The bulk modulus of the 3D polymer was 407 GPa, being slightly smaller than that of diamond.