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

有机薄膜晶体管由于在多种有机材料中具有较高的场效应迁移率而备受关注。然而，在这些有机半导体中，研究人员还没有建立一种可靠的方法来在非常低的密度水平上掺杂，尽管这对无机半导体的技术发展至关重要。本文讨论了在SIO_2栅极绝缘子上采用有机硅烷自组装单层（sam）来控制通道电荷密度的新技术。具有氟和氨基的SAMs已被证明分别在晶体管通道中积累空穴和电子：这些特性是根据SAMs分子的电偶极子效应和有机薄膜与SAMs之间的弱电荷转移来理解的。现场高压x射线衍射实验和第一性原理局域密度泛函计算表明，二维（2D）四边形C60聚合物通过通道向三维（3D）聚合物转变。C60分子沿c轴高度各向异性压缩，在20gpa以上发生不可逆的一阶阶变换。在三维聚合物相中，2+2键保留在二维平面上，而相邻层之间则由3+3键连接。聚合物的体积模量为407 GPa，略小于金刚石的体积模量。

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.