Polarized Infrared Studies on Charge Transport in 4-Hydroxycyanobenzene Single Crystals

4-Hydroxycyanobenzene (4HCB) semiconducting single crystals have been probed by polarized IR radiation under various conditions. Linearly polarized IR spectroscopy was found to be sufficient to identify the main crystal axes, provided that crystallographic and electrical analyses have been carried out at least once on the crystal. Moreover, a 2D anisotropic hydrogen bonding degree, which results to be higher along the axis a (one of the two planar axes), has been found. Static electrical polarization induces a rather large and anisotropic rotation of the 3D electric dipole vector of the crystal (p), which increases its component along the axis a and decreases the one along b (the other planar axis). When the crystal is probed under actual charge transport conditions in a field effect transistor (FET) structure, the IR radiation is more effectively screened along axis a (which presents the highest carrier mobility) than along axis b.