  The surface conductivity is measured by a four-probe technique for pentacene
and rubrene single-crystals laminated on polarized and nearly unpolarized
molecular monolayers with application of perpendicular electric fields. The
polarization of the self-assembled monolayers (SAMs) shifts the threshold gate
voltage, while maintaining a very low subthreshold swing of the single-crystal
devices (0.11 V/decade). The results, excluding influences of parasitic
contacts and grain boundaries, demonstrate SAM-induced nanoscale charge
injection up to ~10^12 cm^-2 at the surface of the organic single crystals.
