To determine the molecular orientation of rubbed and unrubbed poly[4,4′-oxydiphenylene- pyromellitimide] (PMDA-ODA) films, we have measured the infrared (IR) absorption spectra of PMDA-ODA films on Si substrates as a function of the incident angle. The molecular orientation was determined by fitting the incident angle dependence and the IR dichroic ratio with the theoretical curves. The IR absorption was calculated by a transfer matrix method to take account of the multiple reflection and refraction at the interfaces. The vibrational response of the polyimide film in the IR region was represented by a Lorentz oscillator model. We found that the molecules in a spin-coated polyimide film are oriented parallel to the substrate surface with a standard deviation of 6.5°. For a rubbed film, the polymer chains are oriented along the rubbing direction and are tilted up on average by 8.5° from the surface plane. We observed a blueshift of the C=O asymmetric stretching band at oblique incidence. The blueshift is explained by anomalous dispersion of the dielectric constant of the polyimide film, and is reproduced by our calculation.

Using a modified flow-coating method, bottom-gate/bottom-contact type organic field-effect transistors (OFETs) with a highly oriented active layer of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) were fabricated. The flow-coated TIPS-pentacene films were fairly uniform and consisted of arrays of needle-shaped crystals along the flow-coating direction. The uniformity allowed us to determine the contact resistance by a transfer line method. The usefulness of the modified flow-coating method for fabricating high performance OFETs has been demonstrated, and we found that not only the field-effect mobility but also the contact resistance significantly depends on the channel current direction with respect to the flow-coating direction.

We have measured the light emission spectra of a clean Au(111) surface induced by the scanning tunneling microscope (STM). The STM tip was made of pure Au wire. When the tip apex had a truncated shape (in the scanning electron microscope image), multiple peaks were observed whose energies and number depend on the tip shape. These peaks arise from the resonant modes of the localized surface plasmons whose energies are determined by the apex size.

We have determined the orientations of poly[ 4,4^′-oxydiphenylene-pyromellitimide] (PMDA-ODA) molecules in rubbed and unrubbed polyimide films ( ∼120 Å) on Si substrates by polarized IR absorption spectroscopy. We found that for rubbed films the polymer chains are oriented along the rubbing direction and are tilted up on average by 8.5° from the surface plane. We conclude that the polymer chain inclination induced by rubbing determines the tilt of the director of the bulk liquid crystal.