Piezomodulation study of Langmuir–Blodgett films of copper phthalocyanine derivatives

Abstract

A method for quantitative analysis of piezomodulation spectra of a thin film on a substrate, including the internal reflection in the system, is presented. This method is applied to Langmuir–Blodgett (LB) films of copper phthalocyanine (CuPc) derivatives on glass substrates. A uniaxial stress was applied along the symmetry axis of the film. The spectra were measured in the region from 1.5 to 2.4 eV in three configurations; transmission, reflection from the film side, and reflection from the substrate side. The optimum Lorentzian parameters and their changes due to the stress are determined by the least-mean-square fit. The microstructures and electronic states of the LB film are discussed from the stress effects. The very small feature, which is hardly identified in the absorption spectra because of the large Frenkel exciton band, is attributed to a charge transfer (CT) excitation.

Radio Frequency Effect on the Ion Saturation Current

“…A similar red-shift in the peak wavelength was also reported in the piezomodulation study using copper phthalocyanine derivatives. 13) The second idea is based on the point-dipole point-dipole approximation. In a dimer system, it is known that the absorption spectrum shifts from that of the monomer system due to the dipoledipole interactions between molecules.…”

Uniaxial Stress Effect on the Charge Transfer in Highly Oriented Films of Iodinated Palladium Phthalocyanine

“…The PdPc absorption band is an allowed transition and its absorption coefficient is as high as lo6 cm-', so that the change of the reflectivities at the interfaces (such as the interface between nitrogen gas and the film or the interface between the film and the substrate) is of the same order as the change of the transmittance. Specifically, in the case of the absorption band in which several bands overlap, the reflection at the interface plays a crucial role in PA spectroscopy, and should be explicitly taken into account for a quantitative discussion [9]. However, in the case of isolated absorption bands like those of PdPcI,, the following approximation is sufficient for a qualitative discussion: Here, a and d are absorption coefficient of the film and its thickness, respectively.…”

“…It is a quite unusual phenomenon that the intensity of the PdPc absorption band decreases in the lightly doped film and increases in the heavily doped film under a uniaxial stress. The intensity of the PdPc absorption band can decrease under a compression by the enhanced mixing between the Frenkel exciton of PdPc molecules and the charge transfer exciton [9]. However, the intensity never decreases under tensile stress.…”