STRUCTURE CHARACTERIZATION OF THE 2 KINDS OF NANOMETER SIZE ALPHA-FE2O3-STEARATE ALTERNATING LANGMUIR-BLODGETT-FILMS BY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

Structure, infrared optical properties, and molecular orientation of 7 0- and 20-angstrom nanoparticulate alpha-Fe2O3-stearate alternating La ngmuir-Blodgett films were studied by using FTIR absorption spectra an d Kramers-Kronig (KK) analysis. The KK analysis results show that the average refractive indexes of the films are 1.83 (70 angstrom) and 1.6 2 (20 angstrom), respectively. According to the refractive index, exti nction spectra, and the linear infrared dichroic spectra of the films, the molecular orientation was calculated. The orientation angles are 5-degrees and 38-degrees for fatty chains, 80-degrees and 65-degrees f or COO- asymmetric mode, and 55-degrees and 39-degrees for COO- symmet ric mode of stearate ions in 20- and 70-angstrom alpha-Fe2O3-St LB fil ms, respectively. From these results, the carboxylate groups were cons idered to be a relatively spherical symmetric distribution, and on the contrary, the hydrocarbon chains were found almost perpendicular to t he substrate. The band progressions of Fe2O3-St LB films in the range of 1360-1320 cm-1 can be detected, especially in the case of 20-angstr om Fe2O3-St LB films. These indicated that the films possess a high-or der alternating structure. The hexagonal-like close packing (hcp) form of the nanoparticles was considered as a possible structure between t wo stearate ion layers. The obvious hypsochrome shift was observed in the UV-visible spectra of the 20- and 70-angstrom Fe2O3-St films, indi cating the influence of quantum size effect.