Organic superlattice film by alternate deposition of single molecular layers

Abstract

Abstract A 5,10,15,20-tetraphenylporphyrin (H2TPP; C44H30N4) film with an extra-flat surface was prepared on a Si(100) wafer substrate cooled down below 233 K. The organic molecular-beam deposition technique was used for fabrication of the film under ultra-high vacuum between 4 × 10−7 and 4 × 10−8 Pa. The r.m.s roughness determined by atomic-force microscope measurement was 0.22 nm, which is comparable to that of the Si substrate surface. Superlattice films of H2TPP/ZnTPP (5,10,15,20-tetraphenylporphyrinato zinc; C44H28N4Zn) were grown on Si and glass substrates in the same manner. Their periods between 12.1 and 2.37 nm were measured by small-angle X-ray scattering and confirmed by secondary-ion mass spectrometry depth profiling. The Fourier transform infrared spectroscopy measurement of the superlattice film with the minimum period of 2.37 nm indicated that the quasi-planar molecules of H2TPP and ZnTPP inclined at an angle of 75° with respect to the substrate surface. This suggests that an alternating molecular layer deposition of a single molecular layer was attained in the organic film for the first time.