Organic superlattice film by alternate deposition of single molecular layers

Abstract A 5,10,15,20-tetraphenylporphyrin (H 2 TPP; C 44 H 30 N 4 ) 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 H 2 TPP/ZnTPP (5,10,15,20-tetraphenylporphyrinato zinc; C 44 H 28 N 4 Zn) 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 H 2 TPP 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.