PREPARATION AND CHARACTERIZATION OF ORGANIC SUPERLATTICE THIN-FILMS GROWN ON HYDROGENATED SILICON SINGLE-CRYSTAL SUBSTRATES

We have succeeded in preparing very thin (nanometre order) alternating layers that can be called 'organic superlattices' by using a special combination of materials, substrates and deposition conditions with go od verification by various characterization techniques. Specially surf ace-treated single-crystal silicon substrates with hydrogen-terminated dangling bonds on the surface were used to induce van der Waals heter oepitaxial growth. Choice of materials with the appropriate molecular shapes and aggregation force is also important for preparing flat mole cular films. Tetraphenylporphyrins (H2TPP and ZnTPP) and phthalocyanin es were used for this purpose. A molecular beam epitaxy chamber with s pecially designed cells was used with the cooled substrates. Direct pr oof of the alternating composition was given by transmission electron microscopy observation, avoiding decomposition by the electron beam, a nd also by SIMS depth profiling under special conditions to ensure goo d depth resolution. X-ray diffraction in the small-angle region gives the periodicity of the alternating layers, as well as their crystal qu ality. Atomic force microscopy confirms the atomic flatness and also g ives the molecular orientation in the films. Fourier transform infrare d spectroscopy examines the chemical stability of the compounds during deposition and also gives the axial orientation of the molecules in t he films.