Long range order in Si(100) surfaces engineered with porphyrin nanostructures

Abstract

Engineering of Si(100) with ordered organic nanostructures represents an advanced method to manufacture hybrid organic/inorganic systems useful for different applications. Well-ordered and densely packed molecules can be obtained by a self-assembly process that depends on directional inter-molecular interactions such as π–π stacking, electrostatic, dipole–dipole or van der Waals interactions, and other more complex forces. Macrocycles are well known to aggregate both in solution and in thin films as a result of some of the above-mentioned interactions. In our study, Si(100) substrates were functionalized with a covalent 4-ClCH₂C₆H₄SiCl₃ monolayer that binds to the surface using the –SiCl₃ group and leaves a –CH₂Cl group unreacted. The remaining alkyl chloride functionality at the top of the Si(100) substrate allowed additional covalent functionalization with a porphyrin monolayer that resulted in ordered, surface-confined porphyrin assemblies. X-ray photoelectron spectroscopy gave indication of the porphyrin grafting mode. Atomic force microscopy showed a long range order of these nanostructures. Emission measurements confirmed the porphyrin luminescence.