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In this letter, we report the successful growth of an ultrathin organic film on Si(100)-2×1 by reactive coupling of polyimide precursors. Using the molecular layer deposition technique, 1,4-phenylene diamine and pyromellitic dianhydride were sequentially dosed on clean Si(100)-2×1 under ultrahigh vacuum conditions. The interfacial imidization was initiated by thermal curing at 200 °C. High resolution electron energy loss spectroscopy was employed to identify surface species. The spectra show clearly, that an oligimide chain has been formed which stands upright on the substrate. The chain bonds to the silicon substrate via a Si–(NH)–C linkage.

The chemisorption of maleic anhydride on Si(100)-2×1 at room temperature has been studied with scanning tunneling microscopy (STM). We observe that, at low coverages below 0.12 monolayer, the unsaturated organic compound adsorbs almost exclusively on inter-dimer sites and not through a direct [2+2] cycloaddition. The STM images provide evidence that the adsorption of a second maleic anhydride molecule on an adjacent inter-dimer site results in the cleavage of the silicon dimer bond located between the two molecules. The chemisorption of the organic molecules induces a local rearrangement of unsaturated silicon dimers.

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