COPPER PHTHALOCYANINE ON SI(111)-7X7 AND SI(001)-2X1 - AN XPS AES ANDSTM STUDY/

Silicon surfaces with different reconstruction, Si(111)-7X7 and Si(001 )-2X1, are exposed to a molecular beam of copper phthalocyanine. On Si (111) the adsorbate-substrate interaction is strong, as suggested by a partial reduction of copper shown in the XPS spectra and by the evide nce provided by STM of a chemical reaction involving some of the Si ad atoms. As a consequence, the molecules are not imaged at atomic scale by STM. At variance with this behaviour, on the single-domain Si(001)- 2X1 face, the adsorbed molecules are clearly imaged by STM, suggesting an adsorption state more weakly bonded. This is the first observation of Cu phthalocyanine molecules imaged on a silicon surface, and it fu rther illustrates the potential of STM for surface chemistry.