ASPECTS OF FORMALDEHYDE SYNTHESIS ON CU(110) AS STUDIED BY STM

The synthesis of formaldehyde from methanol (both CH3OH and CD3OD) on oxygen-predosed Cu(110) surfaces has been studied using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Sequential STM images show the conversion of methanol to methoxy results in the removal of O from the short sides of the (2 X 1) Cu-O islands present when the surface is dosed with oxygen to give 1/4 monolayer coverage. Methoxy forms a (5 X 2) reconstruction which incorporates added Cu atoms. Detailed observations have been made on the formation of this (5 X 2) methoxy reconstruction. (5 X 2) LEED patterns have also been observed and show diffraction spot absences characteristic of p1g1 or p2mg symmetries. Models for the (5 X 2) methoxy-induced structure are proposed that are consistent with both the STM and LEED data. The decomposition of methoxy to formaldehyde occurs with STM images showing as an initial step the diminishing of the (5 X 2) methoxy islands. This occurs from island edges. Upon island-breakup the added Cu atoms incorporated in the (5 X 2) reconstruction are released causing the expansion of nearby step edges.