Charge transfer of methylene blue molecules on covered Au(111) surffaces

C. VERICAT; F. REMES LENICOV; S. TANCO; G. ANDREASEN; M. E. VELA; R. C. SALVAREZZA

Tucumán

Workshop; National Science Foundation – CONICET Quilmes Nanoscience Workshop: Electronics with Molecules and Quantum Dots; 2003

CONICET

The charge transfer of methylene blue molecules immobilized on different monolayer covered-Au(111) surfaces has been studied by electrochemical techniques complemented by scanning tunneling microscopy. The positively charged methylene blue ions (MB+) are effectively immobilized on negatively charged S and I adlayers. When methylene blue immobilization is made on COO--terminated thiols (mercaptopropionic acid, MPA, and mercaptoundecanoic acid, MUA), the value of Qsurf is markedly reduced, indicating that the electron transfer through hydrocarbon chains is very difficult, although the MB+ is effectively immobilized. electrochemical runs made with methylene blue in solution demonstrate that defects are the main path for electron transfer trough COO--terminated thiol covered Au(111) surfaces. For low-defect COO--terminated thiol adlayers a diode-like effect related to the blocking of the anion-transport through small pores with negatively charged gates is observed.