Infrared spectroscopy of the organic monolayer sandwiched between a Hg electrode and a Si substrate.
We have successfully observed the vibrational spectra of organic monolayers sandwiched between a liquid Hg electrode and a Si substrate by means of a newly developed reflection absorption (RA) device. The vibrational spectra of organic monolayers between two electrodes can be observed under a certain bias voltage. The monolayers were fabricated by the reaction of hydrogen-terminated Si(111) with 1-octadecene. A metal/insulator/semiconductor structure was prepared using liquid Hg as a metal electrode and the organic monolayer as an insulator. Infrared (IR) light entered from the Si substrate side with an incident angle of 75 degrees. The reflected IR light from the metallic Hg was detected by a mercury-cadmium-telluride detector. We obtained RA spectra using a bare H-Si(111) substrate as a reference. The absorbance of the RA spectrum was comparable with that of the transmission spectrum for the octadecyl-terminated Si(111) without Hg. The C-H stretching modes in the CH(2) group show blueshifts, and the C-H antisymmetric stretching modes in the CH(3) are broadened in comparison with the transmission spectrum. Under a certain bias voltage, we observed changes in band shape. We concluded that the variation was due to the temperature increase by resistive heating of the substrate.
Furuhashi
Masayuki
M
The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan.
Yoshinobu
Jun
J