Effect of Cooperative Behavior on Molecular Vibrational IETS Peak Intensities
Contrary to previous theories of the intensity of molecular vibrational energy loss peaks in IETS, we have shown that the second derivative of the tunneling current varies as n4/3 rather than linearly in n, where n is the concentration of molecules adsorbed on the insulator surface during the junction fabrication. This is a result of considering the proper form for the potential in the junction region from a layer of vibrating dipoles with all of its images. Even though obtained with a simple model for the junction, this dependence agrees with the experimental results of LANGAN and HANSMA.
Recently, LANGAN and HANSMA  adsorbed tritiated benzoic acid (C6H5COOH) of concentration c in aqueous solution on an aluminum oxide surface. Using a scintillation counter, they determined that the surface concentration n varied an c1.2. Separately, upon fabricating an Al-Al2O3Pb tunnel junction with benzoic acid adsorbed on the oxide surface at the Al2O3-Pb interface, they found that the intensity of an Inelastic Electron Tunneling (IET) feature at 686 cm-1 varied as c1.6 . Consequently, the IET intensity varies with surface concentration as n1.3±0.1 .
KeywordsBrillouin Zone Adsorbate Layer Tunnel Junction Cooperative Behavior Aluminum Oxide Surface
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