Langmuir-Blodgett films in metal-silicon contacts

To what extent two, four or eight Langmuir-Blodgett films of omega-tricosenoic acid (CH2(CH2)(20)COOH) deposited on a silicon wafer will retard the thermally induced reaction of a superimposed nickel film with the silicon substrate is investigated using MeV He backscattering spectrometry as an analytical tool to detect the presence or absence of a reaction in the range of 200-400 degrees C annealing for 30 min in argon at atmospheric pressure. A few pairs of Langmuir-Blodgett films can raise the onset of a reaction from 200 degrees C to above 400 degrees C. A single pair can do likewise when it is polymerized by a 2 keV electron beam. The hypothesis that the films break down chemically - in the limit to a bare carbon layer - upon thermal annealing or electron-beam irradiation qualitatively explains the observations.