To what extent two, four or eight Langmuir-Blodgett films of omega-tricosenoic acid (CH 2 (CH 2 ) 2 0 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°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°C to above 400°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.