Insulating Films Formed Under Electron and Ion Bombardment

In an evacuated tube in which the slightest traces of organic vapors may occur, even with liquid air cooling, insulating layers are formed on surfaces subject to electron or canal-ray bombardment. These layers may be attributed to carbon compounds, and their formation is related to the polymerization of organic vapors by electrical discharges, $\alpha$-particles, and ultraviolet light. The simple ion-deposition theory is inadequate as the layers are formed only at the point of impact of the rays on the surface. Electrical resistances and break-down potentials were observed for several films. The importance of these deposits in general experimental practice, such as the photometry of mass-spectra, is pointed out, and, amongst others, cases are cited of their influence producing contact potentials, pseudo high vacua, erroneous photographic recording and differential condensation of vapors upon previously bombarded surfaces.