Polish on Metals

Abstract

MR. R. C. FRENCH has reported on electron diffraction experiments on polished metal surfaces (copper, silver).1 The fact that the diffraction rings become more and more diffuse if the surface is carefully polished is, he concludes, an experimental confirmation of Sir George Beilby's theory, which supposes that by careful polishing a metal surface is covered with a thin amorphous layer of the metal as a supercooled liquid. Mr. H. Raether, who is working in this laboratory with a diffraction apparatus,2 has got similar results with polished metals. I do not, however, believe that for the explanation of these results it is necessary to suppose that the size of the crystals which constitute the surface is really altered so very much by the process of polishing. I should like to suggest a simpler explanation. A polycrystalline metal surface which is bombarded with electrons at a grazing angle gives sharp diffraction rings if the surface consists of small lumps which are thin enough to allow the electrons to pass through ; this was first shown by Prof. G. P. Thomson.3 The lumps play the role of the grating, and if by polishing the metal they are levelled, the resolving power of the gratings is gradually diminished (corresponding to the diminished breadth of the gratings).