The Role of Electrostatic Field in the Appearance of a Narrow and Dense Layer of Metal Nanoparticles near the Surface of a Metal-Containing Dielectric after Electron Irradiation

The work proposes a mechanism for the formation of a layered structure of metal nanoparticles in dielectrics irradiated with fast electrons. On the example of silver-containing glass, a model is discussed in which silver nanoparticles can accumulate under the surface in two layers: wide, at the depth of embedded primary electrons (~3 μm for 30 keV), and extremely narrow ~0.1 µm, closer to the surface (at a depth of ~0.5 μm). Both the first and second layers are due to strong electrostatic fields arising in the regions of embedded electrons (space negative charge) and near-surface positive space charge formed by true secondary electron emission. The process of diffusion of polarized silver atoms in the specified inhomogeneous electric field with a secondary electron emission coefficient greater than unity is considered. In the presented model of the distribution of space charge and electric field in silver-containing glass irradiated with fast electrons, an equilibrium profile of the concentration of silver atoms in the near-surface layer is obtained. It is shown that in the formed electric fields it is possible to form a structure with areas of enrichment and depletion of the specified impurity. The calculated values of the equilibrium concentrations of silver atoms at the surface may exceed the corresponding volume values by several times.