Figure 1
(a) The schematic representation of the array with the gradually changing lattice constant. (b) Electron density along the x-direction line passing through the focal spot in three cases. Electron density distribution for the array without the lattice gradient (c) and with the gradient increment g = 0.3 (d). The energy of the incident electron is E = 0.5 and the incident electron beam has unit electron density at the beam center. The obvious focusing effect can be observed in Fig. 1(d) when the array has the lattice gradient.
