Whilst the atomic-level perfection is governed by the wafer's chemical treatment, the macroscopic shape is dependant upon the way in which the crystal is bent into shape. The completed helium atom mirror and exploded schematic. Application of a potential difference between electrodes and crystal cause the crystal to deflect into the lower alumina aperture. Careful control over the boundary conditions set by the aperture and electrode size and dimensions afford control over the macroscopic mirror shape. Control over the silicon chemical preparation allows for atomic-scale perfection.
Geometric optics define the ideal shape of a mirror surface.
In the laboratory, we can approximate this shape by sucking a thin crystal through a carefully defined aperture. The current mirror is shown in figure 2. Meanwhile, we have also researched the ultra-smooth crystal surfaces required for microscopic control. The surfaces are prepared in the cleanrooms of the Semiconductor Physics Group at the Cavendish. Significant research into improved preparation and storage of clean silicon mirrors has been completed.