Surfaces are selected regarding several key properties depending on the application:
- Secondary electron yield:
The number of emitted electrons per incident particle.
- Ionization efficiency:
The fraction of particles that get negatively ionized upon reflection of the surface
- Reflection efficiency:
A measure of the scattering properties of the surface. It indicates the percentage of particles that get reflected into the standardized field of view of the MCP.
- Angular scattering:
Angular resolved charge state dependent scattering properties of the surface.
These properties are measured dependent of primary particle type and energy, and of the angle of incidence of the primary beam upon the surface under test. Some properties are also time dependent and others change when the surface is exposed to UV radiation.
Roughly the investigated surfaces fall into three different groups:
- Metallic surfaces:
These include mono and poly crystalline tunsten and tantalum surfaces. Tungsten surfaces were used in the LENA instrument on IMAGE.
- Insulating surfaces:
Oxydic single crystals like MgO and SrTiO3 fall into this group.
- Multi layer surfaces:
Most of the surfaces fall into this group. The idea is to combine some optimized top layer with an easy to handle substrate with a high flatness. Typical examples are CVD diamond or samples with dielectric layers to absorb UV more efficiently combined with a suitable top layer, i.e. tungsten or MgO.