MCP:End Spoiling
End spoiling in MCPs refers to the deposition of electrode material into the pore by up to several pore diameters at the output surface of the MCP. This technique helps focus the electrons exiting the MCP, reducing their transverse velocity. End spoiling on the output side increases spatial resolution but decreases gain. There is a trade-off between spatial resolution and gain, with a recommended end-spoiling value (h) of approximately 1-2. The value of h represents the ratio of the electrode length (b) to the pore diameter (d).
On the input side of the MCP, end spoiling is also employed with a typical h value between 0.5 and 0.8.
Effects of end spoiling:
- Narrows the electron energy distribution (N(E)), as demonstrated in simulations with varying h values (0, 0.5, 1, and 3).
- Results in a small increase in spatial resolution (around 10%) with an end-spoiling value of 1.5. However, simulations show no systematic change in angle distribution with end spoiling.
- Decreases MCP gain, as the electric field gradient is zero within the electrode length (h), resulting in no gain within that region. This effect has been observed in experiments where gain decreases with increasing end-spoiling values (h = 1.2, 2.2, 3, and 4).
Controlling End Spoiling:
Controlling end spoiling during MCP fabrication is crucial. While RF-magnetron sputtering is a common technique for depositing materials like Ti and Cu, it is not suitable for controlling end spoiling due to its non-line-of-sight deposition nature. Evaporation techniques are necessary to achieve precise control over end spoiling.