IMPROVEMENT OF THE DETECTION EFFICIENCY OF CHANNEL PLATE ELECTRON MULTIPLIER FOR ATOM-PROBE APPLICATION

Improvement of the detection efficiency of microchannel plates (MCPs) is of great importance, especially when it is applied to quantitative measurements. The efficiency is limited by the open area ratio of MCP to a value close to 60%. By applying a small electric field between th e input face of the channel plate and a grid above the face, electrons emitted by ions striking the interchannel web are returned to channel s and then detected. A few attempts have been made in order to quantif y the resulting increase of the detection efficiency. However,the stat istical nature of the field evaporation process in the atom probe make s this quantification rather difficult. We have designed a new detecto r making it possible to quantify easily this improvement. Our results show that the increase in the detection efficiency depends on the elec tric field strength above the front face of the MCP. With a 95% transm ission grid, the maximum detection efficiency obtained with an uncoate d MCP is 85%.