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 the input face of the channel plate and a grid above the face, electrons emitted by ions striking the interchannel web are returned to channels and then detected. A few attempts have been made in order to quantify the resulting increase of the detection efficiency. However, the statistical nature of the field evaporation process in the atom probe makes this quantification rather difficult. We have designed a new detector making it possible to quantify easily this improvement. Our results show that the increase in the detection efficiency depends on the electric field strength above the front face of the MCP. With a 95% transmission grid, the maximum detection efficiency obtained with an uncoated MCP is 85%.