Characterization of Efficiency Enhancement in Microchannel Plate Detectors

Abstract

Abstract. The detection efficiency of a channel-plate detector is mainly determined by the open area ratio of its input face. which is typically 60%-70%. It is known that the efficiency can be enhanced by applying an electric field normal to the channel-plate surface, such that secondary electrons generated when ions strike the channel-plate surface are returned to the detector. This paper characterises the enhancement observed in channel-plate detectors for atom probe and 3-dimensional atom probe applications. In a double channel-plate detector, it was found that improvement in efficiency was approximately 30% as compared to the situation where all secondary events are lost. The secondary electron events are found to have a broader pulse height distribution, with a mean which is a factor of three lower than that of the primary ion events. Using the variation of efficiency with grid voltage, the maximum secondary electron energy was estimated to be IOeV. This value was used to calculate the loss in time and spatial resolution which would result from the detection of secondary electrons. These effects are shown to be acceptably small within a 3-dimensional atom probe detector design, for a wide range of bias voltages. Previous work has suggested that the efficiency gain from a biassed grid drops off at grid fields in the range 25-100V/mm. This effect is shown to have been generated by field fringing effects.

Tomographic Atom Probe: New Dimension in Materials Analysis

“…Studies of precipitation phenomena, grain boundary segregation, and long-range ordering in materials have shown the ability of this instrument to give quantitative materials chemistry results on the nanometer scale. Some recent work has shown that it is possible to increase detection efficiency up to 86% (Deconihout et al, 1995b;Sijbrandij et al, 1996a). The main issue concerns the mass resolution of the instrument.…”

“…Thus it appears that the low detection efficiency makes impossible the study of the earliest stages of ordering phenomena. Some recent work has shown that it is possible to increase detection efficiency up to 86% (Deconihout et al, 1995b;Sijbrandij et al, 1996a). As a result, the number of positioned atoms in 3-D images can be increased by approximately 50%.…”

Absolute Detection Efficiency of a High-Sensitivity Microchannel Plate with Tapered Pores

“…Several attempts to exceed the OAR limit have been made by applying a repelling electric field to reflect secondary electrons back to the MCP surface. 3,17,[19][20][21][22] An essential solution would be to widen the open area. An efficient way to accomplish this goal is to narrow the walls of the pores.…”

Materials Applications of an Advanced 3-Dimensional Atom Probe

“…This causes secondary electrons generated when ions strike the area between the channels to be returned towards the detector. Detection of these electrons increases the efficiency of the detector above the open area ratio of the channel plate (65%) to approximately 80% [6]. Previously, 3DAP instruments have been based around a straight flight path configuration, such that their mass resolution has been limited by ion energy variations to n~/Am=100-200 full width at half maximum (FWHM).…”