Development of an improved field ionization detector incorporating a secondary electron stage

Abstract

Field ionization from sharp tips is attracting increased attention for use in detectors for neutral atomic/molecular species. However, the direct detection of the ionized species typically results in low sensitivities due to the small acceptance angle of the receiving ion-sensitive measurement device (usually a channel electron multiplier) and can result in sputtering damage due to the relatively high mass and energy of the incident ion species. Here we present a design for a field-ionization-based neutral atom detector incorporating a simple secondary electron generating stage. The use of such a stage decouples the field-ionized species from the detected electron signal, thus eliminating any sputtering damage to the channel electron multiplier. The detector armature discussed is shown to exhibit a linear response to neutral gas pressure and a sensitivity that is improved by more than two orders of magnitude over a previous field ionization detector design.

Field ionization detection of helium using a planar array of carbon nanotubes

“…In our case, the sensitivity factor of best fit is 6.2 × 10 7 counts/Torr. Consistent with previous reports, 15,26 we find that α is a function of the history of the device and the channel electron multiplier and thus the absolute count rates of Figs. 2(b) and 3 are not directly comparable.…”

“…A solution to the latter was recently published by our group. 26 Most important is that Fig. 3 Time (s)…”

Improved field emission stability from single-walled carbon nanotubes chemically attached to silicon

“…1. For t < 0.5 h , the field emission is relatively unstable with both V and J fluctuating as a function of time, which is consistent with previous observations [ 25 ] and is most probably related to field-induced desorption of adsorbates, causing fluctuations in both the work function and β [ 26 - 28 ].…”

Focusing of a neutral helium beam below one micron

“…In fact, the number of helium atoms arriving at the detector is much higher, but the very low efficiency of the present-day electron-bombardment detectors (less than 10 −5 ) makes it appear so low. Several groups are currently exploring the possibility of improving the detector efficiency with various means [35][36][37][38][39][40][41], but so far no breakthrough has occurred. The other crucial issue is thermal drift.…”