The development of vacuum measurements down to extremely high vacuum – XHV

A Cylindrical Triode Ultrahigh Vacuum Ionization Gauge with a Carbon Nanotube Cathode

“…To the best of our knowledge, this is the first reported CNT emitter-based ionization gauge whose lower limit of pressure measurement is lower than its hot cathode counterpart [ 5 , 36 ]. It is well-known that in cylindrical triode ionization gauges, X-ray effects are one of the most dominant factors to restrain the extension of the lower limit of pressure measurements of such a gauge [ 1 , 6 ]. This is mainly due to the fact that the X-rays mainly produced by electron-impact on the anode generate a photoelectron current from the ion collector, and thus produce a pressure-independent background current.…”

“…Thus, it can explain the variation of the experimental sensitivity with anode voltage. As is clearly shown in Figure 2, both the electron-impact ionization cross-section and the effective electron path length reach their maximum values at an anode voltage of ~100 V. Consequently, the highest sensitivity is naturally obtained according to Equation (1). In addition, it should be noted that under some anode voltages (e.g., 250 V), the sensitivity derived from experimental testing was higher than the one obtained by theoretical simulation, which is mainly because in the theoretical simulation, only the contribution of gas phase ions was considered.…”

“…In recent years, ultrahigh and extremely high vacuum pressure measurements have become widely demanded in many science and engineering fields [ 1 , 2 , 3 ], including space exploration, surface science, particle accelerator, storage ring, etc. To date, hot cathode and cold cathode ionization gauges are the only practically available electronic vacuum sensors in this pressure region [ 4 , 5 ].…”

“…To date, hot cathode and cold cathode ionization gauges are the only practically available electronic vacuum sensors in this pressure region [ 4 , 5 ]. However, conventional ionization gauges have long-standing intractable problems when measuring extremely low pressure, i.e., X-ray effects, electron-stimulated desorption effects, and outgassing effects [ 1 , 6 , 7 ]. Fortunately, recent studies [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ] have shown that ionization gauges with carbon nanotube (CNT) cathodes have unique advantages, such as low power consumption for electron emissions, fast responses, free from visible to infrared light radiation and thermal radiation, etc., in extremely low pressure measurements, which are largely due to the application of the novel CNT field emission cathode.…”

Development of a new UHV/XHV pressure standard (cold atom vacuum standard)

“…Figure 4. Theoretical loss rate coefficient estimates, kloss (assuming room temperature and zero trap depth) versus background gas species for the following sensor atoms: 7 Li (blue circles), 23 Na (orange squares), 39 K (inverted green triangles), 85 Rb (red triangles), 133 Cs (purple diamonds). These are computed using published C6 coefficients where possible [29][30][31][32], or estimates based on dynamic polarizabilities and the Casimir-Polder integral [33][34][35][36].…”