Low-Voltage Field Ionization of Gases Up to Torr-Level Pressures Using Massive Arrays of Self-Aligned Gated Nanoscale Tips

Large arrays of self-aligned gated nanoscale tips (320000 tips in 32 mm² with average radii <;5 nm) are reported for application as gas ionizers in portable analytical instruments. The fabricated devices are capable of field ionization (FI) of gases at voltages <; 150 V even for helium with the highest ionization potential among molecules. Reliable operation of the devices was demonstrated at pressures as high as 1 Torr in He and 10 Torr in N₂. FI at higher pressures was only prohibited by gas discharge rather than device failure. Ion currents as high as 0.35 nA in N₂ and 0.1 nA in He were generated at a tip-to-gate bias of 200 V. Continuous operation for 10⁴ s at 10 Torr confirmed excellent stability of the device for FI of gases. The device characteristics slowly degraded during continuous operation possibly due to particle adsorption on the tip surface. The device characteristics can be restored by operating the device as a field emitter at pressures <;10^-7 Torr.