{"id":1244,"date":"2013-07-25T18:26:58","date_gmt":"2013-07-25T18:26:58","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/?p=1244"},"modified":"2013-07-25T18:30:14","modified_gmt":"2013-07-25T18:30:14","slug":"self-aligned-gated-tip-arrays-for-low-voltage-high-pressure-field-ionization-of-gases","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/self-aligned-gated-tip-arrays-for-low-voltage-high-pressure-field-ionization-of-gases\/","title":{"rendered":"Self-aligned Gated Tip Arrays for Low-voltage, High-pressure Field Ionization of Gases"},"content":{"rendered":"

Field ion sources operate based on field ionization (FI) phenomena in which an electron tunnels out of a molecule under the influence of a high electric field that lowers and narrows the potential barrier (see Figure 1a). Excellent characteristics in terms of low power consumption, soft-ionization capability, and possibility to operate at high pressures render these devices very attractive for portable analytical instruments. Most commonly, field ionizers are used in field ion mass spectrometers[1<\/a>]<\/sup> and gas chromatography field ion mass spectrometry systems[2<\/a>]<\/sup> for analysis of organic molecules and petroleum products. Field ionizers are also investigated for application in atom beam microscopes for study of surface physics[3<\/a>]<\/sup> and neutron generators for oil-well logging[4<\/a>]<\/sup>. Although promising, application of field ionizers for portable equipment is currently limited by high operating voltages as the state-of-the-art devices require voltages in excess of 500 V to generate ion currents in nA-range needed for most practical applications[5<\/a>]<\/sup>[6<\/a>]<\/sup>[7<\/a>]<\/sup>.<\/p>\n

We designed and fabricated massive arrays of resilient, self-aligned gated nanoscale tips that are capable of field ionizing gases at voltages as low as 150 V. Photolithography and oxidation sharpening were employed to produce a self-aligned device configuration and highly uniform gate and tip dimensions. Electric fields higher than 20 V\/nm can be generated with tip-to-gate biases below 200 V that are sufficient to field ionize even helium, with the highest ionization potential of any molecule. The proposed gated tips (Figure 1b) have average tip radii < 5 nm and gate apertures of 3 \u00b5m. We demonstrated field ionization of nitrogen at pressures as high as 10 Torr with onset fields of 8\u201310 V\/nm and ion currents > 1 nA at 200 V tip-to-gate bias, as shown in Figure 2.<\/p>\n\n\t\t