Miniature vacuum sensor based on gas adsorptions from carbon nanotube field emitters

A mini-type vacuum sensor based upon current enhancement from gas adsorption for multi-walled carbon nanotube (MWNT) field emitters is developed. The current increase rates in low emission state are proportional to gas pressures in nitrogen, hydrogen, and mixed gas environments. The field emission energy distribution (FEED) measurement demonstrated the reductions of electron tunneling energy barriers in H2 and N2 ambiences. The first-principles simulation indicates that the energy barrier reduction, which is related to the surface energy well from nitrogen adsorption, is attributed to the sensing effect for nitrogen. Both experiments and first-principles simulation affirmed that the high MWNT crystallinity benefits the sensing performance. The miniature sensor in millimeter dimensions based on MWNT field emitter with simple diode configuration can operate in a wide vacuum range from 10−7 to 10−2 Pa. The sensor was assembled inside the X-ray tube to measure the in-situ device vacuum, showing great potentials for vacuum electronic device applications.