  Experimental evidences reported in this letter show that the gas ionization
induced positive charge accumulation can lead to the electron field emission
from carbon nanotubes (CNTs) in an electrode system with proper range of gap
spacing, where the CNT film with ethocel was covered with ZnO nanorods. The
hypothesis for illustration is suggested that: 1) the cosmic ray ionization
frequency increases 108~1010 times due to the metastable population resulted
from the interaction between the gases and the CNTs; 2) the flux of positive
charges is enhanced in the converged field due to the ZnO nanostructures. The
resulted positive charge local density is high enough to trigger the field
emission of the CNTs. The methodology may be useful in particle detectors and
ionization gas sensors.
