Enhanced field emission from extremely small metallic microtips

1 .Introduction Electron field emission from microscopic metal cathodes subjected to high electric fields is observed at fields being much below the value predicted by the Fowler-Nordheim law for flab metallic surface.Un derstanding for this phenomenon is important for high field vacuum aplications [1J. This enhanced field emission (EFE) is known to originate from localized microparticles on a broad area cathode 12-51. The characteristic size L of the microtip was estimated to be of order of iO - 1O_8 cm. However,the physical mechanism of EFE is not clear up to now. The case of extremely small microtips is analised below Depending on the correlation of the microtipe size and lengt of elastic (l ) and in elastic ( 1 e electron scattering,three modes of emission may be realized: ballistic (1<> le Ji ).In the later case the principial solution may be obtained by means of hydrodynamic approximation [6] . Otherwise, in the case under consideration, the the analysis should be based upon the directsolution on the kinetic equation for the electron distribution function.For metall microcontacts such a programme in the single-particle approximation is relized in [7]. In this case the energy scattering length 2e Oi le )1/2 >> thus heat discharges in a region of volume 2 , exceeding considerably the region of formation of microtip tunneling resistance ('.3 ). According to [3], it is this particular phenomenon that causes the microtip thermal stability at greater values of the current density.