Thermal instability of molybdenum and silicon tips

Thermal effects in molybdenum and silicon tips are analyzed with the aim of understanding the initiating mechanism of thermal instability leading to vacuum breakdown. A new theoretical treatment is employed to study the thermal response of tip emitters, which takes into account the correlative effect between field emission and its resultant temperature rise at the apex of tips. The results show that for a typical Si tip, thermal instability would occur before the tip temperature reaches its melting point, while thermal effect is not significant in the case of the Mo tip with the same geometry and dimension of a silicon tip. This remarkable difference between two types of tip is mainly due to their large discrepancies in electrical resistivity, but the Nottingham effect contributes significantly as well.