  We report observation of field emission from self-catalyzed GaAs nanowires
grown on Si (111). The measurements are realized inside a scanning electron
microscope chamber with nano-controlled tungsten tip functioning as anode.
Experimental data are analyzed in the framework of Fowler-Nordheim theory. We
demonstrate stable current up to 10$^{-7}$ A emitted from the tip of single
nanowire, with field enhancement factor $\beta$ up to 112 at anode-cathode
distance d=350 nm. A linear dependence of $\beta$ on the anode-cathode distance
is experimentally found. We also show that the presence of a Ga catalyst
droplet suppresses the emission of current from the nanowire tip. This allows
detection of field emission from the nanowire sidewalls, which occurs with
reduced field enhancement factor and stability. This study further extends the
GaAs technology to vacuum electronics applications.
