Single-walled carbon nanotubes (SWCNTs) were assembled onto a tungsten tip and then received heat treatment. After sample heating at different temperatures, mass spectra of residual gas were recorded with a quadrupole mass spectrometer and curves of field emissive current versus anode-cathode voltage were acquired with a field emission microscope (FEM). Water molecules were found to be responsible for the instability of the field emission before the system baking out. The change in relative amount of CO and CO, in the vacuum was interpreted by the existence of carbon and oxygen atoms released from tungsten filament and tip at high temperatures. The alteration in work function and FEM images of SWCNTs arising from the heating treatment was also studied. (C) 2002 Elsevier Science B.V. All rights reserved.