SILICON EMITTER FOR FIELD DESORPTION MASS-SPECTROMETRY

A new ion emitter for field ionization and desorption mass spectrometry has been developed. Very fine silicon whiskers grown on a 60-μm (diameter) tungsten (or tantalum) wire can be used as a strong and efficient emitter. The process of growth is as follows. A small amount of gold is deposited by evaporation on 60-μm tungsten wire. After being preheated in a vacuum chamber, the gold coated tungsten wire is heated by direct electric current in silane gas (SiH4 5 % + Ar 95 %) at a pressure of 180 Torr. Silicon whiskers grow in about 1 min. Pre-treatment, careful control, and high voltage supply during the whisker growth are unnecessary. The total ionizing efficiencies of silicon emitters in FI operation and in FD operation have been measured. The ionization efficiency for acetone in FI operation was 5 X 10-6 A/Torr and that for AMP in FD operation was 1.4 X 10-12 C/μg. The results for other test samples are also described. © 1979, American Chemical Society. All rights reserved.