Method of fabricating a funnel-shaped miniature electrode for use as a

Abstract

A method of fabricating a funnel-shaped miniature electrode with thin walls and very sharp edges for use in a field ionization source for ionizing components of a fluid sample is disclosed, which method includes the use of a female mold, or matrix, formed with a stepped, generally frustoconical-shaped aperture therethrough. The aperture wall includes a plurality of different diameter generally tapered wall sections of decreasing size in going along the aperture axis, with the smallest diameter section at the one end being of short length and small diameter. It is convenient, but not necessary, to coat the aperture wall with a parting layer which aids in the separation of the subsequently-formed miniature funnel-shaped electrode from the female mold and facilitates cleaning of the mold for reuse. Electrically conducting material such as copper, gold, or the like, to form the funnel-shaped electrode then is deposited on the parting layer to the desired thickness to provide the funnel-shaped electrode with the desired strength. For this step physical vapor deposition is preferred because of the flexibility of the process and the extreme accuracy of surface replication that can be achieved, however, any of the coating, plating or like processes can be used. The evaporant beam is directed onto the mold cavity from the large diameter end of the aperture from a source either on axis with the mold or at an angle to the mold axis, and the beam and mold are relatively rotated about such axis during metal deposition although rotation is not necessary with well aligned on axis deposition.