Thermionic emitter for electron microscopy

Claim 1

For use in electronic microscopes, an improved thermionic filament consisting of a one piece metallic conducting wire of circular cross-section made of tungsten or the like, bent into the general shape of an inverter V with two diverging legs in a common plane, and defining: (a) in a first zone, an arcuate point of essentially constant diameter acting as a thermionic cahtode; (b) in a secnd zone, spaced apart from said first zone, said two diverging legs which are of constant diameter; (c) in a third zone, intermediate said first and second zones, two transitional sections, each transitional section extending between one of said legs and one side of said arcuate point; the diameter of said wire where it forms said arcuate point being substantially less than the diameter of said wire in said second zone and the diameter of said wire in each transitional section changing progressively from the greater diameter of said wire in said second zone to the lesser diameter of said wire in said first zone as a result of sharpening of said first and third zone by precision electrolytic shaping.

Claim 18

A method of precision sharpening by electrolytic immersion for the sharpening of fine elongated metallic workpiece progressively from the non-sharpened region of said metallic workpiece, comprising: mounting said workpiece above an electrolytic bath, adjusting the level of the said workpiece with respect to the upper surface of the electrolyte in a still condition, and driving said electrolyte in relative vertical oscillation, at controlled frequency and amplitude during circulation of an electrolysis electrical current thereby to cause cyclic immersion of said workpiece into said electrolytic bath.

Claim 19

A method of precision sharpening by electrolytic immersion for the sharpening of fine elongated metallic workpiece progressively from the non-sharpened region of said metallic workpiece, comprising: mounting said workpiece above an electrolytic bath, adjusting the level of the said workpiece with respect to the upper surface of the electrolyte in a still condition, and driving said electrolyte in relative vertical oscillation, at controlled frequency and amplitude during circulation of an electrolysis electrical current thereby to cause cyclic immersion of said workpiece into said electrolytic bath.

Claim 23

An apparatus used for precision electrolytic sharpening of a small metallic component such as a tungsten filament comprising an electrolyte bath, an electrolyte reservoir at the same level, a lower duct in communication with the bottom of said bath and that of said reservoir, said bath, said lower duct and said reservoir being adapted to contain a determined volume of a suitable electrolyte liquid, said apparatus also comprising a support directly above said electrolyte bath and adapted to hold said component in fixed position in said electrolyte bath, coarse adjustment means for adjusting the height of said support, microscopic adjustment means for fine adjustment of the height of the support, a membrane stretched across the free electrolyte surface in said reservoir, an electro-mechanical vibrator comprising a magnetic coil adapted to vibrate said membrane and said body of electrolyte at a low frequency, means for generating a vibrator driving voltage applied across the terminals of said magnetic coil and having means for controlling the frequency and the intensity of said vibrator driving voltage, and an electrical electrolysis current circuit comprising a submerged electrode in said bath below said component and a second electrode formed by said component.

Claim 24

An apparatus used for precision electrolytic sharpening of a small metallic component such as a tungsten filament comprising an electrolyte bath, an electrolyte reservoir at the same level, a lower duct in communication with the bottom of said bath and that of said reservoir, said bath, said lower duct and said reservoir being adapted to contain a determined volume of a suitable electrolyte liquid, said apparatus also comprising a support directly above said electrolyte bath and adapted to hold said component in fixed position in said electrolyte bath, coarse adjustment means for adjusting the height of said support, microscopic adjustment means for fine adjustment of the height of the support, a membrane stretched across the free electrolyte surface in said reservoir, an electro-mechanical vibrator comprising a magnetic coil adapted to vibrate said membrane and said body of electrolyte at a low frequency, means for generating a vibrator driving voltage applied across the terminals of said magnetic coil and having means for controlling the frequency and the intensity of said vibrator driving voltage, and an electrical electrolysis current circuit comprising a submerged electrode in said bath below said component and a second electrode formed by said component.