Condenser/objective lens SE-I Imaging of chromium-coated biological specimens using a Schottky field emission source

Abstract

We have had experience with high resolution SE-I enriched imaging of chromium(Cr) coated soft and hard biological tissue. SEMs equipped with condenser/objective (c/o) lens stages and LaB6(ISI DS-130) or cold cathode field emission (CFE)(Hitachi S-900) sources operated at high voltage(15-30 KeV) were assessed by the comparison of emission properties and image contrasts generated from ferritin test specimens. Practical source performance during the imaging of metal coated bulk biological tissues is subject to the metal film quality which is responsible for generating accurate topographic contrasts at high magnifications of biologically significant structures in the 1-10 nm range. Recently a thermionically assisted Schottky field emission source(SFE) has been designed for the c/o lens optics of the ISI DS-130 SEM. A practical consideration for the imaging of biological microdomains at high magnification must be: how does the SFE source compare with the LaB6 emitter on the same optical column and can the SFE compare with the CFE for producing quality ultrahigh magnification (500,000x) topographic contrasts in the nanometer range.