Investigation of emitter tips for scanning tunneling microscope-based microprobe systems (original) (raw)
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The spatially controlled field assisted etching method for sharpening metallic tips, in a field ion microscope (FIM), is used to study the evolution of the field emission when the tip apex radius is decreased below 1 nm. Unlike the conventional image formation in a field emission microscope (FEM), we demonstrate that at this scale the field emission is rather confined to atomic sites. A single atom apex fabricated at the end of such tips exhibits an outstanding brightness compared to other atomic tips. The measurements have been repeated for two double atom tips, with different atom-atom separations, and images of atomic field emission localization have also been obtained. We have found that the field emission intensity alternates between adjacent atoms when the applied voltage is gradually increased beyond a threshold value.
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This paper presents the results of a series of tests performed on a set of eld emission electric propulsion (FEEP) emitters, including recording of the current /voltage characteristic curves and ion beam scanning with electrostatic probes. This work was aimed at collecting reliable, systematic thruster performance data to be used as a basis for the de nition of a reference thruster mathematical model (not reported here). Four FEEP emitters with three different slit height values were tested. Thrust produced covered the 1 -170 mN range. Repeatability of thruster performance was found to depend on the degree of wetting of the emitter slit and on the presence of glow discharge between the electrodes. The latter represented an undesired effect and was therefore eliminated after the rst series of experiments. Wetting, on the contrary, proved to be of the utmost importance. In some cases, thruster performance improved by up to as much as 150% within a few days of the beginning of the test, as a result of enhanced slit wetting.