Evaluation of a Neon Focused Field Ion Source: Fabrication and Characteristics
A new type of gaseous field ion source, operated with the inert gas neon, was developed. The source material used was the equiatomic B 2-ordered Ni-Al alloy doped with small amounts of W and C. Small surface protrusions were formed by the field evaporation of the multiphase alloy containing ultrafine spherical precipitates. The emission current-voltage characteristics were recorded as a function of neon gas pressure and source temperature. Total source current densities of up to 6 nA were obtained. A source temperature just above the condensation point of Ne gas was found to generate the highest ion current
A novel approach to gaseous field ion sources for focused ion beam applications
Abstract Experiments have demonstrated that significantly increased angular current densities may be obtained from protrusions formed from ultrafine precipitates compared to the normal field ion specimens. The confinement of the ion-emitting region to the precipitates is an effective method of increasing the angular current density. This type of emitter may be a potential candidate for gaseous focused ion sources.
The field ionization characteristics of individual atomic planes
Abstract A detailed study of the field ionization characteristics of nine different planes of tungsten in the (001)-(011)-(111) standard triangle has been performed as function of tip temperature ( T T ) between 11°K and 86°K, and local radius of curvature ( rT ). The measured helium ion current-voltage characteristic curve for each plane was found to consist of two distinct regimes. The first regime was linear on a log-log plot, and the slope varied from 27 to 41. A modified version of Gomer's model for the very low field ion current fitted the regime I data reasonably well. The second regime of each characteristic curve was quite complicated and exhibited several maxima and minima whose positions were functions of both T T and crystallographic plane. A qualitative explanation for the behavior of the ion current in regime II was given in terms of a patch field model consisting of three dominant spatial regions on the surface of the field ion microscope specimen. In addition, the explanation also considered the role played by a lateral supply of gas atoms on the specimen's surface, and a slowly increasing field dependent radial supply function of gas atoms. It was also found that the probability of ionization was a strong function of both T T , and crystallographic plane. An expression was derived for the temperature dependence of this effect which fitted the data for atomically smooth planes [e.g., the (011) plane]. Finally, the ion current from individual planes was proportional to a power of rT (at constant electric field) which varied between 2.3 and 2.9. This result was at variance with the existing theories of the supply function, and indicated that the shank of the specimen was a significant source of imaging gas atoms.