Sean Kellogg

Mass filtered plasma focused ion beam system

The authors describe an inductively coupled plasma ion source combined with a mass tunable Wien (E × B) filter that is capable of delivering single or mixed gas plasma generated ions. Gases for the RF powered ion source can be premixed or of variable stoichiometry by mixing individual gases. The gas mixtures can contain a variety of elements providing light to heavy gaseous ions which can be selected by mass filtering. Optimization of the plasma source consists of varying parameters such as the RF power, pressure, and gas stoichiometry. Subsequently, the mass filter/plasma-gas ion column can be optimized for a wide range of applications. For example, high resolution imaging using high reduced brightness light ions (e.g., for subsurface imaging) or fast material removal using heavy ions may be accomplished across a wide range of beam currents, typically 10 pA to 10 μA, with the same gas mixture. The authors have examined several candidate species (He+, Ne+, Ar+, Xe+, O2+, O+, O−, N+, N2+, H+, H2+, H3+) and...

Computer modeling of the Schottky electron source

A computer modeling program that is able to imitate the polyhedral shape of the ZrO/W(100) Schottky cathode is used to compute emission parameters such as the electric field distribution and reduced brightness Br for the various observed end form shapes. This program includes the electron–electron interactions in the beam and their effect on Br. A relationship between the axial field factor β = F/Ve and the axial lens factor K = (I′/J)1/2 (where F, Ve, I′, and J are the applied electric field, extraction voltage, beam angular intensity, and surface current density, respectively) was obtained from the data which allow β, K, and the work function to be calculated from experimental I′(Ve) data. In addition, an empirical relation, independent of the end form shapes, was obtained that allows Br to be calculated from the intrinsic reduced brightness. Experimental energy distribution measurements are presented which allows one to compare the energy spread and Br values for emitters with various values of β. An e...

Off-axis modeling and measurement of emission parameters for the Schottky emitter

The optical performance of on- and off-axis emission from the central (001) facet of a Schottky emission (SE) source has been studied using a hybrid experimental and numerical approach, which allows for the simultaneous determination of all key performance measures. A recently developed computer modeling program was instrumental in aiding the discovery of empirical relationships that allow work function (φ), β (where field factor β=F/Ve for emitter surface field F and extraction voltage Ve), and source brightness (Br) to be calculated from on- and off-axis experimental angular intensity (I′) data. Emission parameters F, current density (J), and φ, were determined from experimental data for off-axis emission angle up to 4° in which energy spread (ΔE50) and I′ were directly measured. Also included in this study was the influence of the various end-form shapes of the polyhedral SE source on the various emission parameters. Plots of Br versus ΔE50 for emitters over a range of β, I′, and off-axis angle have be...