Cathode duoplasmatron

In 1967 Liebl reported the development of the first imaging SIMS instrument based on the principle of focused ion beam scanning [24]. This instrument, the ion microprobe mass analyzer, was produced by Applied Research Laboratories (Fig. 4.5). It used an improved hollow cathode duoplasmatron [25] ion source that eliminated filaments used in earlier sources and allowed stable operation with reactive gases. The primary ion beam was mass analyzed for beam purity and focused in a two-lens column to a spot as small as 2 pm. The secondary ions were accelerated from the sample surface into a double focusing mass spectrometer of Mattauch-Herzog geometry. Both positive and negative secondary ions were de-... 

Current density and the type of primary ion have a critical effect on SIMS analyses. High current densities are desirable for rapid profiling and high-sensitivity analysis, whereas low current densities are chosen when the analyte layer is thin or when using static SIMS. Exotic polyatomic ion sources are an area of active research today Re04 [104], SF5+ [105], SF6 , NO, CF3+, C, and many others [106,107], have been reported to provide exceptional enhancement of secondary ion yields and ultrashallow depth profiling. However, the most heavily used ion sources today are the hollow cathode duoplasmatron (Fig. 4.31) [108], the thermal... 

The most common species used with SIMS sources are Ar+, 02+, 0 , and N2+. These ions and other permanent gas ions are formed easily with high brightness and stability with the hollow cathode duoplasmatron. Ar+ does not enhance the formation of secondary ions but is popular in static SIMS, in which analysis of the undisturbed surface is the goal and no enhancement is necessary. 02+ and 0 both enhance positive secondary ion count rates by formation of surface oxides that serve to increase and control the work function of the surface. 02+ forms a more intense beam than 0 and thus is used preferentially, except in the case of analyzing insulators (see Chapter 11). In some cases the sample surface is flooded with 02 gas for surface control and secondary ion enhancement. An N2+ beam enhances secondary ion formation, but not as well as 02+. It is very useful for profiling and analysis of oxide films on metals, however. It also is less damaging to duoplasmatron hollow cathodes and extends their life by a factor of 5 or more compared to oxygen. 

Schnitzer and Anbar s experiments are rather similar to those of Baumann, Heinicke, Kaiser and Bethge Both employed plasma ion sources that employed by Schnitzer and Anbar was a hollow cathode duoplasmatron. Also, both used einzel lenses and momentum/charge analysis. But the different lifetimes of the doubly-charged negative ions studied dictated somewhat different analyses. Baumann, et al. used an electric deflection analysis after the magnetic sector, as already seen, whereas Schnitzer and Anbar employed a Wien velocity filter and einzel lens voltage variation prior to the magnetic sector. 

A cold cathode duoplasmatron is commonly used to produce 2, O, and Ar" (or other inert gases) beams. The pressure in the duoplasmatron during operation will be in the Torr range. As a gas is fed in, a plasma is initiated by a... 

The most popular member of the plasmatron family is the duoplasmatron (O Fig. 50.3). Its idea is that the plasma density between the anode and cathode is greatly increased in a small volume by an intermediate electrode placed between the anode and cathode putting on... 

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