Ion Beam Injector based on High Current LMIS

One of the major advantages of Liquid Metal Alloy Ion Sources (LMAIS) is the capability to emit a broad spectrum of ions from doubly and singly charged ions of nearly the half of the periodic table up to molecular ions or small clusters, consisting of a few atoms and different charge stages. These ion sources, characterized by a high brightness of about 106 A/cm2 sr, low energy spread of some eV and a very compact design are dedicated mostly for focused ion beam (FIB) applications [1] or field emission electric propulsion (FEEP) thrusters in space technology [2]. Normal ions in a wide spectrum of parameters can be provided also by other ion sources. The very special of LM(A)IS are the formation of heavy polyatomic ions from metallic or semiconducting elements, which is of great interest for self-organized surface patterning. So with Bismuth di- and trimer ions regular hexagonal dot structures were obtained after room temperature irradiation of Germanium at normal incidence using a FIB instrument induced by the enormous energy deposition by the heavy projectiles [3, 4]. To employ these heavy ions also for other ion beam systems and especially for larger areas an ion source injector module based on a high current LM(A)IS will be presented. Total emitted ion currents of more than 100 µA can be reached using different types of field emitter in particular porous needles from Tungsten and Rhenium or capillaries, 50 µm inner diameter of Tantalum. Source materials like Ga for tests, Gold (from Au82Si18 alloy), Lead or Bismuth (Bi or Ga38Bi62 alloy) were investigated.
In the injector a nearly parallel ion beam of about 2 mm diameter can be obtained by means of an asymmetric ion-optical Einzel lens. The cluster ion fraction for a certain ion species is in the range of per mil up to a few percent dependent on the emitted elements. A mass separation system (Wien filter) selects the desired ions while a quadrupole is used for beam adjustment and astigmatism correction. High cluster ion currents enable the formation of various nanostructures or even smooth surfaces over an area in cm²-range depending on ion species, energy, fluence and angle of incidence. The LM(A)IS preparation and the performance of the ion beam module at certain experiments will be presented and discussed.

[1] L. Bischoff, Ultramicroscopy 103, 59 (2005).
[2] M. Tajmar and B. Jang, CEAS Space J. 4, 47 (2013).
[3] L. Bischoff, et al., Nucl. Instr. and Meth. B 272,198 (2012).
[4] R. Boettger et al. J. Vac. Sci. Technol. B 30, 06FFF12 (2012).