Point defects in Helium Ion Microscopy: an ionoluminescence study

In Helium Ion Microscopy (HIM) [1] several signals are available to form an image and obtain information on sample properties. Besides secondary electrons and backscattered helium atoms also photons can be utilized. The latter phenomenon is referred to as ionoluminescence (IL). We show how the ion beam can be used to create sub surface luminescence patterns, that can be made visible using optical techniques [2]. The patterned areas are not visible in the obtained images of the sample surface.
Here, we use IL together with HIM to understand the creation of defects and their behaviour in ionic crystals. The emission of the created point defects has been analyzed in dependence of scanning parameters (pixel spacing and primary current). The fluence dependent results can be understood when the different diffusion behaviour of the identified defects is taken into account [3].
In a second step, single pixel exposures have been used to directly measure the surface projected interaction volume of the beam with sodium chloride. The results are compared to different theoretical calculations. We find that in the presented case a minimum density of 3 emission centers per nm^2 is needed for a detectable IL signal [2].
This research is supported by the Dutch Technology Foundation STW, which is the applied science division of NWO, and the Technology Programme of the Ministry of Economic Affairs.
References:
[1] Gregor Hlawacek, et al. Helium ion microscopy. J. Vac. Sci. Technol. B Microelectron. Nanom. Struct., 32(2):020801, 2014.
[2] Vasilisa Veligura, Gregor Hlawacek, Uwe Jahn, Raoul van Gastel, Harold J. W. Zandvliet, and Bene Poelsema. Creation and physical aspects of luminescent patterns using helium ion microscopy. J. Appl. Phys., 115(18):183502, 2014.
[3] Vasilisa Veligura, Gregor Hlawacek, R van Gastel, Harold J. W. Zandvliet, and Bene Poelsema. A high resolution ionoluminescence study of defect creation and interaction. J. Phys. Condens. Matter, 26(16):165401, 2014.