World’s first Rb+ ion microscope images created at CQT
Researchers from the CQT group (Applied Physics, Gijs ten Haaf and Steinar Wouters) have built the world’s first high-resolution ion microscope for rubidium ions (Rb+). Ion microscopes (or focused ion beams) are versatile tools that can both be used for imaging and for manipulation of nanostructures. Imaging is performed in a similar way as done in a scanning electron microscope. The momentum of the ions, that is much higher than that of electrons, can be used to physically sputter material from a substrate or to decompose a precursor gas leaving a deposit on the substrate. Due to their ability to alter substrates at the nanoscale ion microscopes are very useful in the development of integrated circuits (ICs). With the ever decreasing size of the features on ICs there is a push towards ion microscopes with higher resolution. Commercial microscopes based on the gallium liquid metal ion source (Ga-LMIS) reach a resolution down to 5 nm but can not be improved further. Microscopes based on the Helium/Neon gas field ionization source offer a higher resolution but are less suitable for nano-machining. Therefore alternative ion sources based on the Nobel prize winning technique of laser cooling and compression are being developed .
In the past 5 years, an ion source based on the photo-ionization of a laser cooled and compressed atomic beam of rubidium atoms was constructed and tested at the CQT research group . Calculations and simulations show that an ion microscope with this source can achieve a resolution of 1 nm, a major improvement over the Ga-LMIS. The experiment was built up in steps and the performance of each part was verified, starting with the thermal source of the atoms followed by the magneto-optical compressor. In the past two years the photoionization process was optimized and finally the source was mounted on a commercial ion microscope from FEI company. This allowed taking the world’s first Rb+ micrographs of which one of them is shown below. In the coming period the resolution of the machine will be determined and the properties of Rb+ as ion for microscopy will be studied.
This research is supported by the Dutch Technology Foundation STW (part of NOW), FEI Company (now Thermo-Fisher Scientific), Pulsar Physics and Coherent Inc.
 Background information about laser-cooled ion sources can be read here: J. J. McClelland et al. in Applied Physical Reviews 3, 011302 (2016) (or at the arXiv)
 The latest article on the development of the ion source for the Rb+ microscope at CQT can be read here: G. ten Haaf et al. in Physical Review Applied 7, 054013 (2017) (or at the arXiv)