Nanobeam is an advanced technology for the preparation of charged ion beams with a spot diameter of nanometer scale, which is mainly used in high-resolution and high-precision ion beam analysis, ion beam fabrication and ion beam material modification research. The nanobeam devices play an important role in material analysis, micro/nano fabrication, microelectronic device manufacturing and quantum computing. The high-quality ion source is one of the key components of nanobeam device, the performance of which directly affects the resolution and precision of the nanobeam system. However, the conventional ion sources used in this system is limited to available ionic species, large energy spread and complex structure. These issues prevent them from meeting emerging application scenarios that call for multi-ion types and high resolution. This emphasizes how crucial it is to create new kinds of ion sources as soon as possible.
With the development of laser cooling technology, ultracold ions with temperatures in the mK or even μK range can be obtained based on the technology of photoionization of cold atoms and laser cooling of ions. The typical characteristics of low temperature and easy manipulability have greatly promoted the emergence of ultracold ion sources. The ultracold ions exhibit extremely small transverse velocity divergence, which can significantly enhance the brightness and emittance quality parameters of the ion source，bringing tremendous opportunities for the innovation of nano-ion beam technology. Therefore, the research on ultracold ion sources is of great significance for achieving high-quality ion sources with higher brightness, smaller size, lower energy dispersion, more diversified ion species, and simplified structure. Here, we reviewed the recent research progress in ultracold ion sources, introducing the important achievements made in the basic research and application technology development of magneto-optical trap ion sources, cold atomic beam ion sources, and ultracold single ion sources from aspects of preparation principles, generation methods, and typical applications. Finally, we offers a perspective on the future development and application prospects of ultracold ion sources.