A compact UHV negative halogen ion source with narrow energy spread for ion soft-landing study

A compact ultrahigh vacuum negative halogen ion source has been developed to generate ion beams with small energy spread for soft-landing applications. Thermionic emission of a halogen atom from a hot tantalum surface carries an extra electron to form a negative halogen ion. Based on this principle, a tantalum helical ionizer is designed to efficiently produce Cl- ions from Cl atoms generated by CuCl2 decomposition. The intrinsic kinetic energy distribution, quantified by a retarding field energy analyzer, exhibits a full width at half maximum of ∼0.83 eV. Beam profiling confirms a controllable diameter within 8 mm. Isotopes of 35Cl- and 37Cl- have been successfully resolved with a Wien filter. The compact ion source has been integrated into an ion transport study apparatus, with initial experiments verifying ion soft-landing and surface charge dynamics. This ion source provides a reliable tool for probing ion-involved interfacial processes under ultra-high vacuum conditions, while advancing ion chemistry and relating sciences as well.