Selective production of hydrogen ion species at atomically designed nanotips.

Hydrogen scanning ion microscopy systems rely on nanotip gas field ion sources to generate the hydrogen ion beam. The exact structure of the nanotip and the applied electric field are shown to be important. It is demonstrated that hydrogen ion beams are found to occur as mixtures of H, H and H depending on the electric field strength and the nanotip structure. Various nanotips were prepared, including single atom tips (SATs), trimers and other nano-structured tips to compare the contents of hydrogen ion beams. It was found that single atom tips produce primarily H at low operating voltages, but as the voltage is increased, H dominates. For the trimer case, H becomes a significant species and equals the H current but H can be isolated at higher voltages. For the hexamer tip structure, H almost completely dominates with little H being produced. H is only observed in small quantities for all tip structures until a high voltage regime, where apex atom resolution is not observed. Comparisons W SATs and Ir SATs showed similar H/H product ratios indicating the nanotip structure plays a key role in the catalytic formation of H. Temperature affects are also discussed and operating parameters for single species ion beams are discussed.