Experimental Study On The Production Of Negative Ion Copper Clusters And Applications

At the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratories (ORNL), we investigated the formation, production and potential application of negative-ion copper clusters using mass distributions of negative-ion copper clusters obtained by bombarding various copper samples with Cs ions. The Cu samples – in very large mass-selected clusters Cu (e.g. n=54) – included natural Cu, isotopically enriched copper-63 and copper-65, and electroformed ultra-clean Cu. Mass spectra of negative copper cluster produced by Cs sputter source size up to 50 are shown for the first time.

Three main features were observed for all four copper samples: the intensity of copper cluster ion exhibit an even-odd alternation because of electron pairing in the highest occupied molecular orbitals ; a discontinuity in the ion intensity at magic number n = 2, 8, 20, 40 due to close of shell in the shell model; the abundance of a copper cluster has a power-law dependence on its size n. The exponent we measured for the copper cluster was ~ 3. It’s for the first time to report experimental power-law exponent of copper cluster low to 3 which consists of the thermodynamic model and shock wave model.

In addition, by having access to various samples of copper, including isotopically enriched material, we were able to study the formation of clusters involving various combinations of copper-63 and copper-65. A binomial distribution was observed for the formation of Cu clusters from natural Cu and clean Cu samples and it indicates the formation of sputter copper cluster is a random multiple sequential aggregation. It’s for the first time to shown isotopes exhibit binomial distribution inside a metal cluster.

We explored a potential application of copper clusters, utilizing the energy-and-mass-selected copper cluster to prepare nanoporous graphene for applications such as water desalination. Copper clusters of size (n = 3 and 9) and energy 200 keV were applied to bombard the single-layer graphene with various dosages. Raman spectrum and scanning electron microscopy showed diameter around 2 nm defects were created.