Preferential Sputtering of DNA Molecules on a Graphite Surface by Ar Cluster Ion Beam

Abstract

The process of sputtering by bombardment with gas cluster ions was investigated from the perspective of the kinetic energy per constituent atom (E atom ) of an incident cluster ion, which determines the threshold for the formation of craterlike defects by irradiation of an argon gas cluster ion beam (Ar-GCIB) onto a graphite surface. Furthermore, DNA molecules adsorbed on a graphite surface were preferentially sputtered by adjusting E atom of the Ar-GCIB down to this threshold, while the substrate graphite surface retained its carbon lattice structure without the formation of craterlike defects. These results indicate that a GCIB could be used as a primary ion beam for secondary ion mass spectrometry (SIMS), which would enable the preferential analysis of an adsorbed layer on a substrate without causing damage to the substrate.

Matrix‐free detection of intact ions from proteins in argon‐cluster secondary ion mass spectrometry

“…We previously analyzed the traces caused by argon (Ar) cluster ions bombarded on graphite12, 13 and obtained the following result: “the kinetic energy per atom of the cluster ion used for bombardment will almost completely determine the rate at which traces are produced. A certain level of kinetic energy per atom or greater is required for causing traces, and this threshold energy is determined by the cohesive energy of the carbon atoms that constitute graphite.” This result suggests that adjusting the kinetic energy per atom can suppress the damage to the sample.…”

Molecular Depth Profiling with Cluster Ion Beams

“…Enabling low energy per atom sputtering also allows for more controlled sputtering of species in the range of known bond dissociation energies. 95,140 Maintaining the kinetic energy per atom below the bond dissociation energies observed in organic materials (e.g., C-C, C-N, and C-O), which are typically ∼3-5 eV/atom reduces fragmentation significantly. 140 An example of the effect of energy per atom on the fragmentation and sputtering yield of molecular samples is illustrated in Figure 5.40.…”

“…95,140 Maintaining the kinetic energy per atom below the bond dissociation energies observed in organic materials (e.g., C-C, C-N, and C-O), which are typically ∼3-5 eV/atom reduces fragmentation significantly. 140 An example of the effect of energy per atom on the fragmentation and sputtering yield of molecular samples is illustrated in Figure 5.40. Figure 5.40a shows the intensity of fragment ions ( , ) and Na-cationized molecules (•, •) of a small polypeptide consisting of six aspartic acid monomers (Asp) 6 plotted as a function of increasing energy per nucleon (increasing cluster size).…”

New design and development of size‐selected gas cluster SIMS

“…We have investigated the sputtering of DNA molecules adsorbed on a highly oriented pyrolytic graphite (HOPG) by an argon gas cluster ion beam (Ar-GCIB) [11,12]. This study demonstrated that DNA molecules on an HOPG surface can be preferentially sputtered by adjusting E atom of Ar-GCIB without damaging the substrate surface, which suggests that the sputtering process can be controlled by precisely adjusting the cluster size, and has motivated the development of a size-selected GCIB TOF-SIMS, which should be a useful tool for performing SIMS with minimal damage.…”