Over the past few years, gas cluster ion beams (GCIB) has shown great capability of dealing with bio-materials and soft materials owing to its high sputter yield and low damage accumulation that preserved the molecular structures during depth profiling, therefore molecular ion of high mass can be obtained in subsequent analysis. However, although GCIB has lower damage accumulation comparing with C60+ and monoatomic ions, the inevitable alteration in chemical structure can still change the property of remaining surface and gradually affect the accuracy of depth profile. As a result, artifacts can still be observed in the resulting depth profiles. In order to further improve the depth profile of soft materials, low energy O2+ can be used to cosputter the surface to enhance the ionization yield and mask the damage accumulation. While the energy per atom (E/n) is known to be another important factor to the sputter process and previous works concluded higher E/n is beneficial, how the change in E/n affects GCIB-O2+ cosputter depth profile is not clear yet. In this study, bulk poly(ethylene terephthalate) (PET) was chosen as the modeling material and 10-20kV Ar1000-4000 (E/n=2.5-20) with or without 200V O2+ beam was used to cosputter the surface. Spectra at different depths were obtained by a time-of-flight secondary ion mass spectrometer (ToF-SIMS) with pulsed Bi32+ as primary ion to construct the depth profile. After sputtering, the craters were measured by alpha step and atomic force microscopy (AFM) with quantitative imaging mode. The result shows that with higher E/n, the resulting surface is more rough and the surface Young’s modulus became smaller compared with the pristine surface. This result suggested that depolymerization took place. Also, steady-state was not clearly observed in the depth profile, which indicated damage still accumulated. Furthermore, at E/n=20, the sputter rate and secondary ion intensity decreased rapidly. Because the Young’s modulus increased significantly with low roughness, the result suggested that the system reached gel point rapidly. In other words, radical induced cross-link dominated the damage process. With the auxiliary O2+ as cosputter ion, it helps to break the ion-beam induced morphology and enhance the ionization yield that masked damage. As a result, steady-state can be obtained and depth profiles with less artifact were observed.

Effect of energy per atom (E/n) in Ar gas cluster ion beam (GCIB, Arn+) and O2+ cosputter

253rd National Meeting (2017)

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