Effect of Temperature and Energy per Atom (E/n) in Ar Gas Cluster Ion Beam (GCIB, Arn+) on Depth Profile of Organic Thin Film by Secondary Ion Mass Spectroscopy

• Main Authors: Shu-Han Hung, 洪舒涵
• Other Authors: 薛景中
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/752re9

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 106 === Secondary Ion Mass Spectroscopy (SIMS), with its ability to analyze chemical compositions at near surface and along the depth, has been used for decades. However, depth profiles of bio-materials and soft materials are more difficult to obtain due to the fragmentation and transformation of molecules induced by atomic ion sputtering gun. Nevertheless, with more surface-localized energy deposition, gas cluster ion beam (GCIB) could preserve molecular structures during sputtering hence is a promising candidate for analyzing soft materials. Furthermore, by adjusting the energy per atom (E/n) of GCIB, experimental parameters can be optimized. In this work, as modeling system, trehalose thin films on silicon were profiled with 10-20 keV Ar1000-4000+ (E/n = 2.5-20 eV/atom). The spectrum during interlaced sputtering was obtained with Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) with pulsed C60+ as primary ion beam to construct the depth profile. It was found that with higher energy density (E/n ≥ 10 eV/atom), lower intensity of molecular ions was obtained due to fragmentation of the molecules and higher degree of damage. Furthermore, with lower energy density (E/n ≤ 4 eV/atom), suppressed intensity is also observed due to the lower sputtering rate that cannot remove damage sufficiently. Nevertheless, with medium energy density (E/n = 4-10 eV/atom), the introduction and removal of structural damage is balanced hence higher molecular ion intensity is retained. As a result, moderate E/n yield more realistic results. In addition to the E/n, temperature is another factor that influences depth profiles. At higher temperature, molecules become more mobile hence higher sputtering rate is expected and could mask the damage. However, radicals are also more mobile and induce more significant cross-linking that suppress the ion intensity. For lower temperature, radicals would be immobilized but the sputtering rate would also decrease hence it is more difficult to remove damage. In this work, depth profiles of trehalose thin films are conducted under -90 ℃, 25 ℃ and 90 ℃ using Arn+ with different energy density as sputter ions. The results show that enhanced intensity is observed at high temperature due to the enhanced sputter yield. However, no obvious differences are found in depth profiles conducted at low temperature as compared with those at room temperature.