Paper AS-ThA3
On the Way to Optimal 3D Molecular Imaging with ToF-SIMS: A Comparison between C60 Single Beam and Bin/C60 Dual Beam Depth Profiling
Thursday, November 12, 2009, 2:40 pm, Room C2
| Session: |
Chemical State Depth Profiling |
| Presenter: |
S. Muramoto, University of Washington |
| Authors: |
J. Brison, University of Washington
S. Muramoto, University of Washington
D.G. Castner, University of Washington
|
| Correspondent: |
Click to Email |
Many ToF-SIMS 3D molecular images are acquired in the dual beam mode, where a high-energy beam (e.g., Ga+ or Bin+ at 25keV) used at low fluence for analysis is combined with a low-energy beam for sputtering/etching (e.g., C60n+ at 10 keV, Cs+ at 250 eV). Because its fluence is kept below the static limit, the effect of the high-energy analysis beam is sometimes neglected in the data interpretation, with the chemical damage entirely attributed to the etching beam. The influence of the analysis beam on the quality of ToF-SIMS depth profiles has been studied for inorganic samples [1], but no systematic study has been reported for organic samples. Because organic samples, and specifically biological samples and cells, are complex and fragile, a systematic study is necessary to understand, quantify, and model the influence of the ToF-SIMS parameters on the quality of ToF-SIMS 3D molecular images. These parameters include the species, fluence, energy, bombardment angle, and electrical charge of each primary ion beam.
In this paper, we have performed multiple depth profiles of a polymeric sample (100 nm thick tetraglyme on Si) in the single beam mode (C60 for analysis and etching) and compared them to those obtained in the dual beam mode (Bin+ for analysis and C60n+ for etching). For all depth profiles we kept the same parameters for the etching beam (i.e., C60 at 10 keV, 500 x 500 µm2, 1nA) and we varied the analysis conditions (i.e., species, area, energy, and fluence). We found that the analysis beam could significantly improve or degrade the quality of ToF-SIMS depth profiles, depending on the analysis beam parameters. At very low fluence (3 to 8% of the total primary ion fluence, depending on the sample and on the ion species), Bin+ improves the quality of the ToF-SIMS 3D images because of its higher lateral resolution. At higher Bin+ fluences, the high clean up efficiency of the C60 beam [2] can no longer remove the chemical damage induced by the analysis beam and the quality of ToF-SIMS data (molecular signals and interface width) degrades with the increasing Bin+fluence (or decreasing C60 fluence).
[1] T. Grehl, R. Mollers, E. Niehuis, Appl. Surf. Sci. 203-204 (2003) 277.
[2] A. Wucher, J. Cheng, N. Winograd, J. Phys. Chem. C 112 (2008) 16550.