## 3 Results and Discussion
### X-ray Photoelectron Spectroscopy (XPS) Surface Characterization
#### 3.2.2 X-ray Photoelectron Spectroscopy (XPS) Mapping Analysis  
Once the XPS electron spectra were obtained for the chemical states of C 1s, O 1s, F 1s, and Si 2p, the 2D mapping analysis information could be reconstructed for a large area with FDTS SAM film patterns. As shown in Figure 8b-e, the reconstructed mapping image matched decently well with the secondary electron image in Figure 8a. Of note, the secondary electron image obtained with XPS was not as sharp as the counterpart image obtained with AES analysis due to the inherent difference in the category of spatial resolution detection. As shown in Figure 8b, the dark area was free of fluorine elements, while the green area was filled with FDTS SAM molecules. For the O 1s peak, the FDTS SAM film pattern and silicon dioxide pattern were barely distinguished from O 1s peaks  
Figure 6: X-ray photoelectron spectroscopy (XPS) spectra with high resolution of four chemical states in Point 1: C 1s, O 1s, Si 2p, F 1s, and atomic concentration (AC%) of four chemical states in one sampling area.  
Figure 7: X-ray photoelectron spectroscopy (XPS) spectra with high resolution of four chemical states in Point 2: C 1s, O 1s, Si 2p, F 1s, and atomic concentration (AC%) of four chemical states in one sampling area.  
shown in Figure 8c; even the amplitude of the O 1s peak was smaller on the FDTS SAM surface than that of the O 1s peak on a silicon surface. From the results of AES, we observed that there was more oxygen element and more organic contamination on the silicon dioxide surface than FDTS SAM surface, and these two kinds of areas could be differentiated clearly. For the Si 2p peak, the amplitude of Si 2p on the silicon dioxide surface was almost identical to that of Si 2p on the FDTS SAM film pattern. Compared with the AES detection results, we deduced that the detection sensitivity of XPS was higher than the sensitivity of AES. However, different chemical states could be combined for analysis of the FDTS SAM film pattern with XPS. As shown in Figure 8e, O 1s, F 1s, and Si 2p could be combined for mapping analysis since these are the major components of FDTS SAM. The white area was free of three chemical states, while the pink area was covered with these combined chemical states, which matched relatively well with the secondary electron image in Figure 8a.  
To investigate FDTS SAM film patterns in a three-dimensional (3D) manner, we also used an oxygen gas cluster ion beam (GCIB) in cycles to characterize the FDTS SAM film pattern layer by layer, which meant that GCIB etching and XPS detection were performed alternately (one layer etching, one layer XPS). First, GCIB was used to etch one thin layer; then, surfaces images were obtained with XPS for the top surface. The typical etch rate of GCIB is about 8.3 nm/min for a standard PMMA photoresist. One FDTS SAM region was selected for depth profiling. As shown in Figure 9a, after about 20s, the etching curves of C 1s and F 1s were crossed with the etching curve of Si 2p and O 1s, which meant that the silicon dioxide surface underneath FDTS SAM was exposed. The reason was that the silicon dioxide surface was a far more stable surface and provided silicon-related material constantly. The 2D XPS surface images could be incorporated together by overlaying to illustrate the dynamic process shown in Figure 9b, which demonstrates a thin FDTS SAM film patterned on the silicon dioxide layer.  
Figure 8: (a) Induced secondary electron image (SXI) of an area of 50 μm by 50 μm. Reconstructed mapping image of chemical states within the same area shown in (a). (b) O 1s, (c) F 1s, (d) Si 2p, and (e) O 1s+F 1s+Si 2p.