# Paint Removal with Pulsed Laser: Theory Simulation and Mechanism Analysis
## 3 Results and Discussion
### XPS Analysis
#### 3.3.1 C1s XPS Analysis  
The curv--fitted XPS spectra of C1s obtained from the cleaned and untreated surfaces reveals four peaks (Figure 8). The components of C1s spectra for various binding energy values are listed in Table 3. The new components for C1s--C, C\({}_{96.8}\)O\({}_{3.2}\), C\({}_{93.1}\)O\({}_{6.9}\), (-CH\({}_{2}\)CH(C(O)OCH\({}_{3}\))-)\({}_{n}\), (-CH\({}_{2}\)CH(C(O)OH)-)\({}_{n}\), (-CH\({}_{2}\)CH(CH)(CH\({}_{3}\))CH\({}_{2}\)-)\({}_{n}\), (-CH\({}_{2}\)C(CH)(3)(C(O)OCH2 CH3)-)\({}_{n}\), and (-CH\({}_{2}\)C(CH)(3)(C(O)OC(CH\({}_{3}\))\({}_{3}\)-)\({}_{n}\)--were detected and analyzed. The presence of C, C\({}_{96.8}\)O\({}_{3.2}\), C\({}_{93.1}\)O\({}_{6.9}\) indicates that the high laser energy caused the paint to undergo carbonization and combustion during the cleaning process. The content of (-CH\({}_{2}\)CH(C(O)OCH\({}_{3}\))-)\({}_{n}\), (-CH\({}_{2}\)CH(C(O)OH)-)\({}_{n}\), (-CH\({}_{2}\)CHC(CH)\({}_{3}\))CH\({}_{2}\)-)\({}_{n}\) were found to be up to 49.72%, which indicates that a large number of polymer molecular chains were decomposed during the process, such as the breakage of C-C chemical bonds and the rearrangement of C-H chemical bonds. In addition, the presence of (-CH\({}_{2}\)C(CH\({}_{3}\))(C(O)OCH\({}_{2}\)CH\({}_{3}\))-)\({}_{n}\), (-CH\({}_{2}\)C(CH\({}_{3}\))(C(O)OC(CH\({}_{3}\))\({}_{3}\)-)\({}_{n}\) indicated that the O-H and C-H chemical bonds were broken and the C-O and C-C chemical bonds were rearranged [9].  
Compared with the spectra for the untreated surface, the C1s binding energy of the cleaned surface was found to have a shift, and an increase in binding energy. This was due to breakage of C-H chemical bonds in the polymer molecular chain during the laser cleaning process. The density of the electron clouds around the C atom also reduced, increasing the binding ability of the nucleus to the extranuclear electrons, subsequently resulting in an increase in binding energy.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Binding Energy/eV** & **Components** & **Area\%** \\ \hline \multirow{4}{*}{Untreated surface} & 283.97 & C-H, C-C & 2.18 \\  & 284.44 & -CH\({}_{2}\)-, C-C & 32.78 \\  & 284.83 & (-CH\({}_{2}\)C(CH\({}_{3}\))(C(O)OH)-)\({}_{n}\), & 63.02 \\  & 288.37 & (-CH\({}_{2}\)C(CH\({}_{3}\))(C(O)OCH\({}_{3}\))-)\({}_{n}\), & \\  & & O=C-N, C-N & \\ \hline \multirow{4}{*}{Cleaned surface} & 284.50 & C graphite (HOP), i-CH\({}_{3}\), C-H, & 27.41 \\  & 506.803\({}_{2}\), \({}_{93.1}\)O\({}_{6.9}\) & & 16.00 \\  & 284.73 & C graphite, C-C, C-H, C & 16.00 \\  & (-CH\({}_{2}\)CH(C(O)OCH\({}_{3}\))-)\({}_{n}\), & \\  & 285.22 & (-CH\({}_{2}\)CH(C(O)OH)-)\({}_{n}\), & 49.72 \\  & (-CH\({}_{2}\)CHC(CH\({}_{3}\))CH\({}_{2}\)-)\({}_{n}\) & \\  & (-C(CH\({}_{3}\))(C(O)-OCH\({}_{3}\))-CH\({}_{2}\)-)\({}_{n}\), & \\  & 288.72 & (-CH\({}_{2}\)C(CH\({}_{3}\))(C(O)OCH\({}_{3}\))-)\({}_{n}\), & 6.87 \\  & (-CH\({}_{2}\)C(CH\({}_{3}\))(C(O)OCH\({}_{2}\)CH\({}_{3}\))-)\({}_{n}\), & \\  & (-CH\({}_{2}\)C(CH\({}_{3}\))(C(O)OC(CH\({}_{3}\))\({}_{3}\)-)\({}_{n}\) & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Results of the peak separation of XPS C1s spectra, together with the binding energy and relative content of the C1s spectra.  
Figure 11: Curve-fitted Al2p, Ti2p XPS spectra of the cleaned surface.