## 3 Results and Discussion  
### SEM and XPS Results  
In the neutron tube, the Ti film thickness on the target is generally larger than 1 \(\upmu\)m [18; 19]. This is because the mean free path of D\({}^{+}\) is about 0.75-1.03 \(\upmu\)m for energy of primary D\({}^{+}\), varying between 100 keV and 150 keV. In this work, the film coating thickness with untreated OFHC substrates was 2.20 \(\upmu\)m, as shown in Figure 1.  
Generally, surface topography could influence the SEY of the samples. Rougher surfaces may contribute to the decrease of SEY [20]. Thus, SEM topographies of laser treated and untreated OFHC samples before and after film depositions were investigated. The SEM micrographs with 30,000\(\times\), 10,000\(\times\) and 1000\(\times\) magnification of Ti-Zr-V-Hf film with SEM micrographs with cleaned laser processed OFHC substrates are shown in Figure 2. The SEM microstructures of these two kinds of films deposited on the untreated and cleaned laser treated OFHC substrates are analyzed, as shown in Figures 2 and 3. The surface of Ti and Ti-Zr-V-Hf films with cleaned laser processed OFHC substrates was obviously rougher than the ones with cleaned OFHC substrates. The specific surface area of cleaned OFHC was 1.74 m\({}^{2}\)/g. Moreover, the specific surface areas of the Ti and Ti-Zr-V-Hf coated cleaned laserprocessed OFHC substrates were 4.42 m\({}^{2}\)/g and 4.93 m\({}^{2}\)/g, respectively, and that of Ti and Ti-Zr-V-Hf coated cleaned OFHC substrates were 2.41 m\({}^{2}\)/g and 2.52 m\({}^{2}\)/g, respectively. Thus, the specific surface area results were basically in accord with the SEM results. The rougher surface contributed to the SEY decrease of Ti and Ti-Zr-V-Hf films with cleaned laser processed OFHC substrates in contrast to the ones with untreated substrates. The grain size of Ti-Zr-V-Hf film was smaller than the one of Ti film. The morphologies of Ti-Zr-V-Hf and Ti film coatings with cleaned laser processed OFHC substrates indicate the presence of sphere/island-like structures entrenched within uneven pores. For Ti film, this kind of sphere/island-like structures comprise tens of nanometer-sized, sphere-like grains with sizes ranging from 20 to 100 nm. Figures 2a and 3a reveal that the grains of Ti-Zr-V-Hf film are globular-like structures, while the ones of Ti film in Figure 2d are squamous-like structures. The difference in grain structures may be caused by the sputtered target atoms. When the view field is 27.7 \(\upmu\)m, the surface textures of Ti-Zr-V-Hf and Ti film coatings showed in Figure 2b,e are columnar-like structures. It can be speculated that the curves formed after laser processing play an essential role in microstructural evolution during film deposition. Rougher film coating surfaces were obtained with laser processed OFHC substrates, which contribute to the SEY reduction of Ti-Zr-V-Hf and Ti film coatings. The surface average roughnesses (\(R_{a}\)) of bare OFHC and laser treated OFHC were 0.189 \(\upmu\)m and 7.143 \(\upmu\)m, respectively. As shown in Table 1, the surface roughnesses of Ti film and Ti-Zr-V-Hf film on bare OFHC substrates were 0.110 \(\upmu\)m and 0.131 \(\upmu\)m, respectively. When the substrates were cleaned  
Figure 1: FIB-SEM (Focused Ion beam-scanning electron microscope) fracture morphology of Ti film coating with untreated oxygen-free high-conductivity copper (OFHC) substrate. Figure 2: The SEM (Scanning electron microscope) micrographs of the Ti–Zr–V–Hf and Ti film coatings with cleaned laser processed OFHC substrates. (**a–c**) are the SEM images of Ti–Zr–V–Hf film coatings. (**d–f**) are the SEM images of Ti film coatings. laser treated OFHC, the surface roughnesses of Ti film and Ti-Zr-V-Hf film were 6.842 \(\upmu\)m and 6.902 \(\upmu\)m, respectively. It can be concluded that the surface roughnesses of film-coated substrates decreased slightly compared to that of uncoated ones. Moreover, the surface roughnesses of Ti-Zr-V-Hf films were slightly higher than that of Ti films, but lower than that of the substrates.