## 3 Results  
### Effects of Irradiation Time  
The LAB process was effective for the facile CaP coating of the Co-Cr alloy substrate. SEM observation revealed that the laser-irradiated surface of the substrate was roughened at the microscale within 5 min (Figure 2a). As the irradiation time was increased to 30 min, the surface roughness increased further and a rugged micrograin-like structure was formed on the laser-irradiated surface. The untreated and LAB-processed substrates showed SEM-EDX peaks due to Co, Cr and Mo, which are the main component elements of the Co-Cr alloy substrate (Figure 2b). In addition to these peaks from the substrate, Ca and P peaks appeared on the LAB-processed (5 min) substrate. The Ca and P peaks increased in intensity with respect to the Co, Cr and Mo peaks as the irradiation time was extended from 5 to 30 min. The SEM-EDX results indicate that a certain type of CaP compound was precipitated on the laser-irradiated surface of the substrate within 5 min by the LAB process, and the amount of CaP precipitate increased with the irradiation time up to 30 min.  
The LAB process provided area-specific CaP coating on the Co-Cr alloy substrate, as evidenced by a comparison of the irradiated and non-irradiated surfaces of the LAB-processed (30 min) substrate. After the LAB process for 30 min, CaP was precipitated on the laser-irradiated surface (inside the 5 mm diameter region) of the substrate (Figure 2a,b). In contrast, there were no apparent structural changes on the non-irradiated surface (outside the irradiated region) of the same substrate (Figure 2c). Neither Ca nor P was detected on the non-irradiated surface of this substrate by SEM-EDX measurements (data not shown). From these results, the area-specific coating capability of the LAB process using the Co-Cr alloy substrate was confirmed.  
The LAB process caused not only CaP precipitation but also surface oxidation of the Co\(-\)Cr alloy substrate. The crystalline structures of the untreated and LAB-processed (30 min) surfaces were examined by TF-XRD. As shown in Figure 3, diffraction peaks ascribed to cobalt chromite (CoCr\({}_{2}\)O\({}_{4}\)) and chromium oxide (Cr\({}_{2}\)O\({}_{3}\)) were detected after the LAB process for 30 min, which suggests the presence of these metal oxides on the LAB-processed substrate surface. It was not clear whether cobalt oxides (CoO and Co\({}_{3}\)O\({}_{4}\)) coexisted on the LAB-processed substrate surface from the TF-XRD pattern. Despite the presence of CaP on this substrate (see Figure 2b), peaks due to crystalline CaP were not clearly detected, but, instead, a broad halo at around 30\({}^{\circ}\) was observed, which can be ascribed to amorphous CaP (ACP) [20]. These results suggest that the CaP precipitates formed on the LAB-processed substrate were composed mainly of ACP.  
Figure 3: Thin-film X-ray diffraction (TF-XRD) patterns of the surfaces of the untreated and LAB-processed (30 min) Co\(-\)Cr alloy substrates.  
Figure 2: (**a**) Scanning electron microscopy (SEM) images and (**b**) energy-dispersive X-ray (EDX) spectra of the laser-irradiated surfaces of the untreated and LAB-processed (5, 10 and 30 min) Co\(-\)Cr alloy substrates. (**c**) SEM image of the non-irradiated surface of the LAB-processed (30 min) Co\(-\)Cr alloy substrate. The C peak in (**b**) is derived from the carbon coating that was applied to the substrate surface prior to the SEM-EDX analysis.