## 3 Results and Discussion
### Characterization of Morphology and Chemical States of Polycrystalline Diamond Films
#### 3.1.4 Raman Analysis
As the grain size increases and the film becomes more transparent to the visible laser, the H atoms settle in the grain boundary, increasing the v1 and v2 signals. For large grain sizes, there are fewer available sites for the H to settle, and v1, v2, and sp\({}^{2}\) decrease, making the sp3 the dominant contribution. This sample was used for this analysis because the gold-coated silicon AFM tip radius (\(\sim\)50 nm) is much smaller than the grain size (400 nm) of the MCD film grown for 4 h, thus enabling the differentiation of the electrical conduction between grains and grain boundaries. Figure 8A shows the topography mapping from an area of 1 \(\times\) 1 \(\upmu\)m\({}^{2}\), in which enough grains were detected to observe the peaks and valleys. Figure 8B shows the electrical current mapping from the same area mapped in Figure 8A. The white areas observed in Figure 8B represent the maximum current flow (1 \(\times\) 10\({}^{-8}\) A), while the dark areas represent the minimum current flow (1 \(\times\) 10\({}^{-12}\) A) while applying a potential from \(-\)2 V to +2 V. A comparison of Figure 8A,B indicates that areas where the maximum current flow was measured correspond to those areas where the grain boundaries are. Figure 8C shows curves I-V obtained from the spots indicated in Figure 8A. For the spots numbered 4, 5, and 8, for which the AFM tip was located over the grain boundaries, an ohmic response was observed as compared to measurements on spots 1, 2, 3, 6, and 7, on top of grains, for which a minimum current flow was detected. These measurements indicate that the current flows mainly through grain boundaries. In order to confirm the hypothesis on electrical conduction through grain boundaries in the MCD films studied here, different voltages were applied on top of a diamond grain until an electronic current was observed. Figure 8D shows curves I-V for the different voltages applied on spot 3 (\(-\)1.5 to +1.5 and \(-\)3 to +3 V) for which the current was very small. On the other hand, when applying a voltage of around 5 to 5.5 V on spot 3, a small electronic current signal was detected, which increased rapidly at about +8 V, indicating that the electric field extending across the surface of the grains was reaching the grain boundaries to extract electrons much more efficiently. AFM-KPFM current measurements showed that the interior of the grains does not conduct electronic charges, but the grain boundaries do. The electrical current of the grain boundary has a value of 1 \(\times\) 10\({}^{-8}\) A, which is about four orders of magnitude smaller  
Figure 8: Conductive atomic force microscopy (CAFM) from MCD film grown for 4 h with 200 sccm H\({}_{2}\) sccm CH\({}_{4}\) gas flow (see Table 1). (**A**) AFM topography mapping from a 1 \(\times\) 1 \(\upmu\)m area. (**B**) Electrical current mapping. (**C**) Curves I-V from the spots indicated in (**A**). (**D**) Curves I-V for voltages in the range \(-\)10 V to +10 V, applied to spot 3 as shown in (**A**). than the current which would be expected if all the electrons in the dangling bond were free electrons.