# Substrate-Driven Atomic Layer Deposition of High-\(\kappa\) Dielectrics on 2D Materials
## 3 Substrate-Driven ALD of High-\(\kappa\) Dielectrics on 2D Materials
### ALD on Epitaxial Graphene on SiC  
Epitaxial graphene (EG) grown by high-temperature (1600-2000 \({}^{\circ}\)C) thermal decomposition of the SiC(0001) surface typically consists of 1 L graphene on a large percentage of the surface area and 2 L or 3 L graphene regions especially localized at the step edges of the SiC surface terraces [67; 68]. ALD growth of high-\(\kappa\) dielectrics, such as Al\({}_{2}\)O\({}_{3}\) and HfO\({}_{2}\), on epitaxial graphene (EG) on SiC typically results in inhomogeneous coverage [69; 70], mainly on the 2 L or regions with few layers. However, by using highly homogeneous epitaxial graphene consisting of a monolayer for 98% of the surface and a bilayer for the remaining 2%, very uniform and pinhole-free Al\({}_{2}\)O\({}_{3}\) layers have been obtained by direct thermal  
Figure 7: AFM morphology of graphene/copper without **(a)** and with an Al\({}_{2}\)O\({}_{3}\) layer (**b**). Current maps (**c**,**d**) and local I-V curves (**e**,**f**) acquired on graphene/copper and Al\({}_{2}\)O\({}_{3}\)/graphene/copper.  
ALD at 250 \({}^{\circ}\)C without any seeding layer or pre-functionalization [26]. On the other hand, very inhomogeneous ALD coverage has been observed under identical ALD conditions on monolayer graphene transferred on a pristine SiC substrate. This demonstrates that the enhanced reactivity of the epitaxial graphene towards ALD precursors is not related to the SiC substrate but rather to the peculiar EG/SiC interface. Ab initio density functional theory (DFT) calculations demonstrated enhanced adsorption energy for the water molecules (ALD precursor) on 1 L graphene, depending on the n-type doping. Thus, the high doping induced by the buffer layer (between the EG and SiC substrate) on the EG was considered a possible origin of the excellent Al\({}_{2}\)O\({}_{3}\) nucleation. The effectiveness of ALD nucleation has been demonstrated following the evolution of the surface morphology, starting from the as-grown EG surface (Figure 8a) and in the early deposition cycles (10, 20, and 40 cycles) [27] as shown in Figure 8b-d. A coverage level of \(>\)80% was observed already after 10 deposition cycles and 100% after 40 deposition cycles (Figure 8e). The evolution of ALD nucleation during the first few cycles is schematically depicted in Figure 8f, which displays four consecutive steps with an increasing number of ALD cycles (from top to bottom): (1) the formation of the first nuclei on the 1 L EG surface, (2) the increase of pre-existent nuclei and the further nucleation on bare EG, (3) diffusion and coalescence of the islands, and (4) the formation of a complete layer of dielectrics on graphene.  
Figure 9 shows the morphology (a) and current map (b) acquired by C-AFM on a scratch of the Al\({}_{2}\)O\({}_{3}\), demonstrating continuous ultrathin layers (\(\sim\)2.4 nm) of dielectrics with optimal insulator behavior (c,d). The slight fluctuations of the injected current, observable by the current map, through the ultra-thin dielectric layer are related to local changes in the surface roughness, as can be deduced from the comparison between the height and current line profiles. The obtained results have an important impact on devices exploiting epitaxial graphene.