# 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 Monolayer CVD Graphene on the Native Metal Substrates
The electrostatic effect of polar traps causes enhanced adsorption of the water molecules (used as a co-reactant in the thermal ALD process) on the metal-supported 1 L graphene (Figure 5b, upper panel), resulting in improved nucleation of the high-\(\kappa\) dielectric and, consequently, of the surface coverage. Clearly, the transparency to electrostatic fields decreases with an increasing number of graphene layers, thus explaining the poor ALD coverage on multilayer graphene on the same metal substrates. Furthermore, the lack of these polar traps at the 1 L graphene/SiO\({}_{2}\) interface or in HOPG results in low adsorption of the precursor molecules (as illustrated in Figure 5b, lower panel). Using similar deposition parameters, [PERSON] et al. [53] also reported a high coverage level of Al\({}_{2}\)O\({}_{3}\) by ALD on 1 L graphene/Cu. In particular, they explored in detail the impact of the different deposition parameters (temperature, precursor pulse time, and number of ALD cycles) on the uniformity of the high-\(\kappa\) films. As an example, Figure 6 shows the evolution of Al\({}_{2}\)O\({}_{3}\) coverage on 1 L graphene/Cu (a) with an increasing cycle number from 12 cycles (b) to 100 cycles (c) at a temperature of 200 \({}^{\circ}\)C.  
The early-stage nucleation of high-\(\kappa\) dielectrics on graphene/Cu was studied by [PERSON] et al. [64] using scanning transmission electron microscopy (STEM) in the high-angle annular dark field (HAADF) mode. In particular, they investigated the nucleation mode of HfO\({}_{2}\) considering the initial 16 deposition cycles. They proposed Volmer-Weber nucleation mechanism, which involves the initial island formation and the following coalescence of the islands toward the closing of the layer. Furthermore, they found a different HfO\({}_{2}\) nucleation density between the 1 L and 2 L graphene regions. On the 1 L graphene, it was possible to observe by STEM the initial nuclei of the HfO\({}_{2}\) layer, whereas on the 2 L region, the nucleation phenomena were sparsely distributed. Such a difference further confirms the screened substrate effect in the 2 L regions. The electrical insulating properties of thin high-\(\kappa\) dielectrics deposited on metal-supported graphene can be studied with the Conductive Atomic Force Microscopy (C-AFM) technique [65; 66]. Figure 7a,b shows the surface morphologies of the as-grown 1 L graphene/Cu and after ALD of a 10-nm thick Al\({}_{2}\)O\({}_{3}\) layer at a temperature of 250 \({}^{\circ}\)C. The high roughness of the copper substrate made it difficult to evaluate the morphology of the deposited Al\({}_{2}\)O\({}_{3}\) and the coverage fraction. Figure 7c,d shows the corresponding current maps of 1 L graphene/Cu and of Al\({}_{2}\)O\({}_{3}\) (10 nm)/1 L graphene/Cu, acquired  
Figure 6: SEM and AFM images of the graphene/Cu system before (**a**) and after Al\({}_{2}\)O\({}_{3}\) growth by ALD at 200 \({}^{\circ}\)C with 12 (**b**) and 100 (**c**) TMA/H\({}_{2}\)O cycles. Images adapted with permission from [53], copyright the American Chemical Society, 2016.  
using the experimental configuration depicted in the insets of Figure 7e,f. As expected, the conductivity map of the bare graphene/Cu (Figure 7c) exhibited high current flow on the entire investigated area, even for a very low bias (V\({}_{\text{Tip}}\) = 10 mV) applied to the tip. Conversely, the current map acquired on the Al\({}_{2}\)O\({}_{3}\) deposited on the graphene/Cu showed optimal and uniform insulator behavior on the entire investigated surface up to an applied voltage of V\({}_{\text{Tip}}\) = 7 V. No spots associated with the local current flow could be observed, and this is an indication of uniform nucleation and ALD growth of the dielectric on the 1 L graphene/Cu system.