# 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  
When an AD process is carried out on graphene membrane, the underlying substrate can play an important role, because it determines the wettability degree of the graphene surface. This effect has been demonstrated by [PERSON] et al. [21] by performing ALD deposition of Al\({}_{2}\)O\({}_{3}\) on three different kinds of graphene materials: highly oriented pyrolitic graphite (HOPG), 1 L graphene grown by CVD on a copper substrate, and 1 L CVD graphene transferred on a SiO\({}_{2}\) substrate. Figure 4 shows the nucleation mode of the dielectric on the three systems. By performing a deposition process consisting of 100 cycles (in order to obtain a thickness lower than 10 nm) at a temperature of 80 \({}^{\circ}\)C, they found discontinuous coverage both on the HOPG (Figure 4a) and on 1 L graphene transferred on  
Figure 3: (**a**) Schematic of a top-gated graphene transistor with an ALD Al\({}_{2}\)O\({}_{3}\) gate dielectric. (**b**) Capacitance voltage (C-V\({}_{\text{TG}}\)) measurements performed by sweeping V\({}_{\text{TG}}\) from negative to positive values and back using a progressively increasing sweep range. (**c**) Dirac point position (left axis) as a function of the bias sweep range for the forward and backward sweep and the evaluated density N\({}_{\text{ot}}\) of the trapped negative charges by near-interface oxide traps (right axis). Images adapted with permission from [42], copyright American Chemical Society, 2017.  
a SiO\({}_{2}\) substrate (Figure 4b). Using the same ALD conditions, complete coverage on the entire area was instead observed in the case of 1 L graphene residing on the native metal substrate (Cu in this case) (Figure 4c). Uniform coverage was obtained even in the case of ultra-thin (\(\sim\)3 nm) deposited Al\({}_{2}\)O\({}_{3}\) films, as shown in Figure 4d. The authors also investigated the dependence of the Al\({}_{2}\)O\({}_{3}\) coverage on the ALD deposition temperature (in the range from 80 \({}^{\circ}\)C to 200 \({}^{\circ}\)C) for 1 L and multilayer graphene supported by Cu or Ni-Au metal substrates, as well as for HOPG and 1 L graphene transferred onto SiO\({}_{2}\) (Figure 5a). While a coverage percentage \(>\)90% was obtained on the metal-supported 1 L graphene in the considered temperature range, significantly lower coverage values were found for multilayers of graphene on the same metal substrates, with a similar temperature dependence to the case of HOPG and SiO\({}_{2}\)-supported 1 L graphene. Aside from Al\({}_{2}\)O\({}_{3}\), other high-\(\kappa\) dielectrics (such as HfO\({}_{2}\)) grown by ALD showed similar improved ALD growth on the 1 L graphene and Cu system. Figure 4: SEM images of 10 nm Al\({}_{2}\)O\({}_{3}\) grown by ALD on HOPG (**a**), on monolayer CVD-graphene transferred on SiO\({}_{2}\) (**b**), and on monolayer CVD-graphene on the native metal substrate (Cu) (**c**), and an image of 3 nm Al\({}_{2}\)O\({}_{3}\) on monolayer CVD-graphene on Cu (**d**). Images adapted with permission from [21], copyright the American Institute of Physics, 2012. Figure 5: (**a**) The coverage percentage of the Al\({}_{2}\)O\({}_{3}\) grown by ALD on different graphene materials as a function of the growth temperature. (**b**) Schematic of the precursor (H\({}_{2}\)O) adsorption mechanism in the cases of 1 L graphene/metal and HOPG or 1 L graphene/SiO\({}_{2}\) samples. Water molecules are more efficiently adsorbed on the surface of the 1 L graphene/metal system. Images adapted with permission from [21], copyright the American Institute of Physics, 2012. This strongly improved ALD growth was due to the partial transparency of 1 L graphene to the electrostatic fields generated by the polar traps at the graphene/metal interface [23; 24; 25; 63]. Such polar sites are a consequence of charge transfer phenomena between the graphene and metal due to their work function difference and also the crystal and bond distortion.