<i>In Situ</i> Observation of Initial Stage in Dielectric Growth and Deposition of Ultrahigh Nucleation Density Dielectric on Two-Dimensional Surfaces

Several proposed beyond-CMOS devices based on two-dimensional (2D) heterostructures require the deposition of thin dielectrics between 2D layers. However, the direct deposition of dielectrics on 2D materials is challenging due to their inert surface chemistry. To deposit high-quality, thin dielectrics on 2D materials, a flat lying titanyl phthalocyanine (TiOPc) monolayer, deposited via the molecular beam epitaxy, was employed to create a seed layer for atomic layer deposition (ALD) on 2D materials, and the initial stage of growth was probed using <i>in situ</i> STM. ALD pulses of trimethyl aluminum (TMA) and H<sub>2</sub>O resulted in the uniform deposition of AlO<sub><i>x</i></sub> on the TiOPc/HOPG. The uniformity of the dielectric is consistent with DFT calculations showing multiple reaction sites are available on the TiOPc molecule for reaction with TMA. Capacitors prepared with 50 cycles of AlO<sub><i>x</i></sub> on TiOPc/graphene display a capacitance greater than 1000 nF/cm<sup>2</sup>, and dual-gated devices have current densities of 10<sup>–7</sup>A/cm<sup>2</sup> with 40 cycles.