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