Ultrathin Quasi-2D Amorphous Carbon Dielectric prepared from Solution Precursor for Nanoelectronics

Integrating crystalline 2D semiconductors and semimetals channels with 3D bulk amorphous metal oxides generally leads to poor interfaces with high concentrations of traps and scattering centers. Low-dimensional amorphous dielectrics could be ideal for 2D-material-based nanoelectronics with their intrinsic ultrathinness and capability to maintain a smooth and homogenous 2D surface. Here we report the wafer-scale synthesis of ultrathin quasi-2D amorphous carbon with thickness down to 1–2 atomic layers from solution-processable carbon-dot precursors directly on non-catalytic substrates. The prepared one layer of coalesced carbon dots is an atomically thin, mechanically strong amorphous film predominantly composted of sp² carbon with low surface dangling bond density, and their few-layer assemblies are robust nanodielectrics with low leakage current density and high breakdown field strength.<br/><br/>The thickness of the prepared ultrathin quasi-2D amorphous carbon film was characterized precisely based on high-resolution cross-sectional STEM images, giving a thickness of 0.41 ± 0.04 nm. After each deposition-coalescing cycle, the thickness of the film increased precisely by 0.4 nm, which is comparable to the interlayer spacing of graphite, as measured by both AFM and TEM.<br/><br/>With carbon-dot precursors covalently crosslinked together, the prepared ultrathin quasi-2D amorphous carbon film is mechanically robust enough to be transferred to other substrates as a complete and continuous membrane. The transferred quasi-2D amorphous carbon was firstly suspended as freestanding nanomembranes on TEM grid for imaging. The uniform contrast throughout in the low-magnification ADF-STEM image confirms that the film is macroscopically homogenous, and the SAED patterns show a characteristic diffuse halo, which verifies its amorphous nature.<br/><br/>Their mechanical properties were characterized by AFM nanoindentation performed on atomically thin nanomembranes suspended over 1.2 μm wide and 3 μm deep circular holes, giving an extracted high Young’s modulus of 400±100 GPa, which is comparable to that of crystalline graphene and h-BN, further verifies the homogeneity and continuity of the ultrathin quasi-2D amorphous carbon prepared from the assembly and coalescence of carbon dots with strong lateral connections, which are very likely of covalent nature.<br/><br/>The achieved macroscopic uniformity, atomic-level thickness control, and processability allow our quasi-2D amorphous carbon films as dielectric in nanoelectronics devices, where their unique structure and properties were exploited to enable improved device performances. When utilized as gate dielectrics in graphene and 2D metal chalcogenides transistors, compared to amorphous bulk metal oxides, the ultrathin amorphous carbon films with predominant sp² carbon content can form clean interfaces with graphene and 2D metal chalcogenides, which leads to enhanced carrier transport mobility and minimum hysteresis. Compared to polycrystalline 2D h-BN, they have better processability and their amorphous atomic structures lead to drastically lower leakage current density (&lt;10^-4 A/cm² with thickness down to three atomic layers of 1.6 nm) with higher dielectric strength (breakdown field above 20 MV/cm) for substantially reduced power consumption and improved device reliability.<br/><br/>The atomic-level thickness and the presence of large-size carbon rings inside the atomic structure of quasi-2D amorphous carbon also make its multilayered assemblies attractive for insulating ion-transport media in memristors. Their intrinsic ultrathinness and distinctive atomic structures composed of heterogeneous carbon rings offer predefined filament formation pathways across atomically thin films, leading to drastically enhanced switching uniformity, reduced energy consumption (&lt;20 fJ per operation), and faster operating speed (&lt;20 ns) as the switching media for electrochemical memristor, without sacrificing endurance and retention.