Solution-Based Synthesis of Ultrathin Quasi-2D Amorphous Carbon for Nanoelectrics

In the last decade, the research on carbonaceous two-dimensional (2D) materials has drawn a lot of interest from the aspects of both fundamental studies and practical applications. The atomic-scale thickness and unique layered structure make the materials in this family exhibit several distinct optical and electrical properties from their bulk counterparts. Previous studies have mainly focused on the crystalline graphene material. Recently, 2D amorphous carbon is emerging to attract increasing attention since it has shown great potential for applications in various fields. However, synthesis of wafer-scale 2D amorphous carbon with thickness approaching the atomic limit is a substantial challenge. Current approaches to prepare 2D amorphous films rely on the adoption of plasma-enhanced chemical-vapor deposition (CVD) or pulsed laser deposition, where the power provided by the excited species in plasma, or the energetic pulsed laser can lead to the formation of continuous films but is insufficient to promote their crystallization. For both methods, the spatial uniformity and area coverage of the prepared 2D amorphous films could be limited, and especially the film thickness cannot be precisely controlled with atomic level of precision, in particular beyond the first monolayer when the reaction can no longer be catalyzed by the substrate. These limitations have so far prevented their adoption in functional application demonstrations which require films with large-area homogeneity and precisely tunable thickness from monolayer to multilayers, ideally synthesized directly on device substate. 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 noncatalytic substrates. The prepared one layer of coalesced carbon dots is an atomically thin, mechanically strong amorphous film predominantly composed 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. This synthesis strategy is distinct from vacuum depositions, with substantial advantages in enabling a solution-based process that is not only scalable but can be repeated in a layer-by-layer fashion for producing freestanding membranes from 1–2 atomic layers to multi-layered stacks with precisely controlled nanometer thickness. The achieved macroscopic uniformity, atomic-level thickness control, and wafer-scale processability allow engineered incorporation of prepared quasi-2D amorphous carbon films as dielectric in nanoelectronic devices, where their unique structure and properties were exploited to enable enhanced device performance and uniformity.