Fig. 3: Physical properties of quasi-2D amorphous carbon prepared from carbon-dot precursors.

a AFM scan of an ultrathin (1–2 atomic-layer thick) quasi-2D amorphous carbon nanomembrane suspended over a 1.25 μm diameter well. b Height profiles from multiple indentations with the force applied increasing from 2 to 5, 10, 15, and 20 nN from top to bottom, colored from green to red. Force-displacement curves (c, symbols: experimental data; dashed lines: fitting to the linear elastic deformation expression) measured from multiple (five, each represented with a different color) suspended ultrathin membranes, and their extracted 2D Young’s moduli (d, orange represents each sample and green represents the average; error bars represent uncertainties of fitted parameters). e False-colored SEM image of an array of two-terminal devices with 50 μm channel width (W) to measure the lateral resistance of quasi-2D amorphous carbon. Inset: SEM micrograph showing the smallest L_ch down to 35 nm. f Current (I)-voltage (V) curves measured for two-terminal devices shown in (e) with L_ch of 35 nm (black), 65 nm (red), and 85 nm (blue), respectively. g Current density flowing vertically across triple-layered quasi-2D amorphous carbon films (1.2–1.6 nm thick) sandwiched between 5 μm-wide graphene bottom electrodes and 5 μm-wide metal top electrodes. Results from ten devices biased with both polarities were plotted together with each represented by a different color. Inset: SEM micrograph of the graphene/quasi-2D amorphous carbon trilayer/metal capacitor where red dashed lines serve as visual guide to mark the boundary of the graphene bottom electrode. Comparison of the leakage current density (h) and the dielectric breakdown field (i) of quasi-2D amorphous carbon films and h-BN prepared with both mechanical exfoliation and CVD. The leakage current through the exfoliated h-BN and the associated breakdown field in ref. ²¹ and ref. ²² were determined in a single grain using the conductive-AFM with a circular tip-sample contact area with diameter of merely 25 ± 10 nm and 2–4 nm, respectively. j Capacitance-voltage characteristics of a disk-shaped 20 μm-diameter metal/quasi-2D amorphous carbon film (10 sequentially deposited layers, ~4.5 nm thick)/silicon capacitor, measured under different frequencies from 200 kHz (blue), 500 kHz (red), to 1 MHz (black). Arrows mark the voltage sweeping directions during the measurement. k Frequency dependence of ε_r of quasi-2D amorphous carbon film evaluated between 10⁴ and 10⁶ Hz. l Tauc plot with the extrapolation of the linear region (red dashed line) to determine the effective optical bandgap (E_g) of the ultrathin quasi-2D amorphous carbon.