Fig. 1: Wafer-scale ultrathin quasi-2D amorphous carbon prepared by the assembly and coalescence of coal-derived carbon dots.
From: Ultrathin quasi-2D amorphous carbon dielectric prepared from solution precursor for nanoelectronics
a Optical image of an atomically thin quasi-2D amorphous carbon film deposited on a 3-in. diameter SiO2/Si wafer with the normalized total Raman intensity for the D and G bands mapped over 96 points. The color code illustrates a Raman intensity range from 75% to 130% of the average with standard deviation of 10%. b Raman spectra of the carbon-dot assembly as deposited (black dotted line) and after coalescence (red solid line). Si* marks the second-order Raman scattering by optical phonons of silicon. c High-resolution C1s XPS spectrum of the ultrathin quasi-2D amorphous carbon formed on SiO2/Si substrate (black circles), with the fitted curve (brown solid line) showing a single carbon sp2 peak at 284.0 eV, while the film before annealing (blue dashed line) contains a substantial amount of sp3 carbon with a higher binding energy of 284.8 eV. XPS spectrum of crystalline graphene was measured as internal control to mark the position of sp2 carbon peak (red dashed line). Green solid line is the baseline subtracted before fitting. Reconstructed cross-sectional STEM image (part d) and associated contrast intensity profile (part e) of an ultrathin quasi-2D amorphous carbon film deposited on a c-cut sapphire wafer with a Pt protective layer on top. Blue and orange dashed lines serve as visual guide to mark the atomic planes in Pt and sapphire, respectively. Dark red dashed lines mark the material interfaces. f AFM image of ultrathin quasi-2D amorphous carbon film patterned to generate an edge by photolithography and oxygen reactive-ion etching (RIE). Inset: The averaged line cut showing a step height ~0.8 nm. g Film thickness as a function of the number of layers deposited. The red solid line is a linear fitting to the data. Inset: cross-sectional TEM micrograph showing the atomic planes. h Optical image of an ultrathin quasi-2D amorphous carbon membrane transferred to a substrate of Au (200 nm)/SiO2 (90 nm)/Si, after immersing in Au etchant. The area not covered by the transferred film appears as dark blue, while the intact Au region corresponds to the transferred quasi-2D amorphous carbon film. Inset: a magnified view showing an etched pit corresponding to a pin-hole defect in the transferred atomically thin nanomembrane.
