Novel phase Q-carbon thin films exhibit some intriguing features and have been explored for various potential applications. Herein, we report the growth of different Q-carbon structures (i.e., filaments, clusters, and microdots) by varying the laser energy density from 0.5 to 1.0 J/cm2 during pulsed laser annealing of amorphous diamond-like carbon films with different sp3-sp2 carbon compositions. These unique nano- and microstructures of Q-carbon demonstrate exceptionally stable electrochemical performance by cyclic voltammetry, galvanostatic charging-discharging, and electrochemical impedance spectroscopy for energy applications. The temperature-dependent magnetic studies (magnetization vs magnetic field and temperature) reveal the ferromagnetic nature of the Q-carbon microdots. The saturation magnetization and coercive field values decrease from 132 to 14 emu/cc and 155 to 92 Oe by increasing the temperature from 2 to 300 K, respectively. The electrochemical performances of Q-carbon filament, cluster, and microdot thin-film supercapacitors were investigated by two-electrode configurations, and the highest areal specific capacitance of ∼156 mF/cm2 was observed at a current density of 0.15 mA/cm2 in the Q-carbon microdot thin film. The Q-carbon microdot electrodes demonstrate an exceptional capacitance retention performance of ∼97.2% and Coulombic efficiency of ∼96.5% after 3000 cycles due to their expectational reversibility in the charging-discharging process. The kinetic feature of the ion diffusion associated with the charge storage property is also investigated, and small changes in equivalent series resistance of ∼9.5% and contact resistance of ∼9.1% confirm outstanding stability with active charge kinetics during the stability test. A high areal power density of ∼5.84 W/cm2 was obtained at an areal energy density of ∼0.058 W h/cm2 for the Q-carbon microdot structure. The theoretical quantum capacitance was obtained at ∼400 mF/cm2 by density functional theory calculation, which gives an idea about the overall capacitance value. The obtained areal specific capacitance, power density, and impressive long-term cyclic stability of Q-carbon thin-film microdot electrodes endorse substantial promise in high-performance supercapacitor applications.

Out of these, 12 atoms have the potential to switch hybridization between sp2 and sp3, forming dimers. Q-carbon: Ferromagnetic carbon was discovered in Carbon is capable of forming many allotropes (structurally different forms of the same element) due to its valency (tetravalent). Well-known forms of carbon include diamond and graphite. In recent decades, many more allotropes have been discovered and researched, including ball shapes such as buckminsterfullerene and sheets such as graphene. Larger-scale structures of carbon include nanotubes, nan Carb… The Laves graph or K4 crystal is a theoretically predicted three-dimensional crystalline metastable carbon structure in which each carbon atom is bonded to three others, at 120° angles (like graphite), but where the bond planes of adjacent layers lie at an angle of 70.5°, rather than coinciding. M-carbon: Monoclinic C-centered carbon is thought to have been first created in 1963 by compressing graphite at room temperature. Its structure was theorized in 2006, then in 2009 it was related to those experimental observations. Many structural candidates, including bct-carbon, were proposed to be equally compatible with experimental data available at the time, until in 2012 it was shown theoretically that this structure is kinetically the most likely to form from graphite. High-resolution data appeared shortly after, demonstrating that among all structure candidates only M-carbon is compatible with experiment. Metallic carbon: Theoretical studies have shown that there are regions in the phase diagram, at extremely high pressures, where carbon has metallic character. Laser shock experiments and theory indicate that above 600 GPa liquid carbon is metallic. Novamene: A combination of both hexagonal diamond and sp2 hexagons as in graphene. Phagraphene: Graphene-like allotrope with distorted Dirac cones. Prismane C8 is a theoretically predicted metastable carbon allotrope comprising an atomic cluster of eight carbon atoms, with the shape of an elongated triangular bipyramid—a six-atom triangular prism with two more atoms above and below its bases. Protomene: A hexagonal crystal structure with a fully relaxed primitive cell involving 48 atoms. Out of these, 12 atoms have the potential to switch hybridization between sp2 and sp3, forming dimers. Q-carbon: Ferromagnetic carbon was discovered in 2015. T-carbon: Every carbon atom in diamond is replaced with a carbon tetrahedron (hence 'T-carbon'). This was proposed by theorists in 1985. There is evidence that white dwarf stars have a core of crystallized carbon and oxygen nuclei. The largest of these found in the universe so far, BPM 37093, is located 50 light-years (4.7×1014 km) away in the constellation Centaurus. A news…