Cost-Effective Synthesis of Diamond Nano-/Microstructures from Amorphous and Graphitic Carbon Materials: Implications for Nanoelectronics

The synthesis of diamonds with different microstructures is important for various applications including nanoelectronic devices where diamonds can be implemented as heat spreaders. Here we report the synthesis of functional diamond microstructures and coatings, including diamond microfibers, microspheres, tubes, and large-area thin film, using amorphous and graphitic carbon precursors by hot filament chemical vapor deposition. The characteristics of microstructures depend upon initial carbon precursors and their laser annealing pretreatments. Low-cost and abundant carbon precursors act as diamond nucleation sites and accelerate diamond growth, while laser annealing can further promote the nucleation and growth of diamond. As a result, carbon microfibers are converted to diamond microfibers, while large diamond microspheres are formed from multipulse laser-annealed carbon microfibers. Both of the diamond structures consist of 5-fold twinned microcrystallites. Highly dense and phase-pure diamond films are observed using porous carbon seed, and individual diamond tubes with porous walls are obtained by using carbon nanotube hollow fibers. The electron backscatter diffraction analysis confirms the diamond cubic lattice structure, while sharp diamond peaks (1331–1333 cm–1) in Raman spectra demonstrate the excellent diamond quality of prepared diamond microstructures

Highly Stable Electrochemical Supercapacitor Performance of Self-Assembled Ferromagnetic Q‑Carbon

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