Laser-Induced Phosphorus-Doped Conductive Layer Formation on Single-Crystal Diamond Surfaces

Electric-Field Emission Mechanism in Q-Carbon Field Emitters

In this paper, we report the excellent field emission properties of Q-carbon and analyze its field emission characteristics through structural, morphological, and electronic property correlations, supported by density functional theory (DFT) simulation studies. The Q-carbon field emitters show impressive and stable field emission properties, such as a low turn-on electric field of ∼2.38 V/μm, a high emission current density of ∼33 μA/cm², and a critical field of ∼2.44 V/μm for the transition from a linear region to the saturation region in the F-N plot. The outstanding field emission properties of Q-carbon are attributed to (i) a unique sp²/sp³ mixture in Q-carbon, (ii) sp²-bonded highly conductive amorphous carbon-rich channels inside the Q-carbon cluster, (iii) a large local field enhancement due to the local geometry and microstructure of Q-carbon, and (iv) the presence of sp²-bonded amorphous carbon regions in the composite film. The temperature-dependent field emission properties, such as extreme sensitivity and an enhancement in the emission current density with temperature, can be explained by the local density of states near the Fermi level and the excellent thermal stability of the Q-carbon field emitters. From DFT simulation studies, the computed work function and the field-enhancement factor were determined to be 3.62 eV and ∼2300, respectively, which explains the excellent field emission characteristics of Q-carbon. The obtained field emission properties, in most cases, were superior to those from other carbon/diamond-based field emitters, which will open new frontiers in field emission-based electronic applications.

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.

UV Light Irradiation Effects in P-Doped Diamonds: Total Content Determination of Phosphorus Donors

Upon the UV light irradiation of single-crystal diamonds doped with phosphorus, several effects have been observed. The integral intensity of phosphorus lines in FTIR absorption spectra under UV radiation was increased. A saturation effect depending on the power of the laser radiation was demonstrated. Narrowing of the phosphorus lines, as well as the redistribution of the intensities in their doublets caused by the Jahn-Teller distortion of the donor ground state, was observed. It was found that these effects are associated with the decompensation of the phosphorus donors. An easy, fast, sensitive, and nondestructive, fully optical method for the determination of the total phosphorus donor's concentration in semiconducting diamonds, as well as its compensation ratio, was proposed.

Correlated Electrical Conductivities to Chemical Configurations of Nitrogenated Nanocrystalline Diamond Films

Diamond is one of the fascinating films appropriate for optoelectronic applications due to its wide bandgap (5.45 eV), high thermal conductivity (3320 W m−1·K−1), and strong chemical stability. In this report, we synthesized a type of diamond film called nanocrystalline diamond (NCD) by employing a physical vapor deposition method. The synthesis process was performed in different ratios of nitrogen and hydrogen mixed gas atmospheres to form nitrogen-doped (n-type) NCD films. A high-resolution scanning electron microscope confirmed the nature of the deposited films to contain diamond nanograins embedded into the amorphous carbon matrix. Sensitive spectroscopic investigations, including X-ray photoemission (XPS) and near-edge X-ray absorption fine structure (NEXAFS), were performed using a synchrotron beam. XPS spectra indicated that the nitrogen content in the film increased with the inflow ratio of nitrogen and hydrogen gas (IN/H). NEXAFS spectra revealed that the σ*C–C peak weakened, accompanied by a π*C=N peak strengthened with nitrogen doping. This structural modification after nitrogen doping was found to generate unpaired electrons with the formation of C–N and C=N bonding in grain boundaries (GBs). The measured electrical conductivity increased with nitrogen content, which confirms the suggestion of structural investigations that nitrogen-doping generated free electrons at the GBs of the NCD films.