Q‑Carbon as a Corrosion-Resistant Coating

A newly discovered quenched form of carbon, widely known as Q-carbon, thin films are synthesized by the direct conversion of the amorphous carbon layer using the nanosecond pulsed laser annealing technique, and its corrosion-resistant properties, that is, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy technique, are investigated. The unique microstructure and the existence of defects (sp2 content) in sp3-rich Q-carbon are highly desirable for efficient corrosion-resistant performance. The sp3 percentage of the as-grown Q-carbon is measured to be ∼80.5% from the D and G peaks of the Raman and C-1S X-ray photoelectron spectrum. The anti-corrosion properties with inhibition durability of Q-carbon thin films are systematically investigated in various concentrations of Na2SO4 solutions, and the corrosion potential, corrosion current, and corrosion rate of Q-carbon are determined to be −253 V, 30.1 × 10–5 A/cm2, and 0.00528, respectively, for 1 M Na2SO4 solution. Both series and contact resistance decrease from 5498.6 and 821.1 Ω to 698.8 and 124.3 Ω with an increase of Na2SO4 concentration from 0.1 to 1 M, respectively. The small shift of PDP curves toward more negative potential, the shrinkage of the radius of semicircular arcs in the Nyquist plot (Z″ vs Z′), and negligible loss in corrosion resistance (∼78%) are observed for Q-carbon thin film at the immersion time up to 48 h. The unique sp2–sp3 ratio, shorter bond length, compact atomic arrangement, and minimum porosity, along with the high adhesion strength, due to the ultrafast solid–liquid–solid growth route, of Q-carbon thin film on the substrate signify it as a better alternative compared to the existing corrosion-resistant materials

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

Electrochemical Performance of Carbon-Nanotube-Supported Tubular Diamond

Tubular diamond structures with high surface areas are very desirable for various potential electrochemical applications. Here, we report a simple and cost-effective two-step method for the synthesis of a diamond tube with a porous tube wall from carbon nanotube (CNT) hollow fibers via pulsed laser annealing (PLA) and hot filament chemical vapor deposition (HFCVD). These diamond tubes exhibit high double-layer capacitances of 11.65–18.07 mF cm–2, three orders of magnitudes higher than the equivalent flat diamond films. Scanning electron microscopy (SEM) shows the presence of diamond microspheres composed of both micro- and nanocrystallites on the entire tube after 3–6 h HFCVD. The number density of the diamond, the average size of diamond microspheres, and the nanocrystallite content on the microspheres can be controlled by HFCVD time and laser annealing parameters of CNT hollow fibers. The electron back-scattered diffraction analysis shows the crystallographic orientation of the prepared diamond along the ⟨101⟩ plane. Raman spectra show a sharp characteristic/signature diamond peak at ∼1332 cm–1, corresponding to an unstrained high-quality diamond. The magnificent electrochemical performances of these CNT-supported diamond tubes are explained by their significantly enhanced electroactive surface area and the presence of a very small fraction (0.73–1.03%) of sp2 carbon in diamond tubes for electron conduction. The density of states, band gaps, and outmost quantum capacitance (∼200 μF/cm2 at −2.2 V electrode potential) of the tubular diamond are calculated by the density functional theory calculations, which support our experimental findings and suggest its future potentiality as an efficient supercapacitor electrode material

Low-Temperature Spin-Canted Magnetism and Bipolaron Freezing Electrical Transition in Potential Electron Field Emitter NdNiO₃

The orthorhombic nanostructured NdNiO3 is prepared by the sol–gel auto-combustion method, and its temperature-dependent magnetic and electrical transport properties are studied. The electric field emission with density functional theory and current voltage characteristics are also investigated at room temperature. The low-temperature magnetic measurement (magnetization with field and temperature) shows that NdNiO3 undergoes a magnetic phase transition (TN) near 176 K from paramagnetic to spin-canted antiferromagnetic state. The temperature-dependent magnetic susceptibility (χ) reinforced the signature of magnetic phase transition, and it is fitted by the modified Curie–Weiss law. A metal to insulator (MIT) phase transition (∼178 K) is observed above TN from temperature- and frequency-dependent conductivity measurement. It originates due to higher distortion of NiO6 octahedra and bandwidth constriction of NdNiO3 nanostructured compound. The variation of the frequency exponent (n) with temperature illustrates the continuous-time random walk conduction model with bipolaron condensation near MIT and the non-overlapping small polaron tunneling model above room temperature. The spin-resolved density of states calculation exhibits the room temperature paramagnetic phase and metallic nature and helps us to calculate local work function (Φ) ∼5.44 eV. Low turn-on field at 1 μA/cm2 ∼10.5 V/μm and high field emission current density 203 μA/cm2 at 21 V/μm are observed for layered NdNiO3 with a field enhancement factor (β) ∼1230, which promotes NdNiO3 as an efficient field emitter. The current–voltage characteristics of NdNiO3/p-Si heterostructures are also explored for future technological applications

Tubular Diamond as an Efficient Electron Field Emitter

Herein, we present a straightforward and cost-effective procedure for producing conductive diamond tubes on the surface of porous carbon nanotube hollow fibers using successive 10-pulsed laser annealing shots and 6 h of hot filament chemical vapor deposition techniques. Room-temperature Raman and X-ray diffraction spectra reveal the signature T2g peaks near 1332.4 cm–1 and 111 planes of diamonds near 43.9°, respectively. A low turn-on field (ETO) ∼1.85 V/μm@1 μA/cm2 and a threshold field (ETH) ∼2.54 V/μm@10 μA/cm2 were observed for the tubular diamond structures. The field enhancement factor (β) was calculated at 3594 and highly stable field emission current stability was observed over a long period of 4 h. For the first time, a good insight into the field emission results of the diamond is established with the structural, electronic properties, and the work function (φ) ∼4.84 eV analysis conducted by the density functional theory simulation. Finite electronic states at the Fermi level are observed beyond a band gap, and it demonstrates the wide-band gap (4.4 eV) semiconducting nature of the diamond. The Bader charge analysis and maximum entropy method pattern revealed the negative electron affinity of the diamond, and it is responsible for the emission of electrons from the conduction band of the diamond. Besides, the accumulation of charge carriers, which contributes to the electric field emission, takes place due to the weak π bonds of carbon atoms. The low turn-on field, the high field enhancement factor, and the good field emission current stability of tubular diamond offer great prospects for future efficient and low-cost field emission devices

Structural Metamorphosis and Band Dislocation of Trirutile NiTa₂O₆ under Compression

Trirutile NiTa2O6 has been studied under high pressure by in situ Raman and angle-dispersive synchrotron X-ray diffraction techniques. It undergoes a new quenchable phase at high pressures above 11.8 GPa accompanied by softening of the internal modes ν1(A1g), ν1(Eg), and ν6(Eg), and it is denser by 15% compared with its ambient phase. Various Raman-active modes of NiTa2O6 diminished at high pressures due to the distortion of edge-sharing TaO6 octahedra, which was further confirmed by X-ray diffraction and density functional theory results. The equation of state has been determined using the second-order Birch–Murnaghan equation, and the obtained bulk modulus is 199(4) GPa. The pressure and volume dependence of optical lattice vibrational frequencies and their corresponding Grüneisen parameters are calculated, indicating the inconsistency of the trirutile structure at high pressures, which was accompanied by the strong deformation of TaO6 octahedra. Pressure-induced structural metamorphosis and soft-mode-driven displacive transition related to the mechanical instability of NiTa2O6 are examined and decompression results recommend the transition is irreversible

Growth Optimization, Optical, and Dielectric Properties of Heteroepitaxially Grown Ultrawide-Bandgap ZnGa2O4 (111) Thin Film

Figure S1 Figure S

Improved Electrochemical Performance in an Exfoliated Tetracyanonickelate-Based Metal–Organic Framework

Tetracyanonickelate (TCN)-based metal–organic frameworks (MOFs) show great potential in electrochemical applications such as supercapacitors due to their layered morphology and tunable structure. This study reports on improved electrochemical performance of exfoliated manganese tetracyanonickelate (Mn-TCN) nanosheets produced by the heat-assisted liquid-phase exfoliation (LPE) technique. The structural change was confirmed by the Raman frequency shift of the CN band from 2177 to 2182 cm–1 and increased band gap from 3.15 to 4.33 eV in the exfoliated phase. Statistical distribution obtained from atomic force microscopy (AFM) shows that 50% of the nanosheets are single-to-four-layered and have an average lateral size of ∼240 nm2 and thickness of ∼1.2–4.8 nm. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) patterns suggest that the material maintains its crystallinity after exfoliation. It exhibits an almost 6-fold improvement in specific capacitance (from 13.0 to 72.5 F g–1) measured at a scan rate of 5 mV s–1 in 1 M KOH solution. Galvanostatic charge–discharge (GCD) measurement shows a capacity enhancement from ∼18 F g–1 in the bulk phase to ∼45 F g–1 in the exfoliated phase at a current density of 1 A g–1. Bulk crystals exhibit an increasing trend of capacitance retention by ∼125% over 1000 charge–discharge cycles attributed to electrochemical exfoliation. Electrochemical impedance spectroscopy (EIS) demonstrates a 5-fold reduction in the total equivalent series resistance (ESR) from 4864 Ω (bulk) to 1089 Ω (exfoliated). The enhanced storage capacity in the exfoliated phase results from the combined effect of the electrochemical double-layer charge storage mechanism at the nanosheet–electrolyte interface and the Faradic process characteristic of the pseudocapacitive charge storage behavior