NaCl is one of the simplest compounds and was thought to be wellunderstood, and yet, unexpected complexities related to it were uncovered at high pressure and in low-dimensional states. Here, exotic hexagonal NaCl thin films on the (110) diamond surface were crystallized in the experiment following a theoretical prediction based on ab initio evolutionary algorithm USPEX. State-of-the-art calculations and experiments showed the existence of a hexagonal NaCl thin film, which is due to the strong chemical interaction of the NaCl film with the diamond substrate.
Supercapacitors based on carbon nanomaterials
are attracting much
attention because of their high capacitance enabled by large specific
surface area. The introduction of heteroatoms such as N or O enhances
the specific capacitance of these materials. However, the mechanisms
that lead to the increase in the specific capacitance are not yet
well-studied. In this Letter, we demonstrate an effective method for
modification of the surface of carbon nanowalls (CNWs) using DC plasma
in atmospheres of O2, N2, and their mixture.
Processing in the plasma leads to the incorporation of ∼4 atom
% nitrogen and ∼10 atom % oxygen atoms. Electrochemical measurements
reveal that CNWs functionalized with oxygen groups are characterized
by higher capacitance. The specific capacitance for samples with oxygen
reaches 8.9 F cm–3 at a scan rate of 20 mV s–1. In contrast, the nitrogen-doped samples demonstrate
a specific capacitance of 4.4 F cm–3 at the same
scan rate. The mechanism of heteroatom incorporation into the carbon
lattice is explained using density functional theory calculations.
In our research, we analyzed the energy and water consumption in diamond mining and laboratory synthesis operations. We used publicly available reports issued by two market leaders, DeBeers and ALROSA, to estimate water and energy use per carat of a rough diamond. The efficiency of the two most popular synthesis technologies for artificial diamonds—High-Pressure-High-Temperature (HPHT) and Microwave-assisted Chemical Vapor Deposition (M-CVD)—was examined. We found that the modern HPHT presses, with open cooling circuits, consume about 36 kWh/ct when producing gem-quality and average-sized (near-) colorless diamonds. ALROSA and DeBeers use about 96 kWh/ct and 150 kWh/ct, respectively, including all energy required to mine. Energy consumption of M-CVD processes can be different and depends on technological conditions. Our M-CVD machine is the least energy-efficient, requiring about 215 kWh/ct in the single-crystal regime, using 2.45-GHz magnetron for the support synthesis. The M-CVD methods of individual synthetic companies IIa Technology and Ekati Mine are different from our results and equal 77 and 143 kWh/ct, respectively. Water consumption for the HPHT and M-CVD methods was insignificant: approximately zero and 0.002 m3/ct, respectively, and below 0.077 m3/ct for ALROSA-mined diamonds. This study touches upon the impact of the diamond production methods used on the carbon footprint.
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