Diamond with nitrogen: states, control, and applications

The burgeoning multi-field applications of diamond concurrently bring up a foremost consideration associated with nitrogen. Ubiquitous nitrogen in both natural and artificial diamond in most cases as disruptive impurity is undesirable for diamond material properties, eg deterioration in electrical performance. However, the feat of this most common element-nitrogen, can change diamond growth evolution, endow diamond fancy colors and even give quantum technology a solid boost. This perspective reviews the understanding and progress of nitrogen in diamond including natural occurring gemstones and their synthetic counterparts formed by high temperature high pressure (HPHT) and chemical vapor deposition (CVD) methods. The review paper covers a variety of topics ranging from the basis of physical state of nitrogen and its related defects as well as the resulting effects in diamond (including nitrogen termination on diamond surface), to precise control of nitrogen incorporation associated with selective post-treatments and finally to the practical utilization. Among the multitudinous potential nitrogen related centers, the nitrogen-vacancy (NV) defects in diamond have attracted particular interest and are still ceaselessly drawing extensive attentions for quantum frontiers advance.</p

Antibacterial properties of polycrystalline diamond films

Electronic and mechanical properties, and their biocompatibility, make diamond-based materials promising biomedical applications. The cost required to produce high quality single crystalline diamond films is still a hurdle to prevent them from commercial applications, but the emergence of polycrystalline diamond (PCD) films grown by chemical vapour deposition (CVD) method has provided an affordable strategy. PCD films grown on silicon wafer have been used throughout and were fully characterised by SEM, XPS, Raman spectroscopy and FTIR. The samples contain nearly pure carbon, with impurities originated from the CVD growth and the silicon etching process. Raman spectroscopy revealed it contained tetrahedral amorphous carbon with small tensile stress. The sp2 carbon content, comprised between 16.1 and 18.8%, is attributed to the diamond grain boundaries and iron-catalysed graphitisation. Antibacterial properties of PCD films were performed with two model bacteria, i.e. Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) using direct contact and shaking flask methods. The samples showed strong bacteriostatic properties against S. aureus and E. coli with the direct contact method and no influence on planktonic bacterial growth. These results suggest that the bacteriostatic mechanism of PCD films is linked to their surface functional groups (carbon radicals and –NH2 and –COOH groups) and that no diffusible molecules or components were involved

Rational Design of CoOOH/α-Fe₂O₃/SnO₂ for Boosted Photoelectrochemical Water Oxidation: The Roles of Underneath SnO₂ and Surface CoOOH

Hematite (α-Fe2O3) photoanode is a promising candidate for efficient PEC solar energy conversion. However, the serious charge recombination together with the sluggish water oxidation kinetics of α-Fe2O3 still restricts its practical application in renewable energy systems. In this work, a CoOOH/α-Fe2O3/SnO2 photoanode was fabricated, in which the ultrathin SnO2 underlayer is deposited on the fluorine-doped tin oxide (FTO) substrate, α-Fe2O3 nanorod array is the absorber layer, and CoOOH nanosheet is the surface modifier, respectively. The resulting CoOOH/α-Fe2O3/SnO2 exhibited excellent PEC water splitting with a high photocurrent density of 2.05 mA cm–2 at 1.23 V vs RHE in the alkaline electrolyte, which is ca. 3.25 times that of bare α-Fe2O3. PEC characterizations demonstrated that SnO2 not only could block hole transport from α-Fe2O3 to FTO substrate but also could efficiently enhance the light-harvesting property and reduce the surface states by controlling the growth process of α-Fe2O3, while the CoOOH overlayer as cocatalysts could rapidly extract the photogenerated holes and provide catalytic active sites for water oxidation. Benefiting from the synergistic effects of SnO2 and CoOOH, the efficiency of the charge recombination and the overpotential for water oxidation of α-Fe2O3 are obviously decreased, resulting in the boosted PEC efficiency for water oxidation. The rational design and simple fabrication strategy display great potentials to be used for other PEC systems with excellent efficiency

Doomed Couple of Diamond with Terahertz Frequency: Hyperfine Quality Discrimination and Complex Dielectric Responses of Diamond in the Terahertz Waveband

The technology age of terahertz (THz) frequency is coming with tremendous features and astonishing applications in various fields of science. Using THz time domain spectroscopy, we demonstrate experimentally, for the first time, the fingerprint absorption peaks and the complex dielectric response trends in 0.1-3 THz frequency waveband, on intentionally synthesized and processed chemical vapour deposition (CVD) polycrystalline and single-crystal diamond films with systematic quality-difference. The two absorption signatures within the 0.1-3 THz frequency band, in which the atomic vibration is materials-independent, are attributed to the sp2 phonon vibration modes of as-grown graphitic phases and/or defects. Regarding the complex dielectric responses of diamond in THz waveband, scattering effect resulting from the extended grain boundaries associated with concomitant pores (even gaps) (and/or extended crystal cleavage faults associated with amorphous carbon), as well as intrinsic lattice absorption resulting from increased sp2 impurities, have been taken into account. Especially the defect size comparable with the wavelength is also found to play a significant effect on the loss at higher-frequency electromagnetic wave. These findings are expected to promote not only ultra-sensitive quality diagnose for diamond but verification of an ideal transmission material for THz waveband applications

Ensemble cell-wide kinetic modeling of anaerobic organisms to support fuels and chemicals production

Thermophilic microorganisms have garnered the interest of the bioprocess industry due to their high temperature optimal growth conditions. In particular, two phylogenetically close organisms Clostridium thermocellum and Moorella thermoacetica have been focused on in the recent years. While C. thermocellum can metabolize cellulose into biofuels such as ethanol, M. thermoacetica can metabolize syn gas using the unique Wood-Ljungdahl pathway. Despite their increasing role as bio-production platforms, they remain poorly characterized with significant uncertainty in their metabolic repertoire. To this end, we develop cell-wide dynamic models of transcription and metabolism of these two organisms using the concept of Ensemble Modeling (EM) which requires curated genome-scale metabolic (GSM) models of the organisms as its foundation. The second generation GSM for C. thermocellum (iCth446) has been developed, which contains 446 genes and includes 598 metabolites and 637 reactions, along with gene-protein-reaction associations. The GSM is devoid of thermodynamically infeasible cycles and contains elementally and charge-balanced reactions. The GSM was simulated with down-regulation of phosphoenolpyruvate carboxykinase, or down-regulation of malic enzyme and malate dehydrogenase knocked out along with exogenous pyruvate kinase knocked in and lactate dehydrogenase knocked out. The simulations showed higher yield of ethanol production compared to wild-type conditions as observed experimentally. Likewise, the GSM results showed that only lactate hydrogenase knock out did not have any effect on growth rate as observed experimentally. The GSM model for M. thermoacetica has been constructed using a semi-automatic pipeline in the SEED database. This model contains 517 genes and 812 reactions, supplemented with 57 exchange reactions including biomass demand reaction. The GSM will be curated, gap-filled, and incorporated with the estimated growth and non-growth associated ATP (GAM & NGAM) requirements. Steady-state 13C-labelling experiments will be used to validate flux distribution predicted by the GSM, followed by instationary 13Clabeling experiments to identify the robustness of the GSM under various growth conditions with different substrates in distinct growth phases. Ultimately, these experiments will resolve the long-standing debate surrounding the hypothetical incomplete TCA cycle of M. thermoacetica. The constructed stoichiometry representations will subsequently serve as the scaffold for building kinetic model using the EM approach for C. thermocellum and M. thermoacetica. The EM procedure will allow us to integrate substrate-level as well as transcriptional level regulatory interactions into the framework. The constructed kinetic models will be ultimately used to identify the effect of transcription factors as well as enzyme level manipulations on metabolic fluxes leading to explore key metabolic derivers that underpin various biofuels production

Smoothing of single crystal diamond by high-speed three-dimensional dynamic friction polishing: Optimization and surface bonds evolution mechanism

The high-speed three-dimensional movement dynamic friction polishing (3DM-DFP) has been recognized as an efficient approach for ultra-smoothing single crystal diamond (SCD) surface. Continuing from the previous works focusing on the subsurface cleavage of diamond after 3DM-DFP, process optimization and surface reaction evolution mechanism as a fundamental building block is investigated, for the first time, for comprehensively understanding this fast-smoothing manner. By systematically adjusting the controlling factor, stronger load (0.3 MPa) and appropriate duration (0.5 h) as well as moderate sliding speed (in the range of 30 to 45 m s−1) is found to be able to obtain the smooth surface of SCD without uncontacted traces or break-surface cleavage. Subtle residual clues on SCD surface as a function of progressive DFP procedure indicate that Fe catalytic oxidation mainly produce Fe2O3 and partial intermediate oxides Fe1-yO. Meanwhile, the activated oxygen inserts sp3 Csingle bondC bonds could form Csingle bondO or Cdouble bondO and C-O-V (vacancy) at existing reactive surface sites. The (100) favorable Cdouble bondO bonds can be rebuilt if (100) surface is reformed, although the Csingle bondO bonds associated with non-(100) rough surface would replace them during DFP procedure. The formed Csingle bondOsingle bondC and concomitant C-O-V as well as the oxidized graphite give rise to the increase of Csingle bondO proportion, and finally the covered defective graphitic phase has an approximate Csingle bondO/Cdouble bondO ratio of 1.25. All these are endowed potential value for future upgrading of DFP technique for diamond surface smoothing.</div

Morphology-dependent antibacterial properties of diamond coatings

Microorganisms promoted corrosion has caused significant loss to marine engineering and the antibacterial coatings have served as a solution that has gained attention. In this study, the chemical vapour deposition technique has been employed to grow three different types of diamond coatings, namely, ultrananocrystalline diamond (UNCD), nanocrystalline diamond (NCD), and microcrystalline diamond (MCD) coatings. The evolution of associated surface morphology and the surface functional groups of the grown coatings have demonstrated antibacterial activity in seawater environments. It is found that different ratio of sp3/sp2 carbon bonds on the diamond coatings influences their surface property (hydrophobic/hydrophilic), which changes the anti-adhesion behaviour of diamond coatings against bacteria. This plays a critical role in determining the antibacterial property of the developed coatings. The results show that the diamond coatings arising from the deposition process kill the bacteria via a combination of the mechanical effects and the functional groups on the surface of UNCD, NCD, and MCD coatings, respectively. These antibacterial coatings are effective to both Gram-negative bacteria (E. coli) and Gram-positive bacteria (B. subtilis) for 1–6 h of incubation time. When the contact duration is prolonged to 6 h or over, the MCD coatings begin to reduce the bacteria colonies drastically and enhance the bacteriostatic rate for both E. coli and B. subtilis.</p

Polyethylene Waxes with Short Chain Branching via Steric and Electronic Tuning of an 8-(Arylimino)-5,6,7-trihydroquinoline-nickel Catalyst

Ten examples of nickel(II) halide complexes [8-{N(2,4-(C15H13)2-6-RC6H2N)}C9H8N]NiBr2 [R = Me (Ni1), Et (Ni2), iPr (Ni3), Cl (Ni4), or F (Ni5)] and [8-{N(2,4-(C15H13)2-6-RC6H2N)}C9H8N]NiCl2 [R = Me (Ni6), Et (Ni7), iPr (Ni8), Cl (Ni9), or F (Ni10)], each incorporating a sterically encumbered N,N-chelating 8-[2,4-bis(dibenzocycloheptyl)-6-R-phenylimino]-5,6,7-trihydroquinoline ligand, are disclosed. Full details for the preparation of these complexes as well as the zinc-mediated synthesis of precursor ligands L1–L5 are given. Structural characterization of Ni3(H2O), Ni6, Ni7(H2O), and Ni8(H2O) reveals halide-bridged dinuclear structures of the type (N,N)NiX(μ-X)2NiX(N,N) with the ortho-substituted dibenzocycloheptyl groups providing steric protection to each metal center. In the presence of ethylaluminum dichloride (EtAlCl2) or methylaluminoxane (MAO), Ni1–Ni10 displayed high activities for ethylene polymerization [≤6.17 × 106 g of PE (mol of Ni)−1 h–1 for Ni6/EtAlCl2 at 20 °C], generating low-molecular weight polyethylene waxes. Notably, catalysts incorporating a 6-alkyl group (Me, Et, or iPr) as the N-aryl substituent proved to be more active than their 6-halide (Cl or F) counterparts and formed relatively higher-molecular weight polymers (Mw range of 9.1–22.9 kg mol–1) with a narrow dispersity. Moreover, analysis of these waxes by 13C nuclear magnetic resonance spectroscopy showed that they typically possessed short chain branching (>83% methyl) with branching densities of 79–90 branches per 1000 Cs. In addition, chain end analysis revealed the presence of both vinyl (−CH═CH2) and internal vinylene (−CH═CH−) functional groups, highlighting the role of both β-H elimination and isomerization.</p

Evolutionary features of subsurface defects of single crystal diamond after dynamic friction polishing

Due to the fatigue and continuous energy input during high-speed dynamic friction polishing (DFP), the diamond crystal beneath the polished surface (roughness 50 nm) and even preferential crystal cleavage with the non-diamond phase (distributing at the position in micrometers range).</p

Evolutionary features of subsurface defects of single crystal diamond after dynamic friction polishing

Due to the fatigue and continuous energy input during high-speed dynamic friction polishing (DFP), the diamond crystal beneath the polished surface (roughness 50 nm) and even preferential crystal cleavage with the non-diamond phase (distributing at the position in micrometers range).</p