Substitutional Carbon Research Articles

Carbon depth profile and internal stress by thermal energy variation in carbon‐doped TiZrN coating

AbstractDiffusion and bonding behavior of the doped carbon by variation of thermal energy was investigated in terms of carbon depth profile and local atomic structure. The thermal energy of pulsed laser was limited to the range of 20%~50% to dope the carbon and prevent degradation of the coating layer with laser carburization. The doped carbon was confirmed to be distributed to a depth of around 20 nm from the surface at 20% thermal energy by ToF‐SIMS analysis. Carbon diffused at about 400 nm with 50% thermal energy, and most of the carbon spread from the surface to around 80 nm. The EXAFS analysis represented that the peak of the interstitial carbon site was formed at 20% and the ZrN peak shifted toward the ZrC peak by increasing the thermal energy. The analysis of the electronic structure and the bonding state demonstrated that the proportion of substitutional carbon was about 21% at a thermal energy of 50%. The internal stress was calculated using HR‐XRD with a 5‐axes sample stage, which was −453 MPa before doping and then increased to −1494 MPa at 50% because the mixture of interstitial and substitutional carbon increased distortion inside the coating layer. The elastic modulus and hardness were 459 and 37.9 GPa at 50%, respectively, which were improved by 10% and 20% compared to those of the TiZrN coating.

Facile synthesis of graphitic carbon nitride via copolymerization of melamine and TCNQ for photocatalytic hydrogen evolution

Graphitic carbon nitride (g-C3N4) has been regarded as an intriguing photocatalyst applying to hydrogen generation but suffering rapid recombination of photoinduced electron-hole pairs and insufficient absorption under visible light. We developed a novel one-pot thermal copolymerization method of melamine as a precursor and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a comonomer to synthesize modified g-C3N4 (abbreviated as X% TCNQ) for the first time, aiming to directly incorporate TCNQ molecular into carbon nitride skeleton for the substitution of low-electronegative carbon for high-electronegative nitride atom. Results revealed that the as-prepared photocatalysts by copolymerization of melamine with TCNQ retained the original framework of g-C3N4, and dramatically altered the electronic and optical properties of carbon nitride. Various measurements confirmed that as-synthesized samples exhibited larger specific surface areas, faster photogenerated charge transfer and broader optical absorption by decreasing the π-deficiency and extending the π-conjugated system, thus facilitating the photocatalytic activity. Specifically, the 0.3% TCNQ exhibited as high as seven times than the pristine g-C3N4 on photocatalytic H2 generation and kept its photoactivity for five circles. This work highlights a feasible approach of chemical protocols for the molecular design to synthesize functional carbon nitride photocatalysts by copolymerizing appropriate g-C3N4 precursor and comonomers.

Nonmagnetic doping induced quantum anomalous Hall effect in topological insulators

Quantum anomalous Hall effect (QAHE) has been experimentally observed in magnetically doped topological insulators. However, ultra-low temperature (usually below 300 mK), which is mainly attributed to inhomogeneous magnetic doping, becomes a daunting challenge for potential applications. Here, a \textit{nonmagnetic}-doping strategy is proposed to produce ferromagnetism and realize QAHE in topological insulators. We numerically demonstrated that magnetic moments can be induced by nitrogen or carbon substitution in Bi$_2$Se$_3$, Bi$_2$Te$_3$, and Sb$_2$Te$_3$, but only nitrogen-doped Sb$_2$Te$_3$ exhibits long-range ferromagnetism and preserve large bulk band gap. We further show that its corresponding thin-film can harbor QAHE at temperatures of 17-29 Kelvin, which is two orders of magnitude higher than the typical temperatures in similar systems. Our proposed \textit{nonmagnetic} doping scheme may shed new light in experimental realization of high-temperature QAHE in topological insulators.

Theoretical Study of the Si/C Mixed Benzenes and Their Major Valence Isomers

Changes in the structures and relative stabilities of benzene and the major valence isomers fulvene, Dewar benzene, benzvalene, and prismane on the substitution of the skeletal carbons with silicon...

Alteration of the Condylar Oral Bone in Obese and Gastric Bypass Mice

Obesity is the main cause of type 2 diabetes mellitus (T2DM). Roux-en-Y gastric bypass (RYGB) surgery is an effective treatment for this obesity-related health problem. However, the adverse effects of T2DM on bone tissue persist or even aggravate after this surgical procedure. As studies on the mandibular condyle bone are scarce, the aim of the present study was to assess its compositional characteristics in T2DM and RYGB conditions. Thirty-two male C57BL/6 mice at 8 weeks of age were randomly assigned to receive either a high-fat or low-fat diet. After 14 weeks of high-fat diet intake, seven obese mice were subjected to RYGB surgery. All animals were euthanized at the age of 30 weeks. Mandibular bones were removed and the trabecular condyle region was assessed using Raman spectroscopy. A decreased mineralization was observed for both T2DM and RYGB condyle bones when compared to controls, with elevated carbonate substitutions for the RYGB group. No compositional differences in crystallinity and presence of advanced glycation end products were found between the groups, with the exception of an increased presence of N-carboxymethyl-lysine in RYGB bone compared to their T2DM counterpart. Site-specific measurements revealed a non-uniform bone composition, with increasing mineralization and carbonate substitutions towards the centre of the mandibular condyle. T2DM and RYGB surgery affect the mandibular condyle bone quality, as investigated at compositional level. Assessment of bone structural properties and remodelling should be carried out to further explore the effects of T2DM and RYGB surgery on this skeleton area.

Amino pyridine iron(II) complexes: Characterization and catalytic application for atom transfer radical polymerization and catalytic chain transfer

The amino-pyridine ligand scaffold has achieved widespread use for base metal catalysis. Atom Transfer Radical Polymerization (ATRP) is one realm where base metals have achieved success in catalysis, in particular copper and iron. Herein, the synthesis and characterization of two amino-pyridine iron(II) complexes is described where the amino carbon substitution is the point of differentiation. We hypothesized that a sterically hindered, electron rich t-butyl substituent in this position might improve the propensity of said complex to achieve ATRP since inductive electron donation from the t-butyl group may improve catalyst activity and shift the ATRP equilibrium towards the active polymer species and corresponding Fe(III) complex. Dimeric 1 and 2 ([2-[(2,6-Me2-C6H3)NHCH(R)]C5H4N]FeCl2)2 (R = t-butyl or ethyl, respectively) were identified by single crystal X-ray diffraction. Both complexes favor a high-spin iron(II) state, as evidenced by Evans NMR magnetic susceptibility measurements and suggested by gas-phase computations at the M06-L level of theory. Complexes 1 and 2 catalyze styrene polymerization at elevated temperatures (120 °C) and polymerization data suggests that ATRP operates and catalytic chain transfer (CCT) competes at extended reaction times. Complex 1 with its t-butyl substituted amino carbon displays a slightly higher ATRP activity as compared to 2 [kobs(1) = 0.31 h−1; kobs(2) = 0.10 h−1], suggesting the importance of ligand optimization for future iron ATRP catalyst development.

Evaluating the Impact of Future Global Climate Change and Bioeconomy Scenarios on Ecosystem Services Using a Strategic Forest Management Decision Support System

Sustainable Forest Management (SFM) has become an important pillar of modern forest management, and one way to evaluate the sustainability of forestry is to assess long-term supply of ecosystem services (ESs) indicators. The concept of sustainability also has come to include adapting to climate change and the associated dynamic timber markets. This study aims to: 1) incorporate several ESs indicators in a Forest Management Decision Support System (FMDSS) that can deal with climate change and dynamic timber markets; and 2) analyse the impact that intensified forest management, resulting from global change scenarios that represent different levels of climate change mitigation efforts, will have on forest ES indicators in the west of Ireland. A linear programming model that optimized Net Present Value (NPV) from mill-gate sales was previously developed in Remsoft Woodstock, a DSS framework used for strategic forest planning around the world. This Woodstock model was modified to include the effects of global scenarios that include climate change and dynamic timber prices. This model was further developed to include indicators for five ESs (carbon storage in the forest as well as in harvested wood products and carbon substitution, windthrow risk, biodiversity, water quality, and cultural values), to assess the impacts of these global scenarios on the forest landscape and the sustainability of forest management. The ES indicator values were mainly linked to forest age, forest type, and yield tables, and their inclusion in the FMDSS had almost no impact on total model run times. Intensified forest clearfelling, as a result of increasing timber prices associated with most global scenarios, led to increased phosphor emissions to waterbodies, and reductions in windthrow risk and carbon storage. The global scenarios only resulted in minor differences in the indicator values for biodiversity and cultural values. Besides the global scenarios, recent forest policy development and the poor soil conditions in the study area impacted on the results. The developed system, with its innovative method to incorporate climate change and associated market dynamics, could be applied to other forest landscapes in Ireland and Europe, or indeed by any forest company or organisation that uses Remsoft Woodstock.

Effect of substitutional and vacancy defects on the electrical and mechanical properties of 2D-hexagonal boron nitride.

Defects in the nanoscale are common in the 2D materials irrespective of the fabricated method. Material performance gets significantly affected due to the presence of defects in 2D materials. In the present study, electronic and mechanical properties of 2D-hexagonal boron nitride (hBN) are investigated. At the electronic scale, the formation energies, band structures were obtained for pristine and defected hBN. The substitutional defects of carbon (C-at-NS, C-at-BS) and oxygen (O-at-NS, O-at-BS) at boron and nitrogen sites, single vacancy defects (BV, NV) and triangular vacancies (3B + N)v and (3N + B)v of boron and nitrogen, and Stone-Thrower-Wales (STW) type-1 and type-2 defects were considered. We found that with the inclusion of defects in 2D-hBN, the bandgap decreases, and carbon substitution at the boron site produces n-type characteristics, whereas substitution of carbon at the nitrogen site produces p-type characteristics. Boron vacancies increased the p-type character. At the atomistic scale, stiffness, ultimate tensile strength, and fracture strain were simulated for the pristine and defected hBN with molecular dynamics (MD) simulations using Tersoff potential. We found that the vacancy defects dominated by Boron atoms are energetically favorable and shift the electric conductivity from insulating to conducting. The stiffness and ultimate tensile strain of the 2D-hBN in the zigzag direction are higher than that of armchair direction. A strength reduction of around ~ 50% is observed with a defect concentration of 2.1%. It is observed that pristine and defective 2D-hBN is stronger in ZZ than AC configuration. Graphical abstract.

Optimization of Carbon Encapsulated Boron Doping for High‐Performance Bulk Sintered MgB2

Carbon has been a standard doping agent in MgB2 for long time. It, however, has also participated in a non‐uniform distribution of the constituents throughout the bulk MgB2. To address this issue, carbon encapsulated boron (CEB) was used instead of the manually added mixture of boron and carbon. The previous studies confirmed that only low concentrations of carbon in CEB were effective for synthesis of a high‐performance bulk MgB2. Here, a further step in optimization carbon content in CEB is reported. Carbon content in CEB varied as 1, 1.1, 1.35, 1.5, and 1.9 wt%. X‐ray diffraction (XRD) results depict a slight shift in peaks corresponding to a–b plane, indicating carbon substitution into the lattice. High superconducting critical current density in self‐field, such as 660, 550, and 435 kA cm−2, was observed in the samples with 1.5 wt% CEB at 10, 15, and 20 K, respectively. In addition, Jc of 75 kA cm−2 at 2 T and 20 K was observed in the 1.5 wt% CEB sample, which is thrice the value observed in the pure sample, with a minute tradeoff in Tc (around 37.5 K). Scanning electron microscope (SEM) images reveal that small particles of size ranging from 50 to 200 nm contribute to Jc improvement. Energy‐dispersive X‐ray (EDX) results show carbon uniformly distributed throughout the bulk.

Sulfur Incorporation in Hierarchical TiO2 Nanosheet/Carbon Nanotube Hybrids for Improved Lithium Storage Performance

AbstractTo boost the lithium storage performance of TiO2, sulfur was homogeneously incorporated into the hybrids of hierarchical TiO2 nanosheets and carbon nanotubes (CNTs) through a solvothermal‐calcination process. The resulting 0D‐2D‐1D architecture endowed the hybrids with considerable interfaces for lithium accommodation and shortened pathways for lithium diffusion. Moreover, the interplane spacings of TiO2 and CNTs were expanded and their electronic structures were modified atomically, owing to partial sulfur substitution for oxygen and carbon. Benefitting from the simultaneous acceleration of lithium and electron transport as well as the dominated capacitive charge storage mechanism, lithium‐ion batteries based on S−TiO2/CNTs delivered an initial discharge capacity of 870.4 mAh g−1 at 0.2 A g−1, a high‐rate capacity of 119.3 mAh g−1 at 5.0 A g−1 and a reversible capacity of 195.5 mAh g−1 at 2.0 A g−1 after 700 cycles, far superior to the counterpart without sulfur doping and comparable to most reported TiO2‐based nanostructures.

Geochemistry and paleoenvironment of the phosphorites from the Ameki Formation, Niger delta, Nigeria

The phosphorites of the Ameki Formation occur as nodules, pellets as well as primary phosphatic shales and siltstones. Geochemical analysis of the phosphate samples was carried out to determine its chemical composition as well as its depositional environment. The methodology applied include XRF, INAA, XRD and thin section petrography using Polarizing Microscope. The XRF result identified CaO- P2O5- F as the major mineral group, SiO2, Al2O3, Fe2O3, MgO and TiO2, which show minor occurrences and Cr, U, Pb, V, Cu, Zn, Se and Cd that occur in trace amounts. The nodules and pellets are of medium to high grade (25- 34wt% P2O5) whereas the primary phosphatic shales and siltstones are of low to medium grade (4.5– 22wt% P2O5). The phosphorites comprise mostly of francolites. The mean index of refraction estimated by Becke-line method using Standard Polarizing Microscope gave 1.634 and1.636.XRD analysis yielded an average values of 9.243 (± 0.002) A° and 6.715 (± 0.002) A° for a and c crystallographic axes respectively with an axial ratio (c/a) of 0.726for unit cell parameter, suggestive of low degree of carbonate substitution. An increase in P2O5 content is found to be accompanied by increase in CaO, CO2 and F contents, but by a decrease in H2O, organic carbon, SiO2 and Fe contents indicative of amorphous solid phase of calcium phosphate. The phosphorite is interpreted to form under high biologic productive, shelf setting. High nutrient availability in the ancient sea is linked to upwelling along the West African Coastline during the Eocene.
 Keywords: Phosphorites; Geochemistry; Paleoenvironment; Ameki; Francolites; Nodules

Carbon substitution enhanced electronic and optical properties of MgSiP2 chalcopyrite through TB-mBJ approximation

In this work, we used the first-principles calculation based on density functional theory to investigate the effect of carbon substitution on structural, electronic, and optical properties of the MgSiP2 compound. Our calculations for the lattice constants show that both a and c decrease when the C atoms increasingly replace Si atoms in MgSiP2, however, the bulk modulus is found to be increasing. The calculated negative values of the formation energy (Ef) reveal that all MgSi1-xCxP2 alloys are thermodynamically stables. In addition, the substitution of the C atoms leads to a reduction of the value of the band-gap to 1.51 eV, 1.47 eV, and 1.30 eV for x = 0.25, 0.5 and, 0.75 respectively, these values have been calculated using the TB-mBJ approximation. We have calculated also the optical properties and the results show that the average absorption coefficient of MgSi1-xCxP2 alloys is improved in the visible light region (α ∼ 105 cm−1). Therefore, the band-gap values and the high absorption coefficient (α ∼ 105 cm−1) make MgSi1-xCxP2 alloys a promising candidate for photovoltaic applications.

P123: Preliminary evaluation of raman spectroscopy to detect calcifications in excised breast tissue: A prelude to the first in vivo whole breast study

Introduction: Mammographic screening through the NHS Breast Screening Programme (NHSBSP) has limitations, including false positivity (9-13%). Adjunct techniques would support clinical decision making and reduce unnecessary biopsy. Raman spectroscopy is an analytical method that is non-invasive, non-destructive and provides chemical information to distinguish between breast micro-calcifications: Type I (benign) and Type II (malignant). Baker et al (2010) demonstrated that the level of carbonate substitution in type II calcifications can help provide cancer grade.

A Comprehensive Microstructural and Compositional Characterization of Allogenic and Xenogenic Bone: Application to Bone Grafts and Nanostructured Biomimetic Coatings

Bone grafts and bone-based materials are widely used in orthopedic surgery. However, the selection of the bone type to be used is more focused on the biological properties of bone sources than physico-chemical ones. Moreover, although biogenic sources are increasingly used for deposition of biomimetic nanostructured coatings, the influence of specific precursors used on coating’s morphology and composition has not yet been explored. Therefore, in order to fill this gap, we provided a detailed characterization of the properties of the mineral phase of the most used bone sources for allografts, xenografts and coating deposition protocols, not currently available. To this aim, several bone apatite precursors are compared in terms of composition and morphology. Significant differences are assessed for the magnesium content between female and male human donors, and in terms of Ca/P ratio, magnesium content and carbonate substitution between human bone and different animal bone sources. Prospectively, based on these data, bone from different sources can be used to obtain bone grafts having slightly different properties, depending on the clinical need. Likewise, the suitability of coating-based biomimetic films for specific clinical musculoskeletal application may depend on the type of apatite precursor used, being differently able to tune surface morphology and nanostructuration, as shown in the proof of concepts of thin film manufacturing here presented.

Oxytocin and bone quality in the femoral neck of rats in periestropause

The objective of this study is to identify whether oxytocin (OT) contributes to the reduction of osteopenia in the femoral neck of rats in periestropause. Animals in irregular estrous cycles received two NaCl injections (0.15 mol/L) or OT (134 μg/kg) over a 12-h interval, and after thirty-five days without treatments, the biological sample collection was performed. The oxytocin group (Ot) demonstrated the highest enzymatic activity of alkaline phosphatase (p = 0.0138), lowest enzymatic activity of tartrate-resistant acid phosphatase (p = 0.0045), higher percentage of compact bone (p = 0.0359), cortical expression of runt-related transcription factor 2 (p = 0.0101), osterix (p = 0.0101), bone morphogenetic protein-2/4 (p = 0.0101) and periostin (p = 0.0455). Furthermore, the mineral-to-matrix ratio (ν1PO4/Proline) was higher and type-B carbonate substitution (CO3/ν1PO4) was lower (p = 0.0008 and 0.0303) in Ot group. The Ot showed higher areal bone mineral density (p = 0.0050), cortical bone area (p = 0.0416), polar moment of inertia, maximum, minimum (p = 0.0480, 0.0480, 0.0035), bone volume fraction (p = 0.0166), connectivity density (p < 0.0001), maximal load (p = 0.0003) and bone stiffness (p = 0.0145). In Ot percentage of cortical pores (p = 0.0102) and trabecular number (p = 0.0088) was lower. The results evidence action of OT in the reduction of osteopenia, suggesting that it is a promising anabolic strategy for the prevention of primary osteoporosis during the periestropause period.

Enhancement of Jc in C6H16N2 added MgB2 superconductor without carbon substitution for boron

The influence of C6H16N2 addition on the microstructural and superconducting properties of MgB2 was systematically investigated. Unlike previously reported carbon sources, the C6H16N2 additive had no effect on the lattice parameters of MgB2. However, the obvious improvement of critical current density (Jc) was obtained for C6H16N2 added MgB2 without carbon substitution for boron. The average grain size was reduced with the addition of C6H16N2. Additionally, different numbers of spherical MgB2 grains appeared inside the C6H16N2 added MgB2. As the added amount of C6H16N2 increased, the active cross-sectional area fraction (AF) values first increased then decreased. The possible reasons for these results have been discussed. The additive C6H16N2 resulted in a small depression in Tc and slightly increased the ΔTc of MgB2 at 0 T. The Hc2 (T) and Hirr (T) values of C6H16N2 added MgB2 samples are larger than those of pure MgB2 at temperatures below 25 K. It was concluded that the reduced grain size and the improved grain connectivity were mainly correlated with the enhancement of the Jc, Fp, Hc2, and Hirr performances in C6H16N2 added MgB2 superconductors.

Substitutional carbon defects in silicon: A quantum mechanical characterization through the infrared and Raman spectra.

The infrared (IR) and Raman spectra of eight substitutional carbon defects in silicon are computed at the quantum mechanical level by using a periodic supercell approach based on hybrid functionals, an all electron Gaussian type basis set and the CRYSTAL code. The single substitutional C s case and its combination with a vacancy (C s V and C s SiV) are considered first. The progressive saturation of the four bonds of a Si atom with C is then examined. The last set of defects consists of a chain of adjacent carbon atoms C , with i = 1-3. The simple substitutional case, C s , is the common first member of the three sets. All these defects show important, very characteristic features in their IR spectrum. One or two C related peaks dominate the spectra: at 596 cm-1 for C s (and C s SiV, the second neighbor vacancy is not shifting the C s peak), at 705 and 716 cm-1 for C s V, at 537 cm-1 for C and C (with additional peaks at 522, 655 and 689 for the latter only), at 607 and 624 cm-1 , 601 and 643 cm-1 , and 629 cm-1 for SiC , SiC , and SiC , respectively. Comparison with experiment allows to attribute many observed peaks to one of the C substitutional defects. Observed peaks above 720 cm-1 must be attributed to interstitial C or more complicated defects.

Carbon-doped ZnO nanotube-based highly effective hydrogen gas sensor: A first-principles study

The hydrogen gas sensing properties of carbon-doped ZnO nanotube has been theoretically investigated by employing first-principles density functional theory in combination with non-equilibrium Green's function. The figure of merits is creating the new states in ZnO nanotube structure by adding carbon substitution for an oxygen site. The calculation of adsorption energy indicates strong chemical adsorption of hydrogen on the outside and inside of carbon-doped ZnO nanotube. Moreover, density of state, current-voltage and sensor response have been performed for energetically favorable adsorption geometries of hydrogen. The involvement of carbon valence electrons in the chemical adsorption of hydrogen has been examined by partial density of state diagram. The current-voltage diagram of carbon-doped ZnO nanotube indicates negative-differential resistance trend. This trend has been disappeared after the chemical adsorption of hydrogen. The sensor response calculations reveal the high response of the sensor occurs in 3.5 V on the outside and inside of carbon-doped ZnO nanotube.

Research Progress of Electromagnetic Properties of MgB2 Induced by Carbon-Containing Materials Addition and Process Techniques

For the high transition temperature (Tc) and low cost taking both raw materials and fabrication process into account, MgB2 has been a competitive candidate to replace the conventional NiTi superconductor for high-temperature application in fault current limiters, transformers, motors, magnetic resonance imaging, adiabatic demagnetization refrigerators, generators, etc. The carbon-containing materials addition induced high critical current density (Jc) is reviewed based on their influences on the upper critical field (Hc2), flux pinning force, and connectivity. The doping effects were compared in the overview focusing on SiC, organic dopants, and graphene-related dopants. SiC doping is featured for the high-field critical current density, which is caused by the increased Hc2 attributed to the substitution of carbon on boron site and the strong flux pinning force offered by the nanosized secondary phases in the MgB2 matrix. Organic dopants have the advantage over SiC dopant for their relatively homogeneous distribution in the MgB2 matrix based on wet mixing of the organics and the raw boron powders. Low doping level of two-dimensional materials can improve the superconducting properties in all measured fields because of the combined advantages of carbon substitution effect and grain connectivity. MgB2 fabricated with carbon-encapsulated boron also introduces strong flux pinning centers in MgB2, which show weak destruction of the connectivity of the MgB2 grains as reflected by the low-magnetic-supercurrent behavior. High-pressure treatment and diffusion method can fabricate high-density MgB2 superconductors with better connectivity and increase the Jc compared with the in situ and ex situ methods.

Effects of carbon related defects on opto-electronic properties of β-Ga2O3: The first principle calculation

Calculations using the revised Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE06) reveal the opto-electronic effects of carbon in β-Ga2O3. Stable charged states with carbon dopant are proved by phonon calculations which can result in the deep levels in the band gap. Stronger distortion can happen around oxygen sites substituted by carbon than those at gallium sites leading to interactions changing. Temperature and oxygen pressure can have huge effect on the formation of substitutions and the electronic conductivity. As partial oxygen pressure increase, the substitution concentration increases, and decrease with temperature increasing. Electronic conductivity of substitution of carbon at oxygen sites can get enhanced hugely, and it increases with temperature increasing. Besides electronic properties, carbon substitution can also have great impact on optical properties. Red-infrared PL emissions can be induced with substitutions at gallium sites, and yellow and blue emissions can be achieved by substitutions with oxygen in different charged states. The work can effectively predict the impact of carbon substitution in β-Ga2O3 and be useful for improvement of device designs and optimizations.