Substitutional Carbon Research Articles

Mechanism of palladium-catalyzed allylic substitution of tertiary allylic carbonates with sodium sulfinates: unusual bifunctional nucleophile-enabled inner-sphere pathway and origin of regio- and enantioselectivities

DFT calculations were performed to investigate Pd-catalyzed allylic sulfonylation of tertiary allylic carbonates. The bifunctional role of the sulfonate nucleophile enables the C–S bond formation via a unique inner-sphere pathway.

Rat bone responses to hindlimb unloading-reloading: Composition, BMD and mechanical properties

IntroductionBone loss in lower limbs under space microgravity condition can persist even after the astronauts return to Earth's gravitational environment. It is crucial to determine the extent and timing of bone recovery after spaceflight, especially for long-term flights. However, there is a lack of comprehensive descriptions of the recovery of various aspects of bone quality, particularly in terms of compositional characteristics that reflect changes in bone quality. Therefore, the objective of this study is to investigate the alterations in bone mineral density, composition characteristics, and mechanical properties of rat lower limbs during unloading (tail suspension) and the subsequent recovery loading period. MethodsRats were subjected to tail suspension for four weeks (TS4) followed by reloading for an additional four weeks. Bone mineral density (BMD) was measured by μ-CT and analyzed. The mechanical properties of the tibia were assessed by a three-point bending test, and the composition characteristics of bone tissue were evaluated using Raman spectroscopy. Regression analysis was performed to identify main component related to mechanical property. ResultsIn the metaphysis, BMD of the tibia significant decreased, particularly in trabecular bone. Upon reloading, only the cortical bone showed recovery. In the diaphysis, cortical bone remained unchanged during unloading but demonstrated delayed bone loss during the reloading period. Simultaneously, the mechanical properties of tibia experienced a substantial reduction after four weeks of unloading, The stiffness and maximum strength did not fully recover, though the elastic modulus and the ultimate strength were restored following the reloading process. Raman spectroscopy characterization found an increase in the carbonate substitution and crystal crystallinity of the diaphysis after 4 weeks of unloading. There was an intriguing alteration in the mineralized collagen ratio, that an increase was observed in the diaphysis while a decrease was observed in the metaphysis. During 4 weeks of reloading, the compositional characteristics of the diaphysis recovered earlier than those of the metaphysis, with the exception of crystallinity which remained unrecovered. Regression analysis indicated that carbonate replacement has a strong correlation to bone mechanical properties during the 4 weeks of unloading and subsequent 4 weeks of reloading. ConclusionsThe data obtained in this study highlight the incomplete recovery of bone mineral density, mechanical properties, and compositional characteristics during reloading in tail-suspended rats. These findings deepen our understanding of microgravity-induced bone loss and provide valuable information to develop interventions not only for astronauts but also for persons on earth during and after prolonged periods of unloading.

Impurity-induced enhancement of parity-forbidden optical intracenter transitions of shallow donors in silicon

Different defects in silicon crystals cause lattice distortion that may violate selection rules for certain intracenter optical transitions of hydrogen-like donor centers. Perturbations due to large concentration of substitutional donors enhance all parity-forbidden atomic transitions, but cause large concentration broadening of the transition lines, prohibiting observation of transitions at close energies. Substitutional residual carbon atoms in silicon induce, in contrast, a weak-to-moderate broadening of donor absorption lines enabling the resolution of some parity-forbidden intracenter transitions in impurity absorption spectra at moderate donor densities. Binding energies of several series of s- and d-type states were obtained by resolving of intracenter transitions terminating in these states, by low-temperature infrared absorption spectroscopy in carbon-rich and/or heavily doped silicon crystals.

Impact of hair-derived carbon substitution on structural and superconducting properties of MgB2

This study presents a comprehensive analysis of the effects resulting from the substitution of biowaste-derived carbon-dot (CD) from human hair on structural and superconducting properties of MgB2. Syntheses of polycrystalline samples were accomplished through a standard solid-state reaction route. X-ray powder diffraction results confirm the formation of MgB2 as a primary phase in all samples and show the successful substitution of carbon for boron in MgB2. The critical current density, determined at 20 K and 4.5 T, for carbon-substituted MgB2 synthesized at 850 °C was enhanced by more than four times compared with unsubstituted MgB2. The observed improvement is due to the formation of efficient pinning centers resulting from the incorporation of carbon substituting for boron in MgB2. Furthermore, x-ray photoelectron spectroscopy (XPS) confirmed the presence of carbon bonding to boron in MgB2 synthesized with biowaste-derived CDs, indicating successful incorporation into the structure. Ultraviolet photoelectron spectroscopy (UPS) results show that the carbon-substituted MgB2 can lead to changes in the electronic band structure and values of work function. These changes significantly impact the properties of MgB2 materials, including superconducting transition temperature, upper critical field, and critical current density. The XPS and UPS experimental results are in good agreement with density functional theory calculations for MgB2 with and without carbon substitution.

Synthesis and characterization of B-type carbonated hydroxyapatite materials: Effect of carbonate content on mechanical strength and in vitro degradation

The current approach in bone tissue engineering requires resorbable biomaterials that enhance bone formation while maintaining sufficient mechanical stability. In this work, the influence of three levels of B-type carbonate substitution in hydroxyapatite lattice on mechanical strength and degradation rate is analyzed. The inverse aqueous route has been selected as a synthesis method of four powders with carbonate substitution between 4 and 6wt.%. X-ray fluorescence (XRF), (C-S)-Analysis, FT-Infrared, X-ray diffraction, DTA-TG and TEM were used to investigate chemical composition, type of substitution, thermal behaviour, and morphology of the powders. Disc shaped specimens were processed by uniaxial pressing and sintering in argon/CO2 flow. Maximum temperatures of thermal treatment between 750 and 850°C were selected to obtain similar porosity levels for the different compositions. The highest carbonate substituted material (5.3wt.%) presented higher compressive strength and dissolution rate than the other materials showing the beneficial effect of B-type substitution in hydroxyapatite materials for bone repair.

Effect of lepidolite on melting, viscosity and structure of CaO–SiO2 based melt

It will be an economic, environmental-friendly and energy-saving way to utilize lepidolite as a substitution of industrial grade lithium carbonate for preparation of commercial mold flux. Therefore, the melting behavior, viscosity and melt structure of mold fluxes with different lepidolite content were investigated in this study. The results show that the initial melting temperature of the fluxes increases from 1278.4 to 1301.2 K, meanwhile the complete melting temperature increases from 1622.0 to 1674.4 K with the addition of lepidolite from 15.10 to 37.80 wt%. The viscosity of mold fluxes at 1573 K increases from 0.12 to 0.44 Pa s, whereas the break temperature reduces from 1467.7 to 1386.9 K with the increase of lepidolite. The melt structure analyses suggests that the simple structural units, such as Q0, Q1, Q2 and [AlO4]5-- tetrahedral asymmetric stretching reduce; while the complex structural units, like Q3, Q4, [AlO4]5-- tetrahedral symmetric stretching and Al–O–Si bending increase with the addition of lepidolite. These changes suggest that the free oxygen transforms into bridging oxygen and non-bridging oxygen, and the structure of melt becomes more complex when lepidolite is added in the flux.

Structural and Physicochemical Properties of Carbon Doped Boron Nitride Fullerenes: Effect of Doping Level and Atomic Arrangement

AbstractThe effect of carbon doping on the structural and physicochemical properties of B12N12‐xCx [4, 6]‐fullerenes (0 ≤ x ≤ 6) (BNFs) is studied in the frame of the density functional theory. All non‐symmetry related isomers are modeled. Although carbon doping reduces the cohesive energy of the BNFs, most of them remain stable. It is found that the location of carbon atoms in the lowest‐energy isomers follows a definite sequence as the doping level increases. The results indicate that substitutional carbon lowers the gap energy and chemical hardness of BNFs, but it increases their electronegativity and electrophilicity index. Particularly, carbon doping makes BNFs more susceptible to nucleophilic attacks. Additionally, the charge redistribution and structural asymmetry generated by carbon doping endows BNFs with polar character. A dipole alignment parameter is introduced to elucidate some correlation between the atomic arrangement and the polarity of the systems. While carbon doping enhances the capability of BNFs to interact with other chemical species, possible toxicity concerns are highlighted. Finally, possible fingerprints to identify successful carbon doping through infrared and UV–vis spectroscopy are proposed.

Discussion on the Landscape Design of Urban Parks Under the Background of ' Double Carbon '

In view of the landscape design under the background of ' double carbon ', the requirements and principles of practicing ' double carbon ' action are put forward in the planning stage. Based on the existing problems of urban parks and the design idea of ' low carbon ', this study puts forward some design ideas such as carbon emission reduction, carbon substitution, carbon storage and carbon cycle, in order to provide reference value for landscape designers in urban park landscape design.

A Study on Ikaite Growth in the Presence of Phosphate

Phosphate is a common component in natural growth solutions of ikaite. Although phosphate often occurs as a minor constituent, its presence may promote the formation of ikaite as it significantly inhibits the precipitation of calcite. The interactions of phosphate with ikaite and the role of a potential uptake of phosphate by ikaite, however, are poorly understood. In this study, the influence of phosphate on ikaite growth at 1 °C was investigated. Ikaite- and calcite-seeded growth experiments were conducted in cryo-mixed-flow reactors at saturation ratios 1.5 ≤ Ωikaite ≤ 2.9 (Ω = ionic activity product/solubility product). From these growth experiments, the rate constant k = 0.10 ± 0.03 µmol/m2/s and the reaction order n = 0.8 ± 0.3 were derived for ikaite. The reaction order implies a transport- or adsorption-controlled growth mechanism which supports a low energy pathway of ikaite growth via an attachment of hydrous CaCO30 complexes without any extensive dehydration of aqueous species as, for instance, required for calcite growth. A potential depletion of aqueous phosphate due to an uptake by ikaite growth was not detectable. Furthermore, growth retardation by phosphate, as known for calcite growth, was not evident. Thus, a significant incorporation of phosphate into growing ikaite could be precluded for the conditions applied in this study. The observed lack of incorporation of phosphate agrees with the previously suggested growth mechanism via the attachment of hydrous CaCO30 complexes which likely does not facilitate substantial substitution of carbonate by phosphate ions.

Detection of osteoporotic-related bone changes and prediction of distal radius strength using Raman spectra from excised human cadaver finger bones

While osteoporosis is reliably diagnosed using dual energy X-ray absorptiometry (DXA), screening rates are alarmingly low, contributing to preventable fractures. Raman spectroscopy (RS) can detect biochemical changes that occur in bones transcutaneously and can arguably be more accessible than DXA as a fracture risk assessment. A reasonable approach to translate RS is to interrogate phalangeal bones of human hands, where the soft tissues covering the bone are less likely to hamper transcutaneous measurements. To that end, we set out to first determine whether Raman spectra obtained from phalangeal bones correlate with distal radius fracture strength, which can predict subsequent osteoporotic fractures at the spine and hip. We performed RS upon diaphyseal and epiphyseal regions of exposed proximal phalanges from 12 cadaver forearms classified as healthy (n = 3), osteopenic (n = 4), or osteoporotic (n = 5) based on wrist T-scores measured by DXA. We observed a significant decrease in phosphate to matrix ratio and a significant increase in carbonate substitution in the osteoporotic phalanges relative to healthy and osteopenic phalanges. Multivariate regression models produced wrist T-score estimates with significant correlation to the DXA-measured values (r = 0.79). Furthermore, by accounting for phalangeal RS parameters, body mass index, and age, a multivariate regression significantly predicted distal radius strength measured in a simulated-fall biomechanical test (r = 0.81). These findings demonstrate the feasibility of interrogating the phalanges using RS for bone quality assessment of distant clinical sites of fragility fractures, such as the wrist. Future work will address transcutaneous measurement challenges as another requirement for scale-up and translation.

Boosted Redox Kinetics Enabling Na3V2(PO4)3 with Excellent Performance at Low Temperature through Cation Substitution and Multiwalled Carbon Nanotube Cross-Linking.

The open NASICON framework and high reversible capacity enable Na3V2(PO4)3 (NVP) to be a highly promising cathode candidate for sodium-ion batteries (SIBs). Nevertheless, the unsatisfied cyclic stability and degraded rate capability at low temperatures due to sluggish ionic migration and poor conductivity become the main challenges. Herein, excellent sodium storage performance for the NVP cathode can be received by partial potassium (K) substitution and multiwalled carbon nanotube (MWCNT) cross-linking to modify the ionic diffusion and electronic conductivity. Consequently, the as-fabricated Na3-xKxV2(PO4)3@C/MWCNT can maintain a capacity retention of 79.4% after 2000 cycles at 20 C. Moreover, the electrochemical tests at -20 °C manifest that the designed electrode can deliver 89.7, 73.5, and 64.8% charge of states, respectively, at 1, 2, and 3 C, accompanied with a capacity retention of 84.3% after 500 cycles at 20 C. Generally, the improved electronic conductivity and modified ionic diffusion kinetics resulting from K doping and MWCNT interconnecting endows the resultant Na3-xKxV2(PO4)3@C/MWCNT with modified electrochemical polarization and improved redox reversibility, contributing to superior performance at low temperatures. Generally, this study highlights the potential of alien substitution and carbon hybridization to improve the NASICON-type cathodes toward high-performance SIBs, especially at low temperatures.

Maintenance and enhancement of forest ecosystem services: a non-industrial private forest owner perspective

The transition to a fossil-free society in Sweden is expected to cause an increased demand for forest-derived products which may intensify existing conflicts between forest ecosystem services. This study investigated the preferences among non-industrial private forest owners for maintaining multiple forest ecosystem services and their preferences for future forest development. The findings were related to their prioritizations for and knowledge of forest management. The study results were generated through the means of a survey which revealed a consistent high valuation among all respondents of ecosystem services relating to water quality, timber quality, recreation, and biodiversity. A majority of the respondents desired increasing proportions of mixed species and broadleaved stands within the future forest landscape. Certified forest owners who were members of a forest owner association (CMs) prioritized achieving high economic income through roundwood production with strong preferences for the ecosystem services high stand growth and high timber quality. For CMs, carbon substitution was the preferred means of mitigating climate change. Forest owners lacking both certification and membership in a forest owner association ranked the ecosystem services recreation and biodiversity significantly higher, and also preferred retaining more old forest within the landscape. The survey results revealed a higher management activity among CMs, resulting in a more frequent establishment of mixed and broadleaved stands. Forest owners with medium to large scale properties were well-represented within the CM category. The results indicated that while the CMs have stronger preferences for roundwood production compared to owners of small properties, they are also more likely to have taken adaptive measures favoring risk management and biodiversity.

Superhard lithium carbaboride clathrates

Lightweight strong boron-carbon clathrates adopting sodalite structure have been inspirated by the successful synthesis of the SrB3C3 compounds, which assuming the cubic bipartite sodalite structure. In this work, we designed series of stoichiometric LiBxC12-x and Li2BxC12-x (x = 1–6) compounds based on boron substitution of carbon in carbon sodalite structure using first-principles calculations. We found that LiB2C10, LiB3C9, LiB4C8, Li2B3C9 and Li2B4C8 are dynamically stable at high pressure and can be recovered under normal pressure. Strikingly, compared with inserting one Li atom into the B-C framework, inserting two Li atoms exhibit lower enthalpy value and better symmetry. Li2B4C8 is identified as the most stable structure among these compounds, and Li2B4C8 could potentially be synthesized at moderate pressure. The electron localization function calculations reveal that there is a strong covalent bond between B and C atoms in the clathrates, which forming the rigid three - dimensional crystalline networks. Moreover, the estimated Vickers hardness values of these five stable clathrates are 42 ∼ 51 GPa, which can be classified as superhard materials. At the same time, the pure shear strength of LiB2C10 is found to be 48.1 GPa, which exceeds the threshold value of 40 GPa. The pure shear strength of LiB3C9 (38.0 GPa) and Li2B3C9 (38.8 GPa) are found to be close to 40 GPa. Our work presents a new strategy for exploring superhard sodalite-like clathrate candidates.

Carbon Substitution Effect Through the Utilization of Wood Products in Major Carbon-intensive Industries: Focusing on the Construction Industry in Korea

This study aims to examine the carbon substitution effect in Korea's major carbon-intensive industry, the construction industry. To accomplish this, we estimate the factor demand functions for the building construction and maintenance industry as well as the civil construction industry using the SUR model. Subsequently, we conduct a simulation analysis to assess the carbon substitution effect resulting from the replacement of wood with other factor inputs in each industry. The data utilized in this study are gathered from the Bank of Korea's Input-Output table and the Bank of Korea's producer price index. The estimated results of the factor demand functions reveal a substitutive relationship between wood and wood products with processed metal products within the construction industry. The simulation analysis indicates that an 8.75% increase in demand for wood and wood products within the construction industry can lead to the most significant reduction in total greenhouse gas (GHG) emissions for the industry, amounting to 277.52 thousand tons. This study is the first to quantify carbon substitution effects from an economic perspective, thereby contributing to providing insights for governments in formulating policies related to carbon neutrality.

ESCAPE simplified approach designed to evaluate materials sustainability: The case of new adsorbent materials for activated carbon substitution

This paper discusses a novel simplified approach for assessing the sustainability of new material, specifically focusing on the synthesis technology used. The material can be obtained through emerging technologies, even if they are in the early laboratory development stage. The evaluation is conducted by comparing it to a reference material, which could be a natural resource, for instance. This approach can be applied in situations where complete life cycle assessment (LCA) data is unavailable or a comprehensive LCA evaluation is not required. ESCAPE (standing for Evaluation of Sustainability of material substitution using CArbon footPrint by a simplifiEd approach) involves the calculation of two parameters, the embodied energy, and the CO2 footprint, for all steps of the material synthesis procedure. The manuscript discusses in detail for the first time the approach's applicability and potentialities with some examples, devoted to new proposed adsorbents, derived from wastes. For this aim, 50 literature papers are considered and analysed. Surprisingly, the results show that only 28% of the 50 selected materials are in accord with the introduced sustainability index, showing that most of the new proposed adsorbents appear to be not environmentally sustainable.This study's findings highlight the ESCAPE approach's potential in facilitating materials eco-design by identifying the most resource-intensive steps in synthesis procedures. Notably, this approach provides the flexibility to incorporate the energy mixes of different Countries where the new processes may be deployed, enabling sustainability evaluations based on specific locations. This capability opens possibilities for a more comprehensive and context-specific assessment of sustainability in materials development. In essence, ESCAPE serves as a preliminary screening method before conducting an LCA, enabling rapid evaluations. It serves as a valuable tool for researchers and industries aiming to develop sustainable materials, thereby expediting the transition toward a circular economy.

Ultraviolet electronic spectroscopy of heavily substituted naphthalene derivatives

Context. The so-called bump spectral signature observable on interstellar extinction curves, peaking at 217.5 nm, is commonly assigned to π* ← π transitions from carbonaceous carriers, but the exact nature of the carbonaceous carriers remains debated. Aims. To constrain the chemical structures associated with the bump carriers, we record and compare the UV spectra of a large variety of carbonaceous molecules to this interstellar feature. Methods. Large carbonaceous molecules, such as polycyclic aromatic hydrocarbons (PAHs), were produced by a combustion process stabilized at low pressure under rich flame conditions. Species were extracted and probed through resonance enhanced multiphoton ionization spectroscopy coupled to a time-of-flight mass spectrometer. Masses and absorption profiles of the carbonaceous molecules were measured, and their spectra were compared to the bump feature. Results. Species showing a specific mass progression starting at mass 128 u visible up to mass 394 u with a characteristic progression of +14 u present a common electronic absorption band profile peaking asymptotically around 220 nm. The first masses were assigned to a naphthalene C10H8 molecule and two of its derivatives: C10H7CH3 and C10H7C2H5. The mass progression of +14 u is explained by successive H atom substitutions by CH3 functional groups. This mass distribution was thus assigned to naphthalene derivatives with large aliphatic carbon substitution. This derivative family shows an electronic band assigned to S3 ← S0 transitions involving electron promotion within the π aromatic orbitals of the naphathlene chromophore. More importantly, after a few substitutions, the position of the band converges asymptotically to a value close to the interstellar bump signature, independent of the molecule size. Conclusions. Based on the asymptotic behavior of the larger members in the species distribution, a similar band position is expected from double aromatic ring substructures within hydrogenated amorphous carbons (HACs). Similar to the conclusions of previous works, we find substituted naphthalene units as substructures of interstellar HACs to be good candidates as carriers of the bump feature.

Exploring Various Catalysts for Nitrogen Reduction to Ammonia

Electrochemical nitrogen reduction reaction (eNRR), one of the most studied problems in catalysis, has the potential to replace the century-old Haber-Bosch process for ammonia synthesis. However, a low-cost, highly selective and efficient catalyst for eNRR is yet to be discovered. Metal based catalysts have been at the heart of numerous studies for eNRR, however there has been a shift towards metal-free catalysts due to their environmentally benign nature and low cost. In this study, we analyze 2D boron-based electrocatalysts for nitrogen reduction and explore the effect of carbon substitution on their activity. Using first-principles calculations, we demonstrate that pristine and carbon (C) substituted 𝛼 borophene catalyze eNRR at exceptionally low limiting potentials of -0.33 V and -0.25 V, respectively. These 𝛼 borophene based catalysts also show high selectivity towards eNRR over the competing hydrogen evolution reaction (HER). Our results show that C-substituted 𝛼 borophene exhibits outstanding catalytic activity towards eNRR via the distal pathway with a small activation barrier of 0.56 eV, almost half the value reported for Ru (0001). Finally, we identify two novel descriptors, adsorption energy of *NNH and charge transfer to *N2, which can be used in high-throughput screening of catalysts for eNRR. These findings demonstrate the strong potential of metal-free borophene based catalysts for efficient electrochemical reduction of N2, enabling low-cost and sustainable NH3 synthesis.We revisit the nitrogenase FeM cofactor (M=Fe/Mo/V) based catalysts for eNRR to decipher the key mechanism at play. Further, catalysts based on transition metal nitrides (TMNs) and transition metal dichalcogenides (TMDCs) are also being explored for the study and compared with the state-of-the-art materials available. The dominance of one NRR mechanism like the Mars Van Krevelen (MvK) mechanism on TMNs over others like the dissociative NRR is also examined. These findings will provide a more comprehensive and elaborate view of the ammonia synthesis for N2 reduction reaction space.

Complexation of Boron and Aluminum with a Bidentate Hydroxy-BN-naphthalene Ligand

The isoelectronic relationship of 1,2-azaborinine (B=N structural motif) and benzene (C=C) is well documented. Upon deprotonation of the former, the anionic 1,2-azaboratabenzene is obtained, which is isosteric with pyridine (C=N) and has a similar capability as an aromatic N-donor. We present the complexation of boron and aluminum precursors with a κ2-N,O-donating 8-hydroxy-BN-naphthalene ligand (H2(BQ), 1). Six chelate complexes with 1:1 and 2:1 stoichiometries were isolated and characterized by X-ray diffraction analysis and NMR spectroscopy. Comparing the isosteric dimethylaluminum complexes of H2(BQ) and an 8-hydroxyquinoline (HQ’, 2) as a reference allowed us to quantify the influence of a formal substitution of carbon by boron on the structure and the electronic properties: While the structural parameters of the ligands were similar, the electropositive boron atom affected the electron density distributions within the complexes substantially. As the consequence, the Al–N bond was significantly shortened, and the aluminum atom showed a different coordination geometry than in the quinoline analog. Moreover, strong hypsochromic shifts of both the absorption and the emission were observed. The results highlight that the differences between CN and BN polyaromatic complexes are more distinct than between equally charged BN and CC congeners.

Electronic Structure and Surface Chemistry of Hexagonal Boron Nitride on HOPG and Nickel Substrates.

The effect of point defects and interactions with the substrate are shown by density functional theory calculations to be of significant importance for the structure and functional properties of hexagonal boron nitride (h-BN) films on highly ordered pyrolytic graphite (HOPG) and Ni(111) substrates. The structure, surface chemistry, and electronic properties are calculated for h-BN systems with selected intrinsic, oxygen, and carbon defects and with graphene hybrid structures. The electronic structure of a pristine monolayer of h-BN is dependent on the type of substrate, as h-BN is decoupled electronically from the HOPG surface and acts as bulk-like h-BN, whereas on a Ni(111) substrate, metallic-like behavior is predicted. These different film/substrate systems therefore show different reactivities and defect chemistries. The formation energies for substitutional defects are significantly lower than for intrinsic defects regardless of the substrate, and vacancies formed during film deposition are expected to be filled by either ambient oxygen or carbon from impurities. Significantly lower formation energies for intrinsic and oxygen and carbon substitutional defects were predicted for h-BN on Ni(111). In-plane h-BCN hybrid structures were predicted to be terminated by N-C bonding. Substitutional carbon on the boron site imposes n-type semiconductivity in h-BN, and the n-type character increases significantly for h-BN on HOPG. The h-BN film surface becomes electronically decoupled from the substrate when exceeding monolayer thickness, showing that the surface electronic properties and point defect chemistry for multilayer h-BN films should be comparable to those of a freestanding h-BN layer.

Enhancing UV-C Photoelectron Lifetimes for Avalanche-like Photocurrents in Carbon-Doped Bi3O4Cl Nanosheets.

Interlayer electric fields in two-dimensional (2D) materials create photoelectron protecting barriers useful to mitigate electron-hole recombination. However, tuning the interlayer electric field remains challenging. Here, carbon-doped Bi3O4Cl (C:Bi3O4Cl) nanosheets are synthesized using a gas phase protocol, and n-type carriers are acquired as confirmed by the transconductance polarity of nanosheet field effect transistors. Thin C:Bi3O4Cl nanosheets show excellent 266 nm photodetector figures of merit, and an avalanche-like photocurrent is demonstrated. Decaying behaviors of photoelectrons pumped by a 266 nm laser pulse (266 nm photoelectrons) are observed using transient absorption spectroscopy, and a significant 266 nm photoelectron lifetime quality in C:Bi3O4Cl is presented. Built C:Bi3O4Cl models suggest that the interlayer electric field can be boosted by two different carbon substitutions at the inner and outer bismuth sites. This work reports a facile approach to increase the interlayer electric field in Bi3O4Cl for future UV-C photodetector applications.