Nitrogen Incorporation Research Articles

Ultra-dry air plasma treatment for enhancing the dielectric properties of Al2O3-GPTMS-PMMA hybrid dielectric gate layers in a-IGZO TFT applications

We assessed the effects of ultra dry-air plasma surface treatments on the properties of Al2O3-GPTMS-PMMA hybrid dielectric layers for applications to high-performance amorphous Indium Gallium Zinc Oxide (a-IGZO) thin film transistors (TFTs). The hybrid layers were deposited by an easy dip coating sol-gel process at low temperature and then treated with dry-air plasma at 1, 2 and 3 consecutive cycles. Their properties were analyzed as a function of the number of plasma cycles and contrasted with those of the untreated ones. The dielectric characteristics of the hybrid layers were determined from I–V and C–f measurements performed on metal–insulator–metal and metal–insulator–semiconductor devices. The results show that the plasma treatments increase the surface energy and wettability of the hybrid films. There is also a reduction of the OH groups and oxygen vacancies in the hybrid network improving the dielectric properties. The incorporation of nitrogen into the hybrid films surface is also observed. The plasma-treated hybrid dielectric layers were applied as dielectric gate in the fabrication of a-IGZO TFTs. The best electrical performance of the fabricated TFTs was achieved with the 3 cycles plasma-treated hybrid dielectric gate, showing high mobility, 29.3 cm2 V−1 s−1, low threshold voltage, 2.9 V, high I ON/OFF current ratio, 106, and low subthreshold swing of 0.42 V dec−1.

Single-step hydrothermal synthesis of nitrogen-doped ZnO nanostructures and an insight into its electrochemical properties

Zinc oxide (ZnO) nanostructures have been extensively used as electrochemical sensing material for the development of biosensors and bioimplantable devices. It is important to evaluate their electrochemical performance while developing materials with rapid response time and higher sensitivity. Herein, we present a novel one-step low-temperature hydrothermal technique for simultaneous nitrogen doping and growth of ZnO (N-ZnO) nanostructures. Nitrogen addition is expected to enhance the electron mobility and hence the electrical conductivity of ZnO. The nanostructures were characterized by X-ray diffraction, UV–Vis spectroscopy and field emission scanning electron microscopy. The electrochemical properties were studied by electrochemical impedance spectroscopy and cyclic voltammetry using an N-ZnO/Ag/Glass symmetric two-electrode system. The nitrogen addition to ZnO lattice is suggested by XRD peak shift, changing lattice parameters and dislocation density as compared to pristine ZnO. A substantial increase in the electrochemical response and conductivity can be attributed to nitrogen incorporation into ZnO lattice.

An insight on the MoS2 tribo-film formation to determine the friction performance of Mo-S-N sputtered coatings

Amorphous Mo-S-N coatings are known to provide excellent tribological properties in diverse environments due to easy sliding under the influence of MoS 2 tribo-films. However, the role of nitrogen incorporation, the formation mechanism of MoS 2 tribo-film at the sliding interface and the changes in the friction behaviour under different environments are not fully understood. In this study, an amorphous coating with 30 at. % N was deposited in a semi-industrial reactive direct current magnetron sputtering (DCMS) system, using a single MoS 2 target in combination with a secondary plasma source. The coating was predicted to have either a Mo-S-N phase with N filling some of the S sites or a MoS 2 (N 2 ) structure where the gas molecules prevent the formation of a crystalline lamellar structure. Tribological studies performed in vacuum and ambient air resulted in steady-state COF values of 0.03 and 0.15, respectively. High-resolution transmission electron microscopy (HRTEM) analysis performed on the wear-tracks revealed that the low coefficient of friction (COF) in vacuum was attributed to the formation of a thick and continuous lamellar tribo-film with a low amount of nitrogen. Contrarily, in ambient air, the surface oxidation disturbed the formation of a continuous MoS 2 tribo-film from the amorphous coatings, leading to an increase in the COF and wear rate. This study shows through indirect measurements of the chemical composition of the as-deposited coating and wear debris that nitrogen is stored in gaseous form (N 2 ) within the amorphous matrix and is released from the contact during sliding. • Amorphous Mo-S-N coatings with 30 at. % N deposited with high adhesion to steel. • Tribo-film formation and role of N on the lubricating behaviour of Mo-S-N coatings. • COF in vacuum (10 −2 Pa) of 0.03 and in ambient air (24 °C, 20–30% RH) of 0.15. • Low friction in vacuum due to formation of a MoS 2 tribo-layer at the sliding interface. • Higher friction in ambient air due to a surface oxide formed at the interface.

Incorporation-limiting mechanisms during nitrogenation of monolayer graphene films in nitrogen flowing afterglows.

Monolayer graphene films are exposed to the flowing afterglow of a low-pressure microwave nitrogen plasma, characterized by the absence of ion irradiation and significant populations of N atoms and N2(A) metastables. Hyperspectral Raman imaging of graphene domains reveals damage generation with a progressive rise of the D/G and D/2D band ratios following subsequent plasma treatments. Plasma-induced damage is mostly zero-dimensional and the graphene state remains in the pre-amorphous regime. Over the range of experimental conditions investigated, damage formation increases with the fluence of energy provided by heterogenous surface recombination of N atoms and deexcitation of N2(A) metastable species. In such conditions, X-ray photoelectron spectroscopy reveals that the nitrogen incorporation (either as pyridine, pyrrole, or quaternary moieties) does not simply increase with the fluence of plasma-generated N atoms but is also linked to the damage generation. Based on these findings, a surface reaction model for monolayer graphene nitrogenation is proposed. It is shown that the nitrogen incorporation is first limited by the plasma-induced formation of defect sites at low damage and then by the adsorption of nitrogen atoms at high damage.

Influence of nitrogen incorporation on the photocatalytic property of ZnO nanoparticles

Zinc oxide (ZnO) nanoparticles are deliberated as exceptional photocatalyst for organic pollutants degradation. However, their inefficacy under visible light poses a problem for industrial application. Thus, in this work, a route for the synthesis of nitrogen incorporated ZnO nanocomposites was proposed with urea as the nitrogen source. From XRD spectra, the complete incorporation of nitrogen into ZnO lattice was observed. The morphological study was performed using FESEM technique which revealed a major change in the morphology of ZnO nanoparticles after nitrogen incorporation from plate-like to flower-like structures, respectively. Existence of nitrogen in the sample was confirmed through EDX studies which revealed the occurrence of 1.1% nitrogen in the sample. Nitrogen incorporated ZnO nanocomposites exhibited better photocatalytic degradation of methylene blue dye (78%) than ZnO NP (48%) in aqueous medium under visible light illumination within 30 min.

Covalent photofunctionalization and electronic repair of 2H-MoS2via nitrogen incorporation.

A route towards covalent functionalization of chemically inert 2H-MoS2 exploiting sulfur vacancies is explored by means of (TD)DFT and GW/BSE calculations. Functionalization via nitrogen incorporation at sulfur vacancies is shown to result in more stable covalent binding than via thiol incorporation. In this way, defective monolayer MoS2 is repaired and the quasiparticle band structure as well as the remarkable optical properties of pristine MoS2 are restored. Hence, defect-free functionalization with various molecules is possible. Our results for covalently attached azobenzene, as a prominent photo-switch, pave the way to create photoresponsive two-dimensional (2D) materials.

Temperature-Dependent Impedance Spectra of Nitrogen-Doped Ultrananocrystalline Diamond Films Grown on Si Substrates

Nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous-carbon (UNCD/a-C:H) composite films, grown on Si substrates by the coaxial arc plasma gun, were investigated using temperature-dependent impedance spectroscopy. The measurements were carried out in frequency and temperature ranges of 100 Hz–2 MHz and 300–400 K, respectively. Structurally, the nitrogen incorporation into the deposited films as well as sp2/sp3 ratio was studied by X-ray photoemission spectroscopy (XPS), measured with synchrotron radiation. The results of temperature-dependent electrical conductance characterization of the examined films revealed that the heterogeneous structure possesses a low-frequency conduction mechanism with an activation energy of 46 meV. This possibly originated from charge carriers hopping in the deposited composite. Furthermore, the results manifested a relaxation process, with an activation energy of 41 meV, originated from space charges in grain boundaries of the films. Cole-Cole plots of measured and fitted impedance spectra exhibited equivalent resistance due to grain boundaries that are much smaller than that related to UNCD grains. This is owing to the nitrogen incorporated in the composite film inside the grain boundaries instead of the grains. This increases the concentration of charge carriers within the grain boundaries and therefore enhances their conductivity. Moreover, the deduced capacitance corresponding to grain boundaries was larger than that originated from the UNCD grains. This is due to the difference between the grain-size and grain-boundary width of the UNCD/a-C:H composite.

Tissue-specific Isotopic Incorporation Turnover Rates and Trophic Discrimination Factors in the Freshwater Shrimp Macrobrachium borellii (Crustacea: Decapoda: Palaemonidae).

The interpretation of isotopic data in ecology requires knowledge about two factors: turnover rate and the trophic discrimination factor, which have not been well described in freshwater shrimps. We performed a 142-day diet shift experiment on 174 individuals of the omnivorous shrimp Macrobrachium borellii, measured their growth, and temporally serially sampled muscle and hepatopancreas tissue to quantify carbon and nitrogen incorporation rates and isotope discrimination factors. Shrimps were fed with artificial diets (δ13C = -26.1‰, δ15N= 2.1‰) for 45 days in attempt to standardize the shrimps' initial δ13C and δ15N values for subsequent experiments. Shrimps were then fed with another artificial diet (δ13C = -16.1‰, δ15N = 15.8‰) and the change in δ13C and δ15N was observed for a period of 97 days. The trophic discrimination factor (∆) for δ13C was significantly higher in hepatopancreas (0.7 ± 0.36‰) than in muscle (-0.1 ± 0.83‰); however, the opposite was the case for δ15N (1.7 ± 0.43‰ and 3.6 ± 0.42‰, respectively). In the hepatopancreas the mean residence time (τ) of 13C was 26.3 ± 4.3 days compared to a residence time of 16.6 ± 5.51 days for δ15N, whereas the τ in muscle was 75.8 ± 25 days for δ13C and 40 ± 25 days for δ15N. The rate of incorporation of carbon into muscle was higher than that predicted by allometric equations relating isotopic incorporation rate to body mass that was developed previously for invertebrates. Our results support ranges of traditional trophic discrimination factor values observed in muscles samples of different taxa (∆15N around 3‒3.5‰ and ∆13C around 0‒1‰), but our work provides evidence that these traditionally used values may vary in other tissues, as we found that in the hepatopancreas ∆15N is around 1.7‰.

Promoting reactivity of graphene based catalysts to achieve LH mechanism for CO oxidation

In heterogeneous catalysis, the LH (Langmuir Hinshelwood) mechanism is more efficient and recommended over any other mechanism adopted for CO oxidation. However, the LH mechanism over a carbon surface is a challenge and is paused to be applied to any carbon surface in practical application. In this work, we carried out density functional theory to study how the incorporation of nitrogen, boron atom (C→N, C→B) and co-doping on graphene nanoribbons can modify the catalytic activity of the surface and the preference between ER (Eley-Ridel) and LH mechanism is explored. Boron plays a crucial role in the adsorption of both CO and O2, whereas nitrogen doping can only activate O2 molecule through altering the triplet ground state. Considering the activation energy for the first CO2 formation and CO binding strength, we have defined a window to identify the operation of the LH mechanism in the catalysis. 3B edge doped AGNR (armchair graphene nanoribbon doped with three boron atoms at its edge) is identified as an active catalyst for the CO oxidation through the LH mechanism, with the SA (Sabatier activity) and TOF (turnover frequency) values of 0.90 and 2.47, respectively. This approach will help to search for metal-free catalysts for the CO oxidation with the efficient LH mechanism.

High‐Resolution Electronic Excitation and Emission Spectra of Pentacene and 6,13‐Diazapentacene Monomers and Weakly Bound Dimers by Matrix‐Isolation Spectroscopy

N‐Heteropolycycles are among the most promising candidates for applications in organic devices. For this purpose, a profound understanding of the low‐energy electronic absorbance and emission characteristics is of crucial importance. Herein, we report high‐resolution absorbance and fluorescence spectra of pentacene (PEN) and 6,13‐diazapentacene (DAP) in solid neon obtained using the matrix‐isolation technique. Accompanying DFT calculations allow the assignment of specific vibrationally resolved signals to corresponding modes. Furthermore, we present for the first time evidence for the formation of van der Waals dimers of both substances. These dimers exhibit significantly different optical characteristics resulting from the change of electronic properties evoked by the incorporation of sp2 nitrogen into the molecular backbone.

Nitrogen and carbon incorporation in GaNxAs1-x grown in a showerhead MOVPE reactor

The growth of dilute nitrides with metal organic chemical vapor phase epitaxy (MOVPE) presents two major challenges: a low N-incorporation combined with a high impurity density of carbon and hydrogen. For the device implementation the full understanding of the growth of the metastable material and the influence of the parameters on the impurity levels is of high interest. We investigated the N- and C-incorporation in GaNxAs1-x as a reference system in a close coupled showerhead MOVPE reactor to minimize gas-phase reactions for a wide range of growth parameters and precursors. The N-incorporation was always proportional to the N/As-ratio, while the absolute N-molar-flow, growth rate and interaction time show only a minor influence, indicating little gas-phase pre-reactions. Pyrolysis and pre-reactions between radicals on the surface have been taken into account according to the used precursor combination. We identified the group-III-methyl-groups as the major C-source and found a linear correlation between the incorporated N and C. GaN0.01As0.99 could be grown with C-background below 1016 atoms/cm3 for optimized conditions.

Incorporation of nitrogen in diamond films – A new way of tuning parameters for optical passive elements

This paper investigates the impact of nitrogen incorporation in diamond films for the construction of an interferometric sensor to measure displacement. Diamond films with different nitrogen levels (0–5%) were deposited on silicon substrates by microwave plasma enhanced chemical vapor deposition. The structural characteristics of these samples are characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), confocal micro-Raman spectroscopy, and electron energy loss spectroscopy (EELS). The homogeneous and continuous surface morphology of the films is observed through SEM. In the micro-Raman and electron energy loss spectroscopy studies, it is evident that there is a formation of sp2-bonded carbon phases due to the increase in the concentration of nitrogen. This investigation gives a strong basis for utilizing these diamond films as reflective layers in fiber-optic devices. The interferometric measurement setup is constructed as a Fabry-Pérot interferometer. The nitrogen incorporated films are proved to be useful as mirrors as they achieve a measurement signal with high contrast. The achieved visibility values for the investigated samples are higher than 94% in the range of 40–100 μm.

Nitrogen-doped nanoporous graphene induced by a multiple confinement strategy for membrane separation of rare earth.

SummaryRare earth separation is still a major challenge in membrane science. Nitrogen-doped nanoporous graphene (NDNG) is a promising material for membrane separation, but it has not yet been tested for rare earth separation, and it is limited by multi-complex synthesis. Herein, we developed a one-step, facile, and scalable approach to synthesize NDNG with tunable pore size and controlled nitrogen content using confinement combustion. Nanoporous hydrotalcite from Zn(NO3)2 is formed between layers of graphene oxide (GO) absorbed with phenylalanine via confinement growth, thus preparing the sandwich hydrotalcite/phenylalanine/GO composites. Subsequently, area-confinement combustion of hydrotalcite nanopores is used to etch graphene nanopores, and the hydrotalcite interlayer as a closed flat nanoreactor induces two-dimensional space confinement doping of planar nitrogen into graphene. The membrane prepared by NDNG achieves separation of Sc3+ from the other rare earth ions with excellent selectivity (∼3.7) through selective electrostatic interactions of pyrrolic-N, and separation selectivity of ∼1.7 for Tm3+/Sm3+.

Peculiarities of sol-gel synthesis of co-modified by nitrogen and metal ions (Zn2+, Zr4+, Pt2+) semiconductive TiO2 films

According to the XPS investigation of titania films co-modified by nitro gen and metal ions obtained via sol-gel method, the formation of common bonds between elements occurs due to the presence of metal ions. The mechanism of urea thermolysis is changed as a result of the ability of metal ions to form the complex compounds with urea molecules under the reported synthesis conditions that, in turn, depends on the nature of metal ions, leading to the different chemical compositions of materials’ surface. The XPS data show that nitrogen atoms are surrounded by nonmetal ones on the surface of the films modi fied by Zn2+ or Zr4+ ions. It is suggested that no formation of the complexes between Ті, Zn, or Zr atoms with urea occurs due to its protonation through an oxygen atom leading to the formation of O,N-containing reaction products. In the case of Pt2+ doping, the substitutional nitrogen incorporation in the titania lattice, as well as the formation of N-containing fragments, have been detected. The chemical nature of Pt ions allows them to interact with urea molecules through an N atom of the amino group. As a result, the transformation of urea molecules in the complexes occurs at higher temperatures concurrently with the titania crystallization that is recognized as a catalyst for the intermediates of the urea decomposition leading to the formation of common bonds between N and Ti atoms.

Study of the Fluorescence based Applications of Water Soluble (N, P) Doped Carbon Dots Synthesized via Microwave Assisted Green Pyrolysis

Background: Water soluble nitrogen and phosphorus doped carbon dots (CD) have been synthesized using citric acid, tris(2-aminoethyl)amine and orthophosphoric acid via one step microwave assisted pyrolytic method. Methods: The CD synthesized has been characterized using FTIR, UV-Vis, fluorescence spectroscopy and EDAX coupled with SEM techniques. Results: SEM study has shown the formation of nanosized CD with an average size of ~18 nm. Elemental analysis via EDAX has confirmed successful incorporation of nitrogen (30.8% wt) and phosphorus (5.7% wt) atoms in it. The steady state and 3D fluorescence spectroscopic studies have shown its efficient fluorescence emission with emission maxima in the region of ~450 nm. It has shown efficient “turn off” fluorescence behaviour towards transition metal ions like Fe2+ and Co2+ ions and toxic nitrophenolic compounds like p-nitrophenol and picric acid. Its efficient interaction with BSA has been revealed in terms of fluorescence quenching of BSA by steady state, synchronous and 3D fluorescence spectroscopy. It has shown very good in vitro biocompatibility and enhanced cell adhesion properties towards NIH 3T3 fibroblast cells. Moreover, fluorescence microscopy has shown significant uptake of CD by the tested cell line. Conclusion: Such bio-compatible nitrogen and phosphorous doped CD can be potentially useful to estimate metal ions, p-nitrophenol and picric acid using fluorescence spectroscopy and for fluorescence based bio-imaging.

Electrosynthesis of H2O2 over Cobalt-N-Doped Ordered Mesoporous Carbon Materials (Co-N-OMC)

Electrochemical generation of hydrogen peroxide (H2O2) via two-electron oxygen reduction is a promising alternative to the conventional industrial anthraquinone process. The current challenges include discovering a sample and cost-effective electrocatalysts with high activity, selectivity, and stability. Herein, we reported a straightforward preparation of cobalt-N-doped ordered mesoporous carbon (Co-N-OMC) using dry-state low energy ball milling, followed by controlled pyrolysis. This fast, solvent-free, and scalable method used inexpensive materials containing cobalt acetate as the metal precursor, mesoporous SiO2 (KIT6) with a high surface area as the template for controlling the mesoporous structure; and imidazole as carbon and nitrogen sources, allowing simultaneous carbon matrix formation and nitrogen incorporation. Moreover, the Co-N-OMC electrocatalytic performance was compared with various materials, including N-OMC, Co-OMC, OMC, and non-mesoporous carbon, to separately examine each component's role, embedded Co, N dopant, and mesoporous morphology on the catalyst behavior. The optimal Co-N-OMC catalyst displayed an excellent electrocatalytic activity with H2O2 selectivity above 95% in an acid medium at very positive potentials. Furthermore, batch H2O2 electrolysis measurements confirmed the high H2O2 faradaic selectivity over 90% and H2O2 production of 555 mmol g-1 for a 60 min test. Finally, laboratory-scale H2O2 production was demonstrated in a flow electrolytic reactor with a Co−N−OMC cathode layer. The H2O2 electrolysis in flow cell configuration exhibitedabout a five-time-increase in H2O2 production ~ 2900 mmol g-1 for 60 min test with H2O2 faradaic selectivity above 90%. Such a considerable improvement in H2O2 production and selectivity is probably due to cobalt particles' coexistence with nitrogen dopants supported on a mesoporous structure. The optimal loading of cobalt might facilitate the two-electron pathway towards H2O2 generation.In addition, nitrogen dopants and the mesoporous structure may have lowered the ORR overpotential and improved mass transport in the catalyst layer, respectively.

Silicon Phthalocyanine Modified Multi-Walled Carbon Nanotubes As a Novel Metal-Free Catalyst for the Oxygen Electroreduction

Finding an alternative catalysts for the oxygen reduction reaction (ORR) has been a key issue in modern electrocatalysis. Traditional platinum-based catalysts are not viable in the long term and thus much effort has been focused on non-precious metal catalysts. Heteroatom doped and metal-heteroatom co-doped carbon materials have emerged as the main candidate for replacing the platinum-based catalysts. Different MN4 macrocycles, such as metal phthalocyanines and porphyrins, have been studied as promising materials to prepare electrocatalysts for ORR in alkaline media [1]. While the development of non-precious metal and non-metal carbon catalysts has gained a lot of attention recently, non-metal phthalocyanines are a less studied topic [2].In this work a novel catalyst material including multi-walled carbon nanotubes (MWCNT) and silicon phthalocyanine dichloride (SiPcCl2) was synthesised and the electrochemical activity towards the oxygen reduction reaction (ORR) in alkaline media was studied. Different ratios of phthalocyanine-to-nanotubes were pyrolysed at 800 °C. After optimising the ratio of phthalocyanine-to-nanotubes, the pyrolysis process was also carried out at different temperatures, but the results showed that the best temperature for pyrolysis is still 800 °C. ORR activity on SiPc/MWCNT catalyst was studied in 0.1 M KOH by employing rotating disc electrode method. Physical characterisation was carried out with X-ray photoelectron spectroscopy and transmission electron microscopy. The results showed successful incorporation of silicon and nitrogen into the carbon framework. We show that doping MWCNTs with a non-metal phthalocyanine creates a highly active ORR catalyst rivaling the activity of metal-based catalysts in alkaline conditions. This work clearly demonstrates that non-metal macrocyclic compound modified carbons, similar to the the SiPc/MWCNT can be used as alternative cathode catalysts for the metal-air batteries and alkaline membrane fuel cells.[1] Y. Liu, X. Yue, K. Li, J. Qiao, D.P. Wilkinson, J. Zhang, PEM fuel cell electrocatalysts based on transition metal macrocyclic compounds, Coord Chem Rev. 315 (2016) 153-177.[2] K.-K. Türk, K. Kaare, I. Kruusenberg, M. Merisalu, U. Joost, L. Matisen, V. Sammelselg, J.H. Zagal, K. Tammeveski, Oxygen electroreduction on zinc and dilithium phthalocyanine modified multiwalled carbon nanotubes in alkaline media, J. Electrochem. Soc. 164 (2017) H338-H344.

Inhibiting photocatalytic electron-hole recombination by coupling MIL-125(Ti) with chemically reduced, nitrogen-containing graphene oxide

In this study, we fabricated a novel chemically reduced nitrogen containing graphene oxide (CR-N-GO) modified metal organic framework, (MIL-125(Ti)) by one-pot solvo-thermal approach for its application in photocatalytic degradation of xenobiotic organic pollutants. CR-N-GO has nitrogen present as impurity on its surface therefore, aim of this study was to signify the importance of that nitrogen for enhancement of visible light activity of photocatalyst. The r-N-MIL (modified MIL-125(Ti)) photocatalyst was characterized to obtain structural, optical, and surface properties. This characterization suggests mesoporous structures with improved surface roughness and visible light capturing property. Photocatalytic degradation of Rhodamine B (RhB) increased 2.0-fold under visible light compared to that of the pristine MIL-125(Ti). Enhanced photocatalytic activity under visible light was attributed to p states induced by oxygen bonding of MIL-125(Ti) oxo clusters with CR-N-GO, nitrogen incorporation into MIL-125(Ti) from CR-N-GO, localized electronic states of Ti-O-C bonds and mesoporous structure. Moreover, photoexcitation, radical generation, and photocatalytic degradation steps exhibited the photocatalytic degradation mechanism. Furthermore, LC/MS analysis identified chromophore cleavage, ring opening, and mineralization as major photocatalytic degradation pathways. Performance evaluation through catalyst surface efficiency and apparent quantum yield is on par with those of other catalysts and describes r-N-MIL as a fascinating semiconductor photocatalyst.

Iron and nitrogen-doped double gyroid mesoporous carbons for oxygen reduction in acidic environments

Iron- and nitrogen-doped carbon (Fe-N-C) represents a promising class of alternative electrocatalysts to noble metals for the oxygen reduction reaction (ORR) in acidic environments. To make Fe-N-C active, one of the most critical parameters is microporosity, which must be controlled to maximize the active site density. However, the use of microporosity must be optimized for the requirement of high-flux mass transport. Here, we synthesized and demonstrated gyroidal mesoporous Fe-N-C with microporous pore walls as an avenue to combine a high active-site density with favorable mass transport at high flux. The gyroidal mesoporous Fe-N-C catalysts have competitive gravimetric and volumetric ORR activities, comparable to the ORR activity obtained in purely microporous configurations despite having mesoporous features. Our result suggests that the ORR activity of microporous Fe-N-C electrocatalysts can be combined with mesoporosity through the use of mesoporous Fe-N-C with microporous pore walls. We further investigate effects of the nitrogen incorporation method on mesoporous N-doped carbon electrocatalysts. We find that despite having ∼2 × higher N concentration, nitrogen incorporation via NH3 yields similar ORR activity to incorporation via a chemical additive, a finding we attribute to the role of pyridinic and quaternary N in the ORR.

Engineering quantum-coherent defects: The role of substrate miscut in chemical vapor deposition diamond growth

The engineering of defects in diamond, particularly nitrogen-vacancy (NV) centers, is important for many applications in quantum science. A materials science approach based on chemical vapor deposition (CVD) growth of diamond and in situ nitrogen doping is a promising path toward tuning and optimizing the desired properties of the embedded defects. Herein, with the coherence of the embedded defects in mind, we explore the effects of substrate miscut on the diamond growth rate, nitrogen density, and hillock defect density, and we report an optimal angle range for the purposes of engineering coherent ensembles of NV centers in diamond according to our growth parameters. We provide a model that quantitatively describes hillock nucleation in the step-flow regime of CVD growth, shedding insight on the physics of hillock formation. We also report significantly enhanced incorporation of nitrogen at hillock defects, opening the possibility for templating hillock-defect-localized NV center ensembles for quantum applications.