Reproducible graphene synthesis by oxygen-free chemical vapour deposition.

Chemical vapour deposition (CVD) synthesis of graphene on copper has been broadly adopted since the first demonstration of this process1. However, widespread use of CVD-grown graphene for basic science and applications has been hindered by challenges with reproducibility2 and quality3. Here we identify trace oxygen as a key factor determining the growth trajectory and quality for graphene grown by low-pressure CVD. Oxygen-free chemical vapour deposition (OF-CVD) synthesis is fast and highly reproducible, with kinetics that can be described by a compact model, whereas adding trace oxygen leads to suppressed nucleation and slower/incomplete growth. Oxygen affects graphene quality as assessed by surface contamination, emergence of the Raman D peak and decrease in electrical conductivity. Epitaxial graphene grown in oxygen-free conditions is contamination-free and shows no detectable D peak. After dry transfer and boron nitride encapsulation, it shows room-temperature electrical-transport behaviour close to that of exfoliated graphene. A graphite-gated device shows well-developed integer and fractional quantum Hall effects. By highlighting the importance of eliminating trace oxygen, this work provides guidance for future CVD system design and operation. The increased reproducibility and quality afforded by OF-CVD synthesis will broadly influence basic research and applications of graphene.

Dynamic Gate Control of Aryldiazonium Chemistry on Graphene Field-Effect Transistors.

As graphene field-effect transistors (GFETs) are becoming increasingly valued for sensor applications, efficiency and control of their surface functionalization become critical. Here, we introduce an innovative method using a gate electrode to precisely modulate aryldiazonium functionalization directly on graphene devices. Although this covalent chemistry is well-known, we show that its spontaneous reaction on GFETs is highly heterogeneous with a low overall yield. By dynamically tuning the gate voltage in the presence of the reactant, we can quickly enable or suppress the reaction, resulting in a high degree of homogeneity between devices. We are also able to monitor and control functionalization kinetics in real time. The mechanism for our approach is based on electron transfer availability, analogous to chemical, substrate-based, or electrochemical doping, but has the practical advantage of being fully implementable on devices or chips. This work illustrates how powerful the FET platforms are to study surface reactions on nanomaterials in real time.

Visible Out-of-plane Polarized Luminescence and Electronic Resonance in Black Phosphorus.

Black phosphorus (BP) is unique among layered materials because of its homonuclear lattice and strong structural anisotropy. While recent investigations on few-layer BP have extensively explored the in-plane (a, c) anisotropy, much less attention has been given to the out-of-plane direction (b). Here, the optical response from bulk BP is probed using polarization-resolved photoluminescence (PL), photoluminescence excitation (PLE), and resonant Raman scattering along the zigzag, out-of-plane, and armchair directions. An unexpected b-polarized luminescence emission is detected in the visible, far above the fundamental gap. PLE indicates that this emission is generated through b-polarized excitation at 2.3 eV. The same electronic resonance is observed in resonant Raman with the enhancement of the Ag phonon modes scattering efficiency. These experimental results are fully consistent with DFT calculations of the permittivity tensor elements and demonstrate the remarkable extent to which the anisotropy influences the optical properties and carrier dynamics in black phosphorus.

Bioremediation of Unconventional Oil Contaminated Ecosystems under Natural and Assisted Conditions: A Review.

It is a general understanding that unconventional oil is petroleum-extracted and processed into petroleum products using unconventional means. The recent growth in the United States shale oil production and the lack of refineries in Canada built for heavy crude processes have resulted in a significant increase in U.S imports of unconventional oil since 2018. This has increased the risk of incidents and catastrophic emergencies during the transportation of unconventional oils using transmission pipelines and train rails. A great deal of effort has been made to address the remediation of contaminated soil/sediment following the traditional oil spills. However, spill response and cleanup techniques (e.g., oil recuperation, soil-sediment-water treatments) showed slow and inefficient performance when it came to unconventional oil, bringing larger associated environmental impacts in need of investigation. To the best of our knowledge, there is no coherent review available on the biodegradability of unconventional oil, including Dilbit and Bakken oil. Hence, in view of the insufficient information and contrasting results obtained on the remediation of petroleum, this review is an attempt to fill the gap by presenting the collective understanding and critical analysis of the literature on bioremediation of products from the oil sand and shale (e.g., Dilbit and Bakken oil). This can help evaluate the different aspects of hydrocarbon biodegradation and identify the knowledge gaps in the literature.

RDX degradation by chemical oxidation using calcium peroxide in bench scale sludge systems.

The ability of calcium peroxide (CaO2) to degrade hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated soil slurries using CaO2-based modified Fenton oxidation was investigated. Results showed that increasing the CaO2 dose increased degradation rates of RDX and pH. RDX concentrations decreased to below detection after 18 h with 2 M and 2.5 M CaO2, after 30 h with 1.5 M CaO2, after 54 h with 1 M CaO2, but 0.1 M CaO2 achieved no significant RDX removal. Increasing the soil organic matter content decreased the rate and extent of RDX degradation. RDX degradation products 4-nitro-2,4-diazabutanal (NDAB) and methylenedinitramine (MEDINA) were quantified, and the greater accumulation of NDAB than MEDINA suggests denitration of RDX was the most likely initial degradation step. Isotopic ratios for nitrogen and oxygen associated with RDX oxidation are also consistent with either nitrification of NH4+ from soil or precipitation. Existing technologies merely only extract energetics from soils for treatment ex situ, whereas the approach introduced herein destroys RDX in situ with a one-step application.

Case report: Infant with a Fast-growing Soft Tissue Tumor on the Thumb, Revealing a PLAG1-positive Connatal Lipoblastoma.

At the age of 4 months, an infant was presented to us with a nodular subcutaneous tumor on the right thumb measuring 2cm, already seen prenatally via ultrasound. An MRI in sedation performed at the age of 4.5 months had no diagnostic specificity. By a biopsy at the age of 5 months malignancy could be excluded. Finally at the age of 16 months the tumor which had meanwhile grown to a monstrous size (5 cm of diameter) could be entirely removed by microsurgical technique maintaining the integrity of all intrinsic structures. The diagnosis of myxoid lipoblastoma was confirmed. According to literature, Lipoblastomas often present as connatal rapid growing soft tissue tumors and are benign. Total removal is essential for avoiding a local recurrence.

Momentum-Resolved Dielectric Response of Free-Standing Mono-, Bi-, and Trilayer Black Phosphorus.

Black phosphorus (BP), a 2D semiconducting material of interest in electronics and photonics, exhibits physical properties characterized by strong anisotropy and band gap energy that scales with reducing layer number. However, the investigation of its intrinsic properties is challenging because thin-layer BP is photo-oxidized under ambient conditions and the energy of its electronic states shifts in different dielectric environments. We prepared free-standing samples of few-layer BP under glovebox conditions and probed the dielectric response in a vacuum using scanning transmission electron microscopy and electron energy loss spectroscopy (STEM-EELS). Thresholds of the excitation energy are measured at 1.9, 1.4, and 1.1 eV for the mono-, bi-, and trilayer BP, respectively, and these values are used to estimate the corresponding optical band gaps. A comparison of our results with electronic structure calculations indicates that the variation of the quasi-particle gap is larger than that of the exciton binding energy. The dispersion of the plasmons versus momentum for one- to three-layer BP and bulk BP highlights a deviation from parabolic to linear dispersion and strong anisotropic fingerprints.

Second-Order Raman Scattering in Exfoliated Black Phosphorus.

Second-order Raman scattering has been extensively studied in carbon-based nanomaterials, for example, nanotube and graphene, because it activates normally forbidden Raman modes that are sensitive to crystal disorder, such as defects, dopants, strain, and so forth. The sp2-hybridized carbon systems are, however, the exception among nanomaterials, where first-order Raman processes usually dominate. Here we report the identification of four second-order Raman modes, named D1, D1', D2 and D2', in exfoliated black phosphorus (P(black)), an elemental direct-gap semiconductor exhibiting strong mechanical and electronic anisotropies. Located in close proximity to the Ag1 and Ag2 modes, these new modes dominate at an excitation wavelength of 633 nm. Their evolutions as a function of sample thickness, excitation wavelength, and defect density indicate that they are defect-activated and involve high-momentum phonons in a doubly resonant Raman process. Ab initio simulations of a monolayer reveal that the D' and D modes occur through intravalley scatterings with split contributions in the armchair and zigzag directions, respectively. The high sensitivity of these D modes to disorder helps explaining several discrepancies found in the literature.

Plasmonic enhancement of SERS measured on molecules in carbon nanotubes.

We isolated the plasmonic contribution to surface-enhanced Raman scattering (SERS) and found it to be much stronger than expected. Organic dyes encapsulated in single-walled carbon nanotubes are ideal probes for quantifying plasmonic enhancement in a Raman experiment. The molecules are chemically protected through the nanotube wall and spatially isolated from the metal, which prevents enhancement by chemical means and through surface roughness. The tubes carry molecules into SERS hotspots, thereby defining molecular position and making it accessible for structural characterization with atomic-force and electron microscopy. We measured a SERS enhancement factor of 106 on α-sexithiophene (6T) molecules in the gap of a plasmonic nanodimer. This is two orders of magnitude stronger than predicted by the electromagnetic enhancement theory (104). We discuss various phenomena that may explain the discrepancy (including hybridization, static and dynamic charge transfer, surface roughness, uncertainties in molecular position and orientation), but found all of them lacking in enhancement for our probe system. We suggest that plasmonic enhancement in SERS is, in fact, much stronger than currently anticipated. We discuss novel approaches for treating SERS quantum mechanically that appear promising for predicting correct enhancement factors. Our findings have important consequences on the understanding of SERS as well as for designing and optimizing plasmonic substrates.

A field-deployed surface plasmon resonance (SPR) sensor for RDX quantification in environmental waters.

A field-deployable surface plasmon resonance (SPR) sensor is reported for the detection of the energetic material (commonly termed explosives) 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) at ppb concentration in environmental samples. The SPR sensor was first validated under laboratory conditions with uncontaminated natural water samples spiked with known concentrations of RDX near the EPA limit of 2 ppb, which was then applied to monitor environmental samples collected in different downgradient wells near a grenade training range. The SPR sensor was finally tested on the field, where environmental samples were analysed on location in less than 90 minutes per well, which included the time to setup the equipment, sample the well and analyse the sample. The SPR analysis time was less than 45 minutes for equilibration, recalibration and measuring the water sample. Results obtained with the SPR sensors were cross-validated with the standard HPLC method (EPA method 8330b), and they showed good agreement with an accuracy within less than 1.6 ppb for analysis at the sampling sites, and with the relative standard deviation (RSD) better than 20% for field and laboratory measurements. The SPR sensor worked in a range of environmental conditions, including operation from about 0 °C to nearly 30 °C. The instrument was easily deployed near the sampling site using motor vehicles under summer conditions (Lab-in-a-Jeep) and using a sled under winter conditions (Lab-on-a-sled), showcasing the field deployability of the RDX SPR sensor and the possibility of continuously monitoring RDX in the environment.

A Conceptual Model of Fate and Transport Processes for RDX Deposited to Surface Soils of North American Active Demolition Sites.

The use of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) as an energetic material (EM) in ammunition constituents such as detonators, primers, mines, and rocket boosters and in plastic explosives has led to an international warning on possible soil, surface water, and groundwater contamination on military training sites. In Canada, the demolition sites of range training areas are known to be the second most contaminated sites by EM residues in terms of their concentrations in soil after anti-tank ranges. This research proposes a conceptual model of the presence of RDX at the field scale at demolition sites according to previous soil and water characterization studies. This model illustrates the origin of RDX contamination, the main RDX transport pathways and processes, and the main threatened receptors. This conceptual model is of importance to visualize and understand RDX's environmental fate and behavior and to ultimately enable the production of a detailed quantitative model that can help to manage those RDX-contaminated sites.

Polarization-Resolved Raman Study of Bulk-like and Davydov-Induced Vibrational Modes of Exfoliated Black Phosphorus.

Owing to its crystallographic structure, black phosphorus is one of the few 2D materials expressing strongly anisotropic optical, transport, and mechanical properties. We report on the anisotropy of electron-phonon interactions through a polarization-resolved Raman study of the four vibrational modes of atomically thin black phosphorus (2D phosphane): the three bulk-like modes Ag1, B2g, and Ag2 and the Davydov-induced mode labeled Ag(B2u). The complex Raman tensor elements reveal that the relative variation in permittivity of all Ag modes is irrespective of the atomic motion involved lowest along the zigzag direction, the basal anisotropy of these variations is most pronounced for Ag2 and Ag(B2u), and interlayer interactions in multilayer samples lead to reduced anisotropy. The bulk-forbidden Ag(B2u) mode appears for n ≥ 2 and quickly subsides in thicker layers. It is assigned to a Davydov-induced IR to Raman conversion of the bulk IR mode B2u and exhibits characteristics similar to Ag2. Although this mode is expected to be weak, an electronic resonance significantly enhances its Raman efficiency such that it becomes a dominant mode in the spectrum of bilayer 2D phosphane.

Photooxidation and quantum confinement effects in exfoliated black phosphorus.

Thin layers of black phosphorus have recently raised interest owing to their two-dimensional (2D) semiconducting properties, such as tunable direct bandgap and high carrier mobilities. This lamellar crystal of phosphorus atoms can be exfoliated down to monolayer 2D-phosphane (also called phosphorene) using procedures similar to those used for graphene. Probing the properties has, however, been challenged by a fast degradation of the thinnest layers on exposure to ambient conditions. Herein, we investigate this chemistry using in situ Raman and transmission electron spectroscopies. The results highlight a thickness-dependent photoassisted oxidation reaction with oxygen dissolved in adsorbed water. The oxidation kinetics is consistent with a phenomenological model involving electron transfer and quantum confinement as key parameters. A procedure carried out in a glove box is used to prepare mono-, bi- and multilayer 2D-phosphane in their pristine states for further studies on the effect of layer thickness on the Raman modes. Controlled experiments in ambient conditions are shown to lower the A(g)(1)/A(g)(2) intensity ratio for ultrathin layers, a signature of oxidation.

Titanyl phthalocyanine ambipolar thin film transistors making use of carbon nanotube electrodes.

The capability of efficiently injecting charge carriers into organic films and finely tuning their morphology and structure is crucial to improve the performance of organic thin film transistors (OTFTs). In this work, we investigate OTFTs employing carbon nanotubes (CNTs) as the source-drain electrodes and, as the organic semiconductor, thin films of titanyl phthalocyanine (TiOPc) grown by supersonic molecular beam deposition (SuMBD). While CNT electrodes have shown an unprecedented ability to improve charge injection in OTFTs, SuMBD is an effective technique to tune film morphology and structure. Varying the substrate temperature during deposition, we were able to grow both amorphous (low substrate temperature) and polycrystalline (high substrate temperature) films of TiOPc. Regardless of the film morphology and structure, CNT electrodes led to superior charge injection and transport performance with respect to benchmark Au electrodes. Vacuum annealing of polycrystalline TiOPc films with CNT electrodes yielded ambipolar OTFTs.

Biodegradation of nitroglycerin from propellant residues on military training ranges.

Nitroglycerin (NG) is often present in soils and sometimes in pore water at antitank firing positions due to incomplete combustion of propellants. Various degradation processes can contribute to the natural attenuation of NG in soils and pore water, thus reducing the risks of groundwater contamination. However, until now these processes have been sparsely documented. This study aimed at evaluating the ability of microorganisms from a legacy firing position to degrade dissolved NG, as well as NG trapped within propellant particles. Results from the shake-flask experiments showed that the isolated culture is capable of degrading dissolved NG but not the nitrocellulose matrix of propellant particles, so that the deeply embedded NG molecules cannot be degraded. Furthermore, the results from column experiments showed that in a nutrient-poor sand, degradation of dissolved NG may not be sufficiently rapid to prevent groundwater contamination. Therefore, the results from this study indicate that, under favorable soil conditions, biodegradation can be an important natural attenuation process for NG dissolving out of fresh propellant residues. In contrast, biodegradation does not contribute to the long-term attenuation of NG within old, weathered propellant residues. Although NG in these old residues no longer poses a threat to groundwater quality, if soil clean-up of a legacy site is required, active remediation approaches should be sought.

Evaluation of 4DryField® as an Adhesion Prophylaxis in Pediatric Patients: A Propensity-Score Matched Study.

INTRODUCTION: Abdominal adhesions following surgery can lead to complications like intestinal obstruction and pelvic pain. While no molecular therapies currently target the underlying adhesion formation process, various barrier agents exist. 4DryField® has shown promise in reducing bleeding and adhesions in adults. This study aimed to assess its effectiveness in children. METHODS: The study examined all pediatric patients who underwent laparotomy between January 2018 and February 2022. It compared outcomes between those treated with 4DryField® and a control group. Key endpoints included surgical revision, adhesion recurrence, infections, insufficiencies, fever, C-reactive protein (CRP) levels, and time to gastrointestinal passage. RESULTS: In total, 233 children had surgery for bowel adhesions. After propensity score matching, 82 patients were included in the analysis: 39 in the control and 43 in the 4DryField® group. 4DryField® did not affect the readhesion rate. Children in the treatment group had significantly more complications (47 vs. 15%, p = 0.002), more often fever, and higher CRP levels. CONCLUSIONS: 4DryField® did not show potential in reducing adhesion formation, but it was associated with significantly more complications in pediatric patients. Thus, future prospective studies are needed to evaluate the safety and effectiveness of 4DryField® in children.

Intra-arterial delivery of neurospheres into isolated perfused porcine colons: a proof of concept.

Cell replacement in aganglionic intestines is a promising, yet merely experimental tool for the therapy of congenital dysganglionosis of the enteric nervous system like Hirschsprung disease. While the injection of single cells or neurospheres to a defined and very restricted location is trivial, the translation to the clinical application, where large aganglionic or hypoganglionic areas need to be colonized (hundreds of square centimetres), afford a homogeneous distribution of multiple neurospheres all over the affected tissue areas. Reaching the entire aganglionic area in vivo is critical for the restoration of peristaltic function. The latter mainly depends on an intact nervous system that extends throughout the organ. Intra-arterial injection is a common method in cell therapy and may be the key to delivering cells or neurospheres into the capillary bed of the colon with area-wide distribution. We describe an experimental method for monitoring the distribution of a defined number of neurospheres into porcine recta ex vivo, immediately after intra-arterial injection. We designed this method to localize grafting sites of single neurospheres in precise biopsies which can further be examined in explant cultures. The isolated perfused porcine rectum allowed us to continuously monitor the perfusion pressure. A blockage of too many capillaries would lead to an ischaemic situation and an increase of perfusion pressure. Since we could demonstrate that the area-wide delivery of neurospheres did not alter the overall vascular resistance, we showed that the delivery does not significantly impair the local circulation.

Interindividual variability in cold-pressor pain sensitivity is not explained by peripheral vascular responding and generalizes to a C-nociceptor-specific pain phenotype.

ABSTRACT: Pain sensitivity of healthy subjects in the cold-pressor (CP) test was proposed to be dichotomously distributed and to represent a pain sensitivity trait. Still, it has not been systematically explored which factors influence this pain sensitivity readout. The aim of this study was to distinguish potential contributions of local tissue-related factors such as perfusion and thermoregulation or gain settings in nociceptive systems. Cold-pressor-sensitive and CP-insensitive students screened from a medical student laboratory course were recruited for a CP retest with additional cardiovascular and bilateral local vascular monitoring. In addition, comprehensive quantitative sensory testing according to Deutscher Forschungsverbund Neuropathischer Schmerz standards and a sustained pinch test were performed. Cold pressor was reproducible across sessions (Cohen kappa 0.61 ± 0.14, P < 0.005). At 30 seconds in ice water, CP-sensitive subjects exhibited not only more pain (78.6 ± 26.3 vs 29.5 ± 17.5, P < 0.0001) but also significantly stronger increases in mean arterial blood pressure (12.6 ± 9.3 vs 5.6 ± 8.1 mm Hg, P < 0.05) and heart rate (15.0 ± 8.2 vs 7.1 ± 6.2 bpm, P < 0.005), and lower baroreflex sensitivity, but not local or vasoconstrictor reflex-mediated microcirculatory responses. Cold-pressor-sensitive subjects exhibited significantly lower pain thresholds also for cold, heat, and blunt pressure, and enhanced pain summation, but no significant differences in Aδ-nociceptor-mediated punctate mechanical pain. In conclusion, differences in nociceptive signal processing drove systemic cardiovascular responses. Baroreceptor activation suppressed pain and cardiovascular responses more efficiently in CP-insensitive subjects. Cold-pressor sensitivity generalized to a pain trait of C-fiber-mediated nociceptive channels, which was independent of local thermal and vascular changes in the ice-water-exposed hand. Thus, the C-fiber pain trait reflects gain setting of the nociceptive system.

Stable isotopes of nitrate reflect natural attenuation of propellant residues on military training ranges.

Nitroglycerin (NG) and nitrocellulose (NC) are constituents of double-base propellants used notably for firing antitank ammunitions. Nitroglycerin was detected in soil and water samples from the unsaturated zone (pore water) at an active antitank firing position, where the presence of high nitrate (NO3(-)) concentrations suggests that natural attenuation of NG is occurring. However, concentrations alone cannot assess if NG is the source of NO3(-), nor can they determine which degradation processes are involved. To address this issue, isotopic ratios (δ(15)N, δ(18)O) were measured for NO3(-) produced from NG and NC through various controlled degradation processes and compared with ratios measured in field pore water samples. Results indicate that propellant combustion and degradation mediated by soil organic carbon produced the observed NO3(-) in pore water at this site. Moreover, isotopic results are presented for NO3(-) produced through photolysis of propellant constituents, which could be a dominant process at other sites. The isotopic data presented here constitute novel information regarding a source of NO3(-) that was practically not documented before and a basis to study the contamination by energetic materials in different contexts.

Counter-current acid leaching process for the removal of Cu, Pb, Sb and Zn from shooting range soil.

This research explores the performance of a counter-current leaching process (CCLP) for Cu, Pb, Sb and Zn extraction in a polluted shooting range soil. The initial metal concentrations in the soil were 1790 mg Cu/kg, 48,300 mg Pb/kg, 840 mg Sb/kg and 368 mg Zn/kg. The leaching process consisted of five one-hour acid leaching steps, which used 1 M H2SO4 + 4 M NaCl (20 degrees C, soil suspension = 100 g/L) followed by two water rinsing steps. Ten counter-current remediation cycles were completed and the average metal removal yields were 98.3 +/- 0.3% of Cu, 99.5 +/- 0.1% of Pb, 75.5 +/- 5.1% of Sb and 29.1 +/- 27.2% of Zn. The quality of metal leaching did not deteriorate throughout the 10 remediation cycles completed for this study. The CCLP reduced acid and salt use by approximately 68% and reduced water consumption by approximately 60%, exceeding reductions achieved by a standard acid leaching process.