The fabrication of van der Waals heterostructures, artificial materials assembled by individual stacking of 2D layers, is among the most promising directions in 2D materials research. Until now, the ...most widespread approach to stack 2D layers relies on deterministic placement methods, which are cumbersome and tend to suffer from poor control over the lattice orientations and the presence of unwanted interlayer adsorbates. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS
-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors.
2D materials have opened a new field in materials science with outstanding scientific and technological impact. A largely explored route for the preparation of 2D materials is the exfoliation of ...layered crystals with weak forces between their layers. However, its application to covalent crystals remains elusive. Herein, a further step is taken by introducing the exfoliation of germanium, a narrow‐bandgap semiconductor presenting a 3D diamond‐like structure with strong covalent bonds. Pure α‐germanium is exfoliated following a simple one‐step procedure assisted by wet ball‐milling, allowing gram‐scale fabrication of high‐quality layers with large lateral dimensions and nanometer thicknesses. The generated flakes are thoroughly characterized by different techniques, giving evidence that the new 2D material exhibits bandgaps that depend on both the crystallographic direction and the number of layers. Besides potential technological applications, this work is also of interest for the search of 2D materials with new properties.
α‐Germanium crystals are exfoliated using a wet ball‐milling technique to produce α‐germanium nanolayers (α‐Ge NLs) in a process that is upscaled to gram production. The α‐Ge NLs can be redispersed using a shear‐mixer, yielding very stable suspensions. Theoretical calculations predict a thickness‐dependent bandgap of these NLs that is confirmed by electron energy‐loss spectroscopy of α‐Ge NLs with different orientations.
The high field transport characteristics of nanostructured transistors based on layered materials are not only important from a device physics perspective but also for possible applications in next ...generation electronics. With the growing promise of layered materials as replacements to conventional silicon technology, the high current density properties of the layered material titanium trisulfide (TiS3) are studied here. The high breakdown current densities of up to 1.7 × 106 A cm−2 are observed in TiS3 nanoribbon‐based field‐effect transistors, which are among the highest found in semiconducting nanomaterials. Investigating the mechanisms responsible for current breakdown, a thermogravimetric analysis of bulk TiS3 is performed and the results with density functional theory and kinetic Monte Carlo calculations are compared. In conclusion, the oxidation of TiS3 and subsequent desorption of sulfur atoms play an important role in the electrical breakdown of the material in ambient conditions. The results show that TiS3 is an attractive material for high power applications and lend insight into the thermal and defect activated mechanisms responsible for electrical breakdown in nanostructured devices.
TiS3 nanoribbons‐based field‐effect transistors are found to stand one of the highest current densities among nanostructured materials. The mechanisms that lead to the nanodevice breakdown are investigated in the bulk material by thermogravimetric analysis measurements and by density functional theory calculations together with kinetic Monte Carlo simulations, and are found to be due to oxygen‐mediated sulfur desorption.
Abstract
Luminescent defects in hexagonal boron nitride (h-BN) have recently emerged as a promising platform for non-classical light emission. On-chip solutions, however, require techniques for ...controllable in-situ manipulation of quantum light. Here, we demonstrate the dynamic spectral and temporal tuning of the optical emission from h-BN via moving acousto-mechanical modulation induced by stimulated phonons. When perturbed by the propagating acoustic phonon, the optically probed radiative h-BN defects are periodically strained and their sharp emission lines are modulated by the deformation potential coupling. This results in an acoustically driven spectral tuning within a 2.5-meV bandwidth. Our findings, supported by first-principles theoretical calculations, reveal exceptionally high elasto-optic coupling in h-BN of ~50 meV/%. Temporal control of the emitted photons is achieved by combining the acoustically mediated fine-spectral tuning with spectral detection filtering. This study opens the door to the use of sound for scalable integration of h-BN emitters in nanophotonic and quantum information technologies.
The prospect of carbon-based magnetic materials is of immense fundamental and practical importance, and information on atomic-scale features is required for a better understanding of the mechanisms ...leading to carbon magnetism. Here we report the first direct detection of the microscopic magnetic field produced at (13)C nuclei in a ferromagnetic carbon material by zero-field nuclear magnetic resonance (NMR). Electronic structure calculations carried out in nanosized model systems with different classes of structural defects show a similar range of magnetic field values (18-21 T) for all investigated systems, in agreement with the NMR experiments. Our results are strong evidence of the intrinsic nature of defect-induced magnetism in magnetic carbons and establish the magnitude of the hyperfine magnetic field created in the neighbourhood of the defects that lead to magnetic order in these materials.
•Nitrate photoreduction using ilmenite and oxalic acid is feasible in saline water.•Oxalic acid scavenging in presence of Ca2+ hinders the NO3− reduction.•Acidification with HCl limits CaC2O4 ...formation and precipitation.•Ea = 9.8 kJ/mol, which is lower than that reported for catalytic hydrogenation.
As climate change progresses, there is an increasing interest on the use of non-conventional water sources such as brackish or saline waters. Nowadays, the main threat in Europe detected in these waterbodies is nitrate contamination. Within the multiple available methods studied for nitrate reduction, photocatalysis presents promising results, but this technology has not yet been tested in saline water. This work tackles the elimination of nitrate (NO3− =50 mg/L) in brackish and saline water (sea salt = 5–33 g/L) using ilmenite as photocatalyst and oxalic acid as an environmental-friendly reducing agent. The main challenge when working in saline water is to overcome oxalic acid scavenging by Ca2+ present in the water matrix. This can be solved either working at over stoichiometric concentrations of oxalic acid (≈300% stoich. dose) or acidifying the reaction media. The addition of hydrochloric acid ensures the protonation of oxalic acid, reducing drastically its precipitation as CaC2O4. Working at C2O42− = 180 mg/L, FeTiO3 = 450 mg/L and HCl 37% = 13 mM, 73% total nitrogen (TN) elimination was reached after 420 min. Reaction temperature was also evaluated in the range of 20–80 °C, which allowed to calculate the Ea=9.8 kJ/mol. Finally, the effect of dissolved O2 on the TN reduction was assessed. Overall, photocatalytic nitrate reduction presents itself as a feasible technology regardless of the water salinity.
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Experimental and theoretical investigation of the capacity of the natural ilmenite (FeTiO3) to reduce nitrate (NO3−) from ultra-pure and mineral water is presented. A comprehensive mechanism of NO3− ...photocatalytic transformation is proposed regarding the density functional theory (DFT) calculations and the photocatalytic reduction of nitrate. When ultra-pure water is employed, the nitrate is totally converted to NOX (2%) and N2 (98%) after 210 min. Additionally, using the stoichiometric dose of oxalate, the nitrate also vanishes from the mineral water, forming NO2−, NOX, and N2 as products. Thus, the findings reveal that natural ilmenite can be a great candidate for reducing NO3− in contaminated water.
•FeTiO3 is a promising material for the removal of NO3− from water.•Theoretical simulations showed that NO3− and NO2− molecules are adsorbed on FeTiO3 .•In ultrapure water + oxalate, NO3− is completely converted to NOx and N2.•The FeTiO3 photocatalyst demonstrates low-cost and high activity.
Addressing the pressing issue of nitrogen oxides (NOx) pollution requires the identification and optimization of efficient materials for NOx removal. This study rigorously explores franckeite, a ...naturally occurring van-der-Waals heterostructure, for its photocatalytic potential in NOx elimination. Employing ab-initio calculations underpinned by density functional theory (DFT) and the many-body BerkeleyGW (GW) plus Bethe-Salpeter (GW-BSE) approach, we analyze franckeite’s structural, electronic, and optical characteristics, including its absorption spectra. Our experimental data indicate a substantial improvement in NO removal efficiency, ranging from 30% to a remarkable 100% under specific conditions. We find a direct correlation between removal efficiency and gas flow rate; higher rates reduce catalyst-NO interaction time. Additionally, we identify radical species responsible for oxidizing NO to nitrates/nitrites. Franckeite demonstrated both stability and reusability, achieving an average efficiency of 95% during three continuous hours of testing. These findings open new avenues for scaling up the use of Franckeite in environmental applications.
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•Franckeite proposed as photocatalyst for NOx removal.•Up to 100% NO removal efficiency, surpassing prior catalysts.•Radical-mediated NO oxidation mechanism elucidated.•Stable and reusable photocatalyst with 95% effectiveness over 3 h.•Promising for large-scale NOx purification applications.
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