Three-Dimensional Assemblies of Edge-Enriched WSe2 Nanoflowers for Selectively Detecting Ammonia or Nitrogen Dioxide.

Herein, we present, for the first time, a chemoresistive-type gas sensor composed of two-dimensional WSe2, fabricated by a simple selenization of tungsten trioxide (WO3) nanowires at atmospheric pressure. The morphological, structural, and chemical composition investigation shows the growth of vertically oriented three-dimensional (3D) assemblies of edge-enriched WSe2 nanoplatelets arrayed in a nanoflower shape. The gas sensing properties of flowered nanoplatelets (2H-WSe2) are investigated thoroughly toward specific gases (NH3 and NO2) at different operating temperatures. The integration of 3D WSe2 with unique structural arrangements resulted in exceptional gas sensing characteristics with dual selectivity toward NH3 and NO2 gases. Selectivity can be tuned by selecting its operating temperature (150 °C for NH3 and 100 °C for NO2). For instance, the sensor has shown stable and reproducible responses (24.5%) toward 40 ppm NH3 vapor detection with an experimental LoD < 2 ppm at moderate temperatures. The gas detecting capabilities for CO, H2, C6H6, and NO2 were also investigated to better comprehend the selectivity of the nanoflower sensor. Sensors showed repeatable responses with high sensitivity to NO2 molecules at a substantially lower operating temperature (100 °C) (even at room temperature) and LoD < 0.1 ppm. However, the gas sensing properties reveal high selectivity toward NH3 gas at moderate operating temperatures. Moreover, the sensor demonstrated high resilience against ambient humidity (Rh = 50%), demonstrating its remarkable stability toward NH3 gas detection. Considering the detection of NO2 in a humid ambient atmosphere, there was a modest increase in the sensor response (5.5%). Furthermore, four-month long-term stability assessments were also taken toward NH3 gas detection, and sensors showed excellent response stability. Therefore, this study highlights the practical application of the 2H variant of WSe2 nanoflower gas sensors for NH3 vapor detection.

Investigation of the Antibacterial Properties of Silver-Doped Amorphous Carbon Coatings Produced by Low Pressure Magnetron Assisted Acetylene Discharges.

Hospital-acquired infections are responsible for a significant part of morbidity and mortality. Among the possible modes of transmission, this study focuses on environmental surfaces by developing innovative antibacterial coatings that can be applied on interior fittings in hospitals. This work aims to optimize a coating made of an amorphous carbon matrix doped with silver (a-C:H:Ag) produced by a hybrid PVD/PECVD process and to evaluate its antibacterial activity. We present a coating characterization (chemical composition and morphology) as well as its stability in an ageing process and after multiple exposures to bacteria. The antibacterial activity of the coatings is demonstrated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria through several bioassays. Moreover, the data suggest a crucial role of silver diffusion towards the surface and nanoparticle formation to explain the very promising anti-bacterial activities reported in this work.

Atmospheric pressure chemical vapor deposition growth of vertically aligned SnS2 and SnSe2 nanosheets.

Laminated metal dichalcogenides are candidates for different potential applications ranging from catalysis to nanoelectronics. However, efforts are still needed to optimize synthesis methods aiming to control the number of layers, morphology, and crystallinity, parameters that govern the properties of the synthesized materials. Another important parameter is the thickness and the length of the samples with the possibility of large-scale growth of target homogeneous materials. Here, we report a chemical vapor deposition method at atmospheric pressure to produce vertically aligned tin dichalcogenide based-materials. Tin disulfide (SnS2) and tin diselenide (SnSe2) vertically aligned nanosheets have been synthesized and characterized by different methods showing their crystallinity and purity. Homogenous crystalline 2H-phase SnS2 nanosheets with high purity were synthesized with vertical orientation on substrates; sulfur vacancies were observed at the edges of the sheets. Similarly, in the crystalline 2H phase SnSe2 nanosheets selenium vacancies were observed at the edges. Moreover, these nanosheets are larger than the SnS2 nanosheets, show lower nanosheet homogeneity on substrates and contamination with selenium atoms from the synthesis was observed. The synthesized nanomaterials are interesting in various applications where the edge accessibility and/or directionality of the nanosheets play a major role as for example in gas sensing or field emission.

ZnO/Carbon xerogel photocatalysts by low-pressure plasma treatment, the role of the carbon substrate and its plasma functionalization.

ZnO is known to be photocatalytic, but with limited performances due to the strong electron-hole recombination after irradiation. The integration of ZnO nanomaterials on a conductive and high surface area carbon substrate is thus a potential alternative to obtain a significant improvement of the photocatalytic performance. Moreover, the carbon functionalization is expected to have a significant role in the adsorption/degradation mechanisms of dye, due to the difference in wettability or surface charge. In this view, ZnO photocatalytic nanoparticles have been deposited on high surface area carbon xerogel substrate (CXG), using a new and original plasma process, consisting in the degradation of a solid organometallic directly on the carbon substrate (no gaseous precursor). In addition to the ZnO nanoparticle formation, the plasma treatment allows the carbon functionalization. The ZnO/CXG composite has been tested for the degradation of Rhodamine B (RhB) in aqueous media and compared with and O2 or NH3 plasma-treated xerogels (without nanoparticles) to identify the significant role of the substrate and its modification in the RhB adsorption and degradation mechanism. The high photocatalytic activity of ZnO/CXG composite is attributed to (i) the formation of small (8-10 nm) and well-crystallized ZnO nanoparticles anchored to the carbon substrate and (ii) to the modification of the xerogel surface chemistry. Indeed, O2 plasma treatment of the CXG promotes the generation of hydroxyl, carbonyl and carboxyl surface functional groups, which are polar and acidic, while the NH3 plasma treatment mainly leads to the formation of polar and basic amino groups. While both plasma treatments promote the formation of polar functional groups, which enhance the CXG wettability, the formation of acidic groups is identified as beneficial for the adsorption of the RhB dye, while basic groups are detrimental.

High performance of 3D silicon nanowires array@CrN for electrochemical capacitors.

Silicon nanowire (SiNW) arrays were coated with chromium nitride (CrN) for use as supercapacitor electrodes. The CrN layer of different thicknesses was deposited onto SiNWs using bipolar magnetron sputtering method. The areal capacitance of the SiNWs-CrN, as measured in 0.5 M H2SO4 electrolyte, was as high as 180 mF cm-2 at a scan rate of 5 mV s-1 (equivalent to 31.8 mF cm-2 at 1.6 mA cm-2) with an excellent electrochemical retention of 92% over 15 000 cycles. This work paves the way toward using CrN modified 3D SiNWs arrays for micro-supercapacitor application.

Restoring self-limited growth of single-layer graphene on copper foil via backside coating.

The growth of single-layer graphene (SLG) by chemical vapor deposition (CVD) on copper surfaces is very popular because of the self-limiting effect that, in principle, prevents the growth of few-layer graphene (FLG). However, the reproducibility of the CVD growth of homogeneous SLG remains a major challenge, especially if one wants to avoid heavy surface treatments, monocrystalline substrates and expensive equipment to control the atmosphere inside the growth system. We demonstrate here that backside tungsten coating of copper foils allows for the exclusive growth of SLG with full coverage by atmospheric pressure CVD implemented in a vacuum-free furnace. We show that the absence of FLG patches is related to the suppression of carbon diffusion through copper. In the perspective of large-scale production of graphene, this approach constitutes a significant improvement to the traditional CVD growth process since (1) a tight control of the hydrocarbon flow is no longer required to avoid FLG formation and, consequently, (2) the growth duration necessary to reach full coverage can be drastically shortened.