Synthesis and Characterization of Highly Crystalline Vertically Aligned WSe2 Nanosheets

Here, we report on the synthesis of tungsten diselenide (WSe2) nanosheets using an atmospheric pressure chemical vapor deposition technique via the rapid selenization of thin tungsten films. The morphology and the structure, as well as the optical properties, of the so-produced material have been studied using electron microscopies, X-ray photoelectron spectroscopy, photoluminescence, UV–visible and Raman spectroscopies, and X-ray diffraction. These studies confirmed the high crystallinity, quality, purity, and orientation of the WSe2 nanosheets, in addition to the unexpected presence of mixed phases, instead of only the most thermodynamically stable 2H phase. The synthesized material might be useful for applications such as gas sensing or for hydrogen evolution reaction catalysis

Low kinetic energy oxygen ion irradiationof vertically aligned carbon nanotubes

International audienceVertically aligned multiwalled carbon nanotubes (v-CNTs) were functionalized with oxygen groups using low kinetic energy oxygen ion irradiation. X-ray photoelectron spectroscopy (XPS) analysis indicates that oxygen ion irradiation produces three different types of oxygen functional groups at the CNTs surface: epoxide, carbonyl and carboxyl groups. The relative concentration of these groups depends on the parameters used for oxygen ion irradiation. Scanning electron microscopy (SEM) shows that the macroscopic structure and alignment of v-CNTS are not affected by the ion irradiation and transmission electron microscopy (TEM) proves tip functionalization of v-CNTs. We observed that in comparison to oxygen plasma treatment, oxygen ion irradiation shows higher functionalization efficiency and versatility. Ion irradiation leads to higher amount of oxygen grafting at the v-CNTs surface, besides different functional groups and their relative concentration can be tuned varying the irradiation parameters

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.This research work was financed by a grant from the University of Namur. C. Bittencourt and J.-F. Colomer are Research Associates of the National Funds for Scientific Research (FRS-FNRS, Belgium). CB thanks the Belgian Fund for Scientific Research under the FRFC contract CDR J001019. The Electron Microscopy Unit, member of Morph-IM platform from the UNamur, is acknowledged for electron microscopy facilities. The SIAM (Synthesis, Irradiation and Analysis of Matter) and PC2 platforms of the UNamur are acknowledged for XPS and XRD measurements respectively. The STEM measurements were performed in the Laboratorio de Microscopias Avanzadas (LMA) at the Universidad de Zaragoza (Spain). R.A. acknowledges funding from the Spanish MICINN (project grant PID2019-104739GB-100/AEI/10.13039/501100011033), from the Government of Aragon (project DGA E13-17R (FEDER, EU)) and from the European Union H2020 programs “ESTEEM3” (grant number 823717) and “Graphene Flagship – CORE3” (grant number 881603).Peer reviewe

Three-dimensional assemblies of edge-enriched WSe2 nanoflowers for selectively detecting ammonia or nitrogen dioxide

[Image: see text] Herein, we present, for the first time, a chemoresistive-type gas sensor composed of two-dimensional WSe(2), fabricated by a simple selenization of tungsten trioxide (WO(3)) nanowires at atmospheric pressure. The morphological, structural, and chemical composition investigation shows the growth of vertically oriented three-dimensional (3D) assemblies of edge-enriched WSe(2) nanoplatelets arrayed in a nanoflower shape. The gas sensing properties of flowered nanoplatelets (2H-WSe(2)) are investigated thoroughly toward specific gases (NH(3) and NO(2)) at different operating temperatures. The integration of 3D WSe(2) with unique structural arrangements resulted in exceptional gas sensing characteristics with dual selectivity toward NH(3) and NO(2) gases. Selectivity can be tuned by selecting its operating temperature (150 °C for NH(3) and 100 °C for NO(2)). For instance, the sensor has shown stable and reproducible responses (24.5%) toward 40 ppm NH(3) vapor detection with an experimental LoD < 2 ppm at moderate temperatures. The gas detecting capabilities for CO, H(2), C(6)H(6), and NO(2) were also investigated to better comprehend the selectivity of the nanoflower sensor. Sensors showed repeatable responses with high sensitivity to NO(2) 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 NH(3) gas at moderate operating temperatures. Moreover, the sensor demonstrated high resilience against ambient humidity (Rh = 50%), demonstrating its remarkable stability toward NH(3) gas detection. Considering the detection of NO(2) 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 NH(3) gas detection, and sensors showed excellent response stability. Therefore, this study highlights the practical application of the 2H variant of WSe(2) nanoflower gas sensors for NH(3) vapor detection

Thermal stability of oxygen functionalization in v-CNTs by low kinetic energy ion irradiation

International audienceVertically aligned multiwalled carbon nanotubes synthetized by catalytic chemical vapor deposition are irradiated with low kinetic energy oxygen ions to graft oxygen functional groups at their surface. Subsequently, the thermal stability of these functional groups is investigated by heating the sample progressively to 200, 300, 400 and 500 °C. X-Ray photoelectron spectroscopy (XPS) is used to analyze the atomic concentration and chemical configuration at the sample surface after each stage. Scanning and transmission electron microscopies are used to observe the morphology of the nanotubes after the thermal treatment. The solvent-free functionalization is carried out in 10 min reaching an oxygen atomic concentration of 17.2 at.%, with no impurities introduced. At the end of the thermal treatment, the relative oxygen content drops to 5.6 at.%. XPS analysis indicates that four oxygen groups produced by the ion irradiation: epoxide, hydroxyl, carbonyl, and carboxyl groups, with the epoxides being the least stable and the carbonyls the most stable. Combining low kinetic energy ion-irradiation with a post-thermal anneal is shown to be an effective route to simultaneously control both sample oxygen content and the ratio of different oxygenated functional groups