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Soft matter containing Ti3C2Tx MXenes exhibits promising potential in electromechanical sensor development. Current systems suffer from a decrease in sensibility up to complete breakdown due to small structural defects that will be generated during their longtime practical service. Various non-covalent hydrogel systems, based on hydrogen bonding and ionic coupling, have been employed to improve their durability related to their repairability. However, Ti3C2Tx MXenes are not stable in those networks, since they will be irreversibly oxidized in high humidity environment during practical application. Here, we report the use of a novel dynamic covalent bond based network – a MXene acrylate vitrimer network (MAVIN) with a low glass transition temperature, which can not only be repaired fast with high efficiency but also protects the MXenes in sensor applications from oxidation under working conditions. In addition, owing to the strong microwave absorptivity of Ti3C2Tx and of the flexible dynamic covalent bond network, a damaged MAVIN sensor can be repaired by microwave radiation with a high healing efficiency of 92.4% within 1 minute, which is as good as the best healing efficiency reported in literature so far but 30 times faster. With stability at a voltage of 3 V and fast healing demonstrated, MAVIN promises potential usage in reliable and sustainable strain sensors.

WSxC(H) coatings were deposited on single crystal silicon(100) wafers by magnetron co-sputtering and reactive sputtering at various target-substrate distances. Upon increasing the distance, the stoichiometric S/W ratio increases from 0.51 to 1.89. Also, the porosity of coatings gradually augments and a columnar microstructure tends to form. Preferential sulfur resputtering rather than contaminations primarily accounts for the low S/W ratio. TEM reveals randomly oriented WS2(002) platelets in the WSxC coatings when deposited at a large distance, which is supported by XRD. The composite coatings exhibit a decreasing hardness and elastic modulus with increasing target-substrate distance. The triboperformance is strongly affected by the coating composition, the target-substrate distance and the testing environment. Cross-sectional TEM of formed tribofilms reveals an obvious reorientation of WS2(002) basal planes parallel to the plane of sliding, leading to an ultralow friction.

Novel pillared structures were developed from the intercalation of iron-substituted cubic silsesquioxanes in a sodium and an acid-activated montmorillonite nanoclay and evaluated as acid catalysts. Octameric cubic oligosiloxanes were formed upon controlled hydrolytic polycondensation of the corresponding monomer (a diamino-alkoxysilane) and reacted with iron cations to form complexes that were intercalated within the layered nanoclay matrices. Upon calcination iron oxide nanoparticles are formed which are located on the silica cubes (pillars) and on the surfaces of the clay platelets. Acid activation of the nanoclay was performed in order to increase the number of acid active sites in the pristine clay and thus increase its catalytic activity. A plethora of analytical techniques including X-ray diffraction, thermal analyses, Fourier transform infrared, electron paramagnetic resonance, Raman, Mossbauer and X-ray photoelectron spectroscopies and porosimetry measurements were used in order to follow the synthesis steps and to fully characterize the final catalysts. The resulting pillared clays exhibit a high specific area and show significant acid catalytic activity that was verified using the catalytic dehydration of isopropanol as a probe reaction. (C) 2017 Elsevier Inc. All rights reserved.

A series of tungsten oxide-silica (WO3-SiO2) composite nanomaterials were synthesized through a novel, template-free sol-gel method, in which supercritical-CO2 (scCO(2)) was utilized as synthesis medium. The efficacy of the synthesis method stems from a tailored reactor design that allows the contact of the reactants only in the presence of scCO(2). Selected synthetic parameters were screened with the purpose of enhancing the performance of the resulting materials as heterogeneous catalysts in epoxidation reactions with H2O2 as environmentally friendly oxidant. A cyclooctene conversion of 73% with epoxide selectivity of > 99% was achieved over the best WO3-SiO2 catalyst under mild reaction conditions (80 degrees C), equimolar H2O2 amount (1:1) and low WO3 loading (similar to 2.5 wt%). The turnover number achieved with this catalyst (TON = 328), is significantly higher than that of a WO3-SiO2 prepared via a similar sol-gel route but without supercritical CO2, and that of commercial WO3. A thorough characterization with a combination of techniques (ICP-OES, N-2-physisorption, XRD, TEM, STEM-EDX, SEM-EDX, FT-IR and Raman spectroscopy, XPS, TGA and FT-IR analysis of adsorbed pyridine) allowed correlating the physicochemical properties of the WO3-SiO2 nanomaterials with their catalytic performance. The high catalytic activity was attributed to: (i) the very high surface area (892 m(2)/g) and (ii) good dispersion of the W species acting as Lewis acid sites, which were both brought about by the synthesis in supercritical CO2, and (iii) the relatively low hydrophilicity, which was tuned by optimizing the tetramethyl orthosilicate concentration and the amount of basic solution used in the synthesis of the materials. Our optimum catalyst was also tested in the reaction of cyclohexene with H2O2, resulting in cyclohexane diol as main product due to the presence of strong BrOnsted acid sites in the catalyst, whereas the reaction with limonene yielded the internal epoxide as the major product and the corresponding diol as side product. Importantly, the catalyst did not show leaching and could be reused in five consecutive runs without any decrease in activity. (C) 2020 The Authors. Published by Elsevier Ltd.

The effect of the textural properties and morphology of zeolite Y, used as support of iron (Fe) or cobalt (Co) oxides, on the quantity and quality of the multi-wall carbon nanotubes (MWNTs) synthesized by catalytic chemical vapour deposition (CCVD) of acetylene was studied. The parent zeolite Y was modified by various dealumination procedures, namely hydrothermal treatment (steaming), treatment with ammonium hexafluorosilicate (AHFS) and combined steaming-AHFS. The ion-exchange and wet impregnation methods were used for supporting the metals on the zeolite Y samples, with the latter method providing the most effective catalysts for carbon nanotube (CNT) formation. Severe dealumination of zeolite-Y by steaming, which induced the formation of secondary meso/macropores and of relatively large particles/aggregates, resulted in significant decrease in the formation of CNTs compared to the catalysts based on the parent zeolite-Y. Post-treatment of the steamed samples with AHFS had no beneficial effect on the catalysts' activity. Moderate dealumination of the parent zeolite Y by AHFS also inhibited the formation of CNTs, but to a lesser extent compared to the catalysts based on steamed zeolite Y. The TGA studies revealed the presence of carbon phases with different thermal stability in the zeolite-CNT composites, ranging from amorphous carbon to well-graphitized MWNTs. TEM images and micro-Raman spectra taken right after growth confirmed the formation of high quality MWNTs with a low degree of disorder irrespective of the catalysts used, the degree of dealumination of the zeolite Y and the textural and morphological characteristics of the zeolitic support. (c) 2007 Elsevier Inc. All rights reserved. Microporous and Mesoporous Materials

Often metal nitrides posses unique properties for applications, such as great hardness, high melting points, chemical stability, novel electrical and magnetic properties. One route to the formation of metal nitride films is through ion irradiation of metal surfaces. In this report, the results of irradiation of Au(1 1 0) surfaces by nitrogen ions with kinetic energies of 0.5 and 2 keV are studied with high resolution X-ray photoemission spectroscopy. N1s core level spectra show clear evidence for the formation of a gold nitride at, or in close vicinity to, the surface––the first direct observation of nitride formation by this element. Subsurface molecular nitrogen is also observed, the relative concentration of which increases with irradiation energy. We suggest that the subsurface molecular nitrogen is most likely present in the form of trapped bubbles.

In this paper we report a photoelectron spectroscopy (XPS and UPS) study of films of a benzylic amide [2]catenane on Au(1 1 1). We show that this molecule retains its molecular integrity during sublimation and that it chemisorbs on the metal surface. Potassium intercalation modifies the electronic structure of the films. We have observed a reduction of its amide functions and a modification of the charge density of the aromatic rings. The creation of polaron-like states in the gap of the neutral catenane and a decrease in the catenane work function of 0.8 eV have been demonstrated.

Thiol-functionalised catenane and rotaxane thin films were investigated in order to understand the self-assembly of such complex molecules on Au(111). Adsorption from the liquid phase at 300 K leads to the formation of overlayers without long-range order, as evidenced by high-resolution electron energy-loss spectroscopy (HREELS). As expected for thiol adsorption, the sulfur 2p binding energies determined by X-ray photoelectron spectroscopy (XPS) are consistent with the formation of thiolate surface intermediates. The properties of these films are explored as a function of annealing. Changes in vibrational spectra such as the emergence of a AuO band and variations in core-level binding energies and intensities reveal molecular rearrangement due to partial desorption. In addition, based on coherent domain sizes estimated by the angular width of the elastic beam intensity, annealing promotes long-range order within the adlayers.

C60 was deposited on Ni(110), Pt(111) and Ag(111) and annealed at different temperatures. The structural properties of the overlayer were investigated by low-energy electron diffraction, the changes induced by adsorption on its electronic properties were studied by valence band and core-level photoemission spectroscopy and inverse photoemission spectroscopy. On all surfaces C60 is chemisorbed and a clear signature for charge transfer is found for C60 on Ni(110) and Ag(111). Decomposition of C60 takes place on Ni(110) and Pt(111) above 690 K and 560 K respectively. The decomposition is a kinetically limited reaction on both surfaces and on Pt(111) we find a very strongly chemisorbed precursor state for decomposition.

Adsorbate dynamics has received increasing interest over the last years, as it has been realized that the electron dynamics of the substrate can be profoundly affected by adsorbates due to couplings between vibrational and electronic states. Persson has developed a model where the scattering of the conduction electrons by the adsorbate results in a friction force between the adsorbate and the metallic substrate. The model predicts that the dipole-forbidden low-frequency adsorbate modes exhibit anti-absorption peaks, and that the broadband infrared (IR) reflectance change displays a characteristic frequency dependence in the anomalous skin-effect region, with an asymptotic limit in the mid-IR. The friction coefficient, which can be extracted from the asymptotic change of the reflectance, equals the inverse of the electronic contribution to the lifetime of the frustrated parallel translation. This model has been verified by recording simultaneously the direct-current (DC) resistance change, the broadband IR reflectance change and the IR features for various adsorbates on Cu(111) thin films epitaxially grown on TiO 2 (110) substrates. The friction coefficients obtained from the DC resistance change and from the IR reflectance change show good agreement. Coadsorption experiments reveal the marked dependence of the friction coefficient on the adsorbate-induced density of states at the Fermi level ( E F ). Using the Newns–Anderson model for chemisorption, the IR reflectance change of C 60 adsorbed on the following noble metal surfaces: Ag(111), Au(110) and Cu(100), indicates a high density of induced states at E F .

We report here the first results on the thin-film growth of benzylic amide catenanes. The films were deposited onto gold single crystals by two different methods: by sublimation under ultra-high vacuum and by dipping of the substrate into a solution of the catenane. Sublimation yielded well-ordered films (domain diameter~100 A ˚) while dipping produced disordered films. The vibrational and electronic properties of these films were investigated by high-resolution electron energy loss spectroscopy (HREELS) as a function of film thickness. The vibrational spectra indicate that the first layer of catenanes is chemisorbed. © 1998 Elsevier Science S.A. All rights reserved

We have studied the coadsorption of oxygen with a (2 × 2) monolayer of K on graphite. At least three different adsorption phases for oxygen have been found. Different spectroscopic techniques have been used in order to identify the different oxygen species adsorbed on the surface. For low oxygen coverage, the molecules dissociate and form a K2O species. At higher oxygen doses, K2O2 and KO2 are present on the surface up to saturation coverage. XAS yields an O2 bond length of about 1.39 Å for the KO2 in this phase. This species is found to form an ionic complex which is weakly bound to the graphite.

We have studied the vibrational properties of thin C60 overlayers deposited on ideally H-terminated Si(111) surfaces, by multiple infrared reflection and high-resolution electron energy-loss spectroscopies. We find that the SiH interface remains intact upon C60 deposition: the SiH stretching mode frequency, initially at 2083.8 cm−1, shifts downward to 2062 cm−1, and broadens while keeping the same integrated intensity. Due to the symmetry-breaking effect at the surface on the adsorbed C60 molecules, a new IR band is observed at 1445 cm−1 which is mainly s-polarised. No evidence for chemical interaction between C60 and HSi(111)-(1 × 1) is found, pointing to van der Waals-type bonding. From the relative intensities of the dipole-active and -inactive modes in HREELS in the specular direction, and from the angular width of the scattered elastic peak, the growth of an ordered film is inferred.

The magnetic moments of Gd and Fe in gadolinium iron garnet (Gd3Fe5O12) were probed at 77 and 300 K by soft-X-ray magnetic circular dichroism (SXMCD) measurements at the GdMa4,5 and at the FeL2,3 absorption edges. The SXMCD signal at each edge allows one to independently determine the magnetic ordering for each specific ion, and the temperature dependence confirms that the reversal of the macroscopic magnetization is due to the reversal of each local magnetic moment of the Fe and the Gd atoms when the compensation point (Tcomp = 288 K) is crossed. This work therefore demonstrates that SXMCD can probe element and site specific magnetic properties of multi-component systems.

The study of the stretching mode of Li, Na and K on various Cu surfaces show that the force constant of the adsorbate-surface bond depends neither on coverage nor substantially on the particular type of alkali atom. On the Cu(110) surface the spectra also infer that the (1 × 2) reconstruction may be induced by a local coverage less than 0.03 monolayers.

The isothermal dissociation rate of CCH and CH on Ni(111) was measured by following, with HREEL spectroscopy, the intensity of the CH stretching peak as a function of time. By repeating the experiment at several different temperatures we obtained an activation energy of 8 ± 3 kcal/mol for the CCH dissociation reaction and of 12 ± 3 kcal/mol for the CH dissociation reaction. Pre-exponential factors were found to be 10 3±1 s −1 in both cases. Independent thermal desorption spectra show a feature at 470 K and a tail extending up to 600 K. which can be assigned to the CCH dissociation and the CH dissociation respectively. The two experiments are quantitatively consistent.