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Minimizing friction and wear is one of the continuing challenges in many mechanical industries. Recent research efforts have been focused on accelerating the antifriction and antiwear properties of hard coatings through the incorporation of self-lubricant materials or the development of new architectures. In this present study, carbon-rich MoC, MoCN, and multilayer MoC/MoCN coatings were deposited using reactive magnetron sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were used to evaluate their properties, which revealed the presence of ceramic cubic crystallites, covalent bonds between primary elements, and an excess of amorphous carbon (a-C) in all of the coatings. The multilayer architecture and possible segregation of a-C around the ceramic crystallites resulted in improved mechanical properties for all coatings, with MoC/MoCN coatings having a maximum hardness of 21 GPa and elastic modulus of 236 GPa. Friction and wear behavior are initially determined by the structural–composition–property relationships of the respective coatings; later, the tribological characteristics are altered depending on the nature of tribolayer on both mating surfaces at the contact interface. The highest wear resistance of multilayer MoC/MoCN coating (8.7 × 10–8mm3/N m) and MoC coating (3.9 × 10–7mm3/N m) was due to the dissipation of contact stress by the tribofilm consisting of carbon tribo products like graphitic sp2carbon, diamond-like sp3carbon, and pyrrolic-N. On the other hand, MoCN coating depicted a lower wear resistance due to the frequent termination of C–H bonds by N, which restricts the strong formation of tribofilms as well as poor mechanical properties.

We report on a controllable and specific functionalisation route for graphene field-effect transistors (GFETs) for the recognition of small physiologically active molecules. Key element is the noncovalent functionalisation of the graphene surface with perylene bisimide (PBI) molecules directly on the growth substrate. This Functional Layer Transfer enables the homogeneous self-assembly of PBI molecules on graphene, onto which antibodies are subsequently immobilised. The sensor surface was characterised by atomic force microscopy, Raman spectroscopy and electrical measurements, showing superior performance over conventional functionalisation after transfer. Specific sensing of small molecules was realised by monitoring the electrical property changes of functionalised GFET devices upon the application of methamphetamine and cortisol. The concentration dependent electrical response of our sensors was determined down to a concentration of 300 ng ml−1 for methamphetamine.

Covalent functionalization of two‐dimensional molybdenum disulfide (2D MoS2) holds great promise in developing robust organic‐MoS2 hybrid structures. Herein, for the first time, we demonstrate an approach to building up a bisfunctionalized MoS2 hybrid structure through successively reacting activated MoS2 with alkyl iodide and aryl diazonium salts. This approach can be utilized to modify both colloidal and substrate supported MoS2 nanosheets. We have discovered that compared to the adducts formed through the reactions of MoS2 with diazonium salts, those formed through the reactions of MoS2 with alkyl iodides display higher reactivity towards further reactions with electrophiles. We are convinced that our systematic study on the formation and reactivity of covalently functionalized MoS2 hybrids will provide some practical guidance on multi‐angle tailoring of the properties of 2D MoS2 for various potential applications., For the first time, we demonstrate an approach to building up a bisfunctionalized MoS2 hybrid structure through successively treating activated MoS2 with alkyl iodide and aryl diazonium salt. This approach can be used to modify both colloidal and substrate‐supported MoS2 nanosheets.

Tungsten ditelluride (WTe2) is a layered transition metal dichalcogenide (TMD) that has attracted increasing research interest in recent years. WTe2 has demonstrated large non-saturating magnetoresistance, potential for spintronic applications and promise as a type-II Weyl semimetal. The majority of works on WTe2 have relied on mechanically exfoliated flakes from chemical vapour transport (CVT)-grown crystals for their investigations. While producing high-quality samples, this method is hindered by several disadvantages including long synthesis time, high-temperature annealing and an inherent lack of scalability. In this work, a synthesis method is demonstrated that allows the production of large-area polycrystalline films of WTe2. This is achieved by the reaction of pre-deposited films of W and Te at a relatively low temperature of 550 °C. Sputter X-ray photoelectron spectroscopy reveals the rapid but self-limiting nature of the oxidation of these WTe2 films in ambient conditions. The WTe2 films are composed of areas of micrometre-sized nanobelts that can be isolated and offer potential as an alternative to CVT-grown samples. These nanobelts are highly crystalline with low defect densities indicated by transmission electron microscopy and show promising initial electrical results.

Monolayer MoSe2 is a transition metal dichalcogenide with a narrow bandgap, high optical absorbance and large spin-splitting energy, giving it great promise for applications in the field of optoelectronics. Producing monolayer MoSe2 films in a reliable and scalable manner is still a challenging task as conventional chemical vapor deposition (CVD) or exfoliation based techniques are limited due to the small domains/nanosheet sizes obtained. Here, based on NaCl assisted CVD, we demonstrate the simple and stable synthesis of sub-millimeter size single-crystal MoSe2 monolayers with mobilities ranging from 38 to 8 cm2 V−1 s−1. The average mobility is 12 cm2 V−1 s−1. We further determine that the optical responsivity of monolayer MoSe2 is 42 mA W−1, with an external quantum efficiency of 8.22%.

In this work, we present a comprehensive theoretical and experimental study of quantum confinement in layered platinum diselenide (PtSe2) films as a function of film thickness. Our electrical measurements, in combination with density functional theory calculations, show distinct layer-dependent semimetal-to-semiconductor evolution in PtSe2 films, and highlight the importance of including van der Waals interactions, Green’s function calibration, and screened Coulomb interactions in the determination of the thickness-dependent PtSe2 energy gap. Large-area PtSe2 films of varying thickness (2.5–6.5 nm) were formed at 400 °C by thermally assisted conversion of ultra-thin platinum films on Si/SiO2 substrates. The PtSe2 films exhibit p-type semiconducting behavior with hole mobility values up to 13 cm2/V·s. Metal-oxide-semiconductor field-effect transistors have been fabricated using the grown PtSe2 films and a gate field-controlled switching performance with an ION/IOFF ratio of >230 has been measured at room temperature for a 2.5–3 nm PtSe2 film, while the ratio drops to 2 films, consistent with a semiconducting-to-semimetallic transition with increasing PtSe2 film thickness. These experimental observations indicate that the low-temperature growth of semimetallic or semiconducting PtSe2 could be integrated into the back-end-of-line of a silicon complementary metal-oxide-semiconductor process.

Advanced functional materials 2103936 (2021). doi:10.1002/adfm.202103936, Published by Wiley-VCH, Weinheim

Two‐dimensional (2D) molybdenum disulfide (MoS2) holds great promise in electronic and optoelectronic applications owing to its unique structure and intriguing properties. The intrinsic defects such as sulfur vacancies (SVs) of MoS2 nanosheets are found to be detrimental to the device efficiency. To mitigate this problem, functionalization of 2D MoS2 using thiols has emerged as one of the key strategies for engineering defects. Herein, we demonstrate an approach to controllably engineer the SVs of chemically exfoliated MoS2 nanosheets using a series of substituted thiophenols in solution. The degree of functionalization can be tuned by varying the electron‐withdrawing strength of substituents in thiophenols. We find that the intensity of 2LA(M) peak normalized to A1g peak strongly correlates to the degree of functionalization. Our results provide a spectroscopic indicator to monitor and quantify the defect engineering process. This method of MoS2 defect functionalization in solution also benefits the further exploration of defect‐free MoS2 for a wide range of applications., Non‐defective defects: Plot of the intensity of the 2LA(M) peak normalized to A1g peak (I450/I404) as a function of the degree of functionalization. This phenomenological relationship between I450/I404 and the degree of functionalization can potentially serve as a spectroscopic indicator to monitor and quantify the defect engineering process. The inset model depicts the structure of defect‐functionalized MoS2 nanosheets. The R in the model structure is corresponding to the para‐substituent on the phenyl ring.

Monolayer MoSe

Molybdenum dioxide (MoO2) is a layered material which shows promise for a number of applications in the electrochemical energy storage arena. Mostly studied as a bulk layered material, MoO2 has not previously been exfoliated in large quantities. Here we demonstrate the liquid phase exfoliation of MoO2 in the solvent isopropanol, yielding reasonable amounts of good quality nanosheets. However, we found that, when dispersed in isopropanol under ambient conditions, MoO2 nanosheets are gradually oxidized to higher oxides such as MoO3 over a period of days. Conversely, if the nanosheets are processed into dried films immediately after exfoliation, and before oxidation has had a chance to progress, the nanosheets are relatively stable under ambient conditions, remaining unoxidised unless the films are heated. We also found that MoO2 nanosheets can be size selected by controlled centrifugation and show size-dependent optical properties. This allows us to propose spectroscopic metrics which allow concentration- and size-estimation from extinction spectra. Finally, we found that liquid-exfoliated MoO2 nanosheets could be used to produce lithium ion battery anodes with capacities of up to 1140 mA h g−1.

Molybdenum dioxide (MoO

Chlorination remains a big hurdle in membrane technology as the most commonly used membranes for water purification consist of a polyamide top-layer, which is not fully resistant towards chlorine-induced oxidation. In this work, DOW FILMTECTM BW30 membrane elements were systematically chlorinated with NaOCl at pilot-scale under acidic conditions (pH4) at 10 bar for 2.5 h. Variations in membrane performance and their physico- chemical properties were determined by ATR-FTIR, XPS, WD-XRF, SEM, AFM and zeta-potential measurements. With increasing bleaching concentration, both membrane roughness and chlorine incorporation via N- and ring- chlorination increased, while surface charge remained quasi unaltered. Both water flux and salt passage de- creased proportionally over the whole concentration range. Accordingly, positron annihilation lifetime spec- troscopy (PALS) revealed a decrease in the size of the top-layer free-volume elements as chlorine concentration increased, confirming, for the first time in a quantitative manner, the so-called tightening effect. The obtained results also show that thin-film composite (TFC) membranes are altered differently when chlorinated under pressure than via simple immersion, as conventionally performed in literature. ispartof: Journal of Membrane Science vol:551 pages:123-135 status: published

Scanning tunneling microscopy has been used to investigate silicon overgrowth of C 60 on the Si(1 0 0)-2 × 1 surface. It can be shown that crystal morphology and quality is highly dependent on temperature and C 60 coverage. A C 60 coverage of 0.02 ML was used to show the initial stage of silicon overgrowth (1.5 ML of Si), medium stage with crater formation, crater diminution (10 ML of Si) and finally crater overgrowth (100 ML of Si). Crystal quality can be improved by annealing of the stack at 750 °C for several minutes, but SiC formation at 800 °C deteriorates the stack. Segregation of C 60 plays an important role already at low coverage. Nevertheless, C 60 can be enclosed into the crystal within a few monolayers. This has been proven by STM, TEM and SIMS analysis. Higher C 60 coverage leads to 3D islanding, which was proven by STM and LEED, and eventually to polysilicon, shown by STM and TEM. Finally we give a short comparison to the Si(1 1 1)-7 × 7 surface.

The cleaning of silicon (Si) surfaces is a very important issue for the fabrication of novel semiconductor devices on the nanoscale. Established methods for the removal of organic impurities and the native or chemical oxide are often combined with high temperature desorption steps. However, devices with small feature sizes will be unfunctional if, for example, out-diffusion of dopants is not prevented. In this paper we present two possible processes for low-temperature cleaning: an atomic hydrogen source, based on dissociative adsorption of hydrogen at a heated tantalum (Ta) surface and a hydrogen DC plasma source as a part of an UHV cluster tool. The influence of atomic hydrogen on carbon and oxide removal is surveyed and the existing model for native oxide etching with an argon/hydrogen DC plasma is adapted.

Silicon-rich nitride, deposited by LPCVD, is a low stress amorphous material with a high refractive index. After deposition the silicon-rich nitride thin film is annealed at temperatures above 1100 °C to break N H bonds, which have absorption peaks in the wavelength band important for optical telecommunication. However, silicon clustering appears in the thin films when annealing above 1150 °C. Clustering is undesirable in waveguide materials because the localized variations of the refractive index associated with the clusters lead to Raleigh scattering, which can cause significant propagation loss in optical waveguides. This means that the annealing temperature must be high enough to break the N H bonds, but no so high as to produce clusters. Therefore, the process window for an annealing step lies between 1100 and 1150 °C. The chemical composition of amorphous silicon-rich nitride has been investigated by Rutherford back scattering (RBS) and X-ray photoelectron spectroscopy (XPS). The influence of deposition parameters and annealing temperatures on the stoichiometry and the chemical bonds will be discussed. The origin of the clusters has been found to be silicon due to severe silicon out-diffusion from the substrate during annealing at temperatures above 1100 °C.

Thin films of noble-metal-based transition metal dichalcogenides, such as PtSe2, have attracted increasing attention due to their interesting layer-number dependent properties and application potential. While it is difficult to cleave bulk crystals down to mono- and few-layers, a range of growth techniques have been established producing material of varying quality and layer number. However, to date, no reliable high-throughput characterization to assess layer number exists. Here, we use top-down liquid phase exfoliation (LPE) coupled with centrifugation to produce PtSe2 nanosheets of varying sizes and thicknesses with a low degree of basal plane defectiveness. Measurement of the dimensions by statistical atomic force microscopy allows us to quantitatively link information contained in optical spectra to the dimensions. For LPE nanosheets we establish metrics for lateral size and layer number based on extinction spectroscopy. Further, we compare the Raman spectroscopic response of LPE nanosheets with micromechanically exfoliated PtSe2, as well as thin films produced by a range of bottom up techniques. We demonstrate that the Eg 1 peak position and the intensity ratio of the Eg 1/A1g 1 peaks can serve as a robust metric for layer number across all sample types.This will be of importance in future benchmarking of PtSe2 films.