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Graphical abstract Highlights • Surface generation mechanism is studied by MD and experiments. • Slipping processes during material deformation are visualized. • Smaller groove depth and width be generated in comparison to static plowing. • Average machining force is significantly smaller for dynamic plowing. Abstract Dynamic ploughing lithography based on atomic force microscope (AFM) is a promising technique for fabrication of nano structures and devices. This study investigates the material removal mechanism and surface generation in dynamic ploughing of single crystal copper by molecular dynamics (MD) simulations in addition to the experimental tests, and compares it with that of static ploughing lithography. It is found that the material removal in dynamic ploughing is mainly due to downwards and sidewards slipping of workpiece material on the {1 1 1} slip planes and the subsequent elastic recovery, whereas forwards and sidewards slipping account for the material removal in static ploughing. As a result, there is little chip formation in dynamic ploughing, while significant chip formation is observed for static ploughing in both simulations and experiments. In addition, this results in smaller groove depth and width for dynamic ploughing, allowing fabrication of nanostructures with smaller features. The slipping processes in both static and dynamic ploughing can be corresponded with the periodical variations of machining forces. The average machining force in dynamic ploughing is significantly smaller than that in static ploughing. This indicates the possibility of reducing the wear of AFM tip by employing dynamic ploughing lithography, since the tip wear is greatly influenced by the magnitude of machining force. These results reveal the mechanism of material removal and surface generation in dynamic ploughing lithography, which can be of useful reference for its practical application in nanomanufacturing. [ABSTRACT FROM AUTHOR]

The fabrication of periodic nanostructures with a fine control of their dimensions is performed on poly(methyl methacrylate) (PMMA) thin films using an atomic force microscope technique called dynamic plowing lithography (DPL). Different scratching directions are investigated first when generating single grooves with DPL. In particular, the depth, the width and the periodicity of the machined grooves as well the height of the pile-up, formed on the side of the grooves, are assessed. It was found that these features are not significantly affected by the scratching direction, except when processing took place in a direction away from the cantilever probe and parallel to its main axis. For a given scratching direction, arrays of regular grooves are then obtained by controlling the feed, i.e. the distance between two machining lines. A scan-scratch tip trace is also used to reduce processing time and tip wear. However, irregular patterns are created when combining two layers oriented at different angles and where each layer defines an array of grooves. Thus, a “combination writing” method was implemented to fabricate arrays of grooves with a well-defined wavelength of 30 nm, which was twice the feed value utilized. Checkerboard, diamond-shaped, and hexagonal nanodots were also fabricated. These were obtained by using the combination writing method and by varying the orientation and the number of layers. The density of the nanodots achieved could be as high as 1.9 × 10 9 nanodots per mm 2 . [ABSTRACT FROM AUTHOR]

Formation of the double-layer electric field and capacitance of the water-metal interface is of significant interest in physicochemical processes. In this study, we perform first- principles molecular dynamics simulations on the water/Pt(111) interface to investigate the temperature dependence of the compact layer electric field and capacitance based on the calculated charge densities. On the Pt (111) surface, water molecules form ice-like structures that exhibit more disorder along the height direction with increasing temperature. The O H bonds of more water molecules point toward the Pt surface to form Pt H covalent bonds with increasing temperature, which weaken the corresponding O H bonds. In addition, our calculated capacitance at 300 K is 15.2 mF/cm 2 , which is in good agreement with the experimental results. As the temperature increases from 10 to 450 K, the field strength and capacitance of the compact layer on Pt (111) first increase and then decrease slightly, which is significant for understanding the water/Pt interface from atomic level. [ABSTRACT FROM AUTHOR]

Highlights: [•] The surface with hierarchical micro-nano-pillars had the least ice adhesion, which was far less than the surface with micro-pillars and smooth surface without any structure (MN

Highlights: [•] Increasing the height and decreasing the space of the micro-rod may result in Cassie wetting state. [•] Decreasing the height and increasing the space of the micro-rod may result in Wenzel wetting state. [•] A suspended wetting state model due to wall scallops was proposed. [•] The wetting state transition was interpreted by intruding height, de-pinning and sag mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Structure and core level spectra of CoSi 2 -like to Co-rich silicides are discussed. • 200 ML Co on Si(1 1 1) forms a closed metallic Co thin film in contrast to 100 ML. • Thermostable CoSi 2 and Co-Si(1 1 1) ring clusters do not bind CO at RT. • CO adsorption at RT only occurs on Co-rich silicides and metallic Co. We report on the structure and reactivity of the Co-Si polycrystalline surfaces that form at room temperature (RT). Scanning tunneling microscopy (STM) was used to examine the surface morphology while X-ray photoelectron spectroscopy (XPS) was used to detect the chemical states of cobalt and silicon as a function of cobalt coverage. Moreover, XPS measurements after exposing the Co-Si(1 1 1) samples to CO gas provide information about CO adsorption and dissociation. When <5 ML Co is deposited on Si(1 1 1) at RT, most Co atoms diffuse into Si lattice and no CO adsorption is found at RT. This shows that coordination of Co to Si suppresses CO adsorption. Neither Co-induced Si(1 1 1)-ring cluster nor CoSi 2 crystalline film adsorb CO at RT. In contrast, CO adsorption was found at RT for cobalt doses >5 ML, an indication that Co-rich silicides and metallic Co present. The CO adsorption capacity increases with cobalt dose up to 30 ML after which it levels off, an indication that metallic cobalt sites are dominantly exposed on the surface. Furthermore, a closed metal film is formed for 200 ML dose. Some dissociation of CO was observed during heating of the CO-covered samples for Co doses ≥30 ML. [ABSTRACT FROM AUTHOR]

Abstract: Wettability tailoring of patterned silicon surface has great potential in fields producing integrated circuits, solar cells, sensors, detectors, and micro/nano electromechanical systems. The present paper presents a convenient yet effective method of combining reactive ion etching and catalyzed etching to prepare silicon surface with micro–nano dual-scale pillars. The experimental results indicate that the hydrophilic surface transformed to a superhydrophobic surface when micro–nano dual-scale pillars were formed. The surface preserved superhydrophobicity even when the geometric parameters of the micropillars were changed. Overhangs of water drops on steep micro–nano dual-scale pillars result in superhydrophobicity. This method offers a new way for tailoring the wettability of patterned silicon surfaces. [Copyright &y& Elsevier]

[Display omitted] • Water aggregation configurations on Fe (1 1 1) surface were discussed. • The water adsorption layer structures on Fe (1 1 1) at different temperatures were investigated. • H 2 S dissociation paths in aqueous environment on Fe (1 1 1) at 300 K was discussed. • H 2 S dissociation behavior on clean Fe (1 1 1) at 10 K and 300 K was discussed. A wet H 2 S environment can cause significant mechanical failure and corrosion. In this study, we used first principles static and molecular dynamics calculations to investigate the behavior of water adsorption of Fe (1 1 1) at different temperatures, followed by the effect of water molecules on the dissociation of H 2 S on the Fe (1 1 1) surface. At room temperature, the structures of the water layer on the Fe (1 1 1) surface include the H-up and H-down mixed structures. H 2 S molecules exhibit stronger competitiveness in co-adsorption with water molecules. Moreover, because the interaction of H-S in H 2 S molecules can be weakened by hydrogen bonds with water and stronger Fe-H owing to water adsorption on the surface, the induced lower dissociation barriers can be sufficiently overcome at room temperature. Therefore, it can be concluded that conditions such as water adsorption layer and room temperature can promote the dissociation of H 2 S on Fe (1 1 1), which is helpful to understand the H 2 S corrosion process at the metal interface. [ABSTRACT FROM AUTHOR]

We present a simple quick evaluation method on vertical-cavity-surface-emitting laser (VCSEL) structures, which is designed for atomic clock working at high temperature (>350 K), to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) gain peak. The surface and edge electroluminescence (EL) measurements were performed non-destructively on pieces of as-grown VCSEL structures by employing soldered indium (In) contacts. The surface EL spectra determine the CM position, while the edge EL spectra are used to identify the wavelength of ground-state emission from the QW in the active region (QW gain peak). The room temperature EL measurements from a cleaved edge of the VCSEL structures indicate that the QW gain peak is at ∼780.5 nm, while the CM measured in the VCSEL surface emission EL peak (sample B) is at ∼793 nm. When the sample is heated up, the amount of CM shift with temperature can be fitted with Δ λ CM = T × 0.068   nm / K , also corroborated by temperature dependence surface reflectivity measurement, and the gain peak can be fitted with λ QW peak = 780.5 nm   +   T × 0.26   nm / K . The CM and QW gain peak of sample B will be brought into alignment at ∼365 K by fitting curve and this was confirmed by measurement. In summary, the surface and edge EL measurements using soldered In as electrodes can be very useful for post growth non-destructive characterization of VCSELs at different temperature. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Relationship between material removal mode and scratching direction is investigated. • A theoretical model is developed to relate machining depth with normal load. • An optimal machining direction is selected based on the quality of the grooves. Abstract The material removal state, which is closely related to machining quality, is an important factor in any machining process. During the machining using a non-rotational symmetric cutting tool, scratching direction manifests significant influence on the material removal state. In the present study, the relationship between material removal mode and scratching direction was investigated during the nanoscratching process on single crystal copper using an atomic force microscopy (AFM) tip. Considering the installation angle of the cantilever and the height of pile-up, a theoretical model was developed to relate machining depth with normal load for the machining of a single groove. Experimental results revealed that the theoretical normal load model was more suitable when materials were expelled in constant chip formation with small pile-ups. In addition, based on the scratching tests in different directions, the critical included cutting angle determined whether materials were expelled in chip formation or not. The height of pile-up was also influenced by the included cutting angle during the scratching in face-forward direction; however, during the machining in edge-forward direction, the distance between the cutting swept faces formed by the lateral and front edges determined the height of pile-up. Finally, an optimal machining direction is selected based on the quality of the machined grooves, which can be used in the potential application. [ABSTRACT FROM AUTHOR]

In current study, various pore-forming agents were employed for the synthesis of Fe-W-Ti catalysts via sol-gel one-pot approach, and the catalytic performance was investigated for selective catalytic reduction of NO x by ammonia (NH 3 -SCR). Among all the catalysts, Fe 0.2 W 0.2 Ti(U 0.03 , urea-modification) catalyst exhibited more than 95% NO x conversion in range of 240–420 °C, and excellent performance of resistance to SO 2 and H 2 O was observed with a slight decline of NO x conversion to 92%. The characterization results revealed that urea-modified catalyst possessed low crystallinity of TiO 2 with particle size of 3.8 nm and the dispersion of Fe-W species was increased significantly, which could be ascribed to the high specific surface area (144.92 m 2 /g) and superior porous structure. The sufficient strong acid, the remarkable reducibility and the increase in the ratio of divalent iron & adsorbed oxygen may be responsible for the excellent catalytic activity. Moreover, a dramatic drop in the specific surface area and surface acidity of the hydrothermal aged catalyst was observed, and the active species also became agglomerated with FeWO 4 solid solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nucleation of dislocations within the grain boundaries caused plasticity during scratching of polycrystalline gallium arsenide. • The 1/2〈1 1 0〉 is the main type of dislocation responsible for ductile plasticity in polycrystalline GaAs. • Scratching force signature showed a periodic wave crest-trough transition during scratching. • The sub-surface damage was found to reduced with the increase of scratch velocity. This paper used molecular dynamics simulation to reveal the origins of the ductile plasticity in polycrystalline gallium arsenide (GaAs) during its nanoscratching. Velocity-controlled nanoscratching tests were performed with a diamond tool to study the friction-induced deformation behaviour of polycrystalline GaAs. Cutting temperature, sub-surface damage depth, cutting stresses, the evolution of dislocations and the subsequent microstructural changes were extracted from the simulation. The simulated MD data indicated that the deformation of polycrystalline GaAs is accompanied by dislocation nucleation in the grain boundaries (GBs) leading to the initiation of plastic deformation. Furthermore, the 1/2〈1 1 0〉 is the main type of dislocation responsible for ductile plasticity in polycrystalline GaAs. The magnitude of cutting forces and the extent of sub-surface damage were both observed to reduce with an increase in the scratch velocity whereas the cutting temperature scaled with the cutting velocity. As for the depth of the scratch, an increase in its magnitude increased the cutting forces, temperature and damage-depth. A phenomenon of fluctuation from wave crests to wave troughs in the cutting forces was observed only during the cutting of polycrystalline GaAs and not during the cutting of single-crystal GaAs. [ABSTRACT FROM AUTHOR]

• Large area continuous monolayer-WS 2 /SiO 2 /Si and monolayer-WS 2 /GaAs heterostructure are fabricated. • The carrier lifetime for WS 2 /GaAs sample is much larger than that of the WS 2 /SiO 2 sample. • A type-Ⅱ band alignment is confirmed at the WS 2 /GaAs heterointerface. • The conduction band offset is about 1.415 eV while the valence band offset is 0.55 eV. We investigate the carrier dynamics in monolayer-WS 2 /SiO 2 and WS 2 /GaAs heterojunctions using time-resolved photoluminescence in this study. The exciton lifetime and radiative lifetime for WS 2 /GaAs sample were determined to be 497 ps and 46 ns, respectively, which are much larger than those of the WS 2 /SiO 2 sample. Then the energy band structure at the WS 2 /GaAs heterojunction was explored using x-ray photoelectron spectroscopy. A type-Ⅱ band alignment was confirmed at the interface with the conduction band offset about 1.415 eV and valence band offset 0.55 eV, which was further proved by ultraviolet photoelectron spectroscopy. As a result, the WS 2 /GaAs junction facilitated electron and hole separation by the aid of built-in field, and in turn enlarged the carrier lifetime. This work provided a promising integration of 2D materials with traditional bulk semiconductors for future high efficiency, highly reliable applications in photonic and optoelectronic devices. [ABSTRACT FROM AUTHOR]