Abstract: The changes induced by exposing multi-walled carbon nanotubes (CNTs) to atomic nitrogen were analysed by high-resolution transmission electron microscopy (HRTEM), x-ray and ultraviolet photoelectron spectroscopy. It was found that the atomic nitrogen generated by a microwave plasma effectively grafts chemical groups onto the CNT surface altering the density of valence electronic states. HRTEM showed that the exposure to atomic nitrogen does not significantly damage the CNT surface.

Abstract: A parameter study is carried out for an inductively coupled plasma used for the synthesis of carbon nanotubes or carbon nanofibres (CNTs/CNFs), by means of the Hybrid Plasma Equipment Model. The influence of processing parameters including gas ratio for four different gas mixtures typically used for CNT/CNF growth (i.e. CH4/H2, CH4/NH3, C2H2/H2 and C2H2/NH3), inductively coupled plasma (ICP) power (501000 W), operating pressure (10 mTorr1 Torr), bias power (01000 W) and temperature of the substrate (01000 °C) on the plasma chemistry is investigated and the optimized conditions for CNT/CNF growth are analysed. Summarized, our calculations suggest that a lower fraction of hydrocarbon gases (CH4 or C2H2, i.e. below 20%) and hence a higher fraction of etchant gases (H2 or NH3) in the gas mixture result in more 'clean' conditions for controlled CNT/CNF growth. The same applies to a higher ICP power, a moderate ICP gas pressure above 100 mTorr (at least for single-walled carbon nanotubes), a high bias power (for aligned CNTs) and an intermediate substrate temperature.

Abstract: A hybrid model, called the hybrid plasma equipment model, was used to study inductively coupled SF6 plasmas used for Si etching applications. The plasma properties such as number densities of electrons, positive and negative ions, and neutrals are calculated under typical etching conditions. The electron kinetics is analysed by means of the electron energy probability function. The plasma chemistry taking place in pure SF6 and in an Ar/SF6 mixture is also discussed, and finally the effect of the argon fraction on the plasma properties is investigated.

Abstract: The atmospheric pressure dielectric barrier discharge in helium is a pulsed discharge in nature. If during the electrical current pulse a glow discharge is reached, then this pulse will last only a few microseconds in operating periods of sinusoidal voltage with lengths of about 10 to 100 µs. In this paper we demonstrate that right before a glow discharge is reached, the discharge very closely resembles the commonly assumed Townsend discharge structure, but actually contains some significant differing features and hence should not be considered as a Townsend discharge. In order to clarify this, we present calculation results of high time and space resolution of the pulse formation. The results indicate that indeed a maximum of ionization is formed at the anode, but that the level of ionization remains high and that the electric field at that time is significantly disturbed. Our results also show where this intermediate structure comes from.

Abstract: Plasma modelling is an exciting subject in which virtually all physical disciplines are represented. Plasma models combine the electromagnetic, statistical and fluid dynamical theories that have their roots in the 19th century with the modern insights concerning the structure of matter that were developed throughout the 20th century. The present cluster issue consists of 20 invited contributions, which are representative of the state of the art in plasma modelling and numerical simulation. These contributions provide an in-depth discussion of the major theories and modelling and simulation strategies, and their applications to contemporary plasma-based technologies. In this editorial review, we introduce and complement those papers by providing a bird's eye perspective on plasma modelling and discussing the historical context in which it has surfaced.

Abstract: Using a molecular dynamics model the crystallinity of MgxAlyOz thin films with a variation in the stoichiometry of the thin film is studied at operating conditions similar to the experimental operating conditions of a dual magnetron sputter deposition system. The films are deposited on a crystalline or amorphous substrate. The Mg metal content in the film ranged from 100% (i.e. MgO film) to 0% (i.e. Al2O3 film). The radial distribution function and density of the films are calculated. The results are compared with x-ray diffraction and transmission electron microscopy analyses of experimentally deposited thin films by the dual magnetron reactive sputtering process. Both simulation and experimental results show that the structure of the MgAlO film varies from crystalline to amorphous when the Mg concentration decreases. It seems that the crystalline MgAlO films have a MgO structure with Al atoms in between.

Abstract: This paper focuses on the investigation of CF4 decomposition in a low-pressure inductively coupled plasma by means of a global model. The influence of O2 on the CF4 decomposition process is studied for conditions used in semiconductor manufacturing processes. The model is applied for different powers and O2 contents ranging between 2% and 98% in the CF4/O2 gas mixture. The model includes the reaction mechanisms in the gas phase coupled with the surface reactions and sticking probabilities of the species at the walls. The calculation results are first compared with experimental results from the literature (for the electron density, temperature and F atom density) at a specific power, in the entire range of CF4/O2 gas mixture ratios, and the obtained agreements indicate the validity of the model. The main products of the gas mixture, obtained from this model, include CO, CO2 and COF2 together with a low fraction of F2. The most effective reactions for the formation and loss of the various species in this process are also determined in detail. Decomposition of CF4 produces mostly CF3 and F radicals. These radicals also contribute to the backward reactions, forming again CF4. This study reveals that the maximum decomposition efficiency of CF4 is achieved at a CF4/O2 ratio equal to 1, at the applied power of 300 W.

Abstract: Modelling at the molecular or atomic scale can be very useful for obtaining a better insight in plasma medicine. This paper gives an overview of different atomic/molecular scale modelling approaches that can be used to study the direct interaction of plasma species with biomolecules or the consequences of these interactions for the biomolecules on a somewhat longer time-scale. These approaches include density functional theory (DFT), density functional based tight binding (DFTB), classical reactive and non-reactive molecular dynamics (MD) and united-atom or coarse-grained MD, as well as hybrid quantum mechanics/molecular mechanics (QM/MM) methods. Specific examples will be given for three important types of biomolecules, present in human cells, i.e. proteins, DNA and phospholipids found in the cell membrane. The results show that each of these modelling approaches has its specific strengths and limitations, and is particularly useful for certain applications. A multi-level approach is therefore most suitable for obtaining a global picture of the plasma–biomolecule interactions.

Abstract: Experiments have demonstrated the potential selective anticancer capacity of cold atmospheric plasmas (CAPs), but the underlying mechanisms remain unclear. Using computer simulations, we try to shed light on the mechanism of selectivity, based on aquaporins (AQPs), i.e. transmembrane protein channels transferring external H 2 O 2 and other reactive oxygen species, created e.g. by CAPs, to the cell interior. Specifically, we perform molecular dynamics simulations for the permeation of H 2 O 2 through AQP1 (one of the members of the AQP family) and the palmitoyl-oleoyl-phosphatidylcholine (POPC) phospholipid bilayer (PLB). The free energy barrier of H 2 O 2 across AQP1 is lower than for the POPC PLB, while the permeability coefficient, calculated using the free energy and diffusion rate profiles, is two orders of magnitude higher. This indicates that the delivery of H 2 O 2 into the cell interior should be through AQP. Our study gives a better insight into the role of AQPs in the selectivity of CAPs for treating cancer cells.

Abstract: Cold atmospheric plasmas (CAPs) have attracted significant interest for their potential benefits in medical applications, including cancer therapy. The therapeutic effects of CAPs are related to reactive oxygen and nitrogen species (ROS and RNS) present in the plasma. The impact of ROS has been extensively studied, but the role of RNS in CAP-treatment remains poorly understood at the molecular level. Here, we investigate the permeation of RNS and ROS across native and oxidized phospholipid bilayers (PLBs) by means of computer simulations. The results reveal significantly lower free energy barriers for RNS (i.e. NO, NO2, N2O4) and O3 compared to hydrophilic ROS, such as OH, HO2 and H2O2. This suggests that the investigated RNS and O3 can permeate more easily through both native and oxidized PLBs in comparison to hydrophilic ROS, indicating their potentially important role in plasma medicine.

Abstract: A thorough understanding of the skyrmion motion through nanotracks is a prerequisite to realize the full potential of spintronic applications like the skyrmion racetrack memory. One of the challenges is to place the data, i.e. skyrmions, on discrete fixed positions, e.g. below a read or write head. In the domain-wall racetrack memory, one proposed solution to this problem was patterning the nanotrack with notches. Following this approach, this paper reports on the skyrmion mobility through a nanotrack with periodic notches (constrictions) made using variations in the chiral Dzyaloshinskii-Moriya interaction. We observe that such notches induce a coupling between the mobility and the skyrmion breathing mode, which manifests itself as velocity-dependent oscillations of the skyrmion diameter and plateaus in which the velocity is independent of the driving force. Despite the fact that domain walls are far more rigid objects than skyrmions, we were able to perform an analogous study and, surprisingly, found even larger plateaus of constant velocity. For both systems it is straightforward to tune the velocity at these plateaus by changing the design of the notched nanotrack geometry, e.g. by varying the distance between the notches. Therefore, the notch-induced coupling between the excited modes and the mobility could offer a strategy to stabilize the velocity against unwanted perturbations in racetrack-like applications. In the last part of the paper we focus on the low-current mobility regimes, whose very rich dynamics at nonzero temperatures are very similar to the operating principle of recently developed probabilistic logic devices. This proves that the mobility of nanomagnetic structures through a periodically modulated track is not only interesting from a fundamental point of view, but has a future in many spintronic applications.

Abstract: Hydrogen production through photocatalytic water splitting is being developed swiftly to address the ongoing energy crisis. Over the past decade, with the rise of graphene and other two-dimensional (2D) materials, an increasing number of computational and experimental studies have focused on relevant van der Waals (vdW) semiconductor heterostructures for photocatalytic water splitting. In this review, the fundamental mechanism and distinctive performance of type-II and Z-scheme vdW heterostructure photocatalysts are presented. Accordingly, we have conducted a systematic review of recent studies focusing on candidates for photocatalysts, specifically vdW heterostructures involving 2D transition metal disulfides (TMDs), 2D Janus TMDs, and phosphorenes. The photocatalytic performance of these heterostructures and their suitability in theoretical scenarios are discussed based on their electronic and optoelectronic properties, particularly in terms of band structures, photoexcited carrier dynamics, and light absorption. In addition, various approaches for tuning the performance of these potential photocatalysts are illustrated. This strategic framework for constructing and modulating 2D heterostructure photocatalysts is expected to provide inspiration for addressing possible challenges in future studies.

Abstract: Electrophoretic Deposition (EPD) is one of the alternative methods to fabricate and enhance the performance of Li-ion batteries. It enables the fabrication of electrodes with outstanding qualities and different electrochemical properties by the great domination over various parameters. EPD facilitates the processing of electrodes by binder-free grafting of nanomaterials, such as graphene derivatives, carbon nanotube, and nanoparticles, into the battery electrodes. It also enables the assembly of the free-standing electrodes with 3D structure and provides possibilities, such as the fabrication of the electrodes with an oriented microstructure, even on 3D substrates to improve the energy or power density. In this review, after an introduction to EPD, the effect of EPD parameters on the properties of the prepared electrodes is reviewed. Then, EPD is compared with tape cast, and its advantages over the conventional method are evaluated. Also, employing the EPD method as an intermediate process is discussed. Finally, the application of EPD in the fabrication of separators is assessed, and the prospects for the future are described.

Abstract: Energy-dispersive X-ray fluorescence analysis was applied for the analysis of hair. The hair samples were digested in a mixture of nitric and perchloric acid and the heavy metals were precipitated with ammonium pyrrolidine dithiocarbamate. The accuracy, precision and recovery of the method for the elements Fe, Ni, Cu, Zn and Pb were evaluated through the analysis of a standard hair sample. The procedure was applied to the analysis of hair from an occupationally exposed group of Sudanese workers and a control group. The hair of the exposed group showed a range of 80550 ppm Fe, 612 ppm Cu, 57190 ppm Zn and 703700 ppm Pb, while that of the control group had a range of 60310 ppm Fe, 722 ppm Cu, 89170 ppm Zn and 317 ppm Pb.