Abstract: Cold atmospheric plasma (CAP) is a partially ionized gas that gains attention
as a well-tolerated cancer treatment that can enhance anti-tumor immune
responses, which are important for durable therapeutic effects. This review
offers a comprehensive and critical summary on the current understanding of
mechanisms in which CAP can assist anti-tumor immunity: induction of
immunogenic cell death, oxidative post-translational modifications of the
tumor and its microenvironment, epigenetic regulation of aberrant gene
expression, and enhancement of immune cell functions. This should provide
a rationale for the effective and meaningful clinical implementation of CAP. As
discussed here, despite its potential, CAP faces different clinical limitations
associated with the current CAP treatment modalities: direct exposure of
cancerous cells to plasma, and indirect treatment through injection of
plasma-treated liquids in the tumor. To this end, a novel modality is proposed:
plasma-treated hydrogels (PTHs) that can not only help overcome some of the
clinical limitations but also offer a convenient platform for combining CAP
with existing drugs to improve therapeutic responses and contribute to the
clinical translation of CAP. Finally, by integrating expertise in biomaterials and
plasma medicine, practical considerations and prospective for the
development of PTHs are offered.

Abstract: Black phosphorus (BP) has recently triggered an unprecedented interest in the 2D community. However, many of its unique properties are not exploited and the well-known environmental vulnerability is not conquered. Herein, a type-I mixed-dimensional (0D-1D) van der Waals heterojunction is developed, where three-atomic-layer BP quantum dots (QDs) are assembled on a single ZnO nanorod (NR). By adjusting the indium (In) content in ZnO NRs, the degree and even the direction of surface charge transfer doping within the heterojunction can be tuned, which result in selective Raman scattering enhancements between ZnO and BP. The maximal enhancement factor is determined as 4340 for BP QDs with sub-ppm level. Furthermore, an unexpected long-term ambient stability (more than six months) of BP QDs is revealed, which is ascribed to the electron doping from ZnO:In NRs. The first demonstration of selective Raman enhancements between two inorganic semiconductors as well as the improved stability of BP shed light on this emerging 2D material.

Abstract: ZrO2 and HfO2 nanoparticles are homogeneously dispersed in SiO2 matrices (supported film and bulk powders) by copolymerization of two oxozirconium and oxohafnium clusters (M4O(2)(OMc)(12), M= Zr, Hf; OMc = OC(O)-C(CH3)=CH2) with (methacryloxypropyl)trimethoxysilane (MAPTMS, (CH2=C(CH3)C(O)O)-(CH2)(3)Si(OCH3)(3)). After calcination (at a temperature >= 800 degrees C), a silica matrix with homogeneously distributed MO2 nanocrystallites is obtained. This route yields a spatially homogeneous dispersion of the metal precursors inside the silica matrix, which is maintained during calcination. The composition of the films and the powders is studied before and after calcination by using Fourier transform infrared (FTIR) analysis, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The local environment of the metal atoms in one of the calcined samples is investigated by using X-ray Absorption Fine Structure (XAFS) spectroscopy. Through X-ray diffraction (XRD) the crystallization of Hf and Zr oxides is seen at temperatures higher than those expected for the pure oxides, and transmission electron microscopy (TEM) shows the presence of well-distributed and isolated crystalline oxide nanoparticles (540 nm).

Abstract: Methane needle-plane discharge has practical application prospect and scientific research significance since methane conversion heavy oil hydrogenation is formed by coupling methane needle-plane discharge with heavy oil hydrogenation, which can achieve high-efficient heavy oil hydrogenation and increase the yields of high value-added light olefins. In this paper, a two-dimensional fluid model is built up for numerically simulating the methane needle-plane discharge plasma at atmospheric pressure. Spatial and axial distributions of electric intensity, electron temperature and particle densities are obtained. Reaction yields are summarized and crucial pathways to produce various kinds of charged and neutral particles are found out. Simulation results indicate that axial evolutions of CH3+ and CH4+ densities, electric intensity and electron temperature are similar and closely related. The CH5+ and C2H5+ densities first increase and then decrease along the axial direction. The CH3 and H densities have nearly identical spatial and axial distributions. Particle density distributions of CH2, C2H4 and C2H5 are obviously different in the area near the cathode but comparatively resemblant in the positive column region. The CH3+ and CH4+ are produced by electron impact ionizations between electrons and CH4. The CH5+ and C2H5+ are respectively generated by molecular impact dissociations between CH3+ and CH4 and between CH4+ and CH4. Electron impact decomposition between electrons and CH4 is a dominated reaction to produce CH3, CH2, CH and H. The reactions between CH2 and CH4 and between electrons and C2H4 are critical pathways to produce C2H4 and C2H2, respectively. In addition, the yields of electron impact decomposition reactions between electrons and CH4 and reactions between CH2 and CH4 account for 52.15% and 47.85% of total yields of H-2 respectively.

Abstract: The combination of catalysis and nonthermal plasma holds promise for enabling difficult chemical conversions. The possible synergy between both depends strongly on the nature of the reactive plasma species and the catalyst material. In this paper, we show how vibrationally excited species and plasma-generated radicals interact with transition metal catalysts and how changing the catalyst material can improve the conversion rates and product selectivity. We developed a microkinetic model to investigate the impact of vibrational excitations and plasma-generated radicals on the nonoxidative coupling of methane over transition metal surfaces. We predict a significant increase in ethylene formation for vibrationally excited methane. Plasma-generated radicals have a stronger impact on the turnover frequencies with high selectivity toward ethylene on noble catalysts and mixed selectivity on non-noble catalysts. In general, we show how the optimal catalyst material depends on the desired products as well as the plasma conditions.

Abstract: Ammonia is a crucial nutrient used for plant growth and as a building block in the pharmaceutical and chemical industry, produced via nitrogen fixation of the ubiquitous atmospheric N2. Current industrial ammonia production relies heavily on fossil resources, but a lot of work is put into developing nonfossil-based pathways. Among these is the use of nonequilibrium plasma. In this work, we investigated water vapor as a H source for nitrogen fixation into NH3 by nonequilibrium plasma. The highest selectivity toward NH3 was observed with low amounts of added H2O vapor, but the highest production rate was reached at high H2O vapor contents. We also studied the role of H2O vapor and of the plasma-exposed liquid H2O in nitrogen fixation by using isotopically labeled water to distinguish between these two sources of H2O. We show that added H2O vapor, and not liquid H2O, is the main source of H for NH3 generation. The studied catalyst- and H2-free method offers excellent selectivity toward NH3 (up to 96%), with energy consumption (ca. 95–118 MJ/mol) in the range of many plasma-catalytic H2-utilizing processes.

Abstract: Spectacular progress in developing advanced Si circuits with reduced size, along the track of Moore's law, has been relying on necessary developments in wet cleaning of nanopatterned Si wafers to provide contaminant free surfaces. The most efficient cleaning is achieved when complete wetting can be realized. In this work, ordered arrays of silicon nanopillars on a hitherto unexplored small scale have been used to study the wetting behavior on nanomodulated surfaces in a substantial range of surface treatments and geometrical parameters. With the use of optical reflectance measurements, the nanoscale water imbibition depths have been measured and the transition to the superhydrophobic Cassie-Baxter state has been accurately determined. For pillars of high aspect ratio (about 15), the transition occurs even when the surface is grafted with a hydrophilic functional group. We have found a striking consistent deviation between the contact angle measurements and the straightforward application of the classical wetting models. Molecular dynamics simulations show that these deviations can be attributed to the long overlooked atomic-scale surface perturbations that are introduced during the nanofabrication process. When the transition condition is approached, transient states of partial imbibition that characterize intermediate states between the Wenzel and Cassie-Baxter states are revealed in our experiments.

Abstract: Plasma technology is gaining increasing interest for gas conversion applications, such as CO2 conversion into value-added chemicals or renewable fuels, and N2 fixation from the air, to be used for the production of small building blocks for, e.g., mineral fertilizers. Plasma is generated by electric power and can easily be switched on/off, making it, in principle, suitable for using intermittent renewable electricity. In this Perspective article, we explain why plasma might be promising for this application. We briefly present the most common types of plasma reactors with their characteristic features, illustrating why some plasma types exhibit better energy efficiency than others. We also highlight current research in the fields of CO2 conversion (including the combined conversion of CO2 with CH4, H2O, or H2) as well as N2 fixation (for NH3 or NOx synthesis). Finally, we discuss the major limitations and steps to be taken for further improvement.

Abstract: Catalyst preparation with plasmas is increasingly attracting interest. A plasma is a partially ionized gas, consisting of electrons, ions, molecules, radicals, photons, and excited species, which are all active species for catalyst preparation and treatment. Under the influence of plasma, nucleation and crystal growth in catalyst preparation can be very different from those in the conventional thermal approach. Some thermodynamically unfavorable reactions can easily take place with plasmas. Compounds such as sulfides, nitrides, and phosphides that are produced under harsh conditions can be synthesized by plasma under mild conditions. Plasmas can produce catalysts with smaller particle sizes and controllable structure. Plasma is also a facile tool for reduction, oxidation, doping, etching, coating, alloy formation, surface treatment, and surface cleaning in a simple and direct way. A rapid and convenient plasma template removal has thus been established for zeolite synthesis. It can operate at room temperature and allows the catalyst preparation on temperature-sensitive supporting materials. Plasma is typically effective for the production of various catalysts on metallic substrates. In addition, plasma-prepared transition-metal catalysts show enhanced low-temperature activity with improved stability. This provides a useful model catalyst for further improvement of industrial catalysts. In this review, we aim to summarize the recent advances in catalyst preparation with plasmas. The present understanding of plasma-based catalyst preparation is discussed. The challenges and future development are addressed.

Abstract: Industrial production of HCN from NH3 and CH4 not only uses precious Pt or Pt−Rh catalysts but also requires extremely high temperatures (∼1600 K). From an energetic, operational, and safety perspective, a drastic decrease in temperature is highly desirable. Here, we report ammonia reforming of methane for the production of HCN and H2 at 673 K by the combination of CH4/NH3 plasma and a supported Cu/silicalite-1 catalyst. 30% CH4 conversion has been achieved with 79% HCN selectivity. Catalyst characterization and plasma diagnostics reveal that the excellent reaction performance is attributed to metallic Cu active sites. In addition, we propose a possible reaction pathway, viz. E-R reactions with N, NH, NH2, and CH radicals produced in the plasma, for the production of HCN, based on density functional theory calculations. Importantly, the Cu/silicalite-1 catalyst costs less than 5% of the commercial Pt mesh catalyst.

Abstract: Plasma-catalytic CO, hydrogenation for methanol production is gaining increasing interest, but our understanding of its reaction mechanism remains primitive. We present a combined experimental/computational study on plasma-catalytic CO, hydrogenation to CH3OH over a size-selected Cu/gamma-Al2O3 catalyst. Our experiments demonstrate a synergistic effect between the Cu/gamma-Al2O3 catalyst and the CO2/H-2 plasma, achieving a CO2 conversion of 10% at 4 wt % Cu loading and a CH3OH selectivity near 50% further rising to 65% with H2O addition (for a H2O/CO2 ratio of 1). Furthermore, the energy consumption for CH3OH production was more than 20 times lower than with plasma only. We carried out density functional theory calculations over a Cu-13/gamma-Al2O3 model, which reveal that the interfacial sites of the Cu-13 cluster and gamma-Al2O3 support show a bifunctional effect: they not only activate the CO2 molecules but also strongly adsorb key intermediates to promote their hydrogenation further. Reactive plasma species can regulate the catalyst surface reactions via the Eley-Rideal (E-R) mechanism, which accelerates the hydrogenation process and promotes the generation of the key intermediates. H2O can promote the CH3OH desorption by competitive adsorption over the Cu-13/gamma-Al2O3 surface. This study provides new insights into CO2 hydrogenation through plasma catalysis, and it provides inspiration for the conversion of some other small molecules (CH4, N-2, CO, etc.) by plasma catalysis using supported-metal clusters.

Abstract: Since the discovery of graphene, a broad range of two-dimensional (2D) materials has captured the attention of the scientific communities. Materials, such as hexagonal boron nitride (hBN) and the transition metal dichalcogenides (TMDs) family, have shown promising semiconducting and insulating properties that are very appealing for the semiconductor industry. Recently, the possibility of taking advantage of the properties of 2D-based heterostructures has been investigated for low-power nanoelectronic applications. In this work, we aim at evaluating the relation between the nature of the materials used in such heterostructures and the amplitude of the layer-to-layer charge transfer induced by an external electric field, as is typically present in nanoelectronic gated devices. A broad range of combinations of TMDs, graphene, and hBN has been investigated using density functional theory. Our results show that the electric field induced charge transfer strongly depends on the nature of the 2D materials used in the van der Waals heterostructures and to a lesser extent on the relative orientation of the materials in the structure. Our findings contribute to the building of the fundamental understanding required to engineer electrostatically the doping of 2D materials and to establish the factors that drive the charge transfer mechanisms in electron tunneling-based devices. These are key ingredients for the development of 2D -based nanoelectronic devices.

Abstract: The continuous miniaturization of nanodevices, such as transistors, solar cells, and optical fibers, requires the controlled synthesis of (ultra)thin gate oxides (<10 nm), including Si gate-oxide (SiO2) with high quality at the atomic scale. Traditional thermal growth of SiO2 on planar Si surfaces, however, does not allow one to obtain such ultrathin oxide due to either the high oxygen diffusivity at high temperature or the very low sticking ability of incident oxygen at low temperature. Two recent techniques, both operative at low (room) temperature, have been put forward to overcome these obstacles: (i) hyperthermal oxidation of planar Si surfaces and (ii) thermal or plasma-assisted oxidation of nonplanar Si surfaces, including Si nanowires (SiNWs). These nanooxidation processes are, however, often difficult to study experimentally, due to the key intermediate processes taking place on the nanosecond time scale.
In this Account, these Si nano-oxidation techniques are discussed from a computational point of view and compared to both hyperthermal and thermal oxidation experiments, as well as to well-known models of thermal oxidation, including the Deal−Grove, Cabrera−Mott, and Kao models and several alternative mechanisms. In our studies, we use reactive molecular dynamics (MD) and hybrid MD/Monte Carlo simulation techniques, applying the Reax force field. The incident energy of oxygen species is chosen in the range of 1−5 eV in hyperthermal oxidation of planar Si surfaces in order to prevent energy-induced damage. It turns out that hyperthermal growth allows for two growth modes, where the ultrathin oxide thickness depends on either (1) only the kinetic energy of the incident oxygen species at a growth temperature below Ttrans = 600 K, or (2) both the incident energy and the growth temperature at a growth temperature above Ttrans. These modes are specific to such ultrathin oxides, and are not observed in traditional thermal oxidation, nor theoretically considered by already existing models. In the case of thermal or plasma-assisted oxidation of small Si nanowires, on the other hand, the thickness of the ultrathin oxide is a function of the growth temperature and the nanowire diameter. Below Ttrans, which varies with the nanowire diameter, partially oxidized SiNW are formed, whereas complete oxidation to a SiO2 nanowire occurs only above Ttrans. In both nano-oxidation processes at lower temperature (T < Ttrans), final sandwich c-Si|SiOx|a-SiO2 structures are obtained due to a competition between overcoming the energy barrier to penetrate into Si subsurface layers and the compressive stress (∼2−3 GPa) at the Si crystal/oxide interface. The overall atomic-simulation results strongly indicate that the thickness of the intermediate SiOx (x < 2) region is very limited (∼0.5 nm) and constant irrespective of oxidation parameters. Thus, control over the ultrathin SiO2 thickness with good quality is indeed possible by accurately tuning the oxidant energy, oxidation temperature and surface curvature.
In general, we discuss and put in perspective these two oxidation mechanisms for obtaining controllable ultrathin gate-oxide films, offering a new route toward the fabrication of nanodevices via selective nano-oxidation.

Abstract: We study the structural, mechanical and electronic properties of the two-dimensional (2D) allotrope of tin: tinene/stanene using first-principles calculation within density functional theory, implemented in a set of computer codes. Continuing the trend of the group-IV 2D materials graphene, silicene and germanene; tinene is predicted to have a honeycomb lattice with lattice parameter of a(0) = 4.62 angstrom and a buckling of d(0) = 0.92 angstrom. The electronic dispersion shows a Dirac cone with zero gap at the Fermi energy and a Fermi velocity of v(F) = 0.97 x 10(6) m s(-1); including spin-orbit coupling yields a bandgap of 0.10 eV. The monolayer is thermally stable up to 700 K, as indicated by first-principles molecular dynamics, and has a phonon dispersion without imaginary frequencies. We explore applied electric field and applied strain as functionalization mechanisms. Combining these two mechanisms allows for an induced bandgap up to 0.21 eV, whilst retaining the linear dispersion, albeit with degraded electronic transport parameters.

Abstract: Heterostructures of low-dimensional semiconducting materials, such as transition metal dichalcogenides (MX2), are promising building blocks for future electronic and optoelectronic devices. The patterning of one MX2 material on top of another one is challenging due to their structural similarity. This prevents an intrinsic etch stop when conventional anisotropic dry etching processes are used. An alternative approach consist in a two-step process, where a sacrificial silicon layer is pre-patterned with a low damage plasma process, stopping on the underlying MoS2 film. The pre-patterned layer is used as sacrificial template for the formation of the top WS2 film. This study describes the optimization of a cyclic Ar/Cl-2 atomic layer etch process applied to etch silicon on top of MoS2, with minimal damage, followed by a selective conversion of the patterned Si into WS2. The impact of the Si atomic layer etch towards the MoS2 is evaluated: in the ion energy range used for this study, MoS2 removal occurs in the over-etch step over 1-2 layers, leading to the appearance of MoOx but without significant lattice distortions to the remaining layers. The combination of Si atomic layer etch, on top of MoS2, and subsequent Si-to-WS2 selective conversion, allows to create a WS2/MoS2 heterostructure, with clear Raman signals and horizontal lattice alignment. These results demonstrate a scalable, transfer free method to achieve horizontally individually patterned heterostacks and open the route towards wafer-level processing of 2D materials.