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Candidate tungsten armor materials in a magnetic confinement fusion device must be able to withstand thermal variation that leads to internal stresses caused by the impinging heat load. In addition...

Periodic surface structures at the nanometer or micrometer scale have been achieved by various methods, while atomic-scale surface structures over large areas are unavailable. Herein, we report the...

The Hybrid Illinois Device for Research and Applications (HIDRA) at the University of Illinois at Urbana-Champaign is a toroidal plasma device that enables fusion plasma-material interaction testing with both stellarator and tokamak plasmas. HIDRA’s long-pulse steady state stellarator plasmas provide a testbed for plasma facing component (PFC) plasma exposures. The HIDRA Material Analysis Test-stand (HIDRA-MAT) is a material characterization module attached to HIDRA that is being designed and fabricated to include thermal desorption spectroscopy and laser induced breakdown spectroscopy systems for in-vacuo PFC characterization. A specialized rotatable sample holder positions the sample for liquid metal droplet application from a liquid metal droplet injector on HIDRA-MAT. Early experiments look to investigate the effect liquid lithium has on porous tungsten samples’ retention of H, D, and He after plasma exposure. Preliminary results from a dual residual gas analyzer system show the ability to differentiate D2 and He in HIDRA-MAT. This work aims to advance the understanding of liquid metal PFCs and further the design and development of new fusion PFCs and technologies.

Hydrogels provide a solution-mimicking environment for the interaction with living systems that make them desirable for various biomedical and technological applications. Because relevant biologica...

Bacterial adhesion and biofilm formation on the surface of biomedical devices are detrimental processes that compromise patient safety and material functionality. Several physicochemical factors are involved in biofilm growth, including the surface properties. Among these, material stiffness has recently been suggested to influence microbial adhesion and biofilm growth in a variety of polymers and hydrogels. However, no clear consensus exists about the role of material stiffness in biofilm initiation and whether very compliant substrates are deleterious to bacterial cell adhesion. Here, by systematically tuning substrate topography and stiffness while keeping the surface free energy of polydimethylsiloxane substrates constant, we show that topographical patterns at the micron and submicron scale impart unique properties to the surface which are independent of the material stiffness. The current work provides a better understanding of the role of material stiffness in bacterial physiology and may constitute a cost-effective and simple strategy to reduce bacterial attachment and biofilm growth even in very compliant and hydrophobic polymers.

Surface-associated bacterial communities, known as biofilms, are responsible for a broad spectrum of infections in humans. Recent studies have indicated that surfaces containing nanoscale protrusions, like those in dragonfly wings, create a hostile niche for bacterial colonization and biofilm growth. This functionality has been mimicked on metals and semiconductors by creating nanopillars and other high aspect ratio nanostructures at the interface of these materials. However, bactericidal topographies have not been reported on clinically relevant hydrogels and highly compliant polymers, mostly because of the complexity of fabricating nanopatterns in hydrogels with precise control of the size that can also resist aqueous immersion. Here, we report the fabrication of bioinspired bactericidal nanostructures in bacterial cellulose (BC) hydrogels using low-energy ion beam irradiation. By challenging the currently accepted view, we show that the nanostructures grown in BC affect preferentially stiff membranes like those of the Gram-positive bacteria

Bacterial cellulose is a naturally occurring polysaccharide with numerous biomedical applications that range from drug delivery platforms to tissue engineering strategies. BC possesses remarkable biocompatibility, microstructure, and mechanical properties that resemble native human tissues, making it suitable for the replacement of damaged or injured tissues. In this review, we will discuss the structure and mechanical properties of the BC and summarize the techniques used to characterize these properties. We will also discuss the functionalization of BC to yield nanocomposites and the surface modification of BC by plasma and irradiation-based methods to fabricate materials with improved functionalities such as bactericidal capabilities.

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is a linear plasma device being used in plasma source research and development (R&D) for the proposed MPEX. Once the R&D is completed, this device can also be used to perform plasma–material interaction studies. To perform these studies, a new materials analysis and particle probe (MAPP) has been constructed. The MAPP’s components are a sample holder and manipulator and a custom vacuum chamber with ports to facilitate surface chemistry diagnostics. The MAPP’s overall design enables rapid sample turnaround and in vacuo surface characterization. The surface analysis vacuum chamber has ports for x-ray photoelectron spectroscopy, thermal desorption spectroscopy, back-scatter ion scattering spectroscopy, forward-scatter ion scattering spectroscopy, and direct recoil spectroscopy. The sample manipulator and holder is a Lesker/UHV Multi-Centre Analytical Stage, which is used to place the samples in the exposure region of the Proto-MPEX or the analysis position in the MAPP vacuum chamber. The sample holder has a heating capability of up to 1200 °C for heated exposure and for desorption studies. In this work, we present the MAPP’s design and the first tungsten sample exposure with ex situ analysis that shows a surface deposition layer on the exposed target, highlighting the need for additional in situ measurements on the Proto-MPEX.

One of the most significant design challenges for materials performance exposed to extreme environments (e.g., heat, pressure, and radiation) is maintaining structural integrity while preve...

Titanium implant failures are mainly related to stress shielding phenomenon and the poor cell interaction with host bone tissue. The development of bioactive and biomimetic Ti scaffolds for bone regeneration remains a challenge which needs the design of Ti implants with enhanced osseointegration. In this context, 4 types of titanium samples were fabricated using conventional powder metallurgy, fully dense, dense etched, porous Ti, and porous etched Ti. Porous samples were manufactured by space holder technique, using ammonium bicarbonate particles as spacer in three different ranges of particle size (100–200 μm, 250–355 μm and 355–500 μm). Substrates were chemically etched by immersion in fluorhydric acid at different times (125 and 625 s) and subsequently, were characterized from a micro-structural, topographical and mechanical point of view. Etched surfaces showed an additional roughness preferentially located inside pores. In vitro tests showed that all substrates were biocompatible (80% of cell viability), confirming cell adhesion of premioblastic cells. Similarly, osteoblast showed similar cell proliferation rates at 4 days, however, higher cell metabolic activity was observed in fully dense and dense etched surfaces at 7 days. In contrast, a significant increase of alkaline phosphatase enzyme expression was observed in porous and porous etched samples compared to control surfaces (dense and dense etched), noticing the suitable surface modification parameters (porosity and roughness) to improve cell differentiation. Furthermore, the presence of pores and rough surfaces of porous Ti substrates remarkably decreased macrophage activation reducing the M1 phenotype polarization as well M1 cell marker expression. Thus, a successful surface modification of porous Ti scaffolds has been performed towards a reduction on stress shielding phenomenon and enhancement of bone osseointegration, achieving a biomechanical and biofunctional equilibrium., This article is also dedicated to our dear friend and colleague Prof. Juan Jose Pavón, who prematurely passed away early in 2017, his dedication to his work, his students, his friends and family, will always be remembered. This work was supported by the Ministry of Economy and Competitiveness of Spain under the grant MAT2015-71284-P and of the Junta de Andalucía – FEDER (Spain) through the Project Ref. P12-TEP-1401. The authors would like to thank technician J. Pinto for assistance in micro-mechanical testing

In reactor-relevant fusion divertor conditions, tungsten (W) will be used as an armor material due to its excellent thermal properties. It will be exposed to impurities from numerous sources, inclu...

Tungsten is the material of choice as the plasma-facing material in future plasma-burning fusion reactors. During operation, plasma-facing materials will be simultaneously exposed to 14-MeV...

A new generation of biomaterials are evolving from being biologically inert toward bioactive surfaces, which can further interact with biological components at the nanoscale. Here, we present direc...

The plasma surface interactions within a fusion device are one of the limiting factors to long pulse, power generating operation. A plasma facing component material will require effective heat tolerance, minimal erosion yield, and minimal fuel retention properties. Tungsten (W) has been selected as the divertor material for the International Thermonuclear Experimental Reactor (ITER) due to its high thermal conductivity and high sputter threshold. However, when W is exposed to high particle flux (>1022 ions/m2s) at high surface temperatures (>600 °C), the surface will develop defects such as pits, blisters, and nano-structured tendrils, reducing the beneficial properties of W. To overcome this limitation, a more radiation tolerant thin film material could be used, such as lithium (Li). In addition, the lithium film can protect the plasma from high-Z W sputtered atoms. In multiple tokamak devices, a Li wall coating, has improved the plasma performance by reducing fuel recycling from the walls, stabilizing the edge plasma and decreasing the number of edge localized modes (ELMs). Since ELMs help eject impurities from the core plasma, the complete suppression of ELMs is detrimental. Methods to regulate the frequency of ELMs have been investigated using gas puffs. In this work we report a new method to control the ELM frequency by tuning fuel recycling via the intrinsic helium (He) ions produced as ash from the deuterium (D) – tritium (T) fusion reaction. In Li films, one mechanism to retain D is via a chemical interaction between Li, O (oxygen), and D. Previous work has shown that when He ions are introduced with D ions, in a dual beam irradiation of Li films on W, a reduction in the dynamic surface D retention is observed. To further investigate this phenomenon, 1–2 um films of Li on W were exposed to sequential irradiations of D and He. The He fluence was ≈5% of the D (3.3 × 1020 ions/m2). The energies for the He and D ions were 1000 eV and 250 eV/amu, respectively and samples were exposed at room temperature. The surface chemistry was characterized with x-ray photoelectron spectroscopy (XPS) to determine changes in retention. The XPS scans were conducted in-situ and in-operando for the irradiations. Our results showed a decrease in the surface retention when He follows D ions and little change in the retention when D follows He. This indicates that He breaks the D retention mechanism in Li. Keywords: Lithium, Tungsten, Deuterium, In-situ XPS, Plasma facing components, Hydrogen retention

Tungsten is the material of choice for plasma-facing components in the divertor region of future plasma-burning tokamak fusion reactors. However, under low energy helium irradiation at elevated temperatures, significant surface morphology changes are expected, including pores, blisters, and fuzz. Dispersion-strengthened tungsten materials with small additions of transition metal carbide dispersoids have been proposed as an alternative to pure tungsten, as they have shown enhanced thermomechanical properties and possible radiation damage tolerance. However, their response to low energy helium irradiation has yet to be fully elucidated. In this work, dispersion-strengthened tungsten alloys containing 1–10 wt.% tantalum carbide, titanium carbide, or zirconium carbide were exposed to 250 eV helium ions at 600 and 800 °C to a 1 × 1020 cm−2 fluence to understand the early-stage irradiation response to helium bombardment. At 600 °C, nanostructuring is only observed on titanium carbide particles. As the temperature is raised to 800 °C, pores and ripples were developed on tungsten grains for all samples; fiber-form structures and isolated tendril growth is observed only on titanium carbide particles. Minimal surface morphology changes were observed on tantalum carbide and zirconium carbide particles. X-ray photoelectron spectroscopy of the alloyed specimens post-irradiation at 800 °C indicates the formation of zirconium and titanium oxides on the surface. Potential thermodynamic, sputtering, and composition-based formation mechanisms behind the novel nanostructuring and chemistry changes of the complex materials are discussed. Keywords: Dispersion-strengthened tungsten, Tungsten, Helium damage, Tungsten fuzz

The U.S. Fusion Energy Sciences Advisory Committee was charged “to identify the most promising transformative enabling capabilities (TEC) for the U.S. to pursue that could promote efficient advance toward fusion energy, building on burning plasma science and technology.” A subcommittee of U.S. technical experts was formed and received community input in the form of white papers and presentations on the charge questions. The subcommittee identified four “most promising transformative enabling capabilities”: 1. advanced algorithms 2. high critical temperature superconductors 3. advanced materials and manufacturing 4. novel technologies for tritium fuel cycle control. In addition, one second-tier TEC, defined as a “promising transformative enabling capability,” was identified: fast-flowing liquid-metal plasma-facing components. Each of these TECs presents a tremendous opportunity to accelerate fusion science and technology toward power production. Dedicated investment in these TECs for fusion systems is needed to capitalize on the rapid advances being made for a variety of nonfusion applications to fully realize their transformative potential for fusion energy.

Carbon dots (CDs) have recently garnered significant attention owing to their excellent luminescence properties, thereby demonstrating a variety of applications in in vitro and in vivo imaging. Understanding the long-term metabolic fate of these agents in a biological environment is the focus of this work. Here we show that the CDs undergo peroxide catalysed degradation in the presence of lipase. Our results indicate that differently charged CD species exhibit unique degradation kinetics upon being subjected to enzyme oxidation. Furthermore, this decomposition correlates with the relative accessibility of the enzymatic molecule. Using multiple physico-chemical characterization studies and molecular modelling, we confirmed the interaction of passivating surface abundant molecules with the enzyme. Finally, we have identified hydroxymethyl furfural as a metabolic by-product of the CDs used here. Our results indicate the possibility and a likely mechanism for complete CD degradation in living systems that can pave the way for a variety of biomedical applications.

Boronization is a Plasma Facing Component (PFC) conditioning technique widely used in tokamak machines. The National Spherical Torus Experiment-Upgrade (NSTX-U) applied this conditioning, using a plasma glow with a deuterated Trimethyl-boron (d-TMB) and He mixture. The use of boronization during the campaign improved the plasma performance, allowing longer plasma discharges and H-mode access. The chemical state of an ATJ graphite sample, used as a proxy for the NSTX-U PFCs, was monitored in-situ using the Materials Analysis Particle Probe (MAPP) diagnostic and X-ray Photoelectron Spectroscopy (XPS). The XPS data showed a progressive rise (from

One of the major limitations during titanium (Ti) implant osseointegration is the poor cellular interactions at the biointerface. In the present study, the combined effect of recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) and nanopatterned Ti6Al4V fabricated with Directed irradiation synthesis (DIS) is investigated in vitro. This environmentally-friendly plasma uses ions to create self-organized nanostructures on the surfaces. Nanocones (≈36.7 nm in DIS 80°) and thinner nanowalls (≈16.5 nm in DIS 60°) were fabricated depending on DIS incidence angle and observed via scanning electron microscopy. All samples have a similar crystalline structure and wettability, except for sandblasted/acid-etched (SLA) and acid-etched/anodized (Anodized) samples which are more hydrophilic. Biological results revealed that the viability and adhesion properties (vinculin expression and cell spreading) of DIS 80° with BMP-2 were similar to those polished with BMP-2, yet we observed more filopodia on DIS 80° (≈39 filopodia/cell) compared to the other samples (&lt, 30 filopodia/cell). BMP-2 increased alkaline phosphatase activity in all samples, tending to be higher in DIS 80°. Moreover, in the mineralization studies, DIS 80° with BMP-2 and Anodized with BMP-2 increased the formation of calcium deposits (&gt, 3.3 fold) compared to polished with BMP-2. Hence, this study shows there is a synergistic effect of BMP-2 and DIS surface modification in improving Ti biological properties which could be applied to Ti bone implants to treat bone disease.

Low-energy ion irradiation of III-V semiconductor surfaces can lead to the formation of regular hexagonal dot patterns at the surface. We present experimental and computational results for ion irradiation of GaSb surfaces which elucidate the nature of the coupled compositional and morphological pattern-formation mechanisms. We demonstrate by in-situ grazing-incidence small-angle x-ray scattering (GISAXS) and angle-resolved Auger electron spectroscopy (ARAES) that the emergence of an altered compositional depth profile is essential to induce morphological changes at the surface. This morphological evolution of the surface follows nucleation-and-growth kinetics. Furthermore, we show from massive-scale molecular dynamics (MD) simulations that the compositional depth profile evolution leads to thermodynamic phase separation, providing a lateral compositional instability that drives pattern formation. Additionally, high-fluence simulations elucidate the irradiation-induced mechanisms of compositional depth profile formation. Prompt ion effects drive formation of single-element “protoclusters”, predominantly of Sb. Structural and energetic characterization of the simulation results indicate that Sb may be more mobile than Ga, providing a diffusional pathway for long-temporal-scale compositional evolution of the irradiated surface. Our findings motivate the development of new, comprehensive models which consider the total spatial and temporal complexity of multicomponent systems evolving under ion irradiation.

Device-associated infections are one of the deadliest complications accompanying the use of biomaterials, and despite recent advances in the development of anti-biofouling strategies, biomaterials that exhibit both functional tissue restoration and antimicrobial activity have been challenging to achieve. Here, we report the fabrication of bio-inspired bactericidal nanospikes in bacterial cellulose and investigate the mechanism underlying this phenomenon. We demonstrate these structures affects preferentially stiff membranes like those in Gram-positive bacteria, but exhibit cytocompatibility towards mammalian cells, a requisite for tissue restoration. We also reveal the bactericidal activity of the nanospikes is due to a pressure-induced mechanism, which depends on the cell’s adherence time, nanospike’s geometry and spacing, cell shape, and mechanical properties of the cell wall. Our findings provide a better understanding of the mechanobiology of bacterial cells at the interface with nanoscale structures, which is fundamental for the rational design bactericidal topographies.

Bacterial adhesion and biofilm formation on the surface of biomedical devices is a detrimental process that compromises patient safety and material functionality. Several physicochemical factors are involved in biofilm growth, including the surface properties. Among those, material stiffness has recently been suggested to influence microbial adhesion and biofilm growth in a variety of polymers and hydrogels. However, no clear consensus exists about the role of material stiffness on biofilm initiation and whether very compliant substrates are deleterious to bacterial cell adhesion. Here, by systematically tuning substrate topography and stiffness while keeping the surface free energy of polydimethylsiloxane substrates constant, we show that topographical patterns at the micron and submicron scale impart unique properties to the surface that are independent of the material stiffness. The current work provides a better understanding of the role of material stiffness on bacterial physiology and may constitute a cost-effective and simple strategy to reduce bacterial attachment and biofilm growth even in very compliant and hydrophobic polymers.

La colección Colombia hacia una sociedad del conocimiento reúne las contribuciones de la Misión Internacional de Sabios 2019 sobre Educación, Ciencia, Tecnología e Innovación, convocada por el Presidente de la República. Este volumen corresponde a las contribuciones realizadas por el Foco de Tecnologías Convergentes -Nano, Bio, Info y Cogno- e Industrias 4.0, cuyas recomendaciones sobre la educación, la infraestructura digital estratégica, la inversión inteligente, la innovación para crear valor y equidad, la atracción de capital privado y talento internacional, la política pública acompañada de regulaciones modernas, entre otros pilares, conforman una arquitectura crítica para la innovación y la oportunidad global para el país., Vicepresidencia de la República de Colombia, Universidad EAFIT, Universidad del Valle

The percutaneous invasion of microorganisms through damaged skin layers can lead to the onset of infections with potentially life-threatening complications, especially in vulnerable populations like newborns, elderly, and diabetic patients. With the emergence of superbugs that are resistant to almost all the available antibiotics and the unfruitful discovery of new antimicrobial compounds in the last few decades, there is a demand for novel engineering strategies to approach skin and soft tissue infections associated with the used of biomaterials. Naturally occurring anti-biofouling and antimicrobial interfaces based on spatial structure offer an unprecedented opportunity for biomaterial design, as they do not contribute to bacterial resistance, do not pollute the environment, and can be easily implemented in a variety of biomaterial interfaces. In this article, we review the complications caused by biomaterials in contact with the skin, especially those that compromise medical adhesives, sutures, and wound dressing materials. Then, we introduced bioinspired designs that can be implemented in those materials based on nano- and microscale topographies.

Tungsten is the plasma-facing material of choice for the divertor region in ITER as it has favorable properties under ion irradiation. However, tungsten is a very brittle material whose fabrication is complicated by its high melting point and low recrystallization temperature. Spark plasma sintering is a powder consolidation technique that can rapidly compact tungsten powder to high relative densities while preserving fine grain sizes. Dispersing fine transition metal carbide particles within the tungsten matrix has been proposed to enhance the ductility of tungsten by re-arranging the impurity distribution. Tungsten samples consolidated with 0.5–10 wt% zirconium carbide, titanium carbide, or tantalum carbide have been fabricated via spark plasma sintering to >90% relative density. Consolidated samples have transition metal-rich dispersoids uniformly distributed at grain boundaries and within the micron-sized tungsten grains. The presence of the dispersed second phase particles successfully refined the final grain size, as the average grain size decreased from 11 μm for the pure W samples to ~1 μm for the samples with 10 wt% second phase. Correspondingly, the hardness as measured via Vickers hardness rises as the grain size decreases and volume fraction of the second phase increases. XRD and XPS analyses show that formation of tungsten carbide and transition metal oxide complexes alter the impurity distribution and material performance.

The review of recent theoretical and experimental research on the complex surface chemistry processes that evolve from low-Z material conditioning on plasma-facing materials under extreme fusion plasma conditions is presented. A combination of multi-scale computational physics and chemistry modeling with real-time diagnosis of the plasma-material interface in tokamak fusion plasma edge is complemented by ex-vessel in-situ single-effect experimental facilities to unravel the evolving characteristics of low-Z components under irradiation. Effects of the lithium and boron coatings at carbon surfaces to the retention of deuterium and chemical sputtering of the plasma-facing surfaces are discussed in detail. The critical role of oxygen in the surface chemistry during hydrogen-fuel irradiation is found to drive the kinetics and dynamics of these surfaces as they interact with fusion edge plasma that ultimately could have profound effects on fusion plasma confinement behavior. Computational studies also extend in spatio-temporal scales not accessible by empirical means and therefore open the opportunity for a strategic approach at irradiation surface science studies that combined these powerful computational tools with in-vessel and ex-vessel in-situ diagnostics. Keywords: Plasma-material interface, Retention, Sputtering, Lithium, Boron, Quantum-classical molecular dynamics, X-ray photoelectron spectroscopy, Material-analysis particle probe, PACS codes: 28-52.-s, 52.40.Hf, 82.33.Xj, 73.22.-f

The Hybrid Illinois Device for Research and Applications (HIDRA) is a toroidal fusion device at the University of Illinois at Urbana–Champaign, Urbana, IL, USA. HIDRA is the former WEGA stellarator that was operated at the Max Planck Institut fur Plasmaphysik, Greifswald, Germany. The machine is a five-period, $l=2, m=5$ stellarator, with major radius $R_{0}=0.72$ m, and minor radius $a=0.19$ m. Initial heating is achieved with 2.45-GHz electron cyclotron resonance heating and an on-axis magnetic field of $B_{0}=0.087$ T that can go as high as $B_{0}=0.5$ T. HIDRA has the ability to operate as both a stellarator and a tokamak, initially operating in the stellarator mode. The focus of research on HIDRA will be doing dedicated studies on plasma-material interactions (PMIs) using the wealth of knowledge and experience at the Center for Plasma Material Interactions, Urbana, IL, USA. In early 2016, the first experiments were performed on HIDRA. This paper presents some of the first results obtained from the machine such as initial magnetic fields’ measurements and plasma discharges. It also shows the development of the control system being currently implemented and introduces HIDRA-materials analysis tool, the in situ PMI facility that will be mounted on HIDRA in the near future to further enhance the diagnostics and material testing experiments meant to be conducted on the machine.

Directed plasma nanosynthesis (DPNS) is a plasma-based surface modification process used to provide high-fidelity bioactive and bioresorbable interfaces for Mg-based foams having an average 500-μm pore size and containing main components of Al, Zn and Ca at bal., 3.3%, 1.11%, and 0.21%, respectively. Correlations of incident particle energies of 400–700 eV and room temperature, normal and off-normal incidence angles of 0° and 60°, respectively, and high-ion fluence conditions are combined to elicit a bioreactive Mg-foam surface. H2 evolution and pH levels of irradiated and non-irradiated Mg-foams were examined and correlated to the DPNS parameters. In situ X-ray photoelectron spectroscopy and focused ion-beam results have shown that energies of ~ 400–700 eV can control surface topography and composition, which, in turn, controls the foam-corrosion mechanism. Samples are immersed in Dulbecco’s modified eagle media, and a synergistic reaction is found in which the irradiated samples enhance the formation of calcium–phosphate (CaP) phases to CaP ratios close to the hydroxylapatite phase that enhances bone-tissue regeneration. These results lead to a surface modification strategy that adjusts the interaction of the material and the environment without using a coating that could affect the geometry and the bulk properties of the porous material.

Large-scale atomistic computational modeling is critical to developing a fundamental understanding of the driving mechanisms behind ion beam-induced pattern formation on III–V compound semiconductor surfaces. Existing theoretical efforts fail to account for the existence of compositional depth profiles, as observed in experiments, which evolve over time and contribute to the development of lateral compositional instabilities. Another critical knowledge gap in existing theories is the a priori selection of ion-driven compositional mechanisms, so that different models predict the same surface morphology for radically different surface compositions. Atomistic simulations can elucidate key ion-induced compositional mechanisms leading to nonequilibrium compositional depth profiles. Such simulations must be performed on large length scales to enable connection of depth compositional mechanisms to lateral instabilities which ultimately drive patterning. To address these essential knowledge gaps, a 100 × 100 nm 2 GaSb surface was constructed for molecular dynamics simulations with altered composition based on experimental data at the pattern threshold fluence. The surface was then bombarded with 500 eV Kr + ions to a differential fluence of 8.4 × 10 13 cm −2 . In Ga-enriched (Sb-enriched) regions, clusters of Ga (Sb) are observed to form. While the Ga clusters remain amorphous, Sb clusters rapidly crystallize. The crystallization is not directly ion-induced but rather an intrinsic material behavior of pure Sb in response to the ion-induced compositional instability in the surface. To elucidate the ion-driven compositional changes leading to this state, 25 × 25 nm 2 “pristine” 50–50 GaSb crystalline surfaces were irradiated with 500 eV Ne + , Ar + , and Kr + to fluences on the order of 10 16 cm −2 . The ion-induced displacement cascade tends to lead to formation of Sb nanoclusters, while Ga rarely forms clusters but readily bonds to the Sb clusters. While initially the clustering behavior is the same for all ion species, for continued Kr + irradiation the clusters become less prevalent within the material surface.

An innovative PFC diagnostic, the Materials Analysis Particle Probe (MAPP) was used to study the chemistry of Plasma Facing Components (PFCs) in the National Spherical Tokamak Experiment Upgrade (NSTX-U). NSTX-U used boronization as conditioning strategy during the 2015–2016 experimental campaign. Deposition with ∼9.1g of deuterated tri-methyl boron (d-TMB) in a helium glow discharge resulted in coatings with an equivalent thickness of 7.0nm at the lower outer divertor region. MAPP was used to capture for the first time the in-vacuo evolution of the chemical state of ATJ graphite PFCs after boronization and plasma exposure via X-ray Photoelectron Spectroscopy (XPS) on a day-to-day basis. The XPS data shows the formation of B4C on the PFCs surface during boronization. We observed the gradual increase of the B2O3 fraction in the coatings with plasma exposures. In contrast, we measured the formation of non-stoichiometric oxides when the samples were only exposed to residual gases and an argon vent. MAPP data revealed erosion and oxidation of deposited boron coatings over the course of tens of shots (a time resolution improved several orders-of-magnitude compared to post-campaign PFC characterization) that is correlated with the transitory nature of plasma performance enhancement with boron conditioning. Keywords: XPS, Boronized graphite, Conditioning, Plasma facing components, NSTX-U

Tungsten will be used as plasma-facing material in the divertor in ITER, but it undergoes detrimental surface-subsurface morphological changes under irradiation. One type of tungsten that may mitigate such morphologies is porous tungsten due to higher defect sink areal density. While surface nanostructures such as fuzz may compromise plasma performance, their intrinsic porosity offers a proxy for a porous material and strategies to prevent high-Z impurity emission. Liquid metal coatings have been proposed as plasma facing materials to counteract the erosion issues faced by tungsten. Tin-lithium eutectics are an understudied class of potential liquid metal coatings for their low melting points and reduced erosion and fuel retention compared to pure lithium coatings. A 95 at.% tin-lithium eutectic was deposited on fuzzy tungsten samples and exposed to 250 eV deuterium ions at 250 °C and varying fluences. Mitigation of fuzz erosion and deuterium retention were examined post-mortem with SEM and secondary mass ion spectroscopy (SIMS) of tungsten samples and witness samples used to collect eroded material. The SnLi film persisted after irradiation and protected underlying fuzz. SIMS results demonstrate surface mixing of the liquid metal and tungsten substrate and increased lithium erosion at high fluence and non-structured surfaces. The highest concentration and deepest penetration of retained deuterium was observed in the sample exposed to the lowest fluence. Results may indicate intercalation of liquid metal with tungsten tendrils at elevated temperatures. Keywords: Tin-lithium, Fuzzy tungsten, Liquid metal, Erosion, Deuterium retention

Boronization has been effective in reducing plasma impurities and enabling access to higher density, higher confinement plasmas in many magnetic fusion devices. The National Spherical Torus eXperiment, NSTX, has recently undergone a major upgrade to NSTX-U in order to develop the physics basis for a ST-based Fusion Nuclear Science Facility (FNSF) with capability for double the toroidal field, plasma current, and NBI heating power and increased pulse duration from 1–1.5s to 5–8s. A new deuterated tri-methyl boron conditioning system was implemented together with a novel surface analysis diagnostic. We report on the spatial distribution of the boron deposition versus discharge pressure, gas injection and electrode location. The oxygen concentration of the plasma facing surface was measured by in-vacuo XPS and increased both with plasma exposure and with exposure to trace residual gases. This increase correlated with the rise of oxygen emission from the plasma. Keywords: Boronization, Deuterated tri-methyl boron, NSTX-U, Plasma-materials interaction, Surface analysis

The application of lithium to plasma-facing components (PFCs) has long been used as a technique for wall conditioning in magnetic confinement devices to improve plasma performance. Determining the characteristics of PFCs at the time of exposure to the plasma, however, is difficult because they can only be analyzed after venting the vacuum vessel and removing them at the end of an operational period. The Materials Analysis and Particle Probe (MAPP) addresses this problem by enabling PFC samples to be exposed to plasmas, and then withdrawn into an analysis chamber without breaking vacuum. The MAPP system was used to introduce samples that matched the metallic PFCs of the Lithium Tokamak Experiment (LTX). Lithium that was subsequently evaporated onto the walls also covered the MAPP samples, which were then subject to LTX discharges. In vacuo extraction and analysis of the samples indicated that lithium oxide formed on the PFCs, but improved plasma performance persisted in LTX. The reduced recycling this suggests is consistent with separate surface science experiments that demonstrated deuterium retention in the presence of lithium oxide films. Since oxygen decreases the thermal stability of the deuterium in the film, the release of deuterium was observed below the lithium deuteride dissociation temperature. This may explain what occurred when lithium was applied to the surface of the NSTX Liquid Lithium Divertor (LLD). The LLD had segments with individual heaters, and the deuterium-alpha emission was clearly lower in the cooler regions. The plan for NSTX-U is to replace the graphite tiles with high-Z PFCs, and apply lithium to their surfaces with lithium evaporation. Experiments with lithium coatings on such PFCs suggest that deuterium could still be retained if lithium compounds form, but limiting their surface temperatures may be necessary.

Boronization has been used in the National Spherical Torus-Upgrade (NSTX-U) as first wall conditioning technique. The technique decreased the oxygen impurities in the plasma and the O% on the Plasma Facing Components (PFC) as measured with an in-vacuo probe. Samples were extracted from tiles removed from the tokamak for post-mortem and controlled studies. Ex-vessel low energy and fluence D2+ and Ar+ irradiations were characterized in-situ to elucidate surface evolution of a cored graphite sample with an intrinsic concentration of boron from a tokamak environment. In addition, quadrupole mass spectrometer measurements of emitted D-containing species during irradiation, indicate potential retention of D by the boronized graphite interface and correlated back to the surface chemistry evolution. Classical Molecular Dynamics (CMD) simulations were used to investigate the chemistry of the B-C-O-D system. The results suggest that boron coatings retain oxygen by forming oxidized boron states in the presence of deuterium plasmas and corroborate empirical findings. A four times increase in the O% of the boron coatings was observed following in-situ deuterium exposures, in contrast with a reduction of equal magnitude observed after Ar irradiations. These results illustrate the complex chemistry driven by energetic ions at the edge of tokamaks plasmas on the PFCs.

Tungsten is the material of choice for the divertor region of future nuclear fusion reactors, an environment that will expose plasma-facing components (e.g. divertor, etc...) to high temperatures and transient high heat flux events. Under these conditions, recrystallization and grain growth of tungsten can occur, leading to undesirable microstructural and mechanical property changes. Therefore, there is a need to raise the recrystallization temperature of tungsten and limit the kinetics of the recrystallization and grain growth processes. In this work, we examine the effect of different types (TiC vs. TaC vs. ZrC) and different concentrations (1.1 vs. 5 vs. 10 wt.%) of dispersed second phase particles in a tungsten matrix on the high temperature performance. The addition of second-phase particles effectively increases the temperature of and time for recrystallization and slow grain growth; however, the addition of a high weight fraction of particles alters the surface chemistry, which may impact subsequent plasma-surface interactions. These results show that the addition of small concentrations of dispersed particles can be effectively employed in tungsten to raise the upper operating temperature limit for tungsten in a fusion reactor.

Bacterial cellulose (BC) has been used as a scaffold for tissue regeneration (TR). Improving functional TR requires highly selective strategies for specific cell attraction. Embedding iron oxide nanoparticles into a BC matrix can drive magnetically labeled cells to specific tissues where they may begin to heal injured tissue. This article focuses on characterization and in vitro toxicity assessment of magnetic BC (MBC). We proposed to detect the production of radical oxygen species (ROS), esterase activity, and apoptosis to study cytotoxic interactions of MBC within its bioenvironment. Morphological characterization was performed using scanning electron microscopy where evidence shows that the diameter of MBC fibers compared to BC fibers was 33% smaller, and the pore areas were 25% bigger. Cytotoxicity assays in porcine aortic smooth muscle cells exposed for 24 hours to BC, MBC, and poly(ethylene glycol)-coated MBC (MBC-PEG) reveals 96% viability and 9% ROS production for MBC-PEG. In contrast, 25% of cells exposed to MBC were apoptotic, suggesting that even when the cells were metabolically active, MBC can induce damage. These outcomes support the need for more integral assessment in the hopes of assessing the potential biosafety and uses of nanocomposites for TR. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2801-2809, 2016.