Plasma Bombardment Research Articles

Quasi‐Ordered Nanoforests with Hybrid Plasmon Resonances for Broadband Absorption and Photodetection

AbstractWith the continuing development of green energy technology, solar energy is the most widely distributed and easily utilized form of energy in nature. High‐absorption absorbers over a wide spectrum range are beneficial for solar energy harvest. Herein, a fast and efficient method is developed to fabricate a broadband absorber consisting of quasi‐ordered nanoforests and metal nanoparticles using a simple plasma bombardment process on a 4‐inch silicon wafer, offering high throughputs that can meet practical application demands. The absorber exhibits high absorption exceeding 90% from 300 to 2500 nm, good absorption stability with negligible disturbance from the polarization and the incident angle of light. This effective absorption behavior can be ascribed to multilevel hybridization of the plasmon resonances in the hybrid structures and cavity mode resonances inside the nanoforests. Furthermore, the absorber is integrated onto a thermopile for photodetection with largely enhanced photoresponse from 532 to 2200 nm. The photoinduced voltage of the devices shows a large increment of 433% at 100 mW cm−2 light power density, in comparison with a contrast pristine thermopile. It is expected that such a broadband absorber holds great potential for multiple applications, including solar steam generation, photodetection, and solar cells.

Plasma Oxygen Interaction with Organic Polymer Films: A Mechanistic Study

In this presentation, first principles calculations combined with advanced surface diagnostics are used to unravel the mechanisms of plasma oxygen interaction with organic films, of interest for advanced patterning in semiconductor device manufacturing. Results from a combination of X-ray photoelectron spectroscopy (XPS) diagnosed oxygen plasma-exposed polystyrene films and first principles modeling of organic films (polystyrene, polyethylene and derivatives) provide insights into how organic films are oxidized by oxygen atoms. XPS measurements show the rapid formation of C-O structures and their saturation after oxygen exposure on both pristine and argon bombarded polystyrene samples. Quantum mechanics calculations confirm that C-OH formation can be immediate without recourse to previously formed dangling bonds. Multiple oxygen impacts are required for scission of pristine ethylene carbon strands. Therefore, ethylene films can be converted to polyols that are stable, whereas more likely strands are broken before polyol formation through the formation of water and C=O. On the contrary, intermediate compounds with adjacent C=O bonds are not likely to form stable structures. The combination of XPS measurements and modeling imply that the oxidation of polystyrene and polyethylene is self-limiting on both hydrogen saturated and de-hydrogenated (after argon ion plasma bombardment) surfaces.

Effect of electrolytic plasma polishing on microstructural evolution and tensile properties of 316L stainless steel

Electrolytic plasma polishing (EPP) is an advanced technique for high-quality surface finishing of metal and alloy materials. Austenitic 316L stainless steel (SS) is extensively used in various industrial applications due to its excellent comprehensive performance. Therefore, it is widely studied to improve its properties by specific means and methods and expand its scope of application. In this paper, the influence of EPP generated dynamic composite energy on the microstructural evolution and tensile properties of machined 316L SS is investigated. A decrease in the surface roughness (from 0.103 μm to 0.046 μm), average grain size (from 5.65 μm to 5.21 μm), and low angle grain boundaries (LAGBs) are observed, along with an increase in geometrically necessary dislocation density in post EPP samples. Post EPP, grains are found to be predominantly oriented in 〈101〉. Schmid factor variation (from 0.475 to 0.45) shows a reduction in plastic deformability of the material. The yield strength and tensile strength of the material is increased by 8.98% and 4.32%, approximately, after EPP treatment. The dynamic composite energy produced during the EPP process may induce a cavitational effect, causing (i) rupture of the vapor-gaseous envelope, (ii) high-energy plasma bombardment, and (iii) development of annealing stress inside the material, resulting in microstructural evolution of 316L SS.

Structural integrity of DEMO divertor target assessed by neutron tomography

The divertor target plates are the most exposed in-vessel components to high heat flux loads in a fusion reactor due to a combination of plasma bombardment, radiation and nuclear heating. Reliable exhaust systems of such a huge thermal power required a robust and durable divertor target with a sufficiently large heat removal capability and lifetime. In this context, it is pivotal to develop non-destructive evaluation methods to assess the structural integrity of this component that, if compromised could reduced its lifetime. In this work we have demonstrated for the first time the feasibility of using neutron tomography to detect volumetric defects within DEMO divertor mock-ups with a spatial resolution of the order of hundreds of micrometers. Neutron tomography is applicable for studying complex structures, often manufactured from exotic materials which are not favourable for conventional non-destructive evaluation methods. This technique could be effectively used during research and development cycles of fusion component design or for quality assurance during manufacturing.

Activating Titanium Metal with H2 Plasma for the Hydrogen Evolution Reaction.

Developing a high-performance nonprecious metal electrocatalyst for water splitting is a strong demand for the large-scale application of electrochemical H2 production. In this work, we design a facile and scalable strategy to activate titanium metal for the hydrogen evolution reaction (HER) in alkaline media through incorporating hydrogen into the α-Ti crystal lattice by H2 plasma bombardment. Benefiting from the accelerated charge transfer and enlarged electrochemical surface area after H2 plasma treatment, the H-incorporated Ti shows remarkably enhanced HER activity with a much lower overpotential at -10 mA cm-2 by 276 mV when compared to the pristine Ti. It is revealed that the retention of the incorporated H(D) atoms in the Ti crystal lattice during HER accounts for the durable feature of the catalyst. Density functional theory calculations demonstrate the effectiveness of hydrogen incorporation in tuning the adsorption energy of reaction species via charge redistribution. Our work offers a novel route to activate titanium or other metals by H incorporation through a controllable H2 plasma treatment to tune the electronic structure for water splitting reactions.

Charge-Transfer Induced by the Oxygen Vacancy Defects in the Ag/MoO3 Composite System.

In this paper, an Ag/MoO3 composite system was cosputtered by Ar plasma bombardment on a polystyrene (PS) colloidal microsphere array. The MoO3 formed by this method contained abundant oxygen vacancy defects, which provided a channel for charge transfer in the system and compensated for the wide band gap of MoO3. Various characterization methods strongly demonstrated the existence of oxygen vacancy defects and detected the properties of oxygen vacancies. 4-Aminothiophenol (p-aminothiophenol, PATP) was used as a candidate surface-enhanced Raman scattering (SERS) probe molecule to evaluate the contribution of the oxygen vacancy defects in the Ag/MoO3 composite system. Interestingly, oxygen vacancy defects are a kind of charge channel, and their powerful effect is fully reflected in their SERS spectra. Increasing the number of charge channels and increasing the utilization rate of the channels caused the frequency of SERS characteristic peaks to shift. This interesting phenomenon opens up a new horizon for the study of SERS in oxygen-containing semiconductors and provides a powerful reference for the study of PATP.

Evaluation of silicon carbide as a divertor armor material in DIII-D H-mode discharges

Silicon carbide (SiC) represents a promising but largely untested plasma-facing material (PFM) for next-step fusion devices. In this work, an analytic mixed-material erosion model is developed by calculating the physical (via SDTrimSP) and chemical (via empirical scalings) sputtering yield from SiC, Si, and C. The Si content in the near-surface SiC layer is predicted to increase during D plasma bombardment due to more efficient physical and chemical sputtering of C relative to Si. Silicon erosion from SiC thereby occurs primarily from sputtering of the enriched Si layer, rather than directly from the SiC itself. SiC coatings on ATJ graphite, manufactured via chemical vapor deposition, were exposed to repeated H-mode plasma discharges in the DIII-D tokamak to test this model. The qualitative trends from analytic modeling are reproduced by the experimental measurements, obtained via spectroscopic inference using the S/XB method. Quantitatively the model slightly under-predicts measured erosion rates, which is attributed to uncertainties in the ion impact angle distribution, as well as the effect of edge-localized modes. After exposure, minimal changes to the macroscopic or microscopic surface morphology of the SiC coatings were observed. Compositional analysis reveals Si enrichment of about 10%, in line with expectations from the erosion model. Extrapolating to a DEMO-type device, an order-of-magnitude decrease in impurity sourcing, and up to a factor of 2 decrease in impurity radiation, is expected with SiC walls, relative to graphite, if low C plasma impurity content can be achieved. These favorable erosion properties motivate further investigations of SiC as a low-Z, non-metallic PFM.

The Efficiency of DBD Cold Plasma Pen Treatment on the Oyster Mushroom Bacterial Decontamination

Cold plasma provided bacterial inactivation role in food industry. In this study, the cold plasma play a crucial inactivation role when effectively reduces the bacteria colonies on oyster mushroom surface. By development of the dielectric barrier discharge-cold plasma pen (DBD-CPP) system, the mushroom surface was exposed to the cold plasma discharge with variable of exposure treatment time (0 min, 0.5 min, 1 min, 3 min and 5 min) with ~6 kV of power voltage and 5 SLM of atmospheric gas pressure flow rate. In order to identify the reduction of the microbial growth, isolation technique will be carry out by excising the mushroom sample into a suspension and serial dilution follows by identification of its colony morphologies and characteristics. Results screening shows increments of exposure treatment times up to 3 min shows none growth of bacteria colonies. This because the bacteria cell wall was disrupt and destruction by the plasma bombardment. Thus, this study able to extend the lifetime of the mushroom and produce a free microbial fresh mushroom by decontaminate the bacteria on the mushroom surface

Remarkable enhancement of tracking resistance of addition-cure liquid silicone rubber by alkyl-disubstituted ureido siloxane immobilized on the silica filler surface

It is urgent and significant to prepare silicone rubber with excellent tracking resistance in a harsh environment. In this work, alkyl-disubstituted ureido siloxane immobilized on silica (U-SiO2) was prepared by the dehydration condensation of hydrolysates of alkoxy groups in alkyl-disubstituted ureido siloxanes (US) and hydroxyl groups on the silica surface. The effect of U-SiO2 on the tracking resistance of addition-cure liquid silicone rubber (ALSR) was investigated by inclined-plane test (IP test). It was found that U-SiO2 could effectively enhance the tracking resistance of ALSR. Especially, diisopropylureidopropyltriethoxysilane and diisobutylureidopropyltriethoxysilane with isomeric substitution immobilized on silica (DIPUPES-SiO2 and DIBUPES-SiO2) performed the best. With less than 1.00 phr content, ALSR samples could reach 1A4.5 level. The erosion mass was only 0.40 % and 0.62%, respectively. Moreover, ALSR / DIPUPES-SiO2 had excellent water resistance. It could still reach 1A4.5 level and the erosion mass was almost unchanged after ALSR / DIPUPES-SiO2 was immersed in the water for five days. The results of plasma irradiation and thermal treatment showed that U-SiO2 could effectively inhibit the aggregation of platinum in Karstedt's catalyst, which could promote the crosslinking of ALSR chains under the elevated temperature to form a compact ceramic protected layer. It could not only isolate the oxygen and heat and suppress the thermal degradation of ALSR, but also resist the plasma bombardment. Therefore, the tracking resistance of ALSR was remarkably enhanced.

A novel liquid lithium jet-cooled finger-type divertor target concept for fusion power plant application

The divertor target is the most thermally loaded plasma-facing component in a foreseen DEMO reactor and beyond, which has to tolerate the peak high heat fluxes of up to ∼20 MW m−2 produced by intense plasma bombardment, radiation and nuclear heating. However, none of current designs including water-cooled and helium-cooled concepts can satisfy this requirement. Motivated by the excellent power removal capacity of liquid metal coolant and combined with the structure characteristics of the finger-type helium-cooled target, a novel concept of liquid Li jet-cooled finger-type divertor target for DEMO reactors was proposed in this paper. The performance analysis, including thermal-hydraulics analysis, mechanical analysis and MHD effects analysis, have shown that the proposed design can withstand 20 MW m−2 heat load because the temperatures of the structural materials remain within the thermal rules and the maximum thermo-mechanical stress in the VM-W thimble is approximately 484 MPa appearing in the round corner, which is below the 3S m limit at the corresponding temperature. Moreover, a theoretical and empirical analysis has confirmed that MHD effects on pressure drop and heat transfer is rather limited in the design. The comparison of this new design with other representative designs including water-cooled ITER-like target design and helium-cooled modular jet target design has been made, and the results shows that the proposed liquid Li cooled target design has better performance under 20 MW m−2 high heat flux and ∼10 dpa neutron irradiation. Therefore, this design is promising to provide a new option for solving the DEMO reactor divertor heat removal issues. Certainly, a large number of R&D efforts are still needed to ensure the success of this concept, particularly in the areas of materials, fabrication and irradiation.

Modeling and analyzing temperature-dependent parameters of Ni/β-Ga2O3 Schottky barrier diode deposited by confined magnetic field-based sputtering

In this work, the temperature-dependent parameters of Ni/β-Ga2O3 Schottky barrier diode (SBD) were analyzed and modeled. The simulation is to elucidate the physical phenomenon behind this temperature dependence. At room temperature, the deviation of SBD parameters from the ideal case is due to the Schottky barrier height ( inhomogeneity. A model is developed for this inhomogeneity in which an interfacial defected layer (IDL) is formed. Defects (extrinsic states) are related to plasma and Ar atom bombardment used in the confined magnetic field-based sputtering to realize the Ni Schottky contact diffusion in β-Ga2O3. Ni diffuses, upon annealing, to compensate defects in this IDL. It was found that the Schottky barrier height () and threshold voltage decrease with increasing temperature. This decrease is related to intrinsic and extrinsic states (plasma and Ar bombardment). However, the ideality factor (η) increases which is related to the series resistance (R S) increase. The increase is related to the interfacial layer and nickel resistance increase with increasing temperature.

Synthesis of single-walled, bamboo-shaped and Y-junction carbon nanotubes using microwave plasma CVD on low-temperature and chemically processed catalysts

The low temperature nucleation and high yield growth of CNTs with their diverse range of layered structures and shapes is of significant interest to the research community in view of obtaining distinctive properties necessary for specific applications. In this regard, several strategies have been employed to control the growth characteristics of CNTs. In the present investigation, the low temperature growth of CNTs has been enabled using CO2 as a suitable oxidizing gas. CNTs have been grown via an optimum etching process conducted under diffuse plasma generated using a specially designed shadow mask assembly that shields the growth surface from direct plasma bombardment, and subsequent abrasive etching by the reactive plasma species. Furthermore, CO2 as a component in the plasma facilitates the elimination of amorphous carbonaceous components from the surface of the CNTs. The growth of narrow CNTs has been achieved via the formation of a low diameter (~20 nm) catalyst comprised of Fe nano-particles grown in a low temperature (10 °C) chemical process under an inert atmosphere via simultaneous aerial oxidation and neutralization in a single step. Further plasma optimization by controlling the MW power has facilitated the growth of CNTs with controlled diameters, wall numbers and different morphologies (e.g., Y-junction and bamboo-shaped MWCNTs, and very low diameter (~1.5 nm) SWCNTs). The tip growth mechanism for CNT nucleation has been established using HR-TEM, in which the Fe catalyst nanoparticles are detected within the top shell of the growing CNTs.

Persistent Sputtering Yield Reduction in Plasma-Infused Foams.

Aluminum microfoams are found to exhibit persistent sputtering yield reductions of 40%-80% compared to a flat aluminum surface under 100 to 300eV argon plasma bombardment. An analytical model reveals a strong dependency of the yield on the foam geometry and plasma sheath. For foam pore sizes near or larger than the sheath thickness, the plasma infuses the foam and transitions the plasma-surface interactions from superficial to volumetric phenomena. By defining a plasma infusion parameter, the sputtering behavior of foams is shown to be separated into the plasma-facing and plasma-infused regimes. While plasma infusion leads to a larger effective sputtering area, geometric recapture of ejected particles facilitates an overall reduction in yield. For a given level of plasma infusion, the reductions in normalized yield are more pronounced at lower ion energies since angular sputtering effects enable more effective geometric recapture of sputterants.

Modelling of hydrogen atoms reflection from an annealed tungsten fuzzy surfaces

Abstract Modelling of the hydrogen reflection on tungsten smooth and fuzz surfaces under the low-energy hydrogen plasma bombardment has been performed with the three-dimensional kinetic Monte Carlo code SURO-FUZZ. The relative reflection coefficient of hydrogen atoms, i.e. the ratio of reflected hydrogen atoms on the tungsten fuzz surface to that on the tungsten smooth one, is employed to illustrate the change in the hydrogen reflection on the tungsten fuzz and smooth surfaces. The simulated relative reflection coefficient of hydrogen atoms shows a large discrepancy with the measured values obtained in the hydrogen plasma bombardment experiment. The impinging hydrogen particles with a low incident energy result in a small sputtering and large residual nanostructure existing on the tungsten fuzz surface, which lead to a small change in the relative reflection coefficient of hydrogen atoms. The discrepancy between simulations and experiments motivates us to take the impacts of the annealing effect into account in SURO-FUZZ code. Implementation of annealing effect into SURO-FUZZ has been benchmarked against the experimental data. The simulated temporal evolution of the hydrogen reflection coefficient is in reasonable agreement with the experimental data.

Modeling a Ni/β-Ga2O3 Schottky barrier diode deposited by confined magnetic-field-based sputtering

In this work, a detailed numerical simulation is carried out to model the current–voltage characteristics of a nickel/β-Ga2O3 Schottky barrier diode at different temperatures. These SBDs are produced using confined magnetic-field-based sputtering to deposit the nickel (Ni) Schottky contact of the diode. This method reduces the thickness of the defect area created by plasma and argon bombardment, and consequently, the electrical characteristics are less affected by temperature changes or annealing (i.e. the device is more stable). During annealing, Ni diffuses into β-Ga2O3. A model for this diffusion is proposed in this work, in which Ni diffusion reduces the defects produced by plasma and argon bombardment by filling the Ga vacancy. Furthermore, Ni diffusion produces a new interfacial compound, namely at the interface between the Ni and the β-Ga2O3. This new compound layer has different properties than those of β-Ga2O3, in particular, those of the bandgap and the affinity. Finally, the temperature-dependent current-density–voltage (J–V) characteristics are simulated, taking the proposed model into account. A good agreement with measured values is achieved, especially at low forward voltages, which demonstrates the soundness of the proposed model.

Ar plasma-assisted P-doped Ni3S2 with S vacancies for efficient electrocatalytic water splitting.

Doping engineering is considered an effective way to improve the electrocatalytic water splitting performance of catalysts. In this paper, P-doped Ni3S2/NF was prepared by Ar plasma-assisted chemical vapor deposition, where the P dopant was efficiently introduced into Ni3S2/NF under the assistance of Ar plasma. Meanwhile, numerous vacancies were generated due to plasma bombardment. In the doping process, the P dopants replace the S vacancies, which contributes to the strong bonding between the P dopants and Ni3S2. Due to the synergistic effect of the P dopants and S vacancies, the Sv-Ni3S2-xPx-4 catalyst has low HER and OER overpotentials of 89 mV and 216 mV at 10 mA cm-2, with a lower impedance value and good stability. The present work shows a facile route to introduce dopants and vacancies into catalyst materials for adding active sites, eventually improving their electrocatalytic performance.

Plasma-surface interaction experimental device: PSIEC and its first plasma exposure experiments on bulk tungsten and coatings

Abstract A new laboratory-scale linear plasma device, PSIEC (Plasma-Surface Interaction system under Extreme Conditions), has been designed and constructed at Hefei University of Technology, China, to study plasma-material interactions for fusion reactor application. The PSIEC facility can generate continuous plasmas of hydrogen, deuterium, helium, argon and nitrogen. The electron density of these plasmas ranges from the order of magnitude of 1017 to 1018 /m3 and the electron temperature ranges from 1 to 40 eV. The incident ion energy is adjusted by applying a negative bias up to 110 V to the target. The plasma bombarding flux is varied from the order of magnitude of 1021 to 1022 ions/m2/s. Using the PSIEC facility, first plasma exposure experiments have been conducted on bulk tungsten and coatings. The different microstructure of tungsten have been found to lead to different damage effects under helium plasma exposure. Preliminary results allow us to expect nanocrystalline tungsten to be a promising candidate for plasma-facing material, of which the high concentration of intrinsic defects such as grain boundaries and interfaces offers the possibility of improving their irradiation resistance.

Selective etching of hexagonal boron nitride by high-pressure CF4 plasma for individual one-dimensional ohmic contacts to graphene layers

We describe a technique for fabricating one-dimensional Ohmic contacts to individual graphene layers encapsulated in hexagonal boron nitride (h-BN) using CF4 and O2 plasmas. The high etch selectivity of h-BN against graphene (>1000) is achieved by increasing the plasma pressure, which enables etching of h-BN, while graphene acts as an etch stop to protect underlying h-BN. A low-pressure O2 plasma anisotropically etches graphene in the vertical direction, which exposes graphene edges at h-BN sidewalls. Despite the O2 plasma bombardment, the lower h-BN layer functions as an insulating layer. Thus, this method allows us to pattern metal electrodes on h-BN over a second graphene layer. Subsequent electron-beam lithography and evaporation fabricate metal contacts at the graphene edges that are active down to cryogenic temperatures. This fabrication method is demonstrated by the preparation of a graphene Hall bar with a graphite backgate and double bilayer-graphene Hall bar devices. The high flexibility of the device geometries enabled by this method creates access to a variety of experiments on electrostatically coupled graphene layers.

The metal–organic framework UiO-66 with missing-linker defects: A highly active catalyst for carbon dioxide cycloaddition

Metal-organic frameworks (MOFs) have been confirmed to be a promising material for carbon dioxide capture, while the simultaneous capture and conversion of carbon dioxide over the MOF-based catalysts is furthermore being a hot topic. In this work, we demonstrate that the zirconium-based MOF UiO-66 (UiO for University of Oslo) with missing-linker defects is a highly active catalyst for carbon dioxide cycloaddition with an epoxide, which is a reaction with 100% atom economy and broad industrial uses. A facile, rapid, energy-saving and environmentally friendly argon plasma treatment was employed to create the missing-linker defects in UiO-66 without using hazardous chemicals at atmospheric pressure and temperature below 398 K, whereas the bulk structure of UiO-66 remained stable. The energetic argon plasma species decomposed part of the linkers within UiO-66 structure, leaving unsaturated metal sites. The defect concentration in UiO-66 was tuned by changing the plasma bombardment time. After an argon plasma treatment for 30 min, the number of linker deficiencies per Zr6 cluster can reach up to 2.3. The product yield of the UiO-66 with abundant missing-linker defects increased of ca. 43% over the defect-free UiO-66. The crucial role of the missing-linker defects of UiO-66 in the enhancement of the catalytic activity was confirmed. The present study will be helpful for the future preparation of defective MOFs with potential applications not only for carbon dioxide conversion but also for energy storage and conversion.

Synthesis of organic functional thin films and their application tests of graphene based FET

This study investigated on the effects of gate dielectrics for field effect transistors (FETs). The gate dielectrics with organic and inorganic layers were deposited on Si (100) substrates using cyclohexane and tetraethyl orthosilicate (TEOS) by plasma enhanced chemical vapor deposition (PECVD) method. After the Si (100) substrates were dry-cleaned by in situ Ar plasma bombardment with 60 W for 15 min., the gate dielectric plasma polymer thin films deposited under plasma power between 20 W and 60 W with different precursor flow ratio. Also, the active graphene layer was grown on a Ni substrate using CH4 by low-pressure thermal chemical vapor deposition (CVD) method, and the Ni substrate was then etched away. In order to fabricate a back-gate graphene-based FET, the graphene layer was adsorbed onto the plasma-polymer gate dielectric film, then 80 nm thick Au electrodes were finally evaporated onto the graphene using a mask with a gap of 370 nm, and a probe-station system was utilized to characterize the devices. As the plasma power and flow rate of TEOS increases, the gate voltage moves at a positive voltage, indicting p-doping by high fragmented Si and O elements under high plasma power and TEOS flow rate.