Low Energy Hydrogen Plasma Research Articles

Precision defect integrated graphene as reliable support membrane for high-resolution cryo-transmission electron microscopy

Graphene is an excellent support film for high-resolution transmission electron microscopy (TEM) but its use with biological samples, notably in cryo-TEM, is hindered by its inherent hydrophobicity. Whereas surface treatments have been proposed to render graphene hydrophilic, they are often difficult to reproduce due to a lack of information on the structural changes that modify the wetting properties of graphene. This study aims to correlate the atomic structure of graphene with its wetting properties to allow a reproducible protocol to advance its application in cryo-TEM. We follow the change in the atomic structure of graphene as a function of low-energy hydrogen plasma treatment duration on monolayer graphene transferred onto TEM grids. With finely controlled plasma exposure, partial hydrogenation, monoatomic vacancies, and pores of a few nanometers are realized in the graphene. The introduction of defects (vacancies and pores) enables the formation of continuous layers of vitreous ice on TEM grids. Grids with defect-integrated graphene are reproduced and used in the vitrification of the mouse serotonin 5-HT3 receptor, a membrane protein. Single particle analysis of the membrane protein on graphene compared to conventional holey carbon film give insight into the strengths and discretions in using graphene membrane for protein structural studies.

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.

Growth mechanism of subsurface hydrogen cavities in tungsten exposed to low-energy high-flux hydrogen plasma

Due to a lack of direct experimental results, the detailed mechanisms that govern the blistering behavior of tungsten (W) exposed to ITER-relevant condition in nuclear fusion remain unclear. The growth mechanism of hydrogen (H) blisters is one example. In this work, recrystallized W was exposed to H plasma at 50 eV, 1.5×1026m−2, and 573 K. Transmission electron microscopy (TEM) samples were prepared using plasma-focused ion beam (FIB) followed by flash-polishing to effectively remove surface damages induced by FIB. The TEM images revealed that the general blisters observed on the exposed surface are associated with underlying cavities. A considerable amount of dislocations were found in the vicinity of the cavities. Prismatic dislocation loop arrays were observed, including small size 'coffee-bean' prismatic loops and large size prismatic loops. Near the tip of surfaces cavities, evidences for the emission of shear loops were also found. Based on the experimental findings, a multi-stage growth mechanism of H cavities was proposed. The loop-punching mechanism is operative for both very small cavities and cavities with sizes larger than several hundreds of nanometers. Whereas at intermediate sizes, cavities grow by emitting shear loops from the cavity tip.

Surface modification and sputtering of FeCrAl alloys exposed to low-energy hydrogen plasmas

In the present paper processes of sputtering and surface modification of commercial and experimental FeCrAl composites alloyed with yttrium, molybdenum and zirconium were investigated. Using a field-emission scanning electron microscope, it was shown that under the influence of low-energy (500 eV) hydrogen plasma with a flux about 3.2 ⋅ 1020 m–2 ⋅ s–1 and fluence 4 ⋅ 1024 m–2 at Troom, surface morphology develops due to the formation of grooves along grain boundaries, macro- and microcracks, as well as intragranular pits due to the sputtering of precipitates. Determination of the composition of precipitates by an energy dispersive X-ray spectrometer allowed to establish that aluminum oxide is preferentially distributed in the grains of FeCrAl-based alloys, and yttrium oxides are localized along grain boundaries. Results of erosion studies indicated that the sputtering yields for hydrogen on all alloys are 1.05– 0.38 at./ion and doesn’t exceed those for published data for pure iron and chromium. For experimental alloys doped with yttrium and molybdenum found that the obtained sputtering coefficients were in several times lower than for steel SS304 and only one and a half times higher compared to tungsten.

Modulation of the electronic states of perovskite SrCrO3 thin films through protonation via low-energy hydrogen plasma implantation approaches

Hydrogenation of transition metal oxides offers a powerful platform to tailor physical functionalities as well as for potential applications in modern electronic technologies. An ideal nondestructive and efficient hydrogen incorporation approach is important for the realistic technological applications. We demonstrate the proton injection on SrCrO3 thin films via an efficient low-energy hydrogen plasma implantation experiments, without destroying the original lattice framework. Hydrogen ions accumulate largely at the interfacial regions with amorphous character which extend about one-third of the total thickness. The HxSrCrO3 (HSCO) thin films appear like exfoliated layers which however retain the fully strained state with distorted perovskite structure. Proton doping induces the change of Cr oxidation state from Cr4+ to Cr3+ in HSCO thin films and a transition from metallic to insulating phase. Our investigations suggest an attractive platform in manipulating the electronic phases in proton-based approaches and may offer a potential peeling off strategy for nanoscale devices through low-energy hydrogen plasma implantation approaches.

Bubble growth from clustered hydrogen and helium atoms in tungsten under a fusion environment

Bubbles seriously degrade the mechanical properties of tungsten and thus threaten the safety of nuclear fusion devices, however, the underlying atomic mechanism of bubble growth from clustered hydrogen and helium atoms is still mysterious. In this work, first-principles calculations are therefore carried out to assess the stability of tungsten atoms around both hydrogen and helium clusters. We find that the closest vacancy-formation energies of interstitial hydrogen and helium clusters are substantially decreased. The first-nearest and second-nearest vacancy-formation energies close to vacancy–hydrogen clusters decrease in a step-like way to ∼0, while those close to vacancy–helium clusters are reduced almost linearly to ∼−5.46 eV when atom number reaches 10. The vacancy-formation energies closest to helium clusters are more significantly reduced than those nearest to hydrogen clusters, whatever the clusters are embedded at interstitial sites or vacancies. The reduction of vacancy-formation energies results in instability and thus emission of tungsten atoms close to interstitial helium and vacancy–helium clusters, which illustrates the experimental results, that the tungsten atoms can be emitted from the vicinity of vacancy–helium clusters. In addition, the emission of unstable tungsten atoms close to hydrogen clusters may become possible once they are disturbed by the environment. The emission of tungsten atoms facilitates the growth and evolution of hydrogen and helium clusters and ultimately the bubble formation. The results also explain the bubble formation even if no displacement damage is produced in tungsten exposed to low-energy hydrogen and helium plasma.

Combined effects of crystallography, heat treatment and surface polishing on blistering in tungsten exposed to high-flux deuterium plasma

For tungsten exposed to low-energy hydrogen-plasmas, it has been thought that grains with surface normal are most susceptible to blistering while those with surface normal are virtually impervious to it. Here, we report results showing that non-uniformity of blister distribution depends on the state of the surface due to polishing. In electrochemically polished material blisters appear on the grains with all orientations, while in mechanically polished material blister-free areas associated with particular orientations emerge. On the other hand, blistering is shown to have a strong dependence on the level of deformation within particular grains in partially recrystallized material.

Effect of low-energy hydrogen-plasma irradiation on graphite for plasma-facing components

Plasma-facing components (PFCs) in fusion devices inherently suffer from irradiation by hydrogen isotope plasmas. Graphite is used as the first wall of the Korea Superconducting Tokamak Advanced Research (KSTAR) because of its low atomic number and excellent thermal and mechanical properties. In this experiment, the effect of hydrogen-plasma irradiation on the PFCs was studied using KSTAR-like graphite tiles. The tiles were irradiated with low-energy hydrogen plasmas produced by an electron cyclotron resonance system. The changes in the surface morphology and disorders induced in the structure were investigated using field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and electron spin resonance measurements.

Erratum: Controlling protein adsorption on graphene for cryo-EM using low-energy hydrogen plasmas

Nat. Methods 11, 649–652 (2014); published online 20 April 2014; corrected after print 10 June 2014 In the version of this article initially published, the arrow in Figure 1b pointing to the 0–110 reflection was in the incorrect location. The error has been corrected in the HTML and PDF versions of the article.

Controlling protein adsorption on graphene for cryo-EM using low-energy hydrogen plasmas.

Despite its many favorable properties as a sample support for biological electron microscopy, graphene is not widely used because its hydrophobicity precludes reliable protein deposition. We describe a method to modify graphene using a low-energy hydrogen plasma, which reduces hydrophobicity without degrading the graphene lattice. We show that the use of plasma-treated graphene enables better control of protein distribution in ice for electron cryo-microscopy and improved image quality by reducing radiation-induced sample motion.

The improvement of Si0.5Ge0.5/Si interface quality by using low energy hydrogen plasma cleaning process and positron annihilation spectroscopy

Positron Annihilation Spectra (PAS), Raman, and photoluminescence spectroscopy reveal that Si 0.5 Ge 0.5 /Si interface quality can be dramatically improved through a low energy plasma cleaning process using hydrogen. In the PAS, the particularly small values of lifetime and intensity near the Si 0.5 Ge 0.5 /Si interface in the treated sample indicate a 2.25 times reduction in defect concentration. Fewer defects were found in the interface, resulting in a high compressive strain of about 0.36 % in the top layer, which can be observed in Raman spectra, and a 1.39 times increase to the radiative recombination rate for the infrared emission, which can be observed in the photoluminescence spectra. Improved Si 0.5 Ge 0.5 /Si interface quality leads to improved optical and electrical characteristics in SiGe-based devices in a broader range of photovoltaic applications. The PAS is also shown to be a useful metrology tool for quantifying defects in SiGe-based devices.

Optimized Si0.5Ge0.5/Si Interface Quality by the Process of Low Energy Hydrogen Plasma Cleaning and Investigation by Positron Annihilation Spectroscopy

Positron Annihilation Spectra (PAS), Raman, and Photoluminescence spectroscopy reveal that Si0.5Ge0.5/Si interface quality can be significantly improved by the process of low energy plasma cleaning with hydrogen. In the PAS detection, the particularly small value of lifetime and intensity near the Si0.5Ge0.5/Si interface in the sample with the treatment indicate that the defect concentration is successfully reduced 2.25 times. Fewer defects existed in the interface result in the high compressive strain about 0.36% in the top epi-Si0.5Ge0.5 layer, which can be observed in the Raman spectra detection, and stronger radiative recombination rate about 1.39 times for the infrared emission, which can be observed in the photoluminescence spectra. With better interface quality, the SiGe-based devices can have better optical and electrical characteristics for more applications such as solar cells industry. The PAS is also demonstrated that it is the useful methodology tool to quantify the defect information in the SiGe-based devices.

Surface modification and oxidation of Si wafers after low energy plasma treatment in hydrogen, helium and argon

Surface layers of the single crystalline silicon wafers subjected to low-energy hydrogen, helium and argon plasma treatments were investigated using X-ray absorption near edge structure spectroscopy (XANES) with the use of synchrotron radiation. It was shown that a surface silicon oxide layer with a thickness greater than native silicon oxide is formed as a result of such treatment. At the same time, in the investigated wafers the surface layers of a few nanometers appear to contain elemental silicon in a disordered (amorphous) state. Possible clusterization of Si in the surface layers was considered to result from the plasma treatment.

Improved Si0.5Ge0.5/Si interface quality achieved by the process of low energy hydrogen plasma cleaning and investigation of interface quality with positron annihilation spectroscopy

The Positron Annihilation Spectra(PAS), Raman, and Photoluminescencespectroscopy reveal that Si0.5Ge0.5/Si interface quality can be significantly improved by the low energy plasma cleaning process using hydrogen. In the PAS, the particularly small value of lifetime and intensity near the Si0.5Ge0.5/Si interface in the sample with the treatment indicate that the defect concentration is successfully reduced 2.25 times, respectively. Fewer defects existed in the Si0.5Ge0.5/Si interface result in the high compressive strain about 0.36% in the top epi-Si0.5Ge0.5 layer, which can be observed in Raman spectra and stronger radiative recombination rate about 1.39 times for the infrared emission, which can be observed in the photoluminescencespectra. With better Si0.5Ge0.5/Si interface quality, the SiGe-based devices can have better optical and electrical characteristics for more applications in the industry. The PAS is also demonstrated that it is the useful methodology tool to quantify the defect information in the SiGe-based material.

Influence of hydrogen on the thermionic electron emission from nitrogen-incorporated polycrystalline diamond films

Although hydrogen has been shown to enhance the thermionic emission properties of nitrogen-incorporated diamond cathodes, the effect diminishes when these cathodes are heated to temperatures in excess of 700 °C, possibly due to the hydrogen desorbing from the diamond. In order to further examine this behavior, this work examines the thermionic emission properties of a nitrogen-incorporated diamond film grown by chemical vapor deposition in a hydrogen-methane-nitrogen plasma. The film was tested for thermally stimulated electron emission at temperatures ranging from 500 to 900 °C in an as-grown state and after exposure to a hydrogen plasma treatment. Emission current increased, as described by the Richardson equation for thermal emission up to ∼ 700 °C. Above ∼ 800 °C the thermionic emission current was observed to diminish, an effect attributed to the loss of hydrogen from the diamond. Recovery of the hydrogen effect was explored by exposing the diamond film to a low-energy hydrogen plasma. The thermionic emission current at temperatures below ∼700 °C after this hydrogen plasma exposure was observed to increase by four orders of magnitude over the thermionic emission current observed in the initial (as-grown) test. Possible explanations for this emission current increase are discussed.

Hydrogen Blister Formation on Cold-Worked Tungsten with Layered Structure

Low-energy (<100 eV) and high-flux (>1021 m-2s-1) hydrogen plasma exposures were performed on cold-worked powder metallurgy tungsten (PM-W), recrystallized cold-worked PM-W and hot-worked PM-W. Large blisters with a diameter of approximately 100–200 µm were observed only on the surface of cold-worked PM-W. The blister formation mechanism has not been clarified thus far. PM-W has a consisting of 1-µm-thick layers, which is formed by press-roll processing. A detailed observation of the cross section of those blisters shows for the first time that the blisters are formed by cleaving the upper layer along the stratified layer. These experimental results indicate that the manufacturing process of tungsten material is one of the key factors for blister formation on the tungsten surface.

Microscopic and macroscopic damage in metals exposed to LHD divertor plasmas

In order to study erosion/damage processes of the tungsten divertor target, material probe experiments were carried out by exposing tungsten specimens to short pulse helium or hydrogen divertor plasma in LHD (10–20eV, about 1×1022ions/m2s). A narrow ‘footprint’, a trace of local-melting, of divertor plasma was formed on the material probe head along the divertor-leg for both hydrogen and helium discharges. In the specimens located rather far from the footprint, where less loading of particles is expected, remarkable blistering was confirmed for both helium and hydrogen irradiation cases. The erosion of the surface was estimated to be 6.3nm/1s (one discharge), and 4.1nm/24s (19 discharges) for helium and hydrogen, respectively. One should note that erosion due to blistering occurs even for the very low energy hydrogen plasma exposure. It is considered that the abrupt change of specimen temperature due to very high flux particle load may enhance the blistering.

Blister formation on tungsten surface under low energy and high flux hydrogen plasma irradiation in NAGDIS-I

This study presents experimental results on hydrogen blister formation on powder metallurgy tungsten (PM-W) surface under low energy (<100 eV) and high ion flux (>10 21 m −2 s −1) hydrogen plasma irradiation in a divertor plasma simulator-NAGDIS-I. The tungsten samples were exposed to steady-state hydrogen plasma at various sample temperatures and fluences. Hydrogen blister formations are clearly observed on tungsten surface at the surface temperature below 950 K. The blister size is from a few 10 μm to a few 100 μm. It was found that the blister formations obviously depend on the surface temperature and the incident hydrogen ion fluence. No blisters are observed on tungsten surface at the surface temperature above 950 K even if the fluence is high enough.

Electrical activity of grain boundaries in silicon bicrystals and its modification by hydrogen plasma treatment

Electrical activity of grain boundaries (GBs) and its transformation under the influence of low-energy hydrogen plasma treatment in p-type silicon bicrystalline samples cut from EFG silicon polycrystals were investigated. Comprehensive studies have enabled one to investigate the electrical activity of GBs relative to the minority (MIC) and majority (MAC) carriers and to demonstrate the possibility of controlling this activity by different processing methods. These studies allowed for establishing the correlation between the type, structure and individual electrical activity of GBs and also thermal pre-history of samples. Among the tested modes, hydrogenation was found to be the most radical method of electrical activity modification for all types of GBs. In the process, results on hydrogenation of GBs in EFG silicon crystals depend essentially on three factors: type of GBs, state of ribbons (as-grown or annealed) and concurrence of grain boundary dangling bonds and boron passivation effects.

Thin SiGe buffer layer growth by in situ low energy hydrogen plasma preparation

A new method to relax thin constant composition molecular beam epitaxy (MBE) grown SiGe buffer layers on silicon (100) substrates has been studied. A low energy plasma cleaning process (LEPC) using hydrogen prior to deposition can reduce the Si 1− x Ge x layer thickness to approximately 10% of a standard graded buffer. The layers were characterised by secondary ion mass spectroscopy (SIMS), high resolution X-ray diffraction (HRXRD), transmission electron microscopy (TEM), Rutherford backscattering (RBS) and atomic force microscopy (AFM). The threading dislocation density is 10 5 cm –2 (TEM measurement) and is comparable to or even lower than in standard buffers. Ge concentration and Si 1− x Ge x layer thickness are limited by spontaneous relaxation during growth. The critical thickness on hydrogen prepared wafers is reduced to nearly 50% of that prepared in the standard manner. A complete post-epitaxial relaxation has been obtained for a 160-nm-thick Si 0.83Ge 0.17 layer at temperatures as low as 600°C. AFM investigations of such samples show significantly reduced area-RMS values of 0.3–0.9 nm. By means of multistep growth the Ge content can be increased. In a two-step mode thin buffers up to 34% Ge were grown with a high crystal quality.