Hydrogen Plasma Research Articles

Modelling and theoretical understanding of the isotope effect from JET experiments in view of reliable predictions for deuterium-tritium plasmas

This is an overview of the theoretical understanding of the so-called isotope effect in JET hydrogen versus deuterium plasmas. Experimentally, weak to moderate deviations from naive GyroBohm scaling expectations are found for the core heat transport in L and H-modes. The physical mechanisms behind such deviations are analysed in the framework of the gyrokinetic theory. In the case of particle transport, isotope effects are mostly found in the plasma edge where the density is higher in deuterium than in hydrogen plasmas. In general, both the thermal energy and particle confinement increase with increasing main ion mass. A comparison of such results to expectations for deuterium-tritium plasmas in ITER is discussed.

Free-Standing ZnO:Mo Nanorods Exposed to Hydrogen or Oxygen Plasma: Influence on the Intrinsic and Extrinsic Defect States.

Cationic doping of ZnO nanorods has gained increased interest as it can lead to the production of materials with improved luminescent properties, electrical conductivity and stability. We report on various Mo-doped ZnO powders of nanorods synthesized by the hydrothermal growth method. Further annealing or/and cold hydrogen or oxygen plasma modification was applied. The atomic structure of the as-grown and plasma-modified rods was characterized by X-ray diffraction. To identify any possible changes in morphology, scanning electron microscopy was used. Paramagnetic point defects were investigated by electron paramagnetic resonance. In particular, two new types of defects were initiated by the plasma treatment. Their appearance was explained, and corresponding mechanisms were proposed. The changes in the luminescence and scintillation properties were characterized by photo- and radioluminescence, respectively. Charge trapping phenomena were studied by thermally stimulated luminescence. Cold plasma treatment influenced the luminescence properties of ZnO:Mo structures. The contact with hydrogen lead to an approximately threefold increase in intensity of the ultraviolet exciton-related band peaking at ~3.24 eV, whereas the red band attributed to zinc vacancies (~1.97 eV) was suppressed compared to the as-grown samples. The exciton- and defect-related emission subsided after the treatment in oxygen plasma.

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

An overview of recent results obtained at the tokamak ASDEX Upgrade (AUG) is given. A work flow for predictive profile modelling of AUG discharges was established which is able to reproduce experimental H-mode plasma profiles based on engineering parameters only. In the plasma center, theoretical predictions on plasma current redistribution by a dynamo effect were confirmed experimentally. For core transport, the stabilizing effect of fast ion distributions on turbulent transport is shown to be important to explain the core isotope effect and improves the description of hollow low-Z impurity profiles. The L–H power threshold of hydrogen plasmas is not affected by small helium admixtures and it increases continuously from the deuterium to the hydrogen level when the hydrogen concentration is raised from 0 to 100%. One focus of recent campaigns was the search for a fusion relevant integrated plasma scenario without large edge localised modes (ELMs). Results from six different ELM-free confinement regimes are compared with respect to reactor relevance: ELM suppression by magnetic perturbation coils could be attributed to toroidally asymmetric turbulent fluctuations in the vicinity of the separatrix. Stable improved confinement mode plasma phases with a detached inner divertor were obtained using a feedback control of the plasma β. The enhanced D α H-mode regime was extended to higher heating power by feedback controlled radiative cooling with argon. The quasi-coherent exhaust regime was developed into an integrated scenario at high heating power and energy confinement, with a detached divertor and without large ELMs. Small ELMs close to the separatrix lead to peeling-ballooning stability and quasi continuous power exhaust. Helium beam density fluctuation measurements confirm that transport close to the separatrix is important to achieve the different ELM-free regimes. Based on separatrix plasma parameters and interchange-drift-Alfvén turbulence, an analytic model was derived that reproduces the experimentally found important operational boundaries of the density limit and between L- and H-mode confinement. Feedback control for the X-point radiator (XPR) position was established as an important element for divertor detachment control. Stable and detached ELM-free phases with H-mode confinement quality were obtained when the XPR was moved 10 cm above the X-point. Investigations of the plasma in the future flexible snow-flake divertor of AUG by means of first SOLPS-ITER simulations with drifts activated predict beneficial detachment properties and the activation of an additional strike point by the drifts.

Plasma Treatment of Ga‐Doped ZnO Nanorods

A comparative study of structural, optical properties of plasma‐treated Ga‐doped ZnO nanorods (GZO NRs) prepared by hydrothermal growth is presented, which provides an economical technology for fast production. Annealing in air followed by plasma treatment has been found to be an effective way of purification of ZnO NRs. The plasma hydrogenation and oxidation are done at room temperature in an inductively coupled plasma (ICP) reactor. The properties of plasma‐treated GZO NRs are investigated using various characterization methods, such as scanning electron microscopy (SEM), Raman, Fourier transform infrared (FTIR), X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. The SEM confirms the hexagonal shape of all GZO NRs. XPS reveals the presence of metallic Ga as well as Ga2O3 on GZO NRs surface. XRD has detected hexagonal (P63mc) ZnO phase in all samples with additional diffraction pattern in powder that has not been plasma treated. Plasma treatment does not affect the position of FTIR signals but changes the intensity of some absorption peaks. EPR shows a dominant signal with a g‐factor of 1.96. Plasma treatment of GZO samples affects its intensity.

Homoepitaxial overgrowth of (111) diamond films on Au-coated and Ni-coated substrates

Homoepitaxial growth of (111)-oriented diamond films on the Au-coated and Ni-coated diamond substrates by microwave plasma chemical vapor deposition (CVD) has been investigated. The process is involved with overgrowth of CVD diamond on Au and Ni islands formed by hydrogen plasma annealing of the 20 nm Au and Ni film coatings on diamond substrates. Cross-sectional transmission electron microscopy (TEM) observations show that both of the Au and Ni islands as single crystallites are in epitaxy with diamond substrate and no diamond growth occurs on top of those islands in the early stage of diamond deposition. The overgrowth of diamond over the metal islands results in excellent coalescence to form a continuous film with a lower defect density than the film without the metal coating. With such Au and Ni islands, the film stress can be further relaxed as shown with Raman spectroscopy.

EUV-induced hydrogen plasma and particle release

Extreme UV (EUV) lithography is the most advanced lithography technology for creating the patterns for state-of-the-art Integrated Circuits (IC), with critical dimensions down to 10 nm. This resolution is achieved by using a wavelength of 13.5 nm, imaging a reflective reticle onto a wafer via a mirror-based projection system. The system uses a low-pressure hydrogen background gas, which is excited into a low-density hydrogen plasma by the energetic EUV radiation. In the vicinity of the projection mirrors and reticle, this creates an aggressive environment that must be understood and managed to minimize molecular and particle contamination of the critical optical surfaces. In the past 25 years, main focus has been on the interaction between the EUV-induced plasma and the mirror surfaces. To secure best yield, however, focus should also be on the construction and functional surfaces close to the EUV beam. This paper will present details of energies and fluxes of the pulsed EUV-induced plasma, and its interactions with materials and particles.

Controllable Preparation of Spherical Molybdenum Nano-Powders by One-Step Reduction of APM in Radio Frequency Hydrogen Plasma

Spherical molybdenum nano-powders were in-situ ultrafast synthesized from ammonium paramolybdate (APM) raw materials in a one-step reduction method by radio frequency (RF) hydrogen plasma. Due to the extreme conditions of the RF plasma torch such as its high temperature and large temperature gradient, the injected raw APM powder was quickly gasified and then reduced into nano-sized metal molybdenum (Mo) powder. The influences of APM powder delivery rate and H2 concentration on the properties of the obtained powders were investigated. Field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD), nanolaser particle analyzer, and specific surface area method were used to characterize the morphology, phase, and particle size distribution of the powders. The results showed that the nano-sized Mo powder obtained by hydrogen plasma treatment had a quasi-spherical morphology and an average particle size of about 30 nm. The particle size could be successfully adjusted by varying H2 concentrations. In addition, spherical nano-sized MoO3 powder could be obtained when no H2 was added into the RF plasma.

Impact of hydrogen plasma treatment on the electrical performances of ZnO thin-film transistors

In this study, we investigated the effects of hydrogen plasma (H) treatment on the structure, surface morphology, and optical and electronic properties of zinc oxide (ZnO) films, and on the performances of related ZnO thin-film transistors (TFTs). It was found that the performances and stabilities of the ZnO TFTs improved by carrying out the appropriate H plasma treatment. As a result, the ZnO:H (30 s) TFTs were found to exhibit a high field-effect mobility of 18.5 cm2/Vs, small threshold voltage (Vth) of 1.5 V, low sub-threshold swing of 0.32 V/decade, and high on/off current ratio (Ion/Ioff) of 107. These improvements could be attributed to the fact that the H treatment of ZnO was shown to result in the generation of shallow donors and in the defect passivation in ZnO films owing to the formation of HO and VO-H complex bounds. The increase in the carrier concentration and the passivation of the interface trap densities and oxygen vacancies in ZnO TFTs were revealed by X-ray photo-electron spectroscopy (XPS) analysis and density functional theory (DFT) calculations. These high-performance hydrogenated ZnO TFTs obtained as a result may find applications in oxide thin-film electronics.

Atomic layer deposition of AlN on different SiC surfaces

Thin AlN films were grown using a Picosun R-200 atomic layer deposition (ALD) reactor on SiC surfaces with different crystallographic orientation: on-axis 4H-SiC (0001) and 8° off-axis 4H-SiC. TMA (trimethylaluminium) and NH3 were used as precursors while hydrogen and nitrogen plasma were applied for in-situ substrate cleaning. The substrate temperatures were 400 °C and 450 °C, with 20 ALD cycles. The surface morphology was investigated by scanning electron microscopy (SEM), which revealed nanometer-sized islands in all films. The AlN films deposited on on-axis 4H-SiC at 450 °C substrate temperature exhibited a relatively small roughness of about 0.255 nm. The chemical composition and bonding states were investigated by X-ray photoelectron spectroscopy. For all layers, high-resolution XPS showed Al 2p and N 1s spectra that are characteristic of AlN. These results are a good prerequisite of establishing the growth conditions of AlN films for surface acoustic wave (SAW) devices.

A Wearable Respiration Sensor for Real-Time Monitoring of Chronic Kidney Disease.

Human respiration is accompanied with abundant physiological and pathological information, such as the change in ammonia (NH3) content, which is related to chronic kidney disease (CKD); hence, monitoring the breathing behavior helps in health assessment and illness prediction. In this work, a wearable respiration sensor based on CeO2@polyaniline (CeO2@PANI) nanocomposites that underwent a hydrogen plasma treatment is developed. The results unambiguously show that the response of the corresponding nanocomposites is significantly enhanced from 165 to 670% to 100 ppm NH3 compared to the counterpart that did not undergo hydrogen plasma treatment and even reaches 24% to 50 ppb NH3, suggesting its fascinating capability of detecting the trace level of NH3 in human breathing. The superior response for NH3 is ascribed to the stable oxygen vacancies produced by the hydrogen plasma treatment. Furthermore, the clinical tests for patients with uremia suggest that the as-designed sensor has potential applications in clinical monitoring for CKD. Herein, this work offers a new strategy to obtain respiration sensors with high performance and provides a feasible approach for health evaluation and disease monitoring of patients with CKD.

Channel Mobility Boosting in a Poly-Si Channel Using Ge Diffusion Engineering and Hydrogen Plasma Treatment

We demonstrated that channel mobility and cell current could be increased through Ge diffusion engineering and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma treatment in a poly-Si channel. Even though the Ge channel has a higher intrinsic mobility than the Si channel, a typical poly-SiGe channel has inferior channel characteristics due to high interface trap density (D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> ) and bulk trap density caused by Ge. We propose a novel technique to control the Ge profile along the depth direction of the channel to realize lower Ge concentration at the gate dielectric interface and higher Ge concentration at the channel bulk. This Ge profile could achieve reduced D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> and enhanced channel mobility. Furthermore, the bulk traps caused by Ge are effectively reduced by H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma treatment. These techniques increased the channel mobility to 32%, which can help increase the channel mobility of devices where poly-Si channels are used.

The crystallization dependent electron-proton synergistic doping for hydrogenation of WO3 film

Hydrogenation of metallic oxides was effective to modulate the chemical/physical properties and realize various functional applications. Normally, the traditional hydrogenating route always required high temperature annealing in hydrogen gas assisted by noble metal catalyst (Au or Pd et al.) or treatment by hydrogen plasma in vacuum condition. In the current study, we achieved a facile hydrogenation route for WO3 films at ambient conditions by contacting a Zn particle in a diluted acid solution and proposed a so-called electron-proton synergistic doping (EPSD) process. Due to the electrochromic property of WO3 film, the hydrogenation induced color change from transparent to deep-blue could be directly observed by eyesight. In addition, the higher H-doping concentrating in WO3 film would induce much deeper blue color. Results showed that the crystallinity and microstructures of WO3 film dominated the EPSD process, which not only effected the Fermi level difference between the Zn particle and WO3 film, but also changed the migrating barrier of proton at the interface. This macroscopic hydrogenation of WO3 films at ambience conditions showed some potential applications for tunable electrochromic devices.

Hydrogenated Amorphous Titania with Engineered Surface Oxygen Vacancy for Efficient Formaldehyde and Dye Removals under Visible-Light Irradiation.

Hydrogenated crystalized TiO2−x with oxygen vacant (OV) doping has attracted considerable attraction, owing to its impressive photoactivity. However, amorphous TiO2, as a common allotrope of titania, is ignored as a hydrogenated templet. In this work, hydrogenated amorphous TiO2−x (HAm-TiO2−x) with engineered surface OV and high surface area (176.7 cm2 g−1) was first prepared using a unique liquid plasma hydrogenation strategy. In HAm-TiO2−x, we found that OV was energetically retained in the subsurface region; in particular, the subsurface OV-induced energy level preferred to remain under the conduction band (0.5 eV) to form a conduction band tail and deep trap states, resulting in a narrow bandgap (2.36 eV). With the benefits of abundant light absorption and efficient photocarrier transportation, HAm-TiO2−x coated glass has demonstrated superior visible-light-driven self-cleaning performances. To investigate its formaldehyde photodegradation under harsh indoor conditions, HAm-TiO2−x was used to decompose low-concentration formaldehyde (~0.6 ppm) with weak-visible light (λ = 600 nm, power density = 0.136 mW/cm2). Thus, HAm-TiO2−x achieved high quantum efficiency of 3 × 10−6 molecules/photon and photoactivity of 92.6%. The adsorption capabilities of O2 (−1.42 eV) and HCHO (−1.58 eV) in HAm-TiO2−x are both largely promoted in the presence of subsurface OV. The surface reaction pathway and formaldehyde decomposition mechanism over HAm-TiO2−x were finally clarified. This work opened a promising way to fabricate hydrogenated amorphous photocatalysts, which could contribute to visible-light-driven photocatalytic environmental applications.

Low-temperature n-type doping of insulating ultrathin amorphous indium oxide using H plasma-assisted annealing

Low-temperature process compatibility is a key factor in successfully constructing additional functional circuits on top of pre-existing circuitry without corrupting characteristics thereof, a technique that typically requires die-to-die (wafer-to-wafer) stacking and interconnecting. And against thermal annealing, which is mandatory and is possible only globally for activating amorphous oxide semiconductors, the selective control of electrical characteristics of the oxide thin-films for integrated circuit applications is challenging. Here, a low-temperature process that enables n-type doping of the designed region of insulating In2O3 thin-film is demonstrated. A short hydrogen plasma treatment followed by low-temperature annealing is used to increase interstitial and substitutional hydrogen associated bond states creating shallow donor levels in the insulating In2O3 surface to transform the thin-film into an n-type semiconductor. As a result, an In2O3 thin-film transistor with a high on/off current ratio (>108), a field-effect mobility of 3.8 cm2 V−1 s−1, and a threshold voltage of ∼3.0 V has been developed. Compared to performing just thermal annealing, the H-plasma assisted annealing process resulted in an n-type In2O3 thin-film transistor showing similar characteristics, while the processing time was reduced by ∼1/3 and the plasma-untreated area still remained insulating. With further development, the hydrogen plasma doping process may make possible a monolithic planar process technology for amorphous oxide semiconductors.

Evaluation of Hydrogen-Induced Blistering of Mo/Si Multilayers with a Capping Layer

Mo/Si multilayer mirrors are used for extreme ultraviolet (EUV) lithography. The formation of hydrogen-induced blisters in the Mo/Si multilayer is a problem that reduces the reflectance of the mirror. To evaluate the blister-resistance of EUV mirrors, the blister formation processes of Mo/Si multilayers with a capping layer were investigated using a high-frequency hydrogen plasma system as a hydrogen ion source under varying hydrogen ion exposure conditions. As a result, it was observed that blister formation by low-energy hydrogen ion irradiation of about 10 eV increases the blister-occupied area, depending on the amount of the ion dose. Furthermore, the sample was heated to promote the diffusion of hydrogen atoms, and the activation energy of blister formation was examined using the Arrhenius plot of the ion dose required for blister formation with respect to the heating temperature. The analysis showed that when the ion flux is known, the blister formation time can be predicted.

Confinement improvement during detached phase with RMP application in deuterium plasmas of LHD

In order to explore the compatibility of good core plasma performance with divertor heat load mitigation, the interaction between cold edge plasma and core plasma transport, including the edge transport barrier (ETB), has been analysed in the divertor detachment discharges of deuterium plasmas in LHD with resonant magnetic perturbation (RMP) field application. The RMP application introduces a widened edge stochastic layer and sharp boundary in the magnetic field structure between the confinement region and the edge stochastic layer. The widened edge stochastic layer enhances impurity radiation and provides stable detachment operation as compared with the case without RMP. It is found that ETB is formed at the confinement boundary at the onset of detachment transition. However, as the detachment deepens, the resistive pressure gradient-driven MHD mode is excited, which degrades the ETB. At the same time, however, the core transport decreases to keep global plasma stored energy (W p) unchanged, showing clear core-edge coupling. After a gradual increase of density fluctuation during the MHD activity, a spontaneous increase of W p and the recovery of ETB are observed while the detachment is maintained. Then, the coherent MHD mode ceases and ELM-like bursts appear. In the improved mode, impurity decontamination occurs, and the divertor heat load increases slightly. Key controlling physical processes in the interplay between core and cold edge plasma are discussed. A comparison between deuterium and hydrogen plasmas shows that hydrogen plasmas exhibit similar features to the deuterium ones in terms of density and magnetic fluctuations, impurity decontamination towards higher confinement, etc. But most of the features are modest in the hydrogen plasmas and thus no clear confinement mode transition with clear ETB formation is defined. Better global confinement is obtained in the deuterium plasmas than the hydrogen ones at a higher radiation level.

Time-resolved measurement of radical populations in extreme-ultraviolet-light-induced hydrogen plasma

We have investigated hydrogen plasma induced by intense extreme ultraviolet (EUV) radiation by measuring the plasma parameters and population density of radicals, which is expected to clean the tin contamination on the optics in EUV sources, using a time-resolved optical emission spectroscopy. The obtained electron density was n e = (2 ± 0.4) × 1013 cm−3, and the electron temperature was T e = 1 ± 0.2 eV. The electron density was five orders of magnitude higher than that of previous study. The radical population density determined by the experiment was consistent with that calculated with a collisional radiative model, showing excitation and recombination are dominant production processes.

Non-thermal plasma-assisted rapid hydrogenolysis of polystyrene to high yield ethylene

The evergrowing plastic production and the caused concerns of plastic waste accumulation have stimulated the need for waste plastic chemical recycling/valorization. Current methods suffer from harsh reaction conditions and long reaction time. Herein we demonstrate a non-thermal plasma-assisted method for rapid hydrogenolysis of polystyrene (PS) at ambient temperature and atmospheric pressure, generating high yield (>40 wt%) of C1–C3 hydrocarbons and ethylene being the dominant gas product (Selectivity of ethylene, SC2H4 > 70%) within ~10 min. The fast reaction kinetics is attributed to highly active hydrogen plasma, which can effectively break bonds in polymer and initiate hydrogenolysis under mild condition. Efficient hydrogenolysis of post-consumer PS materials using this method is also demonstrated, suggesting a promising approach for fast retrieval of small molecular hydrocarbon modules from plastic materials as well as a good capability to process waste plastics in complicated conditions.

Reversible control of the metal-insulator transition in V2O3 thin films through plasma hydrogenation

We investigate the effect of hydrogen plasma treatment on the metal-insulator transition (MIT) of epitaxial V2O3 films grown on c-Al2O3. The films were exposed to plasma at constant power for varying intervals. With increasing hydrogenation the films display a suppression of the MIT magnitude and temperature due to neutralization of structural defects and passivation of unpaired bonds by incorporation of atomic hydrogen as supported by relaxation in strain by XRD and Raman spectroscopy analysis, while stabilizing the metallic phase due to reduction in Peierls dimerization of V-V bonds. Heating to 350-400 °C the electrical characteristics of the film in the as-grown state are regained showing the possibility of reversibly controlling the MIT characteristics.

Promoted Hydrogenolysis of Furan Aldehydes to 2,5-Dimethylfuran by Defect Engineering on Pd/NiCo2 O4.

Catalytic hydrogenolysis of biobased furan aldehydes (i. e., 5-methylfurfural, 5-hydroxymethylfurfural) to 2,5-dimethylfuran has gained extensive interest for biomass-derived fuels and chemicals. Herein, a class of NiCo2 O4 -supported palladium with considerable oxygen defects was synthesized by hydrogen plasma etching and phosphating methods. The oxygen defects not only promoted the hydrogenation of the C=O group but also enhanced the accessibility of coordinatively unsaturated metal cations with Lewis acidity for the hydrogenolysis of the C-OH group. Meanwhile, the additional Brønsted acidity in Pd/NiCo2 O4-x obtained by phosphating could further strengthen the hydrogenolysis ability by the etherification route of C-OH. Finally, Pd/NiCo2 O4-x exhibited the most effective performance with 2,5-dimethylfuran yields of 92.9 and 90.5 % from 5-methylfurfural and 5-hydroxymethylfurfural, respectively. These catalytic mechanisms were confirmed by in-situ infrared spectroscopy and control experiments. Furthermore, the catalyst showed outstanding recycling stability. This work shows powerful synergistic catalysis in the hydrogenolysis reaction by multifunctional active sites.