RF-PECVD Technique Research Articles

Wear Behavior of DLC Coated HSS with Hydraulic Fluids

The worldwide rotary pump market was estimated at around $5000 million in 2020 and the market is supposed to increase by 20% toward the end of 2026, seeing a compounded annual growth rate of 3% over a period from 2022-2026. The scrapping of an engineered component made from non-renewable resources at an early stage in life due to wear goes against the ethics of the conservation of natural resources as the frictional processes lead to dissipation of a part of input energy. In this context many research works focused on analyzing wear behavior using various formulated and vegetable oils but no works investigated on using hydraulic oils as lubricant for wear preventative nature. The objective of the work was to obtain diamond-like carbon coating on high-speed steel samples and test them for better wear preventative behavior with different hydraulic fluids. The HSS ball sample of 12.7 mm diameter were used as a substrate on which the dlc coating was to be developed using then RF-PECVD technique. The developed DLC coating was characterized by conducting X-Ray diffraction which suggested the coating to be of amorphous structure, Raman spectroscopy which determined the content of graphite (sp2 ) to be 47% and that of diamond (sp3 ) to be 53%.Further nanoindentation was conducted to compare the hardness of the high-speed steel sample before and after coating which was 12.22GPa and 35.56GPa respectively. The four ball test was performed to investigate the anti-wear properties of lubricating oil at specific conditions such as higher load, controlled temperature and constant rotating speed of the ball as per the ASTM D4172. The four ball results show that the coefficient of friction for samples reduces by around 36% when test oil 3 is used in uncoated samples and 48% in coated samples. Also, the wear rate for the test oil 3 for coated samples was found to be 0.7381x10-6 mm/Nm, which is the lowest wear rate among the other test oils. The outcome of the project is the reduction of coefficient of friction by 84% with respect to dry condition when test oil 3 is used. Therefore, it can be deduced that test oil 3 stands out as the most effective lubricant among the trio of test oils.In this direction , further work can be carried out by carrying out four ball tests with lubricant oils in combination with additives to it so as to enhance the base oil property and suppress undesirable base oil properties. Fabrication and manufacturing of the vane model can be done to validate the result with the help of experimental work. Key Word: DLC; HSS; Raman Spectrograph; AFM; 4-Ball Test, Hydraulic Oil.

A comprehensive study of simultaneous RF-PECVD synthesis of n-diamond and carbon nanowalls hybrid structure over a large area

In this study, n-diamond–carbon nanowalls hybrid structure was synthesized on a 4-inch diameter silicon wafer by RF-PECVD technique (type CCP). A comprehensive analysis of the structure was carried out at the beginning of growth and after a long period of synthesis using electron microscopy, transmission microscopy, Raman spectroscopy, and X-ray diffraction techniques. As the analysis showed, feeding carbon monoxide (CO) to a gas mixture of methane (CH4), argon (Ar), and hydrogen (H2) induces the formation of n-diamond particles in a basal layer. By using plasma-enhanced etching in an oxygen-containing medium, carbon nanowalls (CNWs) were successfully removed, and the underlying layer containing n-diamond was analyzed. For the first time, X-ray diffraction results of a separate n-diamond phase were obtained for this layer.

Stepwise tuning of the doping and thickness of a-Si:H(p) emitter layer to improve the performance of c-Si(n)/a-Si:H(p) heterojunction solar cells

Crystalline silicon (c-Si)/ hydrogenated amorphous silicon (a-Si:H) heterojunction (Ag/Al/c-Si(n)/a-Si:H(i)/a-Si:H(p)/ITO/Ag) solar cells were fabricated by RF-PECVD technique. The efficiency (η), short circuit current density (Jsc) and fill factor (FF) of the heterojunction (HJ) solar cells were improved from 10 to 17%, 24 to 32 mA/cm2 and 0.60 to 0.74 respectively through systematic tuning of processing steps; the thickness and doping of a-Si:H(p) layer respectively. High open circuit voltage (Voc) of 705 mV could be achieved by improving the interfaces between the a-Si:H layers and c-Si by inserting an ultrathin intrinsic a-Si:H film using H2 plasma treatment on c-Si(n) wafer and a-Si:H(i) layer respectively. Simultaneously, other solar parameters like Jsc and FF were also improved step by step by carefully adjusting the gas flow rate and deposition time of doped a-Si:H(p) layer. By increasing the doping of a-Si:H(p) layer, electric field at the interface could be enhanced, which led to the immediate separation of electron–hole pair and thus improving the solar cell parameters. This is also confirmed by external quantum efficiency (EQE) spectra measured with and without external reverse bias.

WITHDRAWN: Comparative study of structure, optical properties and residual stress of boron carbide thin films deposited by RF-PECVD and PLD technique

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High open circuit voltage c-Si/a-Si:H heterojunction solar cells: Influence of hydrogen plasma treatment studied by spectroscopic ellipsometry

One sided c-Si/a-Si:H heterojunction solar cells (Ag/Al/c-Si(n)/a-Si:H(i)/a-Si:H(p)/ITO/Ag) with open circuit voltage (Voc) as high as 711 mV were fabricated on double side polished n- type c-Si wafer (thickness 275–325 µm, resistivity of 5–10 Ω cm) by RF-PECVD technique in multi-chamber system. The cells were fabricated with hydrogen plasma treatment of a-Si:H(i) layer of different thicknesses prior to the deposition of top a-Si:H(p) layer. The thickness, optical band gap and microstructure of different a-Si:H layers in the cells were estimated using Spectroscopic ellipsometry. It was observed that hydrogen plasma treatment of a-Si:H (i) layer not only etched out the significant portion of the layer, but also improved the microstructure of the films and passivated the interface defects without deteriorating the electronic transport properties. The Voc of 711 mV is higher than the values reported in literature so far for single sided solar cells. This improvement in Voc is due to reduction of interface recombination sites, passivation of surface dangling bonds and decrease of series resistance with 2 min H2 plasma treatment on a-Si:H(i) layer before deposition of a-Si:H(p) layer, which also improved the short circuit current density (Jsc) and fill factor (FF). The results suggest hydrogen plasma treatment of a-Si:H(i) layer as an alternative approach to achieve surface passivation and improve open circuit voltage of c-Si/a-Si:H heterojunction cells.

Investigation of the effect of RF energy on optical, morphological, chemical and antibacterial properties of PolyTerpenol thin films obtained by RF-PECVD technique

In this study, it was aimed to obtain PolyTerpenol thin films by radio frequency plasma enhanced chemical vapor deposition technique using Terpinen-4-ol essential oil, which is organic compounds. The surface morphology and chemical properties of polymer thin films were investigated by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy. AFM analyzes of PolyTerpenol thin films revealed that the thin films are homogeneous, smooth and nonporous. The optical properties of the thin films were determined using UV–Vis spectrophotometer. When optical band gaps of thin films were examined, it was found that this value varied from 3.83 to 3.20 eV. The extinction coefficients of the obtained thin films according to the increasing RF energy were calculated as 0.0011, 0.0060, 0.0085 and 0.0150, respectively, at a wavelength of 320 nm. In addition, antibacterial effects of these thin films against Escherichia Coli (E.Coli) bacteria were also investigated. The PolyTerpenol thin films were found to have high antibacterial activity against E. Coli bacteria.

Evolution of nanostructure in hydrogenated amorphous silicon thin films with substrate temperature studied by Raman mapping, Raman scattering and spectroscopic ellipsometry

Raman mapping and Raman scattering studies have been performed on hydrogenated silicon thin films deposited at different substrate temperature by rf-PECVD technique. In Raman mapping a clear difference in contrast, corresponding to different phases, was observed for films deposited at substrate temperature (Ts) ≥ 130 °C. The Raman spectra recorded at bright and dark spots in Raman image correspond to nanocrystalline and amorphous phase respectively. The fractional area of bright spots in Raman mapping was found to increase with increasing Ts. Also, the nanocrystalline fraction and size of nanocrystallites is found to increase with increasing Ts. These studies suggest that nucleation sites for the growth of nc-Si:H are formed at substrate temperature as low as 130 °C. With further increase in Ts more and more nucleation sites are formed which subsequently enhance crystallinity in these films. Films deposited at Ts ≥ 150 °C have larger band gap, higher roughness and higher photosensitivity and are of excellent device quality.

Raman and spectroscopic ellipsometry studies of a-Si:H thin films on low-cost photo paper substrate

Photo papers are very light weight, cheapest easily available and compatible with the roll-to-roll printing process. Here we report hydrogenated amorphous silicon (a-Si:H) thin films deposited on photo paper by plasma enhanced chemical vapor deposition (rf-PECVD) technique. A series of intrinsic a-Si-H thin films were deposited by varying the substrate temperature (Ts) between 70 °C – 150 °C. Raman measurement atdifferent positions on the film corresponds to multiphase (amorphous as well as nanocrystalline phase) nature of films. The film having nanocrystalline phase, exhibit higher bandgap and higher photosensitivity (∼ 6 orders of magnitude) as compared to films with pure amorphous phase. The optoelectronic properties of these films are comparable to those on conventional corning 1737 glass substrate.

Structure and mechanical properties of oxygen doped diamond-like carbon thin films

In this study, structure and mechanical properties of doped diamond-like carbon (DLC) films with oxygen were investigated. A mixture of methane (CH4), argon (Ar) and oxygen (O2) was used as feeding gas, and the RF-PECVD technique was used as a deposition method. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and a combination of elastic recoil detection analysis and Rutherford backscattering (ERDA-RBS). Nano-indentation tests were performed to measure hardness. Also, the residual stress of the films was calculated by Stoney equation. The XPS and ERDA-RBS results indicated that by increasing the oxygen in the feeding gas up to 5.6vol.%, the incorporation of oxygen into the films' structure was increased. The ratio of sp2 to sp3 sites was changed by the variation of oxygen content in the film structure. The sp2/sp3 ratios are 0.43 and 1.04 for un-doped and doped DLC films with 5.6vol.% oxygen in the feeding gas, respectively. The Raman spectroscopy (RS) results showed that by increasing the oxygen content in doped DLC films, the amount of sp2 CC aromatic bonds was raised and the hydrogen content reduced in the structure. The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the decrease of hydrogen content and the increase the ratio of CC aromatic to olefinic bonds. Hardness and residual stress of the films were raised by increasing the oxygen content within the films' structure. The maximum hardness (19.6GPa) and residual stress (0.29GPa) were obtained for doped DLC films, which had the maximum content of oxygen in structure, while the minimum hardness (7.1GPa) and residual stress (0.16GPa) were obtained for un-doped DLC films. The increase of sp3 CC bonds between clusters and the decrease of the hydrogen content, with a simultaneous increase of oxygen in the films' structure is the reason for increase of hardness and residual stress.

Effect of RF Power on the Chemical Bonding and Humidity Sensing Properties of a-CN<sub>x</sub> Thin Films

Amorphous carbon nitride (a-CNx) thin films were deposited using radio frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique. A set of a-CNx thin films were prepared using pure methane (CH4) gas diluted with nitrogen (N2) gas. The rf power was varied at 50, 60, 70, 80, 90 and 100 W. The characterization techniques used were Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscope (FESEM). Humidity sensing properties of the a-CNx thin films were investigated by recording their electrical response to relative humidity (RH) at room temperature. Chemical bonding analysis clearly showed the presence of nitrile bands in the deposited films. The FESEM images of the films show a porous, granule-like and dendritic morphology. The average resistance of the a-CNx thin film is changed from 23.7 kΩ to 5.8 kΩ in the range of 5 to 95%RH. The films show a good response and repeatability as a humidity sensing materials. This work showed that rf power has a significant effects on the chemical bonding, morphology and electrical properties of the a-CNx films.

Amorphous and crystalline TiO2 coatings synthesized with the RF PECVD technique from metalorganic precursor

Thin films of titanium dioxide (TiO2) were synthesized with the help of plasma enhanced chemical vapour deposition (RF PECVD) technique, using titanium (IV) ethoxide and gaseous oxygen as precursor compounds. The glow discharge power and the flow rate of oxygen were used as process operational parameters. Phase composition of the films was studied with the X-ray diffraction (XRD) technique, their morphology was followed with the scanning electron microscopy (SEM), elemental composition was investigated with the energy dispersive spectroscopy (EDS) and their thickness and optical properties were assessed with the help of variable angle spectroscopic ellipsometry (VASE) and UV-VIS spectroscopy.The coatings obtained at the glow discharge power of 300 W and the oxygen flow rate of 400 sccm were characterized by the best titanium dioxide stoichiometry and the highest refractive index of 2.2. As deposited, the films had strictly amorphous character. They crystallized after thermal annealing at 500 °C, with an increase of their refractive index to 2.35. Thermal treatment also modified water wettability of the coatings: annealing produced a decrease of water contact angle by more than 30°. An illumination of the films with UV radiation brought about further drop of water contact angle which eventually resulted in a strongly hydrophilic surface.

Electrochemical Deposition of Manganese Oxides on Carbon Nano-Sheets

We have electrodeposited Mn-oxide films on Carbon nano-sheets (CNS), thin (< 10 nm) vertical standing graphitic sheets, having in mind potential energy storage applications of this high-surface-area composite structure. We examined the deposition kinetics of Mn-oxides and physical-chemical properties of Mn-oxide/CNS composite films on substrates ranging from flat to high-aspect-ratio (HAR) Si pillars. We have also explored the possibility to integrate this process into production line typical for microelectronics industry.CNS was grown using RF-PECVD technique [1] onto both blanket 200 mm Si wafers coated with 70 nm thick PVD TiN, and wafer pieces with high-aspect-ratio Si pillars coated with 10 nm ALD TiN. CNS was grown on TiN from CH4/H2mixture [1] to a height of approximately 1 µm.Anodic electrodeposition of Mn-oxide, often also termed electrolytic manganese-dioxide (EMD), was performed on both blanket CNS/TiN/Si and patterned CNS/ALD TiN/Si samples using 0.3 M MnSO4·xH2O + 0.55 M H2SO4aqueous electrolyte. Plating experiments were performed using a three-electrode clip-on Teflon cell connected to a computer controlled Autolab potentiostat PGSTAT100 (Metrohm), with Ag/AgCl as a reference electrode (RE) and Pt mesh as a counter electrode (CE). Characterization of EMD/CNS films was performed using Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS). Figure 1 shows SEM images of as-grown CNS (a) and EMD coverage as a function of deposition current (b and c). EMD is plated galvanostatically, and potential-time responses were analyzed to help optimize deposition parameters for desired film thickness and structural properties. The analysis was based on the theories of galvanostatic nucleation and growth [2], and proposed reaction mechanisms during galvanostatic deposition of EMD [3]. Further surface area enhancement was attempted through EMD/CNS deposition on HAR Si pillars coated with 10 nm ALD TiN. Figure 2 shows HAR ALD TiN/Si pillars before and after CNS and EMD deposition, respectively. CNS coating was applied to various ALD TiN/Si structures having different aspect ratios and spacing between pillars, and then followed by EMD deposition.A typical Raman spectrum of our EMD/CNS structure, shown in Figure 3, contained broad features in the range 450 to 730 cm-1 where characteristic EMD peaks are expected [4 and references therein], and showed characteristic CNS peaks in 1000 to 3500 cm-1range [5]. Thanks to its sensitivity to local structure/symmetry Raman spectroscopy proved to be a useful tool for characterization of disordered and defective EMD. We were able to detect EMD structural changes upon annealing at various temperatures and lithiation in anhydrous propylene carbonate solvent with 1 M LiClO4, and also monitor the effects of plating and post-plating processing on CNS.

Structure, gas-barrier properties and overall migration of poly(lactic acid) films coated with hydrogenated amorphous carbon layers

Hydrogenated amorphous carbon (a-C:H) films were grown on a poly(lactic acid) (PLA) substrate by means of a radiofrequency plasma-enhanced chemical vapour deposition (rf-PECVD) technique with different deposition times (5, 20 and 40min). The main goal of this treatment was to increase the barrier properties of PLA, maintaining its original transparency and colour as well as controlling interactions with food simulants for packaging applications. Morphological, chemical, and mechanical properties of PLA/a-C:H systems were evaluated while permeability and overall migration tests were performed in order to determine the effect of the plasma treatment on the gas-barrier properties of PLA films and their application in food packaging. Morphological results suggested a good adhesion of the deposited layers onto the polymer surface and the samples treated for 5 and 20min only slightly darkened the PLA film. X-ray photoelectron spectroscopy revealed that the structural properties of the carbon layer deposited onto the PLA film depend on the exposure time. PLA/a-C:H system treated for 5min showed the highest barrier properties, while none of the studied samples exceeded the migration limit established by the current legislation, suggesting the suitability of these materials in packaging applications.

Mechanical, photocatalytic and microbiological properties of titanium dioxide thin films synthesized with the sol–gel and low temperature plasma deposition techniques

In this work, selected mechanical, photocatalytic and biological properties of thin titanium dioxide films, synthesized with the sol–gel and radio frequency plasma enhanced chemical vapor deposition (RF PECVD) techniques, were compared. In both cases, austenitic stainless steel was used as a substrate, and titanium organic connections served as TiO2 precursors. Prior to the deposition, several substrates had been surface plasma activated and the film adherence to activated and non-activated surfaces was compared.The TiO2 films deposited with the RF PECVD technique were characterized by better mechanical properties than those of the sol–gel coatings. The bactericidal activity of the plasma deposited films was also higher. All coatings significantly reduced the formation of bacterial biofilm. In the domain of water photowettability, similar photowetting effects were obtained for the PECVD and sol films. Finally, an important finding concerns the photocatalytic properties of amorphous TiO2 coatings, synthesized with the RF PECVD technique.

Optimizing rf Power for Preferential C≡N Bond Formation in a-CNx Thin Films Prepared by rf-PECVD Technique

Effects of rf power on the chemical bonding in carbon nitride films deposited using radio-frequency (rf) plasma enhanced chemical vapor deposition in pure methane and nitrogen gas mixtures were investigated. The rf power was varied from 60 to 100 W. The deposition rate of the films increased constantly with increasing rf power up to 80W, before saturating with further increase in rf power. Fourier transform infra-red spectroscopy (FTIR) studies showed a systematic change in the spectra and revealed three main peaks namely the G-peak, D-peak and C≡N triple bond. This work showed that rf power has significant effects on the chemical bonding of the a-CNx films and the optimum rf power for the high C≡N absorption intensity is 80 W.

Catalyst free carbon nitride nanostructures prepared by rf-PECVD technique on hydrogenated amorphous carbon template

Catalyst free nanostructured carbon nitride thin films were synthesized by radio-frequency plasma enhanced chemical vapour deposition (rf-PECVD) on pre-deposited hydrogenated amorphous carbon layer (C:H). The effects of the morphological and structural properties of the pre-deposited C:H underlayer on the formation and the corresponding carbon nitride nanostructures (ns:CNx) were studied. The C:H underlayers were produced from pure methane plasma while the carbon nitride nanostructure were formed from a mixture of methane and nitrogen. The effects of varying the applied rf powers on the morphological and structural characteristics of the C:H underlayer and the resulting ns:CNx films were determined. The C:H underlayers were studied using Fourier Transform Infrared (FTIR) Spectroscopy and Atomic Force Microscopy (AFM) while Auger Electron Spectroscopy, FTIR Spectroscopy, and Field Emission Scanning Electron Microscopy (FESEM) were used to study the carbon nitride nanostructures product. The results showed that the change in the surface morphology of the C:H has significant influence on the features of the resulting carbon nitride nanostructures.

RF power density dependent phase formation in hydrogenated silicon films

Hydrogenated amorphous and micro/nanocrystalline silicon films have been deposited using RF (13.56 MHz) PECVD technique in the RF power density range of 177 to 885 mW/cm 2 exploiting SiH 4 + H 2 + Ar gaseous mixture. Predominant crystalline phase was observed in the films, as revealed from Raman spectroscopic study, deposited at power densities of 531 and 708 mW/cm 2 and amorphous phase at 177, 354 and 885 mW/cm 2. Amorphous to microcrystalline phase transition occurred near RF power density of 531 mW/cm 2. The high crystalline phase (~ 80%) was found in the film deposited at 708 mW/cm 2. Lower values of bond angle distortion of 6.7 and 5° were found for the films deposited at 531 and 708 mW/cm 2 as compared to bond angle distortion of 8.4, 9.3 and 9.1° for the films deposited at 177, 354 and 885 mW/cm 2, respectively. Plasma parameters extracted from V/I probe and properties of the films revealed contribution of ions to be beneficial for the enhancement of deposition rate of the films. The increased ion energy (sheath field) and ion flux together with SiH x (x = 1,2,3) radicals on growing film surface might help in the enhancement of crystallinity at 708 mW/cm 2.

Evaluation of corrosion resistance of diamond-like carbon films deposited onto AISI 4340 steel

The corrosion resistance of amorphous diamond-like carbon (DLC) coatings deposited by radio frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique on AISI 4340 steel substrates was evaluated under saline (5% NaCl) and acid (1700 ppm H2SO4) atmospheres. The corrosion process was investigated by surface characterization and electrochemical methods, such as potentiostatic polarization and electrochemical impedance spectroscopy (EIS). DLC coatings effectively protected the substrate after 48 h in a salt fog chamber and after the first Kesternich cycle. For comparison, under the same conditions, titanium nitride (TiN) coatings did not protect the substrate even for 2 h of saline exposure and even for the first Kesternich cycle. Although the DLC coatings resisted well to the corrosive action of the aggressive media, nucleation and growth of homogenous and micro-sized pinholes uniformly distributed on DLC coatings were observed as a result of the corrosion processes. The observed results suggest that the development of techniques which would reduce the porosity of the DLC films could promote further improvement on their corrosion protection ability.

Influence of argon dilution on growth and properties of hydrogenated nanocrystalline silicon films

The effect of argon concentration (66–87%) in total gaseous mixture (SiH 4+H 2+Ar) on growth and properties of hydrogenated nanocrystalline silicon films deposited by RF (13.56 MHz) PECVD technique was investigated. Raman and XRD measurements revealed increasing argon fraction favored enhancement of crystallinity, enlargement of crystallites and relaxation of strained bonds. Photoluminescence spectra of nc-Si:H films exhibited two radiative transitions in the photon energy ranges of 2.8–3.1 eV and 1.6–2.1 eV. The high energy PL peaks are attributed to surface effect of the films whereas peaks in the range of 1.6–2.1 eV are due to nanocrystallinity in the films. Argon dilution also helped enhancement of deposition rate and conductivity of the films. A film deposited at 81% of argon fraction possesses high crystallinity (75%), conductivity in the order of 10 −5 (Ω cm) −1, size of the crystallite (Raman=12 nm, XRD=18 nm), and low residual stress (125 MPa).

Amorphous silicon carbide photoelectrode for hydrogen production directly from water using sunlight

Results on the use of amorphous silicon carbide (a-SiC:H) as a photoelectrode in an integrated ‘hybrid’ photoelectrochemical (PEC) cell to produce hydrogen directly from water using sunlight are presented. A high quality a-SiC:H thin film with bandgap >2.0eV was fabricated by RF-PECVD technique using a SiH4, H2 and CH4 gas mixture. Incorporation of the carbon in the a-SiH film not only increased the bandgap, but also led to an increase in corrosion resistance in an electrolyte. Adding H2 during the fabrication process led to a decrease in the density of states (DOS) in the films. Immersing the a-SiC:H(p)/a-SiC:H(i) structure in a pH 2 electrolyte showed excellent durability up to 100 h (so far tested); the photocurrent increased and the photocurrent onset shifted anodically after the 100-h durability test, which is encouraging. It was also found that a SiO x layer is formed on the surface of a-SiC:H when exposed to air, which led to a decrease in the photocurrent, and the photocurrent onset shifted cathodically. We have found that this effect could be removed via a hydrofluoric acid dip and the photocurrent could be increased to over 6mA/cm2 at a potential of −1.4V (versus Ag/AgCl). To boost the photovoltage (potential) required for water splitting, the configuration of a-Si:H tandem (or ‘micromorph’)/a-SiC:H structure (PV/PEC) could be viable for water splitting. As a first step, we integrated amorphous silicon tandem solar cells with an a-SiC:H photoelectrode, which exhibited encouraging results. Finally, via simulation, we showed that using a-SiC:H as a photoelectrode could lead to a solar-to-hydrogen (STH) conversion efficiency >10%.