Substrate Heating Temperature Research Articles

Low-temperature growth at 225 °C and characterization of carbon nanowalls synthesized by radical injection plasma-enhanced chemical vapor deposition

The synthesis of carbon nanowalls (CNWs) necessitated a substrate heating temperature above 600 °C. This study describes a low-temperature growth at 225 °C and characterization of CNWs synthesized by the radical injection plasma-enhanced chemical vapor deposition. To investigate the effect of temperature on the growth process, CNWs were synthesized at various temperatures ranging from 200 °C to 700 °C. The morphology of the CNWs observed with a scanning electron microscope shows that wall density increases as substrate temperature decreases. The Raman spectroscopy analysis indicates that CNWs grown at 225 °C have higher defect levels than those grown at higher temperatures, such as 700 °C. Transmission electron microscopy confirmed the presence of multiple graphene layers in the CNWs grown at 225 °C. The water contact angle results revealed that CNWs grown at 225 °C had higher hydrophobicity than those grown at higher temperatures, opening up the potential for CNW applications.

Activity and Durability of Mn Binary Oxide-Based Electrocatalyst for an Alternative Anode

Compared with alkaline water electrolysis (AWE), proton exchange membrane water electrolysis (PEMWE) has several advantages such as high current density, compact system and high purity of hydrogen gas. However, a conventional anode of PEMWE utilizes precious metal oxide such as iridium oxide (IrO2) with high cost and low resources. Recently, it has been reported that the performance of low-loading IrO2 anodes deteriorates due to the potential fluctuations simulated variable renewable energies [1-2]. Thus, it is required to develop a low-cost catalyst with high durability against the potential fluctuations. We have focused on the tantalum oxide-based electrocatalyst because of its low cost and high chemical stability in acid. In this study, we have investigated on the catalytic activity and durability of Mn added Ta oxide-based thin film (Mn-TaOx) for the alternative anode of PEMWE. For the purpose of improvement of durability, Mn-TaOx coated with ZrO2 fabricated by the Atomic Layer Deposition (ALD) was also prepared to evaluate the durability of potential cycling.A Ti rod was used as the substrate, and Mn-TaOx was prepared by RF magnetron sputtering deposition. Mn disk was used as the sputtering target, and the Ta plate was placed on the Mn target to prepare Mn-TaOx. Mn addition was fixed at 50 at%, and it was controlled by the area ratio considering sputtering rate of Mn and Ta metal. Partial pressure of Ar and O2 gas were kept constant at 0.23 Pa for 20 min during the sputtering. The substrate heating temperature was constant at 673 K during the sputtering. The prepared Mn-TaOx electrode was coated with ZrO2 fabricated by ALD (ZrO2 coating Mn-TaOx). The thickness of coating ZrO2 was varied in the range of 0.5 to 2.0 nm. All electrochemical measurements such as oxygen evolution reaction (OER) was used by conventional three electrode cell in 1 M H2SO4 at 303 K. In addition, electrochemical impedance spectroscopy (EIS) was also performed to estimate several factors such as charge transfer resistance (R ct), film resistance (R film) and so on. The protocol of potential cycling as a durability test was set the potential in the range of 1.5 to 2.0 V with 50 mV s-1 for 10000 cycles, and the slow scan voltammetry was conducted every 2000 cycle in the range of 1.2 to 2.0 V with 5 mV s-1 to compare the OER activity before and after test.The OER current of ZrO2 coating Mn-TaOx was smaller than that of Mn-TaOx without coating (Mn50-TaOx (0 nm)). In particular, the OER current of Mn-TaOx coated with 2 nm of ZrO2 (“2 nm”) was greatly decreased because the film thickness of ZrO2 is too thick so that it has low electric conductivity. Furthermore, the APD-ZrO2 covered on the surface, and it is also hard to react with reactant at active site. From results of EIS, the R ct and R film of “2 nm” increased. On the other hand, the OER current of Mn-TaOx coated with 1 nm of ZrO2 (“1 nm”) did not drastically decrease compared to Mn-TaOx and it was suggested that “1 nm” relatively maintained its activity.Figure 1 shows the geometric current density (i geo) at 2.0 V of ALD-ZrO2 coated on Mn-TaOx after potential cycling. The i geo at 2.0 V of Mn-TaOx without coating also shows in Fig. 1. The i geo of Mn50-TaOx (0 nm) was decreased about half value after 2000 cycles of durability test, but that of Mn-TaOx coated with ZrO2 did not decrease significantly even after 2000 cycles of potential cycling. In particular, the i geo of “1 nm” was the highest current after the 2000 cycles of potential cycling in this study, and the degradation didn’t observe in this cycle range. According to the results from XPS spectrum, a small amount of ZrO2 was detected on the surface of “1 nm” after the potential cycling. The redox peak of Mn(Ⅲ)/(Ⅳ) [3] observed at the ALD-ZrO2 coated on Mn-TaOx was also detected after the potential cycling, so that the Mn species as an active site of Mn-TaOx for the OER was still remained. Therefore, the reason why the “1 nm” was relatively stable is that the amounts of both active and protect site have maintained during the durability test.AcknowledgementThis work is partially supported by Suzuki Foundation.References(1) Ayers, Curr. Opin. Electrochem., 18, 9 (2019).(2) M. Alia, and G. C. Anderson, J. Electrochem. Soc., 166, F282 (2019).(3) Morita, C. Iwakura, and H. Tamura, Electrochim. Acta, 24, 357 (1979). Figure 1

Effects of Oxygen Defects in Zr Oxide-Based Thin Films on Oxygen Reduction Reaction in Acidic Media

The use of carbon-supported platinum as cathode catalysts of polymer electrolyte fuel cells has some problems such as high cost and low amount of resources of platinum. Therefore, we have attempted to develop substitute of platinum based on group 4 metal oxides. In the case of Zr oxide-based powder catalysts, we found that zirconium oxide-based compounds with oxygen defects and deposited carbon derived from organometallic precursors had definite activity of oxygen reduction reaction (ORR) [1][2]. However, the ORR activities of these catalysts still remain low. In order to increase the ORR activity drastically, it is necessary to clarify the catalyst design. This requires an understanding of the active sites and the electron conduction path separately, which were not separated in powder catalysts. On the other hand, Sugino et al. investigated the effect of oxygen vacancies and nitrogen doping on the active site based on first-principles calculations [3]. Defects by oxygen vacancies and nitrogen dopants were introduced into the tetragonal ZrO2(101) slab. It was found that the energy barrier of the rate-determining step, or the removal of adsorbed OH, was comparable to (or only slightly lower than) that of the pristine surfaces, indicating that defects play only a minor role in enhancing the ORR activity. In other words, it was suggested that oxygen vacancies and nitrogen dopants contributed to the emergence of ORR activity by enhancing the electrical conductivity of ZrO2 rather than by forming high quality active sites. Simple models are suitable for experimentally confirming the results of theoretical calculations and for understanding the active sites and the electron conduction paths separately. Therefore, we attempted to prepare nitrogen doped ZrOx nanofilms by RF magnetron sputtering method with different targets and atmospheres and to investigate their potential as model electrodes.ZrOx thin films of ca. 3-5 nm thickness were prepared by RF magnetron sputtering method using glassy carbon (GC) plates as substrates and ZrN or Zr metal plates as targets under Ar, Ar+O2 and Ar+N2. The sputtering power, the deposition time, and the substrate heating temperature were 100 W, 10 min, and 300 ℃, respectively. The flow rates of Ar, O2, and N2 gas were controlled to keep the total chamber pressure at approximately 0.6 Pa. When the gases were mixed, the partial pressure ratio was set to 1:1. Electrode prepared with a ZrN target in Ar was denoted as "ZrN_Ar", and electrodes prepared with a Zr target in Ar:O2 and Ar:N2 were denoted as "Zr_Ar+N2" and "Zr_Ar+O2", respectively. A conventional three-electrode cell was used for electrochemical measurements with Reversible Hydrogen Electrode (RHE) as a reference and a GC plate as a counter electrode in 0.5 M sulfuric acid at 30 ℃. The oxygen reduction current density i ORR (geometric area standard) was calculated by subtracting the current in N2 from the current in O2.Figure 1 shows the effect of sputtering condition on potential-ORR current curves of the ZrOx thin film electrodes. For comparison, the result of the GC substrate only is also plotted as "GC only." The ORR activity of the ZrN_Ar was lower than that of the GC only. In addition, the current of the steady-state cyclic voltammogram of the ZrN_Ar was smaller than that of the GC only. This may be due to the electrochemical oxidation of ZrN surface and the formation of an insulating layer without active sites, presumably Zr hydroxide. On the other hand, the onset potential of the Zr_Ar+N2 and the Zr_Ar+O2 for the ORR were higher than that of the GC only and the Zr_Ar+N2 showed highest ORR activity. The steady-state cyclic voltammograms of the Zr_Ar+N2 and the Zr_Ar+O2 were larger than that of GC only, revealing that these electrodes might have high conductivities. In addition, XPS measurements suggest that the Zr_Ar+N2 contains nitrogen and the Zr_Ar+N2 and the Zr_Ar+O2 have oxygen vacancies. These results suggested that their high ORR activities were caused by nitrogen doping and oxygen defects. Therefore, the electrodes prepared by RF magnetron sputtering method may be able to separate the active sites from the electron conduction by changing the sputtering conditions such as film thickness.AcknowledgementThe authors thank the financial support of the New Energy and Industrial Technology Development Organization (NEDO).References(1) A. Ishihara et al., J. Phys. Chem. C, 123, 18150 (2019).(2) M. Chisaka et al., ACS Omega, 2, 678 (2017).(3) S. Muhammady et al., J. Phys. Chem. C, 126, 15662 (2022). Figure 1

Ni50.8Ti49.2 alloy prepared by double-wire + arc additive manufacturing with a substrate heating temperature of 600 °C

In this study, a Ni50.8Ti49.2 single-walled component was prepared in-situ using double-wire + arc additive manufacturing using a substrate heated to 600 °C and TA1 and ER-Ni wires used as raw materials. The microstructure and properties of the component were thoroughly investigated. The results revealed that Ni4Ti3 precipitated mainly in spherical and needle-like forms, contributing to improved component strength through coherent strain strengthening and lattice distortion, respectively. The maximum hardness value reached an impressive 531 HV0.2. DSC curves showed distinct transformation temperatures: As = −24.8 °C, Af = 11.7 °C, Ms = 12.5 °C, and Mf = −28.1 °C. The presence of the precipitated phase altered the Ni content of the matrix, leading to overlapping peaks during the phase transformation process. After 15 cycles of compression, the component exhibited an unrecoverable strain approaching 1.75 %, demonstrating a certain degree of superelasticity.

Marangoni instability of an evaporating binary mixture droplet

Evaporation of a binary mixture droplet (BMD) is a common natural phenomenon and widely applied in many industrial fields. For the case of a sessile BMD being the only contact-line pinning throughout an entire evaporation, a theoretical model describing the evaporating dynamics is established when considering the comprehensive effect of evaporative cooling, the thermal Marangoni effect, the solutal Marangoni effect, the convection effect, and the Stefan flow. The dynamics of a binary ethanol–water droplet on a heated substrate is simulated using a cylindrical coordinate system. The reasons for Marangoni instability-driven flow (MIF) are discussed, and the influence of initial ethanol concentration and substrate heating temperature are examined. An evaporating BMD first forms a MIF at the contact line and quickly affects the whole droplet. Under the influence of the Marangoni instability, the BMD presents a complex internal flow structure with multiple-vortex and nonlinear temperature and ethanol concentration distributions. The positive feedback induced by vortices and the nonlinear distribution of concentration and temperature promotes the development of a MIF. At low initial ethanol concentrations, the MIF loses its driving force and turns into a stable counterclockwise single-vortex flow as ethanol evaporates completely. However, at high initial ethanol concentrations, the MIF exists in the entire evaporation. Increasing ethanol concentration and substrate heating temperature can delay the appearance of the MIF; ethanol concentration affects the MIF duration time, and heating temperature alters the MIF intensity. To enhance flow intensity and mass transfer of BMDs, the temperature difference should first be increased, followed by increased ethanol concentration.

Clean fabrication strategy of diamond crystals containing nanocomposite films for corrosion and wear protection of AISI-321 alloy

This study focused on the synthesis of Niobium/Hexagonal-Diamond/Amorphous-Carbon (Nb/H-D: a-C) films on AISI-321 alloy. The substrate heating used as a vital deposition parameter to tailor structure of the films in an unbalanced magnetron (UB-M) sputtering system for the first time. The substrate heater temperature (Th) ranged between (RT) to 150 °C. The results indicated that increasing the substrate heater temperature promoted the abundance of hexagonal diamond (H-Diamond) crystals through the solid phase separation. Therefore, the film deposited at the highest temperature (150 °C) demonstrated the highest plenty of H-Diamond. Electrochemical impedance spectroscopy (EIS) measurements (after 2, 8, 24, 72, and 168 h immersion) and polarization tests (after 168 h immersion) disclosed that increasing the substrate heater temperature positively affects the corrosion resistance of (Nb/H-D: a-C) films. The results proved that the film deposited at the highest temperature of 150 °C, demonstrated the exceptional corrosion protection efficiency of 99.69 %. Moreover, this film presented acceptable low-frequency impedance (|Z|10KHz) and total resistance (Rt) values of >108 Ω·cm2 and >117 MΩ·cm2 at all immersion times in 3.5 wt% NaCl solution. The highest abundance of the H-Diamond phase, with remarkable chemical inertness at higher substrate heater temperatures, can be an effective reason for elevating anti-corrosion performance of the films. Additionally, as the substrate heater temperature enhanced from RT to 150 °C, mechanical properties illustrated an remarkable increment trend (increasing hardness from 20 to 32.7 GPa and the elasticity modulus from 407 to 470 GPa). Moreover, the anti-wear performances of the films significantly improved with increasing substrate heater temperature, reducing the wear rate from 9.4 × 10−6 to 9 × 10−7 mm3/N·m. These results are mainly attributed to the highest abundance of the superhard H-Diamond phase in the film deposited at higher substrate heater temperature. In conclusion, the (Nb/H-D: a-C) film synthesized at 150 °C represented a promising candidate for tailoring the electrochemical and anti-wear performances of AISI-321 alloy.

Nanocrystalline gallium nitride electron transport layer for cesium lead bromide photovoltaic power converter in blue light optical wireless power transmission

Nanocrystalline gallium nitride (nc-GaN) layers were deposited by RF magnetron sputtering for the electron transport layer of the cesium lead bromide (CsPbBr3) photovoltaic power converter. We investigated the structural and electrical properties of the nc-GaN layers and found that substrate heater temperature is a key factor to determine the electrical conductivity of the nc-GaN layers. CsPbBr3 photovoltaic power converters with nc-GaN electron transport layers show good photovoltaic performance. The best performance was obtained at the substrate heater temperature of 550 °C and a conversion efficiency of 5.56% (V OC = 1.24 V, J SC = 6.68 mA cm−2, FF = 0.66) under AM1.5 G illumination with a light intensity of 100 mW cm−2. The estimated conversion efficiency under blue light with a wavelength of 450 nm is 28.8%.

Effects of a simulated high-energy space environment on a LaF3/MgF2 multilayer

Due to their low absorption, the LaF3/MgF2 material pair is widely used in the far-ultraviolet space payload. In the space environment, there are plenty of energetic particles (electrons, protons, γ rays, and atomic oxygen) and strong ultraviolet lines. These energetic particles penetrate into the films, and may change the materials’ physical and chemical structures. Hence, these energetic particles and ultraviolet lines may degrade the performance of LaF3/MgF2. We examined the effect of a simulated high-energy space environment on a LaF3/MgF2 multilayer. Dendritic patterns were observed in LaF3/MgF2 multilayer irradiated by the 30 keV electrons. The generation mechanism was proposed. This pattern was gradient wrinkle delamination due to the electric discharge, and it was non-uniform, asymmetric. This problem can be avoided by decreasing the substrate heating temperature and lay number (total thickness), and choosing the fluoride material substrate. The LaF3/MgF2 multilayer demonstrated no changes after the irradiation of the protons, γ rays, atomic oxygen, and ultraviolet lines.

Pinholes in Al/MgF2.

Pinholes in A l/M g F 2 were first inferred by the transmittance enhancement in Larruquert group's research. However, no direct proof was reported to verify the existence of the pinholes in A l/M g F 2. In the past 80years, pinholes were first observed by dark-field microscopy and bright-field microscopy in the transmission mode. They were small and on the order of several hundred nanometers to several micrometers. Essentially, the pinhole was not a real hole, partially because of the lack of the Al element. Increasing the thickness of Al cannot reduce the size of the pinholes. The occurrence of the pinholes was dependent on the deposition rate of the Al film and the substrate heating temperature, and it was independent of the substrate materials. This research eliminates an otherwise easily ignored scattering source, and it will benefit the development of ultra-precise optics, including mirrors for gyro-lasers, the detection of gravitational waves, and coronagraph detection.

Uniaxial in-plane magnetic anisotropy mechanism in Ni, Fe, and Ni-Fe alloy films deposited on single crystal Y-cut 128° LiNbO3 using magnetron sputtering

We investigated the mechanism of induced in-plane uniaxial magnetic anisotropy (Ku) in Nickel (Ni), Iron (Fe), and Ni-Fe alloy films deposited in situ on a single-crystal 128° Y-cut LiNbO3 (LNO) substrate at various substrate heating temperatures (Th) in the range 30–400 °C through radio frequency magnetron sputtering or co-sputtering. The results show that the Ku values for the Ni, Fe, and Ni-Fe alloy films are induced in the (01.2) or (21¯.0) planes of the LNO substrate. The highest value of Ku for the Ni films was observed at Th = 200 °C, which is owing to the increased orientation of the fcc Ni (311) plane. The Ni film with thickness t ∼ 20 nm deposited on the LNO substrate at Th = 200 °C possesses the highest value of Ku. Density functional theory calculations show that the magnetic anisotropic energy on the fcc Ni (311) plane differs depending on the magnetization direction in the in-plane direction in the model. Meanwhile, the value of Ku for the Fe films decreases with an increase in the value of Th because the films with higher Th are polycrystalline and have an oxide layer. The composition dependence of Ku for Ni-Fe alloy films at Th = 30 °C shows a trend similar to the crystal magnetic anisotropy for bulk Ni-Fe alloy. The induced Ku on LNO is attributed to the magnetostriction effect with the change in the crystal orientation of the ferromagnetic metal owing to a strain from the LNO substrate through the thermal expansion during sputtering. These results indicate the origin of the induced Ku in the Ni and Fe based metallic material films deposited on the LNO substrate.

(Digital Presentation) Oxygen Evolution Reaction on Non-Precious Metal Oxide-Based Electrocatalysts With and Without Low Potential Scan in Acidic Solution

Hydrogen energy ministerial meeting (H2 EM 2021) was held on Oct. 4, 2021 by the ministry of economy, trade and industry (METI) of Japanese government as online special event with cabinet members and officials from 29 countries, regions, and organizations. In the industrial session, 4 sessions were held, and the water electrolysis was one of the themes of industrial session. Panelists from several countries introduced state-of-art technologies of water electrolyzer [1]. In our previous study, the hydrogen producing from renewable energies is called as “Green Hydrogen” [2].Proton exchange membrane water electrolysis (PEMWE) has partly commercialized and recently applied its system for the Power-to-Gas (PtG). However, conventional anode is precious metal oxide such as IrO2 and the cost of raw material is expensive. From this point of view, the non-precious metal oxide anode should be required for green hydrogen production. We focused on tantalum and molybdenum oxide-based electrocatalyst (TaOx and MoOx) and have studied its catalytic activity for oxygen evolution reaction (OER) [3]. Moreover, TaOx with Mn addition showed much higher the OER activity than TaOx [4]. In this study, we have applied for MoOx with Mn addition for investigating the catalytic activity for the OER in acidic solution.Ti rod was used as substarate. MoOx was prepared by RF magnetron sputtering method. In the case of fabrication for Mn-MoOx, Mo metal piece for 40% surface area was set on the Mn disc as additional material. Each partial pressure of Ar and O2 gas was adjusted to 0.15 Pa in fabrication of Mn-MoOx. The substrate heating temperature was constant at 673 K during sputtering. We used conventional three electrode cell with each sample as working electrode while the reversible hydrogen electrode (RHE) and carbon plate were used as reference and counter electrode to demonstrate the electrochemical measurement in 1 M H2SO4 solution with saturated nitrogen atmosphere at 303 K. Several samples were demonstrated pretreatment from 0.05 to 1.2 V vs. RHE before the measurement of OER. The slow scan voltammetry was performed from 1.2 to 2.0 V to evaluate the OER activity. We also carried out electrochemical impedance spectroscopy (EIS) to obtain resistance components and semiconducting properties. In addition, samples before and after electrochemical measurement were analyzed by SEM-EDX and XPS.Figure 1 shows the Tafel plots of OER on Mo oxide-based electrocatalysts with and without Mn addition. The current density was based on geometric surface area. In the case of sample performing pretreatment, the Mn-MoOx with pretreatment (Mn-MoOx(Pre)) has obviously higher OER current than MoOx with pretreatment (MoOx(Pre)). Moreover, Mn-MoOx has higher OER current than Mn-MoOx(Pre), and the Tafel slope of OER on Mn-TaOx was 79 mV dec-1 the while the that on the Mn-MoOx(Pre) was 147 mV dec-1. From the results of EIS, the charge transfer resistance of Mn-MoOx was much smaller than that of Mn-MoOx(Pre) while the film resistance of was similar to that of Mn-MoOx(Pre). The results from SEM-EDX revealed that Mn amount in Mn-MoOx after the electrochemical measurement was constant compared to that before electrochemical measurement while Mn amount in Mn-MoOx(Pre) after electrochemical measurement was decreased compared to that before electrochemical measurement. From results from XPS analysis, Mn ratio in the Mn-MoOx after electrochemical measurement was constant compared to that before electrochemical measurement while Mn amount in Mn-MoOx(Pre) after electrochemical measurement was decreased compared to that before electrochemical measurement. Therefore, Mn species still remained on both surface and bulk in the case of Mn-MoOx while it was decreased in the case of Mn-MoOx(Pre). In Fig. 1, The peak over 1.5 V was detected from Tafel plots of both Mn-MoOx and Mn-MoOx(Pre). This peak corresponded to redox peak of Mn(III)/Mn(IV) [5], and it implied that Mn species affected on the OER activity. However, the electric charge of Mn(III)/Mn(IV) of Mn-MoOx was smaller than that of Mn-MnOx(Pre), and it is suggested that not only Mn oxide but also other species such as Mn-Mo compound oxide reacts as an active site of OER on Mn-MoOx.Acknowledgement: This work is partially supported by the Suzuki Foundation.Reference https://www.meti.go.jp/english/press/2021/1008_001.html Ota, A. Ishihara, K. Matsuzawa, and S. Mitsushima, Electrochemistry, 78, 970 (2010). Matsuzawa, S. Hirayama, K. Sumi, A. Ishihara, Abst. PRiME2020, I01F-2492, Online (2020). Matsuzawa, S. Hirayama, Y. Kohara, and A. Ishihara, ECS Trans, 104(8), 431 (2021).M. Morita, C. Iwakura, and H. Tamura, Electrochim. Acta, 24, 357 (1979). Figure 1

Enhancement of Adhesion and Antibending Performance of Ag Circuit on Polyimide Fabricated by Heat‐Assisted Direct Ink Writing Method

Herein, flexible circuits with enhanced adhesion and antibending resistance are fabricated by heat‐assisted direct ink writing. The experimental parameters are explored under different nozzle sizes, angles, heights, direct writing speeds, and heating temperatures by selecting an appropriate extrusion speed. The solvent evaporation caused by heating temperature enables the metal particles to densify quickly to form a conductive path. This method is suitable for fabricating devices on polyimide (PI) with appropriate direct writing parameters and is simple to operate. A flexible Ag circuit with a resistivity of 4.31 × 10−8 Ω m and good resistance after 20 000 consecutive bending cycles is fabricated with a nozzle size of 32G, a nozzle height of 10 μm, a nozzle angle of 90°, an extrusion speed of 5 μm min−1, a substrate heating temperature of 70 °C, and a direct writing speed of 1 mm s−1. Large‐area complex flexible display LED arrays are fabricated using thermally assisted direct ink writing.

Influence of temperatures on structure, thermoelectric, and mechanical properties of nanocrystalline SnSe thin films deposited by thermal evaporation

The Tin Selenide (SnSe) thermoelectric materials’ high heat-electricity inter-conversion capability makes it a potential energy resource material to tap the waste heat from different industrial processing. The present work has optimized parameters for the deposition of single-phase nanocrystalline SnSe thin films using the thermal evaporation technique. The XRD, Raman Spectroscopy, SEM, EDS, Seebeck Coefficient, Electrical Conductivity, and Thermal Conductivity data analyses were used to optimize and establish the structure-thermoelectric property relationship for nanocrystalline SnSe films. The phase analysis of the SnSe thin films deposited at various substrate heating temperatures (Ts) reveals a significant influence of Ts in the evolution of a single phase of SnSe film. The films deposited at Ts ≤ 200 °C evolved with the phases of Sn, Se, and SnSe, whereas films deposited at Ts ≥ 300 °C grew with single-phase polycrystalline SnSe. An increase in crystallite size with a shape transformation from circular to elongated grains was observed with Ts. The maximum ZT value of 0.64 with a power factor value of ~2.2 μWcm-1K-2 at 750 K measuring temperature (Ta) was obtained for the SnSe film deposited at Ts = 300 °C. The change in thermoelectric properties with Ta, including a p-type to n-type transition observed at ~600 K, was correlated with the alteration of structure and the elemental composition of the deposited films after heating at 350 °C. The heating temperature significantly influenced the hardness and elastic modulus values of the films deposited at Ts ≤ 300 °C.

НИЗЬКОТЕМПЕРАТУРНА ІОННО-ПЛАЗМОВА ТЕХНОЛОГІЯ ОСАДЖЕННЯ НАНОСТРУКТУРОВАНИХ ПЛІВОК НІТРИДУ АЛЮМІНІЮ ТА БОРУ

A low-temperature (substrate heating temperature up to 400 °C) ion-plasma technology for the formation of nanostructured AlN and BN films by the method of high-frequency reactive magnetron sputtering of the corresponding targets has been developed (the modernized installation "Cathode-1M"), which has in its technological cycle the means of physical and chemical modification, which allow to purposefully control the phase composition, surface morphology, size and texture of nanocrystalline films. The possibility of using the method of high-frequency magnetron sputtering for deposition of transparent hexagonal BN films in the nanoscale state on quartz and silicon substrates is shown. Atomic force microscopy (AFM) has shown that AlN films can have an amorphous or polycrystalline surface with grain sizes of approximately 20-100 nm, with the height of the nanoparticles varying from 3 to 10 nm and the degree of surface roughness from 1 to 10 nm. It was found that the dielectric penetration of polycrystalline AlN films decreases from 10 to 3.5 at increased frequencies from 25 Hz to 1 MHz, and the peak tangent of the dielectric loss angle reaches 0.2 at 10 kHz. Such features indicate the existence of spontaneous polarization of dipoles in the obtained AlN films. Interest in dielectric properties in AlN / Si structures it is also due to the fact that there are point defects, such as nitrogen vacancies and silicon atoms, which diffuse from the silicon substrate during synthesis and play an important role in the dielectric properties of AlN during the formation of dipoles. The technology makes it possible, in a single technological cycle, to produce multilayer structures modified for specific functional tasks with specified characteristics necessary for the manufacture of modern electronics, optoelectronics and sensorics devices. It should also be noted that the technology of magnetron sputtering (installation "Cathode-1M") is highly productive, energetically efficient and environmentally friendly in comparison with other known technologies for creating semiconductor structures and allows them to be obtained with minimal changes in the technological cycle.

The Impact of Mn addition on Ta Oxide-Based Electrocatalysts for Oxygen Evolution Reaction in Acid

Hydrogen energy ministerial meeting (H2 EM 2020) was held on Oct. 14, 2020 by the ministry of economy, trade and industry (METI) of Japanese government as online special event with cabinet members and officials from 23 countries, regions, and organizations. In the open session, presenter from industrial company of water electrolysis introduced to improve its technologies for producing hydrogen from renewable energies [1]. In our previous study, the hydrogen producing from renewable energies is called as “Green Hydrogen” [2].Polymer electrolyte water electrolysis (PEWE) has partly commercialized and recently applied its system for the Power-to-Gas (PtG). However, conventional anode is precious metal oxide such as IrO2 and the cost of raw material is expensive. Moreover, it is reported that the IrO₂ is afraid to cause the degradation operating by variable renewable energy (VRE) because the catalytic activity of oxygen evolution reaction became lower by potential cycling of VRE simulation [3]. From this point of view, the non-precious metal oxide anode with high durability against VRE should be required for green hydrogen production. We focused on tatanium oxide-based electrocatalyst (TaOx) and have studied its catalytic activity for oxygen evolution reaction (OER) [4]. In this study, we have investigated the catalytic activity of TaOx with and Mn addition for the OER in acidic solution.Ti rod was used as substarate. TaOx was prepared by RF magnetron sputtering method. In the case of fabrication for Mn-TaOx, Ta metal piece for 60% surface area was set on the Mn disc as additional material. Each partial pressure of Ar and O2 gas was adjusted to 0.23 Pa in fabrication of Mn-TaOx. The substrate heating temperature was constant at 673 K during sputtering. We used conventional three electrode cell with each sample as working electrode while the reversible hydrogen electrode (RHE) and carbon plate were used as reference and counter electrode to demonstrate the electrochemical measurement. In order to evaluate the OER activity of samples, the slow scan voltammetry was performed from 1.2 to 2.5 V vs. RHE in 1 M H2SO4 solution with saturated nitrogen atmosphere at 303 K. We also carried out electrochemical impedance spectroscopy (EIS) to obtain resistance components and semiconducting properties.Figure 1 shows the polarization curve of OER on Ta oxide-based electrocatalysts with Mn addition. The results of Ti oxide-based electrocatalysts with Mo addition (Mo-TiOx) that is our past study [4] is also shown in this figure. The current density was based on geometric surface area. According to figure, the Mn-TaOx has obviously higher OER current than that on Mo-TiOx, and the Tafel slope of OER on Mn-TaOx was 105 mV dec-1 the while the that on the Mo-TiOx was 91 mV dec-1. The peak over 1.5 V was detected from polarization curve of Mn-TaOx in Fig. 1. This peak corresponded to Mn ion, and it suggests that Mn species affected on the OER activity while the amounts of Mn on the sample after electrochemical measurement showed below detection limit from XPS analysis. According to these results, the surface of Mn-TaOx was consisted of Ta oxide mainly with very few amount of Mn after electrochemical measurements. From the results of EIS, resistances of film and charge transfer on Mn-TaOx were lower than that of Mo-TiOx. In addition, the slope of Mott-Schottky plots on the Mn-TaOx was much gentle than that on the Mo-TiOx, and it means that the carrier concentration in Mn-TaOx was higher than that in Mo-TiOx. Therefore, the reason why the Mn-TaOx showed higher OER current than the Mo-TiOx is that both factors of electrical conductivity and catalytic activity were improved.Acknowledgement: This work is partially supported by Toyota Mobility Foundation and ENEOS Tonen General Research / Development Encouragement & Scholarship Foundation.Reference https://www.meti.go.jp/english/press/2020/1015_001.htmlK. Ota, A. Ishihara, K. Matsuzawa, and S. Mitsushima, Electrochemistry, 78, 970 (2010).S. M. Alia, and G. C. Anderson, J. Electrochem. Soc., 166, F282 (2019).K. Matsuzawa, S. Hirayama, K. Sumi, A. Ishihara, Abst. PRiME2020, I01F-2492, Online (2020). Figure 1

Time saving technique for studying thermal processes in magnetron sputtering of titanium target

The kinetics of thermal processes on a substrate during magnetron sputtering of a titanium target has been studied. A technique is proposed for reducing the time of the substrate heating temperature measurement, which is useful in performing extensive experiments in multifactorial problems. The selection criterion for the duration of the observation interval can be the relative error in extrapolating the stationary temperature of the substrate. The technique is universal in nature and allows to reduce the time of a single experiment by a factor of 2 - 3 with an error of no more than 5%.

Out-of-Plane Thermal Expansion Coefficient and Biaxial Young’s Modulus of Sputtered ITO Thin Films

This paper proposes a measuring apparatus and method for simultaneous determination of the thermal expansion coefficient and biaxial Young’s modulus of indium tin oxide (ITO) thin films. ITO thin films simultaneously coated on N-BK7 and S-TIM35 glass substrates were prepared by direct current (DC) magnetron sputtering deposition. The thermo-mechanical parameters of ITO thin films were investigated experimentally. Thermal stress in sputtered ITO films was evaluated by an improved Twyman–Green interferometer associated with wavelet transform at different temperatures. When the heating temperature increased from 30 °C to 100 °C, the tensile thermal stress of ITO thin films increased. The increase in substrate temperature led to the decrease of total residual stress deposited on two glass substrates. A linear relationship between the thermal stress and substrate heating temperature was found. The thermal expansion coefficient and biaxial Young’s modulus of the films were measured by the double substrate method. The results show that the out of plane thermal expansion coefficient and biaxial Young’s modulus of the ITO film were 5.81 × 10−6 °C−1 and 475 GPa.

Просветляющие покрытия на основе ZnO, полученные методом электронно-лучевого испарения

In this work, research was carried out to analyze the possibility to fabricate nanostructured antireflection coatings based on ZnO. The dependence of structural features of the film on the substrate heating temperature during deposition of an aluminum-doped zinc oxide (AZO) has been studied. It is shown that it is impossible to obtain the required structural properties of the film by changing one parameter, the substrate temperature during deposition of the material, in the range of 20 – 600 °C. For this purpose, an approach has been suggested, which consists in preliminary deposition of a nanometer-thick Sn layer with subsequent substrate heating up to the temperature of deposition of the main material layer. The optimization of coating deposition conditions led to the fabrication of a medium consisting of many whiskers with transverse dimensions of tens of nanometers and a length of hundreds of nanometers, which are oriented mainly perpendicular to the substrate. It is shown that the gradient nature of a change in the material density, and, hence, in the effective refractive index in the direction perpendicular to the substrate plane, provides antireflection properties of the coating over a wide range of wavelengths as well as in different directions of light propagation.

Temperature Effect of Low-Damage Plasma for Nitrogen-Modification of Graphene

This work investigates temperature effects of low-damage plasma (LD plasma) treatment for nitrogen-modification graphene. Different from traditional nitrogen-modification graphene achieved by ammonia plasma, in this work, it is accomplished by the LD plasma with pure nitrogen. The analyses of Raman and XPS spectra show that the concentration of modified nitrogen raised with the substrate temperature from room temperature to 125 °C. However, the decrease of nitrogen-modification ratio occurred as the substrate heating temperature higher than 150 °C. This might be resulted from the diffusion mechanism of ion species away from the graphene surface. Observed from these experimental results, the highest nitrogen doping ratio on artificial-stacked graphene bilayers (ASGBs) sample occurred at the substrate-heating temperature of 125 °C. Based on the developed method, advantages of nitrogen-modification graphene with less contamination can be achieved for further applications.

Oxygen Evolution Reaction of Mo Oxide-Based Electocatalysts Doped with Different Metals in Acid Solution

At end of February in 2020, Fukushima Hydrogen Energy Research Field (FH2R) has started to operate with a renewable energy-powered 10MW-class hydrogen production unit, which is the largest-class in the world. These kinds of “Green Hydrogen” [1] production technologies will be accelerated not only in Japan but also all over the world because “Global Action Agenda” was released and many presentations were also given by international organizations in Hydrogen energy ministerial meeting (H2 EM 2019) which was held in Tokyo, last year with cabinet members and officials from 35 countries, regions, and organizations.In FH2R, the newest system of water electrolysis has installed. In Japan, not only alkaline water electrolysis (AWE) but also polymer electrolyte water electrolysis (PEWE) have been developed. Compared with AWE, PEWE is partly commercialized procedure to produce the hydrogen with high purity. However, one of the issue of PEWE is iridium oxide (IrO2) anode that is one of the precious metal oxide with poor resources. In order to utilize the PEWE system applying for green hydrogen production in large scale with low cost, we focused on the molybdenum-oxide based electrocatalyst (MoOx) as alternative anode materials because of its low cost compared with precious metal oxide [2-4]. In this study, we have investigated the catalytic activity of oxygen evolution reaction (OER) on MoOx with and without doping.Ti rod was used as substarate. Mo oxide-based electrocatalyst was prepared by RF magnetron sputtering method. Mo disc was used as the sputtering target. In the case of fabrication for Zr- and Ta-MoOx, Zr or Ta piece for 10% surface area was set on the Mo disc as doping material. Each partial pressure of Ar and O2 gas was adjusted to 0.23 Pa in fabrication of MoOx, Zr-MoOx and Ta-TiOx. The substrate heating temperature was constant at 673 K during sputtering. We used conventional three electrode cell with each sample as working electrode while the reversible hydrogen electrode (RHE) and carbon plate were used as reference and counter electrode to demonstrate the electrochemical measurement. In order to evaluate the OER activity of samples, the slow scan voltammetry was performed from 1.2 to 2.5 V vs. RHE in 1 M H2SO4 solution at 303 K. We also carried out electrochemical impedance spectroscopy (EIS) to obtain resistance components and semiconducting properties.Figure 1 shows the slow scan voltammograms of OER on Zr-MoOx, Ta-MoOx, and MoOx. The Zr-MoOx in this study have larger current densities than that of Ta-MoOx and MoOx. It was found that that Zr doping was effective for enhancing the OER activity of MoOx. According to Mott-Schottky plots, all samples whether doping or non-doping showed n-type semiconductor while flat band potential of Zr-MoOx was smaller than that of Ta-MoOx and MoOx.Acknowledgement: This work is partially supported by Toyota Mobility Foundation.Reference K. Ota, A. Ishihara, K. Matsuzawa, and S. Mitsushima, Electrochemistry, 78, 970 (2010).S. Hirayama, A. Ishihara, K. Sumi, K. Ota, and K. Matsuzawa, Proc. 39th Symp. Hydrogen Ener. Syst Soc Jpn (HESS), p.99 (2019) (in Japanese).K. Matsuzawa, K. Sumi, S. Hirayama, Y. Kuroda, S. Mitsushima, K. Ota and A. Ishihara, Abst. 237th ECS Meeting, I02-1551 (2020).S. Hirayama, A. Ishihara, K. Sumi, and K. Matsuzawa, Proc. 27th FCDIC Fuel Cell Symp., P9 (2020) (in Japanese). Figure 1