研究者詳細 - 石川　健治

論文 - 石川　健治

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Effects of Plasma Ions/Radicals on Kinetic Interactions in Nanowall Deposition: A Review 査読有り

Ishikawa, K

ADVANCED ENGINEERING MATERIALS 26 巻 ( 16 ) 頁： 2400679 2024年8月

担当区分：筆頭著者,　最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Engineering Materials

Recent advances in the growth of carbon nanowalls (CNWs) and vertical graphene nanosheets using various plasma-enhanced chemical vapor deposition (PECVD) methods are reviewed in this article. Growth methods are classified into hot- and cold-wall reactors equipped with diverse plasma generation systems, and their respective characteristics are summarized, with particular attention to the behavior of reactive species, such as ions and radicals, generated within the plasma. Recent progress in this research domain is outlined for each method, and an organized account of the chemical kinetic phenomena occurring within the plasma is provided. Finally, future perspectives are discussed. Fundamental data are obtained through real-time in situ measurements of ions and radicals, and the construction of a database from these data offers microscopic insights that significantly enhance processing outcomes for macroscopically controlling the mechanical shapes and chemical properties of CNWs.

DOI： 10.1002/adem.202400679

Future of plasma etching for microelectronics: Challenges and opportunities 査読有り国際共著

Oehrlein, GS; Brandstadter, SM; Bruce, RL; Chang, JP; Demott, JC; Donnelly, VM; Dussart, R; Fischer, A; Gottscho, RA; Hamaguchi, S; Honda, M; Hori, M; Ishikawa, K; Jaloviar, SG; Kanarik, KJ; Karahashi, K; Ko, AKTR; Kothari, H; Kuboi, N; Kushner, MJ; Lill, T; Luan, PS; Mesbah, A; Miller, E; Nath, S; Ohya, Y; Omura, M; Park, C; Poulose, J; Rauf, S; Sekine, M; Smith, TG; Stafford, N; Standaert, T; Ventzek, PLG

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 42 巻 ( 4 ) 頁： 041501 2024年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Vacuum Science and Technology B

Plasma etching is an essential semiconductor manufacturing technology required to enable the current microelectronics industry. Along with lithographic patterning, thin-film formation methods, and others, plasma etching has dynamically evolved to meet the exponentially growing demands of the microelectronics industry that enables modern society. At this time, plasma etching faces a period of unprecedented changes owing to numerous factors, including aggressive transition to three-dimensional (3D) device architectures, process precision approaching atomic-scale critical dimensions, introduction of new materials, fundamental silicon device limits, and parallel evolution of post-CMOS approaches. The vast growth of the microelectronics industry has emphasized its role in addressing major societal challenges, including questions on the sustainability of the associated energy use, semiconductor manufacturing related emissions of greenhouse gases, and others. The goal of this article is to help both define the challenges for plasma etching and point out effective plasma etching technology options that may play essential roles in defining microelectronics manufacturing in the future. The challenges are accompanied by significant new opportunities, including integrating experiments with various computational approaches such as machine learning/artificial intelligence and progress in computational approaches, including the realization of digital twins of physical etch chambers through hybrid/coupled models. These prospects can enable innovative solutions to problems that were not available during the past 50 years of plasma etch development in the microelectronics industry. To elaborate on these perspectives, the present article brings together the views of various experts on the different topics that will shape plasma etching for microelectronics manufacturing of the future.

DOI： 10.1116/6.0003579

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

Minh, NQ; Van Nong, N; Oda, O; Ishikawa, K; Hori, M

VACUUM 224 巻頁： 113180 2024年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Vacuum

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.

DOI： 10.1016/j.vacuum.2024.113180

Epitaxial growth of high-quality GaN with a high growth rate at low temperatures by radical-enhanced metalorganic chemical vapor deposition 査読有り

Dhasiyan, AK; Amalraj, FW; Jayaprasad, S; Shimizu, N; Oda, O; Ishikawa, K; Hori, M

SCIENTIFIC REPORTS 14 巻 ( 1 ) 頁： 10861 2024年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

Using our recently developed radical-enhanced metalorganic chemical vapor deposition (REMOCVD) technique, we have grown gallium nitride (GaN) on bulk GaN and GaN on Si templates. Three features make up this system: (1) applying very high-frequency power (60 MHz) to increase the plasma density; (2) introducing H<inf>2</inf> and N<inf>2</inf> gas in the plasma discharge region to produce active NH<inf>x</inf> radical species in addition to nitrogen radicals; and (3) supplying radicals under remote plasma arrangement with a Faraday cage to suppress charged ions and photons. Using this new REMOCVD system, it was found that high-quality crystals can be grown at lower temperatures than that of MOCVD but the disadvantage was that the growth rate was smaller as 0.2–0.8 μm/h than that by MOCVD. In the present work, we have used a pBN inner shield to prevent the deactivation of radicals to increase the growth rate. The growth conditions such as the plasma power, trimethylgallium (TMG) source flow rate, N<inf>2</inf> + H<inf>2</inf> gas mixture flow rate, and the ratio of N<inf>2</inf>/H<inf>2</inf> were optimized and it was found that the growth rate could be increased up to 3.4 μm/h with remarkably high crystalline quality comparable to that of MOCVD. The XRD-FWHM of GaN grown on the GaN/Si template and the bulk GaN substrate were 977 arcsec and 72 arcsec respectively. This work may be very promising to achieve high-power GaN/GaN devices.

DOI： 10.1038/s41598-024-61501-9

<i>In situ</i> atom-resolved observation of Si (111) 7x7 surface with F radical and Ar ion irradiation simulated atomic layer etching 査読有り

Tsutsumi, T; Asano, A; Kondo, H; Ishikawa, K; Sekine, M; Hori, M

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 42 巻 ( 3 ) 頁： 032603 2024年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Vacuum Science and Technology A Vacuum Surfaces and Films

Ar ions with controlled energy and doses, along with radicals in CF<inf>4</inf> plasma, were irradiated separately onto a Si (111) 7 × 7 surface by using a plasma beam reactor. The crystal structure and the chemical bonds on the surface were analyzed by scanning tunneling microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy without air exposure of the samples. The SiF layer formed by F radical irradiation was completely removed by a desorption reaction induced by heating at 600 °C, resulting in an atomically flat surface that maintained the crystal structure. The 7 × 7 structure, which was reconstructed by each irradiation process alone, was not reconstructed because of the synergistic effects of F radicals and Ar ions in the cyclic CF<inf>4</inf>/Ar plasma used to simulate an atomic layer etching process. The cyclic CF<inf>4</inf>/Ar plasma process inhibited the reconstruction of the crystal structure by forming a mixture region that included Si, F, and C atoms.

DOI： 10.1116/6.0003432

Nitrogen admixture effects on growth characteristics and properties of carbon nanowalls 査読有り Open Access

Christy, PRD; Van Nong, N; Britun, N; Minh, NQ; Nguyen, TTN; Kondo, H; Oda, O; Ishikawa, K; Hori, M

THIN SOLID FILMS 795 巻頁： 140322 2024年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Thin Solid Films

The plasma functionalization of carbon nanowalls (CNWs) is of great interest due to their potential applications in electron field emission and energy storage devices. In this study, the effects of nitrogen on the growth and properties of CNWs are thoroughly investigated by varying a wide range of the N<inf>2</inf> concentrations in the CH<inf>4</inf>/H<inf>2</inf>/N<inf>2</inf> discharge plasma. Nitrogen-doped carbon nanowalls (N–CNWs) were synthesized in a single-step growth using the hydrogen radical injection plasma-enhanced chemical vapor deposition technique. The formation of dense N–CNWs was found to be enhanced by nitrogen and was three times higher in the sample with a 150 sccm N<inf>2</inf> flow rate than in the sample without N<inf>2</inf> addition (N-0). As the N<inf>2</inf> concentration increased from 0 to 200 sccm, the morphology of CNWs changed from relatively straight to curly-like nanowall structures. A high-resolution optical emission spectroscopic observation shows that as N<inf>2</inf> flow increased, CN radicals became the dominant species, suppressing the formation of C<inf>2</inf> and CH. Photoelectron spectroscopy analysis revealed the nitrogen doping effect on graphene layers at high N<inf>2</inf> concentrations. According to Raman and Transmission Electron Microscopy analyses, the N–CNWs had more branched and thicker nanowalls with higher defect concentrations than the N-0 sample. The wettability of N–CNWs was improved, particularly for the sample with a N<inf>2</inf> flow rate of 150 sccm.

DOI： 10.1016/j.tsf.2024.140322

Dissociative properties of C<sub>4</sub>F<sub>6</sub> obtained using computational chemistry 査読有り

Hayashi, T; Ishikawa, K; Sekine, M; Hori, M

JAPANESE JOURNAL OF APPLIED PHYSICS 63 巻 ( 4 ) 頁： 04SP26 2024年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

The electronic properties of C<inf>4</inf>F<inf>6</inf> were investigated by using computational chemistry to clarify the dissociative channels in the process plasma. The results show the mainly ionized ion is C<inf>3</inf>F<inf>3</inf><sup>+</sup> (CF<inf>2</inf>=C=CF<sup>+</sup>; propargyl ion) which is observed in the mass spectrum with the electron energy of 70 eV, and the intermediate molecular structure to produce C<inf>3</inf>F<inf>3</inf><sup>+</sup> ion is methyl allene ion (CF<inf>2</inf>=C=CF-CF<inf>3</inf><sup>+</sup>). The molecular ion C<inf>4</inf>F<inf>6</inf><sup>+</sup> is also mainly produced in the ionization threshold region. For the excited states, the calculated results suggest that CF<inf>2</inf>CFCF + CF<inf>2</inf> dissociation takes place in the energy region higher than 7.0 eV and C<inf>2</inf>F<inf>3</inf> + C<inf>2</inf>F<inf>3</inf> dissociation takes place in the energy region higher than 8.0 eV. In the electron attachment process, the vertical electron attachment energy was calculated as 1.1 eV and the nonadiabatic negative ion energy was −0.2 eV lower than the energy of neutral C<inf>4</inf>F<inf>6</inf>

DOI： 10.35848/1347-4065/ad3166

Inhibition of glutamine metabolism increases sensitivity to plasma-activated medium-induced cytotoxicity 査読有り

Tanaka, S; Hayashi, S; Otsuka, T; Kamiya, T; Ishikawa, K; Hara, H

FREE RADICAL RESEARCH 58 巻 ( 3 ) 頁： 170 - 179 2024年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Free Radical Research

Non-thermal atmospheric pressure plasma (NTP), an ionized gas containing electrons, ions, radicals, and photons, has various biological effects, including wound healing and anticancer effects. Plasma-activated medium (PAM), which is prepared by irradiating medium with NTP, preferentially kills cancer cells. Large amounts of reactive oxygen species (ROS) and reactive nitrogen species (RNS) included in PAM are closely related to its anticancer effects. The precise mechanism of PAM-induced cytotoxicity is not fully understood; however, PAM exposure has been reported to reduce cellular energy metabolism. Glutamine (Gln) is an important amino acid as an energy source in cancer cells. Gln is converted to glutamate by glutaminase (GLS), and is utilized to synthesize ATP and glutathione (GSH). Expression levels of GLS have been shown to be higher in certain types of cancers. In this study, we examined the effects of GLS inhibition on PAM cytotoxicity using breast cancer MDA-MB-231 cells. Pretreatment with BPTES, a glutaminase 1 (GLS1) inhibitor, dose-dependently enhanced PAM-induced cell death. PAM-induced ROS production and γ-H2AX formation, a DNA damage marker, were increased in cells pretreated with BPTES compared with PAM alone. BPTES pretreatment enhanced a PAM-induced decrease in intracellular GSH, indicating the possibility that BPTES reduces the antioxidant capacity of MDA-MB-231 cells. In addition, BPTES pretreatment enhanced PAM-induced loss of the mitochondrial membrane potential and reduction of ATP production. Moreover, GLS1 knockdown promoted PAM-induced cell death. Taken together, the combination of GLS1 inhibitors such as BPTES is considered to be useful for enhancing the cytotoxic effects of PAM against cancer cells.

DOI： 10.1080/10715762.2024.2332343

Plasma-Driven Sciences: Exploring Complex Interactions at Plasma Boundaries 査読有り Open Access

Ishikawa, K; Koga, K; Ohno, N

PLASMA 7 巻 ( 1 ) 頁： 160 - 177 2024年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Plasma

Plasma-driven science is defined as the artificial control of physical plasma-driven phenomena based on complex interactions between nonequilibrium open systems. Recently, peculiar phenomena related to physical plasma have been discovered in plasma boundary regions, either naturally or artificially. Because laboratory plasma can be produced under nominal conditions around atmospheric pressure and room temperature, phenomena related to the interaction of plasma with liquid solutions and living organisms at the plasma boundaries are emerging. Currently, the relationships between these complex interactions should be solved using science-based data-driven approaches; these approaches require a reliable and comprehensive database of dynamic changes in the chemical networks of elementary reactions. Consequently, the elucidation of the mechanisms governing plasma-driven phenomena and the discovery of the latent actions behind these plasma-driven phenomena will be realized through plasma-driven science.

DOI： 10.3390/plasma7010011

Elaborate cooperation of poly(rC)-binding proteins 1/2 and glutathione in ferroptosis induced by plasma-activated Ringer's lactate 査読有り

Jiang, L; Zheng, H; Ishida, M; Lyu, Q; Akatsuka, S; Motooka, Y; Sato, K; Sekido, Y; Nakamura, K; Tanaka, H; Ishikawa, K; Kajiyama, H; Mizuno, M; Hori, M; Toyokuni, S

FREE RADICAL BIOLOGY AND MEDICINE 214 巻頁： 28 - 41 2024年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Free Radical Biology and Medicine

Reactive species are involved in various aspects of neoplastic diseases, including carcinogenesis, cancer-specific metabolism and therapeutics. Non-thermal plasma (NTP) can directly provide reactive species, by integrating atmospheric and interjacent molecules as substrates, to represent a handy strategy to load oxidative stress in situ. NTP causes apoptosis and/or ferroptosis specifically in cancer cells of various types. Plasma-activated Ringer's lactate (PAL) is another modality at the preclinical stage as cancer therapeutics, based on more stable reactive species. PAL specifically kills malignant mesothelioma (MM) cells, employing lysosomal ·NO as a switch from autophagy to ferroptosis. However, the entire molecular mechanisms have not been elucidated yet. Here we studied cytosolic iron regulations in MM and other cancer cells in response to PAL exposure. We discovered that cells with higher catalytic Fe(II) are more susceptible to PAL-induced ferroptosis. PAL caused a cytosolic catalytic Fe(II)-associated pathology through iron chaperones, poly (rC)-binding proteins (PCBP)1/2, inducing a disturbance in glutathione-regulated iron homeostasis. PCBP1/NCOA4-mediated ferritinophagy started at a later phase, further increasing cytosolic catalytic Fe(II), ending in ferroptosis. In contrast, PCBP2 after PAL exposure contributed to iron loading to mitochondria, leading to mitochondrial dysfunction. Therapeutic effect of PAL was successfully applied to an orthotopic MM xenograft model in mice. In conclusion, PAL can selectively sensitize MM cells to ferroptosis by remodeling cytoplasmic iron homeostasis, where glutathione and PCBPs play distinct roles, resulting in lethal ferritinophagy and mitochondrial dysfunction. Our findings indicate the clinical application of PAL as a ferroptosis-inducer and the potential of PCBPs as novel targets in cancer therapeutics.

DOI： 10.1016/j.freeradbiomed.2024.02.001

液中プラズマによるナノグラフェンの高速合成と機能化 Open Access

石川健治, 堤隆義, 近藤博基, 堀勝, 平松美根男

表面と真空 67 巻 ( 2 ) 頁： 77 - 82 2024年2月

Surface sulfurization of amorphous carbon films in the chemistry of oxygen plasma added with SO2 or OCS for high-aspect-ratio etching 査読有り

Ishikawa, K; Nguyen, TTN; Aoki, Y; Sato, H; Kawakami, J; Tsuno, S; Hsiao, SN; Hori, M

APPLIED SURFACE SCIENCE 645 巻頁： 158876 2024年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Surface Science

Etching of oxygen-based plasmas with sulfur dioxide (SO<inf>2</inf>) or carbonyl sulfide (OCS) can form high-aspect-ratio (HAR) features of amorphous carbon films as carbon hard masks (CHM). The etched profiles showing shapes such as bowing or tapering are essentially dependent on the partial pressures of SO<inf>2</inf> or OCS in the O<inf>2</inf> plasma. The surface treated after the OCS-added plasma exhibited strong sulfurization by S<inf>2</inf> and CS species in S 2p of the X-ray photoelectron spectroscopy (XPS). The gas-phase interactions in the sulfur-oxygen-carbon system generated atoms and molecules, such as O, O<sup>+</sup>, and O<inf>2</inf><sup>+</sup>, which etched at the bottom and, conversely, SO, CO, CS, CS<inf>2</inf>, and S<inf>2</inf>, which inhibited isotropic etching at the sidewalls of the HAR features. The chemical reactions of the CS sulfurizing precursors in the gas phase were monitored by comparing their optical emission intensities at a wavelength of 257 nm with those of SO<inf>2</inf> at approximately 320 nm. The optimization of the HAR profiles of the CHM can be controlled by sidewall sulfurization of the CHM to obtain desirable profile shapes for the HAR features.

DOI： 10.1016/j.apsusc.2023.158876

Oxygen radical irradiation transforms an organic fertilizer L-tryptophan into an environment and human-friendly bactericide 査読有り

Iwata, N; Ishikawa, K; Nishikawa, Y; Kato, H; Shimizu, M; Kato, M; Tanaka, H; Ito, M; Hori, M

ENVIRONMENTAL TECHNOLOGY & INNOVATION 33 巻頁： 103496 2024年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Environmental Technology and Innovation

Organic fertilizers are useful in hydroponic agriculture to bring about a sustainable society with minimal pollution. Irradiation of L-tryptophan (L-Trp) solutions with electrically neutral atomic oxygen produces immediate bactericidal activity. After oxygen radical irradiation of an L-Trp-containing Escherichia coli suspension at pH 6.3 for 5 min, a colony-forming unit assay showed a 6-log reduction in the number of surviving E. coli. Kynurenine and N’-formylkynurenine were identified as irradiation products in the solution using liquid chromatography–mass spectroscopy and nuclear magnetic resonance spectroscopy. Tryptophan radicals (Trp•) are precursors of kynurenine and N’-formylkynurenine and are detected using spin-trap electron spin resonance. The bactericidal effect is mediated by central carbon metabolism via enzyme deactivation in E. coli. Enzymatic deactivation via the oxygen radical irradiation of a solution containing the amino acid L-Trp eventually resulted in bacterial death.

DOI： 10.1016/j.eti.2023.103496

High linear energy transfer (LET) nature of alanine radical yield by soft X-ray irradiations studied by electron spin resonance (ESR) applications 査読有り

Nakagawa, S; Yokoya, A; Ohara, M; Usami, N; Asada, M; Fujiwara, M; Nakamura, T; Ishikawa, K

RADIATION PHYSICS AND CHEMISTRY 214 巻頁： 111304 2024年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Radiation Physics and Chemistry

Radicals produced in alanine by irradiation of 2–7 keV X-rays were investigated by ESR applications; i.e., CW-ESR, pulse-ESR and ESR imaging. The relative radical yield decreased with the decreasing photon energy and the increasing dose. The 2D imaging showed that the radical concentration at the surface was extremely low even though the absorption of X-rays exponentially decreased with the penetration depth. The depth of the radical concentration peak was almost the same as the penetration depth for the X-ray irradiation with an energy lower than 5-keV. The product formed by radical recombination was observed by an LC/MS (liquid chromatograph-mass spectrum) analysis. For the soft X-ray irradiation, many radicals will be lost by the efficient radical-radical recombination due to the higher density of the radicals, similar to the high-LET irradiation by heavy ions. The spin-spin relaxation rate (1/T<inf>2</inf>), which correlates with the radical concentration, increased by the decreasing photon energy. The values of 1/T<inf>2</inf> for the soft X-rays were compatible to that for the heavy ions with the high-LET. Based on these observations, it is concluded that the effects of irradiation by soft X-rays are similar to high-LET irradiation.

DOI： 10.1016/j.radphyschem.2023.111304

Science and Applications of Plasma-Activated Solutions: Current Trends and Future Directions 査読有り国際共著

Tanaka H., Mizuno M., Ishikawa K., Miron C., Okazaki Y., Toyokuni S., Nakamura K., Kajiyama H., Ito M., Hori M.

Plasma Medicine 14 巻 ( 1 ) 頁： 67 - 76 2024年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Plasma Medicine

Recent research into plasma-activated solutions has unveiled their considerable potential across a range of applications, including cancer treatment, industrial processes, and environmental management. This review summarizes key findings from recent studies on the effects of plasma-activated solutions, focusing on their ability to induce cell death in glioblastoma cells, enhance ethanol production in yeast, and convert organic compounds into environmentally friendly substances. The review highlights the mechanisms by which plasma-activated solutions exert their effects, such as oxidative stress induction and cellular metabolic alterations. Addition-ally, it discusses the implications of these findings for overcoming challenges in cancer therapy, improving agricultural practices, and developing novel environmental technologies. The ongoing advancements in plasma technology offer promising avenues for future research and applications, underscoring its transformative potential in both scientific and practical domains.

DOI： 10.1615/PlasmaMed.v14.i1.50

Cold Atmospheric Pressure Plasma-Activated Liquids for Cancer Treatment 査読有り

Miron, C; Hiromasa, T; Britun, N; Hashizume, H; Ishikawa, K; Du, LY; Yamakawa, T; Kurebayashi, Y; Kondo, T; Kondo, H; Kajiyama, H; Toyokuni, S; Mizuno, M; Hori, M

ADVANCES IN DIGITAL HEALTH AND MEDICAL BIOENGINEERING, VOL 3, EHB-2023 111 巻頁： 150 - 162 2024年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ifmbe Proceedings

Low-temperature plasma (LTP) is a promising tool that can assist in cancer treatment. Plasma-treated liquids have shown a selective cytotoxic effect on cancer cells attributed to reactive species formed in discharge, but this mechanism is not completely understood. In this study, the chemical compounds formed by plasma irradiation of Ringer’s lactate solutions and their effects on non-tumorigenic breast epithelial cells (MCF-10A) and breast cancer cells (MCF-7) were investigated. Among these compounds, glyceric acid increased the cell viability by more than two-fold compared to the control samples for MCF-10A and MCF-7 cells, whereas the tricarballylic acid had a pronounced cytotoxic effect on the cells when incubated with solutions of 0.6 mM to 50 mM concentrations. A good selectivity in killing the cancer cells was observed when the chemical compounds identified in plasma-treated liquids (such as ethyl acetate, glyceric acid, and tricarballylic acid) were used in a mixture solution of a certain concentration. The results show that the LTP-generated chemical compounds have both, stimulatory and inhibitory effects on cell viability, and the best selectivity is achieved only when these compounds are combined in a certain amount and have a synergistic effect, completely killing only the cancer cells.

DOI： 10.1007/978-3-031-62523-7_17

Bias-supply timing tailored to the aspect ratio dependence of silicon trench etching in Ar plasma with alternately injected C4F8 and SF6 査読有り Open Access

Yoshie, T; Ishikawa, K; Nguyen, TTN; Hsiao, SN; Tsutsumi, T; Sekine, M; Hori, M

APPLIED SURFACE SCIENCE 638 巻頁： 157981 2023年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Surface Science

In semiconductor device fabrication, the feature profiles of a high-aspect-ratio (HAR) Si trench is needed to be controlled considering aspect-ratio-dependent etching (ARDE). This is achieved by a cyclic process in which Ar plasma is sustained while C<inf>4</inf>F<inf>8</inf> and SF<inf>6</inf> are alternately injected and a short-period supply of a substrate bias is provided. Presently, the transient behaviors of gaseous and surface reactions are dynamically revealed by measuring the plasma parameters using a surface wave probe and optical emission spectroscopy. When the etched surface is fluorinated during the cycle, an ARDE-free Si-trench feature profile can be fabricated by controlling the bias-supply timing.

DOI： 10.1016/j.apsusc.2023.157981

An approach to reduce surface charging with cryogenic plasma etching using hydrogen-fluoride contained gases 査読有り

Hsiao S.N., Sekine M., Ishikawa K., Iijima Y., Ohya Y., Hori M.

Applied Physics Letters 123 巻 ( 21 ) 頁： 1 - 4 2023年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

The surface conductivity influences the etched pattern profiles in the plasma process. In the dielectric film etching, it is vital to reduce the charging build-up, which bends the trajectory of incoming ions for highly anisotropic etching. A significant increase in surface electric conductivity of SiO<inf>2</inf> films was observed when exposed to down-flow plasmas containing hydrogen fluoride (HF) at cryogenic temperature (−60 °C). This phenomenon can be attributed to two factors: (i) the absorption of HF and/or its compounds and (ii) the presence of H<inf>2</inf>O, which is likely originating from the etching by-product of SiO<inf>2</inf> and/or within the reactor. Comparing the surface electric resistance of the samples treated with HF plasmas to that of CF<inf>4</inf>/H<inf>2</inf> and C<inf>4</inf>F<inf>8</inf>/H<inf>2</inf> plasmas, we found that HF plasma treatment enables to be approximately three and six orders of magnitude lower. By using in situ x-ray photoemission spectroscopy, it was revealed that the presence of HF and/or its compounds and H<inf>2</inf>O were absorbed on the sample surface at −60 °C. These results strongly suggest that the cryogenic plasma etching with HF-contained gases can be used to alleviate the charge build-up issues.

DOI： 10.1063/5.0173553

Gas-phase study of the behavior of trimethyl gallium and triethyl gallium by optical emission spectroscopy and quadrupole mass spectroscopy for the growth of GaN by REMOCVD (radical-enhanced metalorganic chemical vapor deposition) 査読有り Open Access

Dhasiyan, AK; Jayaprasad, S; Amalraj, FW; Shimizu, N; Oda, O; Ishikawa, K; Hori, M

JAPANESE JOURNAL OF APPLIED PHYSICS 62 巻 ( SN ) 頁： SN1019 2023年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

Metal-organic CVD (MOCVD) is a well-established means of epitaxial growth of III-nitrides in terms of production. To overcome the drawbacks of MOCVD, we have developed a radical-enhanced MOVCVD (REMOCVD) technique which is promising to grow group-III nitride materials at lower temperatures without ammonia gas. The gas phase behavior of trimethyl gallium (TMG) and triethyl gallium (TEG) in the chamber is studied with optical emission spectroscopy (OES) and quadrupole mass spectroscopy. From OES results, it is found that the parasitic reactions due to activated Ga and CN could be avoided by introducing hydrogen as a source gas together with nitrogen gas. The TEG is completely decomposed in REMOCVD at 550 °C which is a much lower temperature compared to TMG in a hydrogen atmosphere. Also, it is found that due to the low decomposition temperature of TEG, TEG contaminated the gas line which needs to be cleaned often.

DOI： 10.35848/1347-4065/acfd34

Deposition of carbon-based materials directly on copper foil and nickel foam as 2D-and 3D-networked metal substrates by in-liquid plasma 査読有り Open Access

Dela Vega, MSDC; Nguyen, TTN; Kondo, H; Tsutsumi, T; Ishikawa, K; Hori, M

PLASMA PROCESSES AND POLYMERS 20 巻 ( 11 ) 頁： 1 - 5 2023年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Plasma Processes and Polymers

In-liquid plasma (ILP) process has been an attractive route for nanomaterial synthesis due to its high-yield production in low-temperature atmospheric pressure conditions. In comparison with conventional ILP synthesis that produces free-standing nanomaterials, this work brings a new perspective on the application of the ILP process through carbon formation directly on ethanol-immersed two-dimensional (foil) and three-dimensional (3D) (foam) metal substrates. Three types of carbon, including graphene, graphitic carbon, and amorphous carbon, were simultaneously produced during plasma discharge. Graphitic and amorphous carbon formed radially and coexisted on the metal substrate surface, while free-standing graphene was produced in ethanol. A conformal coating was achieved on the exterior surface of the 3D-networked substrate. The proposed mechanism for carbon formation on metal substrates is presented here.

DOI： 10.1002/ppap.202300036

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