Ubiquitous organic molecule-based free-standing nanowires with ultra-high aspect ratios

ごくありふれた有機分子からナノ細線をつくり立たせて埋めつくす --立体電子回路や超高感度センサーへ--. 京都大学プレスリリース. 2021-06-30.The critical dimension of semiconductor devices is approaching the single-nm regime, and a variety of practical devices of this scale are targeted for production. Planar structures of nano-devices are still the center of fabrication techniques, which limit further integration of devices into a chip. Extension into 3D space is a promising strategy for future; however, the surface interaction in 3D nanospace make it hard to integrate nanostructures with ultrahigh aspect ratios. Here we report a unique technique using high-energy charged particles to produce free-standing 1D organic nanostructures with high aspect ratios over 100 and controlled number density. Along the straight trajectory of particles penetrating the films of various sublimable organic molecules, 1D nanowires were formed with approximately 10~15 nm thickness and controlled length. An all-dry process was developed to isolate the nanowires, and planar or coaxial heterojunction structures were built into the nanowires. Electrical and structural functions of the developed standing nanowire arrays were investigated, demonstrating the potential of the present ultrathin organic nanowire systems

Formation of Fe Nanoparticles by Ion Implantation Technique for Catalytic Graphitization of a Phenolic Resin

Ion implantation technique was employed to introduce iron nanoparticles (Fe NPs) into a carbon precursor polymer with the aim of forming of a graphitic nanostructure through catalytic graphitization by the introduced Fe NPs. A phenolic resin was implanted by 100 keV Fe+ ions with ion fluence of 1 × 1014–1 × 1016 ions/cm2 at ambient temperature under vacuum, and subsequently heat-treated at 800 °C in a nitrogen gas atmosphere. It was found that the particle size of Fe NPs could be controlled in the range of 5–30 nm by the Fe+ ion fluence. Additionally, it was found that a nanosized turbostratic graphite structure with mean interlayer distance of 0.3531 nm, which is consisted of shell-like carbon layers and intricately distorted carbon layers, was formed around the Fe NPs. The ion implantation technique is one of the advantageous ways to introduce size-controlled fine metal NPs which are effective for the formation of graphitic nanostructure from a carbon precursor polymer

Swelling of radiation-cured polymer precursor powder for silicon carbide by pyrolysis

Ceramic yield, density, volume change and pore size distribution were measured for radiation- and thermally cured PCS powder when they were pyrolyzed in the temperature range of 673–973 K. Higher ceramic yield was obtained for radiation-cured powder due to smaller amount of evolved gas. Temperature dependence of volume change and the total pore volume show that the formation and disappearance of pores in the powders were determined by the volume shrinkage and evolution of decomposed gases. Volume shrinkage narrowed the pore size distribution for radiation-cured powder. For thermally cured powder, the narrowing of size distribution was disturbed by aggregated pores. Smaller amount of evolved gas from radiation-cured powder relative to thermally cured powder prevented the aggregation of pores and provided the narrow size distribution

Influence of gamma ray irradiation on thermal conductivity of bismaleimide-triazine-based insulation tape at cryogenic temperature

近年、大強度加速器を利用した素粒子物理の研究実施を実現するため、MGy級の高放射線環境下で使用可能な超伝導磁石システムが要求されている。この要求に対し、我々は、機械的特性の面において100MGyの耐放射線性を有するエポキシ樹脂とビスマレイミドートリアジン(BT)樹脂を基材としたガラス繊維強化絶縁テープを開発している。一方、絶縁テープ材の熱伝導率は、磁石システム動作中の超伝導コイル温度に影響を及ぼす重要なパラメータの一つである。そこで本報では、熱伝導率測定装置を開発するとともに、ガンマ線照射後の絶縁テープの熱伝導率変化を調べた。その結果、5MGyまでの照射において顕著な熱伝導率の変化は見られず、BT樹脂を用いた絶縁テープが超伝導磁石システムに適用可能であると結論を得た

Formation of Fe Nanoparticles by Ion Implantation Technique for Catalytic Graphitization of a Phenolic Resin

Ion implantation technique was employed to introduce iron nanoparticles (Fe NPs) into a carbon precursor polymer with the aim for formation of graphitic nanostructure through catalytic graphitization by the introduced Fe NPs. A phenolic resin was implanted by 100 keV Fe+ ions with ion fluence of 1E14-1E16 ions/cm^2 at ambient temperature under vacuum, and subsequently heat-treated at 800°C in nitrogen gas atmosphere. It was found that the particle size of Fe NPs could be controlled in the range of 5-30 nm by the Fe+ ion fluence. Additionally, it was found that nano-sized turbostratic graphite structure with mean interlayer distance of 0.3531 nm, which is consisted of shell-like carbon layers and intricately distorted carbon layers, was formed around the Fe NPs. The ion implantation technique is one of the advantageous ways to introduce size-controlled fine metal NPs which are effective for the formation of graphitic nanostructure from a carbon precursor polymer

Changes of oxygen adsorption state of Pt nanoparticle catalyst on the carbon support by the ion irradiation

燃料電池の普及に向けて炭素担持Ptナノ粒子触媒の酸素還元反応（ORR）活性向上が求められているが，我々のグループでは炭素担体を模擬したグラッシーカーボン（GC）基板へのArイオン照射によってORR活性が，未照射試料に比べて2.5倍に向上することを見いだした。イオン照射を用いたGC担体への欠陥導入によるORR活性向上メカニズムを解明するために，本研究ではORR初期過程の酸素吸着に着目し，ORRで電子のやり取りをするPt 5d状態を観測できるPt L3吸収端XAFSの酸素雰囲気でのin situ測定を行った。水素還元直後の純粋Pt状態と酸素暴露状態を観測し，酸素暴露前後のXAFSスペクトルの差分からPtナノ粒子の酸素吸着状態のみを導出し，照射試料と未照射試料を比較した。先行研究からPtへの酸素吸着(Pt-O)に起因するピークを同定し，そのピーク位置を比較すると，照射試料の方が0.7 eV低エネルギーシフトしていることが分かった。これはPt-O反結合性準位の低下を意味するため，反結合準位への電子充填が起こりやすくなることでPt-Oが弱結合化して酸素離脱が容易に変化していることが分かった。240th ECS Meetin

Fabrication of a nitrogen-doped carbon catalyst from a precursor polymer using the electron beam irradiation technique

A novel process for fabricating a nitrogen-doped carbon catalyst from a precursor polymer utilizing the high-energy electron beam (EB) irradiation technique was examined with the aim of simultaneously forming a graphitic nanostructure and nitrogen doping in thermally non-equilibrium conditions. A blend of phenolic resin and cobalt chloride was irradiated by a 2 MeV EB under flowing ammonia gas and heated up to 800 °C. It was found that the EB irradiation produces carbon material with a high content of the graphite phase and enhances the amount of N-doping, especially pyridinic-N, compared with the common heat treatment in an electric furnace. The obtained carbon material exhibited catalytic activity for oxygen reduction reaction (ORR) with an ORR potential of 0.7 V versus RHE and an electron transfer number of 3 in 0.5 M H2SO4

The suppression of oxidative corrosion of carbon by structural change due to ion irradiation

The glassy carbon (GC) has been widely used as an electrode in the field of electrochemistry. Since the carbon corrosion is inevitable because of the carbon oxidization caused by applying voltage in an electrolyte, the GC without the oxidative corrosion has been required. The previous study reported that the ion irradiation into GC leads to more electrochemically stable carbon and the structural change to amorphous carbon. However, it has not been understood the relationship between the microstructure caused by the ion irradiation and its oxidative corrosion. In this study, we have discovered that the ion irradiation at a certain fluence leads to the suppression of corrosion with accompanying the orientation along c-axis.The polished GC substrates were irradiated with 380 keV Ar+ at fluence between 1.0×10^14 and 1.0×10^16 ions/cm^2 at TIARA. We estimated the durability for the corrosion by cyclic voltammetry (CV) before and after the accelerated durability test repeating potential cycling between 1.0 and 1.5 V.From the fluence dependence of CV curves before and after the accelerated durability test for pristine and irradiated GC substrates, we compared the curves before and after. The magnitude of the current in the CV curve for the irradiation below 1.0×10^15 ions/cm^2 increases after the durability test, indicating the electrochemical oxidation of the GC. For the fluence above 7.5×10^15 ions/cm^2, we observed small change in the CV curve after the durability test. We additionally observed slight orientation along c-axis and then the densification at the fluence above 7.5×10^15 ions/cm^2 although amorphous and almost unchanged in the density for 1.0×10^15 ions/cm^2 from TEM and EELS results. These results suggest that the oxidative corrosion was suppressed by the formation of chemically stable surface consisting of c-plane of graphite.第30回日本MRS年次大