Synthesis and formation mechanism of novel double-thick-walled silicon carbide nanotubes from multiwalled carbon nanotubes

　In this study, double-thick-walled (DTW) silicon carbide (SiC) nanotubes, the walls of which comprise connected disordered polycrystalline nanograins, were successfully synthesized for the first time via the reaction of multiwalled carbon nanotubes (MWCNTs) with Si powder. DTW SiC nanotubes exhibit novel properties unlike other SiC nanomaterials, owing to their intriguing geometries. The DTW SiC nanotubes had a wall thickness exceeding 20 nm, regardless of the external diameter, as indicated by transmission electron microscopy results. The DTW SiC nanotubes with a spacing of above 30 nm between the outer and inner nanotubes exhibited perfect double-walled structures. The inner and outer nanotubes were not connected in any region. When all the carbon was transformed into SiC, the volume of carbon increased to 2.2 times the initial value. These results reveal that DTW SiC nanotubes with perfect structures cannot be synthesized without an MWCNT wall thickness of at least 50 nm. Several types of DTW SiC nanotubes with different morphologies, such as diameter, end structure, and distance between the inner and outer nanotubes, were synthesized. The morphology of DTW SiC nanotubes can be controlled by changing the wall thickness and/or diameter of the original MWCNTs and the reaction conditions

Synthesis of Polycrystalline and Amorphous Double-Thick-Walled Silicon Carbide Nanotubes

　The formation of novel structured SiC nanomaterials with new properties is required because there is the possibility that they have novel properties relative to bulk SiC materials. Polycrystalline double-thick-walled (DTW) SiC nanotubes were successful synthesized by the reaction of multi-walled carbon nanotubes with Si powder. We also synthesized novel amorphous DTW SiC nanotubes for the first time.　The degree of crystallinity of the SiC nanotube was decreasing with growing irradiation damage, and the SiC crystals were completely amorphized when irradiated at 3.2 dpa. According to these TEM images, the double-walled structure in the amorphous SiC nanotube was maintained even after ion irradiation. When the irradiation damage increased up to 24.0 dpa, the amorphous DTW SiC nanotube altered to the amorphous SiC nanowire.Materials Research Meeting 202

Ion Irradiation Induced Synthesis of Novel Amorphous Double-Thick-Walled Silicon Carbide Nanotubes

　The synthesis of new structured SiC nanomaterials with novel properties is required because there is the possibility that they have novel properties relative to bulk SiC materials. We also have synthesized polycrystalline double-thick-walled (DTW) SiC nanotubes. Herein, we report the successful synthesis of novel amorphous DTW SiC nanotubes for the first time.　The degree of crystallinity of the SiC nanotube was decreasing with growing irradiation damage, and the SiC crystals were completely amorphized when irradiated at 3.2 dpa. According to these TEM images, the double-walled structure in the amorphous SiC nanotube was maintained even after ion irradiation. When the irradiation damage increased up to 24.0 dpa, the amorphous DTW SiC nanotube altered to the amorphous SiC nanowire.The 9th International Symposium on Surface Science (ISSS9

Synthesis of new structured hybrid carbon nanomaterials by ion irradiation of C-SiC coaxial nanotubes

　これまでに、C-SiC同軸ナノチューブの創製に成功しているが、これらC-SiC同軸ナノチューブのイオン照射を行ったところ、SiCナノチューブ内に新奇カーボンナノ材料の創製に成功したので報告する。　室温におけるイオン照射後のC-SiC同軸ナノチューブの透過型電子顕微鏡(TEM)写真より、外側のSiCはアモルファスに変化するが、内部のカーボン層は結晶性を維持していることが分かった。さらに、元々存在したナノチューブの径方向に垂直なカーボン層だけでなく、径方向に平行な新しいカーボン層が、イオン照射後に出現した。これらの結果から、アモルファスSiCナノチューブ内に、長さ方向に積層した50nm以下の微小円状グラフェンと多層カーボンナノチューブが複合化された新奇構造を有するハイブリッドカーボンナノ材料の創製に成功したことが示唆された。第29回 日本MRS年次大

Precipitation of Pt Nanoparticles inside Ion-Track-Etched Capillaries

円柱状ナノ空間構造内にPt、Auなどの金属ナノ粒子を高密度に集積できれば、触媒反応場や局在型表面プラズモン共鳴吸収による光発熱場としてガス改質材料への応用が期待できる。本研究では、350 MeV Xeイオンビーム照射と化学エッチングよりポリイミドフィルム（厚さ2.5μm）に形成したイオン穿孔（直径約500 nm、長さ2.5μm）内に電子線還元法によりPtナノ粒子の形成を試みた。実験では、塩化白金酸濃度（0.1～10 mM）及び電子線照射量(最大1.4 × 1016 e/cm2)をパラメータに塩化白金酸水溶液中でイオン穿孔膜に2 MVの電子線を照射して試料を作製した。イオン穿孔内に析出したPt粒子の形態及び集積度合は、断面観察試料を作製して走査型電子顕微鏡、透過型電子顕微鏡観察により評価した。その結果、塩化白金酸濃度0.5 mMではイオン穿孔内壁に粒径が5 nm程度のPtナノ粒子が一様に分散して担持し、濃度が10 mMになると100 nm程度の凝集体を形成することがわかった。一方、Ptナノ粒子の形態は電子線照射量に影響されないことがわかった

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

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