Atsumi Miyashita - Academia.edu (original) (raw)
Papers by Atsumi Miyashita
The Japan Society of Applied Physics, 2016
Effects of Surface Modification on Hydriding Property of a Hydrogen Storage Alloy by Short Pulse ... more Effects of Surface Modification on Hydriding Property of a Hydrogen Storage Alloy by Short Pulse Laser Irradiation ○ 阿部 浩之 、下村 拓也 、菖蒲 敬久 、徳平 真之介 、宮下 敦巳 、西村 昭彦 、 大道 博行 、内田 裕久 4 (1.原子力機構量子ビーム高崎、2.原子力機構レーザー研、3.原子 力機構量子ビーム播磨 3.東海大院応用理学 ) Hiroshi Abe, Takuya Shimomura, Takahisa Shobu, Shinnosuke Tokuhira, Atsumi Miyashita, Akihiko Nishimura, Hiroyuki Daido, Hirohisa Uchida (1.JAEA Qubs , 2.JAEA Appl. Laser Tech. Inst., 3.JAEA Qubs SPring-8, 4.Tokai Univ.) E-mail: abe.hiroshi10@jaea.go.jp 【はじめに】 水素吸蔵材料の水素吸蔵能を向上させることは実用上重要であり、それら吸蔵能向上の為に従 来は化学処理[1]やメカニカルアロイング(MA)[2]、メカニカルグラインディング(MG)[3]、更には 荷電粒子照射[4]などといった手法により表面改質を行ってきた。本研究では新たな手法の確立を 進めるべく、短パルスレーザー照射[5]による水素吸蔵能向上を図ることを目的とし、その吸蔵能 向上におけるプロセス解明の足がかりを得る為に、水素吸蔵測定だけでなく放射光や XPS測定な どの表面分析を実施し、レーザー照射による材料表面層の変化を調べた。本研究の水素吸蔵材料 LaNi5 系合金は、ハイブリッドカー(HV)に搭載されているニッケル水素電池や乾電池型蓄電池 (Ni-MH)等の実用材料として利用されている。これら材料の更なる特性向上を目指し、水素吸材料 表面に対して、短パルスレーザー照射技術を利用することによって表面構造変化や水素吸蔵量、 水素吸蔵初期反応速度の変化を測定した。また放射光や XPSを利用して、種々条件による表面構 造変化について歪み測定や表面状態分析を通して、レーザー照射と水素吸蔵能変化の...
Journal of Physics: Condensed Matter, 2021
Co2MnGa is a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. Using spin-polari... more Co2MnGa is a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. Using spin-polarized positron annihilation spectroscopy, we examined a Bridgman-grown Co2MnGa single crystal with a nearly perfect L21-ordered structure and a reference Co2MnAl polycrystal with a Mn–Al-disordered B2 structure. We found that a large amount of magnetic vacancies (more than 100 ppm) were included in the Co2MnGa crystal but not the Co2MnAl crystal. We discuss possible reasons for the inclusion of vacancies, the role of vacancies in the development of the ordered structure, and the electronic states associated with the vacancies. Toward the development of Co2MnGa-based devices, the manners for reducing vacancies as well as the influence of vacancies on the electrical transport properties should be considered.
Physical Review Letters, 2021
Transactions of the Materials Research Society of Japan, 2007
Tungsten tri-oxide (W0a) thin films are prepared by magnetron sputtering and subsequent thermal t... more Tungsten tri-oxide (W0a) thin films are prepared by magnetron sputtering and subsequent thermal treatment. Ion irradiations with ~e+ at 350 keV were performed for the films. Gasocbromic coloration of the irradiated films was observed by a measurement of optical transmittance with the exposure of 1 % hydrogen. The extent of coloration level of the irradiated film with the tluence of lxl0 17 ionslcm 2 is 7.5 times laaer than that of non-irradiated film. W 4f photoemission spectra for the films were measured by x-ray photoelectron spectroscopy. From the fitting analysis for the spectra, the non-irradiated film has only. W+. In the irradiated film with the tluence of lxl0 17 ionslcm 2 , it is estimated that 17% and 4% of the V change into w+ and vt'+, respectively. The irradiation for the films breaks the chemical bonds between tungsten and oxygen, and makes atomic sites of oxygen-deficient tungsten such as w'+ and v+. The improvement ofthe gasocbromic coloration for thew~ films relates to the increment of thew'+ and vt+ sites induced by the irradiation.
Materials Science Forum, 2008
We perform a dynamical simulation of the SiO2/4H-SiC C-face interface oxidation process at 2500K ... more We perform a dynamical simulation of the SiO2/4H-SiC C-face interface oxidation process at 2500K using first-principles molecular dynamics based on plane waves, supercells, and the projector-augmented wave method. The slab model is used for the simulation. Oxygen molecules are dissociated in the SiO2 layers or by Si atoms at the SiO2 interface. The O atoms of the O2 molecule oxidize the C atoms at the SiC interface and form Si-C-O or CO2-C complexes. COx (x=1 or 2) molecules are desorbed from these complexes by thermal motion. COx molecules diffuse in the SiO2 layers when they do not react with dangling bonds. COx molecule formed during C-face oxidation more easily diffuse than those formed during Si-face oxidation in the interface region.
Materials Science Forum, 2007
We performed the dynamical simulation of the SiO2/4H-SiC(0001) interface oxidation process using ... more We performed the dynamical simulation of the SiO2/4H-SiC(0001) interface oxidation process using first-principles molecular dynamics based on plane waves, supercells, and the projector augmented wave method. The slab model has been used for the simulation. The heat-and-cool method is used to prepare the initial interface structure. In this initial interface structure, there is no transition oxide layer or dangling bond at the SiO2/SiC interface. As the trigger of the oxidation process, the carbon vacancy is introduced in the SiC layer near the interface. The oxygen molecules are added one by one to the empty sphere in the SiO2 layer near the interface in the simulation of the oxidation process. The molecular dynamics simulation is carried out at 2500 K. The oxygen molecule is dissociated and forms bonds with the Si atom in the SiO2 layer. The atoms of Si in the SiC layer at the SiO2/4H-SiC(0001) interface are oxidized to form the SiO2 layer. Carbon clusters, which are considered one...
Materials Science Forum, 2010
We perform dynamical simulations of dry oxidation and NO annealing of the SiO2/4H-SiC C-face inte... more We perform dynamical simulations of dry oxidation and NO annealing of the SiO2/4H-SiC C-face interface at 1500K using first-principles molecular dynamics based on plane waves, supercells, and the projector-augmented wave method. The slab model is used for the simulation. In the dry oxidation simulation, O atoms oxidize not only the C atoms at the SiC interface but also second-atomic-layer Si atoms in the SiC layer. Bilayer oxidation occurs in the oxidation process. The formation of C clusters that grow in the c-axis direction is observed. In the simulation of NO annealing, N atoms passivate interface C atoms. The density of N atoms saturates, then N atoms desorb as N2 molecules. CN molecules are formed by the abstraction of C atoms by the N atoms, and the CN molecules readily react at the interface. The formation of a Si3N structure is also observed.
Materials Science Forum, 2005
First-principles calculations for the abrupt SiO2/4H-SiC interfaces accounting for Si-Si bonding ... more First-principles calculations for the abrupt SiO2/4H-SiC interfaces accounting for Si-Si bonding and Nitrogen atom termination have been performed. Interface states due to Si-Si bonds appear at the valence band edge. Interface states at the midgap vanish when N atom terminates the Si dangling bond, but the interface states arising from the Si-N bonds appear at the valence band edge at the same time.
Journal of Materials Chemistry A, 2015
Poly(ether ether ketone)-based graft-type polymer electrolyte membranes solved the trade-off rela... more Poly(ether ether ketone)-based graft-type polymer electrolyte membranes solved the trade-off relationship between conductivity and mechanical properties.
International Journal of Hydrogen Energy, 2016
Mesoscopic Materials and Clusters, 1999
Thin Solid Films, 1999
ABSTRACT In this work, ilmenite structure FeTiO3 thin films on α-Al2O3 (0001) substrates were pre... more ABSTRACT In this work, ilmenite structure FeTiO3 thin films on α-Al2O3 (0001) substrates were prepared by Nd:YAG pulsed laser deposition. Different deposition conditions with different temperatures, and different partial gas pressures of different gases were used. It was found that an epitaxial and stoichiometric FeTiO3 single-crystal film can be prepared at 450°C in several different ambients, including pure argon, vacuum and Ar+5%O2 at different partial pressures respectively. However, the best film was ablated using 5% oxygen and argon gas mixed ambient of 0.01mbar at 450°C. With the temperature lower than 300°C or higher than 500°C, we could not obtain crystalline or even single-phase FeTiO3 film. X-ray diffraction and Rutherford backscattering spectrometry with channeling were used to characterize the films.
Thin Solid Films, 1999
Parametric work has been done to prepare FeTiO3 (FTO) thin films on A-, C-, and R-cut sapphire su... more Parametric work has been done to prepare FeTiO3 (FTO) thin films on A-, C-, and R-cut sapphire substrates. We have found that the preparation of highly oriented FTO films on different cut substrates is strongly dependent on substrate temperature, laser energy density and gas pressure. The orientations of FTO thin film can be controlled both by varying substrate cut direction and laser energy density. By varying the substrate cut directions, epitaxial thin films with high quality have been successfully grown on both A- and C-cut sapphire substrates with different substrate temperatures. The orientation control can also be realized by changing laser energy density, and we have grown both (112̄0) and (0006) oriented films on A-cut substrates with different laser energy densities. Higher laser energy density developed the tendency of film growth along the (0006) direction on A-cut substrates. At the same time, higher laser energy density enhances (0006) film growth on C-cut sapphire too. We have also found that epitaxial films can be grown on A-cut sapphire substrates in a quite large temperature range from 450 to 600°C. However, we have not got epitaxial film on R-cut sapphire substrate in a quite wide temperature range from 300 to 600°C. Probably it can be grown at a higher temperature which now is not accessible to our PLD system.
Surface Review and Letters, 1996
We have performed x-ray absorption measurements of laser-ablated Si particles in vacuum and in He... more We have performed x-ray absorption measurements of laser-ablated Si particles in vacuum and in Hegas environment. It is found that the spatial distributions of laser-ablated particles are very different between the two cases. This suggests that a higher-density region of helium gas is formed at the top of the plume of the ablated particles, and free expansion of particles is restrained by this helium cloud. Moreover, the spectrum obtained at 260 ns indicates that it takes more than 260 ns to form Si clusters. It is also demonstrated that Al particles can be sputtered in vacuum by laser-ablated Si particles if an Al plate is placed in front of the plume.
Physical Review B, 2011
The Doppler broadening of annihilation radiation (DBAR) spectra of Fe, Co, Ni, and Gd polycrystal... more The Doppler broadening of annihilation radiation (DBAR) spectra of Fe, Co, Ni, and Gd polycrystals measured using spin-polarized positrons from a 68 Ge-68 Ga source in magnetic fields exhibited clear asymmetry upon field reversal. The differential DBAR spectra between field-up and field-down conditions were qualitatively reproduced in calculations considering polarization of positrons and electrons. The magnitudes of the field-reversal asymmetry for the Fe, Co, and Ni samples was approximately proportional to the effective magnetization. The magnetic field dependence of the DBAR spectrum for the Fe sample showed hysteresis that is similar to a magnetization curve. These results demonstrate that spin-polarized positron annihilation spectroscopy will be useful in studying magnetic substances.
Journal of Electron Microscopy, 2002
ABSTRACT Implantation with 100 keV C+ ions in a transmission electron microscope (TE... more ABSTRACT Implantation with 100 keV C+ ions in a transmission electron microscope (TEM) was performed in copper at temperatures from 570 to 970 K to reveal the agglomeration process of implanted species immiscible in the substrates. Phase and strain contrast features with diameters of ∼5 nm appeared in Cu TEM samples at a fluence of 1 × 1017 C/cm2, at which carbon concentration and radiation damage were roughly evaluated as 10 at% and four displacements per carbon atom, respectively. The features were determined as carbon onions due to their spherical morphology and concentric graphene shells with the interlayer distance of bulk graphite. The strain contrast around onions indicated that they were embedded in the substrate enhancing isotropic strain. We have further derived evidence on the location of onions, such as the interaction of onions with dislocations and with the sample edge, the latter of which was observed due to irradiation‐enhanced evaporation of Cu. On the other hand, carbon nanocapsules (concentric graphitic spheres with cavities), typically observed in implanted polycrystalline Cu substrates, were formed through the graphitization at substrate grain boundaries and following emission of the encapsulated copper particles.
Journal of Applied Physics, 2001
Copper substrates were implanted with carbon ions at temperature ranging from 570 to 973 K. Impla... more Copper substrates were implanted with carbon ions at temperature ranging from 570 to 973 K. Implantation microstructures were investigated using transmission electron microscopy and high-resolution electron microscopy. Carbon onions and nanocapsules were observed together with amorphous carbon layers. Most of the nanocapsules were found to be hollow and rarely included copper nanoparticles. The encapsulating of Cu nanoparticles with graphene layers, the gradual shrinkage of the encapsulated clusters, and finally the disappearance of the clusters (leaving behind hollow nanocapsules) were observed under electron irradiation at 783 K. Statistics of cluster size as a function of ion fluence, implantation temperature, and substrate crystallinity gave insights into the nucleation processes of onions and nanocapsules. One process involves the formation of graphene layers on grain boundaries to encapsulate copper particles. The other process is the nucleation of graphene cages, probably ful...
The Japan Society of Applied Physics, 2016
Effects of Surface Modification on Hydriding Property of a Hydrogen Storage Alloy by Short Pulse ... more Effects of Surface Modification on Hydriding Property of a Hydrogen Storage Alloy by Short Pulse Laser Irradiation ○ 阿部 浩之 、下村 拓也 、菖蒲 敬久 、徳平 真之介 、宮下 敦巳 、西村 昭彦 、 大道 博行 、内田 裕久 4 (1.原子力機構量子ビーム高崎、2.原子力機構レーザー研、3.原子 力機構量子ビーム播磨 3.東海大院応用理学 ) Hiroshi Abe, Takuya Shimomura, Takahisa Shobu, Shinnosuke Tokuhira, Atsumi Miyashita, Akihiko Nishimura, Hiroyuki Daido, Hirohisa Uchida (1.JAEA Qubs , 2.JAEA Appl. Laser Tech. Inst., 3.JAEA Qubs SPring-8, 4.Tokai Univ.) E-mail: abe.hiroshi10@jaea.go.jp 【はじめに】 水素吸蔵材料の水素吸蔵能を向上させることは実用上重要であり、それら吸蔵能向上の為に従 来は化学処理[1]やメカニカルアロイング(MA)[2]、メカニカルグラインディング(MG)[3]、更には 荷電粒子照射[4]などといった手法により表面改質を行ってきた。本研究では新たな手法の確立を 進めるべく、短パルスレーザー照射[5]による水素吸蔵能向上を図ることを目的とし、その吸蔵能 向上におけるプロセス解明の足がかりを得る為に、水素吸蔵測定だけでなく放射光や XPS測定な どの表面分析を実施し、レーザー照射による材料表面層の変化を調べた。本研究の水素吸蔵材料 LaNi5 系合金は、ハイブリッドカー(HV)に搭載されているニッケル水素電池や乾電池型蓄電池 (Ni-MH)等の実用材料として利用されている。これら材料の更なる特性向上を目指し、水素吸材料 表面に対して、短パルスレーザー照射技術を利用することによって表面構造変化や水素吸蔵量、 水素吸蔵初期反応速度の変化を測定した。また放射光や XPSを利用して、種々条件による表面構 造変化について歪み測定や表面状態分析を通して、レーザー照射と水素吸蔵能変化の...
Journal of Physics: Condensed Matter, 2021
Co2MnGa is a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. Using spin-polari... more Co2MnGa is a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. Using spin-polarized positron annihilation spectroscopy, we examined a Bridgman-grown Co2MnGa single crystal with a nearly perfect L21-ordered structure and a reference Co2MnAl polycrystal with a Mn–Al-disordered B2 structure. We found that a large amount of magnetic vacancies (more than 100 ppm) were included in the Co2MnGa crystal but not the Co2MnAl crystal. We discuss possible reasons for the inclusion of vacancies, the role of vacancies in the development of the ordered structure, and the electronic states associated with the vacancies. Toward the development of Co2MnGa-based devices, the manners for reducing vacancies as well as the influence of vacancies on the electrical transport properties should be considered.
Physical Review Letters, 2021
Transactions of the Materials Research Society of Japan, 2007
Tungsten tri-oxide (W0a) thin films are prepared by magnetron sputtering and subsequent thermal t... more Tungsten tri-oxide (W0a) thin films are prepared by magnetron sputtering and subsequent thermal treatment. Ion irradiations with ~e+ at 350 keV were performed for the films. Gasocbromic coloration of the irradiated films was observed by a measurement of optical transmittance with the exposure of 1 % hydrogen. The extent of coloration level of the irradiated film with the tluence of lxl0 17 ionslcm 2 is 7.5 times laaer than that of non-irradiated film. W 4f photoemission spectra for the films were measured by x-ray photoelectron spectroscopy. From the fitting analysis for the spectra, the non-irradiated film has only. W+. In the irradiated film with the tluence of lxl0 17 ionslcm 2 , it is estimated that 17% and 4% of the V change into w+ and vt'+, respectively. The irradiation for the films breaks the chemical bonds between tungsten and oxygen, and makes atomic sites of oxygen-deficient tungsten such as w'+ and v+. The improvement ofthe gasocbromic coloration for thew~ films relates to the increment of thew'+ and vt+ sites induced by the irradiation.
Materials Science Forum, 2008
We perform a dynamical simulation of the SiO2/4H-SiC C-face interface oxidation process at 2500K ... more We perform a dynamical simulation of the SiO2/4H-SiC C-face interface oxidation process at 2500K using first-principles molecular dynamics based on plane waves, supercells, and the projector-augmented wave method. The slab model is used for the simulation. Oxygen molecules are dissociated in the SiO2 layers or by Si atoms at the SiO2 interface. The O atoms of the O2 molecule oxidize the C atoms at the SiC interface and form Si-C-O or CO2-C complexes. COx (x=1 or 2) molecules are desorbed from these complexes by thermal motion. COx molecules diffuse in the SiO2 layers when they do not react with dangling bonds. COx molecule formed during C-face oxidation more easily diffuse than those formed during Si-face oxidation in the interface region.
Materials Science Forum, 2007
We performed the dynamical simulation of the SiO2/4H-SiC(0001) interface oxidation process using ... more We performed the dynamical simulation of the SiO2/4H-SiC(0001) interface oxidation process using first-principles molecular dynamics based on plane waves, supercells, and the projector augmented wave method. The slab model has been used for the simulation. The heat-and-cool method is used to prepare the initial interface structure. In this initial interface structure, there is no transition oxide layer or dangling bond at the SiO2/SiC interface. As the trigger of the oxidation process, the carbon vacancy is introduced in the SiC layer near the interface. The oxygen molecules are added one by one to the empty sphere in the SiO2 layer near the interface in the simulation of the oxidation process. The molecular dynamics simulation is carried out at 2500 K. The oxygen molecule is dissociated and forms bonds with the Si atom in the SiO2 layer. The atoms of Si in the SiC layer at the SiO2/4H-SiC(0001) interface are oxidized to form the SiO2 layer. Carbon clusters, which are considered one...
Materials Science Forum, 2010
We perform dynamical simulations of dry oxidation and NO annealing of the SiO2/4H-SiC C-face inte... more We perform dynamical simulations of dry oxidation and NO annealing of the SiO2/4H-SiC C-face interface at 1500K using first-principles molecular dynamics based on plane waves, supercells, and the projector-augmented wave method. The slab model is used for the simulation. In the dry oxidation simulation, O atoms oxidize not only the C atoms at the SiC interface but also second-atomic-layer Si atoms in the SiC layer. Bilayer oxidation occurs in the oxidation process. The formation of C clusters that grow in the c-axis direction is observed. In the simulation of NO annealing, N atoms passivate interface C atoms. The density of N atoms saturates, then N atoms desorb as N2 molecules. CN molecules are formed by the abstraction of C atoms by the N atoms, and the CN molecules readily react at the interface. The formation of a Si3N structure is also observed.
Materials Science Forum, 2005
First-principles calculations for the abrupt SiO2/4H-SiC interfaces accounting for Si-Si bonding ... more First-principles calculations for the abrupt SiO2/4H-SiC interfaces accounting for Si-Si bonding and Nitrogen atom termination have been performed. Interface states due to Si-Si bonds appear at the valence band edge. Interface states at the midgap vanish when N atom terminates the Si dangling bond, but the interface states arising from the Si-N bonds appear at the valence band edge at the same time.
Journal of Materials Chemistry A, 2015
Poly(ether ether ketone)-based graft-type polymer electrolyte membranes solved the trade-off rela... more Poly(ether ether ketone)-based graft-type polymer electrolyte membranes solved the trade-off relationship between conductivity and mechanical properties.
International Journal of Hydrogen Energy, 2016
Mesoscopic Materials and Clusters, 1999
Thin Solid Films, 1999
ABSTRACT In this work, ilmenite structure FeTiO3 thin films on α-Al2O3 (0001) substrates were pre... more ABSTRACT In this work, ilmenite structure FeTiO3 thin films on α-Al2O3 (0001) substrates were prepared by Nd:YAG pulsed laser deposition. Different deposition conditions with different temperatures, and different partial gas pressures of different gases were used. It was found that an epitaxial and stoichiometric FeTiO3 single-crystal film can be prepared at 450°C in several different ambients, including pure argon, vacuum and Ar+5%O2 at different partial pressures respectively. However, the best film was ablated using 5% oxygen and argon gas mixed ambient of 0.01mbar at 450°C. With the temperature lower than 300°C or higher than 500°C, we could not obtain crystalline or even single-phase FeTiO3 film. X-ray diffraction and Rutherford backscattering spectrometry with channeling were used to characterize the films.
Thin Solid Films, 1999
Parametric work has been done to prepare FeTiO3 (FTO) thin films on A-, C-, and R-cut sapphire su... more Parametric work has been done to prepare FeTiO3 (FTO) thin films on A-, C-, and R-cut sapphire substrates. We have found that the preparation of highly oriented FTO films on different cut substrates is strongly dependent on substrate temperature, laser energy density and gas pressure. The orientations of FTO thin film can be controlled both by varying substrate cut direction and laser energy density. By varying the substrate cut directions, epitaxial thin films with high quality have been successfully grown on both A- and C-cut sapphire substrates with different substrate temperatures. The orientation control can also be realized by changing laser energy density, and we have grown both (112̄0) and (0006) oriented films on A-cut substrates with different laser energy densities. Higher laser energy density developed the tendency of film growth along the (0006) direction on A-cut substrates. At the same time, higher laser energy density enhances (0006) film growth on C-cut sapphire too. We have also found that epitaxial films can be grown on A-cut sapphire substrates in a quite large temperature range from 450 to 600°C. However, we have not got epitaxial film on R-cut sapphire substrate in a quite wide temperature range from 300 to 600°C. Probably it can be grown at a higher temperature which now is not accessible to our PLD system.
Surface Review and Letters, 1996
We have performed x-ray absorption measurements of laser-ablated Si particles in vacuum and in He... more We have performed x-ray absorption measurements of laser-ablated Si particles in vacuum and in Hegas environment. It is found that the spatial distributions of laser-ablated particles are very different between the two cases. This suggests that a higher-density region of helium gas is formed at the top of the plume of the ablated particles, and free expansion of particles is restrained by this helium cloud. Moreover, the spectrum obtained at 260 ns indicates that it takes more than 260 ns to form Si clusters. It is also demonstrated that Al particles can be sputtered in vacuum by laser-ablated Si particles if an Al plate is placed in front of the plume.
Physical Review B, 2011
The Doppler broadening of annihilation radiation (DBAR) spectra of Fe, Co, Ni, and Gd polycrystal... more The Doppler broadening of annihilation radiation (DBAR) spectra of Fe, Co, Ni, and Gd polycrystals measured using spin-polarized positrons from a 68 Ge-68 Ga source in magnetic fields exhibited clear asymmetry upon field reversal. The differential DBAR spectra between field-up and field-down conditions were qualitatively reproduced in calculations considering polarization of positrons and electrons. The magnitudes of the field-reversal asymmetry for the Fe, Co, and Ni samples was approximately proportional to the effective magnetization. The magnetic field dependence of the DBAR spectrum for the Fe sample showed hysteresis that is similar to a magnetization curve. These results demonstrate that spin-polarized positron annihilation spectroscopy will be useful in studying magnetic substances.
Journal of Electron Microscopy, 2002
ABSTRACT Implantation with 100 keV C+ ions in a transmission electron microscope (TE... more ABSTRACT Implantation with 100 keV C+ ions in a transmission electron microscope (TEM) was performed in copper at temperatures from 570 to 970 K to reveal the agglomeration process of implanted species immiscible in the substrates. Phase and strain contrast features with diameters of ∼5 nm appeared in Cu TEM samples at a fluence of 1 × 1017 C/cm2, at which carbon concentration and radiation damage were roughly evaluated as 10 at% and four displacements per carbon atom, respectively. The features were determined as carbon onions due to their spherical morphology and concentric graphene shells with the interlayer distance of bulk graphite. The strain contrast around onions indicated that they were embedded in the substrate enhancing isotropic strain. We have further derived evidence on the location of onions, such as the interaction of onions with dislocations and with the sample edge, the latter of which was observed due to irradiation‐enhanced evaporation of Cu. On the other hand, carbon nanocapsules (concentric graphitic spheres with cavities), typically observed in implanted polycrystalline Cu substrates, were formed through the graphitization at substrate grain boundaries and following emission of the encapsulated copper particles.
Journal of Applied Physics, 2001
Copper substrates were implanted with carbon ions at temperature ranging from 570 to 973 K. Impla... more Copper substrates were implanted with carbon ions at temperature ranging from 570 to 973 K. Implantation microstructures were investigated using transmission electron microscopy and high-resolution electron microscopy. Carbon onions and nanocapsules were observed together with amorphous carbon layers. Most of the nanocapsules were found to be hollow and rarely included copper nanoparticles. The encapsulating of Cu nanoparticles with graphene layers, the gradual shrinkage of the encapsulated clusters, and finally the disappearance of the clusters (leaving behind hollow nanocapsules) were observed under electron irradiation at 783 K. Statistics of cluster size as a function of ion fluence, implantation temperature, and substrate crystallinity gave insights into the nucleation processes of onions and nanocapsules. One process involves the formation of graphene layers on grain boundaries to encapsulate copper particles. The other process is the nucleation of graphene cages, probably ful...