Microscopy, 2014, Vol. 63, No. S1
i22 Irradiation damage in multicomponent equimolar alloys and high entropy alloys (HEAs)
2
Rutgers Center for Emergent Materials and Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
Takeshi Nagasea,b, Philip D. Rackc,d, and Takeshi Egamic,d,e a
Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan, b Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1, Yamada-Oka, Suita, Osaka 565-0871, Japan, cOak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, U.S, dDepartment of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996, U.S, and e Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, U.S
(1) ZrHfNb equimolar alloys [1, 2] A multicomponent ZrHfNb alloy was prepared by a co-sputtering process using elemental Zr, Hf, and Nb targets using an AJA International ATC 2000-V system. A single-phase bcc solid solution was obtained in the ZrHfNb alloy with an approximately equiatomic ratio of its constituent elements. The irradiation-induced structural change in the ZrHfNb equimolar alloys with the bcc solid solution structure was investigated by HVEM using the Hitachi H-3000 installed at Osaka University. The polycrystalline bcc phase shows high phase stability against irradiation damage at 298 K; the bcc solid solution phase, whose grain size was about 20 nm, remained as a main constituent phase even after the severe irradiation damage that reached 10 dpa. (2) CoCrCuFeNi HEAs [3] A single-phase fcc solid solution was obtained in a CoCrCuFeNi alloy. The microstructure of the alloy depended on the preparation technique: a nanocrystalline CoCrCuFeNi alloy with an approximately equiatomic ratio of its constituent elements was obtained by a co-sputtering process with multi-targets, while polycrystalline structures were formed when the arc-melting method was used. Both nanocrystalline and polycrystalline structures showed high phase stability against fast electron irradiation at temperatures ranging from 298 K to 973 K; a fcc phase remained as the main constituent phase over 40 dpa of irradiation. The grain coarsening of the crystalline phase can be seen during the annealing in a nanocrystalline CoCrCuFeNi alloy, while the irradiation-induced grain coarsening did not occur at 773 K as well as at 298 K.
References 1. Fiebig M., et al., Nature 419, 818 (2002). 2. Choi T. J., et al., Nature Materials 9, 253 (2010) doi: 10.1093/jmicro/dfu067
Observation of the potential distribution in GaN-based devices by a scanning electron microscope Takahiro Karumi1, Shigeyasu Tanaka2, and Takayoshi Tanji2 1
Department of Electrical Engineering and Computer Science, Nagoya University, and 2EcoTopia Science Institute, Nagoya University
References 1. Nagase T., Anada S., Rack P. D., Noh J. H., Yasuda H., Mori H., Egami T.: Intermetallics, 26 (2012) 122–130. 2. Nagase T., Anada S., Rack P. D., Noh J. H., Yasuda H., Mori H., Egami T.: Intermetallics, 38 (2013) 70–79. 3. Nagase T., Rack P. D., Noh J. H., Egami T.: Intermetallics, to be submitted. 4. Egami T., Guo W., Rack P. D., Nagase T.: Metall. Mater. Trans. A, 45 (2014) 180–183. doi: 10.1093/jmicro/dfu054 Observation of vortex domain structures in multiferroic hexagonal manganites RMnO3 by transmission electron microscopy Yoichi Horibe1, Fei-Ting Huang2, Taekjib Choi2, Nara Lee2, and Sang-Wook Cheong2 1
Department of Materials Science & Engineering, Kyushu Institute of Technology, Kita-kyushu, Fukuoka 804-8550, Japan, and
Mapping of the potential distribution using a scanning electron microscope (SEM) has been reported in recent years [1,2] for semiconductors such as Si, GaAs and InP. But, there are no such studies on GaN-based devices, to our knowledge. In this study, we observed two types of GaN-based devices by SEM to see if there is a condition that the contrast matches the potential distribution of the devices. The first device we studied was GaN p-n junction ( p, n ∼5 × 1017 cm−3). The device was cut, and polished from the cross-section to a flat surface. The cross-section was observed by SEM. Fig. 1(a) shows an SEM image taken at 3 kV. The p-region appears bright and the n-region appears dark. The image intensity changes at the position of p-n junction, for which we used electron beam induced current (EBIC) technique to determine the p-n junction position. Fig. 1(b) is a line profile across the p-n junction (broken line) of the SEM image together with a calculated potential distribution (solid line) using p and n concentrations. It can be seen that the contrast profile matches the potential distribution very well. The SEM observations were carried out for several accelerating voltages. But, best result was obtained at 3 kV. For lower accelerating voltages, the image seemed to reflect the surface potential. On the other hand, higher accelerating voltages resulted in blurred images. The second sample was a light emitting diode structure based on AlN where a multiple quantum
Downloaded from http://jmicro.oxfordjournals.org/ at University of Ulster on November 17, 2015
To maintain sustainable energy supply and improve the safety and efficiency of nuclear reactors, development of new and advanced nuclear materials with superior resistance to irradiation damage is necessary. Recently, a new generation of structural materials, termed as multicomponent equimolar alloys and/or high entropy alloys (HEAs), are being developed. These alloys consist of multicomponent elements for maximizing the compositional entropy, which stabilizes the solid solution phase. In this paper, preliminary studies on the irradiation damage in equimolar alloys and HEAs by High Voltage Electron Microscopy (HVEM) are reported [1–4].
Multiferroic hexagonal manganite RMnO3 (R = rare-earth elements) shows improper ferroelectricity accompanied by tilting of MnO5 hexahedra as the primary order parameter. The ferroelectricity is originated from displacements of rare-earth ions along c-axis triggered by the MnO5 hexahedra tilting. Although coupling between ferroelectric and antiferromagnetic domains below the magnetic transition temperature of ∼90 K has been reported from previous work[1], the relationship between the ferroelectric domains and structural domains due to the MnO5 hexahedra tilting has not been wellstudied. In this talk, we will report our studies on unique patterns of ferroelectric antiphase domains with a vorticity in hexagonal RMnO3, obtained from the results of transmission electron microscopy [2]. The electron diffraction patterns obtained at room temperature exhibit superlattice reflection spots due to the MnO5 hexahedra tilting and displacements of rare-earth ions along c-axis, in addition to the fundamental reflections associated with the high symmetry structure with the space group of P63/mmc. Unique antiphase/ferroelectric "cloverleaf-like" domain patterns are clearly observed in dark-field images taken using superlattice spots. The fundamental and superlattice dark-field imaging combined with high-resolution imaging clearly demonstrates that in the cloverleaf-like domain patterns the antiphase and ferroelectric domains arrange periodically with certain rotation direction. In addition, there exist two types of cloverleaf-like domain patterns with the opposite rotations next to each other in the superlattice dark-field images. These results indicate that the cloverleaf-like domain patterns can be considered as the aggregation of vortices and antivortices consisting of ferroelectric and antiphase domains.
i22 Irradiation damage in multicomponent equimolar alloys and high entropy alloys (HEAs)
2
Rutgers Center for Emergent Materials and Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
Takeshi Nagasea,b, Philip D. Rackc,d, and Takeshi Egamic,d,e a
Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan, b Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1, Yamada-Oka, Suita, Osaka 565-0871, Japan, cOak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, U.S, dDepartment of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996, U.S, and e Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, U.S
(1) ZrHfNb equimolar alloys [1, 2] A multicomponent ZrHfNb alloy was prepared by a co-sputtering process using elemental Zr, Hf, and Nb targets using an AJA International ATC 2000-V system. A single-phase bcc solid solution was obtained in the ZrHfNb alloy with an approximately equiatomic ratio of its constituent elements. The irradiation-induced structural change in the ZrHfNb equimolar alloys with the bcc solid solution structure was investigated by HVEM using the Hitachi H-3000 installed at Osaka University. The polycrystalline bcc phase shows high phase stability against irradiation damage at 298 K; the bcc solid solution phase, whose grain size was about 20 nm, remained as a main constituent phase even after the severe irradiation damage that reached 10 dpa. (2) CoCrCuFeNi HEAs [3] A single-phase fcc solid solution was obtained in a CoCrCuFeNi alloy. The microstructure of the alloy depended on the preparation technique: a nanocrystalline CoCrCuFeNi alloy with an approximately equiatomic ratio of its constituent elements was obtained by a co-sputtering process with multi-targets, while polycrystalline structures were formed when the arc-melting method was used. Both nanocrystalline and polycrystalline structures showed high phase stability against fast electron irradiation at temperatures ranging from 298 K to 973 K; a fcc phase remained as the main constituent phase over 40 dpa of irradiation. The grain coarsening of the crystalline phase can be seen during the annealing in a nanocrystalline CoCrCuFeNi alloy, while the irradiation-induced grain coarsening did not occur at 773 K as well as at 298 K.
References 1. Fiebig M., et al., Nature 419, 818 (2002). 2. Choi T. J., et al., Nature Materials 9, 253 (2010) doi: 10.1093/jmicro/dfu067
Observation of the potential distribution in GaN-based devices by a scanning electron microscope Takahiro Karumi1, Shigeyasu Tanaka2, and Takayoshi Tanji2 1
Department of Electrical Engineering and Computer Science, Nagoya University, and 2EcoTopia Science Institute, Nagoya University
References 1. Nagase T., Anada S., Rack P. D., Noh J. H., Yasuda H., Mori H., Egami T.: Intermetallics, 26 (2012) 122–130. 2. Nagase T., Anada S., Rack P. D., Noh J. H., Yasuda H., Mori H., Egami T.: Intermetallics, 38 (2013) 70–79. 3. Nagase T., Rack P. D., Noh J. H., Egami T.: Intermetallics, to be submitted. 4. Egami T., Guo W., Rack P. D., Nagase T.: Metall. Mater. Trans. A, 45 (2014) 180–183. doi: 10.1093/jmicro/dfu054 Observation of vortex domain structures in multiferroic hexagonal manganites RMnO3 by transmission electron microscopy Yoichi Horibe1, Fei-Ting Huang2, Taekjib Choi2, Nara Lee2, and Sang-Wook Cheong2 1
Department of Materials Science & Engineering, Kyushu Institute of Technology, Kita-kyushu, Fukuoka 804-8550, Japan, and
Mapping of the potential distribution using a scanning electron microscope (SEM) has been reported in recent years [1,2] for semiconductors such as Si, GaAs and InP. But, there are no such studies on GaN-based devices, to our knowledge. In this study, we observed two types of GaN-based devices by SEM to see if there is a condition that the contrast matches the potential distribution of the devices. The first device we studied was GaN p-n junction ( p, n ∼5 × 1017 cm−3). The device was cut, and polished from the cross-section to a flat surface. The cross-section was observed by SEM. Fig. 1(a) shows an SEM image taken at 3 kV. The p-region appears bright and the n-region appears dark. The image intensity changes at the position of p-n junction, for which we used electron beam induced current (EBIC) technique to determine the p-n junction position. Fig. 1(b) is a line profile across the p-n junction (broken line) of the SEM image together with a calculated potential distribution (solid line) using p and n concentrations. It can be seen that the contrast profile matches the potential distribution very well. The SEM observations were carried out for several accelerating voltages. But, best result was obtained at 3 kV. For lower accelerating voltages, the image seemed to reflect the surface potential. On the other hand, higher accelerating voltages resulted in blurred images. The second sample was a light emitting diode structure based on AlN where a multiple quantum
Downloaded from http://jmicro.oxfordjournals.org/ at University of Ulster on November 17, 2015
To maintain sustainable energy supply and improve the safety and efficiency of nuclear reactors, development of new and advanced nuclear materials with superior resistance to irradiation damage is necessary. Recently, a new generation of structural materials, termed as multicomponent equimolar alloys and/or high entropy alloys (HEAs), are being developed. These alloys consist of multicomponent elements for maximizing the compositional entropy, which stabilizes the solid solution phase. In this paper, preliminary studies on the irradiation damage in equimolar alloys and HEAs by High Voltage Electron Microscopy (HVEM) are reported [1–4].
Multiferroic hexagonal manganite RMnO3 (R = rare-earth elements) shows improper ferroelectricity accompanied by tilting of MnO5 hexahedra as the primary order parameter. The ferroelectricity is originated from displacements of rare-earth ions along c-axis triggered by the MnO5 hexahedra tilting. Although coupling between ferroelectric and antiferromagnetic domains below the magnetic transition temperature of ∼90 K has been reported from previous work[1], the relationship between the ferroelectric domains and structural domains due to the MnO5 hexahedra tilting has not been wellstudied. In this talk, we will report our studies on unique patterns of ferroelectric antiphase domains with a vorticity in hexagonal RMnO3, obtained from the results of transmission electron microscopy [2]. The electron diffraction patterns obtained at room temperature exhibit superlattice reflection spots due to the MnO5 hexahedra tilting and displacements of rare-earth ions along c-axis, in addition to the fundamental reflections associated with the high symmetry structure with the space group of P63/mmc. Unique antiphase/ferroelectric "cloverleaf-like" domain patterns are clearly observed in dark-field images taken using superlattice spots. The fundamental and superlattice dark-field imaging combined with high-resolution imaging clearly demonstrates that in the cloverleaf-like domain patterns the antiphase and ferroelectric domains arrange periodically with certain rotation direction. In addition, there exist two types of cloverleaf-like domain patterns with the opposite rotations next to each other in the superlattice dark-field images. These results indicate that the cloverleaf-like domain patterns can be considered as the aggregation of vortices and antivortices consisting of ferroelectric and antiphase domains.
