Microscopy, 2014, Vol. 63, No. S1
i14 these images, we could obtain acute and obtuse rhombohedral structures of the crystal unit cells. Moreover, the Pb-Pb correlated images reconstructed from Pb Lα holograms showed a local structure of body center-like 2a0 ×2a0 × 2a0 superlattice, proving a rigid 3D network structural model combining the two kinds of rhombohedrons. This superstructure are believed to play an important role in the relaxor behaviour of PMN at atomic level[3].
References 1. Hayashi K., et al. J. Phys.: Condens. Matter 24, 093201 (2012). 2. Hosokawa S., et al. Phys. Rev. B 87, 094104 (2013). 3. Hu W., et al. Phys. Rev. B 89, 140103(R) (2014). doi: 10.1093/jmicro/dfu047
Motohiro Suzuki* Japan Synchrotron Radiation Research Institute/SPirng-8, Kouto, Sayo, Hyogo 679-5198, Japan
*Email: [email protected] X-ray measurement offers several useful features that are unavailable from other microscopic means including electron-based techniques. By using X-rays, one can observe the internal parts of a thick sample. This technique basically requires no high vacuum environment such that measurements are feasible for wet specimens as well as under strong electric and magnetic fields and even at a high pressure. X-ray spectroscopy using core excitation provides element-selectivity with significant sensitivities to the chemical states and atomic magnetic moments in the matter. Synchrotron radiation sources produce a small and low-divergent X-ray beam, which can be converged to a spot with the size of a micrometer or less using X-ray focusing optics. The recent development in the focusing optics has been driving X-ray microscopy, which has already gone into the era of X-ray nanoscopy. With the use of the most sophisticated focusing devices, an X-ray beam of 7-nm size has successfully been achieved [1]. X-ray microscopy maintains above-mentioned unique features of X-ray technique, being a perfect complement to electron microscopy. In this paper, we present recent studies on magnetic microscopy and local magnetic analysis using hard X-rays. The relevant instrumentation developments are also described. The X-ray nanospectroscopy station of BL39XU at SPring-8 is equipped with a focusing optics consisting of two elliptic mirrors, and a focused X-ray beam with the size of 100 × 100 nm2 is available [2]. Researchers can perform X-ray absorption spectroscopy: nano-XAFS (X-ray absorption fine structure) using the X-ray beam as small as 100 nm. The available X-ray energy is from 5 to 16 keV, which allows nano-XAFS study at the K edges of 3d transition metals, L edges of rare-earth elements and 5d noble metals. Another useful capability of the nanoprobe is X-ray polarization tunability, enabling magnetic circular dichroism (XMCD) spectroscopy with a sub-micrometer resolution. Scanning XMCD imaging, XMCD measurement in local areas, and element-specific magnetometry for magnetic particles/magnetic devices as small as 100 nm can be performed. Nano-XAFS application includes visualization of the chemical state in a particle catalyst [3] and phase-change memory devices [4]. For magnetic microscopic study, magnetization reversal processes of an individual magnetic CoPt dot in bit-patterned media have directly been observed [2]. Imaging of the chemical distribution and magnetic domain evolution in a Nd-Fe-B sintered magnet in demagnetization processes is presented. References 1. Mimura H., Handa S., Kimura T., Yumoto H., Yamakawa D., Yokoyama H., Matsuyama S., Inagaki K., Yamamura K.,
doi: 10.1093/jmicro/dfu041
X-ray STM: Nanoscale elemental analysis & Observation of atomic track Akira Saito1,2, Y. Furudate1,2, Y. Kusui1,2, T. Saito1,2, M. Akai-Kasaya1, Y. Tanaka2, K. Tamasaku2, Y. Kohmura2, T. Ishikawa2, Y. Kuwahara1,2, and M. Aono3 1 Dept. Precision Sci.& Technol.,Graduate School of Engineering, Osaka Univ.,Osaka, Japan, 2RIKEN SPring-8 Center, Sayo-cho, Hyogo, Japan, and 3National Inst. for Materials Science, Tsukuba, Ibaraki, Japan Scanning tunneling microscopy (STM) combined with brilliant X-rays from synchrotron radiation (SR) can provide various possibilities of original and important applications, such as the elemental analysis on solid surfaces at an atomic scale. The principle of the elemental analysis is based on the inner-shell excitation of an elementspecific energy level “under STM observation”. A key to obtain an atomic locality is to extract the element-specific modulation of the local tunneling current (not emission that can damage the spatial resolution), which is derived from the inner-shell excitation [1]. On this purpose, we developed a special SR-STM system and smart tip. To surmount a tiny core-excitation efficiency by hard X-rays, we focused two-dimensionally an incident beam having the highest photon density at the SPring-8. After successes in the elemental analyses by SR-STM [1,2] on a semiconductor hetero-interface (Ge on Si) and metal-semiconductor interface (Cu on Ge), we succeeded in obtaining the elemental contrast between Co nano-islands and Au substrate. The results on the metallic substrate suggest the generality of the method and give some important implications on the principle of contrast. For all cases of three samples, the spatial resolution of the analysis was estimated to be ∼1 nm or less, and it is worth noting that the measured surface domains had a deposition thickness of less than one atomic layer (Fig. 1, left and center). On the other hand, we found that the “X-ray induced atomic motion” can be observed directly with atomic scale using the SR-STM system effectively under the incident photon density of ∼2 x1015 photon/sec/mm2 [3]. SR-STM visualized successfully the track of the atomic motion (Fig. 1, right), which enabled the further analysis on the mechanism of the atomic motion. It is worth comparing our results with past conventional thermal STM observations on the same surface [4], where the atomic motion was found to occur in the 2-dimensional domain. However, our results show the atomic track having a local chain distribution [3]. The above mentioned results will allow us to investigate the chemical analysis and control of the local reaction with the spatial resolution of STM, giving hope of wide applications.
Downloaded from http://jmicro.oxfordjournals.org/ at University of Lethbridge on November 15, 2015
Hard-X-ray magnetic microscopy and local magnetization analysis using synchrotron radiation
Sano Y., Tamasaku K., Nishino Y., Yabashi M., Ishikawa T., Yamauchi K., Nat. Phys. 6, 122 (2010). 2. Suzuki M., Kawamura N., Mizumaki M., Terada Y., Uruga T., Fujiwara A., Yamazaki H., Yumoto H., Koyama T., Senba Y., Takeuchi T., Ohashi H., Nariyama N., Takeshita K., Kimura H., Matsushita T., Furukawa Y., Ohata T., Kondo Y., Ariake J., Richter J., Fons P., Sekizawa O., Ishiguro N., Tada M., Goto S., Yamamoto M., Takata M., Ishikawa T., Phys J..: Conf. Ser. 430, 012017 (2013). 3. Ishiguro N., Uruga T., Sekizawa O., Tsuji T., Suzuki M., Kawamura N., Mizumaki M., Nitta K., Yokoyama T., Tada M., ChemPhysChem 15, 1563 (2014). 4. Richter J.H., Kolobov A.V., Fons P., Wang X., Mitrofanov K.V., Tominaga J., Osawa H., Suzuki M., MRS Proc. 1563, mrss13 (2013).
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Fig. 1. (left) Topographic image and (center) beam-induced tip current image of Ge(111)-Cu (-2V, 0.2 nA). (right) X-ray- induced atomic motion tracks on Ge(111) that were newly imaged by the Xray-STM.
1. Saito A., et al. J.Synchrotron Rad. 13 (2006) 216; Jpn.J.Appl. Phys. 45 (2006) 1913; Surf. Sci. 601 (2007) 5294; Curr. Appl. Phys. 12 (2012) S52-56. 2. Saito A., et al. Surf. Interface Anal. 40 (2008) 1033. 3. Saito A., et al. J. Nanosci. Nanotechnol. 11 (2011) 1873; A. Saito: Chap.31, pp.585-592 in "Fundamentals of Picoscience" (ed. Klaus Sattler, Taylor & Francis Books, 2013). 4. Feenstra R.M., et al. Phys. Rev. Lett. 66 (1991) 3257; I.-S. Hwang et al., Science 265 (1994) 490. doi: 10.1093/jmicro/dfu045
Introduction to advanced image reconstruction methods and compressed sensing in medical computed tomography Hiroyuki Kudo* Division of Information Engineering, Faculty of Engineering, Information and Systems, University of Tsukuba, Tennoudai 1-1-1, Tsukuba 305-8573, Japan
*E-mail: [email protected] Image reconstruction is an important step in electron tomography as well as in medical imaging modalities such as x-ray CT, PET, and SPECT. I have been mainly working on image reconstruction in medical x-ray CT and PET for more than 20 years. Using my past experience and knowledge, this talk will consist of the following two parts. In the first part, we will introduce advanced image reconstruction methods called as “statistical reconstruction” or “iterative reconstruction”. Up to the middle of 2000s, analytical image reconstruction methods such as FBP had been adopted in most commercial x-ray CT scanners. However, the statistical (iterative) reconstruction methods which had been introduced into commercial CT
scanners in the late of 2000s enabled to reconstruct high-quality images from a limited number of projection data, limited-angle projection data, or noisy projection data measured with low radiation exposure. This revolution can be recognized as one of major progresses in CT image reconstruction fields. We will explain the principle of these advanced reconstruction methods. In the second part, we will introduce example research of advanced image reconstruction methods from our recent research. The first work aims at developing an advanced image reconstruction method in electron tomography called as Iterative SEries Reduction (ISER), which allows us to reconstruct high-quality images from a limited number of projection data, limited-angle projection data, or noisy projection data. The method is briefly described as follows. In electron tomography field, research on image reconstruction using Compressed Sensing (CS) approaches began very recently. The proposed ISER method is based on Total Variation (TV) minimization which can be recognized as one of CS approaches. However, to significantly speed up the convergence, we succeeded in combining the TV minimization with the row-actiontype iterative algorithm such as Algebraic Reconstruction Technique (ART) using the mathematical technique called as Proximal Splitting. The second work is on A-MAP (Anatomical MAP) reconstruction and PA-MAP (Probabilistic-Atlas MAP) reconstruction for medical x-ray CT, both of which utilize rather strong a priori information on the object constructed from an image of the same patient taken with another imaging modality (A-MAP) or a collection of images of many patients (PA-MAP). We believe that using such stronger a priori knowledge compared to general a priori knowledge such as TV would be a future direction to be investigated in electron tomography field. Figure 1 shows an example reconstructed image obtained by ISER TV minimization method with real electron tomography data. The sample is Fe-Pt magnetic material provided by Prof. Hata (Kyushu University) and Prof. Murayama (Virginia Institutes of Technology). The number of projection data was 32 and the angular range was limited to 130 degrees (from -65 (deg) to 65 (deg)). We compared reconstructions (vertical slices) by FBP, ART, and ISER methods. The result demonstrates that ISER method significantly reduces streak artifacts and limited-angle blurring artifacts. doi: 10.1093/jmicro/dfu037
Fig. 1. Reconstructions of tilt series of Fe-Pt magnetic material by FBP, ART, and ISER methods. The number of projection data was 32 and the angular range was limited to 130 degrees (from -65 (deg) to 65 (deg)).
Downloaded from http://jmicro.oxfordjournals.org/ at University of Lethbridge on November 15, 2015
References
i14 these images, we could obtain acute and obtuse rhombohedral structures of the crystal unit cells. Moreover, the Pb-Pb correlated images reconstructed from Pb Lα holograms showed a local structure of body center-like 2a0 ×2a0 × 2a0 superlattice, proving a rigid 3D network structural model combining the two kinds of rhombohedrons. This superstructure are believed to play an important role in the relaxor behaviour of PMN at atomic level[3].
References 1. Hayashi K., et al. J. Phys.: Condens. Matter 24, 093201 (2012). 2. Hosokawa S., et al. Phys. Rev. B 87, 094104 (2013). 3. Hu W., et al. Phys. Rev. B 89, 140103(R) (2014). doi: 10.1093/jmicro/dfu047
Motohiro Suzuki* Japan Synchrotron Radiation Research Institute/SPirng-8, Kouto, Sayo, Hyogo 679-5198, Japan
*Email: [email protected] X-ray measurement offers several useful features that are unavailable from other microscopic means including electron-based techniques. By using X-rays, one can observe the internal parts of a thick sample. This technique basically requires no high vacuum environment such that measurements are feasible for wet specimens as well as under strong electric and magnetic fields and even at a high pressure. X-ray spectroscopy using core excitation provides element-selectivity with significant sensitivities to the chemical states and atomic magnetic moments in the matter. Synchrotron radiation sources produce a small and low-divergent X-ray beam, which can be converged to a spot with the size of a micrometer or less using X-ray focusing optics. The recent development in the focusing optics has been driving X-ray microscopy, which has already gone into the era of X-ray nanoscopy. With the use of the most sophisticated focusing devices, an X-ray beam of 7-nm size has successfully been achieved [1]. X-ray microscopy maintains above-mentioned unique features of X-ray technique, being a perfect complement to electron microscopy. In this paper, we present recent studies on magnetic microscopy and local magnetic analysis using hard X-rays. The relevant instrumentation developments are also described. The X-ray nanospectroscopy station of BL39XU at SPring-8 is equipped with a focusing optics consisting of two elliptic mirrors, and a focused X-ray beam with the size of 100 × 100 nm2 is available [2]. Researchers can perform X-ray absorption spectroscopy: nano-XAFS (X-ray absorption fine structure) using the X-ray beam as small as 100 nm. The available X-ray energy is from 5 to 16 keV, which allows nano-XAFS study at the K edges of 3d transition metals, L edges of rare-earth elements and 5d noble metals. Another useful capability of the nanoprobe is X-ray polarization tunability, enabling magnetic circular dichroism (XMCD) spectroscopy with a sub-micrometer resolution. Scanning XMCD imaging, XMCD measurement in local areas, and element-specific magnetometry for magnetic particles/magnetic devices as small as 100 nm can be performed. Nano-XAFS application includes visualization of the chemical state in a particle catalyst [3] and phase-change memory devices [4]. For magnetic microscopic study, magnetization reversal processes of an individual magnetic CoPt dot in bit-patterned media have directly been observed [2]. Imaging of the chemical distribution and magnetic domain evolution in a Nd-Fe-B sintered magnet in demagnetization processes is presented. References 1. Mimura H., Handa S., Kimura T., Yumoto H., Yamakawa D., Yokoyama H., Matsuyama S., Inagaki K., Yamamura K.,
doi: 10.1093/jmicro/dfu041
X-ray STM: Nanoscale elemental analysis & Observation of atomic track Akira Saito1,2, Y. Furudate1,2, Y. Kusui1,2, T. Saito1,2, M. Akai-Kasaya1, Y. Tanaka2, K. Tamasaku2, Y. Kohmura2, T. Ishikawa2, Y. Kuwahara1,2, and M. Aono3 1 Dept. Precision Sci.& Technol.,Graduate School of Engineering, Osaka Univ.,Osaka, Japan, 2RIKEN SPring-8 Center, Sayo-cho, Hyogo, Japan, and 3National Inst. for Materials Science, Tsukuba, Ibaraki, Japan Scanning tunneling microscopy (STM) combined with brilliant X-rays from synchrotron radiation (SR) can provide various possibilities of original and important applications, such as the elemental analysis on solid surfaces at an atomic scale. The principle of the elemental analysis is based on the inner-shell excitation of an elementspecific energy level “under STM observation”. A key to obtain an atomic locality is to extract the element-specific modulation of the local tunneling current (not emission that can damage the spatial resolution), which is derived from the inner-shell excitation [1]. On this purpose, we developed a special SR-STM system and smart tip. To surmount a tiny core-excitation efficiency by hard X-rays, we focused two-dimensionally an incident beam having the highest photon density at the SPring-8. After successes in the elemental analyses by SR-STM [1,2] on a semiconductor hetero-interface (Ge on Si) and metal-semiconductor interface (Cu on Ge), we succeeded in obtaining the elemental contrast between Co nano-islands and Au substrate. The results on the metallic substrate suggest the generality of the method and give some important implications on the principle of contrast. For all cases of three samples, the spatial resolution of the analysis was estimated to be ∼1 nm or less, and it is worth noting that the measured surface domains had a deposition thickness of less than one atomic layer (Fig. 1, left and center). On the other hand, we found that the “X-ray induced atomic motion” can be observed directly with atomic scale using the SR-STM system effectively under the incident photon density of ∼2 x1015 photon/sec/mm2 [3]. SR-STM visualized successfully the track of the atomic motion (Fig. 1, right), which enabled the further analysis on the mechanism of the atomic motion. It is worth comparing our results with past conventional thermal STM observations on the same surface [4], where the atomic motion was found to occur in the 2-dimensional domain. However, our results show the atomic track having a local chain distribution [3]. The above mentioned results will allow us to investigate the chemical analysis and control of the local reaction with the spatial resolution of STM, giving hope of wide applications.
Downloaded from http://jmicro.oxfordjournals.org/ at University of Lethbridge on November 15, 2015
Hard-X-ray magnetic microscopy and local magnetization analysis using synchrotron radiation
Sano Y., Tamasaku K., Nishino Y., Yabashi M., Ishikawa T., Yamauchi K., Nat. Phys. 6, 122 (2010). 2. Suzuki M., Kawamura N., Mizumaki M., Terada Y., Uruga T., Fujiwara A., Yamazaki H., Yumoto H., Koyama T., Senba Y., Takeuchi T., Ohashi H., Nariyama N., Takeshita K., Kimura H., Matsushita T., Furukawa Y., Ohata T., Kondo Y., Ariake J., Richter J., Fons P., Sekizawa O., Ishiguro N., Tada M., Goto S., Yamamoto M., Takata M., Ishikawa T., Phys J..: Conf. Ser. 430, 012017 (2013). 3. Ishiguro N., Uruga T., Sekizawa O., Tsuji T., Suzuki M., Kawamura N., Mizumaki M., Nitta K., Yokoyama T., Tada M., ChemPhysChem 15, 1563 (2014). 4. Richter J.H., Kolobov A.V., Fons P., Wang X., Mitrofanov K.V., Tominaga J., Osawa H., Suzuki M., MRS Proc. 1563, mrss13 (2013).
Microscopy, 2014, Vol. 63, No. S1
i15
Fig. 1. (left) Topographic image and (center) beam-induced tip current image of Ge(111)-Cu (-2V, 0.2 nA). (right) X-ray- induced atomic motion tracks on Ge(111) that were newly imaged by the Xray-STM.
1. Saito A., et al. J.Synchrotron Rad. 13 (2006) 216; Jpn.J.Appl. Phys. 45 (2006) 1913; Surf. Sci. 601 (2007) 5294; Curr. Appl. Phys. 12 (2012) S52-56. 2. Saito A., et al. Surf. Interface Anal. 40 (2008) 1033. 3. Saito A., et al. J. Nanosci. Nanotechnol. 11 (2011) 1873; A. Saito: Chap.31, pp.585-592 in "Fundamentals of Picoscience" (ed. Klaus Sattler, Taylor & Francis Books, 2013). 4. Feenstra R.M., et al. Phys. Rev. Lett. 66 (1991) 3257; I.-S. Hwang et al., Science 265 (1994) 490. doi: 10.1093/jmicro/dfu045
Introduction to advanced image reconstruction methods and compressed sensing in medical computed tomography Hiroyuki Kudo* Division of Information Engineering, Faculty of Engineering, Information and Systems, University of Tsukuba, Tennoudai 1-1-1, Tsukuba 305-8573, Japan
*E-mail: [email protected] Image reconstruction is an important step in electron tomography as well as in medical imaging modalities such as x-ray CT, PET, and SPECT. I have been mainly working on image reconstruction in medical x-ray CT and PET for more than 20 years. Using my past experience and knowledge, this talk will consist of the following two parts. In the first part, we will introduce advanced image reconstruction methods called as “statistical reconstruction” or “iterative reconstruction”. Up to the middle of 2000s, analytical image reconstruction methods such as FBP had been adopted in most commercial x-ray CT scanners. However, the statistical (iterative) reconstruction methods which had been introduced into commercial CT
scanners in the late of 2000s enabled to reconstruct high-quality images from a limited number of projection data, limited-angle projection data, or noisy projection data measured with low radiation exposure. This revolution can be recognized as one of major progresses in CT image reconstruction fields. We will explain the principle of these advanced reconstruction methods. In the second part, we will introduce example research of advanced image reconstruction methods from our recent research. The first work aims at developing an advanced image reconstruction method in electron tomography called as Iterative SEries Reduction (ISER), which allows us to reconstruct high-quality images from a limited number of projection data, limited-angle projection data, or noisy projection data. The method is briefly described as follows. In electron tomography field, research on image reconstruction using Compressed Sensing (CS) approaches began very recently. The proposed ISER method is based on Total Variation (TV) minimization which can be recognized as one of CS approaches. However, to significantly speed up the convergence, we succeeded in combining the TV minimization with the row-actiontype iterative algorithm such as Algebraic Reconstruction Technique (ART) using the mathematical technique called as Proximal Splitting. The second work is on A-MAP (Anatomical MAP) reconstruction and PA-MAP (Probabilistic-Atlas MAP) reconstruction for medical x-ray CT, both of which utilize rather strong a priori information on the object constructed from an image of the same patient taken with another imaging modality (A-MAP) or a collection of images of many patients (PA-MAP). We believe that using such stronger a priori knowledge compared to general a priori knowledge such as TV would be a future direction to be investigated in electron tomography field. Figure 1 shows an example reconstructed image obtained by ISER TV minimization method with real electron tomography data. The sample is Fe-Pt magnetic material provided by Prof. Hata (Kyushu University) and Prof. Murayama (Virginia Institutes of Technology). The number of projection data was 32 and the angular range was limited to 130 degrees (from -65 (deg) to 65 (deg)). We compared reconstructions (vertical slices) by FBP, ART, and ISER methods. The result demonstrates that ISER method significantly reduces streak artifacts and limited-angle blurring artifacts. doi: 10.1093/jmicro/dfu037
Fig. 1. Reconstructions of tilt series of Fe-Pt magnetic material by FBP, ART, and ISER methods. The number of projection data was 32 and the angular range was limited to 130 degrees (from -65 (deg) to 65 (deg)).
Downloaded from http://jmicro.oxfordjournals.org/ at University of Lethbridge on November 15, 2015
References
