Researcher Database

Faculty of Information Science and Technology Electronics for Informatics Advanced Electronics
Associate Professor

Researcher Profile and Settings


  • Faculty of Information Science and Technology Electronics for Informatics Advanced Electronics

Job Title

  • Associate Professor

J-Global ID

Research Interests

  • 薄膜   表面科学   バイオセンサー   カーボンナノチューブ   グラフェン   スピントロニクス   

Research Areas

  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electronic devices and equipment
  • Nanotechnology/Materials / Thin-film surfaces and interfaces
  • Nanotechnology/Materials / Nanomaterials

Academic & Professional Experience

  • 2019/04 - Today 北海道大学 大学院情報科学研究院 特任准教授
  • 2018/04 - 2019/03 Hokkaido University Creative Research Institution
  • 2015/04 - 2018/03 Hokkaido University Creative Research Institution


  • 1997/04 - 2000/03  Hokkaido University  Graduate School of Engineering

Association Memberships

  • Society of Nano Science and Technology   THE JAPAN SOCIETY OF APPLIED PHYSICS   

Research Activities

Published Papers

  • S. Hiura, A. Subagyo, A. Murayama, K. Sueoka
    Appl. Phys. Express 12 (5) 055502:1-5  2019/04 [Refereed][Not invited]
  • Miyatake Y, Kuribayashi-Shigetomi K, Ohta Y, Ikeshita S, Subagyo A, Sueoka K, Kakugo A, Amano M, Takahashi T, Okajima T, Kasahara M
    Scientific reports 8 (1) 14054  2018/09 [Refereed][Not invited]
  • Origami-based self-folding of co-cultured NIH/3T3 and HepG2 cells into 3D microstructure
    Q. He, T. Okajima, H. Onoe, A. Subagyo, K. Sueoka, K. Kuribayashi-Shigetomi
    Scientific Reports 8 4556  2018 [Refereed][Not invited]
  • PingGen Cai, Ryosuke Takahashi, Kaori Kuribayashi-Shigetomi, Agus Subagyo, Kazuhisa Sueoka, John M. Maloney, Krystyn J. Van Vliet, Takaharu Okajima
    BIOPHYSICAL JOURNAL 113 (3) 671 - 678 0006-3495 2017/08 [Refereed][Not invited]
    Changes in the cytoskeletal organization within cells can be characterized by large spatial and temporal variations in rheological properties of the cell (e.g., the complex shear modulus G(star)). Although the ensemble variation in G(star) of single cells has been elucidated, the detailed temporal variation of G(star) remains unknown. In this study, we investigated how the rheological properties of individual fibroblast cells change under a spatially confined environment in which the cell translational motion is highly restricted and the whole cell shape remains unchanged. The temporal evolution of single-cell rheology was probed at the same measurement location within the cell, using atomic force microscopy-based oscillatory deformation. The measurements reveal that the temporal variation in the power-law rheology of cells is quantitatively consistent with the ensemble variation, indicating that the cell system satisfies an ergodic hypothesis in which the temporal statistics are identical to the ensemble statistics. The autocorrelation of G(star) implies that the cell mechanical state evolves in the ensemble of possible states with a characteristic timescale.
  • Direct observation of subsurface charge ordering in Fe3O4(001) by scanning tunneling microscopy/spectroscopy
    S. Hiura, A. Ikeuchi, M. Jochi, R. Yamazaki, S. Takahashi, A. Subagyo, A. Murayama, K. Sueoka
    Applied Physics Express 10 45701  2017 [Refereed][Not invited]
  • M. Sawano, R. Tanaka, R. Takahashi, K. Kurubayashi-Shigetomi, A. Subagyo, K. Sueoka, T. Okajima
    MOLECULAR BIOLOGY OF THE CELL 27 1059-1524 2016 [Not refereed][Not invited]
  • Seiji Takeda, Agus Subagyo, Shu-Ping Hui, Hirotoshi Fuda, Rojeet Shrestha, Kazuhisa Sueoka, Hitoshi Chiba
    ANNALS OF CLINICAL BIOCHEMISTRY 52 (6) 647 - 653 0004-5632 2015/11 [Refereed][Not invited]
    Background Evaluation of low-density lipoprotein oxidation is important in the risk assessment of cardiovascular disease. Atomic force microscope is widely used to evaluate the physical properties including stiffness on a single-particle scale. In this study, the effect of low-density lipoprotein oxidation on the low-density lipoprotein stiffness was investigated using an atomic force microscope. Methods Isolated low-density lipoprotein particles with or without oxidation were densely bound to an Au substrate on mica, and then pressed and deformed by the atomic force microscope tip. The stiffness of each low-density lipoprotein particle was estimated as the elastic modulus obtained by the force curve analysis. Biochemical change of low-density lipoprotein due to oxidation was studied by electrophoresis. Results and conclusion The elastic modulus of low-density lipoprotein particles ranged between 0.1 and 2MPa. The oxidation of low-density lipoprotein increased the number of low-density lipoprotein particles with smaller elastic moduli, indicating the decrease in low-density lipoprotein stiffness. The elastic modulus of low-density lipoprotein might be potentially useful to evaluate low-density lipoprotein oxidation.
  • Satoshi Hiura, Akira Ikeuchi, Soraya Shirini, Agus Subagyo, Kazuhisa Sueoka
    JAPANESE JOURNAL OF APPLIED PHYSICS 54 (8) 08LB02  0021-4922 2015/08 [Refereed][Not invited]
    We report two types of adsorption structures in H/Fe3O4(001) film surfaces and the correlation between OH density and Fe electronic states, which have been studied by scanning tunneling microscopy/spectroscopy (STM/STS). Two types of bright protrusions (BPs), whose lengths along the atomic rows are different, are observed in the STM images. The shorter and longer BPs consist of Fe atoms with one and with two OH groups neighbor, respectively. In addition, STS measurements show the higher local density of states (LDOS) just below the Fermi level of Fe atoms with increasing neighboring OH groups. The variation can be attributed to the difference in the gain of electrons from H atoms, which is due to the difference in the number of neighboring OH groups. These results reveal that surface OH density is a factor for determining the LDOS just below the Fermi level of surface Fe atoms. (C) 2015 The Japan Society of Applied Physics
  • Satoshi Hiura, Akira Ikeuchi, Soraya Shirini, Agus Subagyo, Kazuhisa Sueoka
    PHYSICAL REVIEW B 91 (20) 205411  1098-0121 2015/05 [Refereed][Not invited]
    We report the presence of OH groups on the surfaces of ultrahigh-vacuum-prepared Fe3O4(001) films by means of x-ray photoelectron spectroscopy (XPS). In addition, the variations of Fe electronic states induced by H atoms adsorbed on a Jahn-Teller distorted Fe3O4(001) surface have been studied using in situ scanning tunneling microscopy and scanning tunneling spectroscopy (STS). The obtained XPS spectra of the films have demonstrated the presence of surface OH groups. The STS spectra measured on Fe sites with and without neighboring OH groups have indicated that adsorbed H and their neighboring Fe atoms behave as electron-donor and electron-trapping sites, respectively. This phenomenon changes the Fe atoms from a semiconducting to a metalliclike nature. These local electronic state modifications are related to the occupation of Fe 3d states just below the Fermi level, corresponding to an Fe2+-like state. The orbital occupation can be explained by the gain of electrons from the adsorbed H atoms.
  • Y. Q. Huang, Y. Puttisong, I. A. Buyanova, X. J. Yang, A. Subagyo, K. Sueoka, A. Murayama, W. M. Chen
    APPLIED PHYSICS LETTERS 106 (9) 93109  0003-6951 2015/03 [Refereed][Not invited]
    We investigate ensemble electron spin dephasing in self-assembled InGaAs/GaAs quantum dots (QDs) of different lateral sizes by employing optical Hanle measurements. Using low excitation power, we are able to obtain a spin dephasing time T-2* (in the order of ns) of the resident electron after recombination of negative trions in the QDs. We show that T-2* is determined by the hyperfine field arising from the frozen fluctuation of nuclear spins, which scales with the size of QDs following the Merkulov-Efros-Rosen model. This scaling no longer holds in large QDs, most likely due to a breakdown in the lateral electron confinement. (C) 2015 AIP Publishing LLC.
  • Kaori Kuribayashi-Shigetomi, Ryosuke Takahashi, Agus Subagyo, Kazuhisa Sueoka, Takaharu Okajima
    Hyper Bio Assembler for 3D Cellular Systems 57 - 67 2015/01/01 [Refereed][Not invited]
    The compliant mechanical properties of single cells have been extensively investigated and these properties are known to exhibit a strong dependence on the surrounding environments and also cell types, functions and conditions. An understanding of the cell behavior is important for applications of tissue engineering. Accurate rheological measurements are essential to elucidate the mechanisms of cell integrity and fluidity and are also key to mechanically identifying and separating single cells for cellular and tissue engineering. Of the various existing nano-and micro-rheology techniques, atomic force microscopy (AFM) shows great potential as a minimally invasive method. AFM allows mechanical measurements to be performed without the need for chemical modifications, via nano-scale contact between the AFM probe and the cell surface. In this chapter, we describe a recent advance in which micro-fabricated substrates are used for high-speed, automated AFM rheological measurements on size-and position-controlled cells.
  • Takafumi Yamamura, Takayuki Kiba, Xiaojie Yang, Junichi Takayama, Agus Subagyo, Kazuhisa Sueoka, Akihiro Murayama
    JOURNAL OF APPLIED PHYSICS 116 (9) 94309  0021-8979 2014/09 [Refereed][Not invited]
    The growth-temperature dependence of the optical spin-injection dynamics in self-assembled quantum dots (QDs) of In0.5Ga0.5As was studied by increasing the sheet density of the dots from 2 x 10(10) to 7 x 10(10) cm(-2) and reducing their size through a decrease in growth temperature from 500 to 470 degrees C. The circularly polarized transient photoluminescence (PL) of the resulting QD ensembles was analyzed after optical excitation of spin-polarized carriers in GaAs barriers by using rate equations that take into account spin-injection dynamics such as spin-injection time, spin relaxation during injection, spin-dependent state-filling, and subsequent spin relaxation. The excitation-power dependence of the transient circular polarization of PL in the QDs, which is sensitive to the state-filling effect, was also examined. It was found that a systematic increase occurs in the degree of circular polarization of PL with decreasing growth temperature, which reflects the transient polarization of exciton spin after spin injection. This is attributed to strong suppression of the filling effect for the majority-spin states as the dot-density of the QDs increases. (C) 2014 AIP Publishing LLC.
  • Y. Puttisong, Y. Q. Huang, I. A. Buyanova, X. J. Yang, A. Subagyo, K. Sueoka, A. Murayama, W. M. Chen
    APPLIED PHYSICS LETTERS 105 (13) 132106  0003-6951 2014/09 [Refereed][Not invited]
    We show that circularly polarized emission light from InGaAs/GaAs quantum dot (QD) ensembles under optical spin injection from an adjacent GaAs layer can switch its helicity depending on emission wavelengths and optical excitation density. We attribute this anomalous behavior to simultaneous contributions from both positive and negative trions and a lower number of photo-excited holes than electrons being injected into the QDs due to trapping of holes at ionized acceptors and a lower hole mobility. Our results call for caution in reading out electron spin polarization by optical polarization of the QD ensembles and also provide a guideline in improving efficiency of spin light emitting devices that utilize QDs. (C) 2014 AIP Publishing LLC.
  • Ryosuke Takahashi, Satoshi Ichikawa, Agus Subagyo, Kazuhisa Sueoka, Takaharu Okajima
    ADVANCED ROBOTICS 28 (7) 449 - 455 0169-1864 2014/04 [Refereed][Not invited]
    To investigate the mechanical properties of adherent cells under conditions where cell-to-cell interaction can be prevented and controlled, we used microcontact printing to pattern single cells without intercellular contacts and measured them with a custom-built atomic force microscopy (AFM) system. The motorized AFM system can measure individual cells over a large spatial range, enabling the measurement of cells in a microarray format. We tested single fibroblast cells and found that the power-law of their complex shear modulus is not significantly influenced by cell-to-cell contact. This method is effective for obtaining high-throughput measurements on single cells.
  • PingGen Cai, Ryosuke Takahashi, Kaori Kuribayashi-Shigetomi, Agus Subagyo, Kazuhisa Sueoka, Takaharu Okajima
    To sort living cells according to our needs, it is important to understand how degree cell property measured for cell sorting fluctuates in time. Mechanical property of cells is one of essential indicators for cell sorting. Thus, in this study, we attempted to measure a time evolution of viscoelastic property such as complex shear modulus, G* of single cells adhered on substrates using atomic force microscopy (AFM). We observed that the G* largely fluctuated in time even the cells are placed on substrates in a confined condition. This indicates that in mechanical cell sorting, mechanical fluctuations of cells should be carefully estimated so that cells are precisely separated by taking the measured data involving cell fluctuations into account.
  • Ryosuke Tanaka, Yuki Fujii, Junpei Kikkawa, Kaori Kuribayashi-Shigetomi, Agus Subagyo, Kazuhisa Sueoka, Takaharu Okajima
    Cells rapidly undergo cell division during the embryogenesis. Such dynamic behaviors of cells during the embryogenesis are considered to be strongly associated with their mechanical properties such as cell-cell mechanical interactions and cell stiffness. However, the interplay between the morphogenesis and the mechanical property of whole cell assembly during the developmental process has not been well understood. To exploring the mechanism of forming the whole cell assembly, we proposed atomic force microscopy (AFM) combined with a microarray technique, which allows us to map mechanical property of the whole cell assembly. In this AFM setup, the cell assembly is randomly directed in the microarray well, and thus the average mechanical property of the whole cell assembly can be reconstructed from mapping images obtained from different cell assemblies.
  • Ryosuke Takahashi, Kaori Kuribayashi-Shigetomi, Agus Subagyo, Kazuhisa Sueoka, Takaharu Okajima
    Rheological properties of cells are associated with various cell functions and thus are considered to be an indicator for diagnosing cell disease. Atomic force microscopy (AFM) is a powerful tool for quantifying the mechanical properties of isolated single cells. For example, our AFM technique reported previously revealed that the complex shear modulus of single cells exhibited a large cell-to-cell variation which depended on frequency. By contrast, rheological properties of cell population such as cells in confluent condition have been less understood. Thus, it is valuable to investigate how quantitatively the AFM technique can be applied to cell population such as cells in confluent condition. As a result, rheological properties of cells in confluent conditions can be relatively rapidly measured by our AFM setup modifying a force modulation AFM mode. This suggests that the AFM technique is useful for diagnosing not only single cells but also cell population and cell assembly.
    e-Journal Surf Sci Nanotechnol (Web) 12 26-30 (J-STAGE)  1348-0391 2014 [Not refereed][Not invited]
  • Xiao-Jie Yang, Takayuki Kiba, Takafumi Yamamura, Junichi Takayama, Agus Subagyo, Kazuhisa Sueoka, Akihiro Murayama
    APPLIED PHYSICS LETTERS 104 (1) 12406  0003-6951 2014/01 [Refereed][Not invited]
    We investigate the electron-spin injection dynamics via tunneling from an In0.1Ga0.9As quantum well (QW) to In0.5Ga0.5As quantum dots (QDs) in coupled QW-QDs nanostructures. These coupled nanostructures demonstrate ultrafast (5 to 20 ps) spin injection into the QDs. The degree of spin polarization up to 45% is obtained in the QDs after the injection, essentially depending on the injection time. The spin injection and conservation are enhanced with thinner barriers due to the stronger electronic coupling between the QW and QDs. (C) 2014 AIP Publishing LLC.
    Appl Phys Lett 103 (8) 082405-082405-5  0003-6951 2013/08/19 [Not refereed][Not invited]
  • Ryosuke Takahashi, Kaori Kuribayashi-Shigetomi, Masahiro Tsuchiya, Agus Subagyo, Kazuhisa Sueoka, Takaharu Okajima
    International Symposium on Micro-NanoMechatronics and Human Science, MHS 2013, Nagoya, Japan, November 10-13, 2013 IEEE 1 - 3 2474-378X 2013 [Refereed][Not invited]
  • Mizuno Taichi, Hosoi Hirotaka, Subagyo Agus, Oishi Suguru, Ikeuchi Akira, Hiura Satoshi, Sueoka Kazuhisa
    Jpn J Appl Phys The Japan Society of Applied Physics 51 (8) 08KB03 - 08KB03-4 0021-4922 2012/08/25 [Not refereed][Not invited]
    Fe3O4 is one of the important oxide materials and its surface structure should be well understood to enable application of this material. We report the first noncontact atomic force microscopy (NC-AFM) results for Fe3O4(001) thin films. The observed films were grown homoepitaxially on magnetite thin films substrate. A low-energy electron diffraction pattern shows the well-known (\sqrt{2}\times \sqrt{2})R45° reconstructed structure. The observed minimum step height is 0.21 nm, corresponding to the distance between the same planes. We obtain two types of atomic-scale NC-AFM images. One image shows bright protrusions along the [100] and [010] directions at intervals of 0.84 nm corresponding to a unit cell of the (\sqrt{2}\times \sqrt{2})R45° reconstructed structure. The other image shows a more detailed atomic structure with 0.6 and 0.3 nm corrugations.
  • Ikeuchi Akira, Hiura Satoshi, Mizuno Taichi, Kaji Eisaku, Subagyo Agus, Sueoka Kazuhisa
    Jpn J Appl Phys The Japan Society of Applied Physics 51 (8) 08KB02 - 08KB02-5 0021-4922 2012/08/25 [Not refereed][Not invited]
    We have studied the surface atomic configurations around antiphase domain boundaries (APBs) in epitaxial magnetite (Fe3O4) thin films on MgO(001) by scanning tunneling microscopy (STM). The observed surface of the Fe3O4 films is the B-plane terminating surface with the (\sqrt{2}\times\sqrt{2})R45^{\circ} reconstruction. Several variations of APBs are observed by STM at atomic resolution. The observed APBs are categorized into a APBs labeled by three different phase shift vectors: in-plane 1/4[110], in-plane 1/2[100], and out-of-plane 1/4[101]. We discussed how these APBs appear on the surface. The proportions of the APBs with 1/4[110], 1/2[100], and 1/4[101] shifts are about 38, 1, and 61%, respectively, in our experiment.
  • A. Okada, Y. Mizutani, A. Subagyo, H. Hosoi, M. Nakamura, K. Sueoka, K. Kawahara, T. Okajima
    Appl. Phys. Lett. 99 (26) 263703-1 - 263703-3 0003-6951 2011/12/26 [Refereed][Not invited]
  • Tsubasa Ichikawa, Yuji Sakamoto, Agus Subagyo, Kazuhisa Sueoka
    APPLIED OPTICS 50 (34) H211 - H219 1559-128X 2011/12 [Refereed][Not invited]
    The research on reflectance distributions in computer-generated holograms (CGHs) is particularly sparse, and the textures of materials are not expressed. Thus, we propose a method for calculating reflectance distributions in CGHs that uses the finite-difference time-domain method. In this method, reflected light from an uneven surface made on a computer is analyzed by finite-difference time-domain simulation, and the reflected light distribution is applied to the CGH as an object light. We report the relations between the surface roughness of the objects and the reflectance distributions, and show that the reflectance distributions are given to CGHs by imaging simulation. (C) 2011 Optical Society of America
  • Ichikawa T, Sakamoto Y, Subagyo A, Sueoka K
    Applied optics 50 (34) H211 - 9 0003-6935 2011/12 [Refereed][Not invited]
  • Ichikawa Tsubasa, Sakamoto Yuji, Subagyo Agus, Sueoka Kazuhisa
    PRACTICAL HOLOGRAPHY XXV: MATERIALS AND APPLICATIONS 7957 0277-786X 2011 [Refereed][Not invited]
  • Ishida N, Subagyo A, Ikeuchi A, Sueoka K
    The Review of scientific instruments 80 (9) 093703  0034-6748 2009/09 [Refereed][Not invited]
  • Kaji Eisaku, Subagyo Agus, Arita Masashi, Sueoka Kazuhisa
    JOURNAL OF APPLIED PHYSICS 105 (7) 0021-8979 2009/04/01 [Refereed][Not invited]
  • Takeda Seiji, Nakamura Motonori, Subagyo Agus, Ishii Atsushi, Sueoka Kazuhisa, Mukasa Koichi
    SENSORS AND ACTUATORS B-CHEMICAL 132 (1) 9 - 12 0925-4005 2008/05/28 [Refereed][Not invited]
  • Subagyo A, Sasaki Y, Oka H, Sueoka K
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (12) 4482 - 4485 0370-1972 2007/12 [Refereed][Not invited]
  • Takeda S, Nakamura M, Ishii A, Subagyo A, Hosoi H, Sueoka K, Mukasa K
    Nanoscale research letters 2 (4) 207 - 212 1931-7573 2007/03 [Refereed][Not invited]
  • Eisaku Kaji, Agus Subagyo, Kazuhisa Sueoka
    Physica Status Solidi (C) Current Topics in Solid State Physics 4 (12) 4364 - 4367 1862-6351 2007 [Refereed][Not invited]
    The surface crystallographic structure and magnetic structure of magnetite thin films epitaxially grown on a MgO(001) substrate were investigated by means of a scanning tunnelling microscope (STM), magnetic force microscope (MFM) and Spin-polarized scanning electron microscopy (Spin-SEM). The STM investigation and MFM measurement were performed in-situ and in an ambient condition, respectively. After exposing the sample to air, a Spin-SEM image was acquired. Spin-dependent contrasted SEM images could be obtained after cleaning the sample surfaces. The cleaning procedure is annealing the sample at 250°C in an ultra high vacuum (UHV) below 3 × 10-8 Pa for 3 hours. The STM observation indicates the thin films have antiphase domains and the observed MFM images reflect a cease in micromagnetic domain structures. Spin-SEM images indicate that large-scale magnetic inhomogeneity of a few μm is the inhomogeneity of the perpendicular magnetic moments of the films. Due to the spatial resolution limitation of our Spin-SEM system, the correlation between the fine and coarse magnetic structures of the thin films induced by the antiphase domain boundaries is not clear, however, we have suggested the annealing process alone in a UHV makes the spin configuration of the thin films visible using a conventional Spin-SEM system. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.
  • Kaji Eisaku, Subagyo Agus, Sueoka Kazuhisa
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 12 4 (12) 4364 - 4367 1610-1634 2007 [Refereed][Not invited]
  • Subagyo Agus, Sueoka Kazuhisa
    Jpn J Appl Phys Part 1 45 (3B) 2255 - 2258 0021-4922 2006/03/30 [Not refereed][Not invited]
  • Ishida Nobuyuki, Subagyo Agus, Sueoka Kazuhisa
    INTERNATIONAL JOURNAL OF NANOSCIENCE, VOL 5, NO 6 5 (6) 895 - + 2006 [Refereed][Not invited]
  • Oka Hirofumi, Subagyo Agus, Sueoka Kazuhisa
    INTERNATIONAL JOURNAL OF NANOSCIENCE, VOL 5, NO 6 5 (6) 935 - + 2006 [Refereed][Not invited]
  • Subagyo Agus, Sueoka Kazuhisa
    Jpn J Appl Phys Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physics 44 (7) 5447 - 5450 0021-4922 2005/07/15 [Not refereed][Not invited]
    We report the role of atom defects on the charge freezing of Fe3O4(001) surfaces studied by spin-polarized scanning tunneling microscopy (SP-STM) using a Ni tip. Epitaxially grown Fe3O4(001) films on a MgO(001) substrate were used as samples. Atomically flat surfaces are obtained by annealing in an ultrahigh vacuum and in oxygen. The surfaces exhibit a $(\sqrt{2}\times\sqrt{2})R45$° reconstruction as revealed by STM with a W tip. STM images indicate surface termination at B-sites. An atomic structure with a 0.3 nm periodicity is observed within the cation rows that are aligned along the [110] direction. SP-STM images show a pronouncedly different periodicity of 1.2 nm on areas having surface defects such as cation vacancies. This corrugation with a 1.2 nm periodicity can be attributed to a charge localization of Fe3+ and Fe2+ ions that are trapped by cation vacancies and then isolated from the electron hopping process. The results also indicate the important role of oxygen vacancies in modifying the 1.2 nm periodicity.
  • HIROSE Ryusuke, ARITA Masashi, HAMADA Kouichi, TAKAHASHI Yasuo, SUBAGYO Agus
    Jpn J Appl Phys Part 2 44 (24-27) L790-L792  0021-4922 2005/07/10 [Not refereed][Not invited]
    J Magn Magn Mater 290/291 (Pt.2) 1037 - 1039 0304-8853 2005/04 [Not refereed][Not invited]
  • K Sueoka, A Subagyo, H Hosoi, K Mukasa
    NANOTECHNOLOGY 15 (10) S691 - S698 0957-4484 2004/10 [Refereed][Not invited]
    We review our research on the application of scanning tunnelling microscopy (STM) and non-contact atomic force microscopy (NC-AFM) for magnetic imaging in high spatial resolution even down to the atomic scale. In the first part, we propose a new experimental scheme of spin-polarized STM (SP-STM) with a GaAs spin probe to obtain a large contribution of spin-polarized electrons in the tunnelling current. This is yielded by injecting the spin-polarized photo-excited electrons in an optically pumped GaAs tip into the spin-polarized empty states near the Fermi level of a bcc-Fe(001) surface. According to the bandgap energy of GaAs and the surface state of the sample observed at 0.4 eV above the Fermi level, the spin-dependant electron injection can be achieved by applying a sample bias voltage of -1 V. The tunnel current in the positive bias region depends on the helicity of the circular polarized pumping light, and is modified when the applied magnetic field is reversed. Mapping the current asymmetry provides a spin-dependent SP-STM image. In the second part, we describe the progress towards spin imaging with NC-AFM. The spin imaging can be achieved by detecting short-range magnetic interaction such as exchange interaction between a ferromagnetic tip and a magnetic sample. We demonstrate the capabilities of NC-AFM by imaging the spin structure of an antiferromagnetic NiO(001) surface on the atomic scale. The cross-sectional line profiles of the atomically resolved images obtained using several ferromagnetic tips (Fe, Ni) were analysed by adding the atomic corrugation amplitude on the basis of the periodicity of the image. The results of the analysis show that the difference of the neighbouring maxima depends on the crystal direction. On the other hand, no significant indication of the directional dependency can be seen on the images obtained by using a non-magnetic Si tip. The directional dependency coincides with the antiferromagnetic spin alignment of the NiO(001) surface.
  • Ishida Nobuyuki, Subagyo Agus, Hosoi Hirotaka, Sueoka Kazuhisa, Mukasa Koichi
    Jpn J Appl Phys Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physics 43 (7) 4557 - 4560 0021-4922 2004/07/15 [Not refereed][Not invited]
    We investigated the adsorption structures of K atoms on a GaAs(110) surface as a function of coverage by scanning tunneling microscopy. We found three kinds of adsorption structures, namely, the low-density linear chain, the asymmetric chain and the symmetric chain. At the initial stage with low coverage, K atoms form low-density linear and asymmetric chains. With increasing coverage, low-density linear chains disappeared and the number of asymmetric chains increased. At high adsorption coverage, K atoms began to form symmetric chains, so that the symmetric and asymmetric chains coexisted. The strong dependency of the adsorption structure on the coverage is discussed by considering a recent theoretical work.
  • Oka Hirofumi, Subagyo Agus, Sawamura Makoto, Sueoka Kazuhisa, Mukasa Koichi
    Japanese Journal of Applied Physics 公益社団法人 応用物理学会 41 (7) 4969 - 4972 0021-4922 2002 [Not refereed][Not invited]
    Scanning tunneling microscopy (STM) measurements reveal that Fe thin films epitaxially grown on a MgO(001) substrate under appropriate conditions have an atomic step-terrace surface with a <I>c</I>(2 × 2) surface reconstruction, and that this surface is often accompanied by line-like patterns along the Fe‹110› direction. We have investigated the electronic properties of the patterns in detail by atomically resolved STM. We found that the pattern is a domain phase boundary of the <I>c</I>(2 × 2) domains, and that the domain boundaries consist of atoms exhibiting a (1 × 1) structure. The STM image shows remarkable bias-voltage dependency as indicated by the contrast inversion between the patterns and <I>c</I>(2 × 2) domains as the polarity of the applied bias-voltage is changed, and the contrast achieved its maximum value at +0.2 V. This bias-voltage dependency of the patterns can be explained by the existence of surface states which are observed at around 0.2 eV above the Fermi level on the Fe(001) (1 × 1) surface and 0.4 eV on the <I>c</I>(2 × 2) domains.
  • H Ohno, K Yoh, T Doi, A Subagyo, K Sueoka, K Mukasa
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 19 (6) 2280 - 2283 1071-1023 2001/11 [Refereed][Not invited]
    We report on the growth of planar/patterned Fe thin films on InAs(100) substrates and their subsequent characterization using reflection high-energy electron diffraction, low-energy electron diffraction, superconducting quantum interference device, and four-terminal contact resistance measurements. Epitaxial growth of body-centered-cubic Fe crystal on InAs(100) was verified for growth temperatures of 23 degreesC and 175 degreesC. A patterned Fe wire array showed clear uniaxial shape anisotropy with the easy axis along the wire direction. Its coercive force was found to depend on the growth temperature and the width of the Fe wires. Four-terminal contact resistance measurement of Fe/n-InAs revealed that Fe forms decent ohmic contact to the InAs substrate with a resistivity of the order of 10(-6) Omegacm(2). Samples crown at room temperature showed equally decent or even better magnetic and electrical characteristics than those obtained by higher temperature growth. These results indicate that the Fe/InAs hybrid structures have definite potential for spin-related semiconductor devices with practical process sequences. (C) 2001 American Vacuum Society.
  • Oka Hirofumi, Subagyo Agus, Sawamura Makoto, Sueoka Kazuhisa, Mukasa Kōichi
    Jpn J Appl Phys Publication Office, Japanese Journal of Applied Physics, Faculty of Science, University of Tokyo 40 (6) 4334 - 4336 0021-4922 2001/06/30 [Not refereed][Not invited]
    Fe thin films with flat surfaces are obtained on a MgO(001) substrate at a growth temperature of 550 K. The surfaces with atomically flat and wide terraces exhibit a $c(2{\times}2)$ reconstructed structure. To evaluate the effect of impurity atoms at the surface on the surface structures, scanning tunneling spectroscopy (STS), reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS) studies were performed. The differential conductivity (${dI/dV}$) spectrum of the $c(2{\times}2)$ Fe(001) thin-film surfaces indicates an intense peak at the sample bias voltage of 0.4 V. Since there is no clear evidence of impurity adatoms forming such a surface structure, we expect that the topmost atoms are Fe, and that the observed peak originates from surface states.
  • A Subagyo, K Sueoka, K Mukasa
    NUCLEATION AND GROWTH PROCESSES IN MATERIALS 580 429 - 434 0272-9172 2000 [Refereed][Not invited]
    We reported a scanning tunneling microscopy(STM) observation on the growth mode transition from 2D-nucleation to spiral growth in the epitaxial Fe films on MgO(001). As the growth temperature is increased to above 493 K, a temperature region where the Schwoebel barrier is overcome, the Fe films grow in a 2D-nucleation and growth mode formed atomically flat films. The 2D-nucleation transformed into a spiral growth as increasing film thickness. At a growth temperature of 493 K, the transition of 2D nucleation to the spiral growth was observed at a film thickness of 75 Angstrom. The critical thickness of the emergence of growth transition decreased as the growth temperature is increased.
  • Subagyo Agus, Oka Hirofumi, Eilers Guido, Sueoka Kazuhisa, Mukasa Koichi
    Japanese Journal of Applied Physics 公益社団法人 応用物理学会 39 (6) 3777 - 3779 0021-4922 2000 [Not refereed][Not invited]
    We report the first atomic-resolution scanning tunneling microscopy (STM) image of epitaxial bcc-Fe(001) films grown on MgO(001) substrates. A 50-\AA-thick Fe film grown at a growth temperature of 550 K formed square pyramidal islands with atomically flat terraces. The terraces were found to range between 5 nm and 20 nm in width separated by monoatomic high steps. The film exhibited a (1× 1) unreconstructed structure at a film thickness below 19 \AA; however, a reconstructed surface was found on thicker films. The atomic-resolution STM image and low energy electron diffraction (LEED) observation indicated that the reconstructed structure is a c(2× 2) structure.
  • A Subagyo, K Sueoka, K Mukasa
    IEEE TRANSACTIONS ON MAGNETICS 35 (5) 3037 - 3039 0018-9464 1999/09 [Refereed][Not invited]
    The effects of substrate annealing on the growth morphology of bcc-Fe(001) films epitaxially grown on MgO (001) surfaces have been investigated. Substrate annealing at 1000 degrees C for 30 minutes produced step-terrace surfaces which are the basis of flat and square Fe islands. By increasing the annealing time, the step profiles are improved to form long straight steps. Longer annealing time caused an increase of segregated impurities regions and a reconstruction of the MgO surface. The presence of the segregated impurities and the reconstructed MgO surface negate the annealing effects, i.e. it reduces the step edge growth that enhances the formation of round islands, degrades the uniformity of Fe island size and increases the rms roughness of Fe films.
  • Subagyo Agus, Sueoka Kazuhisa, Mukasa Koichi, Hayakawa Kazunobu
    Japanese Journal of Applied Physics 公益社団法人 応用物理学会 38 (6) 3820 - 3825 0021-4922 1999 [Not refereed][Not invited]
    Substrate preparation procedure dependence of the growth morphology and magnetic properties of 25 ML bcc-Fe(001) thin films epitaxially grown on MgO(001) substrates in a wide range of growth temperature was investigated by means of scanning tunneling microscopy (STM) and superconducting quantum interference device (SQUID). The growth morphology of Fe thin films was uniform both on a polished and on an annealed substrate, but nonuniform on a cleaved substrate. It was very difficult to obtain a flat Fe thin film on the cleaved substrate, and the film became discontinuous at or above a growth temperature of 493 K. At a growth temperature of 550 K, atomically defined terraces of Fe thin films were formed on the annealed substrate but were not formed on the polished substrate. A continuous film grown on the annealed substrate at a temperature of 593 K has a less magnetic anisotropy. The other continuous films have low coercivity of about 8 Oe and a biaxial magnetic anisotropy. The dependency of the growth morphology and magnetic properties of Fe thin films upon substrate preparation procedures concerning the presence of step-terraces on the substrate surface is discussed.
  • SUEOKA Kazuhisa, HOSOYAMA Naoki, SUBAGYO Agus, MUKASA Koichi, HAYAKAWA Kazunobu
    Journal of the Surface Science Society of Japan 日本表面科学会 19 (8) 522 - 526 0388-5321 1998/08/10 [Not refereed][Not invited]


Industrial Property Rights

  • WO/2010/079573:電界効果トランジスタ、その製造方法およびバイオセンサ  2010
    アグス スバギョ, 中村基訓, 山林智明, 高橋理, 菊地洋明, 近藤勝則
  • WO/2009/144902:電界効果トランジスタおよびその製造方法  2009
    菊地洋明, 高橋理, 近藤勝則, 山林智明, 小笠原邦男, 石垣忠, 稗貫豊, 中村基訓, アグス スバギョ

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