Co-reporter:Bashir Ahmad, Muhammad Naeem Ashiq, Muhammad Shuaib Khan, Minoru Osada, Muhammad Najam-Ul-Haq, Irshad Ali
Journal of Alloys and Compounds 2017 Volume 723(Volume 723) pp:
Publication Date(Web):5 November 2017
DOI:10.1016/j.jallcom.2017.06.219
•Simple and economical sol-gel method has been used for the fabrication of materials.•DC resistivity increase with the substituent content.•Curie temperature decrease with Nd-Mn concentration.•Synthesized materials can be used for applications in microwave devices.Technologically important ferrites magnetic materials with nominal composition “Sr2-xNdxCo2MnyFe12-yO22” (x = 0.0 to 0.1 and y = 0.0 to 1.0) were fabricated by the simple sol-gel method. The X-ray diffraction analysis endorsed the formation of well-defined Y-type hexagonal single phase with crystallite size in range of 38–45 nm. Owing to reduction of Fe3+ ions at octahedral site, an increase in DC resistivity was observed from 4.083 × 108 to 2.376 × 109 Ω-cm with the increase in substituents content. The two conduction mechanisms operating in ferri- and paramagnetic regions were shown by Arrhenius plot. It was observed that conduction in ferrimagnetic and paramagnetic regions was governed by the hopping of electrons and polarons, respectively. The decrease in Curie temperature “Tc” (553-423 K) was detected as a factor of Nd-Mn content due to decrease in FeFe interaction at octahedral site. The changes in the values of dielectric constant (ε′), dielectric loss factor (ε″) and tan loss (δ) follow Maxwell-Wagner model. The relatively high resistivity (2.376 × 109 Ω-cm) and low dielectric constants (2.97 at 1 MHz) for the sample with x = 0.1 and y = 1.0 make this material as an excellent candidates for high frequency microwave devices.Download high-res image (210KB)Download full-size image
Co-reporter:Bao-Wen Li; Minoru Osada; Yasuo Ebina; Shigenori Ueda;Takayoshi Sasaki
Journal of the American Chemical Society 2016 Volume 138(Issue 24) pp:7621-7625
Publication Date(Web):June 13, 2016
DOI:10.1021/jacs.6b02722
Multiferroic materials, in which the electronic polarization can be switched by a magnetic field and vice versa, are of fundamental importance for new electronic technologies. However, there exist very few single-phase materials that exhibit such cross-coupling properties at room temperature, and heterostructures with a strong magnetoelectric coupling have only been made with complex techniques. Here, we present a rational design for multiferroic materials by use of a layer-by-layer engineering of 2D nanosheets. Our approach to new multiferroic materials is the artificial construction of high-quality superlattices by interleaving ferromagnetic Ti0.8Co0.2O2 nanosheets with dielectric perovskite-structured Ca2Nb3O10 nanosheets. Such an artificial structuring allows us to engineer the interlayer coupling, and the (Ti0.8Co0.2O2/Ca2Nb3O10/Ti0.8Co0.2O2) superlattices induce room-temperature ferroelectricity in the presence of the ferromagnetic order. Our technique provides a new route for tailoring artificial multiferroic materials in a highly controllable manner.
Co-reporter:Sang Sub Kim, Tran Van Khai, Vadym Kulish, Yoon-Hyun Kim, Han Gil Na, Akash Katoch, Minoru Osada, Ping Wu, and Hyoun Woo Kim
Chemistry of Materials 2015 Volume 27(Issue 12) pp:4222
Publication Date(Web):June 10, 2015
DOI:10.1021/cm504802j
Bandgap engineering of atomically thin 2D crystals is critical for their applications in nanoelectronics, optoelectronics, and photonics. Here, we report a simple but rather unexpected approach for bandgap engineering of muscovite-type mica nanosheets (KAl3Si3O10(OH)2) via controlled molecular thickness. Through density functional calculations, we analyze electronic structures in 2D mica nanosheets and develop a general picture for tunable bandgap narrowing induced by controlled molecular thickness. From conducting atomic force microscopy, we observe an abnormal bandgap narrowing in 2D mica nanosheets, contrary to well-known quantum size effects. In mica nanosheets, decreasing the number of layers results in reduced bandgap energy from 7 to 2.5 eV, and the bilayer case exhibits a semiconducting nature with ∼2.5 eV. Structural modeling by transmission electron microscopy and density functional calculations reveal that this bandgap narrowing can be defined as a consequence of lattice relaxations as well as surface doping effects. These bandgap engineered 2D mica nanosheets open up an exciting opportunity for new physical properties in 2D materials and may find diverse applications in 2D electronic/optoelectronic devices.
Co-reporter:Minoru Osada and Takayoshi Sasaki
Polymer Journal 2015 47(2) pp:89-98
Publication Date(Web):December 10, 2014
DOI:10.1038/pj.2014.111
Hierarchical self‐assembly is a ubiquitous process in nature that underlies the formation of complex biological structures. In recent decades, scientists have aspired to exploit biomimetic approaches to create new artificial materials with hierarchical structures and tailored properties. However, de novo design of such hierarchically structured materials is still a major challenge. In this Focus Review, we provide an overview of new design principles for hierarchical nanoarchitectures using a layer-by-layer (LbL) assembly of two-dimensional (2D) oxide nanosheets. 2D oxide nanosheets have remarkable potential as building blocks for tailoring fusion materials combined with a range of foreign materials such as organic molecules, gels, polymers, and inorganic and metal nanoparticles. The ability to create functionalized, 2D hierarchical systems will lead to various applications in optoelectronics, spinelectronics, energy and environment technologies.
Co-reporter:Minoru Osada, Satoshi Yoguchi, Masayuki Itose, Bao-Wen Li, Yasuo Ebina, Katsutoshi Fukuda, Yoshinori Kotani, Kanta Ono, Shigenori Ueda and Takayoshi Sasaki
Nanoscale 2014 vol. 6(Issue 23) pp:14227-14236
Publication Date(Web):29 Oct 2014
DOI:10.1039/C4NR04465G
Ti1−x−yFexCoyO2 nanosheets are synthesized in which the (Fe/Co) content is systematically controlled in the range of 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.2. A key feature of this new preparation is the use of (Li/Fe)-, (Fe/Co)- and (Li/Co)-co-substituted layered titanates as starting materials. In exfoliated nanosheets, the composition can be intentionally modified by controlled Fe/Co substitution into Ti sites during the solid-state synthesis of the starting layered compounds. The composition of the host layers is maintained in the subsequent exfoliation process, which is very helpful in the rational design of nanosheets through the use of controlled doping. Through this controlled doping, we achieve exquisite control of the electronic properties of Ti1-δO2 nanosheets, including the position of impurity bands, the Fermi energy and ferromagnetic properties. From photoelectron spectroscopy and first-principles studies, we have observed that the use of Fe/Co co-doping with higher Fe and Co oxidation states is necessary to bring the highest occupied Fe/Co impurity states to the Fermi level. This band engineering transforms the Ti1−x−yFexCoyO2 nanosheet into a room-temperature half-metallic ferromagnet, thus accomplishing the main requirements of future spinelectronics.
Co-reporter:Yoon-Hyun Kim, Hyung-Jun Kim, Minoru Osada, Bao-Wen Li, Yasuo Ebina, and Takayoshi Sasaki
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 22) pp:19510
Publication Date(Web):November 5, 2014
DOI:10.1021/am506629g
We investigated high-temperature dielectric responses of high-κ perovskite nanosheet (Ca2Nb3O10), an important material platform for postgraphene technology and ultrascale electronic devices. Through in situ characterizations using conducting atomic force microscopy, we found a robust high-temperature property of Ca2Nb3O10 nanosheet even in a monolayer form (∼2 nm). Furthermore, layer-by-layer assembled nanocapacitors retained both size-free high-εr characteristic (∼200) and high insulation resistance (∼1 × 10–7 A/cm2) at high temperatures up to 250 °C. The simultaneous improvement of εr and thermal stability in high-κ nanodielectrics is of critical technological importance, and perovskite nanosheet has great potential for a rational design and construction of high-temperature capacitors.Keywords: 2D perovskite nanosheet; high-temperature capacitor; in situ characterization; nanodielectric; thermal stability
Co-reporter:Bao-Wen Li, Minoru Osada, Yasuo Ebina, Kosho Akatsuka, Katsutoshi Fukuda, and Takayoshi Sasaki
ACS Nano 2014 Volume 8(Issue 6) pp:5449
Publication Date(Web):May 5, 2014
DOI:10.1021/nn502014c
A systematic study has been conducted to examine the thermal stability of layer-by-layer assembled films of perovskite-type nanosheets, (Ca2Nb3O10–)n (n = 1–10), which exhibit superior dielectric and insulating properties. In-plane and out-of-plane X-ray diffraction data as well as observations by atomic force microscopy and transmission electron microscopy indicated the high thermal robustness of the nanosheet films. In a monolayer film with an extremely small thickness of ∼2 nm, the nanosheet was stable up to 800 °C, the temperature above which segregation into CaNb2O6 and Ca2Nb2O7 began. The critical temperature moderately decreased as the film thickness, or the number of nanosheet layers, increased, and reached 700 °C for seven- and 10-layer films, which is comparable to the phase transformation temperature for a bulk phase of the protonic layered oxide of HCa2Nb3O10·1.5H2O as a precursor of the nanosheet. This thermal stabilization of perovskite-type nanosheets should be associated with restricted nucleation and crystal growth peculiar to such ultrathin 2D bound systems. The stable high-k dielectric response (εr = 210) and highly insulating nature (J < 10–7 A cm–2) remained substantially unchanged even after the nanosheet film was annealed up to 600 °C. This study demonstrates the high thermal stability of 2D perovskite-type niobate nanosheets in terms of structure and dielectric properties, which suggests promising potential for future high-k devices operable over a wide temperature range.Keywords: layer-by-layer assembly; nanodielectrics; perovskite-type nanosheets; thermal stability
Co-reporter:Minoru Osada, Natália Hajduková-Šmídová, Kosho Akatsuka, Satoshi Yoguchi and Takayoshi Sasaki
Journal of Materials Chemistry A 2013 vol. 1(Issue 14) pp:2520-2524
Publication Date(Web):04 Mar 2013
DOI:10.1039/C3TC00952A
We report on a new magneto-plasmonic material consisting of 1 nm thick ferromagnetic nanosheets and Au nanoparticles. The magneto-optical (MO) Kerr spectra of Ti0.8Co0.2O2 nanosheets near Au surfaces showed a gigantic MO response (∼106 deg cm−1) in the visible wavelength region (380–600 nm), not present in Ti0.8Co0.2O2 nanosheets on a bare glass substrate. The observed peaks correspond to intrinsic d–d* electronic transitions in Ti0.8Co0.2O2 and are consistent with the near-field enhancement of the MO response resulting from the spectral overlap of the surface-plasmon-resonance (SPR) in the Au surface with the electronic transitions in Ti0.8Co0.2O2. Similar SPR effects were also achieved in ferromagnetic nanosheet/Au with different compositions and with different separation distances (<5 nm). This demonstration of SPR-enhanced magneto-optics in the ferromagnetic/plasmonic nanosystem may enable designing of nanoarchitectures for miniaturized high-performance MO devices and for remote sensing and imaging of magnetic fields.
Co-reporter:Chulho Jung, Tsuyoshi Ohnishi, Minoru Osada, Kazunori Takada, and Takayoshi Sasaki
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 11) pp:4592
Publication Date(Web):May 31, 2013
DOI:10.1021/am400849z
An approach to fabricate Ba0.5Sr0.5TiO3 (BST) films with a preferred orientation on a glass substrate by pulsed laser deposition was developed. To ensure a preferred crystallographic orientation, we utilized a molecularly thin Ca2Nb3O10 perovskite nanosheet as a seed layer and successfully fabricated BST films with a nearly perfect (100)-axis orientation. The 100 nm films after annealing at 450 °C in air showed a good dielectric performance (εr > 400), which was comparable to the εr value of epitaxially grown films with the same thickness. These results indicate that the nanosheet seed layer plays a crucial role in controlled film growth, realizing a nearly intrinsic performance of BST.Keywords: Ba1−xSrxTiO3; dielectrics; nanosheet; seed layer; thin-film growth;
Co-reporter:Dr. Norihiro Suzuki;Mohamed B. Zakaria;Nagy L. Torad;Dr. Kevin C.-W. Wu;Dr. Yoshihiro Nemoto;Dr. Masataka Imura;Dr. Minoru Osada;Dr. Yusuke Yamauchi
Chemistry - A European Journal 2013 Volume 19( Issue 14) pp:4446-4450
Publication Date(Web):
DOI:10.1002/chem.201203421
Co-reporter:Minoru Osada;Takayoshi Sasaki
Advanced Materials 2012 Volume 24( Issue 2) pp:210-228
Publication Date(Web):
DOI:10.1002/adma.201103241
Abstract
Two-dimensional (2D) nanosheets, which possess atomic or molecular thickness and infinite planar lengths, are regarded as the thinnest functional nanomaterials. The recent development of methods for manipulating graphene (carbon nanosheet) has provided new possibilities and applications for 2D systems; many amazing functionalities such as high electron mobility and quantum Hall effects have been discovered. However, graphene is a conductor, and electronic technology also requires insulators, which are essential for many devices such as memories, capacitors, and gate dielectrics. Along with graphene, inorganic nanosheets have thus increasingly attracted fundamental research interest because they have the potential to be used as dielectric alternatives in next-generation nanoelectronics. Here, we review the progress made in the properties of dielectric nanosheets, highlighting emerging functionalities in electronic applications. We also present a perspective on the advantages offered by this class of materials for future nanoelectronics.
Co-reporter:Minoru Osada;Takayoshi Sasaki
Advanced Materials 2012 Volume 24( Issue 2) pp:
Publication Date(Web):
DOI:10.1002/adma.201290002
Co-reporter:Bao-Wen Li, Minoru Osada, Tadashi C. Ozawa, and Takayoshi Sasaki
Chemistry of Materials 2012 Volume 24(Issue 16) pp:3111
Publication Date(Web):August 2, 2012
DOI:10.1021/cm3013039
Co-reporter:Minoru Osada;Genki Takanashi;Bao-Wen Li;Kosho Akatsuka;Yasuo Ebina;Kanta Ono;Hiroshi Funakubo;Kazunori Takada;Takayoshi Sasaki
Advanced Functional Materials 2011 Volume 21( Issue 18) pp:3482-3487
Publication Date(Web):
DOI:10.1002/adfm.201100580
Abstract
An important challenge in current microelectronics research is the development of techniques for making smaller, higher-performance electronic components. In this context, the fabrication and integration of ultrathin high-κ dielectrics with good insulating properties is an important issue. Here, we report on a rational approach to produce high-performance nanodielectrics using one-nanometer-thick oxide nanosheets as a building block. In titano niobate nanosheets (TiNbO5, Ti2NbO7, Ti5NbO14), the octahedral distortion inherent to site-engineering by Nb incorporation results in a giant molecular polarizability, and their multilayer nanofilms exhibit a high dielectric constant (160–320), the largest value seen so far in high-κ nanofilms with thickness down to 10 nm. Furthermore, these superior high-κ properties are fairly temperature-independent with low leakage-current density (<10−7 A cm−2). This work may provide a new recipe for designing nanodielectrics desirable for practical high-κ devices.
Co-reporter:Minoru Osada, Takayoshi Sasaki, Kanta Ono, Yoshinori Kotani, Shigenori Ueda, and Keisuke Kobayashi
ACS Nano 2011 Volume 5(Issue 9) pp:6871
Publication Date(Web):August 8, 2011
DOI:10.1021/nn200835v
We have investigated the interface electronic states in self-assembled (Ti0.8Co0.2O2/Ti0.6Fe0.4O2)n superlattices by X-ray photoelectron spectroscopy. A charge of about −0.3 electron is transferred from Fe to Co ions across the interface and induces a major reconstruction of the orbital occupation at the interfacial (Ti0.8Co0.2O2/Ti0.6Fe0.4O2) layers. Supported by first-principles calculations, the Co3+ state is partially occupied at the interface by superlattice formation, and this new magnetic state directly influences the coupling between Ti0.8Co0.2O2 and Ti0.6Fe0.4O2 nanosheets. These data indicate that the orbital reconstruction is indeed realized by the interface charge transfer between Co and Fe ions in the adjoined nanosheets, and the generic feature of engineered interfaces can be extended to self-assembled superlattices of oxide nanosheets.Keywords: ferromagnetic nanosheets; interface ferromagnetism; layer-by-layer assembly; orbital reconstruction; X-ray photoemission spectroscopy
Co-reporter:Minoru Osada, Kosho Akatsuka, Yasuo Ebina, Hiroshi Funakubo, Kanta Ono, Kazunori Takada, and Takayoshi Sasaki
ACS Nano 2010 Volume 4(Issue 9) pp:5225
Publication Date(Web):August 24, 2010
DOI:10.1021/nn101453v
Size-induced suppression of permittivity in perovskite thin films is a fundamental problem that has remained unresolved for decades. This size-effect issue becomes increasingly important due to the integration of perovskite nanofilms into high-κ capacitors, as well as concerns that intrinsic size effects may limit their device performance. Here, we report a new approach to produce robust high-κ nanodielectrics using perovskite nanosheet (Ca2Nb3O10), a new class of nanomaterials that is derived from layered compounds by exfoliation. By a solution-based bottom-up approach using perovskite nanosheets, we have successfully fabricated multilayer nanofilms directly on SrRuO3 or Pt substrates without any interfacial dead layers. These nanofilms exhibit high dielectric constant (>200), the largest value seen so far in perovskite films with a thickness down to 10 nm. Furthermore, the superior high-κ properties are a size-effect-free characteristic with low leakage current density (<10−7 A cm−2). Our work provides a key for understanding the size effect and also represents a step toward a bottom-up paradigm for future high-κ devices.Keywords: high-κ dielectrics; layer-by-layer assembly; perovskite nanosheets; size effect
Co-reporter:Bao-Wen Li, Minoru Osada, Tadashi C. Ozawa, Yasuo Ebina, Kosho Akatsuka, Renzhi Ma, Hiroshi Funakubo, and Takayoshi Sasaki
ACS Nano 2010 Volume 4(Issue 11) pp:6673
Publication Date(Web):November 4, 2010
DOI:10.1021/nn102144s
Combining different materials into desired superlattice structures can produce new electronic states at the interface and the opportunity to create artificial materials with novel properties. Here we introduce a new, rather unexpected, and yet simple way to such a superlattice assembly of perovskite oxides: in the Dion−Jacobson phase, a model system of layered perovskites, high-quality bicolor perovskite superlattices (LaNb2O7)nL(Ca2Nb3O10)nC are successfully fabricated by a layer-by-layer assembly using two different perovskite nanosheets (LaNb2O7 and Ca2Nb3O10) as a building block. The artificially fabricated (LaNb2O7/Ca2Nb3O10) superlattices are structurally unique, which is not feasible to create in the bulk form. By such an artificial structuring, we found that (LaNb2O7/Ca2Nb3O10) superlattices possess a new form of interface coupling, which gives rise to ferroelectricity.Keywords: artificial superlattice; ferroelectricity; layer-by-layer assembly; perovskite nanosheets
Co-reporter:Xiaoping Dong, Minoru Osada, Hidekazu Ueda, Yasuo Ebina, Yoshinori Kotani, Kanta Ono, Shigenori Ueda, Keisuke Kobayashi, Kazunori Takada and Takayoshi Sasaki
Chemistry of Materials 2009 Volume 21(Issue 19) pp:4366
Publication Date(Web):August 31, 2009
DOI:10.1021/cm900210m
We report the synthesis of Mn-substituted titania nanosheets and the preparation of room-temperature ferromagnetic thin films via layer-by-layer assembly of these nanosheets. Ti(5.2−2x)/6Mnx/2O2 (x = 0.0−0.4) nanosheets were synthesized by delaminating layered titanates [K0.8Ti(5.2−2x)/3Li(0.8−x)/3MnxO4], in which the Mn content was systematically controlled by Li+ doping. We found that Mn content in the host layers was preserved upon exfoliation, and controlled Mn doping was achieved in exfoliated Ti(5.2−2x)/6Mnx/2O2 (x = 0.0−0.4) nanosheets, where Li+ ions were completely extracted by acid-exchange reaction in the exfoliation process. The multilayer films of Ti(5.2−2x)/6Mnx/2O2 (x = 0.0−0.4) nanosheets exhibit a clear magnetic hysteresis loop at room-temperature in similar to what observed in ferromagnetic Ti1−xCoxO2 nanosheets. Electronic absorption, magnetic circular dichroism, and hard X-ray photoelectron spectroscopy were used to identify Mn-derived states, and analyze the properties of these states related to ferromagnetism. The first-principles calculation of Ti(5.2−2x)/6Mnx/2O2 was also employed to characterize the doping effect on electronic structures.
Co-reporter:Minoru Osada and Takayoshi Sasaki
Journal of Materials Chemistry A 2009 vol. 19(Issue 17) pp:2503-2511
Publication Date(Web):18 Mar 2009
DOI:10.1039/B820160A
Two-dimensional (2D) nanosheets obtained via exfoliation of layered compounds have attracted intense research in recent years. In particular, the development of exotic 2D systems such as stable graphene and transition-metal oxide nanosheets has sparked new discoveries in condensed matter physics and nanoelectronics. Here, we review the progress made in the synthesis, characterization and properties of oxide nanosheets, highlighting emerging functionalities in electronic and spin-electronic applications. We also present a perspective on the advantages offered by this class of materials for future nanotechnology.
Co-reporter:M. Osada;Y. Ebina;H. Funakubo;S. Yokoyama;T. Kiguchi;K. Takada;T. Sasaki
Advanced Materials 2006 Volume 18(Issue 8) pp:1023-1027
Publication Date(Web):7 APR 2006
DOI:10.1002/adma.200501224
2D titania nanosheets are attractive candidates as insulating materials for high-κ dielectrics. Solution-based layer-by-layer deposition combined with an atomically flat SrRuO3 electrode produces atomically uniform multilayer nanofilms. These nanofilms exhibit high relative dielectric constants (ϵr) of approximately 125, even for thicknesses down to 10 nm, in contrast to size- induced degradation typical in high-κ materials (see figure).
Co-reporter:M. Osada;Y. Ebina;K. Takada;T. Sasaki
Advanced Materials 2006 Volume 18(Issue 3) pp:295-299
Publication Date(Web):26 JAN 2006
DOI:10.1002/adma.200501810
A two-dimensional titania nanosheet is proven to be useful as a host for spinelectronic materials. Magneto–optical measurements demonstrate that Co-substituted titania nanosheets (Ti0.8Co0.2O2) act as nanoscale ferromagnetic layers at room temperature, and their multilayer assemblies exhibit robust magnetic circular dichroism (MCD) in the ultraviolet–visible region. The availability of ferromagnetic nanostructures allows the rational design of high-efficiency magneto–optical devices.
Co-reporter:Minoru Osada, Toshiyuki Sakemi, Tetsuya Yamamoto
Thin Solid Films 2006 Volume 494(1–2) pp:38-41
Publication Date(Web):3 January 2006
DOI:10.1016/j.tsf.2005.07.179
We report on Raman scattering studies of Ga-doped ZnO thin films that were grown by intentionally changing oxygen partial pressure in order to study the influences of oxygen partial pressure on local structural properties of this material. Raman spectra of ZnO:Ga (3 wt.% Ga-doped) films revealed vibrational modes at 575 and 630–660 cm− 1 in addition to the host phonons of ZnO. These additional modes correspond to local vibrational modes associated with oxygen vacancy (VO) and Ga impurity (GaZn), respectively. With increasing oxygen partial pressure (oxygen flow rate up to ∼ 10 sccm), the 575-cm− 1 mode decreases in its intensity, indicating the reduced VO concentration. Further increasing oxygen partial pressure (> 10 sccm), we find a substantial disorder apparent in host ZnO phonons and some additional modes. These results suggest that the oxygen-rich condition may cause the formation of compensating-defects such as oxygen interstitials (Oi), Zn vacancy (VZn) and their complexes (GaZn–Oi, GaZn–VZn), strongly reducing carrier concentration in this system.
Co-reporter:Minoru Osada, Natália Hajduková-Šmídová, Kosho Akatsuka, Satoshi Yoguchi and Takayoshi Sasaki
Journal of Materials Chemistry A 2013 - vol. 1(Issue 14) pp:NaN2524-2524
Publication Date(Web):2013/03/04
DOI:10.1039/C3TC00952A
We report on a new magneto-plasmonic material consisting of 1 nm thick ferromagnetic nanosheets and Au nanoparticles. The magneto-optical (MO) Kerr spectra of Ti0.8Co0.2O2 nanosheets near Au surfaces showed a gigantic MO response (∼106 deg cm−1) in the visible wavelength region (380–600 nm), not present in Ti0.8Co0.2O2 nanosheets on a bare glass substrate. The observed peaks correspond to intrinsic d–d* electronic transitions in Ti0.8Co0.2O2 and are consistent with the near-field enhancement of the MO response resulting from the spectral overlap of the surface-plasmon-resonance (SPR) in the Au surface with the electronic transitions in Ti0.8Co0.2O2. Similar SPR effects were also achieved in ferromagnetic nanosheet/Au with different compositions and with different separation distances (<5 nm). This demonstration of SPR-enhanced magneto-optics in the ferromagnetic/plasmonic nanosystem may enable designing of nanoarchitectures for miniaturized high-performance MO devices and for remote sensing and imaging of magnetic fields.
Co-reporter:Minoru Osada and Takayoshi Sasaki
Journal of Materials Chemistry A 2009 - vol. 19(Issue 17) pp:NaN2511-2511
Publication Date(Web):2009/03/18
DOI:10.1039/B820160A
Two-dimensional (2D) nanosheets obtained via exfoliation of layered compounds have attracted intense research in recent years. In particular, the development of exotic 2D systems such as stable graphene and transition-metal oxide nanosheets has sparked new discoveries in condensed matter physics and nanoelectronics. Here, we review the progress made in the synthesis, characterization and properties of oxide nanosheets, highlighting emerging functionalities in electronic and spin-electronic applications. We also present a perspective on the advantages offered by this class of materials for future nanotechnology.
