研究者詳細 - 中嶋　敦

論文 - 中嶋　敦

分割表示 263 件中 61 - 80 件目／全件表示 >>

Formation of a superatom monolayer using gas-phase-synthesized Ta@Si₁₆ nanocluster ions

M. Nakaya, T. Iwasa, H. Tsunoyama, T. Eguchi, A. Nakajima

Nanoscale （Royal Society of Chemistry） 6 （ 24 ） 14702 - 14707 2014年10月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 20403364

The controlled assembly of superatomic nanocluster ions synthesized in the gas phase is a key technology for constructing a novel series of functional nanomaterials. However, it is generally difficult to immobilize them onto a conductive surface while maintaining their original properties owing to undesirable modifications of their geometry and charge state. In this study, it has been shown that this difficulty can be overcome by controlling the donor-acceptor interaction between nanoclusters and surfaces. Cations of Ta-atom-encapsulated Si16 cage nanoclusters (Ta@Si16) behaving as rare-gas-like superatoms are synthesized in the gas phase and deposited on conductive surfaces terminated with acceptor-like C60 and donor-like α-sexithiophene (6T) molecules. Scanning tunneling microscopy and spectroscopy have demonstrated that Ta@Si16 cations can be densely immobilized onto C60-terminated surfaces while retaining their cage shape and positive charge, which is realized by creating binary charge transfer complexes (Ta@Si16+-C60-) on the surfaces. The Ta@Si16 nanoclusters exhibit excellent thermal stability on C60-teminated surfaces similar to those in the gas phase, whereas the nanoclusters destabilize at room temperature on 6T-terminated surfaces owing to the loss of electronic closure via a change in the charge state. This journal is

Access to Document (DOI)

Development of ultrafine multichannel microfluidic mixer for synthesis of bimetallic nanoclusters: Catalytic application of highly monodisperse AuPd nanoclusters stabilized by poly(N-vinylpyrrolidone)

N. Hayashi, Y. Sakai, H. Tsunoyama, A. Nakajima

Langmuir （American Chemical Society） 30 （ 34 ） 10539 - 10547 2014年08月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 07437463

On account of their novel properties, bimetallic nanoparticles and nanoclusters (NCs) are strong potential candidates for optical, magnetic, and catalytic functional materials. These properties depend on the chemical composition and size (number of constituent atoms) of the NCs. Control of size, structure, and composition is particularly important for fabricating highly functional materials based on bimetallic NCs. Size- and structure-controlled synthesis of two-element alloys can reveal their intrinsic electronic synergistic effects. However, because synergistic enhancement of activity is strongly affected by composition as well as by size and structure, controlled synthesis is a challenging task, particularly in catalytic applications. To investigate catalytic synergistic effects, we have synthesized highly monodisperse, sub-2 nm, solid-solution AuPd NCs stabilized with poly(N-vinylpyrrolidone) (AuPd:PVP) using a newly developed ultrafine microfluidic mixing device with 15 m wide multiple lamination channels. The synergistic enhancement for catalytic aerobic oxidation of benzyl alcohol exhibited a volcano-shaped trend, with a maximum at 20-65 at. % Pd. From X-ray photoelectron spectroscopic measurements, we confirmed that the enhanced activity originates from the enhanced electron density at the Au sites, donated by Pd sites. © 2014 American Chemical Society.

Access to Document (DOI)

Electronic states of titanyl phthalocyanine films on alkanethiolate self-assembled monolayers probed by two-photon photoemission

M. Ogura, M. Shibuta, T. Eguchi, A. Nakajima

Journal of Electron Spectroscopy and Related Phenomena （Elsevier Science BV） 195 272 - 277 2014年07月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 0368-2048

We studied both occupied and unoccupied states of titanyl phthalocyanine (TiOPc) films formed on an octanethiolate self-assembled monolayer (SAM) on an Au(1 1 1) surface fabricated in a wet chemical process using two-photon photoemission (2PPE) spectroscopy. A 1.90-nm-thick layer of TiOPc formed an unoccupied state at 2.9 eV above the Fermi level. This state was resonantly enhanced at 4.3-4.4 eV photon energy, suggesting that electrons were excited from the highest occupied molecular orbital of TiOPc. The 2PPE measurements of photon energy dependence and light polarization selectivity revealed that the unoccupied state originates from a charge transfer exciton not observed in organic thin films deposited on bare metallic substrates. The formation of a charge transfer exciton implies that the SAM strongly insulates the molecular monolayer.

Access to Document (DOI)

Investigation of the electronic structures of organolanthanide sandwich complex anions by photoelectron spectroscopy: 4f orbital contribution in the metal-ligand interaction

N. Hosoya, K. Yada, T. Masuda, E. Nakajo, S. Yabushita, A. Nakajima

Journal of Physical Chemistry A （American Chemical Society） 118 （ 17 ） 3051 - 3060 2014年04月

研究論文（学術雑誌）, 最終著者, 責任著者, 査読有り, ISSN 10895639

The electronic structures of lanthanide (Ln) ions sandwiched between 1,3,5,7-cyclooctatetraene (COT), Ln(COT)2-, have been investigated by anion photoelectron spectroscopy. Complexes of 12 Ln atoms were investigated (excluding promethium (Pm), europium (Eu), and ytterbium (Yb)). The 213 nm photoelectron (PE) spectra of Ln(COT)2- exhibit two peaks assignable to the highest occupied molecular orbital (HOMO; e 2u) and the next HOMO (HOMO-1; e2g) approximately at 2.6 and 3.6 eV, respectively, and their energy gap increases as the central metal atom progresses from lanthanum (La) to lutetium (Lu). Since lanthanide contraction shortens the distance between the Ln atom and the COT ligands, the widening energy gap represents the destabilization of the e2u orbital as well as the stabilization of the e2g orbital. Evidence for 4f orbital contribution in the metal-ligand interaction has been revealed by the Ln atom dependence in which the same e2u orbital symmetry enables an interaction between the 4f orbital of Ln atoms and the π orbital of COT. © 2014 American Chemical Society.

Access to Document (DOI)

Formation and electronic structures of organoeuropium sandwich nanowires

N. Hosoya, R. Takegami, J. Suzumura, K. Yada, K. Miyajima, M. Mitsui, M. B. Knickelbein, S. Yabushita, A. Nakajima

Journal of Physical Chemistry A （American Chemical Society） 118 （ 37 ） 8298 - 8308 2014年04月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 1089-5639

Organoeuropium sandwich clusters, comprising europium (Eu) and 1,3,5,7-cyclooctatetraene (COT) (Eun(COT)m), were produced in the gas phase using a laser vaporization synthesis method. Photoionization mass spectra revealed an exclusive Eun(COT)m formation with three compositions: m = n + 1, m = n, and m = n - 1, which, we propose, correspond to full-sandwich, half-sandwich, and inverted-sandwich structures, respectively. The charge distributions, metal-ligand bonding characteristics, and electronic structures of the clusters were comprehensively investigated by photoionization measurements of Eun(COT)m neutrals and by photoelectron spectroscopy of Eun(COT)m- and isoelectronic Ban(COT)m- anions. The results confirmed that (1) highly ionic metal-ligand bonding is formed between Eu2+ and COT2- within the sandwich structure (at the termini, ionic forms are Eu+ and COT-) and (2) size dependence of orbital energy can be explained by the Coulombic interaction of simple point charge models between the detaching electrons and dipoles/quadrupoles. When the terminus of the sandwich clusters is Eu2+, COT2-, or Eu0, the orbital energy of the electron detachment channel at the opposite terminus strongly depends on the cluster size. In this case, the molecular stack behaves as a one-dimensionally aligned dipole; otherwise, it behaves as a quadrupole, and the relationship between cluster size and electron detachment energy is much weaker. The study also reports on the 4f orbital energy in Eu ions and the formation mechanism of organoeuropium sandwich nanowires up to 12 nm in length. The nanowires are formed by successive charge transfer at the terminal part, Eu+ and COT-, which reduces the ionization energy and increases the electron affinity, respectively. (Graph Presented).

Access to Document (DOI)

Physical properties of mononuclear organoeuropium sandwich complexes ligated by cyclooctatetraene and bis(trimethylsilyl)cyclooctatetraene

T. Tsuji, S. Fukazawa, R. Sugiyama, K. Kawasaki, T. Iwasa, H. Tsunoyama, N. Tokitoh, A. Nakajima

Chemical Physics Letters （Elsevier Science） 595-596 144 - 150 2014年03月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 0009-2614

Mononuclear organoeuropium sandwich complexes were synthesized from ligands of 1,3,5,7-cyclooctatetraene (COT) and 1,4- and 1,6-bis(trimethylsilyl)- cyclooctatetraenes (COT″) in a liquid ammonia of europium (Eu) and lithium (Li). Elemental analyses revealed the chemical compositions as [(DME)Li] 2Eu(COT)2 (1) and [(DME)Li]2Eu(COT″) 2 (2). Vibrational analyses and magnetic measurements revealed a ligand-Eu-ligand sandwich structure. The Eu2+ ions induce paramagnetic behaviors at 6-300 K. Although UV-irradiated 1 and 2 emit light of similar color, the quantum yields of their toluene solution widely differ (2.4% and 21%, respectively). The effects of the trimethylsilyl group are evaluated from quantum chemical calculations. © 2014 Elsevier B.V. All rights reserved.

Access to Document (DOI)

Liquid-phase synthesis of multidecker organoeuropium sandwich complexes and their physical properties

T. Tuji, N. Hosoya, S. Fukazawa, R. Sugiyama, T. Iwasa, H. Tsunoyama, H. Hamaki, N. Tokitoh, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 118 （ 11 ） 5896 - 5907 2014年03月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 1932-7447

Multidecker organoeuropium sandwich complexes were synthesized with the organic ligands 1,3,5,7-cyclooctatetraene (COT) and 1,4- and 1,6-bis(trimethylsilyl)cyclooctatetraenes (COT″) in a liquid ammonia solution of europium (Eu) metal. Infrared (IR) absorption and Raman spectroscopies and magnetic measurements were used to identify local structures and charge distributions. It was found that the organoeuropium complexes have Eu2+-COT2- (Eu2+-COT″2-) charge distributions, including a local structure of ligand-Eu-ligand sandwiches. Together with elemental analysis by inductively coupled plasma atomic emission spectroscopy, it is shown that the organoeuropium complexes form a multidecker sandwich structure that is insouble in many solvents. In addition to their paramagnetic behaviors at 150-300 K, the organoeuropium complexes of Eu-COT and Eu-COT″ showed red and orange-red emissions, respectively, under UV irradiation. The introdution of bulky trimethylsilyl groups onto COT prominently enhanced the emission intensity by more than a factor of 10 compared to that of Eu-COT, and similar emission enhancement was observed when ethylenediamine vapor was contacted with Eu-COT solid. The intensity enhancement and the shifts in the emission wavelength are discussed from the viewpoint of orbital interactions between Eu2+ and COT2- (COT″2-). © 2014 American Chemical Society.

Access to Document (DOI)

Formation and control of ultrasharp metal/molecule interfaces by controlled immobilization of size-selected metal nanoclusters onto organic molecular films

M. Nakaya, T. Iwasa, H. Tsunoyama, T. Eguchi, A. Nakajima

Advanced Functional Materials （Wiley-VCH Verlag GMBH） 24 （ 9 ） 1202 - 1210 2014年03月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 1616-301X

The formation of metallic layers on ultrathin molecular films via a well-controlled interface is essential for constructing organic nanodevices composed of metal/molecule/metal sandwich junctions. The scanning tunneling microscopy and spectroscopy studies demonstrate that an ultrasharp metal/molecule interface is realizable by depositing size-selected Ag nanoclusters (Agn) from the gas phase on few-layer films of C 60 molecules. It is also demonstrated that Agn nanoclusters can be immobilized on monolayer films of oligothiophene molecules via C60 molecules, although they three-dimensionally aggregate on bare oligothiophene films. It is also shown that electrons and holes are injected into the topmost layer of C60 films via the Ag n/C60 interface. Moreover, the barrier height for carrier injection at the Agn/C60 interface can be modified depending on the size of Agn nanoclusters and the kinetic energy during the deposition. The present results demonstrate that the controlled immobilization of metallic nanoclusters on molecular films can be used as a fabrication technology for metal/molecule/metal junctions. Metal/molecule heterojunctions are constructed by the controlled immobilization of size-selected Ag nanoclusters (Agn) from the gas phase on ultrathin C60 films. In such heterojunctions, electrons and holes can be precisely injected into the topmost C60 molecules in films via an atomically abrupt metal/molecule interface. The barrier height for carrier injection can be modified. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Access to Document (DOI)

Wavelength dependence of water microdroplet shattering with dual IR lasers and dye sensitization

A. Sugiyama, A. Nakajima

Zeitschrift fur Physikalische Chemie （Walter de Gruyter GMBH） 228 （ 4-5 ） 459 - 470 2014年02月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 0942-9352

We have used time-resolved imaging to examine the effect of incident radiation wavelength in the range 2.75-3.75 μm on the shattering of water microdroplets by single and dual lasers. Dye sensitization of microdroplets was induced by using the water-soluble dye sulforhodamine G; this enabled us to observe both the forward and backward components of fragmented droplets and splashes. Compared with employing a single IR laser, simultaneous illumination by two IR lasers can effectively compress the spatial distribution of small fragments around the absorption maximum for the OH-stretching vibration of liquid water (y=2.75-3.25 μm). Scattering and compression of the fragmented microdroplets after single and dual IR laser irradiation can be explained by conservation of momentum.

Access to Document (DOI)

Probing of an adsorbate-specific excited state on an organic insulating surface by two-photon photoemission spectroscopy

M. Shibuta, H. Hirata, T. Eguchi, A. Nakajima

Journal of the American Chemical Society （American Chemical Society） 136 （ 5 ） 1825 - 1831 2014年01月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 0002-7863

In this study, we investigate the photoexcited electronic states of ferrocene (Fc) molecules adsorbed on an organic insulating surface by two-photon photoemission spectroscopy. This insulating layer, composed of a decanethiolate self-assembled monolayer formed on an Au(111) substrate, enables us to probe the electronically excited states localized at the adsorbed Fc molecules. The adsorbate-specific state is resonantly excited by photons at 4.57 eV, which is 0.5 eV smaller than the energy of the first molecular Rydberg state of free Fc in the gas phase. This result indicates that the electrons are bound to both the excited hole formed in the adsorbate and the positive image charge induced in the substrate. The hybridized electronic characteristics of the adsorbate-specific state are responsible for the strong transition selectivity and short lifetime of the excited state. © 2014 American Chemical Society.

Access to Document (DOI)

Electronic and optical properties of vertex-sharing homo- and hetero-biicosahedral gold clusters

T. Iwasa, K. Nobusada, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 117 （ 46 ） 24586 - 24591 2013年11月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 1932-7447

Electronic and optical properties of vertex sharing homo- and heterobiicosahedral gold clusters [M1M2Au 23(PH3)10(SCH3)5Cl 2]2+ (M1/M2 = Au/Au, Pt/Hg) are investigated by means of density functional computations, focusing on superatom assembly. In the homo clusters, the projected density of states onto the spherical harmonics reveals that each icosahedral unit behaves as a superatom with the Au(6s6p) electrons and electron shell closings of S and P orbitals followed by unoccupied D orbitals; each unit satisfies an 8-electron superatom condition. Because the Au(5d) band appears between the S and P orbitals, the electronic structure is characterized as S, Au(5d)-band, and P. The lowest electronic excitation in the homo cluster is the P to D transition. In the hetero biicosahedral cluster, the central Au atoms of each icosahedron are replaced by Pt and Hg. The HOMO and LUMO are well localized to the PtAu 12 and HgAu12 units, respectively, forming a cluster-assembled heterojunction in a single stable structure. The absorption spectrum of the heterobiicosahedral cluster is characterized by charge transfer from PtAu12 to HgAu12 in the visible region, accompanied by a weak charge transfer in the opposite direction. Despite low numbers of charge carriers, the heterobiicosahedral cluster shows a large dipole moment. © 2013 American Chemical Society.

Access to Document (DOI)

Geometric, electronic, and optical properties of monomer and assembly of endohedral aluminum superatomic clusters

T. Iwasa, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 117 （ 41 ） 21551 - 21557 2013年10月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 1932-7447

Density functional computations are used to evaluate the geometric, electronic, and optical properties of endohedral aluminum clusters X@Al 12 (X = B, Al, Si, P) and their assemblies. All X@Al 12+/0/- clusters are perfect or slightly distorted icosahedral structures, with the exception of Al13+, which is highly distorted. The projected density of states (PDOS) onto the spherical harmonics of monomers clearly reveals superatom behavior and electron shell closings of F orbitals in a 40-electron species. The electronic absorption spectrum of SiAl12 is analyzed in terms of the superatom orbitals. The optimized structures of X@Al12-Y@Al12 (X-Y = Si-Si, B-P, Al-P) dimers are constructed by facing the sides of the monomers in a staggered fashion. The PDOS of the dimers mostly exhibit five hybridizations: S, P, SD, PF, and SDG. The exceptions are HOMO, which possesses a DFG hybridized character and lies between the PF and SDG regions, and LUMO, which possesses a DG hybridized character. By analyzing the simulated absorption spectra of the B@Al12-P@Al12 and Al13-P@Al12 heterodimers, charge transfers from B/Al@Al12 to P@Al12 are found in the visible region, weakly accompanying the opposite charge transfer. The heterodimers have substantial charge carriers, estimated as the difference in electron counts from the closed-shell Si@Al12, with slight charge depletions (∼0.2). The charge distributions in B@Al 12 and P@Al12 are essentially unaltered by the insertion of Si@Al12 into the heterodimer, resulting in that the heterotrimer possesses a larger dipole moment than the heterodimer. © 2013 American Chemical Society.

Access to Document (DOI)

Advanced nanocluster ion source based on high-power impulse magnetron sputtering and time-resolved measurements of nanocluster formation

C.-H. Zhang, H. Tsunoyama, H. Akatsuka, H. Sekiya, T. Nagase, A. Nakajima

Journal of Physical Chemistry A （American Chemical Society） 117 （ 40 ） 10211 - 10217 2013年09月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 1089-5639

We developed a new nanocluster (NC) ion source based on the high-power impulse magnetron sputtering (HiPIMS) technique coupled with a gas flow cell reactor. Silver NC anions (Agn-) with a maximum intensity of 5.5 nA (Ag11-) are generated with the size ranging from the atomic anion to the 70-mer, which is well-controlled by simply adjusting the peak power and repetition rate of the HiPIMS. By time-resolved density profiles of Agn-, we find that the ion beam generated by HiPIMS is characterized by individual 100 ms duration "bunches" below a repetition rate of 10 Hz, which is well-Thermalized with a group velocity of 5 m/s. The high intensity of the NCs is attributable to the high ionization fraction by this HiPIMS ion source, while the underlying mechanism of the flexible size tuning of the ion source is understood by time-resolved mass spectrometry coupled with the sequential growth mechanism; the increment of the density of the target species in the bunches with the peak power and the overlapping of the bunches with the repetition rate cause the formation of large NCs. © 2013 American Chemical Society.

Access to Document (DOI)

Geometric, electronic, and optical properties of a boron-doped aluminum cluster of B₂ Al₂₁^-: A density functional theory study

T. Iwasa, A. Nakajima

Chemical Physics Letters （Elsevier Science BV） 582 100 - 104 2013年09月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 00092614

We present the physicochemical properties for the lowest-energy isomer of a boron-doped aluminum cluster of B2Al21-. The isomer was obtained by basin-hopping minimization based on the density functional theory, starting from a face-sharing bi-icosahedral structure in which two boron atoms were endohedrally doped to each icosahedron. The lowest-energy isomer is a triangular form in which an aluminum cage encapsulates two boron atoms endohedrally. The electronic structure was analyzed by projecting Kohn-Sham orbitals onto the spherical harmonics; occupied and unoccupied frontier orbitals are dominantly G- and H-symmetries, respectively. Optical absorption is mainly assigned to G to H transitions. © 2013 Elsevier B.V. All rights reserved.

Access to Document (DOI)

Development of high-flux ion source for size-selected nanocluster ions based on high-power impulse magnetron sputtering

H. Tsunoyama, C.-H. Zhang, H. Akatsuka, H. Sekiya, T. Nagase, A. Nakajima

Chemistry Letters （Chemical Society of Japan） 42 （ 8 ） 857 - 859 2013年08月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 0366-7022

In this study, we have developed a highly intensive ion source of size-selected nanoclusters based on a high-power impulse magnetron sputtering method. The maximum intensity of the size-selected silver nanocluster anions exceeded that of standard ion sources by more than ten times. The high intensity in the present method was achieved by the high throughput of the ion optics and the high ionization fraction. Fine tuning of the nanocluster size distributions was also demonstrated. © 2013 The Chemical Society of Japan.

Access to Document (DOI)

Development of cluster ion source based on modulated pulse power magnetron sputtering technique

C.-H. Zhang, H. Tsunoyama, H. Akatsuka, H. Sekiya, T. Nagase, A. Nakajima

The 8th Annual IEEE International Conference on Nano/Micro Engineered and Molecular Systems （IEEE） 428 - 431 2013年07月

研究論文（国際会議プロシーディングス）, 共著, 最終著者, 責任著者, 査読有り

A new ion source based on modulated pulse power (MPP) magnetron sputtering (MSP) was developed and demonstrated for cluster production. By employing MPP-MSP, both silver and silicon cluster beams were produced and analyzed by a quadrupole mass spectrometer. It is found that the maximum intensity of silver cluster anions reaches 500 pA, which is considerably higher than that with a conventional DC-MSP. For silicon cluster cation, the overall ion intensity of the cluster beam by MPP-MSP is about three times higher than that generated by DC-MSP. © 2013 IEEE.

Access to Document (DOI)

Study on electronic properties of composite clusters toward nanoscale functional advanced materials

A. Nakajima

Bulletin of the Chemical Society of Japan （Chemical Society of Japan） 86 （ 4 ） 414 - 437 2013年04月

研究論文（学術雑誌）, 単著, 筆頭著者, 最終著者, 責任著者, 査読有り, ISSN 0009-2673

Clusters consisting of 101000 atoms size-dependently exhibit novel electronic and geometric properties. In particular, composite clusters composed of several elements and/or components provide a promising way for a bottom-up approach for designing functional advanced materials, because the functionality of the composite clusters can be optimized not only by the cluster size but also by their compositions. This account surveys recent investigations of composite clusters focusing on the efforts to create a new functional composite cluster by a fine doping or hybridization based on their size-specific electronic properties. Organometallic clusters and caged clusters are demonstrated as a representative example of designing the functionality of magnetism and electronic state structures. In order to create functional nanomaterials, furthermore, a fine controlling methodology of the soft-landing technique has been developed to fix the composite clusters onto a surface decorated with a self-assembled monolayer. The embedded isolation mechanism on the substrate is discussed form the viewpoint of self-assembly phenomena with the molecular ordering of σ σ interaction, and also the electronic structures characterized by molecular ordering of π- π interaction is intrinsically revealed by molecular clusters of -conjugate polyacenes as a model for self-assembled aggregates. © 2013 The Chemical Society of Japan.

Access to Document (DOI)

Imaging and Characterizing Long-Range Surface Plasmon Polaritons Propagating in a Submillimeter Scale by Two-Color Two-Photon Photoelectron Emission Microscopy

M. Shibuta, T. Eguchi, A. Nakajima

Plasmonics （Springer Nature） 8 （ 3 ） 1411 - 1415 2013年04月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 1557-1955

Long-range surface plasmon polaritons (SPPs), which propagate along metal/dielectric interfaces to submillimeter distances in the range of near-infrared (NIR) excitation wavelength, were examined by two-color two-photon photoelectron emission microscopy (2P-PEEM). Interferences between incident NIR photons and SPPs excited by the NIR photons at surface defects were imaged by detecting photoelectrons emitted from a gold surface, assisted by simultaneously irradiated ultraviolet photons which are to overcome the workfunction of the surface. The wavelength of the interference beat depends sensitively on the NIR wavelength. By analyzing the interference beat, the dispersion curve as well as phase and group velocities of SPP's were experimentally obtained. The results closely match the theoretical one based on the Drude free electron model, indicating that two-color 2P-PEEM is applicable not only to the visualization of NIR-excited SPPs but also to the quantitative analysis of its physical properties. This method will be widely used to observe SPPs for various artificial plasmonic devices. © 2013 Springer Science+Business Media New York.

Access to Document (DOI)

Excited electron dynamics at ferrocene-terminated self-assembled monolayers on Au(111): Lengthened lifetime of image potential state

N. Hirata, M. Shibuta, T. Eguchi, A. Nakajima

Chemical Physics Letters （Elsevier Science BV） 561-562 131 - 136 2013年03月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 00092614

Ultraviolet photoemission spectroscopy (UPS) and two-photon photoemission (2PPE) spectroscopy have been employed to investigate the electronic states and the excited electron dynamics of ferrocene (Fc)-terminated self-assembled monolayers (SAMs) on Au(1 1 1). For the 11-ferrocenyl-1-undecanethiol (FcC11-) SAM, an image potential state (IPS) located at EF +3.8 eV was observed by time-resolved 2PPE. Its lifetime, 90 fs, was found to be much shorter than that of decanethiol (C10-) SAM, 11 ps. By forming the C10-SAM beforehand, the IPS lifetime for FcC11-&C10-SAM was lengthened to ∼9 ps; this can enable improvement in molecular ordering and substantial formation of C10 domains. © 2013 Elsevier B.V. All rights reserved.

Access to Document (DOI)

Size and structure dependence of electronic states in thiolate-protected gold nanoclusters of Au₂₅(SR)₁₈, Au₃₈(SR)₂₄, and Au₁₄₄(SR)₆₀

T. Ohta, M. Shibuta, H. Tsunoyama, Y. Negishi, T. Eguchi, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 117 （ 7 ） 3674 - 3679 2013年02月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 19327447

The electronic states of three different sizes of compositionally precise thiolate-protected gold nanoclusters, Au25(SR)18, Au 38(SR)24, and Au144(SR)60 (R = C12H25), have been evaluated by X-ray photoemission spectroscopy. The Au 4f core-levels of the nanoclusters are well reproduced by two spectral components derived from centered core-Au and positively charged shell-Au atoms, the numbers of which are determined based on the atomic structures of the nanoclusters. The spin-orbit splitting of Au 5d5/2 and 5d3/2 in the valence band becomes narrower than that for bulk Au, depending on the cluster size, which is quantitatively characterized by a reduction in the average coordination number of Au. The Au 5d valence-band spectra also show that the charge reorganization of 5d electrons induced by interaction with thiol molecules is more significant for the 5d5/2 than the 5d3/2 orbital. © 2013 American Chemical Society.

Access to Document (DOI)

　前のページ - 次のページ　

中嶋 敦

論文 - 中嶋 敦

中嶋　敦

論文 - 中嶋　敦