研究者詳細 - 中嶋　敦

論文 - 中嶋　敦

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Experimental and theoretical studies on the electronic properties of vanadium-benzene sandwich cluster anions, V_nBz_n+1^- (n = 1-5)

T. Masubuchi, K. Ohi, T. Iwasa, A. Nakajima

Journal of Chemical Physics （American Institute of Physics） 137 （ 22 ） 224305 2012年12月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 00219606

Vanadium-benzene cluster anions, VnBzn+1- (Bz = C6H6) were generated by laser ablation and supersonic jet methods, and studied using photoelectron spectroscopy. The density functional theory was employed to compute their geometric and electronic structures. It is concluded that the V nBzn+1- anions exhibit multiple-decker sandwich structures similar to their corresponding neutrals, and the adiabatic electron affinity increases with the cluster size. Our computation shows that the excess electron of the anion occupies the d orbitals of the vanadium atoms and that it is delocalized one-dimensionally. Furthermore, a very large HOMO-LUMO gap difference between majority and minority spin orbitals is observed for both the neutrals and the anions, and the V nBzn+10/- clusters are found to be completely spin-polarized. These facts confirm the possibility of using V nBzn+1 clusters as spin filters. © 2012 American Institute of Physics.

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Probing buried organic-organic and metal-organic heterointerfaces by hard x-ray photoelectron spectroscopy

M. Shibuta, T. Eguchi, Y. Watanabe, J. Son, H. Oji, A. Nakajima

Applied Physics Letters （American Institute of Physics） 101 （ 22 ） 221603 2012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 0003-6951

We present a nondestructive characterization method for buried hetero-interfaces for organic/organic and metal/organic systems using hard x-ray photoelectron spectroscopy (HAXPES) which can probe electronic states at depths deeper than ∼10 nm. A significant interface-derived signal showing a strong chemical interaction is observed for Au deposited onto a C60 film, while there is no such additional feature for copper phthalocyanine deposited onto a C60 film reflecting the weak interaction between the molecules in the latter case. A depth analysis with HAXPES reveals that a Au-C 60 intermixed layer with a thickness of 5.1 nm is formed at the interface. © 2012 American Institute of Physics.

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Wavelength dependence of IR laser for dual-laser shattering of a water microdroplet

A. Sugiyama, A. Nakajima

Chemistry Letters （Chemical Society of Japan） 41 （ 11 ） 1481 - 1483 2012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 0366-7022

For the single- and dual-laser shattering of water microdroplets, the wavelength dependence of an infrared (IR) laser was experimentally examined in the range 2.253.75 μm using ion current measurements coupled with time-resolved imaging. Compared to a single IR laser, simultaneous illumination by dual IR lasers effectively compresses the spatial distribution of small fragments around the absorption maximum for the OHstretching vibration of liquid water (λ=2.753.25 μm). The effect can be explained by the small penetration depth of the IR laser toward water microdroplets. © 2012 The Chemical Society of Japan.

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Molecular-scale and wide-energy-range tunneling spectroscopy on self-assembled monolayers of alkanethiol molecules

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

ACS Nano （American Chemical Society） 6 （ 10 ） 8728 - 8734 2012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 1936-0851

The electronic properties of alkanethiol self-assembled monolayers (alkanethiolate SAMs) associated with their molecular-scale geometry are investigated using scanning tunneling microscopy and spectroscopy (STM/STS). We have selectively formed the three types of alkanethiolate SAMs with standing-up, lying-down, and lattice-gas phases by precise thermal annealing of the SAMs which are conventionally prepared by depositing alkanethiol molecules onto Au(111) surface in solution. The empty and filled states of each SAM are evaluated over a wide energy range covering 6 eV above/below the Fermi level (E F) using two types of STS on the basis of tunneling current-voltage and distance-voltage measurements. Electronic states originating from rigid covalent bonds between the thiol group and substrate surface are observed near E F in the standing-up and lying-down phases but not in the lattice-gas phase. These states contribute to electrical conduction in the tunneling junction at a low bias voltage. At a higher energy, a highly conductive state stemming from the alkyl chain and an image potential state (IPS) formed in a vacuum gap appear in all phases. The IPS shifts toward a higher energy through the change in the geometry of the SAM from the standing-up phase to the lattice-gas phase through the lying-down phase. This is explained by the increasing work function of alkanethiolate/Au(111) with decreasing density of surface molecules. © 2012 American Chemical Society.

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Dual IR laser shattering of a water microdroplet

A. Sugiyama, A. Nakajima

Applied Physics A: Materials Science and Processing （Springer Nature） 109 （ 1 ） 31 - 37 2012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 0947-8396

Ion desorption from the infrared (IR) laser shattering of water microdroplets (ø90 μm in diameter) was experimentally examined by ion current measurements coupled with time-resolved imaging by a charge-coupled-device camera. When a microdroplet was shattered by simultaneous illumination by two IR lasers (λ=2.9 μm) from both the left- and right-hand sides, the time-resolved imaging shows that a lot of small fragments of splash spread around the droplet. The spatial distributions of the small fragments were symmetrically compressed. The resulting fragment swarm was effectively introduced into a vacuum chamber through an inlet skimmer ø0.3-0.4 mm in diameter. The ion current measured from a 10 -6 mol/m 3 NaCl water solution microdroplet using two lasers was considerably enhanced compared to that by single IR laser shattering. When one of the two IR lasers was delayed by 0-1000 μs, the ion current gradually decreased with the delay time, and dropped substantially at delays longer than 100 ns. The results are ascribed to dynamical processes following the multi-photon excitation. The dual IR laser ablation of a liquid droplet can enhance the efficiency of ion formation with a lower dispersion velocity, which can be conveniently combined with time-of-flight mass spectrometry. © 2012 Springer-Verlag.

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