研究者詳細 - 中嶋　敦

論文 - 中嶋　敦

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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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Geometric, electronic, and optical properties of a superatomic heterodimer and trimer: Sc@Si₁₆-V@Si₁₆ and Sc@Si₁₆-Ti@Si₁₆-V@Si₁₆

T. Iwasa, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 116 （ 26 ） 14071 - 14077 2012年06月

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

The geometric, electronic, and optical properties of a heterodimer and trimer consisting of metal-encapsulating silicon cage clusters, M@Si 16 (M = Sc, Ti, V) with D 4d symmetry, are studied using density functional computations to explore the possibility of using these clusters as building blocks for a nanometer scale heteroassembly. In this study, among the possible low-lying geometries, the linear-form of the hetero-oligomers is adopted as a model system, where the D 4d monomers are covalently bonded by facing their squares in an eclipsed fashion. The heterodimer consisting of halogen-like Sc@Si 16 and alkaline-like V@Si 16 has a dipole moment of 7.63 D, and its occupied and virtual frontier orbitals are localized to V@Si 16 and to Sc@Si 16, respectively. Some of the inner molecular orbitals exhibit superatomic bonding and antibonding character. The electronic excitations involve charge-transfer states mainly from V@Si 16 to Sc@Si 16 in the optical energy region. The linear heterotrimer of Sc@Si 16-Ti@Si 16- V@Si 16, formed by inserting the rare-gas-like Ti@Si 16, has a larger dipole moment of 15.6 D and one or more localized frontier orbitals compared to the dimer. We propose possible formation routes to realize the present hetero-oligomers using photoexcitation or energy-selective electron injection into several LUMOs of the monomers that are suitable for linear-oligomerization. © 2012 American Chemical Society.

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Electronic states of alkanethiolate self-assembled monolayers on Au(111) studied by two-photon photoemission spectroscopy

N. Hirata, M. Shibuta, R. Matsui, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 116 （ 25 ） 13623 - 13628 2012年06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

Two-photon photoemission (2PPE) spectroscopy has been employed to probe the electronic states of n-alkanethiolate self-assembled monolayers (SAMs) on an Au(111) substrate fabricated in a wet chemical process. Electronic states newly formed in the SAM formation were observed below and above the Fermi level (E F) for various alkyl chain lengths of C12-, C18-, and C22-SAMs. At 3.5-3.7 eV above E F, an unoccupied state originating from a bond between gold and sulfur atoms appears, a state that shows little dispersion with parallel to the surface. The peak position of the unoccupied state depends on the substrate temperature, and it was stabilized with increasing temperature; E F +3.7 eV at 85 K and E F +3.5 eV at 330 K for C18-SAM. The stabilization of the state is attributed to the increase of intermolecular interaction at sulfur atoms with their neighboring S atoms, which is caused by a change in the tilt angle of the alkyl chains in the SAM: on increasing the temperature, the interaction between S atoms in the SAM is promoted by the more upright alkyl chains. © 2012 American Chemical Society.

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Charge separation at the molecular monolayer surface: Observation and control of the dynamics

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

Journal of Physical Chemistry Letters （American Chemical Society） 3 （ 8 ） 981 - 985 2012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 1948-7185

Charge separation dynamics relevant to an electron transfer have been revealed by time- and angle-resolved two-photon photoemission spectroscopy for an n-alkanethiolate self-assembled monolayer (SAM) on a Au(111) surface fabricated by a chemical-wet process. The electron was photoexcited into an image potential state located at 3.7 eV above the Fermi level (E F), and it survived well for more than 100 ps on dodecanethiolate (C12)-SAM. The degree of electron separation is precisely controlled by selecting the length of the alkyl chain (C10-C18). We have also evaluated molecular conductivity at the specific electron energy of E F + 3.7 eV. The tunneling decay parameter, β, was fitted by β 90 K = 0.097 Å -1 and β RT = 0.13 Å -1. These values were one order smaller than that at around E F by conventional contact probe methods. © 2012 American Chemical Society.

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Investigation of lanthanide sandwich nanoclusters encapsulated with a cyclo-olefin polymer as a gas barrier

E. Tsunemi, T. Tsuji, S. Fukazawa, H. Tsunoyama, Y. Watanabe, A. Nakajima

Applied Physics Express （Japan Society of Applied Physics） 5 （ 3 ） 035202 2012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 1882-0778

Lanthanide nanoclusters ligated by planar organic molecules have one-dimensional sandwich structures and are air/moisture sensitive. To investigate their optical properties, originating from the lanthanide elements, for novel nanodevices, we preserved the nanoclusters with a cycloolefin polymer as a gas barrier. The technique enabled us to conduct various spectroscopic analyses without oxidation of the samples, such as fluorescence microscopy, photoluminescence, and X-ray absorption fine structure determination, thus revealing that lanthanide sandwich nanoclusters containing europium (Eu) atoms exhibit orange fluorescence attributed to divalent Eu 2+. © 2012 The Japan Society of Applied Physics.

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Anion photoelectron spectroscopy of germanium and tin clusters containing a transition- or lanthanide-metal atom; MGe_n^- (n = 8-20) and MSn_n^- (n = 15-17) (M = Sc-V, Y-Nb, and Lu-Ta)

J. Atobe, K. Koyasu, S. Furuse, A. Nakajima

Physical Chemistry Chemical Physics （Royal Society of Chemistry） 14 （ 26 ） 9403 - 9410 2012年02月

研究論文（学術雑誌）, 最終著者, 責任著者, 査読有り, ISSN 14639076

The electronic properties of germanium and tin clusters containing a transition- or lanthanide-metal atom from group 3, 4, or 5, MGe n (M = Sc, Ti, V, Y, Zr, Nb, Lu, Hf, and Ta) and MSn n (M = Sc, Ti, Y. Zr, and Hf), were investigated by anion photoelectron spectroscopy at 213 nm. In the case of the group 3 elements Sc, Y, and Lu, the threshold energy of electron detachment of MGe n- exhibits local maxima at n = 10 and 16, while in the case of the group 4 elements Ti, Zr, and Hf, it exhibits a local minimum only at n = 16, associated with the presence of a small bump in the spectrum. A similar behavior is observed for MSn n- around n = 16, and these electronic characteristics of MGe n and MSn n are closely related to those of MSi n. Compared to MSi n, however, the larger cavity size of a Ge n cage allows metal atom encapsulation at a smaller size n. A cooperative effect between the electronic and geometric structures of clusters with a large cavity of Ge 16 or Sn 16 is discussed together with the results of experiments that probe their geometric stability via their reactivity to H 2O adsorption. © 2012 the Owner Societies.

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Physical properties of aliphatic monolayer on indium-tin oxide and SnO₂(110) relevant to thermal stability of soft-landed Cr(benzene)₂

S. Nagaoka, K. Horiuchi, M. Shikishima, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 115 （ 49 ） 24215 - 24220 2011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 19327447

The physical properties of surface modified indium-tin oxide (ITO) and SnO 2(110) with an adsorbed aliphatic chain monolayer were studied by soft-landing experiments coupled with infrared (IR) spectroscopy, temperature programmed desorption (TPD) spectroscopy, and scanning probe microscopy. The IR spectra showed that the aliphatic chains of palmitic acid on both the metal oxide surfaces form a crystalline-phase monolayer with an all-trans conformation at room temperature. Gas-phase synthesized Cr(benzene) 2 cations deposited with a hyperthermal energy (20 eV) were used to probe the surface morphology. The IR spectrum after deposition showed that the cations soft-landed after being neutralized and oriented to cant the molecular axes far from the surface normal direction through penetration into the monolayer matrix. The TPD spectrum showed that the desorption activation energy of Cr(benzene) 2 from an aliphatic monolayer on ITO is much lower than that from the aliphatic monolayer on SnO 2 or a self-assembled monolayer of alkanethiol on Au(111). The lower thermal stability of Cr(benzene) 2 on the aliphatic monolayer on ITO can be ascribed to considerable surface roughness of the ITO itself, which can be characterized by scanning probe microscopy. © 2011 American Chemical Society.

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Soft-and reactive-landing of Cr(aniline)₂ sandwich complexes onto self-assembled monolayers: Separation between functional and binding sites

S. Nagaoka, K. Ikemoto, K. Horiuchi, A. Nakajima

Journal of the American Chemical Society （American Chemical Society） 133 （ 46 ） 18719 - 18727 2011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 00027863

Soft-and reactive-landing of gas-phase synthesized cationic Cr(aniline)2 complexes onto self-assembled monolayers of methylterminated (CH3-SAM) and carboxyl-terminated (COOH-SAM) organothiolates coated on gold were performed at hyperthermal collision energy (5-20 eV). The properties of the Cr(aniline)2 complexes on the SAM surfaces were characterized using infrared reflection absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD), together with theoretical calculations based on density functional theory (DFT). For the CH 3-SAM, the Cr(aniline)2 complexes were embedded inside the SAM matrix in a neutral charge state, keeping a sandwich structure. For the COOH-SAM, the IRAS and TPD study revealed that the amine-containing Cr(aniline)2 complexes were bound to the SAM surface in two forms of physisorption and chemical linking through an amide bond. In the desorption, the latter form appeared as the reaction product between organothiolates and Cr(aniline)2 above 400 K, where the organothiolate molecules, forming the SAM, were desorbed from the gold surface. The results show that the hyperthermal depositions onto a COOH-SAM bring about reactive-landing followed by covalent linking of an amide bond between the amine-containing Cr(aniline)2 complexes to the carboxyl-terminated SAM surface, in which the binding sites can be separated from the functional sites of the d-π interaction. © 2011 American Chemical Society.

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Theoretical investigation of a titanium-aniline complex with and without an alkyl chain

T. Iwasa, K. Horiuchi, M. Shikishima, Y. Noguchi, S. Nagaoka, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 115 （ 33 ） 16574 - 16582 2011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 1932-7447

Density functional theory computations are employed to investigate the geometric, electronic, and vibrational properties of a neutral Ti(aniline) experimentally soft-landed onto an alkanethiol self-assembled monolayer (CH-SAM) matrix. Five optimized structures of a bare Ti(aniline) are obtained: Three of the five optimized structures show Ti-phenyl ring bonds with singlet, triplet, and quintet spin states and the other two show Ti-N bonds with triplet and quintet states. For their calculated IR spectra in the range 0-2000 cm -1, the peak position and intensity of the NH2 scissor mode (∼1600 cm-1) are insensitive to the Ti binding and spin states, whereas those of the NH2-C6H5 intergroup stretching (∼1200 cm-1) and NH2 inversion (500-1000 cm-1) modes are sensitive to these factors. To study Ti(aniline) in a CH-SAM matrix, geometric structures of a modeled system of Ti(aniline)-C3H8 are optimized and their infrared reflection absorption spectra are directly calculated by projecting the normal mode derivatives of the dipole moment of the system onto the surface normal. C3H8 stabilizes Ti(aniline) by about 8-10 kcal/mol but causes little change in the IR spectrum in the range 1300-1700 cm-1, except for the quintet state. From a comparison of the predicted IRAS spectra with the experiment, Ti(aniline) in CH-SAM is concluded to be in a triplet state with a Ti-phenyl ring bond. © 2011 American Chemical Society.

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Photoemission enhancement induced by near-fields via local surface plasmon resonance of silver nanoparticles on a hydrogen-terminated Si(111) surface

T. Nakamura, N. Hirata, Y. Sekino, S. Nagaoka, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 114 （ 39 ） 16270 - 16277 2010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 1932-7447

The photoemission enhancement with local surface plasmon resonance (LSPR) was studied by two-photon photoemission (2PPE) spectroscopy for size-selected silver (Ag) and gold (Au) metal nanoparticles (NPs) deposited on a hydrogen-terminated Si(111)-(1 × 1) [H-Si(111)] surface. At 0.0015 monolayer equivalents (MLE) of Ag NPs, the photoemission enhancement was observed at a photon energy of 3.10 eV, which corresponds to the peak energy for the LSPR of isolated Ag NPs. A surface with around 0.005 MLE LSPR of size-selected Ag NPs exhibited three- and four-photon photoemission processes, implying monodispersed Ag NPs on H-Si(111). This enhancement could not be observed for Au NP deposition, even at 1.0 MLE in the photon energy range of 2.90-3.23 eV. Taking into account the polarization and photoemission-angle dependences, the photoemission enhancement could be accounted for by a mechanism involving the near-fields induced by the LSPR of Ag NPs. This mechanism is consistent with an analysis based on the effect of the interparticle distance between Ag NPs on the near-field intensity and polarization. © 2010 American Chemical Society.

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Two-photon photoemission spectroscopy for silver nanoparticles on a hydrogen-terminated Si(111) surface: Metal nanoparticle-enhanced photoemission

T. Nakamura, N. Hirata, S. Nagaoka, A. Nakajima

Chemical Physics Letters （Elsevier Science BV） 489 （ 1-3 ） 69 - 74 2010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 00092614

Two-photon photoemission (2PPE) spectroscopy was employed for size-selected silver nanoparticles (Ag NPs) deposited on a hydrogen-terminated Si(1 1 1) [H-Si(1 1 1)] to reveal photoemission enhancement through local surface plasmon resonance (LSPR). At low coverage of Ag NPs around 0.005 monolayer equivalents (MLE), the photoemission from the H-Si(1 1 1) substrate was enhanced by ∼2 × 102 times. Above 0.10 MLE, in contrast, photoemission from the Ag NPs themselves was observed. From the experimental results of polarization and the photoemission angle dependence, the photoemission enhancement, depending on the coverage of Ag NPs, is attributed to near-fields from LSPR of Ag NPs. © 2010 Elsevier B.V. All rights reserved.

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Size-dependent magnetic properties of naked and ligand-capped nickel nanoparticles

A. Sugiyama, Y. Taguchi, S. Nagaoka, A. Nakajima

Chemical Physics Letters （Elsevier Science BV） 485 （ 1-3 ） 129 - 132 2010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 0009-2614

Ligand-free naked and oleylamine-capped nickel nanoparticles (Ni NPs) were size-selectively prepared in the size ranges of 5-17 nm (naked) and 13-19 nm (capped) in diameter through gas- and liquid-phase syntheses, respectively. As for the magnetic properties of both the naked and oleylamine-capped Ni NPs, the blocking temperatures, TB, increase with the size, where TB for the naked Ni NPs are significantly higher than that for the capped Ni NPs. The results indicate that the ferromagnetic core region of Ni NPs is reduced by the formation of nonmagnetic layers at the surface of the capped NPs, where their thickness is estimated to be 1-2 nm. © 2009 Elsevier B.V. All rights reserved.

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Electronic structure of hydrogen-terminated silicon surfaces [H-Si(111)] studied by two-photon photoemission

T. Nakamura, K. Miyajima, N. Hirata, T. Matsumoto, Y. Morikawa, H. Tada, A. Nakajima

Applied Physics A: Materials Science and Processing （Springer Nature） 98 （ 4 ） 735 - 743 2009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 09478396

The surface and bulk electronic states of hydrogen-terminated Si(111)-(1 × 1) [H-Si(111)] were studied by two-photon photoemission (2PPE) spectroscopy. With the polarization and emission-angle dependence of the 2PPE spectra, five series of electronic structures for H-Si(111) can be identified as A, B, C, D, and E in the 2PPE spectra by fine tuning the exciting photon energy, hv, from 4.23 to 4.90 eV. For hv < 4.6 eV, peak A arises from a surface resonance at a 1.01 eV from EF, and at the photon energy higher than 4.6 eV, peak A indicates photoemission from an intermediate state, corresponding to an image-potential state at 3.61 eV from EF. Other structures, B, C, and D arise from bulk states, while structure E occurs from an electronhole excitation process. This work has revealed the surface resonance and the image-potential state on H-Si(111) for the first time. © Springer-Verlag 2009.

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Characterization of alkyl monolayer covalently bonded to Si(111) and soft-landing of vanadium-benzene sandwich clusters onto the alkyl monolayer substrate

T. Matsumoto, S. Nagaoka, K. Ikemoto, M. Mitsui, M. Ara, H. Tada, A. Nakajima

European Physical Journal D （SPRINGER） 52 （ 1-3 ） 99 - 102 2009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 1434-6060

A hexadecyl monolayer covalently attached to Si(111) surfaces (C 16-Si(111)) was prepared at 200 °C from 1-hexadecene. Formation of the monolayer was characterized by water contact angle measurement, attenuated total reflection infrared (ATR-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Gas phase synthesized vanadium (V)-benzene (Bz) 1:2 (VBz2) sandwich clusters were size-selectively deposited onto the C16-Si(111) substrate thus prepared and an oxidized Si substrate. Investigation of the resultant clusters was implemented by thermal desorption spectroscopy (TDS). About 30 K increase in threshold desorption temperature of the landed clusters was observed on going from the oxidized Si to the C16-Si(111) substrate, a result indicating that the clusters are more strongly bound to the C16-Si(111) than to the oxidized Si. This result was explained by the penetration of the landed clusters into the hexadecyl monolayer. © 2009 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

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An atomic force microscope study of vanadium-benzene sandwich clusters soft-landed on self-assembled monolayers

S. Nagaoka, K. Ikemoto, K. Fujio, K. Hiehata, A. Sasahara, M. Mitsui, H. Onishi, A. Nakajima

European Physical Journal D （Springer Nature） 52 （ 1-3 ） 103 - 106 2009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 1434-6060

Multiple-decker vanadium-benzene sandwich clusters Vn(benzene) n+1 produced by a laser-vaporization synthesis method were soft-landed onto self-assembled monolayers of alkanethiol (C18H-SAM) and fluorinated alkanethiol (C10F-SAM) at 200 K. Noncontact atomic force microscopy has been used to examine the resulting adsorption states of the clusters landed on the SAMs at room temperature. For each SAM substrate, the aggregates of the deposited clusters were observed at the vacancy islands and near the steps of the SAM surface. The result indicates that, at room temperature, the clusters landed on the SAM substrate thermally diffuse on the surface to form columnar-shape islands around the defect sites of the SAM surface. © 2009 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

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Soft-landing experiments of Cr(benzene)₂ sandwich complexes onto a carboxyl-terminated self-assembled monolayer matrix

K. Ikemoto, S. Nagaoka, T. Matsumoto, M. Mitsui, A. Nakajima

Journal of Physical Chemistry C （American Chemical Society） 113 （ 11 ） 4476 - 4482 2009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

Gas-phase synthesized Cr(benzene)2 sandwich complexes were soft-landed onto a carboxyl-terminated selfassembled monolayer (C 15COOH-SAM) on a gold substrate at hyperthermal collision energy (5-20 eV). The deposition process and adsorption properties of the soft-landed complexes were investigated by means of infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD) measurements. With the soft-landing, the Cr(benzene)2 complexes are adsorbed at the SAM surface while keeping their native sandwich structure intact even after the hyperthermal collision event. Moreover, the complexes tend to orient their molecular axes reasonably or comparatively close to the surface normal direction to the SAM surface. This orientation might arise from chemical interactions between the benzene ring in the sandwich complexes and carboxyl groups on the SAM surface. An Arrhenius analysis of the TPD spectra reveals the desorption activation energy of soft-landed complexes as 133 ± 10 kJ/mol, a value which is comparable to typical adsorption heat of chemisorptions. Chemical interactions between the Cr(benzene)2 complexes and carboxyl groups would provide firm trapping of the complexes at the SAM surface, preventing the supported complexes from being desorbed until near room temperature. © 2009 American Chemical Society.

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