Y. Kitahama - Academia.edu (original) (raw)

Papers by Y. Kitahama

Research paper thumbnail of CIDEP study on the flash photolysis of benzoin included in beta-cyclodextrin

Chemical Physics Letters, 1996

The photodissociation reaction of benzoin (Norrish type I) included in a beta-cyclodextrin (CD) c... more The photodissociation reaction of benzoin (Norrish type I) included in a beta-cyclodextrin (CD) cavity in the aqueous phase was studied by using time-resolved ESR and Fourier transform ESR methods. The CIDEP (chemically induced dynamic electron polarization) spectra of alpha-hydroxybenzyl radical and benzoyl radical were carefully investigated in beta-CD, in ethanol, in an ethanol/water mixture, and in saturated aqueous solutions. According to these data and the calculations due to an extended Bloch equation, the spin-lattice relaxation time observed in the beta-CD system was compared to those in homogeneous solutions. It is concluded that dissociation takes place from the excited triplet state of benzoin and the fragment radicals are easily ejected from the cavity of beta-CD to the aqueous phase much faster than the time-resolution (˜ 20 ns) of the present FT-ESR measurement.

Research paper thumbnail of The study on the magnetic field effect and the microwave effect on the photoconductivity observed in the photolysis of N,N,N′,N′-tetramethyl-p-phenylenediamine: theoretical calculation trial by the stochastic Liouville equation

Chemical Physics, 1998

The magnetic field effect on the photoconductivity and photoconductivity detected magnetic resona... more The magnetic field effect on the photoconductivity and photoconductivity detected magnetic resonance spectra observed X X Ž . in the photoionization system of N, N, N , N -tetramethyl-p-phenylenediamine TMPD in alcohol are analyzed by the numerical calculation. The stochastic Liouville equation is applied to the study of the dynamics of the transiently formed Ž . radical-ion pair RIP . We succeeded in estimating the appropriate physical parameters according to the simulation of the line-width and the other observed phenomena. However, we realized that a new model, the formation of a cluster-like network structure between the RIP and the solvent molecules, should be introduced, because the calculation of the RIP dynamics in homogeneous solutions cannot reproduce the experimental results of the viscosity dependence. q 1998 Elsevier Science B.V. All rights reserved. 0301-0104r98r$ -see front matter q 1998 Elsevier Science B.V. All rights reserved.

Research paper thumbnail of Mechanism of Surface-Enhanced Raman Scattering and Its Application to Highly Sensitive Protein Detection

Guang pu xue yu guang pu fen xi = Guang pu

ABSTRACT

Research paper thumbnail of Surface-Enhanced Raman Scattering Imaging: Application and Experimental Approach by Far-Field with Conventional Setup

Sasic/Chemical Imaging, 2010

Research paper thumbnail of Mechanism of surface-enhanced Raman scattering and its application to highly sensitive protein detection

Guang pu xue yu guang pu fen xi = Guang pu, 2009

ABSTRACT

Research paper thumbnail of Different behaviour of molecules in dark SERS state on colloidal Ag nanoparticles estimated by truncated power law analysis of blinking SERS

Phys. Chem. Chem. Phys., 2014

For single colloidal Ag nanoaggregates, covered with either large or small amounts of citrate ani... more For single colloidal Ag nanoaggregates, covered with either large or small amounts of citrate anions, blinking surface-enhanced Raman scattering (SERS) of anionic thiacyanine was measured and analyzed by a truncated power law. The power law without and with an exponential function reproduces a probability distribution for bright and dark SERS events versus their duration times, respectively. On the Ag surface, except for junctions of the nanoaggregate with a large or small amount of the citrate anions, two-dimensional fast or one-dimensional slow random walk of the anionic thiacyanine, respectively, was estimated by the exponents and the truncation times in the power law for the dark SERS events. In addition, the power law exponents for the bright SERS events were derived to be of similar values, indicating a similar molecular random walk near the junction, which may be dominated evenly by a surface-plasmon-enhanced electromagnetic field on the same-sized Ag nanoaggregate. Thus, not only the bright SERS, but also the dark SERS molecular behaviour on the Ag surface was investigated by the truncated power law analysis.

Research paper thumbnail of Protein-mediated sandwich strategy for surface-enhanced Raman scattering: application to versatile protein detection

Analytical chemistry, 2009

For surface-enhanced Raman scattering (SERS)-based protein identification, immunoassay, and drug ... more For surface-enhanced Raman scattering (SERS)-based protein identification, immunoassay, and drug screening, metal sandwich substrates bridged by proteins have been created in the present study. The sandwich architectures are fabricated based on a layer-by-layer (LbL) technique. The first gold monolayer is prepared by the self-assembling of gold nanoparticles on a poly(diallyldimethylammonium chloride) (PDDA)-coated glass slide. The second gold or silver layer is produced by the interactions between proteins in the middle layer of the sandwich architecture and the metal nanoparticles. Highly reproducible surface-enhanced resonance Raman scattering (SERRS) and SERS spectra can be obtained by the present gold-protein-gold (Au/Au) and gold-protein-silver (Au/Ag) sandwiches, and we find that the latter yields about 7 times stronger SERRS than the former. Because of contributions from the two metal layers to the SERS, this sandwich strategy holds great potential in highly sensitive and re...

Research paper thumbnail of Surface Plasmon Excitation and Surface-Enhanced Raman Scattering Using Two-Dimensionally Close-Packed Gold Nanoparticles †

The Journal of Physical Chemistry C, 2009

... Mohammad Kamal Hossain ‡ # , Yasutaka Kitahama ‡ , Vasudevanpillai Biju § , Tamitake Itoh § ,... more ... Mohammad Kamal Hossain ‡ # , Yasutaka Kitahama ‡ , Vasudevanpillai Biju § , Tamitake Itoh § , Tadaaki Kaneko and Yukihiro Ozaki* ‡. Department of Chemistry, School of Science and Technology, Kwansei Gakuin ...

Research paper thumbnail of Tip-Enhanced Raman Spectroscopy Study of Local Interactions at the Interface of Styrene–Butadiene Rubber/Multiwalled Carbon Nanotube Nanocomposites

The Journal of Physical Chemistry C, 2013

ABSTRACT Tip-enhanced Raman scattering (TERS) spectral measurements of nanocomposite styrene–buta... more ABSTRACT Tip-enhanced Raman scattering (TERS) spectral measurements of nanocomposite styrene–butadiene rubber (SBR) and multiwalled carbon nanotubes (MWCNTs) films were used to explore the local molecular interaction between nanocomposites. TERS spectra from geographically separated points were attributable to SBR or MWCNTs, showing great potential for investigating local film inhomogeneity within several tens of nanometers. Such inhomogeneity has never been observed by confocal Raman measurements. TERS bands due to SBR phenyl groups were strong when MWCNT bands were strong, whereas vinyl-group TERS bands were strong when the MWCNT bands were weak. Analysis of the findings suggests that the local distribution of polymer chains is modified with changes in the orientation of the phenyl rings by π–π interactions between the polymer chains and the MWCNTs.

Research paper thumbnail of Truncated Power Law Analysis of Blinking SERS of Thiacyanine Molecules Adsorbed on Single Silver Nanoaggregates by Excitation at Various Wavelengths

The Journal of Physical Chemistry C, 2013

ABSTRACT From blinking surface-enhanced Raman scattering (SERS) of anionic thiacyanine adsorbed o... more ABSTRACT From blinking surface-enhanced Raman scattering (SERS) of anionic thiacyanine adsorbed on single Ag nanoaggregates, the electromagnetic field and the molecular behavior in a nonemissive state were investigated by a truncated power law analysis. The power law that reproduces probability distribution of dark SERS events versus duration time was not truncated often by excitation at long wavelengths; otherwise it was truncated at the long tail. The truncation suggests a high energy barrier from nonemissive to emissive state and a short passage time of molecular random walk to overcome the energy barrier. The energy barrier in blinking SERS likely originates from a nanometer-ordered periodic optical trapping potential well, namely, electromagnetic field around a junction of the Ag nanoaggregate due to coupling of multipolar surface plasmon resonance, which is hardly induced by excitation at long wavelengths. This is consistent with the experimental excitation wavelength dependence of the truncation. At a low concentration of anionic thiacyanine, the power law was truncated at the short tail. The reason may be the short passage time of the molecule on the Ag surface adsorbing a small number of obstacles to reach the junction.

Research paper thumbnail of Surface-Enhanced Phosphorescence Measurement by an Optically Trapped Colloidal Ag Nanoaggregate on Anionic Thiacarbocyanine H-Aggregate

The Journal of Physical Chemistry C, 2013

ABSTRACT A citrate-reduced Ag nanoaggregate was optically trapped on a fiber-shaped H-aggregate o... more ABSTRACT A citrate-reduced Ag nanoaggregate was optically trapped on a fiber-shaped H-aggregate of an anionic thiacarbocyanine dye against Coulomb repulsion by focusing a near-infrared (NIR) laser beam. As the NIR laser power increased, namely, as the Ag nanoaggregate approaches the H-aggregate, phosphorescence from the H-aggregate with the Ag nanoaggregate excited moderately at 514 and 647 nm was strengthened, although that at 568 nm was weakened. By excitation at 568 nm, which was close to a surface plasmon resonance peak of the Ag nanoaggregate, surface-plasmon-enhanced optical trapping potential well might have deepened, and then the Ag nanoaggregate might have approached the H-aggregate too closely to enhance the phosphorescence because of energy transfer to the metal. As the excitation laser intensity increased, namely, as the surface-plasmon-enhanced optical trapping potential well was deepened, the phosphorescence enhancement factor trended upward and then downward by enhancement due to plasmon at a close distance from the Ag surface and the energy transfer at the closer distance, respectively.

Research paper thumbnail of A Raman Spectroscopy Study on Single-Wall Carbon Nanotube/Polystyrene Nanocomposites: Mechanical Compression Transferred from the Polymer to Single-Wall Carbon Nanotubes

The Journal of Physical Chemistry C, 2012

Research paper thumbnail of Power-law statistics in blinking SERS of thiacyanine adsorbed on a single silver nanoaggregate

Physical Chemistry Chemical Physics, 2010

In blinking surface-enhanced Raman scattering (SERS), probability distributions of the bright and... more In blinking surface-enhanced Raman scattering (SERS), probability distributions of the bright and dark events against their duration times are reproduced by a power-law without and with an exponential function, respectively. The truncation at the tail of the power-law suggests not only a potential well but also an energy barrier during a single molecule optical trapping onto the junction.

Research paper thumbnail of A study on the interaction of single-walled carbon nanotubes (SWCNTs) and polystyrene (PS) at the interface in SWCNT–PS nanocomposites using tip-enhanced Raman spectroscopy

Physical Chemistry Chemical Physics, 2013

Normal Raman and tip-enhanced Raman scattering (TERS) spectra were recorded for single-walled car... more Normal Raman and tip-enhanced Raman scattering (TERS) spectra were recorded for single-walled carbon nanotube (SWCNT)-polystyrene (PS) nanocomposites to investigate the distribution of SWCNTs in the nanocomposites and local interactions at an interface between SWCNTs and PS. The normal Raman spectra do not show an evident point-to-point variation. In contrast, in the TERS spectra, Raman bands of SWCNTs show obvious point-to-point shifts; the shifts depend on the points. The shift of the G' band which has high sensitivity to the mechanical compression reflects its distribution at the surface of composites. The shift of the G band arises from two reasons: the disentanglement of SWCNTs in the SWCNT-PS system due to the penetration of PS chains into SWCNT bundles during melt mixing and the mechanical compression distribution from the PS matrix. Moreover, the relative intensity of the G' band and the Raman band of PS at 3058 cm(-1) changes with the points in the TERS spectra of the nanocomposites, which further reflects the dispersion state of SWCNTs in the polymer matrix. This study demonstrates that TERS has great potential to be applied to polymer nanocomposite materials for local structure and function studies.

Research paper thumbnail of Power-law analysis of surface-plasmon-enhanced electromagnetic field dependence of blinking SERS of thiacyanine or thiacarbocyanine adsorbed on single silver nanoaggregates

Physical Chemistry Chemical Physics, 2011

Blinking statistics in surface-enhanced Raman scattering (SERS) of thiacyanine or thiacarbocyanin... more Blinking statistics in surface-enhanced Raman scattering (SERS) of thiacyanine or thiacarbocyanine adsorbed on single Ag nanoaggregates were analyzed by a power law. A power law reproduces the probability distributions of both the bright and dark SERS occurrences against their duration times. As the localized surface plasmon resonance (LSPR) wavelength of a single Ag nanoaggregate approached the excitation wavelength or the excitation laser intensity increases, the power-law exponents were close to -1.5, a value derived from a one-dimensional random walk model. When the LSPR wavelength left the excitation wavelength or the excitation laser intensity decreases, the power-law exponents deviated from -1.5. The decrease in the power-law exponents in the bright SERS, which indicates a decrease in the probabilities of the long-lived bright SERS, and the increase in the power-law exponents in the dark SERS coincide with the increasing shallowness and narrowing of a optical trapping potential well due to a surface-plasmon-enhanced electromagnetic field around a junction of the Ag nanoaggregates excited at a wavelength apart from the LSPR wavelength or under the low laser intensity, i.e., the low original electromagnetic field, respectively.

Research paper thumbnail of Direct conversion of silver complexes to nanoscale hexagonal columns on a copper alloy for plasmonic applications

Physical Chemistry Chemical Physics, 2013

We introduced a novel method for the rapid synthesis of silver nanohexagonal thin columns from an... more We introduced a novel method for the rapid synthesis of silver nanohexagonal thin columns from an aqueous mixture of sodium thiosulfate (Na2S2O3) and silver chloride (AgCl) simply added to a phosphor bronze substrate. The reaction is based on galvanic displacement and the products are potentially useful for plasmonic applications.

Research paper thumbnail of Optical Waveguide Self-Assembled from Organic Dye Molecules in Solution

Nano Letters, 2005

Fiber-shaped H-aggregates with lengths of up to 300 microm are synthesized by self-assembly of th... more Fiber-shaped H-aggregates with lengths of up to 300 microm are synthesized by self-assembly of thiacyanine (TC) dye molecules in solution. Photoluminescence (PL) images and spatially resolved PL spectra of the fibers that are transferred onto a glass substrate reveal that the fibers act as single-mode optical waveguides that propagate PL in the range of 520 to 560 nm over 250 microm without any loss.

Research paper thumbnail of Study of Internal Structure of meso -Tetrakis (4-Sulfonatophenyl) Porphine J-Aggregates in Solution by Fluorescence Microscope Imaging in a Magnetic Field

Langmuir, 2006

To determine the internal molecular arrangement of organic dye aggregates, a technique for observ... more To determine the internal molecular arrangement of organic dye aggregates, a technique for observing the fluorescence microscope image of a solution consisting of dye aggregates in a magnetic field was developed. Using this technique, the fluorescence image of meso-tetrakis (4-sulfonatophenyl) porphine (TPPS) J-aggregates in a solution in a magnetic field of 10 T was observed. It was observed that individual rod-shaped TPPS aggregates (4-20 µm in length) were aligned parallel to the applied field. The polarized absorption spectra of the sample solution were also measured in the fields of up to 10 T. The spectra show the magnetic field dependence of the J-band intensity, reflecting the magnetic alignment of the aggregates. On the basis of the magnetic and optical properties obtained by the experiments, it was proposed that TPPS J-aggregates have a tube-like structure and are constructed from one-dimensional molecular arrays that are stacked parallel to the long axis of the tube.

Research paper thumbnail of pH-Response Mechanism of p -Aminobenzenethiol on Ag Nanoparticles Revealed By Two-Dimensional Correlation Surface-Enhanced Raman Scattering Spectroscopy

The Journal of Physical Chemistry Letters, 2012

The existence of pH-dependent surface-enhanced Raman scattering (SERS) of p-aminobenzenethiol (PA... more The existence of pH-dependent surface-enhanced Raman scattering (SERS) of p-aminobenzenethiol (PATP) on Ag nanoparticles has been confirmed by numerous studies, but its mechanism still remains to be clarified. Discussion of the mechanism is at a standstill because of the lack of a systematic investigation of the process behind the pH-induced variation of the PATP behavior. Two-dimensional correlation spectroscopy is one of the most powerful and versatile spectral analysis methods for investigating perturbation-induced variations in dynamic data. Herein, we have analyzed the pH-dependent behavior of PATP using a static buffer solution with pH ranging from 3.0 to 2.0. The order of the variations in the different vibrational intensities was carefully investigated based on 2D correlation SERS spectroscopy. These results have demonstrated that the very first step of the pH-response process involves protonation of the amine group. The pH-response mechanism revealed is an important new component to our understanding of the origin of the b 2 -type bands of PATP.

Research paper thumbnail of Laser spectroscopy on molecular beam with a time-of-flight mass spectrometer operating in a strong magnetic field

The European Physical Journal D, 2006

Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dy... more Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ionsmass and charge state-was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process through the X 2 Π−A 2 Σ + transition of nitric oxide (NO) molecules. A mass resolution m/∆m ≥ 180 ± 6 was obtained in the field up to 10 T. This was the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong magnetic field up to 10 T. Parent NO + ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T.

Research paper thumbnail of CIDEP study on the flash photolysis of benzoin included in beta-cyclodextrin

Chemical Physics Letters, 1996

The photodissociation reaction of benzoin (Norrish type I) included in a beta-cyclodextrin (CD) c... more The photodissociation reaction of benzoin (Norrish type I) included in a beta-cyclodextrin (CD) cavity in the aqueous phase was studied by using time-resolved ESR and Fourier transform ESR methods. The CIDEP (chemically induced dynamic electron polarization) spectra of alpha-hydroxybenzyl radical and benzoyl radical were carefully investigated in beta-CD, in ethanol, in an ethanol/water mixture, and in saturated aqueous solutions. According to these data and the calculations due to an extended Bloch equation, the spin-lattice relaxation time observed in the beta-CD system was compared to those in homogeneous solutions. It is concluded that dissociation takes place from the excited triplet state of benzoin and the fragment radicals are easily ejected from the cavity of beta-CD to the aqueous phase much faster than the time-resolution (˜ 20 ns) of the present FT-ESR measurement.

Research paper thumbnail of The study on the magnetic field effect and the microwave effect on the photoconductivity observed in the photolysis of N,N,N′,N′-tetramethyl-p-phenylenediamine: theoretical calculation trial by the stochastic Liouville equation

Chemical Physics, 1998

The magnetic field effect on the photoconductivity and photoconductivity detected magnetic resona... more The magnetic field effect on the photoconductivity and photoconductivity detected magnetic resonance spectra observed X X Ž . in the photoionization system of N, N, N , N -tetramethyl-p-phenylenediamine TMPD in alcohol are analyzed by the numerical calculation. The stochastic Liouville equation is applied to the study of the dynamics of the transiently formed Ž . radical-ion pair RIP . We succeeded in estimating the appropriate physical parameters according to the simulation of the line-width and the other observed phenomena. However, we realized that a new model, the formation of a cluster-like network structure between the RIP and the solvent molecules, should be introduced, because the calculation of the RIP dynamics in homogeneous solutions cannot reproduce the experimental results of the viscosity dependence. q 1998 Elsevier Science B.V. All rights reserved. 0301-0104r98r$ -see front matter q 1998 Elsevier Science B.V. All rights reserved.

Research paper thumbnail of Mechanism of Surface-Enhanced Raman Scattering and Its Application to Highly Sensitive Protein Detection

Guang pu xue yu guang pu fen xi = Guang pu

ABSTRACT

Research paper thumbnail of Surface-Enhanced Raman Scattering Imaging: Application and Experimental Approach by Far-Field with Conventional Setup

Sasic/Chemical Imaging, 2010

Research paper thumbnail of Mechanism of surface-enhanced Raman scattering and its application to highly sensitive protein detection

Guang pu xue yu guang pu fen xi = Guang pu, 2009

ABSTRACT

Research paper thumbnail of Different behaviour of molecules in dark SERS state on colloidal Ag nanoparticles estimated by truncated power law analysis of blinking SERS

Phys. Chem. Chem. Phys., 2014

For single colloidal Ag nanoaggregates, covered with either large or small amounts of citrate ani... more For single colloidal Ag nanoaggregates, covered with either large or small amounts of citrate anions, blinking surface-enhanced Raman scattering (SERS) of anionic thiacyanine was measured and analyzed by a truncated power law. The power law without and with an exponential function reproduces a probability distribution for bright and dark SERS events versus their duration times, respectively. On the Ag surface, except for junctions of the nanoaggregate with a large or small amount of the citrate anions, two-dimensional fast or one-dimensional slow random walk of the anionic thiacyanine, respectively, was estimated by the exponents and the truncation times in the power law for the dark SERS events. In addition, the power law exponents for the bright SERS events were derived to be of similar values, indicating a similar molecular random walk near the junction, which may be dominated evenly by a surface-plasmon-enhanced electromagnetic field on the same-sized Ag nanoaggregate. Thus, not only the bright SERS, but also the dark SERS molecular behaviour on the Ag surface was investigated by the truncated power law analysis.

Research paper thumbnail of Protein-mediated sandwich strategy for surface-enhanced Raman scattering: application to versatile protein detection

Analytical chemistry, 2009

For surface-enhanced Raman scattering (SERS)-based protein identification, immunoassay, and drug ... more For surface-enhanced Raman scattering (SERS)-based protein identification, immunoassay, and drug screening, metal sandwich substrates bridged by proteins have been created in the present study. The sandwich architectures are fabricated based on a layer-by-layer (LbL) technique. The first gold monolayer is prepared by the self-assembling of gold nanoparticles on a poly(diallyldimethylammonium chloride) (PDDA)-coated glass slide. The second gold or silver layer is produced by the interactions between proteins in the middle layer of the sandwich architecture and the metal nanoparticles. Highly reproducible surface-enhanced resonance Raman scattering (SERRS) and SERS spectra can be obtained by the present gold-protein-gold (Au/Au) and gold-protein-silver (Au/Ag) sandwiches, and we find that the latter yields about 7 times stronger SERRS than the former. Because of contributions from the two metal layers to the SERS, this sandwich strategy holds great potential in highly sensitive and re...

Research paper thumbnail of Surface Plasmon Excitation and Surface-Enhanced Raman Scattering Using Two-Dimensionally Close-Packed Gold Nanoparticles †

The Journal of Physical Chemistry C, 2009

... Mohammad Kamal Hossain ‡ # , Yasutaka Kitahama ‡ , Vasudevanpillai Biju § , Tamitake Itoh § ,... more ... Mohammad Kamal Hossain ‡ # , Yasutaka Kitahama ‡ , Vasudevanpillai Biju § , Tamitake Itoh § , Tadaaki Kaneko and Yukihiro Ozaki* ‡. Department of Chemistry, School of Science and Technology, Kwansei Gakuin ...

Research paper thumbnail of Tip-Enhanced Raman Spectroscopy Study of Local Interactions at the Interface of Styrene–Butadiene Rubber/Multiwalled Carbon Nanotube Nanocomposites

The Journal of Physical Chemistry C, 2013

ABSTRACT Tip-enhanced Raman scattering (TERS) spectral measurements of nanocomposite styrene–buta... more ABSTRACT Tip-enhanced Raman scattering (TERS) spectral measurements of nanocomposite styrene–butadiene rubber (SBR) and multiwalled carbon nanotubes (MWCNTs) films were used to explore the local molecular interaction between nanocomposites. TERS spectra from geographically separated points were attributable to SBR or MWCNTs, showing great potential for investigating local film inhomogeneity within several tens of nanometers. Such inhomogeneity has never been observed by confocal Raman measurements. TERS bands due to SBR phenyl groups were strong when MWCNT bands were strong, whereas vinyl-group TERS bands were strong when the MWCNT bands were weak. Analysis of the findings suggests that the local distribution of polymer chains is modified with changes in the orientation of the phenyl rings by π–π interactions between the polymer chains and the MWCNTs.

Research paper thumbnail of Truncated Power Law Analysis of Blinking SERS of Thiacyanine Molecules Adsorbed on Single Silver Nanoaggregates by Excitation at Various Wavelengths

The Journal of Physical Chemistry C, 2013

ABSTRACT From blinking surface-enhanced Raman scattering (SERS) of anionic thiacyanine adsorbed o... more ABSTRACT From blinking surface-enhanced Raman scattering (SERS) of anionic thiacyanine adsorbed on single Ag nanoaggregates, the electromagnetic field and the molecular behavior in a nonemissive state were investigated by a truncated power law analysis. The power law that reproduces probability distribution of dark SERS events versus duration time was not truncated often by excitation at long wavelengths; otherwise it was truncated at the long tail. The truncation suggests a high energy barrier from nonemissive to emissive state and a short passage time of molecular random walk to overcome the energy barrier. The energy barrier in blinking SERS likely originates from a nanometer-ordered periodic optical trapping potential well, namely, electromagnetic field around a junction of the Ag nanoaggregate due to coupling of multipolar surface plasmon resonance, which is hardly induced by excitation at long wavelengths. This is consistent with the experimental excitation wavelength dependence of the truncation. At a low concentration of anionic thiacyanine, the power law was truncated at the short tail. The reason may be the short passage time of the molecule on the Ag surface adsorbing a small number of obstacles to reach the junction.

Research paper thumbnail of Surface-Enhanced Phosphorescence Measurement by an Optically Trapped Colloidal Ag Nanoaggregate on Anionic Thiacarbocyanine H-Aggregate

The Journal of Physical Chemistry C, 2013

ABSTRACT A citrate-reduced Ag nanoaggregate was optically trapped on a fiber-shaped H-aggregate o... more ABSTRACT A citrate-reduced Ag nanoaggregate was optically trapped on a fiber-shaped H-aggregate of an anionic thiacarbocyanine dye against Coulomb repulsion by focusing a near-infrared (NIR) laser beam. As the NIR laser power increased, namely, as the Ag nanoaggregate approaches the H-aggregate, phosphorescence from the H-aggregate with the Ag nanoaggregate excited moderately at 514 and 647 nm was strengthened, although that at 568 nm was weakened. By excitation at 568 nm, which was close to a surface plasmon resonance peak of the Ag nanoaggregate, surface-plasmon-enhanced optical trapping potential well might have deepened, and then the Ag nanoaggregate might have approached the H-aggregate too closely to enhance the phosphorescence because of energy transfer to the metal. As the excitation laser intensity increased, namely, as the surface-plasmon-enhanced optical trapping potential well was deepened, the phosphorescence enhancement factor trended upward and then downward by enhancement due to plasmon at a close distance from the Ag surface and the energy transfer at the closer distance, respectively.

Research paper thumbnail of A Raman Spectroscopy Study on Single-Wall Carbon Nanotube/Polystyrene Nanocomposites: Mechanical Compression Transferred from the Polymer to Single-Wall Carbon Nanotubes

The Journal of Physical Chemistry C, 2012

Research paper thumbnail of Power-law statistics in blinking SERS of thiacyanine adsorbed on a single silver nanoaggregate

Physical Chemistry Chemical Physics, 2010

In blinking surface-enhanced Raman scattering (SERS), probability distributions of the bright and... more In blinking surface-enhanced Raman scattering (SERS), probability distributions of the bright and dark events against their duration times are reproduced by a power-law without and with an exponential function, respectively. The truncation at the tail of the power-law suggests not only a potential well but also an energy barrier during a single molecule optical trapping onto the junction.

Research paper thumbnail of A study on the interaction of single-walled carbon nanotubes (SWCNTs) and polystyrene (PS) at the interface in SWCNT–PS nanocomposites using tip-enhanced Raman spectroscopy

Physical Chemistry Chemical Physics, 2013

Normal Raman and tip-enhanced Raman scattering (TERS) spectra were recorded for single-walled car... more Normal Raman and tip-enhanced Raman scattering (TERS) spectra were recorded for single-walled carbon nanotube (SWCNT)-polystyrene (PS) nanocomposites to investigate the distribution of SWCNTs in the nanocomposites and local interactions at an interface between SWCNTs and PS. The normal Raman spectra do not show an evident point-to-point variation. In contrast, in the TERS spectra, Raman bands of SWCNTs show obvious point-to-point shifts; the shifts depend on the points. The shift of the G' band which has high sensitivity to the mechanical compression reflects its distribution at the surface of composites. The shift of the G band arises from two reasons: the disentanglement of SWCNTs in the SWCNT-PS system due to the penetration of PS chains into SWCNT bundles during melt mixing and the mechanical compression distribution from the PS matrix. Moreover, the relative intensity of the G' band and the Raman band of PS at 3058 cm(-1) changes with the points in the TERS spectra of the nanocomposites, which further reflects the dispersion state of SWCNTs in the polymer matrix. This study demonstrates that TERS has great potential to be applied to polymer nanocomposite materials for local structure and function studies.

Research paper thumbnail of Power-law analysis of surface-plasmon-enhanced electromagnetic field dependence of blinking SERS of thiacyanine or thiacarbocyanine adsorbed on single silver nanoaggregates

Physical Chemistry Chemical Physics, 2011

Blinking statistics in surface-enhanced Raman scattering (SERS) of thiacyanine or thiacarbocyanin... more Blinking statistics in surface-enhanced Raman scattering (SERS) of thiacyanine or thiacarbocyanine adsorbed on single Ag nanoaggregates were analyzed by a power law. A power law reproduces the probability distributions of both the bright and dark SERS occurrences against their duration times. As the localized surface plasmon resonance (LSPR) wavelength of a single Ag nanoaggregate approached the excitation wavelength or the excitation laser intensity increases, the power-law exponents were close to -1.5, a value derived from a one-dimensional random walk model. When the LSPR wavelength left the excitation wavelength or the excitation laser intensity decreases, the power-law exponents deviated from -1.5. The decrease in the power-law exponents in the bright SERS, which indicates a decrease in the probabilities of the long-lived bright SERS, and the increase in the power-law exponents in the dark SERS coincide with the increasing shallowness and narrowing of a optical trapping potential well due to a surface-plasmon-enhanced electromagnetic field around a junction of the Ag nanoaggregates excited at a wavelength apart from the LSPR wavelength or under the low laser intensity, i.e., the low original electromagnetic field, respectively.

Research paper thumbnail of Direct conversion of silver complexes to nanoscale hexagonal columns on a copper alloy for plasmonic applications

Physical Chemistry Chemical Physics, 2013

We introduced a novel method for the rapid synthesis of silver nanohexagonal thin columns from an... more We introduced a novel method for the rapid synthesis of silver nanohexagonal thin columns from an aqueous mixture of sodium thiosulfate (Na2S2O3) and silver chloride (AgCl) simply added to a phosphor bronze substrate. The reaction is based on galvanic displacement and the products are potentially useful for plasmonic applications.

Research paper thumbnail of Optical Waveguide Self-Assembled from Organic Dye Molecules in Solution

Nano Letters, 2005

Fiber-shaped H-aggregates with lengths of up to 300 microm are synthesized by self-assembly of th... more Fiber-shaped H-aggregates with lengths of up to 300 microm are synthesized by self-assembly of thiacyanine (TC) dye molecules in solution. Photoluminescence (PL) images and spatially resolved PL spectra of the fibers that are transferred onto a glass substrate reveal that the fibers act as single-mode optical waveguides that propagate PL in the range of 520 to 560 nm over 250 microm without any loss.

Research paper thumbnail of Study of Internal Structure of meso -Tetrakis (4-Sulfonatophenyl) Porphine J-Aggregates in Solution by Fluorescence Microscope Imaging in a Magnetic Field

Langmuir, 2006

To determine the internal molecular arrangement of organic dye aggregates, a technique for observ... more To determine the internal molecular arrangement of organic dye aggregates, a technique for observing the fluorescence microscope image of a solution consisting of dye aggregates in a magnetic field was developed. Using this technique, the fluorescence image of meso-tetrakis (4-sulfonatophenyl) porphine (TPPS) J-aggregates in a solution in a magnetic field of 10 T was observed. It was observed that individual rod-shaped TPPS aggregates (4-20 µm in length) were aligned parallel to the applied field. The polarized absorption spectra of the sample solution were also measured in the fields of up to 10 T. The spectra show the magnetic field dependence of the J-band intensity, reflecting the magnetic alignment of the aggregates. On the basis of the magnetic and optical properties obtained by the experiments, it was proposed that TPPS J-aggregates have a tube-like structure and are constructed from one-dimensional molecular arrays that are stacked parallel to the long axis of the tube.

Research paper thumbnail of pH-Response Mechanism of p -Aminobenzenethiol on Ag Nanoparticles Revealed By Two-Dimensional Correlation Surface-Enhanced Raman Scattering Spectroscopy

The Journal of Physical Chemistry Letters, 2012

The existence of pH-dependent surface-enhanced Raman scattering (SERS) of p-aminobenzenethiol (PA... more The existence of pH-dependent surface-enhanced Raman scattering (SERS) of p-aminobenzenethiol (PATP) on Ag nanoparticles has been confirmed by numerous studies, but its mechanism still remains to be clarified. Discussion of the mechanism is at a standstill because of the lack of a systematic investigation of the process behind the pH-induced variation of the PATP behavior. Two-dimensional correlation spectroscopy is one of the most powerful and versatile spectral analysis methods for investigating perturbation-induced variations in dynamic data. Herein, we have analyzed the pH-dependent behavior of PATP using a static buffer solution with pH ranging from 3.0 to 2.0. The order of the variations in the different vibrational intensities was carefully investigated based on 2D correlation SERS spectroscopy. These results have demonstrated that the very first step of the pH-response process involves protonation of the amine group. The pH-response mechanism revealed is an important new component to our understanding of the origin of the b 2 -type bands of PATP.

Research paper thumbnail of Laser spectroscopy on molecular beam with a time-of-flight mass spectrometer operating in a strong magnetic field

The European Physical Journal D, 2006

Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dy... more Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ionsmass and charge state-was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process through the X 2 Π−A 2 Σ + transition of nitric oxide (NO) molecules. A mass resolution m/∆m ≥ 180 ± 6 was obtained in the field up to 10 T. This was the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong magnetic field up to 10 T. Parent NO + ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T.