Co-reporter:Tomoharu Yamamura;Takamasa Minami
The Journal of Physical Chemistry C November 27, 2008 Volume 112(Issue 47) pp:18340-18349
Publication Date(Web):2017-2-22
DOI:10.1021/jp805978g
Nanosecond pulsed laser ablation of gold with an excitation wavelength of 532 nm was conducted in supercritical CO2 to generate gold nanoparticles, which were then investigated by scanning electron microscopy and small-angle X-ray scattering, and their extinction spectra and simulated extinction spectra were studied. Both the morphology and amount of gold nanoparticles changed significantly with changes in the density of supercritical CO2 during laser ablation. In a gaslike density, a network structure consisting of nanonecklaces was the major product, whereas in a liquidlike density, large nanospheres with an average diameter (⟨D⟩) of 500 nm were produced. After absorption of multiphoton of excitation light, the gold nanonecklaces and large nanospheres were generated by the fragmentation and solidification, respectively, of liquid gold droplets with ⟨D⟩ = 500 nm. The amount of both products changed according to the branching ratio, which determined whether the liquid gold droplets followed the fragmentation or solidification channel. The local structure of supercritical CO2 in the vicinity of the gold nanoparticles determined the preferred reaction channel. A significant change in the branching ratio occurred near the density ρr = 0.7, where both the enhancement of the local density of supercritical CO2 and the degree of solvation of fluid molecules around the gold nanoparticles reached a maximum. To the best of our knowledge, this is the first study to observe the density dependence of morphological changes in gold nanoparticles fabricated by laser ablation in a supercritical fluid and the local structure of the supercritical fluid that determines the morphology and amount of nanoparticles.
Co-reporter:Ken-ichi Saitow, Yoshinori Okamoto, and Yohko F. Yano
The Journal of Physical Chemistry C August 16, 2012 Volume 116(Issue 32) pp:17252-17258
Publication Date(Web):July 24, 2012
DOI:10.1021/jp304109h
The nanosecond pulsed laser ablation of a gold plate at the excitation wavelength of 532 nm was conducted in the supercritical fluid of dipolar trifluoromethane (CHF3). The generation of gold nanoparticles was investigated as a function of the fluid density that corresponded to changes in the permittivity and thermal properties over the wide ranges. The analysis of data from electron microscopy and small-angle X-ray scattering (SAXS) revealed that the principal product is a gold nanonetwork with length up to a few 10 μm and a branched structure. The gold nanonetwork consisted of gold nanospheres with an average diameter of 20 nm and a mass fractal structure. The mass fractal dimension of the nanonetwork changed by the fluid density, and its dimension was attributed to the number of the nanospheres. It was clarified that not the fluid thermal properties but the ambient dielectricity and polarization energy during the ablation are responsible for the morphology and number of gold nanoparticles. This is the first report of (i) fractal structure of gold nanoparticles created by the ablation, (ii) ablation mechanism in dipolar and nondipolar fluids, and (iii) a chemical-free nanoparticle synthesis in a dipolar fluid.
Co-reporter:Daisuke Kajiya, Ken-ichi Saitow
The Journal of Supercritical Fluids 2017 Volume 120, Part 2(Volume 120, Part 2) pp:
Publication Date(Web):1 February 2017
DOI:10.1016/j.supflu.2016.05.050
•Investigation of the entrainer effect using vibrational spectroscopy.•Density dependence of attractive and repulsive energies between solute and solvent.•Attractive energy of ethanol was 4 times greater than that of ethane.•Repulsive energy of ethanol was almost equal to that of ethane.Vibrational Raman spectra of the CC stretching modes for ethane and ethanol were measured in supercritical carbon dioxide (scCO2) at the isotherm of reduced temperature Tr = T/Tc = 1.02 (Tc is the critical temperature) as a function of fluid density, ρr = ρ/ρc, in the range of 0.01–1.5. The peak frequencies of the Raman spectra were analyzed using the perturbed hard-sphere theory, and the attractive and repulsive energy components between solute and solvent were quantified as a function of the fluid density. For ethane, the magnitude of the attractive energy was almost equal to that of the repulsive energy. In contrast, the magnitude of the attractive energy for ethanol was four times greater than that of the repulsive energy. The significant difference in the attractive energies of ethane and ethanol is attributed to the solvation of the CO2 molecules at the oxygen atom of ethanol, according to analyses of local density and quantum chemical calculations. These observations provide useful information to understand the entrainer effect in scCO2.Download high-res image (215KB)Download full-size image
Co-reporter:Daisuke Kajiya, Tomoyuki Koganezawa, and Ken-ichi Saitow
The Journal of Physical Chemistry C 2016 Volume 120(Issue 41) pp:23351-23357
Publication Date(Web):September 26, 2016
DOI:10.1021/acs.jpcc.6b06833
Poly(3-alkylthiophene) (P3AT) is a popular family of π-conjugated polymers used to study polymer-based flexible electronic devices. To enhance the performance of a smart material for wearable or stretchable-skin devices, it is crucial to optimize both the carrier mobility and the film structure. Here, we present the enhancements of hole mobilities of three P3ATs films along the out-of-plane direction using photoconductivity measurements by rubbing. The three P3ATs have the same conjugated backbone but different alkyl side chain (CnH2n+1) lengths of n = 4, 6, and 12. As the alkyl chain length becomes longer, the hole mobility increased up to 5-fold after rubbing. Polarized absorption and grazing-incidence X-ray diffraction measurements indicate the P3AT (n = 12) film has a highly oriented structure in the in-plane direction and increased π–π stacking in the out-of-plane direction after rubbing due to a low tensile modulus from the long alkyl side chain.
Co-reporter:Daisuke Kajiya, Masayoshi Imanishi, and Ken-ichi Saitow
The Journal of Physical Chemistry B 2016 Volume 120(Issue 4) pp:785-792
Publication Date(Web):January 7, 2016
DOI:10.1021/acs.jpcb.5b11740
Vibrational Raman spectra for the C═O stretching modes of three esters with different functional groups (methyl, a single phenyl, and two phenyl groups) were measured in supercritical carbon dioxide (scCO2). The results were compared with Raman spectra for three ketones involving the same functional groups, measured at the same thermodynamic states in scCO2. The peak frequencies of the Raman spectra of these six solute molecules were analyzed by decomposition into the attractive and repulsive energy components, based on the perturbed hard-sphere theory. For all solute molecules, the attractive energy is greater than the repulsive energy. In particular, a significant difference in the attractive energies of the ester–CO2 and ketone–CO2 systems was observed when the methyl group is attached to the ester or ketone. This difference was significantly reduced in the solute systems with a single phenyl group and was completely absent in those with two phenyl groups. The optimized structures among the solutes and CO2 molecules based on quantum chemical calculations indicate that greater attractive energy is obtained for a system where the oxygen atom of the ester is solvated by CO2 molecules.
Co-reporter:Natsumi Ikeda, Tomoyuki Koganezawa, Daisuke Kajiya, and Ken-ichi Saitow
The Journal of Physical Chemistry C 2016 Volume 120(Issue 34) pp:19043-19048
Publication Date(Web):August 9, 2016
DOI:10.1021/acs.jpcc.6b07101
A hybrid solar cell composed of a crystalline semiconductor and polymer film has attracted much attention due to numerous advantages, such as high mobility, long lifetime, and the aqueous solution processing. Recently, the power conversion efficiency (PCE) of the hybrid solar cell of silicon (Si) wafer and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is reported to be higher than that of a commercial amorphous Si solar cell. Here in the Si/PEDOT:PSS hybrid solar cell was prepared using dimethyl sulfoxide (DMSO) as an additive to the PEDOT:PSS solution. The PCE was increased up to 10-fold by the addition of DMSO at a concentration of 5 wt%. Results from grazing-incidence X-ray diffraction, atomic force microscopy, and Raman spectroscopy indicated the 10-fold enhancement was controlled by the nanostructure of the PEDOT:PSS film. The enhanced performance was attributed to (i) an increase of π–π stacking, (ii) shortened distances between π–π planes, (iii) an increase in the quinoid structure of PEDOT, and (iv) reduced PEDOT:PSS particle size. The PCE was also enhanced by a transparent cathode of colloidal Ag nanowires and through the use of a vacuum-free process for preparation of the PEDOT:PSS film.
Co-reporter:Daisuke Kajiya and Ken-ichi Saitow
Nanoscale 2015 vol. 7(Issue 38) pp:15780-15788
Publication Date(Web):25 Aug 2015
DOI:10.1039/C5NR02361K
Hybrid silicon nanocrystal (Si-NC)/poly(3-hexylthiophene) (P3HT) films serve as the active layers of quantum dot/polymer hybrid photovoltaics. To achieve effective photovoltaic properties, it is necessary to enhance the charge carrier mobility and carrier density of the P3HT films. A 50- and 12-fold enhancement of the hole mobility and hole density, respectively, was achieved along the out-of-plane direction of a Si-NC/P3HT hybrid film, which corresponds to the carrier-migration direction between the photovoltaic electrodes. According to time-of-flight, electronic absorption, Raman, atomic force microscopy, photoluminescence lifetime, and X-ray diffraction measurements, the significant enhancement of the mobility and density was attributed to both an increase in the P3HT crystallinity and the dissociation efficiency of P3HT excitons on the addition of Si-NCs to the P3HT films. These enhancements were achieved using a film preparation method developed in the present study, which has been named successive drop casting.
Co-reporter:Daisuke Kajiya
The Journal of Physical Chemistry C 2015 Volume 119(Issue 15) pp:7987-7995
Publication Date(Web):March 23, 2015
DOI:10.1021/jp510675r
Poly(3-hexylthiophene) (P3HT) is used as a conjugated polymer material for the fabrication of organic solar cells. To enhance the performance of the solar cell, it is crucial to improve the charge transport properties of the out-of-plane direction, which corresponds to the direction normal to the cell. The out-of-plane hole mobility in P3HT films before and after rubbing was investigated. The mobility was measured by the time-of-flight method and was enhanced by a factor of 8 with rubbing. The enhancement of mobility is significantly dependent on the regioregularity (RR) of P3HT and is the largest with low RR (91%). The mobility of low RR becomes almost equal to that of high RR (98%) after rubbing. Polarized absorption and Raman spectral measurements, and optical, atomic force, and scanning electron microscopy observations indicate the mobility enhancement can be attributed to aggregation and molecular planarity enhanced by rubbing. Three enhancement factors (EFs) for the mobility, aggregation, and planarity were quantified by changing the RR. It was thus determined that subtle aggregation produces a large mobility enhancement. According to the results of grazing-incidence X-ray diffraction measurement, the increase of face-on component of P3HT by rubbing was observed and corresponds to the increase of π–π staking of thiophene ring along the out-of-plane direction. Evolution from the disordered to the ordered P3HT structure by rubbing significantly improves hole transport in the out-of-plane direction.
Co-reporter:Ken-ichi Saitow, Hidemi Suemori and Hironori Tamamitsu
Chemical Communications 2014 vol. 50(Issue 9) pp:1137-1140
Publication Date(Web):19 Nov 2013
DOI:10.1039/C3CC46566G
Fluorescence-intensity enhancement of dye molecules was investigated using silicon submicron particles as a function of the particle size. Silicon particles with a size of 500 nm gave an enhancement factor up to 180. Measurement of scattering spectra revealed that the localized electric field at the particle enhances the fluorescence intensity.
Co-reporter:Hironori Tamamitsu, Ken-ichi Saitow
Chemical Physics Letters 2014 Volume 591() pp:37-42
Publication Date(Web):20 January 2014
DOI:10.1016/j.cplett.2013.10.066
Highlights
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Enhancement effect in local region elucidated by in situ microscope spectrometer.
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Enhancement effect carefully evaluated by volume and background.
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Enhancement volume estimated from FDTD calculation.
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Enhancement mechanism investigated by λex & λem wavelengths and scattering spectrum.
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Special enhancement substrate prepared by supercritical fluid.
Co-reporter:Hua Sun, Satoshi Miyazaki, Hironori Tamamitsu and Ken-ichi Saitow
Chemical Communications 2013 vol. 49(Issue 87) pp:10302-10304
Publication Date(Web):02 Sep 2013
DOI:10.1039/C3CC43846E
A silicon nanoparticle solution (size ≅ 50 nm) with the concentration of 100 mM, which is contamination free, was synthesized using a ball milling method and was stable for 4 months without aggregation. This stability was responsible for large negative zeta potential on the surface of Si-NPs, established by milling in 2-propanol solvent.
Co-reporter:Shaoyu Wei ; Tomoharu Yamamura ; Daisuke Kajiya
The Journal of Physical Chemistry C 2012 Volume 116(Issue 6) pp:3928-3934
Publication Date(Web):January 6, 2012
DOI:10.1021/jp210080k
White-light-emitting silicon nanocrystals (Si-NCs) ranging from the near UV to the red region were fabricated by pulsed laser ablation (PLA) of a bulk silicon crystal in a supercritical fluid. The broad photoluminescence (PL) spectra, white light continuum, were investigated by measuring time evolution against aging in the atmosphere or oxygen ambience. The results show that the PL intensity of the higher-energy component increases, whereas that of the lower-energy component decreases as aging time increases. According to rate constants of PL intensity enhancement, the increase in the PL intensity was ascribed to the oxidation of the Si-NCs. This enhancement became significant when the sample was generated at the thermodynamic state, showing a critical anomaly of supercritical CO2. That is, rapid cooling of the hot Si-NC in supercritical CO2 immediately after PLA produces a luminescent Si-NC in the blue-green wavelength region. On the basis of PL spectral measurements at five excitation wavelengths, the lower- and higher-energy PL components were assigned to electronic structures arising from the quantum confinement effect of the Si-NC and the electron–hole recombination at the radiative centers at the surface of the Si-NC, respectively.
Co-reporter:Ken-ichi Saitow, Yoshinori Okamoto, and Yohko F. Yano
The Journal of Physical Chemistry C 2012 116(32) pp: 17252-17258
Publication Date(Web):July 24, 2012
DOI:10.1021/jp304109h
The nanosecond pulsed laser ablation of a gold plate at the excitation wavelength of 532 nm was conducted in the supercritical fluid of dipolar trifluoromethane (CHF3). The generation of gold nanoparticles was investigated as a function of the fluid density that corresponded to changes in the permittivity and thermal properties over the wide ranges. The analysis of data from electron microscopy and small-angle X-ray scattering (SAXS) revealed that the principal product is a gold nanonetwork with length up to a few 10 μm and a branched structure. The gold nanonetwork consisted of gold nanospheres with an average diameter of 20 nm and a mass fractal structure. The mass fractal dimension of the nanonetwork changed by the fluid density, and its dimension was attributed to the number of the nanospheres. It was clarified that not the fluid thermal properties but the ambient dielectricity and polarization energy during the ablation are responsible for the morphology and number of gold nanoparticles. This is the first report of (i) fractal structure of gold nanoparticles created by the ablation, (ii) ablation mechanism in dipolar and nondipolar fluids, and (iii) a chemical-free nanoparticle synthesis in a dipolar fluid.
Co-reporter:Daisuke Kajiya and Ken-ichi Saitow
The Journal of Physical Chemistry B 2010 Volume 114(Issue 26) pp:8659-8666
Publication Date(Web):June 11, 2010
DOI:10.1021/jp101217s
Vibrational Raman spectra of the C═C stretching modes of cis- and trans-1,2-dichloroethylene (C2H2Cl2) were measured in supercritical Xe, SF6, CO2, and CHF3. The spectra were collected over a wide range of densities of supercritical fluids at a fixed solute mole fraction and isotherm of Tr = T/Tc = 1.02. In all fluids, as the density increased, the peak frequencies of the C═C stretching modes shifted toward the low-energy side. By analyzing these density dependencies using the perturbed hard-sphere theory, the shifted amounts were characterized into attractive and repulsive components. The attractive shifts of both isomers were almost equivalent in supercritical CHF3, CO2, and SF6, whereas they were significantly larger in supercritical Xe. The attractive shifts obtained experimentally were compared with the ones calculated on the basis of dispersion, dipole−dipole, dipole−induced-dipole, and dipole−quadrupole interactions between solute and solvent molecules. The experimental attractive shifts in supercritical Xe were 2−3 times greater than the calculated shifts. The large attractive shifts were ascribed to both an anisotropic solvation structure and to a strong interaction (charge transfer) between Xe and C2H2Cl2 molecules.
Co-reporter:Daisuke Kajiya and Ken-ichi Saitow
The Journal of Physical Chemistry B 2010 Volume 114(Issue 50) pp:16832-16837
Publication Date(Web):November 29, 2010
DOI:10.1021/jp107820j
Vibrational Raman spectra of the C═C stretching modes of cis-stilbene and cis-1,2-dichloroethylene (C2H2Cl2) were measured in supercritical CO2 in a density range of 0.08 < ρr = ρ/ρc < 1.5 at an isotherm of Tr = T/Tc = 1.02. As the fluid density increased, the peak frequencies of cis-stilbene and cis-C2H2Cl2 shifted toward the low-energy side. The shifted frequencies of cis-stilbene were consistently greater than those of cis-C2H2Cl2 in all density regions, by a factor of 4. By analyzing these density dependencies using the perturbed hard-sphere theory, the shifted frequencies were decomposed into attractive and repulsive components. By quantifying these components as a function of fluid density, we investigated how each solute is solvated in supercritical CO2. The results indicate that the attractive energy between cis-stilbene and CO2 is twice that between cis-C2H2Cl2 and CO2. A local density augmentation around the solute molecule was not observed in the cis-C2H2Cl2/CO2 system, but it was observed in the cis-stilbene/CO2 system because of site-selective solvation around the phenyl group of cis-stilbene. To the best of our knowledge, this is the first time that the site-selective solvation of a solute molecule has been observed using Raman spectral measurements of a solution system. Based on theoretical calculations and Raman spectral measurements of cis-stilbene in the supercritical fluid of dipolar CHF3, it is concluded that a driving force for site-selective solvation is the dispersion force.
Co-reporter:Ken-ichi Saitow and Tomoharu Yamamura
The Journal of Physical Chemistry C 2009 Volume 113(Issue 19) pp:8465-8470
Publication Date(Web):2017-2-22
DOI:10.1021/jp900067s
Nanosecond pulsed laser ablation of bulk silicon crystal upon the excitation of 532 nm was conducted in supercritical CO2 to generate silicon nanocrystals, whose properties were studied by seven experimental methods. According to the photoluminescence spectra and fluorescence microscope images, emissions of near-ultraviolet, violet, blue, green, and red were observed in air, at room temperature, and without cooling in liquid nitrogen or a helium cryogenic system. A preferable emission channel of carriers, generated by photoexcitation of Si/SiO2 of core/shell structure, was responsible for interface states with defect sites. This luminescence process caused color changes and intensity increase, enhanced by a factor of 100, where thermal properties of supercritical CO2 were maximized, due to critical anomaly. It was found that colors and intensities of photoluminescence of silicon nanocrystals are controlled by a cooling rate during ablation, whose quantity is manipulated by the supercritical fluid pressure.
Co-reporter:Daisuke Kajiya and Ken-ichi Saitow
The Journal of Physical Chemistry B 2009 Volume 113(Issue 40) pp:13291-13299
Publication Date(Web):September 14, 2009
DOI:10.1021/jp903240v
Vibrational Raman spectra of the C═C stretching modes of cis- and trans-1,2-dichloroethylene (C2H2Cl2) were measured in supercritical carbon dioxide (CO2). The spectra were collected at a fixed solute mole fraction by varying the fluid density by a factor of 20. As the density increased, the peak frequencies of the C═C stretching modes shifted toward the low-energy side at isotherms of reduced temperature, Tr = T/Tc = 1.02, 1.06, and 1.20. By analyzing these density dependences using the perturbed hard-sphere theory, we decomposed the shifts into attractive and repulsive components. The repulsive shifts of cis-C2H2Cl2 were almost equivalent to those of trans-C2H2Cl2. However, the attractive shifts of nonpolar trans-C2H2Cl2 were significantly greater than those of polar cis-C2H2Cl2 at all densities and temperatures. To evaluate the difference in the isomers, we calculated the attractive shifts of the C═C stretching modes of each isomer, composing of dispersion, dipole-induced-dipole, and dipole−quadrupole interactions between solute C2H2Cl2 and solvent CO2 molecules. These three interactions were quantified by considering molecular configurations and orientations, and solvation structures around the isomers were elucidated by 3D schematic diagrams. As a result, it was shown that the anisotropic solvation structure around trans-C2H2Cl2 was responsible for the larger attractive shifts in the supercritical CO2. The difference of solvation structures between the isomers was significant at Tr = 1.02 but became minor as the temperature increased to Tr = 1.20.
Co-reporter:Daisuke Kajiya, Yutaka Mouri and Ken-ichi Saitow
The Journal of Physical Chemistry B 2008 Volume 112(Issue 27) pp:7980-7983
Publication Date(Web):June 14, 2008
DOI:10.1021/jp803875x
Vibrational Raman spectra of C═C stretching modes of both cis- and trans-1,2-dichloroethylene (C2H2Cl2) were measured as a function of density in supercritical carbon dioxide (CO2). Measurements were performed with solute mole fraction of 0.01 at an isotherm of Tr = T/Tc = 1.02. As the density of CO2 increased, peak frequencies of the C═C stretching modes shifted toward the low energy side. By analyzing these density dependences using perturbed hard-sphere theory, we decomposed the shifted amounts into attractive and repulsive components. The amounts of repulsive shifts were almost equivalent, whereas those of the attractive shifts of trans-C2H2Cl2 were larger than those of cis-C2H2Cl2 at all densities. This means that the nonpolar solute, trans-C2H2Cl2, shows stronger solute—solvent interactions than those of the polar solute cis-C2H2Cl2. The difference of attractive interactions between these isomers is the greatest at a density where local density enhancement of supercritical CO2 reaches the maximum.
Co-reporter:Ken-ichi Saitow Dr.;Yukito Naitoh Dr.;Keisuke Tominaga Dr.;Keitaro Yoshihara Dr.
Chemistry – An Asian Journal 2008 Volume 3( Issue 4) pp:696-709
Publication Date(Web):
DOI:10.1002/asia.200700351
Abstract
We studied photoinduced reactions of diiodomethane (CH2I2) upon excitation at 268 nm in acetonitrile and hexane by subpicosecond–nanosecond transient absorption spectroscopy. The transient spectra involve two absorption bands centered at around 400 (intense) and 540 nm (weak). The transients probed over the range 340–740 nm show common time profiles consisting of a fast rise (<200 fs), a fast decay (≈500 fs), and a slow rise. The two fast components were independent of solute concentration, whereas the slow rise became faster (7–50 ps) when the concentration in both solutions was increased. We assigned the fast components to the generation of a CH2I radical by direct dissociation of the photoexcited CH2I2 and its disappearance by subsequent primary geminate recombination. The concentration-dependent slow rise produced the absorption bands centered at 400 and 540 nm. The former consists of different time-dependent bands at 385 and 430 nm. The band near 430 nm grew first and was assigned to a charge-transfer (CT) complex, CH2I2δ+⋅⋅⋅Iδ−, formed by a photofragment I atom and the solute CH2I2 molecule. The CT complex is followed by full electron transfer, which then develops the band of the ion pair CH2I2+⋅⋅⋅I− at 385 nm on the picosecond timescale. On the nanosecond scale, I3− was generated after decay of the ion pair. The reaction scheme and kinetics were elucidated by the time-resolved absorption spectra and the reaction rate equations. We ascribed concentration-dependent dynamics to the CT-complex formation in pre-existing aggregates of CH2I2 and analyzed how solutes are aggregated at a given bulk concentration by evaluating a relative local concentration. Whereas the local concentration in hexane monotonically increased as a function of the bulk concentration, that in acetonitrile gradually became saturated. The number of CH2I2 molecules that can participate in CT-complex formation has an upper limit that depends on the size of aggregation or spatial restriction in the neighboring region of the initially photoexcited CH2I2. Such conditions were achieved at lower concentrations in acetonitrile than in hexane.
Co-reporter:Yunzi Xin, Takumi Kitasako, Makoto Maeda, Ken-ichi Saitow
Chemical Physics Letters (16 April 2017) Volume 674() pp:
Publication Date(Web):16 April 2017
DOI:10.1016/j.cplett.2017.02.060
•Si NPs synthesized by pulsed laser ablation in different organic solvents.•Carbon atom ratio of solvent molecule controls PL quantum yield and particle size.•Enhancement of PL quantum yield during aging was found.Pulsed-laser ablation of silicon (Si) was conducted in six different organic solvents using a nanosecond laser. Si nanoparticles (Si-NPs) that exhibited blue photoluminescence (PL) were generated in all the solvents, but a significant solvent dependence emerged: particle size, PL spectra, and PL quantum yield (QY). The results of solvent dependence were well characterized using an atomic ratio in a solvent molecule. The highest QY was observed for the smallest Si-NPs (ca. 2 nm) synthesized in 1-octyne. The QY was enhanced by aging in 1-octyne, and its mechanism was attributed to alkyl passivation of dangling bonds on the Si-NPs.
Co-reporter:Ken-ichi Saitow, Hidemi Suemori and Hironori Tamamitsu
Chemical Communications 2014 - vol. 50(Issue 9) pp:NaN1140-1140
Publication Date(Web):2013/11/19
DOI:10.1039/C3CC46566G
Fluorescence-intensity enhancement of dye molecules was investigated using silicon submicron particles as a function of the particle size. Silicon particles with a size of 500 nm gave an enhancement factor up to 180. Measurement of scattering spectra revealed that the localized electric field at the particle enhances the fluorescence intensity.
Co-reporter:Hua Sun, Satoshi Miyazaki, Hironori Tamamitsu and Ken-ichi Saitow
Chemical Communications 2013 - vol. 49(Issue 87) pp:NaN10304-10304
Publication Date(Web):2013/09/02
DOI:10.1039/C3CC43846E
A silicon nanoparticle solution (size ≅ 50 nm) with the concentration of 100 mM, which is contamination free, was synthesized using a ball milling method and was stable for 4 months without aggregation. This stability was responsible for large negative zeta potential on the surface of Si-NPs, established by milling in 2-propanol solvent.
![Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]](http://img.cochemist.com/ccimg/138200/138184-36-8.png)
![Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]](http://img.cochemist.com/ccimg/138200/138184-36-8_b.png)
