Youngku Sohn - Academia.edu (original) (raw)
Papers by Youngku Sohn
Ultrasonics Sonochemistry, 2014
We investigated a facial method to produce silver nanowires with low aspect ratio by fragmentizin... more We investigated a facial method to produce silver nanowires with low aspect ratio by fragmentizing as produced long silver nanowires. The length of silver nanowires can be shortened in a controllable manner by increasing ultrasonication time or ultrasonication power. However, excessively large ultrasonication power caused a problem of agglomeration of nanowires. From UV absorption spectra, it was found that the UV absorption characteristic of silver nanowires is not affected by ultrasonication assisted fragmentation indicating that one dimensional structure of silver nanowires is maintained during the fragmentation process.
Journal of Colloid and Interface Science, 2014
A tetrakis(dibenzylmethanido) Eu(III) complex as a ultraviolet (UV) excited phosphor was synthesi... more A tetrakis(dibenzylmethanido) Eu(III) complex as a ultraviolet (UV) excited phosphor was synthesized, and incorporated with mesoporous silica as core-shell (CS), outer-shell (OS) and intermediate-shell (IS) architectures, using a combination of the self-organization process and the Stöber method. Exciting the Eu(III) complex at UV light produced a strong sensitized red-emission from Eu(III) by energy transfer from the ligand. Phosphor-converted light-emitting diodes (pc-LEDs) were fabricated by casting the powdered complex and the incorporated silica nanoparticles onto a 365-nm InGaN chip, and their optical properties and thermal stability were investigated in terms of the chromaticity index and the intensity decay, respectively. The CS silica nanoparticle casted UV-LED exhibited the best perfomence with strong intensity and excellent thermal stability.
Luminescence : the journal of biological and chemical luminescence, Jan 23, 2015
A silica (SiO2 ) nanoparticle matrix was codoped with luminescent Eu(III) and Tb(III) ions using ... more A silica (SiO2 ) nanoparticle matrix was codoped with luminescent Eu(III) and Tb(III) ions using a modified Stöber method. The effects of fast and slow thermal annealing on photoluminescence profile imaging were examined. Slow annealing treatment suppressed more quenching sites than fast thermal annealing to further increase the photoluminescence signals. The photoluminescence signals observed between 450 and 720 nm were assigned to the (5) D0 → (7) FJ (J = 0,1,2,3,4) of Eu(III) and the (5) D4 → (7) FJ (J = 6,5,4,3) transitions of Tb(III). Photoluminescence was largely sensitized by indirect excitation and was much stronger than that generated by direct excitation. The Eu(III) and Tb(III) ions were doped at lower symmetry sites in the silica matrix. Copyright © 2015 John Wiley & Sons, Ltd.
Scientific reports, 2015
SnO2 has been studied intensely for applications to sensors, Li-ion batteries and solar cells. De... more SnO2 has been studied intensely for applications to sensors, Li-ion batteries and solar cells. Despite this, comparatively little attention has been paid to the changes in morphology and crystal phase that occur on the metal oxide surface during chemical reactions. This paper reports anaerobic and aerobic ethanol and CO oxidation reactions over SnO2 nanoparticles (NPs), as well as the subsequent changes in the nature of the NPs. Uniform SnO2@C core-shells (10 nm) were formed by an aerobic ethanol oxidation reaction over SnO2 NPs. On the other hand, metallic Sn spheres were produced by an anaerobic ethanol oxidation reaction at 450 °C, which is significantly lower than that (1200 °C) used in industrial Sn production. Anaerobic and aerobic CO oxidation reactions were also examined. The novelty of the methods for the production of metallic Sn and SnO2@C core-shells including other anaerobic and aerobic reactions will contribute significantly to Sn and SnO2-based applications.
Journal of the Chemical Society, Dalton Transactions, 1999
ABSTRACT The crystal structure and the luminescence of the complex Na[Eu(DCTA)·H2O]·4H2O (DCTA = ... more ABSTRACT The crystal structure and the luminescence of the complex Na[Eu(DCTA)·H2O]·4H2O (DCTA = trans-cyclohexane-1,2-diyldinitrilotetraacetate) have been determined. In the structure the EuIII is co-ordinated by two nitrogen atoms and four terminal oxygen atoms of two iminodiacetate groups, and two water oxygen atoms which bridge two adjacent EuIII. When the crystals are excited by UV light they produce a very characteristic luminescence responsible for the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions. The energy-level scheme of the 7FJ states and detailed assignments for the observed luminescence lines have been proposed by phenomenological simulation in the framework of the free-ion and crystal-field Hamiltonians. Although an additional correction to the free-ion model is needed for the barycenter shifting due to the complexation, the set of refined crystal-field parameters under C2v site symmetry satisfactorily reproduces the fine splitting of the luminescence lines in the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions. The behavior of the maximum splitting of the 7F1 manifold is also discussed in terms of a scalar crystal-field strength parameter.
Materials Science in Semiconductor Processing, 2014
We synthesized hierarchical flower-like BiOBr x Cl 1 À x (0 r x r 1) microspheres in ethylene gly... more We synthesized hierarchical flower-like BiOBr x Cl 1 À x (0 r x r 1) microspheres in ethylene glycol solvent and examined their fundamental properties by scanning electron microscopy (SEM), X-day diffraction (XRD), UV-visible absorption, Raman, photoluminescence spectroscopy, and BET surface area measurement. Additionally, their adsorption and photocatalytic performance were tested using methyl orange (MO), Rhodamine B (RhB), and methylene blue (MB). The adsorption performance was found to be in the order of BiOCl o BiOBr x Cl 1 À x o BiOBr for MO under dark conditions. For the selected BiOBr 0.7 Cl 0.3 catalyst, the adsorption ability was found to be in the order of MO 5RhB o MB owing to electrostatic interactions between the catalyst and the dye. The photocatalytic dye degradation performance occurred in the order of MB o MO 5 RhB as a result of light absorption by the dye followed by good electron transfer from the conduction band of the dye to that of the catalyst. An indirect chemical probe method was used to examine the roles of active species in the dye-sensitized photodegradation mechanism, which were found to be in the order of d OH E d O 2 À o h þ under visible light irradiation.
Reaction Kinetics, Mechanisms and Catalysis, 2014
CO oxidation to CO 2 by Pd-CeO 2 catalysts was tested by temperatureprogrammed mass spectrometry ... more CO oxidation to CO 2 by Pd-CeO 2 catalysts was tested by temperatureprogrammed mass spectrometry for as-prepared and thermal H 2 -treated Pd-doped CeO 2 catalysts, compared with those of Ag and Au-doped CeO 2 . For the as-prepared samples, the oxidation rate and the T 10 % (the temperature at 10 % CO conversion) occurred in the order of Au & Pd [ Ag ) undoped in the 1st CO oxidation run, while in the 2nd run, the order became Au [ Pd [ Ag ) undoped. For the thermal H 2 -treated samples, the order became Pd [ Au [ Ag [ undoped and Au [ Pd [ Ag [ undoped in the 1st and 2nd CO oxidation runs, respectively. The T 10 % in the 2nd run commonly occurred at much lower temperatures for the metal-doped CeO 2 upon achieving good metal-oxide interfacial contact during the 1st run. The T 10 % of undoped CeO 2 was the most significantly affected by the thermal treatment effects while those of metal-doped CeO 2 catalysts were not greatly affected by the thermal H 2 -treatment. Based on these findings, the metal-support interaction/interface is more important than the surface area, Au (88 m 2 /g) [ Ag (59 m 2 /g) & Pd & undoped.
CrystEngComm, 2014
ABSTRACT Indium sulfide (In2S3) microspheres of (β-) tetragonal phase were synthesized by varying... more ABSTRACT Indium sulfide (In2S3) microspheres of (β-) tetragonal phase were synthesized by varying the indium precursors using a template-free and surfactant-less hydrothermal process at 150 °C. The as-synthesized samples were found to be crystalline and phase pure as confirmed by X-ray diffraction and X-ray photoelectron spectroscopy studies, respectively. Indium precursors play an important role in controlling the shape of the building blocks, i.e. nanoflakes or nanobricks, of In2S3 microspheres. The photocatalytic activity of as-synthesized In2S3 microspheres was tested for the degradation of methylene blue and crystal violet in the presence of visible light produced by an incandescent lamp. The terephthalic acid test using photoluminescence spectroscopy shows hydroxyl radicals as active species for the degradation of organic contaminants. Repeat photocatalysis measurements suggest the high stability of In2S3 microspheres without a change in their morphology and phase.
Applied Surface Science, 2014
Cubic (space group Ia-3, a = 10.49Å) bixbyite two-dimensional thulium(III) oxide nanosquare struc... more Cubic (space group Ia-3, a = 10.49Å) bixbyite two-dimensional thulium(III) oxide nanosquare structure was first prepared, and then fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction crystallography (XRD), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), UV-vis-near IR absorption, Raman, X-ray photoelectron spectroscopy, temperature-programmed reduction and oxidation experiments. The crystal structure was fully refined, and detailed structural parameters were determined on the basis of the Rietveld analysis. High resolution TEM image revealed interplanar distances of 0.26 nm and 0.31 nm corresponding to the (4 0 0) and (2 2 2) planes, respectively. The structure projections of the (4 0 0) and (2 2 2) planes were imaged along [0 1 1] and [1 1 −2] directions, respectively. A broad H 2 reduction peak and a sharp O 2 oxidation peak were found at 688 • C and 123 • C, respectively. CO oxidation activity started to appear at 400-500 • C. The new results of this study further highlight the characteristics and the actual applications of Tm(III) oxide.
The Journal of Physical Chemistry C, 2008
Adsorption and oxidation of phenylacetylene (PA) and phenylmethylacetylene (PMA) on atomic oxygen... more Adsorption and oxidation of phenylacetylene (PA) and phenylmethylacetylene (PMA) on atomic oxygen (O (a) )precovered Cu(111) have been studied by temperature-programmed desorption (TPD) spectroscopy, X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). Oxidation products commonly include H 2 O, CO, and CO 2 , and their yields strongly depend on the O (a) coverage. The desorption profile of parent PA with O (a) coverage is markedly different from that of parent PMA, which is mainly due to that the terminal C-H bond of the acetylene group of PA is more vulnerable to be attacked by the O (a) than the hydrogen of the methyl group of PMA. The reactivity of O (a) is dependent on the O (a) coverage: it decreases with the increase of the coverage. With the increase of O (a) coverage, the H 2 O desorption temperature shifts to a higher temperature. The more active O (a) at low coverage is mainly used for forming H 2 O by cleaving the tC-H (or -CH 3 ) hydrogen; the less active O (a) at high coverage is mainly consumed for CO 2 .
The Journal of Physical Chemistry B, 2010
At high porphyrin densities, the effects of the number and position of the positive charges of th... more At high porphyrin densities, the effects of the number and position of the positive charges of the periphery ring on the stacking of the porphyrin on poly[d(A-T)(2)] was investigated using polarized spectroscopy, including circular and linear dichroism (CD and LD, respectively). The CD spectrum of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin(TMPyP) consisted of two positive bands in the Soret absorption region at low [porphyrin]/[DNA base] ratios (R ratios) and changed to two distinguishable categories of the bisignate CD spectrum with increasing R ratio. These CD spectra were attributed to the monomeric groove binding, and the moderately and extensively stacked TMPyPs. In contrast, trans-bis(N-methylpyridinium-4-yl)porphyrin (trans-BMPyP) dominantly produced a CD spectrum that corresponded to the extensive stacking, except at the lowest R ratio that was used in this work (R = 0.04). However, for cis-bis(N-methylpyridinium-4-yl)porphyrin (cis-BMPyP), the intensity of the apparent bisignate CD signal was too small to assign it to the extensive stacking. Moreover, the shape of the CD spectrum in the DNA absorption region showed that the conformation of poly[d(A-T)(2)] was retained, in contrast to the extensively stacked TMPyP and trans-BMPyP. In the extensively stacked TMPyP- poly[d(A-T)(2)] assembly, the large negative LD signal in the Soret band was observed suggesting that the direction of the molecular planes of TMPyP was close to perpendicular with respect to the orientation axis (flow axis). In contrast, the LD spectrum of the trans-BMPyP-poly[d(A-T)(2)] complex produced positive LD signal in the same wavelength region, suggesting the orientation of the molecular plane was nearly parallel relative to the flow direction. Surprisingly, the LD signal in the DNA absorption region for both of the porphyrins was positive. Therefore, the helix axis of the DNA was near perpendicular relative to the flow direction in the porphyrin-polynucleotide assembly.
Surface Science, 2008
The thermal and photochemistry of tert-butyl iodide (t-buI) on ice films grown on Cu(111) at 100 ... more The thermal and photochemistry of tert-butyl iodide (t-buI) on ice films grown on Cu(111) at 100 K were studied using time-of-flight (TOF) temperature programmed desorption (TPD) mass spectroscopy and Xray photoelectron spectroscopy (XPS). The thermal reaction products include isobutane (i-C 4 H 10 ), isobutene (i-C 4 H 8 ) and minor t-butyl alcohol. In the rising edge of the water desorption at 145K,theparentt−buImoleculedesorbsfromtheiceaswellasotherthermalreactionproducts.Abovethefallingedgeofthewaterdesorptionat145 K, the parent t-buI molecule desorbs from the ice as well as other thermal reaction products. Above the falling edge of the water desorption at 145K,theparentt−buImoleculedesorbsfromtheiceaswellasotherthermalreactionproducts.Abovethefallingedgeofthewaterdesorptionat180 K, the reaction products and the parent molecule desorb from the Cu . For t-buI on bare Cu(111) dosed at 100 K, dominant i-C 4 H 8 , some i-C 4 H 10 and tiny t-buI desorption peaks were observed. This indicates that t-buI promptly dissociates on Cu(111) to form C 4 H 9 and chemisorbed I at 100 K. The C 4 H 9 quickly rearranges, followed by C-H scission to form mainly i-C 4 H 8 , or abstracts H to form some i-C 4 H 10 . The I directly chemisorbs on the Cu(111), evidenced by I(3d) XPS peaks. On ice layer, the most dominant i-C 4 H 10 desorption peak indicates that the C 4 H 9 abstracts H from ice to form C 4 H 10 . For photoirradiation of t-buI on ice, we observed an enhanced t-buI dissociation followed by ejection of reaction products, evidenced by decrease in TPD and C(1s) XPS intensities. No ejection of I-containing molecules was observed. We attribute the t-buI dissociation to solvated electrons in ice. During photoirradiation, I radicals seem to diffuse into the bulk ice to chemisorb on Cu(111), plausibly due to self-diffusion of water. In addition, a preferential desorption of C 4 H 10 and/or an enhanced reaction channel to i-C 4 H 8 by photoirradiation is evidenced by a faster TPD decay rate of C 4 H 10 with photoirradiation time. An increased i-C 4 H 8 TPD peak at 113 K and an appearance of 2 amu desorption could indicate the enhanced channel to i-C 4 H 8 .
Langmuir, 2007
The bonding properties of 1-phenyl-1-propyne (PP, C 6 H 5 CCCH 3 ) on Cu(111) at 100 K have been ... more The bonding properties of 1-phenyl-1-propyne (PP, C 6 H 5 CCCH 3 ) on Cu(111) at 100 K have been studied using temperature-programmed desorption (TPD), and X-ray, ultraviolet, and two-photon photoemission spectroscopies (XPS, UPS, and 2PPE). In TPD, there is no evidence for dissociation. Multilayer desorption occurs at 187 K, and monolayer desorption occurs at 320 (83.5 kJ/mol) and 390 K (102.4 kJ/mol), with the latter dominating. Based on the calibrated C(1s) XPS, the saturation monolayer coverage is one PP per four surface Cu atoms. The broad and asymmetric C(1s) intensity profile of the monolayer can be resolved into three symmetric components, with peaks at 283.6, 284.5, and 285.2 eV and intensities of 2:6:1, respectively. These are attributed, respectively, to acetylenic carbons bound to Cu, phenyl, and methyl carbons. The monolayer valence band ultraviolet photoemission spectrum profile contains four resonances attributable to PP perturbed by interactions with the Cu(111) substrate. With the exception of the highest occupied molecular orbital (HOMO) that is shifted by 0.4 eV, these are uniformly shifted by 1 eV further from the Fermi level for the multilayer. Calculated electron density plots of the occupied orbitals coupled with UPS profiles suggest a spectator role for the phenyl group and bonding to Cu via the acetylenic carbons. The adsorption of 1.0 monolayer (ML) of PP on Cu(111) lowers the work function by 0.85 eV. Using 2PPE, two unoccupied orbitals were identified at 1.0 (U 1 *-LUMO) and 0.6 eV (U 2 *-image state) below the vacuum level. A chemisorption model consistent with these spectroscopic results and the major chemisorption peak in TPD involve di-σ-bonding of the acetylenic carbons to a pair of second-nearest neighbor surface Cu atoms (cross-bridge).
Langmuir, 2009
Gold nanoparticles (Au NPs) were prepared on a native-oxide-covered Si(100) substrate by sputter-... more Gold nanoparticles (Au NPs) were prepared on a native-oxide-covered Si(100) substrate by sputter-deposition followed by thermal annealing. The size of Au NPs could be controlled in the range of 8-48 nm by varying the sputterdeposition time and post-annealing temperature. The interparticle separation was found to be directly related to the size of Au NPs, with smaller separations for particles of smaller size. The surface morphology, crystal structure, and interfacial composition of the chemical states of these supported Au NPs were studied as a function of their average size by using scanning electron microscopy, glancing-incidence X-ray diffraction, and depth-profiling X-ray photoelectron spectroscopy (XPS), respectively. The new Au 4f 7/2 peak found at 1.1-1.2 eV higher in binding energy than that for the metallic Au feature (at 84.0 eV) can be attributed to the formation of Au silicide at the interface between Au NPs and the Si substrate. Depth-profiling XPS experiments revealed no discernible change in the binding energies of the Au silicide and metallic Au 4f features with increasing Ar + sputtering time, indicating that the Au-to-silicide interface is abrupt. Furthermore, the shift in the Au 5d 5/2 valence band to a higher binding energy and the reduction of the Au 5d spin-orbit splitting with increasing Ar + sputtering time also support the formation of Au silicide. No clear evidence for the quantum size effect was observed for the supported NPs. The finite density of state at the Fermi level and the fixed Au 4f 7/2 peak position clearly indicate the metallic nature of the Au silicide at the Au-Si interface.
Journal of Physics: Condensed Matter, 2000
The polarization emission spectrum and the angular dependence of polarization ratio of the blue e... more The polarization emission spectrum and the angular dependence of polarization ratio of the blue emission from KCl:Eu2+ were investigated at 78.8 K. The polarized emission at 420 nm consisted of several components. The angular dependence of polarization ratio of each component is proportional to sin(2icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> ) or -cos(2icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> ), when the exciting light is polarized at
Journal of Physics: Condensed Matter, 2008
The interfacial electronic structure and photoexcitation kinetics of MEH-PPV/P3HT heterolayer fil... more The interfacial electronic structure and photoexcitation kinetics of MEH-PPV/P3HT heterolayer film on gold were studied using two-photon photoemission spectroscopy. We observed that the photoelectron kinetic energy distribution and the photoexcitation kinetics exhibit the characteristics of the MEH-PPV layer, and the absolute two-photon photoemission yield is determined by the P3HT layer. On the basis of the photoexcitation kinetics and the photoelectron
Journal of Materials Science, 2012
Silver nanoparticles supported on anatase TiO 2 nanoparticles have been prepared by deposition-pr... more Silver nanoparticles supported on anatase TiO 2 nanoparticles have been prepared by deposition-precipitation, and characterized by X-ray photoelectron spectroscopy, including scanning electron microscopy, X-ray diffraction crystallography, Raman, and UV-visible absorption spectroscopy. The Ag 3d peak and the X-ray diffraction patterns show characteristics of purely metallic Ag, with no indication of Ag oxide species. Depth-profiling X-ray photoelectron spectroscopy with Ar ? ion beam sputtering show a significant change in Ti 2p, and an asymmetric broadening of Ag 3d to a higher binding energy side. A decrease in major Ti 2p 3/2 at 459.2 eV and a significant increase in lower binding energy peak are due to change in oxidation state of Ti from ?4 to ?3/?2. A broadening of Ag 3d peak with sputtering time is tentatively assigned to a final state quantum size effect. Upon annealing the deposition-precipitation sample, no significant change in Ag 3d peak is observed, while Ti 2p and O 1s XPS intensities are reduced, plausibly due to change in analyzed surface area for TiO 2 . The photocatalytic activity for the photodegradation of methyl orange is dramatically reduced upon high Ag-loading, compared to bare TiO 2 . The X-ray photoelectron spectroscopy of Ag on TiO 2 prepared by an electrochemical deposition reveals that Ag is also metallic, with no evidence of an oxide form. Upon annealing the electrodeposited sample, the Ag 3d peak shifts by ?0.3 eV, while the Ti 2p and O 1s show no critical change in intensity and peak position.
The Journal of Chemical Physics, 2007
Photoexcitation kinetics and interfacial electronic structures of poly[2-methoxy-5(2-ethylhexylox... more Photoexcitation kinetics and interfacial electronic structures of poly[2-methoxy-5(2-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) film on gold have been investigated using two-photon photoemission spectroscopy (2PPE). The authors directly probed a fixed intermediate state located at 0.95 eV above the Fermi level (or 2.95 eV below the vacuum level), assigned to a charged polaron. Based on the power law slope and the 2PPE spectra with laser intensity, they found that the polaron follows a second order bimolecular annihilation process. The 2PPE yield dramatically increases with increasing photon energy. They attribute this to an enhanced dissociation of hotter excitons at higher excitation levels. The work function of MEH-PPV/Au is measured to be 3.9 eV, 1.2 eV downshift from the clean gold, attributable to interface dipole effects. The energy gap between the intermediate polaron state and the hole polaron level is estimated to be 2.45 eV.
![Research paper thumbnail of Luminescence and crystal field parameters of the Na3[Eu(DPA)3]·12H2O complex in a single crystalline state](https://attachments.academia-assets.com/44135063/thumbnails/1.jpg)
](Journal of Alloys and Compounds, 1998
Inorganica Chimica Acta, 2000
Ultrasonics Sonochemistry, 2014
We investigated a facial method to produce silver nanowires with low aspect ratio by fragmentizin... more We investigated a facial method to produce silver nanowires with low aspect ratio by fragmentizing as produced long silver nanowires. The length of silver nanowires can be shortened in a controllable manner by increasing ultrasonication time or ultrasonication power. However, excessively large ultrasonication power caused a problem of agglomeration of nanowires. From UV absorption spectra, it was found that the UV absorption characteristic of silver nanowires is not affected by ultrasonication assisted fragmentation indicating that one dimensional structure of silver nanowires is maintained during the fragmentation process.
Journal of Colloid and Interface Science, 2014
A tetrakis(dibenzylmethanido) Eu(III) complex as a ultraviolet (UV) excited phosphor was synthesi... more A tetrakis(dibenzylmethanido) Eu(III) complex as a ultraviolet (UV) excited phosphor was synthesized, and incorporated with mesoporous silica as core-shell (CS), outer-shell (OS) and intermediate-shell (IS) architectures, using a combination of the self-organization process and the Stöber method. Exciting the Eu(III) complex at UV light produced a strong sensitized red-emission from Eu(III) by energy transfer from the ligand. Phosphor-converted light-emitting diodes (pc-LEDs) were fabricated by casting the powdered complex and the incorporated silica nanoparticles onto a 365-nm InGaN chip, and their optical properties and thermal stability were investigated in terms of the chromaticity index and the intensity decay, respectively. The CS silica nanoparticle casted UV-LED exhibited the best perfomence with strong intensity and excellent thermal stability.
Luminescence : the journal of biological and chemical luminescence, Jan 23, 2015
A silica (SiO2 ) nanoparticle matrix was codoped with luminescent Eu(III) and Tb(III) ions using ... more A silica (SiO2 ) nanoparticle matrix was codoped with luminescent Eu(III) and Tb(III) ions using a modified Stöber method. The effects of fast and slow thermal annealing on photoluminescence profile imaging were examined. Slow annealing treatment suppressed more quenching sites than fast thermal annealing to further increase the photoluminescence signals. The photoluminescence signals observed between 450 and 720 nm were assigned to the (5) D0 → (7) FJ (J = 0,1,2,3,4) of Eu(III) and the (5) D4 → (7) FJ (J = 6,5,4,3) transitions of Tb(III). Photoluminescence was largely sensitized by indirect excitation and was much stronger than that generated by direct excitation. The Eu(III) and Tb(III) ions were doped at lower symmetry sites in the silica matrix. Copyright © 2015 John Wiley & Sons, Ltd.
Scientific reports, 2015
SnO2 has been studied intensely for applications to sensors, Li-ion batteries and solar cells. De... more SnO2 has been studied intensely for applications to sensors, Li-ion batteries and solar cells. Despite this, comparatively little attention has been paid to the changes in morphology and crystal phase that occur on the metal oxide surface during chemical reactions. This paper reports anaerobic and aerobic ethanol and CO oxidation reactions over SnO2 nanoparticles (NPs), as well as the subsequent changes in the nature of the NPs. Uniform SnO2@C core-shells (10 nm) were formed by an aerobic ethanol oxidation reaction over SnO2 NPs. On the other hand, metallic Sn spheres were produced by an anaerobic ethanol oxidation reaction at 450 °C, which is significantly lower than that (1200 °C) used in industrial Sn production. Anaerobic and aerobic CO oxidation reactions were also examined. The novelty of the methods for the production of metallic Sn and SnO2@C core-shells including other anaerobic and aerobic reactions will contribute significantly to Sn and SnO2-based applications.
Journal of the Chemical Society, Dalton Transactions, 1999
ABSTRACT The crystal structure and the luminescence of the complex Na[Eu(DCTA)·H2O]·4H2O (DCTA = ... more ABSTRACT The crystal structure and the luminescence of the complex Na[Eu(DCTA)·H2O]·4H2O (DCTA = trans-cyclohexane-1,2-diyldinitrilotetraacetate) have been determined. In the structure the EuIII is co-ordinated by two nitrogen atoms and four terminal oxygen atoms of two iminodiacetate groups, and two water oxygen atoms which bridge two adjacent EuIII. When the crystals are excited by UV light they produce a very characteristic luminescence responsible for the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions. The energy-level scheme of the 7FJ states and detailed assignments for the observed luminescence lines have been proposed by phenomenological simulation in the framework of the free-ion and crystal-field Hamiltonians. Although an additional correction to the free-ion model is needed for the barycenter shifting due to the complexation, the set of refined crystal-field parameters under C2v site symmetry satisfactorily reproduces the fine splitting of the luminescence lines in the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions. The behavior of the maximum splitting of the 7F1 manifold is also discussed in terms of a scalar crystal-field strength parameter.
Materials Science in Semiconductor Processing, 2014
We synthesized hierarchical flower-like BiOBr x Cl 1 À x (0 r x r 1) microspheres in ethylene gly... more We synthesized hierarchical flower-like BiOBr x Cl 1 À x (0 r x r 1) microspheres in ethylene glycol solvent and examined their fundamental properties by scanning electron microscopy (SEM), X-day diffraction (XRD), UV-visible absorption, Raman, photoluminescence spectroscopy, and BET surface area measurement. Additionally, their adsorption and photocatalytic performance were tested using methyl orange (MO), Rhodamine B (RhB), and methylene blue (MB). The adsorption performance was found to be in the order of BiOCl o BiOBr x Cl 1 À x o BiOBr for MO under dark conditions. For the selected BiOBr 0.7 Cl 0.3 catalyst, the adsorption ability was found to be in the order of MO 5RhB o MB owing to electrostatic interactions between the catalyst and the dye. The photocatalytic dye degradation performance occurred in the order of MB o MO 5 RhB as a result of light absorption by the dye followed by good electron transfer from the conduction band of the dye to that of the catalyst. An indirect chemical probe method was used to examine the roles of active species in the dye-sensitized photodegradation mechanism, which were found to be in the order of d OH E d O 2 À o h þ under visible light irradiation.
Reaction Kinetics, Mechanisms and Catalysis, 2014
CO oxidation to CO 2 by Pd-CeO 2 catalysts was tested by temperatureprogrammed mass spectrometry ... more CO oxidation to CO 2 by Pd-CeO 2 catalysts was tested by temperatureprogrammed mass spectrometry for as-prepared and thermal H 2 -treated Pd-doped CeO 2 catalysts, compared with those of Ag and Au-doped CeO 2 . For the as-prepared samples, the oxidation rate and the T 10 % (the temperature at 10 % CO conversion) occurred in the order of Au & Pd [ Ag ) undoped in the 1st CO oxidation run, while in the 2nd run, the order became Au [ Pd [ Ag ) undoped. For the thermal H 2 -treated samples, the order became Pd [ Au [ Ag [ undoped and Au [ Pd [ Ag [ undoped in the 1st and 2nd CO oxidation runs, respectively. The T 10 % in the 2nd run commonly occurred at much lower temperatures for the metal-doped CeO 2 upon achieving good metal-oxide interfacial contact during the 1st run. The T 10 % of undoped CeO 2 was the most significantly affected by the thermal treatment effects while those of metal-doped CeO 2 catalysts were not greatly affected by the thermal H 2 -treatment. Based on these findings, the metal-support interaction/interface is more important than the surface area, Au (88 m 2 /g) [ Ag (59 m 2 /g) & Pd & undoped.
CrystEngComm, 2014
ABSTRACT Indium sulfide (In2S3) microspheres of (β-) tetragonal phase were synthesized by varying... more ABSTRACT Indium sulfide (In2S3) microspheres of (β-) tetragonal phase were synthesized by varying the indium precursors using a template-free and surfactant-less hydrothermal process at 150 °C. The as-synthesized samples were found to be crystalline and phase pure as confirmed by X-ray diffraction and X-ray photoelectron spectroscopy studies, respectively. Indium precursors play an important role in controlling the shape of the building blocks, i.e. nanoflakes or nanobricks, of In2S3 microspheres. The photocatalytic activity of as-synthesized In2S3 microspheres was tested for the degradation of methylene blue and crystal violet in the presence of visible light produced by an incandescent lamp. The terephthalic acid test using photoluminescence spectroscopy shows hydroxyl radicals as active species for the degradation of organic contaminants. Repeat photocatalysis measurements suggest the high stability of In2S3 microspheres without a change in their morphology and phase.
Applied Surface Science, 2014
Cubic (space group Ia-3, a = 10.49Å) bixbyite two-dimensional thulium(III) oxide nanosquare struc... more Cubic (space group Ia-3, a = 10.49Å) bixbyite two-dimensional thulium(III) oxide nanosquare structure was first prepared, and then fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction crystallography (XRD), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), UV-vis-near IR absorption, Raman, X-ray photoelectron spectroscopy, temperature-programmed reduction and oxidation experiments. The crystal structure was fully refined, and detailed structural parameters were determined on the basis of the Rietveld analysis. High resolution TEM image revealed interplanar distances of 0.26 nm and 0.31 nm corresponding to the (4 0 0) and (2 2 2) planes, respectively. The structure projections of the (4 0 0) and (2 2 2) planes were imaged along [0 1 1] and [1 1 −2] directions, respectively. A broad H 2 reduction peak and a sharp O 2 oxidation peak were found at 688 • C and 123 • C, respectively. CO oxidation activity started to appear at 400-500 • C. The new results of this study further highlight the characteristics and the actual applications of Tm(III) oxide.
The Journal of Physical Chemistry C, 2008
Adsorption and oxidation of phenylacetylene (PA) and phenylmethylacetylene (PMA) on atomic oxygen... more Adsorption and oxidation of phenylacetylene (PA) and phenylmethylacetylene (PMA) on atomic oxygen (O (a) )precovered Cu(111) have been studied by temperature-programmed desorption (TPD) spectroscopy, X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). Oxidation products commonly include H 2 O, CO, and CO 2 , and their yields strongly depend on the O (a) coverage. The desorption profile of parent PA with O (a) coverage is markedly different from that of parent PMA, which is mainly due to that the terminal C-H bond of the acetylene group of PA is more vulnerable to be attacked by the O (a) than the hydrogen of the methyl group of PMA. The reactivity of O (a) is dependent on the O (a) coverage: it decreases with the increase of the coverage. With the increase of O (a) coverage, the H 2 O desorption temperature shifts to a higher temperature. The more active O (a) at low coverage is mainly used for forming H 2 O by cleaving the tC-H (or -CH 3 ) hydrogen; the less active O (a) at high coverage is mainly consumed for CO 2 .
The Journal of Physical Chemistry B, 2010
At high porphyrin densities, the effects of the number and position of the positive charges of th... more At high porphyrin densities, the effects of the number and position of the positive charges of the periphery ring on the stacking of the porphyrin on poly[d(A-T)(2)] was investigated using polarized spectroscopy, including circular and linear dichroism (CD and LD, respectively). The CD spectrum of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin(TMPyP) consisted of two positive bands in the Soret absorption region at low [porphyrin]/[DNA base] ratios (R ratios) and changed to two distinguishable categories of the bisignate CD spectrum with increasing R ratio. These CD spectra were attributed to the monomeric groove binding, and the moderately and extensively stacked TMPyPs. In contrast, trans-bis(N-methylpyridinium-4-yl)porphyrin (trans-BMPyP) dominantly produced a CD spectrum that corresponded to the extensive stacking, except at the lowest R ratio that was used in this work (R = 0.04). However, for cis-bis(N-methylpyridinium-4-yl)porphyrin (cis-BMPyP), the intensity of the apparent bisignate CD signal was too small to assign it to the extensive stacking. Moreover, the shape of the CD spectrum in the DNA absorption region showed that the conformation of poly[d(A-T)(2)] was retained, in contrast to the extensively stacked TMPyP and trans-BMPyP. In the extensively stacked TMPyP- poly[d(A-T)(2)] assembly, the large negative LD signal in the Soret band was observed suggesting that the direction of the molecular planes of TMPyP was close to perpendicular with respect to the orientation axis (flow axis). In contrast, the LD spectrum of the trans-BMPyP-poly[d(A-T)(2)] complex produced positive LD signal in the same wavelength region, suggesting the orientation of the molecular plane was nearly parallel relative to the flow direction. Surprisingly, the LD signal in the DNA absorption region for both of the porphyrins was positive. Therefore, the helix axis of the DNA was near perpendicular relative to the flow direction in the porphyrin-polynucleotide assembly.
Surface Science, 2008
The thermal and photochemistry of tert-butyl iodide (t-buI) on ice films grown on Cu(111) at 100 ... more The thermal and photochemistry of tert-butyl iodide (t-buI) on ice films grown on Cu(111) at 100 K were studied using time-of-flight (TOF) temperature programmed desorption (TPD) mass spectroscopy and Xray photoelectron spectroscopy (XPS). The thermal reaction products include isobutane (i-C 4 H 10 ), isobutene (i-C 4 H 8 ) and minor t-butyl alcohol. In the rising edge of the water desorption at 145K,theparentt−buImoleculedesorbsfromtheiceaswellasotherthermalreactionproducts.Abovethefallingedgeofthewaterdesorptionat145 K, the parent t-buI molecule desorbs from the ice as well as other thermal reaction products. Above the falling edge of the water desorption at 145K,theparentt−buImoleculedesorbsfromtheiceaswellasotherthermalreactionproducts.Abovethefallingedgeofthewaterdesorptionat180 K, the reaction products and the parent molecule desorb from the Cu . For t-buI on bare Cu(111) dosed at 100 K, dominant i-C 4 H 8 , some i-C 4 H 10 and tiny t-buI desorption peaks were observed. This indicates that t-buI promptly dissociates on Cu(111) to form C 4 H 9 and chemisorbed I at 100 K. The C 4 H 9 quickly rearranges, followed by C-H scission to form mainly i-C 4 H 8 , or abstracts H to form some i-C 4 H 10 . The I directly chemisorbs on the Cu(111), evidenced by I(3d) XPS peaks. On ice layer, the most dominant i-C 4 H 10 desorption peak indicates that the C 4 H 9 abstracts H from ice to form C 4 H 10 . For photoirradiation of t-buI on ice, we observed an enhanced t-buI dissociation followed by ejection of reaction products, evidenced by decrease in TPD and C(1s) XPS intensities. No ejection of I-containing molecules was observed. We attribute the t-buI dissociation to solvated electrons in ice. During photoirradiation, I radicals seem to diffuse into the bulk ice to chemisorb on Cu(111), plausibly due to self-diffusion of water. In addition, a preferential desorption of C 4 H 10 and/or an enhanced reaction channel to i-C 4 H 8 by photoirradiation is evidenced by a faster TPD decay rate of C 4 H 10 with photoirradiation time. An increased i-C 4 H 8 TPD peak at 113 K and an appearance of 2 amu desorption could indicate the enhanced channel to i-C 4 H 8 .
Langmuir, 2007
The bonding properties of 1-phenyl-1-propyne (PP, C 6 H 5 CCCH 3 ) on Cu(111) at 100 K have been ... more The bonding properties of 1-phenyl-1-propyne (PP, C 6 H 5 CCCH 3 ) on Cu(111) at 100 K have been studied using temperature-programmed desorption (TPD), and X-ray, ultraviolet, and two-photon photoemission spectroscopies (XPS, UPS, and 2PPE). In TPD, there is no evidence for dissociation. Multilayer desorption occurs at 187 K, and monolayer desorption occurs at 320 (83.5 kJ/mol) and 390 K (102.4 kJ/mol), with the latter dominating. Based on the calibrated C(1s) XPS, the saturation monolayer coverage is one PP per four surface Cu atoms. The broad and asymmetric C(1s) intensity profile of the monolayer can be resolved into three symmetric components, with peaks at 283.6, 284.5, and 285.2 eV and intensities of 2:6:1, respectively. These are attributed, respectively, to acetylenic carbons bound to Cu, phenyl, and methyl carbons. The monolayer valence band ultraviolet photoemission spectrum profile contains four resonances attributable to PP perturbed by interactions with the Cu(111) substrate. With the exception of the highest occupied molecular orbital (HOMO) that is shifted by 0.4 eV, these are uniformly shifted by 1 eV further from the Fermi level for the multilayer. Calculated electron density plots of the occupied orbitals coupled with UPS profiles suggest a spectator role for the phenyl group and bonding to Cu via the acetylenic carbons. The adsorption of 1.0 monolayer (ML) of PP on Cu(111) lowers the work function by 0.85 eV. Using 2PPE, two unoccupied orbitals were identified at 1.0 (U 1 *-LUMO) and 0.6 eV (U 2 *-image state) below the vacuum level. A chemisorption model consistent with these spectroscopic results and the major chemisorption peak in TPD involve di-σ-bonding of the acetylenic carbons to a pair of second-nearest neighbor surface Cu atoms (cross-bridge).
Langmuir, 2009
Gold nanoparticles (Au NPs) were prepared on a native-oxide-covered Si(100) substrate by sputter-... more Gold nanoparticles (Au NPs) were prepared on a native-oxide-covered Si(100) substrate by sputter-deposition followed by thermal annealing. The size of Au NPs could be controlled in the range of 8-48 nm by varying the sputterdeposition time and post-annealing temperature. The interparticle separation was found to be directly related to the size of Au NPs, with smaller separations for particles of smaller size. The surface morphology, crystal structure, and interfacial composition of the chemical states of these supported Au NPs were studied as a function of their average size by using scanning electron microscopy, glancing-incidence X-ray diffraction, and depth-profiling X-ray photoelectron spectroscopy (XPS), respectively. The new Au 4f 7/2 peak found at 1.1-1.2 eV higher in binding energy than that for the metallic Au feature (at 84.0 eV) can be attributed to the formation of Au silicide at the interface between Au NPs and the Si substrate. Depth-profiling XPS experiments revealed no discernible change in the binding energies of the Au silicide and metallic Au 4f features with increasing Ar + sputtering time, indicating that the Au-to-silicide interface is abrupt. Furthermore, the shift in the Au 5d 5/2 valence band to a higher binding energy and the reduction of the Au 5d spin-orbit splitting with increasing Ar + sputtering time also support the formation of Au silicide. No clear evidence for the quantum size effect was observed for the supported NPs. The finite density of state at the Fermi level and the fixed Au 4f 7/2 peak position clearly indicate the metallic nature of the Au silicide at the Au-Si interface.
Journal of Physics: Condensed Matter, 2000
The polarization emission spectrum and the angular dependence of polarization ratio of the blue e... more The polarization emission spectrum and the angular dependence of polarization ratio of the blue emission from KCl:Eu2+ were investigated at 78.8 K. The polarized emission at 420 nm consisted of several components. The angular dependence of polarization ratio of each component is proportional to sin(2icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> ) or -cos(2icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> ), when the exciting light is polarized at
Journal of Physics: Condensed Matter, 2008
The interfacial electronic structure and photoexcitation kinetics of MEH-PPV/P3HT heterolayer fil... more The interfacial electronic structure and photoexcitation kinetics of MEH-PPV/P3HT heterolayer film on gold were studied using two-photon photoemission spectroscopy. We observed that the photoelectron kinetic energy distribution and the photoexcitation kinetics exhibit the characteristics of the MEH-PPV layer, and the absolute two-photon photoemission yield is determined by the P3HT layer. On the basis of the photoexcitation kinetics and the photoelectron
Journal of Materials Science, 2012
Silver nanoparticles supported on anatase TiO 2 nanoparticles have been prepared by deposition-pr... more Silver nanoparticles supported on anatase TiO 2 nanoparticles have been prepared by deposition-precipitation, and characterized by X-ray photoelectron spectroscopy, including scanning electron microscopy, X-ray diffraction crystallography, Raman, and UV-visible absorption spectroscopy. The Ag 3d peak and the X-ray diffraction patterns show characteristics of purely metallic Ag, with no indication of Ag oxide species. Depth-profiling X-ray photoelectron spectroscopy with Ar ? ion beam sputtering show a significant change in Ti 2p, and an asymmetric broadening of Ag 3d to a higher binding energy side. A decrease in major Ti 2p 3/2 at 459.2 eV and a significant increase in lower binding energy peak are due to change in oxidation state of Ti from ?4 to ?3/?2. A broadening of Ag 3d peak with sputtering time is tentatively assigned to a final state quantum size effect. Upon annealing the deposition-precipitation sample, no significant change in Ag 3d peak is observed, while Ti 2p and O 1s XPS intensities are reduced, plausibly due to change in analyzed surface area for TiO 2 . The photocatalytic activity for the photodegradation of methyl orange is dramatically reduced upon high Ag-loading, compared to bare TiO 2 . The X-ray photoelectron spectroscopy of Ag on TiO 2 prepared by an electrochemical deposition reveals that Ag is also metallic, with no evidence of an oxide form. Upon annealing the electrodeposited sample, the Ag 3d peak shifts by ?0.3 eV, while the Ti 2p and O 1s show no critical change in intensity and peak position.
The Journal of Chemical Physics, 2007
Photoexcitation kinetics and interfacial electronic structures of poly[2-methoxy-5(2-ethylhexylox... more Photoexcitation kinetics and interfacial electronic structures of poly[2-methoxy-5(2-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) film on gold have been investigated using two-photon photoemission spectroscopy (2PPE). The authors directly probed a fixed intermediate state located at 0.95 eV above the Fermi level (or 2.95 eV below the vacuum level), assigned to a charged polaron. Based on the power law slope and the 2PPE spectra with laser intensity, they found that the polaron follows a second order bimolecular annihilation process. The 2PPE yield dramatically increases with increasing photon energy. They attribute this to an enhanced dissociation of hotter excitons at higher excitation levels. The work function of MEH-PPV/Au is measured to be 3.9 eV, 1.2 eV downshift from the clean gold, attributable to interface dipole effects. The energy gap between the intermediate polaron state and the hole polaron level is estimated to be 2.45 eV.
Journal of Alloys and Compounds, 1998
Inorganica Chimica Acta, 2000