Showing papers in "Journal of Physical Chemistry B in 2003"
TL;DR: In this paper, the authors describe recent progress in the theory of nanoparticle optical properties, particularly methods for solving Maxwell's equations for light scattering from particles of arbitrary shape in a complex environment.
Abstract: The optical properties of metal nanoparticles have long been of interest in physical chemistry, starting with Faraday's investigations of colloidal gold in the middle 1800s. More recently, new lithographic techniques as well as improvements to classical wet chemistry methods have made it possible to synthesize noble metal nanoparticles with a wide range of sizes, shapes, and dielectric environments. In this feature article, we describe recent progress in the theory of nanoparticle optical properties, particularly methods for solving Maxwell's equations for light scattering from particles of arbitrary shape in a complex environment. Included is a description of the qualitative features of dipole and quadrupole plasmon resonances for spherical particles; a discussion of analytical and numerical methods for calculating extinction and scattering cross-sections, local fields, and other optical properties for nonspherical particles; and a survey of applications to problems of recent interest involving triangula...
9,086 citations
TL;DR: In this paper, the same absorbed photon number, 1.4 × 1014 quanta·cm-2·s-1, of visible (Vis) or ultraviolet (UV) light was evaluated by the decomposition of gaseous 2-propanol (IPA) powders with low nitrogen concentrations (< 0.02) and showed that the isolated narrow band formed above the valence band is responsible for the Vis light response in the present nitrogen doped TiO2.
Abstract: The oxidation power of the TiO2-xNx powders with low nitrogen concentrations (<0.02) was evaluated by the decomposition of gaseous 2-propanol (IPA) under the same absorbed photon number, 1.4 × 1014 quanta·cm-2·s-1, of visible (Vis) or ultraviolet (UV) light. Regardless of the x value, the quantum yield values from irradiating with Vis light was lower than with UV light, which suggests that the isolated narrow band formed above the valence band is responsible for the Vis light response in the present nitrogen doped TiO2. In addition, increasing the nitrogen concentration when irradiating with UV light lowered the quantum yields, indicating that the doping sites could also serve as recombination sites.
1,964 citations
TL;DR: In this paper, the role of rutile in mixed-phase titania photocatalyst was investigated by EPR spectroscopy, showing that the transition points between these two phases allow for rapid electron transfer from pure-phase rutiles to anatase.
Abstract: Charge separation characteristics of a high-activity, mixed-phase titania photocatalyst (Degussa P25) are probed by EPR spectroscopy. While previous proposals consider rutile as a passive electron sink hindering recombination in anatase, this research details the critical and active role of rutile in TiO2 formulations. The inactivity of pure-phase rutile is due in part to rapid rates of recombination. Yet, in mixed-phase TiO2, charges produced on rutile by visible light are stabilized through electron transfer to lower energy anatase lattice trapping sites. These results suggest that within mixed-phase titania (P25) there is a morphology of nanoclusters containing atypically small rutile crystallites interwoven with anatase crystallites. The transition points between these two phases allow for rapid electron transfer from rutile to anatase. Thus, rutile acts as an antenna to extend the photoactivity into visible wavelengths and the structural arrangement of the similarly sized TiO2 crystallites creates ca...
1,878 citations
TL;DR: In this paper, a new classical empirical potential is proposed for water, which uses a polarizable atomic multipole description of electrostatic interactions, and a modified version of Thole's interaction model is used to damp induction at short range.
Abstract: A new classical empirical potential is proposed for water. The model uses a polarizable atomic multipole description of electrostatic interactions. Multipoles through the quadrupole are assigned to each atomic center based on a distributed multipole analysis (DMA) derived from large basis set molecular orbital calculations on the water monomer. Polarization is treated via self-consistent induced atomic dipoles. A modified version of Thole's interaction model is used to damp induction at short range. Repulsion−dispersion (vdW) effects are computed from a buffered 14−7 potential. In a departure from most current water potentials, we find that significant vdW parameters are necessary on hydrogen as well as oxygen. The new potential is fully flexible and has been tested versus a variety of experimental data and quantum calculations for small clusters, liquid water, and ice. Overall, excellent agreement with experimental and high level ab initio results is obtained for numerous properties, including cluster st...
1,315 citations
TL;DR: In this paper, a linear relationship between the contact angle and the water monomer binding energy on graphite was established and a new route to calibrate interaction potential parameters was presented, which was obtained by applying a carbon−oxygen Lennard-Jones potential with parameters eCO = 0.392 kJ mol-1 and σCO = 3.19 A.
Abstract: A systematic molecular dynamics study shows that the contact angle of a water droplet on graphite changes significantly as a function of the water−carbon interaction energy. Together with the observation that a linear relationship can be established between the contact angle and the water monomer binding energy on graphite, a new route to calibrate interaction potential parameters is presented. Through a variation of the droplet size in the range from 1000 to 17 500 water molecules, we determine the line tension to be positive and on the order of 2 × 10-10 J/m. To recover a macroscopic contact angle of 86°, a water monomer binding energy of −6.33 kJ mol-1 is required, which is obtained by applying a carbon−oxygen Lennard-Jones potential with the parameters eCO = 0.392 kJ mol-1 and σCO = 3.19 A. For this new water−carbon interaction potential, we present density profiles and hydrogen bond distributions for a water droplet on graphite.
1,155 citations
TL;DR: In this paper, a multiwalled carbon nanotube-supported Pt (Pt/MWNT) nanocomposites were prepared by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of an ion salt in ethylene glycol solution.
Abstract: Multiwalled carbon nanotube-supported Pt (Pt/MWNT) nanocomposites were prepared by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution. For comparison, a Pt/XC-72 nanocomposite was also prepared by the EG method. The Pt/MWNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal particles with a narrow particle-size distribution. TEM images show that the Pt particle size is in the range of 2-5 nm with a peak at 2.6 nm, which is consistent with 2.5 nm obtained from the XRD broadening calculation. Surface chemical modifications of MWNTs and water content in EG solvent are found to be the key factors in depositing Pt particles on MWNTs. In the case of the direct methanol fuel cell (DMFC) test, the Pt/MWNT catalyst prepared by EG reduction is slightly superior to the catalyst prepared by aqueous reduction and displays significantly higher performance than the Pt/XC-72 catalyst. These differences in catalytic performance between the MWNT-supported or the carbon black XC-72-supported catalysts are attributed to a greater dispersion of the supported Pt particles when the EG method is used, in contrast to aqueous HCHO reduction and to possible unique structural and higher electrical properties when contrasting MWNTs to carbon black XC-72 as a support.
1,150 citations
TL;DR: In this article, the effect of chemical oxidation on the structure of single-walled carbon nanotubes (SWNTs) by using different oxidants was investigated using infrared spectroscopy and transmission electron microscopy (TEM).
Abstract: In the present study, we report the systematic investigation of the effect of chemical oxidation on the structure of single-walled carbon nanotubes (SWNTs) by using different oxidants. The oxidation procedure was characterized by using infrared spectroscopy and transmission electron microscopy (TEM). The SWNTs were produced by chemical vapor deposition (CVD) and oxidized with three kinds of oxidants: (1) nitric acid (2.6 M), (2) a mixture of concentrated sulfuric acid (98 wt %) and concentrated nitric acid (16 M) (v/v = 3/1) and (3) KMnO4. The results reveal that the different functional groups can be introduced when the SWNTs are treated with different oxidants. Refluxing in dilute nitric acid can be considered as a mild oxidation for SWNTs, introducing the carboxylic acid groups only at those initial defects that already exist. The abundance of the carboxylic acid groups generated with this oxidant remained constant along with the treating time. In contrast, sonication of SWNTs in H2SO4/HNO3 increased ...
1,129 citations
TL;DR: In this article, a liquid-phase deposition (LPD) method was used on fused quartz by the liquid phase deposition method from a (NH4)2TiF6 aqueous solution upon addition of boric acid (H3BO3) and calcined at various temperatures.
Abstract: TiO2 thin films were prepared on fused quartz by the liquid-phase deposition (LPD) method from a (NH4)2TiF6 aqueous solution upon addition of boric acid (H3BO3) and calcined at various temperatures. The as-prepared films were characterized with thermogravimetry (TG), Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), UV−Visible spectrophotometry (UV−Vis), scanning electron microscopy (SEM), photoluminescence spectra (PL), and X-ray photoelectron spectroscopy (XPS), respectively. The photocatalytic activity of the samples was evaluated by photocatalytic decolorization of methyl orange aqueous solution. It was found that the as-prepared TiO2 thin films contained not only Ti and O elements, but also a small amount of F, N, and Si elements. The F and N came from the precursor solution, and the amount of F decreased with increasing calcination temperature. Two sources of Si were identified. One was from the SiF62- ions, which were formed by a reaction between the treatment solution and quartz ...
1,111 citations
TL;DR: In this article, field effect transistors (FETs) based on single SnO2 and ZnO nanobelts of thicknesses between 10 and 30 nm have been fabricated.
Abstract: We have fabricated field-effect transistors (FETs) based on single SnO2 and ZnO nanobelts of thicknesses between 10 and 30 nm. Switching ratios as large as 6 orders of magnitude and conductivities as high as 15 (Ω cm)-1 are observed. Annealing SnO2 nanobelt FETs in an oxygen-deficient atmosphere produces a negative shift in gate threshold voltage, indicating doping by the generation of surface oxygen vacancies. This treatment provides an effective way of tuning the electrical performance of the nanobelt devices. The ability of SnO2 FETs to act as gas sensors is also demonstrated. SnO2 FETs with lengths of about 500 nm or less show an anomalous behavior where the conductance cannot be modulated by the gate. ZnO nanobelt FETs are sensitive to ultraviolet light. Both photogeneration of electron−hole pairs and doping by UV induced surface desorption contribute to the conductivity.
1,087 citations
TL;DR: In this article, a very effective and simple way to produce silver colloids for surface-enhanced Raman scattering (SERS) is reported. But this method is not suitable for the use of SERS in high-dimensional data.
Abstract: A very effective and simple way to produce silver colloids for surface-enhanced Raman scattering (SERS) is reported. Reduction of silver nitrate with hydroxylamine hydrochloride at alkaline pH and at room temperature yields highly sensitive SERS colloids within a short time. The so-produced colloids can be used for SERS spectroscopy immediately after preparation. The overall procedure is fast, simple, and characterized by a high preparation success rate. Changing the mixing order and rate of the two involved solutions, silver nitrate and hydroxylamine hydrochloride containing sodium hydroxide, one can control the size and dispersion of the produced colloids. The obtained colloids have been characterized by UV−vis spectroscopy, transmission electron microscopy, and SERS using a 1064 nm laser line on a Fourier transform and a 785 nm laser line on a dispersive Raman spectrometer. The SERS enhancement factor of the hydroxylamine-reduced silver colloids was tested using crystal violet, rhodamine 6G, methylene ...
1,049 citations
TL;DR: The monochromatic incident photon-to-current conversion efficiency (IPCE) from 420 to 600 nm for a DSSC based on NKX-2311 was over 70% with the maximum of 80% at 470 nm, which is almost equal to the efficiency obtained with the N3 dye system.
Abstract: We have developed novel coumarin dyes for use in dye-sensitized nanocrystalline TiO2 solar cells (DSSCs). The absorption spectra of these novel coumarin dyes are red-shifted remarkably in the visible region relative to the spectrum of C343, a conventional coumarin dye. Introduction of a methine unit (−CHCH−) connecting both the cyano (−CN) and carboxyl (−COOH) groups into the coumarin framework expanded the π conjugation in the dye and thus resulted in a wide absorption in the visible region. These novel dyes performed as efficient photosensitizers for DSSCs. The monochromatic incident photon-to-current conversion efficiency (IPCE) from 420 to 600 nm for a DSSC based on NKX-2311 was over 70% with the maximum of 80% at 470 nm, which is almost equal to the efficiency obtained with the N3 dye system. The IPCE performance of DSSCs based on coumarin dyes depended remarkably on the LUMO levels of the dyes, which are estimated from the oxidation potential and 0−0 energy of the dye. The slow charge recombination,...
Columbia University1, Stanford University2, Clemson University3, Brookhaven National Laboratory4, IBM5, University of Notre Dame6, California Institute of Technology7, University of Alabama8, Technische Universität München9, United States Naval Research Laboratory10, Arizona State University11, University of Florida12, University of Minnesota13
TL;DR: The current status of basic electron transfer research, both theoretical and experimental, with emphasis on the distance-dependent measurements, was discussed in this article, where the authors attempted to integrate terminology and notation of solution electron-transfer kinetics with that of conductance analysis.
Abstract: This is the report of a DOE-sponsored workshop organized to discuss the status of our understanding of charge-transfer processes on the nanoscale and to identify research and other needs for progress in nanoscience and nanotechnology. The current status of basic electron-transfer research, both theoretical and experimental, is addressed, with emphasis on the distance-dependent measurements, and we have attempted to integrate terminology and notation of solution electron-transfer kinetics with that of conductance analysis. The interface between molecules or nanoparticles and bulk metals is examined, and new research tools that advance description and understanding of the interface are presented. The present state-of-the-art in molecular electronics efforts is summarized along with future research needs. Finally, novel strategies that exploit nanoscale architectures are presented for enhancing the efficiences of energy conversion based on photochemistry, catalysis, and electrocatalysis principles.
TL;DR: In this article, the existence of ionic liquids of an unexpectedly wide range of liquid fragilities was demonstrated by combining old, unpublished data on ionic liquid containing quaternary ammonium cations with new data on salts of aromatic cations containing a variety of anions.
Abstract: We combine old, unpublished data on ionic liquids containing quaternary ammonium cations with new data on salts of aromatic cations containing a variety of anions, to demonstrate the existence for ionic liquids of an unexpectedly wide range of liquid fragilities. The pattern is one now familiar for other liquids. Here, the pattern is important in determining the relative fluid properties at ambient temperatures. We find that the optimization of ionic liquids for ambient temperature applications requiring low-vapor-pressure fluid phases involves the proper interplay of both cohesive energy and fragility factors. The cohesive energy is discussed in terms of the coulomb and van der Waals contributions to the attractive part of the pair potential. On the basis of the relation between the glass-transition temperature and the molar volume for salts with less-polarizable anions, we find evidence for a broad minimum in the ionic liquid cohesive energy at an internuclear separation of ca. 0.6 nm. This minimum lies...
TL;DR: In this article, the conduction and valence band edges for electronic band gaps and Fermi levels are determined for Ta2O5, TaON, and Ta3N5 by ultraviolet photoelectron spectroscopy (UPS) and electrochemical analyses.
Abstract: The conduction and valence band edges for electronic band gaps and Fermi levels are determined for Ta2O5, TaON, and Ta3N5 by ultraviolet photoelectron spectroscopy (UPS) and electrochemical analyses. Reasonable agreement between the results of the two methods is obtained at the pH at which the ζ potentials of the particles are zero. The tops of the valence bands are found to be shifted to higher potential energies on the order Ta2O5 < TaON < Ta3N5, whereas the bottoms of the conduction bands are very similar in the range −0.3 to −0.5 V (vs NHE at pH = 0). From the results, it is concluded that TaON and Ta3N5 are promixing catalysts for the reduction and oxidation of water using visible light in the ranges λ < 520 nm and λ < 600 nm, respectively. It is also demonstrated that the proposed UPS technique is a reliable alternative to electrochemical analyses for determining the absolute band gap positions for materials in aqueous solutions that would otherwise be difficult to measure using electrochemical methods.
TL;DR: In this article, the central role of the Ag femtosecond radiative lifetime and the spatial distribution of the excited Ag electrons, in the near field and far field optical properties is discussed.
Abstract: Molecular surface enhanced Raman scattering (SERS) in compact clusters of 30−70 nm Ag nanocrystals has shown single molecule Raman scattering cross sections that are orders of magnitude larger than free space single molecule luminescence cross sections. We analyze certain aspects of this phenomenon with new numerical electromagnetic calculations, and we also present new spectral depolarization data for single molecule rhodamine 6G scattering. We stress the central role of the Ag femtosecond radiative lifetime, and the spatial distribution of the excited Ag electrons, in the near field and far field optical properties. The fundamental nature of the Ag plasmon excited-electronic-state changes from a volume excitation to a surface junction excitation as two particles approach each other within 1 nm. Adsorbed molecules in the junction interact directly with the metallic excited-state wave function, showing electron-transfer-initiated photochemistry as well as enhanced Raman scattering. Depolarization studies ...
TL;DR: In this article, the authors distinguish between conventional solar cells and excitonic solar cells (XSCs) by showing that charge carriers are generated and simultaneously separated across a heterointerface.
Abstract: Existing types of solar cells may be divided into two distinct classes: conventional solar cells, such as silicon p−n junctions, and excitonic solar cells, XSCs. Most organic-based solar cells, including dye-sensitized solar cells, DSSCs, fall into the category of XSCs. In these cells, excitons are generated upon light absorption, and if not created directly at the heterointerface as in DSSCs, they must diffuse to it in order to photogenerate charge carriers. The distinguishing characteristic of XSCs is that charge carriers are generated and simultaneously separated across a heterointerface. In contrast, photogeneration of free electron−hole pairs occurs throughout the bulk semiconductor in conventional cells, and carrier separation upon their arrival at the junction is a subsequent process. This apparently minor mechanistic distinction results in fundamental differences in photovoltaic behavior. For example, the open circuit photovoltage Voc in conventional cells is limited to less than the magnitude of...
TL;DR: In this article, the optical properties of metallic nanoparticles with arbitrary shape were studied and the authors performed theoretical calculations of the absorption, extinction, and scattering efficiencies, which can be directly compared with experiments, using the discrete dipole approximation (DDA).
Abstract: We have studied the optical properties of metallic nanoparticles with arbitrary shape. We performed theoretical calculations of the absorption, extinction, and scattering efficiencies, which can be directly compared with experiments, using the discrete dipole approximation (DDA). In this work, the main features in the optical spectra have been investigated depending of the geometry and size of the nanoparticles. The origin of the optical spectra are discussed in terms of the size, shape, and material properties of each nanoparticle, showing that a nanoparticle can be distinguish by its optical signature.
TL;DR: In this article, the interaction between N3, N719, and N712 sensitizers with nanocrystalline TiO2 film was investigated by ATR-FTIR spectroscopy.
Abstract: FTIR spectra of [Ru(dcbpyH2)2(NCS)2] (N3), (Bu4N)2[Ru(dcbpyH)2(NCS)2] (N719), and (Bu4N)4[Ru(dcbpy)2(NCS)2] (N712) complexes measured as solid samples in photoacoustic mode display fine resolution of IR bands and exhibit differences between the cis and the trans carboxylic acid groups. The interaction between N3, N719, and N712 sensitizers with nanocrystalline TiO2 film was investigated by ATR-FTIR spectroscopy. The data show that these complexes are being anchored onto the TiO2 surface in bridging coordination mode using two out of their four carboxylic acid groups, which are trans to the NCS ligand. The effect of protons on both the short circuit photocurrent and the open circuit photovoltage of dye-sensitized nanocrystalline solar cells was scrutinized. For the standard electrolyte formulation employed and TiCl4 treated mesoporous TiO2 films, the monoprotonated form of the N3 dye exhibited superior power conversion efficiency under AM 1.5 sun compared to the four, two, and zero proton sensitizers.
TL;DR: In this article, mesoporous SBA-15 was functionalized by co-condensation of tetraethoxysilane (TEOS) with APTES in a wide range of molar ratios of TEOS in the presence of triblock copolymer P123 under acidic synthetic conditions.
Abstract: The amine moiety is an important functionality for many applications such as enzyme immobilization on porous solid supports. In this study, mesoporous SBA-15 was functionalized by co-condensation of tetraethoxysilane (TEOS) with organosilane (aminopropyl)triethoxysilane (APTES) in a wide range of molar ratios of APTES:TEOS in the presence of triblock copolymer P123 under acidic synthetic conditions. The functionalized materials were characterized by physical adsorption, CHN elemental analysis, and various spectroscopic techniques. The data of FTIR, elemental analysis, XPS, and solid-state NMR demonstrated the incorporation of amine functional groups on the surface and inside the pore walls of the APTES-functionalized SBA-15 samples. The results of SAXS, N2 adsorption, and TEM showed the effect of APTES present in the initial synthesis mixtures on the formation of SBA-15 mesostructure such as structural ordering, pore size, and surface area. Reasons behind the observed strong adverse effect of APTES on SBA...
TL;DR: In this article, a systematic study of surface-enhanced Raman-scattering (SERS) properties of nanosphere lithography (NSL) derived Ag nanoparticles is presented, which demonstrates the necessity of correlating nanoparticle structure and localized surface plasmon resonance (LSPR) spectroscopic data in order to effectively implement SERS on nanofabricated surfaces.
Abstract: This work presents the first systematic study of the surface-enhanced Raman-scattering (SERS) properties of nanosphere lithography (NSL) derived Ag nanoparticles. Furthermore, it demonstrates the necessity of correlating nanoparticle structure and localized surface plasmon resonance (LSPR) spectroscopic data in order to effectively implement SERS on nanofabricated surfaces that have narrow (∼100 nm) LSPR line widths. Using nanoparticle substrates that are structurally well characterized by atomic force microscopy, the relationship between the LSPR extinction maximum (λmax) and the SERS enhancement factor (EF) is explored in detail using the innovative approach of plasmon-sampled surface-enhanced Raman excitation spectroscopy (PS-SERES). PS-SERES studies were performed as a function of excitation wavelength, molecular adsorbate, vibrational band, and molecule-localized resonance or nonresonance excitation. In each case, high S/N ratio spectra are achieved for samples with an LSPR λmax within a ∼120-nm wind...
TL;DR: In this paper, dye-sensitized solar cells have been fabricated based on nanocrystalline TiO2 film derivatized with an amphiphilic polypyridyl ruthenium complex, cis-RuLL(SCN)2 as light-harvester and hexadecylmalonic acid (HDMA) as coadsorbent.
Abstract: Dye-sensitized solar cells have been fabricated based on nanocrystalline TiO2 film derivatized with an amphiphilic polypyridyl ruthenium complex, cis-RuLL‘(SCN)2 (L = 4,4‘-dicarboxylic acid-2,2‘-bipyridine, L‘ = 4,4‘-dinonyl-2,2‘-bipyridine), as light-harvester and hexadecylmalonic acid (HDMA) as coadsorbent. The cells generated a short-circuit photocurrent of 15.2 mA cm-2, an open-circuit photovoltage of 764 mV, and a total power conversion efficiency of 7.8% under simulated full sunlight (air mass 1.5, 100 mW cm-2). Co-grafting enhanced the photocurrent, photovoltage, and overall conversion efficiency considerably with respect to cells containing no HDMA. Devices showed a good stability under light soaking at 55 °C.
TL;DR: In this paper, the extinction spectra of two-dimensional arrays of Au and Ag cylinders and trigonal prisms that have been fabricated with electron beam lithography were studied by using coupled dipole calculations, and the observed spectral variations were in good qualitative agreement with experimental data.
Abstract: In this paper, the electromagnetic interactions between noble metal nanoparticles are studied by measuring the extinction spectra of two-dimensional arrays of Au and Ag cylinders and trigonal prisms that have been fabricated with electron beam lithography. The nanoparticles are typically 200 nm in diameter and 35 nm in height; both hexagonal and square array patterns have been considered with lattice spacings that vary from 230 to 500 nm. The extinction spectra typically have a maximum in the 700−800 nm region of the spectrum, and this maximum blue shifts as lattice spacing is reduced, having typically a 40 nm decrease in λmax for a 100 nm decrease in lattice spacing. The results are similar for the different noble metals, array patterns, and nanoparticle shapes. The extinction spectra have been modeled using coupled dipole calculations, and the observed spectral variations are in good qualitative agreement with experimental data. Moreover, the computational analysis indicates that the blue shifts are due...
TL;DR: In this paper, a series of Bronsted acid−base ionic liquids were derived from the controlled combination of a monoprotonic acid with an organic base under solvent-free conditions.
Abstract: A new series of Bronsted acid−base ionic liquids were derived from the controlled combination of a monoprotonic acid with an organic base under solvent-free conditions. Appropriate amounts of solid bis(trifluoromethanesulfonyl)amide (HTFSI) and solid imidazole (Im) were mixed at various molar ratios to have compositions varying from an equimolar salt to HTFSI- or Im-rich conditions. The mixture at equivalent molar ratio formed a protic neutral salt with a melting point of 73 °C, which was thermally stable at temperatures even above 300 °C. The melting points of other compositions were lower than those of the equimolar salt and Im or HTFSI, giving eutectics between the equimolar salt and HTFSI or Im. Some of the compositions with certain molar ratios of Im and HTFSI were liquid at room temperature. For Im excess compositions, the conductivity was found to increase with increasing Im mole fraction, and the 1H NMR chemical shift of the proton attached to the nitrogen atom of Im was shifted to a lower magneti...
TL;DR: In this paper, Nanocrystalline porous porous nitrogen doped titanium dioxide (TiO2) thin films were prepared by DC magnetron sputtering and characterized by X-ray diffraction, scanning electron microscopy, and optical and photoelectrochemical (PEC) measurements.
Abstract: Nanocrystalline porous nitrogen doped titanium dioxide (TiO2) thin films were prepared by DC magnetron sputtering. Films were deposited in a plasma of argon, oxygen, and nitrogen, with varying nitrogen contents. The films were characterized by X-ray diffraction, scanning electron microscopy, and optical- and photoelectrochemical (PEC) measurements. These studies showed that the films were porous and displaying rough surfaces with sharp, protruding nodules having a crystal structure varying from rutile to anatase depending on the nitrogen content. All nitrogen doped films showed visible light absorption in the wavelength range from 400 to 535 nm. The PEC properties of the thin film electrodes were determined on as-deposited as well as dye-sensitized films. The nitrogen doped TiO2 generated an incident photon-to-current efficiency response in good agreement with the optical spectra. The PEC measurements on dye-sensitized films showed that the electron-transfer properties in the conduction band were similar ...
TL;DR: In this article, the waveguiding behavior of individual zinc oxide (ZnO) nanowires has been characterized with high-resolution optical microscopy, showing a transition from spontaneous to stimulated emission, and analysis of the polarization, line width and line spacing of the laser radiation facilitates identification of the transverse and longitudinal cavity modes and their gain properties.
Abstract: Wide band gap semiconductor nanostructures with near-cylindrical geometry and large dielectric constants exhibit two-dimensional ultraviolet and visible photonic confinement (i.e., waveguiding). Combined with optical gain and suitable resonant feedback, the waveguiding behavior facilitates highly directional lasing at room temperature in controlled-growth nanowires. We have characterized the nanowire emission in detail with high-resolution optical microscopy. The waveguiding behavior of individual zinc oxide (ZnO) nanowires depends on the wavelength of the emitted light and the directional coupling of the photoluminescence (PL) to the emission dipoles of the nanowire. Polarization studies reveal two distinct regimes of PL characterized by coupling to either guided (bound) or radiation modes of the waveguide, the extent of which depends on wire dimensions. Pumping with high pulse energy engenders the transition from spontaneous to stimulated emission, and analysis of the polarization, line width, and line spacing of the laser radiation facilitates identification of the transverse and longitudinal cavity modes and their gain properties. Interpretation of the lasing spectra as a function of pump fluence, with consideration of ZnO material properties and ultrafast excitation dynamics, demonstrates a transition from exciton (fluence 1 IJ/cm 2 ) and gain saturation behavior (fluence > 3 IJ/cm 2 ) modified by the constraints of the nanoscale cylindrical cavity.
TL;DR: In this article, an ionic liquid electrolyte composed of 1-methyl-3-propylimidazolium iodide, 1-ethyl-3]-dimethyl-polypyridyl ruthenium dicyanamide, and lithium iodide (LiI) was combined with an amphiphilic polypyrinyl-rushenium sensitizer to obtain a solar cell based on a solvent-free electrolyte that had an efficiency of 6.6% at an irradiance of air mass 1.5 and >7.1
Abstract: An ionic liquid electrolyte composed of 1-methyl-3-propylimidazolium iodide, 1-methyl-3-ethylimidazolium dicyanamide, and lithium iodide (LiI) was combined with an amphiphilic polypyridyl ruthenium sensitizer to obtain a solar cell based on a solvent-free electrolyte that had an efficiency of 6.6% at an irradiance of air mass 1.5 (AM 1.5, 100 mW cm -2 ) and >7.1% at lower light intensities. This is the first time such a high efficiency was obtained for dye-sensitized solar cells with pure ionic liquid electrolytes. A thin-layer electrochemical cell was used to determine the redox potential of sensitizers anchored on TiO 2 nanocrystalline film by square-wave voltammetry. Laser transient absorbance measurements revealed that a significant enhancement of the device efficiency, after adding LiI to the ionic liquid electrolyte, could be ascribed to an increase in the electron injection yield and dye regeneration rate.
TL;DR: In this article, the authors investigated the effects of chemical modifications of the surface on the extent of nanotube-surfactant interaction and found that intrinsic surface properties such as the PZC (point of zero charge) are greatly affected by the purification method.
Abstract: The insolubility of single-walled carbon nanotubes (SWNT) in either water or organic solvents has been a limitation for the practical application of this unique material. Recent studies have demonstrated that the suspendability of SWNT can be greatly enhanced by employing appropriate surfactants. Although the efficiency of anionic, cationic, and nonionic surfactants has been demonstrated to different extents, the exact mechanism by which carbon nanotubes and the different surfactants interact is still uncertain. To deepen the understanding of this interfacial phenomenon, we have investigated the effects of chemical modifications of the surface on the extent of nanotube-surfactant interaction. Such changes in the surface chemistry of the SWNT can be achieved by simply varying the pretreatment method, which can be acidic or basic. We have found that intrinsic surface properties such as the PZC (point of zero charge) are greatly affected by the purification method. That is, the electrical charge of the SWNT surface varies with the pH of the surrounding media. However, it has been found that during the adsorption of the anionic surfactant sodium dodecylbenzenesulfonate (NaDDBS) on SWNT Coulombic forces do not play a central role, but are overcome by the hydrophobic interactions between the surfactant tail and the nanotube walls. Only at pH values far from the PZC do the Coulombic forces become important. The hydrophobic forces between the surfactant tail and the nanotube determine the structure of the surfactant-stabilized nanotubes. In such a structure, each nanotube is covered by a monolayer of surfactant molecules in which the heads form a compact outer surface while the tails remain in contact with the nanotube walls. It is important to note that although the final configuration can be described as a cylindrical micelle with a nanotube in the center, the mechanism of formation of this structure does not proceed by incorporation of a nanotube into a micelle, but rather by a two-step adsorption that ends up in the formation of a surfactant monolayer.
TL;DR: In this article, the extinction spectra of one-dimensional linear chains and two-dimensional planar arrays of spherical silver nanoparticles were studied, with the focus on the variation of the plasmon resonance wavelength and width with array structure (spacing, symmetry, particle size, and direction).
Abstract: We use high-quality electrodynamics methods to study the extinction spectra of one-dimensional linear chains and two-dimensional planar arrays of spherical silver nanoparticles, placing emphasis on the variation of the plasmon resonance wavelength and width with array structure (spacing, symmetry), particle size, and polarization direction. Two levels of theory have been considered, coupled dipoles with fully retarded interactions and T-matrix theory that includes a converged multipole expansion on each particle. We find that the most important array effects for particles having a radius of 30 nm or smaller are captured by the couple dipole approach. Our calculations demonstrate several surprising effects that run counter to conventional wisdom in which the particle interactions are assumed to be governed by electrostatic dipolar interactions. In particular, we find that for planar arrays of particles with polarization parallel to the plane the plasmon resonance blue shifts as array spacing D decreases fo...
TL;DR: In this paper, the pH-dependent photoluminescence (PL) of MPA-and TGA-stabilized CdTe nanoparticles was systematically investigated before and after addition of poly(acrylic acid) (PAA) into the CdTE solutions.
Abstract: The CdTe nanoparticles were prepared in aqueous solution using different mercaptocarboxylic acids such as 3-mercaptopropionic acid (MPA) and thioglycolic acid (TGA) as stabilizing agents following the synthetic route described in ref 9. The pH-dependent photoluminescence (PL) of MPA- and TGA-stabilized CdTe nanoparticles was systematically investigated before and after addition of poly(acrylic acid) (PAA) into the CdTe solutions. Experimental results reveal that lowering the pH can increase the PL efficiency of both MPA- and TGA-stabilized CdTe. Moreover, the PL of the CdTe can further be increased in the presence of PAA in low pH range. X-ray photoelectron spectroscopy (XPS) was employed to investigate the interaction between the carboxyl groups from PAA and CdTe nanoparticles which were assembled in polymer matrix by a layer-by-layer self-assembly method to exclude interference from other species in CdTe solutions. XPS results demonstrate that the S/Te ratio of CdTe particles decreases after the additio...
TL;DR: In this article, percolation theory is applied to understand the influence of network geometry on the electron transport dynamics in dye-sensitized nanocrystalline TiO2 solar cells, and the predicted results are compared with those measured by transient photocurrent.
Abstract: Percolation theory is applied to understand the influence of network geometry on the electron transport dynamics in dye-sensitized nanocrystalline TiO2 solar cells, and the predicted results are compared with those measured by transient photocurrent. The porosity of the films was varied experimentally from 52 to 71%. Electron transport was modeled using simulated mesoporous TiO2 films, consisting of a random nanoparticle network, and the random-walk approach. The electron transport pathway through the network was correlated with the film porosity and the coordination numbers of the particles in the film. The experimental measurements and random-walk simulations were in quantitative agreement with percolation theory, which predicts a power-law dependence of the electron diffusion coefficient D on the film porosity as described by the relation: D ∝ |P − Pc|μ. The critical porosity Pc (percolation threshold) and the conductivity exponent μ were found to be 0.76 ± 0.01 and 0.82 ± 0.05, respectively. The frac...