The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
James A Mcquillan - One of the best experts on this subject based on the ideXlab platform.
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influence of adsorbed water on phonon and uv induced ir absorptions of tio2 photocatalytic Particle Films
Journal of Physical Chemistry B, 2004Co-Authors: James A McquillanAbstract:The role of adsorbed water in photocatalytic processes on TiO2 surfaces has been addressed using ATR−IR spectroscopy. Changes in the IR spectra of thin Films of Degussa P25 TiO2 photocatalyst have been observed in the presence of adsorbed water and under near-UV light. Removal of adsorbed water results in the appearance of absorption peaks at 828, 745, and 685 cm-1 attributed to TiO2 surface phonon modes. UV irradiation of the dry TiO2 results in a broad IR absorption which toward lower wavenumbers increases in absorbance, reaches a peak at 880 cm-1, and then drops sharply to a minimum absorption at about 750 cm-1. From observations of the behavior of P25 thin Films under a drying regime and comparisons with transient IR studies, the broad absorption generated by the UV light has been assigned to excitation of shallow trap electrons to the conduction band with an excitation energy of ∼0.1 eV.
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an in situ infrared spectroscopic investigation of adsorption of sodium dodecylsulfate and of cetyltrimethylammonium bromide surfactants to tio2 zro2 al2o3 and ta2o5 Particle Films from aqueous solutions
Vibrational Spectroscopy, 2000Co-Authors: Kevin D Dobson, Alisa D Roddicklanzilotta, James A McquillanAbstract:An in situ infrared spectroscopic study is described of the adsorption of the ionic surfactants, sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB), from aqueous solution to metal oxide Particle Films. Thin porous metal oxide Particle Films were prepared by drying of aqueous colloidal dispersions on single internal reflection ZnSe prisms. Analysis of the spectra of SDS in both aqueous solution and adsorbed to positively charged TiO2, ZrO2, Al2O3 and Ta2O5 surfaces indicates that adsorption occurs primarily via electrostatic and hydrogen bonding interactions between the sulfate headgroup and the metal oxide surfaces. The adsorption of CTAB to negatively charged TiO2 and Ta2O5 was observed. The pH dependence of CTAB adsorption to TiO2 indicated that both electrostatic and hydrophobic interactions are important. Langmuir adsorption constants from isotherm data were similar for adsorption of CTAB on TiO2 at pH=6.3 and at pH=11.0 indicating that charge effects are not dominant in this pH range. Use of a single internal reflection prism allowed the displacement of interfacial water by surfactant adsorption to be clearly discerned in the spectra.
Yukihiro Ozaki - One of the best experts on this subject based on the ideXlab platform.
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simple method for preparing controllably aggregated silver Particle Films used as surface enhanced raman scattering active substrates
Langmuir, 2002Co-Authors: Jiawen Hu, Bing Zhao, Weiqing Xu, And Bofu Li, Yukihiro OzakiAbstract:Silver colloids are one of the extensively employed surface-enhanced Raman scattering (SERS) active substrates. To obtain the SERS effect, their aggregation upon addition of analyte is necessary. However, problems of instability and irreproducibility in the magnitude of the signal are caused by the formation of aggregates. Considering that the aggregation of silver colloids is essential to induce small silver clusters, in the present study, we develop a drying process to prepare silver Particle Films (silver clusters) that are supported directly on a glass slide. These silver Particle Films arise through the aggregation of silver colloids occurring in thin water Films supported on a solid substrate. With the evaporation of water, silver clusters are left on the solid substrate. Thus, the assembly meets perfectly the requirement of aggregation of silver colloids and, at the same time, possesses the stability of solidlike SERS-active substrates. We can easily obtain excellent SERS spectra from these silver ...
Jiawen Hu - One of the best experts on this subject based on the ideXlab platform.
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Theoretical consideration on preparing silver Particle Films by adsorbing nanoParticles from bulk colloids to an air-water interface
Langmuir, 2004Co-Authors: Jiawen Hu, Zhong-qun TianAbstract:In our previous paper, a method for preparing enormous surface-enhanced Raman scattering (SERS) active substrates through the aggregation of silver Particles trapped at an air−water interface was reported. Here, further efforts were devoted to investigate the origin of assembling silver Particle Films by adsorbing nanoParticles from bulk colloids to the air−water interface. It was revealed that it is thermodynamically favorable for a colloidal Particle in bulk colloids to adsorb to the air−water interface; however, a finite sorption barrier between it and the nearby Particles usually restrains the adsorption process. When an electrolyte such as KCl, which is commonly used as an activating agent for additional SERS enhancement, was added into silver colloids, it largely reduced the sorption barrier. Thus, silver nanoParticles can break through the sorption barrier, pop up, and be trapped at the air−water interface. The trapped silver Particles are more inclined to aggregate at the interface than those in b...
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simple method for preparing controllably aggregated silver Particle Films used as surface enhanced raman scattering active substrates
Langmuir, 2002Co-Authors: Jiawen Hu, Bing Zhao, Weiqing Xu, And Bofu Li, Yukihiro OzakiAbstract:Silver colloids are one of the extensively employed surface-enhanced Raman scattering (SERS) active substrates. To obtain the SERS effect, their aggregation upon addition of analyte is necessary. However, problems of instability and irreproducibility in the magnitude of the signal are caused by the formation of aggregates. Considering that the aggregation of silver colloids is essential to induce small silver clusters, in the present study, we develop a drying process to prepare silver Particle Films (silver clusters) that are supported directly on a glass slide. These silver Particle Films arise through the aggregation of silver colloids occurring in thin water Films supported on a solid substrate. With the evaporation of water, silver clusters are left on the solid substrate. Thus, the assembly meets perfectly the requirement of aggregation of silver colloids and, at the same time, possesses the stability of solidlike SERS-active substrates. We can easily obtain excellent SERS spectra from these silver ...
M.h. Nayfeh - One of the best experts on this subject based on the ideXlab platform.
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UV photodetectors with thin-film Si nanoParticle active medium
IEEE Transactions on Nanotechnology, 2005Co-Authors: M.h. Nayfeh, O.m. Nayfeh, A. Smith, J. TherrienAbstract:We constructed ultraviolet (UV) photodetectors using thin Films of silicon nanoParticles as active media. The Si nanoParticle Films are electrodeposited at room temperature on Si p-type substrates. Uniform silicon nanoParticles of 1-nm diameter are dispersed from Si wafers using electrochemical etching. The nanoParticles are ultrabright under UV excitation, with nanosecond luminescence time characteristics. Current-voltage (I--V) characteristics indicate a photoconductor in series with a diode-like junction with a large enhancement in the forward current under UV illumination. Our results point to a sensitive UV detector with good visible blindness where the Particle Films effectively constitutes a wide-bandgap material.
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Thin film silicon nanoParticle UV photodetector
IEEE Photonics Technology Letters, 2004Co-Authors: O.m. Nayfeh, A. Smith, J. Therrien, M.h. NayfehAbstract:We constructed ultraviolet (UV) photodetectors by room-temperature deposition of Si nanoParticle Films on Si p-type substrates. Silicon nanoParticles of 1-nm diameter are dispersed from Si wafers using electrochemical etching. The current-voltage characteristics indicate a photoconductor in series with a diode-like junction with a large enhancement in the forward current under UV illumination. With increasing wavelength, the response drops rapidly, dropping to a few percent at 560 nm. These results point to a sensitive UV detector with good visible blindness where the Particle Films effectively constitutes a wide-bandgap material.
A J Mcquillan - One of the best experts on this subject based on the ideXlab platform.
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An in situ infrared spectroscopic study of ligand adsorption from aqueous solutions to cadmium telluride Particle Films
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001Co-Authors: K.t.l De Silva, A J McquillanAbstract:Abstract An in situ infrared spectroscopic study is described of the adsorption of 8-quinolinol, thiosulfate, thiosalicyclic acid and diethyldithiocarbamate from aqueous solution to cadmium telluride (CdTe) Particle Films. Adsorption isotherms and adsorption constants have been derived for 8-quinolinol and thiosulfate adsorbed to CdTe. The presence of a sulfur donor atom within the adsorbate favours adsorption to CdTe. Spectra recorded with carboxylic acids except thiosalicyclic gave no evidence of adsorbed species, due to their inability to displace the passive oxide film from the CdTe surface.
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probing solid solution interfacial chemistry with atr ir spectroscopy of Particle Films
Advanced Materials, 2001Co-Authors: A J McquillanAbstract:Infrared (IR) spectroscopy of thin Particle Films, deposited on an attenuated total reflection (ATR) crystal and immersed in solution, has high potential for investigating the chemistry of solid–solution interfaces. Phenomena that can be studied include pH-dependent adsorption, photosensitization, photocatalysis, and biocompatibility of prosthetic materials. With Films a few micrometers thick, the penetration depth of the evanescent IR wave is sufficient to monitor surface reactions throughout the high surface area Particle film.
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Probing Solid–Solution Interfacial Chemistry with ATR-IR Spectroscopy of Particle Films
Advanced Materials, 2001Co-Authors: A J McquillanAbstract:Infrared (IR) spectroscopy of thin Particle Films, deposited on an attenuated total reflection (ATR) crystal and immersed in solution, has high potential for investigating the chemistry of solid–solution interfaces. Phenomena that can be studied include pH-dependent adsorption, photosensitization, photocatalysis, and biocompatibility of prosthetic materials. With Films a few micrometers thick, the penetration depth of the evanescent IR wave is sufficient to monitor surface reactions throughout the high surface area Particle film.