Showing papers in "Chemistry of Materials in 2003"
TL;DR: In this article, the extinction coefficient per mole of nanocrystals at the first exitonic absorption peak, e.g., for high-quality CdTe, CdSe, and CdS, was found to be strongly dependent on the size of the nanocrystal, between a square and a cubic dependence.
Abstract: The extinction coefficient per mole of nanocrystals at the first exitonic absorption peak, e, for high-quality CdTe, CdSe, and CdS nanocrystals was found to be strongly dependent on the size of the nanocrystals, between a square and a cubic dependence. The measurements were carried out using either nanocrystals purified with monitored purification procedures or nanocrystals prepared through controlled etching methods. The nature of the surface ligands, the refractive index of the solvents, the PL quantum yield of the nanocrystals, the methods used for the synthesis of the nanocrystals, and the temperature for the measurements all did not show detectable influence on the extinction coefficient for a given sized nanocrystal within experimental error.
4,802 citations
TL;DR: In this article, a method was used for preparing gold NRs with aspect ratios ranging from 1.5 to 4.5 for which the surface plasmon absorption maxima are between 600 and 1300 nm.
Abstract: A method is used for preparing gold NRs with aspect ratios ranging from 1.5 to 10 for which the surface plasmon absorption maxima are between 600 and 1300 nm. This method has been adapted from a previously published seed-mediated growth method (Jana et al. Adv. Mater. 2001, 13, 1389). The disadvantages and limitations of the earlier method (i.e., formation of noncylindrical NRs, φ-shaped particles, and formation of a large fraction of spherical particles) have been overcome by use of a hexadecyltrimethylammonium bromide (CTAB)-capped seed instead of a citrate-capped one. In a single-component surfactant system, the silver content of the growth solution was used to grow NRs to a desired length. This results in reproducible formation of NRs with aspect ratios ranging from 1.5 to 4.5. To grow longer NRs with aspect ratios ranging from 4.6 to 10, a binary surfactant mixture composed of benzyldimethylhexadecylammoniumchloride (BDAC) and CTAB was used. NRs are grown in this mixture either by aging or by additio...
4,645 citations
TL;DR: In this article, a review of the area encompassing modified PFSA membranes, alternative sulfonated polymer and their composite membranes, and acid−base complex membranes is presented. But the authors do not discuss the performance of the composite membranes.
Abstract: The state-of-the-art of polymer electrolyte membrane fuel cell (PEMFC) technology is based on perfluorosulfonic acid (PFSA) polymer membranes operating at a typical temperature of 80 °C. Some of the key issues and shortcomings of the PFSA-based PEMFC technology are briefly discussed. These include water management, CO poisoning, hydrogen, reformate and methanol as fuels, cooling, and heat recovery. As a means to solve these shortcomings, high-temperature polymer electrolyte membranes for operation above 100 °C are under active development. This treatise is devoted to a review of the area encompassing modified PFSA membranes, alternative sulfonated polymer and their composite membranes, and acid−base complex membranes. PFSA membranes have been modified by swelling with nonvolatile solvents and preparing composites with hydrophilic oxides and solid proton conductors. DMFC and H2/O2(air) cells based on modified PFSA membranes have been successfully operated at temperatures up to 120 °C under ambient pressure...
1,595 citations
Journal Article•
1,472 citations
TL;DR: A series of 10 2,3,4,5-tetraphenylsiloles with different 1,1-substituents [XYSi(CPh)4] were prepared, and three of them were characterized crystallographically as mentioned in this paper.
Abstract: A series of ten 2,3,4,5-tetraphenylsiloles with different 1,1-substituents [XYSi(CPh)4] were prepared, and three of these, i.e., 1,1,2,3,4,5-hexaphenylsilole [X = Y = Ph (3)], 1-ethynyl-1,2,3,4,5-pentaphenylsilole [X = Ph, Y = C⋮CH (15)], and 1,1-bis(phenylethynyl)-2,3,4,5-tetraphenylsilole [X = Y = C⋮CPh (18)], were characterized crystallographically. The ground- and excited-states of the siloles were influenced by the inductive effect of the 1,1-substituents: with an increase in their electronegativity, the absorption and emission spectra of the siloles bathochromically shifted. A simple and reliable TLC-based method was developed for measurement of the solid-state luminescence spectra of the siloles. When molecularly dissolved in common solvents at room temperature, all the siloles were practically nonemissive (“off”). When poor solvents were added, the silole molecules clustered into nanoaggregates, which turned the emission “on” and boosted the photoluminescence quantum yields by up to 2 orders of m...
1,048 citations
TL;DR: In this article, the formation of nearly monodisperse CdTe nanocrystals was studied, and the ligand effects on the monomers were found to play a more important role than ligand effect on the nanocrystal and the bonding strength and steric effects of ligands dramatically affect the reactivity of monomers and are considered as contributors to the activity coefficients of monomer.
Abstract: The formation of nearly monodisperse CdTe nanocrystalsdots (either zinc blende or wurtzite crystal structure), rods, and tetrapodsin a noncoordinating solvent was studied Several strong ligand effects were observed, and the ligand effects on the monomers were found to play a more important role than the ligand effects on the nanocrystals Experimental results suggest that, instead of monomer concentrations, monomer activities is a more relevant term for understanding the formation of nanocrystals because strong ligands always exist in the reaction solutions The bonding strength and the steric effects of ligands dramatically affect the reactivity of monomers and are considered as contributors to the activity coefficients of monomers The overall optical properties of the as-prepared CdTe nanocrystals are better than those reported in the literature and comparable to the standard CdSe nanocrystal system The configuration of the hydrocarbon chains of the ligands on the surface of each nanocrystal also pla
753 citations
TL;DR: In this paper, a series of new mesoporous silica materials with MCM-41 type of structure containing a homogeneous layer of organic functional groups inside the pores was prepared using a co-condensation method under low surfactant concentration condition.
Abstract: A series of new mesoporous silica materials with MCM-41 type of structure containing a homogeneous layer of organic functional groups inside the pores was prepared using a co-condensation method under low surfactant concentration condition. This reproducible synthetic approach resulted in high surface coverage with several functional groups such as a primary amine, secondary amine, urea, isocyanate, vinyl, and nitrile. In addition, the presence of organoalkoxysilane precursors during the base catalyzed condensation greatly influenced the final particle shape. By changing the precursor or its concentration, the particle morphology was tuned to various shapes, including spheres, tubes, and rods of various dimensions. The synthetic procedures that gave rise to the specific particle morphologies were investigated and the mechanism responsible for shape control was postulated. The structure and functionality of these materials were characterized by field-emission scanning electron microscopy, transmission elec...
749 citations
TL;DR: A surfactant-templated approach was used to synthesize phosphated mesoporous titanium dioxide by incorporating phosphorus from phosphoric acid directly into the framework of TiO2 as discussed by the authors.
Abstract: A surfactant-templated approach was used to synthesize phosphated mesoporous titanium dioxide by incorporating phosphorus from phosphoric acid directly into the framework of TiO2. The resulting materials were characterized by XRD, nitrogen adsorption, TEM, XPS analysis, UV−vis spectroscopy, FT-IR spectroscopy, and isoelectric point measurements. The surface area of phosphated mesoporous TiO2 exceeded 300 m2/g after calcination at 400 °C. It was found that the incorporation of phosphorus could stabilize the TiO2 framework and increase the surface area significantly. This stabilization is attributed to two reasons: the more complete condensation of surface Ti−OH in the as-prepared sample and the inhibition of grain growth of the embedded anatase TiO2 by the interspersed amorphous titanium phosphate matrix during thermal treatment. Both pure and phosphated mesoporous TiO2 show significant activities on the oxidation of n-pentane. The higher photocatalytic activity of phosphated mesoporous TiO2 can be explai...
703 citations
TL;DR: In this paper, Li3xLa(2/3)-x□(1/3)2xTiO3 (0 < x < 0.16) and its related structure materials, the x ≈ 0.1 member exhibits conductivity of 1 × 10-3 S/cm at room temperature with an activation energy of 0.40 eV.
Abstract: To date, the highest bulk lithium ion-conducting solid electrolyte is the perovskite (ABO3)-type lithium lanthanum titanate (LLT) Li3xLa(2/3)-x□(1/3)-2xTiO3 (0 < x < 0.16) and its related structure materials. The x ≈ 0.1 member exhibits conductivity of 1 × 10-3 S/cm at room temperature with an activation energy of 0.40 eV. The conductivity is comparable to that of commonly used polymer/liquid electrolytes. The ionic conductivity of LLT mainly depends on the size of the A-site ion cation (e.g., La or rare earth, alkali or alkaline earth), lithium and vacancy concentration, and the nature of the B−O bond. For example, replacement of La by other rare earth elements with smaller ionic radii than that of La decreases the lithium ion conductivity, while partial substitution of La by Sr (larger ionic radii than that of La) slightly increases the lithium ion conductivity. The high lithium ion conductivity of LLT is considered to be due to the large concentration of A-site vacancies, and the motion of lithium by a...
703 citations
TL;DR: In this article, the intercalation of the cationic biopolymer chitosan in Na+−montmorillonite, providing compact and robust three-dimensional nanocomposites with interesting functional properties.
Abstract: The objective of this work is the intercalation of the cationic biopolymer chitosan in Na+−montmorillonite, providing compact and robust three-dimensional nanocomposites with interesting functional properties. CHN chemical analysis, X-ray diffraction, Fourier transform infrared spectroscopy, scanning transmission electron microscopy, energy-dispersion X-ray analysis, and thermal analysis have been employed in the characterization of the nanocomposites, confirming the adsorption in mono- or bilayers of chitosan chains depending on the relative amount of chitosan with respect to the cationic exchange capacity of the clay. The first chitosan layer is adsorbed through a cationic exchange procedure, while the second layer is adsorbed in the acetate salt form. Because the deintercalation of the biopolymer is very difficult, the −NH3+Ac- species belonging to the chitosan second layer act as anionic exchange sites and, in this way, such nanocomposites become suitable systems for the detection of anions. These mat...
609 citations
TL;DR: In this paper, organic modification with aminopropyl group of two MCM-41 materials having different pore sizes (obtained from trimethylalkylammonium surfactants with different chain sizes (16 and 12 carbon atoms)) has been carried out in order to control the delivery rate of ibuprofen from the siliceous matrix.
Abstract: Organic modification with aminopropyl group of two MCM-41 materials having different pore sizes (obtained from trimethylalkylammonium surfactants with different chain sizes (16 and 12 carbon atoms)) has been carried out in order to control the delivery rate of ibuprofen from the siliceous matrix. This functionalization was performed by two different methods: the as-synthesized MCM-41 sample was treated with aminopropyltrimethoxysilane (method a), and the MCM-41 was first calcined and then funtionalized by reaction with aminopropyltrimethoxysilane (method b). The amount of ibuprofen adsorbed from hexane solution is lower for the C12 derived materials. A slower delivery rate has been observed for method b, whereas a minor influence of the pore size on the delivery rate has been found.
TL;DR: In this paper, anodic alumina (AA) membranes were coated with Al2O3 and ZnO ALD films and subsequently analyzed using cross-sectional scanning electron microscopy (SEM) and electron probe microanalysis (EPMA).
Abstract: Anodic alumina (AA) membranes are composed of highly uniform, nanometer-scale pores arranged in a hexagonal close-packed array. Depositing conformal films inside the nanopores is extremely difficult because the nanopores have an ultrahigh aspect ratio of L/d ≈ 103. Atomic layer deposition (ALD) is a thin film growth technique that can deposit highly uniform films on high-aspect-ratio substrates with monolayer thickness control. In this study, AA membranes were coated with Al2O3 and ZnO ALD films and subsequently analyzed using cross-sectional scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). SEM analysis of individual nanopores revealed that the AA membranes with nanopore diameters of d = 65 nm and lengths of L = 50 μm could be coated conformally by Al2O3 ALD using sufficient reactant exposure times. Zn concentration profiles measured by EPMA following ZnO ALD showed the progressive infiltration of the ZnO ALD into the nanopores with increasing exposure times for aspect ratios as...
TL;DR: In this paper, the influence of silver nanoparticles on the properties of polyvinyl alcohol (PVA) was investigated by mixing a colloidal solution consisting of Silver nanoparticles with a water solution of PVA in appropriate ratios.
Abstract: The influence of silver (Ag) nanoparticles on the properties of poly(vinyl alcohol) (PVA) was investigated. The nanocomposite was prepared by mixing a colloidal solution consisting of silver nanoparticles with a water solution of PVA in appropriate ratios. Composite films with different contents of inorganic phase were obtained after solvent evaporation. The contents of the inorganic phase in the nanocomposites were determined by using atomic absorption spectroscopy (AA) for silver, and were found to be 0.19, 0.33, and 0.73 wt %. Transmission electron microscopy (TEM) of the nanocomposite films revealed the presence of Ag particles with average diameter of 20 nm. Comparison of the thermal properties of the pure polymer and the nanocomposite films showed that the thermal stability is improved by about 40 °C, and the glass transition temperature is shifted to a higher temperature up to 20 °C for the highest content of the nanofiller. An increase in Young's modulus and strength of the nanocomposite was also ...
TL;DR: In this article, in situ synthesis of noble metal (Ag, Au, Pt, Pd) nanoparticles was carried out under ambient conditions in porous cellulose fibers as nanoreactors.
Abstract: In situ synthesis of noble metal (Ag, Au, Pt, Pd) nanoparticles was carried out under ambient conditions in porous cellulose fibers as nanoreactors. Particles of less than 10 nm were readily prepared using the described approach, and monodisperse nanoparticles were obtained under an optimized concentration of the metal precursor solution. The nanoporous structure and the high oxygen (ether and hydroxyl) density of the cellulose fiber constitute an effective nanoreactor for in situ synthesis of metal nanoparticles. The nanopore is essential for incorporation of metal ion and reductant into cellulose fibers as well as for removal of unnecessary byproducts from fibers. This was endorsed by negligible adsorption of metal ion onto nonporous films of poly(vinyl alcohol) and starch. The ether oxygen and the hydroxyl group not only anchor metal ions tightly in cellulose fibers via ion−dipole interactions, but they also stabilize metal nanoparticles by strong bonding interaction with their surface atoms. The prepa...
TL;DR: In this paper, it was shown that a substantial quantity of Li (at least 1.39 Li) may be removed at 55 °C by oxidation of the nonaqueous electrolyte, thus generating H+ which exchange one-for-one with Li+ to form Li2-xHxMnO3.
Abstract: Lithium intercalation compounds based on lithium manganese oxides are of great importance as positive electrodes for rechargeable lithium batteries. It is widely accepted that Li+ may be extracted (deintercalated) from such lithium manganese oxides accompanied by oxidation of Mn up to a maximum oxidation state of +4. However, it has been suggested recently that further Li+ removal may be possible. Among the mechanisms that have been proposed to charge balance the removal of Li+ are Mn oxidation beyond +4 or loss of O2-. To investigate this phenomenon we have selected Li2MnO3, a layered compound Li[Li1/3Mn2/3]O2 with a ready supply of mobile Li+ ions but with all Mn already in the +4 oxidation state. We show that a substantial quantity of Li (at least 1.39 Li) may be removed. At 55 °C this occurs exclusively by oxidation of the nonaqueous electrolyte, thus generating H+ which exchange one-for-one with Li+ to form Li2-xHxMnO3. The presence of H+ between the oxide layers results in a change of the layer stac...
TL;DR: In this article, a combined computational/experimental study on LiNi1/3Co 1/3Mn 1/ 3O2 is presented. And both the experimental and computational data show that LiNi 1 /3Co1/ 3Mn1 /3O2 material is a high-capacity stable electrode for advanced rechargeable lithium ion batteries.
Abstract: A combined computational/experimental study on LiNi1/3Co1/3Mn1/3O2 is presented. Both density functional theory and experiments are used to probe the active redox pairs and changes in electronic structure of LiNi1/3Co1/3Mn1/3O2 during intercalation or deintercalation of Li. The phase stability and voltage curve of this material are also shown in this paper. Both the experimental and computational data show that LiNi1/3Co1/3Mn1/3O2 material is a high-capacity stable electrode for advanced rechargeable lithium ion batteries.
TL;DR: The ability to modify the surface of carbon nanotubes is of crucial importance for their utilization in different applications as discussed by the authors, and in this paper we report on the chemical modification of multi-w...
Abstract: The ability to modify the surface of carbon nanotubes is of crucial importance for their utilization in different applications. In the present paper we report on the chemical modification of multiw...
TL;DR: In this article, the synthesis of magnetite nanoparticles and the further coating of these particles by several types of protective layers is reported, and the synthesis conditions for pure phase magnetite are determined by quantitative analysis of different reaction equilibria involved in magnetite precipitation from aqueous solutions.
Abstract: Magnetic nanoparticles are becoming increasingly important for several biomedical applications. For example, superparamagnetic magnetite nanoparticles with suitable bio-compatible coatings are useful in magnetic resonance imaging, tissue engineering, and drug delivery, etc. In this study we report the synthesis of magnetite nanoparticles and the further coating of these particles by several types of protective layers. Thermodynamic modeling of the chemical system has been adopted as a rational approach to establish routes to better synthesis conditions for pure phase magnetite. Quantitative analysis of different reaction equilibria involved in the precipitation of magnetite from aqueous solutions has been used to determine optimum synthesis conditions. Superparamagnetic magnetite nanoparticles (SPION) with diameters of 6 and 12 nm have been prepared by controlled chemical coprecipitation of magnetite phase from aqueous solutions containing suitable salts of Fe2+ and Fe3+ under inert atmosphere. Pure magne...
TL;DR: In this article, the degradability of polylactide (PLA)/organically modified layered silicate (OMLS) nanocomposites has been investigated under composting.
Abstract: Our ongoing research on the preparation, characterization, materials properties, and biodegradability of polylactide (PLA)/organically modified layered silicate (OMLS) nanocomposites has yielded results for PLA/organically modified synthetic fluorine mica (OMSFM) nanocomposites. Synthetic fluorine mica (SFM), modified with N-(coco alkyl)-N,N-[bis(2-hydroxyethyl)-N-methylammonium cation, was used as an OMLS for the nanocomposites preparation. The internal structure of the nanocomposites in the nanometer range was established using wide-angle X-ray diffraction (WAXD) analyses and transmission electron micrographic (TEM) observations. All nanocomposites exhibited remarkable improvement of various materials properties with simultaneous improvement in biodegradability than that of neat PLA. This is the first report that deals with the ultimate degradability of PLA and corresponding nanocomposites under compost.
TL;DR: In this article, the atomic layer deposition (ALD) was used to grow a thin platinum thin film at 300 °C by using methylcyclopentadienyl trimethylplatinum (MeCpPtMe3) and oxygen as precursors.
Abstract: Platinum thin films were grown at 300 °C by atomic layer deposition (ALD) using (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and oxygen as precursors. The films had excellent uniformity, low resistivity, and low-impurity contents. Structural studies by X-ray diffraction showed that the films were strongly (111) oriented. Growth rates of 0.45 A cycle-1 were obtained with 4 s total cycle times. The film thickness was found to linearly depend on the number of the reaction cycles. Also, the possible reaction mechanism is discussed.
TL;DR: In this paper, the authors developed complexes of magnetite nanoparticles coated with well-defined hydrophilic polymers so that they could be dispersed in aqueous fluids, and the results showed that these polymers can bind irreversibly to magnetite at the physiological pH.
Abstract: Magnetic nanoparticles that display high saturation magnetization and high magnetic susceptibility are of great interest for medical applications. Magnetite nanoparticles display strong ferrimagnetic behavior and are less sensitive to oxidation than magnetic transition metal nanoparticles such as cobalt, iron, and nickel. For in vivo applications, well-defined organic coatings are needed to surround the magnetite nanoparticles and prevent any aggregation. The goal of this research was to develop complexes of magnetite nanoparticles coated with well-defined hydrophilic polymers so that they could be dispersed in aqueous fluids. Focal points have included the following: (1) Investigations of polymer systems that bind irreversibly to magnetite at the physiological pH, (2) the design of block copolymers with anchor and tail blocks to enable dispersion in biological fluids, and (3) investigations of copolymer block lengths to maximize the concentration of bound magnetite. Hydrophilic triblock copolymers with ...
TL;DR: In this paper, the chalcopyrite compounds CuInS2 and CuInSe2 were synthesized by thermal decomposition of molecular single-source precursors.
Abstract: Nanometer-sized particles of the chalcopyrite compounds CuInS2 and CuInSe2 were synthesized by thermal decomposition of molecular single-source precursors (PPh3)2CuIn(SEt)4 and (PPh3)2CuIn(SePh)4, respectively, in the noncoordinating solvent dioctyl phthalate at temperatures between 200 and 300 °C. The nanoparticles range in size from 3 to 30 nm and are aggregated to form roughly spherical clusters of about 500 nm in diameter. X-ray diffraction of the nanoparticle powders shows greatly broadened lines, indicative of very small particle sizes, which is confirmed by TEM. Peaks present in the XRD can be indexed to reference patterns for the respective chalcopyrite compounds. Optical spectroscopy and elemental analysis by energy dispersive spectroscopy support the identification of the nanoparticles as chalcopyrites.
TL;DR: In this article, chemically functionalized multiwalled carbon nanotubes were incorporated into a polymer matrix by in situ polymerization, to improve the transfer of mechanical load through a chemical bond, which was demonstrated by Raman and infrared spectroscopies.
Abstract: Chemically functionalized multiwalled carbon nanotubes were incorporated into a polymer matrix by in situ polymerization, to improve the transfer of mechanical load through a chemical bond, which was demonstrated by Raman and infrared spectroscopies. The resulting composite shows higher storage modulus (E‘) and tensile strength than existing similar composites, with only 1 wt % of functionalized nanotubes. E‘ at 90 °C is increased by an outstanding 1135% and the glass transition temperature is exceptionally raised by ≅40 °C.
TL;DR: In this article, the authors focus on the electrosynthesis, in situ characterization and technological applications of Prussian blue analogues with the generic formula AhMk[Fe(CN)6]l·mH2O, where h, k, l, and m are stoichiometric numbers, A = alkali metal cation, and M is a transition metal.
Abstract: This review focuses on the electrosynthesis, in situ characterization, and technological applications of Prussian blue analogues with the generic formula AhMk[Fe(CN)6]l·mH2O, where h, k, l, and m are stoichiometric numbers, A = alkali metal cation, and M is a transition metal. Six such metal hexacyanoferrate (MHCF) compounds derived from Cu, Pd, In, V, Co, and Ni are featured in this article against the backdrop of the Prussian blue parent compound itself and other related compounds. The use of cyclic voltammetry and complementary techniques including scanning probe microscopies, quartz crystal microgravimetry, and ac impedance spectroscopy, for studying the growth of MHCF films on targeted substrates, is discussed. Spectroelectrochemical in situ characterization of these films in the UV−visible and IR regions is then reviewed. Finally, the use of Prussian blue and its analogues in devices for displays and “smart” windows, photoimaging, environmental remediation, chemical/biological sensing, energy conver...
TL;DR: In this article, a hierarchical structure was made by self-assembly of nano-fibrils of mineralized collagen resembling extracellular matrix, formed by selfassembly of collagen tr...
Abstract: A designed hierarchical structure was made by self-assembly of nano-fibrils of mineralized collagen resembling extracellular matrix. The collagen fibrils were formed by self-assembly of collagen tr...
TL;DR: In contrast to the performance of traditional filled polymer systems, penetrant permeability coefficients in high-free-volume, glassy poly(4-methyl-2-pentyne) (PMP) increase systematically and substantially with increasing concentration of nonporous, nanoscale fumed silica (FS) as discussed by the authors.
Abstract: In contrast to the performance of traditional filled polymer systems, penetrant permeability coefficients in high-free-volume, glassy poly(4-methyl-2-pentyne) (PMP) increase systematically and substantially with increasing concentration of nonporous, nanoscale fumed silica (FS). For instance, the permeability of PMP containing 40 wt % FS to methane is 2.3 times higher than that of the unfilled polymer. Gas and vapor uptake in the PMP/FS nanocomposites is essentially unaffected by the presence of up to 40 wt % FS, while penetrant diffusion coefficients increase regularly with increasing filler content. This increase in diffusivity is responsible for elevated permeability in the PMP/FS nanocomposites. The addition of FS to PMP augments the permeability of large penetrants more than that of small gases, consistent with a reduction in diffusivity selectivity. Consequently, vapor selectivity in the nanocomposites increases with increasing FS concentration. Activation energies of permeation in PMP decrease with...
TL;DR: In this article, a set of ZnO/Al2O3 alloy films was prepared by ALD in a viscous flow reactor using alternating Zn(CH2CH3)2/H2O exposures for ZnAl ALD and alternating Al(CH 3)3/H 2O exposure for Al2O 3 ALD.
Abstract: Atomic layer deposition (ALD) is an ideal technique for fabricating composite thin films. The thickness and stoichiometry of composite thin films prepared using ALD is dependent on the underlying surface chemistry during ALD film growth. A set of ZnO/Al2O3 alloy films was prepared by ALD in a viscous flow reactor using alternating Zn(CH2CH3)2/H2O exposures for ZnO ALD and alternating Al(CH3)3/H2O exposures for Al2O3 ALD. The ZnO reaction cycle percentage was varied from 0 to 100%. The composite film thicknesses were measured using ex situ stylus profilometry and ellipsometry. The atomic composition of the composite films was established by atomic emission spectroscopy. Large deviations were found when the measured thicknesses and compositions were compared with “rule of mixtures” predictions. Many of the ZnO/Al2O3 alloy films showed lower than expected Zn film content and were thinner than predicted by the ALD growth rates of the pure ZnO and Al2O3 films. To understand these discrepancies, in situ quartz ...
TL;DR: In this article, a polyvinyl alcohol (PVA) fiber was electrospun from water using Triton X-100 surfactant to lower the surface tension and showed increased mechanical strength due to increased crystallinity following post-spinning treatment with methanol.
Abstract: Fully (99+ %) hydrolyzed poly(vinyl alcohol) (PVA) was electrospun from water using Triton X-100 surfactant to lower the surface tension. The diameter of the electrospun PVA fibers ranged from 100 to 700 nm. Treatment of the PVA fiber mats with methanol for 8 h stabilized the fibers against disintegration in contact with water. In addition, the mats showed increased mechanical strength due to increased crystallinity following post-spinning treatment with methanol. We suggest that methanol treatment serves to increase the degree of crystallinity, and hence the number of physical cross-links in the electrospun PVA fibers. This may occur by removal of residual water within the fibers by the alcohol, allowing PVA−water hydrogen bonding to be replaced by intermolecular polymer hydrogen bonding resulting in additional crystallization. Potential applications of electrospun PVA include filters, precursors to graphitic fibers, and biomedical materials.
TL;DR: In this paper, mixed platinum−ruthenium nanoparticles are prepared by water-in-oil reverse microemulsions of water/Triton X-100/propanol-2/cyclohexane.
Abstract: Mixed platinum−ruthenium nanoparticles are prepared by water-in-oil reverse microemulsions of water/Triton X-100/propanol-2/cyclohexane. Nanoparticles formed in the microemulsions are characterized by transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffractometry (XRD), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). TEM results show a narrow distribution of Pt−Ru nanoparticles. A homogeneous alloy structure in the bimetallic nanoparticles is indicated by XRD analysis and ED analysis. The composition of the Pt−Ru nanoparticles can be easily controlled by the relative concentration of Pt and Ru in the initial precursor solution. The composition that was in the Pt−Ru nano-alloy is found to be the same as that in the original precursor solution. XPS analysis reveals the presence of Pt and Ru metal as well as some oxide of ruthenium. The effect of precursor concentration on microemulsion drop size was investigated by photo correlation spectroscopy (...
TL;DR: In this paper, surface-coated nanoparticles of LaF3 and LaPO4 doped with the luminescent trivalent lanthanide ions Eu3+, Nd3+, Er3+, Pr3+, Ho3+, and Yb3+ have been prepared.
Abstract: Surface-coated nanoparticles of LaF3 and LaPO4 doped with the luminescent trivalent lanthanide ions Eu3+, Nd3+, Er3+, Pr3+, Ho3+, and Yb3+ have been prepared. These ions emit in the visible and in the near-infrared part of the electromagnetic spectrum. The ions Nd3+, Er3+, Pr3+, and Ho3+ are the main focus in this research because they show emissions in telecommunication windows. The Yb3+ ion is of interest because it can be used as a sensitizer for Er3+. The Eu3+ ion has been used as a probe for the structural environment of the luminescent ion. It is shown that these lanthanide ions are incorporated in the inorganic host of the particles and that the particles are dispersable in organic solvents. The luminescent lifetimes of the ions are increased by orders of magnitude compared to organic complexes, with values ranging from several microseconds for Pr3+ and Ho3+, up to about 200 μs for Nd3+, and 1 ms for Er3+. This increase in the luminescence lifetime is indicative of an effective shielding of the lan...