Ordered nanopillar structured electrodes for depleted bulk heterojunction colloidal quantum dot solar cells.

A bulk heterojunction of ordered titania nanopillars and PbS colloidal quantum dots is developed. By using a pre-patterned template, an ordered titania nanopillar matrix with nearest neighbours 275 nm apart and height of 300 nm is fabricated and subsequently filled in with PbS colloidal quantum dots to form an ordered depleted bulk heterojunction exhibiting power conversion efficiency of 5.6%.

Transfer molding of nanoscale oxides using water-soluble templates.

We report a facile method for creating nanoscopic oxide structures over large areas that is capable of producing high aspect ratio nanoscale structures with feature sizes below 50 nm. A variety of nanostructured oxides including TiO(2), SnO(2) and organosilicates are formed using sol-gel and nanoparticle precursors by way of molding with water-soluble polymeric templates generated from silicon masters. Sequential stacking techniques are developed that generate unique 3-dimensional nanostructures with combinatorially mixed geometries, scales, and materials. Applicable to a variety of substrates, this scalable method allows access to a broad range of new thin film morphologies for applications in devices, catalysts, and functional surface coatings.

Microwave-assisted synthesis of monodispersed CdTe nanocrystals.

High quality and monodispersed CdTe nanocrystals with tunable emission spectra ranging from 516 nm to 650 nm were synthesized by a highly reproducible microwave method.

Nanostructuration of titania films prepared by self-assembly to affect cell adhesion.

Nanostructured and dense titania films prepared by evaporation-induced self-assembly (EISA) are shown to possess tunable topographical nanoscale features on the order 2-12 nm. Thermal treatment (calcination) induces a transition from amorphous titania to crystalline anatase that modifies the chemical and structural properties of the surfaces via the migration of matter. For nanostructured films, the nanoporous network changes from organized ellipsoidal pores, approximately 4 nm x 2 nm, to a grid-like structure with pores on the order of 12 nm, whereas dense films show a slight roughening of the surface. Cells seeded on templated films show measurable, statistically significant differences in morphology compared with cells seeded on dense films. Moreover, although crystallization of templated films results in surfaces that promote less well-spread cells with higher circularities, the opposite trend is observed for dense films. As such, these results represent a new method to tailor interfaces for biomaterial applications, using EISA to control material patterning on the nanoscale. This self-assembly based approach allows the patterning on size scales that are inaccessible by most traditional techniques while offering the added potential to package and control the release of bioactive molecules.

Risk factors for cesarean delivery in preterm, term and post-term patients undergoing induction of labor with an unfavorable cervix.

BACKGROUND/AIMS: To identify risk factors for cesarean delivery in patients with an unfavorable cervix undergoing an indicated induction of labor. METHODS: This is a secondary analysis of combined data from three prospective randomized trials comparing cervical ripening methods in singleton pregnancies with an unfavorable cervix seeking to identify risk factors for cesarean delivery. RESULTS: Nine hundred and five women underwent an induction of labor for a variety of indications. Gestational age ranged from 27.0-42.8 weeks (mean of 37.8 weeks) and initial Bishop's score from 0-6 (mean 2.5). There were 613 vaginal deliveries (67.7%) and 292 cesarean deliveries (32.2%). Factors associated with an increased risk for cesarean delivery included nulliparous status, Bishop's score 40 and diabetes mellitus. CONCLUSIONS: Risk factors for cesarean delivery in women undergoing an indicated induction include a low Bishop's score, high BMI, nulliparity and diabetes.

Pyrolysis, crystallization, and sintering of mesostructured titania thin films assessed by in situ thermal ellipsometry.

In-situ thermal ellipsometric analysis is used to elucidate new and fine-scale details on the thermally driven densification, pyrolysis, crystallization, and sintering of dense and ordered mesoporous titania thin films prepared by evaporation-induced self-assembly. The role of the heating schedule, initial film thickness, nature of the substrate and templating agent, solution aging, and presence of water and other additives in the calcination environment is examined. Each of these parameters is shown to have unique and often substantial effects on the final film structure, while the technique itself provides detailed insight into the chemical origin and evolution of these effects. In-situ monitoring and control over the governing chemical processes, such as high-temperature adsorption phenomena that impact nanocrystal growth, is also demonstrated. The evolution of both the porosity and chemical processes occurring inside these materials are evaluated, including extraction of kinetic parameters for the pyrolysis of the template and crystallization of the matrix walls. The latter is shown to be strongly dependent on the presence of mesoscale ordering with ordered cubic films indicating a 1D diffusion-limited crystallization process and dense films following a 3D diffusion-limited process. Less well-ordered mesoporous films, despite similarities in pore volume and pore size distributions, are kinetically more reminiscent of dense films in terms of crystallization. In-situ thermal ellipsometry, by detailing the evolution of the thermally driven chemistry and ceramization that dictate the final film properties, provides immensely important insight into the synthesis and optimization of advanced functional materials based on titania and other metal oxide thin films.

Acid-base bifunctional and dielectric outer-sphere effects in heterogeneous catalysis: a comparative investigation of model primary amine catalysts.

Dielectric and acid-base bifunctional effects are elucidated in heterogeneous aminocatalysis using a synthetic strategy based on bulk silica imprinting. Acid-base cooperativity between silanols and amines yields a bifunctional catalyst for the Henry reaction that forms alpha,beta-unsaturated product via quasi-equilibrated iminium intermediate. Solid-state UV/vis spectroscopy of catalyst materials treated with salicylaldehyde demonstrates zwitterionic iminium ion to be the thermodynamically preferred product in the bifunctional catalyst. This product is observed to a much lesser extent relative to its neutral imine tautomer in primary amine catalysts having outer-sphere silanols partially replaced by aprotic functional groups. One of these primary amine catalysts, consisting of a polar outer-sphere environment derived from cyano-terminated capping groups, has activity comparable to that of the bifunctional catalyst in the Henry reaction, but instead forms the beta-nitro alcohol product in high selectivity (approximately 99%). This appears to be the first observation of selective alcohol formation in primary amine catalysis of the Henry reaction. A primary amine catalyst with a methyl-terminated outer-sphere also produces alcohol, albeit at a rate that is 50-fold slower than the cyano-terminated catalyst, demonstrating that outer-sphere dielectric constant affects catalyst activity. We further investigate the importance of organizational effects in enabling acid-base cooperativity within the context of bifunctional catalysis, and the unique role of the solid surface as a macroscopic ligand to impose this cooperativity. Our results unequivocally demonstrate that reaction mechanism and product selectivity in heterogeneous aminocatalysis are critically dependent on the outer-sphere environment.

Investigation of the core-shell interface in gold@silica nanoparticles: a silica imprinting approach.

The nature of the self-assembled core-shell interface in gold@silica nanoparticles synthesized via a 3-aminopropyltrimethoxysilane (APTMS) route is investigated using materials synthesis as a sensitive tool for elucidating interfacial composition and organization. Our approach involves condensation of the gold@silica nanoparticles within a silica framework for synthesis of a composite gold-silica material containing approximately 30 wt % gold. This material contains one of the highest gold loadings reported, but maintains gold core isolation as ascertained via a single surface plasmon resonance absorption band frequency corresponding to that of gold nanoparticles in dilute aqueous solution. The immobilized gold cores are subsequently etched using cyanide anion for the synthesis of templated porosity, which corresponds to the space that was occupied by the gold. Characterization of immobilized amines is performed using probe molecule binding experiments, which demonstrate a lack of accessible amines after gold removal. Solid-state 13C CPMAS NMR spectroscopy on these materials demonstrates that the amount of amine immobilization must be less than 10% of the expected yield, assuming that all of the APTMS becomes bound to the gold nanoparticle template. These results require a core-shell interface in the gold@silica nanoparticles that is predominantly occupied by inorganic silicate species, such as Si-O-Si and Si-OH, rather than primary amines. Such a result is likely a consequence of the weak interaction between primary amines and gold in aqueous solution. Our method for investigating the core-shell interface of gold@silica nanoparticles is generalizable for other interfacial structures and enables the synthesis of bulk imprinted silica using colloidal templates.