452 research outputs found
Tuning and Switching a Plasmonic Quantum Dot Sandwich in a Nematic Line Defect
We study the quantum-mechanical effects arising in a single semiconductor
core/shell quantum dot controllably sandwiched between two plasmonic nanorods.
Control over the position and the sandwich confinement structure is achieved by
the use of a linear-trap, liquid-crystal line defect and laser tweezers that
push the sandwich together. This arrangement allows for the study of exciton
plasmon interactions in a single structure, unaltered by ensemble effects or
the complexity of dielectric interfaces. We demonstrate the effect of plasmonic
confinement on the photon-antibunching behavior of the quantum dot and its
luminescence lifetime. The quantum dot behaves as a single emitter when
nanorods are far away from the quantum dot but shows possible multiexciton
emission and a significantly decreased lifetime when tightly confined in a
plasmonic sandwich. These findings demonstrate that liquid crystal defects,
combined with laser tweezers, enable a versatile platform to study plasmonic
coupling phenomena in a nanoscale laboratory, where all elements can be
arranged almost at will.Comment: Supporting information at the en
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Non-linear Electron Transport Kinetics in Nanocrystalline TiO(2) Based Solar Cells
An analytical model describing electron transport in dye-sensitized nanocrystalline TiO(2) solar cells is shown to account for the non-linear dependence of the electron transport rate on the electron concentration. Equations relating the influenece of an exponential distribtuion of surface states to electron transport are derived and verified by intensity-modulated photocurrent spectroscopy measurements. A slope of 69 meV is inferred for the surface-state distribution curve
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Comparison of Dye-Sensitized Rutile- and Anatase-Based TiO2 Solar Cells
The objective of this work is to develop and optimize the new dye-sensitized solar cell technology. In view of the infancy of rutile material development for solar cells, the PV response of the dye-sensitized rutile-based solar cell is remarkably close to that of the anatase-based cell
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Effect of a Coadsorbent on the Performance of Dye-Sensitized TiO2 Solar Cells: Shielding versus Band-Edge Movement
The objective of this research is to determine the operational characteristics key to efficient, low-cost, stable solar cells based on dye-sensitized mesoporous films (in collaboration with DOE's Office of Science Program). Toward this end, we have investigated the mechanism by which the adsorbent chenodeoxycholate, cografted with a sensitizer onto TiO2 nanocrystals, improves the open-circuit photovoltage (VOC) and short-circuit photocurrent density (JSC). We find that adding chenodeoxycholate not only shifts the TiO2 conduction-band edge to negative potentials but also accelerates the rate of recombination. The net effect of these opposing phenomena is to produce a higher photovoltage. It is also found that chenodeoxycholate reduces the dye loading significantly but has only a modest effect on JSC. Implications of these results to developing more efficient cells are discussed
A critical reappraisal of paleomagnetic evidence for Philippine Sea Plate rotation
The kinematic history of the Philippine Sea Plate (PSP) is crucial for interpreting its geological record related to subduction initiation processes and the paleogeography of the junction between the Paleo-Pacific and Tethyan oceanic realms. However, reconstructing PSP's kinematic history is difficult because the plate has been surrounded by subduction zones for most of its history. In absence of marine magnetic anomalies to constrain PSP's motion relative to its neighboring plates, paleomagnetic data may be used as quantitative constraints on its motion. Previous paleomagnetic studies interpreted easterly deflected declinations to infer clockwise rotations of up to 90° since the Eocene. However, rotations inferred from these datasets may also reflect local block rotations related to plate margin deformation. We here re-evaluate to what extent paleomagnetic data from the PSP unequivocally demonstrate plate motion rather than local rotation. To this end, we provide new data from Guam, in the Mariana forearc, and reassess published paleomagnetic data. Our new data from Guam come from two localities in the Eocene, two in the Oligocene, and two in the Miocene. Our compilation assesses data quality against recently defined criteria. Our new results demonstrate that in Guam, declination differences of up to 35° exist in rocks of Eocene age, indicating local rotations. Our compilation identifies both clockwise and counterclockwise rotations from the plate margins, with little confidence which of these would reflect plate-wide rotation. We compiled paleolatitude data from igneous rocks, which we correct for microplate rotation constrained by intra-PSP marine magnetic anomalies and show a northward drift of the PSP of ∼15° since the Eocene, but without a paleomagnetic necessity for major vertical axis rotation. Hence, with the currently available data, rotations of the PSP may be permitted, but are not required. Plate motion is currently better reconstructed from geological constraints contained in circum-PSP orogenic belts
Determining the Locus for Photocarrier Recombination in Dye-Sensitized Solar Cells
We present intensity-modulated photocurrent and infrared transmittance measurements on dye-sensitized solar cells based on a mesoporous titania (TiO2) matrix immersed in an iodine-based electrolyte. Under short-circuit conditions, we show that an elementary analysis accurately relates the two measurements. Under open-circuit conditions, infrared transmittance, and photovoltage measurements yield information on the characteristic depth at which electrons recombine with ions (the ‘‘locus of recombination’’). For one particular series of samples recombination occurred near the substrate supporting the titania film, as opposed to homogeneously throughout the film
A Comparison of the Adaptive Response of Staphylococcus aureus vs. Streptococcus mutans and the Development of Chlorhexidine Resistance
Antimicrobials with nonselective antibacterial efficacy such as chlorhexidine can be effective in reducing biofilm, but bear the risk of inducing resistance in specific bacteria. In clinical practice, bacteria such as Staphylococcus aureus have been found resistant to chlorhexidine, but other bacteria, including Streptococcus mutans, have largely remained susceptible to chlorhexidine despite its widespread use in oral healthcare. Here, we aim to forward a possible reason as to why S. aureus can acquire resistance against chlorhexidine, while S. mutans remains susceptible to chlorhexidine. Measurement of surface-enhanced fluorescence indicated that chlorhexidine caused gradual, but irreversible deformation to adhering green fluorescent S. aureus due to irreparable damage to the cell wall. Concurrently, the metabolic activity of adhering staphylococci was higher than of planktonic bacteria, suggesting efflux mechanisms may have been activated upon cell wall deformation, impeding the buildup of a high chlorhexidine concentration in the cytoplasm and therewith stimulating the development of chlorhexidine resistance in S. aureus. Exposure of S. mutans to chlorhexidine caused immediate, but reversible deformation in adhering streptococci, indicative of rapid self-repair of cell wall damage done by chlorhexidine. Due to cell wall self-repair, S. mutans will be unable to effectively reduce the chlorhexidine concentration in the cytoplasm causing solidification of the cytoplasm. In line, no increased metabolic activity was observed in S. mutans during exposure to chlorhexidine. Therewith, self-repair is suicidal and prevents the development of a chlorhexidine-resistant progeny in S. mutans
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