A semiconductor nanocrystal film is a unique class of nanocomposite, whose collective properties are determined by those of its constituents. Colloidal synthetic methods offer precise size control ...and finely tuned optical properties via quantum confinement, while recent improvements in charge transport through films have led to a variety of optoelectronic applications. However, understanding the role of defects and impurities in doping, crucial for optimizing device performance, has remained more elusive. In this perspective, we review recent progress in understanding and controlling the doping of semiconductor nanocrystal thin films, with a special focus on its relevance to photovoltaic applications. We highlight an array of postsynthetic techniques based on stoichiometric control, metal impurity incorporation, and electrochemical charging. We conclude with a review of the state of the art for nanocrystal photovoltaics, and propose the use of controlled doping and charge balance as a pathway to higher device efficiencies.
Aims. NGC 2992 is an intermediate Seyfert 1 galaxy showing outflows on kilo parsec scales which might be due either to AGN or starburst activity. We therefore aim at investigating its central region ...for a putative starburst in the past and its connection to the AGN and the outflows. Methods. Observations were performed with the adaptive optics near infrared integral field spectrograph SINFONI on the VLT, complemented by longslit observations with ISAAC on the VLT, as well as N- and Q-band data from the Spitzer archive. The spatial and spectral resolutions of the SINFONI data are 50 pc and 83 km s-1, respectively. The field of view of $3\arcsec$ × $3\arcsec$ corresponds to 450 pc × 450 pc. Brγ equivalent width and line fluxes from PAHs were compared to stellar population models to constrain the age of the putative recent star formation. A simple geometric model of two mutually inclined disks and an additional cone to describe an outflow was developed to explain the observed complex velocity field in H2 1–0S(1). Results. The morphologies of the Brγ and the stellar continuum are different suggesting that at least part of the Brγ emission comes from the AGN. This is confirmed by PAH emission lines at 6.2 μm and 11.2 μm and the strength of the silicon absorption feature at 9.7 μm, which point to dominant AGN activity with a relatively minor starburst contribution. We find a starburst age of 40–50 Myr from Brγ line diagnostics and the radio continuum; ongoing star formation can be excluded. Both the energetics and the timescales indicate that the outflows are driven by the AGN rather than the starburst. The complex velocity field observed in H2 1–0S(1) in the central 450 pc can be explained by the superposition of the galaxy rotation and an outflow.
We analyze new spatially resolved integral field spectroscopic H- and K-band data at a resolution of 03 (100 pc) and reanalyze interferometric CO(2-1) line observations of the prototypical merging ...system Arp 220. We find that the majority of the K-band luminosity is due to a 10 Myr old starburst, with a significant contribution from an underlying 1 Gyr old stellar population and a small contribution from stars 8 Myr old. The Calzetti et al. reddening law provides the best fit to photometric data points spanning 0.45-2.12 Delta *mm. Furthermore, estimates of the bolometric luminosity from IRAS fluxes in conjunction with our stellar population analysis indicate that we observe less than 10% of the emitted K-band light. The stellar and CO(2-1) kinematic center of the western nucleus coincides with the compact hot dust emission, indicating that the latter marks the center of the gravitational potential. In the eastern nucleus, the CO(2-1) data are well matched by a model in which the gas orbits around the peak of the dust emission. This, and the similarity of the K-band tracer kinematics, shows that despite the irregular morphology, the eastern nucleus is also a kinematically coherent structure. Comparison of the extinction map with EWCO and EWBr Delta *g maps indicates that the lower half of the eastern nucleus is significantly more extincted than the upper half, suggesting that the lower half is buried in the larger scale gas disk.
We explore hypothetical ecologies to explain diversity among predatory dinosaurs in North America's medial Cretaceous, based on occurrence, tooth morphology, and stable isotope analysis. The ...Mussentuchit local fauna, Utah, USA, is among the best-known terrestrial vertebrate assemblages from the Cretaceous. Study samples include teeth from six microvertebrate sites, ranging in depositional setting from distal floodplain to channel lags. We recognize four theropod morphotypes: a comparatively large theropod (morph 1), a medium-sized dromaeosaurid (morph 2), a small dromaeosaurid (morph 3), and a tooth-morph similar to the genus Richardoestesia (morph 4). These four morphotypes vary significantly in mean size, from 15.1 mm in the largest theropod to 3.7 mm in Richardoestesia. Further, tooth representation from two of the best-sampled microsites (representing a channel/splay and floodplain deposit) show differing patterns of abundances with morphs 1 and 3 having roughly the same abundance in both sites, while morph 2 was more abundant in the floodplain setting and morph 4 was more abundant in the channel/splay. Stable isotope analysis (δ
C; δ
O) of tooth carbonate from the theropod morphotypes, goniopholidid crocodilians, and matrix (to test for diagenesis) from these sites were also analyzed. The theropods show modest differences in δ
C values between each other, with carbonate from the teeth of morphs 1, 3, and 4 being enriched in
C for the channel/splay relative to the floodplain environments, possibly indicative of dietary plasticity in these species. We hypothesize that these data indicate that the Mussentuchit theropods had different niches within the predator guild, suggesting plausible means by which ecospace was divided among the predatory dinosaurs of the Mussentuchit local fauna.
The Southwestern Atlantic Ocean humpback whales wintering ground (breeding stock A) are distributed along the Brazilian coast (5-23°S), and their main mating and calving ground is in the Abrolhos ...Bank. We investigated genetic diversity, population structure, and relatedness of individuals sampled from the entire Southwest Atlantic humpback whale population. A total of 275 individuals sampled from 2 subregions (Abrolhos Bank, n = 229 and Praia do Forte, n = 46) were screened for 9 microsatellite loci. This population showed a high level of allelic diversity (A = 12.1) and a high mean observed heterozygosity (HO = 0.733). No signal of significant genetic bottleneck was detected in accordance with the mitochondrial DNA data. We find no evidence of temporal (between years) genetic structure as well as no genetic differentiation between whales from the 2 subregions of the Brazilian breeding ground. We observed that the proportion of males and females in this population was approximately 1:1, which differs from the male-biased sex ratio observed in other breeding grounds. The data obtained through this study provided no evidence of kinship associations within social groups. Finally, a female sampled off South Georgia Islands showed a putative parent-offspring relationship with a female off Abrolhos Bank, supporting the migratory link between these 2 areas.
A (nano)crystal‐clear view: With doped semiconductor nanocrystals, local chemical events can be probed through their perturbation of the carrier density of the nanocrystal. Examples demonstrate that ...redox processes and ligand chemistry can induce changes in the vacancy density within copper(I) sulfide nanorods, allowing such events to be detected by strong shifts in localized surface plasmon resonance.
A free-boundary approach is applied to derive universal relationships between the excitability and the velocity and the shape of stabilized wave segments in a broad class of excitable media. In the ...earlier discovered low excitability limit wave segments approach critical fingers. We demonstrate the existence of a second universal limit (a motionless circular shaped spot) in highly excitable media. Analytically obtained asymptotic relationships and interpolation formula connecting both excitability limits are in good quantitative agreement with results from numerical simulations.
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