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Although nanotechnology lessons are increasingly integrated into curricula, students still face significant challenges in understanding the characterization techniques used to investigate nanotechn...

Inspired by the rapid rise in efficiencies of lead halide perovskite (LHP) solar cells, lead-free alternatives are attracting increasing attention. In this work, we study the photovoltaic potential of solution-processed antimony (Sb)-based compounds with the formula A3Sb2I9 (A = Cs, Rb, and K). We experimentally determine bandgap magnitude and type, structure, carrier lifetime, exciton binding energy, film morphology, and photovoltaic device performance. We use density functional theory to compute the equilibrium structures, band structures, carrier effective masses, and phase stability diagrams. We find the A-site cation governs the structural and optoelectronic properties of these compounds. Cs3Sb2I9 has a 0D structure, the largest exciton binding energy (175 ± 9 meV), an indirect bandgap, and, in a solar cell, low photocurrent (0.13 mA cm–2). Rb3Sb2I9 has a 2D structure, a direct bandgap, and, among the materials investigated, the lowest exciton binding energy (101 ± 6 meV) and highest photocurrent (1....

Purpose Iron-oxide nanoparticles (IONPs) have shown tremendous utility for enhancing image contrast and delivering targeted therapies. Quantification of IONPs has been demonstrated at low concentrations with gradient echo (GRE) and spin echo (SE), and at high concentrations with echoless sequences such as swept imaging with Fourier transform (SWIFT). This work examines the overlap of IONP quantification with GRE, SE, and SWIFT. Methods The limit of quantification of GRE, SE, inversion-recovery GRE, and SWIFT sequences was assessed using IONPs at a concentration range of 0.02 to 89.29 mM suspended in 1% agarose. Empirically derived limits of quantification were compared with International Union of Pure and Applied Chemistry definitions. Both commercial and experimental IONPs were used. Results All three IONPs assessed demonstrated an overlap of concentration quantification with GRE, SE, and SWIFT sequences. The largest dynamic range observed was 0.004 to 35.7 mM with Feraheme. Conclusions The metrics established allow upper and lower quantitative limitations to be estimated given the relaxivity characteristics of the IONP and the concentration range of the material to be assessed. The methods outlined in this paper are applicable to any pulse sequence, IONP formulation, and field strength. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Iron oxide nanoparticles have great potential as diagnostic and therapeutic agents in cancer and other diseases; however, biological aggregation severely limits their function in vivo. Aggregates can cause poor biodistribution, reduced heating capability, and can confound their visualization and quantification by magnetic resonance imaging (MRI). Herein, we demonstrate that the incorporation of a functionalized mesoporous silica shell can prevent aggregation and enable the practical use of high-heating, high-contrast iron oxide nanoparticles in vitro and in vivo. Unmodified and mesoporous silica-coated iron oxide nanoparticles were characterized in biologically relevant environments including phosphate buffered saline, simulated body fluid, whole mouse blood, lymph node carcinoma of prostate (LNCaP) cells, and after direct injection into LNCaP prostate cancer tumors in nude mice. Once coated, iron oxide nanoparticles maintained colloidal stability along with high heating and relaxivity behaviors (SARFe = 204 W/g Fe at 190 kHz and 20 kA/m and r1 = 6.9 mM(-1) s(-1) at 1.4 T). Colloidal stability and minimal nonspecific cell uptake allowed for effective heating in salt and agarose suspensions and strong signal enhancement in MR imaging in vivo. These results show that (1) aggregation can lower the heating and imaging performance of magnetic nanoparticles and (2) a coating of functionalized mesoporous silica can mitigate this issue, potentially improving clinical planning and practical use.

Lead halide-based perovskite thin films have attracted great attention due to the explosive increase in perovskite solar cell efficiencies. The same optoelectronic properties that make perovskites ideal absorber materials in solar cells are also beneficial in other light-harvesting applications and make them prime candidates as triplet sensitizers in upconversion via triplet-triplet annihilation in rubrene. In this contribution, we take advantage of long carrier lifetimes and carrier diffusion lengths in perovskite thin films, their high absorption cross sections throughout the visible spectrum, as well as the strong spin-orbit coupling owing to the abundance of heavy atoms to sensitize the upconverter rubrene. Employing bulk perovskite thin films as the absorber layer and spin-mixer in inorganic/organic heterojunction upconversion devices allows us to forego the additional tunneling barrier owing from the passivating ligands required for colloidal sensitizers. Our bilayer device exhibits an upconversion efficiency in excess of 3% under 785 nm illumination.

Chemically prepared colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. We now demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single photon emission with optical coherence times as long as 80 ps, an appreciable fraction of their 210 ps radiative lifetimes. These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photon pairs. Our results present a starting point for the rational design of lead halide perovskite-based quantum emitters with fast emission, wide spectral-tunability, scalable production, and which benefit from the hybrid-integration with nano-photonic components that has been demonstrated for colloidal materials., Main text - 20 pages, 4 figures. Supplementary Material - 11 pages, 8 figures

The Ferrozinen assay is applied as an accurate and rapid method to quantify the iron content of iron oxide nanoparticles (IONPs) and can be used in biological matrices. The addition of ascorbic aqcid accelerates the digestion process and can penetrate an IONP core within a mesoporous and solid silica shell. This new digestion protocol avoids the need for hydrofluoric acid to digest the surrounding silica shell and provides and accessible alternative to inductively coupled plasma methods. With the updated digestion protocol, the quantitative range of the Ferrozine assay is 1 - 14 ppm.

Photosynthetic antennae and organic electronic materials use topological, structural, and molecular control of delocalized excitons to enhance and direct energy transfer. Interactions between the transition dipoles of individual chromophore units allow for coherent delocalization across multiple molecular sites. This delocalization, for specific geometries, greatly enhances the transition dipole moment of the lowest energy excitonic state relative to the chromophore and increases its radiative rate, a phenomenon known as superradiance. In this study, we show that ordered, self-assembled light-harvesting nanotubes (LHNs) display excitation-induced photobrightening and photodarkening. These changes in quantum yield arise due to changes in energetic disorder, which in turn increases/decreases excitonic superradiance. Through a combination of experiment and modeling, we show that intense illumination induces different types of chemical change in LHNs that reproducibly alter absorption and fluorescence properties, indicating control over excitonic delocalization. We also show that changes in spectral width and shift can be sensitive measures of system dimensionality, illustrating the mixed 1-2D nature of LHN excitons. Our results demonstrate a path forward for mastery of energetic disorder in an excitonic antenna, with implications for fundamental studies of coherent energy transport.

This Feature describes several methods for the characterization of magnetic nanoparticles in biological matrices such as cells and tissues. The Feature focuses on sample preparation and includes several case studies where multiple techniques were used in conjunction.

A novel meso bi­cyclo­[2.2.2]octene-based compound was obtained from an attempted Diels–Alder reaction. It crystallizes from p-xylene as a hemisolvate., The title tetrone compound, C32H22N2O4S· 0.5C8H10, is the major product (50% yield) of an attempted Diels–Alder reaction of 2-(α-styr­yl)thio­phene with N-phenyl­male­imide (2 equivalents) in toluene. Recrystallization of the resulting powder from p-xylene gave the title hemisolvate; the p-xylene mol­ecule is located about an inversion center. In the crystal, the primary tetrone contacts are between a carbonyl O atom and the four flagpole H atoms of the bi­cyclo­[2.2.2]octene core, forming chains along [001].

Low carrier mobility and lifetime in semiconductor polymers are some of the main challenges facing the field of organic photovoltaics (OPV) in the quest for efficient devices with high current density. Finding novel strategies such as device structure engineering is a key pathway toward addressing this issue. In this work, the light absorption and carrier collection of OPV devices are improved by employment of ZnO nanowire (NW) arrays with an optimum NW length (50 nm) and antireflection (AR) film with nanocone structure. The optical characterization results show that ZnO NW increases the transmittance of the electron transporting layer as well as the absorption of the polymer blend. Moreover, the as-deposited polymer blend on the ZnO NW array shows better charge transfer as compared to the planar sample. By employing PC70BM:PV2000 as a promising air-stable active-layer, power conversion efficiencies of 9.8% and 10.1% are achieved for NW devices without and with an AR film, indicating 22.5% and 26.2% enhancement in PCE as compared to that of planar device. Moreover, it is shown that the AR film enhances the water-repellent ability of the OPV device.

Intern-constructed eportfolios, depicting their work in our NSF-funded REU summer program, were designed to facilitate training and assessment goals. We developed objective structural measures of these eportfolios to strengthen their descriptions and to explore their connections to training outcomes. ePortfolios from the past four years of a summer research program in applied psychology were assessed in terms of objective measures such as number of pages, number of hyperlinks, number of external pages, number of cross-links, number of documents, and the levels of the website in which these attributes were located. There was strong and significant hierarchical organization of these components in the interns’ eportfolios, and differences in objective measures were associated with intern ratings of learning outcomes. These results indicate promise for objective eportfolio measures as an index of training outcomes as well as supporting program assessment goals.

Driving in fog is a potentially dangerous activity that has been investigated in a number of different ways; however, most have focused on identifying the underlying perceptual changes that result in an inability to perceive speed of vehicle motion. Although the previous research has identified the perceptual changes associated with driving in fog and shows that people are highly likely to perceive their speed to be higher than it actually is, these research studies have not investigated driving behavior when drivers are allowed to maintain speed as they feel appropriate and make use of the vehicle's speedometer. In addition, much of the existing research focuses on speed perception and presents a limited view of other driving performance metrics in terms of lane keeping and event detection. The current study addresses these issues utilizing a driving simulator-based method where fog is simulated as a distance dependent contrast reduction while having participants drive at speeds they feel are appropriate. A number of different instructions and speed feedback mechanisms were tested in order to determine how drivers react when driving in varying levels of fog. Results also include lane keeping measures in order to assess whether drivers are willing to drive at speeds where their lane keeping performance is degraded due to the reduced visibility. Results indicate that, in general, drivers do not tend to slow down significantly until visibility distance is drastically reduced by fog; however, lane keeping ability is maintained throughout most of the range of visibility distances. Lane keeping ability was reduced only when fog results in visibility distances

While driving simulators are a valuable tool for assessing multiple dimensions of driving performance under relatively safe conditions, researchers and practitioners must be prepared for participants that suffer from simulator sickness. This paper describes multiple theories of motion sickness and presents a method for assessing and reacting to simulator sickness symptoms. Results showed that this method identified individuals who were unable to complete a driving simulator study due to simulator sickness with greater than 90% accuracy and that older participants had a greater likelihood of simulator sickness than younger participants. Possible explanations for increased symptoms experienced by older participants are discussed as well as implications for research ethics and simulator sickness prevention.

Dark field transmission electron microscopy has been applied herein to visualize the interactions of inorganic nanomaterials with biological systems. This new application of a known technique addresses a deficiency in status quo visualization techniques. High resolution and low noise images can be acquired to locate and identify crystalline nanoparticles in complex biological matrices. Moreover, through the composition of multiple images taken at different angular beam tilts, it is possible to image a majority of nanoparticles present at a site in dark field mode. This facilitates clarity regarding the internalization of nanomaterials in cellular systems. In addition, comparing dark field images recorded at different angular tilts yields insight into the character of nanoparticle faceting.

The current research represents an initial investigation of drivers’ understanding of high beam and low beam headlight patterns in a nighttime driving environment. Fifty-four university students used a highlighter to indicate on a paper diagram of a roadway scene the portion of the scene that they felt their headlights would illuminate. Although the headlight patterns produced by participants varied more than expected, several consistent patterns emerged. Classification and evaluation of these drivers’ responses revealed that many drivers misunderstand the area of the roadway that is illuminated by their headlights. These misunderstandings fall into fairly distinct patterns. The results indicate many drivers possess an incomplete understanding of the pattern of illumination provided by their headlights. These results are consistent with earlier evidence that many road users fail to appreciate the visibility challenges that exist at night.