We examine the effect of strong three-dimensional quantum confinement on the thermopower and electrical conductivity of PbSe nanocrystal superlattices. We show that for comparable carrier ...concentrations PbSe nanocrystal superlattices exhibit a substantial thermopower enhancement of several hundred microvolts per Kelvin relative to bulk PbSe. We also find that thermopower increases monotonically as the nanocrystal size decreases due to changes in carrier concentration. Lastly, we demonstrate that thermopower of PbSe nanocrystal solids can be tailored by charge-transfer doping.
Low stochastics, high sensitivity photoresists remain a goal for EUV lithography. Here we present studies of two polymer systems that attempt to make improvements to these resist characteristics ...using two different chemical approaches. In one system we work on scissionable poly(phthalaldehyde) modified to enable incorporation of photoactive units on each repeat unit of the polymer chain. In a second system we explore peptoid polymers that possess identical molecular size and composition with much higher molecular uniformity than possible by conventional synthetic techniques. We report the results of exposure of these materials to EUV exposures and the chemical changes that occur.
In this work, crystallization kinetics and aggregate growth of poly(3‐ethylhexylthiophene) (P3EHT) thin films are studied as a function of film thickness. X‐ray diffraction and optical absorption ...show that individual aggregates and crystallites grow anisotropically and mostly along only two packing directions: the alkyl stacking and the polymer chain backbone direction. Further, it is also determined that crystallization kinetics is limited by the reorganization of polymer chains and depends strongly on the film thickness and average molecular weight. Time‐dependent, field‐effect hole mobilities in thin films reveal a percolation threshold for both low and high molecular weight P3EHT. Structural analysis reveals that charge percolation requires bridged aggregates separated by a distance of ≈2–3 nm, which is on the order of the polymer persistence length. These results thus highlight the importance of tie molecules and inter‐aggregate distance in supporting charge percolation in semiconducting polymer thin films. The study as a whole also demonstrates that P3EHT is an ideal model system for polythiophenes and should prove to be useful for future investigations into crystallization kinetics.
Recrystallization kinetics and its relationship to charge transport in poly(3‐ethylhexylthiophene) (P3EHT) thin films are investigated using a combination of grazing incidence X‐ray diffraction, optical absorption, and field‐effect transistor measurements. These results show that thin film crystallization kinetics is limited by polymer chain reorganization and that charge percolation depends strongly on the edge‐to‐edge distance between aggregates.
Low stochastics, high sensitivity photoresists remain a goal for EUV lithography. Here we contrast two positive photoresist systems, polypeptoids (PPs) and poly(phthalaldehyde)s (PPAs), both of which ...are selected to minimize chemical stochastics. In the former, a chemically amplified resist with identical molecular weight, composition, and sequence is studied. In the latter, a PPA homopolymer enables preparation of a chemically homogeneous resist which can be chemically scissioned in exposed areas. We report the results of exposure of these materials to DUV, e-beam and EUV radiation and physical changes that occur. In addition, we highlight unexpected observations of the role of sequence on lithographic performance.
Room-level ventilation in schools and universities McNeill, V. Faye; Corsi, Richard; Huffman, J. Alex ...
Atmospheric Environment: X,
January 2022, 2022-Jan, 2022-01-00, 20220101, 2022-01-01, Volume:
13
Journal Article
Peer reviewed
Open access
Ventilation is of primary concern for maintaining healthy indoor air quality and reducing the spread of airborne infectious disease, including COVID-19. In addition to building-level guidelines, ...increased attention is being placed on room-level ventilation. However, for many universities and schools, ventilation data on a room-by-room basis are not available for classrooms and other key spaces. We present an overview of approaches for measuring ventilation along with their advantages and disadvantages. We also present data from recent case studies for a variety of institutions across the United States, with various building ages, types, locations, and climates, highlighting their commonalities and differences, and examples of the use of this data to support decision making.
•Room-level ventilation data supports decision making (filter use, HVAC scheduling).•Controlled release studies provide ventilation data for naturally ventilated spaces.•In situ monitoring of CO2 and PM can provide ventilation insights during occupancy.•Natural ventilation can be high when cross flow is possible (open doors and windows).•Natural ventilation in older buildings in colder climates is often inadequate.
Water interactions with polymers play an important role in nearly all aspects of life. Yet, precise understanding and quantification of such interactions at the molecular level is incomplete because ...many surface sensitive techniques lack the ability to operate under in situ conditions. To fill this gap, we applied tender ambient pressure X-ray photoelectron spectroscopy to study the effect of polymer functional groups, associated interaction types (polar vs ionic), and counterion types on water sorption. Experiments were carried out on model polymer systems of hydrophobic polystyrene, hydrophilic polyvinyl phenol, and charged polystyrene sulfonate thin films. Interaction of water vapor with these polymer surfaces was investigated in situ from ultra-high vacuum up to 100% relative humidity at room temperature. We showed directly at a molecular scale that water sorption is controlled by the polymer’s polar and charged groups. Additionally, counterion specific hydration mechanism on polyelectrolytes were revealed. Overall, these results provide mechanistic insights for the design of polymeric materials with improved properties.
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