Highly Stable Luminous "snakes" from CsPbX3 Perovskite Nanocrystals Anchored on Amine-Coated Silica Nanowires

CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) are known for their exceptional optoelectronic properties, yet the material's instability toward polar solvents, heat, or UV irradiation greatly limits its further applications. Herein, an efficient in situ growing strategy has been developed to give highly stable perovskite NC composites (abbreviated CsPbX3@CA-SiO2) by anchoring CsPbX3 NCs onto silica nanowires (NWs), which effectively depresses the optical degradation of their photoluminescence (PL) and enhances stability. The preparation of surface-functionalized serpentine silica NWs is realized by a sol-gel process involving hydrolysis of a mixture of tetraethyl orthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES), and trimethoxy(octadecyl)silane (TMODS) in a water/oil emulsion. The serpentine NWs are formed via an anisotropic growth with lengths up to 8 μm. The free amino groups are employed as surface ligands for growing perovskite NCs, yielding distributed monodisperse NCs (∼8 nm) around the NW matrix. The emission wavelength is tunable by simple variation of the halide compositions (CsPbX3, X = Cl, Br, or I), and the composites demonstrate a high photoluminescence quantum yield (PLQY 32-69%). Additionally, we have demonstrated the composites CsPbX3@CA-SiO2 can be self-woven to form a porous 3D hierarchical NWs membrane, giving rise to a superhydrophobic surface with hierarchical micro/nano structural features. The resulting composites exhibit high stability toward water, heat, and UV irradiation. This work elucidates an effective strategy to incorporate perovskite nanocrystals onto functional matrices as multifunctional stable light sources

Nanorod Suprastructures from a Ternary Graphene Oxide-Polymer-CsPbX3 Perovskite Nanocrystal Composite That Display High Environmental Stability.

Despite the exceptional optoelectronic characteristics of the emergent perovskite nanocrystals, the ionic nature greatly limits their stability, and thus restricts their potential applications. Here we have adapted a self-assembly strategy to access a rarely reported nanorod suprastructure that provide excellent encapsulation of perovskite nanocrystals by polymer-grafted graphene oxide layers. Polyacrylic acid-grafted graphene oxide (GO-g-PAA) was used as a surface ligand during the synthesis of the CsPbX3 perovskite nanocrystals (NCs), yielding particles (5-12 nm) with tunable halide compositions that were homogeneously embedded in the GO-g-PAA matrix. The resulting NC-GO-g-PAA exhibits a higher photoluminescence quantum yield than previously reported encapsulated NCs while maintaining an easily tunable bandgap, allowing for emission spanning the visible spectrum. The NC-GO-g-PAA hybrid further self-assembles into well-defined nanorods upon solvent treatment. The resulting nanorod morphology imparts extraordinary chemical stability toward protic solvents such as methanol and water and much enhanced thermal stability. The introduction of barrier layers by embedding the perovskite NCs in the GO-g-PAA matrix, together with its unique assembly into nanorods, provides a novel strategy to afford robust perovskite emissive materials with environmental stability that may meet or exceed the requirement for optoelectronic applications

Making Meaning Together: The role of interpretation during a short-term nature excursion

Interpretive nature walks are an important tool for conservation organizations, which use them to educate, and to connect visitors with their sites. Interpretive studies often focus on program outcomes. However, less research exists on how the experience itself is perceived by visitors. Is it primarily a learning process? What role does the guide play, and how does the process of interpretation affect the visitor experience? What implications might this have for interpretive techniques, and for organizations seeking to build supportive stewardship communities? The purpose of this study was to explore how the process of interpretation affects a short-term nature experience by examining it through the lens of both visitor and guide. I accompanied nature walks on Cape Cod, Massachusetts, USA, and subsequently conducted semi-structured interviews with guides and visitors. This provided a trifold perspective on each trip, enabling an examination of the trip as observed by the researcher, and as perceived by both visitor and guide. Learning was an important part of the experience, as expected. However, interviews revealed that a major aspect of a trip is social. A large proportion of respondent narrative was devoted to social observations: about group dynamics; the sharing of knowledge, experience, and personal history; social norms; and the guide’s social aptitude. Information transfer did not always originate with the guide, but resulted from visitor-to-visitor interaction. Visitors learned from each other by comparing past experiences, speculating about observations, and generating questions for the guide. Thus, in addition to receiving knowledge delivered by the guide, visitors were engaged in active, constructive social learning and building and reinforcing common interests. At the same time, they were reinforcing a common identity as members of a particular social “tribe.” Guided nature walks are thus revealed as a social forum for constructive learning. Visitors are not merely passive recipients of knowledge, but active participants in a social learning experience. This discovery has implications for the role of interpreters, their selection, and training. It also offers an opportunity for organizations to use this social aspect as leverage for community-building and development of a stewardship identity among visitors

Making Meaning Together: The role of interpretation during a short-term nature excursion

Interpretive nature walks are an important tool for conservation organizations, which use them to educate, and to connect visitors with their sites. Interpretive studies often focus on program outcomes. However, less research exists on how the experience itself is perceived by visitors. Is it primarily a learning process? What role does the guide play, and how does the process of interpretation affect the visitor experience? What implications might this have for interpretive techniques, and for organizations seeking to build supportive stewardship communities? The purpose of this study was to explore how the process of interpretation affects a short-term nature experience by examining it through the lens of both visitor and guide. I accompanied nature walks on Cape Cod, Massachusetts, USA, and subsequently conducted semi-structured interviews with guides and visitors. This provided a trifold perspective on each trip, enabling an examination of the trip as observed by the researcher, and as perceived by both visitor and guide. Learning was an important part of the experience, as expected. However, interviews revealed that a major aspect of a trip is social. A large proportion of respondent narrative was devoted to social observations: about group dynamics; the sharing of knowledge, experience, and personal history; social norms; and the guide’s social aptitude. Information transfer did not always originate with the guide, but resulted from visitor-to-visitor interaction. Visitors learned from each other by comparing past experiences, speculating about observations, and generating questions for the guide. Thus, in addition to receiving knowledge delivered by the guide, visitors were engaged in active, constructive social learning and building and reinforcing common interests. At the same time, they were reinforcing a common identity as members of a particular social “tribe.” Guided nature walks are thus revealed as a social forum for constructive learning. Visitors are not merely passive recipients of knowledge, but active participants in a social learning experience. This discovery has implications for the role of interpreters, their selection, and training. It also offers an opportunity for organizations to use this social aspect as leverage for community-building and development of a stewardship identity among visitors

Long-Range Exciton Diffusion in Two-Dimensional Assemblies of Cesium Lead Bromide Perovskite Nanocrystals

F\"orster Resonant Energy Transfer (FRET)-mediated exciton diffusion through artificial nanoscale building block assemblies could be used as a new optoelectronic design element to transport energy. However, so far nanocrystal (NC) systems supported only diffusion length of 30 nm, which are too small to be useful in devices. Here, we demonstrate a FRET-mediated exciton diffusion length of 200 nm with 0.5 cm2/s diffusivity through an ordered, two-dimensional assembly of cesium lead bromide perovskite nanocrystals (PNC). Exciton diffusion was directly measured via steady-state and time-resolved photoluminescence (PL) microscopy, with physical modeling providing deeper insight into the transport process. This exceptionally efficient exciton transport is facilitated by PNCs high PL quantum yield, large absorption cross-section, and high polarizability, together with minimal energetic and geometric disorder of the assembly. This FRET-mediated exciton diffusion length matches perovskites optical absorption depth, opening the possibility to design new optoelectronic device architectures with improved performances, and providing insight into the high conversion efficiencies of PNC-based optoelectronic devices

Inequality of Deservingness

This Essay explores how the U.S. tax system—the primary mechanism for distributing antipoverty cash benefits—is poorly suited to evaluating recipients’ deservingness. In doing so, it defines and formalizes the concept of inequality of deservingness, which is dyadic in nature. The first form of such inequality is that of “true deservingness.” True deservingness is somewhat abstract, arising from the distributive justice frameworks that underlie antipoverty program design in the United States. In Part II, the Essay briefly describes the major federal U.S. antipoverty programs, which mostly target support to families with children, people with disabilities, and workers. Working backwards, I then deduce various distributive justice norms that serve as organizing principles for U.S. antipoverty policy. These norms rest on notions of faultlessness, reciprocity, and work effort. The Essay does not defend these norms, but merely identifies them. Inequality of true deservingness refers to the fact that some people are considered deserving of support under these various norms, while others are not. The second form of inequality of deservingness that this Essay considers is that of deservingness as determined by the public benefit system, which I call “deemed deservingness.” Focusing on tax-administered benefits, Part III starts by describing the information that a Form 1040 Individual Income Tax Return gathers about households. This information is necessarily limited; the tax return must be as simple as possible to ease filing for most taxpayers. For instance, while a taxpayer can show whether they are working—which is required to receive the EITC—those who are not working cannot explain why they are not working. Some individuals will thus be deemed deserving or undeserving without being able to provide full context for their actions. As Part III explains, true deservingness and deemed deservingness will not always align. To provide greater texture to this discussion, I describe several taxpayers’ stories based on my former legal aid clients who were excluded from cash antipoverty support. These stories are anonymized, slightly altered amalgams of several clients I represented while directing the low-income taxpayer clinic at Bet Tzedek Legal Service in Los Angeles. Inequality of deservingness is not inherently problematic. Antipoverty programs often draw reasonable boundaries in order to incentivize certain behaviors, limit costs, and encourage public support. It is the incongruity of true deservingness and deemed deservingness that leads to negative outcomes, including unprincipled exclusion of “deserving” individuals, misaligned behavioral incentives, and reduced public support for antipoverty programs. The Essay ends by briefly considering whether reform is necessary and discussing several alternative antipoverty program designs. I conclude that the tax system is ill-equipped to provide inclusive benefits to all people who fit deservingness norms. Policymakers should therefore expand non-tax antipoverty programs to ensure that diverse programs exist to cover the complex scenarios under which households might need support. In addition to federal non-tax programs, I explore several local program models capable of addressing highly individualized needs. The Essay proceeds as follows. Part II describes the major federal antipoverty programs in the United States and deduces the deservingness norms that underlie their eligibility boundaries. It focuses on antipoverty programs administered through the tax system, as these are the largest means-tested cash transfer programs in the United States. Part III describes who is deemed deserving under the tax system and explores how this deemed deservingness fails to align perfectly with the deservingness norms described in Part II. Part IV finishes by discussing the possible negative consequences of such misalignment and considering several policy responses