Real-Time Observation of Nanoscale Kink Band Mediated Plasticity in Ion-Irradiated Graphite: An In Situ TEM Study.

Graphite IG-110 is a synthetic polycrystalline material used as a neutron moderator in reactors. Graphite is inherently brittle and is known to exhibit a further increase in brittleness due to radiation damage at room temperature. To understand the irradiation effects on pre-existing defects and their overall influence on external load, micropillar compression tests were performed using in situ nanoindentation in the Transmission Electron Microscopy (TEM) for both pristine and ion-irradiated samples. While pristine specimens showed brittle and subsequent catastrophic failure, the 2.8 MeV Au2+ ion (fluence of 4.378 × 1014 cm-2) irradiated specimens sustained extensive plasticity at room temperature without failure. In situ TEM characterization showed nucleation of nanoscale kink band structures at numerous sites, where the localized plasticity appeared to close the defects and cracks while allowing large average strain. We propose that compressive mechanical stress due to dimensional change during ion irradiation transforms buckled basal layers in graphite into kink bands. The externally applied load during the micropillar tests proliferates the nucleation and motion of kink bands to accommodate the large plastic strain. The inherent non-uniformity of graphite microstructure promotes such strain localization, making kink bands the predominant mechanism behind unprecedented toughness in an otherwise brittle material.

Real-time insight into the multistage mechanism of nanoparticle exsolution from a perovskite host surface.

In exsolution, nanoparticles form by emerging from oxide hosts by application of redox driving forces, leading to transformative advances in stability, activity, and efficiency over deposition techniques, and resulting in a wide range of new opportunities for catalytic, energy and net-zero-related technologies. However, the mechanism of exsolved nanoparticle nucleation and perovskite structural evolution, has, to date, remained unclear. Herein, we shed light on this elusive process by following in real time Ir nanoparticle emergence from a SrTiO3 host oxide lattice, using in situ high-resolution electron microscopy in combination with computational simulations and machine learning analytics. We show that nucleation occurs via atom clustering, in tandem with host evolution, revealing the participation of surface defects and host lattice restructuring in trapping Ir atoms to initiate nanoparticle formation and growth. These insights provide a theoretical platform and practical recommendations to further the development of highly functional and broadly applicable exsolvable materials.

Negative Thermal Expansion HfV2O7 Nanostructures for Alleviation of Thermal Stress in Nanocomposite Coatings.

A primary mode of failure of thin-film coatings is the mismatch in thermal expansion coefficients of the substrate and the coating, which results in accumulation of interfacial stresses and ultimately in film delamination. While much attention has been devoted to modulation of interfacial bonding to mitigate delamination, current strategies are constrained in their generalizability and have had limited success in imbuing resistance to prolonged thermal cycling. We demonstrate here the incorporation of rigid thermal expansion compensators within polymeric films as a generalizable strategy for minimizing thermal mismatch with the substrate. Nanostructures of the isotropic negative thermal expansion (NTE) material HfV2O7 have been prepared based on the reaction of nanoparticulate precursors. The NTE behavior, derived from transverse oxygen displacement within the cubic structure, has been examined using temperature-variant powder X-ray diffraction, Raman spectroscopy, electron microscopy, and selected-area electron diffraction measurements. HfV2O7 initially crystallizes in a 3 × 3 × 3 superlattice but undergoes phase transformations to stabilize a cubic structure that exhibits strong and isotropic NTE with a coefficient of thermal expansion (CTE) = -6.7 × 10-6 °C-1 across an extended temperature range of 130-700 °C. Incorporation of HfV2O7 in a high-temperature thermoset polybenzimidazole enables the reduction of compressive stress by 67.3% for a relatively small loading of 26.6 vol % HfV2O7. Based on a composite model, we demonstrate that HfV2O7 can reduce the thermal expansion coefficient of polymer nanocomposite films, even at low volume fractions, as a result of its substantially higher elastic modulus compared to the continuous polymer matrix. By changing the volume fraction of HfV2O7, the overall coefficients of thermal expansion of the film can be tuned to match a range of substrates, thereby mitigating thermal stresses and resolving a fundamental challenge for high-temperature composites and nanocomposite coatings.

Examining the Effectiveness of Provider Incentives to Increase CRC Screening Uptake in Neighborhood Healthcare: A California Federally Qualified Health Center.

As an awardee of the Centers for Disease Control and Prevention's Colorectal Cancer Control Program, the California Department of Public Health partnered with Neighborhood Healthcare to implement evidence-based interventions and provider incentives (incentives offered to support staff, e.g., medical assistants, phlebotomists, front office staff, lab technicians) to improve colorectal cancer screening uptake. The objective of this study was to evaluate the effectiveness and cost of the provider incentive intervention implemented by Neighborhood Healthcare to increase colorectal cancer screening uptake. We collected and analyzed process and cost data to assess fecal immunochemical test (FIT) kit return rates to the health centers and the number of completed FIT kits. We estimated the costs of the preexisting interventions and the new interventions. Analyses were conducted for two time periods: preimplementation and implementation. Most Neighborhood Healthcare health centers experienced an increase in the percentage of FIT kit returns (average of 3.6 percentage points) and individuals screened (an average increase of 111 FIT kits per month) from the baseline period through the implementation period. The cost of the incentive intervention for each additional screen was $66.79. In conclusion, the results indicate that incentive programs can have an overall positive impact on both the percentage of FIT kits returned and the number of individuals screened.

Exsolution of Catalytically Active Iridium Nanoparticles from Strontium Titanate.

The search for new functional materials that combine high stability and efficiency with reasonable cost and ease of synthesis is critical for their use in renewable energy applications. Specifically in catalysis, nanoparticles, with their high surface-to-volume ratio, can overcome the cost implications associated with otherwise having to use large amounts of noble metals. However, commercialized materials, that is, catalytic nanoparticles deposited on oxide supports, often suffer from loss of activity because of coarsening and carbon deposition during operation. Exsolution has proven to be an interesting strategy to overcome such issues. Here, the controlled emergence, or exsolution, of faceted iridium nanoparticles from a doped SrTiO3 perovskite is reported and their growth preliminary probed by in situ electron microscopy. Upon reduction of SrIr0.005Ti0.995O3, the generated nanoparticles show embedding into the oxide support, therefore preventing agglomeration and subsequent catalyst degradation. The advantages of this approach are the extremely low noble metal amount employed (∼0.5% weight) and the catalytic activity reported during CO oxidation tests, where the performance of the exsolved SrIr0.005Ti0.995O3 is compared to the activity of a commercial catalyst with 1% loading (1% Ir/Al2O3). The high activity obtained with such low doping shows the possibility of scaling up this new catalyst, reducing the high cost associated with iridium-based materials.

Direct imaging of heteroatom dopants in catalytic carbon nano-onions.

The hollow core, concentric graphitic shells, and large surface area of the carbon nano-onion (CNO) make these carbon nanostructures promising materials for highly efficient catalytic reactions. Doping CNOs with heteroatoms is an effective method of changing their physical and chemical properties. In these cases, the configurations and locations of the incorporated dopant atoms must be a key factor dictating catalytic activity, yet determining a structural arrangement on the single-atom length scale is challenging. Here we present direct imaging of individual nitrogen and sulfur dopant atoms in CNOs, using an aberration-corrected scanning transmission electron microscopy (STEM) approach, combined with electron energy loss spectroscopy (EELS). Inspection of the statistics of dopant configuration and location in sulfur-, nitrogen-, and co-doped samples reveals dopant atoms to be more closely situated to defects in the graphitic shells for co-doped samples, than in their singly doped counterparts. Correlated with an increased activity for the oxygen reduction reaction in the co-doped samples, this suggests a concerted mechanism involving both the dopant and defect.

Epitaxial stabilization versus interdiffusion: synthetic routes to metastable cubic HfO2 and HfV2O7 from the core-shell arrangement of precursors.

Metastable materials that represent excursions from thermodynamic minima are characterized by distinctive structural motifs and electronic structure, which frequently underpins new function. The binary oxides of hafnium present a rich diversity of crystal structures and are of considerable technological importance given their high dielectric constants, refractory characteristics, radiation hardness, and anion conductivity; however, high-symmetry tetragonal and cubic polymorphs of HfO2 are accessible only at substantially elevated temperatures (1720 and 2600 °C, respectively). Here, we demonstrate that the core-shell arrangement of VO2 and amorphous HfO2 promotes outwards oxygen diffusion along an electropositivity gradient and yields an epitaxially matched V2O3/HfO2 interface that allows for the unprecedented stabilization of the metastable cubic polymorph of HfO2 under ambient conditions. Free-standing cubic HfO2, otherwise accessible only above 2600 °C, is stabilized by acid etching of the vanadium oxide core. In contrast, interdiffusion under oxidative conditions yields the negative thermal expansion material HfV2O7. Variable temperature powder X-ray diffraction demonstrate that the prepared HfV2O7 exhibits pronounced negative thermal expansion in the temperature range between 150 and 700 °C. The results demonstrate the potential of using epitaxial crystallographic relationships to facilitate preferential nucleation of otherwise inaccessible metastable compounds.

Shell-Induced Ostwald Ripening: Simultaneous Structure, Composition, and Morphology Transformations during the Creation of Hollow Iron Oxide Nanocapsules.

The creation of nanomaterials requires simultaneous control of not only crystalline structure and composition but also crystal shape and size, or morphology, which can pose a significant synthetic challenge. Approaches to address this challenge include creating nanocrystals whose morphologies echo their underlying crystal structures, such as the growth of platelets of two-dimensional layered crystal structures, or conversely attempting to decouple the morphology from structure by converting a structure or composition after first creating crystals with a desired morphology. A particularly elegant example of this latter approach involves the topotactic conversion of a nanoparticle from one structure and composition to another, since the orientation relationship between the initial and final product allows the crystallinity and orientation to be maintained throughout the process. Here we report a mechanism for creating hollow nanostructures, illustrated via the decomposition of ß-FeOOH nanorods to nanocapsules of α-Fe2O3, γ-Fe2O3, Fe3O4, and FeO, depending on the reaction conditions, while retaining single-crystallinity and the outer nanorod morphology. Using in situ TEM, we demonstrate that the nanostructured morphology of the starting material allows kinetic trapping of metastable phases with a topotactic relationship to the final thermodynamically stable phase.

Small media and client reminders for colorectal cancer screening: current use and gap areas in CDC's Colorectal Cancer Control Program.

INTRODUCTION: CDC's Colorectal Cancer Control Program (CRCCP) funds 25 states and 4 tribal organizations to promote and increase colorectal cancer screening population-wide. The CRCCP grantees must use evidence-based strategies from the Guide to Community Preventive Services, including small media and client reminders. METHODS: To assess the existing resources and needs to promote colorectal cancer screening, we conducted 2 web-based surveys of CRCCP grantees and their community partners. Survey 1 sought to identify priority populations, the number and quality of existing colorectal cancer resources for different population subgroups, and the types of small media and client reminder they were most interested in using. Survey 2 assessed screening messages that were used in the past or might be used in the future, needs for non-English-language information, and preferences for screening-related terminology. RESULTS: In survey 1 (n = 125 from 26 CRCCPs), most respondents (83%) indicated they currently had some information resources for promoting screening but were widely dissatisfied with the quality and number of these resources. They reported the greatest need for resources targeting rural populations (62% of respondents), men (53%), and Hispanics (45%). In survey 2 (n = 57 from 25 CRCCPs), respondents indicated they were most likely to promote colorectal cancer screening using messages that emphasized family (95%), role models (85%), or busy lives (83%), and least likely to use messages based on faith (26%), embarrassment (25%), or fear (22%). Nearly all (85%) indicated a need for resources in languages other than English; 16 different languages were mentioned, most commonly Spanish. CONCLUSION: These findings provide the first picture of CRCCP information resources and interests, and point to specific gaps that must be addressed to help increase screening.

Young persons' access to genitourinary medicine clinics in the UK: a cross-sectional survey.

STUDY DESIGN: This service evaluation of genitourinary medicine (GUM) clinics in the UK was designed to quantify access for young people requesting to be seen and to establish whether they could be seen outside school hours. METHODS: In December 2009 postal questionnaires were sent to all lead clinicians in UK GUM clinics asking when they expected a young person would be offered an appointment and whether it could be outside school hours. Between January and March 2010 trained male and female medical students posing as 16 year olds telephoned all GUM clinics listed on the British Association for Sexual Health and HIV website with symptomatic and asymptomatic scenarios and requested an appointment after school hours. RESULTS: 99% of the 152 responding clinicians estimated that an appointment would be offered within 48 h for both male and female contacts and over 90% could be seen outside school hours whether symptomatic or not. Of the 666 clinic telephone contacts, 88% were offered an appointment within two working days, and 66% were offered an after school appointment within 2 days. There was no significant difference whether the 'patient' was symptomatic or not (87% vs 86%, respectively, p=0.784) in being offered an appointment within two working days. There was variation between countries, with England performing significantly better; 94% were offered an appointment within 2 days versus 58%, 55% and 67% for Wales, Scotland and Northern Ireland, respectively. CONCLUSION: The findings would support the impact and value of process targets on service delivery.

Catalyzing community action within a national campaign: VERB community and national partnerships.

The VERB campaign used a social marketing approach to deliver its message through the mass media, school and community promotions, and partnerships to encourage children aged 9-13 years (tweens) to be physically active every day. This paper presents the VERB campaign's community and national partnership strategy, highlights three successful partnerships, and discusses challenges associated with the efforts. The national advertising generated awareness of and affinity for the product's brand and motivated the primary audience to seek out the product. The campaign's national and community partners were engaged to facilitate a product-distribution channel. The campaign developed a three-pronged partnership strategy to integrate the promotion with the placement of the campaign's product (physical activity): (1) reframe the way physical activity is positioned and delivered; (2) connect the brand to the point-of-purchase; and (3) refer (or drive) the audience to the action outlets, opportunities, places, spaces and programs to purchase the product. The VERB campaign provided partners with marketing training and resources to assist them as they leveraged tweens' brand awareness and supported regular physical activity among tweens. The method of technical assistance and the types of marketing tools were provided in relationship to four characteristics of the partner: (1) partner's network, (2) leaders and champions in the network, (3) partner's financial resources for community campaigns; and (4) partner's understanding of the marketing mindset. Coordinated, collaborative, and strong mass-media and community-based interventions within a national social marketing campaign can sustain the immediate effects of such campaigns.