Symmetry-Defying Iron Pyrite (FeS2) Nanocrystals through Oriented Attachment

A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author’s publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.Iron pyrite (fool's gold, FeS2) is a promising earth abundant and environmentally benign semiconductor material that shows promise as a strong and broad absorber for photovoltaics and high energy density cathode material for batteries. However, controlling FeS2 nanocrystal formation (composition, size, shape, stoichiometry, etc.) and defect mitigation still remains a challenge. These problems represent significant limitations in the ability to control electrical, optical and electrochemical properties to exploit pyrite's full potential for sustainable energy applications. Here, we report a symmetry-defying oriented attachment FeS2 nanocrystal growth by examining the nanostructure evolution and recrystallization to uncover how the shape, size and defects of FeS2 nanocrystals changes during growth. It is demonstrated that a well-controlled reaction temperature and annealing time results in polycrystal-to-monocrystal formation and defect annihilation, which correlates with the performance of photoresponse devices. This knowledge opens up a new tactic to address pyrite's known defect problems

Ionic-passivated FeS2 photocapacitors for energy conversion and storage

This is the publisher's version, also available electronically from http://pubs.rsc.org/en/Content/ArticleLanding/2013/CC/c3cc45088k#!divAbstrac

Charge-Transfer Induced Magnetic Field Effects of Nano-Carbon Heterojunctions

Room temperature magnetic field effects have not been definitively observed in either single-walled carbon nanotubes (SWCNTs) or C60 under a small magnetic field due to their weak hyperfine interaction and slight difference of g-factor between positive and negative polarons. Here, we demonstrate charge-transfer induced magnetic field effects in nano-carbon C60-SWCNT bulk heterojunctions at room temperature, where the mechanism of magnetic field effects is verified using excited state transition modeling. By controlling SWCNT concentrations and interfacial interactions, nano-carbon heterojunctions exhibit tunability of charge-transfer density and room temperature magnetoconductance of 2.8% under 100 mT external magnetic field. External stimuli, such as electric field and photoexcitation, also play an important role in controlling the magnetic field effects of nano-carbon heterojunctions, which suggests that these findings could enable the control of optoelectronic properties of nano-carbon heterojunctions.S.R. thanks the financial support from the Army Research Office - Young Investigator Award (W911NF-14-1-0443) for nanocarbon self-assembly and optoelectronics, and US Department of Energy award (DE-FG02-13ER46937) for organic magnetic study. M.C.H. acknowledges funding from the National Science Foundation (DMR-1006391). T.S. is supported by a National Science Foundation Graduate Research Fellowship and the ANSER Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award Number DE-SC0001059

Wrapping cytochrome c around single-wall carbon nanotube: engineered nanohybrid building blocks for infrared detection at high quantum efficiency

Biomolecule cytochrome c (Cty c), a small molecule of a chain of amino acids with extraordinary electron transport, was helically wrapped around a semiconductive single-wall carbon nanotube (s-SWCNT) to form a molecular building block for uncooled infrared detection with two uniquely designed functionalities: exciton dissociation to free charge carriers at the heterojunction formed on the s-SWCNT/Cty c interface and charge transport along the electron conducting chain of Cty c (acceptor) and hole conducting channel through s-SWCNT (donor). Such a design aims at addressing the long-standing challenges in exciton dissociation and charge transport in an SWCNT network, which have bottlenecked development of photonic SWCNT-based infrared detectors. Using these building blocks, uncooled s-SWCNT/Cyt c thin film infrared detectors were synthesized and shown to have extraordinary photoresponsivity up to 0.77 A W−1 due to a high external quantum efficiency (EQE) in exceeding 90%, which represents a more than two orders of magnitude enhancement than the best previously reported on CNT-based infrared detectors with EQE of only 1.72%. From a broad perspective, this work on novel s-SWCNT/Cyt c nanohybrid infrared detectors has developed a successful platform of engineered carbon nanotube/biomolecule building blocks with superior properties for optoelectronic applications.This work was supported by ARO contract No. ARO-W911NF-12-1-0412, and NSF contracts Nos. NSF-DMR-1105986 and NSF EPSCoR-0903806, and was matching supported by the State of Kansas through Kansas Technology Enterprise Corporation. S.R. thanks the financial support from the Army Research Office-Young Investigator Award (W911NF-14-1–0443) for nanocarbon study. We thank Melisa Xin and Dr. Tanya Simms for their assistance in fabrication of electrodes on devices and AFM characterization, respectively

Polychiral Semiconducting Carbon Nanotube–Fullerene Solar Cells

Single-walled carbon nanotubes (SWCNTs) have highly desirable attributes for solution-processable thin-film photovoltaics (TFPVs), such as broadband absorption, high carrier mobility, and environmental stability. However, previous TFPVs incorporating photoactive SWCNTs have utilized architectures that have limited current, voltage, and ultimately power conversion efficiency (PCE). Here, we report a solar cell geometry that maximizes photocurrent using polychiral SWCNTs while retaining high photovoltage, leading to record-high efficiency SWCNT–fullerene solar cells with average NREL certified and champion PCEs of 2.5% and 3.1%, respectively. Moreover, these cells show significant absorption in the near-infrared portion of the solar spectrum that is currently inaccessible by many leading TFPV technologies

Impact and mechanism of the “three rights separation” of agricultural land on the output efficiency of arable land in China：Based on the production factor perspective

[Objective] Improving the output efficiency of arable land is the core focus of ensuring national food security. The reform of “three rights separation” of agricultural land has significantly increased the enthusiasm of farmers for land management through empowerment, which inevitably has a significant impact on the output efficiency of arable land. The degree of influence and mechanisms involved deserve further investigation. [Methods] Based on the panel data from 146 prefecture-level cities in China from 2013 to 2021, this study first calculated the output efficiency of arable land using the data envelopment analysis (DEA)-Malmquist index method. It then employed a multi-period difference-in-differences test to examine the impact of the “three rights separation” of agricultural land on the output efficiency of arable land. Finally, by constructing a panel fixed effects model with interaction terms, it explored the mechanisms through which the “three rights separation” of agricultural land affects the output efficiency of arable land. [Results] The reform of the “three rights separation” of agricultural, significantly promoted the improvement of the output efficiency of arable land in China. This effect is also reinforced by legal clarity, and the results remains robust after conducting robustness tests such as placebo tests. Heterogeneity analysis revealed that the positive impact of the “three rights separation” of agricultural land on the output efficiency of arable land is more significant in the western region, northeastern region, groups with high per unit sown area planting industry output value, and groups with fiscal support for agriculture below the median level. Mechanism analysis found that the “three rights separation” of agricultural land mainly affects the output efficiency of arable land by weakening the impact of large-scale land management on the output efficiency of arable land and enhancing the impact of rural labor transfer on the output efficiency of arable land. [Conclusion] In the future, China should continue to deepen rural land system reform along the current path, further unleash the policy dividends of the “three rights separation” of agricultural land, and improve the efficiency of arable land resource utilization

Agricultural land management and rural financial development: coupling and coordinated relationship and temporal-spatial disparities in China

Abstract The integrated development of agricultural land and finance not only promotes rural financial innovation and breaks the bottleneck of agricultural financing but also facilitates agricultural land transfer and scaled operations. This leads to the advancement of the effective growth of contemporary agriculture. The reform of the 'separation of three rights' in agricultural land promotes land circulation, which, in turn, offers an institutional guarantee for the tandem development of rural finance and agricultural land management. This paper measures the comprehensive development index of agricultural land management and rural finance in 30 provinces of China from 2005 to 2020. In light of this, it calculates the degree of coupling and coordination between China's agricultural land management and rural financial development. The Dagum Gini coefficient, kernel density, and the Moran index were used to analyze regional differences and patterns of agglomeration. The study found that the degree of coupling coordination between China's agricultural land management and rural finance is increasing annually. However, there remains a significant gap in achieving high-quality coupling. Notably, the growth rate of rural financial development exceeds that of agricultural land management, and hypervariable density is a major source of regional variation. There is polarization in the coupled development of farmland management and rural finance. Provinces in the eastern and central regions tend to be located in the high–high agglomeration (H–H) in terms of the level of development of agricultural land and financial integration, while the western region tends to fall in low–low aggregation (L–L)

Phase Transformation-Induced Tetragonal FeCo Nanostructures

Tetragonal FeCo nanostructures are becoming particularly attractive because of their high magnetocrystalline anisotropy and magnetization achievable without rare-earth elements, . Yet, controlling their metastable structure, size and stoichiometry is a challenging task. In this study, we demonstrate AuCu templated FeCo shell growth followed by thermally induced phase transformation of AuCu core from face-centered cubic to L1₀ structure, which triggers the FeCo shell to transform from the body-centered cubic structure to a body-centered tetragonal phase. High coercivity, 846 Oe, and saturation magnetization, 221 emu/g, are achieved in this tetragonal FeCo structure. Beyond a critical FeCo shell thickness, confirmed experimentally and by lattice mismatch calculations, the FeCo shell relaxes. The shell thickness and stoichiometry dictate the magnetic characteristics of the tetragonal FeCo shell. This study provides a general route to utilize phase transformation to fabricate high performance metastable nanomagnets, which could open up their green energy applications

Synergistic Strain Engineering Effect of Hybrid Plasmonic, Catalytic, and Magnetic Core–Shell Nanocrystals

Hybrid core–shell nanocrystals, consisting of distinct components, represent an emerging functional material system, which could facilitate synergistic coupling effects via integrating drastically different functionalities. Here we report a unique strain engineering effect induced by phase transformation between plasmonic core and magnetic shell materials, which leads to a facile surface reconstruction of bimetallic core–shell nanocrystals to enhance their synergistic magnetic and catalytic properties. This advancement dramatically results in two orders of magnitude enhancement in magnetic coercivity and significant improvement in catalytic activity. Mechanistic studies involving the kinetic measurement and theoretical modeling uncover a structural distortion and surface rearrangement mechanism during the core–shell phase transformation pathway. This facile methodology could potentially open up the new design of multifunctional artificial hybrid nanostructures by the combination of phase transformation and surface engineering for emerging technological applications

Surface-Stress-Induced Phase Transformation of Ultrathin FeCo Nanowires

Ultrathin metal nanowires have attracted wide attention becau se oftheir unique anisotropy and surface-to-volume effects. In this study, we use ultrathin Au nanowires as the templating core to epitaxially grow magnetic iron–cobalt (FeCo) shell through metal-redox with the control on their thickness and stoichiometry. Large surface-stress-induced phase transformation in Au nanowires triggers and stabilizes metastable tetragonal FeCo nanostructure to enhance its magnetic anisotropy and coercivity. Meanwhile, under illumination, plasmon-induced hotspot in ultrathin Au nanowires enables the light-control on magnetic characteristics of FeCo shell. This study demonstrates the feasibility of surface-stress-induced phase transformation to stabilize and control metastable nanostructures for enhanced magnetic anisotropy, which is one of the key properties of functional magnetic materials