Publications by authors named "Tae Hee Han"

161 Publications

Highly Electroconductive and Mechanically Strong TiCT MXene Fibers Using a Deformable MXene Gel.

ACS Nano 2021 Feb 26;15(2):3320-3329. Epub 2021 Jan 26.

Department of Organic and Nano Engineering, Hanyang University, Seoul, 04763, Republic of Korea.

Self-assembly of two-dimensional MXene sheets is used in various fields to create multiscale structures due to their electrical, mechanical, and chemical properties. In principle, MXene nanosheets are assembled by molecular interactions, including hydrogen bonds, electrostatic interactions, and van der Waals forces. This study describes how MXene colloid nanosheets can form self-supporting MXene hydrogels. Three-dimensional network structures of MXene gels are strengthened by reinforced electrostatic interactions between nanosheets. Stable gel networks are beneficial for fabricating highly aligned fibers because MXene gel can endure structural deformation. During wet spinning of highly concentrated MXene colloids in a coagulation bath, MXene sheets can be transformed into perfectly aligned fibers under a mechanical drawing force. Oriented MXene fibers exhibit a 1.5-fold increase in electrical conductivity (12 504 S cm) and Young's modulus (122 GPa) compared with other fibers. The oriented MXene fibers are expected to have widespread applications, including electrical wiring and signal transmission.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsnano.0c10255DOI Listing
February 2021

Carbon nanotube-reduced graphene oxide fiber with high torsional strength from rheological hierarchy control.

Nat Commun 2021 01 15;12(1):396. Epub 2021 Jan 15.

Department of Organic and Nano Engineering, Hanyang University, Seoul, 04763, Republic of Korea.

High torsional strength fibers are of practical interest for applications such as artificial muscles, electric generators, and actuators. Herein, we maximize torsional strength by understanding, measuring, and overcoming rheological thresholds of nanocarbon (nanotube/graphene oxide) dopes. The formed fibers show enhanced structure across multiple length scales, modified hierarchy, and improved mechanical properties. In particular, the torsional properties were examined, with high shear strength (914 MPa) attributed to nanotubes but magnified by their structure, intercalating graphene sheets. This design approach has the potential to realize the hierarchical dimensional hybrids, and may also be useful to build the effective network structure of heterogeneous materials.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-20518-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7810860PMC
January 2021

Licochalcone A inhibits hypoxia-inducible factor-1α accumulation by suppressing mitochondrial respiration in hypoxic cancer cells.

Biomed Pharmacother 2021 Jan 4;133:111082. Epub 2020 Dec 4.

Korea Research Institute of Bioscience and Biotechnology, Daejeon, 34141, South Korea. Electronic address:

Hypoxia-inducible factor (HIF)-1 is an important regulator of the cellular response in the hypoxic tumor environment. While searching for HIF inhibitors derived from natural products that act as anticancer agents, we found that Glycyrrhiza uralensis exerts HIF-1 inhibitory activity in hypoxic cancer cells. Among the five components of G. uralensis, licochalcone A was found to potently suppress hypoxia-induced HIF-1α accumulation and expression of HIF-1α target genes, including GLUT1 and PDK1 in HCT116 cells. Licochalcone A also enhances intracellular oxygen content by directly inhibiting mitochondrial respiration, resulting in oxygen-dependent HIF-1α degradation. Hence, licochalcone A may effectively inhibit ATP production, primarily by reducing the mitochondrial respiration-mediated ATP production rate rather than the glycolysis-mediated ATP production rate. This effect subsequently suppresses cancer cell viability, including that of HCT116, H1299, and H322 cells. Consequently, these results suggest that licochalcone A has therapeutic potential in hypoxic cancer cells.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.biopha.2020.111082DOI Listing
January 2021

Molecular Interaction Regulates the Performance and Longevity of Defect Passivation for Metal Halide Perovskite Solar Cells.

J Am Chem Soc 2020 Nov 16;142(47):20071-20079. Epub 2020 Nov 16.

National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences, School of Physics, and Jiangsu Key Laboratory of Artificial Functional Materials, Nanjing University, Nanjing 210093, China.

Defect passivation constitutes one of the most commonly used strategies to fabricate highly efficient perovskite solar cells (PSCs). However, the durability of the passivation effects under harsh operational conditions has not been extensively studied regardless of the weak and vulnerable secondary bonding between the molecular passivation agents and perovskite crystals. Here, we incorporated strategically designed passivating agents to investigate the effect of their interaction energies on the perovskite crystals and correlated these with the performance and longevity of the passivation effects. We unraveled that the passivation agents with a stronger interaction energy are advantageous not only for effective defect passivation but also to suppress defect migration. The prototypical PSCs treated with the optimal passivation agent exhibited superior performance and operational stability, retaining 81.9 and 85.3% of their initial performance under continuous illumination or nitrogen at 85 °C after 1008 h, respectively, while the reference device completely degraded during that time. This work provides important insights into designing operationally durable defect passivation agents for perovskite optoelectronic devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.0c09560DOI Listing
November 2020

Author Correction: Solid-phase hetero epitaxial growth of α-phase formamidinium perovskite.

Nat Commun 2020 Nov 12;11(1):5880. Epub 2020 Nov 12.

Department of Materials Science and Engineering, California NanoSystems Institute, University of California, Los Angeles, CA, 90095, USA.

A Correction to this paper has been published: https://doi.org/10.1038/s41467-020-19846-y .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-19846-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7661531PMC
November 2020

Solid-phase hetero epitaxial growth of α-phase formamidinium perovskite.

Nat Commun 2020 Nov 2;11(1):5514. Epub 2020 Nov 2.

Department of Materials Science and Engineering, California NanoSystems Institute, University of California, Los Angeles, CA, 90095, USA.

Conventional epitaxy of semiconductor films requires a compatible single crystalline substrate and precisely controlled growth conditions, which limit the price competitiveness and versatility of the process. We demonstrate substrate-tolerant nano-heteroepitaxy (NHE) of high-quality formamidinium-lead-tri-iodide (FAPbI) perovskite films. The layered perovskite templates the solid-state phase conversion of FAPbI from its hexagonal non-perovskite phase to the cubic perovskite polymorph, where the growth kinetics are controlled by a synergistic effect between strain and entropy. The slow heteroepitaxial crystal growth enlarged the perovskite crystals by 10-fold with a reduced defect density and strong preferred orientation. This NHE is readily applicable to various substrates used for devices. The proof-of-concept solar cell and light-emitting diode devices based on the NHE-FAPbI showed efficiencies and stabilities superior to those of devices fabricated without NHE.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-19237-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7608657PMC
November 2020

Rheological Investigation of Relaxation Behavior of Polycarbonate/Acrylonitrile-Butadiene-Styrene Blends.

Polymers (Basel) 2020 Aug 25;12(9). Epub 2020 Aug 25.

Department of Organic and Nano Engineering, Hanyang University, Seoul 04763, Korea.

The rheological properties of polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blends with various blend ratios are investigated at different temperatures to determine the shear dependent chain motions in a heterogeneous blend system. At low frequency levels under 0.1 rad/s, the viscosity of the material with a blend ratio of 3:7 (PC:ABS) is higher than that of pure ABS polymer. As the temperature increases, the viscosities of ABS-rich blends increase rather than decrease, whereas PC-rich blends exhibit decrease in viscosity. Results from the time sweep measurements indicate that ordered structures of PC and the formation and breakdown of internal network structures of ABS polymer occur simultaneously in the blend systems. Newly designed sequence test results show that the internal structures formed between PC and ABS polymers are dominant at low shear conditions for the blend ratio of 3:7 and effects of structural change and the presence of polybutadiene (PBD) become dominant at high shear conditions for pure ABS. The results of yield stress and relaxation time for PC/ABS blends support this phenomenon. The specimen with a blend ratio of 3:7 exhibited the highest value of yield stress at high temperature among others, which implies that the internal structure become stronger at higher temperature. The heterogeneity of ABS-rich blends increases whereas that of PC-rich blends decreases as temperature increases.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/polym12091916DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7563493PMC
August 2020

Selective Disruption of Synaptic BMP Signaling by a Smad Mutation Adjacent to the Highly Conserved H2 Helix.

Genetics 2020 Sep 31;216(1):159-175. Epub 2020 Jul 31.

Section on Cellular Communication, Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892

Bone morphogenetic proteins (BMPs) shape normal development and function via canonical and noncanonical signaling pathways. BMPs initiate canonical signaling by binding to transmembrane receptors that phosphorylate Smad proteins and induce their translocation into the nucleus and regulation of target genes. Phosphorylated Smads also accumulate at cellular junctions, but this noncanonical, local BMP signaling modality remains less defined. We have recently reported that phosphorylated Smad (pMad in ) accumulates at synaptic junctions in protein complexes with genetically distinct composition and regulation. Here, we examined a wide collection of alleles and searched for molecular features relevant to pMad accumulation at synaptic junctions. We found that strong alleles generally disrupt both synaptic and nuclear pMad, whereas moderate alleles have a wider range of phenotypes and can selectively impact different BMP signaling pathways. Interestingly, regulatory mutations reveal that synaptic pMad appears to be more sensitive to a net reduction in Mad levels than nuclear pMad. Importantly, a previously uncharacterized allele, , showed markedly reduced synaptic pMad but only moderately diminished nuclear pMad. The postsynaptic composition and electrophysiological properties of neuromuscular junctions (NMJs) were also altered. Using biochemical approaches, we examined how a single point mutation in could influence the Mad-receptor interface and identified a key motif, the H2 helix. Our study highlights the biological relevance of Smad-dependent, synaptic BMP signaling and uncovers a highly conserved structural feature of Smads, critical for normal development and function.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1534/genetics.120.303484DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7463279PMC
September 2020

Neto-α Controls Synapse Organization and Homeostasis at the Drosophila Neuromuscular Junction.

Cell Rep 2020 07;32(1):107866

Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD, USA. Electronic address:

Glutamate receptor auxiliary proteins control receptor distribution and function, ultimately controlling synapse assembly, maturation, and plasticity. At the Drosophila neuromuscular junction (NMJ), a synapse with both pre- and postsynaptic kainate-type glutamate receptors (KARs), we show that the auxiliary protein Neto evolved functionally distinct isoforms to modulate synapse development and homeostasis. Using genetics, cell biology, and electrophysiology, we demonstrate that Neto-α functions on both sides of the NMJ. In muscle, Neto-α limits the size of the postsynaptic receptor field. In motor neurons (MNs), Neto-α controls neurotransmitter release in a KAR-dependent manner. In addition, Neto-α is both required and sufficient for the presynaptic increase in neurotransmitter release in response to reduced postsynaptic sensitivity. This KAR-independent function of Neto-α is involved in activity-induced cytomatrix remodeling. We propose that Drosophila ensures NMJ functionality by acquiring two Neto isoforms with differential expression patterns and activities.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2020.107866DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7484471PMC
July 2020

Large-scale wet-spinning of highly electroconductive MXene fibers.

Nat Commun 2020 Jun 4;11(1):2825. Epub 2020 Jun 4.

Department of Organic and Nano Engineering, Hanyang University, Seoul, 04763, Republic of Korea.

TiCT MXene is an emerging class of two-dimensional nanomaterials with exceptional electroconductivity and electrochemical properties, and is promising in the manufacturing of multifunctional macroscopic materials and nanomaterials. Herein, we develop a straightforward, continuously controlled, additive/binder-free method to fabricate pure MXene fibers via a large-scale wet-spinning assembly. Our MXene sheets (with an average lateral size of 5.11 μm) are highly concentrated in water and do not form aggregates or undergo phase separation. Introducing ammonium ions during the coagulation process successfully assembles MXene sheets into flexible, meter-long fibers with very high electrical conductivity (7,713 S cm). The fabricated MXene fibers are comprehensively integrated by using them in electrical wires to switch on a light-emitting diode light and transmit electrical signals to earphones to demonstrate their application in electrical devices. Our wet-spinning strategy provides an approach for continuous mass production of MXene fibers for high-performance, next-generation, and wearable electronic devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-16671-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7272396PMC
June 2020

Efficient Flexible Inorganic Perovskite Light-Emitting Diodes Fabricated with CsPbBr Emitters Prepared via Low-Temperature in Situ Dynamic Thermal Crystallization.

Nano Lett 2020 Jun 26;20(6):4673-4680. Epub 2020 May 26.

Department of Materials Science and Engineering, and California Nano Systems Institute, University of California, Los Angeles, California 90095, United States.

The present study systematically investigates the morphology and crystallization process of inorganic CsPbBr perovskite layer films fabricated by thermal coevaporation in conjunction with continuous low-temperature thermal annealing to promote in situ dynamic thermal crystallization. The results confirm for the first time that both the crystal grain size and the compactness of the CsPbBr films can be tuned during the thermal coevaporation fabrication process via in situ dynamic thermal crystallization. The performance of the PeLEDs employing the CsPbBr films as the emitter layer is investigated in detail with respect to the substrate temperature and deposition rate employed during deposition of the CsPbBr film. This study provides guidelines for developing suitable film production processes and highlights future challenges that must be addressed to facilitate the commercial development of large-area, uniform, and flexible perovskite-based optoelectronic devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.nanolett.0c01550DOI Listing
June 2020

Super-Expansion of Assembled Reduced Graphene Oxide Interlayers by Segregation of Al Nanoparticle Pillars for High-Capacity Na-Ion Battery Anodes.

ACS Appl Mater Interfaces 2020 May 14;12(21):23781-23788. Epub 2020 May 14.

Department of Chemical and Biological Engineering, Sookmyung Women's University, 100 Cheongpa-ro 47-gil, Yongsan-gu, Seoul 04310, Republic of Korea.

The applicability of Na-ion batteries is contingent on breakthroughs in alternative electrode materials that have high capacities and which are economically viable. Unfortunately, conventional graphite anodes for Li-ion battery systems do not allow Na-ion accommodation into their interlayer space owing to the large ionic radius and low stabilizing energy of Na in graphite. Here, we suggest a promising strategy for significantly increasing Na capacity by expanding the axial slab space of graphite. We successfully synthesized reconstructed graphite materials via self-assembly of negative graphite oxide (GO) flakes and Al cation (positive) pillars and by subsequent chemical reaction of the obtained Al-GO materials. Al pillars, atomically distributed in graphite interlayers, can extend the slab space by up to ∼7 Å, which is a 2-fold interlayer distance of pristine graphite. An exceptionally high capacity of 780 mAh/g is demonstrated for reconstructed graphite anodes with Al pillars, compared with rGO materials (210 mAh/g). We investigated the electrochemical reaction mechanism and structural changes associated with discharge and charge to emphasize the benefit of using reconstructed graphite as anodes in Na-ion batteries. Our strategy of modifying the interlayer distance by introducing metallic pillars between the layers can help address the low capacity of carbonaceous anodes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.0c00659DOI Listing
May 2020

A 2D Titanium Carbide MXene Flexible Electrode for High-Efficiency Light-Emitting Diodes.

Adv Mater 2020 Jun 30;32(23):e2000919. Epub 2020 Apr 30.

Department of Materials Science and Engineering, Institute of Engineering Research, Research Institute of Advanced Materials, BK21 PLUS SNU Materials Division for Educating Creative Global Leaders, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea.

Although several transparent conducting materials such as carbon nanotubes, graphene, and conducting polymers have been intensively explored as flexible electrodes in optoelectronic devices, their insufficient electrical conductivity, low work function, and complicated electrode fabrication processes have limited their practical use. Herein, a 2D titanium carbide (Ti C ) MXene film with transparent conducting electrode (TCE) properties, including high electrical conductivity (≈11 670 S cm ) and high work function (≈5.1 eV), which are achieved by combining a simple solution processing with modulation of surface composition, is described. A chemical neutralization strategy of a conducting-polymer hole-injection layer is used to prevent detrimental surface oxidation and resulting degradation of the electrode film. Use of the MXene electrode in an organic light-emitting diode leads to a current efficiency of ≈102.0 cd A and an external quantum efficiency of ≈28.5% ph/el, which agree well with the theoretical maximum values from optical simulations. The results demonstrate the strong potential of MXene as a solution-processable electrode in optoelectronic devices and provide a guideline for use of MXenes as TCEs in low-cost flexible optoelectronic devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.202000919DOI Listing
June 2020

PLGA Microspheres with Alginate-Coated Large Pores for the Formulation of an Injectable Depot of Donepezil Hydrochloride.

Pharmaceutics 2020 Apr 1;12(4). Epub 2020 Apr 1.

College of Pharmacy, Chung-Ang University, Seoul 06974, Korea.

As the main symptom of Alzheimer's disease-related dementia is memory loss, patient compliance for donepezil hydrochloride (donepezil), administered as once-daily oral formulations, is poor. Thus, we aimed to design poly(lactic--glycolic acid) (PLGA) microspheres (MS) with alginate-coated large pores as an injectable depot of donepezil exhibiting sustained release over 2-3 weeks. The PLGA MS with large pores could provide large space for loading drugs with high loading capacity, and thereby sufficient amounts of drugs were considered to be delivered with minimal use of PLGA MS being injected. However, initial burst release of donepezil from the porous PLGA MS was observed. To reduce this initial burst release, the surface pores were closed with calcium alginate coating using a spray-ionotropic gelation method. The final pore-closed PLGA MS showed in vitro sustained release for approximately 3 weeks, and the initial burst release was remarkably decreased by the calcium alginate coating. In the prediction of plasma drug concentration profiles using convolution method, the mean residence time of the pore-closed PLGA MS was 2.7-fold longer than that of the porous PLGA MS. Therefore, our results reveal that our pore-closed PLGA MS formulation is a promising candidate for the treatment of dementia with high patient compliance.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/pharmaceutics12040311DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7238133PMC
April 2020

Hybrid Integrated Photomedical Devices for Wearable Vital Sign Tracking.

ACS Sens 2020 06 13;5(6):1582-1588. Epub 2020 Apr 13.

Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States.

In light of the importance of and challenges inherent in realizing a wearable healthcare platform for simultaneously recognizing, preventing, and treating diseases while tracking vital signs, the development of simple and customized functional devices has been required. Here, we suggest a new approach for making a stretchable light waveguide which can be combined with integrated functional devices, such as organic photodetectors (PDs) and nanowire-based heaters, for multifunctional healthcare monitoring. Controlling the reflection condition of the medium gave a solid design rule for strong light emission in our stretchable waveguides. Based on this rule, the stretchable light waveguide (up to 50% strain) made of polydimethylsiloxane was successfully demonstrated with strong emissions. We also incorporated highly sensitive organic PDs and silver nanowire-based heaters with the stretchable waveguide for the detection of vital signs, including the heart rate, deep breathing, coughs, and blood oxygen saturation. Through these multifunctional performances, we have successfully demonstrated that our stretchable light waveguide has a strong potential for multifunctional healthcare monitoring.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acssensors.9b02529DOI Listing
June 2020

A Polymerization-Assisted Grain Growth Strategy for Efficient and Stable Perovskite Solar Cells.

Adv Mater 2020 Apr 8;32(17):e1907769. Epub 2020 Mar 8.

Department of Materials Science and Engineering and California Nano Systems Institute, University of California, Los Angeles, CA, 90095, USA.

Intrinsically, detrimental defects accumulating at the surface and grain boundaries limit both the performance and stability of perovskite solar cells. Small molecules and bulkier polymers with functional groups are utilized to passivate these ionic defects but usually suffer from volatility and precipitation issues, respectively. Here, starting from the addition of small monomers in the PbI precursor, a polymerization-assisted grain growth strategy is introduced in the sequential deposition method. With a polymerization process triggered during the PbI film annealing, the bulkier polymers formed will be adhered to the grain boundaries, retaining the previously established interactions with PbI . After perovskite formation, the polymers anchored on the boundaries can effectively passivate undercoordinated lead ions and reduce the defect density. As a result, a champion power conversion efficiency (PCE) of 23.0% is obtained, together with a prolonged lifetime where 85.7% and 91.8% of the initial PCE remain after 504 h continuous illumination and 2208 h shelf storage, respectively.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201907769DOI Listing
April 2020

Emergence of NDM-4 and OXA-181 carbapenemase-producing Klebsiella pneumoniae.

J Glob Antimicrob Resist 2020 03 13;20:332-333. Epub 2020 Feb 13.

Infectious Diseases Team, Seoul Metropolitan Government Research Institute of Public Health and Environment, Gyeonggi-do, Republic of Korea.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jgar.2020.01.020DOI Listing
March 2020

Room-Temperature, Highly Durable TiCT MXene/Graphene Hybrid Fibers for NH Gas Sensing.

ACS Appl Mater Interfaces 2020 Mar 20;12(9):10434-10442. Epub 2020 Feb 20.

Department of Organic and Nano Engineering, Hanyang University, Seoul, 04763, Republic of Korea.

Graphene-based fibers (GFs) have aroused enormous interest in portable, wearable electronics because of their excellent mechanical flexibility, electrical conductivity, and weavability, which make them advantageous for wearable electronic devices. Herein, we report the development of metal binder-free TiCT MXene/graphene hybrid fibers by a scalable wet-spinning process. These hybrid fibers exhibit excellent mechanical and electrical properties for applications in flexible wearable gas sensors. The synergistic effects of electronic properties and gas-adsorption capabilities of MXene/graphene allow the created fibers to show high NH gas sensitivity at room temperature. The hybrid fibers exhibited significantly improved NH sensing response (Δ/ = 6.77%) compared with individual MXene and graphene. The hybrid fibers also showed excellent mechanical flexibility with a minimal fluctuation of resistance of ±0.2% and low noise resistance even after bending over 2000 cycles, enabling gas sensing during deformation. Furthermore, flexible MXene/graphene hybrid fibers were woven into a lab coat, demonstrating their high potential for wearable devices. We envisage that these exciting features of 2D hybrid materials will provide a novel pathway for designing next-generation portable wearable gas sensors.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.9b21765DOI Listing
March 2020

Steric Impediment of Ion Migration Contributes to Improved Operational Stability of Perovskite Solar Cells.

Adv Mater 2020 Mar 4;32(11):e1906995. Epub 2020 Feb 4.

Department of Materials Science and Engineering and California NanoSystems Institute, University of California Los Angeles, Los Angeles, CA, 90095, USA.

The operational instability of perovskite solar cells (PSCs) is known to mainly originate from the migration of ionic species (or charged defects) under a potential gradient. Compositional engineering of the "A" site cation of the ABX perovskite structure has been shown to be an effective route to improve the stability of PSCs. Here, the effect of size-mismatch-induced lattice distortions on the ion migration energetics and operational stability of PSCs is investigated. It is observed that the size mismatch of the mixed "A" site composition films and devices leads to a steric effect to impede the migration pathways of ions to increase the activation energy of ion migration, which is demonstrated through multiple theoretical and experimental evidence. Consequently, the mixed composition devices exhibit significantly improved thermal stability under continuous heating at 85 °C and operational stability under continuous 1 sun illumination, with an extrapolated lifetime of 2011 h, compared to the 222 h of the reference device.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201906995DOI Listing
March 2020

Graphene Foam Cantilever Produced via Simultaneous Foaming and Doping Effect of an Organic Coagulant.

ACS Appl Mater Interfaces 2020 Mar 6;12(9):10763-10771. Epub 2020 Feb 6.

Department of Organic and Nano Engineering, Hanyang University, Seoul 04763, Republic of Korea.

Inspired by the role of cellular structures, which give three-dimensional robustness to graphene structures, a new type of graphene cantilever with mechanical resilience is introduced. Here, NHSCN is incorporated into graphene oxide (GO) gel using it as a coagulant for GO fiber self-assembly, a foaming agent, and a dopant. Subsequent thermal treatment of the GO fiber at 600 °C results in the evolution of gaseous species from NHSCN, yielding internally porous graphene cantilevers (NS-GF cantilevers). The results reveal that NS-GF cantilevers are doped with N and S and thus exhibit higher electrical conductivity (150 S cm) than that of their nonporous counterparts (38.4 S cm). Unlike conventional fibers, the NS-GF cantilevers exhibit mechanical resilience by bending under applied mechanical force but reverting to the original position upon release. The tip of the NS-GF cantilevers is coated with magnetic FeO particles, and fast mechanical movement is achieved by applying the magnetic field. Since the NS-GF cantilevers are highly conductive and elastic, they are employed as bendable, magnetodriven electrical switches that could precisely read on/off signals for >10 000 cycles. Our approach suggests a robust fabrication strategy to prepare highly electroconductive and mechanically elastic foam structures by introducing unique organic foaming agents.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.9b19498DOI Listing
March 2020

Surface-2D/Bulk-3D Heterophased Perovskite Nanograins for Long-Term-Stable Light-Emitting Diodes.

Adv Mater 2020 Jan 18;32(1):e1905674. Epub 2019 Nov 18.

Department of Materials Science and Engineering and California NanoSystems Institute, University of California, Los Angeles, CA, 90095, USA.

Although metal halide perovskite (MHP) light-emitting diodes (LEDs) have demonstrated great potential in terms of electroluminescence efficiency, the operational stability of MHP LEDs currently remains the biggest bottleneck toward their practical usage. Well-confined excitons/charge carriers in a dielectric/quantum well based on conventional spatial or potential confinement approaches substantially enhance radiative recombination in MHPs, but an increased surface-to-volume ratio and multiphase interfaces likely result in a high degree of surface or interface defect states, which brings about a critical environmentally/operationally vulnerable point on LED stability. Here, an effective solution is suggested to mitigate such drawbacks using strategically designed surface-2D/bulk-3D heterophased MHP nanograins for long-term-stable LEDs. The 2D surface-functionalized MHP renders significantly reduced trap density, environmental stability, and an ion-migration-immune surface in addition to a fast radiative recombination owing to its spatially and potentially confined charge carriers, simultaneously. As a result, heterophased MHP LEDs show substantial improvement in operational lifetime (T : >200 h) compared to conventional pure 3D or quasi-2D counterparts (T : < 0.2 h) as well as electroluminescence efficiency (surface-2D/bulk-3D: ≈7.70 ph per el% and pure 3D: ≈0.46 ph per el%).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201905674DOI Listing
January 2020

Effects of dietary vitamin levels on physiological responses, blood profiles, and reproductive performance in gestating sows.

J Anim Sci Technol 2019 Sep 30;61(5):294-303. Epub 2019 Sep 30.

Department of Agricultural Biotechnology, and Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea.

This study was performed to evaluate the effects of dietary vitamin levels on physiological responses, blood profiles, and reproductive performance in gestating sows. A total of 52 F1 multiparous sows (Yorkshire × Landrace) with an average body weight of 223.5 ± 31.7 kg, an average parity of 6.4 ± 2.7, and an average backfat thickness of 18.5 ± 4.9 mm were divided into four treatment groups considering body weight, backfat thickness, and parity in a completely randomized design with 13 replicates. The treatments were 100% (V1), 300% (V3), 600% (V6) and 900% (V9) of the National Research Council (NRC) . The gestation diet was formulated based on corn-soybean meal (SBM) and contained 3,265 kcal of metabolizable energy (ME)/kg and 12.00% crude protein. During the lactation period, all sows were fed the same commercial lactation diet. There was no significant difference in body weight of gestating sows. However backfat thickness tended to increase when higher levels of vitamins were provided to gestating sows ( < 0.10). When high levels of dietary vitamins were provided, the body weight change of lactating sows increased ( < 0.01). When sows were fed higher levels of vitamins, the feed intake of lactating sows tended to decrease ( = 0.06). There were no treatment differences in the number of total born, born alive, stillbirth piglets, or the body weight of piglets according to different dietary vitamin level. As dietary vitamin level increased, the serum concentration of 25(OH)D in sows at 90 days of gestation linearly increased ( < 0.01). Furthermore, the serum vitamin E level of gestating sows was linearly increased with increasing dietary vitamin level ( < 0.05). The current NRC vitamin requirements are sufficient for gestating sows and higher levels of vitamins in the gestation diet did not show any beneficial effects for gestating and lactating sows.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.5187/jast.2019.61.5.294DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6778853PMC
September 2019

Effects of dietary energy and crude protein levels on growth performance, blood profiles, and carcass traits in growing-finishing pigs.

J Anim Sci Technol 2019 Jul 31;61(4):204-215. Epub 2019 Jul 31.

School of Agricultural Biotechnology, and Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea.

This experiment was conducted to evaluate the effect of dietary energy and crude protein (CP) levels on growth performance, blood profiles, and carcass traits in growing-finishing pigs. A total of 180 crossbred pigs ([Yorkshire × Landrace] × Duroc) with an average body weight of 30.96 ± 3.068 kg were used for a 12-week feeding trial. Experimental pigs were allotted to a 2 × 3 factorial arrangement using a randomized complete block (RCB) design. The first factor was two levels of dietary metabolizable energy (ME) density (13.40 MJ/kg or 13.82 MJ/kg), and the second factor was three dietary CP levels based on subdivision of growing-finishing phases (high: 18%/16.3%/16.3%/13.2% middle: 17%/15.3%/15.3%/12.2% and low: 16%/14.3%/14.3%/11.2%). Average daily gain (ADG) and gain-feed ratio (G:F ratio) decreased as dietary CP level was decreased linearly (linear, < 0.05; < 0.05, respectively) in the early growing period, and G:F ration also decreased as dietary CP level was decreased linearly (linearly, < 0.05) over the whole growing phase. Over the entire experimental period, G:F ratio decreased as dietary ME level decreased ( = 0.01). Blood urea nitrogen (BUN) concentration was increased as dietary energy level decreased in growing period ( < 0.01). During finishing period, total protein concentration was decreased by lower dietary energy level ( < 0.05). In this study, there were no significant differences in proximate factors, physiochemical properties, muscle TBARS assay results, pH changes, or color of pork by dietary treatments. However, saturated fatty acid (SFA) increased ( < 0.01) and polyunsaturated fatty acid (PUFA) decreased ( < 0.05) when ME was decreased by 0.42 MJ/kg in growing-finishing pig diets. In addition, monounsaturated fatty acid (MUFA) tended to increase when CP level was decreased in growing-finishing pig diets ( = 0.06). A growing-finishing diet of 13.82 MJ/kg diet of ME with the high CP level can improve growth performance and show better fatty acids composition of pork.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.5187/jast.2019.61.4.204DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6686147PMC
July 2019

Stiffening of graphene oxide films by soft porous sheets.

Nat Commun 2019 Aug 15;10(1):3677. Epub 2019 Aug 15.

Department of Materials Science and Engineering, Northwestern University, 2220 Campus Dr., Evanston, IL, 60208, USA.

Graphene oxide (GO) sheets have been used as a model system to study how the mechanical properties of two-dimensional building blocks scale to their bulk form, such as paper-like, lamellar-structured thin films. Here, we report that the modulus of multilayer GO films can be significantly enhanced if some of the sheets are drastically weakened by introducing in-plane porosity. Nanometer-sized pores are introduced in GO sheets by chemical etching. Membrane-deflection measurements at the single-layer level show that the sheets are drastically weakened as the in-plane porosity increases. However, the mechanical properties of the corresponding multilayer films are much less sensitive to porosity. Surprisingly, the co-assembly of pristine and etched GO sheets yields even stiffer films than those made from pristine sheets alone. This is attributed to the more compliant nature of the soft porous sheets, which act as a binder to improve interlayer packing and load transfer in the multilayer films.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-019-11609-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6695419PMC
August 2019

A Small-Molecule "Charge Driver" enables Perovskite Quantum Dot Solar Cells with Efficiency Approaching 13.

Adv Mater 2019 Sep 25;31(37):e1900111. Epub 2019 Jul 25.

Department of Materials Science and Engineering and California NanoSystems Institute, University of California, Los Angeles, CA, 90095, USA.

Halide perovskite colloidal quantum dots (CQDs) have recently emerged as a promising candidate for CQD photovoltaics due to their superior optoelectronic properties to conventional chalcogenides CQDs. However, the low charge separation efficiency due to quantum confinement still remains a critical obstacle toward higher-performance perovskite CQD photovoltaics. Available strategies employed in the conventional CQD devices to enhance the carrier separation, such as the design of type-Ⅱ core-shell structure and versatile surface modification to tune the electronic properties, are still not applicable to the perovskite CQD system owing to the difficulty in modulating surface ligands and structural integrity. Herein, a facile strategy that takes advantage of conjugated small molecules that provide an additional driving force for effective charge separation in perovskite CQD solar cells is developed. The resulting perovskite CQD solar cell shows a power conversion efficiency approaching 13% with an open-circuit voltage of 1.10 V, short-circuit current density of 15.4 mA cm , and fill factor of 74.8%, demonstrating the strong potential of this strategy toward achieving high-performance perovskite CQD solar cells.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201900111DOI Listing
September 2019

Tailored nanoplateau and nanochannel structures using solution-processed rutile TiO thin films for complementary and bipolar switching characteristics.

Nanoscale 2019 Aug 11;11(29):13815-13823. Epub 2019 Jul 11.

Division of Materials Science and Engineering, Hanyang University, Seoul 04763, Republic of Korea.

We synthesized two different nanostructures of rutile TiO (r-TiO) thin films on a fluorine-doped tin oxide (FTO) substrate at the lowest temperature reported until now and fabricated resistive random access memory (RRAM) devices with these r-TiO thin films having the stacking sequence of Ag/r-TiO/FTO. Complementary resistive switching (CRS) and bipolar resistive switching (BRS) were observed in different thicknesses of r-TiO based devices. Benefiting from the in situ growth of the solution processed thin films and modulating the reaction growth rates, we successfully attained two different morphologies of r-TiO with a nanoplateau at a controlled deposition rate and pre-defined nanochannels at a higher deposition rate. The RRAM devices with nano-plateaus of r-TiO showed excellent CRS as well as unprecedented simultaneous observations of BRS. These CRS and BRS characteristics were reversible and reproducible. On the other hand, the tailored pre-defined nanochannels in r-TiO led to forming-free BRS with a pulse endurance higher than 10 without any degradation in the high and low resistance states. We propose a plausible switching mechanism of these unprecedented events using various physical and electrical characterization studies of low-temperature processed r-TiO RRAM devices. This work suggests the importance of solution-processed thin film engineering for RRAM switching with reliable and reproducible characteristics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c9nr03465jDOI Listing
August 2019

Monocyte Chemoattractant Protein (MCP)-1 in Rotavirus-Associated White Matter Injury in Newborns.

Neuropediatrics 2019 08 2;50(4):228-234. Epub 2019 Apr 2.

Gyeongsang Institute of Health Science, Gyeongsang National University School of Medicine, Jinju, Republic of Korea.

Recent reports have suggested an association between rotavirus infection and a distinctive pattern of white matter injury (WMI) in neonates with seizures; however, the connection between the two is not fully understood. To evaluate the underlying mechanism, we profiled and compared eight cytokines (IL [interleukin]-1, IL-6, IL-8, IL-10, IFN- [interferon- ], MCP-1 [monocyte chemoattractant protein-1], MIP-1 [macrophage inflammatory protein-1], and TNF- [tumor necrosis factor-]) in the cerebrospinal fluid (CSF) of 33 neonates with seizures who had no other well-known causes of seizures and 13 control patients (rotavirus-induced gastroenteritis but without seizures). Among the 33 neonates with seizures, 9 showed WMI and all were infected with rotavirus (R + W + ). Among the 24 patients without WMI, 11 were infected with rotavirus (R + W - ) and 13 were not (R - W - ).Only MCP-1 and MIP-1 were different between the groups. MCP-1 was increased in R+ W+ compared with R + W- ( < 0.01), R - W- ( < 0.01), and control ( = 0.03) patients. MIP-1 was decreased in R + W+ compared with R - W- ( < 0.01) and control ( < 0.01), but not R + W- ( = 0.23) patients. MCP-1 and MIP-1 are C-C chemokines that recruit immune cells to the site of inflammation. Our pilot study suggests MCP-1-mediated monocyte recruitment may be linked with this complication caused by rotavirus.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1055/s-0038-1677516DOI Listing
August 2019

The effect of diverse metal oxides in graphene composites on the adsorption isotherm of gaseous benzene.

Environ Res 2019 05 30;172:367-374. Epub 2019 Jan 30.

Department of Organic and Nano Engineering, Hanyang University, Seoul 04763, Republic of Korea. Electronic address:

The effective removal technique is necessary for the real world treatment of a hazardous pollutant (e.g., gaseous benzene). In an effort to develop such technique, the adsorption efficiency of benzene in a nitrogen stream (5 Pa (50 ppm) at 50 mL atm min flow rate and 298 K) was assessed against 10 different metal oxide/GO composite materials (i.e., 1: graphene oxide Co (GO-Co (OH)), 2: graphene oxide Cu (GO-Cu(OH)), 3: graphene oxide Mn (GO-MnO), 4: graphene oxide Ni (GO-Ni(OH)), 5: graphene oxide Sn (GO-SnO), 6: reduced graphene oxide Co (rGO-Co(OH)), 7: reduced graphene oxide Cu (rGO-Cu(OH)), 8: reduced graphene oxide Mn (rGO-MnO), 9: reduced graphene oxide Ni (rGO-Ni(OH)), and 10: reduced graphene oxide Sn (rGO-SnO)) in reference to their pristine forms of graphene oxide (GO) and reduced graphene oxide (rGO). The highest adsorption capacities (at 100% breakthrough) were observed as ~23 mg g for both GO-Ni(OH) and rGO-SnO, followed by GO (~19.1 mg g) and GO-Co(OH) (~18.8 mg g). Therefore, the GO-Ni(OH) and rGO-SnO composites exhibited considerably high capacities to treat streams containing >5 Pa of benzene. However, the lowest adsorption capacity was found for GO-MnO (0.05 mg g). Alternately, if expressed in terms of the 10% breakthrough volume (BTV), the five aforementioned materials showed values of 0.50, 0.46, 0.40, 0.44, and 0.39 L g, respectively. The experimental data of target sorbents were fitted to linearized Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich isotherm models. Accordingly, the non-linear Langmuir isotherm model revealed the presence of two or more distinct sorption profiles for several of the tested sorbents. Most of the sorbents showed type-III isotherm profiles where the sorption capacity proportional to the loaded volume.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.envres.2019.01.050DOI Listing
May 2019

Tunable Electronic Properties of Nitrogen and Sulfur Doped Graphene: Density Functional Theory Approach.

Nanomaterials (Basel) 2019 Feb 15;9(2). Epub 2019 Feb 15.

Department of Organic Material Science and Engineering, Pusan National University, 2, Busandaehak-ro 63beon gil, Geumjeong-gu, Busan 46241, Korea.

We calculated the band structures of a variety of N- and S-doped graphenes in order to understand the effects of the N and S dopants on the graphene electronic structure using density functional theory (DFT). Band-structure analysis revealed energy band upshifting above the Fermi level compared to pristine graphene following doping with three nitrogen atoms around a mono-vacancy defect, which corresponds to p-type nature. On the other hand, the energy bands were increasingly shifted downward below the Fermi level with increasing numbers of S atoms in N/S-co-doped graphene, which results in n-type behavior. Hence, modulating the structure of graphene through N- and S-doping schemes results in the switching of "p-type" to "n-type" behavior with increasing S concentration. Mulliken population analysis indicates that the N atom doped near a mono-vacancy is negatively charged due to its higher electronegativity compared to C, whereas the S atom doped near a mono-vacancy is positively charged due to its similar electronegativity to C and its additional valence electrons. As a result, doping with N and S significantly influences the unique electronic properties of graphene. Due to their tunable band-structure properties, the resulting N- and S-doped graphenes can be used in energy and electronic-device applications. In conclusion, we expect that doping with N and S will lead to new pathways for tailoring and enhancing the electronic properties of graphene at the atomic level.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/nano9020268DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6409776PMC
February 2019

Interface and Defect Engineering for Metal Halide Perovskite Optoelectronic Devices.

Adv Mater 2019 Nov 14;31(47):e1803515. Epub 2019 Feb 14.

Department of Materials Science and Engineering and California NanoSystems Institute, University of California, Los Angeles, CA, 90095, USA.

Metal halide perovskites have been in the limelight in recent years due to their enormous potential for use in optoelectronic devices, owing to their unique combination of properties, such as high absorption coefficient, long charge-carrier diffusion lengths, and high defect tolerance. Perovskite-based solar cells and light-emitting diodes (LEDs) have achieved remarkable breakthroughs in a comparatively short amount of time. As of writing, a certified power conversion efficiency of 22.7% and an external quantum efficiency of over 10% have been achieved for perovskite solar cells and LEDs, respectively. Interfaces and defects have a critical influence on the properties and operational stability of metal halide perovskite optoelectronic devices. Therefore, interface and defect engineering are crucial to control the behavior of the charge carriers and to grow high quality, defect-free perovskite crystals. Herein, a comprehensive review of various strategies that attempt to modify the interfacial characteristics, control the crystal growth, and understand the defect physics in metal halide perovskites, for both solar cell and LED applications, is presented. Lastly, based on the latest advances and breakthroughs, perspectives and possible directions forward in a bid to transcend what has already been achieved in this vast field of metal halide perovskite optoelectronic devices are discussed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201803515DOI Listing
November 2019