| 1. |
- Lin, Ci, et al.
(författare)
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Direct Band Gap in Multilayer Transition Metal Dichalcogenide Nanoscrolls with Enhanced Photoluminescence
- 2022
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Ingår i: ACS Materials Letters. - : American Chemical Society (ACS). - 2639-4979. ; 4:8, s. 1547-1555
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Tidskriftsartikel (refereegranskat)abstract
- A direct band gap that solely exists in monolayer semiconducting transition metal dichalcogenides (TMDs) endows strong photoluminescence (PL) features, whereas multilayer TMD structures exhibit quenched PL due to the direct-to-indirect band gap transition. We demonstrate multi-layer TMD (such as MoS2 and WS2) nanoscrolls with a preserved direct band gap fabricated by an effective and facile method of solvent-driven self-assembly. The resultant multi-layer nanoscrolls, exhibiting up to 11 times higher PL intensity than the remanent monolayer, are carefully characterized using PL spectroscopy. Significantly enlarged interlayer distances and modulated interlayer coupling in the fabricated nanostructures are unveiled by cross-sectional scanning transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. The preservation of direct band gap features is further evidenced by density functional theory calculations using the simplified bilayer model with an experimentally obtained 15 & ANGS; interlayer distance. The modulation of the PL intensity as an indicator of the band gap crossover in the TMD nanoscrolls is demonstrated by removing the acetone molecules trapped inside the interlayer space. The general applicability of the method presents an opportunity for large-scale fabrication of a plethora of multilayer TMD nanoscrolls with direct band gaps.
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| 2. |
- Maibach, Julia, 1984, et al.
(författare)
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Toward Operando Characterization of Interphases in Batteries
- 2023
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Ingår i: ACS Materials Letters. - 2639-4979. ; 5:9, s. 2431-2444
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Forskningsöversikt (refereegranskat)abstract
- Electrode/electrolyte interfaces are the most importantand leastunderstood components of Li-ion and next-generation batteries. Animproved understanding of interphases in batteries will undoubtedlylead to breakthroughs in the field. Traditionally, evaluating thoseinterphases involves using ex situ surface sensitiveand/or imaging techniques. Due to their very dynamic and reactivenature, ex situ sample manipulation is undesirable.From this point of view, operando surface sensitivetechniques represent a major opportunity to push boundaries in batterydevelopment. While numerous bulk spectroscopic, scattering, and imagingtechniques are well established and widely used, surface sensitive operando techniques remain challenging and, to a largerextent, restricted to the model systems. Here, we give a perspectiveon techniques with the potential to characterize solid/liquid interfacesin both model and realistic battery configurations. The focus is ontechniques that provide chemical and structural information at lengthand time scales relevant for the solid electrolyte interphase (SEI)formation and evolution, while also probing representative electrodeareas. We highlight the following techniques: vibrational spectroscopy,X-ray photoelectron spectroscopy (XPS), neutron and X-ray reflectometry,and grazing incidence scattering techniques. Comprehensive overviews,as well as promises and challenges, of these techniques when used operando on battery interphases are discussed in detail.
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| 3. |
- Mopoung, Kunpot, et al.
(författare)
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Spin Centers in Vanadium-Doped Cs2NaInCl6 Halide Double Perovskites
- 2024
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Ingår i: ACS Materials Letters. - : AMER CHEMICAL SOC. - 2639-4979. ; 6:2, s. 566-571
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Tidskriftsartikel (refereegranskat)abstract
- We provide direct evidence for a spin-active V4+ defect center, likely in the form of a VO2+ complex, predominantly introduced in single crystals of vanadium-doped Cs2NaInCl6 halide double perovskites grown by the solution-processed hydrothermal method. The defect has C-4v point group symmetry, exhibiting an electron paramagnetic resonance (EPR) spectrum arising from an effective electron spin of S = 1/2 and a nuclear spin of I = 7/2 (corresponding to V-51 with nearly 100% natural abundance). The determined electron g-factor and hyperfine parameter values are g(perpendicular to)= 1.973, g(parallel to) = 1.945, A(perpendicular to) = 180 MHz, and A(parallel to) = 504 MHz, with the principal axis z along a < 001 > crystallographic axis. The controlled growth of V-doped Cs2NaInCl6 in an oxygen-free environment is shown to suppress the V4+ EPR signal. The defect model is suggested to have a VOCl5 octahedral coordination, where one of the nearest-neighbor Cl- of V is replaced by O2-, with octahedral compression along the V-O axis. This VO complex formation competes with the isolated V3+ substitution of In3+, which in turn provides a means for the charge-state tuning of V ions. This finding calls for a better understanding and control of defect formation in solution-grown halide double perovskites, which is critical for optimizing and tailoring material design for solution-processable optoelectronics and spintronics.
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| 4. |
- Nishimura, Naoyuki, et al.
(författare)
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Photon Upconversion from Near-Infrared to Blue Light with TIPS-Anthracene as an Efficient Triplet-Triplet Annihilator
- 2019
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Ingår i: ACS Materials Letters. - : AMER CHEMICAL SOC. - 2639-4979. ; 1:6, s. 660-664
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Tidskriftsartikel (refereegranskat)abstract
- Photon upconversion (PUC) via triplet-triplet annihilation (TTA) from near-infrared (NIR) to blue photons could have important applications especially to bioimaging and drug delivery accompanied by photochemical reaction. The fundamental challenges in achieving this has been the large anti-Stokes shift combined with the need to efficiently sensitize within the biological transparency window (700-900 nm). This calls for materials combinations with minimal energy losses during sensitization and minimal energy requirements to drive efficient TTA. Here, we demonstrate efficient PUC converting from NIR energy to blue photons using the commercially available material 9,10-bis[((triisopropyl)silyl)ethynyl]anthracene (TIPS-Ac) as the annihilator. With a conventional triplet sensitizing system, TIPS-Ac performed TTA with an efficiency of 77 +/- 3% despite a relatively small driving force, compared to conventional TTA material converting from NIR to blue, for the TTA of less than 0.32 eV. Combined with Pt(II) meso-tetraphenyltetrabenzoporphine (PtTPBP), which is a heavy atom triplet sensitizer that directly generates triplets upon NIR photon excitation, the resulting system allowed for an anti-Stokes shift of 1.03 eV. Our results highlight the use of direct triplet generation via NIR excitation as a useful path to achieving large anti-Stokes shift and also show that high TTA efficiencies can be achieved even in the absence of large driving energies for the TTA process.
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| 5. |
- Shi, Rui, et al.
(författare)
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Phonon-Mediated Nonradiative Relaxation in Ln3+-Doped Luminescent Nanocrystals
- 2022
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Ingår i: ACS Materials Letters. - : American Chemical Society (ACS). - 2639-4979. ; 4:10, s. 1882-1903
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Forskningsöversikt (refereegranskat)abstract
- Unsatisfactory photoluminescence efficiency of Ln3+-doped nanocrystals severely restricts their practical application, which has been frequently correlated to the active phonon mediation in the system. Although the phonon-mediated nonradiative relaxation of Ln3+ has been mostly explained by the “energy gap law”, a growing body of observational anomalies raises questions about the general applicability and validity of this phonon frequency-orientated model. For that reason, an improved understanding, questioning commonly accepted views, is needed. Herein the discussion relevant to this topic is reviewed, stressing that for phonon-mediated nonradiative relaxation in Ln3+-doped nanocrystals not only a variety of effects associated with the particle surface but also impacts arising from the nanocrystal interior need to be considered. A clear awareness of these different aspects allows comprehending the delicate electron–lattice interactions in these systems, which is helpful in improving the performance of Ln3+-doped luminescent nanocrystals.
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| 6. |
- Starkholm, Allan, et al.
(författare)
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Gold Polyiodide Hybrid Perovskite Solar Cells
- 2023
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Ingår i: ACS Materials Letters. - : American Chemical Society. - 2639-4979. ; 5, s. 406-412
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present the ionic liquid (IL) synthesis of two novel pseudo-2D perovskite-type gold(III)polyiodide compounds, [DodMe2S][AuI4][I3] (1) and [Et3S][AuI4][I5] (2), and their application as active layers in monolithic solar cells. The compounds are composed of tetraiodoaurate anions and polyiodide entities, infinite polyiodide chains in 1 and pentaiodides in 2, which display short intermolecular contacts resulting in relatively small electronic bandgaps. This work represents the first demonstration of film deposition of gold iodide/polyiodide compounds onto porous monolithic substrates with subsequent solar cell characterization. The devices show promising photovoltaic performance and could unlock new materials design possibilities, ultimately moving away from lead-based photovoltaic materials. These findings further highlight the use of simple polyiodide entities to increase the structural and electronic dimensionality of gold perovskite-type anions. © 2023 The Authors.
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| 7. |
- Wu, Keming, et al.
(författare)
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Surface Reconstruction on Uniform Cu Nanodisks Boosted Electrochemical Nitrate Reduction to Ammonia
- 2022
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Ingår i: ACS Materials Letters. - : American Chemical Society (ACS). - 2639-4979. ; 4, s. 650-656
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Tidskriftsartikel (refereegranskat)abstract
- The Haber-Bosch (HB) process has provided most of commercial ammonia at the expense of high energy consumption and high CO2 emission. Nitrate electroreduction is showing great potential as an alternative route for the green and scale-up synthesis of ammonia at ambient conditions. However, the performance has lagged due to lack of efficient electrocatalysts. In this work, we present the facile synthesis of uniform Cu nanodisks with exposed (111) facets as highly active electrocatalyst for electrochemical ammonia synthesis, delivering a high ammonia yield of 2.16 mg mg-1cat h-1 and a maximum Faradaic efficiency of 81.1% at -0.5 V versus a reversible hydrogen electrode (RHE). The remarkable activity is originated from the surface reconstructed triatomic Cu clusters due to the cathodic deoxygenation process. As a result, the reconstructed surface shows enhanced affinity to the adsorption of nitrate ions which undergo successive break of three N-O bonds, followed by subsequent formation of three N-H bonds to finally form NH3. The present study provides the feasible preparation of Cu based advanced catalysts and a unique insight into the mechanism of nitrate electroreduction.
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| 8. |
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| 9. |
- Yang, Chih-Wen, et al.
(författare)
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Epitaxial Growth and Determination of Band Alignment of Bi2Te3–WSe2 Vertical van der Waals Heterojunctions
- 2020
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Ingår i: ACS Materials Letters. - : American Chemical Society (ACS). - 2639-4979. ; 2:10, s. 1351-1359
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Tidskriftsartikel (refereegranskat)abstract
- Artificial heterojunctions formed by vertical stacking of dissimilar two-dimensional (2D) transition metal dichalcogenide (TMD) monolayer materials in a chosen sequence hold tantalizing prospects for futuristic atomically thin circuits. The emergence of 2D topological insulators (TI), including Bi2Te3, Bi2Se3, and Sb2Te3, represents a new class of 2D building blocks and can complement the existing artificial heterojunctions as a result of their intriguing surface states protected by the time-reversal symmetry. However, the determination of band alignments of such 2D TI/TMD vertical heterojunctions, the key parameter for designing HJ-based electronic/photonic devices, which lies in the development of epitaxy growth, remains in its infancy. Here, we demonstrate the epitaxy growth of 2D TI/TMD vertical heterojunctions comprised of Bi2Te3/WSe2 with atomically clean interfaces that are spectroscopically accessible, and theoretically tractable. Cross-sectional scanning transmission electron microscopy (STEM) images and the presence of interlayer-coupled characteristics from Raman spectroscopy collectively confirm the neat stacking of Bi2Te3/WSe2 with the absence of unwanted containments. Microbeam X-ray photoelectron spectroscopy (ΌXPS) measurement coupled with the density functional theory (DFT) calculations and electrical characteristics of field effect transistors quantitatively reveals the type-II alignment of vertically stacked of quintuple layers (QL) Bi2Te3/WSe2. Meanwhile, the type-III band emerges when transitioning to multi-quintuple layer (MQL) Bi2Te3/WSe2. The finding here provides a well-defined example of the epitaxy growth paradigm, the interlayer coupling-electronic properties relationship, for these emerging 2D TI/TMDs vertical heterojunctions. © 2020 American Chemical Society.
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| 10. |
- Zhou, Shengyang, et al.
(författare)
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Efficient Solar Thermal Energy Conversion and Utilization by a Film of Conductive Metal–Organic Framework Layered on Nanocellulose
- 2022
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Ingår i: ACS Materials Letters. - : American Chemical Society (ACS). - 2639-4979. ; 4, s. 1058-1064
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Tidskriftsartikel (refereegranskat)abstract
- Developing materials for efficient solar thermal energy conversion (STEC) is currently a promising field in energy research. Traditional STEC materials such as carbon and plasmonic nanomaterials have limited efficiency of solar heat utilization, despite their high photothermal conversion efficiency. This paper describes a film composed of hybrid nanofibers of a metal–organic framework layered on cellulose (MC film), resulting in both high photothermal conversion and heat utilization efficiency. The mechanically strong and flexible film can be designed as a solar-driven actuator, enabling large-angle actuation and high contractile power up to 2.5 times greater than that of human muscle. Furthermore, the gathered heat by a MC film-based apparatus can be manipulated to drive solar steam generation for highly efficient seawater desalination, generating clean water at rate of 2.25 kg m–2 h–1 under one-sun irradiation without surface salt accumulation. This work may provide a design rule for developing high-performance STEC systems.
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