ORCID Profile
0000-0002-5151-6360
Current Organisation
University of Leeds
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Publisher: Elsevier BV
Date: 06-2023
Publisher: Wiley
Date: 31-03-2022
Abstract: The interaction of high‐energy electrons and X‐ray photons with beam‐sensitive semiconductors such as halide perovskites is essential for the characterization and understanding of these optoelectronic materials. Using nanoprobe diffraction techniques, which can investigate physical properties on the nanoscale, studies of the interaction of electron and X‐ray radiation with state‐of‐the‐art (FA 0.79 MA 0.16 Cs 0.05 )Pb(I 0.83 Br 0.17 ) 3 hybrid halide perovskite films (FA, formamidinium MA, methylammonium) are performed, tracking the changes in the local crystal structure as a function of fluence using scanning electron diffraction and synchrotron nano X‐ray diffraction techniques. Perovskite grains are identified, from which additional reflections, corresponding to PbBr 2 , appear as a crystalline degradation phase after fluences of 200 e − Å − 2 . These changes are concomitant with the formation of small PbI 2 crystallites at the adjacent high‐angle grain boundaries, with the formation of pinholes, and with a phase transition from tetragonal to cubic. A similar degradation pathway is caused by photon irradiation in nano‐X‐ray diffraction, suggesting common underlying mechanisms. This approach explores the radiation limits of these materials and provides a description of the degradation pathways on the nanoscale. Addressing high‐angle grain boundaries will be critical for the further improvement of halide polycrystalline film stability, especially for applications vulnerable to high‐energy radiation such as space photovoltaics.
Publisher: American Chemical Society (ACS)
Date: 06-09-2019
DOI: 10.1021/JACS.9B07557
Publisher: American Chemical Society (ACS)
Date: 15-08-2016
Abstract: We present a combined scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) investigation into the mode symmetries of plasmonic nanoparticle trimer and tetramer structures. We obtain nanometer-resolved energy loss spectra for both trimer and tetramer structures and compare these to boundary element method simulations. We show that EELS, in conjunction with eigenmode simulations, offers a complete characterization of the in idual superstructures, and we trace the evolution of both optically dark and bright modes and identify multipolar mode contributions. We then apply this technique to tetramer structures that exhibit an expanded range of mode symmetries for two-dimensional and three-dimensional self-assembled geometries. These findings provide a comprehensive experimental account of the available photonic states in self-assembled nanoparticle clusters.
Publisher: American Chemical Society (ACS)
Date: 10-09-2018
DOI: 10.26434/CHEMRXIV.7058033.V1
Abstract: Recent demonstrations of melting in the metal-organic framework (MOF) family have createdinterest in the interfacial domain between inorganic glasses and amorphous organic polymers. Thechemical and physical behaviour of porous hybrid liquids and glasses is of particular interest,though opportunities are limited by the inaccessible melting temperatures of many MOFs. Here,we show that the synthetic processing technique of flux melting, ‘borrowed’ from the inorganicdomain, may be applied to MOFs in order to melt materials which do not possess an accessibleliquid state in their pure form. We employ the high-temperature liquid state of one MOF as a solventfor a secondary, non-melting MOF component. Differential scanning calorimetry, small- and wideangleX-ray scattering, electron microscopy and X-ray total scattering techniques are used to showthe flux melting of the crystalline component within the liquid. Gas adsorption and positronannihilation lifetime spectroscopy measurements show that this results in enhanced, accessibleporosity to a range of guest molecules, in the resultant flux melted MOF glass.
Publisher: American Chemical Society (ACS)
Date: 17-07-2020
DOI: 10.26434/CHEMRXIV.8921765.V1
Abstract: Metal-organic framework crystal-glass composites (MOF-CGCs) are materials in which a crystalline MOF is dispersed within a MOF glass. In this work, we explore the room temperature stabilisation of the open-pore form of MIL-53(Al), usually observed at high-temperature, which occurs upon encapsulation within a ZIF-62(Zn) MOF glass matrix. A series of MOF-CGCs containing different loadings of MIL-53 were synthesised and characterised using X-ray diffraction and nuclear magnetic resonance spectroscopy. An upper limit of MIL-53 that can be stabilised in the composite was determined. The nanostructure of the composites was probed using pair distribution function analysis and scanning transmission electron microscopy. The distribution and integrity of the crystalline component was determined, and these findings related to the MOF-CGC gas adsorption capacity in order to identify the optimal loading necessary for maximum CO 2 sorption capacity.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8SC04044C
Abstract: We show flux melting by using a liquid MOF as a solvent for a secondary, non-melting MOF component.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 24-12-2021
Abstract: The black, photoactive phase of formamidinium (FA) perovskites, which is usually stabilized by cation alloying to avoid the formation of inactive hexagonal phases, is assumed to be cubic. High-resolution microscopy studies by Doherty et al . using nanoscale probes revealed that these FA-rich phases are not cubic but rather undergo slight tilting (by two degrees) of the octahedra. Black phases can have localized regions of hexagonal phases that nucleate degradation. Surface-bound ethylenediaminetetraacetic acid stabilized the tilted phase of pure FA lead triiodide against environmental degradation. —PDS
Publisher: Springer Science and Business Media LLC
Date: 12-06-2019
DOI: 10.1038/S41467-019-10470-Z
Abstract: The majority of research into metal-organic frameworks (MOFs) focuses on their crystalline nature. Recent research has revealed solid-liquid transitions within the family, which we use here to create a class of functional, stable and porous composite materials. Described herein is the design, synthesis, and characterisation of MOF crystal-glass composites, formed by dispersing crystalline MOFs within a MOF-glass matrix. The coordinative bonding and chemical structure of a MIL-53 crystalline phase are preserved within the ZIF-62 glass matrix. Whilst separated phases, the interfacial interactions between the closely contacted microdomains improve the mechanical properties of the composite glass. More significantly, the high temperature open pore phase of MIL-53, which spontaneously transforms to a narrow pore upon cooling in the presence of water, is stabilised at room temperature in the crystal-glass composite. This leads to a significant improvement of CO 2 adsorption capacity.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 29-10-2021
Abstract: Lead halide perovskites can exhibit bright, narrow band photoluminescence but have stability issues related to formation of inactive phases and the loss of lead ions. Hou et al . show that the black, photoactive phase of cesium lead iodide can be stabilized by forming a composite with a glassy phase of a metal-organic framework through liquid-phase sintering. The photoluminescence is at least two orders of magnitude greater than that of the pure perovskite. The glass stabilizes the perovskite under high laser excitation, and about 80% of the photoluminescence was maintained after 10,000 hours of water immersion. —PDS
Publisher: Research Square Platform LLC
Date: 26-04-2023
DOI: 10.21203/RS.3.RS-2747262/V1
Abstract: The stellar optoelectronic properties of metal halide perovskites provide enormous promise for next-generation optical devices with excellent conversion efficiencies and lower manufacturing costs. However, there is a long-standing ambiguity as to whether the perovskite surface/interface ( e.g . structure, charge transfer or source of off-target recombination) or bulk properties are the more determining factor in device performance. We fabricated an array of CsPbI 3 crystal and hybrid glass composites by sintering and globally visualised the property-performance landscape. Our findings reveal that the interface is the primary determinant of the crystal phases, optoelectronic quality, and stability of CsPbI 3 . In particular, the presence of a diffusion "alloying" layer is discovered to be critical for passivating surface traps, and beneficially altering the energy landscape of crystal phases. However, high-temperature sintering results in the promotion of a non-stoichiometric perovskite and excess traps at the interface, despite the short-range structure of halide is retained within the alloying layer. By shedding light on functional hetero-interfaces, our research offers the key factors for engineering high-performance perovskite devices.
Publisher: American Chemical Society (ACS)
Date: 18-04-2019
DOI: 10.26434/CHEMRXIV.7093862.V2
Abstract: The majority of research into metal-organic frameworks (MOFs) focuses on their crystalline nature. However, in recent research the vitrification of a number of MOFs has been revealed. We propose that the solid-liquid phase transitions involved in MOF-glass formation can provide unique opportunities for the creation of a new class of functional, stable and porous composite materials. Described herein is the design, synthesis, and characterisation of novel metal-organic framework (MOF) crystal-glass composites, formed by dispersing crystalline MOFs within a MOF-glass matrix. We demonstrate using structural characterisation and analytical electron tomography, that the coordinative bonding and chemical structure of a MIL-53 crystalline phase are preserved within the ZIF-62 glass matrix. Whilst separated phases, the microdomains of each lie close to one another and possess interfacial interactions which improve the mechanical properties of the composite glass. More significantly, the high temperature open pore phase of MIL-53, which spontaneously transforms to a narrow pore upon cooling, is stabilized at room temperature in the crystal-glass composite. This leads to a significant improvement of CO 2 adsorption capacity.
Publisher: American Chemical Society (ACS)
Date: 16-01-2020
DOI: 10.1021/ACS.NANOLETT.9B04732
Abstract: Vibrational spectroscopies directly record details of bonding in materials, but spatially resolved methods have been limited to surface techniques for mapping functional groups at the nanoscale. Electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope presents a route to functional group analysis from nanoscale volumes using transmitted subnanometer electron probes. Here, we now use vibrational EELS to map distinct carboxylate and imidazolate linkers in a metal-organic framework (MOF) crystal-glass composite material. Domains <100 nm in size are observed using vibrational EELS, with recorded spatial resolution <15 nm at interfaces in the composite. This nanoscale functional group mapping is confirmed by correlated EELS at core ionization edges as well as X-ray energy dispersive spectroscopy for elemental mapping of the metal centers of the two constituent MOFs. These results present a complete nanoscale analysis of the building blocks of the MOF composite and establish spatially resolved functional group analysis using electron beam spectroscopy for crystalline and amorphous organic and metal-organic solids.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Sean Collins.