B21-High Throughput SAXS
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Diamond Proposal Number(s):
[24271, 27588]
Open Access
Abstract: Stimuli-responsive materials are crucial to advance controlled delivery systems for drugs and catalysts. Lyotropic liquid crystals (LLCs) have well-defined internal structures suitable to entrap small molecules and can be broken up into low-viscosity dispersions, aiding their application as delivery systems. In this work, we demonstrate the first example of light-responsive cubic LLC dispersions, or cubosomes, using photoswitchable amphiphiles to enable external control over the LLC structure and subsequent on-demand release of entrapped guest molecules. Azobenzene photosurfactants (AzoPS), containing a neutral tetraethylene glycol head group and azobenzene-alkyl tail, are combined (from 10–30 wt %) into monoolein-water systems to create LLC phases. Homogenization of the bulk LLC forms dispersions of particles, ∼200 nm in diameter with internal bicontinuous primitive cubic phases, as seen using small-angle X-ray scattering and cryo-transmission electron microscopy. Notably, increasing the AzoPS concentration leads to swelling of the cubic lattice, offering a method to tune the internal nanoscale structure. Upon UV irradiation, AzoPS within the cubosomes isomerizes within seconds, which in turn leads to squeezing of the cubic lattice and a decrease in the lattice parameter. This squeeze mechanism was successfully harnessed to enable phototriggerable release of trapped Nile Red guest molecules from the cubosome structure in minutes. The ability to control the internal structure of LLC dispersions using light, and the dramatic effect this has on the retention of entrapped molecules, suggests that these systems may have huge potential for the next-generation of nanodelivery.
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Oct 2022
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E02-JEM ARM 300CF
I15-1-X-ray Pair Distribution Function (XPDF)
I22-Small angle scattering & Diffraction
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Adam F.
Sapnik
,
Irene
Bechis
,
Sean M.
Collins
,
Duncan N.
Johnstone
,
Giorgio
Divitini
,
Andrew J.
Smith
,
Philip A.
Chater
,
Matthew A.
Addicoat
,
Timothy
Johnson
,
David A.
Keen
,
Kim E.
Jelfs
,
Thomas D.
Bennett
Diamond Proposal Number(s):
[20038, 24563]
Open Access
Abstract: Amorphous metal–organic frameworks (MOFs) are an emerging class of materials. However, their structural characterisation represents a significant challenge. Fe-BTC, and the commercial equivalent Basolite® F300, are MOFs with incredibly diverse catalytic ability, yet their disordered structures remain poorly understood. Here, we use advanced electron microscopy to identify a nanocomposite structure of Fe-BTC where nanocrystalline domains are embedded within an amorphous matrix, whilst synchrotron total scattering measurements reveal the extent of local atomic order within Fe-BTC. We use a polymerisation-based algorithm to generate an atomistic structure for Fe-BTC, the first example of this methodology applied to the amorphous MOF field outside the well-studied zeolitic imidazolate framework family. This demonstrates the applicability of this computational approach towards the modelling of other amorphous MOF systems with potential generality towards all MOF chemistries and connectivities. We find that the structures of Fe-BTC and Basolite® F300 can be represented by models containing a mixture of short- and medium-range order with a greater proportion of medium-range order in Basolite® F300 than in Fe-BTC. We conclude by discussing how our approach may allow for high-throughput computational discovery of functional, amorphous MOFs.
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Apr 2021
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E02-JEM ARM 300CF
I15-1-X-ray Pair Distribution Function (XPDF)
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Adam F.
Sapnik
,
Duncan N.
Johnstone
,
Sean M.
Collins
,
Giorgio
Divitini
,
Alice M.
Bumstead
,
Christopher W.
Ashling
,
Philip A.
Chater
,
Dean S.
Keeble
,
Timothy
Johnson
,
David A.
Keen
,
Thomas D.
Bennett
Diamond Proposal Number(s):
[20038, 20198]
Open Access
Abstract: Defect engineering is a powerful tool that can be used to tailor the properties of metal–organic frameworks (MOFs). Here, we incorporate defects through ball milling to systematically vary the porosity of the giant pore MOF, MIL-100 (Fe). We show that milling leads to the breaking of metal–linker bonds, generating additional coordinatively unsaturated metal sites, and ultimately causes amorphisation. Pair distribution function analysis shows the hierarchical local structure is partially retained, even in the amorphised material. We find that solvents can be used to stabilise the MIL-100 (Fe) framework against collapse, which leads to a substantial retention of porosity over the non-stabilised material.
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Mar 2021
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Anna
Abfalterer
,
Javad
Shamsi
,
Dominik J.
Kubicki
,
Christopher N.
Savory
,
James
Xiao
,
Giorgio
Divitini
,
Weiwei
Li
,
Stuart
Macpherson
,
Krzysztof
Gałkowski
,
Judith L.
Macmanus-Driscoll
,
David O.
Scanlon
,
Samuel D.
Stranks
Open Access
Abstract: Optoelectronic devices based on lead halide perovskites are processed in facile ways, yet are remarkably efficient. There are extensive research efforts investigating lead-free perovskite and perovskite-related compounds, yet there are challenges to synthesize these materials in forms that can be directly integrated into thin film devices rather than as bulk powders. Here, we report on the colloidal synthesis and characterization of lead-free, antifluorite Cs2ZrX6 (X = Cl, Br) nanocrystals that are readily processed into thin films. We use transmission electron microscopy and powder X-ray diffraction measurements to determine their size and structural properties, and solid-state nuclear magnetic resonance measurements reveal the presence of oleate ligand, together with a disordered distribution of Cs surface sites. Density functional theory calculations reveal the band structure and fundamental band gaps of 5.06 and 3.91 eV for Cs2ZrCl6 and Cs2ZrBr6, respectively, consistent with experimental values. Finally, we demonstrate that the Cs2ZrCl6 and Cs2ZrBr6 nanocrystal thin films exhibit tunable, broad white photoluminescence with quantum yields of 45% for the latter, with respective peaks in the blue and green spectral regions and mixed systems exhibiting properties between them. Our work represents a critical step toward the application of lead-free Cs2ZrX6 nanocrystal thin films into next-generation light-emitting applications.
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Nov 2020
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I07-Surface & interface diffraction
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Baodan
Zhao
,
Yaxiao
Lian
,
Linsong
Cui
,
Giorgio
Divitini
,
Gunnar
Kusch
,
Edoardo
Ruggeri
,
Florian
Auras
,
Weiwei
Li
,
Dexin
Yang
,
Bonan
Zhu
,
Rachel A.
Oliver
,
Judith L.
Macmanus-Driscoll
,
Samuel D.
Stranks
,
Dawei
Di
,
Richard H.
Friend
Diamond Proposal Number(s):
[17223]
Abstract: Light-emitting diodes based on halide perovskites have recently reached external quantum efficiencies of over 20%. However, the performance of visible perovskite light-emitting diodes has been hindered by non-radiative recombination losses and limited options for charge-transport materials that are compatible with perovskite deposition. Here, we report efficient, green electroluminescence from mixed-dimensional perovskites deposited on a thin (~1 nm) lithium fluoride layer on an organic semiconductor hole-transport layer. The highly polar dielectric interface acts as an effective template for forming high-quality bromide perovskites on otherwise incompatible hydrophobic charge-transport layers. The control of crystallinity and dimensionality of the perovskite layer is achieved by using tetraphenylphosphonium chloride as an additive, leading to external photoluminescence quantum efficiencies of around 65%. With this approach, we obtain light-emitting diodes with external quantum efficiencies of up to 19.1% at high brightness (>1,500 cd m−2).
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Oct 2020
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I06-Nanoscience (XPEEM)
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Diamond Proposal Number(s):
[17563]
Open Access
Abstract: Exchange-bias has been reported in bulk nanocrystalline Fe2MnAl, but individual thin films of this Heusler alloy have never been studied so far. Here we study the structural and magnetic properties of nanocrystalline thin films of Fe2–xMn1+xAl (x = –0.25, 0, 0.25) obtained by sputtering and ex-situ post-deposition annealing. We find that Fe2MnAl films display exchange-bias, and that varying Mn concentration determines the magnitude of the effect, which can be either enhanced (in Fe1.75Mn1.25Al) or suppressed (in Fe2.25Mn0.75Al). X-ray diffraction (XRD) shows that our films present a mixed L21-B2 Heusler structure where increasing Mn concentration favors the partial transformation of the L21 phase into the B2 phase. Scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDX) reveal that this composition-driven L21→B2 transformation is accompanied by phase segregation at the nanoscale. As a result, the Fe2–xMn1+xAl films that show exchange-bias (x = 0, 0.25) are heterogeneous, with nanograins of an Fe-rich phase embedded in a Mn-rich matrix (a non-negative matrix factorisation algorithm was used to give an indication of the phase composition from EDX data). Our comparative analysis of XRD, magnetometry and X-ray magnetic circular dichroism (XMCD), shows that Fe-rich nanograins and Mn-rich matrix are composed of a ferromagnetic L21 phase and an antiferromagnetic B2 phase, respectively, thus revealing that exchange-coupling between these two phases is the cause of the exchange-bias effect. Our work should inspire the development of single-layer, environmentally-friendly spin valve devices based on nanocomposite Heusler films.
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May 2020
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E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Tiarnan A. S.
Doherty
,
Andrew J.
Winchester
,
Stuart
Macpherson
,
Duncan N.
Johnstone
,
Vivek
Pareek
,
Elizabeth M.
Tennyson
,
Sofiia
Kosar
,
Felix U.
Kosasih
,
Miguel
Anaya
,
Mojtaba
Abdi-Jalebi
,
Zahra
Andaji-Garmaroudi
,
E. Laine
Wong
,
Julien
Madéo
,
Yu-Hsien
Chiang
,
Ji-Sang
Park
,
Young-Kwang
Jung
,
Christopher E.
Petoukhoff
,
Giorgio
Divitini
,
Michael K. l.
Man
,
Caterina
Ducati
,
Aron
Walsh
,
Paul A.
Midgley
,
Keshav M.
Dani
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[19023, 19793]
Abstract: Halide perovskite materials have promising performance characteristics for low-cost optoelectronic applications. Photovoltaic devices fabricated from perovskite absorbers have reached power conversion efficiencies above 25 per cent in single-junction devices and 28 per cent in tandem devices. This strong performance (albeit below the practical limits of about 30 per cent and 35 per cent, respectively) is surprising in thin films processed from solution at low-temperature, a method that generally produces abundant crystalline defects. Although point defects often induce only shallow electronic states in the perovskite bandgap that do not affect performance, perovskite devices still have many states deep within the bandgap that trap charge carriers and cause them to recombine non-radiatively. These deep trap states thus induce local variations in photoluminescence and limit the device performance. The origin and distribution of these trap states are unknown, but they have been associated with light-induced halide segregation in mixed-halide perovskite compositions and with local strain, both of which make devices less stable. Here we use photoemission electron microscopy to image the trap distribution in state-of-the-art halide perovskite films. Instead of a relatively uniform distribution within regions of poor photoluminescence efficiency, we observe discrete, nanoscale trap clusters. By correlating microscopy measurements with scanning electron analytical techniques, we find that these trap clusters appear at the interfaces between crystallographically and compositionally distinct entities. Finally, by generating time-resolved photoemission sequences of the photo-excited carrier trapping process, we reveal a hole-trapping character with the kinetics limited by diffusion of holes to the local trap clusters. Our approach shows that managing structure and composition on the nanoscale will be essential for optimal performance of halide perovskite devices.
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Apr 2020
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B21-High Throughput SAXS
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Diamond Proposal Number(s):
[16235]
Open Access
Abstract: Viscoelastic fluids whose rheological properties are tunable with light have the potential to deliver significant impact in fields relying on a change in flow behavior, such as in-use tuning of combined efficient heat-transfer and drag-reduction agents, microfluidic flow and controlled encapsulation and release. However, simple, single-component systems must be developed to allow integration with these applications. Here, we report a single-component viscoelastic fluid, capable of a dramatic light-sensitive rheological response, from a neutral azobenzene photosurfactant, 4-hexyl-4′butyloxymonotetraethylene glycol (C6AzoOC4E4) in water. From cryo-transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and rheology measurements, we observe that the photosurfactant forms an entangled network of wormlike micelles in water, with a high viscosity (28 Pa s) and viscoelastic behaviour. UV irradiation of the surfactant solution creates a less dense micellar network, with some vesicle formation. As a result, the solution viscosity is reduced by four orders of magnitude (to 1.2 × 10−3 Pa s). This process is reversible and the high and low viscosity states can be cycled several times, through alternating UV and blue light irradiation.
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Mar 2020
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I09-Surface and Interface Structural Analysis
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Mojtaba
Abdi-Jalebi
,
Zahra
Andaji-Garmaroudi
,
Stefania
Cacovich
,
Camille
Stavrakas
,
Bertrand
Philippe
,
Johannes M.
Richter
,
Mejd
Alsari
,
Edward P.
Booker
,
Eline M.
Hutter
,
Andrew J.
Pearson
,
Samuele
Lilliu
,
Tom J.
Savenije
,
Hakan
Rensmo
,
Giorgio
Divitini
,
Caterina
Ducati
,
Richard H.
Friend
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[15841]
Abstract: Metal halide perovskites are of great interest for various high-performance optoelectronic applications. The ability to tune the perovskite bandgap continuously by modifying the chemical composition opens up applications for perovskites as coloured emitters, in building-integrated photovoltaics, and as components of tandem photovoltaics to increase the power conversion efficiency. Nevertheless, performance is limited by non-radiative losses, with luminescence yields in state-of-the-art perovskite solar cells still far from 100 per cent under standard solar illumination conditions. Furthermore, in mixed halide perovskite systems designed for continuous bandgap tunability (bandgaps of approximately 1.7 to 1.9 electronvolts), photoinduced ion segregation leads to bandgap instabilities. Here we demonstrate substantial mitigation of both non-radiative losses and photoinduced ion migration in perovskite films and interfaces by decorating the surfaces and grain boundaries with passivating potassium halide layers. We demonstrate external photoluminescence quantum yields of 66 per cent, which translate to internal yields that exceed 95 per cent. The high luminescence yields are achieved while maintaining high mobilities of more than 40 square centimetres per volt per second, providing the elusive combination of both high luminescence and excellent charge transport. When interfaced with electrodes in a solar cell device stack, the external luminescence yield—a quantity that must be maximized to obtain high efficiency—remains as high as 15 per cent, indicating very clean interfaces. We also demonstrate the inhibition of transient photoinduced ion-migration processes across a wide range of mixed halide perovskite bandgaps in materials that exhibit bandgap instabilities when unpassivated. We validate these results in fully operating solar cells. Our work represents an important advance in the construction of tunable metal halide perovskite films and interfaces that can approach the efficiency limits in tandem solar cells, coloured-light-emitting diodes and other optoelectronic applications.
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Mar 2018
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