E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Tiarnan A. S.
Doherty
,
Dominik
Kubicki
,
Stuart
Macpherson
,
Young-Kwang
Jung
,
Duncan
Johnstone
,
Affan
Iqbal
,
Dengyang
Guo
,
Kyle
Frohna
,
Mohsen
Danaie
,
Elizabeth
Tennyson
,
Satyawan
Nagane
,
Anna
Abfalterer
,
Miguel
Anaya
,
Yu-Hsien
Chiang
,
Phillip
Crout
,
Francesco Simone
Ruggeri
,
Sean
Collins
,
Clare
Grey
,
Aron
Walsh
,
Paul
Midgley
,
Samuel
Stranks
Diamond Proposal Number(s):
[20420, 24111]
Abstract: There is currently substantial interest in stabilizing the simple ternary FAPbI3 perovskite because of its near-optimal band gap and superior thermal stability compared to methylammonium-based materials.1 The key challenge of FAPbI3 is the thermodynamic instability of the polymorph required for efficient light harvesting. Without additives, the black photoactive α-polymorph is only stable above ca. 160°C. At room temperature, it is metastable and rapidly transitions to the non-perovskite yellow polymorph. The stabilization of the black polymorph at room temperature can be achieved, for example, by adding a small amount of the pernicious MA through use of methylammonium chloride (in conjunction with formamidinium formate),2 methylammonium thiocyanate,3 or methylammonium formate.4 We have developed a new stabilization strategy which does not involve the addition of MA.5 Instead, it uses a surface-templating agent (EDTA) which modifies the material without incorporating into the structure. We use a combination of scanning electron diffraction (SED) and nuclear magnetic resonance spectroscopies (NMR, NQR) to identify the atomic-level mechanism of action of EDTA in this role. We find that it templates the structure by inducing a small octahedral tilt, only resolvable with local characterization techniques, and imparts remarkable phase stability by arresting transitions to low-dimensional polymorphs. This octahedral tilt engineering strategy is remarkably universal, and we show that it is the intrinsic stabilization mechanism in the state-of-the-art FA-rich mixed-cation materials.
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Feb 2022
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E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Tiarnan A. S.
Doherty
,
Satyawan
Nagane
,
Dominik J.
Kubicki
,
Young-Kwang
Jung
,
Duncan N.
Johnstone
,
Affan N.
Iqbal
,
Dengyang
Guo
,
Kyle
Frohna
,
Mohsen
Danaie
,
Elizabeth M.
Tennyson
,
Stuart
Macpherson
,
Anna
Abfalterer
,
Miguel
Anaya
,
Yu-Hsien
Chiang
,
Phillip
Crout
,
Francesco Simone
Ruggeri
,
Sean M.
Collins
,
Clare P.
Grey
,
Aron
Walsh
,
Paul A.
Midgley
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[20420, 24111]
Abstract: Efforts to stabilize photoactive formamidinium (FA)–based halide perovskites for perovskite photovoltaics have focused on the growth of cubic formamidinium lead iodide (α-FAPbI3) phases by empirically alloying with cesium, methylammonium (MA) cations, or both. We show that such stabilized FA-rich perovskites are noncubic and exhibit ~2° octahedral tilting at room temperature. This tilting, resolvable only with the use of local nanostructure characterization techniques, imparts phase stability by frustrating transitions from photoactive to hexagonal phases. Although the bulk phase appears stable when examined macroscopically, heterogeneous cation distributions allow microscopically unstable regions to form; we found that these transitioned to hexagonal polytypes, leading to local trap-assisted performance losses and photoinstabilities. Using surface-bound ethylenediaminetetraacetic acid, we engineered an octahedral tilt into pure α-FAPbI3 thin films without any cation alloying. The templated photoactive FAPbI3 film was extremely stable against thermal, environmental, and light stressors.
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Dec 2021
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E01-JEM ARM 200CF
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Raj
Pandya
,
Richard Y. S.
Chen
,
Qifei
Gu
,
Jooyoung
Sung
,
Christoph
Schnedermann
,
Oluwafemi S.
Ojambati
,
Rohit
Chikkaraddy
,
Jeffrey
Gorman
,
Gianni
Jacucci
,
Olimpia D.
Onelli
,
Tom
Willhammar
,
Duncan N.
Johnstone
,
Sean M.
Collins
,
Paul A.
Midgley
,
Florian
Auras
,
Tomi
Baikie
,
Rahul
Jayaprakash
,
Fabrice
Mathevet
,
Richard
Soucek
,
Matthew
Du
,
Antonios M.
Alvertis
,
Arjun
Ashoka
,
Silvia
Vignolini
,
David G.
Lidzey
,
Jeremy J.
Baumberg
,
Richard H.
Friend
,
Thierry
Barisien
,
Laurent
Legrand
,
Alex W.
Chin
,
Joel
Yuen-Zhou
,
Semion K.
Saikin
,
Philipp
Kukura
,
Andrew J.
Musser
,
Akshay
Rao
Diamond Proposal Number(s):
[20527]
Open Access
Abstract: Strong-coupling between excitons and confined photonic modes can lead to the formation of new quasi-particles termed exciton-polaritons which can display a range of interesting properties such as super-fluidity, ultrafast transport and Bose-Einstein condensation. Strong-coupling typically occurs when an excitonic material is confided in a dielectric or plasmonic microcavity. Here, we show polaritons can form at room temperature in a range of chemically diverse, organic semiconductor thin films, despite the absence of an external cavity. We find evidence of strong light-matter coupling via angle-dependent peak splittings in the reflectivity spectra of the materials and emission from collective polariton states. We additionally show exciton-polaritons are the primary photoexcitation in these organic materials by directly imaging their ultrafast (5 × 106 m s−1), ultralong (~270 nm) transport. These results open-up new fundamental physics and could enable a new generation of organic optoelectronic and light harvesting devices based on cavity-free exciton-polaritons.
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Nov 2021
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E02-JEM ARM 300CF
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Jingwei
Hou
,
Peng
Chen
,
Atul
Shukla
,
Andraž
Krajnc
,
Tiesheng
Wang
,
Xuemei
Li
,
Rana
Doasa
,
Luiz H. G.
Tizei
,
Bun
Chan
,
Duncan N.
Johnstone
,
Rijia
Lin
,
Tobias U.
Schülli
,
Isaac
Martens
,
Dominique
Appadoo
,
Mark
S'Ari
,
Zhiliang
Wang
,
Tong
Wei
,
Shih-Chun
Lo
,
Mingyuan
Lu
,
Shichun
Li
,
Ebinazar B.
Namdas
,
Gregor
Mali
,
Anthony K.
Cheetham
,
Sean M.
Collins
,
Vicki
Chen
,
Lianzhou
Wang
,
Thomas D.
Bennett
Diamond Proposal Number(s):
[21980, 25140]
Abstract: Lead halide perovskite (LHP) semiconductors show exceptional optoelectronic properties. Barriers for their applications, however, lie in their polymorphism, instability to polar solvents, phase segregation, and susceptibility to the leaching of lead ions. We report a family of scalable composites fabricated through liquid-phase sintering of LHPs and metal-organic framework glasses. The glass acts as a matrix for LHPs, effectively stabilizing nonequilibrium perovskite phases through interfacial interactions. These interactions also passivate LHP surface defects and impart bright, narrow-band photoluminescence with a wide gamut for creating white light-emitting diodes (LEDs). The processable composites show high stability against immersion in water and organic solvents as well as exposure to heat, light, air, and ambient humidity. These properties, together with their lead self-sequestration capability, can enable breakthrough applications for LHPs.
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Oct 2021
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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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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[19130, 20614]
Abstract: Cellulose is crystallized by plants and other organisms into fibrous nanocrystals. The mechanical properties of these nanofibers and the formation of helical superstructures with energy dissipating and adaptive optical properties depend on the ordering of polysaccharide chains within these nanocrystals, which is typically measured in bulk average. Direct measurement of the local polysaccharide chain arrangement has been elusive. In this study, we use the emerging technique of scanning electron diffraction to probe the packing of polysaccharide chains across cellulose nanofibers and to reveal local ordering of the chains in twisting sections of the nanofibers. We then use atomic force microscopy to shed light on the size dependence of the inherent driving force for cellulose nanofiber twisting. The direct measurement of crystalline twisted regions in cellulose nanofibers has important implications for understanding single-cellulose-fibril properties that influence the interactions between cellulose nanocrystals in dense assemblies. This understanding may enable cellulose extraction and separation processes to be tailored and optimized.
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Jan 2021
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[20527]
Open Access
Abstract: Hybrid metal extrusion & bonding (HYB) is a joining method that enables solid-state bonding by combining addition of aluminium filler material through continuous extrusion with pressure exerted by a rotating steel tool. This work presents mechanical and microstructural characterisation of a second generation HYB butt joint of aluminium alloy 6082 and structural steel S355. The ultimate tensile strength was measured to be in the range of 184–220 MPa, which corresponds to 60–72% joint efficiency. Digital image correlation analysis of the strain development during tensile testing revealed that root cracks formed, before the final fracture ran close to the aluminium-steel interface. A significant amount of residual aluminium was found on the steel fracture surface, especially in regions that experienced higher pressure during joining. Scanning and transmission electron microscopy revealed that the bond strength could be attributed to a combination of microscale mechanical interlocking and a discontinuous nanoscale interfacial Al-Fe-Si intermetallic phase layer. Analysis of scanning electron diffraction data acquired in a tilt series, indicated that the polycrystalline intermetallic phase layer contained the cubic αc phase. The results give insight into the bonding mechanisms of aluminium-steel joints and into the performance of HYB joints, which may be used to better understand and further develop aluminium-steel joining processes.
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Nov 2020
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E02-JEM ARM 300CF
I15-1-X-ray Pair Distribution Function (XPDF)
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Shichun
Li
,
Shuwen
Yu
,
Sean M.
Collins
,
Duncan N.
Johnstone
,
Christopher W.
Ashling
,
Adam F.
Sapnik
,
Philip A.
Chater
,
Dean S.
Keeble
,
Lauren N.
Mchugh
,
Paul A.
Midgley
,
David A.
Keen
,
Thomas D.
Bennett
Diamond Proposal Number(s):
[20038, 22632, 21979]
Open Access
Abstract: Metal–organic framework crystal–glass composite (MOF CGC) materials consist of a crystalline MOF embedded within a MOF–glass matrix. In this work, a new synthetic route to these materials is demonstrated through the preparation of two ZIF-62 glass-based CGCs, one with crystalline ZIF-67 and the other with crystalline UiO-66. Previous attempts to form these CGCs failed due to the high processing temperatures involved in heating above the melting point of ZIF-62. Annealing of the ZIF-62 glass above the glass transition with each MOF however leads to stable CGC formation at lower temperatures. The reduction in processing temperatures will enable the formation of a greatly expanded range of MOF CGCs.
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Sep 2020
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[20195, 21979, 20198]
Abstract: Defect engineering can enhance key properties of metal-organic frameworks (MOFs). Tailoring the distribution of de-fects, for example in correlated nanodomains, requires characterization across length scales. However, a critical na-noscale characterization gap has emerged between the bulk diffraction techniques used to detect defect nanodomains and the sub-nanometer imaging used to observe individual defects. Here, we demonstrate that the emerging technique of scanning electron diffraction (SED) can bridge this gap uniquely enabling both nanoscale crystallographic analysis and the low-dose formation of multiple diffraction contrast images for defect analysis in MOFs. We directly image defect nanodomains in the MOF UiO-66(Hf) over an area of ca. 1 000 nm and with a spatial resolution ca. 5 nm to reveal domain morphology and distribution. Based on these observations, we suggest possible crystal growth processes underpinning synthetic control of defect nanodomains. We also identify likely dislocations and small angle grain boundaries, illustrating that SED could be a key technique in developing the potential for engineering the distribution of defects, or “microstruc-ture”, in functional MOF design.
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Jul 2020
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