E02-JEM ARM 300CF
I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[16983, 19130, 20195, 21979, 22395, 20038]
Open Access
Abstract: Characterization of nanoscale changes in the atomic structure of amorphous materials is a profound challenge. Established X-ray and neutron total scattering methods typically provide sufficient signal quality only over macroscopic volumes. Pair distribution function analysis using electron scattering (ePDF) in the scanning transmission electron microscope (STEM) has emerged as a method of probing nanovolumes of these materials, but inorganic glasses as well as metal–organic frameworks (MOFs) and many other materials containing organic components are characteristically prone to irreversible changes after limited electron beam exposures. This beam sensitivity requires ‘low-dose’ data acquisition to probe inorganic glasses, amorphous and glassy MOFs, and MOF composites. Here, we use STEM-ePDF applied at low electron fluences (10 e-/Å2) combined with unsupervised machine learning methods to map changes in the short-range order with ca. 5 nm spatial resolution in a composite material consisting of a zeolitic imidazolate framework glass agZIF-62 and a 0.67([Na2O]0.9[P2O5])-0.33([AlO3/2][AlF3]1.5) inorganic glass. STEM-ePDF enables separation of MOF and inorganic glass domains from atomic structure differences alone, showing abrupt changes in atomic structure at interfaces with interatomic correlation distances seen in X-ray PDF preserved at the nanoscale. These findings underline that the average bulk amorphous structure is retained at the nanoscale in the growing family of MOF glasses and composites, a previously untested assumption in PDF analyses crucial for future non-crystalline nanostructure engineering.
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Oct 2022
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E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Stuart
Macpherson
,
Tiarnan A. S.
Doherty
,
Andrew J.
Winchester
,
Sofiia
Kosar
,
Duncan N.
Johnstone
,
Yu-Hsien
Chiang
,
Krzysztof
Galkowski
,
Miguel
Anaya
,
Kyle
Frohna
,
Affan N.
Iqbal
,
Satyawan
Nagane
,
Bart
Roose
,
Zahra
Andaji-Garmaroudi
,
Kieran W. P.
Orr
,
Julia E.
Parker
,
Paul A.
Midgley
,
Keshav M.
Dani
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[24111, 20420]
Abstract: Understanding the nanoscopic chemical and structural changes that drive instabilities in emerging energy materials is essential for mitigating device degradation. The power conversion efficiency of halide perovskite photovoltaic devices has reached 25.7% in single junction and 29.8% in tandem perovskite/silicon cells1,2, yet retaining such performance under continuous operation has remained elusive3. Here, we develop a multimodal microscopy toolkit to reveal that in leading formamidinium-rich perovskite absorbers, nanoscale phase impurities including hexagonal polytype and lead iodide inclusions are not only traps for photo-excited carriers which themselves reduce performance4,5, but via the same trapping process are sites at which photochemical degradation of the absorber layer is seeded. We visualise illumination-induced structural changes at phase impurities associated with trap clusters, revealing that even trace amounts of these phases, otherwise undetected with bulk measurements, compromise device longevity. The type and distribution of these unwanted phase inclusions depends on film composition and processing, with the presence of polytypes being most detrimental for film photo-stability. Importantly, we reveal that performance losses and intrinsic degradation processes can both be mitigated by modulating these defective phase impurities, and demonstrate that this requires careful tuning of local structural and chemical properties. This multimodal workflow to correlate the nanoscopic landscape of beam sensitive energy materials will be applicable to a wide range of semiconductors for which a local picture of performance and operational stability has yet to be established.
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May 2022
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E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Diamond Proposal Number(s):
[25250, 20420]
Abstract: The interaction of high-energy electrons and X-ray photons with beam-sensitive semiconductors such as halide perovskites is essential for the characterisation and understanding of these optoelectronic materials. Using nano-probe diffraction techniques, which can investigate physical properties on the nanoscale, we perform studies of the interaction of electron and X-ray radiation with state-of-the-art (FA0.79MA0.16Cs0.05)Pb(I0.83Br0.17)3 hybrid halide perovskite films (FA, formamidinium; MA, methylammonium). We track the changes in the local crystal structure as a function of fluence using scanning electron diffraction and synchrotron nano X-ray diffraction techniques. We identify perovskite grains from which additional reflections, corresponding to PbBr2, appear as a crystalline degradation phase after fluences of ∼200 e–Å–2. These changes are concomitant with the formation of small PbI2 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. Our 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.
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Mar 2022
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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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I11-High Resolution Powder Diffraction
I12-JEEP: Joint Engineering, Environmental and Processing
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Kieran W. P.
Orr
,
Sean M.
Collins
,
Emily M.
Reynolds
,
Frank
Nightingale
,
Hanna L. B.
Bostroem
,
Simon J.
Cassidy
,
Daniel M.
Dawson
,
Sharon E.
Ashbrook
,
Oxana
Magdysyuk
,
Paul A.
Midgley
,
Andrew L.
Goodwin
,
Hamish H.-M.
Yeung
Diamond Proposal Number(s):
[20946, 18786]
Open Access
Abstract: Control over the spatial distribution of components in metal–organic frameworks has potential to unlock improved performance and new behaviour in separations, sensing and catalysis. We report an unprecedented single-step synthesis of multi-component metal–organic framework (MOF) nanoparticles based on the canonical ZIF-8 (Zn) system and its Cd analogue, which form with a core–shell structure whose internal interface can be systematically tuned. We use scanning transmission electron microscopy, X-ray energy dispersive spectroscopy and a new composition gradient model to fit high-resolution X-ray diffraction data to show how core–shell composition and interface characteristics are intricately controlled by synthesis temperature and reaction composition. Particle formation is investigated by in situ X-ray diffraction, which reveals that the spatial distribution of components evolves with time and is determined by the interplay of phase stability, crystallisation kinetics and diffusion. This work opens up new possibilities for the control and characterisation of functionality, component distribution and interfaces in MOF-based materials.
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Feb 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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I15-1-X-ray Pair Distribution Function (XPDF)
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Xiao
Hua
,
Alexander S.
Eggeman
,
Elizabeth
Castillo-Martinez
,
Rosa
Robert
,
Harry S.
Geddes
,
Ziheng
Lu
,
Chris J.
Pickard
,
Wei
Meng
,
Kamila M.
Wiaderek
,
Nathalie
Pereira
,
Glenn G.
Amatucci
,
Paul A.
Midgley
,
Karena W.
Chapman
,
Ullrich
Steiner
,
Andrew L.
Goodwin
,
Clare
Grey
Diamond Proposal Number(s):
[17315]
Abstract: Metal fluorides, promising lithium-ion battery cathode materials, have been classified as conversion materials due to the reconstructive phase transitions widely presumed to occur upon lithiation. We challenge this view by studying FeF3 using X-ray total scattering and electron diffraction techniques that measure structure over multiple length scales coupled with density functional theory calculations, and by revisiting prior experimental studies of FeF2 and CuF2. Metal fluoride lithiation is instead dominated by diffusion-controlled displacement mechanisms, and a clear topological relationship between the metal fluoride F− sublattices and that of LiF is established. Initial lithiation of FeF3 forms FeF2 on the particle’s surface, along with a cation-ordered and stacking-disordered phase, A-LixFeyF3, which is structurally related to α-/β-LiMn2+Fe3+F6 and which topotactically transforms to B- and then C-LixFeyF3, before forming LiF and Fe. Lithiation of FeF2 and CuF2 results in a buffer phase between FeF2/CuF2 and LiF. The resulting principles will aid future developments of a wider range of isomorphic metal fluorides.
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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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