E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[28500, 30057, 30160, 30157, 31872]
Open Access
Abstract: Organic molecular crystals encompass a vast range of materials from pharmaceuticals to organic optoelectronics, proteins and waxes in biological and industrial settings. Crystal defects from grain boundaries to dislocations are known to play key roles in mechanisms of growth1,2 and in the functional properties of molecular crystals3,4,5. In contrast to the precise analysis of individual defects in metals, ceramics and inorganic semiconductors enabled by electron microscopy, substantially greater ambiguity remains in the experimental determination of individual dislocation character and slip systems in molecular materials3. In large part, nanoscale dislocation analysis in molecular crystals has been hindered by the low electron doses required to avoid irreversibly degrading these crystals6. Here we present a low-dose, single-exposure approach enabling nanometre-resolved analysis of individual dislocations in molecular crystals. We demonstrate the approach for a range of crystal types to reveal dislocation character and operative slip systems unambiguously.
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Mar 2025
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[28500, 26822, 28789, 30157]
Open Access
Abstract: Waxes comprise a diverse set of materials from lubricants and coatings to biological materials such as the intracuticular wax layers on plant leaves that restrict water loss to inhibit dehydration. Despite the often mixed hydrocarbon chain lengths and functional groups within waxes, they show a propensity for ordering into crystalline phases, albeit with a wealth of solid solution behavior and disorder modes that determine chemical transport and mechanical properties. Here, we reveal the microscopic structure and heterogeneity of replica leaf wax models based on the dominant wax types in the Schefflera elegantissima plant, namely C31H64 and C30H61OH and their binary mixtures. We observe defined grain microstructure in C31H64 crystals and nanoscale domains of chain-ordered lamellae within these grains. Moreover, nematic phases and dynamical disorder coexist with the domains of ordered lamellae. C30H61OH exhibits more disordered chain packing with no grain structure or lamellar domains. Binary mixtures from 0–50% C30H61OH exhibit a loss of grain structure with increasing alcohol content accompanied by increasingly nematic rather than lamellar chain packing, suggesting a partial but limited solid solution behavior. Together, these results unveil the previously unseen microstructural features governing flexibility and permeability in leaf waxes and outline an approach to microstructure analysis across agrochemicals, pharmaceuticals, and food.
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Dec 2024
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E02-JEM ARM 300CF
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Sangcheol
Yoon
,
Braulio
Reyes-Suárez
,
Sang T.
Pham
,
Hervé
Vezin
,
Yeny A.
Tobon
,
Myeongjae
Lee
,
Sam
Mugiraneza
,
Brian Minki
Kim
,
Mariane Yuka Tsubaki
Oide
,
Seongju
Yoo
,
Seunggu
Lee
,
Shu Hui
Wang
,
Sean M.
Collins
,
Christopher M.
Bates
,
Yongsup
Park
,
Bongsoo
Kim
,
G. N. Manjunatha
Reddy
,
Thuc-Quyen
Nguyen
Diamond Proposal Number(s):
[34607]
Abstract: Understanding efficiency–durability relationships and related mitigation strategies is an important step toward the commercialization of organic photovoltaics (OPVs). Here, we report that a photoactivated 6-bridged azide cross-linker (6Bx) improves the morphological stability by suppressing the thermally activated diffusion of (Y6) acceptor molecules in PM6:Y6 bulk-heterojunction (BHJ)-based OPVs. Cross-linked PM6:Y6 (0.05 wt % 6Bx) BHJ OPVs retain 93.4% of the initial power conversion efficiency upon thermal aging at 85 °C for 1680 h (T80 = 3290 h). Molecular origins of enhanced thermal stability are corroborated by optical spectroscopy, surface imaging, 2D solid-state nuclear magnetic resonance (ssNMR), Raman spectroscopy, scanning electron diffraction (SED) measurements, and analysis of the BHJ thin films. The facile single-step cross-linking strategy in conjugation with advanced characterization methods presented in the study paves the way toward developing durable OPVs based on non-fullerene acceptors (NFAs).
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Dec 2024
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E01-JEM ARM 200CF
E02-JEM ARM 300CF
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Open Access
Abstract: Background incl. aims: Conjugated polymers are an important class of organic light emitting diodes (OLEDs) and organic solar cells (OSCs). These materials are predominantly semi-crystalline or amorphous with intricate molecular packing and mixed variety of structural orders and disorders [1]. The susceptibility of these materials to ‘burn-in degradation’ [2] can induce blend-demixing and photo-induced ordering/disordering [3], thereby resulting in the performance losses of the devices [4]. Controlling this performance degradation during operation necessitates an understanding in changes in chemical structures and structural disorders at the nanoscale – the length scale commensurate with the transport of charge carriers. Yet direct nanoscale characterisation is limited for polymer semiconductors and their associated devices due to the irreversible changes in these materials structure when exposed to high-energy ion and electron beam conditions [5]. Here, we advance the structural characterisation of polymer semiconductors, whether in the form of free-standing films or cross-sectioned lamella, using low-dose four-dimesion scanning transmission electron microscopy (4D-STEM), enabling the analysis of the molecular packing, crystallinity, and atomic arrangement in the polymer semiconductors in response to temperature and ion milling-induced damage. Methods: Low-dose 4D-STEM analysis was conducted using established nanobeam scanning electron diffraction alignment at electron Physical Science Imaging Centre (ePSIC), Diamond Light Source. In particular, Merlin-Medipix detector and <1 mrad convergence semi-angle with 1-2 pA in probe current at 300 kV were used to minimize radiolytic damage. We obtained data at a range of camera lengths to enable both mapping of crystalline domains from Bragg scattering as well as reciprocal space (variance measures) and real space electron Pair Distribution Function (ePDF) analysis of disordered and amorphous regions. The materials under examination were free-standing polymer films (F8:F8BT, 1:1), prepared by spin-coating onto PDOT:PSS/ITO/Glass substrates. Subsequently, the multi-layered sample was submerged in deionized water, and the F8:F8BT films were floated onto carbon support films for 4D- STEM analysis. Additionally, we developed cryo-Focused Ion Beam (cryo-FIB) protocols to facilitate the structural examination of the cross-sectioned device model, Glass/ITO/PDOT:PSS/F8:F8BT (1:1). Results: The developed techniques reveal the formation of nano-crystalline domains in the F8:F8BT films after heat treatment. These domains are attributed to the crystallisation of F8 polymers, as evidenced by indexing some diffraction patterns aligning along the zone axis. Additionally, ePDF analysis allows us to characterise the atomic structures in amorphous areas with varying contrast. The analysis indicates that there were no chemical changes in the F8:F8BT blends induced by temperature. However, partial phase segregation occurred, as also supported by low-dose EELS analysis. We extended these analyses to a cross-sectioned device model prepared by cryo-FIB, and the findings demonstrate that our cryo-FIB protocol preserves the crystalinity of the polymer blends. ePDF shows that cryo-FIB milling does not alter the chemical structures of the films, i.e. intramolecular structure, but does affect the intermolecular arrangement. Conclusion: The developed electron microscopy techniques enable the characterisation of microstructures and nanoscale atomic arrangements in beam-sensitive polymer semiconductors, paving a pathway for examining phase segregation and chemical changes resulting from the burn-in degradation. By doing so, effective strategies can be developed to minimise structural degradation in polymer semiconductors, thereby preventing performance losses during operation.
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Oct 2024
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E02-JEM ARM 300CF
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Chao
Sun
,
Christopher M.
Pask
,
Sang T.
Pham
,
Emilio
Rapaccioli
,
Andrew J.
Britton
,
Stuart
Micklethwaite
,
Andrew
Bell
,
Maximilian O.
Besenhard
,
Rik
Drummond-Brydson
,
Ke-Jun
Wu
,
Sean M.
Collins
Diamond Proposal Number(s):
[33373]
Open Access
Abstract: The functional group-directed structures of coordination polymers (CPs) and metal–organic frameworks (MOFs) have made them key candidates for proton exchange membranes in fuel cell technologies. Sulfonate group chemistry is well established in proton conducting polymers but has seen less exploration in CPs. Here, we report solvent-directed crystal structures of Cu2+ and Ca2+ CPs constructed with naphthalenedisulfonate (NDS) and anthraquinone-1,5-disulfonate (ADS) ligands, and we correlate single crystal structures across this set with proton conductivities determined by electrochemical impedance spectroscopy. Starting from the Cu2+-based NDS and aminotriazolate MOF designated Cu-SAT and the aqueous synthesis of the known Ca2+-NDS structure incorporating water ligands, we now report a further five sulfonate CP structures. These syntheses include a direct synthesis of the primary degradation product of Cu-SAT in water, solvent-substituted Ca-NDS structures prepared using dimethylformamide and dimethylsulfoxide solvents, and ADS variants of Cu-SAT and Ca-NDS. We demonstrate a consistent 2D layer motif in the NDS CPs, while structural modifications introduced by the ADS ligand result in a 2D hydrogen bonding network with Cu2+ and aminotriazolate ligands and a 1D CP with Ca2+ in water. Proton conductivities across the set span 10−4 to >10−3 S cm−1 at 80 °C and 95% RH. These findings reveal an experimental structure–function relationship between proton conductivity and the tortuosity of the hydrogen bonding network and establish a general, cross-structure descriptor for tuning the sulfonate CP unit cell to systematically modulate proton conductivity.
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Jun 2024
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E02-JEM ARM 300CF
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Chao
Sun
,
Matthew
Barton
,
Christopher M.
Pask
,
Mohamed
Edokali
,
Lina
Yang
,
Andrew J.
Britton
,
Stuart
Micklethwaite
,
Francesco
Iacoviello
,
Ali
Hassanpour
,
Maximilian
Besenhard
,
Rik
Drummond-Brydson
,
Ke-Jun
Wu
,
Sean M.
Collins
Diamond Proposal Number(s):
[26822, 30160]
Open Access
Abstract: Metal–organic frameworks (MOFs) have emerged as promising candidate materials for proton exchange membranes (PEMs), due to the control of proton transport enabled by functional groups and the structural order within the MOFs. In this work, we report a millifluidic approach for the synthesis of a MOF incorporating both sulfonate and amine groups, termed Cu-SAT, which exhibits a high proton conductivity. The fouling-free multiphase flow reactor synthesis was operated for more than 5 h with no reduction in yield or change in the particle size distribution, demonstrating a sustained space–time yield up to 131.7 kg m−3 day−1 with consistent particle quality. Reaction yield and particle size were controllably tuned by the adjustment of reaction parameters, such as residence/reaction time, temperature, and reagent concentration. The reaction yields from the flow reactor were 10–20% higher than those of corresponding batch syntheses, indicating improved mass and heat transfer in flow. A systematic exploration of synthetic parameters using a factorial design of experiments approach revealed the key correlations between the process parameters and yields and particle size distributions. The proton conductivity of the synthesized Cu-SAT MOF was evaluated in a mixed matrix membrane model PEM with polyvinylpyrrolidone and polyvinylidene fluoride polymers, exhibiting a promising composite conductivity of 1.34 ± 0.05 mS cm−1 at 353 K and 95% relative humidity (RH).
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Sep 2023
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I11-High Resolution Powder Diffraction
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Ashleigh M.
Chester
,
Celia
Castillo-Blas
,
Roman
Sajzew
,
Bruno
Poletto Rodrigues
,
Ruben
Mas Balleste
,
Alicia
Moya
,
Jessica E.
Snelson
,
Sean M.
Collins
,
Adam F.
Sapnik
,
Georgina P.
Robertson
,
Daniel J. M.
Irving
,
Lothar
Wondraczek
,
David A.
Keen
,
Thomas D.
Bennett
Diamond Proposal Number(s):
[20038]
Open Access
Abstract: Recently, increased attention has been focused on amorphous metal-organic frameworks (MOFs) and, more specifically, MOF glasses, the first new glass category discovered since the 1970s. In this work, we explore the fabrication of a compositional series of hybrid blends, the first example of blending a MOF and inorganic glass. We combine ZIF-62(Zn) glass and an inorganic glass, 30Na2O-70P2O5, in an effort to combine the chemical versatility of the MOF glass with the mechanical properties of the inorganic glass. We investigate the interfacial interactions between the two components using pair distribution function analysis and solid state NMR spectroscopy, and suggest potential interactions between the two phases. Thermal analysis of the blend samples indicated that they were less thermally stable than the starting materials, and had a Tg shifted relative to the pristine materials. Annular dark field scanning transmission electron microscopy tomography, X-ray energy dispersive spectroscopy (EDS), nanoindentation and 31P NMR all indicated close mixing of the two phases, suggesting that immiscible blends had formed.
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Sep 2023
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[20198]
Open Access
Abstract: Intentionally disordered metal–organic frameworks (MOFs) display rich functional behaviour. However, the characterisation of their atomic structures remains incredibly challenging. X-ray pair distribution function techniques have been pivotal in determining their average local structure but are largely insensitive to spatial variations in the structure. Fe-BTC (BTC = 1,3,5-benzenetricarboxylate) is a nanocomposite MOF, known for its catalytic properties, comprising crystalline nanoparticles and an amorphous matrix. Here, we use scanning electron diffraction to first map the crystalline and amorphous components to evaluate domain size and then to carry out electron pair distribution function analysis to probe the spatially separated atomic structure of the amorphous matrix. Further Bragg scattering analysis reveals systematic orientational disorder within Fe-BTC’s nanocrystallites, showing over 10° of continuous lattice rotation across single particles. Finally, we identify candidate unit cells for the crystalline component. These independent structural analyses quantify disorder in Fe-BTC at the critical length scale for engineering composite MOF materials.
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May 2023
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E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[30159, 31872]
Abstract: Disorder in organic semiconductors (OSCs) plays a determining role in energy transport properties underpinning optoelectronic device performance [1]. Both energetic disorder native to perfect crystals as well as deviations from crystalline order control transport properties [2,3]. Alongside crystallographic defects like stacking faults and grain boundaries, dislocations that distort molecular packing can introduce exciton- or charge-carrier traps that significantly hamper intermolecular energy transport [4]. Electron microscopy has been a mainstay for probing these crystallographic defects in inorganic semiconductors. Recent progress in atomically resolved electron microscopy has enabled imaging of individual defects in hybrid perovskites [5]. But while hybrid perovskites show structural degradation on the order of <200 e–Å-2 before [6], small molecule OSCs may undergo comparable loss of structure under exposures <30 e–Å-2 [7,8]. Methods that enable the crystallographic analysis of dislocations in beam-sensitive OSCs are therefore a necessary first step to establish their performance effects.
A dislocation is described crystallographically in terms of a displacement vector in the lattice, termed a Burgers vector b. Most attempts to characterize dislocations in organic molecular crystals have relied on techniques at low spatial resolution, including etch pit imaging [9] and scanning probe techniques [10]. These approaches are unable to directly record the crystallography of dislocations or access the nanometre spatial resolution required to isolate individual defects. In contrast, electron microscopy combines the necessary spatial resolution to image the dislocation line as well as the crystallographic detail from electron diffraction to retrieve the Burgers vector. Typically, such an analysis is carried out by many repeated electron beam exposures and sample rotations aimed at identifying the crystal planes associated with a diffraction vector g that are not distorted by the dislocation, a so-called ‘invisibility criterion’ at g.b = 0. Here, we advance this approach for OSCs to carry out unambiguous analysis of the dislocation Burgers vector and type (screw, edge, or mixed) using four-dimensional scanning transmission electron microscopy (4D-STEM) now in a single exposure at a fluence of ~10 e–Å-2.
Thin films of p-terphenyl and anthracene were prepared by solution crystallization as a set of benchmark organic optoelectronic materials [11]. On transfer to a lacey carbon support film for electron microscopy, the draping of the OSC crystals on the support film introduces a small amount of sample bending. This bending defines a set of diffraction conditions that produce ribbons of bright intensity running across images of the film referred to as bend contours. These bend contours exhibit an abrupt shift or break on crossing dislocations unless they satisfy the invisibility criterion. Our 4D-STEM approach specifically supports simultaneous analysis of many lattice planes approximately parallel to the crystal direction perpendicular to the film, i.e. [001] for p-terphenyl and [101] for anthracene. Plotting and fitting the magnitude of breaks in the bend contours as a function of the corresponding diffraction vectors (g) for each plane determines the Burgers vector. For instance, this analysis establishes mixed-type b = [010] dislocations in p-terphenyl and anthracene. These generalizable methods make an analysis of the Burgers vectors of dislocations in beam-sensitive OSC films a routine process. The capability to measure the character and type of dislocations will provide experimental input for models of distortions at these structural defects and enables assessing methods for inhibiting dislocation formation during crystal growth and reducing or removing their deleterious contributions to device performance.
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Mar 2023
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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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