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33 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I10-Beamline for Advanced Dichroism	Switching of the mechanism of charge transport induced by phase transitions in tunnel junctions with large biomolecular cages Nipun Kumar Gupta , Rupali Reddy Pasula , Senthil Kumar Karuppannan , Zhang Ziyu , Anton Tadich , Bruce Cowie , Dong-Chen Qi , Peter Bencok , Sierin Lim , Christian A. Nijhuis Journal Of Materials Chemistry C 446 DOI: 10.1039/D0TC05773H Diamond Proposal Number(s): [22157] Open Access Show Abstract ▼ Abstract: Tunnel junctions based on Fe storing globular proteins are an interesting class of biomolecular tunnel junctions due to their tunable Fe ion loading, symmetrical structure and thermal stability, and are therefore attractive to study the mechanisms of charge transport (CT) at the molecular level. This paper describes a temperature-induced change in the CT mechanism across junctions with large globular (∼25 nm in diameter) E2-proteins bioengineered with Fe-binding peptides from ferritin (E2-LFtn) to mineralise Fe ions in the form of iron oxide nanoparticles (NPs) inside the protein's cavity. The iron oxide NPs provide accessible energy states that support high CT rates and shallow activation barriers. Interestingly, the CT mechanism changes abruptly, but reversibly, from incoherent tunnelling (which is thermally activated) to coherent tunnelling (which is activationless) across the E2-LFtn-based tunnel junctions with the highest Fe ion loading at a temperature of 220–240 K. During this transition the current density across the junctions increases by a factor of 13 at an applied voltage of V = −0.8 V. X-ray absorption spectroscopy indicates that the iron oxide NPs inside the E2-LFtn cages undergo a reversible phase transition; this phase transition opens up new a tunnelling pathway changing the mechanism of CT from thermally activated to activationless tunnelling despite the large size of the E2-LFtn and associated distance for tunnelling.	Mar 2021
I07-Surface & interface diffraction	Electron spin as fingerprint for charge generation and transport in doped organic semiconductors Alberto Privitera , Ross Warren , Giacomo Londi , Pascal Kaienburg , Junjie Liu , Andreas Sperlich , Andreas E. Lauritzen , Oliver Thimm , Arzhang Ardavan , David Beljonne , Moritz Riede Journal Of Materials Chemistry C 210 DOI: 10.1039/D0TC06097F Diamond Proposal Number(s): [20426] Open Access Show Abstract ▼ Abstract: We use the electron spin as a probe to gain insight into the mechanism of molecular doping in a p-doped zinc phthalocyanine host across a broad range of temperatures (80–280 K) and doping concentrations (0–5 wt% of F6-TCNNQ). Electron paramagnetic resonance (EPR) spectroscopy discloses the presence of two main paramagnetic species distinguished by two different g-tensors, which are assigned based on density functional theory calculations to the formation of a positive polaron on the host and a radical anion on the dopant. Close inspection of the EPR spectra shows that radical anions on the dopants couple in an antiferromagnetic manner at device-relevant doping concentrations, thereby suggesting the presence of dopant clustering, and that positive polarons on the molecular host move by polaron hopping with an activation energy of 5 meV. This activation energy is substantially smaller than that inferred from electrical conductivity measurements (∼233 meV), as the latter also includes a (major) contribution from charge-transfer state dissociation. It emerges from this study that probing the electron spin can provide rich information on the nature and dynamics of charge carriers generated upon doping molecular semiconductors, which could serve as a basis for the design of the next generation of dopant and host materials.	Feb 2021
I09-Surface and Interface Structural Analysis	Sb 5s2 lone pairs and band alignment of Sb2Se3 : a photoemission and density functional theory study Christopher H. Don , Huw Shiel , Theodore D. C. Hobson , Christopher N. Savory , Jack E. N. Swallow , Matthew J. Smiles , Leanne A. H. Jones , Thomas J. Featherstone , Pardeep K. Thakur , Tien-lin Lee , Ken Durose , Jonathan D. Major , Vinod R. Dhanak , David O. Scanlon , Tim D. Veal Journal Of Materials Chemistry C 27 DOI: 10.1039/D0TC03470C Diamond Proposal Number(s): [21431] Open Access Show Abstract ▼ Abstract: The presence of a lone pair of 5s electrons at the valence band maximum (VBM) of Sb2Se3 and the resulting band alignments are investigated using soft and hard X-ray photoemission spectroscopy in parallel with density functional theory (DFT) calculations. Vacuum-cleaved and exfoliated bulk crystals of Sb2Se3 are analysed using laboratory and synchrotron X-ray sources to acquire high resolution valence band spectra with both soft and hard X-rays. Utilising the photon-energy dependence of different orbital cross-sections and corresponding DFT calculations, the various orbital contributions to the valence band could be identified, including the 5s orbital's presence at the VBM. The ionization potential is also determined and places the VBM at 5.13 eV below the vacuum level, similar to other materials with 5s2 lone pairs, but far above those of related materials without lone pairs of electrons.	Aug 2020
I15-Extreme Conditions	Cobalt-induced structural modulation in multiferroic Aurivillius-phase oxides Vladimir Koval , Yu Shi , Ivan Škorvánek , Giuseppe Viola , Radovan Bures , Karel Saksl , Pavla Roupcova , Man Zhang , Chenlong Jia , Haixue Yan Journal Of Materials Chemistry C DOI: 10.1039/D0TC01443E Diamond Proposal Number(s): [18273] Show Abstract ▼ Abstract: Attaining robust magnetic long-range order in ferroelectric Aurivillius-phase oxides at room temperature has recently attracted considerable attention of material scientists and engineers for the development of magnetoelectric-active materials in microelectronics and spintronics. Here, we report the structural evolution and its relation to the macroscopic magnetization of the series samples of Aurivillius (Bi4.3Gd0.7)(Fe1-xCox)1+yTi3-2yNbyO15 (x=0, 0.3, 0.5 and y=0, 0.3) compounds prepared by solid state reaction, aiming at shedding light on the Co substitution-induced ferromagnetism at room temperature and above. The Co-free composition showed a single-phase four-layered Aurivillius structure (a space group A21am), while the Co substitution was found to give rise to a mixed-layer structure composed of four- and three-layered phases. Rietveld analysis of the synchrotron X-ray diffraction data showed that the reduction in the number of layers across the Aurivillius morphotropic transition boundary is accompanied by a structural phase transformation from A21am to B2cb. The disordered intergrowth of these phases was evidenced by high-resolution transmission electron microscopy and found to originate from a nanoscale structural modulation occurring at the interface between the two phases. A sextet suggesting a long-range magnetic ordering in the doped samples was deduced from Mössbauer spectra. Magnetic-property measurements, indeed, confirmed a ferromagnetic state of these samples at elevated temperatures. The highest values of the remanent and saturation magnetization at room temperature were obtained for the compositions with x=0.3, in which the occurrence and enhancement of the magnetization can be attributed to the ferromagnetic clustering of the FeO6 and CoO6 octahedra and, partly, also to the spin canting effects and/or a double-exchange magnetic interaction between the mixed valence cobalt through oxygen. The cooperative freezing of randomly distributed Fe-O-Co clusters is suggested to be responsible for the spin glass-like behaviour observed at low temperatures.	May 2020
I16-Materials and Magnetism I22-Small angle scattering & Diffraction	Tailoring liquid crystal honeycombs by head-group choice in bird-like bent-core mesogens Ya-xin Li , Huifang Cheng , Xiangbing Zeng , Yuan Tao , Xiaohong Cheng , Goran Ungar Journal Of Materials Chemistry C 106 DOI: 10.1039/D0TC01879A Open Access Show Abstract ▼ Abstract: We introduce a new class of mesogens that are bird-like in shape and form honeycomb-type supramolecular liquid crystals. They have a bent pi-conjugated aromatic core as wings, a linear or branched chain as the tail and a selection of functional headgroups. Honeycombs of non-centrosymmetric trigonal type (p3m1) are obtained, along with two different complex honeycomb superlattices (p31m and p2gg) and a randomized hexagonal mesophase (p6mm). The key determinant of the self-assembled structure is the nature of interaction of the headgroup with the glycerols at the ends of the wings. The structure depends on whether the sub-columns lying along the edges of the prismatic cells contain pure or mixed headgroups and wing-end hydrogen-bonding groups. Its assembly is further controlled by reducing the tail-chain volume, inducing out-of-plane buckling of the honeycomb. These two modes of symmetry breaking lead to structural polarity both in- and out-of-plane, opening the way to applications in devices relying on properties such as ferroelectricity and second harmonic generation.	May 2020
I07-Surface & interface diffraction	Efficiency enhancement of small molecule organic solar cells using hexapropyltruxene as an interface layer Hanyang Ye , Sameer Vajjala Kesava , Josue Martinez Hardigree , Roisin E. Brown , Giulio Mazzotta , Ross Warren , Peter J. Skabara , Moritz Riede Journal Of Materials Chemistry C 8, 4909 - 4918 DOI: 10.1039/C9TC06845G Diamond Proposal Number(s): [18016] Show Abstract ▼ Abstract: The quenching of excitons in organic solar cells can play a significant role in limiting their power conversion efficiency (PCE). In this article, we investigate the effect of a thin layer of hexapropyltruxene inserted at the interface between the electron donor boron subphthalocyanine chloride (SubPc) and its underlying hole contact in planar heterojunction solar cells. We find that a 3.8 nm hexapropyltruxene interlayer between the molybdenum oxide (MoOx) hole contact and SubPc is sufficient to improve PCE in SubPc/C60 fullerene solar cells from 2.6% to 3.0%, a ∼20% performance improvement. While the absorption stays roughly the same, the comparison of external and internal quantum efficiencies reveals a significant increase in SubPc's contribution to the current for light with wavelengths between 520 and 600 nm. Microstructure and surface morphology assessed with in situ Grazing-Incidence Wide-Angle X-Ray Scattering (GIWAXS) and Atomic Force Microscopy (AFM), are evaluated alongside in situ spectroscopic ellipsometry, and photoluminescence measurements. The microstructural investigations demonstrate changes to the surface and bulk of SubPc grown atop a hexapropyltruxene interlayer indicating that the latter acts as a template layer in a similar way as MoOx. However, the improvement in PCE is found to be mainly via reduced exciton quenching at the MoOx contact with the insertion of the hexapropyltruxene layer.	Apr 2020
B23-Circular Dichroism	Macroscopic chirality of twist-bend nematic phase in bent dimers confirmed by circular dichroism Warren Stevenson , Xiangbing Zeng , Chris Welch , Anil K. Thakur , Goran Ungar , Georg Mehl Journal Of Materials Chemistry C DOI: 10.1039/C9TC05061B Show Abstract ▼ Abstract: Many achiral bent molecules and some polymers with such repeat units exhibit a liquid crystal phase transition between a conventional nematic (N), and a second nematic (Nx) with periodically modulated orientation. Theory predicts several possible structures for the Nx phase, some of which are chiral (helical), and others achiral (e.g. zigzag). Experimentally distinguishing which modulation type is present is non-trivial and the structure is often assumed to be helical despite the other possibilities. Here we use circular dichroism (CD) spectroscopy to directly and unambiguously identify chirality in the Nx phase of two different dimer series, “DTC5Cn” and “CBCnCB”, which vary in (CH2)n spacer length (n=5, 7, 9). In doing so we have determined that the modulation type is helical in all samples. The temperature dependence of the CD signal was also investigated, suggesting that the helical structure progressively unwinds on approach to the high temperature N phase.	Dec 2019
I15-Extreme Conditions	Purification by SPS and formation of a unique 3D nanoscale network: the showcase of Ni–Cr–S H. Groß , T. Dankwort , A.-l. Hansen , U. Schürmann , V. Duppel , M. Poschmann , A. Meingast , D. Groeneveld , J. König , W. Bensch , L. Kienle Journal Of Materials Chemistry C 19 DOI: 10.1039/C9TC04548A Show Abstract ▼ Abstract: The occurrence of a unique 3D nanoscale network in Ni–Cr–S, treated via spark-plasma sintering, was discovered with a variety of ex situ and in situ TEM and XRD techniques. The starting material, consisting of a heterogeneous mixture of different phases, could be purified upon application of the sintering process. The obtained samples showed a network of chemically segregated domains being either Ni rich and Cr deficient or vice versa. These domains could be proven to intergrow fully coherently in 3D, thus establishing a unique microstructure. Electron beam irradiation caused the initial Cr3S4-type structures to transform into the disordered NiAs-type. The disordering is characterised by significant short-range ordering as indicated by the appearance of prominent diffuse scattering. Thermoelectric characterisation at room temperature indicated an n-type semiconductor behaviour with thermal and electrical conductivities similar to usual thermoelectric materials, however with a low Seebeck coefficient and a low power factor of 49.3 μW m−1 K−2.	Oct 2019
B21-High Throughput SAXS	Multimodal control of liquid crystalline mesophases from surfactants with photoswitchable tails Judith E. Houston , Elaine A. Kelly , Margarita Kruteva , Kiriaki Chrissopoulou , Nathan Cowieson , Rachel C. Evans Journal Of Materials Chemistry C 51 DOI: 10.1039/C9TC04079J Diamond Proposal Number(s): [16235] Open Access Show Abstract ▼ Abstract: Non-invasive manipulation of the hierarchical structure of functional materials is a key challenge in the advancement of optoelectronics, energy conversion and storage devices and drug delivery systems. Lyotropic liquids crystals, with their long-range order and a rich array of structures, have long been exploited as soft templates to prepare porous materials. The potential to modify the template structure using an external stimulus such as light could lead to new architectures. Here, using a combination of small-angle X-ray scattering and polarised optical microscopy, we decipher the various structure/self-assembly relationships of neutral surfactants bearing photoswitchable tails, which self-organise into a rich variety of lyotropic liquid crystalline mesophases. Facile, multimodal control of the nanoscale morphology of these single-component systems is achieved through: (i) molecular structure, via careful selection of the alkyl tail/ethylene oxide headgroup lengths; (ii) concentration; (iii) temperature; and (iv) photoisomerisation. The nanoscale architectures range from the weakly concentrated hyperswollen lamellar phases, the more common lyotropic lamellar and hexagonal phases, to pure thermotropic liquid crystals; all of which are accessible at room temperature. Photoisomerisation with UV light leads to the reversible destruction of the liquid crystalline phase, which can be spatially controlled through the use of a mask. This extensive study demonstrates the versatility of neutral photosurfactants and paves the way for new applications, such as photoresponsive templates or drug delivery systems.	Aug 2019
I15-Extreme Conditions	Quenching-assisted actuation mechanisms in core-shell structured BiFeO3−BaTiO3 piezoceramics Ilkan Calisir , Annette K. Kleppe , Antonio Feteira , David A. Hall Journal Of Materials Chemistry C DOI: 10.1039/C9TC01583C Diamond Proposal Number(s): [16390] Show Abstract ▼ Abstract: Electromechanical actuation in piezoceramics is usually enhanced by creating chemically homogeneous materials with structurally heterogeneous morphotropic phase boundaries, leading to abrupt changes in ion displacement directions within the perovskite unit cell. In the present study, an alternative mechanism to enhance electromechanical coupling is found in both chemically and structurally heterogeneous BiFeO3−BaTiO3 lead-free piezoceramics. Such a mechanism is observed in a composition exhibiting core-shell type microstructure, associated with donor-type substitution of Ti4+ for Fe3+, and is primarily activated by thermal quenching treatment. Here, we describe the use of in-situ high-energy synchrotron X-ray powder diffraction upon the application of a high electric field to directly monitor the ferroelectric and elastic interactions between these composite-like components, formed as core and shell regions within grains. Translational short or long-range ordering is observed in the BiFeO3‒depleted shell regions which undergo significant structural alterations from pseudocubic Pm-3m relaxor-ferroelectric in slow-cooled ceramics to rhombohedral R3c or R3m with long-range ferroelectric order in the quenched state. The strain contributions from each component are calculated, leading to the conclusion that the total macroscopic strain arises predominantly from the transformed shell after quenching. Such observations are also complemented by investigations of microstructure and electrical properties, including ferroelectric behaviour and temperature-dependent dielectric properties.	Jul 2019

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