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

Instruments / Technical Area	Publication Details	Published
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
I07-Surface & interface diffraction	Alkyl chain assisted thin film growth of 2,7-dioctyloxy-benzothienobenzothiophene Harald Spreitzer , Benjamin Kaufmann , Christian Ruzié , Christian Rothel , Thomas Arnold , Yves H. Geerts , Christian Teichert , Roland Resel , Andrew O. F. Jones Journal Of Materials Chemistry C 26 DOI: 10.1039/C9TC01979K Diamond Proposal Number(s): [13569] Open Access Show Abstract ▼ Abstract: An understanding of the thin film growth modes of substrate-induced polymorphs allows a deeper insight into the origin of this class of materials. Their onset of crystallisation, the subsequent crystal growth, the evolution of the thin film morphology and the transfer to the equilibrium bulk structure are still not fully understood. This work investigates the thin film formation of a conjugated molecule with terminal alkyl chains. Thin films of 2,7-dioctyloxy[1]benzothieno[3,2-b]benzothiophene were grown by physical vapor deposition on silicon oxide surfaces with varying the film thicknesses from the sub-monolayer regime up to 33 layer thick films. Additionally, the substrate temperature and deposition rate were varied. The films were investigated by atomic force microscopy, X-ray reflectivity and grazing incidence X-ray diffraction. The first growth stage is a closed monolayer with a thickness of 3 nm formed by upright-standing molecules. It is found that the substrate-induced crystal structure is already formed within the first monolayer and continues its growth up to the largest investigated film thickness. The characteristic morphology is terraced islands over the whole thickness range. On top of the first monolayer a morphology with several terrace levels appears, which is associated with a rapid increase of the surface roughness. At larger film thicknesses (≥13 nm) the number of terrace steps does not increase significantly, so that the surface roughness only increases slowly. This work shows that molecules with terminal alkyl chains can form a substrate-induced phase up to large film thicknesses without the appearance of the equilibrium bulk phase.	Jun 2019
I19-Small Molecule Single Crystal Diffraction	The influence of molecular geometry on the efficiency of thermally activated delayed fluorescence Roberto S. Nobuyasu , Jonathan S. Ward , Jamie Gibson , Beth A. Laidlaw , Zhongjie Ren , Przemyslaw Data , Andrei S. Batsanov , Thomas J. Penfold , Martin R. Bryce , Fernando B. Dias Journal Of Materials Chemistry C 7, 6672-6684 DOI: 10.1039/C9TC00720B Diamond Proposal Number(s): [11145] Open Access Show Abstract ▼ Abstract: In this work we successfully developed a strategy for positively influencing the conformation of thermally activated delayed fluorescence (TADF) molecules containing phenothiazine as the electron donor (D) unit, and dibenzothiophene-S,S-dioxide as the acceptor (A), linked in D–A and D–A–D structures. In this strategy the effect of restricted molecular geometry is explored to maximize TADF emission. The presence of bulky substituents in different positions on the donor unit forces the molecules to adopt an axial conformer where the singlet charge transfer state is shifted to higher energy, resulting in the oscillator strength and luminescence efficiency decreasing. With bulky substituents on the acceptor unit, the molecules adopt an equatorial geometry, where the donor and acceptor units are locked in relative near-orthogonal geometry. In this case the individual signatures of the donor and acceptor units are evident in the absorption spectra, demonstrating that the substituent in the acceptor uncouples the electronic linkage between the donor and acceptor more effectively than with donor substitution. In contrast with the axial conformers that show very weak TADF, even with a small singlet triplet gap, molecules with equatorial geometry show stronger oscillator strength and luminescence efficiency and are excellent TADF emitters. Acceptor-substituted molecules 6 and 7 in particular show extremely high TADF efficiency in solution and solid film, even with a singlet–triplet energy gap around 0.2 eV. This extensive study provides important criteria for the design of novel TADF and room temperature phosphorescence (RTP) emitters with optimized geometry.	May 2019
I11-High Resolution Powder Diffraction	Single-phase white-emitting phosphors based on apatite-type gadolinium silicate, Gd 9.33 (SiO 4 ) 6 O 2 doped with Dy 3+ , Eu 3+ and Tb 3+ Melissa M. Rodríguez-garcía , J. A. Gareth Williams , Ivana Radosavljevic Evans Journal Of Materials Chemistry C 71 DOI: 10.1039/C9TC02336D Show Abstract ▼ Abstract: Two series of new apatite-type silicate materials were synthesised and characterised with the aim of achieving white light emission from single-phase phosphors. The Gd9.33(SiO4)6O2 host was doped systematically with Dy3+, Tb3+ and Eu3+ to tune the emission to the white light region. Eight new phosphors with emission very near the ideal white light point are reported. The best properties are found for the 0.5%Tb, 0.03%Eu co-doped Gd9.33(SiO4)6O2, with colour coordinates (0.340, 0.341) and a correlated colour temperature of 5190 K, corresponding to the white light region. The temporal decay of emission from the doped ions was measured following pulsed excitation of the Gd3+ host. An evaluation of energy transfer and quenching effects in the phosphors has been made based on the lifetimes so obtained. In particular, a comparison of the Eu3+ lifetimes in the Dy,Eu co-doped phosphors with those in the Tb,Eu-containing materials suggests quenching of the 5D0 excited state of Eu3+ by the Dy3+ ions. These observations imply that the combination of Eu3+ and Dy3+ ions may not provide optimal efficiencies in phosphors, and that the combination of Eu3+ and Tb3+ is likely to be superior for optimising the emission properties.	May 2019
	A detailed experimental and theoretical study into NaSbS 2 as an emerging solar absorber Winnie W. Leung , Christopher N. Savory , Robert Palgrave , David O. Scanlon Journal Of Materials Chemistry C DOI: 10.1039/C8TC06284F Show Abstract ▼ Abstract: As photovoltaics have grown to become one of the dominant renewable energy generating technologies, attention has fallen upon thin-film materials as a route to lightweight, flexible and portable solar cells. NaSbS2 has recently been proposed as a non-toxic, earth abundant solar absorber for thin-film cells. In this study, we use a combined theoretical and experimental approach to characterize and assess the electronic and optical properties of NaSbS2 as a promising solar absorber. Our results, utilising two theoretical efficiency metrics, demonstrate that NaSbS2 may be limited for use in single-junction cells by a forbidden band gap and slow absorption onset. Other features of its electronic structure, however, indicate that the material may still be promising in thermoelectric applications.	Jan 2019
I20-Scanning-X-ray spectroscopy (XAS/XES)	Interplay between electronic and structural effects on the photoluminescence decay mechanisms in LaPO4·nH2O:Tb3+ and LaPO4:Tb3+ single-crystal nanorods M. T. Colomer , S. Diaz-moreno , A. Tamayo , A. L. Ortiz , J. Chaboy Journal Of Materials Chemistry C DOI: 10.1039/C8TC03187H Diamond Proposal Number(s): [15968] Show Abstract ▼ Abstract: A novel High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy (HERFD-XAS) study at the Tb L3-edge for the rhabdophane-type LaPO4·nH2O:Tb3+ and the monazite-type LaTbPO4:Tb3+ nanorods is reported. We have observed that the changes in the white-line intensity follow a similar trend to that previously observed in the photoluminescence behaviour of these materials. Those changes have been assigned to the localization of the terbium 5d states and the modification induced by the hybridization with the next neighbours as the terbium content is varied. The interplay between electronic (d-states localization) and structural (local disorder) effects is used to explain the different optical behaviour between the two series of nanorods. XAS results indicate that the local ordering is a key factor influencing the different emission efficiency, quenching effect and decay lifetimes observed experimentally for both series of nanorods. The present results indicate that the long lifetime decay process is accounted within a standard single Tb3+ ion scenario, where the structural disorder, favoured by the presence of water molecules in the structure, aids the non-radiative recombination processes. Implications for future use of the white-line intensity in the HERFD-XAS spectra in characterizing other luminescent materials are also discussed.	Oct 2018
B18-Core EXAFS	Direct and continuous hydrothermal flow synthesis of thermochromic phase pure monoclinic VO 2 nanoparticles Delphine Malarde , Ian D. Johnson , Ian J. Godfrey , Michael J. Powell , Giannantonio Cibin , Raul Quesada-cabrera , Jawwad A. Darr , Claire J. Carmalt , Gopinathan Sankar , Ivan P. Parkin , Robert G. Palgrave Journal Of Materials Chemistry C DOI: 10.1039/C8TC00859K Diamond Proposal Number(s): [17147] Open Access Show Abstract ▼ Abstract: Monoclinic vanadium(IV) oxide [VO2(M)] is a widely studied material due to its thermochromic properties and its potential use for energy-efficient glazing applications. VO2(M) nanoparticles can be a great advantage for energy-efficient glazing as below 50 nm the nanoparticles poorly interact with visible wavelengths – resulting in an increase in visible light transmittance whilst maintaining the thermochromic response of the material. The direct synthesis of VO2(M) nanoparticles with effective thermochromic properties will be a step forward towards industrial applications of this material. Unfortunately, many of the synthesis processes reported so far involve multiple steps, including post-treatment, and the synthesis is not always reproducible. In this study, we present the first direct synthesis of pure monoclinic VO2 nanoparticles by continuous hydrothermal flow synthesis (CHFS). TEM images showed that nanoparticles in the size range of 30-40 nm were produced. The VO2(M) nanoparticles also showed good thermochromic properties with a solar modulation (∆Tsol) of 3.8%, as established by UV/Vis spectroscopy. A range of analytical methods was used to characterise the materials, including X-ray absorption spectroscopy (XANES and EXAFS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The influence of niobium (Nb) doping on the physical and thermochromic properties of the VO2 nanoparticles was also explored. Previous work has shown a sharp metal-to-semiconductor transition of VO2 upon incorporation of Nb dopant. The results of the current work suggested these changes are likely due to changes on the local structure of the oxide.	Oct 2018

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