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

Instruments / Technical Area	Publication Details	Published
I15-Extreme Conditions	Pressure-induced chemical decomposition of copper orthovanadate (α-Cu3V2O8) Daniel Díaz-Anichtchenko , Robin Turnbull , Enrico Bandiello , Simone Anzellini , Srungarpu Nagabhusan Achary , Daniel Errandonea Journal Of Materials Chemistry C 43 DOI: 10.1039/D1TC02901K Diamond Proposal Number(s): [21610] Show Abstract ▼ Abstract: The high pressure stability of α-Cu3V2O8 has been investigated via complementary high pressure synchrotron X-ray diffraction experiments and theoretical density functional theory calculations. The results of both experiment and theory are in close agreement. The main result of this work is that α-Cu3V2O8 undergoes a pressure-induced chemical decomposition into CuO and V2O5 at a modest pressure of ∼1.35 GPa according to the experimental observations, and at ∼2.45 GPa according to the calculations. The decomposition is investigated with enthalpy calculations and one of the main driving factors is the stability of the octhedral oxygen-coordination of the metal atoms in the decompositon products. Additionally, we determine the bulk modulus of α-Cu3V2O8 to be the lowest of all known vanadates, at 52(2) GPa, due to its crystal structure, and determine the corresponding isothermal compressibility tensor.	Sep 2021
	Latest directions in p-type transparent conductor design Joe Willis , David O. Scanlon Journal Of Materials Chemistry C 411 DOI: 10.1039/D1TC02547C Open Access Show Abstract ▼ Abstract: Transparent conducting materials (TCMs) are crucial in the operation of modern opto-electronic devices, combining the lucrative properties of optical transparency and electronic conductivity. More than ever we rely on display and touch screens, energy efficient windows and solar cells in our day to day lives. The market for transparent electronics is projected to surpass $3.8 billion by 2026 as the automotive industry seek to incorporate pop-up displays into driver windshields, and the prospect of touch-enabled transparent displays challenges the traditional mouse and keyboard mode of computer operation. However, these new technologies rely heavily on the development of high performance p-type TCMs, a task that has posed a significant challenge to researchers for decades. This review will cover the basic theory and design principles of transparent conductors, followed by an overview of early p-type TCMs and their shortcomings. We discuss the impact of high-throughput screening studies on materials discovery and critically assess the family of p-type halide perovskites that emerged from these, ruling them as unsuitable candidates for high-performance applications. We find that phosphides, selenides, tellurides and halides are the most promising emerging materials, capable of achieving greater valence band dispersion than traditional oxides, and we discuss the challenges facing these more exotic systems. The smorgasbord of materials presented in this review should guide experimental and computational scientists alike in the next phase of p-type transparent conductor research.	Aug 2021
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS I09-Surface and Interface Structural Analysis	Understanding ultrafast charge transfer processes in SnS and SnS 2 : using the core hole clock method to measure attosecond orbital-dependent electron delocalisation in semiconducting layered materials Freddy E. Oropeza , Mariam Barawi , Elena Alfonso Gonzalez , Víctor A. De La Pena O'Shea , Juan F. Trigo , Cecilia Guillén , Fernan Saiz , Ignacio J. Villar-Garcia Journal Of Materials Chemistry C 7 DOI: 10.1039/D1TC02866A Diamond Proposal Number(s): [21754, 22365] Show Abstract ▼ Abstract: SnS and SnS2 are earth abundant layered semiconductors that owing to their optoelectronic properties have been proposed as materials for different photovoltaic, photosensing and photocatalytic applications. The intrinsic efficiency of these materials for such applications is driven by their charge transfer dynamics, which in turn depend on their electronic structure and the interaction of the molecular orbitals involved in the charge transfer process. In this publication, we provide a step-by-step description of the use of the core hole clock method to obtain orbital dependent charge transfer times for SnS2 and SnS down to the attosecond time scale. We use both S 1s and Sn 3d core holes, with natural core hole lifetimes of 1.3 fs and 300 as, as time references to obtain a complete picture of electron delocalisation times across the conduction band of both materials. Ultrafast electron delocalisation times, lower than 5 femtoseconds and as low as tens of attoseconds, are measured for electrons excited to the unoccupied molecular orbitals of both materials. SnS delocalisation times are found to be shorter than those for SnS2 for all probed molecular orbitals, with delocalisation times being more than an order of magnitude shorter for higher lying molecular orbitals. DFT calculations show that charge transfer dynamics are strongly influenced by the interlayer interaction within these materials. The slower delocalisation of electrons in SnS2 can be linked to the restricted out of plane spatial dispersion of the molecular orbitals in the conduction band and consequent limitation of the electron delocalisation pathways. The results presented in this paper highlight the high potential of combining the core hole clock method with high-level DFT calculations to study orbital dependent charge transfer in semiconductor materials for optoelectronic applications down to the attosecond scale.	Jul 2021
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

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