I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[18974]
Abstract: Potassium-ion (K-ion) batteries potentially offer numerous advantages over conventional lithium-ion batteries as a result of the high natural abundance of potassium and its lower positive charge density, compared with lithium. This introduces the possibility of using K-ion in fast charging applications, in which cost effectiveness is also a major factor. Unlike for sodium-ion batteries, graphite can be used as an anode in K-ion cells, for which an extensive supply chain, electrode manufacturing infrastructure, and knowledge already exists. However, the performance of graphite anodes in K-ion cells does not meet expectations, with rapid capacity fading and poor first cycle irreversible capacities often reported. Here we investigate the formation and composition of the solid electrolyte interphase (SEI) as well as K+ insertion in graphite anodes in K-ion batteries. Through the use of energy-tuned synchrotron-based X-ray photoelectron spectroscopy, we make a detailed analysis at three probing depths up to ~50 nm of graphite anodes cycled to various potentials on the first discharge-charge cycle. Extensive SEI formation from a KPF6/DEC:EC electrolyte system is found to occur at low potentials during the insertion of potassium into graphite. During the subsequent removal of potassium from the structure, the thick SEI is partially stripped from the electrode, demonstrating that the SEI layer is unstable and contributes to a significant proportion of the capacity on both discharge and charge. With this in mind, further work is required to develop an electrolyte system with stable SEI layer formation on graphite in order to advance K-ion battery technology.
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Nov 2019
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B21-High Throughput SAXS
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Diamond Proposal Number(s):
[18523]
Abstract: A novel lipopeptide C16KTTβAH was designed that incorporates the KTT tripeptide sequence from “Matrixyl” lipopeptides along with the bioactive βAH (β-alanine-histidine) carnosine dipeptide motif, attached to a C16 hexadecyl lipid chain. We show that this peptide amphiphile self-assembles above a critical aggregation concentration into β-sheet nanotape structures in water, PBS and cell culture media. Nanotape bundle structures were imaged in PBS, the bundling resulting from nanotape associations due to charge screening in the buffer. In addition, hydrogelation was observed and the gel modulus was measured in different aqueous media conditions, revealing tunable hydrogel modulus depending on concentration and nature of the aqueous phase. Stiff hydrogels were observed by direct dissolution in PBS and it was also possible to prepare hydrogels with unprecedented high modulus from low concentration solutions by injection of dilute aqueous solutions into PBS. These hydrogels have exceptional stiffness compared to previously reported β-sheet peptide-based materials. In addition, macroscopic soft threads can be drawn from concentrated aqueous solutions of the lipopeptides which contain aligned nematic structures. The anti-cancer activity of the lipopeptide was assessed using two model breast cancer cell lines, compared to two fibroblast cell line controls. These studies revealed selective concentration-dependent cytotoxicity against MCF-7 cancer cells in a mM concentration range. It was shown that this occurs below the onset of lipopeptide aggregation (i.e. below the critical aggregation concentration), indicating that the cytotoxicity is not related to self-assembly but is an intrinsic property of C16KTTβAH. Finally, hydrogels of this lipopeptide demonstrated slow uptake and release of the dye Congo red, a model diagnostic compound.
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Aug 2019
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Thomas J.
Whittles
,
Tim D.
Veal
,
Christopher N.
Savory
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Peter J.
Yates
,
Philip A. E.
Murgatroyd
,
James T.
Gibbon
,
Max
Birkett
,
Richard J.
Potter
,
Jonathan D.
Major
,
Ken
Durose
,
David O.
Scanlon
,
Vinod R.
Dhanak
Abstract: The earth-abundant semiconductor Cu3BiS3 (CBS) exhibits promising photovoltaic properties and is often considered analogous to the solar absorbers copper indium gallium diselenide (CIGS) and copper zinc tin sulfide (CZTS) despite few device reports. The extent to which this is justifiable is explored via a thorough X-ray photoemission spectroscopy (XPS) analysis: spanning core levels, ionization potential, work function, surface contamination, cleaning, band alignment, and valence-band density of states. The XPS analysis overcomes and addresses the shortcomings of prior XPS studies of this material. Temperature-dependent absorption spectra determine a 1.2 eV direct band gap at room temperature; the widely reported 1.4–1.5 eV band gap is attributed to weak transitions from the low density of states of the topmost valence band previously being undetected. Density functional theory HSE06 + SOC calculations determine the band structure, optical transitions, and well-fitted absorption and Raman spectra. Valence band XPS spectra and model calculations find the CBS bonding to be superficially similar to CIGS and CZTS, but the Bi3+ cations (and formally occupied Bi 6s orbital) have fundamental impacts: giving a low ionization potential (4.98 eV), suggesting that the CdS window layer favored for CIGS and CZTS gives detrimental band alignment and should be rejected in favor of a better aligned material in order for CBS devices to progress.
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Jul 2019
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I07-Surface & interface diffraction
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Mengxue
Chen
,
Dan
Liu
,
Wei
Liu
,
Robert S.
Gurney
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Donghui
Li
,
Jinlong
Cai
,
Emma L. K.
Spooner
,
Rachel C.
Kilbride
,
James D.
Mcgettrick
,
Trystan M.
Watson
,
Zhe
Li
,
Richard A. L.
Jones
,
David G.
Lidzey
,
Tao
Wang
Diamond Proposal Number(s):
[20419]
Abstract: Fluorination of conjugated molecules has been established as an effective structural modification strategy to influence properties, and has attracted extensive attention in organic solar cells (OSCs). Here, we have investigated optoelectronic and photovoltaic property changes of OSCs made of polymer donors with the non-fullerene acceptors (NFAs) ITIC and IEICO and their fluorinated counterparts IT-4F and IEICO-4F. Device studies show that fluorinated NFAs lead to reduced Voc but increased Jsc and FF, and therefore the ultimate influence to efficiency depends on the compensation of Voc loss and gains of Jsc and FF. Fluorination lowers energy levels of NFAs, reduces their electronic bandgaps and red-shifts the absorption spectra. The impact of fluorination on the molecular order depends on the specific NFA, with the conversion of ITIC to IT-4F reduces structural order, which can be reversed after blending with the donor PBDB-T. Contrastingly, IEICO-4F presents stronger π−π stacking after fluorination from IEICO, and this is further strengthened after blending with the donor PTB7-Th. The photovoltaic blends universally present a donor-rich surface region which can promote charge transport and collection towards anode in inverted OSCs. The fluorination of NFAs, however, reduces the fraction of donors in this donor-rich region, consequently encourage the intermixing of donor/acceptor for efficient charge generation.
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Jun 2019
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Abstract: Metal-organic frameworks (MOFs) have shown great promise for sensing of dangerous chemicals, including environmental toxins, nerve agents and explosives. However, challenges remain, such as the sensing of larger analytes and the discrimination between similar analytes at different concentrations. Herein we present the synthesis and development of a new, large-pore MOF for explosives sensing, and demonstrate its excellent sensitivity against a range of relevant explosive compounds including trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN). We have developed an improved, thorough methodology to eliminate common sources of error in our sensing protocol. We then combine this new MOF with two others as part of a three-MOF array for fluorescent sensing and discrimination of five explosives. This sensor works at part-per-million concentrations and importantly, can discriminate explosives with high accuracy without reference to their concentration.
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Mar 2019
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B21-High Throughput SAXS
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Diamond Proposal Number(s):
[18523]
Abstract: The preparation of hydrogels and stable emulsions is important in the formulation of many functional nanostructured soft materials. We investigate the multi-functional self-assembly and bioactivity properties of a novel surfactant-like peptide that shows antimicrobial activity, that is able to form hydrogels without pH adjustment, and is able to stabilize oil-in-water emulsions. Furthermore, we demonstrate on-demand de-emulsification in response to the protease enzyme elastase. We show that the surfactant-like peptide (Ala)9-Arg (A9R) forms β-sheet fibers above a critical aggregation concentration and that water-in-oil emulsions are stabilized by a coating of β-sheet fibers around the emulsion droplets. Furthermore, we demonstrate enzyme-responsive de-emulsification, which has potential in the development of responsive release systems. The peptide shows selective antimicrobial activity against Gram negative pathogens including Pseudomonas aeruginosa, which causes serious infections. Our results highlight the utility of surfactant-like peptides in the stabilization of oil/water emulsions and the potential for these to be used to formulate antimicrobial peptide emulsions which are additionally responsive to protease. The peptide A9R has pronounced antibacterial activity against clinically challenging pathogens, and its ability to form β-sheet fibers plays a key role in its diverse structural properties, ranging from hydrogel formation to emulsion stabilization.
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Feb 2019
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[16202]
Abstract: We demonstrate the emergence and control of magnetic phases between magnetite (Fe3O4), a ferrimagnetic halfmetal, and SrTiO3, a transparent non-magnetic insulator considered the bedrock of oxide-based electronics. The Verwey transition (TV) was detected to persist from bulk-like down to ultrathin Fe3O4 films, decreasing from 117±4 K (38 nm) to 25±4 K (2 nm), respectively. Element-selective electronic and magnetic properties of the ultrathin films and buried interfaces are studied by angle-dependent HAXPES and XMCD techniques. We observe a reduction of Fe2+ ions with decreasing film thickness, accompanied by an increase of Fe3+ ions in both tetrahedral and octahedral sites, and conclude on the formation of a magnetically active ferrimagnetic 2 u.c. γ-Fe2O3 intralayer. In order to manipulate the interfacial magnetic phase, a postannealing process causes the controlled reduction of the γ-Fe2O3 that finally leads to stoichiometric and ferrimagnetic Fe3O4/SrTiO3 (001) heterointerfaces.
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Jan 2019
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[13560]
Abstract: Advanced lithium-ion batteries are of great interest for consumer electronics and electric vehicle applications, however they still suffer from drawbacks stemming from cathode active material limitations (e.g. insufficient capacities and capacity fading). One approach for alleviating such limitations and stabilizing the active material structure may be anion doping. In this work, fluorine and nitrogen are investigated as potential dopants in Li1.02(Ni0.8Co0.1Mn0.1)0.98O2 (NCM-811) as a prototypical nickel-rich cathode active material. Nitrogen doping is achieved by ammonia treatment of NCM in the presence of oxygen, which serves as an unconventional and new approach. The crystal structure was investigated by means of Rietveld and pair distribution function analysis of X-ray diffraction data, which provide very precise information regarding both the average and local structure, respectively. Meanwhile, time-of-flight secondary ion mass spectroscopy was used to assess the efficacy of dopant incorporation within the NCM structure. Moreover, scanning electron microscopy and scanning transmission electron microscopy were conducted to thoroughly investigate the dopant influences on the NCM morphology. Finally, the electrochemical performance was tested via galvanostatic cycling of half- and full-cells between 0.1 and 2 C. Ultimately, a dopant-dependent modulation of the NCM structure was found to enable the enhancement of the electrochemical performance, thereby opening a route to cathode active material optimization.
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Dec 2018
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[17191]
Abstract: Stimuli-responsive nanocarriers based on lipid self-assemblies have the potential to provide targeted delivery of antimicrobial peptides, limiting their side effects while protecting them from degradation in the biological environments. In the present study, we design and characterize a simple pH-responsive antimicrobial nanomaterial, formed through the self-assembly of oleic acid (OA) with the human cathelicidin LL-37 as model for an amphiphilic antimicrobial peptide. Colloidal transformations from core-shell cylindrical micelles with a cross-section diameter of ~ 5.5 nm and a length of ~ 23 nm at pH 7.0, to aggregates of branched thread-like micelles at pH 5.0 were detected using synchrotron small angle X-ray scattering, cryogenic transmission electron microscopy, and dynamic light scattering. Biological in vitro assays using an Escherichia coli bacteria strain showed high antimicrobial activity of the positively charged LL-37/OA aggregates at pH 5.0, which was not caused by the pH conditions themselves. Contrary to that, negligible antimicrobial activity was observed at pH 7.0 for the negatively charged cylindrical micelles. The nanocarrier’s ability to switch its biological activity ‘on’ and ‘off’ in response to changes in pH could be used to focus the antimicrobial peptides’ action to areas of specific pH in the body. The presented findings contribute to the fundamental understanding of lipid-peptide self-assembly, and may open up a promising strategy for designing simple pH-responsive delivery systems for antimicrobial peptides.
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Dec 2018
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E02-JEM ARM 300CF
I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[14925, 10330, 16964]
Abstract: Fuel cells are a key new green technology that have applications in both transport and portable power generation. Carbon supported platinum (Pt) is used as an anode and cathode electrocatalyst in low-temperature fuel cells fuelled with hydrogen or low molecular weight alcohols. The cost of Pt and the limited world supply are significant barriers to the widespread use of these types of fuel cells. Compara-tively palladium has a three times higher abundance in the Earth’s crust. Here a facile, low temperature and scalable synthetic route to-wards 3D nanostructured palladium (Pd) employing electrochemical templating from inverse lyotropic lipid phases is presented. The obtained single diamond morphology Pd nanostructures exhibited excellent catalytic activity and stability towards methanol, ethanol and glycerol oxidation compared to commercial Pd black and the nanostructure was verified by small-angle X-ray scattering (SAXS), scanning tunneling electron microscopy (STEM) as well as by cyclic voltammetry (CV).
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Oct 2018
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