I07-Surface & interface diffraction
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Cem
Ornek
,
Fan
Zhang
,
Alfred
Larsson
,
Mubashir
Mansoor
,
Gary S.
Harlow
,
Robin
Kroll
,
Francesco
Carla
,
Hadeel
Hussain
,
Dirk L.
Engelberg
,
Bora
Derin
,
Jinshan
Pan
Diamond Proposal Number(s):
[23388]
Open Access
Abstract: The passive film stability on stainless steel can be affected by hydrogen absorption and lead to microstructure embrittlement. This work shows that the absorption of hydrogen results in surface degradation due to oxide reduction and ionic defect generation within the passive film, which decomposes and eventually vanishes. The passive film provides a barrier to entering hydrogen, but when hydrogen is formed, atomic hydrogen infuses into the lattices of the austenite and ferrite phases, causing strain evolution, as shown by synchrotron x-ray diffraction data. The vacancy concentration and hence the strains increase with increasing electrochemical cathodic polarization. Under cathodic polarization, the surface oxides are thermodynamically unstable, but the complete reduction is kinetically restrained. As a result, surface oxides remain present under excessive cathodic polarization, contesting the classical assumption that oxides are easily removed. Density-functional theory calculations have shown that the degradation of the passive film is a reduction sequence of iron and chromium oxide, which causes thinning and change of the semiconductor properties of the passive film from n-type to p-type. As a result, the surface loses its passivity after long cathodic polarization and becomes only a weak barrier to hydrogen absorption and hence hydrogen embrittlement.
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Aug 2023
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I07-Surface & interface diffraction
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Cem
Ornek
,
Mubashir
Mansoor
,
Alfred
Larsson
,
Fan
Zhang
,
Gary S.
Harlow
,
Robin
Kroll
,
Francesco
Carla
,
Hadeel
Hussain
,
Bora
Derin
,
Ulf
Kivisäkk
,
Dirk L.
Engelberg
,
Edvin
Lundgren
,
Jinshan
Pan
Diamond Proposal Number(s):
[23388]
Open Access
Abstract: Various mechanisms have been proposed for hydrogen embrittlement of duplex stainless steel, but the causation of hydrogen-induced material degradation has remained unclear. This work shows that phase instability (decomposition) of the austenite phase and ductile-to-brittle transition of the ferrite phase precedes hydrogen embrittlement. In-situ diffraction measurements revealed that Ni-rich sites of the austenite phase decompose into metastable hydrides. Hydride formation is possible by increasing the hydrogen chemical potential during electrochemical charging and low defect formation energy of hydrogen interstitials. Our findings demonstrate that hydrogen embrittlement can only be understood if measured in situ and in real-time during the embrittlement process.
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Jun 2023
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I07-Surface & interface diffraction
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Daniel T. W.
Toolan
,
Michael P.
Weir
,
Shuangqing
Wang
,
Simon A.
Dowland
,
Zhilong
Zhang
,
James
Xiao
,
Jonathan
Rawle
,
Neil
Greenham
,
Richard
Friend
,
Akshay
Rao
,
Richard A. L.
Jones
,
Anthony J.
Ryan
Diamond Proposal Number(s):
[23587]
Open Access
Abstract: Hybrid small-molecule organic semiconductor / quantum dot blend films are attractive for high efficiency low-cost solar energy harvesting devices. Understanding and controlling the self-assembly of the organic semiconductor and quantum dots is crucial in optimising device performance, not only at a lab-scale but for large-scale high-throughput printing and coating methods. Here, in situ grazing incidence X-ray scattering (GIXS) is employed in order to gain direct insights into how small-molecule organic semiconductor / quantum dot blends self-assemble during blade coating. Results show that for two different archetypal organic small molecule:quantum dot blends, small-molecule crystallisation may either occur spontaneously or be mediated by the formation of quantum dot aggregates. Irrespective of the initial crystallisation route, the small-molecule crystallisation acts to exclude the quantum dot impurities from the growing crystalline matrix phase. These results provide important fundamental understanding of structure formation of small organic molecule:quantum dot films prepared via solution processing routes, compatible with large scale deposition manufacturing.
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May 2023
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I07-Surface & interface diffraction
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Alexandra L.
Martin
,
Philip N.
Jemmett
,
Thomas
Howitt
,
Mary H.
Wood
,
Andrew W.
Burley
,
Liam R.
Cox
,
Timothy R.
Dafforn
,
Rebecca J. L.
Welbourn
,
Mario
Campana
,
Maximilian W. A.
Skoda
,
Joseph J.
Thompson
,
Hadeel
Hussain
,
Jonathan L.
Rawle
,
Francesco
Carla
,
Christopher L.
Nicklin
,
Thomas
Arnold
,
Sarah L.
Horswell
Diamond Proposal Number(s):
[14670, 16423, 19542]
Open Access
Abstract: The effect of lipid composition on models of the inner leaflet of mammalian cell membranes has been investigated. Grazing incidence X-ray diffraction and X-ray and neutron reflectivity have been used to characterize lipid packing and solvation, while electrochemical and infrared spectroscopic methods have been employed to probe phase behavior in an applied electric field. Introducing a small quantity of the anionic lipid dimyristoylphosphatidylserine (DMPS) into bilayers of zwitterionic dimyristoylphosphatidylethanolamine (DMPE) results in a significant change in the bilayer response to an applied field: the tilt of the hydrocarbon chains increases before returning to the original tilt angle on detachment of the bilayer. Equimolar mixtures, with slightly closer chain packing, exhibit a similar but weaker response. The latter also tend to incorporate more solvent during this electrochemical phase transition, at levels similar to those of pure DMPS. Reflectivity measurements reveal greater solvation of lipid layers for DMPS > 30 mol %, matching the greater propensity for DMPS-rich bilayers to incorporate water. Taken together, the data indicate that the range of 10–35 mol % DMPS provides optimum bilayer properties (in flexibility and function as a barrier), which may explain why the DMPS content of cell membranes tends to be found within this range.
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Feb 2023
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I07-Surface & interface diffraction
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Philip N.
Jemmett
,
David C.
Milan
,
Richard J.
Nichols
,
Thomas
Howitt
,
Alexandra L.
Martin
,
Thomas
Arnold
,
Jonathan L.
Rawle
,
Christopher L.
Nicklin
,
Timothy R.
Dafforn
,
Liam R.
Cox
,
Sarah L.
Horswell
Diamond Proposal Number(s):
[15539, 18202]
Abstract: Sphingolipids are an important class of lipids found in mammalian cell membranes with important structural and signaling roles. They differ from another major group of lipids, the glycerophospholipids, in the connection of their hydrocarbon chains to their headgroups. In this study, a combination of electrochemical and structural methods has been used to elucidate the effect of this difference on sphingolipid behavior in an applied electric field. N-Palmitoyl sphingomyelin forms bilayers of similar coverage and thickness to its close analogue di-palmitoyl phosphatidylcholine. Grazing incidence diffraction data show slightly closer packing and a smaller chain tilt angle from the surface normal. Electrochemical IR results at low charge density show that the difference in tilt angle is retained on deposition to form bilayers. The bilayers respond differently to increasing electric field strength: chain tilt angles increase for both molecules, but sphingomyelin chains remain tilted as field strength is further increased. This behavior is correlated with disruption of the hydrogen-bonding network of small groups of sphingomyelin molecules, which may have significance for the behavior of molecules in lipid rafts in the presence of strong fields induced by ion gradients or asymmetric distribution of charged lipids.
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Nov 2022
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[21922]
Open Access
Abstract: A high-throughput method for the fabrication of ordered arrays of Au nanoparticles is presented. It is based on pulsed electrodeposition into porous anodic alumina templates. In contrast to many synthesis routes, it is cyanide-free, prior separation of the alumina template from the aluminium substrate is not required, and the use of contaminating surfactants/capping agents often found in colloidal synthesis is avoided. The aspect ratio of the nanoparticles can also be tuned by selecting an appropriate electrodeposition time. We show how to fabricate arrays of nanoparticles, both with branched bases and with hemispherical bases. Furthermore, we compare the different morphologies produced with electron microscopies and grazing-incidence synchrotron X-ray diffraction. We find the nanoparticles are polycrystalline in nature and are compressively strained perpendicular to the direction of growth, and expansively strained along the direction of growth. We discuss how this can produce dislocations and twinning defects that could be beneficial for catalysis.
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May 2022
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[22710]
Open Access
Abstract: The surface region of austenitic stainless steel (SS) is investigated by synchrotron X-ray powder diffraction (XRPD) and X-ray absorption near edge structure (XANES) measurements, because its composition and structure is crucial for the corrosion resistance of SS. Grazing incidence XRPD of a polished AISI 304 bulk steel sample show that the near-surface structure is modified. The concentration of the ferrite phase of Fe, a typical minority phase in AISI 304, increases gradually from 10% to 30% when approaching the surface from 150 nm depth. XANES Fe K-edge investigations of ultra-thin, sputter deposited films also reveal much larger ferrite fractions than expected from the austenitic steel composition of the films. Reasons for the increased ferrite fraction in the surface region of bulk steel and thin films are discussed. However, right at the surface, the trend reverses. Analysis of XANES data for an ultra-thin, 4 nm SS film show that 80% of Fe is oxidized and 20% of metallic Fe is present only in austenite structure, suggesting that ferritic iron is preferentially subject to oxidation. The austenitic Fe is located at more than 2 - 3 nm below the surface where the Ni concentration is > 10%.
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Feb 2022
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I07-Surface & interface diffraction
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[24359, 23666]
Open Access
Abstract: Membranes with high selectivity offer an attractive route to molecular separations, where technologies such as distillation and chromatography are energy intensive. However, it remains challenging to fine tune the structure and porosity in membranes, particularly to separate molecules of similar size. Here, we report a process for producing composite membranes that comprise crystalline porous organic cage films fabricated by interfacial synthesis on a polyacrylonitrile support. These membranes exhibit ultrafast solvent permeance and high rejection of organic dyes with molecular weights over 600 g mol−1. The crystalline cage film is dynamic, and its pore aperture can be switched in methanol to generate larger pores that provide increased methanol permeance and higher molecular weight cut-offs (1,400 g mol−1). By varying the water/methanol ratio, the film can be switched between two phases that have different selectivities, such that a single, ‘smart’ crystalline membrane can perform graded molecular sieving. We exemplify this by separating three organic dyes in a single-stage, single-membrane process.
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Jan 2022
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[18570]
Open Access
Abstract: Planar organic heterostructures are widely explored and employed in photovoltaic cells, light-emitting diodes, and bilayer field-effect transistors. An important role for device performance plays the energy level alignment at the inorganic–organic and organic–organic interfaces. In this work, incremental ultraviolet photoelectron spectroscopy measurements and real-time X-ray scattering experiments are used to thoroughly investigate the thickness-dependent electronic and structural properties of a perfluoropentacene (PFP)-on-[6]phenacene heterostructure. For both materials an incremental increase of the material work function (positive interface dipole) is found. For [6]phenacene, this can be assigned to a thickness-dependent change of molecular arrangement evident from a change of the unit cell volume and a consequential alteration of the ionization energy. In the case of PFP the interface dipole stems from charge transfer from the substrate into unoccupied molecular orbitals resulting in an electrostatic potential on the surface. The magnitude of this potential can be correlated with an increased gap state density resulting from templated structural defects mediated by the bottom layer.
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Dec 2021
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I07-Surface & interface diffraction
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Bin
Yang
,
Marina
Lledos
,
Riaz
Akhtar
,
Giuseppe
Ciccone
,
Long
Jiang
,
Emanuele
Russo
,
Sunil
Rajput
,
Chunyu
Jin
,
Maria
Angelerou
,
Thomas
Arnold
,
Jonathan
Rawle
,
Massimo
Vassalli
,
Maria
Marlow
,
Dave J.
Adams
,
Mischa
Zelzer
Diamond Proposal Number(s):
[16246]
Open Access
Abstract: Controlling supramolecular self-assembly across multiple length scales to prepare gels with localised properties is challenging. Most strategies concentrate on fabricating gels with heterogeneous components, where localised properties are generated by the stimuli-responsive component. Here, as an alternative approach, we use a spiropyran-modified surface that can be patterned with light. We show that light-induced differences in surface chemistry can direct the bulk assembly of a low molecular weight gelator, 2-NapAV, meaning that mechanical gel properties can be controlled by the surface on which the gel is grown. Using grazing incidence X-ray diffraction and grazing incidence small angle X-ray scattering, we demonstrate that the origin of the different gel properties relates to differences in the architectures of the gels. This provides a new method to prepare a single domain (i.e., chemically homogeneous) hydrogel with locally controlled (i.e., mechanically heterogeneous) properties.
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Oct 2021
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