I07-Surface & interface diffraction
|
Diamond Proposal Number(s):
[8117]
Abstract: The crystallization of poly(3-hexylthiophene) (P3HT) to form nanowires has attracted considerable interest because this process significantly increases the hole mobility when compared to amorphous P3HT, leading to improved performance in photovoltaic and other organic electronic devices. However, full characterization of the crystallization self-assembly of the polymer chains in solution has not been achieved yet, due to limited use of
in−situ
not destructive techniques. Here, we investigate the ageing-driven formation and evolution of regioregular (rr) P3HT nanostructures in chlorobenzene solution using small angle neutron scattering (SANS) and UV–Vis spectroscopy. We have monitored how the shape of the rr-P3HT aggregates evolves. The initial states for rr-P3HT chains are the random coils, which straighten to form rods. These subsequently π - π stack to form 2D lamellae, which further stack to create nanowires. The formation of nanowires is promoted both by the length of ageing and by low temperatures (
4∘C
). Temperatures above
>40∘C
reverse the formation of nanowires. Additionally, atomic force microscopy (AFM) and grazing incidence wide angle x-ray scattering (GIWAXS) reveal that the nanowires can be successfully aligned during deposition by off-axis spin coating. Finally, the anisotropic conductivity of the aligned rr-P3HT nanowire films is reported. This is significant for applications such as gas sensing or organic thin film transistors, where increased conductivity and controlled nanostructure are desirable.
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Nov 2019
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
I15-1-X-ray Pair Distribution Function (XPDF)
|
Diamond Proposal Number(s):
[12533]
Abstract: We present new results on solid (monolithic) synthetic C-S-H made at room temperature from easily obtainable calcium sources (calcium oxide, calcium hydroxide) and nanosilica (w/s = 2) with a 2 minute mixing time. Using synchrotron X-ray diffraction combined with TGA/DSC, 29Si NMR and synchrotron pair distribution function (PDF) data we show that the solid C-S-H is crystallographically similar to the more conventionally made synthetic C-S-H slurry. We show that C-S-H is present after 1 day curing (C/S = 0.81) and no X-ray visible portlandite is present at day 3. PDF data shows that the ordered domain size is 2.5 – 4.5 nm, depending on the fit chosen.
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Oct 2019
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I07-Surface & interface diffraction
|
Zahra
Andaji-garmaroudi
,
Mojtaba
Abdi-jalebi
,
Dengyang
Guo
,
Stuart
Macpherson
,
Aditya
Sadhanala
,
Elizabeth M.
Tennyson
,
Edoardo
Ruggeri
,
Miguel
Anaya
,
Krzysztof
Galkowski
,
Ravichandran
Shivanna
,
Kilian
Lohmann
,
Kyle
Frohna
,
Sebastian
Mackowski
,
Tom J.
Savenije
,
Richard H.
Friend
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[17223]
Open Access
Abstract: Mixed‐halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution‐processed triple‐cation mixed‐halide (Cs0.06MA0.15FA0.79)Pb(Br0.4I0.6)3 perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar‐equivalent illumination. It is found that the illumination leads to localized surface sites of iodide‐rich perovskite intermixed with passivating PbI2 material. Time‐ and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide‐rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed‐halide mixed‐cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures.
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Sep 2019
|
|
I09-Surface and Interface Structural Analysis
|
Andrew J.
Naylor
,
Eszter
Makkos
,
Julia
Maibach
,
Niccolo
Guerrini
,
Adam
Sobkowiak
,
Erik
Bjorklund
,
Juan G.
Lozano
,
Ashok
Sreekumar Menon
,
Reza
Younesi
,
Matthew R.
Roberts
,
Kristina
Edström
,
M. Saiful
Islam
,
Peter G.
Bruce
Diamond Proposal Number(s):
[14733, 16629]
Open Access
Abstract: Lithium-rich materials, such as Li1.2Ni0.2Mn0.6O2, exhibit capacities not limited by transition metal redox, through the reversible oxidation of oxide anions. Here we offer detailed insight into the degree of oxygen redox as a function of depth within the material as it is charged and cycled. Energy-tuned photoelectron spectroscopy is used as a powerful, yet highly sensitive technique to probe electronic states of oxygen and transition metals from the top few nanometers at the near-surface through to the bulk of the particles. Two discrete oxygen species are identified, On- and O2-, where n<2, confirming our previous model that oxidation generates localised hole states on O upon charging. This is in contrast to the oxygen redox inactive high voltage spinel LiNi0.5Mn1.5O4, for which no On- species is detected. The depth profile results demonstrate a concentration gradient exists for On- from the surface through to the bulk, indicating a preferential surface oxidation of the layered oxide particles. This is highly consistent with the already well-established core-shell model for such materials. Ab initio calculations reaffirm the electronic structure differences observed experimentally between the surface and bulk, while modelling of delithiated structures shows good agreement between experimental and calculated binding energies for On-.
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Sep 2019
|
|
I09-Surface and Interface Structural Analysis
|
Christian
Baur
,
Ida
Kallquist
,
Johann
Chable
,
Jin Hyun
Chang
,
Rune E.
Johnsen
,
Francisco
Ruiz-zepeda
,
Jean-marcel
Ateba Mba
,
Andrew
Naylor
,
Juan Maria
Garcia-lastra
,
Tejs
Vegge
,
Franziska
Klein
,
Annika R.
Schür
,
Poul
Norby
,
Kristina
Edström
,
Maria
Hahlin
,
Maximilian
Fichtner
Diamond Proposal Number(s):
[19602]
Open Access
Abstract: Lithium-rich transition metal disordered rock salt (DRS) oxyfluorides have the potential to lessen one large bottleneck for lithium ion batteries by improving the cathode capacity. However, irreversible reactions at the electrode/electrolyte interface have so far led to fast capacity fading during electrochemical cycling. Here, we report the synthesis of two new Li-rich transition metal oxyfluorides Li2V0.5Ti0.5O2F and Li2V0.5Fe0.5O2F using the mechanochemical ball milling procedure. Both materials show substantially improved cycling stability compared to Li2VO2F. Rietveld refinements of synchrotron X-ray diffraction patterns reveal the DRS structure of the materials. Based on density functional theory (DFT) calculations, we demonstrate that substitution of V3+ with Ti3+ and Fe3+ favors disordering of the mixed metastable DRS oxyfluoride phase. Hard X-ray photoelectron spectroscopy shows that the substitution stabilizes the active material electrode particle surface and increases the reversibility of the V3+/V5+ redox couple. This work presents a strategy for stabilization of the DRS structure leading to improved electrochemical cyclability of the materials.
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Sep 2019
|
|
I09-Surface and Interface Structural Analysis
|
Abstract: The electronic properties of
CaCuO
2
/
La
0.7
Sr
0.3
MnO
3
(LSMO) superlattices are determined by the electronic structure of the structural units and in particular their interfaces. The electronic structure of LSMO is governed by a metal-insulator transition, which is controlled by the thickness of the units and the sample temperature, resulting in a systematic downward band shift for metallic samples (i.e., thick LSMO units, low temperature). We present a systematic study of the changes in the valence-band structure and screening features in Mn
2
p
and Cu
2
p
core-level spectra. The results show that hybridization of Cu
3
d
orbitals with out-of-plane O
2
p
orbitals can be systematically tuned by controlling the band alignment at the interface via the metal-to-insulator transition of the LSMO units. This opens a new route to rational design of functional interfaces and control of orbital reconstructions.
|
Sep 2019
|
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I09-Surface and Interface Structural Analysis
|
Jack E. N.
Swallow
,
Benjamin A. D.
Williamson
,
Sanjayan
Sathasivam
,
Max
Birkett
,
Thomas J.
Featherstone
,
Philip A. E.
Murgatroyd
,
Holly J.
Edwards
,
Zachary W.
Lebens-higgins
,
David A.
Duncan
,
Mark
Farnworth
,
Paul
Warren
,
Nianhua
Peng
,
Tien-lin
Lee
,
Louis F. J.
Piper
,
Anna
Regoutz
,
Claire J.
Carmalt
,
Ivan P.
Parkin
,
Vin R.
Dhanak
,
David O.
Scanlon
,
Tim D.
Veal
Diamond Proposal Number(s):
[18428]
Open Access
Abstract: Transparent conductors are a vital component of smartphones, touch-enabled displays, low emissivity windows and thin film photovoltaics. Tin-doped In2O3 (ITO) dominates the transparent conductive films market, accounting for the majority of the current multi-billion dollar annual global sales. Due to the high cost of indium, however, alternatives to ITO have been sought but have inferior properties. Here we demonstrate that molybdenum-doped In2O3 (IMO) has higher mobility and therefore higher conductivity than ITO with the same carrier density. This also results in IMO having increased infrared transparency compared to ITO of the same conductivity. These properties enable current performance to be achieved using thinner films, reducing the amount of indium required and raw material costs by half. The enhanced doping behavior arises from Mo 4d donor states being resonant high in the conduction band and negligibly perturbing the host conduction band minimum, in contrast to the adverse perturbation caused by Sn 5s dopant states. This new understanding will enable better and cheaper TCOs based on both In2O3 and other metal oxides.
|
Sep 2019
|
|
B16-Test Beamline
|
Diamond Proposal Number(s):
[8823]
Abstract: Objectives: Yttria Partially Stabilised Zirconia (YPSZ) is a high strength ceramic which has become widely used in porcelain veneered dental copings due to its exceptional toughness. Within these components the residual stress and crystallographic phase of YPSZ close to the interface are highly influential in the primary failure mode; near interface porcelain chipping. In order to improve present understanding of this behaviour, characterisation of these parameters is needed at an improved spatial resolution. Methods: In this study transmission micro-focus X-ray Diffraction, Raman spectroscopy, and focused ion beam milling residual stress analysis techniques have, for the first time, been used to quantify and cross-validate the microscale spatial variation of phase and residual stress of YPSZ in a prosthesis cross-section. Results: The results of all techniques were found to be comparable and complementary. Monoclinic YPSZ was observed within the first 10 μm of the YPSZ-porcelain interface with a maximum volume fraction of 60%. Tensile stresses were observed within the first 150μm of the interface with a maximum value of ≈300MPa at 50μm from the interface. The remainder of the coping was in mild compression at ≈ − 30 MPa, with shear stresses of a similar magnitude also being induced by the YPSZ phase transformation. Significance: The analysis indicates that the interaction between phase transformation, residual stress and porcelain creep at YPSZ-porcelain interface results in a localised porcelain fracture toughness reduction. This explains the increased propensity of failure at this location, and can be used as a basis for improving prosthesis design.
|
Sep 2019
|
|
E01-JEM ARM 200CF
|
Diamond Proposal Number(s):
[16854]
Abstract: 2D crystals are typically uniform and periodic in‐plane with stacked sheet‐like structure in the out‐of‐plane direction. Breaking the in‐plane 2D symmetry by creating unique lattice structures offers anisotropic electronic and optical responses that have potential in nanoelectronics. However, creating nanoscale‐modulated anisotropic 2D lattices is challenging and is mostly done using top‐down lithographic methods with ≈10 nm resolution. A phase transformation mechanism for creating 2D striated lattice systems is revealed, where controlled thermal annealing induces Se loss in few‐layered PdSe2 and leads to 1D sub‐nm etched channels in Pd2Se3 bilayers. These striated 2D crystals cannot be described by a typical unit cells of 1–2 Å for crystals, but rather long range nanoscale periodicity in each three directions. The 1D channels give rise to localized conduction states, which have no bulk layered counterpart or monolayer form. These results show how the known family of 2D crystals can be extended beyond those that exist as bulk layered van der Waals crystals by exploiting phase transformations by elemental depletion in binary systems.
|
Sep 2019
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Diamond Proposal Number(s):
[16188]
Abstract: In die-casting processes, the high cooling rates and pressures affect the alloy solidification and deformation behavior, and thereby impact the final mechanical properties of cast components. In this study, isothermal semi-solid compression and subsequent cooling of aluminum die-cast alloy specimens were characterized using fast synchrotron tomography. This enabled the investigation and quantification of gas and shrinkage porosity evolution during deformation and solidification. The analysis of the 4D images (3D plus time) revealed two distinct mechanisms by which porosity formed; (i) deformation-induced growth due to the enrichment of local hydrogen content by the advective hydrogen transport, as well as a pressure drop in the dilatant shear bands, and (ii) diffusion-controlled growth during the solidification. The rates of pore growth were quantified throughout the process, and a Gaussian distribution function was found to represent the variation in the pore growth rate in both regimes. Using a one-dimensional diffusion model for hydrogen pore growth, the hydrogen flux required for driving pore growth during these regimes was estimated, providing a new insight into the role of advective transport associated with the deformation in the mushy region.
|
Aug 2019
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