I07-Surface & interface diffraction
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Baodan
Zhao
,
Yaxiao
Lian
,
Linsong
Cui
,
Giorgio
Divitini
,
Gunnar
Kusch
,
Edoardo
Ruggeri
,
Florian
Auras
,
Weiwei
Li
,
Dexin
Yang
,
Bonan
Zhu
,
Rachel A.
Oliver
,
Judith L.
Macmanus-driscoll
,
Samuel D.
Stranks
,
Dawei
Di
,
Richard H.
Friend
Diamond Proposal Number(s):
[17223]
Abstract: Light-emitting diodes based on halide perovskites have recently reached external quantum efficiencies of over 20%. However, the performance of visible perovskite light-emitting diodes has been hindered by non-radiative recombination losses and limited options for charge-transport materials that are compatible with perovskite deposition. Here, we report efficient, green electroluminescence from mixed-dimensional perovskites deposited on a thin (~1 nm) lithium fluoride layer on an organic semiconductor hole-transport layer. The highly polar dielectric interface acts as an effective template for forming high-quality bromide perovskites on otherwise incompatible hydrophobic charge-transport layers. The control of crystallinity and dimensionality of the perovskite layer is achieved by using tetraphenylphosphonium chloride as an additive, leading to external photoluminescence quantum efficiencies of around 65%. With this approach, we obtain light-emitting diodes with external quantum efficiencies of up to 19.1% at high brightness (>1,500 cd m−2).
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Oct 2020
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I06-Nanoscience
I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[19308, 16045]
Open Access
Abstract: Understanding the metal–support interaction (MSI) is crucial to comprehend how the catalyst support affects performance and whether this interaction can be exploited in order to design new catalysts with enhanced properties. Spatially resolved soft X-ray absorption spectroscopy (XAS) in combination with Atomic Force Microscopy (AFM) and Scanning Helium Ion-Milling Microscopy (SHIM) has been applied to visualise and characterise the behaviour of individual cobalt nanoparticles (CoNPs) supported on two-dimensional substrates (SiOxSi(100) (x < 2) and rutile TiO2(110)) after undergoing reduction–oxidation–reduction (ROR). The behaviour of the Co species is observed to be strongly dependent on the type of support. For SiOxSi a weaker MSI between Co and the support allows a complete reduction of CoNPs although they migrate and agglomerate. In contrast, a stronger MSI of CoNPs on TiO2 leads to only a partial reduction under H2 at 773 K (as observed from Co L3-edge XAS data) due to enhanced TiO2 binding of surface-exposed cobalt. SHIM data revealed that the interaction of the CoNPs is so strong on TiO2, that they are seen to spread at and below the surface and even to migrate up to ∼40 nm away. These results allow us to better understand deactivation phenomena and additionally demonstrate a new understanding concerning the nature of the MSI for Co/TiO2 and suggest that there is scope for careful control of the post-synthetic thermal treatment for the tuning of this interaction and ultimately the catalytic performance.
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Oct 2020
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I07-Surface & interface diffraction
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Cem
Ornek
,
Alfred
Larsson
,
Gary S.
Harlow
,
Fan
Zhang
,
Robin
Kroll
,
Francesco
Carla
,
Hadeel
Hussain
,
Ulf
Kivisäkk
,
Dirk L.
Engelberg
,
Edvin
Lundgren
,
Jinshan
Pan
Diamond Proposal Number(s):
[23388]
Open Access
Abstract: Grazing-incidence x-ray diffraction was employed to measure, operando, during electrochemical hydrogen charging, the lattice strain development of the near-surface in super duplex stainless steel under applied tensile load. Hydrogen absorption led to the formation of tensile strains in both the austenite (γ) and ferrite (δ) phases perpendicular to the loading axis, whereas compressive strains were formed in the ferrite phase parallel to the loading direction, despite the acting tensile load. The earliest stages of degradation are discussed in light of understanding hydrogen embrittlement.
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Oct 2020
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I07-Surface & interface diffraction
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Cem
Ornek
,
Alfred
Larsson
,
Gary S.
Harlow
,
Fan
Zhang
,
Robin
Kroll
,
Francesco
Carla
,
Hadeel
Hussain
,
Ulf
Kivisäkk
,
Dirk L.
Engelberg
,
Edvin
Lundgren
,
Jinshan
Pan
Diamond Proposal Number(s):
[23388]
Open Access
Abstract: We report the evolution of metastable precursor structures during hydrogen infusion in the near-surface region of a super duplex stainless steel. Grazing-incidence x-ray diffraction was employed to monitor, operando, the lattice degradation of the austenite and ferrite phases. Electrochemical hydrogen charging resulted in the splitting of the diffraction peaks of the austenite phase, suggesting the evolution of a metastable precursor structure. This may be explained by the formation of quasi-hydrides, which convert back into the austenite parent structure during hydrogen effusion. The ferrite showed less lattice deformation than the austenite and no phase transformation.
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Sep 2020
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[21922]
Open Access
Abstract: A method for the electrochemical synthesis of palladium nanowires, using porous alumina templates with diameters of 25 nm and 40 nm, is presented. Through an electrochemical barrier layer thinning step, pulsed electrodeposition can take place directly into the anodized aluminum; without need for extra removal, pore opening, and metal contact coating steps. A digital oscilloscope is used to record and integrate the current, allowing the efficiency of the electrodeposition to be calculated. We discuss how using a large 'off period' allows for the replenishment of the depleted diffusion layer. The nanowires are characterized by using a focused ion beam (FIB) to create cross-sections which can be accessed with a scanning electron microscope (SEM). With grazing-incidence X-ray diffraction (GI-XRD) we find that the nanowires have a slight compressive strain in the direction that they are confined by the pores (0.58 % and 0.51 % for the 25 nm and 40 nm pores respectively). Knowing the strain state of the nanowires inside the template is of importance for the use of templated nanowires in devices. Further characterization is made using high-resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDS), after removal from the alumina templates.
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Aug 2020
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[16299]
Abstract: NixFe3−x
Ni
x
Fe
3
−
x
O4 thin films with varying Ni amount (0 ≤
≤
x ≤
≤
1.5) were deposited on MgO(001) via reactive molecular beam epitaxy. The growth process was monitored during film deposition by means of X-ray diffraction. All prepared films exhibit a well-ordered structure with complete vertical crystallinity throughout the whole film growth and flat surfaces of the final films independent of the Ni amount. An enhancement of the vertical compression in the initial growth continuously decreases up to a film thickness of 8 nm. During further growth, all films exhibit residual and constant vertical compression with lateral adaption of the final films to the substrate lattice, as observed by high energy surface X-ray diffraction experiments. Hard X-ray photoelectron spectroscopy measurements of the final films reveal increasing Fe3+
Fe
3
+
:Fe2+
Fe
2
+
ratios for higher Ni content and point to additional NiO agglomerations within the films exceeding the stoichiometric Ni amount of x = 1.
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Jul 2020
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I07-Surface & interface diffraction
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Michèle
Chevrier
,
Jurgen
Kesters
,
Judith E.
Houston
,
Niko
Van Den Brande
,
Sylvain
Chambon
,
Sébastien
Richeter
,
Bruno
Van Mele
,
Thomas
Arnold
,
Ahmad
Mehdi
,
Roberto
Lazzaroni
,
Philippe
Dubois
,
Rachel C.
Evans
,
Wouter
Maes
,
Sébastien
Clément
Diamond Proposal Number(s):
[13868]
Abstract: Phosphonium‐based polythiophene conjugated polyelectrolytes (CPEs) with three different counterions (dodecylsulfate (DS), octylsulfate (OS) and perfluorooctylsulfonate (PFOS)) are synthesized to determine how the nature of the counterion affects the thermal properties, the self‐assembly in thin films and the performance as cathode interfacial layer in polymer solar cells (PSCs). The counterion has a significant effect on the thermal properties of the CPEs, affecting both their glass transition and crystalline behavior. Grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) studies also indicate that changing the nature of the counterion influences the microstructural organization in thin films (face‐on vs . edge‐on orientation). The affinity of the CPEs with the underlying photoactive layer in PSCs is highly correlated with the counterion species. Finally, in addition to an increase of the power conversion efficiency of ~15% when using these CPEs as cathode interfacial layers in PSCs, a higher device stability is noted, as compared to a reference device with a calcium interlayer.
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Jul 2020
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[18591]
Abstract: Adsorption and incorporation of ions is known to influence the morphology and growth of calcite. Using surface X-ray diffraction, the interfacial structure of calcite in contact with CaCO3, MgCl2, CaCl2 and BaCl2 solutions was determined. All of these conditions yield a comparable interfacial structure, meaning that there is no significant ion adsorption on the terraces under the investigated conditions. This allows for the first time a thorough comparison in all three dimensions with state-of-the-art computer simulations, involving molecular dynamics based on both DFT and two different force field models. Additionally, the simulated structures are used to calculate the corresponding structure factors, which in turn are compared to those obtained from experiment, thereby avoiding the need for fitting or subjective interpretation. In general, there is a good agreement between experiment and the simulations, though there are some small discrepancies in the atomic positions, which lead to an inadequate fit of certain features characteristic of the structure of water at the interface. Of the three simulation methods examined, the DFT results were found to agree best with the experimental structure.
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Jul 2020
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[14937]
Open Access
Abstract: In this study in situ wide angle X-ray scattering (WAXS) has been measured during the spin coating process used to make the precursor films required for the formation of thin films of perovskite. A customized hollow axis spin coater was developed to permit the scattered X-rays to be collected in transmission geometry during the deposition process. Spin coating is the technique most commonly used in laboratories to make thin perovskite films. The dynamics of spin casting MAPbI3-xClx and FAPbI3-xClx films have been investigated and compared to investigate the differences between the dynamics of MAPbI3-xClx and FAPbI3-xClx film formation. In particular we focus on the crystallization dynamics of the precursor film formation. When casting MAPbI3-xClx we observed relatively fast 1D crystallization of the intermediate product MA2PbI3Cl. There was an absence of the desired perovskite phase formed directly; it only appeared after an annealing step which converted the MA2PbI3Cl to MAPbI3. In contrast, slower crystallization via a 3D precursor was observed for FAPbI3-xClx film formation compared to MAPbI3-xClx. Another important finding was that some FAPbI3-xClx perovskite was generated directly during spin casting before annealing. These findings indicate that there are significant differences between the crystallization pathways for these two perovskite materials. These are likely to explain the differences in the lifetime of the resulting perovskite solar cell devices produced using FA and MA cations.
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Jun 2020
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[20426, 24871]
Open Access
Abstract: The real-time morphological evolution of vacuum deposited α-sexithiophene (α-6T) on a weakly interacting (glass) substrate at ambient temperature is reported. In-situ grazing incidence small angle X-ray scattering (GISAXS) enabled the observation of nanoscale aggregates while in-situ grazing incidence wide angle scattering (GIWAXS) allowed the study of the molecular-scale morphology. The in-situ GISAXS measurements revealed that the α-6T growth proceeds via a Stranski-Krastanov mode, whereby 2-4 complete monolayers are deposited followed by subsequent layers formed via island growth. In-situ GIWAXS also showed the evolution of the polymorph composition during the thin film growth. Initially the disordered β-phase and the low-temperature (LT) phase are deposited in nearly equal proportion until a thickness of 8 nm whereby the LT-phase begins to dominate until a final α-6T thickness of 50 nm where the scattering intensity of the LT-phase is more than double that of the β-phase. The change in polymorph composition coincided with an increase in the LT-phase d-spacing, indicating a lattice strain relief as the thin film moves from surface to bulk mediated growth. The GISAXS findings were confirmed through direct imaging using ex-situ atomic force microscopy (AFM) at various thicknesses revealing the existence of both initial monolayers and intermediate and final island morphologies. The findings reveal the real-time morphological evolution of α-6T across both the molecular scale and the nanoscale and highlight the role of strain in polymorph growth. Due to the importance of thin film microstructure in device performance, it is expected that these results will aid in the development of the structure-property relationships necessary to realise the full potential of organic electronics.
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May 2020
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