I07-Surface & interface diffraction
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Shuai
Yuan
,
Lin-Song
Cui
,
Linjie
Dai
,
Yun
Liu
,
Qing-Weii
Liu
,
Yu-Qi
Sun
,
Florian
Auras
,
Miguel
Anaya
,
Xiaopeng
Zheng
,
Edoardo
Ruggeri
,
You-Jun
Yu
,
Yang-Kun
Qu
,
Mojtaba
Abdi-Jalebi
,
Osman M.
Bakr
,
Zhao-Kui
Wang
,
Samuel D.
Stranks
,
Neil C.
Greenham
,
Liang-Sheng
Liao
,
Richard H.
Friend
Diamond Proposal Number(s):
[17223]
Open Access
Abstract: Metal halide perovskite semiconductors have demonstrated remarkable potentials in solution-processed blue light-emitting diodes (LEDs). However, the unsatisfied efficiency and spectral stability responsible for trap-mediated non-radiative losses and halide phase segregation remain the primary unsolved challenges for blue perovskite LEDs. In this study, it is reported that a fluorene-based π-conjugated cationic polymer can be blended with the perovskite semiconductor to control film formation and optoelectronic properties. As a result, sky-blue and true-blue perovskite LEDs with Commission Internationale de l'Eclairage coordinates of (0.08, 0.22) and (0.12, 0.13) at the record external quantum efficiencies of 11.2% and 8.0% were achieved. In addition, the mixed halide perovskites with the conjugated cationic polymer exhibit excellent spectral stability under external bias. This result illustrates that π-conjugated cationic polymers have a great potential to realize efficient blue mixed-halide perovskite LEDs with stable electroluminescence.
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Sep 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[20060]
Open Access
Abstract: The pseudo-layered sulfide NiCr2S4 exhibits outstanding electrochemical performance as anode material in sodium-ion batteries (SIBs). The Na storage mechanism is investigated by synchrotron-based X-ray scattering and absorption techniques as well as by electrochemical measurements. A very high reversible capacity in the 500th cycle of 489 mAh g−1 is observed at 2.0 A g−1 in the potential window 3.0–0.1 V. Full discharge includes irreversible generation of Ni0 and Cr0 nanoparticles embedded in nanocrystalline Na2S yielding shortened diffusion lengths and predominantly surface-controlled charge storage. During charge, Ni0 and Cr0 are oxidized, Na2S is consumed, and amorphous Ni and Cr sulfides are formed. Limiting the potential window to 3.0–0.3 V an unusual nickel extrusion sodium insertion mechanism occurs: Ni2+ is reduced to nanosized Ni0 domains, expelled from the host lattice, and is replaced by Na+ cations to form O3-type like NaCrS2. Surprisingly, the discharge and charge processes comprise Na+ shuttling between highly crystalline NiCr2S4 and NaCrS2 enabling a superior long-term stability for 3000 cycles. The results not only provide valuable insights for the electrochemistry of conversion materials but also extend the scope of layered electrode materials considering the reversible nickel extrusion sodium insertion reaction as new concept for SIBs.
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Sep 2021
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[18768, 22411]
Open Access
Abstract: Human society is facing—among other environmental threats—an enormous challenge due to human activities. The extensive use of high-tech devices and electronics equipment in the daily life makes, among others, rare-earth elements (REEs) recovery from secondary sources highly required. Here, a novel bioMOF-based single-walled carbon nanotube buckypaper (SWCNTBP) is presented as a new and efficient composite material (BioMOF@SWCNT-BP). The flexible and highly crystalline metal–organic framework (MOF), prepared from the natural amino acid L-threonine, has been homogeneously dispersed within the tangled net of a self-standing SWCNT-BP for lanthanides recovery from water. This MOF-carbon-based membrane exhibits high efficiency, either in static or dynamic regimes, in the recovery of lanthanides from aqueous streams outperforming the state-of-the-art. The capture performances of BPs are successfully improved after incorporation of such MOF featuring hexagonal functional channels decorated with the threonine amino acid residues, pointing toward the accessible void spaces, which boosts the capture properties of the final membrane, providing the adaptable functional environment to interact with lanthanides. This material's preparation presents also a potential for large-scale applications with a potential benefit on natural aquatic ecosystems as well. It is highly demanded because REEs from non-recycled waste materials are potential pollutants for surface waters.
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Aug 2021
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[21167]
Open Access
Abstract: New approaches for the engineering of the 3D microstructure, pore modality, and chemical functionality of hierarchically porous nanocarbon assemblies are key to develop the next generation of functional aerogel and membrane materials. Here, interfacially driven assembly of carbon nanotubes (CNT) is exploited to fabricate structurally directed aerogels with highly controlled internal architectures, composed of pseudo-monolayer, CNT microcages. CNT Pickering emulsions enable engineering at fundamentally different length scales, whereby the microporosity, mesoporosity, and macroporosity are decoupled and individually controlled through CNT type, CNT number density, and process energy, respectively. In addition, metal nanocatalysts (Cu, Pd, and Ru) are embedded within the architectures through an elegant sublimation and shock-decomposition approach; introducing the first approach that enables through-volume functionalization of intricate, pre-designed aerogels without microstructural degradation. Catalytic structure–function relationships are explored in a pharma-important amidation reaction; providing insights on how the engineered frameworks enhance catalyst activity. A sophisticated array of advanced tomographic, spectroscopic, and microscopic techniques reveal an intricate 3D assembly of CNT building-blocks and their influence on the functional properties of the enhanced nanocatalysts. These advances set a basis to modulate structure and chemistry of functional aerogel materials independently in a controlled fashion for a variety of applications, including energy conversion and storage, smart electronics, and (electro)catalysis.
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May 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Martin Alexander
Lange
,
Ibrahim
Khan
,
Phil
Opitz
,
Jens
Hartmann
,
Muhammad
Ashraf
,
Ahsanulhaq
Qurashi
,
Leon
Prädel
,
Martin
Panthofer
,
Antje
Cossmer
,
Jens
Pfeifer
,
Fabian
Simon
,
Marcus
Von Der Au
,
Björn
Meermann
,
Mihail
Mondeshki
,
Muhammad Nawaz
Tahir
,
Wolfgang
Tremel
Diamond Proposal Number(s):
[23320]
Open Access
Abstract: A general method to carry out the fluorination of metal oxides with poly(tetrafluoroethylene) (PTFE, Teflon) waste by spark plasma sintering (SPS) on a minute scale with Teflon is reported. The potential of this new approach is highlighted by the following results. i) The tantalum oxyfluorides Ta3O7F and TaO2F are obtained from plastic scrap without using toxic or caustic chemicals for fluorination. ii) Short reaction times (minutes rather than days) reduce the process time the energy costs by almost three orders of magnitude. iii) The oxyfluorides Ta3O7F and TaO2F are produced in gram amounts of nanoparticles. Their synthesis can be upscaled to the kg range with industrial sintering equipment. iv) SPS processing changes the catalytic properties: while conventionally prepared Ta3O7F and TaO2F show little catalytic activity, SPS‐prepared Ta3O7F and TaO2F exhibit high activity for photocatalytic oxygen evolution, reaching photoconversion efficiencies up to 24.7% and applied bias to photoconversion values of 0.86%. This study shows that the materials properties are dictated by the processing which poses new challenges to understand and predict the underlying factors.
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Apr 2021
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Yangkun
He
,
Gerhard H.
Fecher
,
Chenguang
Fu
,
Yu
Pan
,
Kaustuv
Manna
,
Johannes
Kroder
,
Ajay
Jha
,
Xiao
Wang
,
Zhiwei
Hu
,
Stefano
Agrestini
,
Javier
Herrero-Martin
,
Manuel
Valvidares
,
Yurii
Skourski
,
Walter
Schnelle
,
Plamen
Stamenov
,
Horst
Borrmann
,
Liu Hao
Tjeng
,
Rudolf
Schaefer
,
Stuart S. P.
Parkin
,
John Michael D.
Coey
,
Claudia
Felser
Open Access
Abstract: The development of high‐density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat‐assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc, coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2CoSb is introduced as a new hard magnet with potential for thin‐film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m−3 is combined with a saturation magnetization of μ0Ms = 0.52 T at 2 K (2.2 MJ m−3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare‐earth‐free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin–orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m−1 K−1, make Rh2CoSb a candidate for the development of heat‐assisted writing with a recording density in excess of 10 Tb in.−2.
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Oct 2020
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I10-Beamline for Advanced Dichroism
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Yao
Guang
,
Yong
Peng
,
Zhengren
Yan
,
Yizhou
Liu
,
Junwei
Zhang
,
Xue
Zeng
,
Senfu
Zhang
,
Shilei
Zhang
,
David M.
Burn
,
Nicolas
Jaouen
,
Jinwu
Wei
,
Hongjun
Xu
,
Jiafeng
Feng
,
Chi
Fang
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
,
Baoshan
Cui
,
Xixiang
Zhang
,
Guoqiang
Yu
,
Xiufeng
Han
Diamond Proposal Number(s):
[20183, 21868]
Abstract: The emergence of magnetic skyrmions, topological spin textures, has aroused tremendous interest in studying the rich physics related to their topology. While skyrmions promise high‐density and energy‐efficient magnetic memory devices for information technology, the manifestation of their nontrivial topology through single skyrmions and ordered and disordered skyrmion lattices could also give rise to many fascinating physical phenomena, such as chiral magnon and skyrmion glass states. Therefore, generating skyrmions at designated locations on a large scale, while controlling the skyrmion patterns, is the key to advancing topological magnetism. Here, a new, yet general, approach to the “printing” of skyrmions with zero‐field stability in arbitrary patterns on a massive scale in exchange‐biased magnetic multilayers is presented. By exploiting the fact that the antiferromagnetic order can be reconfigured by local thermal excitations, a focused electron beam with a graphic pattern generator to “print” skyrmions is used, which is referred to as skyrmion lithography. This work provides a route to design arbitrary skyrmion patterns, thereby establishing the foundation for further exploration of topological magnetism.
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Aug 2020
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I11-High Resolution Powder Diffraction
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Masoumeh
Keshavarz
,
Elke
Debroye
,
Martin
Ottesen
,
Cristina
Martin
,
Heng
Zhang
,
Eduard
Fron
,
Robert
Küchler
,
Julian A.
Steele
,
Martin
Bremholm
,
Joris
Van De Vondel
,
Hai I.
Wang
,
Mischa
Bonn
,
Maarten B. J.
Roeffaers
,
Steffen
Wiedmann
,
Johan
Hofkens
Diamond Proposal Number(s):
[22020]
Open Access
Abstract: Lead‐free double perovskites have great potential as stable and nontoxic optoelectronic materials. Recently, Cs2AgBiBr6 has emerged as a promising material, with suboptimal photon‐to‐charge carrier conversion efficiency, yet well suited for high‐energy photon‐detection applications. Here, the optoelectronic and structural properties of pure Cs2AgBiBr6 and alkali‐metal‐substituted (Cs1−xYx)2AgBiBr6 (Y: Rb+, K+, Na+; x = 0.02) single crystals are investigated. Strikingly, alkali‐substitution entails a tunability to the material system in its response to X‐rays and structural properties that is most strongly revealed in Rb‐substituted compounds whose X‐ray sensitivity outperforms other double‐perovskite‐based devices reported. While the fundamental nature and magnitude of the bandgap remains unchanged, the alkali‐substituted materials exhibit a threefold boost in their fundamental carrier recombination lifetime at room temperature. Moreover, an enhanced electron–acoustic phonon scattering is found compared to Cs2AgBiBr6. The study thus paves the way for employing cation substitution to tune the properties of double perovskites toward a new material platform for optoelectronics.
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Aug 2020
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B22-Multimode InfraRed imaging And Microspectroscopy
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Open Access
Abstract: There is rising interest on low‐k dielectric materials based on porous metal–organic frameworks (MOFs) for improved electrical insulation in microelectronics. Herein, the concept of MOF dielectric sensor built from a single crystal of HKUST‐1 is demonstrated. Guest encapsulation effects of polar and non‐polar molecules are studied, by monitoring the transient dielectric response and AC conductivity of the crystal exposed to different vapors (water, iodine, methanol, and ethanol). The dielectric properties are measured along the <100> crystal direction in the frequency range of 100 Hz to 2 MHz. The dielectric data show the efficacy of MOF dielectric sensor for discriminating the guest analytes. The time‐dependent transient response reveals dynamics of the molecular inclusion and exclusion processes in the nanoscale pores. Since dielectric response is ubiquitous to all MOF materials (unlike DC conductivity and fluorescence), the results demonstrate the potential of dielectric MOF sensors compared to resistive sensors and luminescence‐based approaches.
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Jul 2020
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I05-ARPES
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Alfred J. H.
Jones
,
Ryan
Muzzio
,
Paulina
Majchrzak
,
Sahar
Pakdel
,
Davide
Curcio
,
Klara
Volckaert
,
Deepnarayan
Biswas
,
Jacob
Gobbo
,
Simranjeet
Singh
,
Jeremy T.
Robinson
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Timur K.
Kim
,
Cephise
Cacho
,
Nicola
Lanata
,
Jill A.
Miwa
,
Philip
Hofmann
,
Jyoti
Katoch
,
Soeren
Ulstrup
Diamond Proposal Number(s):
[24072]
Abstract: The possibility of triggering correlated phenomena by placing a singularity
of the density of states near the Fermi energy remains an intriguing avenue toward engineering the properties of quantum materials. Twisted bilayer gra- phene is a key material in this regard because the superlattice produced by the rotated graphene layers introduces a van Hove singularity and flat bands near the Fermi energy that cause the emergence of numerous correlated phases, including superconductivity. Direct demonstration of electrostatic control of the superlattice bands over a wide energy range has, so far, been critically missing. This work examines the effect of electrical doping on the electronic band structure of twisted bilayer graphene using a back-gated device archi- tecture for angle-resolved photoemission measurements with a nano-focused light spot. A twist angle of 12.2° is selected such that the superlattice Brillouin zone is sufficiently large to enable identification of van Hove singularities and flat band segments in momentum space. The doping dependence of these fea- tures is extracted over an energy range of 0.4 eV, expanding the combinations of twist angle and doping where they can be placed at the Fermi energy and thereby induce new correlated electronic phases in twisted bilayer graphene.
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Jun 2020
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