I06-Nanoscience
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O. J.
Amin
,
S. F.
Poole
,
S.
Reimers
,
L. X.
Barton
,
A.
Dal Din
,
F.
Maccherozzi
,
S. S.
Dhesi
,
V.
Novák
,
F.
Krizek
,
J. S.
Chauhan
,
R. P.
Campion
,
A. W.
Rushforth
,
T.
Jungwirth
,
O. A.
Tretiakov
,
K. W.
Edmonds
,
P.
Wadley
Diamond Proposal Number(s):
[26255, 27845]
Open Access
Abstract: Topologically protected magnetic textures are promising candidates for information carriers in future memory devices, as they can be efficiently propelled at very high velocities using current-induced spin torques. These textures—nanoscale whirls in the magnetic order—include skyrmions, half-skyrmions (merons) and their antiparticles. Antiferromagnets have been shown to host versions of these textures that have high potential for terahertz dynamics, deflection-free motion and improved size scaling due to the absence of stray field. Here we show that topological spin textures, merons and antimerons, can be generated at room temperature and reversibly moved using electrical pulses in thin-film CuMnAs, a semimetallic antiferromagnet that is a testbed system for spintronic applications. The merons and antimerons are localized on 180° domain walls, and move in the direction of the current pulses. The electrical generation and manipulation of antiferromagnetic merons is a crucial step towards realizing the full potential of antiferromagnetic thin films as active components in high-density, high-speed magnetic memory devices.
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May 2023
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I19-Small Molecule Single Crystal Diffraction
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Haofan
Yang
,
Chao
Li
,
Tao
Liu
,
Thomas
Fellowes
,
Samantha Y.
Chong
,
Luca
Catalano
,
Mounib
Bahri
,
Weiwei
Zhang
,
Yongjie
Xu
,
Lunjie
Liu
,
Wei
Zhao
,
Adrian M.
Gardner
,
Rob
Clowes
,
Nigel D.
Browning
,
Xiaobo
Li
,
Alexander J.
Cowan
,
Andrew I.
Cooper
Abstract: Molecular packing controls optoelectronic properties in organic molecular nanomaterials. Here we report a donor–acceptor organic molecule (2,6-bis(4-cyanophenyl)-4-(9-phenyl-9H-carbazol-3-yl)pyridine-3,5-dicarbonitrile) that exhibits two aggregate states in aqueous dispersions: amorphous nanospheres and ordered nanofibres with π–π molecular stacking. The nanofibres promote sacrificial photocatalytic H2 production (31.85 mmol g−1 h−1) while the nanospheres produce hydrogen peroxide (H2O2) (3.20 mmol g−1 h−1 in the presence of O2). This is the first example of an organic photocatalyst that can be directed to produce these two different solar fuels simply by changing the molecular packing. These different packings affect energy band levels, the extent of excited state delocalization, the excited state dynamics, charge transfer to O2 and the light absorption profile. We use a combination of structural and photophysical measurements to understand how this influences photocatalytic selectivity. This illustrates the potential to achieve multiple photocatalytic functionalities with a single organic molecule by engineering nanomorphology and solid-state packing.
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Jan 2023
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I14-Hard X-ray Nanoprobe
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Kyle
Frohna
,
Miguel
Anaya
,
Stuart
Macpherson
,
Jooyoung
Sung
,
Tiarnan A. S.
Doherty
,
Yu-Hsien
Chiang
,
Andrew J.
Winchester
,
Kieran W. P.
Orr
,
Julia E.
Parker
,
Paul D.
Quinn
,
Keshav M.
Dani
,
Akshay
Rao
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[19023, 20420]
Abstract: Halide perovskites perform remarkably in optoelectronic devices. However, this exceptional performance is striking given that perovskites exhibit deep charge-carrier traps and spatial compositional and structural heterogeneity, all of which should be detrimental to performance. Here, we resolve this long-standing paradox by providing a global visualization of the nanoscale chemical, structural and optoelectronic landscape in halide perovskite devices, made possible through the development of a new suite of correlative, multimodal microscopy measurements combining quantitative optical spectroscopic techniques and synchrotron nanoprobe measurements. We show that compositional disorder dominates the optoelectronic response over a weaker influence of nanoscale strain variations even of large magnitude. Nanoscale compositional gradients drive carrier funnelling onto local regions associated with low electronic disorder, drawing carrier recombination away from trap clusters associated with electronic disorder and leading to high local photoluminescence quantum efficiency. These measurements reveal a global picture of the competitive nanoscale landscape, which endows enhanced defect tolerance in devices through spatial chemical disorder that outcompetes both electronic and structural disorder.
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Nov 2021
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E02-JEM ARM 300CF
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Astrid
Weston
,
Yichao
Zou
,
Vladimir
Enaldiev
,
Alex
Summerfield
,
Nicholas
Clark
,
Viktor
Zólyomi
,
Abigail
Graham
,
Celal
Yelgel
,
Samuel
Magorrian
,
Mingwei
Zhou
,
Johanna
Zultak
,
David
Hopkinson
,
Alexei
Barinov
,
Thomas H.
Bointon
,
Andrey
Kretinin
,
Neil R.
Wilson
,
Peter H.
Beton
,
Vladimir I.
Fal’ko
,
Sarah J.
Haigh
,
Roman
Gorbachev
Diamond Proposal Number(s):
[19315, 21597]
Abstract: Van der Waals heterostructures form a unique class of layered artificial solids in which physical properties can be manipulated through controlled composition, order and relative rotation of adjacent atomic planes. Here we use atomic-resolution transmission electron microscopy to reveal the lattice reconstruction in twisted bilayers of the transition metal dichalcogenides, MoS2 and WS2. For twisted 3R bilayers, a tessellated pattern of mirror-reflected triangular 3R domains emerges, separated by a network of partial dislocations for twist angles θ < 2°. The electronic properties of these 3R domains, featuring layer-polarized conduction-band states caused by lack of both inversion and mirror symmetry, appear to be qualitatively different from those of 2H transition metal dichalcogenides. For twisted 2H bilayers, stable 2H domains dominate, with nuclei of a second metastable phase. This appears as a kagome-like pattern at θ ≈ 2°, transitioning at θ → 0 to a hexagonal array of screw dislocations separating large-area 2H domains. Tunnelling measurements show that such reconstruction creates strong piezoelectric textures, opening a new avenue for engineering of 2D material properties.
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May 2020
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Katharina
Zeissler
,
Simone
Finizio
,
Kowsar
Shahbazi
,
Jamie
Massey
,
Fatma Al
Ma’mari
,
David M.
Bracher
,
Armin
Kleibert
,
Mark C.
Rosamond
,
Edmund H.
Linfield
,
Thomas A.
Moore
,
Jörg
Raabe
,
Gavin
Burnell
,
Christopher H.
Marrows
Abstract: Magnetic skyrmions are knot-like quasiparticles. They are candidates for non-volatile data storage in which information is moved between fixed read and write terminals. The read-out operation of skyrmion-based spintronic devices will rely on the electrical detection of a single magnetic skyrmion within a nanostructure. Here we present Pt/Co/Ir nanodiscs that support skyrmions at room temperature. We measured the Hall resistivity and simultaneously imaged the spin texture using magnetic scanning transmission X-ray microscopy. The Hall resistivity is correlated to both the presence and size of the skyrmion. The size-dependent part matches the expected anomalous Hall signal when averaging the magnetization over the entire disc. We observed a resistivity contribution that only depends on the number and sign of skyrmion-like objects present in the disc. Each skyrmion gives rise to 22 ± 2 nΩ cm irrespective of its size. This contribution needs to be considered in all-electrical detection schemes applied to skyrmion-based devices. Not only the area of Néel skyrmions but also their number and sign contribute to their Hall resistivity.
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Oct 2018
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E02-JEM ARM 300CF
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Zupeng
Chen
,
Evgeniya
Vorobyeva
,
Sharon
Mitchell
,
Edvin
Fako
,
Manuel A.
Ortuño
,
Núria
López
,
Sean M.
Collins
,
Paul A.
Midgley
,
Sylvia
Richard
,
Gianvito
Vilé
,
Javier
Pérez-Ramírez
Diamond Proposal Number(s):
[16967]
Abstract: Palladium-catalysed cross-coupling reactions, central tools in fine-chemical synthesis, predominantly employ soluble metal complexes despite recognized challenges with product purification and catalyst reusability. Attempts to tether these homogeneous catalysts on insoluble carriers have been thwarted by suboptimal stability, which leads to a progressively worsening performance due to metal leaching or clustering4. The alternative application of supported Pd nanoparticles has faced limitations because of insufficient activity under the mild conditions required to avoid thermal degradation of the substrates or products. Single-atom heterogeneous catalysts lie at the frontier. Here, we show that the Pd atoms anchored on exfoliated graphitic carbon nitride (Pd-ECN) capture the advantages of both worlds, as they comprise a solid catalyst that matches the high chemoselectivity and broad functional group tolerance of state-of-the-art homogeneous catalysts for Suzuki couplings, and also demonstrate a robust stability in flow. The adaptive coordination environment within the macroheterocycles of ECN facilitates each catalytic step. The findings illustrate the exciting opportunities presented by nanostructuring single atoms in solid hosts for catalytic processes that remain difficult to heterogenize.
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Jun 2018
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I06-Nanoscience
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Peter
Wadley
,
Sonka
Reimers
,
Michal J.
Grzybowski
,
Carl
Andrews
,
Mu
Wang
,
Jasbinder S.
Chauhan
,
Bryan L.
Gallagher
,
Richard P.
Campion
,
Kevin W.
Edmonds
,
Sarnjeet S.
Dhesi
,
Francesco
Maccherozzi
,
Vit
Novak
,
Joerg
Wunderlich
,
Tomas
Jungwirth
Diamond Proposal Number(s):
[16376]
Abstract: Antiferromagnets have several favourable properties as active elements in spintronic devices, including ultra-fast dynamics, zero stray fields and insensitivity to external magnetic fields1. Tetragonal CuMnAs is a testbed system in which the antiferromagnetic order parameter can be switched reversibly at ambient conditions using electrical currents2. In previous experiments, orthogonal in-plane current pulses were used to induce 90° rotations of antiferromagnetic domains and demonstrate the operation of all-electrical memory bits in a multi-terminal geometry3. Here, we demonstrate that antiferromagnetic domain walls can be manipulated to realize stable and reproducible domain changes using only two electrical contacts. This is achieved by using the polarity of the current to switch the sign of the current-induced effective field acting on the antiferromagnetic sublattices. The resulting reversible domain and domain wall reconfigurations are imaged using X-ray magnetic linear dichroism microscopy, and can also be detected electrically. Switching by domain-wall motion can occur at much lower current densities than those needed for coherent domain switching.
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Mar 2018
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Abstract: Arrays of non-interacting nanomagnets are widespread in data storage and processing. As current technologies approach fundamental limits on size and thermal stability, enhancing functionality through embracing the strong interactions present at high array densities becomes attractive. In this respect, artificial spin ices are geometrically frustrated magnetic metamaterials that offer vast untapped potential due to their unique microstate landscapes, with intriguing prospects in applications from reconfigurable logic to magnonic devices or hardware neural networks. However, progress in such systems is impeded by the inability to access more than a fraction of the total microstate space. Here, we demonstrate that topological defect-driven magnetic writing—a scanning probe technique—provides access to all of the possible microstates in artificial spin ices and related arrays of nanomagnets. We create previously elusive configurations such as the spin-crystal ground state of artificial kagome dipolar spin ices and high-energy, low-entropy ‘monopole-chain’ states that exhibit negative effective temperatures.
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Nov 2017
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I05-ARPES
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Jinxiong
Wu
,
Hongtao
Yuan
,
Mengmeng
Meng
,
Cheng
Chen
,
Yan
Sun
,
Zhuoyu
Chen
,
Wenhui
Dang
,
Congwei
Tan
,
Yujing
Liu
,
Jianbo
Yin
,
Yubing
Zhou
,
Shaoyun
Huang
,
H. Q.
Xu
,
Yi
Cui
,
Harold Y.
Hwang
,
Zhongfan
Liu
,
Yulin
Chen
,
Binghai
Yan
,
Hailin
Peng
Diamond Proposal Number(s):
[14132]
Abstract: High-mobility semiconducting ultrathin films form the basis of modern electronics, and may lead to the scalable fabrication of highly performing devices. Because the ultrathin limit cannot be reached for traditional semiconductors, identifying new two-dimensional materials with both high carrier mobility and a large electronic bandgap is a pivotal goal of fundamental research1, 2, 3, 4, 5, 6, 7, 8, 9. However, air-stable ultrathin semiconducting materials with superior performances remain elusive at present10. Here, we report ultrathin films of non-encapsulated layered Bi2O2Se, grown by chemical vapour deposition, which demonstrate excellent air stability and high-mobility semiconducting behaviour. We observe bandgap values of ∼0.8 eV, which are strongly dependent on the film thickness due to quantum-confinement effects. An ultrahigh Hall mobility value of >20,000 cm2 V−1 s−1 is measured in as-grown Bi2O2Se nanoflakes at low temperatures. This value is comparable to what is observed in graphene grown by chemical vapour deposition11 and at the LaAlO3–SrTiO3 interface12, making the detection of Shubnikov–de Haas quantum oscillations possible. Top-gated field-effect transistors based on Bi2O2Se crystals down to the bilayer limit exhibit high Hall mobility values (up to 450 cm2 V−1 s−1), large current on/off ratios (>106) and near-ideal subthreshold swing values (∼65 mV dec–1) at room temperature. Our results make Bi2O2Se a promising candidate for future high-speed and low-power electronic applications.
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Apr 2017
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I05-ARPES
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J.
Riley
,
W.
Meevasana
,
L.
Bawden
,
M.
Asakawa
,
T.
Takayama
,
T.
Eknapakul
,
T.
Kim
,
M.
Hoesch
,
S. K.
Mo
,
H.
Takagi
,
T.
Sasagawa
,
M. S.
Bahramy
,
P. D. C.
King
Diamond Proposal Number(s):
[9500, 11383]
Abstract: Tunable bandgaps, extraordinarily large exciton-binding energies, strong light–matter coupling and a locking of the electron spin with layer and valley pseudospins have established transition-metal dichalcogenides (TMDs) as a unique class of two-dimensional (2D) semiconductors with wide-ranging practical applications. Using angle-resolved photoemission (ARPES), we show here that doping electrons at the surface of the prototypical strong spin–orbit TMD WSe2 , akin to applying a gate voltage in a transistor-type device, induces a counterintuitive lowering of the surface chemical potential concomitant with the formation of a multivalley 2D electron gas (2DEG). These measurements provide a direct spectroscopic signature of negative electronic compressibility (NEC), a result of electron–electron interactions, which we find persists to carrier densities approximately three orders of magnitude higher than in typical semiconductor 2DEGs that exhibit this effect. An accompanying tunable spin splitting of the valence bands further reveals a complex interplay between single-particle band-structure evolution and many-body interactions in electrostatically doped TMDs. Understanding and exploiting this will open up new opportunities for advanced electronic and quantum-logic devices.
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Sep 2015
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