E02-JEM ARM 300CF
|
Diamond Proposal Number(s):
[22549]
Abstract: Monolayer PtSe2 holds great potential in extending 2D devices functionality, but their atomic-level-defect study is still limited. Here, we investigate the atomic structures of lattice imperfections from point to stretched 1D defects in 1T-PtSe2 monolayers, using annular dark-field scanning transmission electron microscopy (ADF-STEM). We show Se vacancies (VSe) have preferential sites with high beam-induced mobility. Diverse divacancies form with paired VSe. We found stretched linear defects triggered by dynamics of VSe that altered strain fields, distinct from the line vacancies in 2H-phase 2D materials. The paired VSe stability and formation possibility of vacancy lines are evaluated by density functional theory. Lower sputtering energy in PtSe2 than that in MoS2 can cause larger possibility of atomic loss compared to diffusion required for creating VSe lines. This provides atomic insights into the defects in 1T-PtSe2 and shows how a deviated 1D structure is embedded in a 2D system without losing atom lines.
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Apr 2022
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I06-Nanoscience
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Dong
Li
,
Bonan
Zhu
,
Dirk
Backes
,
Larissa S. I.
Veiga
,
Tien-Lin
Lee
,
Hongguang
Wang
,
Qian
He
,
Pinku
Roy
,
Jiaye
Zhang
,
Jueli
Shi
,
Aiping
Chen
,
Peter A.
Van Aken
,
Quanxi
Jia
,
Sarnjeet S.
Dhesi
,
David O.
Scanlon
,
Kelvin H. L.
Zhang
,
Weiwei
Li
Diamond Proposal Number(s):
[25425, 26901, 29616]
Abstract: Strain engineering of epitaxial transition metal oxide heterostructures offers an intriguing opportunity to control electronic structures by modifying the interplay between spin, charge, orbital, and lattice degrees of freedom. Here, we demonstrate that the electronic structure, magnetic and transport properties of
La
0.9
Ba
0.1
MnO
3
thin films can be effectively controlled by epitaxial strain. Spectroscopic studies and first-principles calculations reveal that the orbital occupancy in Mn
e
g
orbitals can be switched from the
d
3
z
2
−
r
2
orbital to the
d
x
2
−
y
2
orbital by varying the strain from compressive to tensile. The change of orbital occupancy associated with Mn
3
d
-O
2
p
hybridization leads to dramatic modulation of the magnetic and electronic properties of strained
La
0.9
Ba
0.1
MnO
3
thin films. Under moderate tensile strain, an emergent ferromagnetic insulating state with an enhanced ferromagnetic Curie temperature of 215 K is achieved. These findings not only deepen our understanding of electronic structures, magnetic and transport properties in the
La
0.9
Ba
0.1
MnO
3
system, but also demonstrate the use of epitaxial strain as an effective knob to tune the electronic structures and related physical properties for potential spintronic device applications.
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Apr 2022
|
|
|
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Cyril
Leveille
,
Erick
Burgos-Parra
,
Yanis
Sassi
,
Fernando
Ajejas
,
Valentin
Chardonnet
,
Emanuele
Pedersoli
,
Flavio
Capotondi
,
Giovanni
De Ninno
,
Francesco
Maccherozzi
,
Sarnjeet
Dhesi
,
David M.
Burn
,
Gerrit
Van Der Laan
,
Oliver S.
Latcham
,
Andrey V.
Shytov
,
Volodymyr V.
Kruglyak
,
Emmanuelle
Jal
,
Vincent
Cros
,
Jean-Yves
Chauleau
,
Nicolas
Reyren
,
Michel
Viret
,
Nicolas
Jaouen
Open Access
Abstract: Non-collinear spin textures in ferromagnetic ultrathin films are attracting a renewed interest fueled by possible fine engineering of several magnetic interactions, notably the interfacial Dzyaloshinskii-Moriya interaction. This allows for the stabilization of complex chiral spin textures such as chiral magnetic domain walls (DWs), spin spirals, and magnetic skyrmions among others. We report here on the behavior of chiral DWs at ultrashort timescale after optical pumping in perpendicularly magnetized asymmetric multilayers. The magnetization dynamics is probed using time-resolved circular dichroism in x-ray resonant magnetic scattering (CD-XRMS). We observe a picosecond transient reduction of the CD-XRMS, which is attributed to the spin current-induced coherent and incoherent torques within the continuously varying spin texture of the DWs. We argue that a specific demagnetization of the inner structure of the DW induces a flow of spins from the interior of the neighboring magnetic domains. We identify this time-varying change of the DW texture shortly after the laser pulse as a distortion of the homochiral Néel shape toward a transient mixed Bloch-Néel-Bloch texture along a direction transverse to the DW.
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Mar 2022
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[20426]
Open Access
Abstract: We report on the characterization of the growth of vacuum-deposited zinc phthalocyanine (ZnPc) thin films on glass through a combination of in situ grazing incidence x-ray scattering, x-ray reflectivity, and atomic force microscopy. We found that the growth at room temperature proceeds via the formation of two structurally unique substrate-induced interfacial layers, followed by the growth of the
γ
-ZnPc polymorph thereafter (thickness
≈
1.0
nm). As the growth of the bulk
γ
-ZnPc progresses, a substantial out-of-plane lattice strain (
≈
15
%
relative to
γ
-ZnPc powder) is continually relaxed during the thin film growth. The rate of strain relaxation was slowed after a thickness of
≈
13
nm, corresponding to the transition from layer growth to island growth. The findings reveal the real-time microstructural evolution of ZnPc and highlight the importance of substrate-induced strain on thin film growth.
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Mar 2022
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I09-Surface and Interface Structural Analysis
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Jiaye
Zhang
,
Joe
Willis
,
Zhenni
Yang
,
Xu
Lian
,
Wei
Chen
,
Lai-Sen
Wang
,
Xiangyu
Xu
,
Tien-Lin
Lee
,
Lang
Chen
,
David O.
Scanlon
,
Kelvin H. I.
Zhang
Diamond Proposal Number(s):
[24219]
Open Access
Abstract: Deep UV transparent thin films have recently attracted considerable attention owing to their potential in UV and organic-based optoelectronics. Here, we report the achievement of a deep UV transparent and highly conductive thin film based on Si-doped Ga2O3 (SGO) with high conductivity of 2500 S/cm. The SGO thin films exhibit high transparency over a wide spectrum ranging from visible light to deep UV wavelength and, meanwhile, have a very low work-function of approximately 3.2 eV. A combination of photoemission spectroscopy and theoretical studies reveals that the delocalized conduction band derived from Ga 4s orbitals is responsible for the Ga2O3 films’ high conductivity. Furthermore, Si is shown to act as an efficient shallow donor, yielding high mobility up to approximately 60 cm2/Vs. The superior optoelectronic properties of SGO films make it a promising material for use as electrodes in high-power electronics and deep UV and organic-based optoelectronic devices.
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Mar 2022
|
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E02-JEM ARM 300CF
|
Diamond Proposal Number(s):
[20345]
Abstract: Four-dimensional (4D) scanning transmission electron microscopy is used to study the electric fields at the edges of 2D semiconducting monolayer MoS2. Sub-nanometer 1D features in the 2D electric field maps are observed at the outermost region along zigzag edges and also along nanowire MoS-terminated MoS2 edges. Atomic-scale oscillations are detected in the magnitude of the 1D electromagnetic edge state, with spatial variations that depend on the specific periodic edge reconstructions. Electric field reconstructions, along with integrated differential phase contrast reconstructions, reveal the presence of low Z number atoms terminating many of the uniform edges, which are difficult to detect by annular dark field scanning transmission electron microscopy due to its limited dynamic range. Density functional theory calculations support the formation of periodic 1D edge states and also show that enhancement of the electric field magnitude can occur for some edge terminations. The experimentally observed electric fields at the edges are attributed to the absence of an opposing electric field from a nearest neighbor atom when the electron beam propagates through the 2D monolayer and interacts. These results show the potential of 4D-STEM to map the atomic scale structure and fluctuations of electric fields around edge atoms with different bonding states than bulk atoms in 2D materials, beyond conventional imaging.
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Mar 2022
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I06-Nanoscience
|
Sonka
Reimers
,
Dominik
Kriegner
,
Olena
Gomonay
,
Dina
Carbone
,
Filip
Krizek
,
Vit
Novák
,
Richard P.
Campion
,
Francesco
Maccherozzi
,
Alexander
Bjorling
,
Oliver J.
Amin
,
Luke X.
Barton
,
Stuart F.
Poole
,
Khalid A.
Omari
,
Jan
Michalička
,
Ondřej
Man
,
Jairo
Sinova
,
Tomáš
Jungwirth
,
Peter
Wadley
,
Sarnjeet S.
Dhesi
,
Kevin W.
Edmonds
Diamond Proposal Number(s):
[22437, 2714]
Open Access
Abstract: Efficient manipulation of antiferromagnetic (AF) domains and domain walls has opened up new avenues of research towards ultrafast, high-density spintronic devices. AF domain structures are known to be sensitive to magnetoelastic effects, but the microscopic interplay of crystalline defects, strain and magnetic ordering remains largely unknown. Here, we reveal, using photoemission electron microscopy combined with scanning X-ray diffraction imaging and micromagnetic simulations, that the AF domain structure in CuMnAs thin films is dominated by nanoscale structural twin defects. We demonstrate that microtwin defects, which develop across the entire thickness of the film and terminate on the surface as characteristic lines, determine the location and orientation of 180∘ and 90∘ domain walls. The results emphasize the crucial role of nanoscale crystalline defects in determining the AF domains and domain walls, and provide a route to optimizing device performance.
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Feb 2022
|
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I09-Surface and Interface Structural Analysis
|
Jueli
Shi
,
Ethan A.
Rubinstein
,
Weiwei
Li
,
Jiaye
Zhang
,
Ye
Yang
,
Tien-Lin
Lee
,
Changdong
Qin
,
Pengfei
Yan
,
Judith L.
Macmanus-Driscoll
,
David O.
Scanlon
,
Kelvin H.l.
Zhang
Diamond Proposal Number(s):
[24219]
Open Access
Abstract: Oxide semiconductors are key materials in many technologies from flat-panel displays，solar cells to transparent electronics. However, many potential applications are hindered by the lack of high mobility p-type oxide semiconductors due to the localized O-2p derived valence band (VB) structure. In this work, the VB structure modulation is reported for perovskite Ba2BiMO6 (M = Bi, Nb, Ta) via the Bi 6s2 lone pair state to achieve p-type oxide semiconductors with high hole mobility up to 21 cm2 V−1 s−1, and optical bandgaps widely varying from 1.5 to 3.2 eV. Pulsed laser deposition is used to grow high quality epitaxial thin films. Synergistic combination of hard x-ray photoemission, x-ray absorption spectroscopies, and density functional theory calculations are used to gain insight into the electronic structure of Ba2BiMO6. The high mobility is attributed to the highly dispersive VB edges contributed from the strong coupling of Bi 6s with O 2p at the top of VB that lead to low hole effective masses (0.4–0.7 me). Large variation in bandgaps results from the change in the energy positions of unoccupied Bi 6s orbital or Nb/Ta d orbitals that form the bottom of conduction band. P–N junction diode constructed with p-type Ba2BiTaO6 and n-type Nb doped SrTiO3 exhibits high rectifying ratio of 1.3 × 104 at ±3 V, showing great potential in fabricating high-quality devices. This work provides deep insight into the electronic structure of Bi3+ based perovskites and guides the development of new p-type oxide semiconductors.
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Jan 2022
|
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I09-Surface and Interface Structural Analysis
|
Gian Marco
Pierantozzi
,
Alessandro
De Vita
,
Chiara
Bigi
,
Xin
Gui
,
Hung-Ju
Tien
,
Debashis
Mondal
,
Federico
Mazzola
,
Jun
Fujii
,
Ivana
Vobornik
,
Giovanni
Vinai
,
Alessandro
Sala
,
Cristina
Africh
,
Tien-Lin
Lee
,
Giorgio
Rossi
,
Tay-Rong
Chang
,
Weiwei
Xie
,
Robert J.
Cava
,
Giancarlo
Panaccione
Diamond Proposal Number(s):
[24968]
Open Access
Abstract: We unravel the interplay of topological properties and the layered (anti)ferromagnetic ordering in EuSn2P2, using spin and chemical selective electron and X-ray spectroscopies supported by first-principle calculations. We reveal the presence of in-plane long-range ferromagnetic order triggering topological invariants and resulting in the multiple protection of topological Dirac states. We provide clear evidence that layer-dependent spin-momentum locking coexists with ferromagnetism in this material, a cohabitation that promotes EuSn2P2 as a prime candidate axion insulator for topological antiferromagnetic spintronics applications.
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Jan 2022
|
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I06-Nanoscience
|
S.
Kurdi
,
Y.
Sakuraba
,
K.
Masuda
,
H.
Tajiri
,
B.
Nair
,
G. F.
Nataf
,
M. E.
Vickers
,
G.
Reiss
,
M
Meinert
,
S. S.
Dhesi
,
Massimo
Ghidini
,
Z H
Barber
Diamond Proposal Number(s):
[18932]
Open Access
Abstract: In this work, we investigate the effect of anti-site disorder on the half-metallic properties of a Mn2FeAl Heusler alloy thin film. The film was grown on TiN-buffered MgO 001 substrates via magnetron sputtering. A detailed structural characterization using X-ray diffraction (XRD) and anomalous XRD showed that the film crystallizes in the partially disordered L21B structure with 33% disorder between the Mn(B) and Al(D) sites. We measure a positive anisotropic magnetoresistance in the film, which is an indication of non-half metallic behaviour. Our X-ray magnetic circular dichroism sum rules analysis shows that Mn carries the magnetic moment in the film, as predicted, with a positive Fe moment. Experimentally determined moments correspond most closely with those found by density functional calculated ones for the L21B structure with Mn(B) and Al(D) site disorder, matching the experimental structural analysis. We thus attribute the deviation from half-metallic behaviour to the formation of the L21B structure, which we support by density functional theory calculations. To realize a half-metallic Mn2FeAl film it is important that the inverse Heusler XA structure is stabilized with minimal anti-site atomic disorder.
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Jan 2022
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