|
|
Paulina
Majchrzak
,
Klara
Volckaert
,
Antonija Grubišić
Čabo
,
Deepnarayan
Biswas
,
Marco
Bianchi
,
Sanjoy K.
Mahatha
,
Maciej
Dendzik
,
Federico
Andreatta
,
Signe S.
Grønborg
,
Igor
Markovic
,
Jonathon M.
Riley
,
Jens C.
Johannsen
,
Daniel
Lizzit
,
Luca
Bignardi
,
Silvano
Lizzit
,
Cephise
Cacho
,
Oliver
Alexander
,
Dan
Matselyukh
,
Adam S.
Wyatt
,
Richard T.
Chapman
,
Emma
Springate
,
Jeppe V.
Lauritsen
,
Phil D. C.
King
,
Charlotte
Sanders
,
Jill A.
Miwa
,
Philip
Hofmann
,
Soeren
Ulstrup
Open Access
Abstract: The quasiparticle spectra of atomically thin semiconducting transition metal dichalcogenides (TMDCs) and their response to an ultrafast optical excitation critically depend on interactions with the underlying substrate. Here, we present a comparative time- and angle-resolved photoemission spectroscopy (TR-ARPES) study of the transient electronic structure and ultrafast carrier dynamics in the single- and bilayer TMDCs MoS2 and WS2 on three different substrates: Au(111), Ag(111) and graphene/SiC. The photoexcited quasiparticle bandgaps are observed to vary over the range of 1.9–2.5 eV between our systems. The transient conduction band signals decay on a sub-50 fs timescale on the metals, signifying an efficient removal of photoinduced carriers into the bulk metallic states. On graphene, we instead observe a fast timescale on the order of 170 fs, followed by a slow dynamics for the conduction band decay in MoS
. These timescales are explained by Auger recombination involving MoS
and in-gap defect states. In bilayer TMDCs on metals we observe a complex redistribution of excited holes along the valence band that is substantially affected by interactions with the continuum of bulk metallic states.
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Jul 2021
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B16-Test Beamline
|
A. J.
Blue
,
B.
Gallop
,
T.
Heim
,
C.
Helling
,
K.
Krizka
,
B.
Li
,
C.
Labitan
,
E.
Mladina
,
L.
Poley
,
P. W.
Phillips
,
S. N.
Santpur
,
C. A.
Sawyer
Diamond Proposal Number(s):
[22002]
Open Access
Abstract: Modules for the ATLAS Inner Tracker (ITk) strip tracker include a DC-DC converter circuit glued directly to the silicon sensor which converts the 11 V supplied to the module to the 1.5 V required for the operation of the readout chips. The DC-DC converter unit, consisting of a copper solenoid and custom ASIC, is located directly above the silicon strip sensor and therefore needs to be shielded to protect the sensor from EMI noise created during the operation of the circuit. Despite dedicated shielding, consisting of an aluminium shield box with continuous solder seams encompassing the surface components and a copper layer in the PCB beneath it, module channels connected to sensor strips located beneath the converter circuit were found to show a noise increase. While the DC-DC converter unit causing the underlying EMI noise operates at a frequency of 2 MHz, module characterisation measurements for ITk strip tracker modules are typically performed asynchronously to the DC-DC switching and are therefore averaged over the full range of time bins with respect to the converter frequency. In order to investigate the time dependence of the noise injection relative to the DC-DC switching frequency, a dedicated setup to understand the time-resolved performance change in modules was developed. By using a magnetic field probe to measure the field leaking through the shield box and triggering on its rising edge, data taking could be synchronised with the DC-DC switching. This paper illustrates the concept and setup of such time-resolved performance measurements using magnetic triggering and presents results for the observed effects on signal and noise for ATLAS ITk strip modules from both laboratory and beam tests.
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Jun 2021
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I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[15211, 16099]
Open Access
Abstract: Elemental tin in the α‐phase is an intriguing member of the family of topological quantum materials. In thin films, with decreasing thickness, α‐Sn transforms from a 3D topological Dirac semimetal (TDS) to a 2D topological insulator (TI). Getting access to and making use of its topological surface states is challenging and requires interfacing to a magnetically ordered material. Herein, the successful epitaxial growth of α‐Sn thin films on Co, forming the core of a spin‐valve structure, is reported. Time‐ and element‐selective ferromagnetic resonance experiments are conducted to investigate the presence of spin pumping through the spin‐valve structure. A rigorous statistical analysis of the experimental data using a model based on the Landau–Lifshitz–Gilbert–Slonczewski equation is applied. A strong exchange coupling contribution is found, however no unambiguous proof for spin pumping. Nevertheless, the incorporation of α‐Sn into a spin valve remains a promising approach given its simplicity as an elemental TI and its room‐temperature application potential.
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May 2021
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I10-Beamline for Advanced Dichroism
|
Xiaoqian
Zhang
,
Qiangsheng
Lu
,
Wenqing
Liu
,
Wei
Niu
,
Jiabao
Sun
,
Jacob
Cook
,
Mitchel
Vaninger
,
Paul F.
Miceli
,
David J.
Singh
,
Shang-Wei
Lian
,
Tay-Rong
Chang
,
Xiaoqing
He
,
Jun
Du
,
Liang
He
,
Rong
Zhang
,
Guang
Bian
,
Yongbing
Xu
Diamond Proposal Number(s):
[22532]
Open Access
Abstract: While the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe2, a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature (TC) up to 300 K, an atomic magnetic moment of ~0.21 𝜇B
μ
B
/Cr and perpendicular magnetic anisotropy (PMA) constant (Ku) of 4.89 × 105 erg/cm3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer (TC ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices.
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May 2021
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I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[20748]
Abstract: Over the past four years, the magnetism of 2D magnets has been extensively studied by the full arsenal of probing techniques. 2D magnets can be incorporated to form heterostructures with clean and sharp interfaces, which gives rise to exotic phenomena as a result of the interfacial proximity effect. Here we report a detailed study of the spin (ms) and orbital (ml) moments of an epitaxial (CrSb/Fe3GeTe2)6 superlattice. The synchrotron-radiation based x-ray magnetic circular dichroism (XMCD) technique was performed to probe the microscopic magnetic properties of the superlattices in an elemental resolved manner. We unambiguously obtained a bulk-like moment of Fe3GeTe2 i.e., ms = 1.58 ± 0.2 μB/Fe and ml = 0.22 ± 0.02 μB/Fe. Future works to explore the tuning of the spin polarized band structure of 2D ferromagnetic superlattices will be of great interest and can have strong implications for both fundamental physics and the emerging spintronics technology.
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May 2021
|
|
|
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Abstract: We identify room-temperature converse magnetoelectric effects (CMEs) that are non-volatile by using a single-crystal substrate of PMN–PT (001)pc (pc denotes pseudocubic) to impart voltage-driven strain to a polycrystalline film of Ni. An appropriate magnetic-field history enhances the magnetoelectric coefficient to a near-record peak of ∼10−6 s m−1 and permits electrically driven magnetization reversal of substantial net magnetization. In zero magnetic field, electrically driven ferroelectric domain switching produces large changes of in-plane magnetization that are non-volatile. Microscopically, these changes are accompanied by the creation and destruction of magnetic stripe domains, implying the electrical control of perpendicular magnetic anisotropy. Moreover, the stripe direction can be rotated by a magnetic field or an electric field, the latter yielding the first example of electrically driven rotatable magnetic anisotropy. The observed CMEs are associated with repeatable ferroelectric domain switching that yields a memory effect. This memory effect is well known for PMN–PT (110)pc but not PMN–PT (001)pc. Given that close control of the applied field is not required as for PMN–PT (110)pc, this memory effect could lead the way to magnetoelectric memories based on PMN–PT (001)pc membranes that switch at low voltage.
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Apr 2021
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I18-Microfocus Spectroscopy
|
Diamond Proposal Number(s):
[17304]
Open Access
Abstract: Laser processing is a highly versatile technique for the post-synthesis treatment and modification of transition metal dichalcogenides (TMDCs). However, to date, TMDCs synthesis typically relies on large area CVD growth and lithographic post-processing for nanodevice fabrication, thus relying heavily on complex, capital intensive, vacuum-based processing environments and fabrication tools. This inflexibility necessarily restricts the development of facile, fast, very low-cost synthesis protocols. Here we show that direct, spatially selective synthesis of 2D-TMDCs devices that exhibit excellent electrical, Raman and photoluminescence properties can be realized using laser printing under ambient conditions with minimal lithographic or thermal overheads. Our simple, elegant process can be scaled via conventional laser printing approaches including spatial light modulation and digital light engines to enable mass production protocols such as roll-to-roll processing.
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Mar 2021
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I07-Surface & interface diffraction
|
Open Access
Abstract: Organic semiconductors offer a flexibility in band gap tuning through different molecular lengths and have shown to be promising candidates for high‐performance electronic devices. While electronic properties have been extensively studied in many publications, the topic of thin film structure and molecular packing is still quite neglected. In this work, the thin film crystal structure of [6]phenacene (Fulminene) and [7]phenacene deposited on silicon substrates using the OMBD method as well as further studies with potassium deposition on [6]phenacene are investigated. Ex‐situ X‐ray and optical methods are employed to obtain an insight into the crystal structure and optical properties. The orientation of the molecules and the unit cell structure is calculated from the measured reciprocal space maps. Additionally, the influence of a possible interfacial doping mechanism by deposition of potassium on top of [6]phenacene is investigated. Thin films of [6]phenacene show a high crystallinity with a standing‐up configuration and a similar molecular structure and symmetry compared to [4]phenacene. [7]phenacene features two different apparently thickness‐dependent polymorphs (H and L) with a structure similar to [5]phenacene. These results reveal that odd/even parity, that is, even or odd number of benzene rings, directly influences the phenacene thin film structure.
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Mar 2021
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I05-ARPES
|
S.
Liu
,
W.
Xia
,
K.
Huang
,
Ding
Pei
,
T.
Deng
,
A. J.
Liang
,
J.
Jiang
,
H. F.
Yang
,
J.
Zhang
,
H. J.
Zheng
,
Y. J.
Chen
,
L. X.
Yang
,
Y. F.
Guo
,
M. X.
Wang
,
Z. K.
Liu
,
Y. L.
Chen
Diamond Proposal Number(s):
[25135]
Abstract: Recently, layered copper chalcogenides
Cu
2
X
family
(
X
=
S
,
Se
,
Te
)
has attracted tremendous research interests due to their high thermoelectric performance, which is partly due to the superionic behavior of mobile Cu ions, making these compounds “phonon liquids.” Here, we systematically investigate the electronic structure and its temperature evolution of the less studied single crystal
Cu
2
−
x
Te
by the combination of angle resolved photoemission spectroscopy (ARPES) and scanning tunneling microscope/spectroscopy (STM/STS) experiments. While the band structure of the
Cu
2
−
x
Te
shows agreement with the calculations, we clearly observe a
2
×
2
surface reconstruction from both our low temperature ARPES and STM/STS experiments which survives up to room temperature. Interestingly, our low temperature STM experiments further reveal multiple types of reconstruction patterns, which suggests the origin of the surface reconstruction being the distributed deficiency of liquidlike Cu ions. Our findings reveal the electronic structure and impurity level of
Cu
2
Te
, which provides knowledge about its thermoelectric properties from the electronic degree of freedom.
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Mar 2021
|
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I06-Nanoscience
|
C.
Schmitt
,
L.
Baldrati
,
L.
Sanchez-Tejerina
,
F.
Schreiber
,
A.
Ross
,
M.
Filianina
,
S.
Ding
,
F.
Fuhrmann
,
R.
Ramos
,
F.
Maccherozzi
,
D.
Backes
,
M.-A.
Mawass
,
F.
Kronast
,
S.
Valencia
,
E.
Saitoh
,
G.
Finocchio
,
M.
Klaui
Diamond Proposal Number(s):
[22448]
Abstract: Understanding the electrical manipulation of the antiferromagnetic order is a crucial aspect to enable the design of antiferromagnetic devices working at THz frequencies. Focusing on collinear insulating antiferromagnetic
Ni
O
/
Pt
thin films as a materials platform, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the Néel-vector direction changes. We demonstrate electrical switching between different T domains by current pulses, finding that the Néel-vector orientation in these domains is along [
±
5
±
5
19], different compared to the bulk
⟨
112
⟩
directions. The final state of the in-plane component of the Néel vector
n
IP
after switching by current pulses
j
along the
[
1
±
1
0
]
directions is
n
IP
∥
j
. By comparing the observed Néel-vector orientation and the strain in the thin films, assuming that this variation arises solely from magnetoelastic effects, we quantify the order of magnitude of the magnetoelastic coupling coefficient as
b
0
+
2
b
1
=
3
×
10
7
J
/
m
3
. This information is key for the understanding of current-induced switching in antiferromagnets and for the design and use of such devices as active elements in spintronic devices.
|
Mar 2021
|
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