B18-Core EXAFS
I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[24930, 22629]
Open Access
Abstract: The spectroscopic g-factor of epitaxial thin film Yttrium Iron Garnet (YIG) has been studied using a combination of ferromagnetic resonance spectroscopy and x-ray magnetic circular dichroism. The values obtained by the two techniques are found, within experimental error, to be in agreement using Kittel’s original derivation for the g-factor. For an insulating material with an entirely Fe3+ configuration, a spin mixing correction to Kittel’s derivation of the spectroscopic g-factor, as recently shown by Shaw et al. [Phys. Rev. Lett. 127, 207201 (2021)] for metallic systems, is not required and demonstrates that the spin mixing parameter is small in YIG due to negligible spin–orbit coupling.
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Sep 2022
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[24248]
Open Access
Abstract: Power semiconductor device architectures require the inclusion of a diffusion barrier to suppress or at best prevent the interdiffusion between the copper metallization interconnects and the surrounding silicon substructure. The binary pseudo-alloy of titanium–tungsten (TiW), with >70 at. % W, is a well-established copper diffusion barrier but is prone to degradation via the out-diffusion of titanium when exposed to high temperatures (≥400 ∘C). Here, the thermal stability of physical vapor deposited TiW/Cu bilayer thin films in Si/SiO2(50 nm)/TiW(300 nm)/Cu(25 nm) stacks were characterized in response to annealing at 400 ∘C for 0.5 h and 5 h, using a combination of soft and hard x-ray photoelectron spectroscopy and transmission electron microscopy. Results show that annealing promoted the segregation of titanium out of the TiW and interdiffusion into the copper metallization. Titanium was shown to be driven toward the free copper surface, accumulating there and forming a titanium oxide overlayer upon exposure to air. Annealing for longer timescales promoted a greater out-diffusion of titanium and a thicker oxide layer to grow on the copper surface. However, interface measurements suggest that the diffusion is not significant enough to compromise the barrier integrity, and the TiW/Cu interface remains stable even after 5 h of annealing.
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Apr 2022
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I09-Surface and Interface Structural Analysis
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Huw
Shiel
,
Theodore D. C.
Hobson
,
Oliver S.
Hutter
,
Laurie J.
Phillips
,
Matthew J.
Smiles
,
Leanne A. H.
Jones
,
Thomas J.
Featherstone
,
Jack E. N.
Swallow
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Jonathan D.
Major
,
Ken
Durose
,
Tim D.
Veal
Diamond Proposal Number(s):
[23160]
Open Access
Abstract: Antimony selenide (Sb2
2
Se3
3
) possesses great potential in the field of photovoltaics (PV) due to its suitable properties for use as a solar absorber and good prospects for scalability. Previous studies have reported the growth of a native antimony oxide (Sb2
2
O3
3
) layer at the surface of Sb2
2
Se3
3
thin films during deposition and exposure to air, which can affect the contact between Sb2
2
Se3
3
and subsequent layers. In this study, photoemission techniques were utilized on both Sb2
2
Se3
3
bulk crystals and thin films to investigate the band alignment between Sb2
2
Se3
3
and the Sb2
2
O3
3
layer. By subtracting the valence band spectrum of an in situ cleaved Sb2
2
Se3
3
bulk crystal from that of the atmospherically contaminated bulk crystal, a valence band offset (VBO) of −1.72
−
1.72
eV is measured between Sb2
2
Se3
3
and Sb2
2
O3
3
. This result is supported by a −1.90
−
1.90
eV VBO measured between Sb2
2
O3
3
and Sb2
2
Se3
3
thin films via the Kraut method. Both results indicate a straddling alignment that would oppose carrier extraction through the back contact of superstrate PV devices. This work yields greater insight into the band alignment of Sb2
2
O3
3
at the surface of Sb2
2
Se3
3
films, which is crucial for improving the performance of these PV devices.
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Jun 2021
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I05-ARPES
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D. F.
Liu
,
L. Y.
Wei
,
C. C.
Le
,
H. Y.
Wang
,
X.
Zhang
,
N.
Kumar
,
C.
Shekhar
,
N. B. M.
Schröter
,
Y. W.
Li
,
D.
Pei
,
L. X.
Xu
,
P.
Dudin
,
T. K.
Kim
,
C.
Cacho
,
J.
Fujii
,
I.
Vobornik
,
M. X.
Wang
,
L. X.
Yang
,
Z. K.
Liu
,
Y. F.
Guo
,
J. P.
Hu
,
C.
Felser
,
S. S. P.
Parkin
,
Y. L.
Chen
Diamond Proposal Number(s):
[18005]
Open Access
Abstract: Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Here, we carried out systematic studies on the electronic structure of KMgBi single crystals by combining angle-resolve photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. The flatband was clearly observed near the Fermi level. We also revealed a small bandgap of ∼20 meV between the flatband and the conduction band. These results demonstrate the critical states of KMgBi that transition among various types of Dirac fermions can be tuned in one system.
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Jun 2021
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I09-Surface and Interface Structural Analysis
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C.
Kalha
,
S.
Bichelmaier
,
N. K.
Fernando
,
J. V.
Berens
,
P. K.
Thakur
,
T.-L.
Lee
,
J. J.
Gutiérrez Moreno
,
S.
Mohr
,
L. E.
Ratcliff
,
M.
Reisinger
,
J.
Zechner
,
M.
Nelhiebel
,
A.
Regoutz
Diamond Proposal Number(s):
[19885]
Open Access
Abstract: The binary alloy of titanium-tungsten (TiW) is an established diffusion barrier in high-power semiconductor devices, owing to its ability to suppress the diffusion of copper from the metallization scheme into the surrounding silicon substructure. However, little is known about the response of TiW to high-temperature events or its behavior when exposed to air. Here, a combined soft and hard x-ray photoelectron spectroscopy (XPS) characterization approach is used to study the influence of post-deposition annealing and titanium concentration on the oxidation behavior of a 300 nm-thick TiW film. The combination of both XPS techniques allows for the assessment of the chemical state and elemental composition across the surface and bulk of the TiW layer. The findings show that in response to high-temperature annealing, titanium segregates out of the mixed metal system and upwardly migrates, accumulating at the TiW/air interface. Titanium shows remarkably rapid diffusion under relatively short annealing timescales, and the extent of titanium surface enrichment is increased through longer annealing periods or by increasing the bulk titanium concentration. Surface titanium enrichment enhances the extent of oxidation both at the surface and in the bulk of the alloy due to the strong gettering ability of titanium. Quantification of the soft x-ray photoelectron spectra highlights the formation of three tungsten oxidation environments, attributed to WO2, WO3, and a WO3 oxide coordinated with a titanium environment. This combinatorial characterization approach provides valuable insights into the thermal and oxidation stability of TiW alloys from two depth perspectives, aiding the development of future device technologies.
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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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I06-Nanoscience
I10-Beamline for Advanced Dichroism
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Yu
Yan
,
Xianyang
Lu
,
Bo
Liu
,
Xiaoqian
Zhang
,
Xiangyu
Zheng
,
Hao
Meng
,
Wenqing
Liu
,
Junlin
Wang
,
Iain G.
Will
,
Jing
Wu
,
Ping Kwan Johnny
Wong
,
Jianwang
Cai
,
Jun
Du
,
Rong
Zhang
,
Yongbing
Xu
Diamond Proposal Number(s):
[16538]
Abstract: Perpendicular magnetic anisotropy (PMA) in the Ta/CoFeB/MgO system has been studied using x-ray magnetic circular dichroism and vibrating sample magnetometry. The ratios of the orbital to spin magnetic moments of Co atoms in the Ta/CoFeB/MgO structures with PMA have been found to be enhanced by 100%, compared with the Ta/CoFeB/Ta structure without PMA. The orbital moments of Co are as large as
0.30
μ
B
0.30μB
, more than half of their spin moments in the perpendicularly magnetized Ta/CoFeB/MgO structures. The results indicate that the PMA observed in the CoFeB/MgO structures is related to the increased spin–orbital coupling of the Co atoms. This work offers experimental evidence of the correlation between PMA and the element-specific spin and orbital moments in the Ta/CoFeB/MgO systems.
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Feb 2020
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Open Access
Abstract: An X-ray standing wave (XSW) is created in the overlap region of two coherent X-ray waves, e.g. by diffraction or reflection. The XSW intensity maxima move, when traversing the range of total reflection, causing strong modulation of the photo-excitation of a particular element or atomic species, recorded by electron or X-ray fluorescence spectroscopy. The XSW technique is a Fourier technique, particularly useful for identifying and structurally characterizing diluted, active species. In simple cases, a single XSW measurement allows characterization with pm resolution. Otherwise, employing several XSW measurement, an image can be created by Fourier inversion allowing identifying individual sites. The principle, strength and limitations of the XSW technique are reviewed briefly and we focus on three examples for identifying active sites: catalytically active Al in scolecite, magnetically active and counter-active sites of Mn in GaMnAs and sites on the SrTiO3(001) surface active in the splitting of water.
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Oct 2019
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[21642]
Abstract: A study of a transition from conventional multicomponent alloys to high-entropy alloys (HEAs) is important both for understanding the
formation of HEAs and for proper evaluation of their potential with respect to that of conventional alloys. We report the main result of
such a study performed on (TiZrNbNi)1−xCux metallic glasses (MG) over a broad concentration range x ≤ 0.52 encompassing both high entropy-MGs and Cu-based MGs. A comprehensive study of the composition, homogeneity, thermal stability, atomic structure, electronic
structure, and magnetic susceptibility of 11 alloys has been performed. Thermal analysis revealed a rather weak variation of thermal parameters
and glass forming ability with x. The study of the atomic structure showed a linear variation of average interatomic distances and
atomic volumes close to those predicted by Vegard’s law. The coordination numbers and atomic packing fractions were constant throughout the explored concentration range. The electronic density of states (DOS) showed a split-band structure with DOS close to the Fermi level dominated with d-states of Ti, Zr, and Nb. Accordingly, magnetic susceptibility decreased linearly with x and extrapolated to that of Cu.
Thus, the studied alloys show ideal solution behavior similar to that of binary Cu-Ti, Zr, and Hf MGs. The results are compared with those
for (TiZrNbCu)1−xNix MGs and (CrMnFeCo)1−xNix alloys and their impact on understanding the transition from high-entropy-MGs to
conventional MGs with the same composition is briefly discussed.
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Oct 2019
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I11-High Resolution Powder Diffraction
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Open Access
Abstract: Tungsten bronze (TB) structured materials have attracted attention as possible thermoelectrics because of their complex crystal structure. In this work, a new thermoelectric ceramic with a tetragonal tungsten bronze (TB) structure, Ba6Ti2Nb8O30 (BTN), was prepared by the conventional mixed oxide route with some samples processed by Spark Plasma Sintering (SPS). The addition of MnO enabled the fabrication of high density BTN ceramics at a low sintering temperature of 1580 K in air and by SPS. All samples were annealed in a reducing atmosphere after sintering. X-ray diffraction showed that Ba6Ti2Nb8O30 crystallizes with tetragonal symmetry (P4bm space group). High angle annular dark field-electron energy loss spectroscopy analysis confirmed the proposed crystal structure and provided exact elemental distributions in the lattice, showing higher concentrations of Ti in the 2b lattice sites compared to the 8d lattice sites. XPS showed the presence of two spin-orbit double peaks at 207.7 eV in the reduced BTN samples, confirming the presence of Nb4+ ions. By the use of a sintering aid and optimization of the processing parameters, the ceramics achieved a high power factor of 280 μW/m K2 at 873 K. The BTN ceramics showed phonon-glass-type thermal conduction behavior with a low thermal conductivity of 1.7–1.65 W/m K at 300–873 K. A thermoelectric figure of merit (ZT) of 0.14 was achieved at 873 K. This ZT value is comparable with results for many TB thermoelectrics. However, BTN has the advantage of much easier processing.
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Sep 2019
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