I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[36180]
Abstract: Cr2GaC/C and V2PC/C MAX phase composites were synthesized via a free-radical polymerization–pyrolysis route, achieving > 87 wt% crystalline MAX phase content. SEM/EDS confirms the expected 2:1 atomic ratios of Cr:Ga and V:P, while BET analysis reveals structures with specific surface areas of 344 and 282 m2 g−1 for the Cr2GaC/C and V2PC/C composites, respectively, which are attributed to the porous carbonaceous network. HAXPES verifies core-level signatures consistent with the targeted MAX phases. This approach demonstrates the versatility of sol–gel-derived free-radical polymer networks as reactive precursors for MAX phase formation. The method further provides a foundation for advanced processing strategies, including vat photopolymerization-based additive manufacturing of high-surface-area and complex MAX phase architectures.
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Sep 2026
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[36180]
Abstract: A correlation between depth-resolved defect chemistry and operando electrochemical response is established for compositionally graded gadolinia-doped ceria (GDC)/yttria-stabilized zirconia (YSZ) thin film electrodes. Integration of operando high-temperature scanning surface potential microscopy (HT-SSPM) with depth-resolved hard X-ray photoelectron spectroscopy (HAXPES) enables the relationship between bias-induced contact potential difference (CPD) evolution and spatially resolved Ce3+ distributions across the active film depth. While homogeneous GDC confines oxygen vacancies predominantly near the surface, compositionally graded architectures sustain a subsurface vacancy population extending toward the electrolyte interface. The fully graded structure exhibits steeper and more symmetric CPD gradients under both anodic and cathodic bias, consistent with balanced oxygen reduction and evolution kinetics. Depth-dependent HAXPES indicates that this electrochemical response correlates with enrichment of subsurface Ce3+ states rather than surface composition alone. These findings identify subsurface defect continuity as a key materials parameter influencing ionic transport and interfacial electrochemical behaviour in solid oxide electrodes.
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Aug 2026
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I09-Surface and Interface Structural Analysis
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Leyi
Loh
,
Han
Yan
,
Lixin
Liu
,
Yuan
Chen
,
Esther Lilian
Gray
,
Kamal Kumar
Paul
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Takashi
Taniguchi
,
Kenji
Watanabe
,
Mauro
Brotons-Gisbert
,
Yan
Wang
,
Manish
Chhowalla
Diamond Proposal Number(s):
[38012, 39914, 38086]
Open Access
Abstract: Unintentional doping from dielectrics can impact the electronic properties of two-dimensional transition metal dichalcogenide (2D TMD) semiconductors. Our recent work shows that high-dielectric-constant (k) ZrO2 is an electrostatically inert dielectric for 2D MoS2, supported by X-ray spectroscopy (XPS) and electrical measurements. Here, we expand this work through gate-controlled photoluminescence (PL) of monolayer MoS2 placed on different substrates. MoS2 on ZrO2 exhibits a low carrier concentration, indicated by a small trion-to-exciton ratio (X–/X0) of 0.5, similar to those on high-quality hBN. At a high electrostatic doping of ∼1013 cm–2, MoS2 on high-k ZrO2 reveals a slight exponential dependence of X–/X0 versus carrier concentration, while MoS2 on SiO2 shows strong exponential characteristics even at low gating (1012 cm–2) due to substantial electron doping from substrate-induced disorder tail states. Our findings provide insights into the doping mechanisms in industry-compatible amorphous dielectrics and evaluate their potential for scalable optoelectronic devices.
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Aug 2026
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I09-Surface and Interface Structural Analysis
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Uday
Kushwah
,
Shiyang
Lu
,
Prajna
Bhatt
,
Aysha A.
Riaz
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Marco
Kirm
,
Vitali
Nagirnyi
,
Tanel
Käämbre
,
Johannes
Lischner
,
Anna
Regoutz
,
Juhan Matthias
Kahk
Diamond Proposal Number(s):
[36189]
Open Access
Abstract: Ultrafast scintillators based on ternary hexafluorides are promising for next-generation radiation detectors, which can be used in time-of-flight positron emission tomography. To gain a detailed understanding of the scintillation mechanism in these materials, accurate knowledge of the electronic band structure is required. In this study, photoelectron spectroscopy, density-functional theory, and G0W0 calculations were used to investigate the electronic structure of K2SiF6. The G0W0 calculations predict a wide band gap of 12.4 eV reflecting the strongly ionic character of the bonding. In contrast to predictions from semi-local or hybrid density-functional theory calculations, the large band gap predicted by G0W0 suggests that Auger-Meitner decay of K 3p holes is energetically not allowed and that scintillation via cross-luminescence is possible in this material. However, the poor light-yield observed experimentally indicates that the exclusion of Auger-Meitner decay is not sufficient for good scintillation performance, and cross-luminescence competes with other decay channels.
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Jul 2026
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I09-Surface and Interface Structural Analysis
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Galo J.
Paez Fajardo
,
Daniela E.
Dogaru
,
Hrishit
Banerjee
,
Muhammad
Ans
,
Matthew J. W.
Ogley
,
Veronika
Majherova
,
Gerard
Bree
,
Innes
Mcclelland
,
Shohei
Hayashida
,
Pascal
Puphal
,
Masahiko
Isobe
,
Bernhard
Keimer
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Dave C.
Grinter
,
Pilar
Ferrer
,
Serena A.
Cussen
,
Matthias
Hepting
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[33459, 35075, 36917, 30201]
Open Access
Abstract: Describing lithium-based battery positive electrodes based on different transition metal or oxygen-redox regimes can cause confusion in understanding metal–ligand hybridization, oxygen dimerization and degradation processes. Therefore, it is urgent to investigate the electronic structure of these materials and identify the role each cation and anion has in charge compensation at the subnanoscale. Here, using X-ray resonance photoemission spectroscopy, single-impurity Anderson models, spectral simulations and theoretical calculations, we examine redox mechanisms in positive electrodes during lithium-based battery operation. This approach reconciles the redox description of two positive electrode active materials—LiMn0.6Fe0.4PO4 and LiNiO2—in terms of varying degrees of charge transfer using the Zaanen–Sawatzky–Allen framework. In LiMn0.6Fe0.4PO4, the lack of strong hybridization indicates that the capacity results from the depopulation of metal 3d states, that is, conventional metal redox. However, in cells with LiNiO2-based positive electrodes, negative charge transfer dominates, and redox occurs through the formation and elimination of ligand-hole states. These results clarify the role of oxygen in Ni-rich systems and provide a framework to explain how the charge/discharge capacities are linked to oxygen-dominated states in highly covalent systems, without the need to consider oxygen dimerization.
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Jun 2026
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Abstract: This work reports a systematic investigation of the defect states and carrier compensation mechanisms in Si- and Sn-doped β-Ga2O3 using hybrid density functional theory calculations combined with high-resolution photoemission spectroscopy. The calculations show that Si introduces a shallower donor level ε(0/+1) ≈ 0.17 eV than does Sn (≈0.23 eV). The deeper donor level in Sn results from the stabilization of neutral SnGa via Sn 4d–O 2p hybridization. At higher doping levels, gallium vacancies (VGa) act as the dominant acceptor-type defects. Notably, Sn exhibits a strong tendency to form split-vacancy complexes (Snic-2VGa), with formation energies as low as −1.52 eV under O-rich conditions, indicating their spontaneous formation and self-compensation, whereas the analogous Si-related complexes are significantly less favorable. Electronic structure and orbital analysis reveal that Sn generates localized 5s-derived in-gap states, whereas Si preserves delocalized 3p–O 2p bonding, consistent with the presence of in-gap states in Sn-doped but not Si-doped films. These findings identify dopant–vacancy coupling as the key mechanism governing compensation and provide a mechanistic basis for dopant selection and defect engineering in high-performance β-Ga2O3 devices.
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Apr 2026
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I09-Surface and Interface Structural Analysis
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Hemian
Yi
,
Yunzhe
Liu
,
Chengye
Dong
,
Yiheng
Yang
,
Zi-Jie
Yan
,
Zihao
Wang
,
Lingjie
Zhou
,
Dingsong
Wu
,
Houke
Chen
,
Stephen
Paolini
,
Bing
Xia
,
Bomin
Zhang
,
Xiaoda
Liu
,
Hongtao
Rong
,
Annie G.
Wang
,
Saswata
Mandal
,
Kaijie
Yang
,
Benjamin N.
Katz
,
Lunhui
Hu
,
Jieyi
Liu
,
Tien-Lin
Lee
,
Vincent H.
Crespi
,
Yuanxi
Wang
,
Yulin
Chen
,
Joshua A.
Robinson
,
Chao-Xing
Liu
,
Cui-Zu
Chang
Diamond Proposal Number(s):
[37930]
Abstract: In low-dimensional superconductors, the interplay between quantum confinement and interfacial hybridization effects can reshape Cooper-pair wavefunctions and give rise to unconventional superconducting states. Here we use plasma-free confinement epitaxy assisted by a carbon buffer layer to synthesize a gallium trilayer sandwiched between graphene and a 6H-SiC(0001) substrate. Within this confined gallium layer, we demonstrate interfacial Ising-type superconductivity driven by atomic orbital hybridization. Electrical transport measurements reveal that the in-plane upper critical magnetic field reaches ~21.98 T at T = 400 mK, approximately 3.38 times the Pauli paramagnetic limit. Angle-resolved photoemission spectroscopy measurements, combined with theoretical calculations, confirm the presence of split Fermi surfaces with Ising-type spin textures at the K and K′ valleys of the confined gallium layer, originating from strong hybridization with the SiC substrate. This work establishes a strategy for realizing unconventional pairing wavefunctions through the synergistic combination of quantum confinement and interfacial hybridization effects.
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Apr 2026
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I09-Surface and Interface Structural Analysis
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Muhammad
Ans
,
Eleni
Fiamegkou
,
Ashok S.
Menon
,
Gaurav C.
Pandey
,
Gaolo J.
Paez Fajardo
,
Harry
Gillions
,
Paolo
Melgari
,
Calum
Clenahan
,
Satish
Bolloju
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Serena A.
Cussen
,
Beth I. J.
Johnston
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[38340]
Open Access
Abstract: Lithium nickel oxide (LNO) cathodes offer high capacity for high-energy-density applications but suffer rapid degradation above 4.2 V due to surface and bulk instabilities. Here, we apply an ultrathin aluminum oxide coating using powder atomic layer deposition to improve surface stability. Pouch cell testing shows that coated LNO delivers improved cycling behavior, retaining 91.2% capacity after 100 cycles at C/3. Operando X-ray diffraction reveals that after aging, coated LNO undergoes a less kinetically hindered delithiation, indicating that the surface coating further provides a surface-to-bulk stabilization effect. Postmortem surface sensitive spectroscopy confirms that the aluminum oxide layer (1) scavenges hydrofluoric acid and (2) suppresses surface reconstruction, reducing impedance growth and improving the surface integrity. Overall, the results demonstrate that ultrathin aluminum oxide coatings effectively mitigate interfacial degradation and enhance bulk electrochemical kinetics, providing an effective and scalable approach toward improving the long-term performance of ultra-Ni-rich cathodes.
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Mar 2026
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I09-Surface and Interface Structural Analysis
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Lixin
Liu
,
Han
Yan
,
Leyi
Loh
,
Kamal Kumar
Paul
,
Soumya
Sarkar
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Takashi
Taniguchi
,
Kenji
Watanabe
,
Manish
Chhowalla
,
Yan
Wang
Diamond Proposal Number(s):
[38012, 39914]
Open Access
Abstract: Excellent gate electrostatics in field effect transistors (FETs) based on 2D transition metal dichalcogenide (2D TMD) channels can dramatically decrease static power dissipation. Energy-efficient FETs operate in enhancement mode with a small and positive threshold voltage (Vth) for n-type devices. However, most state-of-the-art FETs based on monolayer MoS2 channel operate in depletion mode with negative Vth due to doping from the underlying dielectric substrate. In this work, we identify key properties of the semiconductor/dielectric interface (MoS2 on industrially relevant high dielectric constant (k) HfO2, ZrO2 and hBN for reference) responsible for realizing enhancement-mode operation of 2D MoS2 channel FETs. We find that hBN and ZrO2 dielectric substrates provide low defect interfaces with MoS2 that enables effective modulation of the Vth using gate metals of different work functions (WFs). We use photoluminescence (PL) and synchrotron X-ray photoelectron spectroscopy (XPS) measurements to investigate doping levels in monolayer MoS2 on different dielectrics with different WF gate metals. We complement the FET and spectroscopic measurements with capacitance-voltage analysis on dielectrics with varying thicknesses, which confirms that Vth modulation in ZrO2 devices is correlated with WF of the gate metals – in contrast with HfO2 devices that exhibit signatures of Vth pinning induced by oxide/interface defect states. Finally, we demonstrate FETs using a 2D MoS2 channel and a 6 nm of ZrO2 dielectric, achieving a subthreshold swing of 87 mV dec−1 and a threshold voltage of 0.1 V. Our results offer insights into the role of dielectric/semiconductor interface in 2D MoS2 based FETs for realizing enhancement mode FETs and highlight the potential of ZrO2 as a scalable high-k dielectric.
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Mar 2026
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I09-Surface and Interface Structural Analysis
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O.
Tkach
,
S.
Fragkos
,
Deepnarayan
Biswas
,
J.
Liu
,
O.
Fedchenko
,
Y.
Lytvynenko
,
S.
Babenkov
,
D.
Zimmer
,
Q. L.
Nguyen
,
S.
Chernov
,
D.
Kutnyakhov
,
M.
Scholz
,
N.
Wind
,
A.
Gloskovskii
,
F.
Pressacco
,
J.
Dilling
,
L.
Bruckmeier
,
M.
Heber
,
L.
Wenthaus
,
G.
Brenner
,
D.
Puntel
,
P. E.
Majchrzak
,
D.
Liu
,
F.
Scholz
,
J. A.
Sobota
,
J. D.
Koralek
,
G.
Dakovski
,
A.
Mehta
,
N.
Sirica
,
M.
Hoesch
,
C.
Schlueter
,
L. V.
Odnodvorets
,
Y.
Mairesse
,
T.-L.
Lee
,
A.
Kunin
,
K.
Rossnagel
,
Z. X.
Shen
,
H. J.
Elmers
,
S.
Beaulieu
,
G.
Schönhense
Abstract: A new type of objective lens has recently been proposed for use in x-ray photoemission electron microscopes (XPEEMs) and momentum microscopes. Adding a ring electrode concentric with the extractor allows the field in the gap between the sample and the extractor to be shaped. Forming a lens field in this gap reduces the field strength at the sample by up to an order of magnitude. This mitigates the risk of field emission, particularly for cleaved samples with sharp edges. A retarding field can redirect all slow electrons, thus eliminating the primary contribution to the space-charge interaction. Here, we present the first experimental investigation of the new lens, examining its performance at photon energies ranging from the extreme ultraviolet (XUV) produced by a high-harmonic generation-based source to soft and hard x rays at two synchrotron facilities. The gap lens in a region without electrodes enables large working distances up to 23 mm. Reduced aberrations allow for larger fields of view in both k-space and real-space imaging, with resolutions comparable to those of conventional cathode lenses. However, field strengths are an order of magnitude smaller. The zero-field mode enables the study of 3D structured objects and is, therefore, beneficial for small cleaved samples as well as for operando devices involving top electrodes. The repeller mode reduces space-charge effects but results in a smaller k-field diameter. This reduction ranges from 10% at hard x-ray energies to 50% in the XUV range. The usable energy interval is also reduced by a factor of two. In time-of-flight XPEEM mode, the raw data show a resolution of 250 nm, which can be improved to better than 100 nm through data processing.
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Mar 2026
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