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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Ziwei J.
Yang
,
Zhuangnan
Li
,
Leyi
Loh
,
James
Moloney
,
John
Walmsley
,
Jiahang
Li
,
Yuan
Chen
,
Lixin
Liu
,
Han
Zang
,
Han
Yan
,
Soumya
Sarkar
,
Jason
Day
,
Yan
Wang
,
Manish
Chhowalla
Diamond Proposal Number(s):
[36790, 39914]
Open Access
Abstract: Metallic, two-dimensional molybdenum disulfide (MoS2) nanosheets show promise for energy storage and catalysis applications. However, current chemical exfoliation methods require more than 48 h to produce milligrams of material, and result in an impure mixture of metallic (1T/1T′, approximately 50%–70%) and semiconducting (2H) phases. Here we demonstrate large-scale and rapid (>600 g h−1) production of nearly pure-phase metallic two-dimensional MoS2 nanosheets using microwave irradiation. Atomic-resolution imaging and X-ray photoelectron spectroscopy show nearly 100% metallic phase in the basal plane. This high purity leads to a large exchange current density (0.175 ± 0.030 mA cm−2) and low Tafel slopes (39–47 mV dec−1) for hydrogen evolution reaction. In supercapacitors and lithium–sulfur pouch-cell batteries, the resulting nanosheets enable a high volumetric capacitance of 753.0 ± 3.6 F cm−3 and a specific capacity of 1,245 ± 16 mAh g−1 (electrolyte-to-sulfur ratio, 2 µl mg−1), respectively. Our method provides a practical pathway for producing high-quality metallic two-dimensional materials for high-performance energy devices.
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Jan 2026
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I09-Surface and Interface Structural Analysis
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Ye
Wang
,
Manish
Chhowalla
,
Yiru
Zhu
,
Tieyuan
Bian
,
Ziwei J.
Yang
,
Yuanyua
Zhao
,
Han
Yan
,
Yang
Li
,
Yan
Wang
,
Feng
Ding
,
Jun
Yin
Diamond Proposal Number(s):
[35092, 30105, 33391, 32963, 38086]
Open Access
Abstract: Engineering chiral optical and electronic properties of materials is interesting for applications in sensing and quantum information. State-of-the-art chiral optoelectronic devices are mostly based on three-dimensional (3D) and quasi-two-dimensional (2D) materials. Here we demonstrate chiral 2D MoS2 with sub-nanometer thickness via chirality transfer from l-/d-penicillamine (l-/d-PEN). We report a giant molar ellipticity of 108 deg·cm2/dmol in monolayer solid-state films, up to 3 orders of magnitude higher than 3D chiral materials. Phototransistors with chiral 2D MoS2 channels exhibit gate-tunable circularly polarized light detection with responsivity of >102 A/W and anisotropy g-factor of 1.98, close to the theoretical maximum of 2.0. The reduced dimensionality magnifies the chirality transfer efficiency, allowing realization of ultrasensitive detectors for circularly polarized photons.
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Oct 2025
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I09-Surface and Interface Structural Analysis
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Han
Yan
,
Yan
Wang
,
Yang
Li
,
Dibya
Phuyal
,
Lixin
Liu
,
Hailing
Guo
,
Yuzheng
Guo
,
Tien-Lin
Lee
,
Minhyuk
Kim
,
Hu Young
Jeong
,
Manish
Chhowalla
Diamond Proposal Number(s):
[30105, 33391, 32963, 38086]
Open Access
Abstract: Two-dimensional transition metal dichalcogenide semiconductors possess ideal attributes for meeting industry scaling targets for transistor channel technology. However, the development of scaled field-effect transistors (FETs) requires industry-compatible gate dielectrics with low equivalent oxide thicknesses. Here we show that zirconium oxide (ZrO2)—an industry-compatible high-dielectric-constant (k) oxide—can form a clean interface with two-dimensional molybdenum disulfide (MoS2). Photoelectron spectroscopy analysis shows that although silicon dioxide and hafnium oxide substrates introduce the doping of MoS2, ZrO2 exhibits no measurable interactions with MoS2. Back-gated monolayer MoS2 FETs using ZrO2 as a dielectric exhibit stable and positive threshold voltages of 0.36 V, subthreshold swings of 75 mV dec−1 and ON currents of more than 400 µA. We also use ZrO2 dielectrics to fabricate p-type tungsten diselenide FETs with ON-state currents of more than 200 µA µm−1. Atomic-resolution imaging of ZrO2 deposited on top of MoS2 reveals a defect-free interface, which leads to top-gated FETs with an equivalent oxide thickness of 0.86 nm and subthreshold swing values of 80 mV dec−1. The clean interface between ZrO2 and monolayer MoS2 allows the effective modulation of threshold voltage in top-gated FETs via gate metal work-function engineering.
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Oct 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[30105, 33391, 38086]
Open Access
Abstract: The clean and reliable transfer of two-dimensional (2D) materials is critical for preserving their intrinsic properties and enabling high-performance device applications. This study presents a method utilizing UV-ozone treated polydimethylsiloxane (UV-PDMS) as a transfer medium to achieve residue-free 2D materials. The UV-PDMS transfer method increases surface rigidity, reduces surface polymeric residues, and ensures intimate contact between 2D materials and target substrates. This is translated into cleaner samples as confirmed by atomic force microscopy (AFM), photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Field-effect transistors (FETs) based on monolayer MoS2 fabricated with UV-PDMS transferred method exhibit lower subthreshold swing, reduced hysteresis, and higher carrier mobility compared to devices fabricated with PDMS transfer. Additionally, vertical solar cells based on multilayer WSe2 prepared with UV-PDMS method demonstrate enhanced fill factor and power conversion efficiency.
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Sep 2025
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I06-Nanoscience (XPEEM)
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Massimo
Ghidini
,
Vladimir
Farenkov
,
Yang
Li
,
Peter J.
Newton
,
Raffaele
Pellicelli
,
Samer
Kurdi
,
Nadia A.
Stelmashenko
,
Francesco
Maccherozzi
,
Crispin H. W.
Barnes
,
Andrew F.
May
,
Manish
Chhowalla
,
Sarnjeet S.
Dhesi
,
Neil D.
Mathur
Diamond Proposal Number(s):
[31793]
Open Access
Abstract: Few-layer flakes of ferromagnetic Fe5–xGeTe2 with x = 0.3 (F5GT) possess a c-axis magnetocrystalline anisotropy that is large enough below ∼200 K to outcompete the easy-plane shape anisotropy, yielding distinctive magnetic microstructures with out-of-plane (OOP) magnetizations. Using photoemission electron microscopy (PEEM) with magnetic contrast from X-ray magnetic circular dichroism (XMCD) to study a thermally demagnetized h-BN-protected nanoflake of F5GT at 110 K, we observe a micron-scale coexistence between domains with OOP magnetizations (∼70% areal fraction) and hitherto unknown domains in which in-plane (IP) magnetization components dominate (∼30% areal fraction). The regions with dominant IP magnetization components do not correlate with small variations of flake thickness (6–10 nm) and instead arise from local changes of magnetocrystalline anisotropy due to a hitherto unidentified chemical inhomogeneity that we suggest to be a higher concentration of Fe vacancies. Our observation of micron-scale inhomogeneity would likely be missed if imaging a single flake orientation and should affect the viability and performance of van der Waals (vdW) spintronic devices with F5GT electrodes.
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Jul 2025
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I06-Nanoscience (XPEEM)
I09-Surface and Interface Structural Analysis
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Yiru
Zhu
,
Zhepeng
Zhang
,
Ye
Wang
,
Soumya
Sarkar
,
Yang
Li
,
Han
Yan
,
Larissa
Ishibe-Veiga
,
Anita
Bagri
,
Ziwei J.
Yang
,
Hugh
Ramsden
,
Goki
Eda
,
Robert L. Z.
Hoye
,
Yan
Wang
,
Manish
Chhowalla
Diamond Proposal Number(s):
[36685, 33391]
Open Access
Abstract: Chalcogen vacancy defects in monolayer transition metal dichalcogenides form in-gap states that can trap excitons, leading to defect-mediated photoluminescence (PL) emission. Here, we show that room-temperature (RT, 300 K) PL from sulfur vacancies in defective monolayer MoS2 is sensitive to doping from dielectric substrates such as SiO2 and HfO2. The defect-mediated PL is observed for monolayer MoS2 on untreated HfO2 but is quenched on untreated SiO2, which is attributed to electron doping of MoS2 on SiO2. Electron doping of MoS2 is confirmed by Raman and synchrotron X-ray photoelectron spectroscopy. Annealing of the SiO2 substrate modifies its surface states, which is reflected in the recovery of the defect-mediated PL emission. The role of substrate-induced doping on sulfur vacancy-mediated PL is further supported by gate-dependent PL measurements. Our results suggest that excess electrons fill the defect energy states from sulfur vacancies in MoS2, reducing the probability of photoexcited carrier occupation and subsequent defect-mediated emission.
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Apr 2025
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I06-Nanoscience (XPEEM)
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Yang
Li
,
Yan
Wang
,
Andrew F.
May
,
Mauro
Fianchini
,
Chiara
Biz
,
Saeyoung
Oh
,
Yiru
Zhu
,
Hu Young
Jeong
,
Jieun
Yang
,
Jose
Gracia
,
Manish
Chhowalla
Diamond Proposal Number(s):
[33245]
Open Access
Abstract: Spin selective catalysis is an emerging approach for improving the thermodynamics and kinetics of reactions. The role of electron spins has been scarcely studied in catalytic reactions. One exception is the oxygen evolution reaction (OER) where strongly correlated metals and oxides are used as catalysts. In OER, spin alignment facilitates the transition of singlet state of the reactant to the triplet state of O2. However, the influence of strong correlations on spin exchange mechanism and spin selective thermodynamics of most catalytic reactions remain unclear. Here we decouple the strongly correlated catalyst from the electrolyte to study spin exchange in two-dimensional (2D) magnetic iron germanium telluride (FGT) heterostructure. We demonstrate that transmission of spin and electrochemical information between the catalyst and the reactant can occur through quantum exchange interaction despite the catalyst of FGT being completely encapsulated by graphene or hexagonal boron nitride (hBN). The strong correlations in FGT that lead to enhanced spin exchange in OER are observed in graphene or hBN layers with thicknesses of up to 6 nm. We demonstrate that spin alignment in FGT leads to a lowering of thermodynamic barrier for adsorption of hydroxide ion and electron transfer to the catalyst. This results in up to fivefold enhancement in OER performance and improved kinetics. Our results provide clear evidence that transmission of both quantum mechanical and electrochemical information through quantum spin exchange interaction in FGT leads to an enhancement in catalytic performance.
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Dec 2024
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I09-Surface and Interface Structural Analysis
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Yiru
Zhu
,
Juhwan
Lim
,
Zhepeng
Zhang
,
Yan
Wang
,
Soumya
Sarkar
,
Hugh
Ramsden
,
Yang
Li
,
Han
Yan
,
Dibya
Phuyal
,
Nicolas
Gauriot
,
Akshay
Rao
,
Robert L. Z.
Hoye
,
Goki
Eda
,
Manish
Chhowalla
Diamond Proposal Number(s):
[30105]
Open Access
Abstract: Atomic defects in monolayer transition metal dichalcogenides (TMDs) such as chalcogen vacancies significantly affect their properties. In this work, we provide a reproducible and facile strategy to rationally induce chalcogen vacancies in monolayer MoS2 by annealing at 600 °C in an argon/hydrogen (95%/5%) atmosphere. Synchrotron X-ray photoelectron spectroscopy shows that a Mo 3d5/2 core peak at 230.1 eV emerges in the annealed MoS2 associated with nonstoichiometric MoSx (0 < x < 2), and Raman spectroscopy shows an enhancement of the ∼380 cm–1 peak that is attributed to sulfur vacancies. At sulfur vacancy densities of ∼1.8 × 1014 cm–2, we observe a defect peak at ∼1.72 eV (referred to as LXD) at room temperature in the photoluminescence (PL) spectrum. The LXD peak is attributed to excitons trapped at defect-induced in-gap states and is typically observed only at low temperatures (≤77 K). Time-resolved PL measurements reveal that the lifetime of defect-mediated LXD emission is longer than that of band edge excitons, both at room and low temperatures (∼2.44 ns at 8 K). The LXD peak can be suppressed by annealing the defective MoS2 in sulfur vapor, which indicates that it is possible to passivate the vacancies. Our results provide insights into how excitonic and defect-mediated PL emissions in MoS2 are influenced by sulfur vacancies at room and low temperatures.
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Jul 2023
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Nuria
Tapia-Ruiz
,
A. Robert
Armstrong
,
Hande
Alptekin
,
Marco A.
Amores
,
Heather
Au
,
Jerry
Barker
,
Rebecca
Boston
,
William R
Brant
,
Jake M.
Brittain
,
Yue
Chen
,
Manish
Chhowalla
,
Yong-Seok
Choi
,
Sara I. R.
Costa
,
Maria
Crespo Ribadeneyra
,
Serena A
Cussen
,
Edmund J.
Cussen
,
William I. F.
David
,
Aamod V
Desai
,
Stewart A. M.
Dickson
,
Emmanuel I.
Eweka
,
Juan D.
Forero-Saboya
,
Clare
Grey
,
John M.
Griffin
,
Peter
Gross
,
Xiao
Hua
,
John T. S.
Irvine
,
Patrik
Johansson
,
Martin O.
Jones
,
Martin
Karlsmo
,
Emma
Kendrick
,
Eunjeong
Kim
,
Oleg V
Kolosov
,
Zhuangnan
Li
,
Stijn F L
Mertens
,
Ronnie
Mogensen
,
Laure
Monconduit
,
Russell E
Morris
,
Andrew J.
Naylor
,
Shahin
Nikman
,
Christopher A
O’keefe
,
Darren M. C.
Ould
,
Robert G.
Palgrave
,
Philippe
Poizot
,
Alexandre
Ponrouch
,
Stéven
Renault
,
Emily M.
Reynolds
,
Ashish
Rudola
,
Ruth
Sayers
,
David O.
Scanlon
,
S.
Sen
,
Valerie R.
Seymour
,
Begoña
Silván
,
Moulay Tahar
Sougrati
,
Lorenzo
Stievano
,
Grant S.
Stone
,
Chris I.
Thomas
,
Maria-Magdalena
Titirici
,
Jincheng
Tong
,
Thomas J.
Wood
,
Dominic S
Wright
,
Reza
Younesi
Open Access
Abstract: Increasing concerns regarding the sustainability of lithium sources, due to their limited availability and consequent expected price increase, have raised awareness of the importance of developing alternative energy-storage candidates that can sustain the ever-growing energy demand. Furthermore, limitations on the availability of the transition metals used in the manufacturing of cathode materials, together with questionable mining practices, are driving development towards more sustainable elements. Given the uniformly high abundance and cost-effectiveness of sodium, as well as its very suitable redox potential (close to that of lithium), sodium-ion battery technology offers tremendous potential to be a counterpart to lithium-ion batteries (LIBs) in different application scenarios, such as stationary energy storage and low-cost vehicles. This potential is reflected by the major investments that are being made by industry in a wide variety of markets and in diverse material combinations. Despite the associated advantages of being a drop-in replacement for LIBs, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviours, for example, different coordination preferences in compounds, desolvation energies, or solubility of the solid–electrolyte interphase inorganic salt components. This demands a more detailed study of the underlying physical and chemical processes occurring in sodium-ion batteries and allows great scope for groundbreaking advances in the field, from lab-scale to scale-up. This roadmap provides an extensive review by experts in academia and industry of the current state of the art in 2021 and the different research directions and strategies currently underway to improve the performance of sodium-ion batteries. The aim is to provide an opinion with respect to the current challenges and opportunities, from the fundamental properties to the practical applications of this technology.
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Jul 2021
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