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Sovizi S, Angizi S, Ahmad Alem SA, Goodarzi R, Taji Boyuk MRR, Ghanbari H, Szoszkiewicz R, Simchi A, Kruse P. Plasma Processing and Treatment of 2D Transition Metal Dichalcogenides: Tuning Properties and Defect Engineering. Chem Rev 2023; 123:13869-13951. [PMID: 38048483 PMCID: PMC10756211 DOI: 10.1021/acs.chemrev.3c00147] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Revised: 08/31/2023] [Accepted: 11/09/2023] [Indexed: 12/06/2023]
Abstract
Two-dimensional transition metal dichalcogenides (TMDs) offer fascinating opportunities for fundamental nanoscale science and various technological applications. They are a promising platform for next generation optoelectronics and energy harvesting devices due to their exceptional characteristics at the nanoscale, such as tunable bandgap and strong light-matter interactions. The performance of TMD-based devices is mainly governed by the structure, composition, size, defects, and the state of their interfaces. Many properties of TMDs are influenced by the method of synthesis so numerous studies have focused on processing high-quality TMDs with controlled physicochemical properties. Plasma-based methods are cost-effective, well controllable, and scalable techniques that have recently attracted researchers' interest in the synthesis and modification of 2D TMDs. TMDs' reactivity toward plasma offers numerous opportunities to modify the surface of TMDs, including functionalization, defect engineering, doping, oxidation, phase engineering, etching, healing, morphological changes, and altering the surface energy. Here we comprehensively review all roles of plasma in the realm of TMDs. The fundamental science behind plasma processing and modification of TMDs and their applications in different fields are presented and discussed. Future perspectives and challenges are highlighted to demonstrate the prominence of TMDs and the importance of surface engineering in next-generation optoelectronic applications.
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Affiliation(s)
- Saeed Sovizi
- Faculty of
Chemistry, Biological and Chemical Research Centre, University of Warsaw, Żwirki i Wigury 101, 02-089, Warsaw, Poland
| | - Shayan Angizi
- Department
of Chemistry and Chemical Biology, McMaster
University, Hamilton, Ontario L8S 4M1, Canada
| | - Sayed Ali Ahmad Alem
- Chair in
Chemistry of Polymeric Materials, Montanuniversität
Leoben, Leoben 8700, Austria
| | - Reyhaneh Goodarzi
- School of
Metallurgy and Materials Engineering, Iran
University of Science and Technology (IUST), Narmak, 16846-13114, Tehran, Iran
| | | | - Hajar Ghanbari
- School of
Metallurgy and Materials Engineering, Iran
University of Science and Technology (IUST), Narmak, 16846-13114, Tehran, Iran
| | - Robert Szoszkiewicz
- Faculty of
Chemistry, Biological and Chemical Research Centre, University of Warsaw, Żwirki i Wigury 101, 02-089, Warsaw, Poland
| | - Abdolreza Simchi
- Department
of Materials Science and Engineering and Institute for Nanoscience
and Nanotechnology, Sharif University of
Technology, 14588-89694 Tehran, Iran
- Center for
Nanoscience and Nanotechnology, Institute for Convergence Science
& Technology, Sharif University of Technology, 14588-89694 Tehran, Iran
| | - Peter Kruse
- Department
of Chemistry and Chemical Biology, McMaster
University, Hamilton, Ontario L8S 4M1, Canada
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2
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Jiang Y, Liu Z, Zhou H, Sharma A, Deng J, Ke C. Physical adsorption and oxidation of ultra-thin MoS 2crystals: insights into surface engineering for 2D electronics and beyond. NANOTECHNOLOGY 2023; 34:405701. [PMID: 37462320 DOI: 10.1088/1361-6528/ace1f7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Accepted: 06/26/2023] [Indexed: 01/25/2024]
Abstract
The oxidation mechanism of atomically thin molybdenum disulfide (MoS2) plays a critical role in its nanoelectronics, optoelectronics, and catalytic applications, where devices often operate in an elevated thermal environment. In this study, we systematically investigate the oxidation of mono- and few-layer MoS2flakes in the air at temperatures ranging from 23 °C to 525 °C and relative humidities of 10%-60% by using atomic force microscopy (AFM), Raman spectroscopy and x-ray photoelectron spectroscopy. Our study reveals the formation of a uniform nanometer-thick physical adsorption layer on the surface of MoS2, which is attributed to the adsorption of ambient moisture. This physical adsorption layer acts as a thermal shield of the underlying MoS2lattice to enhance its thermal stability and can be effectively removed by an AFM tip scanning in contact mode or annealing at 400 °C. Our study shows that high-temperature thermal annealing and AFM tip-based cleaning result in chemical adsorption on sulfur vacancies in MoS2, leading to p-type doping. Our study highlights the importance of humidity control in ensuring reliable and optimal performance for MoS2-based electronic and electrochemical devices and provides crucial insights into the surface engineering of MoS2, which are relevant to the study of other two-dimensional transition metal dichalcogenide materials and their applications.
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Affiliation(s)
- Yingchun Jiang
- Department of Mechanical Engineering, State University of New York at Binghamton, Binghamton, NY 13902, United States of America
| | - Zihan Liu
- Department of Mechanical Engineering, State University of New York at Binghamton, Binghamton, NY 13902, United States of America
| | - Huimin Zhou
- Department of Systems Science and Industrial Engineering, State University of New York at Binghamton, Binghamton, NY 13902, United States of America
| | - Anju Sharma
- Small Scale Systems Integration and Packaging Center, State University of New York at Binghamton, Binghamton, NY 13902, United States of America
| | - Jia Deng
- Department of Systems Science and Industrial Engineering, State University of New York at Binghamton, Binghamton, NY 13902, United States of America
| | - Changhong Ke
- Department of Mechanical Engineering, State University of New York at Binghamton, Binghamton, NY 13902, United States of America
- Materials Science and Engineering Program, State University of New York at Binghamton, Binghamton, NY 13902, United States of America
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Canton-Vitoria R, Hotta T, Xue M, Zhang S, Kitaura R. Synthesis and Characterization of Transition Metal Dichalcogenide Nanoribbons Based on a Controllable O 2 Etching. JACS AU 2023; 3:775-784. [PMID: 37006761 PMCID: PMC10052231 DOI: 10.1021/jacsau.2c00536] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 12/17/2022] [Accepted: 12/19/2022] [Indexed: 06/18/2023]
Abstract
Although the synthesis of monolayer transition metal dichalcogenides has been established in the last decade, synthesizing nanoribbons remains challenging. In this study, we have developed a straightforward method to obtain nanoribbons with controllable widths (25-8000 nm) and lengths (1-50 μm) by O2 etching of the metallic phase in metallic/semiconducting in-plane heterostructures of monolayer MoS2. We also successfully applied this process for synthesizing WS2, MoSe2, and WSe2 nanoribbons. Furthermore, field-effect transistors of the nanoribbons show an on/off ratio of larger than 1000, photoresponses of 1000%, and time responses of 5 s. The nanoribbons were compared with monolayer MoS2, highlighting a substantial difference in the photoluminescence emission and photoresponses. Additionally, the nanoribbons were used as a template to build one-dimensional (1D)-1D or 1D-2D heterostructures with various transition metal dichalcogenides. The process developed in this study offers simple production of nanoribbons with applications in several fields of nanotechnology and chemistry.
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Affiliation(s)
- Ruben Canton-Vitoria
- Department
of Chemistry, Nagoya University, Furo-Cho, Nagoya, Aichi 464-8602, Japan
- Theoretical
and Physical Chemistry Institute, National
Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, Athens 116 35, Greece
| | - Takato Hotta
- Department
of Chemistry, Nagoya University, Furo-Cho, Nagoya, Aichi 464-8602, Japan
| | - Mengsong Xue
- Department
of Chemistry, Nagoya University, Furo-Cho, Nagoya, Aichi 464-8602, Japan
| | - Shaochun Zhang
- Department
of Chemistry, Nagoya University, Furo-Cho, Nagoya, Aichi 464-8602, Japan
| | - Ryo Kitaura
- Department
of Chemistry, Nagoya University, Furo-Cho, Nagoya, Aichi 464-8602, Japan
- International
Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
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Molten Salt-Assisted Catalytic Preparation of MoS2/α-MoO3/Graphene as High-Performance Anode of Li-Ion Battery. Catalysts 2023. [DOI: 10.3390/catal13030499] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/05/2023] Open
Abstract
We report on the facile and scalable catalytic conversion of natural graphite and MoS2 minerals into α-MoO3 nanoribbons incorporated into hexagonal MoS2 and graphene nanosheets, and evaluate the structural, morphological and electrochemical performances of the hybrid nanostructured material obtained. Mechanochemical treatment of raw materials, followed by catalytic molten salt treatment leads to the formation of nanostructures with promising electrochemical performances. We examined the effect of processing temperature on the electrochemical performance of the products. At 1100 °C, an excellent Li-ion storage capacity of 773.5 mAh g−1 is obtained after 180 cycles, considerably greater than that of MoS2 (176.8 mAh g−1). The enhanced capacity and the rate performance of this electrode are attributed to the well-integrated components, characterized by the formation of interfacial molybdenum oxycarbide layer during the synthesis process, contributing to the reduced electrical/electrochemical resistance of the sample. This unique morphology promotes the charge and ions transfer through the reduction of the Li-ion diffusion coefficient (1.2 × 10−18 cm2 s−1), enhancing the pseudocapacitive performance of the electrode; 59.3% at the scan rate of 0.5 mV s−1. This article provides a green and low-cost route to convert highly available natural graphite and MoS2 minerals into nanostructured hybrid materials with promising Li-ion storage performance.
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Mao Q, Zhang Y, Kowalik M, Nayir N, Chandross M, van Duin ACT. Oxidation and hydrogenation of monolayer MoS2 with compositing agent under environmental exposure: The ReaxFF Mo/Ti/Au/O/S/H force field development and applications. FRONTIERS IN NANOTECHNOLOGY 2022. [DOI: 10.3389/fnano.2022.1034795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
An atomistic modeling tool is essential to an in-depth understanding upon surface reactions of transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), with the presence of compositing agents, including Ti and Au, under different environmental exposures. We report a new ReaxFF reactive force field parameter set for Mo, Ti, Au, O, S, and H interactions. We apply the force field in a series of molecular dynamics (MD) simulations to unravel the impact of the Ti dopant on the oxidation/hydrogenation behaviors of MoS2 surface. The simulation results reveal that, in the absence of Ti clusters, the MoS2 surface is ruptured and oxidized at elevated temperatures through a process of adsorption followed by dissociation of the O2 molecules on the MoS2 surface during the temperature ramp. When the MoS2 surface is exposed to H2O molecules, surface hydrogenation is most favored, followed by oxidation, then hydroxylation. The introduction of Ti clusters to the systems mitigates the oxidation/hydrogenation of MoS2 at a low or intermediate temperature by capturing the O2/H2O molecules and locking the O/H-related radicals inside the clusters. However, OH− and H3O+ are emitted from the Ti clusters in the H2O environment as temperature rises, and the accelerating hydrogenation of MoS2 is consequently observed at an ultra-high temperature. These findings indicate an important but complex role of Ti dopants in mitigating the oxidation and hydrogenation of MoS2 under different environmental exposures. The possible mechanisms of oxidation and hydrogenation revealed by MD simulations can give an insight to the design of oxidation resistant TMDs and can be useful to the optical, electronic, magnetic, catalytic, and energy harvesting industries.
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Li W, Shahbazi M, Xing K, Tesfamichael T, Motta N, Qi DC. Highly Sensitive NO2 Gas Sensors Based on MoS2@MoO3 Magnetic Heterostructure. NANOMATERIALS 2022; 12:nano12081303. [PMID: 35458010 PMCID: PMC9027905 DOI: 10.3390/nano12081303] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Revised: 04/07/2022] [Accepted: 04/08/2022] [Indexed: 12/16/2022]
Abstract
Recently, two-dimensional (2D) materials and their heterostructures have attracted considerable attention in gas sensing applications. In this work, we synthesized 2D MoS2@MoO3 heterostructures through post-sulfurization of α-MoO3 nanoribbons grown via vapor phase transport (VPT) and demonstrated highly sensitive NO2 gas sensors based on the hybrid heterostructures. The morphological, structural, and compositional properties of the MoS2@MoO3 hybrids were studied by a combination of advanced characterization techniques revealing a core-shell structure with the coexistence of 2H-MoS2 multilayers and intermediate molybdenum oxysulfides on the surface of α-MoO3. The MoS2@MoO3 hybrids also exhibit room-temperature ferromagnetism, revealed by vibrating sample magnetometry (VSM), as a result of the sulfurization process. The MoS2@MoO3 gas sensors display a p-type-like response towards NO2 with a detection limit of 0.15 ppm at a working temperature of 125 °C, as well as superb selectivity and reversibility. This p-type-like sensing behavior is attributed to the heterointerface of MoS2-MoO3 where interfacial charge transfer leads to a p-type inversion layer in MoS2, and is enhanced by magnetic dipole interactions between the paramagnetic NO2 and the ferromagnetic sensing layer. Our study demonstrates the promising application of 2D molybdenum hybrid compounds in gas sensing applications with a unique combination of electronic and magnetic properties.
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Affiliation(s)
- Wei Li
- School of Chemistry and Physics, Queensland University of Technology, Brisbane, QLD 4001, Australia; (W.L.); (M.S.)
- Centre for Materials Science, Queensland University of Technology, Brisbane, QLD 4001, Australia
| | - Mahboobeh Shahbazi
- School of Chemistry and Physics, Queensland University of Technology, Brisbane, QLD 4001, Australia; (W.L.); (M.S.)
| | - Kaijian Xing
- School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Australia;
| | - Tuquabo Tesfamichael
- Centre for Materials Science, Queensland University of Technology, Brisbane, QLD 4001, Australia
- School of Mechanical, Medical and Process Engineering, Queensland University of Technology, Brisbane, QLD 4001, Australia
- Correspondence: (T.T.); (N.M.); (D.-C.Q.)
| | - Nunzio Motta
- School of Chemistry and Physics, Queensland University of Technology, Brisbane, QLD 4001, Australia; (W.L.); (M.S.)
- Centre for Materials Science, Queensland University of Technology, Brisbane, QLD 4001, Australia
- Correspondence: (T.T.); (N.M.); (D.-C.Q.)
| | - Dong-Chen Qi
- School of Chemistry and Physics, Queensland University of Technology, Brisbane, QLD 4001, Australia; (W.L.); (M.S.)
- Centre for Materials Science, Queensland University of Technology, Brisbane, QLD 4001, Australia
- Correspondence: (T.T.); (N.M.); (D.-C.Q.)
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Yoon A, Kim JH, Lee Z. Elucidation of Novel Potassium-Mediated Oxidation and Etching of Two-Dimensional Transition Metal Dichalcogenides. ACS APPLIED MATERIALS & INTERFACES 2021; 13:49163-49171. [PMID: 34632769 DOI: 10.1021/acsami.1c13607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Preparation of edge-rich two-dimensional (2D) transition metal dichalocogenides (TMDs) has been actively investigated with the aim to improve their electrical and catalytic properties. Here, we elucidate the role of potassium ions in oxidation of TMDs and suggest a consequent novel anisotropic etching mechanism driven by self-running oxide droplets. We discover that potassium-mediated oxidation of MoS2 leads to the formation of K-intercalated hexagonal-phase molybdenum oxides (h-KxMoO3), whereas orthorhombic-phase oxides are formed in the absence of potassium ions. Metastable h-KxMoO3 appears to have decomposed into oxide droplets at higher temperature. Self-running of the oxide droplets leads to layer-by-layer anisotropic etching of MoS2 along the armchair direction. The motion of the droplets appears to be triggered by the surface energy instability between the oxide droplets and the underlying MoS2 layer. This study opens new possibilities to design and manufacture novel edge-rich 2D TMDs that do not follow the equilibrium Wulff shape by modulating their oxidation with the assistance of alkali metals and also offers fundamental insights into the interactions between nanodroplets and 2D materials toward edge engineering.
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Affiliation(s)
- Aram Yoon
- Center for Multidimensional Carbon Materials, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea
| | - Jung Hwa Kim
- Center for Multidimensional Carbon Materials, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
| | - Zonghoon Lee
- Center for Multidimensional Carbon Materials, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea
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8
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Szoszkiewicz R. Local Interactions of Atmospheric Oxygen with MoS 2 Crystals. MATERIALS (BASEL, SWITZERLAND) 2021; 14:5979. [PMID: 34683567 PMCID: PMC8540515 DOI: 10.3390/ma14205979] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 09/29/2021] [Accepted: 10/07/2021] [Indexed: 11/17/2022]
Abstract
Thin and single MoS2 flakes are envisioned to contribute to the flexible nanoelectronics, particularly in sensing, optoelectronics and energy harvesting. Thus, it is important to study their stability and local surface reactivity. Their most straightforward surface reactions in this context pertain to thermally induced interactions with atmospheric oxygen. This review focuses on local and thermally induced interactions of MoS2 crystals and single MoS2 flakes. First, experimentally observed data for oxygen-mediated thermally induced morphological and chemical changes of the MoS2 crystals and single MoS2 flakes are presented. Second, state-of-the-art mechanistic insight from computer simulations and arising open questions are discussed. Finally, the properties and fate of the Mo oxides arising from thermal oxidation are reviewed, and future directions into the research of the local MoS2/MoOx interface are provided.
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Affiliation(s)
- Robert Szoszkiewicz
- Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Żwirki i Wigury 101, 02-089 Warsaw, Poland
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Park S, Garcia‐Esparza AT, Abroshan H, Abraham B, Vinson J, Gallo A, Nordlund D, Park J, Kim TR, Vallez L, Alonso‐Mori R, Sokaras D, Zheng X. Operando Study of Thermal Oxidation of Monolayer MoS 2. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2021; 8:2002768. [PMID: 33977043 PMCID: PMC8097340 DOI: 10.1002/advs.202002768] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Revised: 01/12/2021] [Indexed: 06/12/2023]
Abstract
Monolayer MoS2 is a promising semiconductor to overcome the physical dimension limits of microelectronic devices. Understanding the thermochemical stability of MoS2 is essential since these devices generate heat and are susceptible to oxidative environments. Herein, the promoting effect of molybdenum oxides (MoO x ) particles on the thermal oxidation of MoS2 monolayers is shown by employing operando X-ray absorption spectroscopy, ex situ scanning electron microscopy and X-ray photoelectron spectroscopy. The study demonstrates that chemical vapor deposition-grown MoS2 monolayers contain intrinsic MoO x and are quickly oxidized at 100 °C (3 vol% O2/He), in contrast to previously reported oxidation thresholds (e.g., 250 °C, t ≤ 1 h in the air). Otherwise, removing MoO x increases the thermal oxidation onset temperature of monolayer MoS2 to 300 °C. These results indicate that MoO x promote oxidation. An oxide-free lattice is critical to the long-term stability of monolayer MoS2 in state-of-the-art 2D electronic, optical, and catalytic applications.
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Affiliation(s)
- Sangwook Park
- Department of Mechanical EngineeringStanford UniversityStanfordCA94305USA
- Department of Mechanical EngineeringSeoul National UniversitySeoul08826South Korea
| | - Angel T. Garcia‐Esparza
- Department of Mechanical EngineeringStanford UniversityStanfordCA94305USA
- Stanford Synchrotron Radiation LightsourceSLAC National Accelerator Laboratory2575 Sand Hill RoadMenlo ParkCA94025USA
| | - Hadi Abroshan
- SUNCAT Center for Interface Science and CatalysisSLAC National Accelerator Laboratory2575 Sand Hill RoadMenlo ParkCA94025USA
- School of Chemistry and BiochemistryGeorgia Institute of TechnologyAtlantaGA30332USA
| | - Baxter Abraham
- Stanford Synchrotron Radiation LightsourceSLAC National Accelerator Laboratory2575 Sand Hill RoadMenlo ParkCA94025USA
- Linac Coherent Light SourceSLAC National Accelerator Laboratory2575 Sand Hill RoadMenlo ParkCA94025USA
| | - John Vinson
- National Institute of Standards and Technology100 Bureau DriveGaithersburgMD20899USA
| | - Alessandro Gallo
- SUNCAT Center for Interface Science and CatalysisSLAC National Accelerator Laboratory2575 Sand Hill RoadMenlo ParkCA94025USA
| | - Dennis Nordlund
- Stanford Synchrotron Radiation LightsourceSLAC National Accelerator Laboratory2575 Sand Hill RoadMenlo ParkCA94025USA
| | - Joonsuk Park
- Materials Science and EngineeringStanford UniversityStanfordCA94305USA
| | - Taeho Roy Kim
- Stanford Nano Shared FacilitiesStanford UniversityStanfordCA94305USA
| | - Lauren Vallez
- Department of Mechanical EngineeringStanford UniversityStanfordCA94305USA
| | - Roberto Alonso‐Mori
- Linac Coherent Light SourceSLAC National Accelerator Laboratory2575 Sand Hill RoadMenlo ParkCA94025USA
| | - Dimosthenis Sokaras
- Stanford Synchrotron Radiation LightsourceSLAC National Accelerator Laboratory2575 Sand Hill RoadMenlo ParkCA94025USA
| | - Xiaolin Zheng
- Department of Mechanical EngineeringStanford UniversityStanfordCA94305USA
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Krawczyk M, Pisarek M, Szoszkiewicz R, Jablonski A. Surface Characterization of MoS 2 Atomic Layers Mechanically Exfoliated on a Si Substrate. MATERIALS (BASEL, SWITZERLAND) 2020; 13:E3595. [PMID: 32823911 PMCID: PMC7475815 DOI: 10.3390/ma13163595] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 08/08/2020] [Accepted: 08/12/2020] [Indexed: 11/16/2022]
Abstract
Mo disulfide overlayers with the thickness exceeding 1.77 nm were obtained on Si substrates through mechanical exfoliation. The resulting Mo disulfide flakes were then analyzed ex situ using combination of Auger electron spectroscopy (AES), elastic-peak electron spectroscopy (EPES) and scanning electron microscopy (SEM) in order to characterize their surface chemical composition, electron transport phenomena and surface morphology. Prior to EPES measurements, the Mo disulfide surface was sputter-cleaned and amorphized by 3 kV argon ions, and the resulting S/Mo atomic ratio varied in the range 1.80-1.88, as found from AES measurements. The SEM images revealed single crystalline small-area (up to 15 μm in lateral size) Mo disulfide flakes having polygonal or near-triangular shapes. Such irregular-edged flakes exhibited high crystal quality and thickness uniformity. The inelastic mean free path (IMFP), characterizing electron transport, was evaluated from the relative EPES using Au reference material for electron energies E = 0.5-2 keV. Experimental IMFPs, λ, determined for the AES-measured surface compositions were approximated by the simple function λ = kEp, where k = 0.0289 and p = 0.946 were fitted parameters. Additionally, these IMFPs were compared with IMFPs resulting from the two methods: (i) present calculations based on the formalism of the Oswald et al. model; (ii) the predictive equation of Tanuma et al. (TPP-2M) for the measured Mo0.293S0.551C0.156 surface composition (S/Mo = 1.88), and also for stoichiometric MoS2 composition. The fitted function was found to be reasonably consistent with the measured, calculated and predicted IMFPs. We concluded that the measured IMFP value at 0.5 keV was only slightly affected by residual carbon contamination at the Mo disulfide surface.
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Affiliation(s)
- Mirosław Krawczyk
- Laboratory of Surface Analysis, Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland; (M.P.); (A.J.)
| | - Marcin Pisarek
- Laboratory of Surface Analysis, Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland; (M.P.); (A.J.)
| | - Robert Szoszkiewicz
- Biological and Chemical Research Centre, Faculty of Chemistry, University of Warsaw, Żwirki Wigury 101, 02-089 Warsaw, Poland;
| | - Aleksander Jablonski
- Laboratory of Surface Analysis, Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland; (M.P.); (A.J.)
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