1
|
Chen L, Cheng Z, He S, Zhang X, Deng K, Zong D, Wu Z, Xia M. Large-area single-crystal TMD growth modulated by sapphire substrates. NANOSCALE 2024; 16:978-1004. [PMID: 38112240 DOI: 10.1039/d3nr05400d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
Transition metal dichalcogenides (TMDs) have recently attracted extensive attention due to their unique physical and chemical properties; however, the preparation of large-area TMD single crystals is still a great challenge. Chemical vapor deposition (CVD) is an effective method to synthesize large-area and high-quality TMD films, in which sapphires as suitable substrates play a crucial role in anchoring the source material, promoting nucleation and modulating epitaxial growth. In this review, we provide an insightful overview of different epitaxial mechanisms and growth behaviors associated with the atomic structure of sapphire surfaces and the growth parameters. First, we summarize three epitaxial growth mechanisms of TMDs on sapphire substrates, namely, van der Waals epitaxy, step-guided epitaxy, and dual-coupling-guided epitaxy. Second, we introduce the effects of polishing, cutting, and annealing processing of the sapphire surface on the TMD growth. Finally, we discuss the influence of other growth parameters, such as temperature, pressure, carrier gas, and substrate position, on the growth kinetics of TMDs. This review might provide deep insights into the controllable growth of large-area single-crystal TMDs on sapphires, which will propel their practical applications in high-performance nanoelectronics and optoelectronics.
Collapse
Affiliation(s)
- Lina Chen
- Department of Applied Physics, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China.
| | - Zhaofang Cheng
- Department of Applied Physics, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China.
- MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China
| | - Shaodan He
- Department of Applied Physics, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China.
| | - Xudong Zhang
- Department of Applied Physics, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China.
| | - Kelun Deng
- Department of Applied Physics, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China.
| | - Dehua Zong
- Department of Applied Physics, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China.
| | - Zipeng Wu
- Department of Applied Physics, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China.
| | - Minggang Xia
- Department of Applied Physics, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China.
- MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China
- Shaanxi Province Key Laboratory of Quantum Information and Optoelectronic Quantum Devices, School of Physics, Xi'an Jiaotong University, 710049, People's Republic of China
| |
Collapse
|
2
|
Johnson I, Margetis D. Emergence of local geometric laws of step flow in homoepitaxial growth. Phys Rev E 2022; 105:034802. [PMID: 35428142 DOI: 10.1103/physreve.105.034802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 03/01/2022] [Indexed: 11/07/2022]
Abstract
Below the roughening transition, crystal surfaces exhibit nanoscale line defects, steps, that move by exchanging atoms with their environment. In homoepitaxy, we analytically show how the motion of a step train in vacuum under strong desorption can be approximately described by nonlinear laws that depend on local geometric features such as the curvature of each step, as well as suitably defined effective terrace widths. We assume that each step edge, a free boundary, can be represented by a smooth curve in a fixed reference plane for sufficiently long times. Besides surface diffusion and evaporation, the processes under consideration include kinetic step-step interactions in slowly varying geometries, material deposition on the surface from above, attachment and detachment of atoms at steps, step edge diffusion, and step permeability. Our methodology relies on boundary integral equations for the adatom fluxes responsible for step flow. By applying asymptotics, which effectively treat the diffusive term of the free boundary problem as a singular perturbation, we describe an intimate connection of universal character between step kinetics and local geometry.
Collapse
Affiliation(s)
- Ian Johnson
- Department of Mathematics, University of Maryland, College Park, Maryland 20742, USA
| | - Dionisios Margetis
- Institute for Physical Science and Technology, and Department of Mathematics, and Center for Scientific Computation and Mathematical Modeling, University of Maryland, College Park, Maryland 20742, USA
| |
Collapse
|
3
|
Shi Y, Groven B, Serron J, Wu X, Nalin Mehta A, Minj A, Sergeant S, Han H, Asselberghs I, Lin D, Brems S, Huyghebaert C, Morin P, Radu I, Caymax M. Engineering Wafer-Scale Epitaxial Two-Dimensional Materials through Sapphire Template Screening for Advanced High-Performance Nanoelectronics. ACS NANO 2021; 15:9482-9494. [PMID: 34042437 DOI: 10.1021/acsnano.0c07761] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
In view of its epitaxial seeding capability, c-plane single crystalline sapphire represents one of the most enticing, industry-compatible templates to realize manufacturable deposition of single crystalline two-dimensional transition metal dichalcogenides (MX2) for functional, ultrascaled, nanoelectronic devices beyond silicon. Despite sapphire being atomically flat, the surface topography, structure, and chemical termination vary between sapphire terraces during the fabrication process. To date, it remains poorly understood how these sapphire surface anomalies affect the local epitaxial registry and the intrinsic electrical properties of the deposited MX2 monolayer. Therefore, molybdenum disulfide (MoS2) is deposited by metal-organic chemical vapor deposition (MOCVD) in an industry-standard epitaxial reactor on two types of c-plane sapphire with distinctly different terrace and step dimensions. Complementary scanning probe microscopy techniques reveal an inhomogeneous conductivity profile in the first epitaxial MoS2 monolayer on both sapphire templates. MoS2 regions with poor conductivity correspond to sapphire terraces with uncontrolled topography and surface structure. By intentionally applying a substantial off-axis cut angle (1° in this work), the sapphire terrace width and step height-and thus also surface structure-become more uniform across the substrate and MoS2 conducts the current more homogeneously. Moreover, these effects propagate into the extrinsic MoS2 device performance: the field-effect transistor variability reduces both within and across wafers at higher median electron mobility. Carefully controlling the sapphire surface topography and structure proves an essential prerequisite to systematically study and control the MX2 growth behavior and capture the influence on its structural and electrical properties.
Collapse
Affiliation(s)
| | | | | | - Xiangyu Wu
- IMEC, Kapeldreef 75, 3001 Leuven, Belgium
- Department of Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, 3001 Leuven, Belgium
| | - Ankit Nalin Mehta
- IMEC, Kapeldreef 75, 3001 Leuven, Belgium
- Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200d, 3001 Leuven, Belgium
| | - Albert Minj
- IMEC, Kapeldreef 75, 3001 Leuven, Belgium
- Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200d, 3001 Leuven, Belgium
| | | | - Han Han
- IMEC, Kapeldreef 75, 3001 Leuven, Belgium
| | | | - Dennis Lin
- IMEC, Kapeldreef 75, 3001 Leuven, Belgium
| | | | | | | | | | | |
Collapse
|
4
|
Mortelmans W, El Kazzi S, Nalin Mehta A, Vanhaeren D, Conard T, Meersschaut J, Nuytten T, De Gendt S, Heyns M, Merckling C. Peculiar alignment and strain of 2D WSe 2 grown by van der Waals epitaxy on reconstructed sapphire surfaces. NANOTECHNOLOGY 2019; 30:465601. [PMID: 31426041 DOI: 10.1088/1361-6528/ab3c9b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The increasing scientific and industry interest in 2D MX2 materials within the field of nanotechnology has made the single crystalline integration of large area van der Waals (vdW) layers on commercial substrates an important topic. The c-plane oriented (3D crystal) sapphire surface is believed to be an interesting substrate candidate for this challenging 2D/3D integration. Despite the many attempts that have been made, the yet incomplete understanding of vdW epitaxy still results in synthetic material that shows a crystallinity far too low compared to natural crystals that can be exfoliated onto commercial substrates. Thanks to its atomic control and in situ analysis possibilities, molecular beam epitaxy (MBE) offers a potential solution and an appropriate method to enable a more in-depth understanding of this peculiar 2D/3D hetero-epitaxy. Here, we report on how various sapphire surface reconstructions, that are obtained by thermal annealing of the as-received substrates, influence the vdW epitaxy of the MBE-grown WSe2 monolayers (MLs). The surface chemistry and the interatomic arrangement of the reconstructed sapphire surfaces are shown to control the preferential in-plane epitaxial alignment of the stoichiometric WSe2 crystals. In addition, it is demonstrated that the reconstructions also affect the in-plane lattice parameter and thus the in-plane strain of the 2D vdW-bonded MLs. Hence, the results obtained in this work shine more light on the peculiar concept of vdW epitaxy, especially relevant for 2D materials integration on large-scale 3D crystal commercial substrates.
Collapse
Affiliation(s)
- Wouter Mortelmans
- KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, B-3001, Leuven, Belgium. Imec, Kapeldreef 75, B-3001, Leuven, Belgium
| | | | | | | | | | | | | | | | | | | |
Collapse
|
5
|
Hwang Y, Shin N. Hydrogen-assisted step-edge nucleation of MoSe 2 monolayers on sapphire substrates. NANOSCALE 2019; 11:7701-7709. [PMID: 30946393 DOI: 10.1039/c8nr10315a] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The fabrication of large-area single crystalline monolayer transition metal dichalcogenides (TMDs) is essential for a range of electric and optoelectronic applications. Chemical vapor deposition (CVD) is a promising method to achieve this goal by employing orientation control or alignment along the crystalline lattice of the substrate such as sapphire. On the other hand, a fundamental understanding of the aligned-growth mechanism of TMDs is limited. In this report, we show that the controlled introduction of H2 during the CVD growth of MoSe2 plays a vital role in the step-edge aligned nucleation on a c-sapphire (0001) substrate. In particular, the MoSe2 domains nucleate along the [112[combining macron]0] step-edge orientation by flowing H2 subsequent to pure Ar. Systematic studies, including the H2 introduction time, flow rate, and substrate temperature, suggest that the step-edge aligned nucleation of MoSe2 can be controlled by the hydrogen concentration on the sapphire substrate. These results offer important insights into controlling the epitaxial growth of 2D materials on a crystalline substrate.
Collapse
Affiliation(s)
- Yunjeong Hwang
- Department of Chemical Engineering, Inha University, 100, Inha-ro, Michuhol-Gu, Incheon 22212, Republic of Korea.
| | | |
Collapse
|
6
|
Rahman M, Boggs Z, Neff D, Norton M. The Sapphire (0001) Surface: A Transparent and Ultraflat Substrate for DNA Nanostructure Imaging. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:15014-15020. [PMID: 30110549 DOI: 10.1021/acs.langmuir.8b01851] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Mica is the current substrate of choice for DNA nanostructure imaging, mainly due to its atomically flat surface. However, these mica substrates are often not optically clear. In this work, sapphire has been evaluated as an alternative substrate, with potential to enable parallel optical and AFM studies. Well known for its thermal and chemical properties, sapphire is a hard ionic material with excellent optical properties. Because sapphire lacks the excellent basal cleavage properties of the sheet silicate mica, a process to anneal it at high temperature in water vapor was developed to achieve near atomically smooth (average roughness = 0.141 nm) terraces. AFM imaging was used to determine the dimensions of these terraces and to characterize the morphology of the DNA nanostructures, revealing that their structures were preserved, indicating that annealed c-plane cut (0001) sapphire is a promising substitute for mica as a flat and transparent substrate for DNA nanostructure studies.
Collapse
Affiliation(s)
- Masudur Rahman
- Department of Chemistry , Marshall University , Huntington , West Virginia 25755 , United States
| | - Zachary Boggs
- Department of Chemistry , Marshall University , Huntington , West Virginia 25755 , United States
| | - David Neff
- Department of Chemistry , Marshall University , Huntington , West Virginia 25755 , United States
| | - Michael Norton
- Department of Chemistry , Marshall University , Huntington , West Virginia 25755 , United States
| |
Collapse
|
7
|
Shi X, Xu L, Zhou Y, Zou C, Wang R, Pan G. An in situ study of chemical-mechanical polishing behaviours on sapphire (0001) via simulating the chemical product-removal process by AFM-tapping mode in both liquid and air environments. NANOSCALE 2018; 10:19692-19700. [PMID: 30338330 DOI: 10.1039/c8nr04645j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Chemical-mechanical polishing (CMP) has drawn significant attention as one of the most advanced techniques for achieving an atomic-level smooth surface. However, the mechanism of CMP is still unclear, and the in situ characterization of CMP behaviors at the nanoscale has been a challenge for decades. In this study, we, for the first time, report an in situ study of CMP behaviors on sapphire (0001) via simulating the chemical product-removal process by using atomic force microscopy (AFM) in tapping mode. Through a combination of intensive experimental measurements and detailed structural characterizations, it is shown that the AFM probe in tapping mode can act as a polishing abrasive to realize simultaneous imaging and chemical product removal on sapphire (0001), thus achieving successful in situ characterizations in both liquid and air environments. This work fills in gaps relating to fundamental CMP mechanisms, and provides a new perspective for the study of CMP behaviors on different materials.
Collapse
Affiliation(s)
- Xiaolei Shi
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
| | | | | | | | | | | |
Collapse
|
8
|
Deconvoluting the Photonic and Electronic Response of 2D Materials: The Case of MoS 2. Sci Rep 2017; 7:16938. [PMID: 29209000 PMCID: PMC5717065 DOI: 10.1038/s41598-017-16970-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Accepted: 11/19/2017] [Indexed: 11/26/2022] Open
Abstract
Evaluating and tuning the properties of two-dimensional (2D) materials is a major focus of advancing 2D science and technology. While many claim that the photonic properties of a 2D layer provide evidence that the material is “high quality”, this may not be true for electronic performance. In this work, we deconvolute the photonic and electronic response of synthetic monolayer molybdenum disulfide. We demonstrate that enhanced photoluminescence can be robustly engineered via the proper choice of substrate, where growth of MoS2 on r-plane sapphire can yield >100x enhancement in PL and carrier lifetime due to increased molybdenum-oxygen bonding compared to that of traditionally grown MoS2 on c-plane sapphire. These dramatic enhancements in optical properties are similar to those of super-acid treated MoS2, and suggest that the electronic properties of the MoS2 are also superior. However, a direct comparison of the charge transport properties indicates that the enhanced PL due to increased Mo-O bonding leads to p-type compensation doping, and is accompanied by a 2x degradation in transport properties compared to MoS2 grown on c-plane sapphire. This work provides a foundation for understanding the link between photonic and electronic performance of 2D semiconducting layers, and demonstrates that they are not always correlated.
Collapse
|