An official website of the United States government
Abstract A deeper understanding of resistive switching (RS) in 2D materials is essential for advancing neuromorphic computing. The Dissociation-Diffusion-Adsorption (DDA) model offers a useful framework for probing RS mechanisms in non-volatile memory (NVM) and in-memory computing. We have employed first-principles density functional theory (DFT) to explore dissociation, diffusion, and adsorption phenomena within the DDA model, focusing on the interactions between exemplary metal atoms (Au, Ag, Cu) and monolayer MoS2. Nudged elastic band (NEB) calculations evaluated diffusion barriers in pristine and sulfur-vacancy MoS2. Charged systems were modeled to assess the impact of applied bias on migration pathways. We also examined metal dissociation from bulk electrodes and adsorption at S vacancies. Ag/MoS2shows the lowest dissociation barrier (~0.034 eV), while Au and Cu exhibit similar values (~0.32 eV). These insights highlight Ag as a promising candidate for low-energy RS applications and provide guidance for optimizing switching efficiency in 2D memory devices.
more »
« less
This content will become publicly available on January 1, 2027
2D Indium Oxide at the Epitaxial Graphene/SIC Interface: Synthesis, Structure, Properties, and Devices
Abstract Scaled and high‐quality insulators are crucial for fabricating 2D/3D hybrid vertical electronic devices such as metal‐oxide‐semiconductor (MOS) based Schottky diodes and hot electron transistors, the production of which is constrained by the scarcity of bulk layered wide bandgap semiconductors. In this research, the synthesis of a new 2D insulator, monolayer InO2, which differs in stoichiometry from its bulk form is presented, over a large area (>300 µm2) by intercalating at the epitaxial graphene (EG)/SiC interface. By adjusting the lateral size of graphene through optical lithography prior to the intercalation, the thickness of InO2is tuned such that it is 85% monolayer. The preference for monolayer formation of InO2is explained using molecular dynamics and density functional theory (DFT) calculations. Additionally, the bandgap of InO2is calculated to be 4.1 eV, differing from its bulk form (2.7 eV). Furthermore, MOS‐based Schottky diode measurements on InO2intercalated EG/n‐SiC demonstrate that the EG/n‐SiC junction transforms from ohmic to a Schottky junction upon intercalation, with a barrier height of 0.87 eV and a rectification ratio of ≈105. These findings introduce a new addition to the 2D insulator family, demonstrating the utility of monolayer InO2as a barrier in vertical electronic devices.
more »
« less
- Award ID(s):
- 1539916
- PAR ID:
- 10681085
- Publisher / Repository:
- Wiley-VCH GmbH
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 38
- Issue:
- 6
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The use of metal and semimetal van der Waals contacts for 2D semiconducting devices has led to remarkable device optimizations. In comparison with conventional thin-film metal deposition, a reduction in Fermi level pinning at the contact interface for van der Waals contacts results in, generally, lower contact resistances and higher mobilities. Van der Waals contacts also lead to Schottky barriers that follow the Schottky–Mott rule, allowing barrier estimates on material properties alone. In this study, we present a double Schottky barrier model and apply it to a barrier tunable all van der Waals transistor. In a molybdenum disulfide (MoS2) transistor with graphene and few-layer graphene contacts, we find that the model can be applied to extract Schottky barrier heights that agree with the Schottky–Mott rule from simple two-terminal current–voltage measurements at room temperature. Furthermore, we show tunability of the Schottky barrierin-situusing a regional contact gate. Our results highlight the utility of a basic back-to-back diode model in extracting device characteristics in all van der Waals transistors.more » « less
-
Abstract This study investigates the performance of Ni/Y₂O₃/4H-SiC metal–oxide–semiconductor (MOS) radiation detectors fabricated on 4H-SiC epilayers of 50, 150, and 250 µm thicknesses. The impact of epilayer thickness on electrical behavior, defect dynamics, and alpha particle response in Y₂O₃-gated 4H-SiC detectors is systematically examined. Leveraging the wide bandgap of 4H-SiC and the high dielectric constant and thermal stability of Y₂O₃, the devices are optimized for high-resolution radiation detection in harsh environments. A 40 nm Y₂O₃ dielectric layer, deposited via pulsed laser deposition, retained the Schottky-like behavior and efficient charge transport of the detectors. Device characterization included current–voltage and capacitance–voltage measurements to assess Schottky barrier properties, deep-level transient spectroscopy to analyze defect states, and alpha pulse height spectroscopy to evaluate detection response. The detector with a 250 µm epilayer exhibited lower leakage current and reduced concentrations and capture cross-sections of Z1/2and EH6/7traps—defects known to impair charge collection. However, despite these favorable electrical and defect characteristics, the 250 µm device showed a comparatively lower alpha detection response than thinner epilayer detectors. This behavior suggests an influence of the Y₂O₃/4H-SiC interface, particularly in thicker epilayers, where interfacial states or field distortions may hinder carrier transport. Overall, the findings provide new insights into optimizing thick epilayer MOS detector architectures and underscore the importance of interface engineering to advance robust, high-performance 4H-SiC-based radiation detectors for space, nuclear, and high-energy physics applications.more » « less
-
The realization of air-stable two-dimensional (2D) metals confined at the interface between graphene and SiC has attracted significant attention owing to their distinct properties compared to their bulk counterparts. In this work, we identify two distinct structural phases in a monolayer silver intercalated between graphene and SiC: (i) a moiré pattern arising from the lattice mismatch between graphene and monolayer silver and (ii) a striped reconstruction formed through the interaction with the underlying SiC. Using cryogenic scanning tunneling microscopy combined with density functional theory, we elucidate the origin of the silver striped reconstruction. Driven by the competition between the silver-SiC and the silver-silver interactions within a monolayer, the silver atoms form a one-dimensional Frenkel-Kontorova domain, in which an silver supercell accommodates an supercell of the underlying SiC, which partially relieves tensile strain, otherwise imposed by ideal epitaxy. The strain-induced reconstruction creates a long-range modulation of 2D silver electronic density, giving rise to an electronic state at above the Fermi level in the transition regions between different silver-SiC registries. These findings uncover the important interplay between the structural and electronic properties of intercalated 2D metals and the underlying SiC substrate, providing new insights into substrate-mediated reconstruction and electronic modulation at confined interfaces.more » « less
-
Abstract Chemical vapor deposition (CVD)-grown monolayer (ML) molybdenum disulfide (MoS 2 ) is a promising material for next-generation integrated electronic systems due to its capability of high-throughput synthesis and compatibility with wafer-scale fabrication. Several studies have described the importance of Schottky barriers in analyzing the transport properties and electrical characteristics of MoS 2 field-effect-transistors (FETs) with metal contacts. However, the analysis is typically limited to single devices constructed from exfoliated flakes and should be verified for large-area fabrication methods. In this paper, CVD-grown ML MoS 2 was utilized to fabricate large-area (1 cm × 1 cm) FET arrays. Two different types of metal contacts (i.e. Cr/Au and Ti/Au) were used to analyze the temperature-dependent electrical characteristics of ML MoS 2 FETs and their corresponding Schottky barrier characteristics. Statistical analysis provides new insight about the properties of metal contacts on CVD-grown MoS 2 compared to exfoliated samples. Reduced Schottky barrier heights (SBH) are obtained compared to exfoliated flakes, attributed to a defect-induced enhancement in metallization of CVD-grown samples. Moreover, the dependence of SBH on metal work function indicates a reduction in Fermi level pinning compared to exfoliated flakes, moving towards the Schottky–Mott limit. Optical characterization reveals higher defect concentrations in CVD-grown samples supporting a defect-induced metallization enhancement effect consistent with the electrical SBH experiments.more » « less
