Non-invasive Scanning Raman Spectroscopy and Tomography for Graphene Membrane Characterization

Graphene has extraordinary mechanical and electronic properties, making it a promising material for membrane based nanoelectromechanical systems (NEMS). Here, chemical-vapor-deposited graphene is transferred onto target substrates to suspend it over cavities and trenches for pressure-sensor applications. The development of such devices requires suitable metrology methods, i.e., large-scale characterization techniques, to confirm and analyze successful graphene transfer with intact suspended graphene membranes. We propose fast and noninvasive Raman spectroscopy mapping to distinguish between freestanding and substrate-supported graphene, utilizing the different strain and doping levels. The technique is expanded to combine two-dimensional area scans with cross-sectional Raman spectroscopy, resulting in three-dimensional Raman tomography of membrane-based graphene NEMS. The potential of Raman tomography for in-line monitoring is further demonstrated with a methodology for automated data analysis to spatially resolve the material composition in micrometer-scale integrated devices, including free-standing and substrate-supported graphene. Raman tomography may be applied to devices composed of other two-dimensional materials as well as silicon micro- and nanoelectromechanical systems.Comment: 23 pages, 5 figure

Ultrathin 2D nanosheets of transition metal (hydro)oxides as prospective materials for energy storage devices: A short review

The ultrathin two-dimensional (2D) transition metal oxides and hydroxides (TMO and TMH) nanosheets are attractive for creating high-performance energy storage devices due to a set of unique physical and chemical properties. Flat 2D structure of such materials provides a sufficient number of active adsorption centers, and the ultra-small thickness, on the order of several nanometers, provides fast charge transfer, which significantly improves electronic conductivity. This brief review summarizes recent progress in the synthesis of materials based on ultrathin 2D nanosheets for energy storage applications, including pseudocapacitors, lithium-ion batteries, and other rechargeable devices. The review also presents examples of representative work on the synthesis of ultrathin 2D nanomaterials based on TMO and TMH for various power sources. In conclusion, the article discusses possible prospects and directions for further development of methods and routes for the synthesis of ultrathin two-dimensional transition metal oxides and hydroxides.keywords: two-dimensional materials, transition metal oxides, layered double hydroxides, nanosheets, energy storage devicesDOI: https://doi.org/10.15726/elmattech.2022.1.00

Two-dimensional electronics and optoelectronics

The discovery of monolayer graphene has led to a Nobel Prize in Physics in 2010. This has stimulated research on a wide variety of two-dimensional (2D) layered materials. The coupling of metallic graphene, semiconducting 2D transition metal dichalcogenides (TMDCs) and black phosphorus has attracted tremendous amount of interest in new electronic and optoelectronic applications. Together with other 2D materials such as the wide band gap boron nitride nanosheets (BNNSs), all these 2D materials have led towards an emerging field of van der Waal 2D heterostructures. This book is originally published in Electronics (MDPI) as a special issue of “Two-Dimensional Electronics and Optoelectronics”. The book consists of a total of eight papers, including two review articles, covering important topics of 2D materials. These papers represent some of the important topics on 2D materials and devices. Promises and challenges of 2D materials are discussed herein, which provide a great recent guidance for future research and development

Graphene and molybdenum disulfide hybrids: Synthesis and applications

Graphene and related inorganic two-dimensional (2D) nanomaterials are an exceptional class of compounds with exotic properties that are technologically intriguing. While graphene itself is chemically inert and a gapless semimetal, its isostructural analog, molybdenum disulfide (MOS2) is chemically versatile with band gaps, thereby finding significant use in a myriad of applications. Although these 2D nanomaterials individually possess tremendous authority for various applications, the combination of these materials in the recent past has created a new paradigm in emerging applications. Here, we summarize the current state-of-the-art and progress over the past three years on the development of hybrids of these layered materials. We highlight their pivotal role in electrochemical energy storage, sensing, hydrogen generation by photochemical water splitting and electronic device applications such as field-effect transistors. Perspectives on the challenges and opportunities for the exploration of these 2D layered hybrid materials are put forwardopen1

Two-Dimensional Electronics and Optoelectronics

The discovery of monolayer graphene led to a Nobel Prize in Physics being awarded in 2010. This has stimulated further research on a wide variety of two-dimensional (2D) layered materials. The coupling of metallic graphene, semiconducting 2D transition metal dichalcogenides (TMDCs) and black phosphorus have attracted a tremendous amount of interest in new electronic and optoelectronic applications. Together with other 2D materials, such as the wide band gap boron nitride nanosheets (BNNSs), all these 2D materials have led towards an emerging field of van der Waal 2D heterostructures. The papers in this book were originally published by Electronics (MDPI) in a Special Issue on “Two-Dimensional Electronics and Optoelectronics”. The book consists of eight papers, including two review articles, covering various pertinent and fascinating issues concerning 2D materials and devices. Further, the potential and the challenges of 2D materials are discussed, which provide up to date guidance for future research and development

Prediction of Silicon-Based Layered Structures for Optoelectronic Applications

A method based on the particle swarm optimization (PSO) algorithm is presented to design quasi-two-dimensional (Q2D) materials. With this development, various single-layer and bi-layer materials in C, Si, Ge, Sn, and Pb were predicted. A new Si bi-layer structure is found to have a much-favored energy than the previously widely accepted configuration. Both single-layer and bi-layer Si materials have small band gaps, limiting their usages in optoelectronic applications. Hydrogenation has therefore been used to tune the electronic and optical properties of Si layers. We discover two hydrogenated materials of layered Si8H2 and Si6H2 possessing quasi-direct band gaps of 0.75 eV and 1.59 eV, respectively. Their potential applications for light emitting diode and photovoltaics are proposed and discussed. Our study opened up the possibility of hydrogenated Si layered materials as next-generation optoelectronic devices.Comment: 21 pages,6 figures, 1 tabe