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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Electronic Materials".

Deadline for manuscript submissions: closed (15 July 2021) | Viewed by 61706

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Special Issue Editor

Dr. Rafik Addou

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School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, OR 97331, USA
Interests: 2D materials; scanning probe microscopy; XPS, nanofabrication; thin films, interface and surface science

Special Issue Information

Dear Colleagues,

Since the isolation of the first single layer of graphite (graphene) and the revelation of its outstanding optical, electrical, and mechanical properties, increased interests have focused on all existing layered materials and in developing novel 2D nanomaterials. Two-dimensional materials are extensively used in various 2D/flexible technological applications such as nanoelectronics, optoelectronics, energy, composites, sensing, filtration, nanocoating, life science, and medicine. In the last few years, remarkable efforts have been made towards the growth of high-quality, atomically thin, and large domain films, as well as a realizing electronic grade 2D materials. Except for graphene, immature 2D materials requires tremendous work in making a substantial transition from reporting the fundamental properties and the experimental proof-of-concept (feasibility) to the technology development and validation.

The aim of this Special Issue, entitled “2D Materials for Advanced Devices”, is to offer the latest cutting-edge research and development of 2D technology. This issue seeks to publish recent advances in the synthesis of novel and high-quality 2D materials, device fabrication and testing, integration challenges solving, and surface and interface engineering. Both experimental and theoretical articles will be published in this Special Issue, focusing on the state-of-the-art of recent research on the engineering and developments of 2D materials for advanced devices such as graphene and related materials, hexagonal boron nitride, transition metal dichalcogenides, silicene, phosphorene, tellurene, topological insulators, oxides, nitrides, carbides, hydroxides, perovskites, MOFs, MXenes, etc.

As a renowned expert in the field of 2D nanomaterials, I would like to invite you to submit a manuscript to foster the “2D Materials for Advanced Devices” Special Issue.

Dr. Rafik Addou
Guest Editor

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Keywords

Graphene and its analogs (graphane, graphene oxide, fluorographene, etc.)
Monoelement 2D materials: silicene, germanene, borophene, phosphorene, arsenene, stanene, bismuthene, tellurene, etc.
2D chalcogenides: WSe₂, MoTe₂, TaS₂, GaTe, InSe, Sb₂Te₃, Bi₂Se₃, etc.
2D oxides, carbides, and nitrides
2D perovskites, hydroxides, MOFs, MAX phases, MXenes, metal halides, and other novel 2D materials.
2D Materials engineering: surfaces, interfaces, heterostructures, alloying, passivation, functionalization, etching, 0D and 1D structures from 2D materials, 2D quantum wells, etc.
2D advanced devices and applications
Physics and materials science at 2D limit

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Published Papers (11 papers)

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Research

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12 pages, 2263 KiB

Open AccessArticle

Ion-Locking in Solid Polymer Electrolytes for Reconfigurable Gateless Lateral Graphene p-n Junctions

by Jierui Liang, Ke Xu, Swati Arora, Jennifer E. Laaser and Susan K. Fullerton-Shirey

Materials 2020, 13(5), 1089; https://doi.org/10.3390/ma13051089 - 1 Mar 2020

Cited by 10 | Viewed by 5424

Abstract

A gateless lateral p-n junction with reconfigurability is demonstrated on graphene by ion-locking using solid polymer electrolytes. Ions in the electrolytes are used to configure electric-double-layers (EDLs) that induce p- and n-type regions in graphene. These EDLs are locked in place by two different electrolytes with distinct mechanisms: (1) a polyethylene oxide (PEO)-based electrolyte, PEO:CsClO₄, is locked by thermal quenching (i.e., operating temperature < T_g (glass transition temperature)), and (2) a custom-synthesized, doubly-polymerizable ionic liquid (DPIL) is locked by thermally triggered polymerization that enables room temperature operation. Both approaches are gateless because only the source/drain terminals are required to create the junction, and both show two current minima in the backgated transfer measurements, which is a signature of a graphene p-n junction. The PEO:CsClO₄ gated p-n junction is reconfigured to n-p by resetting the device at room temperature, reprogramming, and cooling to T < T_g. These results show an alternate approach to locking EDLs on 2D devices and suggest a path forward to reconfigurable, gateless lateral p-n junctions with potential applications in polymorphic logic circuits. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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14 pages, 1772 KiB

Open AccessFeature PaperArticle

Monte Carlo Study of Electronic Transport in Monolayer InSe

by Sanjay Gopalan, Gautam Gaddemane, Maarten L. Van de Put and Massimo V. Fischetti

Materials 2019, 12(24), 4210; https://doi.org/10.3390/ma12244210 - 14 Dec 2019

Cited by 16 | Viewed by 4328

Abstract

The absence of a band gap in graphene makes it of minor interest for field-effect transistors. Layered metal chalcogenides have shown great potential in device applications thanks to their wide bandgap and high carrier mobility. Interestingly, in the ever-growing library of two-dimensional (2D) materials, monolayer InSe appears as one of the new promising candidates, although still in the initial stage of theoretical studies. Here, we present a theoretical study of this material using density functional theory (DFT) to determine the electronic band structure as well as the phonon spectrum and electron-phonon matrix elements. The electron-phonon scattering rates are obtained using Fermi’s Golden Rule and are used in a full-band Monte Carlo computer program to solve the Boltzmann transport equation (BTE) to evaluate the intrinsic low-field mobility and velocity-field characteristic. The electron-phonon matrix elements, accounting for both long- and short-range interactions, are considered to study the contributions of different scattering mechanisms. Since monolayer InSe is a polar piezoelectric material, scattering with optical phonons is dominated by the long-range interaction with longitudinal optical (LO) phonons while scattering with acoustic phonons is dominated by piezoelectric scattering with the longitudinal (LA) branch at room temperature (T = 300 K) due to a lack of a center of inversion symmetry in monolayer InSe. The low-field electron mobility, calculated considering all electron-phonon interactions, is found to be 110 cm²V⁻¹s⁻¹, whereas values of 188 cm²V⁻¹s⁻¹ and 365 cm²V⁻¹s⁻¹ are obtained considering the long-range and short-range interactions separately. Therefore, the calculated electron mobility of monolayer InSe seems to be competitive with other previously studied 2D materials and the piezoelectric properties of monolayer InSe make it a suitable material for a wide range of applications in next generation nanoelectronics. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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15 pages, 6214 KiB

Open AccessFeature PaperArticle

Electronic Transport Properties of Silicane Determined from First Principles

by Mohammad Mahdi Khatami, Gautam Gaddemane, Maarten L. Van de Put, Massimo V. Fischetti, Mohammad Kazem Moravvej-Farshi, Mahdi Pourfath and William G. Vandenberghe

Materials 2019, 12(18), 2935; https://doi.org/10.3390/ma12182935 - 11 Sep 2019

Cited by 16 | Viewed by 4296

Abstract

Silicane, a hydrogenated monolayer of hexagonal silicon, is a candidate material for future complementary metal-oxide-semiconductor technology. We determined the phonon-limited mobility and the velocity-field characteristics for electrons and holes in silicane from first principles, relying on density functional theory. Transport calculations were performed using a full-band Monte Carlo scheme. Scattering rates were determined from interpolated electron–phonon matrix elements determined from density functional perturbation theory. We found that the main source of scattering for electrons and holes was the ZA phonons. Different cut-off wavelengths ranging from 0.58 nm to 16 nm were used to study the possible suppression of the out-of-plane acoustic (ZA) phonons. The low-field mobility of electrons (holes) was obtained as 5 (10) cm²/(Vs) with a long wavelength ZA phonon cut-off of 16 nm. We showed that higher electron (hole) mobilities of 24 (101) cm²/(Vs) can be achieved with a cut-off wavelength of 4 nm, while completely suppressing ZA phonons results in an even higher electron (hole) mobility of 53 (109) cm²/(Vs). Velocity-field characteristics showed velocity saturation at 3 × 10⁵ V/cm, and negative differential mobility was observed at larger fields. The silicane mobility was competitive with other two-dimensional materials, such as transition-metal dichalcogenides or phosphorene, predicted using similar full-band Monte Carlo calculations. Therefore, silicon in its most extremely scaled form remains a competitive material for future nanoscale transistor technology, provided scattering with out-of-plane acoustic phonons could be suppressed. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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13 pages, 9064 KiB

Open AccessArticle

New Findings on Multilayer Silicene on Si(111)√3×√3R30°–Ag Template

by Paola De Padova, Amanda Generosi, Barbara Paci, Carlo Ottaviani, Claudio Quaresima, Bruno Olivieri, Marek Kopciuszyński, Lucyna Żurawek, Ryszard Zdyb and Mariusz Krawiec

Materials 2019, 12(14), 2258; https://doi.org/10.3390/ma12142258 - 13 Jul 2019

Cited by 14 | Viewed by 4595

Abstract

We report new findings on multilayer silicene grown on Si(111)√3 × √3 R30°–Ag template, after the recent first compelling experimental evidence of its synthesis. Low-energy electron diffraction, reflection high-energy electron diffraction, and energy-dispersive grazing incidence X-ray diffraction measurements were performed to show up the fingerprints of √3 × √3 multilayer silicene. Angle-resolved photoemission spectroscopy displayed new features in the second surface Brillouin zone, attributed to the multilayer silicene on Si(111)√3 × √3 R30°–Ag. Band-structure dispersion theoretical calculations performed on a model of three honeycomb stacked layers, silicene grown on Si(111)√3 × √3 R30°-Ag surface confirm the experimental results. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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12 pages, 3400 KiB

Open AccessArticle

High-throughput Production of ZnO-MoS₂-Graphene Heterostructures for Highly Efficient Photocatalytic Hydrogen Evolution

by Haocong Dong, Junzhu Li, Mingguang Chen, Hongwei Wang, Xiaochuan Jiang, Yongguang Xiao, Bo Tian and Xixiang Zhang

Materials 2019, 12(14), 2233; https://doi.org/10.3390/ma12142233 - 11 Jul 2019

Cited by 39 | Viewed by 4714

Abstract

High-throughput production of highly efficient photocatalysts for hydrogen evolution remains a considerable challenge for materials scientists. Here, we produced extremely uniform high-quality graphene and molybdenum disulfide (MoS₂) nanoplatelets through the electrochemical-assisted liquid-phase exfoliation, out of which we subsequently fabricated MoS₂/graphene van der Waals heterostructures. Ultimately, zinc oxide (ZnO) nanoparticles were deposited into these two-dimensional heterostructures to produce an artificial ZnO/MoS₂/graphene nanocomposite. This new composite experimentally exhibited an excellent photocatalytic efficiency in hydrogen evolution under the sunlight illumination (

λ > 400 n m

), owing to the extremely high electron mobilities in graphene nanoplatelets and the significant visible-light absorptions of MoS₂. Moreover, due to the synergistic effects in MoS₂ and graphene, the lifetime of excited carriers increased dramatically, which considerably improved the photocatalytic efficiency of the ZnO/MoS₂/graphene heterostructure. We conclude that the novel artificial heterostructure presented here shows great potential for the high-efficient photocatalytic hydrogen generation and the high throughput production of visible-light photocatalysts for industrial applications. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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8 pages, 1542 KiB

Open AccessArticle

High Optical Response of Niobium-Doped WSe₂-Layered Crystals

by Hung-Pin Hsu, Der-Yuh Lin, Jhin-Jhong Jheng, Pin-Cheng Lin and Tsung-Shine Ko

Materials 2019, 12(7), 1161; https://doi.org/10.3390/ma12071161 - 10 Apr 2019

Cited by 7 | Viewed by 3928

Abstract

The optical properties of WSe₂-layered crystals doped with 0.5% niobium (Nb) grown by the chemical vapor transport method were characterized by piezoreflectance (PzR), photoconductivity (PC) spectroscopy, frequency-dependent photocurrent, and time-resolved photoresponse. With the incorporation of 0.5% Nb, the WSe₂ crystal showed slight blue shifts in the near band edge excitonic transitions and exhibited strongly enhanced photoresponsivity. Frequency-dependent photocurrent and time-resolved photoresponse were measured to explore the kinetic decay processes of carriers. Our results show the potential application of layered crystals for photodetection devices based on Nb-doped WSe₂-layered crystals. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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12 pages, 1584 KiB

Open AccessArticle

High-κ Dielectric on ReS₂: In-Situ Thermal Versus Plasma-Enhanced Atomic Layer Deposition of Al₂O₃

by Ava Khosravi, Rafik Addou, Massimo Catalano, Jiyoung Kim and Robert M. Wallace

Materials 2019, 12(7), 1056; https://doi.org/10.3390/ma12071056 - 30 Mar 2019

Cited by 15 | Viewed by 5726

Abstract

We report an excellent growth behavior of a high-κ dielectric on ReS₂, a two-dimensional (2D) transition metal dichalcogenide (TMD). The atomic layer deposition (ALD) of an Al₂O₃ thin film on the UV-Ozone pretreated surface of ReS₂ yields a pinhole free and conformal growth. In-situ half-cycle X-ray photoelectron spectroscopy (XPS) was used to monitor the interfacial chemistry and ex-situ atomic force microscopy (AFM) was used to evaluate the surface morphology. A significant enhancement in the uniformity of the Al₂O₃ thin film was deposited via plasma-enhanced atomic layer deposition (PEALD), while pinhole free Al₂O₃ was achieved using a UV-Ozone pretreatment. The ReS₂ substrate stays intact during all different experiments and processes without any formation of the Re oxide. This work demonstrates that a combination of the ALD process and the formation of weak S–O bonds presents an effective route for a uniform and conformal high-κ dielectric for advanced devices based on 2D materials. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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32 pages, 4212 KiB

Open AccessReview

Oxidic 2D Materials

by Oliver Dubnack and Frank A. Müller

Materials 2021, 14(18), 5213; https://doi.org/10.3390/ma14185213 - 10 Sep 2021

Cited by 3 | Viewed by 3864

Abstract

The possibility of producing stable thin films, only a few atomic layers thick, from a variety of materials beyond graphene has led to two-dimensional (2D) materials being studied intensively in recent years. By reducing the layer thickness and approaching the crystallographic monolayer limit, a variety of unexpected and technologically relevant property phenomena were observed, which also depend on the subsequent arrangement and possible combination of individual layers to form heterostructures. These properties can be specifically used for the development of multifunctional devices, meeting the requirements of the advancing miniaturization of modern manufacturing technologies and the associated need to stabilize physical states even below critical layer thicknesses of conventional materials in the fields of electronics, magnetism and energy conversion. Differences in the structure of potential two-dimensional materials result in decisive influences on possible growth methods and possibilities for subsequent transfer of the thin films. In this review, we focus on recent advances in the rapidly growing field of two-dimensional materials, highlighting those with oxidic crystal structure like perovskites, garnets and spinels. In addition to a selection of well-established growth techniques and approaches for thin film transfer, we evaluate in detail their application potential as free-standing monolayers, bilayers and multilayers in a wide range of advanced technological applications. Finally, we provide suggestions for future developments of this promising research field in consideration of current challenges regarding scalability and structural stability of ultra-thin films. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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27 pages, 7261 KiB

Open AccessFeature PaperReview

Recent Progress in the Synthesis of MoS₂ Thin Films for Sensing, Photovoltaic and Plasmonic Applications: A Review

by Driss Mouloua, Ahmed Kotbi, Geetanjali Deokar, Khaled Kaja, Mimoun El Marssi, My Ali EL Khakani and Mustapha Jouiad

Materials 2021, 14(12), 3283; https://doi.org/10.3390/ma14123283 - 14 Jun 2021

Cited by 50 | Viewed by 9784

Abstract

In the surge of recent successes of 2D materials following the rise of graphene, molybdenum disulfide (2D-MoS₂) has been attracting growing attention from both fundamental and applications viewpoints, owing to the combination of its unique nanoscale properties. For instance, the bandgap of 2D-MoS₂, which changes from direct (in the bulk form) to indirect for ultrathin films (few layers), offers new prospects for various applications in optoelectronics. In this review, we present the latest scientific advances in the field of synthesis and characterization of 2D-MoS₂ films while highlighting some of their applications in energy harvesting, gas sensing, and plasmonic devices. A survey of the physical and chemical processing routes of 2D-MoS₂ is presented first, followed by a detailed description and listing of the most relevant characterization techniques used to study the MoS₂ nanomaterial as well as theoretical simulations of its interesting optical properties. Finally, the challenges related to the synthesis of high quality and fairly controllable MoS₂ thin films are discussed along with their integration into novel functional devices. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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34 pages, 68534 KiB

Open AccessReview

MoS₂/h-BN/Graphene Heterostructure and Plasmonic Effect for Self-Powering Photodetector: A Review

by Umahwathy Sundararaju, Muhammad Aniq Shazni Mohammad Haniff, Pin Jern Ker and P. Susthitha Menon

Materials 2021, 14(7), 1672; https://doi.org/10.3390/ma14071672 - 29 Mar 2021

Cited by 26 | Viewed by 7111

Abstract

A photodetector converts optical signals to detectable electrical signals. Lately, self-powered photodetectors have been widely studied because of their advantages in device miniaturization and low power consumption, which make them preferable in various applications, especially those related to green technology and flexible electronics. Since self-powered photodetectors do not have an external power supply at zero bias, it is important to ensure that the built-in potential in the device produces a sufficiently thick depletion region that efficiently sweeps the carriers across the junction, resulting in detectable electrical signals even at very low-optical power signals. Therefore, two-dimensional (2D) materials are explored as an alternative to silicon-based active regions in the photodetector. In addition, plasmonic effects coupled with self-powered photodetectors will further enhance light absorption and scattering, which contribute to the improvement of the device’s photocurrent generation. Hence, this review focuses on the employment of 2D materials such as graphene and molybdenum disulfide (MoS₂) with the insertion of hexagonal boron nitride (h-BN) and plasmonic nanoparticles. All these approaches have shown performance improvement of photodetectors for self-powering applications. A comprehensive analysis encompassing 2D material characterization, theoretical and numerical modelling, device physics, fabrication and characterization of photodetectors with graphene/MoS₂ and graphene/h-BN/MoS₂ heterostructures with plasmonic effect is presented with potential leads to new research opportunities. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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19 pages, 3207 KiB

Open AccessFeature PaperReview

Contacts for Molybdenum Disulfide: Interface Chemistry and Thermal Stability

by Keren M. Freedy and Stephen J. McDonnell

Materials 2020, 13(3), 693; https://doi.org/10.3390/ma13030693 - 4 Feb 2020

Cited by 11 | Viewed by 5037

Abstract

In this review on contacts with MoS₂, we consider reports on both interface chemistry and device characteristics. We show that there is considerable disagreement between reported properties, at least some of which may be explained by variability in the properties of geological MoS₂. Furthermore, we highlight that while early experiments using photoemission to study the interface behavior of metal-MoS₂ showed a lack of Fermi-level pinning, device measurements repeatedly confirm that the interface is indeed pinned. Here we suggest that a parallel conduction mechanism enabled by metallic defects in the MoS₂ materials may explain both results. We note that processing conditions during metal depositions on MoS₂ can play a critical role in the interface chemistry, with differences between high vacuum and ultra-high vacuum being particularly important for low work function metals. This can be used to engineer the interfaces by using thin metal-oxide interlayers to protect the MoS₂ from reactions with the metals. We also report on the changes in the interfaces that can occur at high temperature which include enhanced reactions between Ti or Cr and MoS₂, diffusion of Ag into MoS₂, and delamination of Fe. What is clear is that there is a dearth of experimental work that investigates both the interface chemistry and device properties in parallel. Full article

(This article belongs to the Special Issue 2D Materials for Advanced Devices)

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