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2515 KiB

Open AccessArticle

Thermal Stability of Epitaxial Graphene Electrodes for Conductive Polymer Nanofiber Devices

by Kyung Ho Kim, Samuel Lara-Avila, Hans He, Hojin Kang, Yung Woo Park, Rositsa Yakimova and Sergey Kubatkin

Crystals 2017, 7(12), 378; https://doi.org/10.3390/cryst7120378 - 14 Dec 2017

Cited by 3 | Viewed by 3793

Abstract

We used large area, monolayer graphene epitaxially grown on SiC (0001) as contact electrodes for polymer nanofiber devices. Our fabrication process, which avoids polymer resist residues on the graphene surface, results in graphene-polyaniline nanofiber devices with Ohmic contacts and electrical conductivity comparable to [...] Read more.

We used large area, monolayer graphene epitaxially grown on SiC (0001) as contact electrodes for polymer nanofiber devices. Our fabrication process, which avoids polymer resist residues on the graphene surface, results in graphene-polyaniline nanofiber devices with Ohmic contacts and electrical conductivity comparable to that of Au-nanofiber devices. We further checked the thermal stability of the graphene contacts to polyaniline devices by annealing up to T = 800 °C, the temperature at which polyaniline nanofibers are carbonized but the graphene electrode remains intact. The thermal stability and Ohmic contact of polymer nanofibers are demonstrated here, which together with the chemical stability and atomic flatness of graphene, make epitaxial graphene on SiC an attractive contact material for future all-carbon electronic devices. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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Review

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84 pages, 10402 KiB

Open AccessFeature PaperReview

Progress in Contact, Doping and Mobility Engineering of MoS₂: An Atomically Thin 2D Semiconductor

by Amritesh Rai, Hema C. P. Movva, Anupam Roy, Deepyanti Taneja, Sayema Chowdhury and Sanjay K. Banerjee

Crystals 2018, 8(8), 316; https://doi.org/10.3390/cryst8080316 - 06 Aug 2018

Cited by 125 | Viewed by 27520

Abstract

Atomically thin molybdenum disulfide (MoS₂), a member of the transition metal dichalcogenide (TMDC) family, has emerged as the prototypical two-dimensional (2D) semiconductor with a multitude of interesting properties and promising device applications spanning all realms of electronics and optoelectronics. While possessing [...] Read more.

Atomically thin molybdenum disulfide (MoS₂), a member of the transition metal dichalcogenide (TMDC) family, has emerged as the prototypical two-dimensional (2D) semiconductor with a multitude of interesting properties and promising device applications spanning all realms of electronics and optoelectronics. While possessing inherent advantages over conventional bulk semiconducting materials (such as Si, Ge and III-Vs) in terms of enabling ultra-short channel and, thus, energy efficient field-effect transistors (FETs), the mechanically flexible and transparent nature of MoS₂ makes it even more attractive for use in ubiquitous flexible and transparent electronic systems. However, before the fascinating properties of MoS₂ can be effectively harnessed and put to good use in practical and commercial applications, several important technological roadblocks pertaining to its contact, doping and mobility (µ) engineering must be overcome. This paper reviews the important technologically relevant properties of semiconducting 2D TMDCs followed by a discussion of the performance projections of, and the major engineering challenges that confront, 2D MoS₂-based devices. Finally, this review provides a comprehensive overview of the various engineering solutions employed, thus far, to address the all-important issues of contact resistance (R_C), controllable and area-selective doping, and charge carrier mobility enhancement in these devices. Several key experimental and theoretical results are cited to supplement the discussions and provide further insight. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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25 pages, 4516 KiB

Open AccessReview

Vertical Transistors Based on 2D Materials: Status and Prospects

by Filippo Giannazzo, Giuseppe Greco, Fabrizio Roccaforte and Sushant S. Sonde

Crystals 2018, 8(2), 70; https://doi.org/10.3390/cryst8020070 - 31 Jan 2018

Cited by 68 | Viewed by 12616

Abstract

Two-dimensional (2D) materials, such as graphene (Gr), transition metal dichalcogenides (TMDs) and hexagonal boron nitride (h-BN), offer interesting opportunities for the implementation of vertical transistors for digital and high-frequency electronics. This paper reviews recent developments in this field, presenting the main vertical device [...] Read more.

Two-dimensional (2D) materials, such as graphene (Gr), transition metal dichalcogenides (TMDs) and hexagonal boron nitride (h-BN), offer interesting opportunities for the implementation of vertical transistors for digital and high-frequency electronics. This paper reviews recent developments in this field, presenting the main vertical device architectures based on 2D/2D or 2D/3D material heterostructures proposed so far. For each of them, the working principles and the targeted application field are discussed. In particular, tunneling field effect transistors (TFETs) for beyond-CMOS low power digital applications are presented, including resonant tunneling transistors based on Gr/h-BN/Gr stacks and band-to-band tunneling transistors based on heterojunctions of different semiconductor layered materials. Furthermore, recent experimental work on the implementation of the hot electron transistor (HET) with the Gr base is reviewed, due to the predicted potential of this device for ultra-high frequency operation in the THz range. Finally, the material sciences issues and the open challenges for the realization of 2D material-based vertical transistors at a large scale for future industrial applications are discussed. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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2878 KiB

Open AccessReview

Van der Waals Heterostructure Based Field Effect Transistor Application

by Jingyu Li, Xiaozhang Chen, David Wei Zhang and Peng Zhou

Crystals 2018, 8(1), 8; https://doi.org/10.3390/cryst8010008 - 26 Dec 2017

Cited by 25 | Viewed by 15310

Abstract

Van der Waals heterostructure is formed by two-dimensional materials, which applications have become hot topics and received intensive exploration for fabricating without lattice mismatch. With the sustained decrease in dimensions of field effect transistors, van der Waals heterostructure plays an important role in [...] Read more.

Van der Waals heterostructure is formed by two-dimensional materials, which applications have become hot topics and received intensive exploration for fabricating without lattice mismatch. With the sustained decrease in dimensions of field effect transistors, van der Waals heterostructure plays an important role in improving the performance of devices because of its prominent electronic and optoelectronic behavior. In this review, we discuss the process of assembling van der Waals heterostructures and thoroughly illustrate the applications based on van der Waals heterostructures. We also present recent innovation in field effect transistors and van der Waals stacks, and offer an outlook of the development in improving the performance of devices based on van der Waals heterostructures. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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8678 KiB

Open AccessReview

Graphene Coated Nanoprobes: A Review

by Fei Hui, Shaochuan Chen, Xianhu Liang, Bin Yuan, Xu Jing, Yuanyuan Shi and Mario Lanza

Crystals 2017, 7(9), 269; https://doi.org/10.3390/cryst7090269 - 08 Sep 2017

Cited by 16 | Viewed by 6556

Abstract

Nanoprobes are one of the most important components in several fields of nanoscience to study materials, molecules and particles. In scanning probe microscopes, the nanoprobes consist on silicon tips coated with thin metallic films to provide additional properties, such as conductivity. However, if [...] Read more.

Nanoprobes are one of the most important components in several fields of nanoscience to study materials, molecules and particles. In scanning probe microscopes, the nanoprobes consist on silicon tips coated with thin metallic films to provide additional properties, such as conductivity. However, if the experiments involve high currents or lateral frictions, the initial properties of the tips can wear out very fast. One possible solution is the use of hard coatings, such as diamond, or making the entire tip out of a precious material (platinum or diamond). However, this strategy is more expensive and the diamond coatings can damage the samples. In this context, the use of graphene as a protective coating for nanoprobes has attracted considerable interest. Here we review the main literature in this field, and discuss the fabrication, performance and scalability of nanoprobes. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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17726 KiB

Open AccessReview

A Review on Metal Nanoparticles Nucleation and Growth on/in Graphene

by Francesco Ruffino and Filippo Giannazzo

Crystals 2017, 7(7), 219; https://doi.org/10.3390/cryst7070219 - 13 Jul 2017

Cited by 35 | Viewed by 8779

Abstract

In this review, the fundamental aspects (with particular focus to the microscopic thermodynamics and kinetics mechanisms) concerning the fabrication of graphene-metal nanoparticles composites are discussed. In particular, the attention is devoted to those fabrication methods involving vapor-phase depositions of metals on/in graphene-based materials. [...] Read more.

In this review, the fundamental aspects (with particular focus to the microscopic thermodynamics and kinetics mechanisms) concerning the fabrication of graphene-metal nanoparticles composites are discussed. In particular, the attention is devoted to those fabrication methods involving vapor-phase depositions of metals on/in graphene-based materials. Graphene-metal nanoparticles composites are, nowadays, widely investigated both from a basic scientific and from several technological point of views. In fact, these graphene-based systems present wide-range tunable and functional electrical, optical, and mechanical properties which can be exploited for the design and production of innovative and high-efficiency devices. This research field is, so, a wide and multidisciplinary section in the nanotechnology field of study. So, this review aims to discuss, in a synthetic and systematic framework, the basic microscopic mechanisms and processes involved in metal nanoparticles formation on graphene sheets by physical vapor deposition methods and on their evolution by post-deposition processes. This is made by putting at the basis of the discussions some specific examples to draw insights on the common general physical and chemical properties and parameters involved in the synergistic interaction processes between graphene and metals. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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1669 KiB

Open AccessReview

Advanced Scanning Probe Microscopy of Graphene and Other 2D Materials

by Chiara Musumeci

Crystals 2017, 7(7), 216; https://doi.org/10.3390/cryst7070216 - 11 Jul 2017

Cited by 27 | Viewed by 14320

Abstract

Two-dimensional (2D) materials, such as graphene and metal dichalcogenides, are an emerging class of materials, which hold the promise to enable next-generation electronics. Features such as average flake size, shape, concentration, and density of defects are among the most significant properties affecting these [...] Read more.

Two-dimensional (2D) materials, such as graphene and metal dichalcogenides, are an emerging class of materials, which hold the promise to enable next-generation electronics. Features such as average flake size, shape, concentration, and density of defects are among the most significant properties affecting these materials’ functions. Because of the nanoscopic nature of these features, a tool performing morphological and functional characterization on this scale is required. Scanning Probe Microscopy (SPM) techniques offer the possibility to correlate morphology and structure with other significant properties, such as opto-electronic and mechanical properties, in a multilevel characterization at atomic- and nanoscale. This review gives an overview of the different SPM techniques used for the characterization of 2D materials. A basic introduction of the working principles of these methods is provided along with some of the most significant examples reported in the literature. Particular attention is given to those techniques where the scanning probe is not used as a simple imaging tool, but rather as a force sensor with very high sensitivity and resolution. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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2571 KiB

Open AccessReview

Synthesis Methods of Two-Dimensional MoS₂: A Brief Review

by Jie Sun, Xuejian Li, Weiling Guo, Miao Zhao, Xing Fan, Yibo Dong, Chen Xu, Jun Deng and Yifeng Fu

Crystals 2017, 7(7), 198; https://doi.org/10.3390/cryst7070198 - 01 Jul 2017

Cited by 147 | Viewed by 25579

Abstract

Molybdenum disulfide (MoS₂) is one of the most important two-dimensional materials after graphene. Monolayer MoS₂ has a direct bandgap (1.9 eV) and is potentially suitable for post-silicon electronics. Among all atomically thin semiconductors, MoS₂’s synthesis techniques are more [...] Read more.

Molybdenum disulfide (MoS₂) is one of the most important two-dimensional materials after graphene. Monolayer MoS₂ has a direct bandgap (1.9 eV) and is potentially suitable for post-silicon electronics. Among all atomically thin semiconductors, MoS₂’s synthesis techniques are more developed. Here, we review the recent developments in the synthesis of hexagonal MoS₂, where they are categorized into top-down and bottom-up approaches. Micromechanical exfoliation is convenient for beginners and basic research. Liquid phase exfoliation and solutions for chemical processes are cheap and suitable for large-scale production; yielding materials mostly in powders with different shapes, sizes and layer numbers. MoS₂ films on a substrate targeting high-end nanoelectronic applications can be produced by chemical vapor deposition, compatible with the semiconductor industry. Usually, metal catalysts are unnecessary. Unlike graphene, the transfer of atomic layers is omitted. We especially emphasize the recent advances in metalorganic chemical vapor deposition and atomic layer deposition, where gaseous precursors are used. These processes grow MoS₂ with the smallest building-blocks, naturally promising higher quality and controllability. Most likely, this will be an important direction in the field. Nevertheless, today none of those methods reproducibly produces MoS₂ with competitive quality. There is a long way to go for MoS₂ in real-life electronic device applications. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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12621 KiB

Open AccessReview

Role of the Potential Barrier in the Electrical Performance of the Graphene/SiC Interface

by Ivan Shtepliuk, Tihomir Iakimov, Volodymyr Khranovskyy, Jens Eriksson, Filippo Giannazzo and Rositsa Yakimova

Crystals 2017, 7(6), 162; https://doi.org/10.3390/cryst7060162 - 02 Jun 2017

Cited by 28 | Viewed by 7963

Abstract

In spite of the great expectations for epitaxial graphene (EG) on silicon carbide (SiC) to be used as a next-generation high-performance component in high-power nano- and micro-electronics, there are still many technological challenges and fundamental problems that hinder the full potential of EG/SiC [...] Read more.

In spite of the great expectations for epitaxial graphene (EG) on silicon carbide (SiC) to be used as a next-generation high-performance component in high-power nano- and micro-electronics, there are still many technological challenges and fundamental problems that hinder the full potential of EG/SiC structures and that must be overcome. Among the existing problems, the quality of the graphene/SiC interface is one of the most critical factors that determines the electroactive behavior of this heterostructure. This paper reviews the relevant studies on the carrier transport through the graphene/SiC, discusses qualitatively the possibility of controllable tuning the potential barrier height at the heterointerface and analyses how the buffer layer formation affects the electronic properties of the combined EG/SiC system. The correlation between the sp²/sp³ hybridization ratio at the interface and the barrier height is discussed. We expect that the barrier height modulation will allow realizing a monolithic electronic platform comprising different graphene interfaces including ohmic contact, Schottky contact, gate dielectric, the electrically-active counterpart in p-n junctions and quantum wells. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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