Editorial

4 pages, 180 KiB

Open AccessEditorial

Special Issue “Fundamentals and Recent Advances in Epitaxial Graphene on SiC”

by Ivan Shtepliuk and Rositsa Yakimova

Appl. Sci. 2021, 11(8), 3381; https://doi.org/10.3390/app11083381 - 09 Apr 2021

Cited by 4 | Viewed by 1334

The aim of this Special Issue is to provide a scientific platform for recognized experts in the field of epitaxial graphene on SiC to present their recent studies towards a deeper comprehension of growth mechanisms, property engineering and device processing. This Special Issue [...] Read more.

The aim of this Special Issue is to provide a scientific platform for recognized experts in the field of epitaxial graphene on SiC to present their recent studies towards a deeper comprehension of growth mechanisms, property engineering and device processing. This Special Issue gives readers the possibility to gain new insights into the nature of buffer layer formation, control of electronic properties of graphene and usage of epitaxial graphene as a substrate for deposition of different substances, including metals and insulators. We believe that the papers published within the current Special Issue develop cumulative knowledge on matters related to device-quality epaxial graphene on SiC, bringing this material closer to realistic practical applications. Full article

(This article belongs to the Special Issue Fundamentals and Recent Advances in Epitaxial Graphene on SiC)

Research

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16 pages, 1356 KiB

Open AccessFeature PaperArticle

Critical View on Buffer Layer Formation and Monolayer Graphene Properties in High-Temperature Sublimation

by Vallery Stanishev, Nerijus Armakavicius, Chamseddine Bouhafs, Camilla Coletti, Philipp Kühne, Ivan G. Ivanov, Alexei A. Zakharov, Rositsa Yakimova and Vanya Darakchieva

Appl. Sci. 2021, 11(4), 1891; https://doi.org/10.3390/app11041891 - 21 Feb 2021

Cited by 3 | Viewed by 2415

Abstract

In this work we have critically reviewed the processes in high-temperature sublimation growth of graphene in Ar atmosphere using closed graphite crucible. Special focus is put on buffer layer formation and free charge carrier properties of monolayer graphene and quasi-freestanding monolayer graphene on [...] Read more.

In this work we have critically reviewed the processes in high-temperature sublimation growth of graphene in Ar atmosphere using closed graphite crucible. Special focus is put on buffer layer formation and free charge carrier properties of monolayer graphene and quasi-freestanding monolayer graphene on 4H–SiC. We show that by introducing Ar at higher temperatures,

T_{Ar}

, one can shift the formation of the buffer layer to higher temperatures for both n-type and semi-insulating substrates. A scenario explaining the observed suppressed formation of buffer layer at higher

T_{Ar}

is proposed and discussed. Increased

T_{Ar}

is also shown to reduce the

s p^{3}

hybridization content and defect densities in the buffer layer on n-type conductive substrates. Growth on semi-insulating substrates results in ordered buffer layer with significantly improved structural properties, for which

T_{Ar}

plays only a minor role. The free charge density and mobility parameters of monolayer graphene and quasi-freestanding monolayer graphene with different

T_{Ar}

and different environmental treatment conditions are determined by contactless terahertz optical Hall effect. An efficient annealing of donors on and near the SiC surface is suggested to take place for intrinsic monolayer graphene grown at 2000

^{\circ}

C, and which is found to be independent of

T_{Ar}

. Higher

T_{Ar}

leads to higher free charge carrier mobility parameters in both intrinsically n-type and ambient p-type doped monolayer graphene.

T_{Ar}

is also found to have a profound effect on the free hole parameters of quasi-freestanding monolayer graphene. These findings are discussed in view of interface and buffer layer properties in order to construct a comprehensive picture of high-temperature sublimation growth and provide guidance for growth parameters optimization depending on the targeted graphene application. Full article

(This article belongs to the Special Issue Fundamentals and Recent Advances in Epitaxial Graphene on SiC)

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12 pages, 2268 KiB

Open AccessArticle

Structural Modifications in Epitaxial Graphene on SiC Following 10 keV Nitrogen Ion Implantation

by Priya Darshni Kaushik, Gholam Reza Yazdi, Garimella Bhaskara Venkata Subba Lakshmi, Grzegorz Greczynski, Rositsa Yakimova and Mikael Syväjärvi

Appl. Sci. 2020, 10(11), 4013; https://doi.org/10.3390/app10114013 - 10 Jun 2020

Cited by 8 | Viewed by 2467

Abstract

Modification of epitaxial graphene on silicon carbide (EG/SiC) was explored by ion implantation using 10 keV nitrogen ions. Fragments of monolayer graphene along with nanostructures were observed following nitrogen ion implantation. At the initial fluence, sp³ defects appeared in EG; higher fluences [...] Read more.

Modification of epitaxial graphene on silicon carbide (EG/SiC) was explored by ion implantation using 10 keV nitrogen ions. Fragments of monolayer graphene along with nanostructures were observed following nitrogen ion implantation. At the initial fluence, sp³ defects appeared in EG; higher fluences resulted in vacancy defects as well as in an increased defect density. The increased fluence created a decrease in the intensity of the prominent peak of SiC as well as of the overall relative Raman intensity. The X-ray photoelectron spectroscopy (XPS) showed a reduction of the peak intensity of graphitic carbon and silicon carbide as a result of ion implantation. The dopant concentration and level of defects could be controlled both in EG and SiC by the fluence. This provided an opportunity to explore EG/SiC as a platform using ion implantation to control defects, and to be applied for fabricating sensitive sensors and nanoelectronics devices with high performance. Full article

(This article belongs to the Special Issue Fundamentals and Recent Advances in Epitaxial Graphene on SiC)

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12 pages, 1054 KiB

Open AccessArticle

Raman 2D Peak Line Shape in Epigraphene on SiC

by Jan Kunc and Martin Rejhon

Appl. Sci. 2020, 10(7), 2354; https://doi.org/10.3390/app10072354 - 30 Mar 2020

Cited by 5 | Viewed by 3303

Abstract

We measured a 2D peak line shape of epitaxial graphene grown on SiC in high vacuum, argon and graphene prepared by hydrogen intercalation from the so called buffer layer on a silicon face of SiC. We fitted the 2D peaks by Lorentzian and [...] Read more.

We measured a 2D peak line shape of epitaxial graphene grown on SiC in high vacuum, argon and graphene prepared by hydrogen intercalation from the so called buffer layer on a silicon face of SiC. We fitted the 2D peaks by Lorentzian and Voigt line shapes. The detailed analysis revealed that the Voigt line shape describes the 2D peak line shape better. We have determined the contribution of the homogeneous and inhomogeneous broadening. The homogeneous broadening is attributed to the intrinsic lifetime. Although the inhomogeneous broadening can be attributed to the spatial variations of the charge density, strain and overgrown graphene ribbons on the sub-micrometer length scales, we found dominant contribution of the strain fluctuations. The quasi free-standing graphene grown by hydrogen intercalation is shown to have the narrowest linewidth due to both homogeneous and inhomogeneous broadening. Full article

(This article belongs to the Special Issue Fundamentals and Recent Advances in Epitaxial Graphene on SiC)

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15 pages, 2520 KiB

Open AccessArticle

Electrochemical Deposition of Copper on Epitaxial Graphene

by Ivan Shtepliuk, Mikhail Vagin and Rositsa Yakimova

Appl. Sci. 2020, 10(4), 1405; https://doi.org/10.3390/app10041405 - 19 Feb 2020

Cited by 14 | Viewed by 5361

Abstract

Understanding the mechanism of metal electrodeposition on graphene as the simplest building block of all graphitic materials is important for electrocatalysis and the creation of metal contacts in electronics. The present work investigates copper electrodeposition onto epitaxial graphene on 4H-SiC by experimental and [...] Read more.

Understanding the mechanism of metal electrodeposition on graphene as the simplest building block of all graphitic materials is important for electrocatalysis and the creation of metal contacts in electronics. The present work investigates copper electrodeposition onto epitaxial graphene on 4H-SiC by experimental and computational techniques. The two subsequent single-electron transfer steps were coherently quantified by electrochemistry and density functional theory (DFT). The kinetic measurements revealed the instantaneous nucleation mechanism of copper (Cu) electrodeposition, controlled by the convergent diffusion of reactant to the limited number of nucleation sites. Cu can freely migrate across the electrode surface. These findings provide fundamental insights into the nature of copper reduction and nucleation mechanisms and can be used as a starting point for performing more sophisticated investigations and developing real applications. Full article

(This article belongs to the Special Issue Fundamentals and Recent Advances in Epitaxial Graphene on SiC)

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Review

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19 pages, 4138 KiB

Open AccessReview

Twistronics in Graphene, from Transfer Assembly to Epitaxy

by Di Wu, Yi Pan and Tai Min

Appl. Sci. 2020, 10(14), 4690; https://doi.org/10.3390/app10144690 - 08 Jul 2020

Cited by 9 | Viewed by 4833

Abstract

The twistronics, which is arising from the moiré superlattice of the small angle between twisted bilayers of 2D materials like graphene, has attracted much attention in the field of 2D materials and condensed matter physics. The novel physical properties in such systems, like [...] Read more.

The twistronics, which is arising from the moiré superlattice of the small angle between twisted bilayers of 2D materials like graphene, has attracted much attention in the field of 2D materials and condensed matter physics. The novel physical properties in such systems, like unconventional superconductivity, come from the dispersionless flat band that appears when the twist reaches some magic angles. By tuning the filling of the fourfold degeneracy flat bands, the desired effects are induced due to the strong correlation of the degenerated Bloch electrons. In this article, we review the twistronics in twisted bi- and multi-layer graphene (TBG and TMG), which is formed both by transfer assembly of exfoliated monolayer graphene and epitaxial growth of multilayer graphene on SiC substrates. Starting from a brief history, we then introduce the theory of flat band in TBG. In the following, we focus on the major achievements in this field: (a) van Hove singularities and charge order; (b) superconductivity and Mott insulator in TBG and (c) transport properties in TBG. In the end, we give the perspective of the rising materials system of twistronics, epitaxial multilayer graphene on the SiC. Full article

(This article belongs to the Special Issue Fundamentals and Recent Advances in Epitaxial Graphene on SiC)

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32 pages, 6981 KiB

Open AccessReview

Electronic and Transport Properties of Epitaxial Graphene on SiC and 3C-SiC/Si: A Review

by Aiswarya Pradeepkumar, D. Kurt Gaskill and Francesca Iacopi

Appl. Sci. 2020, 10(12), 4350; https://doi.org/10.3390/app10124350 - 24 Jun 2020

Cited by 12 | Viewed by 4252

Abstract

The electronic and transport properties of epitaxial graphene are dominated by the interactions the material makes with its surroundings. Based on the transport properties of epitaxial graphene on SiC and 3C-SiC/Si substrates reported in the literature, we emphasize that the graphene interfaces formed [...] Read more.

The electronic and transport properties of epitaxial graphene are dominated by the interactions the material makes with its surroundings. Based on the transport properties of epitaxial graphene on SiC and 3C-SiC/Si substrates reported in the literature, we emphasize that the graphene interfaces formed between the active material and its environment are of paramount importance, and how interface modifications enable the fine-tuning of the transport properties of graphene. This review provides a renewed attention on the understanding and engineering of epitaxial graphene interfaces for integrated electronics and photonics applications. Full article

(This article belongs to the Special Issue Fundamentals and Recent Advances in Epitaxial Graphene on SiC)

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20 pages, 2618 KiB

Open AccessFeature PaperReview

Atomic Layer Deposition of High-k Insulators on Epitaxial Graphene: A Review

by Filippo Giannazzo, Emanuela Schilirò, Raffaella Lo Nigro, Fabrizio Roccaforte and Rositsa Yakimova

Appl. Sci. 2020, 10(7), 2440; https://doi.org/10.3390/app10072440 - 03 Apr 2020

Cited by 15 | Viewed by 3654

Abstract

Due to its excellent physical properties and availability directly on a semiconductor substrate, epitaxial graphene (EG) grown on the (0001) face of hexagonal silicon carbide is a material of choice for advanced applications in electronics, metrology and sensing. The deposition of ultrathin high-k [...] Read more.

Due to its excellent physical properties and availability directly on a semiconductor substrate, epitaxial graphene (EG) grown on the (0001) face of hexagonal silicon carbide is a material of choice for advanced applications in electronics, metrology and sensing. The deposition of ultrathin high-k insulators on its surface is a key requirement for the fabrication of EG-based devices, and, in this context, atomic layer deposition (ALD) is the most suitable candidate to achieve uniform coating with nanometric thickness control. This paper presents an overview of the research on ALD of high-k insulators on EG, with a special emphasis on the role played by the peculiar electrical/structural properties of the EG/SiC (0001) interface in the nucleation step of the ALD process. The direct deposition of Al₂O₃ thin films on the pristine EG surface will be first discussed, demonstrating the critical role of monolayer EG uniformity to achieve a homogeneous Al₂O₃ coverage. Furthermore, the ALD of several high-k materials on EG coated with different seeding layers (oxidized metal films, directly deposited metal-oxides and self-assembled organic monolayers) or subjected to various prefunctionalization treatments (e.g., ozone or fluorine treatments) will be presented. The impact of the pretreatments and of thermal ALD growth on the defectivity and electrical properties (doping and carrier mobility) of the underlying EG will be discussed. Full article

(This article belongs to the Special Issue Fundamentals and Recent Advances in Epitaxial Graphene on SiC)

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