Molecular Beam Epitaxy of Boron Nitride and Graphene layers and heterostructures.

Lead Research Organisation: University of Nottingham
Department Name: Sch of Physics & Astronomy

Abstract

We will grow high-quality, large-area epitaxial layers and heterostructures composed of boron nitride, graphene and related compounds using molecular beam epitaxy (MBE). These graphene/boron nitride heterostructures are members of a new class of multilayer ("vertical transport") electronic devices in which charge carriers can move perpendicular to the plane of the graphene layers. We will identify and optimise the conditions for growth of single atomic layers of boron nitride and graphene, followed by the programmed growth and processing of heterostructures in which single or multiple layers of graphene and boron nitride are grown sequentially to provide architectures by which new types of band-structure engineered functional device can be realised. In February 2013 EPSRC supported our proposed research by awarding us an Equipment Grant to purchase a custom designed molecular beam epitaxy (MBE) system dedicated to the growth of epitaxial layers and heterostructures composed of graphene and boron nitride. The University of Nottingham regards this project as strategically important and is supporting it by providing the cost of installation of the new MBE system and the initial running costs for 2 years. We are now applying for this new grant to secure the research staff (1.5 of PDRA) to run the proposed 3-year project.

Planned Impact

Who will benefit from the proposed research?
1) The UK academic and industrial community who are engaged in graphene engineering research will benefit by the provision of revolutionary, MBE grown graphene-based heterostructure materials and devices.
2) UK manufacturers of graphene based electronic, opto-electronic and spintronic devices.
3) Innovators in any field where graphene or boron nitride are required.
4) Members of the wider society, who can benefit from the novel device structures resulting from this new engineering project.

Together with a commercial manufacturer of MBE equipment, we will develop a custom-designed system for the growth of graphene/boron nitride heterostructures, which will be unique. If the project is successful, the MBE manufacturer will use this knowledge to develop production MBE systems for graphene based devices. The resulting production MBE systems will bring graphene research from University to Industry. This will enable the UK Industry to be in world-leading position for the manufacture of graphene-based devices.

Industrial and academic users will benefit from access to a wide range of high quality graphene-based heterostructure materials and devices produced in the unique, world-class, MBE facility. They will also benefit from the expertise and knowledge-base developed by the investigators, PDRAs and PhD students involved in this project. Production of the first graphene MBE layers at Nottingham in 2014 will coincide with the opening of the National Graphene Institute, whose scientists will therefore have access to our material.

In order to publicise our results we will, in addition to the standard forms of research dissemination in high profile journals, introduce a number of additional activities to highlight our research and the availability of our materials to potential third party collaborators. These will include the organisation of workshop in year 3, to disseminate the results of this project to other researchers on graphene, nitride and the wider academic and industrial semiconductor community within the UK. The availability of material for collaborators will be publicised at the Open Days and also through e-newsletters and national and international conferences.

We will visit UK companies to discuss results and to give seminars where requested. Researchers from Nottingham are active participants in the UK Nitride Consortium (UKNC) and we are a partner institution of the EPSRC National Centre for III-V Technologies (supplying spintronic material) and will exploit these links to ensure the maximum number of beneficiaries in the semiconductor community are aware of this research.

In addition to the impact arising from research outputs, we highlight the output of trained researchers, who will provide a new generation of talent for the developing industry related to graphene based electronic and optoelectronic materials.

The establishment of the new MBE growth facilities for graphene/boron nitride at Nottingham will provide a new source of material for graphene engineering in the UK Universities and Industry. This will generate new research programmes between Nottingham and other groups involved in graphene research within the UK.

Publications

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Cheng T (2018) High-temperature molecular beam epitaxy of hexagonal boron nitride layers in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena

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Cheng T (2016) High temperature MBE of graphene on sapphire and hexagonal boron nitride flakes on sapphire in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena

 
Description We have studied the high-temperature molecular beam epitaxy (MBE) of graphene and hBN monolayers. Graphene grown by high temperature MBE on hexagonal boron nitride (hBN) forms continuous domains with dimensions of order 20 µm, and exhibits moiré patterns with large periodicities, up to ~30 nm, indicating that the layers are highly strained. Topological defects in the moiré patterns are observed and attributed to the relaxation of graphene islands which nucleate at different sites and subsequently coalesce. In addition, cracks are formed leading to strain relaxation, highly anisotropic strain fields, and abrupt boundaries between regions with different moiré periods. These cracks can also be formed by modification of the layers with a local probe resulting in the contraction and physical displacement of graphene layers. The Raman spectra of regions with a large moiré period reveal split and shifted G and 2D peaks confirming the presence of strain. We report the use of a novel atomic carbon source for the MBE of graphene layers on hBN flakes and on sapphire wafers at substrate growth temperatures of 1400C. The source produces a flux of predominantly atomic carbon, which diffuses through the walls of a Joule-heated tantalum tube filled with graphite powder. We demonstrate deposition of carbon on sapphire with carbon deposition rates up to 12 nm/h. Atomic force microscopy measurements reveal the formation of hexagonal moiré patterns when graphene monolayers are grown on hBN flakes. The Raman spectra of the graphene layers grown on hBN and sapphire with the sublimation carbon source and the atomic carbon source are similar, whilst the nature of the carbon aggregates is different - graphitic with the sublimation carbon source and amorphous with the atomic carbon source.Our work demonstrates a new approach to the growth of epitaxial graphene and a means of generating and modifying strain in graphene. The growth and properties of hexagonal boron nitride (hBN) have recently attracted much attention due to applications in graphene-based monolayer thick two dimensional (2D)-structures and at the same time as a wide band gap material for deep-ultraviolet device (DUV) applications. Our results demonstrate that PA-MBE growth at temperatures 1400C can achieve mono- and few-layer thick hBN with a control of the hBN coverage and atomically flat hBN surfaces which is essential for 2D applications of hBN layers. The hBN monolayer coverage can be reproducible controlled by the PA-MBE growth temperature, time and B:N flux ratios. Significantly thicker hBN layers have been achieved at higher B:N flux ratios. However, by decreasing the MBE growth temperature below 1250C we observe a rapid degradation of the optical properties of hBN layers. Therefore, high-temperature PA-MBE, above 1250C is a viable approach for the growth of high-quality hBN layers for 2D and DUV applications.
Exploitation Route Lattice-matched graphene on hexagonal boron nitride is expected to lead to the formation of a band gap but requires the formation of highly strained material and has not been yet
realized. Our work demonstrates a new approach to the MBE growth of epitaxial graphene and a means of generating and modifying strain in graphene. The growth and properties of hexagonal boron nitride (hBN) have recently attracted much attention due to applications in graphene-based monolayer thick two dimensional (2D)-structures and at the same time as a wide band gap material for deep-ultraviolet device (DUV) applications. High-temperature PA-MBE, above 1250C is a viable approach for the growth of high-quality hBN layers for 2D and DUV applications.
Sectors Agriculture, Food and Drink,Digital/Communication/Information Technologies (including Software),Education,Electronics,Energy,Environment,Healthcare

 
Description Lattice-matched graphene on hexagonal boron nitride is expected to lead to the formation of a band gap but requires the formation of highly strained material and has not been yet realized. Our work demonstrates a new approach to the MBE growth of epitaxial graphene and a means of generating and modifying strain in graphene. The growth and properties of hexagonal boron nitride (hBN) have recently attracted much attention due to applications in graphene-based monolayer thick two dimensional (2D)-structures and at the same time as a wide band gap material for deep-ultraviolet device (DUV) applications. High-temperature PA-MBE, above 1250C is a viable approach for the growth of high-quality hBN layers for 2D and DUV applications. The development of group III nitrides allows researchers worldwide to consider AlGaN based light emitting diodes as a possible new alternative DUV light source for water purification and surface decontamination. Hexagonal boron nitride has a potential advantage over AlGaN in such DUV structures due to the possibility of more efficient p- and n-doping.
First Year Of Impact 2016
Sector Agriculture, Food and Drink,Creative Economy,Digital/Communication/Information Technologies (including Software),Education,Electronics,Energy,Environment
Impact Types Economic

 
Description Leverhulme Trust Research Grant
Amount £132,073 (GBP)
Organisation The Leverhulme Trust 
Sector Academic/University
Country United Kingdom
Start 02/2015 
End 02/2018
 
Description Strain-engineered graphene: growth, modification and electronic properties
Amount £910,916 (GBP)
Funding ID EP/P019080/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 02/2017 
End 01/2020
 
Description Prof Novikov's video press release 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Prof Novikov's video press release, prepared by Nottingham press office for the Opening Day of the graphene MBE facilities on the 08.01.2015 (https://mediaspace.nottingham.ac.uk/media/Growing+graphene+%E2%80%93+blue+sky+research+attempts+to+replicate+nature/1_rwzc7u6k/ or
on YouTube https://www.youtube.com/watch?v=A6obEfjWj3Y
Year(s) Of Engagement Activity 2015
URL https://www.youtube.com/watch?v=A6obEfjWj3Y