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.
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.
Organisations
Publications
Novikov S
(2017)
Unintentional boron incorporation in AlGaN layers grown by plasma-assisted MBE using highly efficient nitrogen RF plasma-sources
in Journal of Crystal Growth
Pierucci D
(2018)
Van der Waals epitaxy of two-dimensional single-layer h-BN on graphite by molecular beam epitaxy: Electronic properties and band structure
in Applied Physics Letters
Román R
(2021)
Band gap measurements of monolayer h-BN and insights into carbon-related point defects
in 2D Materials
Summerfield A
(2018)
Moiré-Modulated Conductance of Hexagonal Boron Nitride Tunnel Barriers.
in Nano letters
Summerfield A
(2016)
Erratum: Strain-Engineered Graphene Grown on Hexagonal Boron Nitride by Molecular Beam Epitaxy.
in Scientific reports
Summerfield A
(2016)
Strain-Engineered Graphene Grown on Hexagonal Boron Nitride by Molecular Beam Epitaxy.
in Scientific reports
Thomas J
(2020)
Step-flow growth of graphene-boron nitride lateral heterostructures by molecular beam epitaxy
in 2D Materials
Vuong T
(2017)
Deep ultraviolet emission in hexagonal boron nitride grown by high-temperature molecular beam epitaxy
in 2D Materials
Wrigley J
(2021)
Epitaxy of boron nitride monolayers for graphene-based lateral heterostructures
in 2D Materials
| 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 (hBN) 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 high-temperature molecular beam epitaxy (HT-MBE) growth of epitaxial graphene and a means of generating and modifying strain in graphene. Graphene grown by HT-MBE on hexagonal boron nitride forms continuous domains with dimensions of order 20 µm, and exhibits moiré patterns with large periodicities, indicating that the layers are highly strained. We demonstrate that aligned, lattice-matched graphene can be grown by HT-MBE using substrate temperatures in the range 1600-1710 °C and coexists with a topologically modified moire´ pattern with regions of strained graphene which have giant moire´ periods up to ~80 nm. Raman spectra reveal narrow redshifted peaks due to isotropic strain, while the giant moire´ patterns result in complex splitting of Raman peaks due to strain variations across the moire´ unit cell. We believe that the novel material that can be grown using HT-MBE shows great promise both in realizing the long-standing objective of the introduction of a bandgap into graphene and the exploration of one-dimensional conductors and their junctions. The growth of graphene by MBE using different carbon sources is attracting attention as a means of producing high-quality graphene layers. It is well-established that high-temperature sublimation of graphite produces a flux containing a mixture of carbon clusters including C1, C2 and C3. A novel atomic carbon source was used to grow graphene layers by MBE on hBN and sapphire at substrate temperatures of ~1400 °C. Our AFM measurements reveal the formation of hexagonal moiré patterns on the surface of graphene monolayers on hBN flakes. The amount of non-graphene carbon on the surface is reduced for the layers grown with the atomic carbon source when compared with a carbon sublimation source. However, further experimental studies involving both atomic and standard sublimation carbon sources are required to establish which carbon clusters C1 or C3 are more beneficial for the growth of high quality graphene layers by MBE. 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. HT-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. Our results demonstrate that PA-MBE at growth temperatures of 1390C can achieve mono- and few-layer thick hBN with a control of the hBN coverage and atomically flat hBN surfaces. 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 the higher B:N flux ratios. With the decrease of the PA-MBE growth temperature below 1250C we observe rapid degradation of the optical properties of hBN layers. We have studied high-temperature PA-MBE of hBN layers using a high-efficiency RF plasma source with high active nitrogen fluxes and a nitrogen flow rate of 7 sccm. Despite the more than three-fold increase in nitrogen flux, we did not see any dramatic increase in the growth rates of hBN layers in comparison with the layers grown with the standard nitrogen RF plasma source. This means that the growth rate of hBN layers is controlled by the boron arrival rate and that all our hBN layers are grown under strongly N-rich conditions. This is in stark contrast to the standard group-III-rich optimum PA-MBE conditions required for the growth of high-quality AlGaInN layers. The morphology of the hBN grown with the high-efficiency RF source is significantly different. We achieved an increase of the hBN thickness by decreasing the MBE temperature. However, decreasing the growth temperature resulted in a deterioration of the optical properties of hBN layers. We have demonstrated lower defect-related absorption in the range 5.0 to 5.5 eV for hBN layers grown with a high-efficiency RF plasma nitrogen source in comparison to data from the hBN samples grown with the standard RF plasma source. We exploit the scalable approach of HT-MBE to grow high-quality monolayer boron nitride on HOPG graphite substrates. We combine deep-ultraviolet photoluminescence and reflectance spectroscopy with atomic force microscopy to reveal the presence of a direct gap of energy 6.1 eV in the single hBN atomic layers, thus confirming a crossover to direct gap in the monolayer limit. |
| 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 | Growth of hexagonal boron nitride for deep ultraviolet photonics, quantum emitters and van der Waals substrates |
| Amount | £1,027,022 (GBP) |
| Funding ID | EP/V05323X/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 07/2021 |
| End | 07/2024 |
| Description | Leverhulme Trust Research Grant RPG-2014-129 "Molecular Beam Epitaxy for Graphene/Boron Nitride electronics" |
| Amount | £132,073 (GBP) |
| Organisation | The Leverhulme Trust |
| Sector | Charity/Non Profit |
| 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 | Public |
| Country | United Kingdom |
| Start | 02/2017 |
| End | 01/2021 |
| 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 |