Micro-spectroscopic soft X-ray studies of low-cost epitaxial graphene and adsorbates

Lead Research Organisation: University of Warwick
Department Name: Physics

Abstract

Graphene - the remarkable two-dimensional material whose discoverers were awarded a Nobel prize - may revolutionise the electronics industry. This depends on controlling the electronic properties of the material AND on making such material cheaply. In ordinary three-dimensional materials like silicon, control is achieved by introducing impurities into the material ("doping"). It is not possible to dope graphene conventionally without destroying some of the electronic properties that make it so attractive in the first place. An alternative is "transfer doping" where we place certain molecules on top of the graphene sheet and they add or remove electrons without damaging the sheet's superb electrical properties. We will also need to examine the effects of the substrate that the graphene sheet lies on.

In this project we will investigate the electronic structure of graphene on different substrates and with different molecules on top of it. This will be done using a technique called "angle resolved photoemission spectroscopy", or ARPES, in which we knock electrons out of the graphene using soft X-ray photons and calculate their momentum and energy to build up a complete picture of the electronic structure. However, we will be using advanced ARPES systems at major X-ray facilties in France, Italy and elsewhere which are capable of making these measurements on tiny length scales - less than one micrometre. This will enable us to work out changes in the electronic structure of graphene made in a very cheap and simple way in our lab using the same techniques likely to be employed by the electronics industry. Unlike expensive crystalline substrates, our samples are made on cheap metal foils and are not uniform so we need spatial resolution in the ARPES measurement.

A key part of our project is building up collaborations with theoretical physicists who will be able to help us understand and predict the changes of electronic properties of our cheap, industrially relevant graphene. Such a predictive ability will be a big step forward in bringing graphene to real-world applications in areas such as information technology, advanced detectors and energy efficiency.

Planned Impact

Graphene has the long-term potential to revolutionise electronics, with a correspondingly broad base of beneficiaries. How could our work contribute to this wide impact? We see a chain of beneficiaries arising from this project. Initially we will contribute to the understanding of the electronic structure of graphene as it is likely to be mass-produced, on cheap metal foil substrates, and of the effects of transfer doping by adsorption or contamination. This fundamental knowledge will benefit scientists in the field and guide further experimental and theoretical work (see "academic beneficiaries"). We will ensure this impact by dissemination, including organising a follow-up meeting to our successful workshop in Warwick, and direct collaboration development during the project. Subsequently, the knowledge developed will feed into more technologically orientated work - for example, by providing more accurate electrical conduction parameters to engineers designing graphene-based devices. The recently announced Graphene Hub, publicity activities organised through the syncrotron facilities and business engagement partners (Science City, Warwick Ventures), and our own outreach work will all help in ensuring effective knowledge transfer beyond academic materials science. During the project we will continue to contribute to our successful schools outreach programme across the Physics and Chemistry departments (outlined in the impact plan).
 
Description Graphene is a remarkable material, a honeycomb of carbon atoms just one atomic layer thick. Because it is as thin as any material can be, other atoms and molecules stuck on to it can change its properties drastically. A really critical property is the electrical conduction of graphene. We have shown that the electrical properties of graphene can be controllably altered by adding oxygen or nitrogen atoms to the honeycomb of carbon. We have performed these experiments on graphene fabricated by a cheap and scalable method, so our results are applicable to graphene material presently under investigation for industrial scale applications such as for advanced electronics, sensors and solar power. We were also able to distinguish between the effects of oxygen present on graphene just due to natural exposure to air and oxygen atoms adsorbed on the graphene deliberately. We have developed theoretical collaborations both within Warwick and beyond to further understand graphene growth and electronic structure.
Exploitation Route Our results are important for the many researchers in industry and academia looking to exploit graphene as an electronic material. We have also developed important collaborations with theoretical physicists both in Warwick and externally which are producing on-going new predictions of graphene's properties in the presence of real defects and adsorbates. During this work we also developed a lot of expertise with using graphene oxide (GO) to support nano-sized samples for transmission electron microscopy (TEM). These GO TEM sample supports are now commercially available and manufactured in the UK.
Sectors Chemicals,Digital/Communication/Information Technologies (including Software),Electronics,Energy

URL http://www.warwick.ac.uk/graphene
 
Description Our results are of interest to scientists and engineers looking to use graphene as an electronic material. We have provided some fundamental insights into the electronic structure of real graphene with surface contamination as well as graphene doped deliberately by atomic adsorption. We are publicising the results at the moment: several invited talks at international conferences and working towards high-impact papers. Subsequent impact will flow from these efforts. We also developed important European connections, notably by winning time at two major facilities (the Elettra and Soleil synchrotrons in Italy and France respectively), invited attendance at EUROCASE conference 2013 (Chantilly, France) and an invited seminar at Technische University Eindhoven (July 2014). Our synchrotron experience has been fed into developments at the I05 beamline at Diamond Light Source. Furthermore, graphene oxide supports for transmission electron microscopy developed and exploited during this project are now commercially available, fabricated in the UK and developed with the help of a PhD student placement via the Midlands Physics Alliance Graduate School (MPAGS). Finally the microscopy aspect of our work (including many beautiful images) has led to several schools outreach activities, including hands-on microscopy in primary schools and participation in a Smallpeice Trust physics/engineering workshop.
First Year Of Impact 2013
Sector Chemicals,Education,Manufacturing, including Industrial Biotechology,Other
Impact Types Economic

 
Description PhD studentship AR
Amount £71,640 (GBP)
Organisation Government of Malaysia 
Sector Public
Country Malaysia
Start 05/2014 
End 05/2018
 
Description Nano-ARPES facility at Diamond Light Source 
Organisation Diamond Light Source
Country United Kingdom 
Sector Academic/University 
PI Contribution Use experience from our nano-ARPES work on graphene to assist in commissioning of new branch of I05 beamline at Diamond Light Source - Dr. Pavel Dudin.
Collaborator Contribution Experience and expertise in materials and nano-ARPES.
Impact paper submitted to 2D Materials including data from commissioning beam time.
Start Year 2015
 
Description Theoretical collaboration - Dr. Paul Mulheran 
Organisation University of Strathclyde
Country United Kingdom 
Sector Academic/University 
PI Contribution Experimental data and high performance computing. Modelling graphene / metal surface growth.
Collaborator Contribution Theoretical modelling and high performance computing.
Impact Paper in APL Materials. External contribution to supervision of a PhD student at the Complexity DTC in Warwick.
Start Year 2012
 
Description Smallpeice Trust 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Schools
Results and Impact Students understood more about how physics and engineering are linked and enthusiastically asked questions.

Part of long-term goal of increasing STEM participation among students. Teachers could use material in classroom discussion.
Year(s) Of Engagement Activity 2013
URL http://www.smallpeicetrust.org.uk/
 
Description schools microscopy work 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach Local
Primary Audience Schools
Results and Impact Microscope kit borrowed by Coventry primary school for 1 term. Gavin Bell assisted with set-up and did one session with year 1 pupils. All 300 pupils at the school had a chance to do hands-on microscopy.

Head of science at the school developed activities to specifically link to Coventry LEA's science strategy. Plan to develop a Warwick / RMS joint kit specifically for Coventry schools. Demand increasing year-on-year for kits.
Year(s) Of Engagement Activity 2013,2014
URL http://www.rms.org.uk/outreach/activitykit