Professor Jamie Warner
Department of Materials
Tel: +44 1865 273700 (switchboard)
Fax: +44 1865 273789 (general fax)
Nanostructured Materials Group
Selected Corresponding Author Publications:
- A. W. Robertson, G-D. Lee, K. He, C. Gong, Q. Chen, E. Yoon, A. I. Kirkland, J. H. Warner, Atomic Structure of Sub-Nanometer Pores in Graphene, ACS Nano, Accepted in Press (2015)
- C. Gong, A. W. Robertson, K. He, G-D. Lee, E. Yoon, C. Allen, A. I. Kirkland, J. H. Warner, Thermally Induced Dynamics of Dislocations in Graphene at Atomic Resolution, ACS Nano, 9, 10066-10075 (2015)
- A. W. Robertson, G-D. Lee, K. He, Y. Fan, C. S. Allen, S. Lee, H. Kim, E. Yoon, H. Zheng, A. I. Kirkland, J. H. Warner. Partial Dislocations in Graphene and Their Atomic Level Migration Dynamics. Nano Letters, 15, 5950-5955 (2015)
- J. S. Kim, J. H. Warner, A. W. Robertson, A. I. Kirkland, Formation of Klein Edge Doublets from Graphene Monolayers, ACS Nano, 9, 8916-8922 (2015)
- Q. Chen, A. W. Robertson, K. He, C. Gong, E. Yoon, G-D. Lee, J. H. Warner, Atomic Level Distributed Strain within Graphene Divacancies from Bond Rotations, ACS Nano, 9, 8599-8608 (2015)
- Q. Chen, A-L. Koh, A. W. Robertson, K. He, S. Lee, E. Yoon, G-D. Lee, R. Sinclair, J. H. Warner, Rotating Anisotropic Crystalline Silicon Nanoclusters in Graphene, ACS Nano, 9, 9497-9506 (2015)
- K. He, A. W. Robertson, C. Gong, C. S. Allen, Q. Xu, H. Zandbergen, A. I. Kirkland, J. H. Warner, Controlled Formation of Closed-Edge Nanopores in Graphene, Nanoscale, 7, 11602-11610 (2015)
- S. Wang, X. Wang, J. H. Warner, All Chemical Vapour Deposition Growth of MoS2:h-BN Vertical van der Waals Heterostructures, ACS Nano 9, 5246-5254, (2015)
- K. He, A. W. Robertson, Y. Fan, C. S. Allen, Y-C. Lin, K. Suenaga, A. I. Kirkland, J. H. Warner, Temperature Dependence of the Reconstruction of Zig-Zag Edges in Graphene, ACS Nano, 9, 4786-4795, (2015)
- Y. Rong, K. He, M. Pacios, A. W. Robertson, H. Bhaskaran, J. H. Warner, Controlled Preferential Oxidation of Grain Boundaries in Monolayer Tungsten Disulfide for Direct Optical Imaging, ACS Nano, 9, 3695-3703, (2015)
- Z. He, Y. Sheng, Y. Rong, G-D, Lee, J. Li, J. H. Warner, Layer-Dependent Modulation of Tungsten Disulfide Photoluminescence by Lateral Electric Fields, ACS Nano, 9, 2740, (2015)
- C. Gong, K. He, A. W. Robertson, E. Yoon, G-D. Lee, J. H. Warner, Spatially Dependent Lattice Deformations for Dislocations at the Edges of Graphene, ACS Nano, 9, 656-662, (2015)
- Y. Rong, J. H. Warner, Wired Up: Interconnecting Two-Dimensional Materials with One-Dimensional Atomic Chains, ACS Nano, Perspective Article, 8, 11907-11912 (2014).
- K. He, A. W. Robertson, S. Lee, E. Yoon, G-D. Lee, J. H. Warner, Extended Klein Edges in Graphene, ACS Nano, 8, 12272-12279, (2014)
- J. H. Warner, Y-C. Lin, K. He, M. Koshino, K. Suenaga, Stability and Spectroscopy of Single Nitrogen Dopants in Graphene at Elevated Temperatures, ACS Nano, 8, 11806-11815, (2014)
- S. Wang, Y. Rong, Y. Fan, M. Pacios, H. Bhaskaran, K. He, J. H. Warner, Shape Evolution of Monolayer MoS2 Crystals Grown by Chemical Vapour Deposition, Chemistry of Materials, 26, 6371-6379, (2014)
- J. H. Warner, Y-C. Lin, K. He, M. Koshino, K. Suenaga, Atomic Level Spatial Variations of Energy States Along Graphene Edges, Nano Letters, 14, 6155-6159 (2014)
- G-D. Lee, E. Yoon, K. He, A. Robertson, Jamie. H. Warner, Detailed Formation Processes of Stable Dislocations in Graphene, Nanoscale, 6, 14836-14844, (2014).
- Y. Rong, Y. Fan, A-L. Koh, A. W. Robertson, K. He, S. Wang, H. Tan, R. Sinclair, J. H. Warner, Controlling Sulphur Precursor Addition for Large Single Crystal Domains of WS2, Nanoscale, 6, 12096-12103 (2014)
- Y. Fan, K. He, H. Tan, S. Speller, and J. H. Warner, Crack-Free Growth and Transfer of Continuous Monolayer Graphene Grown on Melted Copper, Chemistry of Materials, 26, 4984–4991 (2014)
- A. W. Robertson, G-D. Lee, K. He, E. Yoon, A. I. Kirkland, J. H. Warner. The Role of the Bridging Atom in Stabilizing Odd Numbered Graphene Vacancies. Nano Letters, 14, 3972–3980, (2014)
- Z. He, K. He, A. W. Robertson, A. I. Kirkland, D. Kim, J. Ihm, E. Yoon, G-D. Lee, J.H. Warner, Atomic Structure and Dynamics of Metal Dopant Pairs in Graphene. Nano Letters, 14, 3766–3772, (2014)
- A. W. Robertson, G.D. Lee, K. He, E. Yoon, A. I. Kirkland, J. H. Warner, Stability and Dynamics of the Tetravacancy in Graphene, Nano Letters, 14, 1634-1642 (2014)
- A. W. Robertson, K. He, A. I. Kirkland, J. H. Warner, Inflating Graphene with Atomic Scale Blisters, Nano Letters, 14, 908-814, (2014)
- A. W. Robertson, C. Ford, K. He, A. I. Kirkland, A. A. R. Watt, J. H. Warner, PbTe Nanocrystal Arrays on Graphene and the Structural Influence of Capping Ligands, Chemistry of Materials, 26, 1567-1575, (2014)
- K. He, G-D. Lee, A. W. Robertson, E. Yoon, J. H. Warner, Hydrogen-Free Graphene Edges, Nature Communications, 5, 3040 (2014)
- J. H. Warner, G-D. Lee, K. He, A. W. Robertson, E. Yoon, A. I. Kirkland, Bond Length and Charge Density Variations within Extended Arm Chair Defects in Graphene. ACS Nano, 7, 9860-9866, (2013)
- J. H. Warner, Y. Fan, A. W. Robertson, K. He, E. Yoon, G. D. Lee, Rippling Graphene at the Nanoscale Through Dislocation Addition. Nano Letters, 13, 4937-4944, (2013)
- J. H. Warner, Z. Liu, K. He, A. W. Robertson, K. Suenaga, Sensitivity of Graphene Edge States to Surface Adatom Interactions. Nano Letters, 13, 4820-4826, (2013)
- A. W. Robertson, B. Montanari, K. He, C. S. Allen, Y. A. Wu, N. Harrison, A. I. Kirkland, J. H. Warner, Structural Reconstruction of the Graphene Monovacancy, ACS Nano, 7, 4495-4502, (2013)
- A. W. Robertson, J. H. Warner, Atomic Resolution Imaging of Graphene by Transmission Electron Microscopy, Nanoscale (Feature Article), 5, 4079-4093 (2013)
- A. W. Robertson, B. Montanari, K. He, J. Kim, C. S. Allen, Y. A. Wu, J. Olivier, J. Neethling, N. Harrison, A. I. Kirkland, J. H. Warner, Dynamics of Single Fe Atoms in Graphene Vacancies, Nano Letters, 13, 1468-1475 (2013)
- A. W. Robertson, C. S. Allen, Y. A. Wu, K. He, J. Olivier, J. Neethling, A. I. Kirkland, J. H. Warner, Spatial Control of Defect Creation in Graphene at the Nanoscale, Nature Communications, 3, 1144 (2012)
- C. S. Allen, A. R. Robertson, A. I. Kirkland, J. H. Warner, The Identification of Inner Tube Defects in Double-Wall Carbon Nanotubes, Small, 8, 3810-3815, (2012)
- J. H. Warner, E. R. Margine, M. Mukai, A. W. Robertson, F. Giustino, A. I. Kirkland, Dislocation Driven Deformations in Graphene. Science, 337, 209-212 (2012).
- J. H. Warner, M. Mukai, A. I. Kirkland. The Atomic Structure of ABC Rhombohedral Stacked Trilayer Graphene. ACS Nano, 6, 5680-5686, (2012)
- Y. Wu, Y. Fan, S. Speller, G. Creeth, J. Sadowski, K. He, A. W. Robertson, C. Allen, J. H. Warner. Large Single Crystals of Graphene on Melted Copper using Chemical Vapour Deposition. ACS Nano, 6, 5010-5017, (2012).
- A. W. Robertson, A. Bachmatiuk, Y. A. Wu, F. Schaeffel, B. Buechner, M. Ruemelli, J. H. Warner, Structural Distortions in Few Layer Graphene from Creases, ACS Nano, 5, 9984-9991, (2011)
- C. S. Allen, Y. Ito, A. W. Robertson, H. Shinohara, J. H. Warner, Two-Dimensional Coalescence Dynamics of Encapsulated Metallofullerenes in Carbon Nanotubes. ACS Nano, 5, 10084-10089 (2011).
- F. Schaeffel, M. Wilson, J. H. Warner, Motion of Light Adatoms and Molecules on the Surface of Few-Layer Graphene. ACS Nano, 5, 9428-9441, (2011)
- J. H. Warner, N. P. Young, A. I. Kirkland, G. A. D. Briggs, Resolving Strain in Carbon Nanotubes at the Atomic Level, Nature Materials, 10, 958-962, (2011)
- Y. A. Wu, A. W. Robertson, F. Shaeffel, S. C. Speller, J. H. Warner, Aligned Rectangular Few-Layer Graphene Domains on Copper Surfaces, Chemistry of Materials, 23, 4543-4547, (2011).
- A. W. Robertson, A. Bachmatiuk, Y. A. Wu, F. Schaffel, B. Rellinghaus, B. Buchner, M. H. Rummeli, J. H. Warner, Atomic Structure of Interconnected Few Layer Graphene Domains, ACS Nano, 5, 6610–6618, (2011)
- A. Robertson, J. H. Warner, Hexagonal single crystal domains of few layer graphene on copper foils. Nano Letters, 11, 1182-1189 (2011)
- F. Shaeffel, M. Wilson, A. Bachmatiuk, M. Rummeli, U. Queitsch, B. Rellinghaus, G. A. D. Briggs, J. H. Warner, Atomic Resolution Imaging of the Edges of Catalytically Etched Suspended Few Layer Graphene. ACS Nano, 5, 1975-1983, (2011)
- J. Luo, P. Tian, C-T. Pan, A. Robertson, J. H. Warner, E. Hill, G. A. D. Briggs. Ultralow Secondary Electron Emission of Graphene. ACS Nano, 5, 1047-1055, (2011)
- J. H. Warner, S. Plant, N. P. Young, K. Porfyrakis, A. Kirkland, G. A. D. Briggs, Atomic Scale Growth Dynamics of Nanocrystals within Nanotubes. ACS Nano, 5, 1410-1417 (2011)
- Featured as a ‘Research Highlight’, Nanoscience: Glimpses of Crystal Growth, Nature, 470, 142 (2011)
- M. Zaka, Y. Ito, H. Wang, W. Yan, A. Robertson, Y. A. Wu, M. H. Rummeli, D. Staunton, T. Hashimoto, J. J. L. Morton, A. Ardavan, G. A. D. Briggs, J. H. Warner, Electron paramagnetic resonance investigations of purified catalyst-free single-walled carbon nanotubes. ACS Nano, 4, 7708-7716 (2010)
- H. Wang, J. Luo, A. Robertson, Y. Ito, W. Yan, V. Lang, M. Zaka, F. Schaffel, M. H. Rummeli, G. A. D. Briggs, J. H. Warner. High performance field effect transistors from solution processed carbon nanotubes. ACS Nano, 4, 6659-6664 (2010)
- J. H. Warner, M. Wilson, Elastic distortions of carbon nanotubes induced by chiral fullerene chains. ACS Nano, 4, 4011-4016, (2010)
- J. H. Warner, M. H. Rummeli, A. Backmatiuk, B. Buchner, Atomic resolution imaging and topography of hexagonal boron nitride sheets produced by chemical exfoliation. ACS Nano, 4, 1299-1304, (2010)
- J. H. Warner, M. H. Rummeli, A. Bachmatiuk, M. Wilson, B. Buchner. Examining Co Based Nanocrystals on Graphene Using Low-Voltage Aberration Corrected Transmission Electron Microscopy. ACS Nano, 4, 470-476, 2010
- J. H. Warner, Y. Ito, M. H. Rümmeli, B. Büchner, H. Shinohara, G. A. D. Briggs, Capturing the motion of molecular nanomaterials encapsulated within carbon nanotubes with ultrahigh temporal resolution. ACS Nano, 3, 3037-3044 (2009)
- J. H. Warner, M. H. Rümmeli, L. Ge, T. Gemming, B. Montanari, N. M. Harrison, B. Büchner, G. A. D. Briggs, Structural transformations in graphene studied with high spatial and fast temporal resolution, Nature Nanotechnology, 4, 500 (2009)
- J. H. Warner, Y. Ito, M. H. Rümmeli, T. Gemming, B. Büchner, H. Shinohara, G. A. D. Briggs, One-Dimensional confined motion of single metal atoms inside double-walled carbon nanotubes, Physical Review Letters, 9, 195504 (2009)
- J. H. Warner, F. Schäffel, G. Zhong, M. H. Rümmeli, B. Büchner, J. Robertson, G. A. D. Briggs, Investigating the diameter dependent stability of single-walled carbon nanotubes, ACS Nano, 3, 1557 (2009)
- J. H. Warner, F. Schaeffel, M. Ruemmeli, B. Buechner, Examining the edges of few-layer graphene sheets, Chemistry of Materials, 21, 2418 (2009)
- J. H. Warner, M. H. Ruemmeli, T. Gemming, B. Buechner, G. A. D. Briggs, Direct imaging of rotational stacking faults in few layer graphene, Nano Letters, 9, 102-106 (2009)
- J. H. Warner, Y. Ito, M. Zaka, L. Ge, T. Akachi, H. Okimoto, K. Porfyrakis, A. A. R. Watt, H. Shinohara, G. A. D. Briggs, Rotating fullerene chains in carbon nanopeapods. Nano Letters, 8, 2328-2335, (2008)
Selected as a ‘Research Highlight’ by Nature Nanotechnology, 3, p452 (2008)
- J. H. Warner, A. A. R. Watt, L. Ge, K. Porfyrakis, T. Akachi, H. Okimoto, Y. Ito, A. Ardavan, B. Montanari, J. H. Jefferson, N. M. Harrison, H. Shinohara, G. A. D. Briggs, Dynamics of paramagnetic metallofullerenes in carbon nanotube peapods. Nano Letters, 8, 1005-1010 (2008)
- J. H. Warner, Self-assembly of ligand-free PbS nanocrystals into nanorods and their nanosculpturing by electron-beam irradiation. Advanced Materials, 20, 784-787 (2008)
Selected as ‘Advances in Advance’ by the editor, and selected for Wiley’s Materials View, March edition 2008.
- J. H. Warner, R. D. Tilley, Synthesis and self-assembly of triangular and hexagonal CdS nanocrystals. Advanced Materials, 17, 2997-3001 (2005)
Second most downloaded article, December 2005
- J. H. Warner, A. Hoshino, K. Yamamoto, R. D. Tilley, Water-soluble photoluminescent silicon quantum dots. Angewandte Chemie Int. Ed. 44, 4550 (2005)
Selected by the editors as ‘Very Important Paper’
Sensor Technology Based on Large Area Synthetic Graphene
Sensor technology, such as touch screen displays and pressure/strain sensors, will be developed using graphene. The graphene will be synthetic and of large area, produced using metal catalyst assisted chemical vapour deposition. Processing methods for transferring the graphene onto transparent flexible polymer substrates will be developed. This project aims at bringing graphene into application and will utilize recent advances within the group for producing outstanding synthetic graphene material. Optical and electron beam lithography will be used to pattern the graphene and metal electrodes for devices. Interfacing with computer hardware will be undertaken to achieve functioning sensor technology.
Also see homepages: Jamie Warner
Direct electron beam lithography of graphene
J H Warner
Graphene holds a lot of promise for electronic applications. In order to be an effective semiconductor in transistors it is desirable for the width of graphene channels to be sub-10nm. This project will focus on fabricating sub-10nm features in graphene using the novel concept of direct electron beam lithography. Electron beam irradiation will be used to directly sputter carbon atoms from graphene with the aim of fabricating structures for nanoelectronic devices. Graphene structures such as nanoribbons will be produced and implemented in field effect transistors. This will involve fabricating graphene nanoelectronic devices that are compatible with high resolution transmission electron microscopy. Parameters that enable control over the graphene sputtering process will be elucidated. Atomic structure will be gained by aberration-corrected HRTEM and correlated with the electronic device properties.
Also see homepages: Jamie Warner
Synthesis of large area graphene sheets using chemical vapour deposition
J H Warner
The 2D crystalline nature of graphene makes it suitable for large area transparent conducting electrodes. Recent advances in chemical vapour deposition (CVD) methods now permit a route to making large area sheets. This project will focus on understanding the growth mechanisms behind CVD grown graphene and then developing approaches to improve the atomic structure and electronic properties. Insights into the structure will be gained using atomic-resolution imaging with low-voltage aberration-corrected high resolution transmission electron microscopy. Techniques to transfer the sheets to transparent substrates, such as glass or flexible polymers will be examined and the sheet resistance determined. Methods to incorporate dopants into the CVD growth process will be pursued with the aim of improving conductivity. Controlling the number of graphene layers grown by CVD will be investigated.
Also see homepages: Jamie Warner
Structural studies of Graphene and other 2D crystals with single atom sensitivity
Jamie Warner, Angus Kirkland
Graphene is a 2D crystal only one atom thick and is ideal for studying individual atoms by transmission electron microscopy. This project will focus on understanding fundamental crystal defects in graphene and other 2D crystals such as boron nitride, MoS2 and WS2. Mono-vacancies and the other non-6 member ring structures that exist in the unique 2D crystal. It will also investigate the grain boundary interface between two graphene domains with the aim of mapping out the unique atomic stitching that occurs. Graphene will be grown by chemical vapour deposition. This project will use Oxford's state-of-the-art aberration-corrected high resolution transmission electron microscope, equipped with a monochromator for the electron beam to give unprecedent spatial resolution at a low accelerating voltage of 80 kV. Advanced image analysis techniques, including exit-wave reconstruction, and comparison to image simulations will be utilized for a deeper understanding of the atomic structure.
Nanoscale patterning of graphene for electronic devices
J H Warner
One of the key challenges limiting 2D electronics is the ability to pattern features on the 10nm scale with high uniformity across a wafer. Field effect transistors comprised of graphene nanoribbons exhibit large on/off ratios only when their channel widths are sub-10nm. At this small size scale the structure of the edges plays a role in their transport properties. Developing methods to control the edge atomic structure is important and it will lead to uniform structures with tailored properties. This project aims to develop top-down lithographic approaches to achieving nanoscale structures in 2D sheets of graphene that are then incorporated into electronic devices. Graphene nanoribbon field effect transistors will be fabricated that are compatible with electron microscopy. Low-voltage aberration-corrected high resolution transmission electron microscopy will be used to characterize the atomic structure. The goal is to improve the performance of graphene nanoribbon field effect transistors by cleaning up the atomic disorder at the edges. Other methods to improve the atomic ordering at the edges such as Joule heating will be examined whilst inside the aberration-corrected HRTEM. The main focus of this project is to develop nanoscale patterning techniques that are scalable, rapid and provide uniformity across a large area.
Also see homepages: Jamie Warner
Spectroscopy and device applications of monolayer semiconductors coupled to optical microcavities
Prof Jamie Warner, Prof Jason Smith
Monolayer semiconductor materials such as WS2 and MoSe2 display strong optical transitions that are attractive for nanoscale optoelectronic devices. These properties can be both enhanced and harnessed by coupling the materials to optical microcavities, opening possibilities for fast optical switches, ultra-low threshold lasers, and advanced quantum light sources. This project brings together the expertise of two leading research groups in 2D materials (Prof Jamie Warner) and in microcavity photonics (Prof Jason Smith). The project will build on some preliminary work which provides first demonstrations of basic phenomena, and will develop the experiments further to investigate ‘strong coupling’ (ie the creation of polaritons - part electronic excitation, part photon) and the switching of polariton states to realise ambient temperature devices.
Graphene based 2D nanoelectronics
Graphene has exceptional electronic properties, combined with a 2D structure that makes it attractive for a wide range of electronic applications. Other 2D crystals such as MoS2 and BN have similar 2D structure, but are semiconducting and insulating. This project will focus on the fabrication and characterization of nanoelectronic devices such as field effect transistors and ultrathin optoelectronic devices using 2D crystals. It will involve working in a clean-room environment using electron beam lithography to fabricate nanostructured electrodes and the patterning of graphene from the top down. The graphene and other 2D materials will be available within the group and are grown by chemical vapour deposition. The aim of this project is to solve processing and materials issues that currently limit the potential of 2D materials in electronics.
Also see homepages: Jamie Warner
Graphene electrodes for nanocrystal solar cells
Jamie Warner and Andrew Watt
Graphene is an ideal 2D material for utilization as a transparent conducting electrode in photovoltaics (solar cells). High efficiency photovoltaic devices will require the effective integration of other nanomaterials with graphene to produce hybrid nanosystems. Inorganic nanocrystals such as PbS, ZnSe, TiO2 and Si, have unique semiconducting properties with band gaps that span from the near-IR to UV. This project will focus on synthesizing inorganic nanocrystals using solution-phase chemistry. Control over the shape to tailor spherical, rod and branched structures will be investigated. Variation of surface state morphology will be conducted through various chemical approachs to control the inter-nanocrystal interactions. Synthetic graphene will be produced using chemical vapour deposition. Composite hybrid devices will be fabricated that use synthetic graphene as a working transparent conducting electrode and the inorganic nanocrystal as the active functional nanomaterial.
Integrating Inorganic Nanocrystals into Graphene Devices
Utilizing graphene in opto-electronic devices will require the effective integration of other nanomaterials to produce hybrid nanosystems. Inorganic nanocrystals such as PbS, ZnSe, TiO2 and Si, have unique semiconducting properties with band gaps that span from the near-IR to UV. This project will focus on synthesizing novel inorganic nanocrystals using solution-phase chemistry. Control over the shape to tailor spherical, rod and branched structures will be investigated. Variation of surface state morphology will be conducted through various chemical approachs to control the inter-nanocrystal interactions. Synthetic graphene will be produced using chemical vapour deposition. Composite hybrid devices will be fabricated that use synthetic graphene as a working transparent conducting electrode and the inorganic nanocrystal as the active functional nanomaterial. Viability in photodetectors and photo-catalysis will be explored.
Also see homepages: Jamie Warner
Insulating and Semiconducting 2D crystals for electronic applications
Graphene is a semi-metal 2D crystal, Boron Nitride (BN) an insulating 2D crystal, and MoS2/WS2 are semiconducting 2D crystals. Realizing the potential of 2D crystals in electronic applications requires all 3 of these variants. We have undertaken years of research in growing graphene crystals by chemical vapour deposition and can now produce high quality materials. However, further improvement is needed to advance the synthesis of BN and MoS2/WS2 2D crystals to obtain similar quality films. In this project 2D crystals will be synthesized by chemical vapour deposition to produce materials with varying band structure. New synthetic strategies will be developed in order to produce large single crystal structures on a variety of substrates compatible with device processing. The atomic structure of the new 2D crystals will be characterized using advanced electron microscopy (scanning electron microscopy and transmission electron microscopy). The electronic properties of the new materials will be analysed by fabricating nanoelectronic devices such as transistors. This is a unique opportunity to undertake a project involving new materials synthesis, characterization of the atomic structure, and implementation in nanoelectronic transistor arrays. The project is well integrated into the group's goals by developing new 2D crystals that will have large up-take amongst other researchers for applications ranging from flexible electronics, pressure sensors, optical detectors, LEDs and solar cells.
Also see homepages: Jamie Warner
Nanomaterials for quantum technologies
Professor G. A. D. Briggs, Dr K. Porfyrakis, Dr J. H. Warner and Dr E. A. Laird
Quantum information processing offers one of the most exciting challenges in the study and development of nanomaterials. It is at the cutting edge of quantum nanoelectronics, and Oxford is part of the world-wide endeavour to develop scalable quantum computers. Instead of classical bits of information, these will work with qubits (quantum bits). We need materials with quantum states that can be individually controlled and measured, and yet which are sufficiently robust against decoherence that they can sustain a sequence of quantum manipulations and interactions. We lead the world in using the new family of fullerene materials (popularly known as Bucky balls), which can be used to contain atomic species inside a cage that separates them from the environment. We can store the quantum information in an electron or nuclear spin, and exchange it between the two. We can manipulate and characterize the spin states by electron paramagnetic resonance and also optically. By creating entanglement between several spins, it is possible to develop sensors that exceed the standard quantum limit. A core thrust of our research is to incorporate molecular materials in working devices for practical quantum technologies. There will be several projects with these nanomaterials, ranging from synthesis and microscopy to experimental implementation of candidate schemes for quantum computing. The research is highly interdisciplinary, and there is scope for a range of skills and interests from materials science and chemistry to experimental quantum physics. There may be possibilities for industrial support and for international travel and collaboration.
Carbon-based quantum devices characterised electrically and by imaging
Dr E. A. Laird, Dr J. H. Warner and Professor G. A. D. Briggs
Carbon nanomaterials are attractive materials for electronic devices, especially for quantum computers using the spin of single electrons. One challenge in realising these applications is that the detailed device structure cannot be fully controlled during fabrication. The aim of this project is to characterize the same devices both through electrical measurements and by high-resolution electron microscopy, with the aim of understanding the electronic properties in terms of the atomic structure.
The goal of project will be to determine how the bandstructure and spin-orbit coupling of carbon nanotubes depend on the atomic structure – in particular on the chirality, which describes how the carbon atoms are aligned. Through aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), it is possible to measure the chiral indices of individual nanotubes, but so far this has not been performed on nanotubes integrated into electronic devices. You will combine these two kinds of measurement by incorporating a TEM window into existing fabrication technology for ultra-low-disorder nanotubes. You will then make electrical measurements of selected devices in a dilution refrigerator, with the aim of correlating the measured spin-orbit coupling to the previously determined chirality and comparing with existing theoretical predictions.
Coupling molecular spins to valley-spin qubits in carbon nanotubes
Professor G. A. D. Briggs, Dr J. H. Warner, Dr K. Porfyrakis and Dr E. A. Laird
Carbon-based quantum technologies require the ability to transfer quantum information from one form to another. Valley-spin qubits (so called because of the hybridisation between electron spin states and the valleys in the band structure of the nanotube) enable single states to be manipulated and measured in electron dipole spin resonance, but the coherence times are not long enough for scaleable quantum computing. Molecular qubits are known from ensemble experiments to have useful quantum coherence times, but to exploit these in useful devices we must have ways to measure them individually. By attaching molecules to the nanotube, and transferring quantum states between the nanotube and the molecule, it should be possible to exploit the best of each. The storage time can be increased a further thousandfold by using molecular nuclear spins as a further resource.
Successful development of this scheme will require nanofabrication of the devices, attachment of the spin-bearing molecules, microscopy of the resulting structures, and magnetic resonance at cryogenic temperatures. This project will involve training in nanofabrication, together with electron microscopy and low-temperature electronic measurements. Aspects of the project will be undertaken in collaboration with other members of the laboratory. The goal will be to show that quantum information can be effectively transferred between the nanotube device and the spin states of the attached molecules. This will be achieved by entangling quantum mechanically the molecular spin with an electron spin on the nanotube, and measuring the molecular spin state through its effect on the electron.
Also see a full listing of New projects available within the Department of Materials.