Dr Jamie Warner
106. J. Luo, W. Ouyang, X. Li, Z. Jin, L. Yang, C. Chen, J. Zhang, Y. Li, J. H. Warner, L-M. Peng, Q. Zheng, J. Zhu, Pointwise Plucking of Suspended Carbon Nanotubes. Nano Letters, 12, 3363-3367 (2012).
105. C. S. Allen, A. R. Robertson, A. I. Kirkland, J. H. Warner, The Identification of Inner Tube Defects in Double-Wall Carbon Nanotubes, Small, Accepted 2012
104. J. H. Warner, E. R. Margine, M. Mukai, A. W. Robertson, F. Giustino, A. I. Kirkland, Dislocation Driven Deformations in Graphene. Science, 337, 209 (2012).
103. L. D. Nyamen, V. S. R. R. Pullabhotla, A. A. Nejo, P. T. Ndifon, J. H. Warner, N. Revaprasadu, Synthesis of anisotropic PbS nanoparticles using heterocyclic dithiocarbamate complexes. Dalton Transactions, 41, 8297-8302, (2012)
102. J. H. Warner, M. Mukai, A. I. Kirkland. The Atomic Structure of ABC Rhombohedral Stacked Trilayer Graphene. ACS Nano, 6, 5680-5686, (2012)
101. M. J. Holmes, Y. S. Parks, X. Wang, C. C. S. Chan, B. P. L. Reid, H. Kim, J. Luo, J. H. Warner, R. A. Taylor, Optical Studies of GaN nanocolumns containing InGaN quantum disks and the effect of strain relaxation on the carrier distribution. Phys. Stat. Sol. C. 9, 712-714 (2012)
100. M. Fouquet, B. C. Bayer, S. Esconjaurequi, R. Blume, J. H. Warner, S. Hofmann, R. Schlogl, C. Thomsen, J. Robertson, Highly chiral-selective growth of single-walled carbon nanotubes with a simple monometallic Co catalyst. Phys. Rev. B. 85, 235411 (2012)
99. 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).
98. J. Moghul, Y. Wu, J. H. Warner, Mechanical Response of Few-Layer Graphene Films on Copper. Scripta Materialia, 67, 273-276, (2012)
97. G.Zhong, J. H. Warner, M. Fouquet, A. W. Robertson, B. Chen, J. Robertson, Growth of Ultrahigh Density Single-Walled Carbon Nanotube Forests by Improved Catalyst Design, ACS Nano, 6, 2893-2903 (2012)
96. I. Ibrahim, A. Bachmatiuk, J. H. Warner, B. Büchner, G. Cuniberti, M. H. Rümmeli, CVD grown horizontally aligned single wall carbon nanotubes: Synthesis routes and growth mechanisms. Small 8, 1973-1992 (2012)
95. B. Li, H. Cao, J. Yin, Y. A. Wu, J. H. Warner, Synthesis and separation of dyes via Ni@reduced graphene oxide nanostructures. Journal of Materials Chemistry, 22, 1876-1883, (2012)
94. A. Wongariyakawee, F. Schaeffel, J. H. Warner, D. O’Hare, Surfactant directed synthesis of calcium aluminium layered double hydroxides nanoplatelets. Journal of Materials Chemistry, 22, 7751-7756, (2012)
93. H. Cao, X. Wu, G. Yin, J. H. Warner, Synthesis of Adenine Modified Reduced Graphene Oxide Nanosheets. Inorganic Chemistry, 51, 295-2960 (2012)
92. M.T. Cole, K. Hou, J.H. Warner, J.S. Barnard, K. Ying, Y. Zhang, C. Li, K.B.K. Teo, W.I. Milne, In-situ deposition of sparse vertically aligned carbon nanofibres on catalytically activated stainless steel mesh for field emission applications. Diamond & Related Materials, 23, 66-71,(2012)
91. Y. A. Wu, J. H. Warner, Shape and Property Control of Mn Doped ZnSe Quantum Dots: From Branched to Spherical. Journal of Materials Chemistry, 22, 417-424, (2012).
90. Y. S. Chaudhary, T. W. Woolerton, C. S. Allen, J. H. Warner, E. Pierce, S. W. Ragsdale, F. A. Armstrong. Visible Light-Driven CO2 Reduction by Enzyme Coupled CdS Nanocrystals. Chemical Communications, 48, 58-60, (2012)
89. 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)
88. 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).
87. 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)
86. 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)
85. 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).
84. 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)
83. I. Ibrahim, A. Bachmatiuk, F. Borrnert, J. Bluher, U. Wolff, J. H. Warner, B. Buchner, C. Cuniberti, M. H. Rummeli. Optimizing substrate surface and catalyst conditions for high yield chemical vapor deposition grown epitaxially aligned single-walled carbon nanotubes, Carbon 49, 5029-5037 (2011)
82. M. J. Holmes, Y. S. Park, X. Wang, C. C. S. Chan, B. P. L. Reid, H. Kim, R. A. Taylor, J. H. Warner, J. Luo, Optical studies on a single GaN nanocolumn containing a single InxGa1-xN quantum disk, Applied Physics Letters, 98, 251908 (2011)
81. E. J. Lawrence, G. G. Wildgoose, L. Aldous, Y. A. Wu, J. H. Warner, R. G. Compton, 3-Aryl-3-(trifluoromethyl)diazirines as versatile photoactivated "linker" molecules for the improved covalent modification of graphitic and carbon nanotube surfaces, Chemistry of Materials , 23, 3740–3751 (2011)
80. H. Wang, J. Luo, F. Schaeffel, M. Ruemmeli, G. A. D. Briggs, J. H. Warner, Carbon Nanoelectronic Devices Compatible with Transmission Electron Microscopy. Nanotechnology, 22, 245305 (2011)
79. Y. A. Wu, A. Kirkland, F. Schaeffel, K. Porfyrakis, N. P. Young, G. A. D. Briggs, J. H. Warner. Utilizing Boron Nitride Sheets as thin supports for high resolution imaging of nanocrystals. Nanotechnology, 22, 195603 (2011)
78. A. Robertson, J. H. Warner, Hexagonal single crystal domains of few layer graphene on copper foils. Nano Letters. 11, 1182-1189 (2011)
77. A. Scott, A. Dianat, F. Borrnert, A. Bachmatiuk, S. Zhang, J. H. Warner, E. Borowiak-Palen, M. Knupfer, B. Buchner, G. Cuniberti, M. H. Rummeli, The catalytic potential of high k dielectrics for graphene formation. Applied Physics Letters. 98, 073110 (2011)
76. 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)
75. B. Li, H. Cao, J. Shao, M. Qu, J. H. Warner, Superparamagnetic Fe3O4 Nanocrystals@Graphene Composites for Energy Storage Devices. Journal of Materials Chemistry. 21, 5069-5075 (2011)
74. 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)
73. 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)
72. J. K. Sprafke, S. D. Stranks. J. H. Warner, R. J. Nicholas, H. L. Anderson, Noncovalent Binding of Carbon Nanotubes by Porphyrin Oligomers. Angewandte Chemie International Edition, 50, 2313-2316 (2011)
71. C. J. Wang, Y. A. Wu, R. M. J. Jacobs, J. H. Warner, G. R. Williams, D. O’Hare, Reverse Micelle Synthesis of Co-Al LDHs: Control of Particle Size and Magnetic Properties. Chemistry of Materials. 23, 171-180, (2011).
70. 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)
69. 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)
68. F. Schaffel, J. H. Warner, A. Bachmatiuk, U. Queitsch, B. Rellinghaus, B. Buchner, L. Schultz, M. H. Rummeli, Tracking down the catalytic hydrogenation of multilayer graphene. Physica Status Solid C. 7, 2731-2734 (2010)
67. S. Gorantla, F. Borrnert, A. Bachmatiuk, M. Dimitrakopoulou, R. Schonfelder, F. Schaffel, J. Thomas, T. Gemming, J. H. Warner, B. I. Yakobson, J. Eckert, B. Buchner, M. H. Rummeli, In-situ observations of fullerene fusion and endocytotic entry into carbon nanotubes. Nanoscale 2, 2077-2079, (2010)
66. J. H. Warner, M. H. Rummeli, A. Bachmatiuk, B. Buchner, Examining the stability of folded graphene edges against electron beam induced sputtering with atomic resolution. Nanotechnology 21, 325702 (2010)
65. M. H. Rummeli, A. Bachmatiuk, A. Scott, F. Borrnert, J. H. Warner, V. Hoffman, J-H. Lin, G. Cuniberti, B. Buechner, Direct Low Temperature Nano-Graphene Synthesis over a Dielectric Insulator. ACS Nano, 4, 4206-4210 (2010)
64. J. H. Warner, M. Wilson, Elastic distortions of carbon nanotubes induced by chiral fullerene chains. ACS Nano, 4, 4011-4016, (2010)
63. R. M. Brown, Y. Ito, J. H. Warner, A. Ardavan, H. Shinohara, G. A. D. Briggs, J. J. L. Morton, Spin coherence times of metallofullerenes: Y, Sc, La@C82. Physical Review B, 82, 033410 (2010)
62. R. J. Nicholls, K. Sader, J. H. Warner, S. R. Plant, K. Porfyrakis, P. D. Nellist, G. A. D. Briggs, D. J. H. Cockayne, Direct imaging and chemical identification of the encapsulated metal atoms in bimetallic endofullerene peapods. ACS Nano, 4, 3943-3948 (2010)
61. A. Bachmatiuk, F. Borrnert, F. Schaeffel, M. Zaka, G. S. Martynkowa, D. Placha, R. Schoenfelder, P. M. F. J. Costa, N. Ioannides, J. H. Warner, R. Klingeler, B. Buchner, M. H. Rummeli, The formation of stacked-cup carbon nanotubes using chemical vapour deposition from ethanol over silica. Carbon, 48, 3175-3181 (2010)
60. J. H. Warner, The influence of the number of layers of graphene on the atomic resolution images obtained from aberration-corrected high resolution transmission electron microscopy. Nanotechnology, 21, 255707 (2010)
59. J. Luo, J. H. Warner, C. Feng, Y. Yao, Z. Jin, H. Wang, C. Pan, S. Wang, L. Yang, Y. Li, J. Zhang, A. A. R. Watt, L. Peng, J. Zhu, G. A. D. Briggs, Ultrahigh secondary electron emission of carbon nanotubes. Applied Physics Letters, 96, 213113 (2010)
58. F. Borrnert, S. Gorantla, A. Bachmatiuk, J. H. Warner, I. Ibrahim, J. Thomas, T. Gemming, J. Eckert, G. Cuniberti, B. Buchner, M. H. Rummeli, In-situ observations of self-repairing single-walled carbon nanotubes. Physical Review B. 81, 201401(R) (2010)
57. J. H. Warner, M. H. Ruemmeli, A. Bachmatiuk, B. Buchner, Structural transformations of carbon chains inside nanotubes. Physical Review B. 81, 155419 (2010)
56. F. Borrnert, C. Borrnert, S. Gorantla, X. Liu, A. Bachmatiuk, J-O. Joswig, F. R. Wagner, F. Schaffel, J. H. Warner, R. Schonfelder, B. Rellinghaus, T. Gemming, J. Thomas, M. Knupfer, B. Buchner, M. H. Rummeli, Single-wall-carbon-nanotube/single-carbon-chain molecular junctions. Physical Review B. 81, 085439 (2010)
55. R. Beal, A. Stavrinados, J. H. Warner, J. Smith, H. Assender, A. A. R. Watt, The molecular structure of polymer-fullerene composite solar cells and its influence on device performance. Macromolecules, 43, 2343-2348, (2010)
54. 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)
53. M. Zaka, J. H. Warner, Y. Ito, J. J. L. Morton, M. H. Rummeli, T. Pichler, A. Ardavan, H. Shinohara, G. A. D. Briggs. Exchange Interactions of Spin-Active Metallofullerenes in Solid-State Carbon Networks. Physical Review B 81, 075424 (2010).
52. 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)
51. Y. Ito, J. H. Warner, M. Zaka, R. Pfeiffer, T. Aono, N. Izumi, H. Okimoto, J. J. L. Morton, A. Ardavan, H. Shinohara, H. Kuzmany, H. Peterlik, G. A. D. Briggs, Controlling Intermolecular Spin Interactions of La@C82 in Empty Fullerene Matrices Physical Chemistry Chemical Physics. 12,1618-1623 (2010)
50. S. Gorantla, F. Borrnert, A. Bachmatiuk, M. Dimitrakopoulou, F. Schaffel, R. Schonfelder, J. Thomas, T. Gemming, J. H. Warner, G. Cuniberti, J. Eckert, B. Buchner, M. H. Rummeli, Enhanced π-π Interactions Between a C60 Fullerene and a Buckle Bend on a Double-Walled Carbon Nanotube. Nano Research 3, 92-97 (2010)
49. H. Cao, H. Zheng, K. Liu, X. Zhang, J. H. Warner, Bioinspired Peonylike b-Ni(OH)2 Nanostructures with Enhanced Electrochemical Activity and Superhydrophobicity. ChemPhysChem, 11,489-494 (2010)
48. F. Shaffel, J. H. Warner, A. Bachmatiuk, B. Rellinghaus, B. Buchner, L. Schultz, M. H. Rummeli, On the catalytic hydrogenation of graphite for graphene nanoribbon fabrication. Physica Status Solidi (b), 246, 2540-2544 (2009)
47. M. H. Holmes, Y. S. Park, J. H. Warner, R. A. Taylor, Quantum confined Stark effect and corresponding lifetime reduction in a single InxGa1-xN quantum disk. Applied Physics Letters, 95, 181910 (2009)
46. A. Bachmatiuk, F. Borrnert, M. Grobosch, F. Schaffel, U. Wolff, A. Scott, M .Zaka, J. H. Warner, R. Klingeler, M. Knupfer, B. Buchner, M. H. Rummeli, Investigating the graphitization mechanism of SiO2 nanoparticles in CVD. ACS Nano, 3, 4098-4104 (2009)
45. S. Tetali, M. Zaka, R. Schoenfelder,; A. Bachmatiuk, F. Boerrnert, I. Ibrahim, J. Lin, G. Cuniberti, J. H. Warner, B. Buechner, M. Rummeli, Unravelling the mechanisms behind mixed catalysts for the high yield production of single walled carbon nanotubes. ACS Nano, 3, 3839-3844 (2009).
44. G. Zhong, S. Hofmann, F. Yan, H. Telg, J. H. Warner, D. Eder, C. Thomsen, W. Milne, J. Robertson, Acetylene: a key growth precursor for single-walled carbon nanotube forests Journal of Physical Chemistry C. 113, 17321-17325, 2009
43. A. Stavrinados, S. Xu, J. H. Warner, J. L. Hutchinson, J. M. Smith, A. A. R. Watt, Superstructures of PbS nanocrystals in a conjugated polymer and the aligning role of oxidation. Nanotechnology, 20, 445608 (2009)
42. 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)
41. 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, p500 (2009)
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
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
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
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.
Also see homepages: Jamie Warner
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.