Dr Jason Smith
Leader of the Photonic Nanomaterials Group (PNG) in which research is focused on optical and electronic properties of solid state nanostructures for applications such as optoelectronics devices, quantum information processing and photovoltaics. At present the Group’s research involves two such systems - semiconductor nanocrystals and colour centres in diamond which we investigate using luminescence-based optical techniques. More information about our research can be found in the project descriptions below, or on the PNG website.
Excitons in semiconductor nano-heterostructures
E. Tyrrell, S. Fairclough, Dr. A.A.R. Watt, Dr. J.M. Smith
Semiconductor nanocrystals with strong optical transitions are becoming increasingly important in a wide range of applications in fields as diverse as medicine, renewable energy, and telecommunications. In nanocrystals made from a single constituent material choosing the size also determines other important optical properties, such as the luminescence lifetime and linewidth. However it is also possible to grow heterostructures of different materials, to explore different quantum confinement geometries which modify the behaviour in both quantitative and qualitative fashion. In this project we focus on a particular design of nanocrystal - the 'type II' nano heterostructure - in which electrons and holes are spatially separated in different core and shell regions, all within a few-nanometres diameter crystal! These nanocrystals are particularly attractive for use in solar cells, and in optical amplifiers and lasers. The project involves both experimental and theoretical approaches to determine the design rules and optical properties of these materials.
High Q optical microcavities for solid state cavity QED
P. Dolan, Dr. G. Hughes, Dr. J.M. Smith
In this project we are developing large arrays of high quality tunable optical microcavities and using them to modify the photon emission properties of nanomaterials such as diamond colour centres and semiconductor nanocrystals. The project focuses on the basic science of the emitter/cavity quantum systems, and explores their use as single photon sources, microlasers, and in a range of sensing and spectroscopic applications. Collaborators include the University of Strathclyde, the University of Bristol, and the University of Melbourne.
Enhancing the efficiency of thin film solar cells using optical confinement
M. Wincott, A. Powell, Dr. H.E. Assender, Dr. A.A.R. Watt, Dr. J.M. Smith
Thin film solar cells offer an inexpensive means to generate clean energy, but current efficiencies are limited to around five percent, about three times lower than commercial polycrystalline silicon cells. One of the main reasons behind the low efficiency is that a tension exists between the desire to absorb as much as possible of the incident light, in which case the optical path length should be thick (at least several hundred nanometres), and the desire to extract the photogenerated charge carriers efficiently from the cell, in which case the exciton transport path length should be short (no more than a few tens of nanometers). Most attempts to solve this problem involve using a thick cell, and focusing the advanced aspects of cell design on building in some means for ensuring a short transport path length. Here we take the opposite viewpoint; that the optical path can be elongated for a given cell geometry by the use of wave guiding and cavitation, thereby reducing the burden placed on the transport related features of the device. This new project involves the design, fabrication, and testing of devices that explore this theme by employing inexpensive approaches to encourage light to propagate in the plane of the film.
Roll-to-roll processing of organic electronics
Dr G.A.W. Abbas, Z. Ding, Dr. H.E. Assender
Electronics components that can be manufactured using roll-to-roll processing offer the possibility of lower cost devices as well as those that might be mechanically flexible in use. Roll-to-roll (R2R) processing, using a flexible substrate (typically a polymer film) allows for cheap production of many components very rapidly, with low energy requirements. Key areas of exploitation of this technology include flexible displays, but there is also a wealth of lower-cost applications. Tagging and tracking of fast moving consumer goods is an example technology that truly exploit the very low-cost nature of the production and in which the manufacturing is closely linked to the manufacturing routes currently exploited for e.g. packaging technologies. This project seeks to exploit the existing industrialised technology of vacuum R2R processing, widely used for example in the packaging industry, to develop the manufacture of very low cost organic field-effect transistor (OFET)-based devices and circuits. This manufacturing route, like solvent based systems, is cheap and provides flexible product, and we can exploit high electrical mobility molecular semiconductors. Additional advantages of the solvent-free vacuum processes include: a) likely enhanced web-speed, b) integration with vacuum-based metal deposition for conducting channels, and metal or ceramic deposition for barrier layers and possible interfacial modification, and c) the ability to deposit multiple thin layers to build up device structures without solvent interactions with underlying layers. The project will exploit our existing R2R web processing facility to explore the principal manufacturing challenges to R2R vacuum production of OFET devices: 1) selection and adaptation of materials to vacuum deposition integrated with design of suitable circuitry, 2) patterning of the semiconductor and insulator layers to allow the formation of circuit connections between devices and 3) reliability of manufacture to be able to produce arrays of multiple transistors for circuits. It will allow us to explore and develop the deposition of molecular semiconductor and dielectric materials and then the subsequent reliability and thermo-mechanical resilience of the resulting product such that it might need to withstand, for example, during a lamination process.
4 public active projects
P. R. Dolan, G. M. Hughes, F. Grazioso, B. R. Patton, and J. M. Smith, Femtoliter tunable optical cavity arrays, Optics Lett. (in press).
F. Grazioso, B. R. Patton, and J. M. Smith, A high stability beam-scanning confocal optical microscope for low temperature operation, Review of Scientific Instruments 81, (2010).
C. A. Cattley, A. Stavrinadis, R. Beal, J. Moghal, A. G. Cook, P. S. Grant, J. M. Smith, H. E. Assender, and A. A. R. Watt, Colloidal synthesis of lead oxide nanocrystals for photovoltaics, Chem. Comm. 46, 2802 (2010).
R. M. Beal, A. Stavrinadis, J. H. Warner, J. M. Smith, H. E. Assender, and A. A. R. Watt, The molecular structure of polymer-fullerene composite solar cells and its influence on device performance, Macromolecules 43, 2343 (2010).
A. Stavrinadis, J. M. Smith, C. A. Cattley, A. G. Cook, P. S. Grant, and A. A. R. Watt, SnS/PbS nanocrystal heterojunction photovoltaics, Nanotechnology 21, 185202 (2010).
A. Stavrinadis, S. Xu, J. H. Warner, J. Hutchison, J. M .Smith and A. A. R. Watt, Superstructures of PbS nanocrystals in a conjugated polymer and the aligning role of oxidation, Nanotechnology 20, 445608 (2009).
D. J. Keeble, E. A. Thomsen, A. Stavrinadis, I. D. W. Samuel, J. M. Smith, and A. A. R. Watt, Paramagnetic point defects and charge carriers in PbS and CdS nanocrystal polymer composites, J. Phys. Chem. C 113, 17306 (2009).
S. C. Benjamin, B. W. Lovett, and J. M. Smith, Prospects for measurement based quantum computing using solid state spins, Laser & Photonics Reviews, 3, 556 (2009).
P. K. Santra, R. Viswanatha, S. Daniels, N. L. Pickett, J. M Smith, P. O'Brien and D. D. Sarma, Investigation of the internal heterostructure of highly luminescent quantum dot - quantum well nanocrystals, J. Am. Chem. Soc. 131, 470 (2009).
B. A. Fairchild, P. Olivero, A. D. Greentree, F. Waldermann, R. A. Taylor, J. M. Smith, S. Rubanov, S. Huntington, B. Gibson, D. N. Jamieson, and S. Prawer, Fabrication of ultra thin membranes from single crystal diamond for photonic and NEMS applications, Advanced Materials 20, 4793 (2008).
A. Stavrinadis, R. Beal, J. M. Smith, H. E. Assender, and A. A. R. Watt, Direct formation of PbS nanorods in a conjugated polymer, Advanced Materials 20, 3105 (2008).
S. H. Kim, P. H. Sher, Y. B. Hahn, and J. M. Smith, Luminescence from single CdSe nanocrystals embedded in ZnO thin films using atomic layer deposition, Nanotechnology 19, 365202 (2008).
P. A. Dalgarno, J. M .Smith, J. MacFarlane, B. D. Gerardot, K. Karrai, A. Badolato, P. M. Petroff, and R. J. Warburton, Coulomb interactions in single charged self-assembled quantum dots: Radiative lifetime and recombination energy, Phys. Rev. B 77, 245311 (2008).
P. A. Dalgarno, M. Ediger, B. D. Gerardot, J. M. Smith, S. Seidl, M. Kroner, K. Karrai, P. M. Petroff, A. O. Govorov, and R. J. Warburton, Optically induced hybridization of a quantum dot state with a filled continuum, Phys. Rev. Lett. 100, 176801 (2008).
P. H. Sher, J. M. Smith, P. A. Dalgarno, R. J. Warburton, X. Chen, P. J. Dobson, S. M. Daniels, N. L. Pickett, and P. O'Brien, Power law carrier dynamics in semiconductor nanocrystals at nanosecond time scales, Appl. Phys. Lett. 92, 101111 (2008).
S. Seidl, M. Kroner, P. A. Dalgarno, A. Hogele, J. M. Smith, M. Ediger, B. D. Gerardot, J. M. Garcia, P. M. Petroff, K. Karrai, and R. J. Warburton, Absorption and photoluminescence spectroscopy on a single self-assembled charge-tunable quantum dot, Phys. Rev. B 72 195339 (2005).
P. A. Dalgarno, J. M. Smith, B. D. Gerardot, A. O. Govorov, K. Karrai, P. M. Petroff, and R. J. Warburton, Dark exciton decay dynamics of a semiconductor quantum dot, Phys. Stat. Solid. A-Applications and Materials Science 202 p.2591-2597 (2005).
A. J. Moore, J. Smith, and N. J. Lawson, Volume three-dimensional flow measurements using wavelength multiplexing, Optics Lett. 30, p.2569 (2005).
J. M. Smith, P. A. Dalgarno, R. J. Warburton, A. O. Govorov, K. Karrai, B. D. Gerardot and P. M. Petroff, Voltage control of the spin dynamics of an exciton in a semiconductor quantum dot, Phys. Rev. Lett. 94, 197402 (2005).
M. Ediger, P. A. Dalgarno, J. M. Smith, B. D. Gerardot, R. J. Warburton, K. Karrai and P. M. Petroff, Controlled generation of neutral, negatively-charged and positively-charged excitons in the same single quantum dot, Appl. Phys. Lett. 86, 2119209 (2005).
B. Urbaszek, E. J. McGhee, J. M. Smith, R. J. Warburton, K. Karrai, B. D. Gerardot, J. M. Garcia and P. M. Petroff, Charged excitons in individual quantum dots: effects of vertical electric fields and optical pump power, Physica E 17, 35 (2003).
J. M. Smith, P. A. Dalgarno, B. Urbaszek, E. J. McGhee, G. S. Buller, G. J. Nott and R. J. Warburton, Carrier storage and capture dynamics in quantum-dot heterostructures, Appl. Phys. Lett. 82, 3761 (2003).
M. A. Malik, P. O'Brien, S. Norager and J. Smith, Gallium arsenide nanoparticles: synthesis and characterisation, J. Mater. Chem. 13, 2591 (2003).
J. M. Smith, G. S. Buller, D. Marshall, A. Miller and C. C. Button, Microsecond carrier lifetimes in InGaAsP quantum wells emitting at lambda=1500 nm, Appl. Phys. Lett. 80, 1870 (2002).
J. M. Smith, P. A. Hiskett, I. Gontijo, L. Purves and G. S. Buller, A picosecond time-resolved photoluminescence microscope with detection at wavelengths greater than 1500 nm, Rev. Sci. Instrum. 72, 2325 (2001).
J. M. Smith, P. A. Hiskett and G. S. Buller, Picosecond time-resolved photoluminescence at detection wavelengths greater than 1500 nm, Opt. Lett. 26, 731 (2001).
P. A. Hiskett, J. M. Smith, G. S. Buller and P. D. Townsend, Low-noise single-photon detection at wavelength 1550 nm.Electron. Lett. 37, 1081 (2001).
S. Pellegrini, G. S. Buller, J. M. Smith, A. M. Wallace and S. Cova, Laser-based distance measurement using picosecond resolution time-correlated single-photon counting, Meas. Sci. Technol. 11, 712 (2000).
P. A. Hiskett, G. S. Buller, A. Y. Loudon, J. M. Smith, I. Gontijo, A. C. Walker, P. D. Townsend and M. J. Robertson, Performance and design of InGaAs/InP photodiodes for single- photon counting at 1550 nm, Appl. Optics 39, 6818 (2000).
High Q optical microcavities for solid state cavity QED
Dr Jason Smith
We are currently developing large arrays of high quality tunable optical microcavities and using them to modify the photon emission properties of nanomaterials such as diamond colour centres and semiconductor nanocrystals. Our work focuses on cavity fabrication, the basic science of the emitter/cavity quantum systems, and exploring their use as single photon sources, microlasers, and in a range of sensing and spectroscopic applications. The new project will involve further developing the cavity fabrication techniques (using focused ion beam milling), and performing experiments to characterise the cavities and the cavity/emitter systems. Particular directions of focus may include increasing the cavity quality factors sufficiently to enter the strong coupling regime, developing nanocrystal-based semiconductor microlasers, or exploring their use in advanced sensing and optical characterisation applications.
Also see homepages: Jason Smith
Semiconductor nanocrystal sensors
Dr Jason Smith
Semiconductor nanocrystals grown by wet chemical methods are rapidly becoming a key functional material that are finding applications in fields as diverse as life sciences, solar power generation, and telecommunications. It is well known that the chemistry of the nanocrystals’ surface profoundly affects their electronic properties, and the fluorescence from single nanocrystals displays a number of interesting dynamic phenomena such as random blinking and spectral drift due to the Quantum Confined Stark Effect which can potentially be harnessed for use as sensors of the local environment. The aim of this project will be to develop techniques for using changes in the fluorescence properties of nanocrystals to sense changes in the surroundings. It will build on recent work to develop a fluidics device and electrical gating structures compatible with single nanocrystal photoluminescence measurements.
Also see homepages: Jason Smith
Optical resonators in ultrapure diamond
Dr Jason Smith
Diamond is optically transparent throughout the infrared, visible and into the ultraviolet region of the spectrum, and its refractive index is relatively insensitive to temperature, making it highly attractive for producing stable optical resonator structures. Such structures could have a number of uses, from classical optical switches, to microcavities for housing quantum bits (qubits) for quantum computing. The difficulty is that processing diamond into microstructures is highly challenging as its chemical inertness makes it resistant to most etches. New plasma etching techniques developed by our collaborators at the University of Strathclyde Institute of Photonics look extremely promising in this regard, and the project will be to design and characterize resonators and waveguides based on thin films of diamond. The project will also involve interaction with the Quantum Photonics group at the University of Bristol.
Also see homepages: Jason Smith
Mapping the structure and composition of heterostructured semiconductor nanoparticles using the scanning transmission electron microscope
Prof P D Nellist, Dr J M Smith
Heterostructured semiconducting nanoparticles show the greatest potential in terms of being able to control and harness quantum properties at room temperature with applications in healthcare, photovoltaics, sensing and optoelectronic devices, spintronic, quantum computation & information processing. Measuring the structure and composition variations at atomic resolution, however, presents a severe characterisation challenge. Recent technological developments in scanning transmission electron microscopy have allowed imaging and spectroscopy measurements to be made routinely at atomic resolution. The aim of this project is to use the capabilities of STEM to make quantitative measurements of structure and composition of heterostructured semiconducting nanoparticles, which can then be related to the optical response of the nanoparticles and used to guide the synthesis and applications of the nanoparticles.
Engineering excitons in semiconductor nanocrystals
Dr Jason Smith and Dr Andrew Watt
The ability to grow heterostructured semiconductor nanocrystals using wet chemical techniques opens up a plethora of new possibilities for engineering their optical and electrical properties. For instance (i) in type II heterostructures, the electron and hole that form the ‘exciton’ are separated spatially, so that optical gain can be generated; and (ii) alloyed structures have recently been grown in which luminescence blinking is absent – a discovery that may hold the key to developing nanocrystal-based LEDs, sensors, and even quantum optical devices. The aim of this project will be to investigate the excitonic behaviour of heterostructured and alloyed nanocrystals. In particular, low temperature spectroscopy of single nanocrystals will be used to gain information free from inhomogeneous and thermal broadening. Experimental results will be compared with theory developed in-house. Applicants interested in the synthesis of alloyed and heterostructured nanocrystals will also be considered.
Also see a full listing of New projects available within the Department of Materials.