School of Physics and Astronomy

Dr Kevin Donovan

Kevin

Reader in Molecular Physics

Email: k.j.donovan@qmul.ac.uk
Telephone: 020 7882 3410
Room Number: G.O. Jones Building, Room 117

Teaching

My teaching

I am currently responsible for teaching;

Thermodynamics (SPA5219), a second year module covering thermodynamics.

Electromagnetic Waves and Optics (SPA5222), a second year module covering physical and geometric optics.

Research

Research Interests:

My research interests

1. Single Walled Carbon Nanotubes. The induced polarisability of single walled carbon nanotubes, SWCNTs, has provided a powerful tool for their study. While there is no permanent dipole moment  the induced dipole can be substantial at even moderate fields allowing the manipulation of the SWCNTs under the action of various forces. This leads to several related but seperate studies;

(i) Dielectrophoresis.The differential polarisability of different species of SWCNT, specifically metallic and semiconducting, make the dielectrophoretic force an interesting candidate for use in the separation of SWCNTs. In a non-uniform electric field the induced dipole experiences a dielectrophoretic translational force and the motion of nanotubes under the action of such forces is the subject of study. Of particular interest is the relationship between Brownian and viscous forces and their action on nanoscale objects compared with the more familiar mesoscale objects described by classical hydrodynamics

 (ii) The Kerr Effect. In a uniform electric field, SWCNTs in suspension will experience a rotational torque and can be made to rotate in viscous media. The consequent alignment renders a previously  isotropic suspension anisotropic and thus birefringent (refractive index depending on polarisation state of light). The study of rotational dynamics of nanoscale objects becomes possible by imposing transient electric fields.

(iii) Induced Dichroism. Similarly, in a uniform field the isotropic sample will become increasingly dichroic (absorption depending on polarisation state of light) as alignment proceeds. Dynamic studies are undertaken of induced linear dichroism in order to more closely relate the dynamics of nanoscale objects to their well studied mesoscale counterparts.

(iv) Rheology of SWCNT suspensions. The application of a controllable torque and the measurement of the dynamic response of SWCNTs allows study of the efffect of the SWCNTs on the viscosity of their local environment and how the nanotube concentration affects this.

(v) Other CNTs; All of the previously referred to techniques are applicable to Double Walled Nanotubes, DWNTs, and Multi-Walled Nanotubes, MWNTs and these too are under study.

2. Charge carrier transport on Polydiacetylene Single Crystals.

Electron (hole) transport on the backbone of conjugated polymers might be considered to be similar to that in silicon as both are covalently bonded structures. The conjugated polymer backbone is one dimensional in contrast to the three dimensional silicon lattice and this difference in dimensionality will make a difference to transport properties. Certain conjugated polymers of the polydiacetylene group may be grown first as macroscopic monomer single crystals and these may be subsequently polymerised to give macroscopic polymer single crystals. Such highly perfect single crystal polymers offer a unique opportunity to study the transport of free carriers on a conjugated one dimensional backbone.

Such studies have revealed, through transient photoconductivity techniques, a unique behaviour that comes about as a result of their one dimensionality. The electrons (holes) in the conduction (valence) band in this one dimensional semiconductor, strongly couple with lattice distortions and travel with the distortion as solitons or solectrons, at around the velocity of sound independent of the applied electric field. Further, the dissipation of these solectrons by phonon scattering is extremely weak and the saturated velocity is reached at very low electric fields.

Transient photoconductivity studies.
The technique of photoconductivity including time resolved photoconductivity with temporal resolution covering times from 100 picoseconds to DC is used to study the effects of reduced dimensionality on charge transport. The high end of this temporal resolution is among the fastest achieved anywhere, worldwide. The Auston switch technique has been developed to this end with a novel application for samples suspended in solvents and contained in an integrated co-axial geometry cell based around the Auston technique.

The Solectron Field Effect Transistor, SFET.

Given the transport properties of polydiacetylenes described above, it is of interest to use the polydiacetylene chains as the channel between source and drain electrodes on a single crystal. The solectron will travel at the velocity of sound ( 2 km/s) even at very low source-drain voltages (electric field) and the creation of a field effect transistor, FET, by addition of a gate electrode above the channel and separated from it by a thin insulator layer will exhibit unusual current-voltage characteristics. Specifically the solectron FET, SFET, can be expected to operate at very low power compared with conventional devices. Because the single crystal character of the polydiacetylene does not allow doping it is necessary to introduce the carriers into the channel by using an injecting electrode for the source. A further potential problem is that the trapping of an electron within the channel at a defect will result in an impediment to introduction of further carriers due to Coulomb repulsion. Highly perfect crystals are therefore needed and it is possible to obtain crystals with an on chain defect separation of 500 microns. If the channel length is much shorter than this the problem should not arise.

3. Charge Transport;  Other organic materials demonstrate the effects of reduced dimensionality on charge transport. This is a situation commonly encountered when the condensed matter is held together by a mixture of Van der Waals and covalent bonding and has consequences for the rate of trapping and bimolecular recombibnation which have been studied.

The charge transport in a range of organic materials has been studied and these include;

(i) Columnar, Discotic Liquid Crystals.

(ii) Carbon nanotubes.

(iii) Polydiacetylene conjugated polymers. 

(iv) Langmuir Blodgett multilayers.

Publications

  • Arenas-Guerrero P, Delgado ÁV, Donovan KJ et al. (2018). Determination of the size distribution of non-spherical nanoparticles by electric birefringence-based methods.. nameOfConference
  • Arenas-Guerrero P, Jiménez ML, Scott K et al. (2017). Electric birefringence of carbon nanotubes: Single- vs double-walled. nameOfConference
  • (2016). Significance of bundling effects on carbon nanotubes' response to hydrostatic compression. nameOfConference
  • Velarde MG, Chetverikov AP, Ebeling W et al. (2014). On the electron transport in polydiacetylene crystals and derivatives. nameOfConference
  • Donovan KJ, Scott K (2013). Anomalous intrinsic viscosity of octadecylamine-functionalised carbon nanotubes in suspension.. nameOfConference
  • Donovan KJ, Scott K (2012). Anomalous effective hydrodynamic radius of octadecylamine functionalised single walled carbon nanotubes. nameOfConference
  • Robb-Smith TJ, Donovan KJ, Scott K et al. (2011). Induced electro-optic effects in single-walled carbon nanotubes. I. Polarizability of metallic nanotubes. nameOfConference
  • Robb-Smith TJ, Donovan KJ, Scott K et al. (2011). Induced electro-optic effects in single-walled carbon nanotubes. II. Hydrodynamics of nanotubes in viscous media. nameOfConference
  • Preece MMPINSPRASKKJDAJA (2010). Design and Synthesis of Novel Calamitic and Discotic Materials Based on the Photorefractive Carbazole Unit. nameOfConference
  • Donovan KJ, Scott K, Somerton M et al. (2006). Transient photocurrents in a charge transfer complex of trinitrofluorenone with a carbazole substituted discotic liquid crystal. nameOfConference
  • Donovan KJ, Scott K (2005). Transient electric birefringence in suspensions of single-walled carbon nanotubes. nameOfConference
  • Lutz T, Donovan KJ (2005). Macroscopic scale separation of metallic and semiconducting nanotubes by dielectrophoresis. nameOfConference
  • Bunning JC, Donovan KJ, Bushby RJ et al. (2005). Electron photogeneration in a triblock co-polymer discotic liquid crystal. nameOfConference
  • Scott K, Somerton M, Bunning JC et al. (2005). Bimolecular recombination on carbon nanotubes. nameOfConference
  • DONOVAN KJ (2005). Charge Transport in Discotic Liquid Crystals. Proc.Int.Symp. Superfunctionality Organic Devices, IPAP Conf. Series 6, 38
  • Bushby RJ, Donovan KJ, Kreouzis T et al. (2005). Molecular engineering of triphenylene-based discotic liquid crystal conductors. nameOfConference
  • (2004). Enhanced conduction in the discotic mesophase. nameOfConference
  • Bunning JC, Donovan KJ, Scott K (2004). Observation of transient photocurrents on suspended nanotubes. nameOfConference
  • Donovan KJ, Kreouzis T, Scott K et al. (2003). Molecular engineering the phototransport properties of discotic liquid crystals. nameOfConference
  • Bushby RJ, Lozman OR, Bunning JC et al. (2003). Photoconducting discotic liquid crystals. nameOfConference
  • Bunning JC, Donovan KJ, Kreouzis T et al. (2003). Quantum efficiencies of photogeneration in discotic liquid crystals. Part 2: Electric field and temperature dependence. nameOfConference
  • Scott K, Donovan KJ, Kreouzis T et al. (2003). Quantum efficiency of photogeneration in discotic liquid crystals: Part 1: Temperature and wavelength dependence. nameOfConference
  • Pecchia A, Lozman OR, Movaghar B et al. (2002). Photoconductive transients and one-dimensional charge carrier dynamics in discotic liquid crystals. nameOfConference
  • Boden N, Bushby RJ, Donovan K et al. (2001). 2,3,7, 8,12,13-Hexakis[2-(2-methoxyethoxy)ethoxy]-tricycloquinazoline: a discogen which allows enhanced levels of n-doping. nameOfConference
  • Kreouzis T, Donovan KJ, Boden N et al. (2001). Temperature-independent hole mobility in discotic liquid crystals. nameOfConference
  • Liu Q (2000). Enhanced electronic transport properties in complementary binary discotic liquid crystal systems. nameOfConference
  • Donovan KJ, Wilson EG (2000). Bimolecular recombination quenching in Langmuir Blodgett multilayers. nameOfConference
  • (2000). Influence of electric field on interwell tunneling rate in quasi two dimensional organic quantum wells. nameOfConference
  • (2000). On the non-Arrhenius temperature dependence of the interwell electron tunneling rate in quasi two dimensional organic quantum wells. nameOfConference
  • (2000). Deconvolution of time of flight photocurrent transients and electronic response time in columnar liquid crystals. nameOfConference
  • (2000). Measurement of intermolecular electron current in supramolecular assemblies created by the Langmuir-Blodgett technique. nameOfConference
  • (1999). Carrier range on finite, isolated molecular wires in a monomer crystalline matrix: Example: Polydiacetylene, 4BCMU. nameOfConference
  • (1999). DC photoconduction action spectra in thin film polymer crystals of 3 and 4BCMU polydiacetylene. nameOfConference
  • (1999). Carrier range on conjugated polymers as molecular wires. Example: Polydiacetylene, 4BCMU. nameOfConference
  • (1999). Carrier range and photocarrier generation efficiency on thin-film crystalline-conjugated polymers. nameOfConference
  • (1998). One dimensional carrier trapping in the crystalline phase of a columnar liquid crystal. nameOfConference
  • (1998). Time resolved electron motion on isolated polymer chains in solution. nameOfConference
  • (1998). Charge dynamics and recombination kinetics in columnar discotic liquid crystals. nameOfConference
  • Clark TR, Kenney ME (1996). Electron tunnelling rates as a function of intermolecular distance, measured in a Langmuir-Blodgett assembly. nameOfConference
  • Boden N, Bushby RJ, Clements J et al. (1995). Mechanism of charge transport in discotic liquid crystals.. nameOfConference
  • Clark TR, Batzel DA, Kenney ME (1994). Comparison of tunnelling rates in two Langmuir-Blodgett quantum well structures differing only in barrier width. nameOfConference
  • Bonnett R, Wilkins RF, Paradiso R et al. (1994). Determination of the parallel and perpendicular intermolecular tunnelling rates in two Langmuir-Blodgett quantum well systems. nameOfConference
  • (1994). Control of electron transfer in a nanostructure assembled from organic molecules. nameOfConference
  • Batzel DA, Kenney ME (1994). Comparison of tunneling rates in two Langmuir-Blodgett quantum well structures differing only in barrier width. nameOfConference
  • Sudiwala RV, Wilson EG, Bonnett R et al. (1994). Determination of the parallel and perpendicular intermolecular tunnelling rates in two Langmuir-Blodgett quantum well systems. nameOfConference
  • Wilkins RF, Paradiso R, Clark TR et al. (1993). Determination of anisotropic electron transport properties of two Langmuir-Blodgett organic multiple quantum wells. nameOfConference
  • Donovan KJ, Elkins JWP, Wilson EG (1993). Novel coulomb glass creation in electronic one dimensional systems. nameOfConference
  • (1993). Novel Coulomb glass creation in electronic one dimensional systems. nameOfConference
  • (1993). Electron-electron interactions and coulomb glass creation in electronic one dimensional systems. nameOfConference
  • Clark TR, Kenney ME (1992). Electron transport across organic quantum wells: new results on amphiphilic phthalocyanines. nameOfConference
  • (1992). Fast photoconduction in Langmuir-Blodgett multilayers of polydiacetylenes. nameOfConference
  • (1991). Reply by K J Donovan and E G Wilson. nameOfConference
  • (1991). The effect of electric field on the bimolecular recombination rate in a one-dimensional polymer single crystal. nameOfConference
  • (1991). The inchworm memory - progress towards a new Langmuir Blodgett molecular electronic device. nameOfConference
  • (1991). Carrier recombination in polydiacetylenes the scaling with sample size. nameOfConference
  • (1991). The effect of electric field on the bimolecular recombination rate in a one dimensional polymer single crystal. nameOfConference
  • (1991). Carrier recombination in polydiacetylenes: The scaling with sample size. nameOfConference
  • (1991). Effect of electric field on the bimolecular recombination rate in a one dimensional polymer single crystal. nameOfConference
  • (1991). Inchworm memory. Progress towards a new Langmuir Blodgett molecular electronic device. nameOfConference
  • (1991). Temporal resolution of electron motion along a molecular wire in solution. nameOfConference
  • (1990). The field-independent early-time drift velocity of carriers in polydiacetylenes: Solitary-wave acoustic polaron or dispersive trap-limited transport in 1D?. nameOfConference
  • Burrows PE, Donovan KJ, Wilson EG (1989). Electron motion perpendicular to Langmuir-Blodgett multilayers of conjugated macrocyclic compounds: The organic quantum well. nameOfConference
  • Wilson G (1989). Non-solitonic nature of picosecond photoconductivity in trans-polyacetylene. nameOfConference
  • (1989). The observation of electron motion along individual polydiacetylene chains in solution: The molecular wire. nameOfConference
  • (1989). The search for east transits using the Auston switch technique in single crystal polydiacetylenes. nameOfConference
  • (1989). Unipolar carrier transport in quasi one dimensional systems:- novel results in polydiacetylene. nameOfConference
  • (1989). Electron motion perpendicular to Langmuir-Blodgett multilayers of conjugated macrocyclic compounds. The organic quantum well. nameOfConference
  • (1988). Organic quantum wells:- Electron transport across Langmuir-Blodgett films of conjugated organic molecules. nameOfConference
  • (1986). Temperature dependence of pulsed photocurrents in the one-dimensional semiconductor pdats. nameOfConference
  • (1986). SOLITARY WAVE ACOUSTIC POLARON MOTION ON POLYDIACETYLENE CHAINS.. nameOfConference
  • (1985). Micro-engineering of a novel organic molecular electronic structure. nameOfConference
  • (1985). Carrier trapping in one-dimensional systems: Example organic PDATS. nameOfConference
  • (1984). Anomalous electric field dependence of carrier drift in one-dimensional systems. Example: Organic PDA-TS. nameOfConference
  • (1981). Demonstration of an ultra-high mobility organic polymer. nameOfConference
  • (1981). Photocarrier creation in one dimension. nameOfConference
  • (1979). Demonstration of high-mobility one-dimensional semiconducting polymers. nameOfConference

PhD Supervision

This is not an exhaustive list and I would be happy to discuss other project possibilities.

Project Title
Carbon nanotubes in suspension; Rotation & translation of mesoscopic cylinders in electric fields.
Creating organic field effect transistors using polymer single crystals.