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
  • Sun YW, Hernández I, González J et al. (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
  • Boden N, Bushby RJ, Lozman OR et al. (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
  • Kreouzis T, Scott K, Donovan KJ et al. (2000). Enhanced electronic transport properties in complementary binary discotic liquid crystal systems. nameOfConference
  • Elliott JE, Jeong IS, Scott K et al. (2000). Bimolecular recombination quenching in Langmuir Blodgett multilayers. nameOfConference
  • Donovan KJ, Elliott JE, Jeong IS et al. (2000). Influence of electric field on interwell tunneling rate in quasi two dimensional organic quantum wells. nameOfConference
  • Jeong IS, Scott K, Donovan KJ et al. (2000). On the non-Arrhenius temperature dependence of the interwell electron tunneling rate in quasi two dimensional organic quantum wells. nameOfConference
  • Donovan KJ, Kreouzis T (2000). Deconvolution of time of flight photocurrent transients and electronic response time in columnar liquid crystals. nameOfConference
  • Donovan KJ, Elliott JE, Scott K et al. (2000). Measurement of intermolecular electron current in supramolecular assemblies created by the Langmuir-Blodgett technique. nameOfConference
  • Spagnoli S, Donovan KJ, Scott K et al. (1999). Carrier range on finite, isolated molecular wires in a monomer crystalline matrix: Example: Polydiacetylene, 4BCMU. nameOfConference
  • Donovan KJ, Scott K, Spagnoli S et al. (1999). DC photoconduction action spectra in thin film polymer crystals of 3 and 4BCMU polydiacetylene. nameOfConference
  • Donovan KJ, Spagnoli S (1999). Carrier range on conjugated polymers as molecular wires. Example: Polydiacetylene, 4BCMU. nameOfConference
  • Donovan KJ, Scott K, Spagnoli S (1999). Carrier range and photocarrier generation efficiency on thin-film crystalline-conjugated polymers. nameOfConference
  • Donovan KJ, Kreouzis T, Boden N et al. (1998). One dimensional carrier trapping in the crystalline phase of a columnar liquid crystal. nameOfConference
  • Donovan KJ, Hargrave P, Scott K et al. (1998). Time resolved electron motion on isolated polymer chains in solution. nameOfConference
  • Boden N, Bushby RJ, Clements J et al. (1998). Charge dynamics and recombination kinetics in columnar discotic liquid crystals. nameOfConference
  • Donovan KJ, Elliott JE, Scott K et al. (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
  • Donovan KJ, Elliot J, Scott K et al. (1994). Comparison of tunnelling rates in two Langmuir-Blodgett quantum well structures differing only in barrier width. nameOfConference
  • Donovan KJ, Scott K, Sudiwala RV et al. (1994). Determination of the parallel and perpendicular intermolecular tunnelling rates in two Langmuir-Blodgett quantum well systems. nameOfConference
  • Scott K, Sudiwala RV, Donovan KJ et al. (1994). Control of electron transfer in a nanostructure assembled from organic molecules. nameOfConference
  • Donovan KJ, Scott K, Sudiwala RV 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
  • Donovan KJ, Elkins JWP, Wilson EG (1993). Novel Coulomb glass creation in electronic one dimensional systems. nameOfConference
  • Donovan KJ, Elkins JWP, Wilson (1993). Electron-electron interactions and coulomb glass creation in electronic one dimensional systems. nameOfConference
  • Donovan KJ, Paradiso R, Scott K et al. (1992). Electron transport across organic quantum wells: new results on amphiphilic phthalocyanines. nameOfConference
  • Donovan KJ, Sudiwala RV, Wilson EG (1992). Fast photoconduction in Langmuir-Blodgett multilayers of polydiacetylenes. nameOfConference
  • Donovan KJ, Wilson EG (1991). Reply by K J Donovan and E G Wilson. nameOfConference
  • Donovan KJ, Elkins JWP, Wilson EG (1991). The effect of electric field on the bimolecular recombination rate in a one-dimensional polymer single crystal. nameOfConference
  • Burrows PM, Donovan KJ, Scott K et al. (1991). The inchworm memory - progress towards a new Langmuir Blodgett molecular electronic device. nameOfConference
  • Donovan KJ, Willock DJ, Wilson EG (1991). Carrier recombination in polydiacetylenes the scaling with sample size. nameOfConference
  • Donovan KJ, Elkins JPW, Wilson EG (1991). The effect of electric field on the bimolecular recombination rate in a one dimensional polymer single crystal. nameOfConference
  • Donovan KJ, Elkins JPW, Wilson EG (1991). Effect of electric field on the bimolecular recombination rate in a one dimensional polymer single crystal. nameOfConference
  • Burrows PM, Donovan KJ, Scott K et al. (1991). Inchworm memory. Progress towards a new Langmuir Blodgett molecular electronic device. nameOfConference
  • Donovan KJ, Wilson EG (1991). Temporal resolution of electron motion along a molecular wire in solution. nameOfConference
  • Donovan KJ, Wilson EG (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
  • Bleier H, Donovan K, Friend RH et al. (1989). Non-solitonic nature of picosecond photoconductivity in trans-polyacetylene. nameOfConference
  • Donovan KJ, Wilson EG (1989). The observation of electron motion along individual polydiacetylene chains in solution: The molecular wire. nameOfConference
  • Donovan KJ, Wilson EG (1989). The search for east transits using the Auston switch technique in single crystal polydiacetylenes. nameOfConference
  • Donovan KJ, Fisher NE, Wilson EG (1989). Unipolar carrier transport in quasi one dimensional systems:- novel results in polydiacetylene. nameOfConference
  • Burrows PE, Donovan KJ, Wilson EG (1989). Electron motion perpendicular to Langmuir-Blodgett multilayers of conjugated macrocyclic compounds. The organic quantum well. nameOfConference
  • Ahmed FR, Burrows PE, Donovan KJ et al. (1988). Organic quantum wells:- Electron transport across Langmuir-Blodgett films of conjugated organic molecules. nameOfConference
  • Donovan KJ, Wilson EG (1986). Temperature dependence of pulsed photocurrents in the one-dimensional semiconductor pdats. nameOfConference
  • Donovan KJ, Wilson EG (1986). SOLITARY WAVE ACOUSTIC POLARON MOTION ON POLYDIACETYLENE CHAINS.. nameOfConference
  • Donovan KJ, Freeman PD, Wilson EG (1985). Micro-engineering of a novel organic molecular electronic structure. nameOfConference
  • Donovan KJ, Wilson EG (1985). Carrier trapping in one-dimensional systems: Example organic PDATS. nameOfConference
  • Movaghar B, Murray DW, Donovan KJ et al. (1984). Anomalous electric field dependence of carrier drift in one-dimensional systems. Example: Organic PDA-TS. nameOfConference
  • Donovan KJ, Wilson EG (1981). Demonstration of an ultra-high mobility organic polymer. nameOfConference
  • Donovan KJ, Wilson EG (1981). Photocarrier creation in one dimension. nameOfConference
  • Donovan KJ, Wilson EG (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.