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

2016

Significance of bundling effects on carbon nanotubes' response to hydrostatic compression
Sun YW, Hernández I, González J et al.
Journal of Physical Chemistry C, Volume 120, issue 3, page 1863, 28th January 2016.
DOI: 10.1021/acs.jpcc.5b09082

2014

On the electron transport in polydiacetylene crystals and derivatives
Velarde MG, Chetverikov AP, Ebeling W et al.
EPL, Volume 106, issue 2, 1st April 2014.
DOI: 10.1209/0295-5075/106/27004

2013

Anomalous intrinsic viscosity of octadecylamine-functionalised carbon nanotubes in suspension.
Donovan KJ, Scott K
J Chem Phys, Volume 138, issue 24, page 244902, 28th June 2013.
DOI: 10.1063/1.4811279

2012

Anomalous effective hydrodynamic radius of octadecylamine functionalised single walled carbon nanotubes
Donovan KJ, Scott K
CARBON, Volume 50, issue 10, page 3807, 1st August 2012.
DOI: 10.1016/j.carbon.2012.04.007

2011

Induced electro-optic effects in single-walled carbon nanotubes. I. Polarizability of metallic nanotubes
Robb-Smith TJ, Donovan KJ, Scott K et al.
PHYS REV B, Volume 83, issue 15, 7th April 2011.
DOI: 10.1103/PhysRevB.83.155414

Induced electro-optic effects in single-walled carbon nanotubes. II. Hydrodynamics of nanotubes in viscous media
Robb-Smith TJ, Donovan KJ, Scott K et al.
PHYS REV B, Volume 83, issue 15, 7th April 2011.
DOI: 10.1103/PhysRevB.83.155415

2010

Design and Synthesis of Novel Calamitic and Discotic Materials Based on the Photorefractive Carbazole Unit
Preece MMPINSPRASKKJDAJA
Mol. Crys. Liq. Crys, Volume 84, issue 518, page 84, 1st January 2010.
DOI: 10.1080/15421400903568054

2006

Transient photocurrents in a charge transfer complex of trinitrofluorenone with a carbazole substituted discotic liquid crystal
Donovan KJ, Scott K, Somerton M et al.
CHEM PHYS, Volume 322, issue 3, page 471, 20th March 2006.
DOI: 10.1016/j.chemphys.2005.09.036

2005

Transient electric birefringence in suspensions of single-walled carbon nanotubes
Donovan KJ, Scott K
PHYS REV B, Volume 72, issue 19, 1st November 2005.
DOI: 10.1103/PhysRevB.72.195432

Macroscopic scale separation of metallic and semiconducting nanotubes by dielectrophoresis
Lutz T, Donovan KJ
CARBON, Volume 43, issue 12, page 2508, 1st October 2005.
DOI: 10.1016/j.carbon.2005.05.002

Electron photogeneration in a triblock co-polymer discotic liquid crystal
Bunning JC, Donovan KJ, Bushby RJ et al.
CHEM PHYS, Volume 312, issue 1-3, page 145, 6th June 2005.
DOI: 10.1016/j.chemphys.2004.11.032

Bimolecular recombination on carbon nanotubes
Scott K, Somerton M, Bunning JC et al.
Phys. Rev. B, Volume 71, issue 8, page 085412-1, 1st February 2005.
DOI: 10.1103/PhysRevB.71.085412

Charge Transport in Discotic Liquid Crystals
DONOVAN KJ
1st January 2005.

Molecular engineering of triphenylene-based discotic liquid crystal conductors
Bushby RJ, Donovan KJ, Kreouzis T et al.
OPTO-ELECTRON REV, Volume 13, issue 4, page 269, 1st January 2005.

2004

Enhanced conduction in the discotic mesophase
Boden N, Bushby RJ, Lozman OR et al.
Molecular Crystals and Liquid Crystals, Volume 410, 1st December 2004.
DOI: 10.1080/15421400490434324

Observation of transient photocurrents on suspended nanotubes
Bunning JC, Donovan KJ, Scott K
J APPL PHYS, Volume 96, issue 7, page 3939, 1st October 2004.
DOI: 10.1063/1.1789268

2003

Molecular engineering the phototransport properties of discotic liquid crystals
Donovan KJ, Kreouzis T, Scott K et al.
MOLECULAR CRYSTALS AND LIQUID CRYSTALS, Volume 396, page 91, 1st January 2003.
DOI: 10.1080/15421400390213221

Photoconducting discotic liquid crystals
Bushby RJ, Lozman OR, Bunning JC et al.
ORGANIC PHOTONIC MATERIALS AND DEVICES V, Volume 4991, page 222, 1st January 2003.
DOI: 10.1117/12.478360

Quantum efficiencies of photogeneration in discotic liquid crystals. Part 2: Electric field and temperature dependence
Bunning JC, Donovan KJ, Kreouzis T et al.
MOLECULAR CRYSTALS AND LIQUID CRYSTALS, Volume 397, page 563, 1st January 2003.
DOI: 10.1080/15421406390214194

Quantum efficiency of photogeneration in discotic liquid crystals: Part 1: Temperature and wavelength dependence
Scott K, Donovan KJ, Kreouzis T et al.
MOLECULAR CRYSTALS AND LIQUID CRYSTALS, Volume 397, page 553, 1st January 2003.
DOI: 10.1080/15421400390214185

2002

Photoconductive transients and one-dimensional charge carrier dynamics in discotic liquid crystals
Pecchia A, Lozman OR, Movaghar B et al.
PHYS REV B, Volume 65, issue 10, 1st March 2002.
DOI: 10.1103/PhysRevB.65.104204

2001

2,3,7, 8,12,13-Hexakis[2-(2-methoxyethoxy)ethoxy]-tricycloquinazoline: a discogen which allows enhanced levels of n-doping
Boden N, Bushby RJ, Donovan K et al.
LIQ CRYST, Volume 28, issue 12, page 1739, 1st December 2001.
DOI: 10.1080/02678290110082383

Temperature-independent hole mobility in discotic liquid crystals
Kreouzis T, Donovan KJ, Boden N et al.
J CHEM PHYS, Volume 114, issue 4, page 1797, 22nd January 2001.
DOI: 10.1063/1.1334958

PhD Supervision

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