University of Surrey

Test tubes in the lab Research in the ATI Dance Research

Exciton dynamics in polymer wrapped carbon nanotubes

Siddique, Sofia (2015) Exciton dynamics in polymer wrapped carbon nanotubes Doctoral thesis, University of Surrey.

[img] Text
Sofia Siddique_Thesis_6067742_year2014.pdf - Thesis (version of record)
Restricted to Registered users only
Available under License Creative Commons Attribution Non-commercial Share Alike.

Download (6MB)
[img] Text
2014_08_13_Author_Deposit_Agreement_Sofia Siddique_6067742.docx - Other
Available under License Creative Commons Attribution Non-commercial Share Alike.

Download (42kB)


This thesis describes an experimental study of exciton recombination in isolated semiconducting single-wall carbon nanotubes synthesised by different methods and wrapped in different polymers PFO (9,9-dioctylfluorenyl-2,7-diyl), PFO-BPy (9,9-Dioctyfluorenyl-2,7-diyl-Bipyridine) and P3HT (poly 3-hexylthiophene). We present a comprehensive study using femtosecond transient absorption measurements of the kinetics of exciton recombination, where diffusion of excitons in the confined one-dimensional system significantly affects their optical and electronic properties. In all studied samples of isolated nanotubes, an exciton-exciton process dominated the recombination under high excitation, and exhibited a distinct crossover to a diffusion-limited regime with anomalous kinetics at late times. We attribute the reaction-diffusion crossover to a finite reaction probability per exciton-exciton encounter. We have demonstrated a methodology to determine the microscopic parameters controlling reaction and diffusion processes, based on measurements at high initial density where the optical absorption is fully saturated. In studies of the same nanotube species synthesized by both HiPCO (high pressure catalytic decomposition of carbon monoxide) and CoMoCAT (cobalt and molybdenum catalysts based chemical vapour deposition technique) methods and wrapped by different polymers, the exciton reaction probability was approximately constant, corresponding to on average one in five exciton-exciton interactions resulting in an exciton recombination. On the other hand, there was significant variation in the diffusive hopping time for samples synthesized by different processes or subject to different processing. This is consistent with the wide range of values for the diffusion coefficient reported in the literature. We have found that excitons in nanotubes synthesized by the HiPCO are more mobile than CoMoCAT nanotubes, by a factor of ~2 for nanotubes wrapped in P3HT. This may be associated with a lower defect concentration in HiPCO nanotubes compared to CoMoCAT. The nanomaterials studied in this thesis are promising for nanotube-organic hybrids based light emitting and harvesting devices. Our findings will not only facilitate the selection of materials in these applications but also represent experimental data that challenges existing theoretical models for kinetics of non-equilibrium stochastic systems.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors :
Date : 27 February 2015
Contributors :
Depositing User : Sofia Siddique
Date Deposited : 09 Mar 2015 12:36
Last Modified : 17 May 2017 14:24

Actions (login required)

View Item View Item


Downloads per month over past year

Information about this web site

© The University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom.
+44 (0)1483 300800