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Author:
Jacobsson, T. Jesper (Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry)
Title:
Synthesis and characterisation of ZnO nanoparticles.An experimental investigation of some of their size dependent quantum effects
Department:
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry
Publication type:
Student thesis
Language:
English
Level:
Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
Educational program:
Master Programme in Chemical Engineering
Uppsok:
Technology
Pages:
73
Series:
UPTEC K, ISSN 1650-8297; 10003
Year of publ.:
2010
URI:
urn:nbn:se:uu:diva-121715
Permanent link:
http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121715
Subject category:
Materials Chemistry
Inorganic Chemistry
SVEP category:
Materials chemistry
Inorganic chemistry
Keywords(en) :
ZnO, nanoparticles, quantum dots, Sol-gel, Time resolved UV-Vis spectroscopy, fluorescence, Raman, Phonon spectrum, Synthesis, XRD
Abstract(en) :

ZnO nanoparticles in the size range 2.5–7 nm have been synthesised by a wet chemical method where ZnO particles were grown in basic zinc acetate solution. The optical band gap increases when the size of the particles decreases. An empirical relation between the optical band gap given from absorption measurements, and particle size given from XRD measurements has been developed and compared to other similar relations found in the literature.

   Time resolved UV-Vis spectroscopy has been used to follow the growth of particles in situ in solution. The data show that the growth mechanism not can be described by a simple Oswald ripening approach and nor by an exclusive agglomeration of smaller clusters into larger particles. The growth mechanism is more likely a combination of the proposed reaction themes. The data also reveal that particle formation do not demand a heating step for formation of the commonly assumed initial cluster Zn4O(CH3COO)6.

   Steady state fluorescence has been studied as a function of particle size during growth in solution. These measurements confirm what is found in the literature in that the visible fluorescence is shifted to longer wavelengths and loses in intensity as the particles grow. Some picosecond spectroscopy has also been done where the UV fluorescence has been investigated. From these measurements it is apparent that the lifetime of the fluorescence increases with particle size.

    The phonon spectrum of ZnO has been studied with Raman spectroscopy for a number of different particle sizes. From these measurements it is clear that there is a strong quenching of the phonons due to confinement for the small particles, and the only clearly observed vibration is one at 436 cm-1 which intensity strongly increases with particle size.   

Supervisor:
Edvinsson, Tomas (Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry)
Examiner:
Boschloo, Gerrit (Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry)
Westin, Gunnar (Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry)
Available from:
2010-05-05
Created:
2010-03-29
Last updated:
2010-05-05
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