Mike Lazell's Homepage
Research Interests
I am a postdoctoral research associate
with the Prof. Paul
O'Brien group at Imperial
College of Science, Technology and
Medicine,Dept.
of Chemistry, in the Barton
lab. I am current working on quantum dots of semiconductor
materials and
Chemical Vapour Deposition (CVD) of these
materials.
Some of the posters I have presented recently
Nanoparticles
- Does Size Really Matter
CVD
- The Search for New Precursors
and some leaflets
which detail some of the work that I have been doing here at ICSTM.
Nanoparticles - An Introduction
Research into small particles
can be traced back to Faraday’s work on gold colloids in 1857. Ostwald’s
publication of “The World
Of Neglected Dimensions” drew attention to this then new field of chemistry
suggested the size of colloidal
particles and the idea of a gradual transition between molecular and colloidal
states. These particles
are often less than 20 nm in diameter and are now often referred to as
quantum dots,
Q-particles, artificial
atoms (because of their hydrogen like electronic structure) and microelectrodes
(due to
the similarity in reactions
of colloidal particles and compact electrodes) are of interest to scientists
in a wide
range of disciplines. The
synthesis of stable robust colloidal particles is a considerable challenge
to chemists
and material scientists.
Even the most advanced methods of atomic manipulation (scanning tunnelling
microscope) cannot produce
devices smaller than 10 nm, therefore chemical methods need to be employed
to
produce materials exhibiting
quantum behaviour.Physical chemists and physicists have investigated the
novel
properties of small particles
which can often be attributed the large surface area or the restriction
of electronic
entities within the nanocrystal
core.
The synthesis of nanocrystalline
materials has developed in the fields of colloid and organometallic chemistry,
where the growth of small
particles has been achieved by restricting growth using either kinetics
or surface
species to passivate particles.
Nanocrystals are particles in the 1-20 nm size range and although small,
most
retain a certain degree
of crystallinity. It is for particles this small, that the properties are
in a transitionary state
between molecules and bulk
material. Such small particles interact with light predominantly by absorption,
not
by scattering, allowing
powerful optical methods to be used for analysis of the properties, for
example, kinetic
studies for the detection
of short lived intermediates. The study of small particles includes quantum
dots of
semiconductors which have
unusual properties.
The properties of a bulk
semiconductor are not dictated by single atoms, but are a result of a periodic
array of
a large number of molecules
or atoms in a crystal lattice. A transition from bulk semiconductor behaviour
to
molecular properties is
observed as smaller particles are investigated. In this transitionary range,
catalytic,
electronic and optical properties
change drastically. Non linear optical properties have been reported in
quantum dots due to the
presence of charge carriers trapped in surface defects. The optical non
linearity of a
polymer matrix containing
50 Å CdS or PbS nanoparticles was found to be controlled by surface
treatment with
ammonia.
Catalytic properties of metal
quantum dots have also been investigated. A 10-4
M dispersion of 7 nm diameter
Ag colloids in an organic
solute yields free radicals when exposed to UV light. Each radical transfers
an electron
to a colloidal particle
which can store a large number of electrons. Under static conditions, a
number of
electrons can reside on
a particle producing a negative potential high enough for hydrogen evolution.
2(CH3)2COH
+ AgnX-®
2(CH3)2CO
+ 2H+ + Agn(X+2)-
Agn(X+2)-
+ 2H+ ®
AgnX-
+ H2
(n = agglomeration number)
2(CH3)2COH ® 2(CH3)2CO + H2
Quantum size effects in semiconductors
nanoparticles are probably of the most interest. The synthesis of
semiconductor nanoparticles
started in the 1980’s, with the aim of splitting water, reducing it to
hydrogen by
photo-induced electrons
and oxidising it to oxygen by photo-induced holes but was unsuccessful.
General route to Nanoparticles
- Schematic
ã M. Lazell and Paul O'Brien
Ph.D Research
I studied at Queen
Mary and Westfield College, Dept.
of Chemistry, with Dr.
Alice C. Sullivan. The thesis was entitled
Metallasiloxanes; synthesis, characterisation and their applications.
Abstract
Various molecular metallasiloxane compounds
containing the M-O-Si unit have been reviewed. These compounds have
been
prepared using suitable metal reagents
and the dilithium disiloxanediolate or the dilithium silanediolate.
The catalytic activity
for ring-opening polymerisation of cyclic
siloxanes and their potential use as novel single source precursors for
lithium metal
oxides is investigated.
Chapter 1 describes the metallasiloxane
compounds derived from dilithium silanediolate and various metal chlorides.
The X-ray
crystal structures of the compounds [Cr(OSiPh2OSiPh2O)2]-m-[Li(py)2]2
and [Co((OSiPh2)2O)((OSiPh2)3O)]-m-
[Li(py)2]2
are
presented. In addition the results
of attempts to elucidate the factors which might affect the formation of
ring expanded products
are discussed.
Chapter 2 describes the literature
dealing with anionic polymerisation of cyclic siloxanes. The synthesis
and structural
characterisation of [{O(Ph2SiONa)2}4].NaOH.H2O.8pyridine.(toluene)
and [K{O(Ph2SiO)2SiPh2OH}]2
is described. The inactivity
of the potassium compound towards ring-opening
polymerisation of cyclic siloxanes is discussed in the context of currently
accepted mechanistic features of this process.
Chapter 3 describes the use of lithium
bridged metallasiloxanes, for example ‘[LiM{O(SiPh2O)2}3].4LiCl.4THF’,
M = Nb or Ta,
as novel single source precursors for
lithium metal oxides. The thermal decomposition of these precursors
was performed under
vacuum and in air and the results showed
that atmosphere is important in determining the purity of the lithium metal
oxide. Also
the solvent which the compound is prepared
in is important as this changes the purity of the oxides produced;
the presence of
pyridine has an adverse effect.
The deposition of these oxides onto silicon wafers is carried out with
very promising results for
LiMO3,
M = Nb or Ta.
One of the crystals structures in my thesis
[{O(Ph2SiONa)2}4].NaOH.H2O.8pyridine.(toluene)
A copy of my most recent Curriculum
Vitae
Hobbies
I have a Suzuki GSXR-750 which is my third
bike. My previous bikes were an Aprilia RS125 and a Honda RVF 400R,
see some piccy's below.
I have the gold/silver/black one above (not me riding it).
Some Interesting Links
Garbage
Homepage
Prodigy
Homepage
James
D. Mathew's NC35 Homepage
Star
Trek Homepage
Star
Wars Homepage
Dr.
WHO Homepage
South
Park Homepage
MP3's
Superbikes
Some Chemistry Links
Lancaster
chemicals
Sigma/Aldrich/Fluka
BIDS
British
Library
OPAC
97
RSC
Homepage
New
Scientist
Science
jobs
Some Computer Links
Watford
Electronics
Insight
Simply
Computers
Novatech
Dell
Hewlett
Packard
Audio Links
Garbage:
Push It
Prodigy:
Breathe, Firestarter
Sports Links
NFL
Cricket
(Lords)
PAPress
Tennis
(Wimbledon)
E-mail me at m.r.lazell@ic.ac.uk
This Chemistry
on Web site owned by Dr. Mike
Lazell.
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