Vol.
BID,
Supplement
CHINESE
JOURNAL
OF
LASERS
Particle
Dynamics
in Laser Ablation
Plume
During Nanoparticle Synthesis
(Invited)
April,
2001
Tatsuo
OKADA
Junichi
MURAMOTO
Yoshiki
NAKATA
Mitsuo
MAEDA
(Graduate School
oj
InjOT'1nation
Science
and
Electrical Engineering,
Kyushu University,
Fukuoka
812-8581,
Japan)
Abstract
Particle
dynamics
in laser
ablation
plume
in the
background
gas
during
nano-particlesynthesis
are
described,
based
on
the results
of
the
imaging
diagno
stics.
Laser-inducedfluorescence
(LIF)
, a
newly
developed re-decomposition
LIF
(Red-
LIF)
and
Rayleigh
scatteri
ng
have
been used to visualize the
behaviors
of
atomic
and
molecular
species,
clusters
andnano-particles,
respectively.
The
influences
of
the kind
of
the
background
gas
on
the
formation
process
of
the
nanoparticle
and
of
an
external
electric
field on the
nano-particle
b
ehavior
are
described.
Key
words
laser
ablation,
nanoparticle,
clusters,
plume
dynamics,
imaging
spectrosco
py,
Raylei
gh
sca
ttering,
laser-induced fluorescence
1 Introduction
Laser
ablation
in a
background
gas
has
been
widely
used to
synthesize
the
nanoparticle
[l .2)
and
nano-composite
thin
films[
3.1)
. In
the
application
of
these
nano-structured
materials,
the
control
of
the
size
of
the
synthesized
nanoparticle
is
very
important.
For
instance,
it
is
reported
that
the
photo-
lumine
cence
property
of
Si
nanoparticles
largely
depends
on
their
sizes[5).
In
order
to
develop
the
process
technique
for
size-controlled
nanoparticle
synthesis,
understanding
of
the
formation
process
of
nanoparticle
in
the
laser
ablation
plume
is
required.
That
is,
there
still
are
open
questions
about
when,
where
and
how
nanoparticles
are
formed
in
the
ablation
plume.
Several
gro
up
s
have
been discussing
the
formation
dynamics
of
nanoparticle
in
the
laser
ablation
plume
generated
using
ns-pulsed lasers
such
as
excimer
lasers
and
Q-switched
Nd
: Y
AG
lasers,
based on
the
experimental
results
and
theoretical
consideration.
Muramoto
et
al. applied
imaging
spectro
co pic
techniques
based
on
laser-induced
fluorescence
(LIF)
and
Rayleigh
scattering
(RS)
to
the
visualization
of
the
particle
behavior
in the a
blation
plum
e
during
Si
nano
particle
synthesis.
They
found
that
Si
atoms
started
to
disappear
in
the
central
part
of
the
plume
O.
1
~
O.
2
ms
after
ablation
in
10
Torr
He
and
the
Si
dimmers
were
observed
at
the
same
stage[6.
7).
Murakami
et
al.
tried to
detect
Si
nanoparticles
by
X
-r
ay
absorption
spectroscopy,
but
they
failed[8).
More
rece
n
tly
Geohegan
et
al.
applied
photo
l
uminescence
technique
(PL)
to
image
Si
nanoparticles
synthesized
and
suspended
in the
plume
[9).
They
found
as
reported
by
Muramoto
et
ai. ,
that
on-set
times
for
nanoparticle
formation
after
pulsed laser
ablation
were
O.
15-0
. 2
ms
in 10
Torr
He
and
3
ms
in
1
Torr
Ar.
Makimura
et
al.
also
observed
the
growing
Si
nanoparticle
in
time
period
of
O.
6
~
1. 0
ms
after
ablation
by
a
newly
developed
plasma
emission
from
laer-decomposed
nanoparticle[lO).
However,
these
measurement
techniques
have
some
limitations,
which
causes
arguments
on
the
formation
dynamics
of
nanoparticles.
LIF
can
detect
only
atomic
and
small
molecules.
RS
is
not
so
sensitive
as
to
detect
the
nanoparticles
of
less
than
1
nm
in
diameter.
Therefore
the
on-set
time
for
nanoparticle
formation
can
not
be discussed based
on
RS
data.
In
order
to
apply
PL
to
the
detection
of