355Laboratory Analyses
For conventional SEM analysis, samples must be nonvolatile in order to survive
t
he
h
igh-vacuum
e
nvironment
a
nd
c
onductive
t
o
p
revent
c
harging
b
y
t
he
i
ncident
e
lectron
b
eam.
N
onconductive
s
amples
a
re
t
ypically
c
oated
w
ith
a
t
hin
(
2–10nm)
l
ayer
o
f
C
,
A
u,
o
r
I
r.
T
hese
r
equirements
a
re
e
ased
w
ith
a
n
E
SEM,
w
hich
ca
n
o
per-
ate
u
nder
v
arious
s
ample-chamber
at
mospheres.
P
owdered
s
amples
a
re
t
ypically
adhered to a specimen stub using conductive tape or adhesive, or set into epoxy
r
esin
a
nd
p
olished.
A
nalysts
m
ust
t
ake
p
articular
ca
re
t
o
e
nsure
t
hat
t
he
s
ample
i
s
a
dequately
d
ispersed.
C
ommon
me
thods
o
f
d
ispersion
i
nclude
s
onication
us
ing
v
ari-
ous
s
olvents
a
nd
r
epeated
c
ontact
t
ransfers.
D
ispersion
w
ill
d
epend
he
avily ...