<s>
Passivation	B-Application
,	O
in	O
physical	O
chemistry	O
and	O
engineering	O
,	O
refers	O
to	O
coating	O
a	O
material	O
so	O
it	O
becomes	O
"	O
passive	O
"	O
,	O
that	O
is	O
,	O
less	O
readily	O
affected	O
or	O
corroded	O
by	O
the	O
environment	O
.	O
</s>
<s>
Passivation	B-Application
involves	O
creation	O
of	O
an	O
outer	O
layer	O
of	O
shield	O
material	O
that	O
is	O
applied	O
as	O
a	O
microcoating	O
,	O
created	O
by	O
chemical	O
reaction	O
with	O
the	O
base	O
material	O
,	O
or	O
allowed	O
to	O
build	O
by	O
spontaneous	O
oxidation	O
in	O
the	O
air	O
.	O
</s>
<s>
As	O
a	O
technique	O
,	O
passivation	B-Application
is	O
the	O
use	O
of	O
a	O
light	O
coat	O
of	O
a	O
protective	O
material	O
,	O
such	O
as	O
metal	O
oxide	O
,	O
to	O
create	O
a	O
shield	O
against	O
corrosion	O
.	O
</s>
<s>
Passivation	B-Application
of	O
silicon	O
is	O
used	O
during	O
fabrication	B-Architecture
of	O
microelectronic	O
devices	O
.	O
</s>
<s>
In	O
electrochemical	O
treatment	O
of	O
water	O
,	O
passivation	B-Application
reduces	O
the	O
effectiveness	O
of	O
the	O
treatment	O
by	O
increasing	O
the	O
circuit	O
resistance	O
,	O
and	O
active	O
measures	O
are	O
typically	O
used	O
to	O
overcome	O
this	O
effect	O
,	O
the	O
most	O
common	O
being	O
polarity	O
reversal	O
,	O
which	O
results	O
in	O
limited	O
rejection	O
of	O
the	O
fouling	O
layer	O
.	O
</s>
<s>
When	O
exposed	O
to	O
air	O
,	O
many	O
metals	O
naturally	O
form	O
a	O
hard	O
,	O
relatively	O
inert	O
surface	O
layer	O
,	O
usually	O
an	O
oxide	O
(	O
termed	O
the	O
"	O
native	O
oxide	O
layer	O
"	O
)	O
or	O
a	O
nitride	O
,	O
that	O
serves	O
as	O
a	O
passivation	B-Application
layer	I-Application
.	O
</s>
<s>
In	O
the	O
case	O
of	O
silver	O
,	O
the	O
dark	O
tarnish	O
is	O
a	O
passivation	B-Application
layer	I-Application
of	O
silver	O
sulfide	O
formed	O
from	O
reaction	O
with	O
environmental	O
hydrogen	O
sulfide	O
.	O
</s>
<s>
(	O
In	O
contrast	O
,	O
metals	O
such	O
as	O
iron	O
oxidize	O
readily	O
to	O
form	O
a	O
rough	O
porous	O
coating	O
of	O
rust	B-Application
that	O
adheres	O
loosely	O
and	O
sloughs	O
off	O
readily	O
,	O
allowing	O
further	O
oxidation	O
.	O
)	O
</s>
<s>
The	O
passivation	B-Application
layer	I-Application
of	O
oxide	O
markedly	O
slows	O
further	O
oxidation	O
and	O
corrosion	O
in	O
room-temperature	O
air	O
for	O
aluminium	O
,	O
beryllium	O
,	O
chromium	B-Language
,	O
zinc	B-Application
,	O
titanium	O
,	O
and	O
silicon	O
(	O
a	O
metalloid	O
)	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
the	O
semiconductor	B-Architecture
device	I-Architecture
fabrication	I-Architecture
,	O
such	O
as	O
silicon	O
MOSFET	B-Architecture
transistors	I-Architecture
and	O
solar	O
cells	O
,	O
surface	B-Application
passivation	I-Application
refers	O
not	O
only	O
to	O
reducing	O
the	O
chemical	O
reactivity	O
of	O
the	O
surface	O
but	O
also	O
to	O
eliminating	O
the	O
dangling	O
bonds	O
and	O
other	O
defects	O
that	O
form	O
electronic	O
surface	O
states	O
,	O
which	O
impair	O
performance	O
of	O
the	O
devices	O
.	O
</s>
<s>
Surface	B-Application
passivation	I-Application
of	O
silicon	O
usually	O
consists	O
of	O
high-temperature	O
thermal	B-Algorithm
oxidation	I-Algorithm
.	O
</s>
<s>
The	O
conditions	O
necessary	O
,	O
but	O
not	O
sufficient	O
,	O
for	O
passivation	B-Application
are	O
recorded	O
in	O
Pourbaix	O
diagrams	O
.	O
</s>
<s>
Some	O
corrosion	O
inhibitors	O
help	O
the	O
formation	O
of	O
a	O
passivation	B-Application
layer	I-Application
on	O
the	O
surface	O
of	O
the	O
metals	O
to	O
which	O
they	O
are	O
applied	O
.	O
</s>
<s>
Alclading	O
,	O
which	O
metallurgically	O
bonds	O
thin	O
layers	O
of	O
pure	O
aluminium	O
or	O
alloy	O
to	O
different	O
base	O
aluminium	O
alloy	O
,	O
is	O
not	O
strictly	O
passivation	B-Application
of	O
the	O
base	O
alloy	O
.	O
</s>
<s>
Chromate	O
conversion	O
is	O
a	O
common	O
way	O
of	O
passivating	O
not	O
only	O
aluminium	O
,	O
but	O
also	O
zinc	B-Application
,	O
cadmium	O
,	O
copper	O
,	O
silver	O
,	O
magnesium	O
,	O
and	O
tin	B-Protocol
alloys	O
.	O
</s>
<s>
In	O
carbon	O
quantum	O
dot	O
(	O
CQD	O
)	O
technology	O
,	O
CQDs	O
are	O
small	O
carbon	O
nanoparticles	O
(	O
less	O
than	O
10	O
nm	O
in	O
size	O
)	O
with	O
some	O
form	O
of	O
surface	B-Application
passivation	I-Application
.	O
</s>
<s>
Ferrous	O
materials	O
,	O
including	O
steel	O
,	O
may	O
be	O
somewhat	O
protected	O
by	O
promoting	O
oxidation	O
(	O
"	O
rust	B-Application
"	O
)	O
and	O
then	O
converting	O
the	O
oxidation	O
to	O
a	O
metalophosphate	O
by	O
using	O
phosphoric	O
acid	O
and	O
add	O
further	O
protection	O
by	O
surface	O
coating	O
.	O
</s>
<s>
As	O
the	O
uncoated	O
surface	O
is	O
water-soluble	O
,	O
a	O
preferred	O
method	O
is	O
to	O
form	O
manganese	O
or	O
zinc	B-Application
compounds	O
by	O
a	O
process	O
commonly	O
known	O
as	O
parkerizing	O
or	O
phosphate	O
conversion	O
.	O
</s>
<s>
One	O
common	O
mode	O
of	O
corrosion	O
in	O
corrosion-resistant	O
steels	O
is	O
when	O
small	O
spots	O
on	O
the	O
surface	O
begin	O
to	O
rust	B-Application
because	O
grain	O
boundaries	O
or	O
embedded	O
bits	O
of	O
foreign	O
matter	O
(	O
such	O
as	O
grinding	O
swarf	O
)	O
allow	O
water	O
molecules	O
to	O
oxidize	O
some	O
of	O
the	O
iron	O
in	O
those	O
spots	O
despite	O
the	O
alloying	O
chromium	B-Language
.	O
</s>
<s>
Some	O
grades	O
of	O
stainless	O
steel	O
are	O
especially	O
resistant	O
to	O
rouging	O
;	O
parts	O
made	O
from	O
them	O
may	O
therefore	O
forgo	O
any	O
passivation	B-Application
step	O
,	O
depending	O
on	O
engineering	O
decisions	O
.	O
</s>
<s>
Common	O
among	O
all	O
of	O
the	O
different	O
specifications	O
and	O
types	O
are	O
the	O
following	O
steps	O
:	O
Prior	O
to	O
passivation	B-Application
,	O
the	O
object	O
must	O
be	O
cleaned	O
of	O
any	O
contaminants	O
and	O
generally	O
must	O
undergo	O
a	O
validating	O
test	O
to	O
prove	O
that	O
the	O
surface	O
is	O
'	O
clean.	O
'	O
</s>
<s>
Passivating	O
temperatures	O
can	O
range	O
from	O
ambient	O
to	O
60°C	O
,	O
or	O
,	O
while	O
minimum	O
passivation	B-Application
times	O
are	O
usually	O
20	O
to	O
30	O
minutes	O
.	O
</s>
<s>
After	O
passivation	B-Application
,	O
the	O
parts	O
are	O
neutralized	O
using	O
a	O
bath	O
of	O
aqueous	O
sodium	O
hydroxide	O
,	O
then	O
rinsed	O
with	O
clean	O
water	O
and	O
dried	O
.	O
</s>
<s>
The	O
passivation	B-Application
process	O
removes	O
exogenous	O
iron	O
,	O
creates/restores	O
a	O
passive	O
oxide	O
layer	O
that	O
prevents	O
further	O
oxidation	O
(	O
rust	B-Application
)	O
,	O
and	O
cleans	O
the	O
parts	O
of	O
dirt	O
,	O
scale	O
,	O
or	O
other	O
welding-generated	O
compounds	O
(	O
e.g.	O
</s>
<s>
Passivation	B-Application
processes	O
are	O
generally	O
controlled	O
by	O
industry	O
standards	O
,	O
the	O
most	O
prevalent	O
among	O
them	O
today	O
being	O
ASTM	O
A	O
967	O
and	O
AMS	O
2700	O
.	O
</s>
<s>
These	O
industry	O
standards	O
generally	O
list	O
several	O
passivation	B-Application
processes	O
that	O
can	O
be	O
used	O
,	O
with	O
the	O
choice	O
of	O
specific	O
method	O
left	O
to	O
the	O
customer	O
and	O
vendor	O
.	O
</s>
<s>
The	O
"	O
method	O
"	O
is	O
either	O
a	O
nitric	O
acid-based	O
passivating	O
bath	O
,	O
or	O
a	O
citric	O
acid-based	O
bath	O
,	O
these	O
acids	O
remove	O
surface	O
iron	O
and	O
rust	B-Application
,	O
while	O
sparing	O
the	O
chromium	B-Language
.	O
</s>
<s>
Sodium	O
dichromate	O
is	O
often	O
required	O
as	O
an	O
additive	O
to	O
oxidise	O
the	O
chromium	B-Language
in	O
certain	O
'	O
types	O
 '	O
of	O
nitric-based	O
acid	O
baths	O
,	O
however	O
this	O
chemical	O
is	O
highly	O
toxic	O
.	O
</s>
<s>
With	O
citric	O
acid	O
,	O
simply	O
rinsing	O
and	O
drying	O
the	O
part	O
and	O
allowing	O
the	O
air	O
to	O
oxidise	O
it	O
,	O
or	O
in	O
some	O
cases	O
the	O
application	O
of	O
other	O
chemicals	O
,	O
is	O
used	O
to	O
perform	O
the	O
passivation	B-Application
of	O
the	O
surface	O
.	O
</s>
<s>
Various	O
testing	O
methods	O
are	O
available	O
to	O
determine	O
the	O
passivation	B-Application
(	O
or	O
passive	O
state	O
)	O
of	O
stainless	O
steel	O
.	O
</s>
<s>
Electro-chemical	O
testers	O
can	O
also	O
be	O
utilized	O
to	O
commercially	O
verify	O
passivation	B-Application
.	O
</s>
<s>
The	O
surface	O
of	O
titanium	O
and	O
of	O
titanium-rich	O
alloys	O
oxidizes	O
immediately	O
upon	O
exposure	O
to	O
air	O
to	O
form	O
a	O
thin	O
passivation	B-Application
layer	I-Application
of	O
titanium	O
oxide	O
,	O
mostly	O
titanium	O
dioxide	O
.	O
</s>
<s>
Titanium	O
can	O
be	O
anodized	O
to	O
produce	O
a	O
thicker	O
passivation	B-Application
layer	I-Application
.	O
</s>
<s>
As	O
with	O
many	O
other	O
metals	O
,	O
this	O
layer	O
causes	O
thin-film	O
interference	O
which	O
makes	O
the	O
metal	O
surface	O
appear	O
colored	O
,	O
with	O
the	O
thickness	O
of	O
the	O
passivation	B-Application
layer	I-Application
directly	O
effecting	O
the	O
color	O
produced	O
.	O
</s>
<s>
Nickel	O
can	O
be	O
used	O
for	O
handling	O
elemental	O
fluorine	O
,	O
owing	O
to	O
the	O
formation	O
of	O
a	O
passivation	B-Application
layer	I-Application
of	O
nickel	O
fluoride	O
.	O
</s>
<s>
In	O
the	O
area	O
of	O
microelectronics	O
and	O
photovoltaic	O
solar	O
cells	O
,	O
surface	B-Application
passivation	I-Application
is	O
usually	O
implemented	O
by	O
thermal	B-Algorithm
oxidation	I-Algorithm
at	O
about	O
1000°C	O
to	O
form	O
a	O
coating	O
of	O
silicon	O
dioxide	O
.	O
</s>
<s>
Surface	B-Application
passivation	I-Application
is	O
critical	O
to	O
solar	O
cell	O
efficiency	O
.	O
</s>
<s>
The	O
effect	O
of	O
passivation	B-Application
on	O
the	O
efficiency	O
of	O
ranges	O
from	O
3-7	O
%	O
.	O
</s>
<s>
The	O
easiest	O
and	O
most	O
widely	O
studied	O
method	O
to	O
improve	O
perovskite	O
solar	O
cells	O
is	O
passivation	B-Application
.	O
</s>
<s>
A	O
small	O
molecule	O
with	O
the	O
function	O
of	O
passivation	B-Application
is	O
some	O
kind	O
of	O
square	O
that	O
can	O
be	O
inserted	O
where	O
there	O
is	O
an	O
empty	O
space	O
and	O
then	O
a	O
complete	O
layer	O
is	O
obtained.These	O
molecules	O
will	O
generally	O
have	O
lone	O
electron	O
pairs	O
or	O
pi-electrons	O
,	O
so	O
they	O
can	O
bind	O
to	O
the	O
defective	O
states	O
on	O
the	O
surface	O
of	O
the	O
cell	O
film	O
and	O
thus	O
achieve	O
passivation	B-Application
of	O
the	O
material	O
.	O
</s>
<s>
In	O
addition	O
,	O
passivation	B-Application
not	O
only	O
improves	O
the	O
photoelectric	O
conversion	O
efficiency	O
of	O
perovskite	O
cells	O
,	O
but	O
also	O
contributes	O
to	O
the	O
improvement	O
of	O
device	O
stability	O
.	O
</s>
<s>
For	O
example	O
,	O
adding	O
a	O
passivation	B-Application
layer	I-Application
of	O
a	O
few	O
nanometers	O
thickness	O
can	O
effectively	O
achieve	O
passivation	B-Application
with	O
the	O
effect	O
of	O
stopping	O
water	O
vapor	O
intrusion	O
.	O
</s>
