<s>
Surface-enhanced	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
or	O
surface-enhanced	B-Algorithm
Raman	I-Algorithm
scattering	I-Algorithm
(	O
SERS	O
)	O
is	O
a	O
surface-sensitive	O
technique	O
that	O
enhances	O
Raman	B-Architecture
scattering	I-Architecture
by	O
molecules	O
adsorbed	O
on	O
rough	O
metal	O
surfaces	O
or	O
by	O
nanostructures	O
such	O
as	O
plasmonic-magnetic	O
silica	O
nanotubes	O
.	O
</s>
<s>
The	O
electromagnetic	O
theory	O
proposes	O
the	O
excitation	O
of	O
localized	O
surface	O
plasmons	O
,	O
while	O
the	O
chemical	O
theory	O
proposes	O
the	O
formation	O
of	O
charge-transfer	B-Algorithm
complexes	I-Algorithm
.	O
</s>
<s>
The	O
chemical	O
theory	O
is	O
based	O
on	O
resonance	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
,	O
in	O
which	O
the	O
frequency	O
coincidence	O
(	O
or	O
resonance	O
)	O
of	O
the	O
incident	O
photon	O
energy	O
and	O
electron	O
transition	O
greatly	O
enhances	O
Raman	B-Architecture
scattering	I-Architecture
intensity	O
.	O
</s>
<s>
In	O
order	O
for	O
scattering	O
to	O
occur	O
,	O
the	O
plasmon	O
oscillations	B-Algorithm
must	O
be	O
perpendicular	O
to	O
the	O
surface	O
;	O
if	O
they	O
are	O
in-plane	O
with	O
the	O
surface	O
,	O
no	O
scattering	O
will	O
occur	O
.	O
</s>
<s>
It	O
is	O
because	O
of	O
this	O
requirement	O
that	O
roughened	O
surfaces	O
or	O
arrangements	O
of	O
nanoparticles	O
are	O
typically	O
employed	O
in	O
SERS	O
experiments	O
as	O
these	O
surfaces	O
provide	O
an	O
area	O
on	O
which	O
these	O
localized	O
collective	O
oscillations	B-Algorithm
can	O
occur	O
.	O
</s>
<s>
The	O
dipolar	O
term	O
contributes	O
to	O
the	O
plasmon	O
oscillations	B-Algorithm
,	O
which	O
leads	O
to	O
the	O
enhancement	O
.	O
</s>
<s>
First	O
,	O
the	O
field	O
enhancement	O
magnifies	O
the	O
intensity	O
of	O
incident	O
light	O
,	O
which	O
will	O
excite	O
the	O
Raman	O
modes	O
of	O
the	O
molecule	O
being	O
studied	O
,	O
therefore	O
increasing	O
the	O
signal	O
of	O
the	O
Raman	B-Architecture
scattering	I-Architecture
.	O
</s>
<s>
Resonance	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
explains	O
the	O
huge	O
enhancement	O
of	O
Raman	B-Architecture
scattering	I-Architecture
intensity	O
.	O
</s>
<s>
As	O
only	O
the	O
dipole	O
transition	O
leads	O
to	O
Raman	B-Architecture
scattering	I-Architecture
,	O
the	O
higher-order	O
transitions	O
will	O
cause	O
a	O
decrease	O
in	O
the	O
overall	O
efficiency	O
of	O
the	O
enhancement	O
.	O
</s>
<s>
Such	O
substrates	O
can	O
be	O
fabricated	O
on	O
a	O
wafer	O
scale	O
and	O
label-free	O
superresolution	O
microscopy	O
has	O
also	O
been	O
demonstrated	O
using	O
the	O
fluctuations	O
of	O
surface	B-Algorithm
enhanced	I-Algorithm
Raman	I-Algorithm
scattering	I-Algorithm
signal	O
on	O
such	O
highly	O
uniform	O
,	O
high-performance	O
plasmonic	O
metasurfaces	O
.	O
</s>
<s>
Due	O
to	O
their	O
unique	O
physical	O
and	O
chemical	O
properties	O
,	O
two-dimensional	O
(	O
2D	O
)	O
materials	O
have	O
gained	O
significant	O
attention	O
as	O
alternative	O
substrates	O
for	O
surface-enhanced	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
SERS	O
)	O
.	O
</s>
<s>
The	O
term	O
surface	B-Algorithm
enhanced	I-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
implies	O
that	O
it	O
provides	O
the	O
same	O
information	O
that	O
traditional	O
Raman	O
spectroscopy	O
does	O
,	O
simply	O
with	O
a	O
greatly	O
enhanced	O
signal	O
.	O
</s>
