Biomedical Engineering Reference
In-Depth Information
a
b Copper foil
c
Glass
100 µm
Agarose/etchant
H
Substrate
500 µm
500 µm
·
Sensitizing solution
·
Activating bath
·
Cu solution
d
e
Copper foil
250 µm
Agarose
Metallization time
FIGURE 1.35
Depositing. and. etching. of. posts. and. wells. using. agarose. stamps.. (a-c:. Smoukov,.
S.K.,.K.J.M..Bishop,.R..Klajn,.C.J..Campbell,.and.B.A..Grzybowski,.“Cutting.into.solids.with.micro-
patterned.gels,”.
Adv. Mater
..17,.1361,.2005;.d.and.e:.Smoukov,.S.K.,.K.J.M..Bishop,.R..Klajn,.C.J..
Campbell,.and.B.A..Grzybowski,.“Freestanding.three-dimensional.copper.foils.prepared.by.electro-
less.deposition.on.micropatterned.gels,”.
Adv. Mater.
.17,.751,.2005..Reproduced.with.permission.
from.Wiley-VCH.Verlag.GmbH.&.Co..KGaA.)
1.8 Nanofabrication Techniques
In many applications, UV light does not provide enough resolution to deine the features nec-
essary to probe a given phenomenon. his textbook is not the place to review the vast array of
techniques—many under intense development—that exist for fabricating nanoscale objects, but
we will cite two broad families because of their widespread use:
electron beam lithography
and
scanning probe lithography
. Unfortunately, both are
serial patterning
techniques—patterning
twice as many features takes twice as long.
1.8.1 Electron Beam Lithography
Electron beam lithography
uses the electron gun of a scanning electron microscope (SEM;
the same gun used for imaging) to inject a highly focused beam of electrons into the sample
(
Figure 1.36
). he e-beam resist is usually a thin layer of PMMA, which is a positive e-beam
resist; SU-8 is a negative e-beam resist. Unfortunately, the patterning resolution is dictated not
so much by the e-beam spot size (which can be focused down to ~1 nm diameter by accelerat-
ing the e-beam to voltages >100 kV) but by the secondary electrons emitted by the sample in
a circumference that can vary from 10 to 100 nm (depending on the material and charging
conditions).
1.8.2 Scanning Probe Lithography
Scanning probe lithography
uses a sharp tip in proximity (not necessarily in contact) with the
surface of interest. he tip, an integral part of a
scanning probe microscope
(SPM), is typically
used to image the surface. A proximity signal (e.g., a tunneling current, or the delection of the
cantilever where the tip is mounted) is used to adjust the vertical distance between the tip holder
and the sample as the tip is scanned across the sample. To perform nanoscale lithography, the
tip of the SPM is used to modify the surface (
Figure 1.36
)—either indentation, (electro)chemical
