Biomedical Engineering Reference
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Fig. 1.4 (a) SEM image of an AAO nanopore array consisting of 75 nm diameter pores (b) SEM
of AAO nanopores shrunk using the ALD process to a final pore size of 15 nm [
63
], reprinted with
permission (c) SEM of nanopore array formed through FIB milling to form 200 nm pores in a
45
5 nm thick free standing Al
2
O
3
membrane (d) Atomic force microscope scan of a 5
5
Al
2
O
3
nanopore array consisting of 200 nm nanopores, formed using the FIB tool
decompositional sputtering processes [
89
,
90
]. Al
2
O
3
membranes were formed
through a combination of ALD and standard microfabrication processes resulting
in low stress, 45-60 nm thick free standing membranes. In addition, these mem-
branes were mechanically more robust than their SiO
2
counterparts as compressive
thermal stress was reduced during fabrication. Nanopores formed in Al
2
O
3
mem-
branes exhibited state of the art noise performance and allowed for true VLSI device
level integration due to the rapid, low temperature fabrication process developed.
1.3.3.1 Nanopore Nucleation and Expansion Kinetics
SiO
2
and various metal halides/oxides including CaF
2
, AlF
3
,Al
2
O
3
, MgO and TiO
x
exhibit unique sputtering characteristics under an intense electron beam. The
formation of trenches and slots in these material systems has been previously
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