Biomedical Engineering Reference
In-Depth Information
types of nanomaterials, and it is likely to revolutionize the way we make materials.
It requires a thorough understanding of the short-range forces of attraction, such as Van
der Waals forces, electrostatic forces, and a variety of interatomic or intermolecular
forces. Since it is not possible to have various minute things come together without
some attractive force or active fi eld of force in the region, having the fundamental
forces “doing all the work” for us is the key principle underlying this approach.
Some examples of such a synthesis route starting from atoms and molecules are
methods like self-assembly of nanoparticles or monomer/polymer molecules,
chemical or electrochemical reactions for precipitation of nanostructures, sol-gel
processing, laser pyrolysis, chemical vapor deposition (CVD), plasma or fl ame
spraying synthesis, and atomic or molecular condensation. The bio-assisted synthe-
sis of nanomaterials also belongs to this approach (Sarikaya et al.
2003
) . However,
despite being so promising and inviting, our ability to build things from the bottom
up is fairly limited in scope. While we can assemble relatively simple structures, we
cannot produce complex, integrated devices using the bottom-up approach. Any
kind of overall ordered arrangement aside from repeating regular patterns cannot be
done without some sort of top-down infl uence, like lithographic patterning. Until
we have fully mastered the bottom-up synthesis approach, we will not be able to
fully exploit its speed and accuracy. The important factor is that they are two differ-
ent approaches to creating nanostructures which can be applied according to the
specifi c needs for each application, often in a complementary way.
1.1
Nanofabrication by Top-Down Methods
Top-down methods were originally introduced as a new set of manufacturing tools
to solve specifi c industrial problems in micromachining, such as the microelectro-
mechanical systems (MEMS) devices. At the nanoscale though, these methods are
generally not suitable for production on a very large scale because they presently
encounter technological limitation and require extremely long and costly processes.
Nonetheless, they represent some of the most common approaches now used to pat-
tern surfaces and create three-dimensional (3-D) features on substrates. Over the
past decades, there has been a wide variety of top-down manufacturing techniques
that have been implemented using different media that span from chemical and
electrochemical means to photofabrication, laser machining, electron- and ion-beam
milling (IBM), plasma etching and powder blasting. Here, we describe only the
most common techniques used for nano- or nanobio-related applications.
1.1.1
Nanolithography
Nanolithography is one of the most established techniques for making nanostruc-
tured materials and patterns. Nanolithography derives its name from the Greek
words
nanos
(dwarf),
lithos
(rock), and
grapho
(to write), which literally means
“small writing on rocks.” This technique is based on depositing, etching, or writing
