NANOSCALE DEVICES: APPLICATIONS AND MODELING - Bio-Inspired and Nanoscale Integrated Computing - page 35

The well established materials of the microelectronics industry, such as silicon,
dielectrics, and metal layers, also represent a very important category of materials
necessary in nanodevices. Not only can many nanoscale devices be made using
only these materials and standard microfabrication processes, but in many other
cases at least part of the structure of a nanodevice involves these materials and
processes. We will talk more about this later in the chapter, but for now let us
focus on objects that are more ''nano'' by nature.
2.2.1. Molecules
We know that a molecule is a collection of atoms of either one element or several
different elements. Most of the molecules we are familiar with (for example from
our high school chemistry) are made of a relatively small number of atoms.
Consider the water molecule. It has one oxygen and two hydrogen atoms.
However, there is no reason why we could not have much bigger molecules that
include hundreds or even thousands of atoms—as a matter of fact, we do! Let us
go back and think about our nanodevices for a moment. We estimated that a
typical nanodevice would have hundreds or thousands of atoms in it. Can we say a
nanodevice is a molecule? In reality, many nanodevices could be considered
molecules. Many would be a system of several molecules put together or with
other structures in a certain fashion. The term molecular electronics is quite
commonly used these days. One difference between these molecules and the more
''traditional'' molecules that we remember from good old high school chemistry is
that there the molecule was a concept describing the smallest building blocks of a
much larger substance. When we say a nanodevice can be thought of as
a molecule, we are really only emphasizing the fact that it is a stable collection
of a number of atoms, and not necessarily a unit that is going to be used to build a
macroscopic substance. Also, when one thinks of a molecule, the first examples
that usually come to mind are rather small ones that contain only a few atoms
(such as the hydrogen or benzene molecules), although much larger molecules are
also commonplace (such as many polymer molecules or the DNA that can reach
macroscopic length scales). Nanodevices, if one wants to call them molecules, are
usually very large molecules.
2.2.2. Nanoparticles
One important set of ''objects'' that are very useful to the world of nanotechnol-
ogy is nanoparticles. As the name implies, a nanoparticle is a particle that has
dimensions on the order of a few nanometers. This typically includes a few
thousands of atoms. Nanoparticles can be made from various materials. Many
metals, for instance, form good nanoparticles. Nanoparticles containing more
than one element can also be formed. Again, what is really important about a
nanoparticle is the fact that it is small enough such that the quantum effects and
large surface-to-volume ratio effect discussed before are dominant in it, to the
extent that its properties can no longer be described by the same general properties