Biomedical Engineering Reference
In-Depth Information
Chapter 1
Fundamentals on Bionanotechnologies
Abstract This is the introductory chapter of the topic. The basic theoretical and
experimental facts regarding the application of electronics at the nanoscale and
for biological systems are developed here. Transport phenomena at the nanoscale,
the principles of nanotechnologies, the physical properties of biological materials,
and micro/nanofluidics are reviewed and explained in this chapter. The knowledge
gained in this chapter will then be used in the entire topic.
1.1
Transport Phenomena at the Nanoscale
When electronic devices are scaled down from few microns up to nanoscale,
they become comparable with living organisms, such as bacteria, viruses, or the
dimensions of DNA bases. The nanoscale is represented in Fig. 1.1 . This fact is of
paramount importance for sensing, detecting, or manipulating microorganisms or
biomolecules.
The reduced nanometer dimensions of electronic devices changes completely
the transport properties. A nanoscale device is an electron device where one, two,
or even all three spatial dimensions have few nm. If at a scale of few microns
any electronic device can be described by macroscopic physical equations such as
Ohm's law, at the nanoscale, microscopic equations are replaced by equations based
on quantum mechanics. Quantum mechanical effects manifest at the nanoscale even
at room temperature.
A homogenous semiconductor has a conduction band (the first empty band), a
valence band (the last occupied band), and a bandgap that separates them. The
distribution function of charge carriers in these bands is described by the Fermi-
Dirac function
f.E/ D 1= f 1 C expÅ’.E E F /=k B T g ;
(1.1)
where E F is the Fermi energy level. In semiconductors, the Fermi level is located
inside the energy bandgap. In Fig. 1.2 , we have displayed the Fermi function at two
temperatures.
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