Biomedical Engineering Reference
In-Depth Information
It is the fi rst crystalline 2-D-material with unique properties, which makes it
interesting both for fundamental science and for future applications. The Manchester
group succeeded by using an optical method, an Atomic Force Microscope (AFM)
with which they were able to identify fragments made up of only a few layers, or
even monolayer-that's how graphene was identifi ed [
4
,
5
].
Nanoparticles in the Nature and How Long the Adventure
in the Nanospace Was?
It was Democritus of Abdera in ancient Greece who fi rst told that the matter must
have smallest, invisible particle retaining all properties of that matter [
2
]. Democritus'
model was a small, invisible non-particulated sphere. Athomos in Greek's means:
non-dividable. In his vision it contained no electrons or nucleus. This was the fi rst
atomic model ever designed.
He drew his model to show that all atoms are indestructible and unchangeable.
Democritus also knew that atoms are different in size. He thought they were differ-
ent in shape and temperature, as well. Much later on, in modern era it has been
determined that radius of He atom for example is in the range of nano-values [
2
].
John Dalton in 1803 was the fi rst to seriously revise Democritus's theory [
2
].
He stated that atom is particulated and gave the fi rst taw model which was then
modifi ed with work of many scientists such as: Rutherford, Bohr, etc. [
2
].
However, Ernst Rutherford has proved that the nuclei of certain light elements,
such as nitrogen, could be 'disintegrated' by the impact of particles coming from a
radioactive source, and that during this process fast protons were emitted. It was the
fi rst artifi cially induced nuclear reaction and it would change the world forever.
Along with the eventual founding of CERN in 1954, it would lead to nuclear power
and the atomic bombs that devastated Hiroshima and Nagasaki in World War Two.
What did Bohr improve on atomic structure? Rutherford's atomic theory
described an atomic model with all the mass concentrated in a nucleus with electrons
circling the nucleus in a fi xed orbit. This theory was shown incorrect by using
Maxwell's equations, which states since the electrons are moving in a circular
motion, they are accelerating. Accelerating electrons means they are emitting radia-
tion and therefore losing energy and would eventually spiral in motion toward the
nucleus and collapse [
2
]. Bohr's insight was that he declared an electron could orbit
the nucleus but only in discrete orbits which didn't emit radiation. An electron
moves to a higher orbit, with a larger radius, by absorbing radiation (a photon) and
in contrast will emit a photon of energy when the electron moves to a lower orbit
with a smaller radius. Each orbit corresponds to an angular momentum value relat-
ing to Planck's constant (
h
) divided by 2
. Insights regarding radiation and atoms
were taken from Planck's Quantum Theory [
2
]. Bohr proposed that the outer orbits
could accommodate more electrons than the inner orbits.
In total, the atomic
structure theory that Bohr proposed included an atom which was 1/10,000 the
size of the atoms proposed by other scientists.
ˀ
