Nanomaterials Flashcards
Importance of Surface Area when it comes to nanomaterials
As the size of particle decreases greater proportion of atom are
found at the surface for e.g.
Size 30 nm- 5% of atom on its surface
Size 10 nm- 20% of atom on its surface
Size 3 nm- 50% of atom on its surface
Nanomaterials have a much greater surface area to volume
ratio than their conventional forms, which can lead to greater
chemical reactivity and affect their strength.
Quantum Effect
Quantum size effect describes the physics of
electron properties in solids with great reductions in particle
size.
In Bulk the properties of any material are basically the average of the properties of its constituent atoms, as you go smaller and smaller after a point the averaging no longer works.
The quantum confinement effect can be observed
once the diameter of particle is of the same magnitude
as the wavelength of electron
Responsible for
increase of energy gap between energy state and band
gap.
At nano scale materials suddenly show different properties, Eg : copper becomes transparent, silicon turns into a conductor.
Classification of Nanomaterials
Zero dimension (quantum dots)
One dimension (quantum wires, rods)
Two dimension (plates, network, quantum wells)
Three dimension (fullerenes- C60)
Nanomaterial - synthesis and processing
Can be thought of top down or bottom up, as in either to assemble atoms together or to dis-assemble (break, or dissociate) bulk solids into finer pieces until they are constituted of only a few atoms.
Fullerenes
Fullerenes are spherical carbon-cage molecules with sixty (C60) or more
carbon atoms. A hollow pure carbon molecule in which
atom lies at the vertices of polyhedron with 12 pentagonal faces and any
number of hexagonal faces.
Each carbon is bound to other three carbon in pseudo spherical arrangement
of alternating pentagonal and hexagonal rings in the manner of soccer ball. They measure about 0.7-1.5 nm in
diameter.
Heat resistant and super conductivity.
Google Fullerenes and understand the structure.
Quantum dots
Quantum dots are tiny semiconducting crystal, this means this
particle can either conduct or resist depending upon
temperature and purity of lab. There size ranges between
2-10nm. Governed by quantum mechanics. One of the unique
property of quantum dots is their emission color depend upon
their size. The bigger the quantum dot bigger will be the wavelength and smaller the frequency it will emit. This means larger quantum dot will emit red light and smaller will emit blue.
Bohr Radius
The average distance between an electron and a hole in a
exciton is called the Excited Bohr Radius. When the size of the semiconductor falls below the Bohr Radius, the
semiconductor is called a quantum dot.
Applications of Quantum dots
Monitoring cancer cells and observe its evolution.
Could be armed with tumor fighting therapies to diagnose and treat cancer.
Prone to degradation allowing longer operational time.
Used to produce inexpensive quality white light.
Produce white light by intermixing red, green, and blue emitting dots homogenously
within the phosphor.
Solar Cells and Photovoltaics
~60% efficiency in electricity production while being $100 or less per
square meter of paneling necessary.
Effective due to quantum dots’ ability to preferentially absorb and emit
radiation that results in optimal generation of electric current and voltage.
Carbon nanotubes (CNT)
Long hollow structure wall, formed by one atom thick graphene. Rolled at specific chiral angle. Radius and rolling angle decides properties.
Great mechanical, electronic and thermal properties. High tensile strength, can be semiconducting or metallic.
Very Light and strong.
Classification of Carbon Nanotubes
Single Walled :
armchair - metallic
zigzag - semiconducting
chiral - semiconducting
Multi walled -metallic
Method of preparation.
Arc Method
Laser Method
Chemical deposition method
Electrical Conductivity of carbon nanotubes
Function of their
chirality, degree of twist as well as diameter, metallic or semi conductor.
Most conductive fibers known, Highest current density too.
Single wall nanotubes can route electrical speed up to 10 GHz.
Strength and Elasticity of carbon nanotubes
Ultimate high strength fiber, stiffer than steel and are resistant to
damage from physical forces. Pressing on the tip of nanotubes
will cause it to bend without damage to the tip. microscopy. The current Young’s modulus value for single walled nanotubes is about 1 Tera Pascal.
Thermal conductivity and High aspect ratio of carbon nanotubes.
Exhibit superconductivity below 20
°K, very high thermal conductivity. The high aspect ratio means that lower loading of CNTs is needed than to other conductive material.
