2. Unit I:
Application of
1. Zero-dimensional Nanoparticles
2. Quantum dots for Solar Cells, LEDS, bio-sensing
3. Molecular Electronics
4. Nanotube/Nanowire based FET
5. Nanoporus materials & its applications
2
30. Material Classes, Structure, and Properties
30
Classes of Materials
If you stop for a moment and look around you, you will notice a wide variety of materials, either
artificially produced by humans or naturally existing in nature.
Both types can be categorized in particular classes to provide a better understanding of their similarities
and differences.
we distinguish seven classes: metallic, ceramic, polymeric, composite, electronic, biomaterials, and
nanomaterials.
However, as you will note, some materials have characteristics across various classes .
Metallic Materials
Metallic materials consist principally of one or more metallic elements, although in some cases small
additions of nonmetallic elements are present.
Examples of metallic elements are copper, nickel, and aluminum, whereas examples of nonmetallic
elements are carbon, silicon, and nitrogen.
When a particular metallic element dissolves well in one or more additional elements, the mixture is
called a metallic alloy.
The best example of a metallic alloy is steel, which is composed of iron and carbon.
Metallic materials exhibit metallic-type bonds and thus are good thermal and electrical conductors and
are ductile, particularly at room temperature
31. Ceramic Materials:
Ceramic materials are composed of at least two different elements.
31
Among the ceramic materials, we can distinguish those that are predominantly ionic in nature (these consist
of a mixture of metallic elements and nonmetallic elements) and those that are covalent in nature (which
consist mainly of a mixture of nonmetallic elements).
Examples of ceramic materials are glasses, bricks, stones, and porcelain.
Because of their ionic and covalent types of bonds, ceramic materials are hard, brittle, and good insulators.
In addition, they have very good corrosion resistance properties.
Polymeric Materials:
Polymeric materials consist of long molecules composed of manyorganic molecule units, called mer
(therefore the term polymer).
Polymers are typically divided into natural polymers such as wood, rubber, and wool; biopolymers such as
proteins, enzymes, and cellulose; and synthetic polymers such as Teflon and Kevlar.
Among the synthetic polymers there are elastomers, which exhibit large elongations and low strength, and
plastics, which exhibit large variations in properties. Polymeric materials are in general good insulators
and have good corrosion resistance
Composite Materials
Composite materials are formed of two or more materials with verydistinctive properties, which act
synergistically to create properties that cannot be achieved by each single material alone.
Typically, one of the materials of the composite acts as a matrix, whereas the other materials act as
reinforcing phases. Composite materials can be classified as metal-matrix, ceramic-matrix, or polymer-matrix.
For each of these composite materials, the reinforcing phases can be a metal, a ceramic, or a polymer,
depending on the targeted applications.
32. Electronic Materials
3
2
The electronic class of materials is a bit broader than the previous classes because electronic materials can
encompass metals, ceramics, and polymers, such as
the metal copper that is used as interconnects in most electronic chips,
the ceramic silica that is used as optical fibers, and
the polymer polyamides, which are used as a dielectric.
However, the term electronic material is used to describe materials that exhibit semiconductor properties.
The most important of these materials is silicon, which is used in practically all electronic components.
Other materials such as germanium and gallium arsenide are also part of this class.
Biomaterials
The biomaterials class is related to any material, natural or synthetic, that is designed to mimic, augment, or
replace a biological function. Biomaterials should be compatible with the human body and not induce rejection.
This class of materials is rather broad and can comprise metals, ceramics, polymers, and composites.
Typically these materials are used in prostheses, implants, and surgical instruments.
Biomaterials should not be confused with bio-based materials, which are the material parts of our body, such
as bone.
Nanomaterials
The nanomaterial class of materials is extremely broad because it can include all the previous classes of
materials, provided they are composed of a structural component at the nanoscale or they exhibit one of the
dimensions at the nanoscale.
33. Nanomaterials
Nanomaterials are typically categorized as 0-D (nanoparticles), 1-D (nanowires, nanotubes,and nanorods),
2-D (nanofilms and nanocoatings), or 3-D (bulk), which represent the number of dimensions that are not at
the nanoscale.
Everything is made of atoms. How do we know? It is a hypothesis that has been confirmed in several ways.
Toillustrate the idea of how small an atom is, observe Figure . If a strawberry is magnified to the size of
the Earth, the atoms in the strawberry are approximately the size of the original strawberry.
33
34. Q. Let’s now ask another question, which is: What are the properties of these entities called atoms?
We shall divide the properties of atoms into two main categories, namely inertia and forces.
1. The property of inertia: If a particle is moving, it keeps going in the same direction unless forces act on it.
2.The existence of short-range forces: They hold the atoms together in various combinations in a complicated way.
3.What are these short-range forces? These are, of course, the electrical forces.
4.What is it in the atom that can produce such an effect?
5.To answer this question, consider the Bohr atomic model, depicted in Figure.
34
35. Let’s now think about another aspect: What is particular about particles such as electrons, protons, neutrons,
and photons?
Newton thought that light was made up of particles and therefore should behave the way particles do.
And in fact light does behave like particles.
However, this is not the whole story. Light also behaves like a wave.
Q. How can particles such as electrons and light exhibit this dual behavior? We don’t know.
For the time being we need to accept this, keeping in mind that on a small scale the world behaves in a
very different way. It is hard for us to imagine this because we have evolved in a different kind of world.
However, we can still use our imagination. This is the field of quantum mechanics.
This idea claims that we are not allowed to know simultaneously the definite location and the definite speed
of a particle. This is called the Heinserberg Uncertainty Principle.
In other words, we can only say that there is a probability that a particle will have a position near some
coordinate x. This is akin to watching Shaquille O’Neal throw a basketball to the basket. You can’t say that he
is going to hit the basket for sure! There is also a certain probability
Q.This explains a very mysterious paradox, which is this: If the atoms are made of plus and minus charges,
why don’t the electrons get closer? Why are atoms so big? Why is the nucleus at the center with electrons
around it? What keeps the electrons from simply falling in?
Ans: The answer is that if the electrons were in the nucleus, we would know their position and then they
would have to have a very high speed, which would lead to them breaking away from the nucleus.
35
36. So far, when we have been talking about atoms, we have considered their lowest possible energy
configuration. But it turns out that electrons can exist in higher-energy configurations. Are those energies
arbitrary????
Ans: The answer is no. In fact, atoms interchange energy in a very particular away. An
analogous idea is to have people exchange paper currency. Imagine that I want to buy
a CD that costs Rs17 and that I only have Rs5 bills. Further imagine that the
CD store only has Rs5 bills in the cash register. In this case, the CD I want to
buy will cost either Rs15 or Rs20, depending on which party wants to assume the loss.
Atoms are very similar. They can only exchange certain “Rs bills.” For simplicity, let’s
look at the hydrogen atom. As shown in this figure, the ground energy for the hydrogen
atom is −13.6 eV (electron volts). Why is it negative?
The reason is because electrons have less energy when located in the atom than when outside the atom.
Therefore, −13.6 eV is the energy required to remove the electron from the ground energy level. If an atom is
in one of the excited states E1, E2, and so on, it does not remain in that state forever. Sooner or later it drops
to a lower state and radiates energy in the form of light???
ifwe have equipment of very high resolution, we will see that what we thought was a single shell actually
consists of several subshells close together in energy.
Weare still left with one thing to worry about, and that is: How many electrons can we have in each
state? To understand this problem, we should consider that electrons not only move around the nucleus but
also spin while moving. In addition, we should consider a fundamental principle of atomic science, which is
the exclusion principle.
In other words, it is not possible for two electrons to have the same momentum, be at the same location,
and spin in the same direction. What is the consequence of this?
36
38. 3
8
This procedure of classification by dimensions allows nanomaterials to be identified and classified in a 3-D
space. The distances x, y, and z represent dimensions below 100 nm.
As we look in more detail at the aforementioned categories, the straightforward nature of 0-D and 1-D
nanomaterials speak for themselves, and we will look at their synthesis, characterization, properties, and
applications in further detail in next few classes.
For us to begin thinking in more detail about 2-D and 3-D nanomaterials, we need a stronger
understanding of their classification.
• terials
With that in mind, we start by discussing 2-D nanoma
2-D nanomaterial is a single-layer material, with a
thickness below 100 nm and length and width that
exceed nanometer dimensions.
However, as discussed, a material may be
categorized as a nanomaterial simply on the basis of
its internal structural dimensions, regardless of its
exterior material dimensions.
The inclusion of these internal structural qualifications is part of what makes the classification of 2-D
nanomaterials more complex.
A 2-D nanomaterial is shown with a particular internal structure,
composed of crystals (or grains) with nanoscale dimension.
This 2-D nanomaterial may be called a nanocrystalline film
because of two features: (1) the material exhibits an overall exterior
thickness with nanoscale dimensions, and (2) its internal structure is
also at the nanoscale
Two-dimensional nanomaterial with
thickness and internal structure at the
nanoscale
39. Two-dimensional nanomaterial with
thickness at the nanoscale and internal
structure at the microscale
The above example helps illustrate two possible ways of categorizing of 2-D nanomaterials, both these
restrictions do not need to be in place for the material to be considered a nanomaterial.
if the exterior thickness remains at the nanoscale, it is possible for
the same to have a larger (above 100 nm) internal grain structure and
still qualify the entire material as a nanoscale material.
These examples help point out how the internal structural
dimensions and external surface dimensions are independent
variables for the categorization of 2-D nanomaterials.
The way 2-D nanomaterials are produced adds to the complexity
of their categorization. Generally, 2-D nanomaterials, are deposited on
a substrate or support with typical dimensions above the nanoscale.
In these cases, the overall sample thickness dimensions become
a summation of the film’s and substrate’s thickness.
When this occurs, the 2-D nanomaterial can be considered a
nanocoating .
Yet at times when the substrate thickness does have
nanoscale dimensions or when multiple layers with thicknesses
at the nanoscale are deposited sequentially, the 2-D nanomaterial
can be classified as a multilayer 2-D nanomaterial.
Within each layer, the internal structure can be at the nanoscale or
above it
Two-dimensional nanomaterials with
thickness at the nanoscale, internal structure
at the nanoscale/ microscale, and deposited
as a nanocoating on a substrate of any
dimension
40. Two-dimensional nanocrystalline
and microcrystalline multilayered
nanomaterials.
Since we now have several working models for the categorization of
2-D nanomaterials, let’s move on to 3-D nanomaterials.
bulk nanomaterials are materials that do not have any dimension at the
nanoscale.
However, bulk nanomaterials still exhibit features at the nanoscale.
bulk nanomaterials with dimensions larger than the nanoscale
can be composed of crystallites or grains at the nanoscale,
as shown in Figure below:
Three-dimensional nanocrystalline
nanomaterial in bulk form
40
Another group of 3-D nanomaterials are the so-called
nanocomposites.
These materials are formed of two or more materials with very
distinctive properties that act synergistically to create properties
that cannot be achieved by each single material alone.
The matrix of the nanocomposite, which can be polymeric, metallic,
or ceramic, has dimensions larger than the nanoscale, whereas the
reinforcing phase is commonly at the nanoscale
Distinctions are based on the types of reinforcing nanomaterials
added, such as nanoparticles, nanowires, nanotubes, or nanolayers.
Within the nanocomposite classification, we should also consider
materials with multinanolayers composed of various materials or
sandwiches of nanolayers bonded to a matrix core.
41. Summary of 2-D and 3-D crystalline structures.
41
Matrix-reinforced and layered nanocomposites
42. Basic types of large-scale nanomaterials bulk forms. The filler materials, whether 0-D, 1-D, or
2-D nanomaterials are used to make film and bulk nanocomposites.
42
44. 4
4
Many applications, especially in nanoelectronics, require the use of various kinds of physical features, such
as channels, grooves, and raised lines, that are at the nanoscale (see Figure 1)
Two-dimensional nanomaterials containing patterns of
features (e.g., channels, holes).
Nanocopper interconnects used in electronic devices. The
copper lines were produced by electrodeposition of copper
on previously patterned channels existent in the dielectric
material.
(Courtesy of Jin An and P. J. Ferreira, University of
Texas at Austin.
45. • Nanofilms, nanocoatings, and multilayer 2-D nanomaterials can be patterned with various features at
various scales.
•In the case of multilayered nanomaterials, the patterns can be made on any layer. These patterns can
have different geometries and dimensions at the nanoscale or at larger scales.
Most electronic materials fall into the category of patterned 2-D nanomaterials.
Figure below broadly summarizes types of nanomaterials in relation to their dimensionalities:
45
46. Size Effects:Surface-to-Volume Ratio Versus Shape
One of the most fundamental differences between nanomaterials and larger-scale materials is that
nanoscale materials have an extraordinary ratio of surface area to volume.
Though the properties of traditional large-scale materials are often determined entirely by the properties of
their bulk, due to the relatively small contribution of a small surface area, for nanomaterials this surface-to-
volume ratio is inverted, as we will see shortly.
Asa result, the larger surface area of nanomaterials (compared to their volume) plays a larger role in
dictating these materials’ important properties.
This inverted ratio and its effects on nanomaterials properties is a key feature of nanoscience and
nanotechnology.
For these reasons, a nanomaterial’s shape is of great interest because various shapes will produce distinct
surface-to-volume ratios and therefore different properties.
How to calculate the surface-to-volume ratios in nanomaterials with different shapes and to illustrate the
effects of their diversity?
46
