Applied Nanochemistry/Lecture No. 1,2,3,4/Lecture No. 1,2,3,4

Dr. Prakash JhaDr. Prakash JhaSchool of Chemical Sciences,School of Chemical Sciences,

CUG,Gujarat CUG,Gujarat 14-02-201314-02-2013

Prakash_cjha@yahoo.comPrakash_cjha@yahoo.com

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Unit I:

Application of1. Zero-dimensional Nanoparticles2. Quantum dots for Solar Cells, LEDS, bio-sensing3. Molecular Electronics4. Nanotube/Nanowire based FET5. Nanoporus materials & its applications

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Material Classes, Structure, and Properties 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 similaritiesand 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

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Ceramic Materials:Ceramic materials are composed of at least two different elements.

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 insulatorsand have good corrosion resistanceComposite MaterialsComposite 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.

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Electronic MaterialsThe 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.NanomaterialsThe 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.

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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.

To illustrate 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.

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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.

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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 avery 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 somecoordinate 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.

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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???

if we 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.

We are 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?

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General characteristics of nanomaterial classes and their dimensionality

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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.

• With that in mind, we start by discussing 2-D nanomaterials

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 becategorized 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

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.

Two-dimensional nanomaterial with thickness at the nanoscale and internal structure at the microscale

if the exterior thickness remains at the nanoscale, it is possible forthe 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 complexityof 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

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Two-dimensional nanocrystalline and microcrystalline multilayered

nanomaterials.

Since we now have several working models for the categorization of2-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 nanoscalecan be composed of crystallites or grains at the nanoscale,as shown in Figure below:

Three-dimensional nanocrystalline nanomaterial in bulk form

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.

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Summary of 2-D and 3-D crystalline structures.

Matrix-reinforced and layered nanocomposites

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Basic types of large-scale nanomaterials bulk forms. The filler materials, whether 0-D, 1-D, or2-D nanomaterials are used to make film and bulk nanocomposites.

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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 ofTexas at Austin.

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• 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 canhave 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:

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Size Effects:Surface-to-Volume Ratio Versus ShapeOne 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.

As a 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?

Thank you for your kind Thank you for your kind attention!!!!!!!attention!!!!!!!

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