Nanomaterials: Classification, Properties, and Applications - PDF

Here is the text from the images converted into a structured markdown format. ## Classification - Classification is based on the number of dimensions, which are not confined to the nanoscale range (<100 nm). - (1) zero-dimensional (0-D) - (2) one-dimensional (1-D) - (3) two-dimensional (2-D) - (4)...

Here is the text from the images converted into a structured markdown format. ## Classification - Classification is based on the number of dimensions, which are not confined to the nanoscale range (<100 nm). - (1) zero-dimensional (0-D) - (2) one-dimensional (1-D) - (3) two-dimensional (2-D) - (4) three-dimensional (3-D) The image shows a diagram of nanomaterials by dimension: ### 1-D Two dimensions (x,y) at nanoscale, other dimension (L) is not $d \leq 100 nm$ Nanowires, nanorods, and nanotubes ### 0-D All dimensions (x,y,z) at nanoscale $|d \leq 100nm$ Nanoparticles ### 2-D One dimension (t) at nanoscale, other two dimensions $(L_x, L_y)$ are not $t \leq 100nm$ Nanocoatings and nanofilms ## Zero-dimensional nanomaterials - Materials wherein all the dimensions are measured within the nanoscale (no dimensions, or 0-D, are larger than 100 nm). - The most common representation of zero-dimensional nanomaterials are nanoparticles. - Nanoparticles can: - Be amorphous or crystalline - Be single crystalline or polycrystalline - Be composed of single or multi-chemical elements - Exhibit various shapes and forms - Exist individually or incorporated in a matrix - Be metallic, ceramic, or polymeric ## One-dimensional nanomaterials - One dimension that is outside the nanoscale. - This leads to needle like-shaped nanomaterials. - 1-D materials include nanotubes, nanorods, and nanowires. - 1-D nanomaterials can be: - Amorphous or crystalline - Single crystalline or polycrystalline - Chemically pure or impure - Standalone materials or embedded in within another medium - Metallic, ceramic, or polymeric ## Two-dimensional nanomaterials - Two of the dimensions are not confined to the nanoscale. - 2-D nanomaterials exhibit plate-like shapes. - Two-dimensional nanomaterials include nanofilms, nanolayers, and nanocoatings. - 2-D nanomaterials can be: - Amorphous or crystalline - Made up of various chemical compositions - Used as a single layer or as multilayer structures - Deposited on a substrate - Integrated in a surrounding matrix material - Metallic, ceramic, or polymeric The image shows a cross section of 2-D nanomaterials F-TEOS, $t \approx 100nm$ ## Three-dimensional nanomaterials - Bulk nanomaterials are materials that are not confined to the nanoscale in any dimension. These materials are thus characterized by having three arbitrarily dimensions above 100 nm. - Materials possess a nanocrystalline structure or involve the presence of features at the nanoscale. - In terms of nanocrystalline structure, bulk nanomaterials can be composed of a multiple arrangement of nanosize crystals, most typically in different orientations. - With respect to the presence of features at the nanoscale, 3-D nanomaterials can contain dispersions of nanoparticles, bundles of nanowires, and nanotubes as well as multinanolayers. The image shows a three-dimensional space illustration including 0-D, 1-D, 2-D, and 3-D nanomaterials. | Material Type | Description | | :------------- | :------------------------------------------- | | 0-D | All dimensions at the nanoscale | | 1-D | Two dimensions at the nanoscale | | 2-D | One dimension at the nanoscale | | 3-D | No dimensions at the nanoscale, | Illustration of Crystalline Structures: - Nanocrystalline - Microcrystalline - Large-Scale Forms - One layer - Substrate - Multiple layers ## Matrix-reinforced and layered nanocomposites The image is an illustration of Matrix-reinforced and layered 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. - Matrix reinforced with nanoparticles - Matrix reinforced with nanowires/nanotubes - Laminates - Sandwiches ## Quantum effects - The overall behavior of bulk crystalline materials changes when the dimensions are reduced to the nanoscale. - For 0-D nanomaterials, where all the dimensions are at the nanoscale, an electron is confined in 3-D space. No electron delocalization (freedom to move) occurs. - For 1-D nanomaterials, electron confinement occurs in 2-D, whereas delocalization takes place along the long axis of the nanowire/rod/tube. - In the case of 2-D nanomaterials, the conduction electrons will be confined across the thickness but delocalized in the plane of the sheet. ## Electrons confinement - For 0-D nanomaterials the electrons are fully confined. - For 3-D nanomaterials the electrons are fully delocalized. - In 1-D and 2-D nanomaterials, electron confinement and delocalization coexist. - The effect of confinement on the resulting energy states can be calculated by quantum mechanics, as the “particle in the box” problem. An electron is considered to exist inside of an infinitely deep potential well (region of negative energies), from which it cannot escape and is confined by the dimensions of the nanostructure. ## Energies $(0-D) \quad E_n = \frac{\pi^2 \hbar^2}{2mL^2}(n_x^2 + n_y^2 + n_z^2)$ $(1-D) \quad E_n= \frac{\pi^2 \hbar^2}{2mL^2}(n_x^2 + n_y^2)$ $(2-D) \quad E_n = \frac{\pi^2 \hbar^2}{2mL^2}(n_x^2)$ where h=h/2π, h is Planck's constant, m is the mass of the electron, I is the width (confinement) of the infinitely deep potential well, and nx, ny, and nz are the principal quantum numbers in the three dimensions x, y, and z. The smaller the dimensions of the nanostructure (smaller L), the wider is the separation between the energy levels, leading to a spectrum of discreet energies. ## What's different at the nanoscale? Each of the different sized arrangement of gold atoms absorbs and reflects light differently based on its energy levels, which are determined by size and bonding arrangement. This is true for many materials when the particles have a size that is less than 100 nanometers in at least one dimension. ## 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 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 * **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 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. * **Electronic Materials** * 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. * 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. ## General characteristics of nanomaterial classes and their dimensionality | Dimensionality | Class 1 Discrete nano-objects | Class 2 Surface nano-featured materials | Class 3 Bulk nano-structured materials | | :------------- | :----------------------------------- | :---------------------------------------- | :--------------------------------------- | | 0-D | Nanoparticles (smoke, diesel fumes) | Nanocrystalline films | Nanocrystalline materials | | 1-D | Nanorods and tubes (carbon nanotubes) | Nano interconnects | Nanotube-reinforced composites | | 2-D | Nanofilms, foils (gilding foil) | Nano surface layers | Multilayer structures | 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. and 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 be categorized as a nanomaterial simply on the basis of its internal structural dimensions, regardless of its exterior material dimensions. Illustration of $t \leq 100 nm$ - Nanocrystalline, - Microcrystalline 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. This illustration - Nanoscale - Bulk 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) Nanofilms, nanocoatings, and multilayer 2-D nanomaterials can be patterned with various features at various scales. ## 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. As a result, the larger surface area of nanomaterials (compared to their volume) plays a larger role in dictating these materials' important properties. Surface-to-Volume Ratio (nm³) Illustration is as follows: - sphere - cylinder - cube