纳米材料基础(英文ppt)

MTX9100 Nanomaterjalid
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Fundamentals of nanomaterials
Lecture 5
OUTLINE
-What can nanomaterials be? -What is a dimension? - Does size mean a lot? -What is a potential well?

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), and (4) three-dimensional (3-D).
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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
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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
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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
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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.
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Three-dimensional space showing the relationships among 0-D, 1-D, 2-D, and 3-D nanomaterials.
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Summary of 2-D and
3-D crystalline structures
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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 9 commonly at the nanoscale.

Carbon
Carbon is a basic element of life Carbon is special because of its ability to bond to many elements in many different ways It is the sixth most abundant element in the universe The most known types of carbon materials: diamond; graphite; fullerenes; and carbon nanotubes
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Carbon materials
2s and 2p electrons available for bonding
Diamond and graphite are two
allotropes of carbon:
pure forms of the same element that differ in structure.
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DIAMOND
- chemical bonding is purely covalent - highly symmetrical unit cell - extremely hard - low electrical conductivity - high thermal conductivity (superior) - optically transparent - used as gemstones and industrial grinding, machining and cutting
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GRAPHITE
? Layered structure with strong bonding within the planar layers and weak, van der Waals bonding between layers ? Easy interplanar cleavage, applications as a lubricant and for writing (pencils) ? Good electrical conductor ? Chemically stable even at high temperatures ? excellent thermal shock resistance
Applications:
Commonly used as heating elements (in non- oxidizing atmospheres), metallurgical crucibles, casting molds, electrical contacts, brushes and resisto1r3s, high temperature refractories, welding electrodes, air purification systems, etc.

Graphite
Graphite is a layered compound. In each layer, the carbon atoms are arranged in a hexagonal lattice with separation of 0.142 nm, and the
distance between planes is 0.335 nm
The acoustic and thermal properties of graphite are highly anisotropic, since phonons propagate very quickly along the tightly-bound planes, but are slower to travel from one plane to another.
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https://www.sodocs.net/doc/6e13745549.html,/wiki/Graphite

Graphene
Graphene is an one-atom-thick planar sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. It can be viewed as an atomic-scale chicken wire made of carbon atoms and their bonds
The carbon-carbon bond
length in graphene is about
0.142 nm. Graphene is the
basic structural element of
some carbon allotropes
including graphite, carbon
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nanotubes and fullerenes.

Allotropes of carbon
3D 0D
1D
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a) diamond b) graphite c) lonsdaleite
(hexagonal diamond) d) - f) fullerenes (C60, C540, C70); g) amorphous carbon h) carbon nanotube
2D - ???
Wikipedia

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SCIENCE, June 2010
If there's a rock star in the world of materials, it's graphene: single-atom–thick sheets of carbon prized for
its off-the-charts ability to conduct electrons and for being all but transparent.
Those qualities make graphene a tantalizing alternative for use as a transparent conductor, the sort now found in everything from computer displays and flat panel TVs to ATM touch screens and solar cells. But the material has been tough to manufacture in anything larger than flakes a few centimeters across. Now researchers have managed to create rectangular sheets of graphene 76 centimeters in the diagonal direction and even use them to create a working touchscreen display
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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.
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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.
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