nanostructured materials | Cheat Sheet Nanotechnology

Introduction

1. What is nanoscale: nm

2. What is nanomaterials:

Subtances where at least 1 dimension is from 1-100nm

Possess diffirent properties compared to macro/bulk materials

3. Nanomaterials vs bulk:

Large size different behavior in collisions with atoms.

The effects of quantum confinement on electrical,thermal, and optical properties become

significant at about this size.

Reduce imperfection.

Very high fraction of their atoms on their surface.

These atoms are very different from the ones located in side the object.

Change energy band (Eg), density of states (DOS).

4. History of Nanomaterials & Technology:

The history of nanomaterials took an interesting turn in the 20th century.

Japanese professor Norio Taniguchi gives a name to the new field in a scientific paper titled:

"On the Basic Concept of 'Nano-Technology.

5. Classification of nanostructured materials:

Zero-dimensional (0-D) objects have nanometer feature size in every direction: Quantum dots,

nanoparticles, and fullerenes.

One-dimensional (1-D) objects have nanometer size in two directions but larger, e.g.,

micrometer, length in the third: GaAs nanowire/nanofiber, carbon nanotubes

Two-dimensional (2-D) objects are atomically thin sheets of materials: graphene

Three- dimensional (3-D) are nanoporous or nanostructured materials: ceramic, porous metals,

zeolites.

6. Formation of Nanostructure materials:

Top Down Methods (μm to 10 nm) Mechanical grinding:

Top down approach refers to slicing or milling of a bulk material to get nanosized particles.

Milling is a typical top down method in making nanoparticles.

The biggest problem with top down approach is the imperfection of surface structure and

significant crystallographic damage to the processed patterns.

Bottom up approach refers to the build up of a material from the bottom: atom by atom,

molecule by molecule or cluster by cluster.

7. Properties of Nanomaterials:

The reduction of a material dimension has pronounced effects on its physical, mechanical and

chemical properties.

In most cases though, the values of these properties are very different from those in the bulk,

depending on:

the size

morphology of the nanomaterials

7.1. Surface area to volume ratio:

Due to their small dimensions, nanomaterials have extremely large surface area to volume

ratio.

The large surface area to volume ratio of nanoparticles opens many possibilities for creating

new materials and facilitating chemical processes.

S/V = 3/r

Partial preview of the text

Download nanostructured materials and more Cheat Sheet Nanotechnology in PDF only on Docsity!

Introduction

1. What is nanoscale: nm

2. What is nanomaterials:

 Subtances where at least 1 dimension is from 1-100nm

 Possess diffirent properties compared to macro/bulk materials

3. Nanomaterials vs bulk:

 Large size different behavior in collisions with atoms.  The effects of quantum confinement on electrical,thermal, and optical properties become significant at about this size.  Reduce imperfection.  Very high fraction of their atoms on their surface.  These atoms are very different from the ones located in side the object.  Change energy band (Eg), density of states (DOS).

4. History of Nanomaterials & Technology:

 The history of nanomaterials took an interesting turn in the 20th century.  Japanese professor Norio Taniguchi gives a name to the new field in a scientific paper titled: "On the Basic Concept of 'Nano-Technology.

5. Classification of nanostructured materials:

 Zero-dimensional (0-D) objects have nanometer feature size in every direction: Quantum dots, nanoparticles, and fullerenes.  One-dimensional (1-D) objects have nanometer size in two directions but larger, e.g., micrometer, length in the third: GaAs nanowire/nanofiber, carbon nanotubes  Two-dimensional (2-D) objects are atomically thin sheets of materials: graphene  Three- dimensional (3-D) are nanoporous or nanostructured materials: ceramic, porous metals, zeolites.

6. Formation of Nanostructure materials:

 Top Down Methods (μm to 10 nm) Mechanical grinding:  Top down approach refers to slicing or milling of a bulk material to get nanosized particles.  Milling is a typical top down method in making nanoparticles.  The biggest problem with top down approach is the imperfection of surface structure and significant crystallographic damage to the processed patterns.  Bottom up approach refers to the build up of a material from the bottom: atom by atom, molecule by molecule or cluster by cluster.

7. Properties of Nanomaterials:

 The reduction of a material dimension has pronounced effects on its physical, mechanical and chemical properties.  In most cases though, the values of these properties are very different from those in the bulk, depending on:  the size  morphology of the nanomaterials

7.1. Surface area to volume ratio:

 Due to their small dimensions, nanomaterials have extremely large surface area to volume ratio.  The large surface area to volume ratio of nanoparticles opens many possibilities for creating new materials and facilitating chemical processes.  S/V = 3/r

 The total surface energy increases with the overall surface area, which is in turn strongly dependent on the dimension of material.  Nanostructures and nanomaterials possess a large fraction of surface atoms per unit volume.  The ratio of surface atoms to interior atoms changes dramatically if one successively divides a macroscopic object into smaller parts.  Changes in the size range of nanometers → great changes in the physical and chemical properties of the materials.  Due to the vast surface area, all nanostructured materials possess a huge surface energy → thermodynamically unstable or metastable.  Great challenges in fabrication and processing of nanomaterials is to overcome the surface energy and to prevent the nanostructures or nanomaterials from growth in size, driven by the reduction of overall surface energy.  Surface energy, 𝛾, by definition, is the energy required to create a unit area of “new” surface  The energy required to get new surfaces back to its original position will be equal to the number of broken bonds, Nb, multiplying by half of the bond strength, 𝜖 𝜌!: surface atomic density, the number of atoms per unit area on the new surface

7.2. Melting point:

 A number of studies reveal that the melting point of metals such as In, Sn, Pb, Bi, Cd, Al, Ag, and Au decreases with decreasing their size particularly below 30 nm.  The materials at nanoscale melt at lower temperatures than bulk materials.  Generally, the Tm of a bulk material is not dependent on its size.  Tm of the nanomaterial decreases with the decrease in grain size.  The decrease Tm can be on the order of tens to hundreds of degrees for metals with nm dimensions.  The change of Tm can be attributed to the large surface to volume ratio than bulk materials that affects their thermodynamic properties  The high-surface area to volume ratio of the nanoparticles, which in turn have high-surface energies; hence, the activation energy required for the melting of the surface atoms is lower than the bulk.

7.3. Coefficient of Thermal Expansion:

 Nanocrystalline materials have a large amount of interfacial volume; hence, coefficient of thermal expansion (CTE) is expected to be higher than coarsegrained material.

7.4. Electrical conductivity:

 Electrical conductivity decreases with the reduction of dimensions, due to:  The increased surface scattering  The band gap becomes wider, the conductivity decreases and the density of states decreases  However, it can be increased, due to the better ordering in micro-structure. Example: Polymeric fibres.  Nanomaterials are used as very good separator plates in batteries. High surface area → high electron current.

7.5. Magnetic properties:

 The magnetic properties of nanomaterials depend strongly on size of material:  Ferromagnetic particles become unstable, can switch the polarization directions and become paramagnetic.  Thus magnetization gets max. value.  The magnetization vectors of different domain in the sample are not all parallel to each other → overall magnetization is decreased.

nanostructured materials, Cheat Sheet of Nanotechnology

Related documents

Partial preview of the text

Download nanostructured materials and more Cheat Sheet Nanotechnology in PDF only on Docsity!

Introduction

1. What is nanoscale: nm

2. What is nanomaterials:

 Subtances where at least 1 dimension is from 1-100nm

 Possess diffirent properties compared to macro/bulk materials

3. Nanomaterials vs bulk:

4. History of Nanomaterials & Technology:

5. Classification of nanostructured materials:

6. Formation of Nanostructure materials:

7. Properties of Nanomaterials:

7.1. Surface area to volume ratio:

7.2. Melting point:

7.3. Coefficient of Thermal Expansion:

7.4. Electrical conductivity:

7.5. Magnetic properties: