Nano structures.pptx

Nanoscience is the study of phenomena and manipulation of
materials at atomic, molecular, and macromolecular scales, where
properties differ significantly from those at a larger scale.
Nanotechnology is the design, characterization, production, and
application of structures, devices, and systems by controlling the
shape and size at the nanometer scale.

A Nanostructured material(or a nanomaterial) is defined as a solid
material characterized by at least one dimension in the nanometer
range. A nanostructure basically comprises an atom (nanoparticle) or
an aggregate of atoms forming a cluster of dimensions less than 100nm.
The cluster formed can be viewed as a subdivision of a Bulk material,
and having dimensions less than the Characteristic length of certain
phenomena
Nano structures are those which have a characteristic length scale
within 100nm. Particle diameter, grain size, layer thickness, or width of
a conduction line on a device are examples of length scales.
Nanostructures

 Nanostructure materials are materials with different structures in
the range of nanometers (typically 1–100 nm)
 Nano surfaces, cylindrical nanotubes, and nanospheres are
common nanostructures.
 Nanostructure materials exhibit novel and astonishing properties
that are entirely different from their bulk material counterparts
 The properties of nanostructures always depend on the size,
shape, and morphology of the nanostructures, and hence they can
be tuned
 Therefore nanostructure materials are garnering great attention
for their potential to advance and improve currently existing
devices as well as to develop future ones

In recent years, nanosized structures have attracted much attention
from the research community owing to their extraordinary physical,
chemical, mechanical, and electrical properties.
Significance of Nanostructures:
 In nanoelectronics, silicon may soon be replaced by carbon nanotubes to
develop lighter yet efficient microchips and devices
 With growing energy demands, solar panels and hydrogen fuel cells can be
developed using nano structural components to increase their efficiency
 In the field of nanomedicine, biocompatible tunneling nanotubes can help to
deliver drugs to precise targets and monitor health conditions. Creating
functional organic or synthetic nano-structural components for medically
implanted devices is certainly challenging,.

To improve air quality, catalysts made from nanoparticles are used to
transform hazardous gases released from industries and automobiles into
harmless gases
Nanoscale structures (nanoscale rods, rings, beams, plates, and shells) have
been implemented in fundamental structural parts of various
nanoelectromechanical systems (NEMS). NEMS-based devices include
nanomechanical resonators, nanoscale mass sensors, electromechanical
nanoactuators, and nano energy harvesters

Classification of nanostructure materials is based on
 Origin
 Dimension
 And Structure
Classification on the basis of Origin
1. Natural nanomaterial: coming from resources of nature, these
are viruses, proteins, and antibodies. Some minerals like clay,
gelatin, natural colloids, shells, coral, etc are natural
nanomaterials.
2. Artificial nanomaterials: those which are prepared
deliberately through well-defined mechanical and fabrication
processes, like carbon nanotubes, quantum dots, and
semiconductor nanoparticles

Classification on the basis of Materials
1. Carbon-based material: mostly carbon-composed, hollow
spheres (fullerenes) or tubes (nanotubes), these have wide
potential applications.
2. Metal-based materials: Quantum dots, nanogold, nano
silver, and metal oxides like TiO2 are examples of it.
3. Dendrimers: nanosized polymers built from branched units are
dendrimers. Surfaces of dendrimers have branch ends
performing a special function. They are used in drug delivery.
4. Composites: these are bulk-type materials

A nanomaterial is an object that has at least one dimension in the
nanometer scale

NANOSCIENCE IN NATURE: A GREAT STARTING
POINT

Nanoscience in Nature: a great starting point
The interaction of light, water, and
other materials with these
nanostructures gives the natural
materials some remarkable properties
which can be appreciated at the macro
scale.
The chemical identity and properties of a substance depend upon its
molecular structure

Clays
Clays are a type of layered silicate that is characterized by a fine
2D crystal structure

NATURAL COLLOIDS
• Colloid
• Invisible to the naked eye
• Can’t be separated by filtration
• Do not settle down
• Usually particle size 1 – 1000
nanometer
• Visible to the naked eye
• Can be separated by filtration
• Dispersed material is usually solid
• Particles can be settled down
• Usually particle size larger than 1
micrometer
Suspension
• There are different types of dispersed material

NATURAL COLLOIDS SUCH AS MILK AND BLOOD
All these materials have the characteristic of scattering light and often
their color (as in the case of blood and milk) is due to the scattering of
light by the nanoparticles that make them up.

Paper and cotton
high strength, durability, and absorbency of cotton are due
to the nanoscale arrangement of the fibers.

Classification on the basis of Dimensions

Classification on the basis of Dimensions
1. Zero-dimensional:
 These are the materials wherein all the dimensions are within the
nanoscale. The most common representation of 0D nanomaterials
areNanoparticles – Quantum Dots
 They have no dimension or 0-D, outside the nanoscale (larger than
100nm)
 These are nanoparticles that might be crystalline, amorphous, single
crystalline, or polycrystalline.
 The term nanoparticles encompass all 0-D nanosized building
blocks (regardless of size and morphology).

 They are composed of single or multi-chemical elements
 They exhibit various shapes and forms
 They exist individually or incorporated in a matrix
 They may be metallic, ceramic, or polymeric.
 In the past 10 years, significant progress has been seen in 0-D
nanoparticles.
 In well-controlled dimensions a variety of properties has been
developed for the fabrication of 0-D NMs.
 Recently, 0-D such as uniform particle arrays (quantum dots) and
heterogenous particle arrays, core-shell quantum dots have been
used in LEDs, solar cells, and single electron transistors

23
Electrons confined in all the
3Ds Discrete Energy levels

1. One-dimensional (1-D):
 These are the materials with one dimension that is outside the
nanoscale This leads to needle-like-shaped nanomaterials. 1D
materials include Nanotubes, Nanorods, and Nanowires
- These materials could be
 Amorphous or Crystalline
 Single crystalline or Polycrystalline
 Chemically pure or impure
 Stand-alone materials or embedded in within another
medium
 Metallic, ceramic, or polymeric

 The one-dimensional materials have been extensively studied
because of both their functional properties and highly controllable
morphology.
 From the past decade, they have been used in research and
development.
 They play an important role as both interconnects and the key units
in fabricating electronic, optoelectronic nanoscale dimensions,

Electrons confined in 2ds as in
quantum wires: electrons can
freely and easily move in 1D
25

1. Two-dimensional (2D):
 These are the materials with two of the dimensions that are not
confined to the Nanoscale or two dimensions of the material are
outside the Nanoscale. 2D Nanomaterials exhibit plate-like shapes
which include Nanofilms, Nanolayers, and Nanocoating.
 2D nanostructures have two dimensions outside the nanometric size
range (100nm).
 They are made up of various compositions like multi and single-
layered structures.
 They are also integrated into the surrounding matrix material
 Interesting structures for the investigation and development of novel
applications in sensors, photocatalysts, nanocontainers,
nanoreactors, and templates for 2D structures of materials.

- These materials could 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

27
2D nanostructure – If 1D is
Confined to nano range While
another 2D remains Large –
Quantum well (thin Films.
Electrons can easily move in 2
dimensions.

1. Three-dimensional (3D):
 Bulk nanomaterials are materials that are not confined to the
nanoscale in any dimension. (all 3D are above 100nm. 3D
nanostructures have three dimensions outside/above the
nanometric size range(100nm).
- Bulk Materials possess
 a nanocrystalline structure
 can be composed of multiple arrangements of nanosize crystals,
most typically in different orientations.
 With respect to the presence of features at the nanoscale, 3D
nanomaterials can contain dispersions of nanoparticles, bundles
of nanowires and nanotubes as well as multi-nanolayers

 Due to their large surface area, these Bulk materials have attracted
considerable research interest.
 These are very much important materials due to their wide range of
applications in areas of catalysis, magnetic material, and electrode
material for batteries.
 Due to their large surface area these have been used in research
for transporting of molecules due to their porosity.

THE DENSITY OF STATES
29
 The density of states of a system describes the number of
states of each energy level that is available to be occupied by
an electron per unit interval of energy

32
and
QUANTUM CONFINEMENT
DIMENSIONALITY

Metal (conductor), Insulator, and Semiconductor
Conduction
band (empty)
Valence band
(full)ll)
band gap
band gap
Electronicband theory

When a Bulk metal particle is reduced to a size of a few tens or hundreds of
atoms, the density of states changes dramatically. The changes observed in the
electronic structure during the transition of a bulk material to a large nanocluster
and then to a small nanocluster of tens of atoms are as per the figure.
Bulk material Large cluster Small cluster

 When the particle size is reduced such that it has a few hundred
atoms or less, the continuous density of states changes to a set
of discrete energy levels
 In small nanocrystals, the electronic energy levels are not
continuous as in the bulk but are discrete (finite density of states),
because of the confinement of the electronic wavefunction to the
physical dimensions of the particles
 This phenomenon is called quantum confinement and therefore
nanocrystals are also referred to as quantum dots (QDs).

 In any material, substantial variation of fundamental electrical and
optical properties with reduced size will be observed when the
energy spacing between the electronic levels exceeds the thermal
energy (kt)
 The small cluster is analogous to a molecule having discrete
energy levels
 Moreover, nanocrystals possess a high surface area and a large
fraction of the atoms in ananocrystal areon its surface.
 Since this fraction depends largely on the size of the particle (30%
for a 1-nm crystal, 15% for a 10-nm crystal), it can give rise to size
effects in the chemical and physical properties of the nanocrystal

• Decrease in the size of the nanoscale structure cause a color change

The number of electrons plotted as a function of energy for
conduction electrons delocalized in one, two, and three dimensions
provide the density of states which is given by the slopes of the
curves N(E) Vs E. Density of states D(E) = dN/dE. This means the
number of electrons in an interval of energy is proportional to the
density of states at that energy

N(E)
Energy E
3D
2D
1D
Energy E
D(E)
1 Dim
2 Dim
3 Dim

It is observed that the density of states decreases with increasing
energy for one dimension, remains constant for two dimensions, and
increases with increasing energy for three dimensions. Thus the
density of states is different for all three cases.

Energylevelsin metallicandsemiconductor nanoparticles
The density of states in metal (A) and semiconductor
(B) nanocrystals. In each case, the density of states is
discrete at the band edges. The Fermi level is in the
center of a band in metal, so kT will exceed the level
spacing even at low temperatures and small sizes.
Nevertheless, metal nanoparticles of very small size can
exhibit insulating properties.

Dependence of density of states and number of electrons on energy
 The Number of electrons N(E) increases with the energy E for all
four structures. Which means they differ only qualitatively
 The density of states differs dramatically for each of the
nanostructure types
 The nature of dimensionality and the confinement associated with
each of the nanostructures have a profound effect on the
properties
 The above considerations can be used to predict the properties
 On the other hand, we can also identify the structure based on the
properties

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