By Prof. Beer Pal Singh
TOP-DOWN AND BOTTOM-UP APPROACHES FOR
SYNTHESIS OF NANOMATERIALS
Synthesis of nanomaterials and nanostructures are the important aspect of
nanoscience and nanotechnology. New physical properties and applications of nanomaterials
are only possible when nanostructured materials are made available with desired size, shape,
morphology, crystal structure and chemical composition. These notes provide a clear and
concise understanding on Top-down and Bottom-up approaches for synthesis of
nanomaterials.
Introduction:
✓ Nanotechnology is an emerging area of research which has a potential in replacement of
conventional micron technologies and gives size dependent properties of the functional
materials.
✓ The interest in nanoscience (science of low dimensional systems) is a realization of a
famous statement by Feynman that "There's a Plenty of Room at the Bottom".
✓ Based on Feynman’s idea, K. E. Drexler advanced the idea of “molecular
nanotechnology” in 1986 in the book Engines of Creation, where he postulated the
concept of using nanoscale molecular structures to act in a machine like manner to guide
and activate the synthesis of larger molecules.
✓ When the dimension of a material is reduced from a large size, the properties remain the
same at first, then small changes occur, until finally, when the size drops below 100 nm,
dramatic changes in properties can occur.
✓ If only one dimension of a three-dimensional nanostructure is of nanoscale, the structure
is referred to as a quantum well; if two dimensions are of nanometer scale, the structure is
referred to as a quantum wire; and if all three dimensions are of nanometer scale, the
structure is referred to as a quantum dot.Hence a quantum dot has all three dimensions in
the nanorange and is the ultimate example of nanomaterials.
✓ The word quantum is associated with these three types of nanostructures because changes
in properties arise from the physics of quantum-mechanics.
Key issues in the fabrication of Nanomaterials:
The interest in synthesis of nanomaterials has grown because of their distinct optical,
magnetic, electronic, mechanical, and chemical properties compared with those of the bulk
materials.
, By Prof. Beer Pal Singh
The fabrication and process are the key issues in nanoscience and nanotechnology to
explore the novel properties and phenomena of nanomaterials to realize their potential
applications in science and technology. Many technological approaches/methods have been
explored to fabricate nanomaterials.
Followings are the key issues or challenges in the fabrication of nanostructured materials
using any process or technique:
• Can you Control the particle size ?
• Can you control the shape of nanoparticles ?
• Can you control the structure either crystalline or amorphous?
• Particle size distribution (monodespersive: all particles are of same size).
Semiconductor Nanoparticles
Nanoparticle have recently attracted significant attention from the materials
science community. Nanoparticle, particles of the material with diameter in
range 1 to 20 nm, promise to play a significant role in developing technologies.
✓ They exhibit unique physical properties that give rise to many potential applicaltions in
areas such as nonlinear optics, luminescence, elctronics, catalyst, solar energy
conversion, and optoelectronics .
✓ Two fundamental factors, both related to the size of the individual nanocrystal are
responsible for these unique properties. The first is the large surface to volume ratio, and
the second factor is the quantum confinement effect.
✓ The wide band gap II-VI semiconductor are of current interest. For optoelectronics
applications such as blue lasers, light emitting diodes, photonic crystals and optical
devieces based on non linear properties.
✓ The properties of semiconductor nanoparticles strongly depend on its size, shape,
composition, crystallinity and structure.
✓ It is a great challenge and prominent aim to precisely control these parameters of
nanoparticles for the synthetic nanotechnologists.
✓ The exposure of exact size and shape controlled synthesis of nanostructure materials is
becoming a great challenge for the nanotechnologists.
Magnetic Nanoparticles:
✓ Magnetic materials are also strongly affected by the small size scale of nanoparticles.
Magnetic nanoparticles are being looked at for applications in cancer diagnosis and
treatment.
TOP-DOWN AND BOTTOM-UP APPROACHES FOR
SYNTHESIS OF NANOMATERIALS
Synthesis of nanomaterials and nanostructures are the important aspect of
nanoscience and nanotechnology. New physical properties and applications of nanomaterials
are only possible when nanostructured materials are made available with desired size, shape,
morphology, crystal structure and chemical composition. These notes provide a clear and
concise understanding on Top-down and Bottom-up approaches for synthesis of
nanomaterials.
Introduction:
✓ Nanotechnology is an emerging area of research which has a potential in replacement of
conventional micron technologies and gives size dependent properties of the functional
materials.
✓ The interest in nanoscience (science of low dimensional systems) is a realization of a
famous statement by Feynman that "There's a Plenty of Room at the Bottom".
✓ Based on Feynman’s idea, K. E. Drexler advanced the idea of “molecular
nanotechnology” in 1986 in the book Engines of Creation, where he postulated the
concept of using nanoscale molecular structures to act in a machine like manner to guide
and activate the synthesis of larger molecules.
✓ When the dimension of a material is reduced from a large size, the properties remain the
same at first, then small changes occur, until finally, when the size drops below 100 nm,
dramatic changes in properties can occur.
✓ If only one dimension of a three-dimensional nanostructure is of nanoscale, the structure
is referred to as a quantum well; if two dimensions are of nanometer scale, the structure is
referred to as a quantum wire; and if all three dimensions are of nanometer scale, the
structure is referred to as a quantum dot.Hence a quantum dot has all three dimensions in
the nanorange and is the ultimate example of nanomaterials.
✓ The word quantum is associated with these three types of nanostructures because changes
in properties arise from the physics of quantum-mechanics.
Key issues in the fabrication of Nanomaterials:
The interest in synthesis of nanomaterials has grown because of their distinct optical,
magnetic, electronic, mechanical, and chemical properties compared with those of the bulk
materials.
, By Prof. Beer Pal Singh
The fabrication and process are the key issues in nanoscience and nanotechnology to
explore the novel properties and phenomena of nanomaterials to realize their potential
applications in science and technology. Many technological approaches/methods have been
explored to fabricate nanomaterials.
Followings are the key issues or challenges in the fabrication of nanostructured materials
using any process or technique:
• Can you Control the particle size ?
• Can you control the shape of nanoparticles ?
• Can you control the structure either crystalline or amorphous?
• Particle size distribution (monodespersive: all particles are of same size).
Semiconductor Nanoparticles
Nanoparticle have recently attracted significant attention from the materials
science community. Nanoparticle, particles of the material with diameter in
range 1 to 20 nm, promise to play a significant role in developing technologies.
✓ They exhibit unique physical properties that give rise to many potential applicaltions in
areas such as nonlinear optics, luminescence, elctronics, catalyst, solar energy
conversion, and optoelectronics .
✓ Two fundamental factors, both related to the size of the individual nanocrystal are
responsible for these unique properties. The first is the large surface to volume ratio, and
the second factor is the quantum confinement effect.
✓ The wide band gap II-VI semiconductor are of current interest. For optoelectronics
applications such as blue lasers, light emitting diodes, photonic crystals and optical
devieces based on non linear properties.
✓ The properties of semiconductor nanoparticles strongly depend on its size, shape,
composition, crystallinity and structure.
✓ It is a great challenge and prominent aim to precisely control these parameters of
nanoparticles for the synthetic nanotechnologists.
✓ The exposure of exact size and shape controlled synthesis of nanostructure materials is
becoming a great challenge for the nanotechnologists.
Magnetic Nanoparticles:
✓ Magnetic materials are also strongly affected by the small size scale of nanoparticles.
Magnetic nanoparticles are being looked at for applications in cancer diagnosis and
treatment.
