Nanotechnology involves designing and manufacturing devices at the nanoscale, measured in nanometers. There are two main approaches to nanofabrication - top-down, which starts with larger materials and machines them into nanostructures, and bottom-up, which builds nanostructures from atoms and molecules using self-assembly. Current nanofabrication techniques include lithography methods like electron beam lithography, focused ion beam lithography, nanoimprint lithography, and scanning probe lithography. Bottom-up methods include chemical vapor deposition, physical vapor deposition, and dip pen lithography. While nanotechnology holds promise for applications in computing, medicine, and other fields, health and environmental concerns surround the potential impacts of nanomaterials if inh

1. Introduction
Nanotechnology
Nano is the design and manufacture of devices with dimensions
measured in nanometers. One nanometeris 10 -9
meter, or a
millionth of a millimeter.
Nanofabrication is of interest to computerengineers because it
opens the door to super-high density
microprocessor s and memory chip s. It has been suggested that
each data bit could be stored in a single atom .
Carrying this further, a single atom might even be able to represent
a byte or word of data.
,So we need to talk about :Nanofabrication has also caught the
attentionof the medical industry, the military, and the aerospace
industry.
There are several ways that nanofabrication might be done. One
method involves scaling down integrated-circuit ( IC ) fabrication
that has been standard since the 1970s, removing one atom at a time
until the desired structureemerges. A more sophisticated
hypothetical scheme involves the assembly of a chip atom-by-atom;
this would resemble bricklaying. An extension of this is the notion
that a chip might assemble itself atom-by-atomusing programmable
nanomachines. Finally, it has been suggested that a so-
called biochip might be grown like a plant from a seed; the
componentswould form by a process resembling cell division in
living things.

2. Current research
Nanomaterials
Bottom-up approaches
Top-down approaches
Functional approaches
Biomimetic approaches
Speculative
Nanotechnology as defined by size is naturallyvery broad,
includingfields of science as diverse as surface science, organic
chemistry, molecularbiology, semiconductor
physics, microfabrication, molecularengineering, etc.
The associated research and applicationsare equallydiverse,
ranging from extensions of conventional device physics to
completelynew approachesbased upon molecular self-assembly,
from developing new materials with dimensions on the nanoscale
to direct controlof matter on the atomic scale.
Applications
 MOSFET's being made of small nanowires ~10 nm in length. Here is a simulation of such
a nanowire.
 carbonnano tube
 cmos
 bacteriostatic silver nanoparticles
nanofabrication techniques:
1.Top Down.
A.
scanning probe lithography

3. 
atomic force microscopes (AFMs)

Scanning probemicroscopes(SPMs)

. Scanning tunneling microscopes (STMs)
B.
soft lithography,
C.
focused beam lithography
D.
nanoimprint lithography
2.bottom up.
There are two pathways to approach nanoscale. One can
start from bigger material and machine it down all the way
down to the nanoscale. This is similar to carving a small
sculpture out of big rock of stone. The craftmen has to chisel
down the stone until the perfect shape is emerged. However,
this method may require a large amount of material and lot of
it will go to waste. The other nanofabrication pathway is
bottom up approach. Here, nanotechnologist would start with
much smaller materials such as atoms and molecules and
build a nanostructure using them as a building block.
Although, this method would provide great flexibility and low
material wastage, controlling matter in this scale with such a
precision is still a challenging task. Bottom up method
primarily rely on the concept of “self-assembly” where
molecules are encouraged to assemble themselves in to
more ordered structures.

4. Top down methods
The most top down fabrication techniqueis nanolithography. In this
process, required material is protected by a mask and the exposed
material is etched away. Depending upon the level of resolution
required for features in the final product, etching of the base
material can be done chemically using acids or mechanically using
ultraviolet light, x-rays or electron beams. This is the technique
applied to the manufacture of computerchips
Top down approachesare primarily used for surface patterningof
micro/nanoscalefeatures in a desired substrate. The well-developed
patteringtechniquesinclude, scanning probelithography, soft
lithography, focused beam lithography and nanoimprint lithography
scanning probe lithography
Scanning probe microscopes(SPMs)
provides a great way
to probe in to the
nanoscale world.
Similarly one can use
SPMs to manipulate
things in the
nanoscale too. SPMs
or more specifically in an atomic force microscopes (AFMs)

5. physically make contact with the
specimen during the scanning. Same
strategy can be used to scratch,
dimple or score a soft surface as the
tip is dragged along the surface.
They have been used to create
wonderful creations
and art at the nanoscale.
Scanning tunneling microscopes (STMs)
have been used by scientist to create atomic level
manipulations either by pushing individual atoms or picking
up the individual atoms through making a temporary bond
between the tip and the atom and then place it at a desired
location.

7. Although, SPMs can be very precise and can manage matter
at the smallest scale possible this technique suffer from limited
scalability and slowness. Although, the rate of production can
be increased with operating number of tips at a single time, its
output cannot compete with the other techniques. Hence, this
technique is appreciated as suitable to create works of art and
wonderful structures, it may not be able to satisfy demand of
the mass.
Focused beam lithography
As the name suggests, focused beam lithography take use of
electron or ion beam focused in to a resist surface to generate
patterns by exposing the surface followed by removing the
resist through a chemical process.
If electron beams are used, lithography can be used on an
electron-sensitive resist film. Most widely use material for this
is polymethylmethacrylate. Electron beam can induce very
precise patterns to the resist surface in the scale of 3-4 nm if
required. Electron beam lithography can be carried out in a
modified electron microscope.
Focused ion beam lithography uses an ion beam to induce
high-resolution patterns in a resist. This technique has found
applications in semiconductor industry for
1.mask repairing and
2.device modification.

8. Unlike electron beam, ion beam has comparatively low
backscattering and higher exposure sensitivity. It can also be
used as a precise milling tool.
Soft lithography
Soft lithography is the technique of transfer or fabricate a
structure by stams and molds made of elastomeric materials.
The most widely used elastomeric material used in this
technique is polydimethylsiloxane(PDMS) due to its favorable
properties. This technique has found much interest due to its
simplicity and low cost. In fact, it’s possible to make submicron
length scale dimensions with relative ease with ordinary
chemical apparatus.

9. The complete lithographic process consist of two main steps.
First, precisely fabricated masks made by AFM, electronor ion
beam lithography are used to transfer the pattern in to the
elastomeric element or stamp. Then the elastomeric elements
are used to pattern features back in to a desired surface using
an ink or a polymer. Both molecular level and solid inks are
used in the stamping.
Nanoimprint lithography

10. Nanoimprint lithography (NIL) is widely used technique to
imprint micro/nanoscalepatternswithlow cost, highthroughput
and high resolution. Unlike soft lithography, NIL uses a hard
mold to create patterns on a resist through direct mechanical
deformation and therefore achieve limitations set by light
diffraction or beam scattering in conventional lithographic
processes. The resolution of the NIL primarily limited by the
resolution of the template feature. The masks can be made of
number of different substrates such as glass, silicone,
polymers, etc.
Nanoimprint lithography has found applications in organic light
emitting diode fabrication and sensor fabrication.
Bottom up approaches
Bottom up approaches rely on self assembly to build
nanostructures with chemical or physical guidance. Here we
discuss few of mostly used bottom up approaches in the field
of nanofabrication.
Chemical and physical vapor deposition
Vapor deposition techniques are the most widely used bottom
up nanofabrication approach in nanotechnology research and
industry alike. There are two types of vapor deposition
techniques: chemical and physical.

11. In chemical vapor deposition (CVD), coating chamber is filled
with a precursor gas or gasses that can take a reaction with
one or more heated objects in the chamber that needed to be
coated. The chemical reactions occur at the interface of the
gas and the solid producing a thin sold film on the surface.
There are number of CVD variants developed for specific
applications such as spray assisted vapor deposition, aerosol
assisted chemical vapor deposition, metalorganic chemical
vapor deposition, etc. This technique is quite versatile and can
be used to apply wide range of materials in to a substrate.This
technique is widely used in semiconductor and ceramic
industry.
In the physical vapor deposition(PVD) involves vaporization of
a material through heating, electron beam, ion beam, plasma
or laser followed by solidification of the material back at the
surface of the substrate that needed to be coated. There are
no chemical interactions occur in surface of the material. PVD
is usually carried out in high vacuum environment to enhance
the affectivity of the coating by reducing interactions with other
atoms. This technique also has found applications in metal
coating, glass and semiconductor industry.

12. Dip pen lithography
Dip pen lithography (DPN) is a nanofabrication technique that
is based on scanning probe microscopy technique. In contrast
to the scanning probe lithography, which induce structural
deformation in to a substrate, it uses an ink to write a pattern
on a surface. This is exactly similar to using a stylus that
needed to be dipped in ink before writing, but at nanoscale.
There are instruments developed with more than 50,000 DPN
tips in parallel to increase the fabrication throughput. This
technique has been used to transfer nanoscale structures with
organic or biological molecules.

13. Self assembly
Theirs is a fundamental limitation with all the assembling
techniques that we have discussed so far. These techniques
requires too much work to precise handling and keeping track
of everything every time. Wealways take controlwhere should
things be and where they shouldn’t. Self-assembly relies onthe
technique that you just mix the chemicals together and it’s us
to the molecules themselves to sort it out to make a
nanostructure. But a question arises, that is what would drive
them to make these structures.
The main driving force behind this technique is common to
everything in this universe. No matter how big or small,
everything attempts to lower the energy level that is associate
with them. When molecules are mixed together, they sort in
such a way that their energy is at a minimum level. In fact self
assembly is the pathway nature has taken to build amazing
nanostructures. Mastering this technique would allow us to
build everything from basic molecules. It’s hypothesized that
on day we will grow our own food, cloths, computers and just
about everything we need in a molecular factory that we may
have in our houses. Although seem strange and far stretched,
this is theoretically possible.

14. The driving forces of self-assembly are forces like hydrogen
and van der Waal forces which are much weaker than the
covalent bonds that hold molecules together. These weaker
coulombic forces are found in many places in the world from
water to DNA molecules.
There are other interactions such as hydrophobic interactions
that allow hydrophobic materials to bind together in aqueous
medium. The particles may not have a total charge yet they
bind together to reduce the surface area that expose to the
aqueous surrounding.
Molecules also can be self-assembled in to a reconstructed
nanostructuredriven by favorable attractionbetween particular
atoms and molecules sometimes even making strong covalent
bonds. The perfect example is assembly of fatty thiolmolecules
on a silver or gold surface.
Self assembly can also be driven by templates. Molecularlevel
templates such as spheres, tubes and bi-planes can be made
with self-assembly of surfactant molecules that can be
solidified with different means. These template shapes can be
changed by varying concentration, pH, temperature, etc.

15. Nano crystal growth

16. Over the years nanotechnologies have achieved great control
over crystal growth at nanoscale. This paves the way to grow
crystalswith desired shape and sizes of various metallic, metal
oxide and semiconductor materials. Crystals can be grown
from precursor solutions containing a seed crystal. Growth of
the crystal can be changed by controlling growth parameters
such as surfactants and capping agents, temperature, pH,
various ions present. Applications for these custom made
nanocrystals in the rise especially in photovoltaic, photo
catalytic, composites and optical applications.
A major study published more recently in Nature
Nanotechnology suggests some forms of carbon nanotubes –
a poster child for the "nanotechnology revolution" – could be
as harmful as asbestos if inhaled in sufficient
quantities. Anthony Seaton of the Institute of Occupational
Medicine in Edinburgh, Scotland, who contributed to the
article on carbon nanotubes said "We know that some of
them probably have the potential to cause mesothelioma. So
those sorts of materials need to be handled very
carefully."[75]
In the absence of specific regulation forthcoming

17. from governments, Paull and Lyons (2008) have called for an
exclusion of engineered nanoparticles in food.[76]
A
newspaper article reports that workers in a paint factory
developed serious lung disease and nanoparticles were found
in their lungs
Implications
An area of concern is the effect that industrial-scale
manufacturing and use of nanomaterials would have on
human health and the environment, as suggested
by nanotoxicology research. ;For these reasons, some groups
advocate that nanotechnology be regulated by governments.
Others counter that overregulation would stifle scientific
research and the development of beneficial
innovations. Public health research agencies, such as
the National Institute for Occupational Safety and Health are
actively conducting research on potential health effects
stemming from exposures to nanoparticles

18. Some nanoparticle products may have unintended
consequences. Researchers have discovered
that bacteriostatic silver nanoparticles used in socks to
reduce foot odor are being released in the wash. These
particles are then flushed into the waste water stream and
may destroy bacteria which are critical components of natural
ecosystems, farms, and waste treatment processes.
Public deliberations on risk perception in the US and UK
carried out by the Center for Nanotechnology in Society found
that participants were more positive about nanotechnologies
for energy applications than for health applications, with
health applications raising moral and ethical dilemmas such
as cost and availability
.
Health and environmental concerns
Nanofibers are used in several areas and in different
products, in everything from aircraft wings to tennis rackets.
Inhaling airborne nanoparticles and nanofibers may lead to a
number of pulmonary diseases, e.g. fibrosis.]
Researchers
have found that when rats breathed in nanoparticles, the
particles settled in the brain and lungs, which led to significant
increases in biomarkers for inflammation and stress
response]
and that nanoparticles induce skin aging through
oxidative stress in hairless mice.
A two-year study at UCLA's School of Public Health found lab
mice consuming nano-titanium dioxide showed DNA and

19. chromosome damage to a degree "linked to all the big killers
of man, namely cancer, heart disease, neurological disease
and aging"