1.
INNTRODUCTION
2. HISTORY OF NANOTECHNOLOGY
3. NANOTECHNOLOGY TOOLS
4. NANOTECHNOLOGY SIZE CONCERNS
5. TRADITONAL APPORACH “TOP-DOWN-APPORACH”
6. ACCOMPLISHMENT OF NANOTECHNOLOGY
7. APPLICATIONS
8. ROLE FOR ENGINEERING
9. HOW LONG?
10. INDIAN SCENARIO
11. ADVANTAGES
12. NANO PROBLEMES AND LIMITATION 13. CONCLUSION
14. REFERENCES
Introduction
Molecular nanotechnology or Nanotechnology is the name given
to a specific sort of manufacturing technology to build things from
the atom up, and to rearrange matter with atomic precision. In
other words, we can say that nanotechnology is a three
dimensional structural control of material and devices at
molecular level. The nanoscale structures can be prepared,
characterized, manipulated, and even visualized with tools.
“Nanotechnology is a tool-driven field."
Other terms, such as molecular engineering or molecular
manufacturing are also often applied when describing this
emerging technology. This technology does not yet exist. But,
scientists have recently gained the ability to observe and
manipulate atoms directly. However, this is only one small aspect
of a growing array of techniques in nanoscale science and
technology. The ability to make commercial products may yet be a
few decades away.
“Nanotechnology is Engineering, Not Science.”
The central thesis of nanotechnology is that almost any chemically
stable structure that is not specifically disallowed by the laws of
physics can in fact be built. Theoretical and computational models
indicate that molecular manufacturing systems are possible —
that they do not violate existing physical law. These models also
give us a feel for what a molecular manufacturing system might
look like. Melting pot of science combining applications of physics,
chemistry, biology, electronics and computers. Today, scientists are
devising numerous tools and techniques that will be needed to
transform nanotechnology from computer models into reality
Nanotechnology is often called the science of the small. It is
concerned with manipulating particles at the atomic level, usually
in order to form new compounds or make changes to existing
substances. Nanotechnology is being applied to problems in
electronics, biology, genetics and a wide range of business
applications.
Matter is composed of small atoms that are closely bound
together, making up the molecular structure, which, in turn
determines the density of the concerned material. Since different
factors such as molecular density, malleability, ductility and
surface tension come into play, nanosystems have to be designed
in a cost effective manner that overrides these conditions and
helps to create machines capable of withstanding the vagaries of
the environment.
Let us take the case of metals. Metals, solids in particular, consist
of atoms held together by strong structural forces, which enable
metals to withstand high temperatures. Depending upon the
exertion of force or heat, the molecular structure bends in a
particular fashion, thereby acquiring a definite space in the form
of a lattice structure. When the bonding is strong, the metal is able
to withstand pressure. Else it becomes brittle and finally breaks
up. So, only the strongest, the hardest, the highest melting point
metals are worth considering as parts of nanomachines.
The trick is to manipulate atoms individually and place them
exactly where needed, to produce the desired structure. It is a
challenge for the scientists to understand the size, shape, strength,
force, motion and other properties while designing the nano
machines. The idea of nanotechnology is therefore to master over
the characteristics of matter in an intelligent manner to develop
highly efficient systems.
The key aspect of nanotechnology is that nanoscale materials
offer different chemical and physical properties than the bulk
materials, and that these properties could form the basis of new
technologies.
For example, scientists have learned that the electronic--and
hence optical--properties of nanometer-size particles can be tuned
by adjusting the particle size. According to a recent study by a
group at Georgia Institute of Technology, when gold metal is
reduced to nanosize rods, its fluorescence intensity is enhanced
over 10 million-fold. The study found that the wavelength of the
emitted light increases linearly with the rod length, while the light
intensity increases with the square of the rod length.
2. HISTORY OF NANOTECHNOLOGY
Any advanced research carries inherent risks but nanotechnology
bears a special burden. The field's bid for respectability is colored
by the association of the word with a cabal of futurist who foresee
nano as a pathway to a techno-utopia: unparalleled prosperity,
pollution-free industry, even something resembling eternal life.
In 1986-five years after IBM researchers Gerd Binnig and Heinrich
Rohrer invented the scanning tunneling microscope, which
garnered them the Nobel Prize-the book Engines of Creation, by K.
Eric Drexler, created a sensation for its depiction of godlike control
over matter. The book describes self-replicating nanomachines
that could produce virtually any material good, while reversing
global warming, curing disease and dramatically extending life
spans. Scientists with tenured faculty positions and NSF grants
ridiculed these visions, noting that their fundamental
improbability made them an absurd projection of what the future
holds.
But the visionary scent that has surrounded nanotechnology ever
since may provide some unforeseen benefits. To many
nonscientists, Drexler's projections for nanotechnology straddled
the border between science and fiction in a compelling way. Talk
of cell-repair machines that would eliminate aging as we know it
and of home food-growing machines that could produce victuals
without killing anything helped to create a fascination with the
small that genuine scientists, consciously or not, would later use
to draw attention to their work on more mundane but eminently
more real projects. Certainly labeling a research proposal
"nanotechnology" has a more alluring ring than calling it "applied
mesoscale materials science."
Less directly, Drexler's work may actually draw people into science.
His imaginings have inspired a rich vein of science-fiction literature
. As a subgenre of science fiction-rather than a literal prediction of
the future-books about Drexlerian nanotechnology may serve the
same function as Star Trek does in stimulating a teenager's interest
in space, a passion that sometimes leads to a career in aeronautics
or astrophysics.
The danger comes when intelligent people take Drexler's
predictions at face value. Drexlerian nanotechnology drew
renewed publicity last year when a morose Bill Joy, the chief
scientist of Sun Microsystems, worried in the magazine Wired
about the implications of nanorobots that could multiply
uncontrollably.
A spreading mass of
self-replicating robots-what Drexler has labeled "gray goo"-could
pose enough of a threat to society, he mused, that we should
consider stopping development of nanotechnology. But that
suggestion diverts attention from the real nano goo: chemical and
biological weapons.
3. NANOTECHNOLOGY TOOLS
What would it mean if we could inexpensively make things with
every atom in the right place? For starters, we could continue the
revolution in computer hardware right down to molecular gates
and wires -- something that today's lithographic methods (used to
make computer chips) could never hope to do. We could
inexpensively make very strong and very light materials:
shatterproof diamond in precisely the shapes we want, by the ton,
and over fifty times lighter than steel of the same strength.
We could make a Cadillac that weighed fifty kilograms, or a full-
sized sofa you could pick up with one hand. We could make
surgical instruments of such precision and deftness that they could
operate on the cells and even molecules from which we are made
-- something well beyond today's medical technology. The list goes
on -- almost any manufactured product could be improved, often
by orders of magnitude.
3.1 THE ADVANTAGES OF POSITIONAL CONTROL
One of the basic principles of nanotechnology is positional control.
At the macroscopic scale, the idea that we can hold parts in our
hands and assemble them by properly positioning them with
respect to each other goes back to prehistory:
At the molecular scale, the idea of holding and positioning
molecules is new and almost shocking. However, as long ago as
1959 Richard Feynman, the Nobel prize winning physicist, said that
nothing in the laws of physics prevented us from arranging atoms
the way we want: "...it is something, in principle, that can be
done; but in practice, it has not been done because we are too
big."
Before discussing the advantages of positional control at the
molecular scale, it's helpful to look at some of the methods that
have been developed by chemists -- methods that don't use
positional control, but still let chemists synthesize a remarkably
wide range of molecules and molecular structures.
3.2 SELF ASSEMBLY
The ability of chemists to synthesize what they want by stirring
things together is truly remarkable. Imagine building a radio by
putting all the parts in a bag, shaking, and pulling out the radio --
fully assembled and ready to work! Self assembly -- the art and
science of arranging conditions so that the parts themselves
spontaneously assemble into the desired structure -- is a well
established and powerful method of synthesizing complex
molecular structures.
A basic principle in self assembly is selective stickiness: if two
molecular parts have complementary shapes and charge
patterns -- one part has a hollow where the other part has a
bump, and one part has a positive charge where the other part
has a negative charge -- then they will tend to stick together in one
particular way. By shaking these parts around -- something which
thermal noise does for us quite naturally if the parts are floating in
solution -- the parts will eventually, purely by chance, be brought
together in just the right way and combine into a bigger part. This
bigger part can combine in the same way with other parts, letting
us gradually build a complex whole from molecular pieces by
stirring them together and shaking.
Many viruses use this approach to make more viruses -- if you stir
the parts of the T4 bacteriophage together in a test tube, they will
self assemble into fully functional viruses
3.3 POSITIONAL DEVICES AND POSITIONALLY
CONTROLLED REACTIONS
While self assembly is a path to nanotechnology, by itself it would
be hard pressed to make the very wide range of products
promised by nanotechnology. We don't know how to self
assemble shatterproof diamond, for example. During self assembly
the parts bounce around and bump into each other in all kinds of
ways, and if they stick together when we don't want them to stick
together, we'll get unwanted globs of random parts. Many types of
parts have this problem, so self assembly won't work for them. To
make diamond, it seems as though we need to use
indiscriminately sticky parts (such as radicals, carbenes and the
like). These parts can't be allowed to randomly bump into each
other (or much of anything else, for that matter) because they'd
stick together when we didn't want them to stick together and
form messy blobs instead of precise molecular machines.
We can avoid this problem if we can hold and position the parts.
Even though the molecular parts that are used to make diamond
are both randomly and very sticky (more technically, the barriers
to bond formation are low and the resulting covalent bonds are
quite strong), if we can position them we can prevent them from
bumping into each other in the wrong way. When two sticky parts
do come into contact with each other, they'll do so in the right
orientation because we're holding them in the right orientation. In
short, positional control at the molecular scale should let us make
things which would be difficult or impossible to make without it. If
we are to position molecular parts we must develop the molecular
equivalent of "arms" and "hands." We'll need to learn what it
means to "pick up" such parts and "snap them together."
We'll have to understand the precise chemical reactions that such
a device would use. One of the first questions we'll need to
answer is: what does a molecular-scale positional device look like?
Current proposals are similar to macroscopic robotic devices but
on a much smaller scale. The illustrations ( Fig 1 & 2 ) show a
design for a molecular-scale robotic arm proposed by Eric Drexler,
a pioneering researcher in
the field. Only 100 nanometers high and 30 nanometers in
diameter, this rather squat design has a few million atoms and
roughly a hundred moving parts. It uses no lubricants, for at this
scale a lubricant molecule is more like a piece of grit. Instead, the
bearings are "run dry" as described in the following paragraph.
Fig 1 Drexler’s proposed robotic arm Running bearings dry should
work both because the diamond surface is very slippery and
because we can make the surface very smooth -- so smooth that
there wouldn't even be molecular-sized asperities or
imperfections that might catch or grind against each other.
Computer models support our intuition: analysis of the bearings
shown here using computational chemistry programs shows they
should rotate easily.
3.4 STIFFNESS
Molecular arms will be buffeted by something we don't worry
about at the macroscopic scale: thermal noise. This makes
molecular-scale objects wiggle and jiggle, just as Brownian motion
makes small dust particles bounce around at random. The critical
property we need here is stiffness. Stiffness is a measure of how
far something moves when you push on it. If it moves a lot when
you push on it a little, it's not very stiff. If it doesn't budge when
you push hard, it's very stiff.
3.5 SCANNING TUNNELING MICROSCOPE (STM)
The STM is a device that can position a tip to atomic precision near
a surface and can move it around. The scanning tunneling
microscope is conceptually quite simple. It uses a sharp,
electrically conductive needle to scan a surface. The position of
the tip
of the needle is controlled to within 0.1 angstrom (less than the
radius of a hydrogen atom) using a voltage-controlled piezoelectric
drive. When the tip is within a few angstroms of the surface and a
small voltage is applied to the needle, a tunneling current flows
from the tip to the surface. This tunneling current is then detected
and amplified, and can be used to map the shape of the surface,
such as a blind man tapping in front of him with his cane, we can
tell that the tip is approaching the surface and so can "feel" the
outlines of the surface in front of us
Fig. 2 Cross section of a stiff manipulator arm showing its range of
motion Many different types of physical interactions with the
surface are used to detect its presence. Some scanning tunneling
microscopes literally push on the surface -- and note how hard the
surface pushes back. Others connect the surface and probe to a
voltage source, and measure the current flow when the probe gets
close to the surface. A host of other probe-surface interactions can
be measured, and are used to make different types of STMs. But in
all of them, the basic idea is the same: when the sharp tip of the
probe approaches the surface a signal is generated -- a signal
which lets us map out the surface being probed.
The STM cannot only map a surface; in many cases the probe-
surface interaction changes the surface as well. This has already
been used experimentally to spell out molecular words, and the
obvious opportunities to modify the surface in a controlled way
are being investigated both experimentally and theoretically.
4. NANOTECHNOLOGY SIZE CONCERNS
4.1 MEMS: MICRO INFORMATION SEEKERS
Micro-electromechanical system (MEMS) combines computers
with tiny mechanical devices such as sensors, valves, gears, and
actuators embedded in semiconductor chips. These elements are
embedded in the mainframe of the system for carrying out the
bigger task. As the elements are capable of carrying out varying
tasks, they are usually reffered to as ‘smart matter’.
Nanotechnology is often confused with related fields such as
MicroElectroMechanical Systems (MEMS) and molecular
electronics. Table below, illustrates the most basic differences
among these various efforts, which do have some overlap. In the
case of MEMS, it helps to remember that while the two
technologies differ by a factor of about 1000 in linear dimension,
this translates to a factor of a billion in volume—very different
indeed. Also, as MEMS researchers point out, MEMS is not a goal
but a working technology, rapidly growing into a major industry
Table: How micro- and nanotechnologies compare It may be
pointed out that making an organic compound using traditional
synthetic chemistry is not an example of nanotechnology. By
contrast, the use of self-assembly techniques to make small
molecular components coalesce or unite into a macro-cyclic
molecule having multi-nanometer dimensions can legitimately be
considered nanotechnology.
4.2 QUANTUM UNCERTAINTY PRINCIPLE
An early concern regarding the feasibility of nanotechnology
involved quantum uncertainty: would it make these systems
unreliable? Quantum uncertainty says that particles must be
described as small smears of probability, not as points with
perfectly defined locations. This is, in fact, why the atoms and
molecules in the simulations felt so soft and smooth: their
electrons are smeared out over the whole volume of the
molecule, and these electron clouds taper off smoothly and softly
toward the edges. Atoms themselves are a bit uncertain in
position, but this is a small effect compared to thermal vibrations.
Initially, it will be possible to build nanomachines and molecular-
manufacturing systems that work a particular sort of environment,
say, an electric or magnetic field (biological mechanisms are an
existence proof), but in the long run, there will be no need to do
so. Nanomachines can be built from the more stable sorts of
structure. This has been demonstrated by control of molecular
electric dipoles, nanoswitches, nanowires and devices like
Scanning Tunneling Microscope. Molecular nanotechnology falls
entirely within the realm of the possible.
