05-01-2010, 04:26 PM
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ABSTRACT
Imagine a supercomputer no bigger than a human cell. Imagine a four-person, surface-to-orbit spacecraft no larger or more expensive than the family car. Imagine attaining immortality by drinking a medicine. These are just a few products expected from Nanotechnology.
Nanotechnology is molecular manufacturing or, more simply, building things one atom or molecule at a time with programmed nanoscopic robot arms; Nanotechnology proposes the construction of novel molecular devices possessing extraordinary properties. The trick is to manipulate atoms Individually and place them exactly where needed to produce the desired Structure.
The goal of early nanotechnology is to produce the first nano-sized robot Arm capable of manipulating atoms and molecules into a useful product or Copies of itself. Nanotechnology will arrive with the development of the first "Universal Assembler" that has the ability to build with single atoms anything one's software defines. This paper deals with the various possible applications of nanotechnology and the process involved.
INTRODUCTION
The industrial revolution, electricity, computers, Internet and now the next big thing is Nanotechnology. Technically Nanotechnology is defined as an anticipated manufacturing technique by which one can be given thorough and inexpensive control over the structure of matter. These structures are known as nanostructures. The term Nanotechnology was first introduced by Richard Feynman in 1959 and K Eric Drexler popularized it in 1986 in the book ËœEngines of Creationâ„¢.
It is also defined as the ability by which we can arrange atoms by given each its place and thus forms the structure in nanometer scale. Nanotechnology deals with matter at atomic levels. The term nano is derived from Greek word dwarf. Here it refers to one billionth of a meter or (10-9).
The central thesis of Nanotechnology is that almost all chemically stable structures that can be specified can also built. Nanotechnology puts the power of creation in human hands.
NANOSTRUCTURE
Nanostructures must be assembled from some building blocks. These fundamental building blocks are created from atoms of 91 naturally occurring elements. It is inefficient to start with individual atoms due to the slowness and less strength of materials. Usually nanostructures are built, starting with larger building blocks or molecules as components.
Nanostructures are new semi molecular building blocks to assemble Nanostructures.Two of these Nanostructures are Nanotubes & Nanorods that can be made out of silicon, other semiconductors, metals, or even insulators. These Nanorods are made using clever solution chemistry methods, but they can then self assemble into larger Nanoscale structures.
Nanotubes and Nanowires
Graphite is used as a lubricant and in pencils. It is formed out of sheets of carbon atoms linked together hexagonally like chicken wire. Nanoscientists are very interested in them because when rolled into tubes they exhibit some amazing properties. These cylinders of graphite are called carbon Nanotubes.When the roll is only one sheet of carbon atoms thick they are called single walled carbon Nanotubes. Nanotubes are the first nanomaterials engineered at the molecular level, and they exhibit physical and chemical properties that are truly breathtaking.
Carbon NanoTube
Nanotubes show tensile strength greater than 60 times to high-grade steel. Nanotubes are not only strong but they are also very light and flexible. They are used in aeroplane design.
Nanotubes show excellent electrical properties. Scientists tested Nanotubes and found that they behaved like superconductors. Current theory holds that they can act as either superconductors or semiconductors based depending on the exact proportions of the tube and which materials other than carbon are introduced into the tube matrix.
Not all Nanotubes are manufactured out of carbon. Silicon Nanotubes are also common though Nanotubes of silicon are called as Nanowires.
Nanotube and Nanowire research are hot topics both for science and industry. IBM have already used nanotubes to craft usable transistors with properties exceeding those of their pure silicon cousins and some nanotubes based logic gates have been produced.
TOOLS TO MAKE NANOSTRUCTURES¦.
There are mainly two approaches for the development of Nanostructures. They are:
Top-Down Approach
Bottom-Up approach
Top-down approach is an engineering approach for the construction of Nanoscopic devices. Here we take a large structure and divide it into smaller structures iteratively. Bottom-Up approach deals with building up a Nanostructure by starting from a single atom.
Scanning probe instruments
Creating structures at Nanoscale required them to be manipulated at Nanoscale.For these various instruments were used .The scanning probe instruments form the basis of these. Scanning probe instruments cannot only be used to see Nanostructure but also to manipulate them. The principle is used as dragging finger. Just as we scratch a soft surface we can modify the structure. Similarly with the tip of the scanning probe we manipulate the structure by dragging the tip above the surface.
Scanning probes are used to demonstrate and test some fundamental scientific concepts ranging through structural chemistry, electrical interactions and magnetic behaviors.
Scanning probe surface assembly is inherently very elegant, but it suffers three limitations:
It is relatively expensive
It is relatively slow.
It cannot satisfy mass demand.
Nanoscale Lithography
The word lithography originally referred to making objects from stones. A lithograph is an image that is produced by carving a pattern on the stone, inking the stone and then pushing the inked stone onto the paper.
Nanoscale lithography really can™t use visible light because the wavelength of visible light is at least 400 nanometers, so structures smaller than that are difficult to make directly using it. This is one of the reasons that continuing Moiré™s law into the nanoscale will Require entirely new preparation methods.
Dip Pen Nanolithography
One way to construct arbitrary structures on surfaces is to write them in exactly the same way that we write ink lines using a fountain pen. To make such lines at the nanoscale it is necessary to have a nanopen. Fortunately AFM tips are ideal nanopens. Dip pen nanolithography is named after the old-fashioned dip pen that was used in schoolrooms in the 19th century. The principle of DPN is shown in the figure.
In DPN a reservoir of Ëœinkâ„¢ (atoms or molecules) is stored on the top of the scanning probe tip, which is manipulated across the surface, leaving lines and patterns behind. Using this technique any complex structure can be realized because AFM tips are relatively easy to manupulate. This fact makes DPN the technique of choice for creating new and complex structures in small volumes the disadvantage of this technique is that it is very slow.
E-Beam Lithography
We mentioned that current light based industrial lithography is limited to creating features no smaller than the wavelength used. Even though we can in principle get around this restriction by using light of smaller wavelengths, this solution can generate other problems. Smaller-wavelength light has higher energy, so it can have nasty side effects like blowing the feature we are trying to create right off the surface.
An alternate way of getting around the problem is to use electrons instead of light. This E-beam lithography can be used to make structures at the nanoscale. Figure shows two electrodes that are made using E-beam lithography to align platinum nanowires. The structure lying across the nanoscale electrodes is a single molecule, a carbon nanotube.
E-beam lithography also has applications in current microelectronics manufacturing and is one approach that will be used to keep Mooreâ„¢s law on track until size-dependent properties truly assert themselves.
Nanosphere Liftoff Lithography
If marbles are placed together on a board as tightly as possible, they will form a tight group with each marble surrounded by six others. If this array was spray-painted from the top and then the marbles were tipped off the board. The paint would appear as a set of painted dots each shaped like a triangle with concave edges. Now if the marbles are nanoscale marbles, so are the painted dots.
The technique is called nanosphere liftoff lithography. Importantly, this liftoff nanolithography, unlike DPN or scanning probe but like nanostamp, is parallel. Many nanosphers can be placed on the surface, so that regular arrays of many dots can be prepared.
Self-Assembly
The problems with most of the techniques for assembling nanostructures that we have seen so far is that are too munch like work. It is glorious if we could just mix chemicals together and get nanostructures by letting the molecules sort themselves out.
One approach to nanofabrication attempts to do exactly this. It is called self-asseembly.The idea behind self-assembly is that molecules will always seek the lowest energy level available to them. If bonding to an adjacent molecule accomplishes this, they will bond. If reorienting their physical positions does the trick, then they will reorient. The forces involved in self-assembly are generally weaker than the bonding forces that hold molecules together.
They correspond to weaker aspects of Coloumbic interactions and are found in many places throughout nature. In self-assembly, the nano builder introduces particular atoms or molecules onto a surface or onto a preconstructed nanostructure. The molecules then align themselves into particular positions, sometimes forming weak bonds and sometimes forming strong covalent ones, inorder to minimize the total energy. One of the huge advantages of such assembly is that large structures can be prepared in this way, so it is not necessary to tailor individually the specific nanostructures.
Self-assembly is not limited to electronics applications. Self-assembled structures can be used for something as mundane as protecting a surface against corrosion or making a surface slippery, sticky, wet, or dry. Self-assembly is probably the most important of the nanoscale fabrication techniques because of its generality, its ability to produce structures at different length scales, and its low cost.
Nanoscale Crystal Growth
Crystal growth is another sort of self-assembly. Crystals like salt that are made of ions are called ionic crystals. Those made of atoms are called atomic crystals, and those made of molecules are called molecular crystals. So salt is an ionic crystal and sugar is a molecular crystal.
Crystal growth is partly art, partly science. Crystals can be grown from solution using seed crystals, which involves putting a small crystal into the presence of more of its component materials and allowing those components to mimic the pattern of the small crystal or seed. Silicon boules, the blocks used for making microchips, are made or Ëœdrawnâ„¢ in this way.
Polymerization
Polymers are very large molecules. They can be upward of millions atoms in size, made by repetitive formation of the bond from one small molecular unit to the next. Polymerization is a very commonly used scheme for making nanoscale materials and even much larger ones-epoxy adhesives work by making extended polymers upon mixing the two components of the epoxy. Controlled polymerization, in which one manometer at a time is added to the next, is very important for specific elegant structures.
TOOLS FOR MEASURING THE PROPERTIES OF NANOSTUCTURES
Scanning Probe Instruments
Some of the first tools to help launch the nanoscience revolution were the so-called scanning probe instruments. The idea is a simple one: if you rub your finger along a surface, it is easy to distinguish velvet from steel or wood from tar. The different materials exert different forces on your finger as you drag it along the different surfaces. In these experiments your finger acts like a force measurement structure. It is easy to slide across a satin sheet than across warm tar because the warm tar exerts a stronger force dragging back the finger. This is the idea of the scanning force microscope, one of the common types of scanning probe.
In scanning probe measurements, the probe, also called a tip, slides along a surface in the same way your finger does. The probe is of nanoscale dimensions, often only a single atom in size where it scans the target. As the probe slides, it can measure several different properties, each of which corresponds to a different scanning probe measurement. For example, in Atomic Force Microscopy (AFM), electronics are used to measure the force exerted on the probe tip as it moves along the surface.
In Scanning Tunneling Microscopy (STM), the amount of electric current flowing between a scanning tip and a surface is measured. Depending on the way the measurement is done, STM can be used either to test the local geometry or the local electrical conducting characteristics.
In Magnetic Force Microscopy (MFM). The tip that scans across the surface is magnetic. It is used to sense the local magnetic structure on the surface. The MFM tip works in a similar way to the reading head on a hard disk drive or audio cassette player.
Other types of scanning microscopyâ„¢s also exist. They are referred to as scanning probe microscopyâ„¢s because all are based on the general idea of the STM.In all of them, the important idea is that a nanoscale tip that slides or scans over the surface is used to investigate nanoscale structure by measuring forces, currents, magnetic drag, chemical identity, or other specific properties.
Spectroscopy
Spectroscopy refers to shining light of a specific color on a sample and observing the absorbtion, scattering or other properties under those conditions. Spectroscopy is a much older, more general t than scanning probes microscopy and it offers many complementary insights.
Magnetic Resonance Imaging, or MRI is another type of Spectroscopy that may be familiar from its medical applications. Many sorts of Spectroscopy using different energies of light are used in the analysis of nanostructures.
Visible light cannot be used for the spectroscopy analysis of nanostructures because the wavelength of light is between 400nm and 900nm.So light of lesser wavelength is used for analysis. Spectroscopy is of great importance for characterising nanostructure en masse, but most types of Spectroscopy do not tell us about structures on the nanoscale of nanometers.
Electrochemistry
Electrochemistry deals with how the chemical processes can be changed by the application of electrical currents, and how electric currents can be generated from chemical reactions. The most common Electrochemistry devices are batteries that produce energy from chemical reactions. The opposite process is seen in electroplating, wherein metals are made to form on surfaces because positively charged metal ions absorb electrons from the current flowing through the surface to be neutral plated and become neural metals.
Electrochemistry is broadly used in the manufacturing of nanostructure, but it can also be used in their analysis. The nature of the surface atoms in an array can be measured directly using Electrochemistry, and advanced electrochemical technique scanning are often used both to construct and to investigate nanostructures.
Electron Microscopy
These methods are based on the use of electrons rather than light to examine the structure and behavior of the material. There are different types of Electron Microscopy, but they are all based on the same general idea. Electrons are accelerated passed through samples. As the electrons encounter nuclei and other electrons, they scatter. By collecting the electrons we can construct an image that describes where the particles were that scattered the electrons did not make it through. This is called Transmission Electron Microscopy (TEM).
TEM images can have resolution sufficient to see individual atoms, but samples must often be stained before they can be imaged. Additionally TEM can only measure physical structure, not forces like those from magnetic or electric fields. Still, Electron Microscopy has many uses and is broadly used in nanostructure analysis and interpretation.
APPLICATIONS
With the development of Nanotechnology it expects to find applications in various fields. The various applications of Nanotechnology are:
Nano Computers
Nanotechnology is focusing on projects, which can be implemented in bettering our lives. Pervasive computing is an area where a lot of Nanotechnology projects are currently active. If we want to design a chip to fit into our fingertip controlling a music system then solution lies with Nanotechnology.
While making a microprocessor we handle big groups of semiconductor molecules and structure them into the form we need. This form of handling of matter produces severe limitations as to how small these circuits can be made. Present day lithographic technologies are at 0.13 microns. After 0.13 microns it is very difficult to etch the circuits precisely and effectively on the silicon substrate. This is where Nanotechnology steps in. Nanotechnology offers convenience to bulk technology.
Computing giant IBM has come up with a new kind of memory using a technology called ËœMillipede Technologyâ„¢ which makes use of an array of AFM probes to make marks on a polymer surface for storing data. Each tip writes a bit of 50nm on the polymer, which stores data.
Todayâ„¢s best storage devices are capable of storing data up to 2Giga bits per square cm where as Nanotechnology increases the memory to 80Giga bits per square cm using a single AFM tip. The main advantage of using such technology, other than the small sizes, is the power consumption.
Material Technology
It is another major area, which will be affected by Nanotechnology. A nanotube is one such innovation, which can change almost all the areas that we are familiar with. The advantage of using nanotubes is that it is possible to control the way these crystals are developed for applications. Electrical and other properties of materials made using nanotubes can be made to fit precise specifications.
Scientists have begun to mix and match the attractive properties of certain chemicals to produce materials and fabrics that are stronger or more resistant. One company has already reengineered cotton with an outer structure resistant to wrinkles and stains. Nanotubes are also innovations of material technology, which can suit precise mechanical and electrical properties.
Medicine
With the development of Nanotechnology we can even replace operations. The concept used here is ËœMicro encapsulationâ„¢ a Nanotechnology technique, which will help doctors to control precisely the rate at which medicine, are supplied to patient body. One of the major medicinal breaks through in the area of Nanotechnology is the discovery of composite structure of carbon called ËœBucky ballsâ„¢ or C60 molecules. Bucky balls were discovered by Richard Smalley.The main advantage of using bucky balls are that they are extremely small (1nm long) and non-toxic. These spherical particles are very smooth. The body easily excretes them, which make them perfect as drug delivery mechanisms.
Using bucky balls medicines could be delivered to the body orally and then the body eliminates it without any side effects .It is possible to attach the needed drugs on the bucky balls. This is much easier and effective than the conventional capsule approach. In capsules a mixture of drugs is delivered into the body, a major part of which is eliminated by the body.
Another exciting property that Nanotechnology presents is the ability to have minute machines traveling inside our body protecting us from the inside.
These nanodoctors will be able to find and repair damage at the cellular level. For this to be possible molecular assemblers with better capabilities than the current STM are needed. Nanorobots are also similar to Nanodoctors.
The concept of Nanotechnology powered has a long way to go before it can become a reality. This technology is mainly aimed to treat cancer cells and sometimes even suggest cures.
Nanoelectronics
Instead of burning features on to a Si chip nanolectronics are built atom by atom through carefully controlled chemical reactions that will eventually allow for faster information processing. Nanoelectronics will be able to down size transistors producing tera scale integrated chips containing more than a trillion transistors.
Nano LED
This is a novel light source system that uses LED to produce a pulse of 50pico sec to 2nano sec between wavelength of 370nm and 660nm.Today nanoled emits blue, red, UV, amber light.
Applications of Nano LED
Illumination: It is highly efficient than conventional light build, it consumes only 15 watts compared to traditional traffic lights which consume 150 watts and so can be used for traffic lights which are expected to burn for more than a decade continuously. More over they are compact, have low power consumption and low heat.
Replacement of Flash lamps: Flash lamps which are heavier and cost more will be replaced by Nano LED in their applications because of their low cost and portability.
Sensors: Sensors are highly sensitive systems that can be used to warn of presence of chemicals in air or water. Nano LED is more flexible than conventional sensors because the chemical substance can alter the surface structure of LED.
In Computing and electronic devices: Further miniaturization in circuits is done to increase processing power and speed of devices. It can be used in Nanodevices where Ultra fast clocks are required for faster computation and for running the device at rates greater than 1GHz.
Optical Devices: Nano LED based on silicon is used in telecommunication industry for long and medium range data transmission via glass optical fibres by conducting pulses of laser light.
FUTURE APPLICATIONS
Scientist are just beginning to explore and manipulate the inner workings of an atomic universe using Nanotechnology, the crucial convergence of biology, chemistry and electronics that is poised to revolutionize science.
In future with the invention of Robotic arm Nanotechnology will evolve into reality. The applications of Nanotechnology in future are expected to be in the areas of:
Medicine
Environmental
Robotics
Nano Electronics
Material Innovations
Pharmaceuticals
IT field
CONCLUSION
Many of the concepts that Nanotechnology presents may look impossible now but they may not be so far away. Nanotechnology is nearer than we can think. The Nano storm will catch us quietly. The only difference being that it will come in a silent subdued manner much like how we used and embraced artificial fibres over the years without knowing it & it will make a tremendous impact on our lives.
REFERENCES
Nanotechnology “ The Next Big Idea By Mark Ratner
Daniel Ratner
Digit November 2001
Web.me.unr.edu/me372/Spring2001/Nanotechnology.pdf
CONTENTS
1. INTRODUCTION 1
2. NANOSTRUCTURE 2
3. TOOLS TO MAKE NANOSTRUCTURES 5
4. TOOLS FOR MEASURING THE PROPERTIES OF NANOSTUCTURES 13
5. APPLICATIONS 17
6. FUTURE APPLICATIONS 23
7. CONCLUSION 24
8. REFERENCES 25
