What is nanotechnology?

All matter is made up of atoms. Atoms are typically about 1 Angstrom in size; 1 A = 10^-10 metres. Another commonly used unit is 1 nanometer, which is 10 times larger. One nanometer is 10^-9 metres, or one-thousandth of a micron. Cells, for instance, are microns in size and can be seen with the help of a microscope. 

Many atoms together form molecules, either simple ones like water (H2O) or complicated long biological chains that can have more than 1000 atoms in them. Matter of the scale of 1 to 100 nanometers thus has aggregates of atoms, not enough to form large, visible objects of everyday life but not simple enough to be explained on the basis of interaction of a few atoms. These are the typical sizes of interest in nanotechnology.

This is a field of applied science with numerous technological applications. The applications are interesting to an engineer, while the underlying physics and chemistry are interesting to a scientist. Hence this field has been the focus of much attention in recent years.

The science

Materials reduced to the nanoscale can suddenly show very different properties compared to what they exhibit on a macroscale, enabling unique applications.

All these happen because of a number of reasons. First of all, the physics of small (atomic and molecular) sizes is governed by quantum mechanics. This means that there are large deviations from Newton's laws at this scale. Even at the microscopic (cell) scale these effects are not seen. But they definitely affect materials at the nano-scale. Other than this, physical properties of the system such as mechanical (shape), electrical (insulating or not), optical (transparent or not) change.

For instance, copper which is normally opaque become transparent on the nano-scale. Aluminium, which is the basis for most food-wrappers today, becomes combustible. Incredibly, gold becomes a liquid at room temperature, while silicon which is normally a good insulator, becomes a conductor.

Much of the fascination with nanotechnology is due to these unique quantum and surface phenomena that matter exhibits at the nanoscale.

The tools

The field developed because of the ability to control and manipulate individual atoms and molecules. The precise tools include

. the Scanning Tunneling Microscope (STM) and

. the Atomic Force Microscope (AFM).

In order to see structures at the nanoscale, the tip of the scanning probe itself must be smaller than a nanometer or so.


The fullerenes

The invention of the STM  development led to the discovery of fullerenes in 1986 and carbon nanotubes a few years later. Buckminsterfullerene is a molecule cotaining 60 atoms of Carbon. It is also called the bucky ball since it looks like a football. It turns out to be the simplest form of exotic carbon structures called fullerenes.

They have high tensile strength, high electrical conductivity, high ductility, high resistance to heat, and relative chemical inactivity. Because of this they have many applications and are the subject of much research.

Nanolithography 

Once these tools became available, the fascinating art of nanolithography took off.  Lithography is the art of making patterns on moulds and then repeatedly printing the pattern. In nanolithography, a large-scale material is taken and is reduced in size to a nanoscale pattern. An AFM tip is used to deposit a chemical upon a surface in a desired pattern. This is currently used in the fabrication of semiconductor integrated circuits.

Quantum dots

In another development, the synthesis and properties of semiconductor nanocrystals was studied; This led to a fast increasing number of metal oxide nanoparticles of quantum dots. Quantum dots are nanocrystal semi-conductors made by lithography. They have applications in transistors, solar cells, LEDs, and diode lasers.  Their use as bits in a future quantum computer is being explored.

Some of the pure science interest in nanotechnology is in quantum dots and nanotubes. Industry however, has focussed on the manufacture of various polymers and used the advantage of nanoparticles in bulk form, for instance, in suntan lotion and other cosmetics protective coatings, drug delivery, and stain resistant clothing.

The manufacture of polymers based on molecular structure, and the design of computer chip layouts based on surface science, are other important applications.

In fact, it is a highly multidisciplinary field, and is related to widely different fields such as applied physics, materials science, interface and colloid science, device physics, self-replicating machines and robotics, chemical engineering, mechanical engineering, biological engineering, and electrical engineering.

BOX Atomic Force Microscope (AFM)

The figure shows a typical AFM setup. A microfabricated cantilever with a sharp silicon tip is placed on the surface of the sample. Just as your car goes up and down over a bumpy road so that you feel all the bumps, the very sharp tip is deflected by features on a sample surface. The tip itself is a nanometer or so in size. A laser beam reflects off the back side of the cantilever. So as the tip of the cantilever goes up and down, the light from the laser beam goes up and down as well. This light is measured by a set of photodetectors, which allow the deflection to be measured. This measurement is assembled into an image of the surface, accurate to better than a nanometer.


FIG: Buckminsterfullerene C60, also known as the buckyball

FIG: Space-filling model of the nanocar on a surface, using fullerenes as wheels.

FIG: Image of surface reconstruction on a clean Gold surface using scanning tunneling microscopy. The individual atoms composing the material are visible. Surface reconstruction causes the surface atoms to deviate from the bulk crystal structure, and arrange in columns several atoms wide with regularly-spaced pits between them.

FIG: Typical AFM setup.