Introduction to Nanotechnology

The nano in nanotechnology has its roots in ancient Greek word “nanos” which means “dwarf”. Today nano is used as prefix which indicates “billionth” or a factor of 10^-9. Coupling the word nano with the unit meter gives us nanometer which indicates a unit of spatial measurement that is one billionth of a meter. With this in mind, nanotechnology is defined as science, engineering, and technology conducted at the scale that range between 1 and 100nm.

On Dec. 29, 1959, at Caltech or California Institute of Technology, Noble Laureate Richard P. Feynman gave a talk at the annual meeting of the American Physical Society that has become one of the twentieth century's classic science lectures titled „There's Plenty of Room at the Bottom“. In this lecture R. Feynman one of great minds of twentieth century presented a technological vision of extreme miniaturization several years before the world chip became part of the electronics. He had also talked about the problem of manipulating and controlling things at small scale. The general idea of this lecture was to build nano objects atom by atom or molecule by molecule.

Figure 1 - Richard P. Feynamn

In this lecture R. Feynman said: “…I am not afraid to consider the final question as to whether, ultimately-in the great future-we can arrange the atoms the way we want; the very atoms, all the way down! What would happen if we could arrange the atoms one by one the way we want them...“

How to get to nanometer size?

Let’s get a better perspective of a nanometer scale. If we have a meter and divide it into 100 equal pieces, each piece would be one centimeter in size. This is the size of pinky finger or sugar cube. If we cut up centimeter into ten equal pieces, each piece would be one millimeter. Just to get better perspective thinnest phones today are between 4 and 5 mm. Objects that are small as a millimeter can be seen with the naked eye, but when object dimensions fall below a millimeter, they can be hard to see.

If you cut millimeter into one thousand equal pieces, each piece would be a micrometer long. Micrometer is equal to one millionth of a meter. The diameter of hair is a about forty to fifty micrometers wide. Red blood cells are six to ten micrometers in diameter. Many types of bacteria typically measure five to twenty micrometers. Things on this scale usually can’t be seen with our eyes but rather can be visualized with magnifying glass or light microscope.

If we cut a micrometer up into one thousand equal pieces, each piece would be a nanometer long. In other words, a nanometer is equal to one-billionth of a meter. When things are this small, we can’t observe them with our eyes or a light microscope. Objects this small require a special tool for imaging. Things of nanometer scale include: viruses (30 – 50 nm), DNA (2 nm), buck balls (1 nm in diameter) and carbon nanotubes (~1 nm in diameter). Atoms are smaller than a nanometer. One atom measures ~0.1 to 0.3 nm, depending on the element type.

The following video gives good explanation of what does word nano mean?

Good example of miniaturization are cellphones. If we look back to year 1985 when cellphones where about the size of walkie-talkie the miniaturization process change the size and performance of these devices. Today phones or smartphones are computers that fit in your hand and are incomparable to performance of 80s computers and cellphones. They are not just computers, but they are also GPS, radio and a lifeline to the internet and can fit in our pocket.

Figure 2 - Mobile phone (Vodafone VT1) in 1985

Figure 3 - Samsung Galaxy S5 in 2015

So with help of nanotechnology, mobile phones will become more flexible, become water resistant (some of them already are), in-built projectors, 3D screens and more. Generally they will evolve in terms of performance and features.  For future of mobile phone watch the following video.

Nanotechnology, in one sense, is the natural continuation of the revolution that we have witnessed over the last decade, in which millionth of a meter electronics (micro-electronics) have become commonplace, enabling the construction of higher quality materials and devices, and allowing the localization of multiple applications on equivalent or even smaller areas.

So far, the miniaturization ability of microelectronics has allowed the integration or placement of thousands of chips into areas no larger than those used previously. Further miniaturization with the help of nano-technology would allow the placement of millions of currently available electronic devices over an area with dimensions in the millimeters. In another pertinent example, a team from the Technion leveraged the power of nanotechnology to engrave the content of the Old Testament on a piece of silicon smaller than 1 mm x 1 mm.

Surface to volume ratio

Surface area to volume ratio increases with the decrease in the characteristic dimensions of a material and vice versa. As material size decreases, a greater portion of the atoms are found at the surface compared to those inside. Because growth and catalytic chemical reactions occur at material surfaces, a given mass of nanomaterial will be much more reactive than the same mass of material made up of larger particles. Experiments showed that some of materials that are inert in their bulk form are reactive when produced in a nanoscale form.

A silicon cube with a characteristic size of 10nm has about 6250 unit cells. The size of the silicon unit cell is 0.543 nm. How many of them fit in cube?

$$\begin{align} & V={{\left( 10\text{ nm} \right)}^{3}}=1\cdot {{10}^{-24}}{{\text{m}}^{\text{3}}} \\ & {{V}_{uc}}={{\left( 0.543\text{ nm} \right)}^{3}}=1.60103\cdot {{10}^{-28}}{{\text{m}}^{\text{3}}} \\ & \underline{{{\text{n}}_{uc}}=8\text{ }} \\ & \rho =\frac{{{n}_{uc}}}{{{V}_{uc}}}=\frac{8}{1.60103\cdot {{10}^{-28}}}=4.99678\cdot {{10}^{28}}\text{atoms/}{{\text{m}}^{\text{3}}} \\ & n=\rho {{V}_{uc}}=4.99678\cdot {{10}^{28}}\cdot 1\cdot {{10}^{-24}}=49967.8 \\ & n\approx 50000 \\ \end{align}$$

So there are 50000 atoms in silicon cube of 10 nm size. The number of unit cells on each face is around 350 there is about 680 atoms on each surface of the nanocube giving total of 4100 atoms on all nanocube faces. When this number is compared to total number of atoms in nanocube brings us to conclusion that approximately 10 % of the atoms in the nanocube are located on the surface. If we analyze the piece of silicon that is 10 cm2 and 1 µm in thickness this leads to the conclusion that only 0.03 % of the silicon atoms in the structure are available on the surface.

Therefore, nanomaterials have a much greater surface area per unit volume compared with larger particles. This leads to nanoparticles that are more chemically reactive, because molecules at the surface of a material do not have full allocation of covalent bonds and are in an energetically unstable state. Since many more molecules located at the surface are in energetically unstable states, nanomaterials are more reactive compared to the non-nanoscale material. With the high reactivity, almost all types of nanomaterials are capable of catalyzing reactions and free nanomaterials tend to agglomerate into bigger particles.

Owing to the specific physiochemical properties of nanoparticles, they are expected to interact with substances such as proteins, lipids, carbohydrates, nucleic acids, ions, minerals and water present in food, biological, or desalination processes. Other potential applications for this reactivity are drug delivery, clothing insulation, and more.