1
Introduction to Nanotechnology

1.1 Introduction

The word nano is from the Greek word "Nanos" meaning dwarf. It is a prefix used to describe "one billionth" of something, or 0.000?000?001; the prefix that means very, very small. Nanoscience is a part of science that studies small stuff and it is all sciences that work with the very small such as biology, chemistry, or physics. Nanotechnology is the art and science of making very small useful things, including advances in all industries, together with the electronic, chemical, and pharmaceutical.

Nanotechnology is the engineering of functional systems at the molecular scale. This covers both current work and concepts that are more advanced. Nanotechnology is sometimes referred to as a general-purpose technology. That is because in its advanced form it will have significant impact on almost all industries and all areas of society. It will offer better built, longer lasting, cleaner, safer, and smarter products for the home, for communications, for medicine, for transportation, for agriculture, and for industry in general. A key understanding of nanotechnology is that it offers not just better products but a vastly improved manufacturing process. The power of nanotechnology can be encapsulated in an apparently simple device called a personal nanofactory that may sit on your countertop or desktop. Packed with miniature chemical processors, computing, and robotics, it will produce a wide range of items quickly, cleanly, and inexpensively, building products directly from blueprints. Nowadays, nanotechnology has great impact on the development of a wide range of science and technology, including information technology () that provides smaller, faster, more energy-efficient and powerful computing, and other IT-based systems; energy that provides more efficient and cost-effective technologies for energy production such as in solar cells, fuel cells, batteries, and biofuels; consumer goods that provide food and beverages for advanced packaging materials, sensors, and lab-on-chips for food quality testing, appliances and textiles for stain-proof, water-proof and wrinkle-free textiles, household and cosmetics for self-cleaning and scratch-free products, paints, and better cosmetics; and medicines that provide technology for imaging, cancer treatment, medical tools, drug delivery, diagnostic tests, and drug development [1-7].

1.2 Importance of Size in Nanotechnology

The nanoscale size effect can be summarized as follows:

• Realization of miniaturized devices and systems while providing more functionality;
• Attainment of high surface-area-to-volume ratio;
• Manifestation of novel phenomena and properties, including changes in the following:
  • Physical properties (e.g. melting point),
  • Chemical properties (e.g. reactivity),
  • Electrical properties (e.g. conductivity),
  • Mechanical properties (e.g. strength),
  • Optical properties (e.g. light emission).

For instance, when carbon is a pure solid, it is found as graphite or diamond. On the nanoscale, carbon takes on very different structures and therefore provides different properties.

1.3 Approaches in Nanotechnology

Nanofabrication aims at building nanoscale structures (0.1-100?nm), which can act as components, devices, or systems with desired properties, performance, reliability, and reproducibility, in large quantities at low cost. Nanofabrication is used in several industrial applications including the following:

• Information storage,
• Optoelectronics,
• Sensors,
• Microelectromechanical () devices,
• Power semiconductors,
• Pharmaceuticals,
• Biomedical applications,
• Microelectronics (chips).

About 1020 transistors (or 10 billion for every person in the world) are manufactured every year based on (very large-scale integration), (ultralarge-scale integration), and (giga-scale integration). Variations of this versatile technology are used for flat-panel displays, microelectromechanical systems (), as well as for chips for DNA screening. More conventional applications of nanofabrication can be seen in the information storage of computers, cell phones, and digital sound and images. Nanostructures and devices can be accomplished by two approaches: top-down and bottom-up methods.

1.3.1 Top-Down Approach

In this method, large objects are modified to give smaller features. Examples are film deposition and growth, nanoimprint/lithography, etching technology, mechanical polishing. The top-down approach uses the traditional methods to pattern a bulk wafer following two processes:

• Adding a layer of material over the entire wafer and patterning that layer through photolithography;
• Patterning bulk silicon by etching away certain areas.

Problems with the top-down process are as follows:

• Cost of new machines and clean room environments grows exponentially with newer technologies.
• Physical limits of photolithography are becoming a problem.
• With smaller geometries and conventional materials, heat dissipation is a problem.

1.3.2 Bottom-Up Approach

In this method, small building blocks are produced and assembled into larger structures. Examples are chemical synthesis, laser trapping, self-assembly, colloidal aggregation, etc. It is the opposite of the top-down approach. Instead of taking material away to make structures, the bottom-up approach selectively adds atoms to create structures. Molecular assembly is like a Lego set of 90 atoms that we can use to build anything from the bottom up. You just use every atom that you want. All of the elements in the periodic table can be mixed and matched.

The ideas behind the bottom-up approach are based on the following:

• Nature uses the bottom-up approach:
  • Cells,
  • Crystals,
  • Humans.
• Chemistry and biology can help assemble and control growth.

Why is Bottom-up Processing Needed?

• It allows smaller geometries than photolithography.
• Certain structures such as carbon nanotubes and Si nanowires are grown through a bottom-up process.
• New technologies such as organic semiconductors employ bottom-up processes to pattern them.
• It can make formation of films and structures much easier.
• It is more economical than top-down in that it does not waste material to etching.

Applications of bottom-up processing are as follows:

• Self-organizing deposition of silicon nanodots,
• Formation of nanowires,
• Nanotube transistor,
• Self-assembled monolayers,
• Carbon nanotube interconnects.

Ability to synthesize nanoscale building blocks with control on size and composition are under rapid development for further assembling into larger structures with designed properties that will revolutionize materials manufacturing for metals, ceramics, and polymers at exact shapes without machining as well as to be lighter, stronger, and programmable materials and have lower failure rates and reduced life-cycle costs. Also, bioinspired, multifunctional, and adaptive materials as well as self-healing materials are in concern.

Challenges ahead are as follows:

• Synthesis, large-scale processing,
• Making useful, viable composites,
• Multiscale models with predictive capability,
• Analytical instrumentation.

Self-assembly can be defined as coordinated actions of independent entities under local control of driving forces to produce large, ordered structures or to achieve a desired group effect. The driving force of self-assembly is usually based on the interplay of thermodynamics and kinetics such as chemically controlled self-assembly, physically controlled self-assembly, and flip-up principles and spacer techniques.

The future of top-down and bottom-up processing is based on many new applications and can be summarized as follows:

• Top-down processing has been and will be the dominant process in semiconductor manufacturing.
• Newer technologies such as nanotubes and organic semiconductors will require a bottom-up approach for processing.
• Self-assembly eliminates the need for photolithography.
• Bottom-up processing will become more and more prevalent in semiconductor manufacturing.

1.4 Impact of Nanotechnology

Basic advancements in science and technology come about twice a century and lead to massive wealth creation. There are incredible opportunities for nanotechnology to impact all aspects of the economic spectrum. Revolutionary forces have built commonality in railroad, auto, computer, and nanotech that all are enabling technologies.

The importance of nanotechnology is summarized here.

1.4.1 Sensors for the Automotive Industry

Automotive electronics to grow to $300 billion by 2020. The pressure to keep the cost of devices low is enormous. Sensors in use now...