Nanotechnology is an emerging technology with applications in several scientiﬁc and research ﬁelds, such as information and communication technology, electronics, energy, biology, medical technology, etc. The term nanotechnology comes from the combination of two words: the Greek numerical preﬁx nano referring to a billionth and the word technology. Technology is generally considered to be at a size below 0.1µm or 100nm (a nanometer is one billionth of a meter, 10-9 m). Nanoscale science (or nanoscience) studies the phenomena, properties, and responses of materials at atomic, molecular, and macromolecular scales, and in general at sizes between 1 and 100nm.
In this scale, and especially below 5nm, the properties of matter differ signiﬁcantly from that at a larger particulate scale.
Nanotechnology is then the design, the manipulation, the building, the production and application, by controlling the shape and size, the properties-responses and functionality of structures, and devices and systems of the order or less than 100 nm. Nanotechnology is considered an emerging technology due to the possibility to advance well-established products and to create new products with totally new characteristics and functions with enormous potential in a wide range of applications.
In addition to various industrial uses, great innovations are foreseen in information and communication technology, in biology and biotechnology, in medicine and medical technology, in metrology, etc.
According to this theory electrons are conﬁned in all three dimensions causing matter to behave completely different in terms of its optical and electronic properties.
When the dimension of a material approaches the electron wavelength in one or more dimensions, quantum mechanical characteristics of the electrons that are not manifest in the bulk material can start to contribute too even dominate the physical properties of the material . Besides quantum size effects, the nanomaterials behavior is different due to surface effects which dominate as nanocrystal size decreases. Reducing the size of a crystal from 30 to 3nm, the number of atoms on its surface increases from 5% to 50% beginning to perturb the periodicity of the “inﬁnite” lattice. In that sense, atoms at the surface have fewer direct neighbors than atoms in the bulk and as a result they are less stabilized than bulk atoms . The origin of the quantum size effects strongly depends on the type of bonding in the crystal.
For metals, the electron mean free path(MFP) determine the thermal and electrical conductivity and affects the color of the metal. For most of the metals, MFP is of the order of 5–50nm. Reducing further this threshold, the electrons begin to scatter off the crystal surface, and the resistivity of the particles increases. For very small metal particles, the conduction and valence bands begin to break down into discrete levels. For gold particles, this causes a change in color from red to orange at sizes around1.5nm. Quantum Dots In a bulk semiconductor electrons can freely move within an area from a few nanometers to a few hundred of nanometers as deﬁned by the Bohr radius. Thus continuous conduction and valence energy bands exist which are separated by an energy gap. Contrary, in a quantum dot, where excitons can not move freely, discrete atomic like states with energies that are determined by the quantum dot radius appear. The effect of quantum conﬁnement has a great technological interest from semiconductors and optoelectronics to biological applications.
Different methods for the synthesis of nanoengineered materials and devices can accommodate precursors from solid, liquid, or gas phases and encompass a tremendously varied set of experimental techniques. A detailed presentation of these is beyond the scope of this review. In general, however, most synthetic methods can be classiﬁed into two main approaches: “top-down” and “bottom-up” approaches and combinations. “Top-down” (photolithography, micro contact printing) techniques begin with a macroscopic material or group of materials and incorpor ate smaller-scale details into them, whereas “bottom-up” (organic-synthesis, self-assembly) approaches begin by designing and synthesizing custom-made molecules that have the ability to self-assemble or self-organize into higher order mesoscale and macroscale structures. Bottom-up approach aims to guide the assembly of atomic and molecular constituents into organized surface structures through processes inherent in the manipulated system. One example of the bottom-up approach is self-assembly. Self-assembly is the fundamental principle which generates structural organization on all scales from molecules to galaxies. It is a method of integration in which the components spontaneously assemble, until a stable structure of minimum energy is reached.
Energy is one of the most challenging needs of humanity, and is highest on the list of priorities and requisites for human welfare. According to the International Energy Agency (IEA), World’s primary energy demand will increase by 36% between 2008 and 2035. Electricity demand is expected to grow by 2:2% per year. Between 2008 and 2035 .Taking in account the CO2 emissions and the global climate change impact on life and the health of the planet renewable energy sources will have to play a central role in moving the world onto a more secure, reliable, and sustainable energy path. Solar energy is the most abundant, inexhaustible and clean of all the renewable energy resources till date. The power from sun intercepted by the earth is about 1:81011 MW, which is many times larger than the present rate of all the energy consumption. Photovoltaic technology is one of the ﬁnest ways to harness the solar power . Figure 1.9 shows the history of conﬁrmed “champion” laboratory cell efﬁciencies. The performance of conventional solar cells is approaching a plateau; only incremental improvements have been accomplished in the last decade despite dedicated R&D effort. Tandem solar cells based on III–V materials have achieved the highest efﬁciencies of any present photovoltaic device exceeding 40% recently However, the cost of these devices is very high. Limiting their application to space applications. The efﬁciencies reached with commercial solar cell modules are signiﬁcantly lower than those of the best laboratory cells due to losses incurred during scale up. The typical size of “champion laboratory cells” is in the square centimeter range or even below, facilitating the collection of photocurrent.
The great development in Nanotechnology has given birth to the need of knowing of the dimensions that characterize its nanostructure. This lead to the appearance of a new scientiﬁc ﬁeld called Nanometrology. Nanometrology is the science and practice of measurement of functionally important, mostly dimensional parameters and components with at least one critical dimension which is smaller than 100nm. Success in nanomanufacturing of devices will rely on new nanometrologies needed to measure basic materials properties including their sensitivities to environmental conditions and their variations, to control the nanofabrication processes and materials functionalities, and to explore failure mechanisms. In order to study and explore the complex nanosystems, highly sophisticated experimental, theoretical, and modeling tools are required. Especially, the visualization, characterization, and manipulation of materials and devices require sophisticated imaging and quantitative techniques with spatial and temporal resolutions on the order of 106 and below to the molecular level. In addition, these techniques are critical for understanding the relationship and interface between nanoscopic and mesoscopic/macroscopic scales, a particularly important objective for biological and medical applications.
The need for better characterization at the nanoscale derives from the correlation between the macroscopic functional properties with the nanoscale structural characteristics of nanomaterials which is a prerequisite for the development of emerging low-cost manufacturing technological ﬁelds such as organic electronics. These include organic solar cells (OPVs), organic light emitting diodes (OLEDs) and organic ﬁeld-effect transistors (OFETs), and others. Insights on the nanomorphology as well as the conduction mechanisms at the various interfaces that exist in these multilayered devices are crucial for the development of the plastic electronic technology and the construction of better products. Examples of important tools available at the moment include highly focused synchrotron X-ray sources and related techniques that provide detailed molecular structural information by directly probing the atomic arrangement of atoms; scanning probe microscopy that allow three-dimensional-type topographical atomic and molecular views or optical responses of nanoscale structures.
Consequently, today’s suite of metrology tools has been designed to meet the needs of exploraory nanoscale research. New techniques, tools, instruments and infrastructure will be needed to support a successful nanomanufacturing industry. The currently available metrology tools are also beginning to reach the limits of resolution and accuracy and are not expected to meet future requirements for nanotechnology or nanomanufacturing. This combination over comes the difﬁculties that originate from low signal since the Raman systems have limit in lateral resolution of 300m and require high laser power for surface investigation because the measured Raman intensity is six orders of magnitude lower than the excitation power. Thus, TERS is a promising technique and we can see it in the near future to be used for probing the chemical analysis of very small areas and for the imaging of nanostructures and biomolecules such as proteins. New approaches have to be developed and existing ones based on XPS, X-ray absorption spectroscopy, SPM and SIMS have to be improved in terms of better spectral and spatial resolution, better contrast and better sensitivity or elements and molecular species. Ideally new methods should have capabilities to work in situ, at ambient air and/or in liquid surroundings. However, clever new approaches need to be developed. For this, it is required to understand the fundamental mechanisms by which the probes of the nanometrology measuring systems interact with the materials and objects that are being measured. Finally, even with the vast array of current tools available, the important question is whether or not they are providing the required information or reams of inconsequential data. Revolutionary approaches to the nanometrology needed may be required in the near future and therefore, revolutionary and not just evolutionary instrumentation and metrology are needed.