Nanotechnology ("nanotech") is manipulation of matter on an atomic, molecular, and supramolecular scale. The earliest, widespread description of nanotechnology referred to the particular technological goal of precisely manipulating atoms and molecules for fabrication of macroscale products, also now referred to as molecular nanotechnology. A more generalized description of nanotechnology was subsequently established by the National Nanotechnology Initiative, which defines nanotechnology as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers. This definition reflects the fact that quantum mechanical effects are important at this quantum-realm scale, and so the definition shifted from a particular technological goal to a research category inclusive of all types of research and technologies that deal with the special properties of matter which occur below the given size threshold. It is therefore common to see the plural form "nanotechnologies" as well as "nanoscale technologies" to refer to the broad range of research and applications whose common trait is size. Because of the variety of potential applications (including industrial and military), governments have invested billions of dollars in nanotechnology research. Through 2012, the USA has invested $3.7 billion using its National Nanotechnology Initiative, the European Union has invested $1.2 billion, and Japan has invested $750 million.
Nanotechnology as defined by size is naturally very broad, including fields of science as diverse as surface science, organic chemistry, molecular biology, semiconductor physics, energy storage, microfabrication, molecular engineering, etc. The associated research and applications are equally diverse, ranging from extensions of conventional device physics to completely new approaches based upon molecular self-assembly, from developing new materials with dimensions on the nanoscale to direct control of matter on the atomic scale.
Scientists currently debate the future implications of nanotechnology. Nanotechnology may be able to create many new materials and devices with a vast range of applications, such as in nanomedicine, nanoelectronics, biomaterials energy production, and consumer products. On the other hand, nanotechnology raises many of the same issues as any new technology, including concerns about the toxicity and environmental impact of nanomaterials, and their potential effects on global economics, as well as speculation about various doomsday scenarios. These concerns have led to a debate among advocacy groups and governments on whether special regulation of nanotechnology is warranted.
A self-assembled monolayer (SAM) is an organized layer of amphiphilic molecules in which one end of the molecule, the "head group" shows a specific, reversible affinity for a substrate. SAMs also consist of a tail with a functional group at the terminal end. SAMs are created by the chemisorption of hydrophilic head groups onto a substrate from either the vapor or liquid phase followed by a slow two-dimensional organization of hydrophobic tail groups. Initially, adsorbate molecules form either a disordered mass of molecules or form a "lying down phase", and over a period of minutes to hours, begin to form crystalline or semicrystalline structures on the substrate surface. Areas of close-packed molecules nucleate and grow until the surface of the substrate is covered in a single monolayer.
Selecting the type of head group depends on the application of the SAM. Typically, head groups are connected to an alkyl chain in which the terminal end can be functionalized (i.e. adding –OH, –NH3, or –COOH groups) to vary the wetting and interfacial properties. Substrates can be planar surfaces, such as silicon and metals, or curved surfaces, such as nanoparticles. Alkanethiols are the most commonly used molecules for SAMs. They are used on noble metal substrates because of the strong affinity of sulfur for these metals. Silanes are generally used on nonmetallic oxide surfaces. Metal substrates for use in SAMs can be produced through physical vapor deposition techniques, electrodeposition or electroless deposition.
Nadrian C. Seeman is an American chemist known as the founder of the field of DNA nanotechnology beginning in the early 1980s. Seeman's laboratory published the synthesis of the first three-dimensional nanoscale object, a cube made of DNA, in 1991, and the concepts of DNA nanotechnology later found further applications in DNA computing, DNA nanorobotics, and self-assembly of nanoelectronics. Seeman won the 1995 Feynman Prize in Nanotechnology "for developing ways to construct three-dimensional structures, including cubes and more complex polyhedra, from synthesized DNA molecules" and shared the 2010 Kavli Prize in Nanoscience for "development of unprecedented methods to control matter on the nanoscale".
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