Self-assembled monolayer

Part of a series of articles on Molecular self-assembly

Self-assembled monolayer Supramolecular assembly DNA nanotechnology
See also Nanotechnology
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Self assembled monolayers (SAMs) are surfaces consisting of a single layer of molecules on a substrate. Molecular self-assembly is the process by which Molecules adopt a defined arrangement without guidance or management from an outside source A supramolecular assembly or "supermolecule" is a well defined complex of molecules held together by noncovalent bonds. DNA nanotechnology is a subfield of Nanotechnology which seeks to use the unique Molecular recognition properties of DNA and other Nucleic acids Nanotechnology, sometimes shortened to nanotech, refers to a field of Applied science whose theme is the control of matter on an Atomic and Molecular In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Rather than having to use a technique such as chemical vapor deposition or molecular beam epitaxy to add molecules to a surface (often with poor control over the thickness of the molecular layer), self assembled monolayers can be prepared simply by adding a solution of the desired molecule onto the substrate surface and washing off the excess. Chemical vapor deposition (CVD is a Chemical process used to produce high-purity high-performance solid materials Molecular beam Epitaxy (MBE, is one of several methods of depositing Single crystals It was invented in the late 1960s at Bell Telephone Laboratories Self-assembly is a term used to describe processes in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific local A monolayer is a single closely packed layer of atoms molecules or cells

A common example is an alkane thiol on gold. In Organic chemistry, a thiol is a compound that contains the functional group composed of a Sulfur atom and a Hydrogen atom (-SH Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Sulfur has particular affinity for gold, with a binding energy in the range of 20–35 kcal/mol (85–145 kJ/mol). Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Binding energy is the Mechanical energy required to disassemble a whole into separate parts This article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy. The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity An alkane with a thiol head group will stick to the gold surface and form an ordered assembly with the alkyl chains packing together due to van der Waals forces. Alkanes, also known as Paraffins are Chemical compounds that consist only of the elements Carbon (C and Hydrogen (H (i The Van der Waals equation is an Equation of state that can be derived from a special form of the potential between a pair of molecules (hard-sphere repulsion For alkyl thiols on gold, the extended alkyl chains typically orient with an angle of ~30 degrees from the perpendicular of the substrate, and are assumed to be in a fully extended linear arrangement. There has been a great deal of work done determining the process by which alkyl thiol on gold assemblies are produced. It is generally thought that alkyl thiol molecules first bind to the gold surface in a 'lying down' position, where the alkyl chain tails of the molecules lie flat on the gold surface. The thiol interaction provides about 20–30 kcal/mol (85–130 kJ/mol) of driving force for the initial binding, which is modeled as a Langmuir binding isotherm. The Langmuir equation or Langmuir isotherm or Langmuir adsorption equation relates the coverage or Adsorption of molecules on a solid surface to Gas These binding events continue until the lying down molecules are dense enough on the surface to interact with each other. At some point the alkyl chains lift off the substrate and point outwards, tethered by the thiol anchor to the surface. There is a shift to a mixture of lying down molecules and island domains of upright alkyl chains, tilted at 30 degrees to the normal. At this stage binding kinetics become more complex and can no longer be modeled with a simple Langmuir binding isotherm. Over time the island domains merge and cover the bulk of the substrate, and the process can be compared to a 2-D crystallization process on a surface. Alkyl thiol SAMs exhibit grain boundaries and defects even after long periods of assembly. The initial stage of SAM formation usually takes minutes or less under the normal conditions of 0. 1-10 mmol/L thiol concentration in a solvent. More ordering of the assembly can take place over days or months, depending on the molecules involved.

A variety of other self-assembled monolayers can be formed, although there is always debate about the degree to which systems self-assemble. Alkyl thiols are known to assemble on many metals, including silver, copper, palladium, and platinum. Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Palladium (pronounced \pəˈleɪdiəm\ is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it palladium after the Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Alkyl silane molecules (e. Silane is a Chemical compound with Chemical formula Si[[hydrogen H]]4 g. octadecyltrichlorosilane) are another well-known example of self-assembly on silicon oxide surfaces and potentially be of greater technical relevance than alkyl thiol assembly on metals. Octadecyltrichlorosilane ( OTS, or n -octadecyltrichlorosilane) is an Organometallic chemical The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide Alkyl carboxylates are known to assemble on a variety of surfaces, such as aluminium and mica. A carboxylate anion is an Ion with Negative charge that contains the group -COO&minus WikipediaNaming The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially Silicon has been used through the reaction of silicon hydride surface and a radical generator, such as heat, UV or radical initiator molecule, or with reagents such as Grignard and chlorosilanes. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The Grignard reaction, named for the French chemist François Auguste Victor Grignard, is an organometallic Chemical reaction in which Alkyl - Once assembly has been accomplished, chemistry can be performed on the layer, especially if self-assembly places a reactive functional group on the outside of the monolayer. In Organic chemistry, functional groups are specific groups of Atoms within Molecules that are responsible for the characteristic Chemical reactions

SAMs have several applications in scientific research; they tend to have quite different chemical kinetics than the same molecules in another form, because of their exposed, 2-dimensional distribution, and as such are useful for some chemical and biochemical experiments. Chemical kinetics, also known as reaction kinetics is the study of rates of chemical processes A chemical substance is a Material with a definite chemical composition. Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as They can also be used for simulation of biological membranes and as substrates for cell culture. Cell culture is the process by which prokaryotic, or eukaryotic cells are grown under controlled conditions As technology develops to control the functional groups present in SAMS, either by direct deposition of molecules with those groups or by chemical modification of the layer, many other applications are also developing, for example in nanoscale fabrication of electronics. The nanoscopic scale usually refers to structures with a Length scale applicible to Nanotechnology, usually cited as 1-100 Nanometers The nanoscopic scale Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical

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