An "amorphous solid" is a solid Solid is one of the major states of matter. It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a gas does. The atoms in a solid are tightly bound to each other, in which there is no long-range order In physics, long-range order characterizes physical systems in which remote portions of the same sample exhibit correlated behavior of the positions of the atoms The atom is a basic unit of matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons . The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain. (Solids in which there is long-range atomic order are called crystallines A crystal or crystalline solid is a solid material, whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography. The process of crystal formation via mechanisms of crystal growth is called or morphous). Most classes of solid materials can be found or prepared in an amorphous form. For instance, common window glass Glass is an amorphous solid material. Glasses are typically brittle, and often optically transparent. Glass is commonly used for windows, bottles, and eyewear; examples of glassy materials include soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovy-glass, and aluminium oxynitride. The term glass developed in the late Roman is an amorphous solid, many polymers A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties (such as polystyrene Polystyrene (IUPAC Poly(1-phenylethane-1,2-diyl)), abbreviated following ISO Standard PS, is an aromatic polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. Polystyrene is one of the most widely used kinds of plastic) are amorphous, and even foods such as cotton candy Cotton candy , candy floss (British English), fairy floss (Australian English) is a form of spun sugar. Since it is mostly air, servings are large. Cotton candy is often served at fairgrounds or circuses. Food coloring is used to change the natural white color. A typical serving on a stick is at least one ounce and contains about 105 to 115 are amorphous solids.

In principle, given a sufficiently high cooling rate, any liquid can be made into an amorphous solid. Cooling reduces molecular mobility. If the cooling rate is faster than the rate at which molecules can organize into a more thermodynamically In science, thermodynamics is the study of energy conversion between heat and mechanical work, and subsequently the macroscopic variables such as temperature, volume and pressure. The first to give a concise definition of the subject was Scottish physicist William Thomson who in 1854 stated that: favorable crystalline state, then an amorphous solid will be formed. Because of entropy considerations, many polymers can be made amorphous solids by cooling even at slow rates. In contrast, if molecules have sufficient time to organize into a structure with two- or three-dimensional order, then a crystalline (or semi-crystalline) solid will be formed. Water is one example. Because of its small molecular size and ability to quickly rearrange, it cannot be made amorphous without resorting to specialized hyperquenching techniques.

Amorphous materials can also be produced by additives which interfere with the ability of the primary constituent to crystallize. For example, addition of soda Sodium Carbonate , Na2CO3, is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate; and is domestically well known for its everyday use as a water softener. It has a cooling alkaline taste, and can be extracted from the ashes of many plants. It is to silicon dioxide The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with a chemical formula of Si results in window glass, and the addition of glycols A geminal diol has two hydroxyl groups bonded to the same atom. Examples include methanediol H2C2 and 1,1,1,3,3,3-hexafluoropropane-2,2-diol (F3C)2C(OH)2, the hydrated form of hexafluoroacetone to water Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state, water vapor or steam results in a vitrified solid.

Some materials, such as metals, are difficult to prepare in an amorphous state. Unless a material has a high melting temperature (as ceramics do) or a low crystallization energy (as polymers tend to), cooling must be done extremely rapidly. As the cooling is performed, the material changes from a supercooled liquid Liquid is one of the three classical states of matter. Like a gas, a liquid is able to flow and take the shape of a container, but, like a solid, it resists compression. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly constant density. A distinctive property of the liquid state is surface tension,, with properties one would expect from a liquid state States of matter are the distinct forms that different phases of matter take on. Historically, the distinction is made based on qualitative differences in bulk properties. Solid is the state in which matter maintains a fixed volume and shape; liquid is the state in which matter maintains a fixed volume but adapts to the shape of its container; and material, to a solid. The temperature at which this transition occurs is called the glass transition temperature Glass transition or vitrification refers to the transformation of a glass-forming liquid into a glass, which usually occurs upon rapid cooling. It is a dynamic phenomenon occurring between two distinct states of matter , each with different physical properties. Upon cooling through the temperature range of glass transition (a "glass or Tg.

Contents

Definition

It is difficult to make a distinction between truly amorphous solids and crystalline solids if the size of the crystals is very small. Even amorphous materials have some short-range order at the atomic length scale due the nature of chemical bonding A chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction. The strength of bonds varies considerably; there are &. Furthermore, in very small crystals A crystal or crystalline solid is a solid material, whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography. The process of crystal formation via mechanisms of crystal growth is called a large fraction of the atoms The atom is a basic unit of matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons . The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain are located at or near the surface of the crystal; relaxation of the surface and interfacial effects distort the atomic positions, decreasing the structural order. Even the most advanced structural characterization techniques, such as x-ray diffraction and transmission electron microscopy, have difficulty in distinguishing between amorphous and crystalline structures on these length scales.

The transition from the liquid state to the glass, at a temperature below the equilibrium melting point of the material, is called the glass transition Glass transition or vitrification refers to the transformation of a glass-forming liquid into a glass, which usually occurs upon rapid cooling. It is a dynamic phenomenon occurring between two distinct states of matter , each with different physical properties. Upon cooling through the temperature range of glass transition (a "glass. The glass transition temperature, Tg, is the temperature at which an amorphous solid, such as glass or a polymer, becomes brittle on cooling, or soft on heating. More specifically, it defines a pseudo second order phase transition in which a supercooled melt yields, on cooling, a glassy structure and properties similar to those of crystalline materials e.g. of an isotropic solid material [1]. Tg is usually applicable to wholly or partially amorphous solids such as common glasses and plastics (organic polymers). Below the glass transition temperature, Tg, amorphous solids are in a glassy state [2] and most of their joining bonds are intact. In inorganic glasses, with increased temperature more and more joining bonds are broken by thermal fluctuations so that broken bonds (termed configurons) begin to form clusters. Above Tg these clusters become macroscopic large facilitating the flow of material. In organic polymers, secondary, non-covalent bonds between the polymer chains become weak above Tg. Above Tg glasses and organic polymers become soft and capable of plastic deformation without fracture. This behavior is one of the things which make most plastics useful [3]. It is important to note that the glass transition temperature is a kinetic parameter, and thus parametrically depends on the melt cooling rate. Thus the slower the melt cooling rate, the lower Tg. In addition, Tg depends on the measurement conditions, which are not universally defined [4]. The glass transition temperature is approximately the temperature at which the viscosity Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. For example, high-viscosity felsic magma will create a tall, steep stratovolcano, because it cannot flow far before it cools, while low-viscosity mafic lava will create a wide, shallow-sloped shield volcano. All real fluids have some of the liquid exceeds a certain value (about 1012 Pa·s Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensional stress. In everyday terms , viscosity is "thickness". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. Viscosity describes a fluid's internal resistance to). The transition temperature depends on cooling rate, with the glass transition occurring at higher temperatures for faster cooling rates. The precise nature of the glass transition is the subject of ongoing research. While it is clear that the glass transition is not a first-order thermodynamic transition (such as melting), there is debate as to whether it is a higher-order transition such percolation type transformation [5], or merely a kinetic effect.

Amorphous thin films

Amorphous phases are important constituents of thin films Thin films are thin material layers ranging from fractions of a nanometre to several micrometres in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction, which are solid layers of a few nm to some tens of µm thickness deposited upon an underlying substrate. So-called structure zone models were developed to describe the microstructure and morphology of thin films as a function of the homologeous temperature Th that is the ratio of deposition temperature over melting temperature [6][7]. According to these models, a necessary (but not sufficient) condition for the occurrence of amorphous phases is that Th has to be smaller than 0.3, that is the deposition temperature must be below 30% of the melting temperature. For higher values, the surface diffusion of deposited atomic species would allow for the formation of crystallites with long range atomic order.

Regarding their applications, amorphous metallic layers played an important role in the discussion of a suspected superconductivity Superconductivity is an electrical resistance of exactly zero which occurs in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes in 1911. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is also characterized by a phenomenon called the Meissner in amorphous metals [8]. Today, optical coatings made from TiO2, SiO2 The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with a chemical formula of Si , Ta2O5 etc. and combinations of them in most cases comprise of amorphous phases of these compounds. Much research is carried out into thin amorphous films as a gas separating membrane layer [9]. The technologically most important thin amorphous film is probably represented by few nm thin SiO2 layers serving as isolator above the conducting channel of a metal-oxide semiconductor field-effect transistor MOSFET The metal–oxide–semiconductor field-effect transistor is a device used for amplifying or switching electronic signals. The basic principle of the device was first proposed by Julius Edgar Lilienfeld in 1925. In MOSFETs, a voltage on the oxide-insulated gate electrode can induce a conducting channel between the two other contacts called source. Also, hydrogenated amorphous silicon Amorphous silicon is the non-crystalline allotropic form of silicon. It can be deposited in thin films at low temperatures onto a variety of substrates, which offers some unique capabilities in a variety of electronics, a-Si:H in short, is of technical significance for thin film solar cells. In case of a-Si:H the missing long-range order between silicon atoms is partly induced by the presence by hydrogen in the percent range.

The occurrence of amorphous phases turned out as a phenomenon of particular interest for studying thin film growth. Remarkably, the growth of polycrystalline films is often preceded by an initial amorphous layer, the thickness of which may amount to only a few nm. The most investigated example is represented by thin multicrystalline silicon films, where such an initial amorphous layer was observed in many studies, see for instance [10]. Wedge-shaped polycrystals were identified by transmission electron microscopy Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a to grow out of the amorphous phase only after the latter has exceeded a certain thickness, the precise value of which depends on deposition temperature, background pressure and various other process parameters. The phenomenon has been interpreted in the framework of Ostwald’s rule Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to elemental solids. The complete morphology of a material is described by of stages [11] that predicts the formation of phases to proceed with increasing condensation time towards increasing stability [8][10]. Experimental studies of the phenomenon require a clearly defined state of the substrate surface and its contaminant density etc., upon which the thin film is deposited.

References

  1. ^ The TUPAC (rapper)Compendium of Chemical Terminology, 66, 583 (1997).
  2. ^ A. Varshneya. Fundamentals of inorganic glasses. Boston, Academic Press (1994).
  3. ^ But such behavior is not exhibited by crosslinked thermosetting plastics which, once cured, are set for life and will shatter rather than deform, never becoming plastic again when heated, nor melting
  4. ^ O. V. Mazurin, Yu. V. Gankin: "Glass transition temperature: problems of measurements and analysis of the existing data"; Proceedings, International Congress on Glass, July 1-6, 2007, Strasbourg, France
  5. ^ M.I. Ojovan. Glass formation in amorphous SiO2 as a percolation phase transition in a system of network defects. J. Exp. Theor. Phys. Let., 79 (12) 632-634 (2004)
  6. ^ B. A. Movchan and A. V. Demchishin (1969). "Study of the structure and properties of thick vacuum condensates of nickel, titanium, tungsten, aluminium oxide and zirconium dioxide". Phys. Met. Metallogr. 28: 83–90.
  7. ^ J.A. Thornton (1974). "Influence of apparatus geometry and deposition conditions on the structure and topography of thick sputtered coatings". J. Vac. Sci. Tech. 11: 666–670. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1116/1.1312732.
  8. ^ a b Buckel, W. (1961). "The influence of crystal bonds on film growth". Elektrische en Magnetische Eigenschappen van dunne Metallaagies. Leuven, Belgium.
  9. ^ R.M. de Vos, H. Verweij (1998). "High-Selectivity, High-Flux Silica Membranes for Gas Separation". Science 279 (5357): 1710. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1126/science.279.5357.1710. PMID A PMID is a unique number assigned to each PubMed citation of life sciences and biomedical scientific journal articles. The related Pubmed Central archive may additionally assign a separate number, a PMCID (PubMed Central Identifier), normally written with a PMC prefix 9497287.
  10. ^ a b M. Birkholz, B. Selle, W. Fuhs, S. Christiansen, H. P. Strunk, and R. Reich (2001). "Amorphous-crystalline phase transition during the growth of thin films: the case of microcrystalline silicon". Phys. Rev. B 64: 085402. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1103/PhysRevB.64.085402.
  11. ^ W. Ostwald (1897). "Studien über die Umwandlung fester Körper". Z. Phys. Chem. 22: 289–330.

External links

Categories: Phases of matter | Amorphous solids Categories: Amorphous matter | Solids | Glass physics

 

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