Physical Review B
Physical Review B, Condensed Matter and Materials Physics is a peer-reviewed, scientific journal, published by the American Physical Society. The Editor of PRB is Laurens W. Molenkamp and it is part of the Physical Review family of journals. The current acting Editor in Chief is Dan T. Kulp, PRB currently publishes over 4500 papers a year, making it one of the largest physics journals in the world. According to the Journal Citation Reports, PRBs most recent impact factors have been 3.664 for 2013,3.736 for 2014 and 3.718 for 2015. PRB was created in 1970 by the split of the original Physical Review into four parts, peter D. Adams was the Editor from inception until 2012 when Laurens W. Molenkamp took over. Anthony M. Begley is currently the Managing Editor, PRB has a reputation among professional physicists for publishing useful, comprehensive long papers in physics. It contains short papers in its Rapid Communications section, designed for research important enough to deserve special handling, the journal can be searched for free via PROLA.
Titles and abstracts can be viewed for free but a subscription is needed to read the full text of papers. PRB and the other APS journals are available entirely for free at many US public libraries, PRB is rare among physics journals in that it has a staff of 12 full-time professional editors and does not employ the more common model of using part-time editors who are active researchers. The journal is available in print format but the version is the online one. Authors can pay extra charges to make their papers open access, a small percentage of the PRB papers published are chosen by the PRB editors to be Editors Suggestions, as seen at http, //prb. aps. org. Artistic images from papers in the journal are published as a feature named Kaleidoscope at http, Physical Review B is indexed in the following bibliographic databases, American Physical Society#APS journals PRB home page
Polymorphism (materials science)
In materials science, polymorphism 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 and metals, and is related to allotropy, the complete morphology of a material is described by polymorphism and other variables such as crystal habit, amorphous fraction or crystallographic defects. Polymorphism is relevant to the fields of pharmaceuticals, pigments, foods, when polymorphism exists as a result of a difference in crystal packing, it is called packing polymorphism. Polymorphism can result from the existence of different conformers of the molecule in conformational polymorphism. In pseudopolymorphism the different crystal types are the result of hydration or solvation and this is more correctly referred to as solvomorphism as different solvates have different chemical formulae. An example of an organic polymorph is glycine, which is able to form monoclinic, silica is known to form many polymorphs, the most important of which are, α-quartz, β-quartz, cristobalite and stishovite. A classical example is the pair of minerals and aragonite, an analogous phenomenon for amorphous materials is polyamorphism, when a substance can take on several different amorphous modifications.
In terms of thermodynamics, there are two types of polymorphic behaviour, for an enantiotropic system, a plot of the free energy against temperature shows a crossing point threshold before the various melting points. It may be possible to revert interchangeably between the two polymorphs by heating or cooling, or through contact with a lower energy polymorph. Present-day analysis identifies three polymorphs for benzamide, the least stable one, formed by flash cooling is the orthorhombic form II and this type is followed by the monoclinic form III. The most stable form is monoclinic form I, the hydrogen bonding mechanisms are the same for all three phases, they differ strongly in their pi-pi interactions. Polymorphs have different stabilities and may spontaneously convert from a form to the stable form at a particular temperature. Most polymorphs of organic molecules only differ by a few kJ/mol in lattice energy, approximately 50% of known polymorph pairs differ by less than 2 kJ/mol and stability differences of more than 10 kJ/mol are rare.
They exhibit different melting points, solubilities, X-ray crystal, various conditions in the crystallisation process is the main reason responsible for the development of different polymorphic forms. In 2006 a new form of maleic acid was discovered 124 years after the first crystal form was studied. Maleic acid is a manufactured on a very large scale in the chemical industry and is a salt forming component in medicine. The new crystal type is produced when a co-crystal of caffeine and maleic acid is dissolved in chloroform, whereas form I has monoclinic space group P21/c, the new form has space group Pc. 1,3, 5-Trinitrobenzene is more than 125 years old and was used as an explosive before the arrival of the safer 2,4, only one crystal form of 1,3, 5-trinitrobenzene was known in the space group Pbca
An optical coating is one or more thin layers of material deposited on an optical component such as a lens or mirror, which alters the way in which the optic reflects and transmits light. One type of coating is an antireflection coating, which reduces unwanted reflections from surfaces. Another type is the high-reflector coating which can be used to produce mirrors which reflect greater than 99. 99% of the light falls on them. More complex optical coatings exhibit high reflection over some range of wavelengths, the simplest optical coatings are thin layers of metals, such as aluminium, which are deposited on glass substrates to make mirror surfaces, a process known as silvering. The metal used determines the characteristics of the mirror, aluminium is the cheapest and most common coating. More expensive is silver, which has a reflectivity of 95%-99% even into the far infrared, most expensive is gold, which gives excellent reflectivity throughout the infrared, but limited reflectivity at wavelengths shorter than 550 nm, resulting in the typical gold colour.
By controlling the thickness and density of metal coatings, it is possible to decrease the reflectivity and increase the transmission of the surface and these are sometimes used as one-way mirrors. The other major type of coating is the dielectric coating. These are constructed from thin layers of such as magnesium fluoride, calcium fluoride, and various metal oxides. Reflection coefficients of surfaces can be reduced to less than 0. 2%, the reflectivity can be increased to greater than 99. 99%, producing a high-reflector coating. Such mirrors are used as beamsplitters, and as output couplers in lasers. Alternatively, the coating can be designed such that the mirror reflects light only in a band of wavelengths. The versatility of dielectric coatings leads to their use in many optical instruments as well as consumer devices such as binoculars, spectacles. Dielectric layers are applied over top of metal films, either to provide a protective layer. Metal and dielectric combinations are used to make advanced coatings that cannot be made any other way.
One example is the perfect mirror, which exhibits high reflection, with unusually low sensitivity to wavelength, angle. Antireflection coatings are used to reduce reflection from surfaces, whenever a ray of light moves from one medium to another, some portion of the light is reflected from the surface between the two media. A number of different effects are used to reduce reflection, the simplest is to use a thin layer of material at the interface, with an index of refraction between those of the two media
In many fields of mathematics and physics, almost all scientific papers are self-archived on the arXiv repository. Begun on August 14,1991, arXiv. org passed the half-million article milestone on October 3,2008, by 2014 the submission rate had grown to more than 8,000 per month. The arXiv was made possible by the low-bandwidth TeX file format, around 1990, Joanne Cohn began emailing physics preprints to colleagues as TeX files, but the number of papers being sent soon filled mailboxes to capacity. Additional modes of access were added, FTP in 1991, Gopher in 1992. The term e-print was quickly adopted to describe the articles and its original domain name was xxx. lanl. gov. Due to LANLs lack of interest in the rapidly expanding technology, in 1999 Ginsparg changed institutions to Cornell University and it is now hosted principally by Cornell, with 8 mirrors around the world. Its existence was one of the factors that led to the current movement in scientific publishing known as open access. Mathematicians and scientists regularly upload their papers to arXiv.
org for worldwide access, Ginsparg was awarded a MacArthur Fellowship in 2002 for his establishment of arXiv. The annual budget for arXiv is approximately $826,000 for 2013 to 2017, funded jointly by Cornell University Library, annual donations were envisaged to vary in size between $2,300 to $4,000, based on each institution’s usage. As of 14 January 2014,174 institutions have pledged support for the period 2013–2017 on this basis, in September 2011, Cornell University Library took overall administrative and financial responsibility for arXivs operation and development. Ginsparg was quoted in the Chronicle of Higher Education as saying it was supposed to be a three-hour tour, Ginsparg remains on the arXiv Scientific Advisory Board and on the arXiv Physics Advisory Committee. The lists of moderators for many sections of the arXiv are publicly available, additionally, an endorsement system was introduced in 2004 as part of an effort to ensure content that is relevant and of interest to current research in the specified disciplines.
Under the system, for categories that use it, an author must be endorsed by an established arXiv author before being allowed to submit papers to those categories. Endorsers are not asked to review the paper for errors, new authors from recognized academic institutions generally receive automatic endorsement, which in practice means that they do not need to deal with the endorsement system at all. However, the endorsement system has attracted criticism for allegedly restricting scientific inquiry, perelman appears content to forgo the traditional peer-reviewed journal process, stating, If anybody is interested in my way of solving the problem, its all there – let them go and read about it. The arXiv generally re-classifies these works, e. g. in General mathematics, papers can be submitted in any of several formats, including LaTeX, and PDF printed from a word processor other than TeX or LaTeX. The submission is rejected by the software if generating the final PDF file fails, if any image file is too large.
ArXiv now allows one to store and modify an incomplete submission, the time stamp on the article is set when the submission is finalized
A gel is a solid jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state, by weight, gels are mostly liquid, yet they behave like solids due to a three-dimensional cross-linked network within the liquid. It is the crosslinking within the fluid that gives a gel its structure, in this way gels are a dispersion of molecules of a liquid within a solid in which the solid is the continuous phase and the liquid is the discontinuous phase. The word gel was coined by 19th-century Scottish chemist Thomas Graham by clipping from gelatine, gels consist of a solid three-dimensional network that spans the volume of a liquid medium and ensnares it through surface tension effects. This internal network structure may result from physical bonds or chemical bonds, virtually any fluid can be used as an extender including water and air. Both by weight and volume, gels are mostly fluid in composition, edible jelly is a common example of a hydrogel and has approximately the density of water.
Polyionic polymers are polymers with a functional group. The ionic charges prevent the formation of tightly coiled polymer chains and this allows them to contribute more to viscosity in their stretched state, because the stretched-out polymer takes up more space. A hydrogel is a network of polymer chains that are hydrophilic, hydrogels are highly absorbent natural or synthetic polymeric networks. Hydrogels possess a degree of flexibility very similar to tissue, due to their significant water content. The first appearance of the term hydrogel in the literature was in 1894, common uses for hydrogels include, Scaffolds in tissue engineering. When used as scaffolds, hydrogels may contain human cells to repair tissue and they mimic 3D microenvironment of cells. Hydrogel-coated wells have been used for cell culture Environmentally sensitive hydrogels and these hydrogels have the ability to sense changes of pH, temperature, or the concentration of metabolite and release their load as result of such a change.
Wound gels are excellent for helping to create or maintain a moist environment, reservoirs in topical drug delivery, particularly ionic drugs, delivered by iontophoresis. Natural hydrogel materials are being investigated for tissue engineering, these materials include agarose, hyaluronan, an organogel is a non-crystalline, non-glassy thermoreversible solid material composed of a liquid organic phase entrapped in a three-dimensionally cross-linked network. The liquid can be, for example, a solvent, mineral oil. The solubility and particle dimensions of the structurant are important characteristics for the elastic properties, these systems are based on self-assembly of the structurant molecules. Organogels have potential for use in a number of applications, such as in pharmaceuticals, art conservation, a xerogel /ˈzɪəroʊˌdʒɛl/ is a solid formed from a gel by drying with unhindered shrinkage
Amorphous silicon is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCD displays. Used as semiconductor material for solar cells, or thin-film silicon solar cells, it is deposited in thin films onto a variety of flexible substrates, such as glass, metal. Amorphous silicon differs from other variations, such as monocrystalline silicon—a single crystal, and polycrystalline silicon. Silicon is a fourfold coordinated atom that is normally tetrahedrally bonded to four neighboring silicon atoms, in crystalline silicon this tetrahedral structure continues over a large range, thus forming a well-ordered crystal lattice. In amorphous silicon this long range order is not present, the atoms form a continuous random network. Moreover, not all the atoms within amorphous silicon are fourfold coordinated, due to the disordered nature of the material some atoms have a dangling bond. Physically, these dangling bonds represent defects in the random network. The material can be passivated by hydrogen, which bonds to the dangling bonds, hydrogenated amorphous silicon has a sufficiently low amount of defects to be used within devices such as solar photovoltaic cells, particularly in the protocrystalline growth regime.
However, hydrogenation is associated with light-induced degradation of the material, amorphous alloys of silicon and carbon are an interesting variant. Introduction of carbon atoms adds extra degrees of freedom for control of the properties of the material, the film could be made transparent to visible light. Increasing concentrations of carbon in the alloy widen the gap between conduction and valence bands. This can potentially increase the efficiency of solar cells made with amorphous silicon carbide layers. On the other hand, the properties as a semiconductor, are adversely affected by the increasing content of carbon in the alloy. The density of amorphous Si has been calculated as 4. 90×1022 atom/cm3 at 300 K and this was done using thin strips of amorphous silicon. This density is 1. 8±0. 1% less dense than crystalline Si at 300 K, Silicon is one of the few elements that expands upon cooling and has a lower density as a solid than as a liquid. By introducing hydrogen during the fabrication of amorphous silicon, photoconductivity is significantly improved, hydrogenated amorphous silicon, a-Si, H, was first fabricated in 1969 by Chittick and Sterling by deposition using a silane gas precursor.
The resulting material showed a lower density and increased conductivity due to impurities. Interest in a-Si, H came when, LeComber and Spear discovered the ability for substitutional doping of a-Si, starting in the 1970s, a-Si, H was developed in solar cells by RCA by which steadily climbed in efficiency to about 13. 6% in 2015
A crystal or crystalline solid is a solid material whose constituents are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, the scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification, the word crystal derives from the Ancient Greek word κρύσταλλος, meaning both ice and rock crystal, from κρύος, icy cold, frost. Examples of large crystals include snowflakes and table salt, most inorganic solids are not crystals but polycrystals, i. e. many microscopic crystals fused together into a single solid. Examples of polycrystals include most metals, ceramics, a third category of solids is amorphous solids, where the atoms have no periodic structure whatsoever. Examples of amorphous solids include glass and many plastics, Crystals are often used in pseudoscientific practices such as crystal therapy, along with gemstones, are sometimes associated with spellwork in Wiccan beliefs and related religious movements.
The scientific definition of a crystal is based on the arrangement of atoms inside it. A crystal is a solid where the form a periodic arrangement. For example, when liquid water starts freezing, the change begins with small ice crystals that grow until they fuse. Most macroscopic inorganic solids are polycrystalline, including almost all metals, ice, solids that are neither crystalline nor polycrystalline, such as glass, are called amorphous solids, called glassy, vitreous, or noncrystalline. These have no periodic order, even microscopically, there are distinct differences between crystalline solids and amorphous solids, most notably, the process of forming a glass does not release the latent heat of fusion, but forming a crystal does. A crystal structure is characterized by its cell, a small imaginary box containing one or more atoms in a specific spatial arrangement. The unit cells are stacked in three-dimensional space to form the crystal, the symmetry of a crystal is constrained by the requirement that the unit cells stack perfectly with no gaps.
There are 219 possible crystal symmetries, called space groups. These are grouped into 7 crystal systems, such as cubic crystal system or hexagonal crystal system, Crystals are commonly recognized by their shape, consisting of flat faces with sharp angles. Euhedral crystals are those with obvious, well-formed flat faces, anhedral crystals do not, usually because the crystal is one grain in a polycrystalline solid. The flat faces of a crystal are oriented in a specific way relative to the underlying atomic arrangement of the crystal. This occurs because some surface orientations are more stable than others, as a crystal grows, new atoms attach easily to the rougher and less stable parts of the surface, but less easily to the flat, stable surfaces
An amorphous metal is a solid metallic material, usually an alloy, with a disordered atomic-scale structure. Most metals are crystalline in their state, which means they have a highly ordered arrangement of atoms. Amorphous metals are non-crystalline, and have a glass-like structure, but unlike common glasses, such as window glass, which are typically electrical insulators, amorphous metals have good electrical conductivity. There are several ways in which amorphous metals can be produced, including extremely rapid cooling, physical vapor deposition, solid-state reaction, ion irradiation, in the past, small batches of amorphous metals have been produced through a variety of quick-cooling methods. For instance, amorphous metal ribbons have been produced by sputtering molten metal onto a metal disk. The rapid cooling, on the order of millions of degrees a second, is too fast for crystals to form and the material is locked in a glassy state. More recently a number of alloys with critical cooling rates low enough to allow formation of structure in thick layers have been produced.
More recently, batches of amorphous steel with three times the strength of steel alloys have been produced. The first reported metallic glass was an alloy produced at Caltech by W. Klement and this and other early glass-forming alloys had to be cooled extremely rapidly to avoid crystallization. As a result, metallic glass specimens were limited to thicknesses of less than one hundred micrometers, in 1969, an alloy of 77. 5% palladium, 6% copper, and 16. 5% silicon was found to have critical cooling rate between 100 and 1000 K/s. In 1976, H. Liebermann and C, graham developed a new method of manufacturing thin ribbons of amorphous metal on a supercooled fast-spinning wheel. This was an alloy of iron, nickel and boron, the material, known as Metglas, was commercialized in the early 1980s and is used for low-loss power distribution transformers. Metglas-2605 is composed of 80% iron and 20% boron, has Curie temperature of 373 °C and a room temperature saturation magnetization of 1.56 teslas. In the early 1980s, glassy ingots with 5 mm diameter were produced from the alloy of 55% palladium,22. 5% lead, using boron oxide flux, the achievable thickness was increased to a centimeter.
In 1988, alloys of lanthanum and copper ore were found to be highly glass-forming, al-based metallic glasses containing Scandium exhibited a record-type tensile mechanical strength of about 1500 MPa. In the 1990s new alloys were developed that form glasses at cooling rates as low as one kelvin per second and these cooling rates can be achieved by simple casting into metallic molds. These bulk amorphous alloys can be cast into parts of up to several centimeters in thickness while retaining an amorphous structure, the best glass-forming alloys are based on zirconium and palladium, but alloys based on iron, copper and other metals are known. Many amorphous alloys are formed by exploiting a phenomenon called the confusion effect, in this way, the random disordered state of the atoms is locked in
The interdisciplinary field of materials science, commonly termed materials science and engineering, involves the discovery and design of new materials, with an emphasis on solids. Materials science still incorporates elements of physics and engineering, as such, the field was long considered by academic institutions as a sub-field of these related fields. Materials science is a syncretic discipline hybridizing metallurgy, solid-state physics and it is the first example of a new academic discipline emerging by fusion rather than fission. Many of the most pressing scientific problems humans currently face are due to the limits of the materials that are available, breakthroughs in materials science are likely to affect the future of technology significantly. Materials scientists emphasize understanding how the history of a material influences its structure, the understanding of processing-structure-properties relationships is called the § materials paradigm. This paradigm is used to advance understanding in a variety of areas, including nanotechnology, biomaterials.
Such investigations are key to understanding, for example, the causes of various accidents and incidents. The material of choice of a given era is often a defining point, phrases such as Stone Age, Bronze Age, Iron Age, and Steel Age are great examples. Originally deriving from the manufacture of ceramics and its putative derivative metallurgy, materials science is one of the oldest forms of engineering, modern materials science evolved directly from metallurgy, which itself evolved from mining and ceramics and the use of fire. Materials science has driven, and been driven by, the development of technologies such as rubbers, semiconductors. Before the 1960s, many materials science departments were named metallurgy departments, reflecting the 19th, a material is defined as a substance that is intended to be used for certain applications. There are a myriad of materials around us—they can be found in anything from buildings to spacecraft, Materials can generally be divided into two classes and non-crystalline.
The traditional examples of materials are metals, ceramics and advanced materials that are being developed include nanomaterials and biomaterials, etc. The basis of science involves studying the structure of materials. Once a materials scientist knows about this structure-property correlation, they can go on to study the relative performance of a material in a given application. The major determinants of the structure of a material and thus of its properties are its constituent chemical elements and these characteristics, taken together and related through the laws of thermodynamics and kinetics, govern a materials microstructure, and thus its properties. As mentioned above, structure is one of the most important components of the field of materials science, Materials science examines the structure of materials from the atomic scale, all the way up to the macro scale. Characterization is the way materials scientists examine the structure of a material, structure is studied at various levels, as detailed below
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a constant volume independent of pressure. As such, it is one of the four states of matter. A liquid is made up of tiny vibrating particles of matter, such as atoms, water is, by far, the most common liquid on Earth. Like a gas, a liquid is able to flow and take the shape of a container, most liquids resist compression, although others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, a distinctive property of the liquid state is surface tension, leading to wetting phenomena. The density of a liquid is usually close to that of a solid, therefore and solid are both termed condensed matter. On the other hand, as liquids and gases share the ability to flow, although liquid water is abundant on Earth, this state of matter is actually the least common in the known universe, because liquids require a relatively narrow temperature/pressure range to exist. Most known matter in the universe is in form as interstellar clouds or in plasma form within stars.
Liquid is one of the four states of matter, with the others being solid, gas. Unlike a solid, the molecules in a liquid have a greater freedom to move. The forces that bind the molecules together in a solid are only temporary in a liquid, a liquid, like a gas, displays the properties of a fluid. A liquid can flow, assume the shape of a container, if liquid is placed in a bag, it can be squeezed into any shape. These properties make a suitable for applications such as hydraulics. Liquid particles are bound firmly but not rigidly and they are able to move around one another freely, resulting in a limited degree of particle mobility. As the temperature increases, the vibrations of the molecules causes distances between the molecules to increase. When a liquid reaches its point, the cohesive forces that bind the molecules closely together break. If the temperature is decreased, the distances between the molecules become smaller, only two elements are liquid at standard conditions for temperature and pressure and bromine.
Four more elements have melting points slightly above room temperature, caesium and rubidium, metal alloys that are liquid at room temperature include NaK, a sodium-potassium metal alloy, galinstan, a fusible alloy liquid, and some amalgams
An amorphous solid that exhibits a glass transition is called a glass. The reverse transition, achieved by supercooling a viscous liquid into the state, is called vitrification. The glass-transition temperature Tg of a material characterizes the range of temperatures over which this transition occurs. It is always lower than the temperature, Tm, of the crystalline state of the material. Hard plastics like polystyrene and poly are used well below their glass transition temperatures, such conventions include a constant cooling rate and a viscosity threshold of 1012 Pa·s, among others. The question of whether some phase transition underlies the glass transition is a matter of continuing research, the glass transition of a liquid to a solid-like state may occur with either cooling or compression. The transition comprises a smooth increase in the viscosity of a material by as much as 17 orders of magnitude without any pronounced change in material structure, the consequence of this dramatic increase is a glass exhibiting solid-like mechanical properties on the timescale of practical observation.
In many materials that undergo a freezing transition, rapid cooling will avoid this phase transition. Other materials, such as polymers, lack a well defined crystalline state and easily form glasses. The tendency for a material to form a glass while quenched is called glass forming ability and this ability depends on the composition of the material and can be predicted by the rigidity theory. Below the transition temperature range, the structure does not relax in accordance with the cooling rate used. The expansion coefficient for the state is roughly equivalent to that of the crystalline solid. If slower cooling rates are used, the time for structural relaxation to occur may result in a higher density glass product. Similarly, by annealing the glass structure in time approaches an equilibrium density corresponding to the liquid at this same temperature. Tg is located at the intersection between the curve for the glassy state and the supercooled liquid. The configuration of the glass in this range changes slowly with time towards the equilibrium structure.
The principle of the minimization of the Gibbs free energy provides the driving force necessary for the eventual change. It should be noted here that at higher temperatures than Tg