Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.
Molybdenum disulfide is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is MoS
2.
In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The octahedron has eight faces, hence the prefix octa. The octahedron is one of the Platonic solids, although octahedral molecules typically have an atom in their centre and no bonds between the ligand atoms. A perfect octahedron belongs to the point group Oh. Examples of octahedral compounds are sulfur hexafluoride SF6 and molybdenum hexacarbonyl Mo(CO)6. The term "octahedral" is used somewhat loosely by chemists, focusing on the geometry of the bonds to the central atom and not considering differences among the ligands themselves. For example, [Co(NH3)6]3+, which is not octahedral in the mathematical sense due to the orientation of the N−H bonds, is referred to as octahedral.
A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for sulfides, selenides, tellurides, and polonides, rather than oxides. Many metal ores exist as chalcogenides. Photoconductive chalcogenide glasses are used in xerography. Some pigments and catalysts are also based on chalcogenides. The metal dichalcogenide MoS2 is a common solid lubricant.
Tungsten disulfide is an inorganic chemical compound composed of tungsten and sulfur with the chemical formula WS2. This compound is part of the group of materials called the transition metal dichalcogenides. It occurs naturally as the rare mineral tungstenite. This material is a component of certain catalysts used for hydrodesulfurization and hydrodenitrification.
Tantalum(IV) sulfide is an inorganic compound with the formula TaS2. It is a layered compound with three-coordinate sulfide centres and trigonal prismatic or octahedral metal centres. It is structurally similar to molybdenum disulfide MoS2, and numerous other transition metal dichalcogenide materials. The 1T-TaS2 polytype exhibits some unusual properties. In common with many other transition metal dichalcogenide (TMD) compounds, which are metallic at high temperatures, it exhibits a series of charge-density-wave (CDW) phase transitions at low temperatures. It is unusual amongst them in showing a low-temperature insulating state, which is believed to arise from electron correlations, similar to many oxides. The insulating state is commonly attributed to a Mott state. It is also superconducting under pressure or upon doping, with a familiar dome-like phase diagram as a function of dopant, or substituted isovalent element concentration. 1T-TaS2 is unique, not only amongst TMDs but also amongst 'quantum materials', in showing a metastable metallic state at low temperatures. Switching from the insulating to the metallic state can be achieved either optically or by the application of electrical pulses. The metallic state is persistent at low temperatures (below ~20K), but its lifetime can be tuned by changing the temperature. The metastable state lifetime can also be tuned by strain. The electrically-induced switching between states is of current interest, because it can be used for ultrafast energy-efficient memory devices. Because of the frustrated triangular arrangement of localized electrons, the material is suspected to behave as a quantum spin liquid. It has been the subject of numerous studies as a host for intercalation of electron donors.
A copper indium gallium selenide solar cell is a thin-film solar cell used to convert sunlight into electric power. It is manufactured by depositing a thin layer of copper, indium, gallium and selenium on glass or plastic backing, along with electrodes on the front and back to collect current. Because the material has a high absorption coefficient and strongly absorbs sunlight, a much thinner film is required than of other semiconductor materials.
Titanium diselenide (TiSe2) also known as titanium(IV) selenide, is an inorganic compound of titanium and selenium. In this material selenium is viewed as selenide (Se2−) which requires that titanium exists as Ti4+. Titanium diselenide is a member of metal dichalcogenides, compounds that consist of a metal and an element of the chalcogen column within the periodic table. Many exhibit properties of potential value in battery technology, such as intercalation and electrical conductivity, although most applications focus on the less toxic and lighter disulfides, e.g. TiS2.
Tungsten diselenide is an inorganic compound with the formula WSe2. The compound adopts a hexagonal crystalline structure similar to molybdenum disulfide. Every tungsten atom is covalently bonded to six selenium ligands in a trigonal prismatic coordination sphere while each selenium is bonded to three tungsten atoms in a pyramidal geometry. The tungsten–selenium bond has a length of 0.2526 nm, and the distance between selenium atoms is 0.334 nm. It is a well studied example of a layered material. The layers stack together via van der Waals interactions. WSe2 is a very stable semiconductor in the group-VI transition metal dichalcogenides.
Transition-metal dichalcogenide (TMD or TMDC) monolayers are atomically thin semiconductors of the type MX2, with M a transition-metal atom (Mo, W, etc.) and X a chalcogen atom (S, Se, or Te). One layer of M atoms is sandwiched between two layers of X atoms. They are part of the large family of so-called 2D materials, named so to emphasize their extraordinary thinness. For example, a MoS2 monolayer is only 6.5 Å thick. The key feature of these materials is the interaction of large atoms in the 2D structure as compared with first-row transition-metal dichalcogenides, e.g., WTe2 exhibits anomalous giant magnetoresistance and superconductivity.
A two-dimensional semiconductor is a type of natural semiconductor with thicknesses on the atomic scale. Geim and Novoselov et al. initiated the field in 2004 when they reported a new semiconducting material graphene, a flat monolayer of carbon atoms arranged in a 2D honeycomb lattice. A 2D monolayer semiconductor is significant because it exhibits stronger piezoelectric coupling than traditionally employed bulk forms. This coupling could enable applications. One research focus is on designing nanoelectronic components by the use of graphene as electrical conductor, hexagonal boron nitride as electrical insulator, and a transition metal dichalcogenide as semiconductor.
Molybdenum(IV) telluride, molybdenum ditelluride or just molybdenum telluride is a compound of molybdenum and tellurium with formula MoTe2, corresponding to a mass percentage of 27.32% molybdenum and 72.68% tellurium. It can crystallise in two dimensional sheets which can be thinned down to monolayers that are flexible and almost transparent. It is a semiconductor, and can fluoresce. It is part of a class of materials called transition metal dichalcogenides. As a semiconductor the band gap lies in the infrared region. This raises the potential use as a semiconductor in electronics or an infrared detector.
Platinum diselenide is a transition metal dichalcogenide with the formula PtSe2. It is a layered substance that can be split into layers down to three atoms thick. PtSe2 can behave as a metalloid or as a semiconductor depending on the thickness.
Niobium diselenide or niobium(IV) selenide is a layered transition metal dichalcogenide with formula NbSe2. Niobium diselenide is a lubricant, and a superconductor at temperatures below 7.2 K that exhibit a charge density wave (CDW). NbSe2 crystallizes in several related forms, and can be mechanically exfoliated into monatomic layers, similar to other transition metal dichalcogenide monolayers. Monolayer NbSe2 exhibits very different properties from the bulk material, such as of Ising superconductivity, quantum metallic state, and strong enhancement of the CDW.
Verbeekite is a rare mineral consisting of palladium diselenide PdSe2. This transition metal dichalcogenide has an unusual monoclinic structure, with pairs of selenium atoms existing as dimers forming layers between palladium atom sheets. Unit cell dimensions are: a = 6.710, b = 4.154, c = 8.914 Å, β = 92.42 °, V = 248.24 Å3. Palladium diselenide has five polymorphs. Verbeekite can be synthesised at 11.5 GPa pressure and 1300 °C.
Rhenium diselenide is an inorganic compound with the formula ReSe2. It has a layered structure where atoms are strongly bonded within each layer. The layers are held together by weak Van der Waals bonds, and can be easily peeled off from the bulk material.
Rhenium disulfide is an inorganic compound of rhenium and sulfur with the formula ReS2. It has a layered structure where atoms are strongly bonded within each layer. The layers are held together by weak Van der Waals bonds, and can be easily peeled off from the bulk material.
Two dimensional hexagonal boron nitride is a material of comparable structure to graphene with potential applications in e.g. photonics., fuel cells and as a substrate for two-dimensional heterostructures. 2D h-BN is isostructural to graphene, but where graphene is conductive, 2D h-BN is a wide-gap insulator.
Tantalum diselenide is a compound made with tantalum and selenium atoms, with chemical formula TaSe2, which belongs to the family of transition metal dichalcogenides. In contrast to molybdenum disulfide (MoS2) or rhenium disulfide (ReS2, tantalum diselenide does not occur spontaneously in nature, but it can be synthesized. Depending on the growth parameters, different types of crystal structures can be stabilized.
