Names | |
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IUPAC name Platinum silicide | |
Identifiers | |
3D model (JSmol) | |
PubChem CID | |
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Properties | |
PtSi | |
Molar mass | 223.169 g·mol−1 |
Appearance | Orthorhombic crystals [1] |
Density | 12.4 g/cm3 [1] |
Melting point | 1,229 °C (2,244 °F; 1,502 K) [1] |
Structure | |
Orthorhombic [2] | |
Pnma (No. 62), oP8 | |
a = 0.5577 nm, b = 0.3587 nm, c = 0.5916 nm | |
Formula units (Z) | 4 |
Hazards | |
Flash point | Non-flammable |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Platinum silicide, also known as platinum monosilicide, is the inorganic compound with the formula PtSi. It is a semiconductor that turns into a superconductor when cooled to 0.8 K. [3]
The crystal structure of PtSi is orthorhombic, with each silicon atom having six neighboring platinum atoms. The distances between the silicon and the platinum neighbors are as follows: one at a distance of 2.41 angstroms, two at a distance of 2.43 angstroms, one at a distance of 2.52 angstroms, and the final two at a distance of 2.64 angstroms. Each platinum atom has six silicon neighbors at the same distances, as well as two platinum neighbors, at a distance of 2.87 and 2.90 angstroms. All of the distances over 2.50 angstroms are considered too far to really be involved in bonding interactions of the compound. As a result, it has been shown that two sets of covalent bonds compose the bonds forming the compound. One set is the three center Pt–Si–Pt bond, and the other set the two center Pt–Si bonds. Each silicon atom in the compound has one three center bond and two center bonds. The thinnest film of PtSi would consist of two alternating planes of atoms, a single sheet of orthorhombic structures. Thicker layers are formed by stacking pairs of the alternating sheets. The mechanism of bonding between PtSi is more similar to that of pure silicon than pure platinum or Pt2Si, though experimentation has revealed metallic bonding character in PtSi that pure silicon lacks. [4]
PtSi can be synthesized in several ways. The standard method involves depositing a thin film of pure platinum onto silicon wafers and heating in a conventional furnace at 450–600 °C for a half an hour in inert ambients. The process cannot be carried out in an oxygenated environment, as this results in the formation of an oxide layer on the silicon, preventing PtSi from forming. [5]
A secondary technique for synthesis requires a sputtered platinum film deposited on a silicon substrate. Due to the ease with which PtSi can become contaminated by oxygen, several variations of the methods have been reported. Rapid thermal processing has been shown to increase the purity of PtSi layers formed. [6] Lower temperatures (200–450 °C) were also found to be successful, [7] higher temperatures produce thicker PtSi layers, though temperatures in excess of 950 °C formed PtSi with increased resistivity due to clusters of large PtSi grains. [8]
Despite the synthesis method employed, PtSi forms in the same way. When pure platinum is first heated with silicon, Pt2Si is formed. Once all the available Pt and Si are used and the only available surfaces are Pt2Si, the silicide will begin the slower reaction of converting into PtSi. The activation energy for the Pt2Si reaction is around 1.38 eV, while it is 1.67 eV for PtSi.
Oxygen is extremely detrimental to the reaction, as it will bind preferably to Pt, limiting the sites available for Pt–Si bonding and preventing the silicide formation. A partial pressure of O2 as low at 10−7 has been found to be sufficient to slow the formation of the silicide. To avoid this issue inert ambients are used, as well as small annealing chambers to minimize amount of potential contamination. [5] The cleanliness of the metal film is also extremely important, and unclean conditions result in poor PtSi synthesis. [7]
In certain cases an oxide layer can be beneficial. When PtSi is used as a Schottky barrier, an oxide layer prevents wear of the PtSi. [5]
PtSi is a semiconductor and a Schottky barrier with high stability and good sensitivity, and can be used in infrared detection, thermal imaging, or ohmic and Schottky contacts. [9] Platinum silicide was most widely studied and used in the 1980s and 90s, but has become less commonly used, due to its low quantum efficiency. PtSi is now most commonly used in infrared detectors, due to the large size of wavelengths it can be used to detect. [10] It has also been used in detectors for infrared astronomy. It can operate with good stability up to 0.05 °C. Platinum silicide offers high uniformity of arrays imaged. The low cost and stability makes it suited for preventative maintenance and scientific infrared imaging.
Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, lead, and flerovium are below it. It is relatively unreactive.
A semiconductor is a material that has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity generally falls as its temperature rises; metals behave in the opposite way. Its conducting properties may be altered in useful ways by introducing impurities ("doping") into the crystal structure. When two differently doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers, which include electrons, ions, and electron holes, at these junctions is the basis of diodes, transistors, and most modern electronics. Some examples of semiconductors are silicon, germanium, gallium arsenide, and elements near the so-called "metalloid staircase" on the periodic table. After silicon, gallium arsenide is the second-most common semiconductor and is used in laser diodes, solar cells, microwave-frequency integrated circuits, and others. Silicon is a critical element for fabricating most electronic circuits.
Silane (Silicane) is an inorganic compound with chemical formula SiH4. It is a colourless, pyrophoric, toxic gas with a sharp, repulsive, pungent smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Silane with alkyl groups are effective water repellents for mineral surfaces such as concrete and masonry. Silanes with both organic and inorganic attachments are used as coupling agents. Silanes are commonly used to apply coatings to surfaces or as an adhesion promoter.
The Schottky diode, also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes.
In semiconductor production, doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties. The doped material is referred to as an extrinsic semiconductor.
Tungsten(VI) fluoride, also known as tungsten hexafluoride, is an inorganic compound with the formula WF6. It is a toxic, corrosive, colorless gas, with a density of about 13 kg/m3 (22 lb/cu yd). It is one of the densest known gases under standard conditions. WF6 is commonly used by the semiconductor industry to form tungsten films, through the process of chemical vapor deposition. This layer is used in a low-resistivity metallic "interconnect". It is one of seventeen known binary hexafluorides.
In chemistry, a dangling bond is an unsatisfied valence on an immobilized atom. An atom with a dangling bond is also referred to as an immobilized free radical or an immobilized radical, a reference to its structural and chemical similarity to a free radical.
Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There are a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or by various performance metrics, such as spectral response. Semiconductor-based photodetectors typically use a p–n junction that converts photons into charge. The absorbed photons make electron–hole pairs in the depletion region. Photodiodes and photo transistors are a few examples of photo detectors. Solar cells convert some of the light energy absorbed into electrical energy.
Indium antimonide (InSb) is a crystalline compound made from the elements indium (In) and antimony (Sb). It is a narrow-gap semiconductor material from the III-V group used in infrared detectors, including thermal imaging cameras, FLIR systems, infrared homing missile guidance systems, and in infrared astronomy. Indium antimonide detectors are sensitive to infrared wavelengths between 1 and 5 μm.
A silicide is a type of chemical compound that combines silicon and a usually more electropositive element.
Beryllium oxide (BeO), also known as beryllia, is an inorganic compound with the formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except diamond, and exceeds that of most metals. As an amorphous solid, beryllium oxide is white. Its high melting point leads to its use as a refractory material. It occurs in nature as the mineral bromellite. Historically and in materials science, beryllium oxide was called glucina or glucinium oxide, owing to its sweet taste.
An infrared detector is a detector that reacts to infrared (IR) radiation. The two main types of detectors are thermal and photonic (photodetectors).
Indium arsenide, InAs, or indium monoarsenide, is a narrow-bandgap semiconductor composed of indium and arsenic. It has the appearance of grey cubic crystals with a melting point of 942 °C.
An ohmic contact is a non-rectifying electrical junction: a junction between two conductors that has a linear current–voltage (I–V) curve as with Ohm's law. Low-resistance ohmic contacts are used to allow charge to flow easily in both directions between the two conductors, without blocking due to rectification or excess power dissipation due to voltage thresholds.
Silanes are saturated chemical compounds with the empirical formula SixHy. They are hydrosilanes, a class of compounds that includes compounds with Si−H and other Si−X bonds. All contain tetrahedral silicon and terminal hydrides. They only have Si−H and Si−Si single bonds. The bond lengths are 146.0 pm for a Si−H bond and 233 pm for a Si−Si bond. The structures of the silanes are analogues of the alkanes, starting with silane, SiH4, the analogue of methane, continuing with disilane Si2H6, the analogue of ethane, etc. They are mainly of theoretical or academic interest.
In solid-state physics, a metal–semiconductor (M–S) junction is a type of electrical junction in which a metal comes in close contact with a semiconductor material. It is the oldest practical semiconductor device. M–S junctions can either be rectifying or non-rectifying. The rectifying metal–semiconductor junction forms a Schottky barrier, making a device known as a Schottky diode, while the non-rectifying junction is called an ohmic contact.
Direct bonding, or fusion bonding, describes a wafer bonding process without any additional intermediate layers. The bonding process is based on chemical bonds between two surfaces of any material possible meeting numerous requirements. These requirements are specified for the wafer surface as sufficiently clean, flat and smooth. Otherwise unbonded areas so called voids, i.e. interface bubbles, can occur.
Chromium(II) silicide or chromium disilicide is an inorganic compound of chromium and silicon. Its chemical formula is CrSi2. It is a p-type thermoelectric semiconductor with an indirect bandgap of 0.35 eV.
Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.
Iron monosilicide (FeSi) is an intermetallic compound, a silicide of iron that occurs in nature as the rare mineral naquite. It is a narrow-bandgap semiconductor with a room-temperature electrical resistivity of around 10 kΩ·cm and unusual magnetic properties at low temperatures. FeSi has a cubic crystal lattice with no inversion center; therefore its magnetic structure is helical, with right-hand and left-handed chiralities.