Monthly Archives: January 2017

Zinc Oxide Nanoparticles

ZINC OXIDE (ZnO) NANOPARTICLES

Nanotechnology research has gained momentum in the recent years by providing innovative solutions in the field of biomedical, materials science, optics and electronics. Nanoparticles are essentially a varied form of basic elements derived by altering atomic and molecular properties of elements. This article elaborates on the properties and applications of zinc oxide nanoparticles. Zinc oxide (ZnO) nanopowders are available as powders and dispersions. These nanoparticles exhibit antibacterial, anti-corrosive, antifungal and UV filtering properties. Zinc is a Block D, Period 4 element while Oxygen is a Block P, Period 2 element. Some of the synonyms of zinc oxide nanoparticles are oxydatum, zinci oxicum, permanent white, ketozinc and oxozinc.

Zinc oxide (ZnO) nanoparticles have their own importance due to their vast area of applications, e.g. gas sensor, chemical sensor, bio-sensor, cosmetics, storage, optical and electrical devices window materials for displays, solar cells, and drug-delivery. ZnO is an attractive material for short-wavelength optoelectronic applications owing to its wide band gap 3.37 eV, large bond strength, and large exciton binding energy (60 meV) at room temperature. As a wide band gap material, ZnO is used in solid state blue to ultraviolet (UV) optoelectronics, including laser developments. In addition, due to its non-symmetric crystallographic phase ZnO shows the piezoelectric property, which is highly useful for the fabrication of devices, such as electromagnetic coupled sensors and actuators.

Zinc Oxide NPs Lite

Crystalline ZnO has a wurtzite (B4) crystal structure at ambient conditions. The ZnO wurtzite structure has a hexagonal unit cell with two lattice parameters a and c belongs to the space group of C4 6V or P63mc. Figure 1 clearly shows that the structure is composed of two interpenetrating hexagonal closed packed (hcp) sub lattices.

Zinc oxides nanoparticles show a pronounced biological activity. They are used both independently and in complexes with organic compounds. These nanoparticles are not only capable of inhibiting aggregation of colloid solutions and increase their stability but also can deliver medical preparations to the target location of pathological process. In particular, nanozinc has been used in nonorganic complexes with different chemical elements such as ZnS, ZnO etc.

Properties of Zinc oxide Nanoparticles

Nanosized particles of semiconductor materials have gained much more interest in recent years due to their desirable properties and applications in different areas such as catalysts, sensors, photoelectron devices, highly functional and effective devices. These nanomaterials have novel electronic, structural and thermal properties which are of high scientific interests in basic and applied fields.

Zinc oxide (ZnO) is a wide band gap semiconductor with an energy gap of 3.37 eV at room temperature. It has been used considerably for its catalytic, electrical, optoelectronic, and photochemical properties. ZnO nanostructures have a great advantage to apply in a catalytic reaction process due to their large surface area and high catalytic activity. Since zinc oxide shows different physical and chemical properties depending upon the morphology of nanostructures, by not only various synthesis methods but also the physical and chemical properties of synthesized zinc oxide are to be investigated in terms of its morphology.

Properties
Chemical Symbol ZnO
Molar Mass 81.40 g/mol
Melting Point 1975 °C
Boiling Point 2360 °C
Density 65600 kg/m3
Electronic config.  Zinc [Ar] 3d10 4s2
Oxygen [He] 2s2 2p4
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Applications of Zinc Oxide Nanoparticles

ZnO nanomaterials have been used as semiconductors in microelectronic devices and for accelerating degradation of water pollutants via photocatalytic activity. Due to its inherent ability to absorb UV irradiation and optical transparency, ZnO nanoparticles are used in the cosmetic industry, typically in sunscreens and facial creams. Their recognized antibacterial properties are also encouraging a variety of antimicrobial applications.

ZnO nanoparticles have gained interest in other biomedical applications based on their high stability, inherent photoluminescence properties which can be useful in biosensing applications, wide band-gap semiconductor properties useful in photo catalytic systems and promotion of reactive oxygen species generation.

ZnO nanoparticles have recently shown promising application as cholesterol biosensors, dietary modulators for hydrolase activity relevant to controlling diabetes and hyperlipaemia, as well as cell imaging. Additionally, ZnO nanoparticles are favourable in modulating allergic reactions via inhibition of mast cell degranulation. The diversity of these activities has popularized ZnO nanomaterials in interdisciplinary research communities involving physicists, chemists and biologists.

ZnO is nontoxic; it can be used as photocatalytic degradation materials of environmental pollutants. Bulk and thin films of ZnO have demonstrated high sensitivity for many toxic Gases. Researchers concluded that the potential use of ZnO nanoparticles for antibacterial activity. Extensive discussion was centered on the antibacterial activity of ZnO nanoparticles coupled with a number of influenced factors impacting the activity. Mainly, by improving factors like UV illumination, ZnO particle size, concentration, morphology, and surface modification, powerful antibacterial results would be obtained.

In addition to the above applications, i.e., gas sensors, chemical and biosensors, light emitting diodes, photo-detectors, and photo catalytic application, ZnO nanoparticles also exhibit tremendous UV-blocking properties. Generally, sunlight consists of three types of UV radiation, i.e., UV-A (320–400 nm), UV-B (290–320 nm), and UV-C (250–290 nm). Generally, to protect the skin, materials having UV-blocking properties are added to cosmetic formulations. For the protection of skin from UV-A radiation,

ZnO nanoparticles provided an effective UV-blocking material compared to TiO2. Generally, ZnO nanoparticles effectively absorb UV-A radiation rather than scatter it, but TiO2 usually scatters these wavelengths. Although ZnO absorption for UV-A radiation is good compared to TiO2, photocatalytic activity hinders its possible application in cosmetic formulations. In addition, due to the high photo catalytic activity of ZnO, reactive oxygen species are generated, which can oxidize ingredients involved in the cosmetic formulation.

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Titanium Dioxide Nanoparticles

Titanium Dioxide Nanoparticles

Titanium Dioxide Nanoparticles: Nanoparticles research presents wide scope for the development of novel solutions in the field of healthcare, cosmetics, optics and electronics. Altering their molecular and atomic states results in unexpected outcomes, which may not be possible by using the materials in their original states. This article deals with the properties and applications of titanium oxide nanoparticles.

Titanium Dioxide Nanoparticles

Titanium Dioxide Nanoparticles

TiO2 is available in the form of nanocrystals or nanodots having a high surface area. They exhibit magnetic properties. Titanium belongs to Block D, Period 4 while oxygen belongs to Block P, Period 2 of the periodic table. Titanium oxide is also known as flamenco, rutile, titanium dioxide and dioxotitanium. Titanium Dioxide nanoparticles are known for their ability to inhibit bacterial growth and prevent further formation of cell structures.

Nanoscale TiO2 that is manufactured for specific applications is by approximately a factor of 100 finer than the TiO2 pigments and has other physical properties. The production volume of nanoscale Titanium oxide amounts to less than 1 percent that of TiO2 pigments. Nanoscale titanium oxides are not used as food additives. Currently, they are mainly found in high-factor sun protection creams, textile fibers or wood preservatives. For a long time, sun creams have been manufactured adding titanium oxide micro particles that gave the products a pasty, sticky consistency. Leaving a visible film, application of such sun creams was not easy and not pleasing to the skin.

Titanium Dioxide Nanoparticles

Titanium Dioxide Nanoparticles

Sun creams that contain the transparent nanoscale TiO2 can be applied much more easily. In addition, their protective effect against harmful UV radiation is much better. At present, high sun protection factors can only be achieved using nanoscale TiO2. In recent years, metal oxide nanoparticles have attracted much attention by their potential application in diverse fields including catalysis, magnetic recording media, microelectronics and medicine. For example, TiO2 nanoparticles are very important due to their various applications like removing the environmental pollution, sterilization and restraining virus, defending UV, keep rust away, and de-pigment.

TiO2 is a multifaceted compound. TiO2 is also a potent photo catalyst that can break down almost any organic compound when exposed to sunlight, and a number of companies are seeking to capitalize on titanium oxide’s reactivity by developing a wide range of environmentally beneficial products, including self-cleaning fabrics, auto body finishes, and ceramic tiles. Also one development is a paving stone that uses the catalytic properties of TiO2 to remove nitrogen oxide from the air, breaking it down into more environmentally benign substances that can then be washed away by rainfall.

Properties of Titanium Dioxide:

Titanium dioxide mostly occurs together with other types of rock, thus must be separated from these. Ilmenite (FeTiO3) is one of the most well-known minerals. Different methods are used for refinement.

TiO2 is a highly insoluble thermally stable. Titanium source suitable for glass, optic and ceramic applications. Oxide compounds are not conductive to electricity. However, certain perovskite structured oxides are electronically conductive finding application in the cathode of solid oxide fuel cells and oxygen generation systems. They are compounds containing at least one oxygen anion and one metallic cation. They are typically insoluble in aqueous solutions (water) and extremely stable making them useful in ceramic structures as simple as producing clay bowls to advanced electronics in light weight structural components in aerospace and electrochemical applications such as fuel cells in which they exhibit ionic conductivity. Metal oxide compounds are basic anhydrides and can therefore react with acids as well as with strong reducing agents in redox reactions.

Properties
Chemical Symbol TiO2
Molar Mass 79.9378 g/mol
Melting Point 1843 ° C
Boiling Point 2972 ° C
Density 4.23 g/cm3
Electronic config. Titanium [Ar] 3d24s2
Oxygen [He] 2s22p4
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The great versatility of titanium dioxide is owing to its various forms and sizes. These oxides may be used in the form of micro scale pigments or as nano-objects. Their crystal structures may vary depending on the arrangement of TiO2 atoms, one differentiates between rutile and anatase modifications.

TiO2 is mostly used as white pigment because of its high diffraction index, strong light scattering, incident-light reflection capability and a high UV resistance that make TiO2 the standard pigment found in white dispersion paints with high hiding power. Since light scattering does not occur anymore in nanoscale particles, the white TiO2 pigments used are almost exclusively rutile modification particles with grain sizes in the micrometer range. These white pigments are not only found in paints and dyes but also in varnishes, plastics, paper and textiles.

Applications of Titanium Dioxide:

TiO2 involve removing the ripening hormone ethylene from areas where perishable fruits, vegetables, and cut flowers are stored. Also titanium dioxide nanoparticles are used for stripping organic pollutants such as trichloroethylene and methyl-tert-butyl ether from water and degrading toxins produced by blue green algae.

Titanium Dioxide Nanoparticles

Titanium Dioxide Nanoparticles

TiO2 is a well-known photo catalyst for water and air treatment as well as for catalytic production of gases. The general scheme for the photo catalytic destruction of organics begins with its excitation by supra band-gap photons and continues through redox reactions where OH-radicals, formed on the photo catalyst surface play a major role.

TiO2 is non-toxic and therefore is used in cosmetic products (sunscreens, lipsticks, body powder, soap, pearl essence pigments and tooth pastes) and also in special pharmaceutics. TiO2 is even used in food stuffs. TiO2 photo catalytic characteristics are greatly enhanced due to the advent of nanotechnology.

Titanium Dioxide Nanoparticles

Titanium Dioxide Nanoparticles

Photo catalytic Applications: Photo catalysis refers to the chemical reaction that occurs when light strikes a chemical compound that is light sensitive. When light strikes TiO2, a chemical reaction repeated in the immediate region and causes the breakdown of organic toxins, odors and more.

Environmental improvement applications: TiO2 remove environmental pollution substances, such as NOx emitted by exhaust gas etc. from the atmosphere.
Titanium Dioxide Nanoparticles

Pharmaceutical applications: Sterilization, restraining virus, TiO2 photo catalyst can destroy the membrane of cells, solid the proteins of viruses, restrain the virus activation and catching them. It kills bacteria’s up to 99.97%. TiO2 can kill coliform, green suppuration bacillus, golden grape coccus, mildew and suppuration fungus etc. The ability of sterilization can be tested through coliform and golden grape coccus.

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Titanium Nitride Nanoparticles Application

Titanium Nitride Nanoparticles Application

Titanium Nitride Nanoparticles Application: Nanoparticles research has become an area of interest to scientists due to the unexpected results produced by altering the atomic and molecular properties of elements. This article deals with the properties and applications of titanium nitride nanoparticles.

Titanium Nitride Nanoparticles Application

Titanium Nitride Nanoparticles

Titanium nitride (TiN) is available in coated, dispersed and ultra high purity forms. Their high hardness, high temperature chemical stability, high melting point, infrared absorption and UV shielding find a number of useful applications. Titanium belongs to Block D, Period 4 while nitrogen belongs to Block P, Period 2 of the periodic table. Some of the alternate names of titanium nitride are tinite, nitridotitanium and azanylidynetitanium. It is important to maintain dryness while storing these nanoparticles and also avoid any stress on them.

Titanium Nitride Nanoparticles Application

Titanium Nitride Nanoaprticles

Transition metal nitrides, especially titanium nitride (TiN), have been studied for the last three decades due to the unique combination of their material properties. Metallic behavior of TiN combined with its hardness and chemical stability has attracted attention in microelectronics research.

Titanium nitride (TiN) attracts attention due to its plasmonic resonance located in the visible and near-infrared range where important spectral regions such as biological transparency and telecommunication windows are present. Moreover, TiN provides superior material properties such as high melting temperature, corrosion resistance and bio-compatibility for real-world plasmonic applications. Recently, researchers have shown that TiN nanoparticles can provide comparable field enhancement and better absorption efficiency in the biological transparency window when compared to Au particles. Use of TiN for photo thermal therapy requires the availability of colloidal nanoparticles that exhibit plasmonic properties similar to optimized thin film samples. However, powder production of TiN for optical use has not been studied extensively.

PROPERTIES OF TITANIUM NITRIDE

Titanium nitride (TiN) films demonstrate excellent mechanical properties like hardness, high wear resistance and good chemical inertness. Mentioned films are also important for their biocompatibility, resistance against corrosion and reduction of the bacterial colonization. They offer many applications such as contact layers in semiconductors, anticorrosive, hardening coatings for tools and protective antireflective coatings for displays.

Titanium nitride is deposited by both physical and chemical vapor deposition techniques. Chemical vapor deposition from titanium tetrachloride and a nitrogen and hydrogen mixture is thermodynamically favorable at 850°C but temperatures above 1000°C and as high as 2000°C are generally used for durable machine tool coatings since this produces high quality very hard wearing TiN. However these conditions are too harsh to be applied to integrated circuits and limits coating applications on glass. Physical vapor deposition from Ti targets and nitrogen in argon produces high purity TiN on temperature sensitive substrates, such as those used in IC technology, but unsuitable for large area deposition.

Properties
Chemical Symbol TiN
Molar Mass 61.87 g/mol
Melting Point 2950 ° C
Crystal Phase Cubic
Density 4.23 g/cm3
Electronic config. Titanium [Ar] 3d24s2
Oxygen [He] 2s22p3
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APPLICATIONS OF TITANIUM NITRIDE NANOPOWDER

TiN is widely being used on wear surfaces like cutting tools to enhance life of cutting tools / wear surfaces. A coating of 1-4 microns are applied on the substrate in a vacuum chamber by vaporizing titanium directly from solid metal( high purity) to vapor stage (ion) & allowed to react with nitrogen, the high potential difference between substrate & cathode (Titanium rod) attracts the titanium ions on the substrate, where it reacts with nitrogen & forms TiN.

Thin layers of titanium nitride with a thickness in the range of a few micrometers are used for wear protection of tools. Layers with high nitrogen content, e.g. TiN1.0, give the coated parts a gold-like color. Titanium nitride powders with a particle size from nano to micrometers are used as additive in the production of wear-resistant sintered materials like hard metals, silicon nitride or cermets. Furthermore it is added to plastics, particularly to PET. TiN improves the thermal properties of the material and allows increasing the production output of PET bottles. According to the German Foods and Commodities Ordinance the addition of titanium nitride is limited to 20 mg TiN per kg PET. Pure TiN powers can be used to manufacture ceramic crucibles or evaporation boats in which metals are melted.

TiN are used in artificial limbs and for Barrier layer in contact and interconnect metallization. These nanoparticles are also used as Biological materials cutting tools, Gate electrode in metal-oxide-semiconductor (MOS) transistors, Low-barrier Schottky diode, Optical devices in aggressive environments and in Plastic molds.

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Titanium Carbide Nanoparticle

TITANIUM CARBIDE NANOPARTICLE (TiC)

Titanium Carbide Nanoparticle: Scientific research on nanoparticles has discovered the most unexpected behavior of elements by altering their atomic and molecular states. These unexpected properties have found a variety of applications in fields such as biomedicine, pharmaceuticals, electronics and optics etc. This article deals with the properties and applications of titanium carbide nanoparticles.

Titanium carbide, (TiC) is an extremely hard (Mohs 9-9.5) refractory ceramic material, similar to tungsten carbide. It has the appearance of black powder with the sodium chloride (face-centered cubic) crystal structure. It occurs in nature as a form of the very rare mineral khamrabaevite. Titanium carbide is used in preparation of cermets, which are frequently used to machine steel materials at high cutting speed. It is also used as an abrasion-resistant surface coating on metal parts, such as tool bits and watch mechanisms. Titanium carbide is also used as a heat shield coating for atmospheric entry of spacecraft.

Titanium Carbide Nanoparticle

Titanium Carbide Nanoparticle

Titanium carbide is a synthetic, super-hard, high-melting and heat-resistant material which is widely used for manufacturing metal-working tools, protective coatings and carbide steel. Producing nanoscale titanium carbide allows new applications including different types of composite materials.

Titanium carbide nanoparticles (nano-TiC) is a typical transition metal carbide, which shows not only small size, distribution uniformity, specific surface area and high surface activity, but also high thermal stability, antioxidation, strength, hardness, nice thermal conductivity, toughness, electrical conductivity, and so on. Because of its advantages, TiC has been widely applied in biosensors, methanol electro oxidation, super capacitor, direct fuel cells, energy-related applications and also in many other fields.

Titanium carbide nanoparticles possess high purity, narrow range particle size distribution and larger specific surface area. Also, nano TiC has a good conductivity and chemical inert ability as compared to steel and iron. Its melting point is about 3160 °C. TiC nanoparticles are an essential component of cemented carbide with high hardness, corrosion resistance, thermal stability, etc. Also, it is often used in manufacturing of wear-resistant materials, cutting tools, mold, metal melting crucible and many other fields.

Properties of Titanium carbide nanoparticles:

Titanium Carbide (TiC) Nanoparticles, nanodots or nanopowder are black spherical high surface area particles. Nanoscale Titanium Carbide Particles are typically 10 – 100 nanometers (nm) with specific surface area (SSA) in the 100 – 130 m2 /g range. Nano Titanium Carbide Particles are also available in passivated, high purity, coated and dispersed forms.

Properties
Chemical Symbol TiC
Molar Mass 59.89 g/mol
Melting Point 3160 °C
Boiling Point 4820 °C
Density 4.93 g/cm3
Electronic config. Titanium [Ar] 3d24s2
Carbon [He] 2s22p4

Titanium Carbide Nanoparticle: Applications

The application of nano materials in coating can improve the abrasion resistance, corrosion resistance and oxidative stability. A large amount of researches have proved that the application of silicon carbide nanopowder, Zirconium carbide nanoparticles, Titanium carbide nanopowder, Titanium nitride nanoparticles, Boron carbide nanopowder to the compound coating of metal can give super abrasion resistance and self-lubrication. Its abrasion resistance is 100 times higher than bearing steel, friction coefficient being 0.06~0.1, and meanwhile it is also equipped with high-temperature stability and abrasion resistance. The application of nano technology to the key parts of engineer of liquid rocket can largely lengthen the service life of these parts.

Nano TiC is used in manufacturing of wear-resistant materials like cutting tools, mold and metal melting crucible etc. Application of Nano TiC can be used in powder metallurgy industry to produce ceramics, hard alloy spare parts, drawing die and hard alloy mold. Also, Nano titanium carbide ceramic is a good optical material. TiC nanopowder coating can improve the alloy, abrasive steel bearings, nozzles, cutting tools wear resistance. Titanium carbide nanoparticles can be used in abrasive and mold industry to replace Aluminum oxide, silicon carbide, boride silicon and chromic oxide. Its grinding capacity is as good as artificial diamond. TiC is highly conductive in nature so it is also used to enhance the conductivity of materials and as a nucleating agent.

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Tin Selenide

TIN SELENIDE

Tin Selenide: Extensive attention has been paid in search of new semiconducting materials for efficient solar energy conversion. Metal chalcogenides offer a wide range of optical band gaps suitable for various optical and optoelectronic applications.

Tin Selenide

Tin Selenide

Tin Selenide: also known as stannous selenide, is an inorganic compound with the formula (SnSe), where Tin has a +2 oxidation state. Tin (II) selenide is a narrow band-gap (IV-VI) semiconductor and has received considerable interest for applications including low-cost photovoltaics and memory-switching devices. Tin (II) selenide is a typical layered metal chalcogenide; that is, it includes a Group 16 anion (Se2−) and an electropositive element (Sn2+), and it is arranged in a layered structure.

Tin (II) selenide exhibits low thermal conductivity as well as reasonable electrical conductivity, creating the possibility of it being used in thermoelectric materials. Metal selenides have attracted considerable attention due to their interesting properties and potential applications. Tin Selenide (SnSe), a member of group IV-VI semiconductors is one of the promising materials from its applications point of view. SnSe in bulk crystalline and thin film form has been used as memory switching devices, holographic recording systems, and infrared electronic devices.

The bulk properties of SnSe have been analyzed by several researchers and concluded that it belongs to the class of layered semiconductors. SnSe has direct band gap of about 1.2 eV and indirect band gap 1.30 eV. As SnSe has the energy gap of about 1.0 eV it may be utilized as an efficient material for solar energy conversion. Tin selenide (SnSe) is a p-type semiconductor having a narrow band gap (1–1.1 eV), whose constituent elements are abundant in nature and hence it is worth to investigate the development of this material for photovoltaic applications.

Researchers investigated a number of methods to prepare SnSe thin films and powder via brush plating, electro-deposition, spray pyrolysis, hot wall deposition, chemical vapor deposition, vacuum evaporation, chemical bath deposition, atomic layer deposition, laser ablation and D.C. Magnetron sputtering.

Tin Selenide

light-emitting-diodes-history

Tin Selenide (SnSe) is a narrow band gap, binary IV–VI semiconductor, suitable for various optoelectronic applications like memory switching devices, photovoltaic, light emitting devices (LED), and holographic recording systems. Tin selenide is a narrow band-gap (IV-VI) semiconductor and has received considerable interest for applications including low-cost photovoltaics and memory-switching devices.

Tin Selenide

PVPanels

Tin Selenide

Power Switching Devices watlow

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Silicon Wafers Application

Silicon Wafers Application

Silicon Wafers Application: Silicon is the second most common element on Earth and it is the seventh-most common element in the entire universe. It is the most common semi conductor and the most widely used in the electronic and technology sector. There are different silicon fabrication methods including the horizontal gradient freeze method, the horizontal Bridgeman method, the vertical Bridgeman method, the vertical gradient freeze and finally the Czochralski pulling method.

During the growth process to obtain the derived purity, different intentional dopants are added. These introduced impurities can change the electrical properties of the silicon, which can be useful depending on what the silicon is ultimately being produced for. Boron, aluminum, nitrogen, gallium and indium are just some of the silicon dopants that can be introduced during the growth process. Depending on what level the silicon has been doped, the semiconductor can be considered extrinsic or degenerate. Extrinsic would be lightly to moderately doped whereas degenerate semiconductors act more as conductors because of the high levels of doping that occurs during the fabrication.

Silicon Wafers Application

Silicon Wafers Application

Silicon Wafers Application: Silicon wafers are a key component in integrated circuits. Integrated circuits are, simply put, a composite of various electronic components that are arranged to perform a specific function. Silicon is the principle platform for semiconductor devices. A wafer is a thin slice of this semiconductor material, which serves as the substrate for microelectronic devices built in and over the wafer.

Types of Wafer Substrates

Single Element Semiconductors

Silicon, Si is the most common semiconductor having atomic number 14, energy gap Eg = 1.12 eV, indirect band gap; crystal structure-diamond, lattice constant-0.543 nm, thermal conductivity 1.31 W/cm-oC, melting point 1414 oC due to these properties ingle crystal Si can be processed into wafers up to 300 mm in diameter and having excellent mechanical properties in MEMS applications.

Silicon on Insulator (SOI)

Only a thin layer on the surface of a silicon wafer is used for making electronic components; the rest serves essentially as a mechanical support. The role of SOI is to electronically insulate a fine layer of monocrystalline silicon from the rest of the silicon wafer. Integrated circuits can then be fabricated on the top layer of the SOI wafers using the same processes as would be used on plain silicon wafers. The embedded layer of insulation enables the SOI-based chips to function at significantly higher speeds while reducing electrical losses. The result is an increase in performance and a reduction in power consumption. There are two types of SOI wafers. Thin film SOI wafers have a device layer 1.5 m.

Wafer bonding. – In this process the surface of two wafers are coated with an insulating layer (usually oxide). The insulating layers are then bonded together in a furnace creating one single wafer with a buried oxide layer (BOX) sandwiched between layers of semiconductor. The top of the wafer is then lapped and polished until a desired thickness of semiconductor above the BOX is achieved.

SIMOX – Separation by Implantation of Oxide. In this process a bulk semiconductor wafer is bombarded with oxygen ions, creating a layer of buried oxide. The thickness of intrinsic semiconductor above the box is determined by the ion energy. Anneal reinforces Si-O bonds in the BOX.

Smart Cut – The wafer bonding method is used to form the BOX, but instead of lapping off excess semiconductor (which is wasteful) a layer of hydrogen is implanted to a depth specifying the desired active layer of semiconductor. Anneal at ~500 oC splits the wafer along the stress plane created by the implanted hydrogen. The split wafer may then be reused to form other SIO wafers.

III-V Semiconductors

Silicon Wafers Application: Gallium Arsenide (GaAs): After silicon second the most common semiconductor is GaAs having energy gap Eg = 1.43 eV, direct band gap; crystal structure – zinc blend, thermal conductivity 0.46 W/cm-oC, thermally unstable above 600 oC. Due to evaporation they does not form sufficient quality native oxide and mechanically fragile. Due to direct band gap commonly used to fabricate light emitting devices. Because of higher electron and hole mobilities, use for the variety of high-speed electronic devices. The band gap can be readily engineered by forming ternary compounds based on GaAs, e.g. AlGaAs.

Gallium Nitride (GaN): The wide band gap of III-V semiconductor with direct bandgap 3.5 eV wide; among very few semiconductors capable of generating blue radiation. GaN is used for blue LEDs and lasers; intrinsically n-type semiconductor but can be doped p-type. GaN is formed as an epitaxial layer. The Lattice mismatch remains a problem, creating a high defect density. Incorporation of Indium (InxGa1-xN) allows control of emission from green to violet (high and low In content respectively). GaN can also be used in UV detectors that do not respond to visible light. GaN has a Wurtzite(W) or Zinc Blend(ZB) crystal structure

Gallium Phosphide (GaP): The properties of GaP like Crystal structure zinc blend; Lattice constant [A] 5.45; Density [g/cm3] 4.14; Melting point [oC] 1457, due to these properties of GaP the wafers are used in Semiconductor industry.

Other Binary Semiconductors

Silicon carbide (SiC): The semiconductor featuring energy gap Eg = 2.9 -3.05 eV (wide band gap semiconductor), indirect band gap; SiC can be obtained in several polytypes- most common hexagonal in the form of either 4H or 6H polytypes; parameters vary depending on polytype; Intrinsically n-doped; p-type doping and n-type conductivity control can be obtained by doping with aluminum and nitrogen respectively. SiC features higher than Si and GaAs electron saturation velocity; excellent semiconductor but difficult and expensive to fabricate single-crystal wafers; excellent for high power, high temperature applications; SiC is closely lattice matched to GaN, has a thermal expansion coefficient close to GaN, and is available in both conductive and semi-insulating substrates.

Fiber Optic

Silicon is the most economical IR material available. Both P-type and N-type substrates are acceptable for IR optics provided that they offer transmission greater than 50% in the 1.5 to 6 micron wavelength. Generally speaking, for N-type, the resistivity should be greater than 20 ohm-cm and, for P-type, greater than 40 ohm-cm. For use in the near IR, this is not so critical, but for applications for the far IR, resistivity can be critical.

Uses of Silicon Wafers

Silicon wafers primary use is in integrated circuits. Integrated circuits power many of the devices that modern society uses every day. Computers and smart phones are just two of the devices that are dependent on this technology. Although other semiconductors have been tested overtime, silicon has proved to be stable option. Other uses include sensors, such as the tire pressure sensor system, and solar cells. Silicon wafers absorb the photons in sunlight and this in turn creates electricity.

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Silicon Carbide Powder Application

Silicon Carbide Powder Application

Silicon Carbide Powder Application: Silicon Carbide is the only chemical compound of carbon and silicon. It was originally produced by a high temperature electro-chemical reaction of sand and carbon. Silicon carbide is an excellent abrasive and has been produced and made into grinding wheels and other abrasive products for over one hundred years. Today the material has been developed into a high quality technical grade ceramic with very good mechanical properties. It is used in abrasives, refractories, ceramics, and numerous high-performance applications. The material can also be made an electrical conductor and has applications in resistance heating, flame igniters and electronic components. Structural and wear applications are constantly developing.

Silicon Carbide Powder Application

Silicon Carbide Powder Application

Silicon carbide is composed of tetrahedral (structure) of carbon and silicon atoms with strong bonds in the crystal lattice. This produces a very hard and strong material. Silicon carbide is not attacked by any acids or alkalis or molten salts up to 800°C. In air, SiC forms a protective silicon oxide coating at 1200°C and is able to be used up to 1600°C. The high thermal conductivity coupled with low thermal expansion and high strength gives this material exceptional thermal shock resistant qualities. Silicon carbide ceramics with little or no grain boundary impurities maintain their strength to very high temperatures, approaching 1600°C with no strength loss. Chemical purity, resistance to chemical attack at temperature, and strength retention at high temperatures has made this material very popular as wafer tray supports and paddles in semiconductor furnaces.

Production of Silicon Carbide

SiC powders are produced predominantly via the traditional Acheson method where a reaction mixture of green petroleum coke and sand is heated to 2500°C using two large graphite electrodes. Due to the high temperatures, the Acheson process yields the alpha form of SiC, i.e. hexagonal or Rhombohedral (α-SiC). The SiC product, usually in the form of a large chunk, is broken, sorted, crushed, milled, and classified into different sizes to yield the commercial grades of SiC powder. To produce ultrafine SiC powder, the finest grade of the Acheson product is further milled, typically for days, and then acid-treated to remove metallic impurities. Fine SiC powder can also be produced using a mixture of fine powders of silica and carbon reacted at lower temperatures for short periods of time followed by quenching to prevent grain growth.

Silicon Carbide Powder Application

Silicon Carbide Powder Application

SiC fibers are produced via the pyrolysis of organosilicon polymers, such as polycarbosilane, and are commercially available. Briefly, the process consists of melt-spinning the polycarbosilane at approximately 300°C, unfusing with thermal oxidation at 110-200°C, and baking at 1000-1500°C under a flow of inert gas. Nicalon fibers are known for their excellent mechanical properties when used as reinforcement in ceramic matrix composites. (CMC). The drawback of Nicalon fibers has been their oxygen and free-carbon contents, which limit their high temperature applications. Recently, however, Hi-Nicalon SiC fibers have been introduced with much lower oxygen content. At present, much of the work in the SiC fiber reinforced CMC development is using Hi-Nicalon SiC fibers. Another method for producing SiC fibers is via the CVD method. In this process, SiC is deposited from the gas phase on a tungsten wire used as the substrate.

SiC whiskers, which are nearly single crystals, are produced (grown) using different methods, including the heating of coked rice hulls, reaction of silanes, reaction of silica and carbon, and the sublimation of SiC powder. In some cases a third element used as a catalyst, such as iron, is added to the reacting materials to facilitate the precipitation of the SiC crystals. In this arrangement, the mechanism for the SiC whisker growth is called the vapor liquid-solid (VLS) mechanism. SiC whiskers are in the order of microns in diameter and grow several hundred microns in length. Currently, commercially available SiC whiskers are produced using the rice-hull process with the whisker growth being largely of VLS mechanism due to the absence of a catalyst.

Properties of silicon carbide

Oxidation Resistance

In general, SiC has excellent oxidation resistance up to 1650°C. Oxidation resistance, however, depends largely on the amount of open porosity and particle size, which determine the surface area exposed to oxygen. The higher is the surface area the higher is the oxidation rate. Kinetically, SiC is stable in air up to ~1000°C.

Density and Porosity

Density, ρ, of a material is a measure of the mass, m, per unit volume, V, and is reported in units such as g/cm3, lb/in3, etc. Factors affecting the density include the size and atomic weight of the elements comprising the material, the tightness of packing of the atoms in the crystal structure, and the amount of porosity in the microstructure.

Porosity, which is occasionally reported along with density, is another important physical property used to indicate the amount of free space, i.e. not occupied by solid material. Porosity in general, open or closed, is very detrimental to the strength of the material, which is inversely exponentially proportional to the total porosity. Open porosity reduces the oxidation resistance of the non-oxide materials by allowing oxygen gas diffusion. In addition, a material with open porosity presents out gassing problems under high vacuum conditions. Therefore, it is very important to accurately measure total porosity and determine what percentage is open porosity.

Silicon Carbide Powder Application: Flexural Strength

The flexural strength is defined as a measure of the ultimate strength of a specified beam in bending. The beam is subjected to a load at a steady rate until rupture takes place. If the material is ductile, like most metals and alloys, the material bends prior to failure. On the other hand, if the material is brittle, such as ceramics and graphite, there would be a very slight bending followed by a catastrophic failure. There are two standard tests to determine the flexural strength of materials: the four-point test and the three-point test. In the four-point test, the specimen is symmetrically loaded at two locations that are situated one quarter of the overall span between two support spans. In the three-point test, the load is applied at the middle of the specimen between two support bearings.

Silicon Carbide Powder Application: Thermal Conductivity

Due to its high thermal conductivity, silicon carbide is a very attractive material for high temperature applications. From the device design point of view, the thermal conductivity of SiC exceeds that of Cu, BeO, Al2O3, and AlN. The thermal conductivity of SiC single crystal has been reported as high as 500 W/m⋅K. However, most commercial SiC grades have thermal conductivity in the range 50-120 W/m⋅K. The high thermal conductivity of other commercial SiC products, such as POCO’s SUPERSiC, is attributed to the absence of thermal-conduction-inhibiting impurities on the crystal grain boundaries. Basically, SUPERSiC is a continuous phase of SiC with no obvious grain boundaries.

Silicon Carbide Powder Application

There are many uses of Silicon Carbide in different industries. Its physical hardness makes it ideal to be used in abrasive machining processes like grinding, honing, sand blasting and water jet cutting.

The ability of Silicon Carbide to withstand very high temperatures without breaking or distorting is used in the manufacture of ceramic brake discs for sports cars. It is also used in bulletproof vests as an armor material and as a seal ring material for pump shaft sealing where it frequently runs at high speed in contact with a similar silicon carbide seal. One of the major advantages in these applications being the high thermal conductivity of Silicon Carbide which is able to dissipate the frictional heat generated at a rubbing interface.

The high surface hardness of the material lead to it being used in many engineering applications, in which high degree of sliding, erosive and corrosive wear resistance is required. Typically this can be in components used in pumps or for example as valves in oilfield applications where conventional metal components would display excessive wear rates that would lead to rapid failures.

Silicon Carbide Powder Application

Silicon

The unique electrical properties of the compound as a semiconductor make it ideal for manufacturing ultra fast and high voltage light emitting diodes, MOSFETs and thyristors for high power switching.

Silicon Carbide Powder Application

The material’s low thermal expansion coefficient, hardness, rigidity and thermal conductivity make it an ideal mirror material for astronomical telescopes. Silicon Carbide fibers, known as filaments are used to measure gas temperatures in an optical technique called thin filament pyrometry.

It is also used in heating elements where extremely high temperatures need to be accommodated. It is even used in nuclear power to provide structural supports in high temperature gas cooled reactors.

Silicon CarbideContact Us for Silicon Carbide Powder
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Platinum Nanopowder

PLATINUM NANOPOWDER

Platinum Nanopowder: Nanoparticles are significant scientific tools that are being explored in various technological and pharmacological fields. They are a link between larger materials and molecular or atomic structures. They are unique because of their large surface area. Platinum is one of the rarest and most expensive metals. It has high corrosion resistance and numerous catalytic applications including automotive catalytic converters and petrochemical cracking catalysts. Platinum nanoparticles are usually used in the form of colloid or suspension in a fluid. They are the subject of extensive research due to their antioxidant properties.

Platinum Nanopowder: Metal nanoparticles (MNPs), in particular, platinum nanoparticles (PtNps) can possess a wide range of properties that can be used for many practical applications. Nanostructured materials show much interdisciplinary applications. Both chemical and physical properties was found to be fruitful and, in many cases, fascinating in this nanosize range. MNPs are of interest due to their special properties in many aspects, such as catalysis and applications in optical devices.

Platinum Nanopowder

Platinum Nanopowder

Platinum Nanopowder: Due to potential technological interests of PtNps, the study and synthesis of nanoparticles was a very active field of research during last year’s. Platinum- containing films could be used for enzyme immobilization, optical applications, and catalytic activity. For instance, the enhanced catalytic activity of PtNps plays an important role in the reduction of pollutant gases exhausted from automobiles. Particularly, these studies of nanostructured materials show a strong dependence of their properties on size and shape.

The chemical method is relatively easy and inexpensive, with some difficulties to place and align the resulting nanostructures in desired configurations or patterns. Pt metal nanoparticles have been usually prepared by impregnation and reduction of Pt metal precursors in a micro porous support.

The stability of PtNps is of great importance to the development of efficient and durable proton exchange membrane fuel cells and the coalescence of PtNps is responsible for a reduction in the electrochemically active surface area that reduces cell performance. Furthermore, PtNps is used widely in the electronics industry for the manufacturing of conductive thick film circuits and internal electrodes of multilayer ceramic capacitors.

PROPERTIES OF PLATINUM NANOPARTICLES

Many physical and chemical properties of modern materials for electronics, optics, chemical re- actions, and other high-tech applications depend closely on the manufacturing process. Synthesis and processing of MNPs pose a number of difficulties, especially in terms of reactivity and agglomeration. The remarkable reactivity of MNPs, which makes them potential candidates, as catalysts, is associated to their high fraction of surface atoms as compared to conventional bulk materials.

Properties
Chemical Symbol Pt
Molar Mass 195.08 g/mol
Melting Point 1772 ° C
Boiling Point  3827 ° C
Density 21.45 g/cm3
Electronic config. [Xe]4f145d96s1

Catalytic Properties

Platinum NPs are used as catalysts for proton exchange membrane fuel cell (PEMFC), for industrial synthesis of nitric acid, reduction of exhaust gases from vehicles and as catalytic nucleating agents for synthesis of magnetic NPs. NPs can act as catalysts in homogeneous colloidal solution or as gas-phase catalysts while supported on solid state material. The catalytic reactivity of the NP is dependent on the shape, size and morphology of the particle.

One type of platinum NPs that have been researched on are colloidal platinum NPs. Monometallic and bimetallic colloids have been used as catalysts in a wide range of organic chemistry, including, oxidation of carbon monoxide in aqueous solutions, hydrogenation of alkenes in organic or biphasic solutions and hydrosilylation of olefins in organic solutions. Colloidal platinum NPs protected by Poly (N-isopropylacrylamide) was synthesized and their catalytic properties measured. It was determined that they were more active in solution and inactive when phase separated due to its solubility being inversely proportional to temperature.

Optical Properties

Platinum NPs exhibit fascinating optical properties. Being a free electron metal NP like silver and gold, its linear optical response is mainly controlled by the surface plasmon resonance. Surface plasmon resonance occurs when the electrons in the metal surface are subject to an electromagnetic field that exerts a force on the electrons and cause them to displace from their original positions.

Platinum Nanopowder: APPLICATIONS

Hydrogen fuel cells

Among the precious metals, platinum is the most active toward the hydrogen oxidation reaction that occurs at the anode in hydrogen fuel cells. In order to meet cost reductions of this magnitude, the Pt catalyst loading must be decreased. Two strategies have been investigated for reducing the Pt loading: the binary and ternary Pt-based alloyed nanomaterials and the dispersion of Pt-based nanomaterials onto high surface area substrates.

Methanol fuel cells

The methanol oxidation reaction occurs at the anode in direct methanol fuel cells (DMFCs). Platinum is the most promising candidate among pure metals for application in DMFCs. Platinum has the highest activity toward the dissociative adsorption of methanol. However, pure Pt surfaces are poisoned by carbon monoxide, a byproduct of methanol oxidation. Researchers have focused on dispersing nanostructured catalysts on high surface area supporting materials and the development of Pt-based nanomaterials with high electro catalytic activity toward MOR to overcome the poisoning effect of CO.

Drug Delivery

A topic of research within the field of nanoparticles is how to use these small particles for drug delivery. Depending on particle properties, nanoparticles may move throughout the human body are promising as site-specific vehicles for the transport of medicine.

Current research using platinum nanoparticles in drug delivery uses platinum-based carries to move antitumor medicine. In one study, platinum nanoparticles of diameter 58.3 nm were used to transport an anticancer drug to human colon carcinoma cells, HT-29. Uptake of the nanoparticles by the cell involves compartmentalization of the nanoparticles within lysosomes. The high acidity environment enables leaching of platinum ions from the nanoparticles, which the researchers identified as causing the increased effectiveness of the drug.

In another study, Pt nanoparticles of diameter 140 nm was encapsulated within a PEG nanoparticles to move an antitumor drug, Cisplatin, within a prostate cancer cell (LNCaP/PC3) population. Use of platinum in drug delivery hinges on its ability to not interact in a harmful manner in healthy portions of the body while also being able to release its contents when in the correct environment.

Platinum Nanopowder


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Gold Tin Solder Paste

Gold Tin Solder Paste Application

Gold Tin Solder Paste Application: Soldering is an important technique in the assembly of electronic products. To make a sound solder joint, the choice of solder materials is very important. Solder ability, melting point, strength, Young’s modulus, thermal expansion coefficient, thermal fatigue, creep properties and creep resistance will affect the quality of a solder joint.

Solders are generally described as fusible alloys with liquidus temperature below 400° C (750°F). The elements commonly used in solder alloys are tin (Sn), lead (Pb), silver (Ag), bismuth (Bi), indium (In), antimony (Sb) and cadmium (Cd). In addition to tin-lead alloys, binary solder alloys include tin-silver, tin-antimony, tin-indium, tin-bismuth, lead-indium and lead-bismuth. Ternary alloys include tin-lead-silver, tin-lead-bismuth and tin-lead-indium.

Gold Tin Solder Paste Application

Gold Tin Solder Paste Application

Gold-tin solder paste is used in a variety of high-reliability applications, where its high melting point, non-creep, high-tensile stress, thermal and electrical conductivity, as well as proven usage life makes it a standard “known-good” material.

Nanoshel Gold Tin solder paste is formulated for automated high-speed, high-reliability, single or multi point dispensing equipment. It also functions well in hand-held applications. Highly accurate volumes can be dispensed using either pneumatic or positive displacement devices. Optimal dispensing performance is dependent on storage conditions, equipment type, and set up.

Nanoshel Gold Tin solder paste (80Au/20Sn) has a melting point of 280°C (556°F). It can be made into solder paste form with various options to address specific applications. Gold-tin solder paste is generally used in applications that require a high melting temperature (over 150°C), good thermal fatigue properties and high temperature strength. It is also used in applications that require a high tensile strength and high corrosive resistance or in step soldering applications where the paste will not melt during a subsequent low-temperature reflux process. For these reasons, Nanoshel Au/Sn solder paste is widely used in military, aerospace and medical applications.

PROPERTIES OF GOLD TIN SOLDER PASTE

Some principal physical properties of Au/Sn solder paste are in table, by which the advantages of Au/Sn solder could be identified as follows:

Properties
Density 14.7 g.cm-3
Coefficient of thermal expansion 16×10-6 /° C
Thermal Conductivity 57 W.m-1K -1
Tensile Strength 275 MPa
Young’s modulus 68 GPa
Shear Modulus 25 GPa
Poisson’s ration 0.405
Electrical resistivity 16.4 × 10-8 Ω.m
Elongation 2 %

The alloy has high yield strength at ambient temperature and even at assembly temperatures of 250-260 °C, it is still strong enough to maintain hermeticity. Material strength is comparable to that of high temperature brazing materials, but with the benefit of much lower processing temperatures.

Good wet ability; meanwhile, due to similar compositions, Au/Sn solder has a good compatibility with Au metallization due to low leaching rate to thin Au coatings; no migration problems like Ag etc.

Low viscosity; the alloy has low enough viscosity in liquid form that it can fill large gaps. In addition, Au/Sn solder has high corrosion creep resistances good thermal and electrical conductivities. The disadvantages of Au/Sn solder include high cost, brittleness, low elongation and difficult to process.

Gold Tin Solder Paste Application: Au/Sn SOLDER PASTE

Nanoshel Au/Sn eutectic alloy has a melting temperature of 280°C high strength, Flux less, high thermal and electrical conductivity, good wet ability, low viscosity, good solder ability, high corrosion and creep resistance. It has been widely used in the applications in lid sealing and component attachment of ceramic packaging for microelectronic and optoelectronic components Au/Sn can dramatically increase the reliability and thermal/electrical conductivity for the packaging of these components.

Au/Sn Solder paste is used in die bonding (high brightness LEDs, peltier elements and power semiconductors) for vehicle installations, lightings, thermoelectric exchange modules and others. Also in sealing (crystal devices and SAW devices) for mobile communications, base stations, MEMS sensors and others.

Since eutectic Au/Sn has a much higher melting point than Sn96.5Ag3.5 solder (280 °C versus 221 °C), it is incompatible with the organic materials widely used with electronic packaging. However, many high-reliability solder applications exist where the unique combination of mechanical and thermal requirements make eutectic Au/Sn the optimal choice. These applications include, but are by no means limited to, lid sealing, RF and DC feed-through attach on optoelectronic packaging, and laser diode die attach.

Au/Sn solder must be applied properly to get good joining results. The main effects to the joints quality include: Au/Sn solder composition, surface quality of work pieces and preforms (for instance, oxides, contamination and flatness, etc.), processing conditions (like furnace temperature profile, peak temperature, forming gas and tools).

As a hard solder alloy, the alloy also becomes very attractive to flip-chip bonding where the active area of the device is next to sub mount. In this case, a solder alloy like Au/Sn with good thermal and electrical conductivities is particularly needed. Au/Sn performs also have applications in microwave systems assembly and other fields. With the superior properties of Au/Sn and the advantages of using preforms, Au/Sn will become more popular and even necessary in packaging applications

Gold Tin Solder Paste Application


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From us, you can easily purchase Gold Tin Solder Paste Application at great prices. Place online order and we will dispatch your order through DHL, FedEx, UPS. You can also request for a quote by mailing us at sales@nanoshel.com Contact: +1 302 268 6163 (US and Europe), Contact: +91-9779550077 (India). We invite you to contact us for further information about our company and our capabilities. At Nanoshel, we could be glad to be of service to you. We look forward to your suggestions and feedback.


Functionalized Multiwalled Carbon Nanotubes

Functionalized Multiwalled Carbon Nanotubes

Functionalized Multiwalled Carbon Nanotubes (MWCNTs) are made of many graphene layers and the diameter can be up to 100 nm. Two main models describe MWCNTs: (i) the Russian doll model or coaxial cylindrically curved model in which many graphene layers are rolled up and arranged in a cylindrical fashion, and (ii) the parchment model in which a single graphene layer is scrolled as a parchment (Figure 5a and c respectively). A further evolution of the coaxial cylindrically curved model is the coaxial cylindrically poligonized.

Functionalized Multiwalled Carbon Nanotubes

Functionalized Multiwalled Carbon Nanotubes

The electronic structure of a MWCNT is considered as the sum of the electronic structures of the constituent nanotubes. Thereby, we state that in the limit of the large nanotube diameter, all the nanotubes properties correspond to those of graphite. The interlayer distance in MWCNTs is equal to the interlayer distance in graphite (3.35 Å). These interactions are not sufficient to correlate the chirality of near tubes and MWCNTs are a mix of achiral shells. The result is that the lattice structures of the inner and outer layers are generally incommensurate.

Functionalized Multiwalled Carbon Nanotubes

Functionalized Multiwalled Carbon Nanotubes

Solubilization

Pristine nanotubes are insoluble in aqueous media and this has been a major technical roadblock for their biological and biomedical applications. However, recent advances in chemical modification and functionalization methods have lead to Solubilization and dispersion of CNTs in water, thereby facilitating their handling and processing in physiological environments. Generally, dispersion or Solubilization of carbon nanotubes can be achieved by three methods: (i) dispersion upon oxidative acid treatments; (ii) non covalent functionalization iii) covalent functionalization.

Functionalization

Functionalized carbon nanotubes (fCNT) can play an important role in many applications, especially in biomedical -applications of CNTs. Recently; they have been functionalized with several bioactive moieties like proteins, carbohydrates, nucleic acids, anticancer drugs, antibodies and enzymes. Functionalizing the nanotubes makes them soluble in water and various solvents facilitating dispersion, manipulation, sorting and separation. Functionalization with organic, inorganic or bioactive molecules also helps in the interfacing of nanotubes with other materials to form bioconjugates.

Nanotubes can be functionalized by both covalent and non-covalent methods.

Non-covalent functionalization is based on van der Waals, hydrophobic or π-π interactions, and it is particularly interesting because it does not perturb the electronic structure of CNTs and of SWCNTs in particular. This functionalization involves weak forces, and so some applications are prevented. The systems, in fact, are not only difficult to control but also difficult to characterize. The amount of weakly bound molecules is not always calculable; moreover, especially in solution, other interactions can occur and these molecules can be replaced by solvent. Anyway, many examples of non covalent interaction are reported: surfactants are widely used to exfoliate bundles of SWCNTs, as well as ionic liquids in order to facilitate CNTs manipulation and further reactions. CNTs wrapping by polymers, including DNA, have been studied; also proteins are able to non covalently interact with CNTs and these are often used for bio-sensor applications.

Covalent functionalization, of CNTs can be achieved either by oxidation to develop carboxylic groups on their surface or by the attachment of hydrophilic moieties using addition reactions. The covalent bond ensures the stability of the moieties during manipulation as well as allows the further derivatization of the different functional groups on the nanotubes.

CNTs are functionalized by not reversible attachment of appendage on the sidewalls and on the tips. Also in this case, many different approaches are reported. Briefly, reactions can be performed at the sidewall site (sidewall functionalization) or at the defect sites (defect functionalization), usually localized on the tips.

Functionalized Multiwalled Carbon Nanotubes

Functionalized Multiwalled Carbon Nanotubes

Functionalized -MWCNTs are not modified in their electronic structure and new properties can be added by means of functionalization. Instead, electronic properties of SWCNTs are perturbed by covalent functionalization and double bonds are irreversibly lost. This may affect conductive property, preventing further CNT applications.

Functionalized Multiwalled Carbon Nanotubes


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