Semiconductor-polishing slurries. One of the most well-established and widespread uses of nanoparticles today occurs during chemical mechanical planarization (CMP), a highly precise polishing process that is used during the production of integrated circuits on semiconductor chips. During CMP, nanoscaled particles of abrasive materials — typically oxides of aluminum and zirconium, colloidal or fumed silica, and cerium, with particle diameters of 20–300 nm in dia. — are formulated in a polishing slurry that is used to make the metal and dielectric layers on silicon wafers smooth and defect-free.

Shown here is a bundle of single-walled nanotubes Credit: Reprinted with permission from Nanomix, Inc.

Representative companies that produce nanoscaled particles for use in CMP slurries, and the slurries themselves, include Cabot Microelectronics (Boston, Mass.; cabot-corp.com, Rohm and Haas Electronic Materials CMP Technologies (Marlborough, Mass.; electronicmaterials.rohmhaas.com), Honeywell (Morris Township, N.J.; honeywell.com), Bayer AG (Leverkusen, Germany; bayer.com), DA NanoMaterials LLC (a joint venture between DuPont and AirProducts Nanomaterials; Tempe, Ariz.; nanoslurry.com), Eka Chemicals (ekachemicals.com), Praxair Surface Technologies (North Haven, Conn., Praxair.com), Nanophase Technologlies (Romeoville, Ill.; nanophase.com), and others.

Polymeric composites. In recent years, a variety of advanced composite materials have been developed by adding relatively small amounts of carbon nanotubes and/or nanoscaled particles of various other materials to polymeric resins. The resulting nanocomposite that can demonstrate a range of improved material characteristics, such as electrical conductivity, catalytic activity, hardness and scratch resistance, fire retardancy, diffusion-barrier characteristics (such as reduced gas permeability), and even self-cleaning capabilities and anti-microbial properties.

Compared to conventional macroscopic fillers, additives and reinforcement materials, the addition of nanoscaled particles calls for much lower loading levels. For instance, a nanocomposite typically contains just 3–5 wt.% nanosized clay or other nanoparticles, while conventional reinforced composites typically require the addition of 20–40 wt.% micrometer-sized fillers, such as talc, mica, calcium carbonate, asbestos, graphite, silica-based fillers and various oxides. Higher loading rates lead to tradeoffs, such as higher density, increased brittleness, and decreased polymer clarity (micrometer-sized inclusions lead to a loss of transparency because they scatter light). This is not the case when relatively minute proportions of nanoscaled particles are used instead.

Nanofluor Y75N from Precision Polymer Engineering Ltd. (Blackburn, England; www.prepol.com) is a fluoroelastomer that demonstrates improved chemical resistance and gas permeability thanks to the addition of semi-crystalline, perfluorinated nanoparticles. The material’s high fluorine content significantly reduces gas permeability compared to standard fluoroelastomers and perfluoroeslastomers, which leads to reduced swelling from exposure to solvents, says the firm. And, unlike other reinforced polymers, which become opaque when macroscaled metallic or carbon-based fillers are added, Nanofluor Y75N’s nanoscaled additives allow it to remain transparent. According to the company, the material can withstand temperatures ranging from –20 to 180°C.

A growing number of established companies and more-recent startups are developing plastic nanocomposites. These include DuPont Co. (Wilmington, Del.; dupont.com), BASF AG (Ludwigshafen, Germany; bas-ag.de), Degussa AG (Dusseldorf, Germany; degussa.com), Honeywell (Morris Township, N.J.; honeywell.com), Ube Industries (Tokyo, Japan; ube-ind.co.jp), Mitsubishi Gas Chemical Co. (Tokyo, Japan; mgc.co.jp); Bayer AG (Leverkusen, Germany; bayer.com), Hybrid Plastics (Fountain Valley, Calif.; hybridplastics.com), Nanogate Advanced Materials (nanogate.com), a joint venture between Nanogate Technologies GmbH (Saarbruecken, Germany, nanogate.com) and Air Products and Chemicals (Lehigh Valley, Pa.; airproducts.com), Nanocor (Arlington Heights, Ill.; nanocor.com), RTP Company (Winona, Minn.; rtpcompany.com), and others.

Advanced ceramics. Traditionally, high-performance ceramics are made from powders whose constituent particles have a diameter of just under one micrometer, or 1,000 nanometers. However, while finished ceramic components are typically resistant to high temperatures and corrosion, they are also brittle and hard to work with. In recent years, improvements have been demonstrated by producing ceramics from powders consisting of much smaller particles — say, 100 nanometers in diameter or less.

For instance, nanoscaled powders of zirconia (ZrO₂) and alumina (Al₂O₃) are being used as a component in structural ceramics, to improve toughness and resistance to fracture and chipping. Such improved ceramics are increasingly making their way into industrial equipment that tends to experience high temperatures, harsh operating conditions and excessive wear, such as pump components, cutting tools and extrusion dies, bearings and seals, high-temperature filters and membranes, refractory materials, catalysts, advanced sensors, electronic components, and automotive engine components.

Another benefit arises from the use of nanoscaled ceramic powders. Since there is a strong relationship between sintering temperature and particle size, the ability to reduce the particle size of the initial material to about 20 nanometers has been shown to reduce the sintering temperature for zirconia, from 1,400°C to 1,110°C (for more details, see Reference [2]).

Consumer products. Makers of sunscreens, cosmetics and other personal-care products have discovered that the use of nanometer-scaled versions of common additives can improve the effectiveness and aesthetic appeal of many products, compared to conventional formulations. For instance, with the advent of affordable methods to produce and use nanoscaled particles of the common ultraviolet-light blockers titanium dioxide (TiO₂) and zinc oxide (ZnO), sunscreen manufacturers are already using these broad-spectrum UV-blocking agents to produce transparent lotions that are aesthetically superior to the opaque white oxide creams that are the hallmark of surfers and lifeguards. Similarly, nanoparticles of TiO₂ are also being used to add UV-blocking functionality to varnishes, textile fibers and packaging films.

QuantumSphere (Costa Mesa, Calif.; qsinano.com) is supplying nanoscaled silver to improve the therapeutic cosmetics and skin-care products that are designed for acne sufferers produced by Dermacia, Inc. (Santa Ana, Calif.; dermacia.com). The companies claim that at nanoscaled proportions, silver provides enhanced anti-microbial, sun protection and other properties to the end products. Dermacia also offers therapeutic cosmetics that use other nanoscaled additives, including a complex that is said to promote healing for burn victims and post-surgical patients.

CEVP’s NanoGrowth fabrication system allows carbon nanotubes to be grown at room temperature, using plasma-enhanced CVD under vacuum conditions Source: CEVP Ltd.

Gas sensors and other analytical devices. Thanks to their extraordinary surface area, and increased reactivity and catalytic properties, many nanoscaled materials are also being exploited to develop highly sensitive gas sensors and other analytical devices, such as those used to check food quality, improve disease detection, and monitor potential chemical, environmental, biological, radiological and nuclear hazards. The goal is to produce advanced sensors that can collect, process and communicate massive amounts of data, quickly and reliably, with minimal size, weight and power consumption.

Resistive, metal oxide gas sensors (using, for instance, nanoscaled oxides of zinc, tin, titanium and iron) rely on a change in electrical conductivity at the surface of the sensor, as it comes in contact with the target gas. The use of nanoscaled particles of key materials can greatly increase gas-detection sensitivity, selectivity and response time by drastically increasing the amount of reactive surface area on the probe tip. Applied Sciences (Cedarville, Ohio; apsci.com), GSI Creos Corp. (Tokyo, Japan; gsi.co.jp), Nanomix (Emeryville, Calif.; nano.com), Molecular Nanosystems (Palo Alto, Calif.; monano.com), Carbon Solutions (Riverside, Calif.; carbonsolution.com), NanoScale Materials (Manhattan, Kan.; nanmatinc.com), Nanomaterials Research LLC (Longmont, Colo.; nrcorp.com), and Synkera Technologies (Longmont, Colo.; synkera.com) are among the growing list of companies that are involved in this arena.

Similar advances are being pursued in gas chromatography. For instance, miniaturized gas chromatography (GC) modules for gas analyzers have historically been limited to applications involving the measurement of organic compounds. However, SLS Microtechnology GmbH (Hamburg, Germany; sls-micro-technology.de) and researchers from the Technical University of Hamburg-Harburg (Hamburg-Harburg, Germany; tu-harburg.de) have developed a fabrication process to produce a miniature GC system that relies on singled-walled carbon nanotubes packed on a silicon wafer.

As reported in Chemical Engineering (April 2005), SLS Microtechnology’s miniature GC columns are produced by etching 44 channels (each 70 mm long, 70 micrometers wide, and 40 micrometers deep) into a silicon wafer. The channels are then coated with a metal catalyst (such as Fe, Ni or Co), and single-walled nanotubes are grown on the catalyst using thermal CVD of acetylene. As the CVD process continues, a forest of nanotubes grows in the channel, until they are about 40 micrometers long. The trench is then capped with a glass cover by an anodic bonding process.

The chip can be incorporated into SLS’s miniaturized GC module, GCM-5000, which is the size of a credit card. The new system claims to be able to resolve inorganic gases such as CO₂, NOx and O₂, and is designed for applications such as process control, environmental monitoring, threat assessment, and the determination of the heating value of hydrocarbon mixtures, according to the company.

Catalyic and photocatalytic applications. The enormous surface area advantage of nanoscaled particles also supports the development of highly effective catalysts for various chemical process operations and pollution-control applications. The fact that these scaled-down particles have a proportionately greater number of atoms on their surface, compared to their interior, leads to greater reactivity, which has inspired most of the major catalyst makers, including Engelhard Corp. (Iselin, N.J.; englhard.com) and Johnson Matthey (Wayne, Pa.; matthey.com) to pursue catalyst advances based on nanoscaled materials.

Similarly, when exposed to ultraviolet (UV) light, photocatalytic substances such as the anatase form of titanium dioxide (TiO₂; but not the rutile form), strongly absorb UV radiation. In the presence of water, oxygen and UV light, such substances generate free radicals that decompose unwanted chemical substances, and reduce the adhesive forces that bind dirt and algae to various surfaces. This photocatalytic effect is also being exploited for various commercial applications, such as water and air purification, or to impart self-cleaning, anti-microbial and anti-algae properties to various surfaces.

BASF AG (Ludwigshafen, Germany; bas-ag.de), Bayer AG (Ludwigshafen, Germany; bas-ag.de), Degussa AG (Dusseldorf, Germany; degussa.com); Dendritech (Midland, Mich.; dendritech.com) are among the companies involved in developing advanced coatings based on nanotechnology-related advances.

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