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18.10.2013
Nanotechnology Parade. A Brief Overview of the Nominated Technologies
The procedure for collecting applications to be nominated for the International Nanotechnology Award RUSNANOPRIZE 2013 has drawn to a close. The Award was established by OJSC RUSNANO and the Fund for Infrastructure and Educational Programs, and aims to draw public attention to cutting-edge scientific research in the field of nanotechnology, which have proven their practical importance, i.e. have been put into industrial production. The theme of the Award this year was “Nanomaterials and Surface Modification”. We are presenting a series of articles with a brief overview of the nominated technologies.
As expected, the topic of nanomaterials caused the most widespread interest among potential candidates for the Award. It is this area that has the largest number of technologies ready for industrial use. In total, 38 applications were submitted. Following a preliminary screening of the applications for compliance with the formal requirements, 23 applications were admitted to the competition.
All of the applications can be provisionally divided into 6 groups:
- nanostructured metals and alloys
- nanocomposite polymers and nanomodifiers
- materials and technologies for micro- and nanoelectronics
- technologies for modifying and researching surfaces at nanometer-scale
- biomedical materials and technologies
- equipment to create nanomaterials, surface modifications and also to measure and control the features and characteristics of nanomaterials and surfaces.
It should be made clear immediately that the division of the groups is very provisional. Most of the applications in the development and production of equipment were aimed at the microelectronics market. Another example is the nanodiamonds that we already mentioned in previous articles. This nanomaterial can be used as a modifier, an additive that can change the properties of familiar materials, and is also widely used in biomedical technology. Nevertheless, the technology review will be carried out on the selected six groups.
The aim of this article and those that follow it in this series does not include an analysis of the actual applications submitted—how strong they are from the point of view of the Award. This task is being worked on by a serious team of international experts and the results of their work will be announced in late September, when a short-list of candidates will be announced. We will try here to review the technologies, what they mean, and what benefits they can provide for the development of the relevant sectors.
Metals and Alloys
Managing the size and nature of the interaction between grains in the structure of metal makes it possible to achieve totally new features for common, well-known materials such as copper, aluminum, titanium, etc. Two industrial technologies for nanostructuring metals have been nominated for the Award—severe plastic deformation (SPD) and equal channel angular pressing (ECAP). Both technologies are based on the work of Soviet and post-Soviet scientific schools (see, for example, here).
The essence of both approaches is that with local deformations at high pressures, structures with smaller grain size form in metal. This makes it possible to improve by tens of percents, and sometimes exponentially, such characteristics as strength, resistance to corrosion and metal fatigue. ECAP technology has been successfully implemented in the production of copper targets for the microelectronic industry, and SPD technology is used in the manufacture of medical goods made from titanium (dental implants), as well as for the manufacture of high-capacity aluminum wires.
Conductors, or to be more precise, superconductors, have been assigned a separate task. As part of the international project to build the ITER thermonuclear reactor, a team of Russian scientists developed the technology of composite superconducting materials. Based on this technology, industrial production of wires is already underway in the amount of tens of tones. The wires are needed to create a super-strong magnetic field in the reactor; with a cross-section of less than 10 microns this wire can carry a current of more than 300 amps. Physically, what happens is that in the structure of one metal, for example copper, a large number of nano-scale fibers of another metal, for example niobium, are formed. This results in a combination of qualities, like high conductivity and strength, which are not possible when using regular materials.
The high strength and corrosion resistance of metals with a nano-scale grain structure comes from nano-crystal surface technology. Theoretical calculations have predicted that thermodynamically stable nano-scale grains can, in certain conditions, arise in nickel and tungsten. These conditions have been created and currently Ni-W surfaces on gold electronic contact plates make it possible to save up to 2/3 of the precious metals and, in some cases, to do without gold altogether.
Polymer Materials, Additives, Modifiers
The most indicative example of the use of nanoparticles to modify the properties of known materials is nanodiamonds, which we have already covered in the previous articles. Nanodiamonds are used on an industrial scale as an additive in lubricants. This makes it possible to reduce friction more than ten-fold and increase by up to 50% the life-span of rubbing parts and units. In polymer materials nanodiamonds can also add new properties, in particular, they increase the thermal conductivity of polymers and they provide resistance to high temperatures and radiation. Technologies using nanodiamonds accounted for three of the 23 submissions admitted to the competition
For many years, the scientific community has widely discussed the potential of using carbon nanotubes as modifiers in polymer materials. Now this possibility has been implemented on an industrial scale. Valuable consumer properties have been achieved in materials such as packaging film (ESD protection), pipes made from high pressure polyethylene and polycarbonate building panels (in the latter two cases, the use of nanotubes can significantly reduce process losses when processing the final products).
A whole range of technologies for the use of nanoparticles of metal oxides (zinc, titanium, aluminum, etc.) in protective polymer and emulsion coatings have been developed by American specialists. This includes the technology for producing the nanoparticles themselves along with the surface modification technologies and dispersion technologies. The variety of technological approaches is dictated by the wide range of tasks in which these nanoparticles “work”: cosmetics and veterinary (sunscreens, anti-inflammatory and anti-bedsore powder), architecture (self-cleaning coating for glass), the automotive industry (protection against scratches and UV light), energy (coatings for solar cells), and more.
Biological Nanomaterials and Nanosystems
If the contenders for the RUSNANOPRIZE 2013 are anything to go by, applied nanotechnologies in biological systems are developing in two main areas—medicine delivery technology (more broadly—the creation of new medications) and technology in which biological systems are used as a structured nanomaterial.
The developments of Professor Langer (MIT, USA) and Professor Farokhzad (Harvard Medical School, USA) fall into the first category. They are creating combined nanoparticles, the surfaces of which are covered with biological ligands, i.e. molecules that recognize specific targets in the body, for example, the surface of cancer cells. The interior of the nanoparticles is composed of biologically inert polymer which binds the active substance, for example docetaxel, which is traditionally used in chemotherapy. These particles may circulate for a long time and be retained in the blood, and so they accumulate only around the tumor cells. As a result, the concentration of the toxic substance in the tumor can increase by a factor of 10,000 compared with conventional chemotherapy methods. Based on this technology, in particular, drugs have been created for the treatment of brain tumors, which are difficult to treat with traditional methods.
Nanodiamonds act in a similar way by absorbing the cytotoxic drug and accumulating in the tumor tissues, creating an increased concentration of the active agent. Professor Ho (The Jane and Jerry Weintraub Center for Reconstructive Biotechnology, USA) has shown the effectiveness of this combined preparation for treating breast and liver cancer, which does not respond well to conventional chemotherapy.
Professor Mirkin (Northwestern University, USA) has developed and widely implemented biosensor technology based on gold nanoparticles with attached fragments of nucleic acid (so-called “spherical nucleic acid”). These biosensors work to diagnose a range of diseases—where the detection of DNA or RNA in a solution is necessary (e.g., the recognition of viral infections). However, the most impressive progress has been achieved in methods to detect specific sequences of nucleotides directly in the living cell.
Gold nanoparticles with fragments of nucleic acid carrying a sequence complementary to the target, can easily penetrate the cell (for the body, they are not toxic or immunogenic, i.e. they don’t elicit an immune response or allergic reaction). The nucleotide sequence of interest to the researcher is “closed” by a short complementary fragment with a fluorescent tag. When this tag is selected in such a way that when connected the fluorescence is switched off and the tag is not visible. However, in the presence of the target RNA sequence in the cell cytoplasm, the tagged fragment competes for space with the nanoparticles, the tag falls in the solution and begins to glow. As a result, the outlined technique makes it possible to identify specific mRNA in a living cell, i.e., actually see the process of reading certain genes. Quite quickly both the fluorescent tag and the nanoparticles leave the cell, and the cell remains alive and functional.
Perhaps an extreme case of the second field, where a biological system is used as a technological material, is being developed by Professor Angela Belcher from MIT (USA). Prof. Belcher used the ability of virus particles to self-assemble. She created a genetic construct, in which the bacteriophage particles (a virus that infects bacteria) are “dressed” in inorganic material such as gold or cobalt oxide. The biological principle of self-assembly provides the following combination of properties:
- a very high level of ordering of particles at the molecular level (all virus particles are equal)
- the ease of production of the process—the biological systems can be prepared in large quantities at relatively low cost (the viruses “assemble themselves”)
- the environmental safety of the technology—almost all the processes occur at room temperature without the use of toxic or potent chemicals.
Using viral self-assembly technology, it was possible to get nanomaterials that can act as components in traditional lithium-ion batteries. These batteries will be very small and comparable to existing technical specifications.
Surface Modification
The topic of imparting certain properties to surfaces with nanostructured coatings was already partly dealt with in the section on nanomodifiers for polymers. Here we look at technologies that were developed to modify the surface properties of certain products.
Professor Varanasi (MIT, USA) has developed a special technology for constructing surfaces to give them not only the desired level of hydrophobicity, but also manageable wettability and the ability to control the run-off speed for a specific liquid on a given surface. The approach is based on selecting a certain combination of a solid porous support which is soaked with a hydrophobic liquid and retains it on the surface of the material. Researchers have very clearly demonstrated the benefits of its technology for bottles of ketchup, shampoo, toothpaste and other situations where thick and viscous liquids remain at the bottom of containers.
Another approach to the use of hydrophobic surfaces is being developed by a British company. Their technology is based on the vacuum deposition (vapor deposition, plasma-stimulated) of a special polymer coating, which protects the entire unit from moisture. The technology has been implemented and fine-tuned on an industrial scale, for example, for consumer electronics. The applied film is about 100 nanometers thick, it is not visible, it is not felt, and does not interfere with the device’s performance, but it repels water and acts as a general waterproof case. In a video demonstration a British scientist drops his smartphone in the toilet, then cheerfully plucks it out and answers a call.
Against this backdrop, the Russian technology of galvanizing steel surfaces looks a little prosaic. Our scientists have developed a method, which they have successfully tested in industrial conditions, to “saturate” the surface layer of steel products with zinc using thermal diffusion. The uniqueness of this development is in the special properties of the nano-powder — the metal particles are smaller than 100 nm and are covered with a layer of porous oxide. First of all, this makes it possible to cover even difficult surface details with powder and, secondly, it ensures a high concentration of zinc vapor on the steel surface. The technology has been installed at Pervouralsk New Pipe Plant (Chelpipe Group) to manufacture tubes. Thermal-diffused zinc acts as a hermetic sealant in tube connections and has proven to be highly effective in trial operations at a number of oil companies.
Semiconductors: Traditional Approaches, New Achievements
One rapidly developing sector in the semiconductor industry is technology for LED lighting. A team of Russian scientists proposed a solution to a serious obstacle to improving the efficiency of light-emitting diodes, namely, the problem of photon emissions from the active region of light generation. The technology for creating nano-scale structures on sapphire substrates for LEDs based on InAlGaN / GaN multiple quantum wells was theoretically substantiated, experimentally validated and commercialized. Moreover, the structure of the active region itself was optimized. As a result, it was possible to significantly reduce the contribution of non-radiative processes and reduce losses due to internal reflection of photons in the active region. In total, the technology has improved the external quantum yield of LEDs by up to 60%.
Professor Ruskin from Belgium (Université Catholique de Louvain) presented another mainstream area in microelectronics, namely improvements in SOI (silicon on insulator) technology. SOI technology itself, where the substrate used for transistors is not a thick silicon layer, but rather a sandwich, in which an oxide layer insulates the technological silicon layer from the remaining parts of the substrate, is considered a promising avenue for the miniaturization of microprocessors. Professor Ruskin suggested adding another layer to the “sandwich”, saturated with ordered defects in polycrystalline silicon. This fundamentally improves the characteristics of the devices created on the substrate. The French company that mass-produces the substrate using SOI technology believes that Professor Ruskin’s technology will form the basis for the production of electronic “brains” for all personal gadgets in the near future. In addition, the technology has a lot of specialized uses.
Interesting developments in nanolithography were also presented. Traditionally in microelectronics photosensitive polymer is used, which is applied to the surface and illuminates the desired area through a special stencil. This technology has limitations in spatial resolution—it is limited to the diffraction limit of the light. A proposal from a team of authors from Sweden suggests a method for applying a pattern on a surface by imprinting, similar to the way in which an inked stamp is applied to paper and leaves a mark on documents. Scientists have tried to adopt this approach for a long time, but were prevented by a number of serious obstacles—in high definition it is only possible to leave a few imprints, the printing field was small (about 30 microns), because of this the whole process took too long. The proposed technology overcomes these limitations. So, a substrate of 6 inches can be processed in just a few minutes.
Formation of Nanostructures: Chips for Cloaks of Invisibility
Professor Whitesides (Harvard University, USA) introduced a number of approaches for the formation of local relief elements, the most original of which he called “nanoskiving” (from the English ‘skive’—slice off a thin layer, chip). This technology is amazing due to its simplicity and low cost on the one hand, and its huge potential on the other. Basically, this approach involves creating a regular relief on the surface of a solid polymer with submicron resolution. This is currently easy with the help of optical and laser technology. Then a metal film of about 30 nm in thickness is deposited on the surface of the polymer with the relief. A layer of epoxy resin is placed on top, and then, using an ultramicrotome, you get a thin section in a random plane. The thickness of the slice is limited by the capabilities of the ultramicrotome and in modern devices can be up to 30 nm. Let’s assume that the cut was in a plane perpendicular to the median plane of the deposited metal film. In this case, the researcher gets a sheet of polymer material (slice) with a width and a length of up to several millimeters, in which there is a “thread”—a layer of metal film, repeating the regular relief of the initial polymer. The typical dimensions of such structures are tens of nanometers in diameter (the thickness of the initial film X thickness of the slice) and up to millimeters in length. By stacking layers on a specific substrate, using a pincers under an optical microscope, it is possible to form a three-dimensional spatial structure from these “threads”. After treatment in a plasma chamber the polymers are scraped off and metal structures remain. So, this approach combines:
- topological control up to 30 nm in two of the three measurements
- the ability to create macro-objects from nanostructures (characteristic dimensions—mm)
- extremely simple equipment and infrastructure (no need for clean rooms, high vacuum, etc.).
The most popular such technology may come from the developers of metamaterials (for example to provide objects with the property of invisibility at optical wavelengths). This is where it is important to be able to simultaneously control the characteristics of the material both at the level of nanometers and at the macro level. However, the question of industrial adaptability, obviously, still requires some study.
Equipment for Nanoelectronics and More
Two well-known technologies used in the semiconductor industry were nominated for the RUSNANOPRIZE 2013 award as designs for scientific and limited-edition industrial equipment. These are the so-called ALD technology (atomic layer deposition, a patent has been filed by a Finnish company) and MOCVD (metal organic chemical vapor deposition, a patent has been filed by a German company). Both techniques ensure the production of thin layers of certain substance on the surface of a silicon substrate. In the case of ALD, the growth of a new structure is due to the arranging of the atoms or molecules on the edge of the already existing film. Therefore, a very thin film is obtained (up to one layer of atoms) that is very uniform in thickness and in composition. In the case of MOCVD, a metal compound in gaseous form is placed in the reaction chamber, where it is deposited on the substrate surface, and then the metal atoms are released by chemical reagents or thermal decomposition of the organic matter. This technology has a wide range of possibilities as regards selecting materials and is one of the fundamental technologies in modern microelectronics
Finally, a very promising area for research into nanostructures is being developed at the equipment level by a Russian company. The so-called scanning probe microscopy (SPM) is based on two technological solutions. Firstly, a very sharp needle (radius of curvature at the tip up to 1 nm) can be brought very close to the surface and record the forces between the tip and the surface area of a few nanometers. The forces may be very different, depending on the material and properties of the needle and also the properties of the surface itself. In the simplest case, the needle is attracted or repelled by van der Waals forces, but there may be magnetic, electrical, adhesive and other interactions. Secondly, a special scanning system makes it possible to move the needle on the surface with angstrom accuracy. That is, the needle touches the surface, moving from point to point, and the researcher receives a map of the distribution of the properties of interest in a selected area of the specimen. For example, this may simply be the relief—the size of nanostructures. The ability to measure electrical and magnetic properties with nanometer resolution makes SPM a very popular approach for the development of new semiconductor materials and nanoelectronic devices.
D.S. Andreyuk, Vice President, Nanotechnological Society of Russia