Functional nanocoatings: trends and prospects
The nanocoatings can improve the following characteristics: hardness and wear resistance (cutting tools, heads of hard drives); resistance to high temperatures and corrosive environments (turbine blades); anti-adhesive properties (punches); impermeability/hermeticity (microelectronics, OLED-displays); sliding/friction (tribology); hydrophobicity and oleophobicity (touch screens); hydrophilicity (activation before coating); biocompatibility (medical implants); bactericidal (medical instruments). In addition, the formation of functional coatings with desired properties, such as dielectric or conductive (in combination with transparency and flexibility), a heat-conducting or insulating, etc. is possible. Micro- and nanoelectronics, photovoltaics today are unthinkable without film technologies.
reduction of process temperature (important for plastic substrates);
cost reduction and simplification of the equipment (for example, due to the exclusion of the vacuum system);
uniformity of the coating over a larger area;
ability to apply roll-to-roll (R2R) processing;
flexibility of coatings (flexible electronics);
absence of pores (hermeticity).
Graphene will definitely stand out among the many promising nanomaterials and coatings. The development of industrial technology of its synthesis (in particular, using the substrate made of silicon carbide) is under the spotlight of leading researchers. Parylene nanocoating have no pores, therefore, can successfully be used for forming the dielectric layers in the OTFT-matrices and for sealing of OLED-displays and printed circuit boards. Diamond-like nanocoatings (ta-C, a-C: H) have the broadest application from a tribology and biomedicine to reduction of gas permeability of PET containers.
Promising technologies include the formation of self-organized nanostructures by ion bombardment of the surface at a certain angle or by the use of block copolymers. One of the already implemented applications is the manufacturing of wire grid polarizer (WGP) for LCD-displays. In the future we can expect increased use of self-assembly of nanocoatings.
Speaking about the problems of development of this area in the Russian nanoindustry it should be noted shortages in many regions of the service centers for restoration coatings (for example, on cutting tools), as well as the need for the introduction of nanocoatings in the power engineering and healthcare. But the most important are the need to restore the lost positions of Russian applied science and technology, and the creation of conditions for promotion of domestic high-tech developments. It is no secret that many of the imported equipment and technologies, including in the field of nanocoating, are based on Russian ideas and developments (for example, MEVVA – Metal Vapor Vacuum Arc). The goal is to make them profitable to implement in Russia.
First, let’s look at how the ratio of the number of atoms located on the surface of the body, to the number of atoms in the body changes. For convenience of calculation, let us consider the spherical body shape. For the body of radius r, the total number of molecules NV equals:
where Vm is the volume of one molecule.
The number of molecules located on the surface of a sphere:
where Sm is the cross sectional area of a single molecule.
Then the ratio of the number of atoms on the surface to the total number of atoms:
For a single molecule the ratio is equals 1:
where rm is the radius of a single molecule.
We have got an easy and obvious rule – the number of atoms on the surface of the sphere is less than the volume as much as the radius of a molecule is less than the radius of the sphere. From a radius of 1 nm to the radius of 1 m, the ratio will vary a billion times!
Physical conclusion is obvious: when working with nanoparticles, the role of the surface is crucial and nanocoatings deposited on the surface of the nanoparticles can dramatically change the properties of the latter.
It can be argued that nanocoatings, which alter the functional properties of the nanoparticles are central to nanotechnology. Already we can give two examples of nanoparticles with nanocoatings:
colloidal quantum dots (the semiconductor inside and the SAW on the surface) are used in practice by such industry giants as Sony and LG in the production of high brightness and contrast monitors;
biomarkers based on gold nanoparticles with attached oligonucleotides, antibodies or ligands.
Biomarkers are composed of a gold core, to which surface biological molecules are sewn. Due to plasmon resonance, leading to increased light scattering, such biomarkers are easily measured by optical microscopy, and due to the high electron density they are well visible in the transmission electron microscope1. In atomic force microscopy the gold particles allow to visualize individual acts of DNA hybridization2.
It should be noted that the global market for biomarkers has already reached several billion dollars annually. So, in pregnancy tests (to detect the hormone human chorionic gonadotropin) conjugates of gold nanoparticles with antibodies are used. Buying immunochromatographic tests, we also acquire gold nanoparticles with functional nanocoatings.
Gold nanoparticles find new applications in biology and medicine, in particular, in portable sensors for viral and bacterial infections. The high sensitivity of these particles combines with ease of use, safety, reliability, and that much important, with budget price. Now environmentally friendly manufacturing of metal nanoparticles, for example, using plant extracts are actively developed3.
A separate, important and useful topic are nanocoatings for macroscopic bodies, such as thin waxy film to protect the car body or hydrophobic protection from contamination for glass. But perhaps it is not as exciting as coating of the nanoparticles. Many new discoveries, ideas and technological implementations in the field of nanocoating of the nanoparticles are yet to come. Also a lot of problems that must be addressed. I would like to wish all the enthusiasm and success in this way.
Nanocoatings replaced the traditional technology of functional coatings. The use of nanomaterials and nanocoatings in mechanical engineering is topical primarily for the aerospace industry, propulsion engineering and automotive industry. Although the core competence of SemiTEq is the development and production of systems for the manufacturing of electronic components, equipment for the deposition of functional nanocoatings is a close area for us. The applied technologies are basically similar, but the only difference is the need to apply coatings on machine parts and tools. It does not require peculiar to our equipment cleanliness and quality of so-called "thin films", which greatly simplifies the task.
Functional nanocoating is just a new trend, however, we note the constant growth of this market segment. Among the promising technologies should pay attention to atomic layer deposition (ALD). This technology provides the ability to control the properties of materials at the atomic level when applying layers of different elemental composition, structure and thickness to achieve the required characteristics. The range of practical applications of ALD involves thin-film coatings not only in photovoltaics and optics, but also in hardening of glass, biocompatible coatings, protection against tarnishing and corrosion, as well as in the formation of various functional nanocoatings.
There is a growing use of reliable and universal processes of physical vapour deposition (PVD) for various products, including cutting tools. One of the most popular and common in this area are the gas-thermal sputtering and ion-plasma magnetron sputtering.
New technologies for the production of nanostructured coatings replace the outdated and environmentally harmful (in particular, galvanic technology), while there is no significant rise of cost of the process. In my opinion, the most interesting projects carried out Keldysh Research Centre and VIAM developing, in particular, nozzles and turbine blades with nanostructured coatings. I believe that functional nanocoatings have a great future and a huge field of applications, which over time will expand.
The role of nanotechnology in today’s market of innovative materials is characterized by high rates of development of functional nanocoatings. Major target segments are construction, coatings that protect from the external environment, the military industrial complex (corrosion protection and textiles), household goods (easy-clean and anti-microbial coatings), automotive (corrosion protection and hydrophobic coatings).
Growing demand for nanocoating is associated with the rapid development of the market of nanomaterials. Thus, only in the United States over the past five years, the market ща nanomaterials grew more than three times. For nanocoatings average annual growth estimate of 43%. In the EU and North America, as well as in Japan the long-term programs of development and introduction of nanomaterials are implemented. The main problem should be considered the practical development of technologies that will allow the production of the required volumes of nanomaterials that are competitive on the markets. Due to this, the production of nanomaterials in recent years, surely becomes industrial. In particular, it reduces the cost of production of carbon nanotubes. Researches in this area are conducted in MEPhI, Lomonosov MSU, MISIS, PFUR, MUCTR, the number of laboratories and research groups in Rybinsk, Izhevsk, Novosibirsk. US and NATO, Japan invested hundreds of millions of dollars in research and production of nanomaterials, manufacturing of equipment and structures with nanocoatings. Russia and those international associations, in which she plays a significant role (BRICS, CSTO, Eurasian Union) should also to pay essential attention to these questions, in order not to fall out of the scientific and technological competition.
Experts expect much from the massive use of nanocoatings in the energetics. It is expected that in the nearest future for energetics will account for about 13% of world consumption of nanoproducts, and in the foreseeable future developments in nanotechnology will help to make a revolutionary leap in the development of the production and conversion of energy. Given the low diversification of the Russian economy, the relationship between the financial sector and energy prices, such developments can hit it. It should be noted that the Russian government last year approved the forecast of national science and technological development up to 2030, in which new materials and nanotechnologies are included among the priority areas of development of science and technology.
As noted above, the production of nanocoatings is already an important segment of nanotechnology. An important area will be the development of self-cleaning and self-healing coatings. Modification of the adhesion of surfaces will significantly change the number of traditional technologies, for example, in the construction of pipelines, which is important for the oil industry.
In connection with our topic the projects for the production of innovative ceramic coatings for industry, aircraft and medicine are interesting, which implements nanotechnology centre SYGMA.Novosibirsk of Technopark of Novosibirsk Akademgorodok. In particular, they are developing ceramic scalpels, heavy-duty ceramic coatings for industrial machinery, as well as a special ceramic coating for aluminum engine parts for unmanned aerial vehicles, which reduces friction and increases the service life of machinery. This is a great example of cooperation between technopark, the regional branch of Russian Academy of Sciences and the regional government. This collaborative model should be implemented in other regions. ■