Researchers from the National Research Nuclear University MEPhI and Immanuel Kant Baltic State Federal University (BFU) have proposed the use of novel thin films to drastically minimize friction to enhance the durability of surfaces in mechanisms.
This study could be crucial for various fields, ranging from medicine to space technologies.
Thin films are solid state substances that can be only several atomic layers thick. Usually, their properties are considerably different from the properties of the original substances on the macroscale.
Vyacheslav Fominski, Project Supervisor, National Research Nuclear University MEPhI
“The areas of their application keep expanding and include nanoelectronics, optoelectronics, spintronics, electro- and photocatalysis, as well as such important fields of economics as space technologies and instrument building. Micromodule devices for space crafts and medical technologies are also promising areas in which thin films can be used,” added Fominski.
Metal chalcogenides—compounds of transition metals containing sulfur, selenium and tellurium—can be used to decrease friction and offer solutions to several problems.
The first ever experiments for achieving thin films from these materials started in the 1980s. At that time, the researchers were specifically interested in the potential of the films to tweak their properties when there is a change in their structure or layer thickness.
As part of the latest research, Russian researchers analyzed the films that were made up of four elements: sulfur, molybdenum, hydrogen and carbon. Initially, laser impulses (dozens of nanoseconds duration) were aimed at carbon and molybdenum targets to generate plasma flows of these materials.
Upon being modified into the gas phase, carbon and molybdenum reacted with hydrogen sulfide that was pumped in the experimental chamber, and the reaction product deposited on a steel base.
Through this process, chemically active atoms of hydrogen and sulfur could make their way into the growing coating. The atoms collectively formed a thin film on the metal. The film’s properties are dependent on the mode of laser-plasma flow production and the concentration of components.
This method is known as reactive pulsed laser deposition and offers more streamlined and dense layers. It enables researchers to modify various parameters of the experiment, thereby influencing the structure of the final products.
Several research centers, including MEPhI and BFU, have been actively developing this robust tool for making special nanostructures.
The thickness of the thin films created by the team was less than 0.5 μm but minimized friction by more than 10 times: the friction factor of a steel ball that slides along a steel plate without any conventional liquid lubricating oils was never more than 0.03 (at standard conditions and −100 °C). This is the same factor that skates have on ice.
The research that involved the development of coating technology, getting experimental samples and quantifying their properties was performed under the supervision of Vyacheslav Fominski (MEPhI) under RSF support. The analytical part of the study was conducted at BFU under the supervision of Petr Shvets in the framework of a state order.
Fominski, V., et al. (2020) Specific Features of Reactive Pulsed Laser Deposition of Solid Lubricating Nanocomposite Mo–S–C–H Thin-Film Coatings. Nanomaterials. doi.org/10.3390/nano10122456.