applications include barrier layers, transistor gates, and interconnects. Ru films can be deposited by chemical vapor deposition using volatile complexes such as ruthenium tetroxide and the organoruthenium compound (cyclohexadiene)Ru(CO)3. Catalysis Many ruthenium-containing compounds exhibit useful catalytic properties. The catalysts are conveniently divided into those that are soluble in the reaction medium, homogeneous catalysts, and those that are not, which are called heterogeneous catalysts. Homogeneous catalysis Solutions containing ruthenium trichloride are highly active for olefin metathesis. Such catalysts are used commercially for the production of polynorbornene for example. Well defined ruthenium carbene and alkylidene complexes show similar reactivity but are only used on small-scale. The Grubbs' catalysts for example have been employed in the preparation of drugs and advanced materials. Ruthenium complexes are highly active catalysts for transfer hydrogenations (sometimes referred to as "borrowing hydrogen" reactions). Chiral ruthenium complexes, introduced by Ryoji Noyori, are employed for the enantioselective hydrogenation of ketones, aldehydes, and imines. A typical catalyst is (cymene)Ru(S,S-TsDPEN): A Nobel Prize in Chemistry was awarded in 2001 to Ryōji Noyori for contributions to the field of asymmetric hydrogenation. Heterogeneous catalysis Ruthenium-promoted cobalt catalysts are used in Fischer-Tropsch synthesis. Emerging applications Some ruthenium complexes absorb light throughout the visible spectrum and are being actively researched for solar energy technologies. For example, ruthenium-based compounds have been used for light absorption in dye-sensitized solar cells, a promising new low-cost solar cell system. Many ruthenium-based oxides show very unusual properties, such as a quantum critical point behavior, exotic superconductivity (in its strontium ruthenate form), and high-temperature ferromagnetism. Health effects Little is known about the health effects of ruthenium and it is relatively rare for people to encounter ruthenium compounds. Metallic ruthenium is inert (is not chemically reactive). Some compounds such as ruthenium oxide (RuO4) are highly toxic and volatile. See also Airborne radioactivity increase in Europe in autumn 2017 Notes References Bibliography External links Ruthenium at The Periodic Table of Videos (University of Nottingham) Nano-layer of ruthenium stabilizes magnetic sensors Chemical elements Noble metals Precious metals Transition metals Native element minerals Chemical elements with hexagonal close-packed structure