AbstractNanocluster diamonds can be synthesized in open air on stainless steel and molybdenum substrates with a hybrid cold atmospheric plasma source using air plasma and an air + alcohol mixture. At microwave powers below 300 W and at gas flow rates below 300 sccm the temperature of a thermally insulated steel substrate placed 1.5 cm from the hollow cathode caused by the air plasma were less than 600 °C. 200 nm thick coatings with nanocluster diamond grains and aggregates exhibiting diamond peaks in the Raman spectra at 1 325 cm−1 on stainless steel and at 1 322 cm−1 on Mo were formed after 1 h on untreated substrates.magnified image