A method to determine the sticking coefficient of precursor molecules used in atomic layer deposition (ALD) will be introduced. The sticking coefficient is an interesting quantity for comparing different ALD processes and reactors but it cannot be observed easily. The method relies on free molecular flow in nanoscale cylindrical holes. The sticking coefficient is determined for tetrakis(dimethylamino) titanium in combination with ozone. The proposed method can be applied independent of the type of reactor, precursor delivery system and precursors. (C) 2009 Elsevier B. V. All rights reserved.