High-temperature interaction of nitrogen with thin iron films: Thermal desorption kinetics studies combined with microstructure analysis of Fe–N films

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Abstract
The interaction of nitrogen with thin iron films at 673 K has been studied by means of thermal desorption mass spectrometry (TDMS) and a combination of scanning electron microscopy and transmission electron microscopy. TDMS spectra indicate the coexistence of atomic and molecular states of nitrogen adsorbed at 673 K and at a nitrogen pressure of 0.75 Pa. The origin of the molecular state is discussed as an intermediate state towards dissociative adsorption of nitrogen. Reconstruction of the polycrystalline iron film occurs as a result of both nitrogen interaction at 673 K and thermal desorption by heating the sample substrate to 950 K. The Fe grains become finer and the Fe film surface shows an increase in roughness upon interaction with nitrogen at 673 K. TDMS heating involves annealing of the Fe film and decomposition of the “surface nitrides.” The bulk structure of the Fe film is affected by the nitrogen-induced reconstruction of its topmost surface region.