Structures of Yb nanoparticle thin films grown by deposition in He and N2 gas atmospheres: AFM and x-ray reflectivity studies

Nanoparticles of lanthanide metals and their compounds are important from the viewpoint of both basic research and application to many functional devices. In the present work, a gas deposition technique was employed to prepare thin films composed of ytterbium (Z = 70) nanoparticles on a glass substrate. The influence of deposition conditions such as deposition temperature, time and gas pressure was studied in detail. In addition to an ordinary inert gas such as He, the possible use of N-2 was investigated. As a result of combined analysis using atomic force microscopy (AFM) and x-ray reflectivity, it was found that spherical nanoparticles of around 1-140 nm in diameter can be obtained upon deposition in both He and N-2 atmospheres. The thin film is not amorphous but fcc crystals of metallic ytterbium with a small amount of hcp phase are mainly formed. When exposed to air, the top surface is covered by an oxide layer due to natural oxidation. The thickness and density were in the range of 5-30 nm and 4-9 g cm(-3), respectively, depending on the deposition conditions. As only small amounts of nitrides were formed during deposition in an N-2 atmosphere in many cases, it was concluded that the use of N-2 can be a feasible alternative to the ordinary gas deposition method with an inert gas. Finally, some self-organized hexagonally shaped structures, which are more frequently observed upon deposition in N-2, are reported.