Jaroslava Lavková

Preparation of Magnetron Sputtered Thin Cerium Oxide Films with a Large Surface on Silicon Substrates Using Carbonaceous Interlayers

The study focuses on preparation of thin cerium oxide films with a porous structure prepared by rf magnetron sputtering on a silicon wafer substrate using amorphous carbon (a-C) and nitrogenated amorphous carbon films (CNx) as an interlayer. We show that the structure and morphology of the deposited layers depend on the oxygen concentration in working gas used for cerium oxide deposition. Considerable erosion of the carbonaceous interlayer accompanied by the formation of highly porous carbon/cerium oxide bilayer systems is reported. Etching of the carbon interlayer with oxygen species occurring simultaneously with cerium oxide film growth is considered to be the driving force for this effect resulting in the formation of nanostructured cerium oxide films with large surface. In this regard, results of oxygen plasma treatment of a-C and CNx films are presented. Gradual material erosion with increasing duration of plasma impact accompanied by modification of the surface roughness is reported for both types of films. The CNx films were found to be much less resistant to oxygen etching than the a-C film.

Nanoporous Ptn+–CeOx catalyst films grown on carbon substrates

Deposition of the Pt doped cerium oxide catalyst layers on carbon nanotubes and flat carbon substrates by magnetron sputtering leads to growth of solid solution films composed of nanorods oriented perpendicularly to the substrate surface forming fractal like highly porous structure. The films contain only cationic Pt2+ and Pt4+. Cerium oxide is partially reduced. The catalyst films reveal high catalytic activity as anode catalyst in proton exchange membrane fuel cells. Preparation of nanoporous structures by sputtering shows that this technique is suitable for preparation of catalyst for micro fuel cell systems made by planar technology.

Sputtering of Spherical SiO 2 Samples

Dust grains in the interplanetary environment can be basically found in two locations—floating in the free space or attached to a surface of asteroids, comets, or moons. They are sputtered by the impacts of energetic ions, and this process supplies the interplanetary space with heavy elements. The sputtering yield is generally estimated on the basis of laboratory investigations of planar samples. We use silica micrometer-sized spherical grains as a prototype of a space-borne dust, bombard them by 2-keV Ar ions, and monitor the influences of simultaneous application of the electron beam as well as the electric field at the dust surface on the sputtering yield. We found that the increase in the sputtering yield due to the electron impact is much larger than expected and it can enhance the sputtering yield by a factor of 1.6 in a comparison with the sole ion bombardment. On the other hand, the influence of the electric field is not so strong (if any) and it is masked by electron impacts in our experiment. Sputtering of the grains fixed at a surface by 30-keV Ga ions revealed that the angular profile of the yield is flatter than that frequently used for a description of the sputtering process. Finally, we compare these results with the published sputtering yield values.