Iron structures from pyrite ion bombardment

FERRON J.; RUANO G.

Bexco, Busan

Congreso; International Vacuum Congress. IVC 20; 2016

IUVSTA

The alteration ofmatter by ion bombardment is a wide branch of material science that has been deeplystudied. It is, however, again under an enormous renewed interest due to theposibilities of using such tecniques in nanostructure production. For instance,in recent works we studied the diffusion mechanisms ruling the nanostructureformation in Cu(100) under keV N+ ion bombardment. In the currentwork, we focus our interest in the development of iron structures by energeticH+ and He+ from minerals containing Fe2+. Besidesnanostructure development, this work has also implications in astrophysics,since this mechanism is the responsible of the astrophysical surface bodiesmodifications by the solar wind. We can gain, for instance, information aboutthe aging of airless bodies immersed in the outer space. Pyrite (FeS2) is anaturally abundant mineral, with cubic (Pa3 symmetry) structure, it isdiamagnetic and semiconductor in its native form. An industrial commodity inthe production of iron and sulfuric acid, this inexpensive material is objectof study in basic science in a broad spectrum of topics ranging from primordialbiochemistry to nanometric semiconductors development. From the astrophysicalpoint of view the presence of pyrite in outspace bodies has been linked even tothe origin of life. Our efforts are devoted to generation of small metallicdomains through ion bombardment, and fully characterize them from a chemicalpoints of view. We studied using X rayphotoemission spectroscopy (XPS) the changes in the chemistry of the FeS2substrate upon increasing exposure to 4.5 keV He+ ions. We found atransition from Fe2+ to Fe0 upon ion bombardment. We alsodetected the dangling S product of the broken S-Fe and S-S bonds, that has beenpreviously reported for in vacuum sample mechanical cleavage. Once the reducediron was obtained, we studied the film stability. In this way, we exposed thesystem to air and a diluted solution (10 vol) of H2O2 toproduce oxidation and confirm the presence of metallic Fe. While roomtemperature air exposure oxidizes the iron, observed by means of XPS, the solutionof H2O2, diluted enough to prevent chemical attack to freshpyrite removed all the transformed region.