Atomic radical abatement of organic impurities from electron beam deposited metallic structures

Focused electron beam induced processing (FEBIP) of volatile organometallic precursors has become an effective and versatile method of fabricating metal-containing nanostructures. However, the electron stimulated decomposition process responsible for the growth of these nanostructures traps much of the organic content from the precursor’s ligand architecture, resulting in deposits composed of metal atoms embedded in an organic matrix. To improve the metallic properties of FEBIP structures, the metal content must be improved. Toward this goal, the authors have studied the effect of atomic hydrogen (AH) and atomic oxygen (AO) on gold-containing deposits formed from the electron stimulated decomposition of the FEBIP precursor, dimethyl-(acetylacetonate) gold(III), $AuIII(acac)Me2$⁠. The effect of AH and AO on nanometer thick gold-containing deposits was probed at room temperature using a combination of x-ray photoelectron spectroscopy (XPS), scanning Auger electron spectroscopy, and atomic force microscopy (AFM). XPS revealed that deposits formed by electron irradiation of $AuIII(acac)Me2$ are only ≈10% gold, with ≈80% carbon and ≈10% oxygen. By exposing deposits to AH, all of the oxygen atoms and the majority of the carbon atoms were removed, ultimately producing a deposit composed of ≈75% gold and ≈25% carbon. In contrast, all of the carbon could be etched by exposing deposits to AO, although some gold atoms were also oxidized. However, oxygen was rapidly removed from these gold oxide species by subsequent exposure to AH, leaving behind purely metallic gold. AFM analysis revealed that during purification, removal of the organic contaminants was accompanied by a decrease in particle size, consistent with the idea that the radical treatment of the electron beam deposits produced close packed, gold particles. The results suggest that pure metallic structures can be formed by exposing metal-containing FEBIP deposits to a sequence of AO followed by AH.