Reactions of Ions with Adsorbed Me₃PtCpMe: The Role of Ion Identity

Abstract

In focused ion-beam-induced deposition (FIBID) processes, the deposition rate and deposit composition are determined by the interplay between ion-induced deposition and sputtering of the deposited atoms. To provide independent insights into these two facets of FIBID, an ultrahigh vacuum (UHV) surface science approach employing in situ X-ray photoelectron spectroscopy (XPS) and mass spectrometry (MS) has been used to study how the identity of incident ions (Z = He, Ne, Ar, H 2 or D 2 ) influences ioninduced (i) deposition from adsorbed Me 3 PtCpMe and (ii) sputtering of the PtC x films created from Me 3 PtCpMe. For each of the ions studied, the initial decomposition/deposition step could be described as Me 3 PtCpMe (ads) + Z (g) + → PtC 9−x(ads) + xCH 4(g) + H 2(g) although the rate and extent of carbon loss from the Me 3 PtCpMe precursor depended on the ion identity, with heavier ions (Ar + , Ne + ) leading to faster and more extensive fragmentation. For the heavier ions, these findings were ascribed to direct momentum/energy transfer between incident ions and adsorbed precursor molecules, while for the lighter ions, there is an increasing contribution from secondary electrons generated by ion−substrate interactions. While the Pt atom purity associated with ion-induced precursor decomposition was lower for the lighter ions, ioninduced sputtering of PtC x films by lighter ions produced the greatest increase in metal content (i.e., purity), due to the extremely poor mass match with Pt. Indeed, sputtering of nanometer-thick PtC x films by H 2 + /D 2 + produced essentially pure Pt films, as measured by XPS. Increasing the substrate temperature during sputtering, however, inhibited the purification process. The results of these findings in the context of FIBID, conducted in the presence of a constant partial pressure of precursor molecules, are also discussed.