Electron-beam induced deposition and autocatalytic decomposition of Co(CO)₃NO

Abstract

SummaryThe autocatalytic growth of arbitrarily shaped nanostructures fabricated by electron beam-induced deposition (EBID) and electron beam-induced surface activation (EBISA) is studied for two precursors: iron pentacarbonyl, Fe(CO)5, and cobalt tricarbonyl nitrosyl, Co(CO)3NO. Different deposits are prepared on silicon nitride membranes and silicon wafers under ultrahigh vacuum conditions, and are studied by scanning electron microscopy (SEM) and scanning transmission X-ray microscopy (STXM), including near edge X-ray absorption fine structure (NEXAFS) spectroscopy. It has previously been shown that Fe(CO)5 decomposes autocatalytically on Fe seed layers (EBID) and on certain electron beam-activated surfaces, yielding high purity, polycrystalline Fe nanostructures. In this contribution, we investigate the growth of structures from Co(CO)3NO and compare it to results obtained from Fe(CO)5. Co(CO)3NO exhibits autocatalytic growth on Co-containing seed layers prepared by EBID using the same precursor. The growth yields granular, oxygen-, carbon- and nitrogen-containing deposits. In contrast to Fe(CO)5 no decomposition on electron beam-activated surfaces is observed. In addition, we show that the autocatalytic growth of nanostructures from Co(CO)3NO can also be initiated by an Fe seed layer, which presents a novel approach to the fabrication of layered nanostructures.

On the Principles of Tweaking Nanostructure Fabrication via Focused Electron Beam Induced Processing Combined with Catalytic Growth Processes

“…Figure 3) with granular morphology occurs without electron irradiation. A closely related AG experiment conducted on EBID deposits on an ultrathin Si 3 N 4 membrane yielded a maximum thickness of 5 nm, [33] which would be probably sufficient to attenuate the AES signals from the bulk accordingly. In contrast to the previous investigation of Fe(CO) 5 on Ag(111), no preferred grain orientation induced by the underlying anisotropic surface can be observed.…”

“…This is especially remarkable since EBISA did not work for Co(CO) 3 SiO x /Si 3 N 4 , substrates which worked well with Fe(CO) 5 . [33] This aspect is interesting because it reflects a delicate chemical sensitivity of the EBISA process depending on the actual choice of one of the two precursors, which are otherwise apparently similar. Furthermore, the probed deposit sites fabricated from Co(CO) 3 NO contain no carbon, but a similar elemental composition compared to previous reports of FEBIP experiments with the same precursor, [33,40,41] i.e., about 50 at% Co and varying contents of O and N. We cannot conclude about the exact chemical nature of the deposits, however, a Co oxidation state higher than zero is likely, as it was reported for similar systems as well, e.g., for EBID and autocatalytic growth with Co(CO) 3 NO on Si 3 N 4 -membranes [33] and thermal decomposition of Co 2 (CO) 8 on titanate nanowires.…”

“…[33] This aspect is interesting because it reflects a delicate chemical sensitivity of the EBISA process depending on the actual choice of one of the two precursors, which are otherwise apparently similar. Furthermore, the probed deposit sites fabricated from Co(CO) 3 NO contain no carbon, but a similar elemental composition compared to previous reports of FEBIP experiments with the same precursor, [33,40,41] i.e., about 50 at% Co and varying contents of O and N. We cannot conclude about the exact chemical nature of the deposits, however, a Co oxidation state higher than zero is likely, as it was reported for similar systems as well, e.g., for EBID and autocatalytic growth with Co(CO) 3 NO on Si 3 N 4 -membranes [33] and thermal decomposition of Co 2 (CO) 8 on titanate nanowires. [42] The formation of carbon-free deposits from Co(CO) 3 NO on amorphous carbon was recently also reported in a UHV study by Rosenberg et al [43] They observe the formation of (CO) x OCoN (x = 1-2) upon 500 eV electron irradiation of an adsorbed Co(CO) 3 NO layer at a substrate temperature of −168 °C.…”

“…electron spectroscopy (AES). Both precursors are chosen due to their property to grow autocatalytically, [21,33] their ease of handling, i.e., high vapor pressure, and especially due to the prospect to fabricate magnetic nanostructures. [15,34,35] Overall the present study reveals partially unexpected differences in the chemical selectivity of the two similar precursors and hints new protocols to fabricate nanostructures in a controlled manner.…”

Additive Nano-Lithography with Focused Soft X-rays: Basics, Challenges, and Opportunities

“…Recent developments in X-ray optics have pushed this parameter below 10 nm [44,45]. Finally, STXM can be employed for an in-situ analysis of the metallic deposits directly after fabrication by means of resonant imaging and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to evaluate confinement, growth rates, oxidation state and chemical purity [21,22,46,47]. X-ray magnetic circular dichroism (XMCD) can be used to characterize magnetic deposits with respect to their magnetization and coercivity [48].This review presents some basic principles of X-ray optics and X-ray microscopy as well as X-ray beam dosimetry that are relevant for FXBID experiments.…”