Role of Low-Energy Electrons (<35 eV) in the Degradation of Fe(CO)₅ for Focused Electron Beam Induced Deposition Applications: Study by Electron Stimulated Desorption of Negative and Positive Ions

Abstract

Fe(CO) 5 is one of the most common precursors used in focused electron beam induced deposition (FEBID). Since high-energy electrons interacting with matter produce large amounts of secondary electrons with energies <50 eV, those generated within the substrate in FEBID are expected to play a major role in the dissociation process of the precursor molecules. The aim of this study is to identify the role of the secondary electrons in the deposition process of Fe(CO) 5 and the relevant dissociation mechanisms, using an electron stimulated desorption system with 4−33 eV electrons. The desorption of charged fragments from thin films of Fe(CO) 5 , condensed on Xe or onto a Pt foil, was measured as a function of incident electron energy, incident current, and thickness of both Fe(CO) 5 and Xe films. Both dissociative electron attachment (DEA) and dipolar dissociation (DD) are involved in the production of anions, specifically, C − and O − , and Fe(CO) x − (x = 0−4). Cations C + , O + , CO + , and Fe(CO) x + (x = 0−4) were detected with desorption thresholds in the ∼15−25 eV range. These fragments are produced via direct dissociative processes. This study reveals the detailed dissociation mechanisms of Fe(CO) 5 induced by low-energy electron impact by the direct observation of Fe(CO) x fragments under different conditions, thus confirming the frequently proposed mechanisms of deposition of Fe by FEBID.

Dissociative electron attachment and electronic excitation in Fe(CO)5

“…10 Attachment rates of slow electrons to Fe(CO) 5 (and also Fe(CO) n , n = 0 − 4) were measured using a flowing afterglow Langmuir probe apparatus by Shuman et al 11 A study of processes involving positive ions-complementary to the present investigationhas been performed by Lacko et al 12 A preliminary account of a study involving negative ion intermediates was presented in conference proceedings. 13 Processes induced by electron transfer in Rydberg atom collisions were studied by Buathong et al 14 Related to the present work are also condensed phase studieselectron induced degradation of condensed Fe(CO) 5 by electron stimulated desorption has been studied by Massey et al 15,16 and Hauchard and Rowntree 17 -and studies on argon nanoparticles by Lengyel et al 18,19 Electron affinity of Fe(CO) − 4 , required for the interpretaion of the present data, was determined by anion photoelectron spectroscopy by Engelking and Lineberger. 20 Electron-induced decomposition of Fe(CO) 5 has so far been probed experimentally with respect to identifying which fragmentation pathways occur, which electron energy ranges are relevant and, in some cases, determining absolute cross sections.…”

Suppression of low-energy dissociative electron attachment in Fe(CO)5 upon clustering

“…Massey et al [ 20 ] have recently probed the anion desorption from iron pentacarbonyl thin films condensed on xenon upon electron irradiation and reported no desorption signals below 5 eV. The authors attributed this primarily to low desorption probability of fragments produced at low electron energies.…”

“…This is in very good agreement with the present results on anion synthesis in pure Fe(CO) 5 clusters. As already mentioned, Massey et al [ 20 ] studied degradation of Fe(CO) 5 films condensed on a xenon spacer on platinum foil by electron stimulated desorption. They did not observe any anion desorption at electron energies below 4 eV and strong desorption signals in the energy range 5–20 eV.…”

The role of low-energy electrons in focused electron beam induced deposition: four case studies of representative precursors

“…The threshold is thus generally higher than that for DEA and ND but lower than that for DI. To our knowledge there are no current gas phase studies on DD of relevant FEBID precursors and generally DD is not a very efficient process (see T. D. Märk and references therein on pages 276–277 in [ 27 ]) It is, however, worth mentioning that a recent study on electron-stimulated negative ion desorption from Fe(CO) 5 films shows a significant contribution to the desorption yield from dipolar dissociation [ 45 ].…”