Dissociative electron attachment to Pt(PF₃)₄—a precursor for Focused Electron Beam Induced Processing (FEBIP)

Abstract

Experimental absolute cross sections for dissociative electron attachment (DEA) to Pt(PF(3))(4) are presented. Fragment anions resulting from the loss of one, two, three and four PF(3) ligands as well as the Pt(PF(3))F(-) and the F(-) ions were observed. The parent anion Pt(PF(3)) is too short-lived to be detected. The dominant process is loss of one ligand, with a very large cross section of 20 000 pm(2); the other processes are about 200× weaker, with cross sections around 100 pm(2), the naked Pt(-) anion is formed with a cross section of only 1.8 pm(2). The resonances responsible for the DEA bands were assigned based on comparison with electron energy-loss spectra and spectra of vibrational excitation by electron impact. Bands around 0.5 eV and 2 eV were assigned to shape resonances with single occupation of virtual orbitals. A DEA band at 5.9 eV was assigned to a core-excited resonance corresponding to an electron very weakly bound to the lowest excited state. An F(-) band at 12.1 eV is assigned to a core excited resonance with a vacancy in an orbital corresponding to the 2nd ionization energy of the PF(3) ligand. Implications of these findings for FEBIP are discussed.

Understanding the electron-stimulated surface reactions of organometallic complexes to enable design of precursors for electron beam-induced deposition

“…Collectively, these observations indicate that the initial step in the decomposition of adsorbed Pt(PF 3 ) 4 molecules proceeds via cleavage of one of the metal-ligand bonds and loss of one PF 3 group [38]. A comparison of gas phase and surface science studies leads to the same conclusion as for MeCpPtMe 3 ; notably, that dissociation of adsorbed Pt(PF 3 ) 4 precursor molecules in EBID occurs via a DEA process, with the low-energy electrons being produced by the interaction of the primary beam with the substrate [38,58]. The overall deposition process can be represented by the following equation,…”

Absolute cross sections for dissociative electron attachment and dissociative ionization of cobalt tricarbonyl nitrosyl in the energy range from 0 eV to 140 eV

“…We have recently presented absolute partial cross sections for fragment formation through DEA of cobalt tricarbonyl nitrosyl, 21 and relative cross sections for another standard FEBID precursor molecule trimethyl(methylcyclopentadienyl)platinum(IV). 22 These and other recent studies 23,24,43 reveal that DEA induces mainly incomplete fragmentation of the parent compound, in the energy range <10 eV, and may thus be responsible for the inclusion of non-metal contaminants in FEBID structures. However, as discussed earlier, dissociative ionisation is also operative in the secondary electron energy region, and for Co(CO) 3 NO this process leads predominantly to the formation of the bare metal cation, Co + , through complete decomposition of the precursor.…”

“…To our knowledge, however, DEA has to date not been accounted for in MC simulations dealing with FEBID, and although it is clear that further studies are necessary to confirm their relevance and especially how the DEA processes are influenced by the supporting surface, recent investigations indicate strongly that DEA may play a pivotal role in FEBID. [21][22][23][24][25]46 In particular, this applies to the purity of the deposit and the broadening of the deposits beyond the diameter of the electron beam, which are currently the main challenges that need to be addressed to further enhance the applicability of FEBID as a standard tool in nano-fabrication. Like DEA, absolute cross sections for DI of relevant FEBID precursor molecules are scarce.…”

“…7,20 At those energies, dissociative electron attachment (DEA) is the only efficient fragmentation mechanism and, in that context, its potential role in FEBID has been discussed in some detail. [21][22][23][24][25] Although DEA is the only effective electron induced dissociation mechanism below the ionization limit of the respective molecules, SEs and BSEs, with incident energies close to and above the ionization limit of the respective molecules, can also cause fragmentation through dissociative ionization (DI). This is a non-resonant process, but can nonetheless be very efficient at fairly low incident energies (typically, in the range 10-50 eV).…”

Sub-10 nm writing: focused electron beam-induced deposition in perspective

“…While the key role of SEs was generally assumed for decades [3], it was not demonstrated until recently that SEs indeed dominate the chemistry in FEBIP. For instance, experiments with MeCpPtMe 3 [18] and Pt(PF 3 ) 4 [19] show that the most favorable channels for electron-induced dissociation in the gas phase are active at 0-1 eV (see Fig. 1a).…”