How do the electron-driven reactions depend on the chemical properties of the precursor molecules?

Combined experimental and theoretical insight is needed to establish quantitative criteria on how the electron-driven reactions depend on the chemical properties of precursor molecules. This approach has provided guidelines leading to design principles for novel precursors. Also, design rules for FEBID precursors derived from experimental observation have been discussed in a recent review:

• Julie A. Spencer, Samantha G. Rosenberg, Michael Barclay, Yung-Chien Wu, Lisa McElwee-White, D. Howard Fairbrother:
  Understanding the electron-stimulated surface reactions of organometallic complexes to enable design of precursors for electron beam-induced deposition,
  Appl. Phys. A 117 (2014) 1631.

Bimetallic precursors with quasi metallic band structure - unusual DEA pattern

DEA processes continuously spanning the energy range of 0 eV up to 20 eV and leading even to complete loss of the ligands has been observed for HFeCo₃(CO)₁₂. This results from the favourable effect of closely spaced occupied and unoccupied molecular energy levels, i.e., a quasi metallic band structure of the metal core within the precursor. This general behaviour has been confirmed for two other bimetallic precursors (H₂FeRu₃(CO)₁₃, η⁵-CpFe(CO)₂Mn(CO)₅):

• Ragesh Kumar T.P., Ragnar Bjornsson, Sven Barth, Oddur Ingólfsson:
  Formation and decay of negative ion states up to 11 eV above the ionization energy of the nanofabrication precursor HFeCo₃(CO)₁₂,
  Chem. Sci. 8 (2017) 5949-5952.

(η³-C₃H₅)Ru(CO)₃Br - persistent halide ligands drive loss of other ligands

A combined experimental and theoretical has brought forward the picture that halide ligands that are persistent during the initial electron-precursor interaction stabilize the metal-centered anionic precursor fragments. This provides additional energy that drives further ligand loss. Given that the halide can be removed by post-deposition treatment, they can thus act as promoters of precursor fragmentation:

• Rachel M. Thorman, Ragnar Bjornsson, Oddur Ingólfsson:
  Computational study of dissociative electron attachment to π-allyl ruthenium (II) tricarbonyl bromide,
  Eur. Phys. J. D 70 (2016) 164.

• Rachel M. Thorman, Joseph A. Brannaka, Lisa McElwee-White, Oddur Ingolfsson:
  Low energy electron-induced decomposition of (η³-C₃H₅)Ru(CO)₃Br, a potential focused electron beam induced deposition precursor with a heteroleptic ligand set,
  Phys.Chem.Chem.Phys. 19 (2017) 13264-13271.

Pt(PF₃)₄ - non-bonding excited states drive neutral dissociation

Quantum chemical calculation on Pt(PF₃)₄ have revealed that neutral excitation processes lead to a multitude of non-bonding excited states indicating that neutral dissociation which has been mainly neglected so far due to experimental difficulties in fact plays a significant role in precursor fragmentation:

• M. Zlatar, M. Allan, J. Fedor:
  Excited States of Pt(PF₃)₄ and Their Role in Focused Electron-Beam Nanofabrication,
  J. Phys. Chem. C 120 (2016) 10667–10674.

Cisplatin - facile formation of pure Pt

Experimental evidence indicates that the properties of FEBID precursors can in fact be tuned by suitably selected ligands leading to deposits with increased metal content. In fact, electron irradiation of cisplatin leads to pure Pt pointing to a favourable effect of NH₃ and Cl ligands:

• Jonas Warneke, Markus Rohdenburg, Yucheng Zhang, Juraj Orzagh, Alfredo Vaz, Ivo Utke, Jeff Th.M. De Hosson, Willem F. van Dorp, Petra Swiderek:
  Role of NH₃ in the electron-induced reactions of adsorbed and solid cisplatin,
  J. Phys. Chem. C 120 (2016) 4112-4120.

Silanes - the role of chlorine substitution on eletron-induced fragmentation mechanisms

Chlorine substitution at the silicon atom of silacyclohexane switches on DEA fragmentation channels while in the unsubstituted compound, only fragmentation via dissociative ionization (DI) has been observed:

• Elías H. Bjarnason, Benedikt Ómarsson, Nanna Rut Jónsdóttir, Ingvar Árnason,
  Oddur Ingólfsson:
  Dissociative electron attachment and dissociative ionization of 1,1-dichloro-1-silacyclohexane and silacyclohexane,
  International Journal of Mass Spectrometry 370 (2014) 39–43.

• Ragesh Kumar T P, Sangeetha Hari, Krishna K Damodaran, Oddur Ingólfsson, Cornelis W. Hagen:
  Electron beam induced deposition of silacyclohexane and dichlorosilacyclohexane: the role of dissociative ionization and dissociative electron attachment in the deposition process,
  Beilstein J. Nanotechnol. 8 (2017) 2376–2388.

Cr(0)(C₆H₆)(CO)₃ - facile removal of the neutral benzene ligand

Fragments formed by loss of the neutral benzene ligand following electron attachment to Cr(0)(C₆H₆)(CO)₃ have been observed with high intensity. This is in contrast to the anionic cyclopentadienyl ligand of complexes such as MeCpPtMe₃ which produce a deposit with high carbon content due to persistence of the anionic MeCp ligand:

• Janina Kopyra, Paulina Maciejewska, Jelena Maljković:
  Dissociative electron attachment to coordination complexes of chromium: chromium(0) hexacarbonyl and benzene-chromium(0) tricarbonyl,
  Beilstein J. Nanotechnol. 8 (2017) 2257–2263.