Identifying and Rationalizing the Differing Surface Reactions of Low-Energy Electrons and Ions with an Organometallic Precursor

Abstract

Surface reactions of electrons and ions with physisorbed organometallic precursors are fundamental processes in focused electron and ion beam-induced deposition (FEBID and FIBID, respectively) of metal-containing nanostructures. Markedly different surface reactions occur upon exposure of nanometer-scale films of (η5-Cp)­Fe­(CO)2Re­(CO)5 to low-energy electrons (500 eV) compared to argon ions (860 eV). Electron-induced surface reactions are initiated by electronic excitation and fragmentation of (η5-Cp)­Fe­(CO)2Re­(CO)5, causing half of the CO ligands to desorb. Residual CO ligands decompose under further electron irradiation. In contrast, Ar+-induced surface reactions proceed by an ion–molecule momentum/energy transfer process, causing the desorption of all CO ligands without significant ion-induced precursor desorption. This initial decomposition step is followed by ion-induced sputtering of the deposited atoms. The fundamental insights derived from this study can be used not only to rationalize the composition of deposits made by FEBID and FIBID but also to inform the choice of a charged particle deposition strategy and the design of new precursors for these emerging nanofabrication tools.

Low Energy Electron- and Ion-Induced Surface Reactions of Fe(CO)5 Thin Films

“…In a recent paper, we compared the low energy (<1 keV) electron-and argon ion-induced decomposition reactions of thin films of adsorbed CpFe(CO) 2 Re(CO) 5 on a cooled gold substrate. 37 This study revealed that the electron and argon ion-induced decomposition of adsorbed CpFe(CO) 2 Re(CO) 5 were significantly different, giving support to the collision cascade model dominating deposition in the ion-limited regime of FIBID. To explore the extent to which these differences apply to other precursors we have used in situ XPS in the present investigation to compare and contrast the low energy electron-(500 eV) and Ar + (1200−3000 eV) induced reactions with thin films of adsorbed Fe(CO) 5 on a cooled (143 K) Au substrate.…”

“…The similar rate and extent of carbon and oxygen loss strongly suggests that this process is a consequence of CO desorption, consistent with previous studies of other metal carbonyls exposed to low energy electrons. 24,[29][30][31]37 Figure 2b plots the relative abundance of graphitic carbon (open squares) and oxide oxygen (blue squares) upon irradiation with 500 eV electrons, as measured by the graphitic C(1s) and oxide O(1s) XPS peaks (Figure 1), respectively. These two species show a near identical kinetic dependence, indicating that they are likely produced by the same process and with equal efficiency.…”

“…Examining Figures 1 and 2, it is evident that the electroninduced reactions of adsorbed Fe(CO) 5 proceed in two regimes, similar to other carbonyl-containing organometallic species. [29][30][31]37 The first regime, operative at electron doses < ≈ 20 mC/cm 2 , is characterized primarily by the loss of CO ligands. This process which accompanies precursor decomposition can be described as…”

Highly-efficient growth of cobalt nanostructures using focused ion beam induced deposition under cryogenic conditions: application to electrical contacts on graphene, magnetism and hard masking

“…This can be achieved through cooling the substrate below the precursor condensation temperature. [19][20][21][22][23][24] This Cryo-FIBID approach holds an enormous potential for rapid patterning of metallic micro/nano-deposits. For example, optimized W-C cryo-deposits with a resistivity of 800 •cm were obtained using 50 C/cm 2 Ga + dose and applied as electrical contacts to measure semiconducting nanowires.…”

Optimization of Pt-C Deposits by Cryo-FIBID: Substantial Growth Rate Increase and Quasi-Metallic Behaviour

“…The viability of Pt deposition by Cryo-FIBID is reinforced by previous investigations that have demonstrated that focused electron beam irradiation under cryogenic conditions (Cryo-FEBID) of the (CH 3 ) 3 Pt(CpCH 3 ) precursor is feasible [ 16 ]. Additionally, recent theoretical work has emphasized the advantages of ion versus electron precursor decomposition under cryogenic conditions for the metallic content of the deposits [ 17 ].…”