Irradiation-driven molecular dynamics simulation of the FEBID process for Pt(PF₃)₄

Abstract

This paper presents a detailed computational protocol for the atomistic simulation of formation and growth of metal-containing nanostructures during focused electron beam-induced deposition (FEBID). The protocol is based upon irradiation-driven molecular dynamics (IDMD), a novel and general methodology for computer simulations of irradiation-driven transformations of complex molecular systems by means of the advanced software packages MBN Explorer and MBN Studio. Atomistic simulations performed following the formulated protocol provide valuable insights into the fundamental mechanisms of electron-induced precursor fragmentation and the related mechanism of nanostructure formation and growth using FEBID, which are essential for the further advancement of FEBID-based nanofabrication. The developed computational methodology is general and applicable to different precursor molecules, substrate types, and irradiation regimes. The methodology can also be adjusted to simulate the nanostructure formation by other nanofabrication techniques using electron beams, such as direct electron beam lithography. In the present study, the methodology is applied to the IDMD simulation of the FEBID of Pt(PF3)4, a widely studied precursor molecule, on a SiO2 surface. The simulations reveal the processes driving the initial phase of nanostructure formation during FEBID, including the nucleation of Pt atoms and the formation of small metal clusters on the surface, followed by their aggregation and the formation of dendritic platinum nanostructures. The analysis of the simulation results provides spatially resolved relative metal content, height, and growth rate of the deposits, which represents valuable reference data for the experimental characterization of the nanostructures grown by FEBID.

Atomistic simulation of the FEBID-driven growth of iron-based nanostructures

“…17 The MBN Studio toolkit 18 has been utilized to create the systems, prepare all necessary input files and analyze simulation outputs. The step-by-step protocol of the multiscale IDMD-based simulation of the FEBID process 11,15 has been described in detail in the earlier study 19 and is therefore only briefly recapped below. Interatomic interactions involving the precursor molecules are described using the reactive CHARMM (rCHARMM) force field.…”

“…The initial geometry of a Fe(CO) 5 molecule has been determined via density-functional theory (DFT) calculations using Gaussian 09 software 46 and then optimized using MBN Explorer. 17 The rCHARMM parameters for a Fe(CO) 5 molecule have been evaluated from a series of DFT-based potential energy scans, following the protocol employed in the earlier studies 19,43 for W(CO) 6 and Pt(PF 3 ) 4 precursors. The parameters of the bonded and angular interactions for Fe(CO) 5 are listed in Table 1.…”

“…The interaction between iron atoms in the formed metalcontaining structures has been described by means of the many-body embedded-atom-model (EAM) potential 47 taken from the NIST Interatomic Potentials Repository. ‡ Following the earlier IDMD-based studies of FEBID, 11,15,19 the SiO 2 -H substrate has been fixed in space in the course of simulations for computational speed-up. The adsorbed precursor molecules and fragments interact with the substrate via van der Waals forces described by means of the Lennard-Jones potential:…”

“…In the present study, a layer of Fe(CO) 5 with the dimensions of 20 nm  20 nm has been created using MBN Studio, 18 optimized using the velocity quenching algorithm, softly deposited onto the SiO 2 -H substrate and thermalized at 300 K for 0.3 ns using the Langevin thermostat with a damping time of 0.2 ps. 19 The simulations have been performed using the Verlet integration algorithm with a time step of 1 fs and reflective boundary conditions. The linked cell algorithm 17 with a cell size of 10 Å has been employed for the more efficient evaluation of interatomic interactions between particles of the system.…”

“…The IDMD approach also enables monitoring and predicting the morphology of the FEBID nanostructures on the atomistic level. 11,15 Our recent study 19 provided a detailed description of the IDMD-based computational methodology for modeling the formation and growth of FEBID nanostructures. Different computational aspects of the methodology and the key input parameters describing the precursor molecules, the substrate, and the irradiation and replenishment conditions were systematically described.…”