Strategies for the immobilization of nanoparticles using electron beam induced deposition

Abstract

The mechanism of electron-beam-induced immobilization of nanoparticles on a substrate has been studied both experimentally and theoretically. Experiments have been performed for the case of 200-350 nm Co-Ni nanoparticles secured to a substrate using a 30 keV electron beam. Atomic force microscopy studies reveal that the fixing occurs due to the formation of a deposit beneath the nanoparticles, causing strong bonding to the substrate, even for a thin layer. Measurements of the lateral forces required to displace the immobilized nanoparticles have shown that a deposit layer of 0.5 nm results in a tenfold increase in the bonding strength. A comparison of measured profiles with the results of computer simulations clearly reveals that the major role in the formation of the deposit is played by low-energy electrons generated by energetic primary electrons in both the nanoparticles and substrate. It is also shown that the efficiency of bonding decreases with decreasing energy of primary electrons. Different strategies for electron-beam-induced immobilization of nanoparticles and optimization of the processes are discussed.

Selected immobilization of individual nanoparticles by spot-exposure electron-beam-induced deposition

“…26). This different distribution of deposit could account for the different failure mechanism that occurs when secured parti-cles are forcibly displaced -here we observe adhesion between particle and deposit to fail, whereas following areal exposure 26 we found adhesion between deposit and substrate to fail.…”

“…Our Monte Carlo simulations have been described in a previous study. 26 For a large number of incident primary electrons, we calculate the subsequent trajectories as they scatter within the system along with the trajectories of generated electrons including cascades of secondaries. From these we determine the flux of secondaries passing through the surface.…”

“…42 This description of the electron scattering has been shown to give a sound description of SE and backscattered electron yields over a wide range of energies, as well as a good account of the angular and energy distributions of SEs. 26 The surface of the nanoparticle+substrate system at which growth of deposit occurs is described by a set of points r S , which evolve in time. Growth causes the surface to advance in a direction normal to the instantaneous surface profile, at a rate…”

“…[20][21][22][23][24] In these applications EBID forms a blanket of deposit covering the nanoscale objects to hold them in place. 19 Recently we have demonstrated 25,26 that due to the penetration depth of the energetic PEs used for EBID, deposit forms not only on the surfaces directly exposed to the electron beam, but also in regions of geometrical shadow, such as the underside of exposed nanoparticles and the underlying surface. Furthermore, a thin layer of deposit formed in the vicinity of the point of contact of a nanoparticle and substrate can therefore be used to secure the nanoparticle in place, with a ten-fold increase observed in the lateral force required to displace a nanoparticle following the deposition of a sub-nanometer thickness of deposit.…”

Fabrication and Evaluation of Nanoparticle‐Based Biosensors

“…These nanoparticles have been widely used for making single electron transistors, memory storage devices, nanoscale photodetectors, nanoantennas, nanophotonic/plasmonic waveguides, and integrated circuits such as immobilization of 200 -to 350 -nm Co/Ni nanoparticles on a substrate using electron -beam induced deposition [60] .…”