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

The use of spot-exposure electron-beam-induced deposition (EBID) to immobilize targeted nanoparticles on a substrate is demonstrated, and investigated using experiment and simulation. Nanoparticles are secured in place through the build-up of carbonaceous material that forms in the region between a particle and substrate when an energetic electron beam is focused onto the particle and projected through to the substrate. Material build-up directly affects the strength of adhesion to the surface, and can be controlled through electron dosage and beam energy. By selectively immobilizing specific particles within surface agglomerations and removing the excess, we illustrate the potential for spot-exposure EBID as a new technique for nanofabrication.

Proximity effects in free-standing EBID structures.

Proximity effects causing thickening and bending of closely spaced, free-standing pillars grown by electron-beam-induced deposition are investigated. It is shown that growth of a new pillar induces deposition of a layer of additional material on the side of already grown pillars facing the new pillar. We present experimental results which suggest that the bending of pillars is caused by shrinkage of the newly formed layer on exposure to the primary electron beam.

Strategies for the immobilization of nanoparticles using electron beam induced deposition.

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.