Oct 14, 2008
Nanoparticle immobilisation using electron-beam induced deposition
An important area of nanotechnology is the fabrication of hybrid devices in which one or more nanoparticles play the role of the key functional elements. Examples include the use of nanoparticles in single-electron transistors, memory storage devices, nanoscale photodetectors and plasmonic waveguides. An essential aspect of the fabrication of such devices is a technique that enables the reliable bonding of nanoparticles to specific locations.
Electron-beam induced deposition (EBID) offers this possibility. In this process, surface-adsorbed gas molecules are dissociated forming a volatile fraction and a solid residue by secondary electrons emitted when a high energy (10–200 keV) incident electron beam is targeted at a material. In the past this solid residue has been used to fabricate nanostructures and to “clamp” nanoparticles to substrates through blanket coverage.
Now, work in the nanoscience groups at the University at Bath using nanoparticles synthesised at INSA de Toulouse and published in the journal Nanotechnology has shown that nanoparticles can be secured in place using a much smaller amount of EBID residue than previously believed. A 10-fold increase in the force required to dislodge nanoparticles has been measured using AFM for deposit thicknesses of just 0.5 nm. Computer simulations have been used to reveal the basic mechanism underlying this efficient bonding: enhanced deposition occurs near where the nanoparticle contacts the substrate, resulting in “welding” from beneath.
This finding is important as reducing the thickness of deposit needed to immobilise nanoparticles also reduces the possible modification of their electronic, optical or magnetic properties that can result from coverage by the EBID residue, affecting their functionality. The high resolution of modern electron beams (~1 nm) means EBID immobilisation can be used to secure individual nanoparticles, while beam control as used in electron-beam lithography could enable larger-scale organisation of nanoparticles. Starting from a particle monolayer you can envisage patterning by sweeping an electron beam across the surface in a predefined path, securing in place those particles beneath the electron beam and allowing excess particles to be removed by agitation in a solvent bath to lift them into suspension.
About the author
Dan Burbridge is currently studying for a PhD at the University of Bath, researching applications of electron-beam-induced deposition. Dr Sergey Gordeev is an experimental scientist interested in areas of nanofabrication and AFM. Dr Simon Crampin is a computational theoretician with interests in electronic structure and dynamics, and nanoscale physics. Guillaume Viau is a professor of the Department de Genic Physique at INSA de Toulouse working in areas of synthesis and characterisation of nanoparticles.