Atomic force microscopy (AFM) has been explored in recent years to pattern nanoparticles and organic/biomolecules on solid surfaces. In particular, dip-pen nanolithography (DPN) has been successfully demonstrated to 'write' molecules on a surface by using an AFM tip coated with desired molecular 'ink' (1, 2). AFM has also been used to push (slide) and arrange nanoparticles on solid surfaces (3-4). Application of an electric field between the AFM probe and substrate is known to produce effects like oxidation of surfaces and curing of polymers (5). However, use of electric fields in DPN has been limited to electrochemical reduction of metals on surfaces (6, 7).
In this work we demonstrate the direct deposition of gold nanoparticles on solid surfaces using electric field assisted DPN (E-DPN). Bias voltage applied to AFM probes coated with gold nanoparticles is found to play a critical role in releasing the particles onto a substrate. E-DPN has also been used on metal (nickel) substrates to ionize localized regions. Metal chelating peptides coated on AFM probes can then attach to metal ions present in these regions on the substrate. Deposition has been accomplished using both contact and tapping modes, which creates many possible applications of positioning and subsequently imaging nanoparticles and biomolecules on various surfaces.
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