Direct and controlled manipulation of nanometer-sized particles using the non-contact atomic force microscope

In this paper, we present techniques for the direct and controlled manipulation of nanoscale three-dimensional (3D) features using the non-contact atomic force microscope (NC-AFM). A systematic examination of the nature of NC-AFM images of such 3D features leads us to propose two distinct protocols for nanomanipulalion. The first protocol consists of switching off the NC-AFM feedback loop just as the tip approaches a nanofeature of interest. This results in tip-nanofeature contact and causes the feature to be 'pushed' along the surface as the tip continues to move laterally. The second protocol exploits a peculiar feature of the NC-AFM which produces reversal of contrast of nanofeatures from positive to negative in NC-AFM images, due to a feedback instability. The contrast reversal, which is likely to be universal to NC-AFM, occurs with changes in imaging conditions and potentially leads to tip-sample contact, thereby allowing manipulation. This second technique has the advantage of easier identification of the manipulation regime and the potential for manipulating features that are only a few nm in size. We demonstrate the viability of these two protocols by directly manipulating gold particles of diameters 5 and 15 nm into predetermined patterns on a mica surface. We also illustrate a simple, generic approach that is useful for obtaining detailed information on the mechanism of any manipulation based on the scanning probe microscope.