Precise positioning of nanoparticles on surfaces using scanning probe lithography

Two new methods have been developed to precisely position gold nanoparticles on surfaces. The surface-active nanoparticles have a shell of a mixed monolayer comprised of alkanethiol and alkanedithiol molecules to anchor particles to gold surfaces via sulfur-gold chemisorption. In the first method, regions of an alkanethiol self-assembled monolayer (SAM) are shaved by the AFM tip under high force in a solution containing nanoparticles. Nanoparticles then adsorb onto the exposed areas defined by the shaving track of the tip. In a second method, the AFM tip is coated with nanoparticles. Under low force, AFM images are acquired and the nanoparticles remain on the tip. When higher load is applied, areas of the SAM matrix are uncovered and nanoparticles are deposited following the scanning track of the AFM tip. Thus, the 3D positions of the nanoparticles are precisely controlled. The nanostructures are characterized in situ with the same tip at reduced load. Individual particles within the nanopatterns can be resolved by AFM. In both methods, the matrix SAM effectively resists the nonspecific binding of nanoparticles, and prevents lateral diffusion of nanoparticles. The high spatial precision offered by AFM lithography is advantageous for fabrication of nanoparticle-based nanodevices.