Template assisted electrostatic Au nanoparticle assembly

Abstract

Single electron transistors fabricated using template assisted self-assembled nanoparticles has recently gained much interest for possible application to future nanoelectronic devices [1,2]. Here, we present a method where convection driven nanoparticle assembly on structural templates were enhanced by the application of an electrostatic field between the substrate and electrolyte. Array of 80 x 80 nm2 holes were patterned in 150 nm thick PMMA using electron beam lithography. A drop of solution containing high density 20 nm diameter Au nanoparticles was placed on the patterned surface and 1~3 V was applied between the solution and substrate to initiate electrophoresis. As shown in Fig. 1(a), nanoparticles were assembled mostly inside the resist hole structural template and not on the resist surface. The nanoparticle diameter dnc / linewidth lW = 0.25 which means that the maximum number of nanoparticle density per hole for monolayer coverage is 9. however, we observed an average site density ~ 4.5. This was attributed to electrostatic repulsion of existing nanparticles, preventing high density assembly. The 70 nm line pattern template showed higher nanoparticle density (~60% coverage) suggesting linear template structures are more favorable for high level integration. High dnc/lW = 0.75 gave lower nanoparticle density which may limit minimum pattern width for template assisted electrostatic assembly.