title: Assembly of metal nanoparticles into nanogaps.
abstract: The directed assembly of nanoparticles and nanoscale materials onto specific locations of a surface is one of the major challenges in nanotechnology. Here we present a simple and scalable method and model for the assembly of nanoparticles in between electrical leads. Gold nanoparticles, 20 nm in diameter, were assembled inside electrical gaps ranging from 15 to 150 nm with the use of positive ac dielectrophoresis. In this method, an alternating current is used to create a gradient of electrical field that attracts particles in between the two leads used to create the potential. Assembly is achieved when dielectrophoretic forces exceed thermal and electrostatic forces; the use of anchoring molecules, present in the gap, improves the final assembly stability. We demonstrate with both experiment and theory that nanoparticle assembly inside the gap is controlled by the applied voltage and the gap size. Experimental evidence and modeling suggest that a gap-size-dependent threshold voltage must be overcome before particle assembly is realized. Assembly results as a function of frequency and time are also presented. Assembly of fewer than 10 isolated particles in a gap is demonstrated. Preliminary electrical characterization reveals that stable conductance of the assembled particles can be achieved.
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Barsotti
authors.forename: Michael D
authors.initials: MD
authors.lastname: Vahey
authors.forename: Ryan
authors.initials: R
authors.lastname: Wartena
authors.forename: Yet-Ming
authors.initials: YM
authors.lastname: Chiang
authors.forename: Joel
authors.initials: J
authors.lastname: Voldman
authors.forename: Francesco
authors.initials: F
authors.lastname: Stellacci
mesh_terms: D003460:Crystallization / Q000379:methods*; D004586:Electrophoresis / Q000379:methods*; D006046:Gold / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008839:Microelectrodes; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D006046:Gold