Metal Films Prepared by Stepwise Assembly. 2. Construction and Characterization of Colloidal Au and Ag Multilayers

Abstract

This manuscript describes the stepwise, ligand-directed assembly, characterization, and prospective applications of three-dimensional Au and Ag nanoparticle, multlilayered films. Films were prepared by successive treatments of a Au nanoparticle monolayer with a bifunctional cross-linker and colloidal Au or Ag solutions. Changes in film electrical and optical properties are reported for a series of bifunctional cross-linkers of varying molecular lengths. Interestingly, these films exhibit Beer's law behavior despite the presence of strong interparticle optical coupling. Multilayer films with greater than six exposures to 2-mercaptoethylamine and Au colloid were highly conductive and resembled bulk Au in appearance. In contrast, films of similar particle coverage generated using a longer cross-linker (1,6-hexanedithiol) exhibited higher transmission in the near-infrared region and exhibited a reduced conductivity. Measurement of the multilayer morphology with atomic force microscopy , electrostatic force microscopy, and field emission scanning electron microscopy revealed a porous, discontinuous morphology composed of large, continuous regions of aggregated nanoparticles. This, in turn, results in a surface roughness contribution to surface plasmon scattering and surface-enhanced Raman scattering observed for Au, Au/Ag, and Ag colloid multilayers. Particulate multilayer films made using horseradish peroxidase as a cross-linker remained enzymatically active, even beneath three layers of colloidal Au. Multilayers could also be prepared on surfaces patterned by microcontact printing. These data show how Au colloid multilayers grown in solution are a viable alternative to evaporated metal films for a number of applications.

Optical Properties and Ultrafast Dynamics of Metallic Nanocrystals

“…A monolayer of nanoparticles is then assembled and covered with another layer of dithiols upon which another layer of nanoparticles can be prepared. In this method, alternating layers of nanoparticles of different size as well as different composition can be used, as shown by Rao and coworkers (160) as well as by Natan and coworkers (161). Studies were performed regarding the collective optical and conductive properties as a function of the number of deposited layers as well as the nature of the crosslinker.…”

RIR-MAPLE deposition of plasmonic silver nanoparticles

“…Other methods, such as self-assembly [11] and adsorption of nanoparticles onto oppositely charged substrates [12], provide precise control of the nanoparticle film. Yet, these techniques are specifically designed for certain substrates or nanoparticle material systems.…”

Location Control of Nanoparticles Using Combination of Top-down and Bottom-up Nano-fabrication

“…Also, gold allows for the covalent attachment of thiolated ligands to the particle surface [21,22]. The optical and electrical properties of layer by layer self-assembled films comprised of Au or Ag nanoparticles and various organic compounds have been investigated [23][24][25][26][27][28][29]. Furthermore, layer-by-Layer self-assembly of composite thin films of cadmium sulfide nanoparticle and alkanedithiol was achieved on a gold substrate by an alternate immersion into solutions of dithiols and solution containing CdS nanoparticle [30,31].…”