This study utilizes the “bricks” and “mortar” approach to assemble representative organic and inorganic nanostructures into functional hybrid nanomaterials. Zero-dimensional spherical nanoparticles, one-dimensional silver nanowires, and two-dimensional silver nanoplates represent the inorganic functional nanostructured “bricks”. Functional-group bearing polystyrene₂-polyethyleneoxide₁ (PS₂-PEO ₁) star polymer, poly(allylamine hydrochloride), and poly(styrene sulfonate) were employed as the “mortar”. Mechanical, optical, and electrical properties of the resulting organic/inorganic microstructures were investigated to establish structure-property relationships. Beyond the design, fabrication, and characterization of these novel hybrid nanomaterials two potential applications have been explored: (1) ultra-thin composite film-based pressure sensor and (2) single nanoparticle SERS-based chemical sensors.

One-dimensional silver nanowires (diameter = 80 ± 5 nm, length = 6 ± 2 µm) were sandwiched into layer-by-layer (LbL) polyelectrolyte film to yield a series of robust freestanding ultrathin structures (< 100 nm thick). The sandwich architecture allows facile control over volume fraction of silver nanowires (2.5 ≤ &PHgr; ≤ 22.5%), and hence their composite Young’s moduli. Furthermore, the composite film was found to be conductive (110–660 S/cm) within the range of volume fraction in par with percolation threshold predicted for a two-dimensional film. Subsequently, an array of silver nanowires was unidirectionally aligned by means of Langmuir-Blodgett (LB) technique. The unidirectionally oriented silver nanowires were sandwiched into LbL film to give an anisotropic nanocomposite film with much stiffer (fivefold) mechanical response in the direction of nanowire orientation. In addition to their tailored mechanical and electrical properties, these films are robust and can be easily transferred onto various microfabricated substrates. To fabricate these nanostructures, two experimental techniques were developed to characterize the micromechanical properties of the nanocomposite film and array of one-dimensional metallic nanostructures: interferometry of bulged film and buckling of array of highly-oriented nanowires, respectively.

Next, using the same silver nanowire building block a different design of organic/inorganic hybrid nanostructures was explored. With the aid of a three-arm (X-PEO)1-(PS1-Y)2 star polymer linker, spherical gold nanoparticles were assembled onto a silver nanowire surface. We demonstrated that such hybrid, silver-gold nanowires resembling nanocobs, possess significant SERS ability and can serve as bright anisotropic SERS-markers for Raman-based chemical sensor. The influence of core nanostructure geometries (1-D silver nanowire versus 2-D silver nanoplates) were subsequently investigated for their single-nanoparticle hybrid SERS-enhancing ability and control over optical plasmon absorption within the visible and near infrared range. In the latter design, an improved design of SERS-nanostructure was explored by replacing the three-arm star polymer with polyelectrolyte “mortar” which can absorb chemical analytes into the intra-particle “hot-spots”.