Preparation of Two-Dimensional Arrays of Ag Nanopaticles for Laser Interrogation.

A nanoparticle is a collection of thousands of atoms in a typically spherical shape with a diameter of 1 to 100 nm. These particles are bits of matter that lie somewhere between the atom and the bulk. Their chemical and physical properties are of considerable importance in understanding finite-sized systems. Silver nanoparticles passivated with dodecanethiol have been synthesized. A tremendous advantage of forming passivated nanoparticles is the ease of particle size-selection with organic solvents. Size-selected silver nanoparticles have been characterized by Ultraviolet-Visible Absorption and Fourier Transform Infrared Spectroscopies. These particles have an average diameter of approximately 40 nm. A two-dimensional crystalline array of Ag nanoparticles will be formed on a Langmuir Trough. This array or monolayer will be transferred by the Langmuir-Schaefer method to a clean glass slide. The supported array will be mounted in a high vacuum chamber for laser interrogation. In bulk metal, the energy of excited electrons will be dissipated by the phonons or lattice modes. In a small particle, the lattice modes are quite different than in the bulk and may not be as effective in quenching the electrons. Therefore, in a finite-sized particle, it is hypothesized that the excited electrons will escape the metal. Low intensity light of the second harmonic of a Nd:YAG laser (532 nm) will be directed onto the array to excite electrons and the intensity of the ejected electrons will be measured