Our research group has developed a cluster tool system that addresses the above issues. The system consists of a nanoparticle deposition unit, an electron-beam evaporation unit for the deposition of thin films, and a pulsed DC sputtering unit for the deposition of thick layers of metals and insulators. The nanoparticle deposition system is based on sputtering, thus allowing the deposition of nanoparticles of any material that can be sputtered. In addition, nanoparticle deposition can be carried out at room temperature, making it possible to deposit the nanoparticles on a variety of substrates including flexible substrates. Size selection of nanoparticles is achieved by using a quadrupole mass filter with the capability to provide as low as 2% size control. The nanoparticle deposition unit, the electron beam evaporation unit and the DC sputtering unit are all housed inside an ultra-high vacuum chamber to ensure high purity and good surface properties of the nanoparticles. We have used this technique to fabricate nanoparticles of a variety of metals and semiconductors with sizes ranging from 2 nm to 30 nm with less than 5% size variation and demonstrated the viability of the system for the fabrication of nanoparticle based electronic and photonic devices.
The nanoparticles deposited in this system are not uniformly distributed, however, most show physical separation from each other. This is due to the charged nature of the nanoparticles creating inter-particle repulsion. In order to create ordered nanoparticles, we have developed a system where the charged nanoparticles can be physically manipulated through the application of an external electric field. The system consists of an electrode mounted on a platform with x,y,z motion and rotation capability. The displacement in the z-direction (vertical) is of nanometer sensitivity which allows the probe to be placed in close proximity to the substrate. The ordering of the nanoparticles is achieved through x,y or rotational scanning of the electrode with an applied voltage, We have demonstrated various ordering of nanoparticles using this technique. We have also extended the technique to order neutral nanoparticles by inducing image charge on the nanoparticles through the electrode and then manipulating the particles. We have also demonstrated that the technique can be used to order magnetic nanoparticles by using a magnetic tip instead of an electrode. In this poster, we will present details of the nanoparticle ordering system, describe the mechanisms affecting the ordering and present experimental results.