Professor Michael Becker is the William H. Hartwig Faculty Fellow in Electrical Engineering and the current Graduate Studies Committee Chairman for the Materials Science and Engineering Graduate Program.
In the course of his interdisciplinary research on nanomaterials synthesis and applications, he and his colleagues invented a process for nanoparticle manufacturing by laser ablation of a microparticle aerosol (LAMA). (figure 1) The microparticle feedstock is entrained in an inert carrier gas at room temperature and pressure for transport to the laser ablation region. The result is a nanoparticle aerosol of the feedstock material.
The LAMA process can generate in aerosol form many types of inorganic nanoparticles: metal, alloy, semiconductor, and dielectric materials. Its key features include the generation of uncoated nanoparticles without any organic surfactant or coating, and the generation of unagglomerated nanoparticles.
LAMA generated nanoparticles are deposited on substrates or into liquids by high velocity impaction from a supersonic jet into vacuum. (figure 2)
An example LAMA process application is silver nanoparticles (nano-silver) for electrical, thermal, and packaging applications. Nano-silver exhibits high electrical and thermal conductivity and strong bond strength for an extremely low process temperature. It is suitable for application to polymer and flexible substrates. Experimental results show that nano-silver has high conductivity and density at a remarkably low process temperature. (figures 3 and 4)
The range of applications for LAMA generated nanoparticles spans electronic materials, photonic materials, thermal bonding materials, membrane and catalyst materials, and more.
Figure 1. LAMA process for producing and depositing uncoated nanoparticles.
Figure 2. (Left) Diagram of a flat-plate supersonic nozzle for nanoparticle deposition by impaction. Typical nozzle diameter is d = 0.25 mm. (Right) Nanoparticle velocity vs. axial distance in the supersonic jet plotted for several diameters of silver nanoparticles. The carrier gas is He, and the asymptotic velocity is shown for reference.
Figure 3. Plan-view SEM micrographs of nano-silver films; a) as-deposited from ~7 nm primary nanoparticles, and annealed at b) 125˚C, c) 150˚C, and d) 200˚C.
Figure 4. Increase in electrical conductivity and density for annealed nano-silver films as a percentage of bulk silver.