Charging and Heating Dynamics of Nanoparticles in Nonthermal Plasmas

Proposal Title: Charging and Heating Dynamics of Nanoparticles in Nonthermal Plasmas

Principal Investigator: Kortshagen, Uwe R.

Institution: University of Minnesota-Twin Cities

Proposal No: CBET-0903842

Various aspects of 'dusty' or 'complex' plasmas have continued to excite the plasma com-munity since the 1980s. The first wave of interest was sparked by the detrimental effects of the formation of nanoparticles during the manufacture of microelectronic devices. In parallel, the discovery of exciting new physical phenomena in strongly coupled plasmas gave birth to the booming field of complex plasma studies. Recently a new focus of attention has emerged: Using reactive dusty plasmas as controllable sources of nanoparticles. These nanoparticles have interesting physical and chemical properties that make them promising for novel applications. However, even after more than a decade of study, some of the most basic physical processes of such 'nanodusty' plasmas are still poorly understood. Moreover, due to the difficulties of preparing well-characterized experimental systems of 'nanodusty' plasmas, most of our knowledge is based on models that lack experimental verification.

The overall objective of this research is to study the fundamental dynamics of nanoparticle charging and heating in highly defined, well-characterized low temperature plasma environments. To achieve this objective, a unique process to synthesize highly monodisperse, luminescent nanocrystals with well-defined diameters in the range of 3-20 nm will be used; these particles will be injected into carefully designed and characterized test plasmas. For the nanoparticle charging problem, experiments will be performed with size-controlled nanoparticles to test whether the orbital-motion-limited theory or a theory accounting for collisional effects needs to be used for small nanoparticles. Another high-risk/high-reward experiment will attempt to measure, for the first time, the charge distribution of nanoparticles immersed in a plasma. Results of these experiments will provide new information for accompanying modeling studies. For nanoparticle heating in plasmas, a set of first-ever experiments will be performed using 'nanoparticle thermometers' to study the average temperature of monodisperse nanoparticles in plasmas as well as to gain information about their temperature distribution function. One set of experiments will exploit the temperature-dependence of the photoluminescence of nanoparticles to gain information about particle temperatures. Another set of experiments will use the nanoparticles' microstructure to determine whether the particle temperature reached or exceeded the particles? crystallization temperature. Results of these experiments will be compared to numerical models for particle heating.

This research has a wide range of broader impacts. On the technical side, it will build the scientific foundation for the use of plasmas as sources of functional nanoparticles for uses in nanotechnology. It will also serve as a springboard for a number of education and outreach activities. These include K-12 outreach through local public school districts; involvement of undergraduates in research; training of graduate and undergraduate students in a highly interdisciplinary research environment; teaching of new interdisciplinary graduate courses; fostering greater involvement of women and underrepresented groups in our graduate research programs; and active engagement with industry.