Research

1.     Wetting-Dewetting Transitions of ultra-thin Films

The objective of this project is to identify atomic-scale mechanisms that cause wetting-dewetting transitions of thin metal films on silicon substrates. Cross-section in -situ TEM experiments are carried out on various metal film that are low-temperature deposited on silicon substrates. The research activities are funded through an NSF-CAREER award (NSF-DMR 0955638).

Studies to investigate the onset of deleting  i.e., hole formation in thin metal films on SrTiO3 substrates are currently initiated. We study the onset of grain boundary grooving and spinodal instabilities of thin films on a micro- to nanosecond time scale with in situ dynamic TEM experiments. This project is carried out in collaboration with Drs. G. Campbell and T. Lagrange at LLNL and is funded through my grant from the UCOP/UC Lab Fee Program.

2.     Reliability Physics: Dielectric Breakdown of Dielectric Films

The objective of this activity is the fundamental atomic-scale characterization of defect structure evolution in ultrathin films under applied electrical stress. Novel in situ TEM experiments are used to study time-dependent dielectric breakdown through electrical biasing inside the TEM.  For high-k dielectric interfaces we have found that soft and hard breakdown behavior correlates with specific types of defects and their kinetic evolution.  Such experiments are novel and incur controversy in a field that is heavily dominated by regulated reliability studies in semiconductor science and technology.  However, we believe that a new approach to atomic-scale characterization will lead the way for the development of next generation device structures and sub-13nm technology.

3.     Fundamental Mechanisms during Field-assisted Sintering

Despite the broad application of electric field assisted sintering through FAST and SPS processing, the fundamental atomic-scale mechanisms that lead to enhanced materials consolidation in the presence of electrical fields, currents and/or heating rates remain unclear.  We use specially designed in situ TEM experiments to separate the effects of electrical fields and heating rates to identify operative consolidation mechanisms. The in situ TEM studies are designed to systematically reproduce conditions that are characteristic for macroscopic FAST/SPS processing. Recently we have observed neck formation between individual agglomerated nanoparticles as a result of the application of electrical current directly to the particles. Further experiments demonstrate that the presence of carbon significantly reduces the sintering temperatures due to oxidation-reduction reactions while ripening is dominant over densification in the absence of carbon. Most recently, we were able to provide for the first time direct experimental evidence for previously postulated surface cleaning effects required during the initial stage of densification. The results suggest that dielectric breakdown is necessary to occur for dielectric surface layers before current-assisted densification can proceed. The research activators are funded through a UC Laboratory Fee Grant.

Recently we have received funding from the Army Research Office for a comprehensive analysis of Flash Sintering of yttrium-stabilized ZrO2 by using a combination of in-situ TEM and macroscopic EFAS techniques.