Program Highlights

How? We use optical microscopy to determine the dynamics of photo-generated charges in individual semiconductor nanowire hetero-structures.

Transparent conducting oxide play a key role in photovoltaic (PV) devices. There has been much recent interest in finding alternative indium (In) free TCOs and even better performing alternative candidates to substitute for standard ITO.  The driving factors are: scarcity, unintended interfacial phenomena, rapid price increase and global politics associated with In metal in ITO. TCOs based on titanium (Ti) doped tungsten oxide (WO3) thin films were studied in this project. X-ray photoelectron spectroscopy (XPS) analyses provided the chemical and electronic structure changes in the Ti-doped WO3 thin films. The studies when combined with optical studies enabled engineering the materials with desired TCO properties.

In March-April 2015, approximately 50 PREM students, faculty and other volunteers visited six rural schools in the towns of Yabucoa and San Lorenzo, Puerto Rico. The activities included short talks and hands-on demonstrations from the Nanodays (NISENet) kits and others developed by our program. Over 800 students, teachers and parents participated in this effort to reach minority and geographically isolated communities. 

MoS₂ single crystals were transferred onto the edge of a p-Si/SiO₂ wafer, forming an abrupt heterogeneous junction diode at the MoS₂/p-Si interface. When electrically characterized as a field effect transistor, MoS₂ exhibits an n-type response and can be doped in the presence of ultraviolet (UV) light. Its simple design coupled with the ability to rectify AC signals, sense UV light, and reversibly tune these diodes makes them inexpensive, multifunctional, and usable as active or passive components in complex electronics.

Fungal infections such as candidiasis represent an important human health concern worldwide due to high mortality rates, of more than 50%, specifically in those people who are immunocompromised.  In particular risk are those patients undergoing chemotherapy, that suffer from AIDS and those who receive an organ transplant.  Other concerns include the side effects of the current antifungal drugs and the emergence of multidrug resistant organisms. 

In organic photovoltaics, the role of hot charge-transfer (CT) excitons on free carrier generation is currently under intense debate. In this project, we carry out first-principles time-dependent density functional theory calculations to examine hot CT dissociation in polymer/fullerene heterojunctions. We reveal that whether or not hot CT states promote charge separation depends on excitation spectral range and crystallinity of the donor and acceptor phases. We find that while the crystallinity of the donor phase underlies the energy dependence of CT exciton dissociation, the crystallinity of the acceptor determines charge separation efficiency. We propose a theory that can reconcile contradictory experimental observations and provide insight into hot CT dissociation. Crucially, the timescale of hot CT dissociation is found to be comparable to the timescale of its relaxation to the lowest-lying CT state, which is localized in all interfacial models studied.

According to the World Health Organization (WHO), more than 1.5 million children die each year due to rotavirus contamination in drinking water.