Contact-free conductivity probing of metal nanowire films using THz reflection spectroscopy.

We utilize time-domain Terahertz (THz) reflectivity measurements for characterizing the surface conductivity of Polyethylene-terephthalate coated with nanowire (NW) films to form novel transparent electrodes (TE). We find good correspondence between the film conductivity and the THz-field reflectivity that provide uniquely desirable means for non-destructive, contactless conductivity measurements of large area NW-based-TEs. We demonstrate the robustness of THz reflectivity measurements to deviations invoked on NW film composition and film uniformity. The dependence of THz reflectivity on area NW coverage follows an anisotropic effective medium model for the dielectric constant.

The effects of sample conductivity on the efficacy of dynamic nuclear polarization for sensitivity enhancement in solid state NMR spectroscopy.

In recent years dynamic nuclear polarization (DNP) has greatly expanded the range of materials systems that can be studied by solid state NMR spectroscopy. To date, the majority of systems studied by DNP were insulating materials including organic and inorganic solids. However, many technologically-relevant materials used in energy conversion and storage systems are electrically conductive to some extent or are employed as composites containing conductive additives. Such materials introduce challenges in their study by DNP-NMR which include microwave absorption and sample heating that were not thoroughly investigated so far. Here we examine several commercial carbon allotropes, commonly employed as electrodes or conductive additives, and consider their effect on the extent of solvent polarization achieved in DNP from nitroxide biradicals. We then address the effect of sample conductivity systematically by studying a series of carbons with increasing electrical conductivity prepared via glucose carbonization. THz spectroscopy measurements are used to determine the extent of µw absorption. Our results show that while the DNP performance significantly drops in samples containing the highly conductive carbons, sufficient signal enhancement can still be achieved with some compromise on conductivity. Furthermore, we show that the deleterious effect of conductive additives on DNP enhancements can be partially overcome through pulse-DNP experiments.

Strong coupling of collective intermolecular vibrations in organic materials at terahertz frequencies.

Several years ago, strong coupling between electronic molecular transitions and photonic structures was shown to modify the electronic landscape of the molecules and affect their chemical behavior. Since then, this concept has evolved into a new field known as polaritonic chemistry. An important ingredient in the progress of this field was the demonstration of strong coupling with intra-molecular vibrations, which enabled the modification of processes occurring at the electronic ground-state. Here we demonstrate strong coupling with collective, inter-molecular vibrations occurring in organic materials in the low-terahertz region ([Formula: see text]1012 Hz). Using a cavity filled with α-lactose molecules, we measure the temporal evolution and observe coherent Rabi oscillations, corresponding to a splitting of 68 GHz. These results take strong coupling into a new class of materials and processes, including skeletal polymer motions, protein dynamics, metal organic frameworks and other materials, in which collective, spatially extended degrees of freedom participate in the dynamics.