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Electron-phonon interaction (EPI) is the influence of structural dynamics on charge-carrier’s band structure, by changes in the potential acting on a charge carrier due to atomic displacements. When the atomic displacements are anharmonic, and the quasi-harmonic approximation is no longer sufficient, the existing theory fails to explain or predict the macroscopic properties of the material. In quantum confined systems with dielectric mismatch between well and barrier, the effect of atomic displacements on the dielectric environment of charge carriers is greater due to dielectric confinement. 2D hybrid halide perovskites (HHPs) are easy to synthesize, easily tunable dielectric confined materials with pronounced optical response, even at room temperature. Recent studies show the effect of anharmonicity on the optical properties of 3D perovskites and strong EPI in 2D HHPs, affected by temperature. I aim to investigate the effect of anharmonicity on the dielectric environment of charge carriers in prototypical dielectric confined 2D HHPs, using various methods of optical spectroscopy. I hypothesize that anharmonicity would decrease the excitonic binding energy and electron-phonon scattering, due to more efficient charge screening and phonon-phonon scattering.

Dynamic Nuclear Polarization (DNP) is the most widespread and ubiquitous technique for signal enhancement in Nuclear Magnetic Resonance (NMR). The gain in signal intensity is achieved by polarization transfer from the highly-polarized electron spins to the nuclear spins of interest. The home-build DNP/EPR spectrometer in the laboratory of Prof. Songi Han at UCSB allowed for the first time direct observation of the electron spin dynamics in the course of DNP experiment at NMR-relevant magnetic field (≥ 7 Tesla); measurement of electron relaxation times T1 and T2 and electron-electron spin diffusion rate by Electron-Electron DOuble resonance (ELDOR) under DNP conditions. I will present how the addition of 200 GHz arbitrary pulse shaping extended the ability to manipulate the electron spins in both EPR and DNP experiments. Specifically, up to a factor of five improvement in DNP performance was observed when a train of chirp pulses (chirp-DNP) was substituted for conventional, continuous wave microwave irradiation. The combination of shaped-pulse ELDOR together with DNP profile lineshape analysis allowed us to conclude that the gain in performance in chirp-DNP is due to recruitment of additional electron spins that participate in DNP via cross effect (CE) mechanism as opposed to the indirect CE (iCE) mechanism that dominates in the conventional CW DNP experiments under similar conditions.
In addition to serving as the source of the polarization, the electron spins can have other, sometimes detrimental, effects on the NMR spectra such as shifting the position of the peaks (Paramagnetic Shift) and decreasing resolution by linewidth increase (Paramagnetic relaxation) collectively known as paramagnetic effects (PE). We have recently observed the reversal of PE upon microwave irradiation in DNP experiments at liquid helium temperatures. WE suggest that the the origin of the observed effect stems from the REversal of PRE by electron Spin SaturatION (REPRESSION) effect which was traced to the shortening of the electron phase memory time, Tm, with electron spin bath saturation by microwave irradiation.

In nature, bacteria form differentiated multicellular communities, known as biofilms. The coordinated actions of many cells, communicating and dividing labor, improve the ability of the community to attach to hosts and protect it from environmental assaults.Bacterial biofilms are associated with persistent bacterial infections, and thus pose a global threat of extreme clinical importance. Bacteria in a biofilm are significantly more resistant to antibiotics than free-living bacteria. Our work provides two novel explanations of this phenotypic antibiotic resistance: a structural mineral component defending the bacterial colony, and the ability of community members to communicate and coordinate activities using RNA transfer.