Solvent Toolkit for Electrochemical Characterization of Hybrid Perovskite Films.

Organohalide lead (hybrid) perovskites have emerged as competitive semiconducting materials for photovoltaic devices due to their high performance and low cost. To further the understanding and optimization of these materials, solution-based methods for interrogating and modifying perovskite thin films are needed. In this work, we report a hydrofluoroether (HFE) solvent-based electrolyte for electrochemical processing and characterization of organic-inorganic trihalide lead perovskite thin films. Organic perovskite films are soluble in most of the polar organic solvents, and thus until now, they were not considered suitable for electrochemical processing. We have enabled electrochemical characterization and demonstrated a processing toolset for these materials utilizing highly fluorinated electrolytes based on a HFE solvent. Our results show that chemically orthogonal electrolytes based on HFE solvents do not dissolve organic perovskite films and thus allow electrochemical characterization of the electronic structure, investigation of charge transport properties, and potential electrochemical doping of the films with in situ diagnostic capabilities.

Buckled diamond-like carbon nanomechanical resonators.

We have developed capacitively-transduced nanomechanical resonators using sp(2)-rich diamond-like carbon (DLC) thin films as conducting membranes. The electrically conducting DLC films were grown by physical vapor deposition at a temperature of 500 °C. Characterizing the resonant response, we find a larger than expected frequency tuning that we attribute to the membrane being buckled upwards, away from the bottom electrode. The possibility of using buckled resonators to increase frequency tuning can be of advantage in rf applications such as tunable GHz filters and voltage-controlled oscillators.

Spectral mapping of the third-order optical nonlinearity of glass-metal nanocomposites.

By tuning wavelengths of the femtosecond pump and probe pulses we mapped the nonlinear absorption of copper-glass nanocomposites within 520-620 nm range. At the pump intensity of 3 GW/cm(2), the induced transmission rise was as high as 20%. The imaginary part of the third-order optical susceptibility of the nanocomposites as a function of the probe wavelength reproduced well the spectral profile of the surface plasmon resonance in copper. In contrast, the imaginary part of the third-order optical susceptibility as a function of the pump wavelength did not reproduce the plasmon profile being wider than the latter.