Research
Here in the Krummel Lab, we like to push the boundaries of current technology in optics and spectroscopy to probe the dynamics and structures of molecular systems that could never be measured before. We have two 100kHz laser systems for 2D IR and electronic spectroscopies, as well as a 1kHz system for transient absorption and a wet lab for chemical synthesis and sample preparation.
Charge Transfer Dynamics in 2D Nano-Materials
Thermalization loss of absorbed solar energy above the semiconducting active-material bandgap is the largest limiting factor of efficiency in solar energy conversion devices1. Extraction of highly excited (hot) charge carriers before thermalization loss can improve device efficiency by up to 33%2. Single monolayer transition metal dichalcogenides (2D TMDs) are a promising active material for hot carrier devices due to their broad visible light absorption, atomically thin structure, and slow hot carrier cooling3. A crucial step towards design of commercial hot carrier devices is understanding how operational device conditions affect hot carrier dynamics. We have measured for the first time hot carrier extraction in a monolayer MoS2 electrochemical cell under applied bias via broadband femtosecond transient absorption spectroscopy. We observe ultrafast extraction of hot carriers (< 50 fs) before exciton formation (~ 0.5 ps), which may explain the high photocurrent yields observed in our device. The future of this project will be to convert our transient absorption laser into a 2D white-light spectrometer for further investigation of electronic state dynamics within solar energy conversion devices.
Visualizing Structure and Dynamics of Room Temperature Ionic Liquids with 2D-IR
Room temperature ionic liquids represent a class of molten salts which are the subject of growing interest for their potential applications in a wide array of chemical systems. Additionally there is significant interest in understanding how additives and contaminants impact the properties of RTIL mixtures. To that end, we employ nonlinear spectroscopy to study RTILs, with recent work focusing on the impact of water.
100 kHz Mid-IR OPCPA Laser Source for Use in 2D IR Microscopy
To more efficiently image, we developed a higher repetition rate mid-IR laser system, demonstrating for the first time 2D IR spectroscopy at 100 kHz. Achieving this higher repetition rate was accomplished by utilizing advances in diode pumped ytterbium (Yb) oscillators and amplifiers, and is based on an optical parametric chirped-pulse amplifier (OPCPA) utilizing magnesium doped periodically poled lithium niobate (MgO:PPLN) followed by difference frequency generation (DFG) in zinc germanium diphosphide (ZGP). Using this system, we have successfully studied spatially dependent vibrational dynamics of room temperature ionic liquids in microdroplets as well when acting as an elctrolyte between copper electrodes.
