Department of Physics Colloquium

Guest speaker: Peter Grütter (FRSC) Department of Physics, McGill University
Thursday, 2 November 2017 - 3:00 pm to 4:00 pm
Off-campus address: 
25 Templeton St, room 233
Registration required: 
Cost to attend: 
Free of charge
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Title: Ultrafast time resolution in AFM measurements of charge transport in sustainable energy materials

Abstract:  One of the Grand Challenges for humanity in the 21st Century is sustainable energy generation and storage. This translates to major opportunities for AFM to help addressed relevant materials issues if ultrafast time resolution in the localized measurement of electronic properties can be achieved. In this presentation, I will give an overview of our recent successes at characterizing surface potentials using AFM-based techniques on time scales down to atto seconds.We have combined a UHV AFM system with a fs laser excitation system tunable in the optical spectrum. By developing a new pump-probe method we can measure ultrafast decay times using AFM/EFM as a spatial detector. We have applied this technique to 2D and organic systems as well as GaAs and LiNbO3 to measure ultrafast charge carrier decay times as well as mobility. We will also discuss the fundamental time limits achievable using the AFM probe as a detector in pump-probe experiments, in fact we have recently achieved a time resolution of 25 atto seconds!A major challenge in the widespread deployment of sustainable energy sources such as solar and wind is maintaining grid stability. Distributed energy storage in electrical vehicle batteries connected to the grid is an option. We have used a newly developed AFM/EFM technique to spatially determine variations in Li transport mechanism in LiFePO4, a model cathode material. We applied voltage pulses to the sample and observed the resultant fast time decay of the electrostatic forces due to the mobility of Li ions using a time averaging technique. By combining our ultrafast AFM techniques with SEM, TOF-SIMS and EBSD as well as comparison to DFT calculations we show that ionic transport in these materials must be regarded as a collective effect due to the significant contributions by ion-ion and ion-polaron interactions to the measured activation energies.

Refreshments will be served at 2:30 p.m. (BEFORE the seminar) in room ARC 233