Cinematography of Charge: The Art of Making Movies of Electrons

Internal Seminar: Keshav Dani, Assistant Professor, Femtosecond Spectroscopy (Dani Unit)

Abstract:
The flow of electrons in materials drives almost all of technology today – from our ability to generate electricity from light in solar cell devices, to transistors in modern computing machines. The ability to directly image the flow of this charge promises to deepen our understanding of the fundamental processes involved and potentially drive future technology. However, the motion of charge happens on the nanometer lengthscale, and on the femtosecond timescale, thus requiring the development of sophisticated techniques with simultaneous high spatial and high temporal resolution – a non-trivial endeavour. Over the past five years at OIST, the Femtosecond Spectroscopy Unit has been involved in an effort to achieve exactly this – combine ultrafast optical pulses that give you femtosecond temporal resolution with the imaging techniques of electron microscopes that give you nanometer scale spatial resolution. Thereby we succeeded in making a movie – lasting just a few trillionths of a second, of the motion of electrons after light is absorbed in a solar cell structure, thus capturing the essence of a very important 21st century technology. We will end by discussing how our movie and the technique in general can contribute to future understanding of physical phenomena at the nano-, femto- scale.