The ability to directly probe ultrafast phenomena on the nanoscale is essential to our understanding of excitation dynamics on surfaces and in nanomaterials. Recently, a new ultrafast scanning tunneling microscope technique that couples terahertz pulses to the scanning probe tip of an STM was demonstrated (THz-STM), showing photoexcitation dynamics of a single InAs nanodot with simultaneous 0.5 ps time resolution and 2 nm spatial resolution under ambient conditions. Operation of THz-STM in ultrahigh vacuum now makes it possible to spatially-resolve subpicosecond dynamics of single molecules and silicon surfaces with atomic precision. THz-STM also makes it possible to coherently control currents at the tunnel junction, as well as drive tunnel currents exceeding 1011 A/cm2 through a single atom over sub-picosecond time scales. However, more work is needed to better understand the nature of terahertz-pulse-induced tunnel currents and nanoscale photoexcitation dynamics in various material systems using THz-STM. This talk will discuss how ultrafast THz-STM works, recent progress, operation in ambient versus UHV, and how THz-STM can provide new insight into ultrafast dynamics on the atomic scale, which is essential for the development of novel silicon nanoelectronics and molecular-scale devices operating at terahertz frequencies.

Advances in ultrafast terahertz scanning tunneling microscopy

2019 Fall National Meeting

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