A scanning tunneling microscope (STM) capable of performing
pump–probe
spectroscopy integrates unmatched atomic-scale resolution with high
temporal resolution. In recent years, the union of electronic, terahertz,
or visible/near-infrared pulses with STM has contributed to our understanding
of the atomic-scale processes that happen between milliseconds and
attoseconds. This time-resolved STM (TR-STM) technique is evolving
into an unparalleled approach for exploring the ultrafast nuclear,
electronic, or spin dynamics of molecules, low-dimensional structures,
and material surfaces. Here, we review the recent advancements in
TR-STM; survey its application in measuring the dynamics of three
distinct systems, nucleus, electron, and spin; and report the studies
on these transient processes in a series of materials. Besides the
discussion on state-of-the-art techniques, we also highlight several
emerging research topics about the ultrafast processes in nanoscale
objects where we anticipate that the TR-STM can help broaden our knowledge.