Vedran Jelic

Imaging ultrafast dynamics on the nanoscale with a THz-STM

We detail a new ultrafast scanning tunneling microscopy technique called THz-STM that uses terahertz (THz) pulses coupled to the tip of a scanning tunneling microscope (STM) to directly modulate the STM bias voltage over subpicosecond time scales [1]. In doing so, THz-STM achieves ultrafast time resolution via a mode complementary to normal STM operation, thus providing a general ultrafast probe for stroboscopic pump-probe measurements. We use THz-STM to image ultrafast carrier trapping into a single InAs nanodot and demonstrate simultaneous nanometer (2 nm) spatial resolution and subpicosecond (500 fs) temporal resolution in ambient conditions. Extending THz-STM to vacuum and low temperature operation has the potential to enable studies of a wide variety of subpicosecond dynamics on materials with atomic resolution.

Ultrafast THz-pulse-induced tunneling dynamics in an STM

We have recently developed an ultrafast terahertz-pulse-coupled scanning tunneling microscope (THz-STM) that can image nanoscale dynamics with simultaneous 0.5 ps temporal resolution and 2 nm spatial resolution under ambient conditions. Broadband THz pulses that are focused onto the metallic tip of an STM induce sub-picosecond voltage transients across the STM junction, producing a rectified current signal due to the nonlinear tunnel junction currentvoltage (I-V) relationship. We use the Simmons model to simulate a tunnel junction I-V curve whereby a THz pulse induces an ultrafast voltage transient, generating milliamp-level rectified currents over sub-picosecond timescales. The nature of the ultrafast field emission tunneling regime achieved in the THz-STM is discussed.

Ultrafast Terahertz Scanning Tunneling Microscopy with Atomic Resolution

We demonstrate that ultrafast terahertz scanning tunneling microscopy (THz-STM) can probe single atoms on a silicon surface with simultaneous sub-nanometer and sub-picosecond spatio-temporal resolution. THz-STM is established as a new technique for exploring high-field non-equilibrium tunneling phenomena with single atom precision.

Imaging ultrafast nanoscale dynamics with a THz-pulse-coupled STM

An ultrafast terahertz (THz) pulse coupled to the tunnel junction of a scanning tunnelling microscope (STM) is found to produce a subpicosecond rectified current pulse that can be detected by the STM electronics. We use these THz-induced current pulses to develop a new type of ultrafast STM and demonstrate its unprecedented simultaneous 2 nm spatial resolution and 500 fs temporal resolution under ambient laboratory conditions [1]. The terahertz-pulse-coupled STM (THz-STM) is used to image the ultrafast capture of photoexcited carriers into a single InAs nanodot to show its unique capabilities (Fig. 1).