Advances in ultrafast scanning tunneling microscopy

Abstract

Time resolved tunnel current was measured over 4 orders of magnitude in separation between tip and sample using an ultrafast scanning tunneling microscope (USTM). These measurements reveal two distinct regimes for tip height dependence of the signal. In addition, we report 900 femtosecond temporal resolution with a sensitivity of 20 mV/√Hz in USTM measurements of voltage pulses on a coplanar transmission line, and we show that the microscope operates as a high impedance probe.

Ultrafast Scanning Tunneling Microscopy Using a Photoexcited Low-Temperature-Grown GaAs Tip

“…The second pulse at 27 ps is a reflection off the end of the stripline. Unlike previous results [1][2][3][4][5], the waveforms flom the tip in contact and in tunneling mode have the same shape and are flee from other spurious signals. The width of the first pulse in tunneling regime is 3.3 ps indicating a temporal resolution of 1.7 ps after deconvolution.…”

“…In the quest for atomic spatial and picosecond temporal resolutions, several groups [1][2][3][4][5] have integrated an STM tip with an ultrafast optoelectronic switch that gates the tunneling current from the tip. We report a novel ultrafast STM tip consisting of a cleaved GaAs substrate with a 1-pm thick epilayer of low-temperature grown GaAs (LT-GaAs) deposited on the face.…”

Real-space imaging of transient carrier dynamics by nanoscale pump–probe microscopy

“…Hamers et al determined the recombination lifetime of photoexcited carriers in Si, in their pioneering work, by analyzing the observed surface photovoltage (SPV) by simulation [10], and a method that involves the combined use of an optical pulse pair and STM was proposed as photoconductive-gate STM (PG-STM) [11][12][13][14][15][16][17][18]. However, the spatial and temporal resolutions of the former method were limited to the 1 µm scale and laser-pulse repetition rate, respectively, and the PG-STM probes dI/dV or the quantity mediating the signal rather than the transient effect itself [18].…”

Measuring voltage transients with an ultrafast scanning tunneling microscope

“…Based on the PC sampling technique, another approach has been introduced by Weiss et al 3 They reported picosecond and subpicosecond 4 time resolution with a photoconductively gated scanning tunneling microscope. Their results have been confirmed by two other groups.…”