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Title: Ultrafast scanning tunneling microscopy

I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of themore » time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.« less
Authors:
 [1]
  1. California Univ., Berkeley, CA (United States). Dept. of Physics|[Lawrence Berkeley Lab., CA (United States)
Publication Date:
OSTI Identifier:
270266
Report Number(s):
LBL--38594
ON: DE96013134; CNN: Contract N000-14.93.105.36.
DOE Contract Number:
AC03-76SF00098
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Sep 1995
Research Org:
Lawrence Berkeley Lab., CA (United States)
Sponsoring Org:
USDOE, Washington, DC (United States);Office of Naval Research, Washington, DC (United States);Advanced Research Projects Agency, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; 44 INSTRUMENTATION, INCLUDING NUCLEAR AND PARTICLE DETECTORS; 66 PHYSICS; MICROSCOPY; TUNNEL EFFECT; RESOLUTION; LASERS; SUPERCONDUCTING JUNCTIONS; SWITCHES; SURFACES; PULSED IRRADIATION; LASER RADIATION