AVS 58th Annual International Symposium and Exhibition
    Nanometer-scale Science and Technology Division Tuesday Sessions
       Session NS+AS-TuA

Paper NS+AS-TuA10
Two-Color Ultrafast-Laser-Assisted STM

Tuesday, November 1, 2011, 5:00 pm, Room 203

Session: Frontiers in Nanoscale Imaging and Characterization
Presenter: Nicholas Camillone, Brookhaven National Laboratory
Authors: A. Dolocan, Brookhaven National Laboratory
D. Acharya, Brookhaven National Laboratory
P. Zahl, Brookhaven National Laboratory
P. Sutter, Brookhaven National Laboratory
N. Camillone, Brookhaven National Laboratory
Correspondent: Click to Email
Substrate–adsorbate charge transfer and carrier-mediated substrate–adsorbate energy transfer are central to photoinduced surface chemistry. To investigate fundamental links between surface electron dynamics and heterogeneous photocatalysis we are developing an ultrafast-laser-excited scanning tunneling microscopy approach to probing surface electron dynamics with simultaneous subnanometer spatial and subpicosecond temporal resolution. Historically, thermal effects associated with laser power variations have presented a major hurdle to progress. In particular, thermal load modulations due to optical interference have been a barrier to observing dynamics at timescales on the order of the temporal width of the laser pulses. In this talk we present results from a new two-color method that completely eliminates this interference. We will show results for two cases: (1) where the tip is retracted from the surface far enough to prohibit tunneling, and (2) where the tip is within tunneling range of the surface. A delay-modulation technique isolates the two-color photo-emission from concurrent one-color two-photon photoemission and the conventional tunneling current, and also enables subpicosecond time-resolved detection of the photoexcited surface electrons. Advantages of the two-color approach are highlighted by comparison with the one-color case where optical interference causes current modulations that are orders of magnitude larger than the desired signal. The two-color approach represents an important step toward the ultimate goal of simultaneous subnanometer and subpicosecond measurement of surface electron dynamics.