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Gutjahr-Löser, Th., Hornsteiner, A., Krieger, W., Walther, H.

Laser-frequency mixing in a scanning tunneling microscope at 1.3 (mu)m
Journal of Applied Physics 85, (9),pp 6331-6336 (1999)
The radiation of two single-mode diode lasers at 1.3 mu m is focused into the tunneling junction of a scanning tunneling microscope, and gigahertz difference-frequency signals radiated from the tip are detected. Simultaneous measurements of the bias-voltage dependence of the mixing signal and the tunneling current for different surface samples show that the mixing process is due to the nonlinearity of the static current-voltage characteristic of the tunneling junction. The coupling of the laser radiation into the junction conforms to antenna theory. The experimental results are compared with previous measurements at a laser wavelength of 9.3 mu m. Surface images produced by means of the difference-frequency signal show the chemical contrast between micron-sized Au islands and a graphite substrate.

ki-1999-l01