Microwave Frequency Comb from a Semiconductor in a Scanning Tunneling Microscope. (20th December 2016)

• Record Type: Journal Article
• Authors: Hagmann, Mark J.; Yarotski, Dmitry A.; Mousa, Marwan S.
• Editors: Thuvander, Mattias; Cairney, Julie; Gerstl, Stephan
• Is Part Of: Microscopy and microanalysis. Volume 23:Number 2(2017)
• Page Start: 443
• Page End: 448
• Publication Date: 2016-12-20
• Subjects: scanning tunneling microscopy, -- scanning probe microscopy, -- microwave frequency comb, -- spreading resistance, -- laser-assisted tunneling; Microscopy -- Periodicals; Microchemistry -- Periodicals; 502.82
• DOI: 10.1017/S1431927616012563
• Languages: English
• ISSNs: 1431-9276

Abstract

Abstract: Quasi-periodic excitation of the tunneling junction in a scanning tunneling microscope, by a mode-locked ultrafast laser, superimposes a regular sequence of 15 fs pulses on the DC tunneling current. In the frequency domain, this is a frequency comb with harmonics at integer multiples of the laser pulse repetition frequency. With a gold sample the 200th harmonic at 14.85 GHz has a signal-to-noise ratio of 25 dB, and the power at each harmonic varies inversely with the square of the frequency. Now we report the first measurements with a semiconductor where the laser photon energy must be less than the bandgap energy of the semiconductor; the microwave frequency comb must be measured within 200 μ m of the tunneling junction; and the microwave power is 25 dB below that with a metal sample and falls off more rapidly at the higher harmonics. Our results suggest that the measured attenuation of the microwave harmonics is sensitive to the semiconductor spreading resistance within 1 nm of the tunneling junction. This approach may enable sub-nanometer carrier profiling of semiconductors without requiring the diamond nanoprobes in scanning spreading resistance microscopy.