Dual modulation STM: Simultaneous high-resolution mapping of the differential conductivity and local tunnel barrier height demonstrated on Au(111)

We present a scanning tunneling microscopy (STM) technique to simultaneously measure the topography, the local tunnel barrier height (d I/d Z), and the differential conductivity (d I/d V). We modulate the voltage and tip piezo with small sinusoidal signals that exceed the cut-off frequency of the ST...

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Bibliographic Details
Published in:Journal of applied physics 2021-06, Vol.129 (22)
Main Authors: Oldenkotte, V. J. S., Witmans, F. J., Siekman, M. H., de Boeij, P. L., Sotthewes, K., Castenmiller, C., Ackermann, M. D., Sturm, J. M., Zandvliet, H. J. W.
Format: Article
Language:English
Subjects:
Applied physics
Feedback loops
Lock in amplifiers
Modulation
Scanning tunneling microscopy
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Summary:We present a scanning tunneling microscopy (STM) technique to simultaneously measure the topography, the local tunnel barrier height (d I/d Z), and the differential conductivity (d I/d V). We modulate the voltage and tip piezo with small sinusoidal signals that exceed the cut-off frequency of the STM electronics and feed the tunneling current into two lock-in amplifiers (LIAs). We derive and follow a set of criteria for the modulation frequencies to avoid any interference between the LIA measurements. To validate the technique, we measure Friedel oscillations and the subtle tunnel barrier difference between the h c p and f c c stacked regions of the Au(111) herringbone reconstruction. Finally, we show that our method is also applicable to open feedback loop measurements by performing grid I( V) spectroscopy.
ISSN:0021-8979
1089-7550
DOI:10.1063/5.0051403