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arXiv · 0907.0130

The tip-sample water bridge and light emission from scanning tunnelling microscopy

Michael G Boyle·J Mitra·Paul Dawson
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Abstract

Light emission spectrum from a scanning tunnelling microscope (LESTM) is investigated as a function of relative humidity and shown to be a novel and sensitive means for probing the growth and properties of a water meniscus in the nm-scale. An empirical model of the light emission process is formulated and applied successfully to replicate the decay in light intensity and spectral changes observed with increasing relative humidity. The modelling indicates a progressive water filling of the tip-sample junction with increasing humidity or, more pertinently, of the volume of the localized surface plasmons responsible for light emission; it also accounts for the effect of asymmetry in structuring of the water molecules with respect to polarity of the applied bias. This is juxtaposed with the case of a non-polar liquid in the tip-sample nano cavity where no polarity dependence of the light emission is observed. In contrast to the discrete detection of the presence/absence of water bridge in other scanning probe experiments by measurement of the feedback parameter for instrument control LESTM offers a means of continuously monitoring the development of the water bridge with sub-nm sensitivity. The results are relevant to applications such as dip-pen nanolithography and electrochemical scanning probe microscopy.

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Michael G Boyle, J Mitra, Paul Dawson. 2009-07-01. The tip-sample water bridge and light emission from scanning tunnelling microscopy. https://doi.org/10.1088/0957-4484%2F20%2F33%2F335202

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