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

Authors
  • Boyle, Michael G
  • Mitra, J
  • Dawson, Paul
Type
Published Article
Journal
Nanotechnology
Publisher
IOP Publishing
Publication Date
Aug 19, 2009
Volume
20
Issue
33
Pages
335202–335202
Identifiers
DOI: 10.1088/0957-4484/20/33/335202
PMID: 19636103
Source
Medline
License
Unknown

Abstract

The light emission spectrum from a scanning tunnelling microscope (LESTM) is investigated as a function of relative humidity and shown to provide a novel and sensitive means for probing the growth and properties of a water meniscus on the nanometre 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 the polarity of the applied bias. This is juxtaposed with the case of a non-polar liquid in the tip-sample nanocavity where no polarity dependence of the light emission is observed. In contrast to the discrete detection of the presence/absence of a water bridge in other scanning probe experiments through measurement of the feedback parameter for instrument control, LESTM offers a means of continuously monitoring the development of the water bridge with sub-nanometre sensitivity. The results are relevant to applications such as dip-pen nanolithography and electrochemical scanning probe microscopy.

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