Text and Data Mining valid from 2016-09-19
Received: 17 February 2016
Accepted: 17 August 2016
First Online: 19 September 2016
: R.H. is co-founder of Neaspec GmbH, a company producing scattering-type scanning near-field optical microscope systems such as the ones used in this study. All other authors declare no competing financial interests.