Research data supporting “Tracking Optical and Electronic Behaviour of Quantum Contacts in Sub-Nanometre Plasmonic Cavities”

This file describes the contents of the data archive.  We have included both our original data files, and the processed data as plotted in the paper as tab-separated text files.  Our original data is archived in the widely-used HDF5 format; there is a free viewer available for this format from https://www.hdfgroup.org.

Fig_3: This folder contains tab-separated data corresponding to Figure 3.  For (a) and (c), the spectra are given in one 2D file, and the wavelength/x axis values are separately tabulated.  The plots (b) and (d) are given as two-column spreadsheets.

Fig_4: Figure 4 contains a number of parts – the spectra in (a) and (b) are given in the same format as for Figure 3 (NB this is the same data as in Figure 3(c), but zoomed in and presented differently).  The remaining traces are presented as multi-column spreadsheets.  For (d)-(f), data points with similar conductance values have been averaged together.  Therefore, for each point, the values given are means and standard deviations of the averaged data points.  Raw data is available in the HDF5 file.

Fig_5: Figure 5 is in the same format as figure 4, with the exception of the X axis; the cantilever_deflection.tsv file gives the amount the cantilever was bent (which maps approximately to force) for each step in the experiment.  In the case of (c)-(e), data are presented in the same format as Figure 4 (d)-(f), but the X axis is in steps.  To convert these X axes into deflection, use the values to index the cantilever_deflection values.

Fig_6: This is a pair of electron microscope images; the originals are presented here.

original_data.h5
The original data from which the figures 3-5 are plotted is held in the file “original_data.h5”.  Within this file there are three “groups” (analogous to folders):
• classical_spherical_scan_1 holds the original data for Fig. 3(a) and (b)
• spherical_scan_1 holds the original data for Fig. 3(c) and (d) and Fig. 4
• echem_scan contains the original data for Fig. 5
Each of these groups contains a number of datasets.  Unless specified, one of the axes of the dataset is experiment step – this corresponds to time, and (as the tips are generally brought together at a constant speed) can be locally mapped to the position of the cantilever bases.  It should be noted that, as the cantilever flexes, this can be interpreted as the amount the cantilever is deflected when the tips are in contact.  Dataset names and meanings are given below:
• conductance: conductance values between the tips, in units of G0
• current: measured current values in Amperes, from which conductance is calculated
• voltage: applied voltage for the electrical measurement
• force_x, force_y: AFM position sensitive diode readings for torsion (x) and deflection (y) of the cantilever
• position: position of the PI nanopositioning stage in x, y and z as reported from its capacitive position sensors.  NB there is an artefact from its analogue to digital conversion that we have corrected before using the values.  X (the first column) is the tip approach direction.
• spectra: spectra (background-subtracted and normalised) taken at each experimental step, in the “axial” polarisation
• spectra2: spectra (background-subtracted and normalised) taken at each experimental step, in the “transverse” polarisation
• wavelength: wavelength values for each column in spectra
• wavelength2: wavelength values for each column in spectra2
• step: this varies depending on the experiment due to software improvements:
   o classical_spherical_scan_1: the distance moved in microns between steps
   o echem_scan: the position of the stage in microns relative to its starting position
   o spherical_scan_1: the step number since the start of the scan
• timeStamps (where present): time values for each step