Following the publication of Friday of Stripy Nanoparticles Revisited, one colleague wrote the following to me “I guess now you have to reply to Francesco’s response“.
My hope is that scientists will read carefully both articles, as well as the primary articles, and come to their own conclusions regarding the existence and properties of stripy nanoparticles. Having said that, I am happy to discuss any particular question asked by readers (within time constraints…).
Here, I comment just on one particular point which relates to simple understanding of scanning microscopy and to our first argument, i.e. that the images are not compatible with the stripy hypothesis for basic geometric reasons: if stripes are regularly spaced in 3D they cannot be in a 2D projection.
In the response, the authors address this point as follow:
Hence, the central argument in Lévy’s paper is based on two assumptions: (1) an STM tip moves horizontally on a sample, and (2) tunneling currents flow perfectly vertically from the tip into the substrate holding the sample. Both assumptions are invalid. In reality, the tip follows the contour of the sample. [ 23 ] The correct projection of the sample features being imaged with STM is onto the true tip trajectory, not onto an imaginary flat line. If we assume a tip trajectory that maintains a constant distance from the particle’s center of mass (hence making a semicircular trajectory), then images of the idealized particle shown in ref. [ 1 ] would be projected onto such a semicircle and consequently should show stripes with a spacing of ∼ 1 nm. It should be noted that, were the tip to really move horizontally over the sample, there would be no feedback needed, no feedback loop-artifact possible, and the whole interpretation of the images presented in ref. [ 1 ] (feedback loop artifacts) would be in contradiction with the initial argument
Our argument is not based on the assumption that “an STM tip moves horizontally on a sample“. Indeed, during a standard STM scan, the feedback loop attempts to keep the tip-sample distance constant and therefore the tip follows the contour. We simply state the obvious, i.e. that an STM image is a 2D projection of a 3D surface. Each line in an STM image represents (as a color) the vertical movement of the tip as a function of the horizontal displacement. Incidentally, if scanning microscopy worked as described in the paragraph quoted above, the image of a square area… would not be square since each line would have different length depending on the topology of the surface.