Nanoscale dielectric microscopy of non-planar samples by lift-mode electrostatic force microscopy

Abstract

Lift-mode electrostatic force microscopy (EFM) is one of the most convenient imaging modes to study the local dielectric properties of non-planar samples. Here we present the quantitative analysis of this imaging mode. We introduce a method to quantify and subtract the topographic crosstalk from the lift-mode EFM images, and a 3D numerical approach that allows for extracting the local dielectric constant with nanoscale spatial resolution free from topographic artifacts. We demonstrate this procedure by measuring the dielectric properties of micropatterned SiO 2 pillars and of single bacteria cells, thus illustrating the wide applicability of our approach from materials science to biology.

Internal Hydration Properties of Single Bacterial Endospores Probed by Electrostatic Force Microscopy

“…EFM is a scanning probe microscopy technique sensitive to the local dielectric properties of the samples. 33,34 Examples showing this ability include numerous applications to samples of non-biological origin (thin and thick oxides, 35 polymer films, [36][37][38] nanowires, 39 nanotubes 40,41 or nanoparticles [42][43][44][45] ), and of biological origin (single bacterial cells, 46,47 single virus particles, 45 solid supported biomembranes, 48 protein complexes 49 or DNA molecules). 50 EFM has two important properties relevant for the present application, namely, (i)…”

“…To obtain these images we used the topographic images and an approach curve measured on a bare part of the substrate (Figure 1m, black line), as explained elsewhere. 47 The resulting intrinsic capacitance gradient images are Figure 1o). Altogether, these results imply that the variation in the lift EFM capacitance gradient images observed at increasing environmental humidity conditions is directly related to a variation in the electric permittivity properties of the endospore, and not to a change in the endospore dimensions.…”

“…47 Briefly, during the first pass the topographic line is obtained in conventional intermittent contact mode, followed by a second pass, in which the tip moves at a constant height from the measured sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 sensitivity down to ~0.002 aF/nm. Capacitance gradient approach curves have also been measured on given points of the sample.…”

“…around the tip and in the sample (an example is shown in Figure 3c), from which we derive the Maxwell stress tensor on the tip surface, and, by integration of it on the surface of the tip, we obtain the electrostatic force. 47 Software routines written in Matlab (Mathworks Inc.) have been To determine the internal electric permittivities of the core and shell, we proceeded in a two step process. In the first step we determined the equivalent homogeneous electric permittivity, ε r,eff , of the endospore (and bacterial cell), by following a fitting procedure similar to the one detailed elsewhere, [45][46][47] Transmission Electron Microscopy imaging.…”

“…47 Software routines written in Matlab (Mathworks Inc.) have been To determine the internal electric permittivities of the core and shell, we proceeded in a two step process. In the first step we determined the equivalent homogeneous electric permittivity, ε r,eff , of the endospore (and bacterial cell), by following a fitting procedure similar to the one detailed elsewhere, [45][46][47] Transmission Electron Microscopy imaging. Mature bacterial endospores and vegetative cells were directly fixed with 2.5% glutaraldehyde and post fixated with 2% osmium tetroxide.…”