Nondestructive thickness measurement of biological layers at the nanoscale by simultaneous topography and capacitance imaging

Abstract

Nanoscale capacitance images of purple membrane layers are obtained simultaneously to topography in a nondestructive manner by operating alternating current sensing atomic force microscopy in jumping mode. Capacitance images show excellent agreement with theoretical modeling and prove to be a noninvasive method for measuring the thickness of purple membrane layers beyond the single monolayer limit with nanoscale lateral spatial resolution. With the ability of spatially resolving the capacitance while preserving the sample from damaging, this technique can be applied for nanoscale thickness measurement of other biological layers and soft materials in general.

Nanoscale capacitance microscopy of thin dielectric films

“…10 we demonstrated that simultaneous capacitance and topographic profiling measurements on a micro/ nanopatterned dielectric film allow one estimating in a very quantitatively way the thickness of the film at the nanoscale with high vertical resolution.…”

“…The remaining contributions conform the stray capacitance contribution that can be subtracted from the experiments following an appropriate calibration procedure as previously reported. 1,6,10 In order to arrive at an analytical expression for the apex capacitance in the presence of a thin dielectric film, we will restrict ourselves to the model system depicted in Fig. 1͑b͒.…”

“…For thin dielectric films, the power of NCM resides in the ability to quantify intrinsic properties, including film thickness 5 and dielectric constant, 6 with lateral spatial resolution well beyond the limit of conventional ellipsometry, reflectance spectroscopy, 7 and capacitance metrology. 8,9 In two recent papers, 6,10 we have demonstrated the quantitative measurement of the dielectric constant and the thickness of thin insulating films at the nanoscale. To extract these parameters, we have used the following logarithmic expression of the capacitance probed by the nanometric tip apex on the thin dielectric film, C apex dielectric ͑z, r ,h͒ = 2 0 R ln ͫ 1 + R · ͑1 − sin 0 …”

Ultrahigh dielectric constant of thin films obtained by electrostatic force microscopy and artificial neural networks

“…13,14 Unfortunately, the effect of the electrostatic field under these restrictions has not been studied in detail since previous theoretical works focused on dielectric thin films over metallic substrates. 15,16 In this article, we combine numerical methods and artificial neural networks 17 (ANNs) to simulate the electrostatic interaction between an EFM tip and a thin film. Using the electrostatic force as input patterns to the ANN, we establish that the thin film sample can be replaced by a simple semiinfinite sample characterized by an effective dielectric constant.…”

Enhanced dielectric constant resolution of thin insulating films by electrostatic force microscopy

“…12 EFM is currently used to determine the static dielectric constants of thin films of a few nanometers thickness directly deposited on a metallic electrode. The dielectric constant can be determined by comparison of the experimental results with simple analytical expressions 13,14,15 . For metallic samples, the tip-sample interaction is very well understood and the force, as well as the force gradient, can be determined by using a simple analytical model.…”