Visibility of weak contrasts in subsurface scattering near-field microscopy

Coupling model for an extended-range plasmonic optical transformer scanning probe

“…[10][11][12] Increasing the working distance of such a system is a key limitation for subsurface imaging. 13 One approach is a superlens 14 that uses negative refraction to achieve, in principle, a perfect imaging system that retains all wave vectors of the source. Another related approach is evanescent wave amplification, where planar structures induce convergence in the near field.…”

Exploring the detection limits of infrared near-field microscopy regarding small buried structures and pushing them by exploiting superlens-related effects

“…The samples have been investigated by evaluating the optical amplitude s 2 images of the second demodulation order (unless otherwise stated), in order to have the background suppressed while on the other hand having sufficient overall signal strength. The SNOM images were acquired with a tapping amplitude of 60 nm as a compromise between mechanical stability, high contrast and low noise [19]. A pixel size of 20 nm and a sampling time of 30 ms/pixel have been chosen.…”

“…We image small metallic nanoparticles below a Si 3 N 4 -membrane and vary membrane thickness and particle size. In order to be comparable with the previous reported results [18,19], we first choose a wavenumber for imaging and modelling where the permittivity of the cover layer is positive. TEM imaging enables a correct attribution between structure size and the corresponding optical signals, which in turn are compared with a simple model calculation yielding quite good agreement.…”

“…By using the AFM in tapping mode and evaluating the amplitude s n for higher demodulation orders n of the tapping frequency, the background is suppressed, however at the cost of lower overall signal strength [13]. Since the near-fields penetrate into a dielectric sample, non-destructive imaging of subsurface structures is possible up to a depth of about 100 nm, although with a loss in resolution and signal strength [16][17][18][19][20][21][22]. Even larger probing depths can be reached by the use of superlenses [23][24][25][26].…”

“…The change of contrast [18] and visibility [19] of subsurface structures with different tapping amplitudes as well as the influence of the demodulation order [18] have already been investigated on structures with a size of about 100 nm, which is much larger than the resolution of s-SNOM at the surface. All these measurements have been performed at wavenumbers where the permittivity of the cover layer was positive (ε > 0).…”