5.2 Microscopy and Spectroscopy
139
Fig. 5.4 Off-resonantly excited sample emission from a monolayer-WS 2 –hBN stack on photonic
nanostructures. The wavelength-integrated signal is spatially resolved on the spectrometer’s CCD
camera for direct luminescence mapping, as the false-colour intensity profiles in logarithmic (left)
and linear (right) intensity scale show. Top: enhanced local PL from the stack on a circular in-plane
DBR-based optical microcavity (CIDBROM). Bottom: Signal from a similar stack on a reference
hole. Data replotted from author’s work published in [6]
emission signal locally with the help of a probe tip, s-SNOM detects the scattered
signal from the surface of a sample at the laser-light-irradiated tip’s position. In fact,
s-SNOM measures two effects simultaneously, local electric fields and differences of
the material properties caused by corresponding variations of the scattering efficiency
[11]. Thus, its measurement result can also have some spectroscopic material-sensing
contribution.
A home-built s-SNOM setup can be based on a modified AFM near-field microscope [12]. It uses a metallized AFM tip oscillating at a fundamental frequency. Its
apex is illuminated by a laser beam, which is focused down by a paraboloidal mirror from the side. Usually, the tip is kept at a constant time-averaged distance from
the surface while the sample is raster scanned with a piezo-based XY-translation
stage. Owing to the scanning-probe scheme using an AFM tip, s-SNOM measurements simultaneously yield the topography of the specimen by the setup’s AFM
functionality and the spectroscopic near-field information via the tip-scattered light.
This method can be for instance used to characterise spatial field distributions in
139
Fig. 5.4 Off-resonantly excited sample emission from a monolayer-WS 2 –hBN stack on photonic
nanostructures. The wavelength-integrated signal is spatially resolved on the spectrometer’s CCD
camera for direct luminescence mapping, as the false-colour intensity profiles in logarithmic (left)
and linear (right) intensity scale show. Top: enhanced local PL from the stack on a circular in-plane
DBR-based optical microcavity (CIDBROM). Bottom: Signal from a similar stack on a reference
hole. Data replotted from author’s work published in [6]
emission signal locally with the help of a probe tip, s-SNOM detects the scattered
signal from the surface of a sample at the laser-light-irradiated tip’s position. In fact,
s-SNOM measures two effects simultaneously, local electric fields and differences of
the material properties caused by corresponding variations of the scattering efficiency
[11]. Thus, its measurement result can also have some spectroscopic material-sensing
contribution.
A home-built s-SNOM setup can be based on a modified AFM near-field microscope [12]. It uses a metallized AFM tip oscillating at a fundamental frequency. Its
apex is illuminated by a laser beam, which is focused down by a paraboloidal mirror from the side. Usually, the tip is kept at a constant time-averaged distance from
the surface while the sample is raster scanned with a piezo-based XY-translation
stage. Owing to the scanning-probe scheme using an AFM tip, s-SNOM measurements simultaneously yield the topography of the specimen by the setup’s AFM
functionality and the spectroscopic near-field information via the tip-scattered light.
This method can be for instance used to characterise spatial field distributions in