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5 Optical Measurement Techniques
Fig. 5.5 Example of a raster scan PL image obtained for a 2D heterostructure (sketched in the
inset) with approximately 1-µm lateral resolution. The here displayed false-colour map with spatial
intensity profile (intensity linearly increasing from black to white) is based on the spectrallyintegrated emission covering all output from WS 2 and WSe 2 monolayers and heterobilayers (HBL).
The HBL region is boxed as a guide to the eyes. The arrow indicated one direction, from which
spot-specific spectra were shown in a waterfall diagram in [2] (not shown here). In fact, since
spectra are available for every spot, this method is known as hyperspectral imaging. Reproduced
with permission. [2] Copyright 2020 Springer Nature
sub-micron optical structures combined with 2D materials [6] (see Fig. 5.7, and for
cross-sectional line-outs see Fig. 5 of [6]).
In s-SNOM measurements, the probe tip acts as a nano-antenna. It scatters a
part of the near-field wave into the far-field. The scattered light, which is nonlinearly
modulated at the frequency of the tip oscillation, is then collected by the paraboloidal
mirror and detected using a photodetector in the intensity detection scheme. For
extraction of the near-field signature, the detected signal is demodulated at the third
harmonic of the tip’s oscillation frequency. The spatial resolution of such apparatus
is of the order of 20–50 nm [13].
5.2.3 Time-Integrated Detection
Commonly, microscopy and spectroscopy are performed in a time-integrating detection scheme, which acquires signal over time following an excitation process. This
detection method averages over time and provides time-integrated information about
a system, with the spectral resolution and signal sensitivity depending on the dis-
5 Optical Measurement Techniques
Fig. 5.5 Example of a raster scan PL image obtained for a 2D heterostructure (sketched in the
inset) with approximately 1-µm lateral resolution. The here displayed false-colour map with spatial
intensity profile (intensity linearly increasing from black to white) is based on the spectrallyintegrated emission covering all output from WS 2 and WSe 2 monolayers and heterobilayers (HBL).
The HBL region is boxed as a guide to the eyes. The arrow indicated one direction, from which
spot-specific spectra were shown in a waterfall diagram in [2] (not shown here). In fact, since
spectra are available for every spot, this method is known as hyperspectral imaging. Reproduced
with permission. [2] Copyright 2020 Springer Nature
sub-micron optical structures combined with 2D materials [6] (see Fig. 5.7, and for
cross-sectional line-outs see Fig. 5 of [6]).
In s-SNOM measurements, the probe tip acts as a nano-antenna. It scatters a
part of the near-field wave into the far-field. The scattered light, which is nonlinearly
modulated at the frequency of the tip oscillation, is then collected by the paraboloidal
mirror and detected using a photodetector in the intensity detection scheme. For
extraction of the near-field signature, the detected signal is demodulated at the third
harmonic of the tip’s oscillation frequency. The spatial resolution of such apparatus
is of the order of 20–50 nm [13].
5.2.3 Time-Integrated Detection
Commonly, microscopy and spectroscopy are performed in a time-integrating detection scheme, which acquires signal over time following an excitation process. This
detection method averages over time and provides time-integrated information about
a system, with the spectral resolution and signal sensitivity depending on the dis-