138
5 Optical Measurement Techniques
as particularly shiny areas under above-band photoexcitation, facilitating identification of the monolayered regions drastically which can be used during monolayerstransferring endeavours [6].
5.2.2 Spatial Distribution
One-shot imaging with cameras—either of type charged-coupled device (CCD)
or complementary metal-oxide-semiconductor (CMOS)—connected to microscope
setups can provide easy access to high-quality visualisation of sample materials.
However, the recorded intensity profile only carries information about the spatial
domain and some differences in surface reflectance and composition (without spectral resolution).
1 An example of spatial µPL distributions for 2D-materials stacks on
patterned surfaces for PL modifications is for instance given in Fig. 5.4, shown in
linear (right) as well as logarithmic (left) intensity scale for a grating (upper panel)
and reference hole (lower panel).
Similarly, spatially-integrated spectroscopy with or without the use of a microscope does not provide any information about spatial distributions, but merely reveals
spectral signatures. Thus, raster scanning the focal spot of the given light source of
a spectroscopy method is used to obtain spatially-resolved spectral information.
Hereby, the resolution is determined by the magnification of the optics and spatial
filtering methods. Raster scans can be performed both in 1D and 2D,
2 resulting in
hyperspectral imaging (see Fig. 5.5). In addition, spatially-resolved spectra can be
obtained when the real-space image is projected via lenses onto the entrance slit
of an imaging spectrometer’s monochromator, which delivers spatial information in
the direction of the slit wavelength-resolved on a monochromator-attached imaging CCD. By raster scanning in the perpendicular direction, one can also obtain 2D
spatial distributions from such spatially-1D single-shot acquisition mode.
Typically, Raman and fluorescence (luminescence) spectroscopy with spatial resolution is widely used to investigate structured surfaces and microscopic materials,
such as 2D-material flakes and their artificial stacks [2, 7–10]. For example, comparisons of Raman and PL spectra for monolayer and few-layer systems can already
be well performed by hyperspectral line scans (see for instance the Supporting Information section of [8]), for which the sample is scanned in one direction using a
high-precision translation stage, e.g., driven by piezo actuators. Spatial information
can further be obtained by sheet-/surface-sensitive nonlinear frequency conversion
techniques, the signal of which can be mapped [8] (see Fig. 5.6).
Another approach to gain information about spatial profiles and optical properties
can be obtained by SNOM and scattering-type SNOM. While the former collects
1 Amendment: Note that also imaging spectrometer cameras in µPL setups can often well resolve
projected sample images, when the spectrometer with fully-open slit is operated in non-dispersive
mode.
2 Amendment: Or even 3D, focal plane by plane scanned in confocal microscopy.
5 Optical Measurement Techniques
as particularly shiny areas under above-band photoexcitation, facilitating identification of the monolayered regions drastically which can be used during monolayerstransferring endeavours [6].
5.2.2 Spatial Distribution
One-shot imaging with cameras—either of type charged-coupled device (CCD)
or complementary metal-oxide-semiconductor (CMOS)—connected to microscope
setups can provide easy access to high-quality visualisation of sample materials.
However, the recorded intensity profile only carries information about the spatial
domain and some differences in surface reflectance and composition (without spectral resolution).
1 An example of spatial µPL distributions for 2D-materials stacks on
patterned surfaces for PL modifications is for instance given in Fig. 5.4, shown in
linear (right) as well as logarithmic (left) intensity scale for a grating (upper panel)
and reference hole (lower panel).
Similarly, spatially-integrated spectroscopy with or without the use of a microscope does not provide any information about spatial distributions, but merely reveals
spectral signatures. Thus, raster scanning the focal spot of the given light source of
a spectroscopy method is used to obtain spatially-resolved spectral information.
Hereby, the resolution is determined by the magnification of the optics and spatial
filtering methods. Raster scans can be performed both in 1D and 2D,
2 resulting in
hyperspectral imaging (see Fig. 5.5). In addition, spatially-resolved spectra can be
obtained when the real-space image is projected via lenses onto the entrance slit
of an imaging spectrometer’s monochromator, which delivers spatial information in
the direction of the slit wavelength-resolved on a monochromator-attached imaging CCD. By raster scanning in the perpendicular direction, one can also obtain 2D
spatial distributions from such spatially-1D single-shot acquisition mode.
Typically, Raman and fluorescence (luminescence) spectroscopy with spatial resolution is widely used to investigate structured surfaces and microscopic materials,
such as 2D-material flakes and their artificial stacks [2, 7–10]. For example, comparisons of Raman and PL spectra for monolayer and few-layer systems can already
be well performed by hyperspectral line scans (see for instance the Supporting Information section of [8]), for which the sample is scanned in one direction using a
high-precision translation stage, e.g., driven by piezo actuators. Spatial information
can further be obtained by sheet-/surface-sensitive nonlinear frequency conversion
techniques, the signal of which can be mapped [8] (see Fig. 5.6).
Another approach to gain information about spatial profiles and optical properties
can be obtained by SNOM and scattering-type SNOM. While the former collects
1 Amendment: Note that also imaging spectrometer cameras in µPL setups can often well resolve
projected sample images, when the spectrometer with fully-open slit is operated in non-dispersive
mode.
2 Amendment: Or even 3D, focal plane by plane scanned in confocal microscopy.