30
2 Entering a Two-Dimensional Materials World
Fig. 2.7 Angle-resolved spectroscopy of an hBN-encapsulated monolayer of WSe 2 exhibiting
multiple excitonic features and phonon sidebands, which were attributed in the literature to neutral as well as charged excitons (X and X ± , respectively) and exciton complexes, such as neutral/charged biexcitons (XX/XX − ), z-mode excitons (X D,g , “grey”, i.e. not totally dark) and optical
(op.) and acoustic (ac.) dark-exciton (X D ) phonon sidebands (PSB), respectively. a Overview spectrum given as contour diagram with energy versus emission angle (false-colour scale: intensity
increases towards dark blue). b Angle-integrated spectrum (red boxed in a) exhibiting different
excitonic intensity peaks. c Radiation profile of the out-of-plane emitting bright (lateral) exciton
and the in-plane emitting ‘grey’ exciton (a dark exciton with out-of-plane dipole orientation, i.e.
z polarisation), obtained under a cross-polarised detection scheme, showing good agreement with
the expected profile highlighted by simulated data. Reproduced under the terms of the CC-BY 4.0
Licence (http://creativecommons.org/licenses/by/4.0/). [47] Copyright 2020 The Author(s), published by Springer Nature
2.3 Graphene and Related Materials
A 2D World Opened Up for Use
While the fascination for graphene has continuously grown, graphene and many of
its derivatives have not really conquered the electronics market yet. Nevertheless,
graphene has become an important platform for 2D-materials research as well as
device prototyping, and many review articles such as the one by Novoselov et al. [163]
have pointed out a roadmap for graphene, and even for materials beyond graphene
[116]. Although popular for its electronic features, it has also become appealing
for light–matter interaction studies [164]. Since the beginning of the past decade,
graphene has been widely employed and studied for the development of novel electrooptical devices, among others as transparent electrodes [165], for photovoltaic [166]
or plasmonic devices [164, 167, 168], in optical modulators [169], and sensing/sensor
devices [170–172].
The Rise of Graphene
Based on its remarkable properties such as a broad spectral bandwidth and high electron mobility, high-performance photodetectors were envisaged for graphene [13],
and numerous examples indicate the successful use in this regard [173–177], including laser-defined functionalised graphene photodetectors with extraordinary linear
2 Entering a Two-Dimensional Materials World
Fig. 2.7 Angle-resolved spectroscopy of an hBN-encapsulated monolayer of WSe 2 exhibiting
multiple excitonic features and phonon sidebands, which were attributed in the literature to neutral as well as charged excitons (X and X ± , respectively) and exciton complexes, such as neutral/charged biexcitons (XX/XX − ), z-mode excitons (X D,g , “grey”, i.e. not totally dark) and optical
(op.) and acoustic (ac.) dark-exciton (X D ) phonon sidebands (PSB), respectively. a Overview spectrum given as contour diagram with energy versus emission angle (false-colour scale: intensity
increases towards dark blue). b Angle-integrated spectrum (red boxed in a) exhibiting different
excitonic intensity peaks. c Radiation profile of the out-of-plane emitting bright (lateral) exciton
and the in-plane emitting ‘grey’ exciton (a dark exciton with out-of-plane dipole orientation, i.e.
z polarisation), obtained under a cross-polarised detection scheme, showing good agreement with
the expected profile highlighted by simulated data. Reproduced under the terms of the CC-BY 4.0
Licence (http://creativecommons.org/licenses/by/4.0/). [47] Copyright 2020 The Author(s), published by Springer Nature
2.3 Graphene and Related Materials
A 2D World Opened Up for Use
While the fascination for graphene has continuously grown, graphene and many of
its derivatives have not really conquered the electronics market yet. Nevertheless,
graphene has become an important platform for 2D-materials research as well as
device prototyping, and many review articles such as the one by Novoselov et al. [163]
have pointed out a roadmap for graphene, and even for materials beyond graphene
[116]. Although popular for its electronic features, it has also become appealing
for light–matter interaction studies [164]. Since the beginning of the past decade,
graphene has been widely employed and studied for the development of novel electrooptical devices, among others as transparent electrodes [165], for photovoltaic [166]
or plasmonic devices [164, 167, 168], in optical modulators [169], and sensing/sensor
devices [170–172].
The Rise of Graphene
Based on its remarkable properties such as a broad spectral bandwidth and high electron mobility, high-performance photodetectors were envisaged for graphene [13],
and numerous examples indicate the successful use in this regard [173–177], including laser-defined functionalised graphene photodetectors with extraordinary linear