18
2 Entering a Two-Dimensional Materials World
Fig. 2.1 a Schematically indicated spectral map of 2D materials and the typical applications for
each frequency range. Corresponding to their energy gaps, different materials address different
spectral regions, as shown here at the examples of (b) hBN, c TMDCs (here MoS 2 ), d black
phosphorus and e graphene (see gap information and band structure diagrams displayed). Large gap
van-der-Waals materials act as insulators, whereas gapless materials can be very good conductors.
In-between lie medium-sized gaps, which are attractive for optoelectronic applications. Reproduced
with permission. [9] Copyright 2014 Springer Nature
Potential Application Reviews and Excitonic Features
Naturally, potential applications of ultrathin 2D materials had come into focus quickly
[9–20] (cf. Fig. 2.1). Nonetheless, a lot of fundamentals regarding mechanical, electronic, and optical properties, as well as synthesis, remained for exploration. On top,
2D semiconductors have offered a unique platform for investigations on a vast pool of
excitonic species [21]. This goes beyond the neutral excitonic species with peculiar
Rydberg-like characteristics [22–25]. Such pool includes trions [26, 27], biexcitons
[28] and dark exciton states [29].
With time, more and more aspects of the (monolayer) 2D semiconductor’s valley dichroism [30, 31], valley coherence [32], pseudo-spin texture within the light
cone [33], their (density and temperature-dependent) dynamics [34–41], radiativelylimited dephasing (temperature-dependent homogeneous broadening) [35], diffusion
[42], dissociation [43], orientation [44], selection rules [45], fine-structure [46, 47],
exciton or trion g-factors [48–50], electronic dispersion [51], optical dispersion [33,
2 Entering a Two-Dimensional Materials World
Fig. 2.1 a Schematically indicated spectral map of 2D materials and the typical applications for
each frequency range. Corresponding to their energy gaps, different materials address different
spectral regions, as shown here at the examples of (b) hBN, c TMDCs (here MoS 2 ), d black
phosphorus and e graphene (see gap information and band structure diagrams displayed). Large gap
van-der-Waals materials act as insulators, whereas gapless materials can be very good conductors.
In-between lie medium-sized gaps, which are attractive for optoelectronic applications. Reproduced
with permission. [9] Copyright 2014 Springer Nature
Potential Application Reviews and Excitonic Features
Naturally, potential applications of ultrathin 2D materials had come into focus quickly
[9–20] (cf. Fig. 2.1). Nonetheless, a lot of fundamentals regarding mechanical, electronic, and optical properties, as well as synthesis, remained for exploration. On top,
2D semiconductors have offered a unique platform for investigations on a vast pool of
excitonic species [21]. This goes beyond the neutral excitonic species with peculiar
Rydberg-like characteristics [22–25]. Such pool includes trions [26, 27], biexcitons
[28] and dark exciton states [29].
With time, more and more aspects of the (monolayer) 2D semiconductor’s valley dichroism [30, 31], valley coherence [32], pseudo-spin texture within the light
cone [33], their (density and temperature-dependent) dynamics [34–41], radiativelylimited dephasing (temperature-dependent homogeneous broadening) [35], diffusion
[42], dissociation [43], orientation [44], selection rules [45], fine-structure [46, 47],
exciton or trion g-factors [48–50], electronic dispersion [51], optical dispersion [33,