13.3 Van-der-Waals Heterostructures
399
(a)
(b)
Fig. 13.26 a Example of van-der-Waals heterostructure from various 2D materials as proposed in [1326]. Reprinted
with permission, ©2013, Springer Nature. b Van-der-Waals heterostructure with twisted layers. Adapted from [1328],
reprinted with permission, ©2018, Springer Nature
Fig. 13.27 Resistance of
BN-graphene-BN
van-der-Waals
heterostructure (insets
show optical image and
cross section TEM as well
as the device and its
schematic measurement
scheme). Adapted
from [1331]
The field effect for a graphene layer between BN flakes is shown in Fig. 13.27. The measured mobility
(at room temperature) is in the range of 10
5 cm
2 /Vs for a 2D carrier density below 1 × 10
12 cm
−2 and
thus larger than values achieved for InSb or InAs [1331]. Van-der-Waals heterostructures of boron
nitride and graphene are reviewed in [1332].
The effect of surrounding media via the modified dielectric screening on excitons has been mentioned
already above [1319, 1320]. Encapsulation by h-BN monolayers can enhance the luminescence yield
and reduce the recombination time constant of a TMDC monolayer, as demonstrated in [1334] for a
three monolayer h-BN/WS 2 /h-BN heterostructure.
Generally, in van-der-Waals heterostructures, the weak interlayer bonding allows a new degree
of freedom, the twist angle ϑ (cf. Fig. 13.25b for twist of two graphene layers) between two 2D
crystals (Fig. 13.26b). The situation is similar to the twist boundary between two grains (Sect. 4.4.3).
This rotation causes the formation of moiré patterns that are directly observable in STM images as
depicted in Fig. 13.28. The physical properties of the heterostructure can drastically depend on the
twist angle [1335]. A prominent consequence is the periodic modification of the energy landscape for
399
(a)
(b)
Fig. 13.26 a Example of van-der-Waals heterostructure from various 2D materials as proposed in [1326]. Reprinted
with permission, ©2013, Springer Nature. b Van-der-Waals heterostructure with twisted layers. Adapted from [1328],
reprinted with permission, ©2018, Springer Nature
Fig. 13.27 Resistance of
BN-graphene-BN
van-der-Waals
heterostructure (insets
show optical image and
cross section TEM as well
as the device and its
schematic measurement
scheme). Adapted
from [1331]
The field effect for a graphene layer between BN flakes is shown in Fig. 13.27. The measured mobility
(at room temperature) is in the range of 10
5 cm
2 /Vs for a 2D carrier density below 1 × 10
12 cm
−2 and
thus larger than values achieved for InSb or InAs [1331]. Van-der-Waals heterostructures of boron
nitride and graphene are reviewed in [1332].
The effect of surrounding media via the modified dielectric screening on excitons has been mentioned
already above [1319, 1320]. Encapsulation by h-BN monolayers can enhance the luminescence yield
and reduce the recombination time constant of a TMDC monolayer, as demonstrated in [1334] for a
three monolayer h-BN/WS 2 /h-BN heterostructure.
Generally, in van-der-Waals heterostructures, the weak interlayer bonding allows a new degree
of freedom, the twist angle ϑ (cf. Fig. 13.25b for twist of two graphene layers) between two 2D
crystals (Fig. 13.26b). The situation is similar to the twist boundary between two grains (Sect. 4.4.3).
This rotation causes the formation of moiré patterns that are directly observable in STM images as
depicted in Fig. 13.28. The physical properties of the heterostructure can drastically depend on the
twist angle [1335]. A prominent consequence is the periodic modification of the energy landscape for