398
13 Two-Dimensional Semiconductors
Fig. 13.24 Plane-view of
the electron wave function
of the exciton ground state
in MoS 2 monolayer in a
real space and b k-space.
Adapted from [1299],
reprinted with permission,
©2013 APS. c Schematic
1s and 2s exciton wave
functions with different
sensing of the lowenvironment
(c)
13.3 Van-der-Waals Heterostructures
Let’s recall that graphite is a stacked arrangement of graphene layers. It is called the ’Bernal’-phase or
-stacking and relates to the AB- or 2H-stacking like in a hcp crystal (Fig. 13.25a). Other meta-stable
arrangements are the AA’-stackings (twisted bilayer graphene), in which the crystallographic axes of
the two layers have an arbitrary angle ϑ between zero and 30
◦ as depicted in Fig. 13.25b); the stacking
vor ϑ = 0 is also termed AA. Electronic properties depend on the twist angle [1321]. A refined
theory considering the super-periodicities (moiré pattern) of interlayer hopping potential has been
reported in [1322, 1323]. The different stackings can be distinguished, e.g., in infrared spectroscopic
imaging [1324].
As an extension of this concept, van-der-Waals heterostructures been conceived [1326, 1327] which
consist of vertically stacked atomic sheets of various 2D materials, a kind of molecular LEGO
™
(Fig. 13.26a). Virtually any combination is possible for various electronic, sprintronic and photonic
applications [1329, 1330]. An advantage is the well controlled tunneling effect by the present exact
layer thicknesses in the device.
Fig. 13.25 Vertical stacking phases of graphene in a AB-type, Bernal-stacking and b AA’-type, non-Bernal stacking.
The rotation angle ϑ is indicated. Adapted from [1325]
13 Two-Dimensional Semiconductors
Fig. 13.24 Plane-view of
the electron wave function
of the exciton ground state
in MoS 2 monolayer in a
real space and b k-space.
Adapted from [1299],
reprinted with permission,
©2013 APS. c Schematic
1s and 2s exciton wave
functions with different
sensing of the lowenvironment
(c)
13.3 Van-der-Waals Heterostructures
Let’s recall that graphite is a stacked arrangement of graphene layers. It is called the ’Bernal’-phase or
-stacking and relates to the AB- or 2H-stacking like in a hcp crystal (Fig. 13.25a). Other meta-stable
arrangements are the AA’-stackings (twisted bilayer graphene), in which the crystallographic axes of
the two layers have an arbitrary angle ϑ between zero and 30
◦ as depicted in Fig. 13.25b); the stacking
vor ϑ = 0 is also termed AA. Electronic properties depend on the twist angle [1321]. A refined
theory considering the super-periodicities (moiré pattern) of interlayer hopping potential has been
reported in [1322, 1323]. The different stackings can be distinguished, e.g., in infrared spectroscopic
imaging [1324].
As an extension of this concept, van-der-Waals heterostructures been conceived [1326, 1327] which
consist of vertically stacked atomic sheets of various 2D materials, a kind of molecular LEGO
™
(Fig. 13.26a). Virtually any combination is possible for various electronic, sprintronic and photonic
applications [1329, 1330]. An advantage is the well controlled tunneling effect by the present exact
layer thicknesses in the device.
Fig. 13.25 Vertical stacking phases of graphene in a AB-type, Bernal-stacking and b AA’-type, non-Bernal stacking.
The rotation angle ϑ is indicated. Adapted from [1325]