230
8 Conclusion and Outlook
Semiconductor nanomaterials research has entered the stage of industrial applications with quantum dots being used as high-brightness, high colour-purity luminescent nanostructures for display technologies, or even acting as single-photon emitters
for quantum information systems, or as light-absorbing structures for highly-sensitive
photodetectors. Synthesis of quantum materials has evolved to that extent that colloidal quantum dots and other nanoparticles are synthesised in solution with prospects
of mass producibility and device integration. Remarkably, institutes worldwide are
pioneering many topics in this field and numerous companies use highly innovative
concepts to exploit the benefits of such quantum structures. For instance, prominent
display manufacturers are currently developing new display technologies based on
colloidal quantum dots light sources or graphene-based lighting and flexible electrodes.
In addition, natural quantum materials, such as layered two-dimensional (2D) systems, have been in the focus for more than a decade, with graphene as the prominent
conductive example, and transition-metal dichalcogenides (TMDCs) and hexagonal boron nitride (hBN) as the semiconducting and insulating counterparts, respectively. 2D-materials research is a hot topic of functional nanomaterials science and
has received unrivalled attention in the international science community. Recently,
2D-materials research was considered among the top 10 topics of interest by key
scientific journals. Their properties in the monolayer and few-layer regimes give
access to intriguing physics, while the possibility to stack 2D materials vertically
enables enormous variability in terms of van-der-Waals epitaxy, which is layer-bylayer arrangement or growth of 2D materials that are linked to their neighbouring
material sheets by van-der-Waals forces. The high surface-to-bulk ratio, quantum
confinement and the broken symmetry of 2D semiconductors, such as TMDCs or
the post-TMDC materials (e.g. group-III monochalcogenides), are responsible for
considerable changes in optoelectronic properties when the layer number approaches
the monolayer limit, or the environment of ultrathin flakes is altered, or the stacking
of layered structures is varied. Those changes can be of great importance to device
design principles.
From this, innovative potential applications for such materials can be deduced,
covering the fields of electronics, optoelectronics, energy, or sensing. 2D materials
with their mechanical strength and flexibility also allow one to envisage flexible
devices and to target applications, which require bendable substrates or materials.
Most strikingly, 2D semiconductors in the monolayer and few-layer regime offer a
wide range of band gaps, huge exciton binding energies, strong light–matter interaction and even polarisation dichroism. Band gaps from a few milli-electron-volts
to several electron-volts were reported for 2D materials, and peculiarities, such as
the valley Hall effect, enable the design of future valleytronic devices that exploit
the spin-selectivity of the time-reversal-symmetry-broken electronic band structure.
In recent years, different applications were addressed or suggested, depending on
the material properties, ranging from electrodes in batteries and channel-materials
in transistors to ultrasensitive photodetectors or molecular sensors. For instance, 2D
materials such as the conducting graphene can be used for the generation of broadband tunable THz sources or sensors, TMDCs employed as active medium and the
8 Conclusion and Outlook
Semiconductor nanomaterials research has entered the stage of industrial applications with quantum dots being used as high-brightness, high colour-purity luminescent nanostructures for display technologies, or even acting as single-photon emitters
for quantum information systems, or as light-absorbing structures for highly-sensitive
photodetectors. Synthesis of quantum materials has evolved to that extent that colloidal quantum dots and other nanoparticles are synthesised in solution with prospects
of mass producibility and device integration. Remarkably, institutes worldwide are
pioneering many topics in this field and numerous companies use highly innovative
concepts to exploit the benefits of such quantum structures. For instance, prominent
display manufacturers are currently developing new display technologies based on
colloidal quantum dots light sources or graphene-based lighting and flexible electrodes.
In addition, natural quantum materials, such as layered two-dimensional (2D) systems, have been in the focus for more than a decade, with graphene as the prominent
conductive example, and transition-metal dichalcogenides (TMDCs) and hexagonal boron nitride (hBN) as the semiconducting and insulating counterparts, respectively. 2D-materials research is a hot topic of functional nanomaterials science and
has received unrivalled attention in the international science community. Recently,
2D-materials research was considered among the top 10 topics of interest by key
scientific journals. Their properties in the monolayer and few-layer regimes give
access to intriguing physics, while the possibility to stack 2D materials vertically
enables enormous variability in terms of van-der-Waals epitaxy, which is layer-bylayer arrangement or growth of 2D materials that are linked to their neighbouring
material sheets by van-der-Waals forces. The high surface-to-bulk ratio, quantum
confinement and the broken symmetry of 2D semiconductors, such as TMDCs or
the post-TMDC materials (e.g. group-III monochalcogenides), are responsible for
considerable changes in optoelectronic properties when the layer number approaches
the monolayer limit, or the environment of ultrathin flakes is altered, or the stacking
of layered structures is varied. Those changes can be of great importance to device
design principles.
From this, innovative potential applications for such materials can be deduced,
covering the fields of electronics, optoelectronics, energy, or sensing. 2D materials
with their mechanical strength and flexibility also allow one to envisage flexible
devices and to target applications, which require bendable substrates or materials.
Most strikingly, 2D semiconductors in the monolayer and few-layer regime offer a
wide range of band gaps, huge exciton binding energies, strong light–matter interaction and even polarisation dichroism. Band gaps from a few milli-electron-volts
to several electron-volts were reported for 2D materials, and peculiarities, such as
the valley Hall effect, enable the design of future valleytronic devices that exploit
the spin-selectivity of the time-reversal-symmetry-broken electronic band structure.
In recent years, different applications were addressed or suggested, depending on
the material properties, ranging from electrodes in batteries and channel-materials
in transistors to ultrasensitive photodetectors or molecular sensors. For instance, 2D
materials such as the conducting graphene can be used for the generation of broadband tunable THz sources or sensors, TMDCs employed as active medium and the