214
7 Structuring Possibilities
a homobilayer. In the example here, these are composed of two WS 2 monolayers
with distinct stacking-twist angles achieved by the choice of growth parameters.
Firstly, a source substrate was prepared by depositing 5 nm WO 3 on a sapphire or
SiO 2 /Si substrate using physical vapour deposition (PVD). The source substrate
was placed face-to-face atop another sapphire or SiO 2 /Si substrate, which was the
bilayer-growth substrate. During the first growth, WS 2 monolayers were grown on
the growth substrate at 950
◦ C. In the second growth step, a new source substrate was
placed face-to-face onto the growth substrate, which carried the WS 2 monolayers
formed during the first-step growth.
In such a two-step-growth scenario utilised in [14], the monolayers grown during the first step provide seeding sites for the material deposited during the second
growth. In that example, the second growth step took place for WS 2 at 850
◦ C, resulting in homobilayer growth of WS 2 with an AA’ or AB stacking mode. Remarkably,
these two different stacking modes were determined by adjusting the growth parameters of the WS 2 monolayers obtained during the initial growth step. The amount of
sulfur can be adjusted during the first-step growth, which favours either a sulfur-rich
environment or a WO 3 -rich environment. It was found previously in [15] that the
sulfur-rich environment results in sulfur-terminated WS 2 monolayers, whereas the
WO 3 -rich environment was found to give tungsten-terminated WS 2 monolayers. In
the preferential two-step bilayer-growth performed for the study of [14], the former
case triggered the AB stacking of the homobilayers, whereas the latter triggered the
AA’ stacking of the homobilayers.
7.2 Patterning and Assembly
In the following, common concepts for the production and assembly of nanostructured systems are briefly summarised. Thereby, “top–down” and “bottom–up” nanotechnological approaches are addressed which can be utilised to achieve various
nanoscale components for optoelectronic and quantum technological devices. Typical scenarios are the achievement of confinement potentials or waveguides structures
in semiconductor devices through patterning, as well as electrical contacting schemes
through metal deposition on masked surfaces or nanoparticle growth through synthesis in solution and induced-/self-assembly on exposed substrate facets.
7.2.1 Lithography, Deposition and Etching
Translating patterns from a design template into a solid has wide use in the production
and development of nanotechnological devices. To manipulate (VIS–IR) light on the
length scale of its wavelength, microstructuring with sub-micrometer precision is
required. This can be conveniently achieved using optical lithography for masking
of a sample surface. Commonly, a photosensitive resist is exposed by a shadow mask
and the defined pattern in the resist is developed for subsequent etching.
7 Structuring Possibilities
a homobilayer. In the example here, these are composed of two WS 2 monolayers
with distinct stacking-twist angles achieved by the choice of growth parameters.
Firstly, a source substrate was prepared by depositing 5 nm WO 3 on a sapphire or
SiO 2 /Si substrate using physical vapour deposition (PVD). The source substrate
was placed face-to-face atop another sapphire or SiO 2 /Si substrate, which was the
bilayer-growth substrate. During the first growth, WS 2 monolayers were grown on
the growth substrate at 950
◦ C. In the second growth step, a new source substrate was
placed face-to-face onto the growth substrate, which carried the WS 2 monolayers
formed during the first-step growth.
In such a two-step-growth scenario utilised in [14], the monolayers grown during the first step provide seeding sites for the material deposited during the second
growth. In that example, the second growth step took place for WS 2 at 850
◦ C, resulting in homobilayer growth of WS 2 with an AA’ or AB stacking mode. Remarkably,
these two different stacking modes were determined by adjusting the growth parameters of the WS 2 monolayers obtained during the initial growth step. The amount of
sulfur can be adjusted during the first-step growth, which favours either a sulfur-rich
environment or a WO 3 -rich environment. It was found previously in [15] that the
sulfur-rich environment results in sulfur-terminated WS 2 monolayers, whereas the
WO 3 -rich environment was found to give tungsten-terminated WS 2 monolayers. In
the preferential two-step bilayer-growth performed for the study of [14], the former
case triggered the AB stacking of the homobilayers, whereas the latter triggered the
AA’ stacking of the homobilayers.
7.2 Patterning and Assembly
In the following, common concepts for the production and assembly of nanostructured systems are briefly summarised. Thereby, “top–down” and “bottom–up” nanotechnological approaches are addressed which can be utilised to achieve various
nanoscale components for optoelectronic and quantum technological devices. Typical scenarios are the achievement of confinement potentials or waveguides structures
in semiconductor devices through patterning, as well as electrical contacting schemes
through metal deposition on masked surfaces or nanoparticle growth through synthesis in solution and induced-/self-assembly on exposed substrate facets.
7.2.1 Lithography, Deposition and Etching
Translating patterns from a design template into a solid has wide use in the production
and development of nanotechnological devices. To manipulate (VIS–IR) light on the
length scale of its wavelength, microstructuring with sub-micrometer precision is
required. This can be conveniently achieved using optical lithography for masking
of a sample surface. Commonly, a photosensitive resist is exposed by a shadow mask
and the defined pattern in the resist is developed for subsequent etching.