154
5 Optical Measurement Techniques
Fig. 5.11 Example measurement showing the linear optical response for a WS 2 /WSe 2 heterobilayer structure (on hBN) as studied in [2]. a PL spectrum recorded spatially-resolved for the
heterobilayer (here spatially integrated over a certain heterobilayer region) exhibiting numerous
features at 10 K, in semilogarithmic representation. Next to monolayer A-excitonic signatures for
the individual TMDCs, pronounced interlayer features labelled IL1–4 are obtained. b Corresponding reflection contrast spectrum for the same flake (spatially-integrated over a certain heterobilayer
region from spatially-resolved data), showing absorption signatures and strong energetic congruence of features from a and b. Remarkably, the energy-split indirect excitons at long wavelengths
indicate a noticeable influence of moiré patterns according to the literature (cf. [63]). Note the linear
scale here, indicating a pronounced oscillator strength of these optical IL transitions. Additional
interlayer features (IL1,2) between the monolayer resonances have been attributed to moiré states
in good spectral agreement with the aforementioned literature. Also see corresponding lifetimes
obtained from preliminary investigations shown in Fig. 5.9. a, b Reproduced with permission. [2]
Copyright 2019 Springer Nature
(ionised excitons) becomes dominant
11 which can radiate out of the exciton mode as
well (cf. [66], which discusses off-resonantly and resonantly excited Fourier-spaceresolved emission spectra, and references therein).
Typical non-resonantly CW-excited PL spectra show multiple emission modes
and background features (see for instance [46, 66], and inset in Fig. 5.17(d) in the
section below), whereas pulsed measurements can reveal the decay times of bright
species (cf. [5, 7, 31, 33], and see Fig. 5.9). Additionally, time-resolved spectra can
even indicate transfer rates between populations in excitation modes that feed each
others.
11 The interested reader is referred to the semiconductor luminescence equations, see e.g., [18].
5 Optical Measurement Techniques
Fig. 5.11 Example measurement showing the linear optical response for a WS 2 /WSe 2 heterobilayer structure (on hBN) as studied in [2]. a PL spectrum recorded spatially-resolved for the
heterobilayer (here spatially integrated over a certain heterobilayer region) exhibiting numerous
features at 10 K, in semilogarithmic representation. Next to monolayer A-excitonic signatures for
the individual TMDCs, pronounced interlayer features labelled IL1–4 are obtained. b Corresponding reflection contrast spectrum for the same flake (spatially-integrated over a certain heterobilayer
region from spatially-resolved data), showing absorption signatures and strong energetic congruence of features from a and b. Remarkably, the energy-split indirect excitons at long wavelengths
indicate a noticeable influence of moiré patterns according to the literature (cf. [63]). Note the linear
scale here, indicating a pronounced oscillator strength of these optical IL transitions. Additional
interlayer features (IL1,2) between the monolayer resonances have been attributed to moiré states
in good spectral agreement with the aforementioned literature. Also see corresponding lifetimes
obtained from preliminary investigations shown in Fig. 5.9. a, b Reproduced with permission. [2]
Copyright 2019 Springer Nature
(ionised excitons) becomes dominant
11 which can radiate out of the exciton mode as
well (cf. [66], which discusses off-resonantly and resonantly excited Fourier-spaceresolved emission spectra, and references therein).
Typical non-resonantly CW-excited PL spectra show multiple emission modes
and background features (see for instance [46, 66], and inset in Fig. 5.17(d) in the
section below), whereas pulsed measurements can reveal the decay times of bright
species (cf. [5, 7, 31, 33], and see Fig. 5.9). Additionally, time-resolved spectra can
even indicate transfer rates between populations in excitation modes that feed each
others.
11 The interested reader is referred to the semiconductor luminescence equations, see e.g., [18].