SUPPORTING INFORMATION

FESEM

S1.  FESEM images of (a) W_bulk and (b) W_exfoliated samples.

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Optical conductivity

The optical conductivity (σ_opt) has been calculated using Eq. (11). In MoS₂ samples, σ_opt rises with increasing energy. In the visible region (lower energy), the spectra reveals maximas of conductivity which are blue shifted (shifted towards higher energy) for M_exfoliated samples as compared to M_bulk samples (see Fig. S2(a)). These peaks are at selective energies due to the fact that, at these energies, the incident photons have induced greater excitation of electrons in the sample. In the higher energy or ultraviolet region of incident spectrum, nanosheet thin films are more optically conducting than the bulk films. Moving to WS₂ samples, the bulk WS₂ doesn’t show much variation in conductivity but in exfoliated WS₂ there are peaks in the spectrum just like M_exfoliated samples (Fig. S2(b)).

S2.  Plot of optical conductivity (σ_opt) with incident energy (hν) for (a) M_bulk, M_exfoliated and (b) W_bulk, W_exfoliated.

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Optical density & skin depth

As optical density is directly proportional to α(see Eq. 10), maximum density is achieved at energies of inter-band optical transitions as shown in Fig. S3. Skin depth is basically a measure of penetration of radiation into the thin film. Mathematically, it is just the reciprocal of absorption coefficient (Eq. 9). Looking at the variation of skin depth with wavelength for our samples in Fig. S4, the penetration minimizes at the wavelengths corresponding to inter-band transitions or excitonic peaks. This is because at these points, the absorption coefficient maximizes and the electromagnetic radiation gets absorbed and therefore, the skin depth drops.

S3.  Variation of optical density with incident energy (hν) for (a) M_bulk, M_exfoliated and (b) W_bulk, W_exfoliated.

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S4.  Plot of skin depth (δ) vs incident energy (hν) for (a) M_bulk, M_exfoliated and (b) W_bulk, W_exfoliated.

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Urbach Energy (E_u)

To derive the structural order in the samples, Urbach Energy (E_u) plays an important role as described in theory. The obtained values for all the samples are listed in Table 1. From the table, E_u is higher for the bulk samples as compared to their respective nanosheets. This implies that the nanosheets obtained after liquid exfoliation are more ordered. This reconfirms the XRD results in which we observed that the M_exfoliated and W_exfioliated samples are oriented in a single crystalline phase (002), whereas, the XRD patterns of M_bulk and W_bulk consisted of various phases. Therefore, there is more order in the obtained nanosheets of MoS₂ and WS₂.

S5.  Plot of urbach energy (E_u) with incident energy (hν) for (a) M_bulk, M_exfoliated and (b) W_bulk, W_exfoliated.

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Single Sellmeier Model (SSM)

S6.  Plot of (n²–1)^–1 v/s λ^–2 for (a) M_bulk, M_exfoliated and (b) W_bulk, W_exfoliated.

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