206
B. P. Majee and A. K. Mishra
Fig. 16 a SEM images of an interconnected network of vertically oriented few-layer MoS 2
nanosheets. SERS spectra of b R6G and c MO dyes at different concentrations. d Raman intensity
versus dye concentration of R6G and MO molecules for 611 and 1180 cm −1 peaks, respectively.
Adapted with permission from [46]. Copyright 2020 American Chemical Society
indicates the presence of large number of thin edges. These edges are helpful for
improved light adsorption by multiple reflection and larger accessible surface area
for improved dye adsorption [46]. Figure 16b, c show the SERS signals for R6G and
MO molecules adsorbed on the surface of MoS 2 /Si at different concentrations (10
−6
to10
−10 M), respectively. The higher concentrations of dye molecules show higher
peak intensities. In this study, we observed the variation of Raman intensities of 611
and 1180 cm
−1 peaks versus dye concentration for R6G and MO molecules, respectively. We found that the slope of 611 cm
−1 (of R6G) is higher than the 1180 cm
−1
(of MO) as shown in Fig. 16d, suggesting higher enhancement factor (EF) for R6G
compared to MO.
We calculated the EF for both molecules and found value of EF of 8.6 × 10
4 and
5.8 × 10
4 for R6G and MO molecules, respectively. The high detection limit i.e.
up to sub-nanomolar concentration (10
−10 M) can be attributed to the Herzberg −
Teller vibronic coupling in different resonances in analyte/VFL-MoS 2 system. Both
the molecules show absorption in the visible range (R6G-526 nm and MO-467 nm),
which is very close to the resonance with the excitation laser source of wavelength
532 nm. Hence, three different mechanisms responsible for the enhancement are
molecular resonance, CT resonance and the surface interaction between MoS 2 and
B. P. Majee and A. K. Mishra
Fig. 16 a SEM images of an interconnected network of vertically oriented few-layer MoS 2
nanosheets. SERS spectra of b R6G and c MO dyes at different concentrations. d Raman intensity
versus dye concentration of R6G and MO molecules for 611 and 1180 cm −1 peaks, respectively.
Adapted with permission from [46]. Copyright 2020 American Chemical Society
indicates the presence of large number of thin edges. These edges are helpful for
improved light adsorption by multiple reflection and larger accessible surface area
for improved dye adsorption [46]. Figure 16b, c show the SERS signals for R6G and
MO molecules adsorbed on the surface of MoS 2 /Si at different concentrations (10
−6
to10
−10 M), respectively. The higher concentrations of dye molecules show higher
peak intensities. In this study, we observed the variation of Raman intensities of 611
and 1180 cm
−1 peaks versus dye concentration for R6G and MO molecules, respectively. We found that the slope of 611 cm
−1 (of R6G) is higher than the 1180 cm
−1
(of MO) as shown in Fig. 16d, suggesting higher enhancement factor (EF) for R6G
compared to MO.
We calculated the EF for both molecules and found value of EF of 8.6 × 10
4 and
5.8 × 10
4 for R6G and MO molecules, respectively. The high detection limit i.e.
up to sub-nanomolar concentration (10
−10 M) can be attributed to the Herzberg −
Teller vibronic coupling in different resonances in analyte/VFL-MoS 2 system. Both
the molecules show absorption in the visible range (R6G-526 nm and MO-467 nm),
which is very close to the resonance with the excitation laser source of wavelength
532 nm. Hence, three different mechanisms responsible for the enhancement are
molecular resonance, CT resonance and the surface interaction between MoS 2 and