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We report a comprehensive van der Waals density functional theory study on the adsorption characteristics of four canonical and six epigenetically modified DNA nucleobases on single-layer molybdenum disulfide (SL-MoS2) substrates. All the considered nucleobases are physisorbed on SL-MoS2 with a modest electron transfer, ranging from 0.007e− to 0.041e−, from the adsorbates to SL-MoS2. Upon the physisorption of adenine, cytosine, guanine, and thymine on the SL-MoS2 sheet, the work function is decreased by 0.29, 0.09, 0.54, and 0.01 eV, respectively. It is shown that the bandgap of SL-MoS2 can be significantly reduced, by as much as 30%, through the adsorption of nucleobase molecules as the induced molecular flat bands tend to appear either in the energy gap region or in the vicinity of the valence band maximum. We unfold the emergence of distinct electron energy loss spectra upon nucleobase adsorption which may serve as potential probes for selective detection of nucleobase molecules in prospective DNA sequencing applications based on SL-MoS2.

Sensing ultra-low levels of toxic chemicals such as H 2 S is crucial for many technological applications. In this report, employing density functional theory (DFT) calculations, we shed light on the underlying physical phenomena involved in the adsorption and sensing of the H 2 S molecule on both pristine and strained single-layer molybdenum disulfide (SL-MoS 2 ) substrates. We demonstrate that the H 2 S molecule is physisorbed on SL-MoS 2 for all values of strain, i.e. from À8% to +8%, with a modest electron transfer, ranging from 0.023e À to 0.062e À , from the molecule to the SL-MoS 2 . According to our calculations, the electron-donating behaviour of the H 2 S molecule is halved under compressive strains. Moreover, we calculate the optical properties upon H 2 S adsorption and reveal the electron energy loss (EEL) spectra for various concentrations of the H 2 S molecule which may serve as potential probes for detecting H 2 S molecules in prospective sensing applications based on SL-MoS 2 . † Electronic supplementary information (ESI) available: The zero-crossing energies in the real part of dielectric function (3 1 ) spectra for pristine and H 2 S adsorbed SL-MoS 2 under different strains and concentrations of gas molecules. In addition, coordinates of the rst ten peaks in the EEL spectra are given for different strains and concentrations of H 2 S molecules on the SL-MoS 2 . See Fig. 10 The imaginary (3 2 ) part of the dielectric function for pristine and H 2 S adsorbed SL-MoS 2 for (a) À8 percent to (h) +8 percent strained substrates with 2-percent intervals. Moreover, the influence of concentration is also shown.This journal is Fig. 11 Electron energy loss (EEL) spectra for the adsorption of up to four H 2 S molecules in the supercell of SL-MoS 2 for in-plane light polarization under the application of biaxial strains from (a) À8% to (h) +8% with 2-percent intervals. 3460 | Nanoscale Adv., 2019, 1, 3452-3462 This journal is

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