Treatments in common hydroxide based species such as water and alcohol did not show PL enhancement. It is likely that the surface and defects in M o S 2 have already been exposed to air and moisture before treatments, and the defects on the surface are likely filled by adsorbed water or -OH groups. On the other hand, in cases of chlorine based treatments (D CE, DCB) a marginal PL enhancement was observed. This result indicates that there is a relatively strong interaction between chlorine-based molecules and the surface of MoS2, which was reported previously for DCE. This motivated the selection of DCB/DCE (9/1 v/v%) as the solvent choice for treatment by TFS I, which was found to give the optimum treatment conditions, although other solvents were also effective. [0065] To clarify the role of TFS I in passivating the surface of MoS2, N-Phenyl-bis(trifluoromethanesulfonimide) (Ph-TFS I) was introduced as a control reagent. MoS₂ monolayers were treated with Ph-TFS I in a solution of DCB/DCE (9/1 v/v%) using the identical treatment procedure as TFS I (materials and methods). Figs. See 15A, 15B shows the pump- power dependence on PL and QY for Ph-TFS I treated and as-exfoliated monolayers. The Ph- TFS I solution does not significantly alter the QY relative to the original as-exfoliated sample. Considering that the only difference between TFS I and Ph-TFS I is the replacement of hydrogen with a phenyl group, hydrogen is believed to play a critical role in the passivation of defect sites leading to the enhancement of QY. [0066] A wide variety of possible defect sites have been observed in MoS2, both through scanning tunneling microscopy (STM) or through transmission electron microscopy (TEM). The Do S for the most commonly observed defect, sulfur vacancies (V s) as well as a vacancy site with -21- Attorney Docket: 2015-159-02 Lawrence Berkeley National Laboratory an adsorbed -OH group are shown in Fig. 16A. Both of these scenarios induce midgap trap states which can induce defect-mediated Auger recombination and quench the PL. To determine the possible mechanism of the treatment we examined several plausible scenarios. Firstly, due to the high stability of its ionic state, which arises from the delocalization of the anion charge on the nitrogen it is highly unlikely that the TFSI anion passivates the surface. Passivation of dangling bonds at the vacancy site by hydrogen was also considered, and DoS calculations show that the midgap states are removed when the three dangling bonds which occur at the sulfur vacancy site are passivated by hydrogen as shown in Fig. 16B. This scenario was also found to be improbable however, since it is highly energetically unfavorable (Fig. 16C); additionally, hydrogenation of Mo in MoS₂ has been found to be unlikely in previous reports. Claims What is claimed is:

Treatments in common hydroxide based species such as water and alcohol did not show PL enhancement. It is likely that the surface and defects in M o S 2 have already been exposed to air and moisture before treatments, and the defects on the surface are likely filled by adsorbed water or -OH groups. On the other hand, in cases of chlorine based treatments (D CE, DCB) a marginal PL enhancement was observed. This result indicates that there is a relatively strong interaction between chlorine-based molecules and the surface of MoS2, which was reported previously for DCE. This motivated the selection of DCB/DCE (9/1 v/v%) as the solvent choice for treatment by TFS I, which was found to give the optimum treatment conditions, although other solvents were also effective. [0065] To clarify the role of TFS I in passivating the surface of MoS2, N-Phenyl-bis(trifluoromethanesulfonimide) (Ph-TFS I) was introduced as a control reagent. MoS₂ monolayers were treated with Ph-TFS I in a solution of DCB/DCE (9/1 v/v%) using the identical treatment procedure as TFS I (materials and methods). Figs. See 15A, 15B shows the pump- power dependence on PL and QY for Ph-TFS I treated and as-exfoliated monolayers. The Ph- TFS I solution does not significantly alter the QY relative to the original as-exfoliated sample. Considering that the only difference between TFS I and Ph-TFS I is the replacement of hydrogen with a phenyl group, hydrogen is believed to play a critical role in the passivation of defect sites leading to the enhancement of QY. [0066] A wide variety of possible defect sites have been observed in MoS2, both through scanning tunneling microscopy (STM) or through transmission electron microscopy (TEM). The Do S for the most commonly observed defect, sulfur vacancies (V s) as well as a vacancy site with -21- Attorney Docket: 2015-159-02 Lawrence Berkeley National Laboratory an adsorbed -OH group are shown in Fig. 16A. Both of these scenarios induce midgap trap states which can induce defect-mediated Auger recombination and quench the PL. To determine the possible mechanism of the treatment we examined several plausible scenarios. Firstly, due to the high stability of its ionic state, which arises from the delocalization of the anion charge on the nitrogen it is highly unlikely that the TFSI anion passivates the surface. Passivation of dangling bonds at the vacancy site by hydrogen was also considered, and DoS calculations show that the midgap states are removed when the three dangling bonds which occur at the sulfur vacancy site are passivated by hydrogen as shown in Fig. 16B. This scenario was also found to be improbable however, since it is highly energetically unfavorable (Fig. 16C); additionally, hydrogenation of Mo in MoS₂ has been found to be unlikely in previous reports. Claims What is claimed is:

Treatments in common hydroxide based species such as water and alcohol did not show PL enhancement. It is likely that the surface and defects in M o S 2 have already been exposed to air and moisture before treatments, and the defects on the surface are likely filled by adsorbed water or -OH groups. On the other hand, in cases of chlorine based treatments (D CE, DCB) a marginal PL enhancement was observed. This result indicates that there is a relatively strong interaction between chlorine-based molecules and the surface of MoS2, which was reported previously for DCE. This motivated the selection of DCB/DCE (9/1 v/v%) as the solvent choice for treatment by TFS I, which was found to give the optimum treatment conditions, although other solvents were also effective. [0065] To clarify the role of TFS I in passivating the surface of MoS2, N-Phenyl-bis(trifluoromethanesulfonimide) (Ph-TFS I) was introduced as a control reagent. MoS₂ monolayers were treated with Ph-TFS I in a solution of DCB/DCE (9/1 v/v%) using the identical treatment procedure as TFS I (materials and methods). Figs. See 15A, 15B shows the pump- power dependence on PL and QY for Ph-TFS I treated and as-exfoliated monolayers. The Ph- TFS I solution does not significantly alter the QY relative to the original as-exfoliated sample. Considering that the only difference between TFS I and Ph-TFS I is the replacement of hydrogen with a phenyl group, hydrogen is believed to play a critical role in the passivation of defect sites leading to the enhancement of QY. [0066] A wide variety of possible defect sites have been observed in MoS2, both through scanning tunneling microscopy (STM) or through transmission electron microscopy (TEM). The Do S for the most commonly observed defect, sulfur vacancies (V s) as well as a vacancy site with -21- Attorney Docket: 2015-159-02 Lawrence Berkeley National Laboratory an adsorbed -OH group are shown in Fig. 16A. Both of these scenarios induce midgap trap states which can induce defect-mediated Auger recombination and quench the PL. To determine the possible mechanism of the treatment we examined several plausible scenarios. Firstly, due to the high stability of its ionic state, which arises from the delocalization of the anion charge on the nitrogen it is highly unlikely that the TFSI anion passivates the surface. Passivation of dangling bonds at the vacancy site by hydrogen was also considered, and DoS calculations show that the midgap states are removed when the three dangling bonds which occur at the sulfur vacancy site are passivated by hydrogen as shown in Fig. 16B. This scenario was also found to be improbable however, since it is highly energetically unfavorable (Fig. 16C); additionally, hydrogenation of Mo in MoS₂ has been found to be unlikely in previous reports. Claims What is claimed is:

Treatments in common hydroxide based species such as water and alcohol did not show PL enhancement. It is likely that the surface and defects in M o S 2 have already been exposed to air and moisture before treatments, and the defects on the surface are likely filled by adsorbed water or -OH groups. On the other hand, in cases of chlorine based treatments (D CE, DCB) a marginal PL enhancement was observed. This result indicates that there is a relatively strong interaction between chlorine-based molecules and the surface of MoS2, which was reported previously for DCE. This motivated the selection of DCB/DCE (9/1 v/v%) as the solvent choice for treatment by TFS I, which was found to give the optimum treatment conditions, although other solvents were also effective. [0065] To clarify the role of TFS I in passivating the surface of MoS2, N-Phenyl-bis(trifluoromethanesulfonimide) (Ph-TFS I) was introduced as a control reagent. MoS₂ monolayers were treated with Ph-TFS I in a solution of DCB/DCE (9/1 v/v%) using the identical treatment procedure as TFS I (materials and methods). Figs. See 15A, 15B shows the pump- power dependence on PL and QY for Ph-TFS I treated and as-exfoliated monolayers. The Ph- TFS I solution does not significantly alter the QY relative to the original as-exfoliated sample. Considering that the only difference between TFS I and Ph-TFS I is the replacement of hydrogen with a phenyl group, hydrogen is believed to play a critical role in the passivation of defect sites leading to the enhancement of QY. [0066] A wide variety of possible defect sites have been observed in MoS2, both through scanning tunneling microscopy (STM) or through transmission electron microscopy (TEM). The Do S for the most commonly observed defect, sulfur vacancies (V s) as well as a vacancy site with -21- Attorney Docket: 2015-159-02 Lawrence Berkeley National Laboratory an adsorbed -OH group are shown in Fig. 16A. Both of these scenarios induce midgap trap states which can induce defect-mediated Auger recombination and quench the PL. To determine the possible mechanism of the treatment we examined several plausible scenarios. Firstly, due to the high stability of its ionic state, which arises from the delocalization of the anion charge on the nitrogen it is highly unlikely that the TFSI anion passivates the surface. Passivation of dangling bonds at the vacancy site by hydrogen was also considered, and DoS calculations show that the midgap states are removed when the three dangling bonds which occur at the sulfur vacancy site are passivated by hydrogen as shown in Fig. 16B. This scenario was also found to be improbable however, since it is highly energetically unfavorable (Fig. 16C); additionally, hydrogenation of Mo in MoS₂ has been found to be unlikely in previous reports. Claims What is claimed is: