Temperature and Power Dependent Photoluminescent Spectroscopy of MoS$_2$

We report temperature and power dependent photoluminescence (PL) of molybdenum disulphide (mos). Mechanical exfoliation of mos, from bulk provides single-layer flakes which are then transferred either to sapphire substrates or suspended over holes in Si/Si$_3 $N$_4$. We measure temperature dependence from $\approx$100\,K to 400\,K and power dependence from $\approx$6\,$\mu$W to $\approx$7\,mW using an Argon laser at 514.5\,nm and a HeNe laser at 632.8$\,$nm. The PL spectrum exhibits a main exitonic peak(A) at $\approx$1.87\,eV which consist of both neutral excitons and charged trions (A- or A+) [1]. The A exciton peak and the A- exciton peak redshift and broaden with increasing temperature and power. Along with the A peak, we observe a lower energy bound exciton (BE) that is likely related to defects. The BE,a broad peak centred at $\approx$1.7\,eV, linearly redshifts and narrows with increasing power. The power dependence of both the main and bound peak saturates above 0.5\,mW. Raman temperature and power dependence will also be discussed [2]. \\[4pt] [1] KF. Mak et al. Nat. Mat 12,207(2013).\\[0pt] [2] R.Yan and J.R.Simpson, S. Bertolazzi and J. Brivio, M. Watson, X.Wu and A. Kis, T.Luo, H.G.Xing, A.R. Hight Walker, (submitted ACS Nano 2013)