Photoluminescence of Monolayer MoS 2 on LaAlO 3 and SrTiO 3 substrates

Transcription

1 Electronic Suppleentary Material (ES for anoscale. This journal is The Royal Society of Cheistry 214 Suppleentary nforation for Photoluinescence of Monolayer MoS 2 on LalO 3 and SrTiO 3 substrates Yuanyuan Li a, Zeing Qi *a, Miao Liu b, Yuyin Wang a, Xuerui Cheng c, Guobin Zhang a, Liusi Sheng a a ational Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, nhui, 2329, China b Environental Energy Technologies Division, Lawrence Berkeley ational Laboratory, C 9472, US c Departent of Technology and Physics, Zhengzhou University of Light ndustry, Zhengzhou 452, China 1. Calculation of the enhanceent factor for Raan and Photoluinescence (PL intensity noralization. The enhanceent factor is defined as 1 freesanding MoS2 onsubstrate MoS2. The calculation ethod is based on the odel including optical interference and absorption effects due to the substrate geoetry, which is described in Ref. 1 By ultiplying 1 for each easured Raan and PL spectru, the optical interference effect attributed to the different saples is eliinated and intrinsic difference between each syste can be copared. Fig.S1(a 1 shows the calculated enhanceent factor of onolayer to four-layer MoS 2 on SiO 2, LalO 3, Gel-fil and SrTiO 3 substrate. Fig.S1(b and (c show the coparison of the raw and noralized Raan and PL spectra of onolayer MoS 2 on different substrates. 2. Thickness-dependence of Raan spectra for MoS 2 on different substrates Fig.S2 shows the noralized Raan spectra of 1-4L MoS 2 on different types of substrates. 1

2 Fro the Raan spectra, for each kind of substrate, both E 1 2g and 1g odes of MoS 2 are clearly observed. The dependence of these two ode frequencies on layer thickness exhibits siilar trend for four selected substrates, i.e. E 1 2g ode oves to lower frequency end while 1g ode shifts to higher frequency end when the nuber of layers increases. 3. Thickness-dependence of PL spectra for MoS 2 on different substrates Fig.S3 shows the noralized PL spectra of 1-4L MoS 2 on different substrates. t is known that, for onolayer MoS 2, PL spectru is coposed with two excitonic peaks and B, associated with direct optical transitions fro the lowest conduction bands to the highest spin-split valence bands. 2 Fro Fig.S3, both excitonic peaks can be clearly observed in all saples. Meanwhile, all the saples show very siilar thickness-dependence, i.e. when the nuber of layers decreases, the intensity of peak draatically increases and reaches to the axiu for onolayer thin fil, due to the indirect-to-direct band transition. For the bilayer saples, we also observed an eission peak around 1.55 ev (Peak which is ascribed to indirect band transition. Besides the change of peak intensity, the position and shape of peak also changes with thin fil thickness. Peak oves to higher energy end when thin fil thickness decreases. 4. The fitting of PL spectra of onolayer MoS 2 on different substrates. We fit the experiental PL data of onolayer MoS 2 on SiO 2, LalO 3, Gel-fil and SrTiO 3 substrate. The fits are coposed by three Lorenz functions corresponding neutral excitons (, trions ( - and the direct band transition (peak B. The fitting results are shown in Fig.S4. 5. The electron density calculation We estiate the electron density in onolayer MoS 2 fro the analysis of PL intensity of neutral excitons and trions eissions. ccording to ass action odel which is based on the dynaic equilibriu between neutral excitons (, free electrons and trions ( -, the following relationship is obtained: 3-5 2

3 3 exp( 4 ( 2 T k E T k n B b B e el h Where k B is the Boltzann constant, E b is the trion binding energy (~2 ev, 6 T is the teperature. e (.35, (.8 and (1.15 are the effective ass of neutral excitons, trions and electrons, respectively, where is the ass of free electrons. 7 and are the population of neutral exciton and trion, repectively. n el is the electron density. To establish the relationship between PL intensity and the population of neutral exciton and trion, we consider a three level odel that includes a trion, an exciton and the ground state. 8 Based on this odel, the PL intensity weight can be related to the population of neutral exciton and trion as: 1 total Where and are integrated PL intensity of neutral exciton and trion, respectively. and are the relative decay rate of the neutral exciton and trion, respectively. The value of is ~.15 according to Mouri et al. s study. 8 Cobining the three level odel and ass action odel, the n el can be expressed as: exp( 4 ( (1 2 T k E T k n B b B e total total el h References 1. Michele Buscea, G.. S., Herre S.J. van der Zant and ndres Castellanos-Goez. ano Res 214.

4 2. Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Phys Rev Lett 21, 15, ( Siviniant, J.; Scalbert, D.; Kavokin,. V.; Coquillat, D.; Lascaray, J. P. Phys Rev B 1999, 59, (3, Ross, J. S.; Wu, S. F.; Yu, H. Y.; Ghiire,. J.; Jones,. M.; ivazian, G.; Yan, J. Q.; Mandrus, D. G.; Xiao, D.; Yao, W.; Xu, X. D. at Coun 213, Ron,.; Yoon, H. W.; Sturge, M. D.; Manassen,.; Cohen, E.; Pfeiffer, L.. Solid State Coun 1996, 97, (9, Mak, K. F.; He, K. L.; Lee, C.; Lee, G. H.; Hone, J.; Heinz, T. F.; Shan, J. at Mater 213, 12, (3, Cheiwchanchanangij, T.; Labrecht, W. R. L. Phys Rev B 212, 85, (2. 8. Mouri, S.; Miyauchi, Y.; Matsuda, K. ano Lett 213, 13, (12,

5 Figure.S1. (a.the calculated enhanceent factor of onolayer to 4-layer MoS 2 on SiO 2, LO,Gel-fil and STO substrates. (b. The raw and noralized Raan spectra of onolayer MoS 2 on different substrates. (c. The raw and noralized PL spectra of onolayer MoS 2 on different substrates. 5

6 Figure S1. oralized Raan spectra, frequencies of the 1g and E 1 2g odes and the difference between the two odes of onolayer to 4-layer MoS 2 on SiO 2, LO, STO and Gel-fil substrates. 6

7 Figure S3. Thickness-dependent of the noralized PL spectra of MoS 2 on SiO 2, LO, Gel-fil and STO substrates. The inserts are PL spectra of substrates. 7

8 Figure.S4. The fitting of PL spectra of onolayer MoS 2 on SiO 2 (a, LO (b,gel-fil (c,sto (d substrates. The open circle sybols are experiental data. The thin solid lines are the Lorentz functions that copose the fit. 8