single-layer transition metal dichalcogenides MC2 Period 1 1 H 18 He 2 Group 1 2 Li Be Group 13 14 15 16 17 18 B C N O F Ne 3 4 Na K Mg Ca Group 3 4 5 6 7 8 9 10 11 12 Sc Ti V Cr Mn Fe Co Ni Cu Zn Al Ga Si P Ge As S Se Cl Br Ar Kr 5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te l Xe 6 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 7 Fr Ra Ac Rf Db Sg Bh Hs Mt Uun Uuu Uub Uuq Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 3
band structure in MoS2-5 -4 bulk (2H) -5-4 bilayer layer -5-4 monolayer binding energy (ev) -3-2 -1 0 1 binding energy (ev) -3-2 -1 0 1 binding energy (ev) -3-2 -1 0 1 2 2 2.... indirect band gap inversion symmetry indirect band gap inversion symmetry direct band gap no inversion symmetry 5 calculations after: Tawinan Cheiwchanchamnangij et al., Phys. Rev. B 85, 205302 (2012)
single layer MoS2 transistors SiO 2 Gates HfO 2 Monolayer MoS 2 Leads Drain Top gate Monolayer MoS 2 Source HfO 2 SiO 2 Si substrate B. Radisavljevic et al., Nat. Nano. 6, 147 (2011)
angle-resolved photoemission (ARPES): a direct view at the band structure n ASTRID2 h e - electron analyzer
introduction and materials: graphene, single layer MoS2 semiconducting single layer MoS2 and WS2 metallic single layer dichalcogenides: TaS2
creating epitaxial single-layer MoS2 Signe G. Sørensen et al., ACS Nano 8, 6788 (2014) Mo Au(111) SL MoS 2 BL MoS 2 Signe G. Sørensen et al., Langmuir 35, 9700 (2015)
Au S E bin = 0.0 ev 0.0 proj. bulk K gap edge K 0.5 K K K K E bin = 1.4 ev E bin (ev) 1.0 1.5 0.31 ev K K 2.0 E bin = 1.6 ev 2.5-1.3 0.0 1.3 k x (Å -1 ) 1 Å -1 E bin = 2.0 ev Wencan Jin et al., PRL 111, 106801 (2013) Jill Miwa et al., Physical Review Letters 114, 046802 (2015). see also: Yi Zhang et al., Nat. Nano. 9, 111 (2014). calc.: Z. Y. Zhu et al., Phys. Rev. B 84, 153402 (2012)
Calculated bands MoS2 on Au(111) 4 Freestanding MoS 2 /Au(111) E-E F (ev) 2 0-2 -4 M K M K M Albert Bruix et al., Phys. Rev. B 93, 165422 (2015).
Giant Spin-Splitting in Single Layer WS2 1.0 MoS2 m*= 0.55 me 1.0 WS2 m*= 0.35 me E bin (ev) 1.5 1.5 2.0 2.0-0.3 0.0 0.3 k (Å -1 ) -0.2 0.0 0.2 k (Å -1 ) Jill Miwa et al., Physical Review Letters 114, 046802 (2015). Maciek Dendzik et al., Physical Review B 92, 245442 (2051).
time-resolved ARPES ARTEMIS t = -500 fs -0.5-0.5 0.0 0.0 0.5 max 1.0 time delay min 2.0 probe n ¹ s n Le 0.5 1.0 1.5 D C C t = 100 fs -1.0 Ebin (ev) Ebin (ev) -1.0 1.4 1.6 1.8 2.0 1.5 2.0 1.4 1.6 1.8 2.0 k (Å ) k (Å-1) difference t = 100 fs pump pos hydrogen SiC(0001) 0 neg 1.4 1.6 1.8 2.0 k (Å-1)
excited free carriers in single layer MoS2 K 784 nm 1.6 ev CB 615 nm 2.0 ev CB VB VB -1 gap K continuum gap K K E bin (ev) 0 1 E F 2 3 min max 0.00 0.65 1.30 k x (Å -1 ) neg 0 pos 0.00 0.65 1.30 k x (Å -1 ) 0.00 0.65 1.30 k x (Å -1 ) Antonija Grubisic Cabo et al., Nano Letters,15, 5883 (2015).
single layer MoS2: dynamics and band gap E bin (ev) -1.0 0.0 1.0 2.0 1.0 K 1.3 k x (Å -1 ) 1.6 0 30 60 90 120 The band gap is only 1.95 ev (2.8 ev in the free layer) 0.52 1.43 pos 0 neg t (fs) Antonija Grubisic Cabo et al., Nano Letters,15, 5883 (2015).
graphene / MoS2 heterostructure on SiC 0 M K K h = 70 ev b K M M h = 70 ev K max E bin (ev) 2 min 4 K M M K K K K M M K
excited carrier density and band shift 0.0-0.1 MoS 2 /G MoS 2 /Au E gap (ev) -0.2-0.3-0.4 0.0 0.5 theory: A. Steinhoff et al., Nano Lett. 14, 3743 (2015). ( 500 mev renormalization for n 10 12 / cm 2 ) 1.0 n h (10 12 /cm 2 ) 1.5 2.0 band gap renormalization in free-standing MoS2: A. Chernikov et al., Nat. Photonics 9, 466 (2015) A. Chernikov et al. Phys. Rev. Lett. 115, 126802 (2015) Søren Ulstrup et al. ACS Nano 10, 6315 (2016).
introduction and materials: graphene, single layer MoS2 semiconducting single layer MoS2 and WS2 metallic single layer dichalcogenides: TaS2
single-layer transition metal dichalcogenides Period 1 1 H MC2 18 He 2 Group 1 2 Li Be Group 13 14 15 16 17 18 B C N O F Ne 3 4 Na K Mg Ca Group 3 4 5 6 7 8 9 10 11 12 Sc Ti V Cr Mn Fe Co Ni Cu Zn Al Ga Si P Ge As S Se Cl Br Ar Kr 5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te l Xe 6 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 7 Fr Ra Ac Rf Db Sg Bh Hs Mt Uun Uuu Uub Uuq Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr -4 single layer WS2 single layer TaS2 E F -E (ev) -2 0 2 28 4 M K M M K M
real 2D: Charge Density Waves E empty E F full k y 0 E=E F k x k x
2D nesting and charge density wave E empty E F full k y 0 E=E F k x k x
(thin) 2H-TaS2 single layer 1H-NbSe2 bulk: TCDW=33 K TSC=9.5 K bulk @ 100 mk: I Guillamón et al., NJP 13, 103020 (2011) 10 Å T = 45 K 8 nm film (insulating for thinner films) 10 Å M. Ugeda et al., Nat. Phys. 12, 92 (2016), TCDW<45 K X. Xi et al., Nat. Nano. 10, 765 (2015), TCDW=145 K T = 5 K Ayari et al., J. Appl. Phys. 101, 014507, (2007)
growth of single layer TaS2 8.94 Å Bare Au 10 nm Height (Å) 8 6 4 2 0 TaS 2 Au step 10 20 30 x (nm) Charlotte Sanders et al., Physical Review B 94, 081404(R) (2016).
Charge Density Wave? Superconductivity? a) b) 72 1.5Å pm 2nm 5 nm 1.0 Å -1 10 di / dv (a.u.) 5 0-0.5 0 0.5 V S (V) Charlotte Sanders et al., Physical Review B 94, 081404 (R) (2016). T=4.7 K
Conclusions For single layers of MoS2 on Au(111) (metal) the band gap is very strongly renormalized, by 900 mev, and not sensitive to additional excited carriers. For MoS2 on graphene, the band gap renormalization due to the graphene is only small (200 mev) but there is a considerable additional effect due to the excited carriers. Single layer TaS2 is strongly electron-doped on Au(111). It remains metallic with no charge density wave down to 4.7 K. The properties of 2D materials can be drastically changed by their environment. Jill Miwa et al., Physical Review Letters 114, 046802 (2015). Antonija Grubisic Cabo et al., Nano Letters,15, 5883 (2015). Maciek Dendzik et al., Physical Review B 92, 245442 (2015). Søren Ulstrup et al. ACS Nano 10, 6315 (2016). Charlotte Sanders et al., Physical Review B 94, 081404(2016).