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1、Two-dimensional semiconductor,Outlook,Electronics of 2D materials1. Scaling of the semiconductor generation2.Electronic engineering of TMDCStrong confinement of monolayer TMDCsIndirect to direct band gap transitionExcitonic transitionsInversion symmetry breaking of monolayer TMDCs1. Nonlinearity (Pi
2、ezo, SHG)2. Nonequivalent valley index,Insulator, semiconductor and conductor,Semiconductor and human daily life,Point-contact transistor-first transistor ever made,The first point-contact transistor.,Technology generation-need broad exploration,45 nm 2007,22 nm 2011,32 nm 2009,14 nm 2013,10 nm 2015
3、,7 nm 2017,Beyond 2020,QW III-V device,Carbon Nanotube1 nm diameter,Graphene1 atom thick,Nature Nanotechnology 6, 147 (2011),Why 2D semiconductor,From Wiki,Molybdenite,Nature Nanotech. 7, 699 (2012),Different stacking phases of the MoS2,Cleaved by blade and tweezers,Single-layer MoS2 transistors,Nat
4、ure Nanotechnology 6, 147 (2011).,MoS2 transistors with 1 nm gate lengths,Science 354, 99 (2016).,Wafer scale monolayer MoS2,Nature 520, 656 (2015),Carbon nanotube computer,Inorganic nanowireCarbon nanotubes,Precisely place and orientationComplex fabrication techniques,Nature 501, 526 (2013),Self-as
5、sembly graphene-MoS2-graphene heterostructures,Nature Nanotechnolgoy DOI: 10.1038/NNANO.2016.115.,TEM characteristics,Nature Nanotechnolgoy DOI: 10.1038/NNANO.2016.115.,Transistor of graphene/MoS2/graphene,Nature Nanotechnolgoy DOI: 10.1038/NNANO.2016.115.,Self-assembled 2D circuit,Nature Nanotechno
6、lgoy DOI: 10.1038/NNANO.2016.115.,Outlook,Electronics of 2D materials1. Electronic engineering of TMDC2.Transistors built on black phosphorousStrong confinement of monolayer TMDCsIndirect to direct band gap transitionExcitonic transitionsInversion symmetry breaking of monolayer TMDCs1. Nonlinearity
7、(Piezo, SHG)2. Nonequivalent valley index,Bulk Quadrilayer Bilayer monolayer,Atomic structure and electronic band structure of MoS2,Nano Lett. 2010, 10, 12711275,PL and quantum yield of MoS2,PRL 105, 136805 (2010),21,Excitation 488 nmDetection 640nm,Si/MoS2 pn heterojunction,22,APL 104, 193508 (2014
8、),Homojunction LEDs,Nature Nanotech. 9, 268 (2014) Nature Nanotech. 9, 262 (2014) Nature Nanotech. 9, 257 (2014),Homojunction LEDs,Nature Nanotech. 9, 268 (2014)Nature Nanotech. 9, 262 (2014)Nature Nanotech. 9, 257 (2014),2D exciton,PRL 113, 076802 (2014),Charles Kittel, Introduction to solid state
9、physics,Monolayer WS2 Rydberg series,PRL 113, 076802 (2014),Binding energy: 320 meV,Probing dark state in monolayer WS2,Binding energy: 700 meV,Nature 513, 214 (2014).,First-principle calculation,Nature 513, 214 (2014).,Binding energy: 700 meV,Control of neutral and charged excitons emission,Nature
10、Comm. 4, 1474 (2013).,Control of neutral and charged excitons emission,Nature Comm. 4, 1474 (2013).,Higher modulation bandwidthSmall emission linewidth,High Q cavityStrong confinement factor,Monolayer WS2 excitonic laser,Nature Photonics 9, 733 (2015).,WGM modes,190 fs, 80 MHz, excitation Q2600,Natu
11、re Photonics 9, 733 (2015).,Observation of monolayer lasing,Nature Photonics 9, 733 (2015).,Long wavelength WGM,Nature Photonics 9, 733 (2015).,Characterizations of 2D excitonic lasing,Nature Photonics 9, 733 (2015).,Strong confinement of monolayer TMDC,Electronic structure evolution: indirect band
12、gap to direct band gap.Direct band gap of the monolayer TMDC enables light emission.Large exciton binding energy: robust excitonic phenomena even at room temperature.Large trion binding energy.,Outlook,Electronics of 2D materials1. Electronic engineering of TMDC2.Transistors built on black phosphoro
13、usStrong confinement of monolayer TMDCsIndirect to direct band gap transitionExcitonic transitionsInversion symmetry breaking of monolayer TMDCs1. Nonlinearity (Piezo, SHG)2. Nonequivalent valley index,Symmetry for phase and layer dependent,Bulk 3R,Bulk or even-layers 2H,Monolayer,With inversion sym
14、metryIndirect bandgap,Without inversion symmetryIndirect bandgap,Without inversion symmetryDirect bandgap,arXiv: 1304.4289v1 (2013),Angular dependent SHG of monolayer MoS2,WiKi,SHG determines the grain size,Science 344, 488 (2014),Science 344, 488 (2014),SHG mapping,SHG vs TEM,DF-STEM,Layer number d
15、ependence of SHG,Nano Lett. 13, 3329 (2013).,SHG from 3R stacking phase,Light: Sci. & Appl. 5, e16131 (2016).,Light: Sci. & Appl. 5, e16131 (2016).,Layer number dependence of SHG,Light: Sci. & Appl. 5, e16131 (2016).,Layer number dependence of SHG,Piezoelectricity of MoS2,Nature 514, 470 (2014).,J.
16、Phys. Chem. Lett.3, 2871 (2012).,Nature 514, 470 (2014).,Piezoelectricity MoS2,Piezoelectricity of MoS2,Nature Nanotech. 10, 151 (2015).,Valley index,Valleytronics: Use valley index for encoding informationGeneration and detectionHow to generate and control valley carrier?Nonequivalent valley carrie
17、rs: how to measurable it associated with valley index?,Valley contrasting properties by ISB,Valley contrasting propertiesOpposite & m for a time reversal pair of valleysNecessary condition: inversion symmetry breaking (ISB),Valley optical selection rule,Nature Comm. 3, 887 (2012).,PRB 77, 235406 (20
18、08).,Nature Nanotech. 7, 490 (2012); Nature Nanotech. 7, 494 (2012); Nature Comm. 3, 887 (2012).,Circularly polarized light boosts valleytronics,Chiral light-emitting transistor,Science 344, 725 (2014).,Triangular warping,arXiv: 1410.0615v1,Electrical control of circularly polarized emission,Science
19、 344, 725 (2014).,Light: Sci. & Appl. 6, e124 (2014).,Electrical valley generation and detection in monolayer TMDCs,TMDC: long lifetime of polarized hole and spin-valley locking.Ferromagnetic semiconductor: conductivity matching and high spin injection efficiency.,Nat. Nanotech. 11, 598, (2016).,WS2
20、/(Ga, Mn)As heterostructure,No defect emission.Suppression of B exciton emission.,Nat. Nanotech. 11, 598, (2016).,Electrical Valley excitation in WS2,Outward B,Inward B, = -14.8%, = 16.2%,Nat. Nanotech. 11, 598, (2016).,Magnetic field dependent,Nat. Nanotech. 11, 598, (2016).,Valley exciton generati
21、on efficiency,Non-perfect spin polarization.Valley scattering.Joule heating.,Nat. Nanotech. 11, 598, (2016).,Valley contrasting Berry curvature,PRL 99, 236809 (2007).,The valley Hall effect,Science 344, 1489 (2014).,ISB of monolayer TMDC,ISB enables SHG in monolayer TMDC and provides an all-optical
22、technique for material characteristics.ISB enables piezoelectricity of monolayer TMDC and provides mechanical-to-electrical energy conversion.ISB protects the non-equivalent valleys (K and K), may open an avenue to the valleytronics.,A new platform for vdWs heterostructures,Nature 499, 419 (2013).,Transfer method:Assemble the vdWs heterostructures with clean interface.Edge contact:Electrical access and tune each active 2D materials.,vdWs heterostructures,Thank you for your attention.,Yu Ye (叶堉）ye_http:/,
