Peb siv lub sijhawm thiab lub kaum sab xis-daws teeb pom kev zoo photoemission spectroscopy (tr-ARPES) los tshawb nrhiav kev hloov pauv them ceev heev hauv epitaxial heterostructure ua los ntawm monolayer WS2 thiab graphene. Qhov heterostructure no ua ke cov txiaj ntsig ntawm lub semiconductor ncaj qha nrog kev sib txuas spin-orbit muaj zog thiab kev sib cuam tshuam lub teeb muaj zog nrog cov ntawm semimetal tuav cov massless carriers nrog kev txav mus los siab heev thiab lub neej ntev spin. Peb pom tias, tom qab photoexcitation ntawm resonance rau A-exciton hauv WS2, cov qhov photoexcited sai sai hloov mus rau hauv txheej graphene thaum cov electrons photoexcited tseem nyob hauv txheej WS2. Lub xeev transient sib cais them tau pom tias muaj lub neej ntawm ~ 1 ps. Peb muab peb cov kev tshawb pom rau qhov sib txawv hauv qhov chaw scattering tshwm sim los ntawm kev sib raug zoo ntawm WS2 thiab graphene bands raws li qhia los ntawm high-resolution ARPES. Ua ke nrog spin-selective optical excitation, qhov kev tshawb nrhiav WS2 / graphene heterostructure yuav muab lub platform rau kev txhaj tshuaj optical spin zoo rau hauv graphene.
Qhov muaj ntau yam khoom siv ob-seem sib txawv tau qhib qhov ua tau los tsim cov qauv tshiab thaum kawg nyias nyias nrog cov haujlwm tshiab kiag li raws li kev tshuaj ntsuam dielectric thiab ntau yam teebmeem sib ze (1-3). Cov khoom siv pov thawj-ntawm-lub hauv paus ntsiab lus rau kev siv yav tom ntej hauv thaj chaw ntawm cov khoom siv hluav taws xob thiab optoelectronics tau pom tseeb (4-6).
Ntawm no, peb tsom mus rau epitaxial van der Waals heterostructures uas muaj monolayer WS2, ib qho semiconductor ncaj qha nrog kev sib txuas spin-orbit muaj zog thiab kev sib cais ntawm cov qauv band vim yog qhov tawg inversion symmetry (7), thiab monolayer graphene, ib qho semimetal nrog cov qauv conical band thiab kev txav mus los siab heev (8), loj hlob ntawm hydrogen-terminated SiC (0001). Cov cim qhia thawj zaug rau kev hloov pauv them ceev ceev (9–15) thiab qhov sib thooj-induced spin-orbit coupling effects (16–18) ua rau WS2 / graphene thiab cov heterostructures zoo sib xws cog lus rau cov neeg sib tw yav tom ntej optoelectronic (19) thiab optospintronic (20) daim ntawv thov.
Peb tau teem sijhawm los qhia txog txoj kev so ntawm cov khub electron-hole photogenerated hauv WS2 / graphene nrog lub sijhawm- thiab lub kaum sab xis-daws teeb meem photoemission spectroscopy (tr-ARPES). Rau lub hom phiaj ntawd, peb ua kom lub heterostructure zoo siab nrog 2-eV twj tso kua mis pulses resonant rau A-exciton hauv WS2 (21, 12) thiab eject photoelectrons nrog lub sijhawm thib ob-ncua sij hawm probe pulse ntawm 26-eV photon zog. Peb txiav txim siab lub zog kinetic thiab lub kaum sab xis emission ntawm cov photoelectrons nrog lub hemispherical analyzer ua haujlwm ntawm lub twj tso kua mis-probe qeeb kom nkag mus rau lub zog-, lub zog-, thiab lub sijhawm-daws teeb meem carrier dynamics. Lub zog thiab lub sijhawm daws teeb meem yog 240 meV thiab 200 fs, feem.
Peb cov txiaj ntsig muab cov pov thawj ncaj qha rau kev hloov pauv ceev ceev ntawm cov txheej epitaxially, lees paub thawj cov cim qhia raws li txhua txoj kev kho qhov muag hauv cov qauv sib xws sib dhos nrog cov txheej txheem azimuthal sib dhos ntawm cov txheej (9–15). Tsis tas li ntawd, peb qhia tias qhov kev hloov pauv them no yog asymmetric heev. Peb cov kev ntsuas qhia txog lub xeev tsis tau pom dua uas tau cais them nrog cov electrons photoexcited thiab qhov nyob hauv WS2 thiab graphene txheej, feem, uas nyob rau ~ 1 ps. Peb txhais peb cov kev tshawb pom hauv cov nqe lus ntawm qhov sib txawv hauv qhov chaw sib kis rau electron thiab qhov hloov pauv los ntawm kev sib raug zoo ntawm WS2 thiab graphene bands raws li qhia los ntawm kev daws teeb meem siab ARPES. Ua ke nrog spin- thiab hav-selective optical excitation (22–25) WS2 / graphene heterostructures yuav muab lub platform tshiab rau kev txhaj tshuaj optical ultrafast rau hauv graphene.
Daim Duab 1A qhia txog kev ntsuas ARPES siab uas tau txais nrog lub teeb helium ntawm cov qauv band raws li ΓK-kev taw qhia ntawm epitaxial WS2/graphene heterostructure. Lub Dirac cone pom tias yog qhov-doped nrog Dirac point nyob ~ 0.3 eV saum toj no qhov sib npaug ntawm cov tshuaj lom neeg muaj peev xwm. Sab saum toj ntawm spin-split WS2 valence band pom tias yog ~ 1.2 eV hauv qab qhov sib npaug ntawm cov tshuaj lom neeg muaj peev xwm.
(A) Cov duab hluav taws xob sib npaug ntsuas raws li ΓK-kev taw qhia nrog lub teeb helium tsis muaj polarized. (B) Cov duab hluav taws xob rau qhov qeeb ntawm lub twj tso kua mis-probe ntsuas nrog p-polarized extreme ultraviolet pulses ntawm 26-eV photon zog. Cov kab grey thiab liab uas muaj kab txaij cim qhov chaw ntawm cov kab profiles siv los rho tawm cov chaw siab tshaj plaws hauv daim duab 2. (C) Cov kev hloov pauv ntawm lub twj tso kua mis ntawm 200 fs tom qab photoexcitation ntawm lub zog photon ntawm lub twj tso kua mis ntawm 2 eV nrog lub twj tso kua mis fluence ntawm 2 mJ / cm2. Kev nce thiab poob ntawm cov photoelectrons tau qhia ua xim liab thiab xiav, raws li. Cov thawv qhia thaj chaw ntawm kev koom ua ke rau cov kab cim ntawm lub twj tso kua mis-probe uas tau pom hauv daim duab 3.
Daim Duab 1B qhia txog daim duab tr-ARPES ntawm cov qauv band ze rau WS2 thiab graphene K-points ntsuas nrog 100-fs extreme ultraviolet pulses ntawm 26-eV photon zog ntawm qhov tsis zoo pump-probe qeeb ua ntej tuaj txog ntawm lub twj tso kua mis pulse. Ntawm no, qhov kev sib cais spin tsis daws teeb meem vim yog qhov kev puas tsuaj ntawm cov qauv thiab qhov muaj 2-eV pump pulse uas ua rau qhov chaw them dav ntawm cov yam ntxwv spectral. Daim Duab 1C qhia txog kev hloov pauv ntawm lub twj tso kua mis ntawm photocurrent nrog rau Daim Duab 1B ntawm qhov qeeb pump-probe ntawm 200 fs qhov twg lub teeb liab pump-probe ncav cuag nws qhov siab tshaj plaws. Cov xim liab thiab xiav qhia txog kev nce thiab poob ntawm photoelectrons, raws li.
Yuav kom tshuaj xyuas qhov kev nplua nuj no kom ntxaws ntxiv, peb xub txiav txim siab qhov chaw siab tshaj plaws ntawm WS2 valence band thiab graphene π-band raws li cov kab dashed hauv daim duab 1B raws li tau piav qhia ntxaws hauv Cov Khoom Siv Ntxiv. Peb pom tias WS2 valence band hloov mus rau saum 90 meV (Daim duab 2A) thiab graphene π-band hloov mus rau hauv qab 50 meV (Daim duab 2B). Lub neej exponential ntawm cov kev hloov pauv no pom tias yog 1.2 ± 0.1 ps rau valence band ntawm WS2 thiab 1.7 ± 0.3 ps rau graphene π-band. Cov kev hloov pauv siab tshaj plaws no muab pov thawj thawj zaug ntawm kev them nqi ib ntus ntawm ob txheej, qhov twg ntxiv qhov them zoo (tsis zoo) nce (txo) lub zog khi ntawm cov xeev hluav taws xob. Nco ntsoov tias qhov kev hloov pauv ntawm WS2 valence band yog lub luag haujlwm rau lub teeb liab twj tso kua mis-probe hauv thaj chaw cim los ntawm lub thawv dub hauv daim duab 1C.
Kev hloov pauv ntawm qhov chaw siab tshaj plaws ntawm WS2 valence band (A) thiab graphene π-band (B) ua haujlwm ntawm kev ncua sijhawm ntawm lub twj tso kua mis-probe ua ke nrog kev sib haum xeeb (cov kab tuab). Lub neej ntawm WS2 hloov pauv hauv (A) yog 1.2 ± 0.1 ps. Lub neej ntawm graphene hloov pauv hauv (B) yog 1.7 ± 0.3 ps.
Tom ntej no, peb muab lub teeb liab twj tso kua mis sib xyaw ua ke rau ntawm cov cheeb tsam uas cov thawv xim qhia hauv daim duab 1C thiab kos cov lej suav uas tau los ua ib qho kev ua haujlwm ntawm kev ncua sij hawm twj tso kua mis hauv daim duab 3. Kab nkhaus 1 hauv daim duab 3 qhia txog qhov dynamics ntawm cov photoexcited carriers ze rau hauv qab ntawm cov kab conduction ntawm WS2 txheej nrog lub neej ntawm 1.1 ± 0.1 ps tau los ntawm kev sib haum xeeb rau cov ntaub ntawv (saib Cov Khoom Siv Ntxiv).
Cov kab ntsuas ntawm lub twj tso kua mis raws li kev ua haujlwm ntawm kev ncua sijhawm tau los ntawm kev koom ua ke ntawm cov photocurrent hla thaj chaw qhia los ntawm cov thawv hauv daim duab 1C. Cov kab tuab yog exponential haum rau cov ntaub ntawv. Nkhaus (1) Cov pej xeem thauj khoom hloov pauv hauv cov kab conduction ntawm WS2. Nkhaus (2) Lub teeb liab ntawm lub twj tso kua mis ntawm π-band ntawm graphene saum toj no qhov sib npaug ntawm cov tshuaj lom neeg muaj peev xwm. Nkhaus (3) Lub teeb liab ntawm lub twj tso kua mis ntawm π-band ntawm graphene hauv qab qhov sib npaug ntawm cov tshuaj lom neeg muaj peev xwm. Nkhaus (4) Lub teeb liab ntawm lub twj tso kua mis hauv cov kab valence ntawm WS2. Lub neej pom tias yog 1.2 ± 0.1 ps hauv (1), 180 ± 20 fs (nce) thiab ~2 ps (poob) hauv (2), thiab 1.8 ± 0.2 ps hauv (3).
Hauv cov kab nkhaus 2 thiab 3 ntawm daim duab 3, peb qhia lub teeb liab twj-probe ntawm graphene π-band. Peb pom tias qhov nce ntawm cov electrons saum toj no qhov sib npaug ntawm cov tshuaj lom neeg muaj peev xwm (kab nkhaus 2 hauv daim duab 3) muaj lub neej luv dua (180 ± 20 fs) piv rau qhov poob ntawm cov electrons hauv qab qhov sib npaug ntawm cov tshuaj lom neeg muaj peev xwm (1.8 ± 0.2 ps hauv kab nkhaus 3 daim duab 3). Ntxiv mus, qhov pib nce ntawm photocurrent hauv kab nkhaus 2 ntawm daim duab 3 pom tias tig mus ua qhov poob ntawm t = 400 fs nrog lub neej ntawm ~ 2 ps. Qhov tsis sib xws ntawm qhov nce thiab poob pom tias tsis muaj nyob rau hauv lub teeb liab twj-probe ntawm cov monolayer graphene uas tsis tau npog (saib daim duab S5 hauv Cov Khoom Siv Ntxiv), qhia tias qhov tsis sib xws yog qhov tshwm sim ntawm kev sib txuas ntawm cov txheej hauv WS2 / graphene heterostructure. Qhov kev soj ntsuam ntawm qhov nce luv luv thiab qhov poob ntev ntev saum toj thiab hauv qab qhov sib npaug ntawm lub peev xwm tshuaj lom neeg, feem, qhia tau hais tias cov electrons raug tshem tawm ntawm txheej graphene thaum lub sijhawm photoexcitation ntawm heterostructure. Yog li ntawd, txheej graphene dhau los ua tus nqi zoo, uas yog sib xws nrog qhov nce ntawm lub zog khi ntawm π-band pom hauv daim duab 2B. Qhov kev hloov pauv ntawm π-band tshem tawm tus Tsov tus tw siab-zog ntawm qhov sib npaug Fermi-Dirac faib tawm los ntawm saum toj no qhov sib npaug ntawm lub peev xwm tshuaj lom neeg, uas ib feem piav qhia txog kev hloov pauv ntawm lub cim ntawm lub twj tso kua mis-probe teeb liab hauv nkhaus 2 ntawm daim duab 3. Peb yuav qhia hauv qab no tias qhov cuam tshuam no tau txhim kho ntxiv los ntawm kev poob ib ntus ntawm cov electrons hauv π-band.
Qhov xwm txheej no tau txais kev txhawb nqa los ntawm lub teeb liab ntawm lub twj tso kua mis ntawm WS2 valence band hauv nkhaus 4 ntawm daim duab 3. Cov ntaub ntawv no tau txais los ntawm kev sib koom ua ke ntawm cov suav hla thaj chaw uas muab los ntawm lub thawv dub hauv daim duab 1B uas ntes cov electrons photoemitted los ntawm valence band ntawm txhua qhov kev ncua sij hawm ntawm lub twj tso kua mis. Hauv cov kab yuam kev sim, peb tsis pom qhov qhia txog qhov muaj cov qhov hauv valence band ntawm WS2 rau txhua qhov kev ncua sij hawm ntawm lub twj tso kua mis. Qhov no qhia tau tias, tom qab photoexcitation, cov qhov no tau rov ua kom sai sai ntawm lub sijhawm luv dua piv rau peb qhov kev daws teeb meem lub sijhawm.
Yuav kom muab tau pov thawj kawg rau peb qhov kev xav ntawm kev sib cais ntawm tus nqi ceev heev hauv WS2/graphene heterostructure, peb txiav txim siab tus naj npawb ntawm cov qhov uas tau hloov mus rau txheej graphene raws li tau piav qhia meej hauv Cov Khoom Siv Ntxiv. Hauv ntej, qhov kev faib hluav taws xob transient ntawm π-band tau haum nrog Fermi-Dirac faib. Tus naj npawb ntawm cov qhov ces tau suav los ntawm cov txiaj ntsig rau lub peev xwm tshuaj transient thiab qhov kub hluav taws xob. Qhov tshwm sim tau pom hauv daim duab 4. Peb pom tias tag nrho cov lej ntawm ~ 5 × 1012 qhov / cm2 tau hloov los ntawm WS2 mus rau graphene nrog lub neej exponential ntawm 1.5 ± 0.2 ps.
Kev hloov pauv ntawm tus lej ntawm cov qhov hauv π-band ua ib qho kev ua haujlwm ntawm kev ncua sijhawm ntawm lub twj tso kua mis-probe ua ke nrog kev sib haum xeeb exponential uas ua rau lub neej ntawm 1.5 ± 0.2 ps.
Los ntawm cov kev tshawb pom hauv daim duab 2 txog 4, daim duab me me hauv qab no rau qhov kev hloov pauv them ceev heev hauv WS2/graphene heterostructure tshwm sim (Daim duab 5). Photoexcitation ntawm WS2/graphene heterostructure ntawm 2 eV feem ntau populates A-exciton hauv WS2 (Daim duab 5A). Cov kev txhawb nqa hluav taws xob ntxiv hla Dirac point hauv graphene nrog rau ntawm WS2 thiab graphene bands muaj zog ua tau tab sis tsis tshua muaj txiaj ntsig zoo. Cov qhov photoexcited hauv valence band ntawm WS2 raug rov ua dua los ntawm cov electrons los ntawm graphene π-band ntawm lub sijhawm luv dua piv rau peb qhov kev daws teeb meem lub sijhawm (Daim duab 5A). Cov electrons photoexcited hauv conduction band ntawm WS2 muaj lub neej ntawm ~ 1 ps (Daim duab 5B). Txawm li cas los xij, nws yuav siv sijhawm ~ 2 ps los rov ua dua cov qhov hauv graphene π-band (Daim duab 5B). Qhov no qhia tau hais tias, ntxiv rau kev hloov pauv electron ncaj qha ntawm WS2 conduction band thiab graphene π-band, cov kev so kom txaus ntxiv - tej zaum los ntawm cov xwm txheej tsis zoo (26) - yuav tsum tau txiav txim siab kom nkag siab txog tag nrho cov dynamics.
(A) Photoexcitation ntawm resonance rau WS2 A-exciton ntawm 2 eV txhaj cov electrons rau hauv conduction band ntawm WS2. Cov qhov sib xws hauv valence band ntawm WS2 tam sim ntawd rov qab los ntawm cov electrons los ntawm graphene π-band. (B) Cov photoexcited carriers hauv conduction band ntawm WS2 muaj lub neej ntawm ~ 1 ps. Cov qhov hauv graphene π-band nyob rau ~ 2 ps, qhia txog qhov tseem ceeb ntawm cov channel scattering ntxiv qhia los ntawm cov xub dashed. Cov kab dub dashed hauv (A) thiab (B) qhia txog kev hloov pauv band thiab kev hloov pauv hauv cov tshuaj lom neeg muaj peev xwm. (C) Hauv lub xeev transient, WS2 txheej yog negatively charged thaum graphene txheej yog positively charged. Rau spin-selective excitation nrog lub teeb ci polarized, cov photoexcited electrons hauv WS2 thiab cov qhov sib xws hauv graphene yuav tsum qhia txog qhov sib txawv spin polarization.
Hauv lub xeev transient, cov electrons photoexcited nyob hauv lub conduction band ntawm WS2 thaum cov qhov photoexcited nyob hauv π-band ntawm graphene (Daim Duab 5C). Qhov no txhais tau tias txheej WS2 muaj nqi tsis zoo thiab txheej graphene muaj nqi zoo. Qhov no suav nrog qhov hloov pauv ntawm lub ncov transient (Daim Duab 2), qhov tsis sib xws ntawm lub teeb liab graphene pump-probe (cov nkhaus 2 thiab 3 ntawm Daim Duab 3), qhov tsis muaj qhov hauv valence band ntawm WS2 (cov nkhaus 4 Daim Duab 3), nrog rau cov qhov ntxiv hauv graphene π-band (Daim Duab 4). Lub neej ntawm lub xeev sib cais no yog ~ 1 ps (cov nkhaus 1 Daim Duab 3).
Cov xwm txheej zoo sib xws uas tau sib cais los ntawm cov nqi tau pom nyob rau hauv cov qauv van der Waals uas ua los ntawm ob lub semiconductors uas muaj qhov sib txawv nrog hom II band alignment thiab staggered bandgap (27–32). Tom qab photoexcitation, cov electrons thiab qhov tau pom tias txav mus rau hauv qab ntawm conduction band thiab mus rau sab saum toj ntawm valence band, feem, uas nyob hauv cov txheej sib txawv ntawm heterostructure (27–32).
Hauv qhov xwm txheej ntawm peb WS2/graphene heterostructure, qhov chaw zoo tshaj plaws rau ob qho tib si electrons thiab qhov yog nyob rau ntawm Fermi theem hauv cov hlau graphene txheej. Yog li ntawd, ib tug yuav xav tias ob qho tib si electrons thiab qhov sai sai hloov mus rau graphene π-band. Txawm li cas los xij, peb cov kev ntsuas qhia meej meej tias qhov hloov qhov (<200 fs) yog qhov ua tau zoo dua li qhov hloov hluav taws xob (~ 1 ps). Peb muab qhov no rau qhov sib raug zoo ntawm WS2 thiab cov graphene bands raws li tau qhia hauv daim duab 1A uas muab ntau dua ntawm cov xwm txheej kawg rau qhov hloov qhov piv rau qhov hloov hluav taws xob raws li tau xav tsis ntev los no los ntawm (14, 15). Hauv qhov xwm txheej tam sim no, xav tias ~ 2 eV WS2 bandgap, graphene Dirac point thiab equilibrium tshuaj muaj peev xwm nyob ~ 0.5 thiab ~ 0.2 eV saum toj no nruab nrab ntawm WS2 bandgap, feem, rhuav tshem electron-qhov symmetry. Peb pom tias tus lej ntawm cov xeev kawg muaj rau kev hloov qhov yog ~ 6 npaug loj dua li kev hloov hluav taws xob (saib Cov Ntaub Ntawv Ntxiv), yog vim li cas kev hloov qhov yuav tsum tau ceev dua li kev hloov hluav taws xob.
Txawm li cas los xij, daim duab me me ntawm qhov pom kev hloov pauv them ceev ceev heev yuav tsum xav txog qhov sib tshooj ntawm cov orbitals uas tsim cov haujlwm A-exciton nthwv dej hauv WS2 thiab graphene π-band, feem, cov channel sib txawv ntawm electron-electron thiab electron-phonon scattering suav nrog cov kev txwv uas tsim los ntawm momentum, zog, spin, thiab pseudospin kev txuag, kev cuam tshuam ntawm plasma oscillations (33), nrog rau lub luag haujlwm ntawm qhov ua tau displacevive excitation ntawm coherent phonon oscillations uas yuav cuam tshuam rau kev hloov pauv them (34, 35). Tsis tas li ntawd, ib tug yuav xav tias seb lub xeev hloov pauv them uas pom muaj cov nqi hloov pauv excitons lossis cov khub electron-qhov dawb (saib Cov Ntaub Ntawv Ntxiv). Kev tshawb nrhiav theoretical ntxiv uas mus dhau qhov ntau thiab tsawg ntawm daim ntawv tam sim no yog qhov yuav tsum tau ua kom meej cov teeb meem no.
Hauv kev xaus lus, peb tau siv tr-ARPES los kawm txog kev hloov pauv ntawm cov txheej txheem ultrafast hauv epitaxial WS2 / graphene heterostructure. Peb pom tias, thaum zoo siab ntawm resonance rau A-exciton ntawm WS2 ntawm 2 eV, cov qhov photoexcited sai sai hloov mus rau hauv txheej graphene thaum cov electrons photoexcited tseem nyob hauv txheej WS2. Peb tau hais qhov no rau qhov tseeb tias tus lej ntawm cov xwm txheej kawg muaj rau kev hloov pauv qhov loj dua li rau kev hloov pauv electron. Lub neej ntawm lub xeev transient sib cais them tau pom tias yog ~ 1 ps. Ua ke nrog kev hloov pauv optical spin-selective siv lub teeb ci ntsa iab (22–25), kev hloov pauv them ultrafast pom tau yuav nrog los ntawm kev hloov pauv spin. Hauv qhov no, WS2 / graphene heterostructure uas tau tshawb nrhiav yuav siv tau rau kev txhaj tshuaj optical spin rau hauv graphene ua rau cov khoom siv optospintronic tshiab.
Cov qauv graphene tau loj hlob ntawm cov khoom lag luam semiconducting 6H-SiC (0001) wafers los ntawm SiCrystal GmbH. Cov wafers N-doped tau nyob rau ntawm-axis nrog qhov tsis raug hauv qab 0.5 °. Lub SiC substrate tau hydrogen-etched kom tshem tawm cov khawb thiab tau txais cov tiaj tiaj tiaj. Lub ntsej muag huv si thiab atomically tiaj tus Si-terminated ces graphitized los ntawm annealing cov qauv hauv Ar huab cua ntawm 1300 ° C rau 8 feeb (36). Txoj kev no, peb tau txais ib txheej carbon qhov twg txhua qhov thib peb carbon atom tsim covalent bond rau SiC substrate (37). Cov txheej txheem no tau hloov mus rau hauv tag nrho sp2-hybridized quasi dawb-sawv ntsug qhov-doped graphene ntawm hydrogen intercalation (38). Cov qauv no hu ua graphene / H-SiC (0001). Tag nrho cov txheej txheem tau ua tiav hauv lub chaw loj hlob Black Magic lag luam los ntawm Aixtron. Kev loj hlob ntawm WS2 tau ua tiav hauv lub tshuab hluav taws xob kub-phab ntsa los ntawm kev tso cov pa tshuaj lom neeg qis (39, 40) siv cov hmoov WO3 thiab S nrog qhov sib piv ntawm 1: 100 ua cov khoom ua ntej. Cov hmoov WO3 thiab S tau khaws cia ntawm 900 thiab 200 ° C, raws li. Cov hmoov WO3 tau muab tso ze rau ntawm lub substrate. Argon tau siv ua cov roj nqa nrog cov dej ntws ntawm 8 sccm. Lub siab hauv lub tshuab hluav taws xob tau khaws cia ntawm 0.5 mbar. Cov qauv tau piav qhia nrog lub tshuab hluav taws xob theem nrab, lub zog atomic microscopy, Raman, thiab photoluminescence spectroscopy, nrog rau kev siv hluav taws xob qis zog. Cov kev ntsuas no tau qhia ob qho chaw sib txawv ntawm WS2 ib leeg-crystalline qhov twg ΓK- lossis ΓK'-kev taw qhia tau sib phim nrog ΓK-kev taw qhia ntawm cov txheej graphene. Qhov ntev ntawm sab ntawm thaj chaw sib txawv ntawm 300 thiab 700 nm, thiab tag nrho cov kev pab them nqi WS2 tau kwv yees li ~ 40%, tsim nyog rau kev tshuaj xyuas ARPES.
Cov kev sim ARPES zoo li qub tau ua tiav nrog lub tshuab ntsuas hemispherical (SPECS PHOIBOS 150) siv lub tshuab ntsuas hluav taws xob uas txuas nrog lub zog rau kev kuaj pom ob-seem ntawm lub zog hluav taws xob thiab lub zog. Unpolarized, monochromatic He Iα hluav taws xob (21.2 eV) ntawm qhov chaw tso tawm He siab (VG Scienta VUV5000) tau siv rau txhua qhov kev sim photoemission. Lub zog thiab kev daws teeb meem angular hauv peb cov kev sim tau zoo dua 30 meV thiab 0.3 ° (sib raug rau 0.01 Å−1), feem. Tag nrho cov kev sim tau ua nyob rau hauv chav tsev kub. ARPES yog ib qho txheej txheem rhiab heev rau saum npoo. Txhawm rau tshem tawm cov photoelectrons los ntawm ob qho tib si WS2 thiab txheej graphene, cov qauv nrog WS2 tsis tiav ntawm ~ 40% tau siv.
Lub tr-ARPES teeb tsa yog raws li 1-kHz Titanium:Sapphire amplifier (Coherent Legend Elite Duo). 2 mJ ntawm lub zog tso zis tau siv rau kev tsim cov harmonics siab hauv argon. Lub teeb ultraviolet hnyav dhau los ntawm lub grating monochromator tsim cov 100-fs probe pulses ntawm 26-eV photon zog. 8mJ ntawm lub zog tso zis amplifier tau xa mus rau hauv lub optical parametric amplifier (HE-TOPAS los ntawm Light Conversion). Lub teeb liab teeb liab ntawm 1-eV photon zog tau raug ob npaug zaus hauv beta barium borate crystal kom tau txais 2-eV twj tso kua mis pulses. Cov kev ntsuas tr-ARPES tau ua tiav nrog lub hemispherical analyzer (SPECS PHOIBOS 100). Lub zog tag nrho thiab kev daws teeb meem lub sijhawm yog 240 meV thiab 200 fs, raws li.
Cov ntaub ntawv ntxiv rau tsab xov xwm no muaj nyob rau ntawm http://advances.sciencemag.org/cgi/content/full/6/20/eaay0761/DC1
Qhov no yog ib tsab xov xwm qhib rau kev nkag mus tau raws li cov nqe lus ntawm daim ntawv tso cai Creative Commons Attribution-NonCommercial, uas tso cai siv, faib tawm, thiab rov ua dua tshiab hauv txhua qhov chaw, tsuav yog qhov kev siv tsis yog rau kev lag luam thiab muab cov haujlwm thawj zaug raug hais kom raug.
LUS CEEV: Peb tsuas thov koj qhov chaw nyob email kom tus neeg uas koj pom zoo rau nplooj ntawv ntawd paub tias koj xav kom lawv pom nws, thiab nws tsis yog cov ntawv xa tsis raug cai. Peb tsis khaws cov chaw nyob email twg li.
Lo lus nug no yog rau kev sim seb koj puas yog tib neeg tuaj xyuas thiab tiv thaiv kev xa cov ntawv spam tsis siv neeg.
Los ntawm Sven Aeschlimann, Antonio Rossi, Mariana Chavez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Peb qhia txog kev sib cais ntawm tus nqi ceev heev hauv WS2 / graphene heterostructure uas tej zaum yuav ua rau muaj kev txhaj tshuaj optical spin rau hauv graphene.
Los ntawm Sven Aeschlimann, Antonio Rossi, Mariana Chavez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Peb qhia txog kev sib cais ntawm tus nqi ceev heev hauv WS2 / graphene heterostructure uas tej zaum yuav ua rau muaj kev txhaj tshuaj optical spin rau hauv graphene.
© 2020 American Association rau Advancement of Science. Tag nrho cov cai. AAAS yog ib tug khub ntawm HINARI, AGORA, OARE, CHORUS, CLOCKSS, CrossRef thiab COUNTER.Science Advances ISSN 2375-2548.
Lub sijhawm tshaj tawm: Tsib Hlis-25-2020