Peb siv lub sij hawm- thiab lub kaum sab xis daws teeb meem photoemission spectroscopy (tr-ARPES) los tshawb xyuas ultrafast charge transfer nyob rau hauv epitaxial heterostructure ua los ntawm monolayer WS2 thiab graphene. Qhov no heterostructure sib txuas cov txiaj ntsig ntawm qhov sib txawv ncaj qha semiconductor nrog lub zog spin-orbit coupling thiab muaj zog lub teeb teeb meem kev sib cuam tshuam nrog cov semimetal hosting massless carriers nrog tsis tshua muaj siab mus thiab ntev spin lifetime. Peb pom tias, tom qab photoexcitation ntawm resonance rau A-exciton nyob rau hauv WS2, lub photoexcited qhov sai hloov mus rau hauv graphene txheej thaum lub photoexcited electrons tseem nyob rau hauv lub WS2 txheej. Cov txiaj ntsig tau sib cais nyob rau hauv lub xeev tau pom tias muaj lub neej ntawm ∼1 ps. Peb ntaus nqi peb qhov kev tshawb pom rau qhov sib txawv ntawm qhov chaw tawg ntawm qhov chaw tshwm sim los ntawm kev sib raug zoo ntawm WS2 thiab graphene bands raws li qhia los ntawm cov kev daws teeb meem siab ARPES. Ua ke nrog spin-xaiv kho qhov muag excitation, tshawb xyuas WS2 / graphene heterostructure yuav muab lub platform rau kev txhaj tshuaj kho qhov muag zoo rau hauv graphene.
Qhov muaj ntau yam khoom siv ob sab sib txawv tau qhib qhov muaj peev xwm los tsim cov tshiab tshiab thaum kawg nyias heterostructures nrog kev ua haujlwm tshiab tag nrho raws li kev tshuaj ntsuam xyuas dielectric thiab ntau yam cuam tshuam sib thooj (1-3). Cov ntaub ntawv pov thawj-ntawm-txoj cai rau kev siv yav tom ntej hauv kev siv hluav taws xob thiab optoelectronics tau raug pom zoo (4-6).
Ntawm no, peb tsom mus rau epitaxial van der Waals heterostructures muaj xws li monolayer WS2, ib tug ncaj-gap semiconductor nrog muaj zog spin-orbit coupling thiab ib tug loj spin splitting ntawm band qauv vim tawg inversion symmetry (7), thiab monolayer graphene, ib tug semimetal. nrog conical band qauv thiab tsis tshua muaj neeg nqa khoom txav tau yooj yim (8), loj hlob ntawm hydrogen-tawm TSI(0001). Thawj qhov qhia txog kev hloov pauv ceev ceev (9-15) thiab qhov sib thooj-vim qhov sib thooj-vim qhov sib txuas ntawm qhov sib txuas (16-18) ua rau WS2 / graphene thiab cov heterostructures zoo sib xws rau cov neeg sib tw rau yav tom ntej optoelectronic (19) thiab optospintronic (20) daim ntawv thov.
Peb tau teeb tsa los nthuav tawm txoj hauv kev so ntawm photogenerated electron-qhov khub hauv WS2 / graphene nrog lub sijhawm- thiab lub kaum sab xis daws teeb meem photoemission spectroscopy (tr-ARPES). Rau lub hom phiaj ntawd, peb excite lub heterostructure nrog 2-eV twj pulses resonant rau A-exciton hauv WS2 (21, 12) thiab eject photoelectrons nrog lub sij hawm ncua sij hawm soj ntsuam mem tes ntawm 26-eV photon zog. Peb txiav txim siab kinetic zog thiab emission lub kaum sab xis ntawm lub photoelectrons nrog ib tug hemispherical analyzer raws li ib tug muaj nuj nqi ntawm lub twj tso kua mis sojntsuam ncua kom nkag tau mus rau lub zog-, lub zog-, thiab lub sij hawm-kho cov cab kuj dynamics. Lub zog thiab lub sijhawm daws teeb meem yog 240 meV thiab 200 fs, feem.
Peb cov txiaj ntsig tau muab cov pov thawj ncaj qha rau kev hloov pauv ceev ceev ntawm cov txheej txheem epitaxially aligned, lees paub thawj cov cim qhia raws li cov txheej txheem kho qhov muag hauv cov txheej txheem sib dhos zoo sib xws nrog cov txheej txheem azimuthal arbitrary azimuthal cov txheej txheem (9-15). Tsis tas li ntawd, peb qhia tau hais tias qhov kev them nqi no yog asymmetric heev. Peb cov kev ntsuas qhia tau hais tias yav dhau los tsis tau saib xyuas tus nqi sib cais nyob rau hauv lub xeev nrog photoexcited electrons thiab qhov nyob rau hauv WS2 thiab graphene txheej, feem, uas nyob rau ∼1 ps. Peb txhais peb qhov kev tshawb pom nyob rau hauv cov nqe lus ntawm qhov sib txawv ntawm qhov chaw tawg rau electron thiab qhov hloov pauv los ntawm kev sib raug zoo ntawm WS2 thiab graphene bands raws li qhia los ntawm high-resolution ARPES. Ua ke nrog spin- thiab hav-xaiv kho qhov muag excitation (22–25) WS2 / graphene heterostructures yuav muab lub platform tshiab rau kev txhaj tshuaj ultrafast optical spin rau hauv graphene.
Daim duab 1A qhia txog qhov kev ntsuas siab ARPES tau txais nrog lub teeb helium ntawm cov qauv band raws ΓK-kev taw qhia ntawm epitaxial WS2 / graphene heterostructure. Lub Dirac lub khob hliav qab tau pom tias yog lub qhov-doped nrog Dirac taw tes nyob rau ∼0.3 eV saum toj no qhov sib npaug tshuaj muaj peev xwm. Sab saum toj ntawm spin-split WS2 valence band pom tias yog ∼1.2 eV hauv qab qhov sib npaug tshuaj muaj peev xwm.
(A) Equilibrium photocurrent ntsuas raws ΓK-kev taw qhia nrog lub teeb helium unpolarized. (B) Photocurrent rau qhov tsis zoo twj tso kua mis-kev sojntsuam ncua kev ntsuas nrog p-polarized huab ultraviolet pulses ntawm 26-eV photon zog. Dashed grey thiab liab kab cim txoj hauj lwm ntawm cov kab profiles siv los rho tawm lub caij nyoog ncov txoj hauj lwm hauv daim duab 2. (C) Pump-induced hloov ntawm photocurrent 200 fs tom qab photoexcitation ntawm lub twj tso kua mis photon zog ntawm 2 eV nrog lub twj tso kua mis fluence 2 mJ/cm2. Tau txais thiab poob ntawm photoelectrons yog qhia hauv liab thiab xiav, feem. Cov thawv ntawv qhia txog thaj tsam ntawm kev sib koom ua ke rau lub twj tso kua mis-kev sojntsuam cov cim qhia hauv daim duab 3.
Daim duab 1B qhia txog tr-ARPES snapshot ntawm cov qauv band ze rau WS2 thiab graphene K-cov ntsiab lus ntsuas nrog 100-fs ultraviolet pulses ntawm 26-eV photon zog ntawm qhov tsis zoo twj tso kua mis-kev sojntsuam ncua ua ntej tuaj txog ntawm lub twj tso kua mis pulse. Ntawm no, qhov sib cais ntawm qhov sib cais tsis raug daws vim yog cov qauv degradation thiab muaj 2-eV twj mem tes uas ua rau qhov chaw them nqi nthuav dav ntawm cov yam ntxwv spectral. Daim duab 1C qhia txog lub twj tso kua mis-induced hloov ntawm lub photocurrent nrog rau fig. 1B ntawm lub twj tso kua mis-kev sojntsuam ncua ntawm 200 fs qhov twg lub twj tso kua mis-probe teeb liab mus txog nws qhov siab tshaj plaws. Liab thiab xiav xim qhia tau tias nce thiab poob ntawm photoelectrons, feem.
Txhawm rau txheeb xyuas qhov kev nplua nuj nyob hauv qhov kev nthuav dav ntxiv, peb thawj zaug txiav txim siab qhov chaw siab tshaj plaws ntawm WS2 valence band thiab graphene π-band raws cov kab dashed hauv daim duab 1B raws li tau piav qhia hauv kev nthuav dav hauv Cov Khoom Siv Ntxiv. Peb pom tias WS2 valence band hloov los ntawm 90 meV (Fig. 2A) thiab cov graphene π-band hloov los ntawm 50 meV (Fig. 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 cov pov thawj thawj zaug ntawm kev them nyiaj ib ntus ntawm ob txheej, qhov twg ntxiv qhov zoo (tsis zoo) tus nqi nce (qis) lub zog khi ntawm lub xeev hluav taws xob. Nco ntsoov tias qhov upshift ntawm WS2 valence band yog lub luag hauj lwm rau lub tseem ceeb twj tso kua mis-kev sojntsuam teeb liab nyob rau hauv lub cheeb tsam uas cim los ntawm lub thawv dub nyob rau hauv daim duab 1C.
Hloov nyob rau hauv lub ncov txoj hauj lwm ntawm WS2 valence band (A) thiab graphene π-band (B) raws li ib tug muaj nuj nqi ntawm twj tso kua mis sojntsuam ncua ua ke nrog exponential fits (cov kab tuab). Lub neej ntawm WS2 hloov pauv hauv (A) yog 1.2 ± 0.1 ps. Lub neej ntawm graphene hloov hauv (B) yog 1.7 ± 0.3 ps.
Tom ntej no, peb muab lub twj tso kua mis-kev sojntsuam lub teeb liab hla cov cheeb tsam uas qhia los ntawm cov thawv xim hauv daim duab 1C thiab npaj cov txiaj ntsig suav nrog kev ua haujlwm ntawm lub twj tso kua mis-kev sojntsuam ncua sijhawm hauv daim duab 3. Curve 1 hauv daim duab 3 qhia txog kev ua haujlwm ntawm lub twj tso kua mis. photoexcited carriers nyob ze rau hauv qab ntawm cov conduction band ntawm WS2 txheej nrog lub neej ntawm 1.1 ± 0.1 ps tau los ntawm exponential haum rau cov ntaub ntawv (saib Cov Khoom Siv Ntxiv).
Pump-probe traces raws li kev ua haujlwm ntawm kev ncua tau txais los ntawm kev sib koom ua ke cov photocurrent hla thaj chaw uas tau qhia los ntawm cov thawv hauv daim duab 1C. Cov kab tuab yog exponential haum rau cov ntaub ntawv. Curve (1) Cov neeg caij tsheb thauj mus los nyob rau hauv kev sib txuas ntawm WS2. Curve (2) Pump-probe teeb liab ntawm π-band ntawm graphene saum toj ntawm qhov sib npaug tshuaj muaj peev xwm. Curve (3) Pump-probe teeb liab ntawm π-band ntawm graphene hauv qab qhov sib npaug tshuaj muaj peev xwm. Curve (4) Net twj tso kua mis sojntsuam teeb liab hauv valence band ntawm WS2. Lub neej nyob tau pom tias yog 1.2 ± 0.1 ps hauv (1), 180 ± 20 fs (tau) thiab ∼2 ps (poob) hauv (2), thiab 1.8 ± 0.2 ps hauv (3).
Nyob rau hauv curves 2 thiab 3 ntawm daim duab 3, peb qhia lub twj tso kua mis-probe teeb liab ntawm graphene π-band. Peb pom tias qhov nce ntawm electrons saum toj no qhov sib npaug tshuaj muaj peev xwm (kov 2 hauv daim duab 3) muaj lub neej luv dua (180 ± 20 fs) piv rau qhov poob ntawm electrons hauv qab qhov sib npaug tshuaj muaj peev xwm (1.8 ± 0.2 ps hauv nkhaus 3. Daim duab 3). Tsis tas li ntawd, qhov pib nce ntawm photocurrent nyob rau hauv nkhaus 2 ntawm daim duab 3 yog pom tias tig mus rau poob ntawm t = 400 fs nrog lub neej ntawm ∼2 ps. Lub asymmetry ntawm qhov nce thiab poob yog pom tias tsis tuaj nyob rau hauv lub twj tso kua mis-kev sojntsuam teeb liab ntawm uncovered monolayer graphene (saib daim duab S5 nyob rau hauv cov ntaub ntawv ntxiv), qhia tias asymmetry yog ib tug tshwm sim ntawm interlayer coupling nyob rau hauv lub WS2 / graphene heterostructure. Kev soj ntsuam ntawm lub sijhawm luv luv thiab lub neej nyob ntev poob saum toj thiab hauv qab ntawm qhov sib npaug tshuaj muaj peev xwm, feem, qhia tau hais tias cov hluav taws xob tau raug tshem tawm ntawm graphene txheej thaum photoexcitation ntawm heterostructure. Raws li qhov tshwm sim, cov txheej graphene ua rau muaj txiaj ntsig zoo, uas zoo ib yam nrog kev nce hauv kev khi zog ntawm π-band pom hauv daim duab 2B. Lub downshift ntawm π-band tshem tawm lub siab-zog tus Tsov tus tw ntawm equilibrium Fermi-Dirac tis los ntawm saum toj no lub equilibrium tshuaj muaj peev xwm, uas ib feem piav qhia txog kev hloov ntawm cov cim ntawm lub twj tso kua mis-probe teeb liab nyob rau hauv nkhaus 2 ntawm daim duab 3. Peb yuav qhia hauv qab no hais tias cov nyhuv no yog ntxiv txhim khu kev qha los ntawm lub sij hawm poob ntawm electrons nyob rau hauv lub π-band.
Qhov xwm txheej no tau txais kev txhawb nqa los ntawm net twj tso kua mis-kev sojntsuam teeb liab ntawm WS2 valence band nyob rau 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 muab los ntawm lub thawv dub hauv daim duab 1B uas ntes cov electrons photoemitted los ntawm lub valence band ntawm txhua lub twj tso kua mis-kev sojntsuam qeeb. Hauv qhov kev sim ua yuam kev, peb pom tsis muaj qhov qhia tau tias muaj qhov nyob hauv qhov valence band ntawm WS2 rau ib qho twj tso kua mis-kev sojntsuam qeeb. Qhov no qhia tau hais tias, tom qab photoexcitation, cov qhov no tau rov qab sai sai ntawm lub sijhawm luv luv piv rau peb lub cev kev daws teeb meem.
Txhawm rau muab cov ntaub ntawv pov thawj zaum kawg rau peb qhov kev xav ntawm kev sib cais ntawm ultrafast charge nyob rau hauv WS2 / graphene heterostructure, peb txiav txim siab tus naj npawb ntawm qhov hloov mus rau graphene txheej raws li tau piav qhia hauv cov khoom siv ntxiv. Nyob rau hauv luv luv, lub transient hluav taws xob faib ntawm π-band tau haum nrog Fermi-Dirac tis. Tus naj npawb ntawm qhov tau muab xam los ntawm cov txiaj ntsig tshwm sim rau cov tshuaj muaj peev xwm hloov pauv thiab hluav taws xob kub. Cov txiaj ntsig tau pom hauv daim duab 4. Peb pom tias tag nrho cov naj npawb ntawm ∼5 × 1012 qhov / cm2 raug xa los ntawm WS2 rau graphene nrog lub neej exponential ntawm 1.5 ± 0.2 ps.
Kev hloov ntawm tus naj npawb ntawm qhov nyob rau hauv π-band raws li kev ua haujlwm ntawm lub twj tso kua mis-kev sojntsuam ncua ua ke nrog exponential haum yielding lub neej ntawm 1.5 ± 0.2 ps.
Los ntawm cov kev tshawb pom hauv Fig. 2 mus rau 4, daim duab microscopic hauv qab no rau kev hloov pauv ceev ceev hauv WS2 / graphene heterostructure tshwm sim (Fig. 5). Photoexcitation ntawm WS2 / graphene heterostructure ntawm 2 eV dominantly populates A-exciton hauv WS2 (Fig. 5A). Ntxiv cov hluav taws xob excitations hla Dirac taw tes hauv graphene nrog rau ntawm WS2 thiab graphene bands muaj zog tuaj yeem ua tau tab sis tsis tshua muaj txiaj ntsig. Lub photoexcited qhov nyob rau hauv lub valence band ntawm WS2 yog refilled los ntawm electrons los ntawm lub graphene π-band ntawm lub sij hawm teev luv luv piv rau peb lub cev kev daws teeb meem (Fig. 5A). Lub photoexcited electrons nyob rau hauv conduction band ntawm WS2 muaj lub neej ntawm ∼1 ps (Fig. 5B). Txawm li cas los xij, nws yuav siv ∼2 ps txhawm rau txhawm rau txhawm rau lub qhov hauv graphene π-band (Fig. 5B). Qhov no qhia tau hais tias, ib sab ntawm kev hloov hluav taws xob ncaj qha ntawm WS2 conduction band thiab graphene π-band, ntxiv txoj hauv kev so-tejzaum nws los ntawm cov xeev tsis raug (26)-yuav tsum tau txiav txim siab kom nkag siab tag nrho cov dynamics.
(A) Photoexcitation ntawm resonance rau WS2 A-exciton ntawm 2 eV txhaj cov electrons rau hauv cov conduction band ntawm WS2. Cov qhov sib thooj hauv valence band ntawm WS2 yog tam sim ntawd rov qab los ntawm electrons los ntawm graphene π-band. (B) Cov neeg nqa khoom photoexcited nyob rau hauv kev coj ua band ntawm WS2 muaj lub neej ntawm ∼1 ps. Lub qhov nyob rau hauv lub graphene π-band nyob rau ∼2 ps, qhia qhov tseem ceeb ntawm cov kev faib tawm ntxiv uas qhia los ntawm cov xub dashed. Dub dashed kab nyob rau hauv (A) thiab (B) qhia band hloov thiab hloov nyob rau hauv tshuaj muaj peev xwm. (C) Nyob rau hauv lub sijhawm luv luv, WS2 txheej yog tsis zoo them thaum lub graphene txheej yog zoo them. Rau spin-xaiv excitation nrog ncig polarized lub teeb, lub photoexcited electrons nyob rau hauv WS2 thiab cov sib thooj qhov nyob rau hauv graphene yuav tsum qhia opposite spin polarization.
Nyob rau hauv lub sij hawm luv luv, lub photoexcited electrons nyob rau hauv conduction band ntawm WS2 thaum lub photoexcited qhov nyob rau hauv lub π-band ntawm graphene (Fig. 5C). Qhov no txhais tau hais tias WS2 txheej tsis zoo raug them thiab cov txheej graphene raug them zoo. Qhov no suav nrog kev hloov pauv hloov pauv hloov pauv (Daim duab 2), qhov asymmetry ntawm graphene twj tso kua mis-kev sojntsuam teeb liab (kov 2 thiab 3 ntawm daim duab 3), qhov tsis muaj qhov nyob hauv valence band ntawm WS2 (kov 4 Fig. 3) , nrog rau cov qhov ntxiv hauv graphene π-band (Fig. 4). Lub neej ntawm lub xeev sib cais yog ∼1 ps (kov 1 daim duab 3).
Zoo sib xws cov nqi sib cais ntawm lub xeev tau pom nyob rau hauv kev cuam tshuam ntawm van der Waals heterostructures ua los ntawm ob qhov sib txawv ncaj qha semiconductors nrog hom II band alignment thiab staggered bandgap (27-32). Tom qab photoexcitation, cov electrons thiab qhov tau pom sai sai txav mus rau hauv qab ntawm lub conduction band thiab mus rau sab saum toj ntawm lub valence band, feem, uas nyob rau hauv sib txawv txheej ntawm lub heterostructure (27-32).
Nyob rau hauv cov ntaub ntawv ntawm peb WS2 / graphene heterostructure, lub energetically nyiam tshaj qhov chaw rau ob qho tib si electrons thiab qhov yog nyob rau hauv Fermi theem nyob rau hauv lub metallic graphene txheej. Yog li ntawd, ib tug yuav cia siab tias ob qho tib si electrons thiab qhov ceev hloov mus rau graphene π-band. Txawm li cas los xij, peb qhov kev ntsuas tau qhia meej tias qhov hloov pauv ntawm qhov (<200 fs) yog qhov ua tau zoo dua li kev hloov hluav taws xob (∼1 ps). Peb ntaus nqi qhov no rau cov txheeb ze zog sib raug zoo ntawm WS2 thiab cov graphene bands raws li qhia nyob rau hauv daim duab 1A uas muaj ib tug loj tus naj npawb ntawm muaj nyob rau kawg lub xeev rau lub qhov hloov dua siab tshiab piv rau electron hloov lwm lub tsev raws li tsis ntev los no npaj los ntawm (14, 15). Nyob rau hauv cov ntaub ntawv no, piv txwv li ib tug ∼2 eV WS2 bandgap, lub graphene Dirac point thiab equilibrium tshuaj muaj peev xwm nyob rau hauv ∼0.5 thiab ∼0.2 eV saum nruab nrab ntawm WS2 bandgap, ntsig txog, tawg electron-qhov symmetry. Peb pom tias tus naj npawb ntawm cov xeev zaum kawg rau lub qhov hloov pauv yog ∼6 npaug ntau dua rau kev hloov hluav taws xob (saib cov khoom siv ntxiv), uas yog vim li cas qhov hloov pauv yuav tsum ceev dua li kev hloov hluav taws xob.
Ib daim duab microscopic tiav ntawm qhov pom kev hloov pauv hloov pauv ntawm ultrafast asymmetric yuav tsum, txawm li cas los xij, kuj tseem xav txog qhov sib tshooj ntawm lub orbitals uas ua rau A-exciton yoj ua haujlwm hauv WS2 thiab graphene π-band, raws li, sib txawv electron-electron thiab electron-phonon scattering. cov channel suav nrog cov kev txwv tsis pub dhau lub zog, lub zog, tig, thiab kev txuag pseudospin, cuam tshuam ntawm plasma oscillations (33), nrog rau lub luag hauj lwm ntawm ib tug ua tau displacive excitation ntawm coherent phonon oscillations uas tej zaum yuav kho kom haum tus nqi pauv (34, 35). Tsis tas li ntawd, ib tus yuav xav tias seb qhov kev hloov pauv hauv lub xeev puas muaj cov nqi hloov pauv excitons lossis cov khoom siv hluav taws xob dawb dawb (saib Cov Khoom Siv Ntxiv). Kev tshawb nrhiav theoretical ntxiv uas dhau mus dhau ntawm cov ntaub ntawv tam sim no yuav tsum tau qhia meej txog cov teeb meem no.
Hauv cov ntsiab lus, peb tau siv tr-ARPES los kawm ultrafast interlayer tus nqi hloov pauv hauv epitaxial WS2 / graphene heterostructure. Peb pom tias, thaum zoo siab ntawm resonance rau A-exciton ntawm WS2 ntawm 2 eV, lub photoexcited qhov hloov mus rau hauv graphene txheej sai sai thaum lub photoexcited electrons tseem nyob rau hauv WS2 txheej. Peb ntaus nqi qhov no rau qhov tseeb tias tus naj npawb ntawm cov xeev zaum kawg rau lub qhov hloov pauv loj dua rau kev hloov hluav taws xob. Lub neej ntawm cov nqi sib cais nyob rau hauv lub xeev tau pom tias yog ∼1 ps. Ua ke nrog spin-xaiv optical excitation siv lub voj voog polarized (22-25), qhov pom kev hloov pauv ceev ceev tuaj yeem nrog kev hloov pauv. Hauv qhov no, kev tshawb xyuas WS2 / graphene heterostructure yuav siv tau rau kev txhaj tshuaj kho qhov muag zoo rau hauv graphene uas ua rau cov khoom siv optospintronic tshiab.
Cov qauv graphene tau loj hlob ntawm kev lag luam semiconducting 6H-SiC(0001) wafers los ntawm SiCrystal GmbH. Cov N-doped wafers nyob rau-axis nrog miscut hauv qab 0.5 °. SiC substrate yog hydrogen-etched kom tshem tawm khawb thiab tau txais cov tiaj tiaj tiaj tiaj. Qhov huv si thiab atomically tiaj tus Si-terminated nto ces graphitized los ntawm annealing tus qauv hauv Ar cua ntawm 1300 ° C rau 8 min (36). Txoj kev no, peb tau txais ib txheej carbon uas txhua peb cov pa roj carbon atom tsim ib daim ntawv cog lus rau SiC substrate (37). Cov txheej no tau hloov mus ua kiag li sp2-hybridized quasi dawb-sawv qhov-doped graphene ntawm hydrogen intercalation (38). Cov qauv no raug xa mus rau graphene / H-SiC (0001). Tag nrho cov txheej txheem tau ua nyob rau hauv kev lag luam Black Magic loj hlob chamber los ntawm Aixtron. Kev loj hlob WS2 tau ua tiav hauv cov txheej txheem kub-phab ntsa reactor los ntawm cov tshuaj tsis tshua muaj tshuaj vapor deposition (39, 40) siv WO3 thiab S hmoov nrog qhov loj piv ntawm 1: 100 ua ntej. WO3 thiab S hmoov tau khaws cia ntawm 900 thiab 200 ° C, raws li. WO3 hmoov tau muab tso rau ze rau ntawm lub substrate. Argon tau siv los ua cov pa roj nrog cov dej ntws ntawm 8 sccm. Lub siab nyob rau hauv lub reactor tau khaws cia ntawm 0.5 mbar. Cov qauv kuaj pom muaj cov khoom siv hluav taws xob thib ob, atomic force microscopy, Raman, thiab photoluminescence spectroscopy, nrog rau cov hluav taws xob qis hluav taws xob. Cov kev ntsuas no tau nthuav tawm ob qhov sib txawv WS2 ib leeg-crystalline domains qhov twg yog ΓK- lossis ΓK'-kev taw qhia yog ua raws li ΓK-kev taw qhia ntawm graphene txheej. Domain side lengths txawv ntawm 300 thiab 700 nm, thiab tag nrho WS2 kev pab them nqi yog kwv yees li ∼40%, haum rau ARPES tsom xam.
Cov kev sim ARPES zoo li qub tau ua nrog lub ntsuas hemispherical (SPECS PHOIBOS 150) siv lub tshuab hluav taws xob sib txuas-cov cuab yeej ntsuas rau ob sab kev tshawb pom ntawm hluav taws xob hluav taws xob thiab lub zog. Unpolarized, monochromatic Nws Iα hluav taws xob (21.2 eV) ntawm lub siab ntws ntws tawm (VG Scienta VUV5000) tau siv rau txhua qhov kev sim photoemission. Lub zog thiab qhov kev daws teeb meem ntawm peb qhov kev sim tau zoo dua li 30 meV thiab 0.3 ° (xws li 0.01 Å−1), feem. Txhua qhov kev sim tau ua nyob rau hauv chav tsev kub. ARPES yog ib qho txheej txheem nto-rhiab heev. Txhawm rau tshem tawm cov duab hluav taws xob los ntawm ob qho tib si WS2 thiab txheej graphene, cov qauv uas tsis tiav WS2 kev pab them nqi ntawm ∼40% tau siv.
Kev teeb tsa tr-ARPES yog raws li 1-kHz Titanium: Sapphire amplifier (Coherent Legend Elite Duo). 2 mJ ntawm cov zis hluav taws xob tau siv los ua kom muaj kev sib haum xeeb siab hauv argon. Qhov tshwm sim ultraviolet lub teeb dhau los ntawm grating monochromator ua 100-fs sojntsuam pulses ntawm 26-eV photon zog. 8mJ ntawm lub tshuab hluav taws xob tso zis hluav taws xob raug xa mus rau hauv lub tshuab hluav taws xob optical parametric (HE-TOPAS los ntawm Lub Teeb Hloov). Lub teeb liab beam ntawm 1-eV photon zog yog zaus-ob zaug hauv beta barium borate siv lead ua kom tau txais 2-eV twj pulses. Kev ntsuas tr-ARPES tau ua nrog lub ntsuas hemispherical (SPECS PHOIBOS 100). Tag nrho lub zog thiab kev daws teeb meem ntawm lub cev yog 240 meV thiab 200 fs, feem.
Cov ntaub ntawv ntxiv rau tsab xov xwm no muaj nyob ntawm http://advances.sciencemag.org/cgi/content/full/6/20/eaay0761/DC1
Qhov no yog ib tsab xov xwm qhib tau muab faib raws li cov ntsiab lus ntawm Creative Commons Attribution-NonCommercial daim ntawv tso cai, uas tso cai rau siv, faib, thiab luam tawm nyob rau hauv ib qho nruab nrab, tsuav yog qhov tshwm sim ntawm kev siv tsis yog rau kev lag luam kom zoo dua thiab muab cov haujlwm qub kom zoo. hais.
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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 nthuav tawm ultrafast nqi sib cais nyob rau hauv WS2 / graphene heterostructure tejzaum nws ua rau kev kho qhov muag spin txhaj 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 nthuav tawm ultrafast nqi sib cais nyob rau hauv WS2 / graphene heterostructure tejzaum nws ua rau kev kho qhov muag spin txhaj rau hauv graphene.
© 2020 American Association rau Advancement of Science. Txhua txoj cai. AAAS yog ib tug khub ntawm HINARI, AGORA, OARE, CHORUS, CLOCKSS, CrossRef thiab COUNTER.Science Advances ISSN 2375-2548.
Post lub sij hawm: May-25-2020