Sisebenzisa i-photoemission spectroscopy exazululwe ngexesha kunye ne-angle (tr-ARPES) ukuphanda ukudluliselwa kwetshaja okukhawulezayo kwi-epitaxial heterostructure eyenziwe nge-monolayer WS2 kunye ne-graphene. Olu lwakhiwo lwe-heterostructure ludibanisa iingenelo ze-semiconductor ye-direct-gap ene-spin-orbit coupling enamandla kunye nokusebenzisana okunamandla kokukhanya kunye nezo ze-semimetal hosting massless carriers ezine-mobility ephezulu kakhulu kunye nobomi obude be-spin. Sifumanisa ukuba, emva kwe-photoexcitation kwi-resonance kwi-A-exciton kwi-WS2, imingxunya ye-photoexcited idlulela ngokukhawuleza kwi-graphene layer ngelixa ii-electron ze-photoexcited zihlala kwi-WS2 layer. Imeko ye-transient ephumayo ehlukaniswe yi-charge ifunyenwe inobomi obuyi-∼1 ps. Sithi iziphumo zethu zibangelwa kukungafani kwendawo ye-scattering phase ebangelwa kukulungelelaniswa okunxulumeneyo kwee-WS2 kunye nee-graphene bands njengoko kutyhilwe yi-high-resolution ARPES. Ngokudibeneyo ne-spin-selective optical excitation, i-WS2/graphene heterostructure ephandiweyo inokubonelela ngeqonga lokufaka i-optical spin ephumelelayo kwi-graphene.
Ukufumaneka kwezinto ezininzi ezahlukeneyo ezinemilinganiselo emibini kuvule ithuba lokwenza izakhiwo ezintsha ezibhityileyo ezinemisebenzi emitsha ngokupheleleyo esekelwe kuvavanyo lwe-dielectric olulungiselelwe wena kunye neziphumo ezahlukeneyo ezibangelwa kukusondela (1–3). Izixhobo zobungqina bomgaqo-nkqubo wezicelo zexesha elizayo kwicandelo le-elektroniki kunye ne-optoelectronics ziye zafezekiswa (4–6).
Apha, sigxila kwi-epitaxial van der Waals heterostructures equka i-monolayer WS2, i-semiconductor ethe ngqo ene-spin-orbit coupling enamandla kunye nokwahlukana okukhulu kwe-spin structure ye-band ngenxa yokwaphuka kwe-inversion symmetry (7), kunye ne-monolayer graphene, i-semimetal ene-conical band structure kunye ne-carrier movement ephezulu kakhulu (8), ekhuliswe kwi-hydrogen-terminated SiC(0001). Iimpawu zokuqala zokudluliselwa kwe-ultrafast charge (9–15) kunye ne-proximity-induced spin-orbit coupling effects (16–18) zenza i-WS2/graphene kunye ne-heterostructures ezifanayo zibe ngabaviwa abathembisayo kwizicelo ze-optoelectronic zexesha elizayo (19) kunye ne-optospintronic (20).
Sizimisele ukutyhila iindlela zokuphumla zee-electron-hole pairs ezenziwe nge-photogenerated kwi-WS2/graphene nge-time-and-angle-resolved photoemission spectroscopy (tr-ARPES). Ngenxa yoko, sivuselela i-heterostructure ngee-2-eV pump pulses ezihambelana ne-A-exciton kwi-WS2 (21, 12) kwaye sikhuphe ii-photoelectrons nge-time-delayed probe pulse yesibini kwi-26-eV photon energy. Sichonga amandla e-kinetic kunye ne-emission angle yee-photoelectrons nge-hemispherical analyzer njengomsebenzi we-pump-probe delay ukuze sifumane ukufikelela kwi-momentum-, energy-, kunye ne-time-resolved carrier dynamics. Isisombululo samandla kunye nexesha yi-240 meV kunye ne-200 fs, ngokwahlukeneyo.
Iziphumo zethu zibonelela ngobungqina obuthe ngqo bokudluliselwa kwetshaja ye-ultrafast phakathi kweeleya ezilungelelaniswe ngokwe-epitaxially, ziqinisekisa izibonakaliso zokuqala ezisekelwe kwiindlela ze-all-optical kwi-heterostructures ezifanayo ezihlanganiswe ngesandla kunye nokulungelelaniswa kwe-azimuthal okungacwangciswanga kweeleya (9-15). Ukongeza, sibonisa ukuba olu dluliselo lwetshaja alulingani kakhulu. Ukulinganisa kwethu kubonisa imeko ye-transient engabonwanga ngaphambili ene-electrons kunye nemingxuma efumaneka kwi-WS2 kunye ne-graphene layer, ngokulandelanayo, ehlala ixesha elingange-∼1 ps. Sitolika iziphumo zethu ngokweemahluko kwisithuba se-scattering phase sokudluliselwa kwe-electron kunye nemingxuma okubangelwa kukulungelelaniswa okunxulumeneyo kwe-WS2 kunye ne-graphene bands njengoko kutyhilwe yi-high-resolution ARPES. Idityaniswe ne-spin- kunye ne-valley-selective optical excitation (22-25) I-WS2/graphene heterostructures inokubonelela ngeqonga elitsha lokufakwa kwe-ultrafast optical spin kwi-graphene.
Umfanekiso 1A ubonisa umlinganiselo we-ARPES ophakamileyo ofunyenwe ngesibane se-helium sesakhiwo sebhendi ecaleni kwe-ΓK-direction ye-epitaxial WS2/graphene heterostructure. I-Dirac cone ifunyenwe ine-hole-doped apho i-Dirac point ibekwe kwi-∼0.3 eV ngaphezulu kwe-equilibrium chemical potential. Umphezulu we-spin-split WS2 valence band ufunyenwe ukwi-∼1.2 eV ngaphantsi kwe-equilibrium chemical potential.
(A) I-photocurrent elinganayo elinganiswe kwicala le-ΓK ngesibane se-helium esingapholiyo. (B) I-Photocurrent yokulibaziseka kwe-pump-probe engalunganga elinganiswe ngee-pulses ze-ultraviolet ezigqithisileyo ze-p-polarized kwi-26-eV photon energy. Imigca engwevu nebomvu eqhekekileyo iphawula indawo yeeprofayili zomgca ezisetyenziselwa ukukhupha izikhundla ze-transient peak kwiFig. 2. (C) Utshintsho olubangelwa yi-pump lwe-photocurrent engama-200 fs emva kwe-photoexcitation kwi-pump photon energy ye-2 eV ene-pump fluence ye-2 mJ/cm2. Ukwanda kunye nokulahleka kwe-photoelectrons kuboniswe ngombala obomvu noluhlaza okwesibhakabhaka, ngokulandelelana. Iibhokisi zibonisa indawo yokudibanisa ii-traces ze-pump-probe eziboniswe kwiFig. 3.
Umfanekiso 1B ubonisa umfanekiso we-tr-ARPES wesakhiwo sebhendi esikufutshane ne-WS2 kunye ne-graphene K-points ezilinganiswe ngee-100-fs extreme ultraviolet pulses kwi-26-eV photon energy kwi-negative pump-probe delay ngaphambi kokufika kwe-pump pulse. Apha, ukuqhekeka kwe-spin akusonjululwanga ngenxa yokuwohloka kwesampulu kunye nobukho be-2-eV pump pulse ebangela ukwanda kwetshaja yesithuba kwiimpawu ze-spectral. Umfanekiso 1C ubonisa utshintsho olubangelwa yi-pump lwe-photocurrent malunga noMfanekiso 1B kwi-pump-probe delay ye-200 fs apho isignali ye-pump-probe ifikelela kwi-high yayo. Imibala ebomvu neluhlaza okwesibhakabhaka ibonisa ukufumana nokulahleka kwee-photoelectrons, ngokwahlukeneyo.
Ukuze sihlalutye olu tshintsho lutyebileyo ngeenkcukacha ezithe vetshe, siqala ngokumisela iindawo zencochoyi ye-WS2 valence band kunye ne-graphene π-band kwimigca enee-dash kwiFig. 1B njengoko kuchaziwe ngokweenkcukacha kwiSupplementary Materials. Sifumanisa ukuba i-WS2 valence band itshintsha nge-90 meV (Fig. 2A) kwaye i-graphene π-band itshintsha nge-50 meV (Fig. 2B). Ixesha elide lokutshintsha kwezi nguqu lifunyenwe liyi-1.2 ± 0.1 ps kwi-valence band ye-WS2 kunye ne-1.7 ± 0.3 ps kwi-graphene π-band. Ezi ncochoyi ze-peak zibonelela ngobungqina bokuqala bokutshaja kwe-transient layers ezimbini, apho i-positive positive (negative) charge eyongezelelweyo inyusa (inciphisa) amandla okubopha e-electronic states. Qaphela ukuba i-upshift ye-WS2 valence band inoxanduva lwesignali ye-pump-probe evelele kwindawo ephawulwe yibhokisi emnyama kwiFig. 1C.
Utshintsho kwindawo ephezulu ye-WS2 valence band (A) kunye ne-graphene π-band (B) njengomsebenzi wokulibaziseka kwe-pump-probe kunye nokulingana kwe-exponential (imigca etyebileyo). Ubomi be-WS2 shift in (A) yi-1.2 ± 0.1 ps. Ubomi be-graphene shift in (B) yi-1.7 ± 0.3 ps.
Okulandelayo, sidibanisa isignali ye-pump-probe kwiindawo eziboniswe ziibhokisi ezinemibala kwiFig. 1C size sibonise ukubalwa okuphumayo njengomsebenzi wokulibaziseka kwe-pump-probe kwiFig. 3. I-Curve 1 kwiFig. 3 ibonisa i-dynamics ye-photoexcited carriers kufutshane nezantsi kwebhendi yokuqhuba yomaleko we-WS2 kunye nobomi be-1.1 ± 0.1 ps efunyenwe kwi-exponential fit kwidatha (jonga kwi-Supplementary Materials).
I-Pump-probe traces njengomsebenzi wokulibaziseka ofunyenwe ngokuhlanganisa i-photocurrent phezu kwendawo eboniswe ziibhokisi ezikuMfanekiso 1C. Imigca etyebileyo ihambelana nedatha. I-Curve (1) Inani labantu abathwala i-transient kwi-conduction band ye-WS2. I-Curve (2) I-Pump-probe signal ye-π-band ye-graphene ngaphezulu kwe-equilibrium chemical potential. I-Curve (3) I-Pump-probe signal ye-π-band ye-graphene ngaphantsi kwe-equilibrium chemical potential. I-Curve (4) I-Net pump-probe signal kwi-valence band ye-WS2. Ixesha lobomi lifunyenwe liyi-1.2 ± 0.1 ps kwi-(1), 180 ± 20 fs (gain) kunye ne-∼2 ps (loss) kwi-(2), kunye ne-1.8 ± 0.2 ps kwi-(3).
Kwimiqolo yesi-2 neyesi-3 yoMfanekiso 3, sibonisa isignali ye-pump-probe ye-graphene π-band. Sifumanisa ukuba ukuzuza kwee-electron ngaphezulu kwe-equilibrium chemical potential (i-curve 2 kuMfanekiso 3) kunobomi obufutshane kakhulu (180 ± 20 fs) xa kuthelekiswa nokulahleka kwee-electron ngaphantsi kwe-equilibrium chemical potential (1.8 ± 0.2 ps kwi-curve 3 uMfanekiso 3). Ngaphezu koko, ukuzuza kokuqala kwe-photocurrent kwi-curve 2 yoMfanekiso 3 kufunyenwe kujika kube yilahleko kwi-t = 400 fs kunye nobomi be-∼2 ps. Ukungalingani phakathi kokuzuza kunye nokulahlekelwa kufunyenwe kungekho kwisignali ye-pump-probe ye-uncovered monolayer graphene (jonga umfanekiso S5 kwiZixhobo ezongezelelweyo), okubonisa ukuba ukungalingani kubangelwa kukudibana kwe-interlayer kwi-heterostructure ye-WS2/graphene. Ukuqwalaselwa kokufumana inzuzo yexesha elifutshane kunye nokulahleka kwexesha elide ngaphezulu nangaphantsi kwe-equilibrium chemical potential, ngokwahlukeneyo, kubonisa ukuba ii-electron zisuswa ngokufanelekileyo kwi-graphene layer xa i-photoexcitation ye-heterostructure iphuma. Ngenxa yoko, i-graphene layer iba ne-positive charge, ehambelana nokwanda kwamandla okubopha e-π-band efunyenwe kwiFig. 2B. Ukwehla kwe-π-band kususa umsila wamandla aphezulu wokusasazwa kwe-equilibrium Fermi-Dirac ukusuka ngaphezulu kwe-equilibrium chemical potential, echaza ngokuyinxenye utshintsho lwesignali ye-pump-probe kwi-curve 2 yeFig. 3. Siza kubonisa ngezantsi ukuba esi siphumo siphuculwa ngakumbi kukulahleka okwethutyana kwee-electron kwi-π-band.
Le meko ixhaswa yisignali ye-net pump-probe ye-WS2 valence band kwi-curve 4 yoMfanekiso 3. Le datha ifunyenwe ngokuhlanganisa ukubalwa kwendawo enikwe yibhokisi emnyama kwiMfanekiso 1B ebamba ii-electron ezikhutshwa yi-valence band kuzo zonke ii-pump-probe delays. Ngaphakathi kwi-error bar zovavanyo, asifumani sibonakaliso sokuba kukho imingxunya kwi-valence band ye-WS2 kuyo nayiphi na i-pump-probe delay. Oku kubonisa ukuba, emva kwe-photoexcitation, le mingxunya igcwaliswa ngokukhawuleza ngexesha elifutshane xa kuthelekiswa nesisombululo sethu sexesha.
Ukubonelela ngobungqina bokugqibela kwingcamango yethu yokwahlulwa kwe-charge okusheshayo kwi-WS2/graphene heterostructure, sichonga inani lemingxuma edluliselwe kwi-graphene layer njengoko kuchaziwe ngokweenkcukacha kwi-Supplementary Materials. Ngamafutshane, ukusasazwa kwe-elektroniki okuguquguqukayo kwe-π-band kwafakelwa usasazo lwe-Fermi-Dirac. Inani lemingxuma labalwa ukusuka kwixabiso eliphumayo le-transient chemical potential kunye nobushushu be-elektroniki. Isiphumo siboniswe kwiFig. 4. Sifumanisa ukuba inani lilonke lemingxuma eyi-∼5 × 1012/cm2 idluliselwa ukusuka kwi-WS2 ukuya kwi-graphene ngobomi be-exponential obuyi-1.5 ± 0.2 ps.
Utshintsho lwenani lemingxuma kwi-π-band njengomsebenzi wokulibaziseka kwe-pump-probe kunye nokulingana kwe-exponential okuvelisa ubomi be-1.5 ± 0.2 ps.
Kwizinto ezifunyenweyo kwiMifanekiso 2 ukuya ku-4, kuvela umfanekiso olandelayo we-microscopic wokudluliselwa kwetshaja ekhawulezayo kwisakhiwo se-WS2/graphene heterostructure (Umzobo 5). I-Photoexcitation yesakhiwo se-WS2/graphene heterostructure kwi-2 eV igcwalisa kakhulu i-A-exciton kwi-WS2 (Umzobo 5A). Ukuvuselelwa kwe-elektroniki okongeziweyo kwi-Dirac point kwi-graphene kunye naphakathi kwe-WS2 kunye neebhendi ze-graphene kunokwenzeka ngamandla kodwa akusebenzanga kakuhle. Imingxunya ye-photoexcited kwibhendi ye-valence ye-WS2 izaliswa zii-electron ezivela kwibhendi ye-graphene π kwixesha elifutshane xa kuthelekiswa nesisombululo sethu sexesha (Umzobo 5A). Ii-electron ze-photoexcited kwibhendi yokuqhuba ye-WS2 zinobomi be-∼1 ps (Umzobo 5B). Nangona kunjalo, kuthatha i-∼2 ps ukuzalisa imingxunya kwibhendi ye-graphene π (Umzobo 5B). Oku kubonisa ukuba, ngaphandle kokudluliselwa ngqo kwee-electron phakathi kwebhendi yokuqhuba ye-WS2 kunye nebhendi ye-graphene π, iindlela ezongezelelweyo zokuphumla—mhlawumbi ngokusebenzisa iimeko ezingalunganga (26)—kufuneka ziqwalaselwe ukuze kuqondwe ngokupheleleyo iintshukumo.
(A) I-Photoexcitation xa ivakala kwi-WS2 A-exciton kwi-2 eV ifaka ii-electron kwi-conduction band ye-WS2. Imingxunya ehambelanayo kwi-valence band ye-WS2 igcwaliswa ngoko nangoko zii-electron ezivela kwi-graphene π-band. (B) Ii-photoexcited carriers kwi-conduction band ye-WS2 zinobomi be-∼1 ps. Imingxunya kwi-graphene π-band iphila ixesha elingange-∼2 ps, nto leyo ebonisa ukubaluleka kweendlela ezongezelelweyo zokusasazeka eziboniswa ziintolo eziqhekekileyo. Imigca emnyama eqhekekileyo kwi-(A) kunye ne-(B) ibonisa utshintsho lwebhendi kunye notshintsho kwi-chemical potential. (C) Kwimeko ye-transient, umaleko we-WS2 utshajwa kakubi ngelixa umaleko we-graphene utshajwa kakuhle. Kwi-spin-selective excitation enokukhanya okujikelezileyo, ii-photoexcited electron kwi-WS2 kunye nemingxunya ehambelanayo kwi-graphene kulindeleke ukuba zibonise i-spin polarization eyahlukileyo.
Kwimeko yesikhashana, ii-electron eziphuma kwi-photoexcited zihlala kwibhendi yokuqhuba ye-WS2 ngelixa imingxuma ye-photoexcited ikwibhendi ye-π ye-graphene (Umzobo 5C). Oku kuthetha ukuba umaleko we-WS2 utshajiswe kakubi kwaye umaleko we-graphene utshajiswe kakuhle. Oku kubangela utshintsho lwe-transient peak (Umzobo 2), i-asymmetry yesignali ye-graphene pump-probe (ii-curves 2 kunye ne-3 zoMfanekiso 3), ukungabikho kwemingxuma kwibhendi ye-valence ye-WS2 (i-curve 4 Umfanekiso 3), kunye nemingxuma eyongezelelweyo kwibhendi ye-graphene π (Umzobo 4). Ubomi bale meko yahlulwe yi-charge yi-∼1 ps (i-curve 1 Umfanekiso 3).
Iimeko ezifanayo ze-transient ezahlulwe ngokutshaja ziye zabonwa kwi-van der Waals heterostructures ezinxulumeneyo ezenziwe ngee-semiconductors ezimbini ze-direct-gap ezine-type II band alignment kunye ne-staggered bandgap (27-32). Emva kwe-photoexcitation, ii-electron kunye neengxobo zifunyenwe zihamba ngokukhawuleza ziye ezantsi kwe-conduction band nakwi-top ye-valence band, ngokwahlukeneyo, ezikwii-layers ezahlukeneyo ze-heterostructure (27-32).
Kwimeko yesakhiwo sethu se-WS2/graphene heterostructure, indawo efanelekileyo kakhulu yamandla kwii-electron kunye nemingxuma ikwinqanaba le-Fermi kumaleko we-graphene yesinyithi. Ke ngoko, umntu angalindela ukuba zombini ii-electron kunye nemingxuma zidlulela ngokukhawuleza kwi-graphene π-band. Nangona kunjalo, imilinganiselo yethu ibonisa ngokucacileyo ukuba ukudluliselwa kwemingxuma (<200 fs) kusebenza kakuhle kakhulu kunokudluliselwa kwe-electron (∼1 ps). Sithi oku kubangelwa kukulungelelaniswa kwamandla okunxulumene kwe-WS2 kunye neebhendi ze-graphene njengoko kutyhilwe kwiFig. 1A enika inani elikhulu leemeko zokugqibela ezikhoyo zokudluliselwa kwemingxuma xa kuthelekiswa nokudluliselwa kwe-electron njengoko bekulindelwe kutshanje yi (14, 15). Kwimeko yangoku, xa sicinga nge-∼2 eV WS2 bandgap, i-graphene Dirac point kunye ne-equilibrium chemical potential zifumaneka kwi-∼0.5 kunye ne-∼0.2 eV ngaphezulu kombindi we-WS2 bandgap, ngokulandelanayo, ziphula ulungelelwaniso lwe-electron-hole. Sifumanisa ukuba inani leemeko zokugqibela ezikhoyo zokudluliselwa kwemingxunya likhulu ngokuphindwe ka-∼6 kunezokudluliselwa kwee-electron (jonga kwi-Supplementary Materials), yiyo loo nto ukudluliselwa kwemingxunya kulindeleke ukuba kube ngokukhawuleza kunokudluliselwa kwee-electron.
Umfanekiso opheleleyo we-microscopic wokudluliselwa kwe-charge okungabonakaliyo okubonakalayo, nangona kunjalo, kufuneka uqwalasele ukudibana phakathi kwee-orbitals ezenza umsebenzi we-A-exciton wave kwi-WS2 kunye ne-graphene π-band, ngokulandelanayo, iindlela ezahlukeneyo ze-electron-electron kunye ne-electron-phonon scattering kuquka imida ebekwe yi-momentum, energy, spin, kunye ne-pseudospin conservation, impembelelo ye-plasma oscillations (33), kunye nendima ye-displacitive excitation ye-coherent phonon oscillations enokuthi ilawule ukudluliselwa kwe-charge (34, 35). Kwakhona, umntu unokuqikelela ukuba imeko yokudluliselwa kwe-charge ebonweyo iquka ii-excitons zokudluliselwa kwe-charge okanye ii-pairs ze-electron-hole zasimahla (jonga i-Supplementary Materials). Kufuneka uphando olongezelelweyo oluya ngaphaya kobubanzi bephepha langoku ukuze kucaciswe le micimbi.
Ngamafutshane, sisebenzise i-tr-ARPES ukufunda ukudluliselwa kwe-ultrafast interlayer charge kwi-epitaxial WS2/graphene heterostructure. Sifumanise ukuba, xa sichukunyiswa yi-resonance kwi-A-exciton ye-WS2 kwi-2 eV, imingxunya ye-photoexcited idlulela ngokukhawuleza kwi-graphene layer ngelixa ii-electron ze-photoexcited zihlala kwi-WS2 layer. Sithi oku kungenxa yokuba inani leemo zokugqibela ezikhoyo zokudluliselwa kwe-hole likhulu kunezo zokudluliselwa kwe-electron. Ixesha lobomi be-charge-separated transient state lifunyenwe liyi-∼1 ps. Ngokudibeneyo ne-spin-selective optical excitation kusetyenziswa ukukhanya okujikelezileyo (22–25), ukudluliselwa kwe-ultrafast charge okubonweyo kunokukhatshwa kukudluliselwa kwe-spin. Kule meko, i-WS2/graphene heterostructure ephandiweyo ingasetyenziselwa ukufaka i-optical spin ephumelelayo kwi-graphene okubangela izixhobo ezintsha ze-optospintronic.
Iisampulu ze-graphene zikhuliswe kwii-wafers ze-6H-SiC(0001) ezithengiswayo ezivela kwiSiCrystal GmbH. Ii-wafers ezine-N zazikwi-axis ene-miscut engaphantsi kwe-0.5°. I-substrate ye-SiC yachetywa nge-hydrogen ukuze kususwe imikrwelo kwaye kufunyanwe ii-terraces ezithe tyaba eziqhelekileyo. Umphezulu ococekileyo nothe tyaba we-Si-evalwe nge-atomic emva koko wahluzwa nge-graphit ngokufaka isampuli kwi-atmosphere ye-Ar kwi-1300°C imizuzu esi-8 (36). Ngale ndlela, sifumene umaleko omnye wekhabhoni apho i-atom nganye yesithathu yekhabhoni yakha i-covalent bond kwi-substrate ye-SiC (37). Olu maleko lwaguqulwa lwaba yi-graphene exutywe ngokupheleleyo ye-sp2-hybridized quasi free-standing hole-doped graphene ngokusebenzisa i-hydrogen intercalation (38). Ezi sampuli zibizwa ngokuba yi-graphene/H-SiC(0001). Yonke le nkqubo yenziwe kwigumbi lokukhula le-Black Magic elithengiswayo elivela kwi-Aixtron. Ukukhula kwe-WS2 kwenziwe kwi-reactor eqhelekileyo yodonga olushushu ngokufaka umphunga wekhemikhali ophantsi koxinzelelo (39, 40) kusetyenziswa iipowder ze-WO3 kunye ne-S ezinomlinganiselo wobunzima we-1:100 njengezinto ezingaphambili. Iipowder ze-WO3 kunye ne-S zigcinwe kwi-900 kunye ne-200°C, ngokulandelelana. Ipowder ye-WO3 ibekwe kufutshane ne-substrate. I-Argon isetyenziswe njengegesi yokuthwala enokuhamba kwe-8 sccm. Uxinzelelo kwi-reactor lugcinwe kwi-0.5 mbar. Iisampuli zibonakaliswe nge-secondary electron microscopy, i-atomic force microscopy, i-Raman, kunye ne-photoluminescence spectroscopy, kunye ne-low-energy electron diffraction. Ezi zilinganiso zityhile ii-domains ezimbini ezahlukeneyo ze-WS2 single-crystalline apho i-ΓK- okanye i-ΓK'-direction ihambelana ne-ΓK-direction ye-graphene layer. Ubude becala ledomeyini bahluka phakathi kwe-300 kunye ne-700 nm, kwaye ugubungela lonke i-WS2 luqikelelwa kwi-∼40%, olufanele uhlalutyo lwe-ARPES.
Uvavanyo lwe-static ARPES lwenziwe nge-hemispherical analyzer (SPECS PHOIBOS 150) kusetyenziswa inkqubo ye-charge-coupled device-detector ukuze kufunyanwe amandla e-electron kunye ne-momentum. I-unpolarized, monochromatic He Iα radiation (21.2 eV) yomthombo we-high-flux He discharge source (VG Scienta VUV5000) yasetyenziswa kuzo zonke iimvavanyo ze-photoemission. Amandla kunye nesisombululo se-angular kwiimvavanyo zethu zazingcono kune-30 meV kunye ne-0.3° (ehambelana ne-0.01 Å−1), ngokwahlukeneyo. Zonke iimvavanyo zenziwe kubushushu begumbi. I-ARPES yindlela evakalelwa kakhulu ngumphezulu. Ukukhupha ii-photoelectrons kwi-WS2 kunye nomgangatho we-graphene, kwasetyenziswa iisampulu ezine-WS2 coverage engaphelelanga ye-∼40%.
Useto lwe-tr-ARPES lwalusekelwe kwi-amplifier ye-1-kHz Titanium:Sapphire (Coherent Legend Elite Duo). I-2 mJ yamandla okukhupha asetyenziselwe ukuvelisa i-harmonics ephezulu kwi-argon. Ukukhanya okugqithisileyo kwe-ultraviolet okubangelwe kudlule kwi-monochromator ye-grating evelisa ii-pulses ze-probe ze-100-fs kumandla e-photon e-26-eV. I-8mJ yamandla okukhupha i-amplifier ithunyelwe kwi-amplifier ye-optical parametric (HE-TOPAS evela kwi-Light Conversion). I-signal beam kwi-1-eV photon energy yaphindaphindwa kabini kwi-beta barium borate crystal ukuze kufunyanwe ii-pulses ze-2-eV pump. Ukulinganiswa kwe-tr-ARPES kwenziwe nge-hemispherical analyzer (SPECS PHOIBOS 100). Amandla apheleleyo kunye nesisombululo sexesha yayiyi-240 meV kunye ne-200 fs, ngokwahlukeneyo.
Izinto ezongezelelweyo zeli nqaku zifumaneka apha http://advances.sciencemag.org/cgi/content/full/6/20/eaay0761/DC1
Eli linqaku elivulelekileyo elisasazwa phantsi kwemigaqo yelayisensi yeCreative Commons Attribution-NonCommercial, evumela ukusetyenziswa, ukusasazwa, kunye nokuveliswa kwakhona kuyo nayiphi na indlela, okoko nje ukusetyenziswa okubangelwayo kungekuko inzuzo yezorhwebo kwaye ukuba umsebenzi wokuqala ucatshulwe ngokufanelekileyo.
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Lo mbuzo ngowokuvavanya ukuba ungumntu ondwendweleyo okanye awunguye, kwaye uthintele ukuthunyelwa kwe-spam ngokuzenzekelayo.
NguSven Aeschlimann, Antonio Rossi, Mariana Chávez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Sityhila ukwahlulwa kwetshaja ekhawulezayo kakhulu kwisakhiwo se-WS2/graphene esinokuthi sivumele i-optical spin injection kwi-graphene.
NguSven Aeschlimann, Antonio Rossi, Mariana Chávez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Sityhila ukwahlulwa kwetshaja ekhawulezayo kakhulu kwisakhiwo se-WS2/graphene esinokuthi sivumele i-optical spin injection kwi-graphene.
© 2020 Umbutho waseMelika wokuPhucula iNzululwazi. Onke Amalungelo Agciniwe. I-AAAS ngumlingane we-HINARI, i-AGORA, i-OARE, i-CHORUS, i-CLOCKSS, i-CrossRef kunye ne-COUNTER.I-Science Advances ISSN 2375-2548.
Ixesha lokuthumela: Meyi-25-2020