Sisebenzisa i-photoemission spectroscopy exazululwe ngesikhathi kanye ne-angle (tr-ARPES) ukuphenya ukudluliselwa kweshaja okusheshayo kakhulu ku-heterostructure ye-epitaxial eyenziwe nge-monolayer WS2 kanye ne-graphene. Lesi sakhiwo se-heterostructure sihlanganisa izinzuzo ze-semiconductor ye-direct-gap ene-spin-orbit coupling enamandla kanye nokusebenzisana okunamandla kwe-light-matter nalezo ze-semimetal hosting massless carriers ezinokunyakaza okuphezulu kakhulu kanye nokuphila isikhathi eside kwe-spin. Sithola ukuthi, ngemva kwe-photoexcitation ekuphenduleni kwe-A-exciton ku-WS2, izimbobo ze-photoexcited zidlulela ngokushesha kungqimba lwe-graphene kuyilapho ama-electron e-photoexcited ehlala kungqimba lwe-WS2. Isimo se-transient esihlukaniswe ngeshaja esiphumelayo sitholakala sinokuphila isikhathi esingu-∼1 ps. Sithi okutholakele kwethu kuhlukile esikhaleni sesigaba sokuhlakazeka okubangelwa ukulingana okuhlobene kwama-WS2 nama-graphene band njengoba kwembulwe yi-ARPES enesinqumo esiphezulu. Ngokuhambisana ne-spin-selective optical excitation, i-WS2/graphene heterostructure ehloliwe ingahlinzeka ngeplatifomu yokufaka i-optical spin ephumelelayo ku-graphene.
Ukutholakala kwezinto eziningi ezahlukene ezinezinhlangothi ezimbili kuvule ithuba lokudala izakhiwo ezintsha ezihlukene ekugcineni ezinemisebenzi emisha ngokuphelele esekelwe ekuhlolweni kwe-dielectric okwenziwe ngokwezifiso kanye nemiphumela ehlukahlukene ebangelwa ukusondela (1–3). Amadivayisi obufakazi bezimiso zezinhlelo zokusebenza zesikhathi esizayo emkhakheni we-elekthronikhi kanye ne-optoelectronics atholakale (4–6).
Lapha, sigxila kuma-heterostructures epitaxial van der Waals aqukethe i-monolayer WS2, i-semiconductor eqondile ene-spin-orbit coupling enamandla kanye nokuhlukaniswa okukhulu kwe-spin kwesakhiwo se-band ngenxa yokwephulwa kwe-inversion symmetry (7), kanye ne-monolayer graphene, i-semimetal enesakhiwo se-conical band kanye nokuhamba okuphezulu kakhulu kwe-carrier (8), ekhuliswe ku-hydrogen-terminated SiC(0001). Izinkomba zokuqala zokudluliselwa kwe-ultrafast charge (9-15) kanye nemiphumela ye-spin-orbit coupling ebangelwa ukusondelana (16-18) zenza i-WS2/graphene kanye nama-heterostructures afanayo abe yizimbangi ezithembisayo zezinhlelo zokusebenza ze-optoelectronic zesikhathi esizayo (19) kanye ne-optospintronic (20).
Siqale ukwembula izindlela zokuphumula zama-electron-hole pair akhiqizwa nge-photogenerated ku-WS2/graphene nge-photoemission spectroscopy enesikhathi kanye ne-angle-resolved (tr-ARPES). Ngaleyo njongo, sivusa i-heterostructure ngama-pulse e-2-eV pump ahambisana ne-A-exciton ku-WS2 (21, 12) bese sikhipha ama-photoelectron nge-pulse ye-probe eyephuzile yesibili ku-26-eV photon energy. Sinquma amandla e-kinetic kanye ne-engeli yokukhishwa kwama-photoelectron nge-hemispherical analyzer njengomsebenzi wokulibaziseka kwe-pump-probe ukuze sifinyelele ku-momentum-, energy-, kanye ne-time-resolved carrier dynamics. Isixazululo samandla nesikhathi singama-240 meV kanye nama-200 fs, ngokulandelana.
Imiphumela yethu inikeza ubufakazi obuqondile bokudluliselwa kweshaja okusheshayo phakathi kwezingqimba eziqondiswe ngendlela ye-epitaxially, okuqinisekisa izinkomba zokuqala ezisekelwe kumasu e-all-optical kuma-heterostructures afanayo ahlanganiswe ngesandla anokulungiswa kwe-azimuthal okungahleliwe kwezingqimba (9-15). Ngaphezu kwalokho, sibonisa ukuthi lokhu kudluliswa kweshaja akulingani kakhulu. Ukulinganisa kwethu kwembula isimo sesikhashana esihlukaniswe ngeshaja esingakaze sibonwe ngaphambili esinama-electron ane-photoexcited kanye nezimbobo ezitholakala kungqimba lwe-WS2 kanye ne-graphene, ngokulandelana, esiphila isikhathi esingama-∼1 ps. Sichaza okutholakele kwethu ngokwehluka kwesikhala sesigaba sokuhlakazeka sokudluliselwa kwe-electron kanye nezimbobo okubangelwa ukulungiswa okuhlobene kwama-WS2 nama-graphene band njengoba kwembulwe yi-ARPES enesinqumo esiphezulu. Kuhlanganiswe nokuvuselelwa kwe-optical kwe-spin- kanye ne-valley-selective (22-25) ama-heterostructures e-WS2/graphene anganikeza ipulatifomu entsha yokufaka i-ultrafast optical spin ephumelelayo ku-graphene.
Isithombe 1A sibonisa ukulinganiswa kwe-ARPES okunesinqumo esiphezulu okutholwe ngesibani se-helium sesakhiwo sebhendi eceleni kwe-ΓK-direction ye-epitaxial WS2/graphene heterostructure. Ikhoni ye-Dirac itholakale inembobo lapho iphuzu le-Dirac litholakala ku-∼0.3 eV ngaphezu kwekhono lamakhemikhali e-equilibrium. Ingxenye ephezulu yebhendi ye-valence ye-WS2 e-spin-split itholakale ku-∼1.2 eV ngaphansi kwekhono lamakhemikhali e-equilibrium.
(A) I-photocurrent yokulingana elinganiswe ngendlela ye-ΓK ngesibani se-helium esingavulwanga. (B) I-Photocurrent yokulibaziseka kwe-pump-probe okunegative okulinganiswe ngama-pulse e-ultraviolet avulwa kakhulu e-p-polarized ku-26-eV photon energy. Imigqa empunga nebomvu egqagqene iphawula indawo yamaphrofayili omugqa asetshenziselwa ukukhipha izikhundla ze-transient peak ku-Fig. 2. (C) Izinguquko ezibangelwa yi-pump ze-photocurrent engu-200 fs ngemuva kwe-photoexcitation ku-photon energy ye-pump photon engu-2 eV ene-pump fluence engu-2 mJ/cm2. Ukuzuza nokulahlekelwa kwama-photoelectron kuboniswa ngokubomvu nangokuluhlaza okwesibhakabhaka, ngokulandelana. Amabhokisi abonisa indawo yokuhlanganiswa kwe-pump-probe traces eboniswe ku-Fig. 3.
Isithombe 1B sibonisa isithombe se-tr-ARPES sesakhiwo sebhendi esiseduze ne-WS2 kanye nama-graphene K-points alinganiswe ngama-pulse e-ultraviolet aqine kakhulu angu-100-fs kumandla e-photon angu-26-eV ekubambezelekeni kwe-pump-probe okungekuhle ngaphambi kokufika kwe-pulse yephampu. Lapha, ukuhlukana kwe-spin akuxazululwa ngenxa yokuwohloka kwesampula kanye nokuba khona kwe-pulse yephampu engu-2-eV okubangela ukwanda kweshaja yesikhala kwezici ze-spectral. Isithombe 1C sibonisa izinguquko ezibangelwa yi-pump ze-photocurrent maqondana ne-Fig. 1B ekubambezelekeni kwe-pump-probe okungu-200 fs lapho isignali ye-pump-probe ifinyelela khona esiphezulu. Imibala ebomvu neluhlaza okwesibhakabhaka ikhombisa inzuzo nokulahlekelwa kwama-photoelectron, ngokulandelana.
Ukuze sihlaziye lokhu kuguquguquka okucebile ngemininingwane eminingi, siqala ngokunquma izindawo ze-transient peak ze-WS2 valence band kanye ne-graphene π-band emigqeni enemigqa egqamile ku-Fig. 1B njengoba kuchaziwe ngokuningiliziwe ku-Supplementary Materials. Sithola ukuthi i-WS2 valence band ishintsha phezulu ngo-90 meV (Fig. 2A) kanye ne-graphene π-band ishintsha phansi ngo-50 meV (Fig. 2B). Isikhathi sokuphila salezi zinguquko sitholakala singu-1.2 ± 0.1 ps ye-valence band ye-WS2 kanye no-1.7 ± 0.3 ps ye-graphene π-band. Lezi zinguquko ze-peak zinikeza ubufakazi bokuqala bokushaja kwe-transient kwezingqimba ezimbili, lapho ishaja eyengeziwe (engemihle) ikhulisa (inciphisa) amandla okubopha ezimo ze-elekthronikhi. Qaphela ukuthi i-upshift ye-WS2 valence band inesibopho sesignali evelele ye-pump-probe endaweni ephawulwe ibhokisi elimnyama ku-Fig. 1C.
Ushintsho endaweni ephakeme yebhendi ye-valence ye-WS2 (A) kanye nebhendi ye-graphene π (B) njengomsebenzi wokubambezeleka kwe-pump-probe kanye nokulingana kwe-exponential (imigqa ejiyile). Isikhathi sokuphila se-WS2 shift in (A) singu-1.2 ± 0.1 ps. Isikhathi sokuphila se-graphene shift in (B) singu-1.7 ± 0.3 ps.
Okulandelayo, sihlanganisa isignali ye-pump-probe ezindaweni ezikhonjiswe ngamabhokisi anombala ku-Fig. 1C bese sihlela ukubalwa okuphumayo njengomsebenzi wokubambezeleka kwe-pump-probe ku-Fig. 3. I-Curve 1 ku-Fig. 3 ikhombisa ukuguquguquka kwabathwali be-photoexcited eduze nephansi kwebhendi yokuqhuba yengqimba ye-WS2 ngokuphila okungu-1.1 ± 0.1 ps okutholwe ngokufanelana kwedatha (bheka Izinto Ezingeziwe).
Imikhondo ye-pump-probe njengomsebenzi wokulibaziseka okutholakele ngokuhlanganisa i-photocurrent endaweni ekhonjiswe emabhokisini ku-Fig. 1C. Imigqa ewugqinsi ifanelana nedatha. I-Curve (1) Inani labathwali besikhashana ebhendini lokuqhuba le-WS2. I-Curve (2) Isignali ye-pump-probe yebhendi ye-π ye-graphene ngaphezu kwe-equilibrium chemical potential. I-Curve (3) Isignali ye-pump-probe yebhendi ye-π ye-graphene ngaphansi kwe-equilibrium chemical potential. I-Curve (4) Isignali ye-net pump-probe ebhendini ye-valence ye-WS2. Isikhathi sokuphila sitholakala singu-1.2 ± 0.1 ps ku-(1), 180 ± 20 fs (inzuzo) kanye no-∼2 ps (ukulahlekelwa) ku-(2), kanye no-1.8 ± 0.2 ps ku-(3).
Kuma-curve 2 no-3 ku-Fig. 3, sibonisa isignali ye-pump-probe ye-graphene π-band. Sithola ukuthi inzuzo yama-electron ngaphezu kwe-equilibrium chemical potential (i-curve 2 ku-Fig. 3) inokuphila okufushane kakhulu (180 ± 20 fs) uma kuqhathaniswa nokulahlekelwa kwama-electron ngaphansi kwe-equilibrium chemical potential (1.8 ± 0.2 ps ku-curve 3 ku-Fig. 3). Ngaphezu kwalokho, inzuzo yokuqala ye-photocurrent ku-curve 2 ku-Fig. 3 itholakala iphenduka ukulahlekelwa ku-t = 400 fs kanye nokuphila okungu-∼2 ps. I-asymmetry phakathi kwenzuzo nokulahlekelwa itholakala ingekho ku-pump-probe signal ye-uncovered monolayer graphene (bheka umfanekiso S5 ku-Supplementary Materials), okubonisa ukuthi i-asymmetry iwumphumela wokuhlanganiswa kwe-interlayer ku-heterostructure ye-WS2/graphene. Ukuqaphela inzuzo yesikhashana kanye nokulahlekelwa isikhathi eside ngaphezu nangaphansi kwamandla e-equilibrium chemical, ngokulandelana, kubonisa ukuthi ama-electron asuswa kahle ku-graphene layer lapho kuphuma i-photoexcitation ye-heterostructure. Ngenxa yalokho, ungqimba lwe-graphene luba ne-positive charge, okuhambisana nokwanda kwamandla okubopha e-π-band okutholakala ku-Fig. 2B. Ukwehla kwe-π-band kususa umsila wamandla aphezulu wokusatshalaliswa kwe-equilibrium Fermi-Dirac ngaphezu kwamandla e-equilibrium chemical, okuchaza ngokwengxenye ushintsho lwesibonakaliso sesignali ye-pump-probe ku-curve 2 ye-Fig. 3. Sizobonisa ngezansi ukuthi lo mphumela uthuthukiswa kakhulu ukulahleka kwesikhashana kwama-electron ku-π-band.
Lesi simo sisekelwa isignali ye-net pump-probe yebhendi ye-WS2 valence ku-curve 4 ye-Fig. 3. Le datha itholwe ngokuhlanganisa ukubalwa kwendawo enikezwe yibhokisi elimnyama ku-Fig. 1B elibamba ama-electron akhishwa nge-photoemission avela kubhendi ye-valence kuzo zonke izikhathi zokulibaziseka kwe-pump-probe. Ngaphakathi kwemigqa yephutha lokuhlola, asitholi sibonakaliso sokuba khona kwemigodi kubhendi ye-valence ye-WS2 yanoma yikuphi ukulibaziseka kwe-pump-probe. Lokhu kubonisa ukuthi, ngemva kokukhipha i-photoexcitation, le migodi igcwaliswa ngokushesha ngesikhathi esifushane uma kuqhathaniswa nesinqumo sethu sesikhathi.
Ukuze sinikeze ubufakazi bokugcina bombono wethu wokuhlukaniswa kweshaja okusheshayo kakhulu kusakhiwo se-WS2/graphene heterostructure, sinquma inani lemigodi edluliselwe kungqimba lwe-graphene njengoba kuchaziwe ngokuningiliziwe ku-Supplementary Materials. Ngamafuphi, ukusatshalaliswa kwe-electronic transient kwe-π-band kwafakwa ukusatshalaliswa kwe-Fermi-Dirac. Inani lemigodi labe selibalwa kusukela kumanani atholakele we-transient chemical potential kanye nokushisa kwe-electronic. Umphumela uboniswe ku-Fig. 4. Sithola ukuthi inani eliphelele lemigodi engu-∼5 × 1012/cm2 idluliselwa kusuka ku-WS2 iye ku-graphene ngokuphila kwesikhathi eside okungu-1.5 ± 0.2 ps.
Ukushintsha kwenani lezimbobo ku-π-band njengomsebenzi wokubambezeleka kwe-pump-probe kanye nokulingana kwe-exponential okunikeza impilo yonke engu-1.5 ± 0.2 ps.
Kusukela kokutholakele ku-Figs. 2 kuya ku-4, kuvela isithombe esilandelayo esincane kakhulu sokudluliselwa kweshaja okusheshayo ku-heterostructure ye-WS2/graphene (Isithombe 5). I-Photoexcitation ye-heterostructure ye-WS2/graphene ku-2 eV igcwalisa kakhulu i-A-exciton ku-WS2 (Isithombe 5A). Ukwengezwa komoya kagesi ngaphesheya kwephuzu le-Dirac ku-graphene kanye naphakathi kwama-WS2 nama-graphene band kungenzeka ngamandla kodwa kuncane kakhulu ukusebenza kahle. Izimbobo ezi-photoexcited ku-valence band ye-WS2 zigcwaliswa ngama-electron avela ku-graphene π-band ngesikhathi esifushane uma kuqhathaniswa nesinqumo sethu sesikhathi (Isithombe 5A). Ama-electron a-photoexcited ku-conduction band ye-WS2 anempilo ye-∼1 ps (Isithombe 5B). Kodwa-ke, kuthatha i-∼2 ps ukugcwalisa izimbobo ku-graphene π-band (Isithombe 5B). Lokhu kubonisa ukuthi, ngaphandle kokudluliselwa kwe-electron ngqo phakathi kwebhendi yokuqhuba i-WS2 kanye nebhendi ye-graphene π, izindlela ezengeziwe zokuphumula—mhlawumbe ngezimo zokukhubazeka (26)—zidinga ukucatshangelwa ukuze kuqondwe amandla aphelele.
(A) I-Photoexcitation lapho i-resonance i-WS2 A-exciton ku-2 eV ifaka ama-electron ebhendini lokuhambisa i-WS2. Izimbobo ezihambisanayo ebhendini le-valence le-WS2 zigcwaliswa ngokushesha ngama-electron avela ebhendini le-graphene π. (B) Abathwali be-photoexcited ebhendini lokuhambisa i-WS2 banesikhathi sokuphila esingu-∼1 ps. Izimbobo ebhendini le-graphene π zihlala isikhathi esingu-∼2 ps, okubonisa ukubaluleka kweziteshi ezengeziwe zokuhlakazeka eziboniswa yimicibisholo ephukile. Imigqa emnyama ephukile ku-(A) kanye no-(B) ikhombisa ukushintsha kwebhendi kanye nezinguquko emandleni amakhemikhali. (C) Esimweni esidlulayo, ungqimba lwe-WS2 lushajwa kabi kuyilapho ungqimba lwe-graphene lushajwa kahle. Ngokuvuselelwa okukhethayo kwe-spin ngokukhanya okujikelezayo okuhlanganisiwe, ama-electron ephukile ku-WS2 kanye nezimbobo ezihambisanayo ku-graphene kulindeleke ukuthi zibonise i-spin polarization ephambene.
Esimweni esishintshashintshayo, ama-electron aphumayo ahlala ebhendini lokuhambisa i-WS2 kuyilapho imigodi ephumayo itholakala ebhendini le-π le-graphene (Umfanekiso 5C). Lokhu kusho ukuthi ungqimba lwe-WS2 lushajwe kabi kanti ungqimba lwe-graphene lushajwe kahle. Lokhu kuchaza ukushintshashintsha kwe-peak okushintshashintshayo (Umfanekiso 2), ukungalingani kwesignali ye-graphene pump-probe (ama-curve 2 no-3 ku-Umfanekiso 3), ukungabikho kwemigodi ebhendini le-valence le-WS2 (i-curve 4 Umfanekiso 3), kanye nemigodi eyengeziwe ebhendini le-graphene π (Umfanekiso 4). Isikhathi sokuphila salesi simo esihlukaniswe ngokushaja singu-∼1 ps (i-curve 1 Umfanekiso 3).
Izimo ezifanayo zesikhashana ezihlukaniswe ngokushaja ziye zabonwa kuma-heterostructures ahlobene e-van der Waals enziwe ngama-semiconductor amabili e-direct-gap ane-type II band alignment kanye ne-staggered bandgap (27-32). Ngemva kwe-photoexcitation, ama-electron kanye nezimbobo kutholakale ukuthi ahamba ngokushesha aye phansi kwe-conduction band kanye naphezulu kwe-valence band, ngokulandelana, atholakala ezingqimbeni ezahlukene ze-heterostructure (27-32).
Endabeni yesakhiwo sethu se-WS2/graphene heterostructure, indawo engcono kakhulu yamandla ama-electron kanye nemigodi isezingeni le-Fermi kungqimba lwe-graphene yensimbi. Ngakho-ke, umuntu angalindela ukuthi womabili ama-electron kanye nemigodi adlulela ngokushesha ku-graphene π-band. Kodwa-ke, izilinganiso zethu zibonisa ngokusobala ukuthi ukudluliselwa kwemigodi (<200 fs) kusebenza kahle kakhulu kunokudluliselwa kwe-electron (∼1 ps). Sithi lokhu kubangelwa ukulungelelaniswa kwamandla okuhlobene kwe-WS2 kanye ne-graphene bands njengoba kwembulwe ku-Fig. 1A okunikeza inani elikhulu lezimo zokugcina ezitholakalayo zokudluliselwa kwemigodi uma kuqhathaniswa nokudluliselwa kwe-electron njengoba kulindelwe muva nje yi-(14, 15). Kulesi simo samanje, uma sicabanga nge-∼2 eV WS2 bandgap, i-graphene Dirac point kanye ne-equilibrium chemical potential zitholakala ku-∼0.5 kanye no-∼0.2 eV ngaphezu kwe-maphakathi ne-WS2 bandgap, ngokulandelana, ziphula ukulingana kwe-electron-hole. Sithola ukuthi inani lezimo zokugcina ezitholakalayo zokudluliselwa kwemigodi likhulu ngokuphindwe ka-∼6 kunezokudluliselwa kwama-electron (bheka Izinto Ezingeziwe), yingakho ukudluliselwa kwemigodi kulindeleke ukuthi kube ngokushesha kunokudluliselwa kwama-electron.
Isithombe esiphelele esincane kakhulu sokudluliswa kweshaja okungabonakali okusheshayo kufanele, nokho, sicabangele ukuhlangana phakathi kwama-orbitals akha umsebenzi wegagasi le-A-exciton ku-WS2 kanye ne-graphene π-band, ngokulandelana, iziteshi ezahlukene zokusabalala kwe-electron-electron kanye ne-electron-phonon kufaka phakathi imikhawulo ebekwa ukugcinwa kwe-momentum, amandla, i-spin, kanye ne-pseudospin, ithonya le-plasma oscillations (33), kanye nendima yokuvuselelwa okungenzeka kwe-displacitive kwe-coherent phonon oscillations okungase kuqondise ukudluliswa kweshaja (34, 35). Futhi, umuntu angacabanga ukuthi isimo sokudluliswa kweshaja esibonwe siqukethe ama-exciton okudluliselwa kweshaja noma ama-pair amahhala e-electron-hole (bheka Izinto Ezingeziwe). Kudingeka olunye ucwaningo lwethiyori oludlula ububanzi bephepha lamanje ukuze kucaciswe lezi zinkinga.
Ngamafuphi, sisebenzise i-tr-ARPES ukutadisha ukudluliselwa kweshaja ye-ultrafast interlayer ku-heterostructure ye-epitaxial WS2/graphene. Sithole ukuthi, lapho sishukunyiswa yi-resonance ku-A-exciton ye-WS2 ku-2 eV, imigodi ye-photoexcited idlulisela ngokushesha ku-graphene layer kuyilapho ama-electron e-photoexcited ehlala ku-WS2 layer. Sithi lokhu kungenxa yokuthi inani lezimo zokugcina ezitholakalayo zokudluliselwa kwembobo likhulu kunezokudluliselwa kwama-electron. Isikhathi sokuphila sesimo sesikhashana esihlukaniswe ngeshaja sitholakale singama-∼1 ps. Ngokuhambisana nokuvuselelwa kwe-optical optical okukhethayo kusetshenziswa ukukhanya okujikelezile okuhlanganisiwe (22-25), ukudluliselwa kweshaja ye-ultrafast okubonwe kungahambisana nokudluliselwa kwe-spin. Kulesi simo, i-heterostructure ye-WS2/graphene ehloliwe ingasetshenziswa ekufakweni kwe-optical spin ephumelelayo ku-graphene okuholela kumadivayisi amasha e-optospintronic.
Amasampula e-graphene akhuliswe kuma-wafer e-6H-SiC(0001) e-commercial semiconducting avela ku-SiCrystal GmbH. Ama-wafer ane-N aye-on-axis ene-miscut engaphansi kuka-0.5°. I-substrate ye-SiC yaqoshwa nge-hydrogen ukuze kususwe imihuzuko futhi kutholakale ama-terrace ajwayelekile ayisicaba. Ubuso obuhlanzekile nobusicaba obuqediwe nge-atomic babe sebuqoshwa nge-graphit ngokufaka isampula emoyeni we-Ar ku-1300°C imizuzu engu-8 (36). Ngale ndlela, sithole ungqimba olulodwa lwe-carbon lapho i-athomu ngayinye yesithathu ye-carbon yakha isibopho se-covalent ku-substrate ye-SiC (37). Lolu ngqimba lwabe seluguqulwa lwaba yi-graphene ene-hole-doped doped exubile ngokuphelele ye-sp2-hybrided quasi free-standing nge-hydrogen intercalation (38). Lawa masampula abizwa ngokuthi i-graphene/H-SiC(0001). Yonke inqubo yenziwa ekamelweni lokukhula le-Black Magic elithengiswayo elivela ku-Aixtron. Ukukhula kwe-WS2 kwenziwa ku-reactor ejwayelekile yodonga olushisayo ngokufaka umhwamuko wamakhemikhali ophansi (39, 40) kusetshenziswa izimpushana ze-WO3 kanye ne-S ezinesilinganiso sobunzima esingu-1:100 njengezinto ezingaphambili. Izimpushana ze-WO3 kanye ne-S zigcinwe ku-900 kanye no-200°C, ngokulandelana. Impushana ye-WO3 ibekwe eduze kwe-substrate. I-Argon isetshenziswe njengegesi yokuthwala enokuhamba okungu-8 sccm. Ingcindezi ku-reactor igcinwe ku-0.5 mbar. Amasampula abonakala nge-secondary electron microscopy, i-atomic force microscopy, i-Raman, kanye ne-photoluminescence spectroscopy, kanye ne-low-energy electron diffraction. Lezi zilinganiso zembule izizinda ezimbili ezihlukene ze-WS2 single-crystalline lapho i-ΓK- noma i-ΓK'-direction ihambisana ne-ΓK-direction yengqimba ye-graphene. Ubude bezinhlangothi zesizinda bebuhluka phakathi kuka-300 no-700 nm, kanti ukumbozwa okuphelele kwe-WS2 kulinganiselwa ku-∼40%, okufanelekela ukuhlaziywa kwe-ARPES.
Ukuhlolwa kwe-static ARPES kwenziwe nge-hemispherical analyzer (SPECS PHOIBOS 150) kusetshenziswa uhlelo lwe-charge-coupled device-detector ukuthola amandla e-electron kanye ne-momentum enezinhlangothi ezimbili. Imisebe ye-He Iα engashintshiwe, e-monochromatic (21.2 eV) yomthombo wokukhipha i-He ephezulu (VG Scienta VUV5000) yasetshenziswa kuzo zonke izivivinyo ze-photoemission. Amandla kanye ne-angle resolution kuzivivinyo zethu kwakungcono kune-30 meV kanye ne-0.3° (okuhambisana ne-0.01 Å−1), ngokulandelana. Zonke izivivinyo zenziwa ekushiseni kwegumbi. I-ARPES iyindlela ezwela kakhulu ebusweni. Ukukhipha ama-photoelectron kokubili ku-WS2 kanye ne-graphene layer, kwasetshenziswa amasampula ane-WS2 coverage engaphelele engu-∼40%.
Ukusethwa kwe-tr-ARPES kwakusekelwe ku-amplifier ye-Titanium:Sapphire engu-1-kHz (i-Coherent Legend Elite Duo). Amandla okukhipha angu-2 mJ asetshenziselwa ukukhiqiza ama-harmonics aphezulu ku-argon. Ukukhanya okukhulu kwe-ultraviolet okwaphumela kudlule ku-monochromator ye-grating ekhiqiza ama-pulse e-probe angu-100-fs kumandla e-photon angu-26-eV. Amandla okukhipha angu-8mJ athunyelwe ku-amplifier ye-optical parametric (i-HE-TOPAS evela ku-Light Conversion). Ukukhanya kwesignali kumandla e-photon angu-1-eV kwaphindwa kabili ku-beta barium borate crystal ukuthola ama-pulse e-pump angu-2-eV. Ukulinganiswa kwe-tr-ARPES kwenziwa nge-hemispherical analyzer (SPECS PHOIBOS 100). Amandla aphelele kanye nesisombululo sesikhathi kwakungu-240 meV kanye no-200 fs, ngokulandelana.
Izinto ezengeziwe zalesi sihloko ziyatholakala ku-http://advances.sciencemag.org/cgi/content/full/6/20/eaay0761/DC1
Lesi yisihloko esivulelekile esisatshalaliswa ngaphansi kwemigomo yelayisensi ye-Creative Commons Attribution-NonCommercial, evumela ukusetshenziswa, ukusatshalaliswa, kanye nokukhiqizwa kabusha kunoma iyiphi indlela, inqobo nje uma ukusetshenziswa okuphumelayo kungengenxa yenzuzo yezentengiselwano futhi uma nje umsebenzi wokuqala ucashunwe kahle.
QAPHELA: Sicela ikheli lakho le-imeyili kuphela ukuze umuntu oncoma ikhasi azi ukuthi ubufuna alibone, nokuthi akulona iposi elingafuneki. Asithathi noma yiliphi ikheli le-imeyili.
Lo mbuzo ungowokuhlola ukuthi ungumuntu ovakashile noma cha nokuvimbela ukuthunyelwa kogaxekile okuzenzakalelayo.
Ngu Sven Aeschlimann, Antonio Rossi, Mariana Chávez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Sembula ukuhlukaniswa kweshaja okusheshayo kakhulu kusakhiwo se-WS2/graphene esivumela ukujova kwe-optical spin ku-graphene.
Ngu Sven Aeschlimann, Antonio Rossi, Mariana Chávez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Sembula ukuhlukaniswa kweshaja okusheshayo kakhulu kusakhiwo se-WS2/graphene esivumela ukujova kwe-optical spin ku-graphene.
© 2020 Inhlangano YaseMelika Yokuthuthukiswa Kwesayensi. Wonke Amalungelo Agodliwe. I-AAAS inguzakwethu we-HINARI, AGORA, OARE, CHORUS, CLOCKSS, CrossRef kanye ne-COUNTER.Science Advances ISSN 2375-2548.
Isikhathi sokuthunyelwe: Meyi-25-2020