Sisebenzisa i-photoemission spectroscopy exazululwe isikhathi ne-engeli (tr-ARPES) ukuze siphenye ukudluliswa kweshaji okushesha kakhulu ku-epitaxial heterostructure eyenziwe nge-monolayer WS2 ne-graphene. Lesi sakhiwo se-heterostructure sihlanganisa izinzuzo ze-semiconductor ye-direct-gap ene-spin-orbit coupling eqinile kanye nokusebenzisana okuqinile kwe-light-matter nalezo ze-semimetal hosting massless carriers ezinokuhamba okuphezulu kakhulu nempilo ende ye-spin. Sithola ukuthi, ngemva kwe-photoexcitation ekukhanyeni kwe-A-exciton ku-WS2, izimbobo ezine-photoexcited zidlulisela ngokushesha kungqimba lwe-graphene kuyilapho ama-electron e-photoexcited ehlala kusendlalelo se-WS2. Isimo sesikhashana esihlukaniswe ngokukhokhiswa sitholakala sinesikhathi sokuphila esingu-∼1 ps. Sibeka esikutholile ngenxa yomehluko esikhaleni sesigaba esihlakazekayo esibangelwa ukuqondana okuhlobene kwe-WS2 namabhendi e-graphene njengoba kuvezwe i-ARPES yokulungiswa okuphezulu. Ngokuhlanganiswa ne-spin-selective Optical excitation, i-WS2/graphene heterostructure ephenyiwe ingase inikeze inkundla yomjovo osebenza kahle we-optical spin ku-graphene.
Ukutholakala kwezinto eziningi ezihlukene ezinezinhlangothi ezimbili kuvule ithuba lokudala ama-heterostructures anoveli ekugcineni azacile anokusebenza okusha ngokuphelele okusekelwe ekuhlolweni kwe-dielectric okuhambisanayo kanye nemiphumela ehlukahlukene ebangelwa ukusondela (1-3). Imishini yobufakazi bezimiso zezinhlelo zokusebenza zesikhathi esizayo emkhakheni we-electronics kanye ne-optoelectronics yenziwe (4-6).
Lapha, sigxila ku-epitaxial van der Waals heterostructures ehlanganisa i-monolayer WS2, i-semiconductor enegebe eliqondile eline-spin-orbit coupling eqinile kanye nokuhlukaniswa okukhulu kwe-spin kwesakhiwo sebhendi ngenxa yokulinganisa okuphukile kwe-inversion (7), kanye ne-monolayer graphene, i-semimetal. ene-conical band structure kanye nokuhamba kwe-carrier ephezulu kakhulu (8), etshalwe ku-hydrogen-terinated I-SiC(0001). Izinkomba zokuqala zokudluliswa kwenkokhiso esheshayo (9–15) kanye nemiphumela yokuhlanganisa i-spin-orbit eyenziwe ukusondela (16–18) zenza i-WS2/graphene nama-heterostructures afanayo athembisayo ezicelo ze-optoelectronic (19) zesikhathi esizayo ne-optospintronic (20).
Sizimisele ukuveza izindlela zokuphumuza zamapheya e-electron-hole enziwe isithombe ku-WS2/graphene nge-photoemission spectroscopy (tr-ARPES) enesikhathi ne-engeli. Ngaleyo njongo, sijabulela i-heterostructure nge-2-eV futha yamaphaphu ahambisana ne-A-exciton ku-WS2 (21, 12) futhi sikhipha ama-photoelectrons anomshini wokuhlola obambezeleke okwesibili ku-26-eV photon energy. Sinquma amandla e-kinetic kanye ne-engeli yokukhishwa kwama-photoelectrons nge-hemispherical analyzer njengomsebenzi wokulibaziseka kwephampu ukuze uthole ukufinyelela ku-dynamics-, energy-, kanye ne-dynamics yenkampani yenethiwekhi exazululwe. Ukulungiswa kwamandla nesikhathi kungu-240 meV no-200 fs, ngokulandelana.
Imiphumela yethu ihlinzeka ngobufakazi obuqondile bokudluliswa kwenkokhiso esheshayo phakathi kwezendlalelo eziqondaniswe ne-epitaxially, okuqinisekisa izinkomba zokuqala ezisekelwe kumasu okubona konke kuma-heterostructures ahlanganiswe ngesandla afanayo nokuqondanisa kwe-azimuthal okungafanele kwezingqimba (9-15). Ngaphezu kwalokho, sibonisa ukuthi lokhu kudluliselwa kwenkokhiso ku-asymmetric ephezulu. Izilinganiso zethu zembula isimo sesikhashana esingazange sibonwe ngaphambili esihlukaniswe ngenkokhelo esinama-electron ane-photoexcited nezimbobo ezitholakala kungqimba ye-WS2 ne-graphene, ngokulandelanayo, ehlala ∼1 ps. Sihumusha esikutholile ngokuya ngomehluko esikhaleni sesigaba sokuhlakazeka se-electron kanye nokudluliswa kwembobo okubangelwa ukuqondana okuhlobene kwamabhendi e-WS2 nama-graphene njengoba kuvezwe i-ARPES yokulungiswa okuphezulu. Ihlanganiswe ne-spin- and valley-selective Optical excitation (22–25) WS2/graphene heterostructures ingase inikeze inkundla entsha yomjovo osebenza kahle we-ultrafast optical spin ku-graphene.
Umfanekiso 1A ubonisa isilinganiso esiphezulu se-ARPES esitholwe ngesibani se-helium sesakhiwo sebhendi eduze ne-ΓK-direction ye-epitaxial WS2/graphene heterostructure. Ikhoni ye-Dirac itholakala ine-hole-doped ngephoyinti le-Dirac elitholakala ~0.3 eV ngaphezu kwamandla amakhemikhali okulinganisa. Ingaphezulu lebhendi ye-valence ye-spin-split WS2 itholakala ingu-∼1.2 eV ngaphansi kwamandla amakhemikhali okulinganisa.
(A) I-Equilibrium photocurrent ilinganiswa ngokuhambisana ne-ΓK-direction ngesibani se-helium esingahlukanisiwe. (B) I-Photocurrent yokulibaziseka kwephampu-probe okukalwa nge-p-polarized extreme ultraviolet pulses ku-26-eV photon energy. Imigqa empunga edayishiwe nebomvu imaka indawo yamaphrofayela omugqa asetshenziselwa ukukhipha izindawo eziphakeme ezidlulayo ku-Fig. 2. (C) Izinguquko ezidalwe yiphampu ze-photocurrent 200 fs ngemva kwe-photoexcitation ku-pump photon energy engu-2 eV ngepump fluence. kwe 2 mJ/cm2. Ukuzuza nokulahlekelwa kwama-photoelectrons kuboniswa ngokubomvu nokuluhlaza okwesibhakabhaka, ngokulandelana. Amabhokisi abonisa indawo yokuhlanganisa yokulandela umkhondo wepompo eboniswe ku-Fig. 3.
Umfanekiso 1B ubonisa isifinyezo se-tr-ARPES sesakhiwo sebhendi esiseduze ne-WS2 kanye namaphoyinti e-graphene K alinganiswa ngama-100-fs ama-ultraviolet pulses adlulele ku-26-eV amandla e-photon ekubambezelekeni kwephampu-probe ngaphambi kokufika kwe-pump pulse. Lapha, ukuhlukaniswa kwe-spin akuxazululwa ngenxa yokonakaliswa kwesampula kanye nokuba khona kwe-pulse yepompo engu-2-eV ebangela ukunwetshwa kweshaja yesikhala izici ze-spectral. Umfanekiso 1C ubonisa izinguquko ezibangelwa iphampu ze-photocurrent ngokuphathelene ne-Fig. 1B ekubambezelekeni kwephampu-probe engu-200 fs lapho isignali ye-pump-probe ifinyelela ubukhulu bayo. Imibala ebomvu neluhlaza okwesibhakabhaka ibonisa ukuzuza nokulahlekelwa ama-photoelectrons, ngokulandelana.
Ukuze sihlaziye lokhu kuguquguquka okucebile ngemininingwane eyengeziwe, siqale sithole izindawo eziphakeme ezidlulayo zebhendi ye-valence ye-WS2 kanye nebhendi ye-graphene π eduze kwemigqa enedeshi ku-Fig. 1B njengoba kuchazwe ngokuningiliziwe kokuthi Okubalulekile Okungeziwe. Sithola ukuthi ibhendi ye-valence ye-WS2 ishintsha phezulu ngo-90 meV (Fig. 2A) futhi i-graphene π-band ishintshela phansi ngo-50 meV (Fig. 2B). Ukuphila kwe-exponential kwalawa mashifu kutholakala kungu-1.2 ± 0.1 ps kubhendi ye-valence ye-WS2 kanye no-1.7 ± 0.3 ps we-graphene π-band. Lawa mashifu aphezulu ahlinzeka ngobufakazi bokuqala bokushajwa kwesikhashana kwezendlalelo ezimbili, lapho ukushaja okwengeziwe okuyiphozithivu (negative) kwenyusa (kwehla) amandla abophezelayo ezifunda ze-elekthronikhi. Qaphela ukuthi i-upshift yebhendi ye-valence ye-WS2 ibophezelekile ngesignali ye-pump-probe evelele endaweni ephawulwe ngebhokisi elimnyama ku-Fig. 1C.
Ushintsho endaweni ephakeme kakhulu yebhendi ye-valence ye-WS2 (A) kanye ne-graphene π-band (B) njengomsebenzi wokulibaziseka kwephampu kanye nokulingana komchazi (imigqa ewugqinsi). Isikhathi sokuphila sokushintsha kwe-WS2 ku-(A) ngu-1.2 ± 0.1 ps. Isikhathi sokuphila sokushintsha kwe-graphene ku-(B) ngu-1.7 ± 0.3 ps.
Okulandelayo, sihlanganisa isignali ye-pump-probe phezu kwezindawo ezikhonjiswe amabhokisi anemibala ku-Fig. 1C futhi sihlele izibalo eziwumphumela njengomsebenzi wokulibaziseka kwephampu ku-Fig. 3. Ijika 1 ku-Fig. 3 libonisa amandla abathwali abanezithombe ezijabulile eduze naphansi kwebhendi yokuqhuba yongqimba lwe-WS2 nempilo yonke engu-1.1 ± 0.1 ps etholwe kusukela ekulinganeni komchazi kuya idatha (bona Izinto Ezikwengeza).
Ukulandelela i-Pump-probe njengomsebenzi wokubambezeleka okutholwe ngokuhlanganisa i-photocurrent endaweni ekhonjiswe amabhokisi aku-Fig. 1C. Imigqa ewugqinsi ilingana kahle nedatha. Ijika (1) Inani lenkampani yenethiwekhi yesikhashana kubhendi yokuqhuba ye-WS2. Ijika (2) Isignali ye-Pump-probe ye-π-band ye-graphene ngaphezu kwamandla amakhemikhali okulingana. Ijika (3) Isignali ye-Pump-probe ye-π-band ye-graphene ngaphansi kwamandla amakhemikhali okulinganisa. Ijika (4) Isignali ye-Net ye-pump-probe kubhendi ye-valence ye-WS2. Ukuphila konke kutholakala kungu-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).
Kumajika 2 no-3 we-Fig. 3, sibonisa isignali ye-pump-probe ye-graphene π-band. Sithola ukuthi ukuzuza kwama-electron ngaphezu kwamandla amakhemikhali okulinganisa (ijika lesi-2 ku-Fig. 3) linokuphila okufushane kakhulu (180 ± 20 fs) uma kuqhathaniswa nokulahlekelwa kwama-electron ngaphansi kwamandla amakhemikhali okulinganisa (1.8 ± 0.2 ps ku-curve 3) Umfanekiso wesi-3). Ngaphezu kwalokho, inzuzo yokuqala ye-photocurrent ku-curve 2 ye-Fig. 3 itholakala ukuthi iphenduke ibe ukulahlekelwa ku-t = 400 fs nempilo yonke engu-∼2 ps. I-asymmetry phakathi kwenzuzo nokulahlekelwa itholakala ingekho kusignali yephampu-probe ye-graphene ye-monolayer engamboziwe (bona i-fig. S5 kokuthi Izinto Ezingeziwe), okubonisa ukuthi i-asymmetry iwumphumela wokuhlangana kwe-interlayer ku-WS2/graphene heterostructure. Ukubhekwa kwenzuzo yesikhashana kanye nokulahlekelwa okuhlala isikhathi eside ngenhla nangaphansi kwamandla amakhemikhali okulinganisa, ngokulandelanayo, kubonisa ukuthi ama-electron akhishwa kahle kungqimba lwe-graphene phezu kwe-photoexcitation ye-heterostructure. Ngenxa yalokho, ungqimba lwe-graphene luba nokushajwa kahle, okuhambisana nokwanda kwamandla okubopha we-π-band etholakala ku-Fig. 2B. I-downshift ye-π-band isusa umsila wamandla aphezulu wokusatshalaliswa kwe-Fermi-Dirac kusuka ngenhla kwamandla amakhemikhali okulinganisa, okuchaza ngokwengxenye ukuguqulwa kophawu lwesignali yephampu ku-curve 2 ye-Fig. 3. Sizokwenza bonisa ngezansi ukuthi lo mphumela uthuthukiswa nakakhulu ukulahleka kwesikhashana kwama-electron ku-π-band.
Lesi simo sisekelwa isignali ye-net pump-probe yebhendi ye-valence ye-WS2 ku-curve 4 ye-Fig. 3. Le datha itholwe ngokuhlanganisa izibalo endaweni enikezwe ibhokisi elimnyama ku-Fig. 1B elithwebula ama-electron athathwe ku-Fig. ibhendi ye-valence kukho konke ukubambezeleka kwe-pump-probe. Ngaphakathi kwemigoqo yephutha yokuhlola, asitholi inkomba yokuba khona kwezimbobo kubhendi ye-valence ye-WS2 nganoma yikuphi ukulibaziseka kwephampu. Lokhu kubonisa ukuthi, ngemva kwe-photoexcitation, lezi zimbobo zigcwaliswa kabusha ngokushesha ngesilinganiso sesikhathi esifushane uma kuqhathaniswa nokulungiswa kwethu kwesikhashana.
Ukuze sinikeze ubufakazi bokugcina be-hypothesis yethu yokuhlukaniswa kwenkokhiso esheshayo ku-WS2/graphene heterostructure, sinquma inani lezimbobo ezidluliselwe kusendlalelo se-graphene njengoba kuchazwe ngokuningiliziwe kokuthi Okubalulekile Okungeziwe. Ngamafuphi, ukusatshalaliswa kwe-electronic kwesikhashana kwe-π-band kufakwe ukusatshalaliswa kwe-Fermi-Dirac. Inani lezimbobo labe selibalwa kusukela kumanani angumphumela wamandla wesikhashana amakhemikhali kanye nezinga lokushisa likagesi. Umphumela uboniswa ku-Fig. 4. Sithola ukuthi ingqikithi yenani le-~5 × 1012 izimbobo/cm2 idluliswa isuka ku-WS2 iye ku-graphene nge-exponential yokuphila engu-1.5 ± 0.2 ps.
Ukushintsha inani lezimbobo kubhendi engu-π njengomsebenzi wokulibaziseka kwephampu kanye nokulingana okubonakalayo okunikeza impilo yonke engu-1.5 ± 0.2 ps.
Kusukela kokutholwe ku-Fig. 2 kuya ku-4, isithombe esincanyana esilandelayo sokudluliswa kweshaja esheshayo ku-WS2/graphene heterostructure siyavela (Fig. 5). I-Photoexcitation ye-WS2/graphene heterostructure ku-2 eV igcwala kakhulu i-A-exciton ku-WS2 (Fig. 5A). Izivuso ze-elekthronikhi ezengeziwe kulo lonke iphoyinti le-Dirac ku-graphene kanye naphakathi kwe-WS2 namabhendi e-graphene zingenzeka ngamandla kodwa zisebenza kancane kakhulu. Izimbobo ezinezithombe ezijabulile kubhendi ye-valence ye-WS2 zigcwaliswa kabusha ama-electron asuka ku-graphene π-band ngesilinganiso sesikhathi esifushane uma kuqhathaniswa nokulungiswa kwethu kwesikhashana (Fig. 5A). Ama-electron ane-photoexcited kubhendi yokuqhuba ye-WS2 anesikhathi sokuphila esingu-∼1 ps (Fig. 5B). Nokho, kuthatha ∼2 ps ukugcwalisa kabusha izimbobo ku-graphene π-band (Fig. 5B). Lokhu kukhombisa ukuthi, ngaphandle kokudluliswa kwe-electron eqondile phakathi kwebhendi yokuqhuba i-WS2 kanye ne-graphene π-band, izindlela zokuphumula ezengeziwe—mhlawumbe ngezimo zokukhubazeka (26)—zidinga ukucatshangelwa ukuze kuqondwe ukuguquguquka okugcwele.
(A) I-Photoexcitation ngokuzwakalayo kwe-WS2 A-exciton ku-2 eV ijova ama-electron kubhendi yokuqhuba ye-WS2. Izimbobo ezihambisanayo kubhendi ye-valence ye-WS2 zigcwaliswa kabusha ngokushesha ngama-electron asuka ku-graphene π-band. (B) Izinkampani zenethiwekhi ezinezithombe ezijabulile kubhendi yokuqhuba ye-WS2 zinesikhathi sokuphila esingu-∼1 ps. Izimbobo ku-graphene π-band ziphila ∼2 ps, okubonisa ukubaluleka kweziteshi ezengeziwe zokuhlakaza eziboniswa ngemicibisholo edayishiwe. Imigqa enedeshi emnyama ku-(A) kanye no-(B) ikhombisa ukushintsha kwebhendi kanye nezinguquko kumandla amakhemikhali. (C) Esimeni sesikhashana, isendlalelo se-WS2 sishajwa kabi kuyilapho ungqimba lwe-graphene lushajwe kahle. Ukuze uthole injabulo ekhethiwe e-spin enokukhanya kwe-circularly polarized, ama-electron e-photoexcited ku-WS2 kanye nezimbobo ezihambisanayo ku-graphene kulindeleke ukuthi zibonise i-spin polarization ephambene.
Esimeni sesikhashana, ama-electron ajabulile ahlala kubhendi yokuqhuba ye-WS2 kuyilapho izimbobo ezinezithombe ezijabulisayo zitholakala ku-π-band ye-graphene (Fig. 5C). Lokhu kusho ukuthi isendlalelo se-WS2 sishajwe kabi futhi isendlalelo se-graphene sishajwe kahle. Lokhu kubala amashifu aphezulu esikhashana (Umfanekiso 2), i-asymmetry yesignali ye-graphene futha-probe (amajika 2 no-3 we-Fig. 3), ukungabikho kwezimbobo kubhendi ye-valence ye-WS2 (ijika 4 Fig. 3) , kanye nezimbobo ezengeziwe ku-graphene π-band (Fig. 4). Ukuphila kwalesi simo sokuhlukaniswa kwenkokhelo ngu-∼1 ps (ijika 1 Fig. 3).
Izimo ezifanayo zesikhashana ezihlukaniswe ngecala ziye zabonwa kuma-heterostructures ahlobene we-van der Waals enziwe ngamasemiconductors amabili aqondile anegebe lokuqondanisa kwebhendi yohlobo lwe-II kanye ne-bandgap enyakazayo (27-32). Ngemuva kwe-photoexcitation, ama-electron kanye nezimbobo zitholakale zihamba ngokushesha phansi kwebhendi ye-conduction nangaphezulu kwe-valence band, ngokulandelanayo, etholakala ezingxenyeni ezahlukene ze-heterostructure (27-32).
Esimeni sethu se-WS2/graphene heterostructure, indawo evumayo kakhulu yakho kokubili ama-electron nezimbobo isezingeni le-Fermi kungqimba lwe-graphene yensimbi. Ngakho-ke, umuntu angalindela ukuthi kokubili ama-electron nezimbobo zidlulisele ngokushesha ku-graphene π-band. Kodwa-ke, izilinganiso zethu zibonisa ngokusobala ukuthi ukudluliswa kwembobo (<200 fs) kusebenza kahle kakhulu kunokudluliselwa kwe-electron (∼1 ps). Lokhu sikubalula ekuqondaneni okunamandla okuhlobene kwe-WS2 namabhendi e-graphene njengoba embulwe ku-Fig. 1A enikeza ngenani elikhulu lezimo zokugcina ezitholakalayo zokudlulisa imbobo uma kuqhathaniswa nokudluliswa kwama-electron njengoba muva nje kulindelwe ngo-(14, 15). Esimeni samanje, uma kubhekwa ibhendi engu-~2 eV WS2, iphoyinti le-graphene Dirac namandla amakhemikhali okulinganisa atholakala ~0.5 kanye no-0.2 eV ngaphezu kwemaphakathi ne-WS2 bandgap, ngokulandelanayo, ukugqama kwe-electron-hole symmetry. Sithola ukuthi inombolo yezifunda zokugcina ezitholakalayo zokudlulisa imbobo ∼inkulu ngokuphindwe ka-6 kuneyokudluliswa kwe-electron (bona Okubalulekile Okungeziwe), yingakho ukudluliswa kwembobo kulindeleke ukuthi kusheshe kunokudlulisa i-electron.
Isithombe esiphelele se-microscopic esiboniwe sokudluliswa kwe-ultrafast asymmetric charge kufanele, nokho, siphinde sicabangele ukugqagqana phakathi kwama-orbitals akha umsebenzi wegagasi we-A-exciton ku-WS2 kanye ne-graphene π-band, ngokulandelanayo, ukuhlakazeka kwe-electron-electron kanye ne-electron-phonon. iziteshi ezihlanganisa izithiyo ezibekwe umfutho, amandla, ukujikeleza, kanye nokugcinwa kwe-pseudospin, ithonya le-plasma ama-oscillations (33), kanye nendima yesasasa elingase libe khona le-oscillations ehambisanayo yephonon engase ilamule ukudluliswa kwenkokhiso (34, 35). Futhi, umuntu angase aqagele ukuthi ingabe isimo sokudlulisa inkokhiso esibhekiwe siqukethe ama-exciton okudlulisa inkokhiso noma amapheya amahhala e-electron-hole (bona Izinto Ezingeziwe). Uphenyo olwengeziwe lwethiyori oludlulela ngale kobubanzi bephepha lamanje luyadingeka ukuze kucaciswe lezi zindaba.
Kafushane, sisebenzise i-tr-ARPES ukutadisha ukudluliswa kwenkokhiso ye-interlayer ye-ultrafast ku-epitaxial WS2/graphene heterostructure. Sithole ukuthi, uma sijatshuliswa ukuzwakala kwe-A-exciton ye-WS2 ku-2 eV, izimbobo ezine-photoexcited zidlulisela ngokushesha kungqimba lwe-graphene kuyilapho ama-electron e-photoexcited ehlala kusendlalelo se-WS2. Lokhu sikuchasise ngokuthi inani lezifunda zokugcina ezitholakalayo zokudlulisa imbobo likhulu kunelokudluliswa kwe-electron. Impilo yesikhashana ehlukaniswe nenkokhelo itholwe ingu-∼1 ps. Ngokuhambisana ne-spin-selective Optical excitation kusetshenziswa ukukhanya okuyisiyingi (22–25), ukudluliswa kweshaja okubonwayo okubonwayo kungase kuhambisane nokudluliswa kwe-spin. Kulokhu, i-WS2/graphene heterostructure ephenyiwe ingase isetshenziselwe umjovo osebenza kahle we-optical spin ku-graphene okuholela kumadivayisi anoveli e-optospintronic.
Amasampula e-graphene akhuliswe kuma-wafers we-semiconducting we-6H-SiC(0001) avela ku-SiCrystal GmbH. Amawafa e-N-doped ayeku-eksisi nokunqunywa okungalungile ngaphansi kuka-0.5°. I-substrate ye-SiC yayifakwe i-hydrogen ukuze isuse imihuzuko futhi ithole amasimu ayisicaba avamile. Indawo ehlanzekile neyisicaba ye-athomu enqanyuliwe ka-Si yabe isidwetshwa ngokudonsa isampula emkhathini we-Ar ku-1300°C imizuzu engu-8 (36). Ngale ndlela, sithole ungqimba olulodwa lwekhabhoni lapho i-athomu ngayinye yesithathu ye-carbon yenza isibopho esihlangene ku-substrate ye-SiC (37). Lesi sendlalelo sabe sesiguqulwa saba i-sp2-hybridized quasi free-standing hole-doped graphene ngokuphelele nge-hydrogen intercalation (38). Lawa masampuli abizwa ngokuthi i-graphene/H-SiC(0001). Lonke lolu hlelo lwenziwa ekamelweni lokukhula le-Black Magic elivela e-Aixtron. Ukukhula kwe-WS2 kwenziwa kureactor evamile yodonga olushisayo ngokufakwa komhwamuko wamakhemikhali wokucindezela okuphansi (39, 40) kusetshenziswa izimpushana ze-WO3 kanye ne-S ezinesilinganiso esikhulu esingu-1:100 njengamazandulela. Izimpushana ze-WO3 ne-S zazigcinwa ku-900 no-200 ° C, ngokulandelana. I-WO3 powder ibekwe eduze kwe-substrate. I-Argon yayisetshenziswa njengegesi yenethiwekhi ngokugeleza kwe-8 sccm. Ingcindezi ku-reactor igcinwe ku-0.5 mbar. Amasampula abonakala nge-electron microscopy yesibili, i-atomic force microscopy, i-Raman, ne-photoluminescence spectroscopy, kanye ne-low-energy diffraction. Lezi zilinganiso zembule izizinda ezimbili ezihlukene ze-WS2 zekristalu eyodwa lapho i-ΓK- noma i-ΓK'-direction ihambisana ne-ΓK-direction yesendlalelo segraphene. Ubude bezinhlangothi zesizinda bahluka phakathi kuka-300 no-700 nm, futhi isamba sokufakwa kwe-WS2 salinganiselwa ku-∼40%, sifanele ukuhlaziywa kwe-ARPES.
Ukuhlola okumile kwe-ARPES kwenziwa nge-hemispherical analyzer (SPECS PHOIBOS 150) kusetshenziswa isistimu yesitholi sedivayisi ehlanganisiwe yokushaja ukuze kutholwe izinhlangothi ezimbili zamandla e-electron kanye nomfutho. I-unpolarized, monochromatic He Iα radiation (21.2 eV) yomthombo wokukhipha i-He discharge we-flux ephezulu (VG Scienta VUV5000) isetshenziswe kukho konke ukuhlolwa kwe-photoemission. Amandla nokulungiswa kwe-angular ekuhloleni kwethu bekungcono kunokungu-30 meV no-0.3° (okuhambisana no-0.01 Å−1), ngokulandelanayo. Konke ukuhlola kwenziwa ngezinga lokushisa legumbi. I-ARPES iyindlela ezwela kakhulu endaweni. Ukuze kukhishwe ama-photoelectrons kusuka kukho kokubili i-WS2 nesendlalelo se-graphene, amasampula anokufakwa kwe-WS2 okungaphelele okungu-~40% asetshenzisiwe.
Ukusethwa kwe-tr-ARPES bekusekelwe ku-1-kHz Titanium:Sapphire amplifier (Coherent Legend Elite Duo). I-2 mJ yamandla okukhiphayo isetshenziselwe ukukhiqizwa okuphezulu kwe-harmonics ku-argon. Umphumela wokukhanya okweqile kwe-ultraviolet kudlule ku-grating monochromator ekhiqiza ama-pulses e-probe angu-100-fs ku-26-eV photon energy. I-8mJ yamandla okukhipha i-amplifier ithunyelwe ku-optical parametric amplifier (HE-TOPAS kusuka ku-Light Conversion). I-beta yesignali ku-1-eV photon energy iphindwe kabili ku-beta barium borate crystal ukuze kutholwe ama-pulses epompo angu-2-eV. Izilinganiso ze-tr-ARPES zenziwe nge-hemispherical analyzer (SPECS PHOIBOS 100). Amandla esewonke kanye nokulungiswa kwesikhashana kube ngu-240 meV no-200 fs, ngokulandelana.
Izinto ezingeziwe zalesi sihloko zitholakala ku-http://advances.sciencemag.org/cgi/content/full/6/20/eaay0761/DC1
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QAPHELA: Sicela ikheli lakho le-imeyili kuphela ukuze umuntu omncomayo ikhasi azi ukuthi ubufuna alibone, nokuthi aliyona i-imeyili eyimfucuza. Asithathi noma yiliphi ikheli le-imeyili.
Lo mbuzo owokuhlola ukuthi uyisivakashi esingumuntu noma cha kanye nokuvikela 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 ku-WS2/graphene heterostructure evumela umjovo we-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 ku-WS2/graphene heterostructure evumela umjovo we-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 sokuthumela: May-25-2020