Hoʻohana mākou i ka manawa a me ka angle-resolved photoemission spectroscopy (tr-ARPES) no ka noiʻi ʻana i ka hoʻoili uku ultrafast i kahi heterostructure epitaxial i hana ʻia me ka monolayer WS2 a me ka graphene. Hoʻohui kēia heterostructure i nā pōmaikaʻi o kahi semiconductor pololei-gap me ka hui ʻana o ka spin-orbit ikaika a me ka launa pū ʻana o nā mea māmā me nā mea o ka semimetal e hoʻokipa ana i nā mea lawe nui ʻole me ka neʻe kiʻekiʻe loa a me nā ola lōʻihi. ʻIke mākou, ma hope o ka photoexcitation ma ka resonance i ka A-exciton ma WS2, ua hoʻololi koke nā puka photoexcited i ka papa graphene aʻo nā electrons photoexcited e noho ana i ka papa WS2. Loaʻa ka hopena o ke kūlana transient i hoʻokaʻawale ʻia i ka uku i ke ola o ~1 ps. Hāʻawi mākou i kā mākou ʻike i nā ʻokoʻa o ka hoʻopuʻi ʻana i ka manawa i hoʻokumu ʻia e ka alignment pili o WS2 a me nā graphene band e like me ka mea i hōʻike ʻia e ARPES kiʻekiʻe. I ka hui pū ʻana me ka spin-selective optical excitation, hiki i ka WS2 / graphene heterostructure i noiʻi ʻia ke hāʻawi i kahi kahua no ka hoʻoheheʻe ʻana i ka optical spin i ka graphene.
ʻO ka loaʻa ʻana o nā mea ʻelua-dimensional he nui i wehe i ka hiki ke hana i ka moʻolelo hope loa heterostructures lahilahi me nā hana hou loa e pili ana i ka screening dielectric i hoʻopaʻa ʻia a me nā hopena pili kokoke (1-3). Ua ʻike ʻia nā mea hōʻoia-o-principle no nā noi e hiki mai ana ma ke kahua o ka uila a me ka optoelectronics (4-6).
Maʻaneʻi, nānā mākou i nā epitaxial van der Waals heterostructures me ka monolayer WS2, kahi semiconductor pololei-gap me ka hoʻohui ʻana i ka spin-orbit ikaika a me ka hoʻokaʻawale nui ʻana o ka hale hui ma muli o ka haki ʻana o ka inversion symmetry (7), a me ka monolayer graphene, he semimetal. me ka hoʻolālā hui conical a me ka neʻe ʻana o ka mea lawe kiʻekiʻe loa (8), i ulu ma ka hydrogen-terminated SiC(0001). ʻO nā hōʻailona mua no ka hoʻoili kālā ultrafast (9-15) a me nā hopena pili pili i ka spin-orbit (16-18) e hana i ka WS2 / graphene a me nā heterostructures like e hoʻohiki nei i nā moho no ka optoelectronic (19) a me optospintronic (20) e hiki mai ana.
Hoʻomaka mākou e hōʻike i nā ala hoʻomaha o nā paʻi electron-hole i haku ʻia ma WS2/graphene me ka manawa a me ka angle-resolved photoemission spectroscopy (tr-ARPES). No ia kumu, hoʻohauʻoli mākou i ka heterostructure me 2-eV pump pulses resonant i ka A-exciton ma WS2 (21, 12) a hoʻokuʻu i nā photoelectrons me ka lua o ka manawa hoʻopaneʻe puʻupuʻu ma 26-eV photon ikehu. Hoʻoholo mākou i ka ikehu kinetic a me ka huina hoʻokuʻu ʻana o nā photoelectrons me kahi mea hoʻoponopono hemispherical ma ke ʻano he hana o ka hoʻopaneʻe ʻana i ka pauma no ka loaʻa ʻana o ka manawa i ka momentum-, ikehu-, a me ka hoʻoholo ʻana i ka manawa. ʻO ka mana a me ka hoʻonā manawa he 240 meV a me 200 fs.
Hāʻawi kā mākou mau hopena i ka hōʻike pololei no ka hoʻoili kālā ultrafast ma waena o nā papa epitaxially aligned, e hōʻoia ana i nā hōʻailona mua e pili ana i nā ʻenehana āpau-optical i nā heterostructures i hui pū ʻia me ka lima azimuthal alignment o nā papa (9-15). Eia kekahi, hōʻike mākou he asymmetric loa kēia hoʻoili kālā. Hōʻike kā mākou ana i kahi mokuʻāina transient i hoʻokaʻawale ʻole ʻia me ka photoexcited electrons a me nā lua i loaʻa i ka papa WS2 a me ka graphene, kēlā me kēia, e ola ana no ~1 ps. Wehewehe mākou i kā mākou ʻike ma ke ʻano o nā ʻokoʻa o ka hoʻopuehu ʻana i ka manawa no ka electron a me ka hole hoʻoili i hoʻokumu ʻia e ka alignment pili o WS2 a me nā kaula graphene e like me ka mea i hōʻike ʻia e ARPES kiʻekiʻe. Hoʻohui pū ʻia me ka spin- a me ke awāwa-koho o ka hoʻoulu ʻana o ka optical excitation (22-25) WS2/graphene heterostructures hiki ke hāʻawi i kahi kahua hou no ka ultrafast optical spin injection maikaʻi i ka graphene.
Hōʻike ka Figure 1A i kahi ana ARPES hoʻonā kiʻekiʻe i loaʻa me kahi kukui helium o ka hale hui ma ke kuhikuhi ΓK o ka epitaxial WS2 / graphene heterostructure. ʻIke ʻia ka pahu Dirac i hole-doped me ke kiko Dirac i loaʻa ∼0.3 eV ma luna aʻe o ka hiki kemika equilibrium. ʻIke ʻia ʻo ka luna o ka puʻupuʻu WS2 valence spin-split ∼1.2 eV ma lalo o ka hiki kemika equilibrium.
(A) Equilibrium photocurrent i ana ma ka ΓK-direction me ke kukui helium unpolarized. (B) Kiʻi kiʻi no ka hoʻopaneʻe ʻino-ʻimi noiʻi maikaʻi ʻole i ana ʻia me ka p-polarized kiʻekiʻe ultraviolet pulses ma 26-eV photon ikehu. ʻO nā laina ʻeleʻele hina a ʻulaʻula e hōʻailona i ke kūlana o nā ʻaoʻao laina i hoʻohana ʻia no ka unuhi ʻana i nā kūlana kiʻekiʻe transient ma Fig. o 2 mJ/cm2. Hōʻike ʻia ka loaʻa a me ka nalowale o nā photoelectrons i ka ʻulaʻula a me ka uliuli. Hōʻike nā pahu i ka ʻāpana o ka hoʻohui ʻana no nā ʻāpana ʻimi-pume i hōʻike ʻia ma ke kiʻi 3.
Hōʻike ka Kiʻi 1B i kahi kiʻi kiʻi tr-ARPES o ka hale hui kokoke i ka WS2 a me ka graphene K-points i ana ʻia me 100-fs kiʻekiʻe ultraviolet pulses ma 26-eV photon ikehu ma ka hoʻopaneʻe ʻino-probe lohi ma mua o ka hiki ʻana mai o ka pulse pump. Maʻaneʻi, ʻaʻole i hoʻoholo ʻia ka ʻoki ʻana ma muli o ka hoʻohaʻahaʻa ʻana o ka laʻana a me ka loaʻa ʻana o ka pulse pump 2-eV e hoʻonui ai i ka hoʻonui ʻia o nā hiʻohiʻona spectral. Hōʻike ka Figure 1C i nā hoʻololi ʻana o ka paʻi kiʻi e pili ana i ka Fig. 1B ma kahi hoʻolōʻihi ʻana i ka pauma o 200 fs kahi i hiki ai ka hōʻailona ʻumeke i kona kiʻekiʻe. Hōʻike nā kala ʻulaʻula a me ka uliuli i ka loaʻa a me ka nalowale o nā photoelectrons.
No ke kālailai ʻana i kēia waiwai waiwai i nā kikoʻī hou aʻe, e hoʻoholo mua mākou i nā kūlana kiʻekiʻe transient o ka hui valence WS2 a me ka graphene π-band ma nā laina i kahakaha ʻia ma Fig. ʻIke mākou i ka neʻe ʻana o ke kāʻei valence WS2 i 90 meV (Fig. 2A) a ʻo ka graphene π-band e hoʻololi i lalo e 50 meV (Fig. 2B). Ua ʻike ʻia ke ola exponential o kēia mau hoʻololi ʻana he 1.2 ± 0.1 ps no ka hui valence o WS2 a me 1.7 ± 0.3 ps no ka pūna graphene π. Hāʻawi kēia mau hoʻololi kiʻekiʻe i nā hōʻike mua o ka hoʻopiʻi ʻana o nā papa ʻelua, kahi e hoʻonui ai ka uku maikaʻi (negative) (hōʻemi) i ka ikehu paʻa o nā mokuʻāina uila. E hoʻomaopopo ʻo ka piʻi ʻana o ka hui valence WS2 ke kuleana no ka hōʻailona pahū-probe koʻikoʻi ma kahi i kaha ʻia e ka pahu ʻeleʻele ma Fig. 1C.
E hoʻololi i ke kūlana kiʻekiʻe o ka WS2 valence band (A) a me ka graphene π-band (B) ma ke ʻano he hana o ka hoʻolāʻihi ʻana i ka pauma-probe a me nā kiko exponential (laina mānoanoa). ʻO ke ola o ka hoʻololi WS2 ma (A) he 1.2 ± 0.1 ps. ʻO ke ola o ka hoʻololi graphene ma (B) he 1.7 ± 0.3 ps.
A laila, hoʻohui mākou i ka hōʻailona pump-probe ma luna o nā wahi i hōʻike ʻia e nā pahu kala i ka Fig. nā mea lawe photoexcited kokoke i ka lalo o ka hui conduction o ka papa WS2 me ke ola o 1.1 ± 0.1 ps i loaʻa mai kahi exponential kūpono i ka ʻikepili (e nānā i nā Mea Hoʻohui).
Pump-probe traces e like me ka hana o ka lohi i loaʻa ma ka hoʻohui ʻana i ka photocurrent ma luna o ka wahi i hōʻike ʻia e nā pahu ma Fig. 1C. He kūpono nā laina mānoanoa i ka ʻikepili. Pipi (1) Ka heluna kanaka lawe kaʻa i ka hui alakaʻi o WS2. Pipi (2) Hōʻailona hoʻopaʻa ʻana o ka π-band o ka graphene ma luna aʻe o ka hiki kemika equilibrium. Pipi (3) Hōʻailona hoʻopaʻa ʻana o ka π-band o ka graphene ma lalo o ka hiki kemika equilibrium. Pipi (4) hōʻailona pauma-ʻimi noiʻi ma ka pūna valence o WS2. Loaʻa nā manawa ola he 1.2 ± 0.1 ps i (1), 180 ± 20 fs (loaʻa) a me ~2 ps (losses) ma (2), a me 1.8 ± 0.2 ps i (3).
Ma nā kaha 2 a me 3 o ke kiʻi 3, hōʻike mākou i ka hōʻailona pahū o ka graphene π-band. ʻIke mākou he ʻoi aku ka pōkole o ka loaʻa ʻana o nā electrons ma luna aʻe o ka equilibrium kemika (curve 2 ma Fig. 3) i ke ola pōkole loa (180 ± 20 fs) i hoʻohālikelike ʻia me ka nalowale o nā electrons ma lalo o ka hiki kemika equilibrium (1.8 ± 0.2 ps ma ka pihi 3. Fig. 3). Eia kekahi, ʻike ʻia ka loaʻa mua o ke kiʻi kiʻi ma ka pihi 2 o Fig. 3 i lilo i poho ma t = 400 fs me ke ola o ~2 ps. ʻO ka asymmetry ma waena o ka loaʻa a me ka nalowale ʻike ʻia ʻaʻole i loaʻa i ka hōʻailona pahū-probe o ka monolayer graphene i wehe ʻole ʻia (e ʻike i ka fig. S5 ma nā Mea Hoʻohui), e hōʻike ana i ka asymmetry he hopena o ka hoʻohui ʻana i waena o ka WS2/graphene heterostructure. ʻO ka ʻike ʻana i ka loaʻa pōkole a me ka nalowale lōʻihi ma luna a ma lalo o ka hiki kemika equilibrium, kēlā me kēia, e hōʻike ana e hoʻoneʻe maikaʻi ʻia nā electrons mai ka papa graphene ma luna o ka photoexcitation o ka heterostructure. ʻO ka hopena, lilo ka papa graphene i ka hoʻopiʻi maikaʻi, e kūlike me ka piʻi ʻana o ka ikehu hoʻopaʻa o ka π-band i loaʻa ma ka Fig. 2B. ʻO ka iho o ka π-band e hoʻoneʻe i ka huelo ikehu kiʻekiʻe o ka equilibrium Fermi-Dirac puʻunaue mai luna aʻe o ka equilibrium chemical potential, e wehewehe ana i ka hoʻololi ʻana o ka hōʻailona o ka hōʻailona pump-probe ma ka pihi 2 o Fig. 3. hōʻike ma lalo e hoʻonui hou ʻia kēia hopena e ka nalowale o nā electrons i loko o ka π-band.
Kākoʻo ʻia kēia hiʻohiʻona e ka hōʻailona pume-probe upena o ka hui valence WS2 ma ka ʻaoʻao 4 o Fig. 3. Ua loaʻa kēia mau ʻikepili ma o ka hoʻohui ʻana i nā helu ma luna o ka wahi i hāʻawi ʻia e ka pahu ʻeleʻele ma Fig. 1B e hopu ana i nā electrons photoemited mai. ka puana valence i na lohi pauma. Ma loko o nā pahu hewa hoʻokolohua, ʻaʻole mākou e ʻike i kahi hōʻailona no ka loaʻa ʻana o nā lua ma ka hui valence o WS2 no ka lohi ʻana o ka pauma. Hōʻike kēia, ma hope o ka photoexcitation, ua hoʻopiha hou ʻia kēia mau puka i kahi manawa pōkole i hoʻohālikelike ʻia i kā mākou hoʻonā kino.
No ka hāʻawi ʻana i ka hōʻoia hope loa no kā mākou kuhiakau o ka hoʻokaʻawale ʻana i ka ultrafast charge i ka WS2/graphene heterostructure, hoʻoholo mākou i ka helu o nā puka i hoʻololi ʻia i ka papa graphene e like me ka mea i wehewehe ʻia ma nā Mea Hoʻohui. I ka pōkole, ua hoʻokomo ʻia ka puʻupuʻu uila transient o ka π-band me kahi mahele Fermi-Dirac. A laila helu ʻia ka helu o nā puka mai nā waiwai i loaʻa no ka hiki kemika transient a me ka wela uila. Hōʻike ʻia ka hopena ma Fig. 4. Ua ʻike mākou ua hoʻololi ʻia ka huina o ~5 × 1012 puka / cm2 mai WS2 a i graphene me ke ola exponential o 1.5 ± 0.2 ps.
Hoʻololi i ka helu o nā puka i loko o ka π-band ma ke ʻano he hana o ka hoʻopaneʻe ʻana i ka pauma-probe me ka exponential fit e hāʻawi i ke ola o 1.5 ± 0.2 ps.
Mai nā ʻike ma Fig. 2 a 4, e puka mai ana ke ki'i microscopic no ka ho'oili uku ultrafast i ka WS2/graphene heterostructure (Fig. 5). ʻO Photoexcitation o ka WS2 / graphene heterostructure ma 2 eV nui ka populate i ka A-exciton ma WS2 (Fig. 5A). ʻO nā mea hoʻoulu uila hou aʻe ma ka lae Dirac ma ka graphene a ma waena o WS2 a me nā pūʻulu graphene hiki ke ikaika akā ʻoi aku ka maikaʻi. Hoʻopiha hou ʻia nā puka kiʻi kiʻi i loko o ka pā valence o WS2 e nā electrons mai ka graphene π-band ma kahi manawa pōkole e hoʻohālikelike ʻia i kā mākou hoʻonā kino (Fig. 5A). ʻO nā electrons photoexcited i loko o ka hui conduction o WS2 ke ola o ~1 ps (Fig. 5B). Eia naʻe, he ∼2 ps e hoʻopiha hou i nā puka o ka graphene π-band (Fig. 5B). Hōʻike kēia, ma waho aʻe o ka hoʻoili electron pololei ma waena o ka hui hoʻokele WS2 a me ka graphene π-band, pono e noʻonoʻo ʻia nā ala hoʻomaha ʻē aʻe - ma o nā mokuʻāina hemahema (26) - pono e noʻonoʻo ʻia e hoʻomaopopo i ka dynamics piha.
(A) Photoexcitation ma resonance i ka WS2 A-exciton ma 2 eV injects electrons i loko o ka conduction band o WS2. Hoʻopiha koke ʻia nā lua e pili ana i ka hui valence o WS2 e nā electrons mai ka graphene π-band. (B) Loaʻa i nā mea lawe kiʻi paʻi kiʻi i ka hui conduction o WS2 ke ola o ~1 ps. Noho nā puka i loko o ka graphene π-band no ~2 ps, e hōʻike ana i ke koʻikoʻi o nā ala hoʻopuehu hou i hōʻike ʻia e nā pua i ʻoki ʻia. Hōʻike nā laina kaha ʻeleʻele ma (A) a me (B) i ka hoʻololi ʻana o ka band a me nā loli i ka hiki ke kemika. (C) Ma ka moku'āina transient, ua hoʻopiʻi maikaʻi ʻia ka papa WS2 i ka wā e hoʻopiʻi maikaʻi ʻia ka papa graphene. No ka wiliwili koho me ka malamalama polarized circularly, nā electrons photoexcited ma WS2 a me nā lua e pili ana i ka graphene e manaʻo ʻia e hōʻike i ka polarization milo.
Ma ka moku'āina transient, noho nā electrons photoexcited i ka hui conduction o WS2 aʻo nā puka photoexcited aia ma ka π-band o graphene (Fig. 5C). 'O ia ho'i, ua ho'opi'i maika'i 'ia ka papa WS2 a ua ho'opi'i maika'i 'ia ka papa graphene. ʻO kēia ka helu no ka neʻe ʻana o ka piko transient (Fig. 2), ka asymmetry o ka graphene pump-probe signal (curves 2 a me 3 o Fig. 3), ka nele o nā puka ma ka hui valence o WS2 (curve 4 Fig. 3) , a me na puka hou ma ka graphene π-band (Fig. 4). ʻO ke ola o kēia mokuʻāina i hoʻokaʻawale ʻia he ∼ 1 ps (ka pihi 1 Fig. 3).
Ua ʻike ʻia nā mokuʻāina transient hoʻokaʻawale like ʻole i nā heterostructure van der Waals pili i hana ʻia i loko o ʻelua semiconductors-gap pololei me ke ʻano II band alignment a staggered bandgap (27-32). Ma hope o ka photoexcitation, ua ʻike ʻia nā electrons a me nā lua e neʻe wikiwiki i lalo o ka hui conduction a i ka piko o ke kaula valence, i kēlā me kēia, aia i nā papa like ʻole o ka heterostructure (27-32).
I ka hihia o kā mākou WS2/graphene heterostructure, ʻo ka wahi i makemake nui ʻia no nā electrons a me nā lua aia ma ka pae Fermi i ka papa graphene metala. No laila, manaʻo kekahi e hoʻololi koke nā electron a me nā lua i ka graphene π-band. Eia naʻe, ʻoi aku ka maikaʻi o kā mākou ana ʻana i ka hoʻololi ʻana o ka lua (<200 fs) ma mua o ka hoʻoili electron (∼1 ps). Hāʻawi mākou i kēia i ka alignment ikaika pili o ka WS2 a me nā kaula graphene e like me ka hōʻike ʻana ma ka Fig. 1A e hāʻawi ana i kahi helu nui o nā mokuʻāina hope loa i loaʻa no ka hoʻololi ʻana i ka lua i hoʻohālikelike ʻia me ka hoʻoili uila e like me ka mea i manaʻo ʻia e (14, 15). I kēia manawa, me ka mana'o 'ana he ∼2 eV WS2 bandgap, aia ka graphene Dirac point a me equilibrium kemikala hiki ke loa'a ~0.5 a ~0.2 eV ma luna o ka waena o ka WS2 bandgap, e wawahi ana i ka electron-hole symmetry. ʻIke mākou ʻo ka helu o nā mokuʻāina hope loa i loaʻa no ka hoʻololi ʻana he 6 mau manawa ʻoi aku ka nui ma mua o ka hoʻoili electron (e nānā i nā Mea Hoʻohui), ʻo ia ke kumu i manaʻo ʻia e ʻoi aku ka wikiwiki o ka hoʻololi ʻana ma mua o ka hoʻoili electron.
ʻO ke kiʻi microscopic piha o ka ultrafast asymmetric charge transfer i ʻike ʻia, akā naʻe, e noʻonoʻo pū i ka uhi ʻana ma waena o nā orbital i hana i ka hana hawewe A-exciton ma WS2 a me ka graphene π-band, kēlā me kēia, nā electron-electron a me electron-phonon scattering. nā kahawai me nā kaohi i kau ʻia e ka momentum, ka ikehu, ka milo, a me ka mālama ʻana i ka pseudospin, ka mana o ka oscillations plasma (33), a me ke kuleana o kahi hoʻohiwahiwa displacive o nā oscillations phonon coherent e hiki ke hoʻololi i ka hoʻoili kālā (34, 35). Eia kekahi, e noʻonoʻo paha kekahi inā ʻo ka mokuʻāina hoʻoili kālā i ʻike ʻia me nā excitons hoʻoili kālā a i ʻole nā pālua electron-hole manuahi (e nānā i nā Mea Hoʻohui). Pono nā noiʻi noʻonoʻo ʻē aʻe i ʻoi aku ma mua o ke ʻano o ka pepa o kēia manawa e wehewehe i kēia mau pilikia.
I ka hōʻuluʻulu ʻana, ua hoʻohana mākou i ka tr-ARPES e aʻo i ka ultrafast interlayer charge transfer i kahi epitaxial WS2/graphene heterostructure. Ua ʻike mākou, i ka wā i hauʻoli ai i ka resonance i ka A-exciton o WS2 ma 2 eV, ua hoʻololi koke nā puka photoexcited i ka papa graphene aʻo nā electrons photoexcited e noho ana i ka papa WS2. Ua hoʻohālikelike mākou i kēia no ka nui o nā mokuʻāina hope loa no ka hoʻoili ʻana o ka lua ma mua o ka hoʻoili electron. Ua ʻike ʻia ke ola o ka mokuʻāina transient i hoʻokaʻawale ʻia he ∼1 ps. I ka hui pū ʻana me ka spin-selective optical excitation me ka hoʻohana ʻana i ke kukui polarized circularly polarized (22–25), hiki ke hui pū ʻia ka hoʻoili ʻana o ka ultrafast charge me ka hoʻololi ʻana. I kēia hihia, hiki ke hoʻohana ʻia ka WS2 / graphene heterostructure i noiʻi ʻia no ka hoʻokele ʻana o ka optical spin i loko o ka graphene e hopena ai i nā polokalamu optospintronic novel.
Ua ulu ʻia nā laʻana graphene ma nā wafers semiconducting 6H-SiC(0001) mai SiCrystal GmbH. ʻO nā wafers N-doped ma ka axis me kahi kuhi hewa ma lalo o 0.5 °. ʻO ka substrate SiC i kālai ʻia i ka hydrogen e wehe i nā ʻōpala a loaʻa i nā ʻāina pālahalaha maʻamau. ʻO ka maʻemaʻe a me ka atomically flat Si-terminated ili i laila graphitized ma ka annealing i ka hāpana ma Ar lewa ma 1300°C no 8 min (36). Ma kēia ala, ua loaʻa iā mākou kahi papa kalapona hoʻokahi kahi i hoʻokumu ai kēlā me kēia kolu kalapona i kahi paʻa covalent i ka substrate SiC (37). A laila ua hoʻololi ʻia kēia papa i loko o ka graphene sp2-hybridized quasi free-standing hole-doped graphene ma o ka hydrogen intercalation (38). Kuhi ʻia kēia mau laʻana he graphene/H-SiC(0001). Ua hana ʻia ke kaʻina holoʻokoʻa i loko o kahi keʻena ulu ulu ʻo Black Magic mai Aixtron. Ua hoʻokō ʻia ka ulu ʻana o WS2 i loko o kahi reactor pā wela maʻamau e ka haʻahaʻa haʻahaʻa haʻahaʻa kemika vapor deposition (39, 40) me ka hoʻohana ʻana i nā pauka WO3 a me S me ka lakio nui o 1:100 e like me nā precursors. Ua mālama ʻia nā pauka WO3 a me S ma 900 a me 200 ° C. Hoʻokomo ʻia ka pauka WO3 kokoke i ka substrate. Ua hoʻohana ʻia ʻo Argon ma ke ʻano he mea lawe kinoea me ke kahe o 8 sccm. Ua mālama ʻia ke kaomi i loko o ka reactor ma 0.5 mbar. Ua ʻike ʻia nā laʻana me ka microscopy electron lua, microscopy atomic ikaika, Raman, a me ka spectroscopy photoluminescence, a me ka diffraction electron haʻahaʻa. Ua hōʻike ʻia kēia mau ana i ʻelua mau kikowaena WS2 hoʻokahi-crystalline kahi i hoʻopili ʻia ai ka ΓK- a i ʻole ka ΓK'- kuhikuhi me ke kuhikuhi ΓK o ka papa graphene. Ua ʻokoʻa ka lōʻihi o ka ʻaoʻao ma waena o 300 a me 700 nm, a ʻo ka nui o ka uhi ʻana o WS2 ua kokoke i ~40%, kūpono no ka loiloi ARPES.
Ua hana ʻia nā hoʻokolohua static ARPES me kahi mea hoʻoponopono hemispherical (SPECS PHOIBOS 150) me ka hoʻohana ʻana i kahi ʻōnaehana hoʻopaʻa hoʻohui ʻia no ka ʻike ʻelua-dimensional o ka ikehu electron a me ka manawa. Unpolarized, monochromatic He Iα radiation (21.2 eV) o kahi kiʻekiʻe-flux He discharge kumu (VG Scienta VUV5000) ua hoʻohana 'ia no nā hoʻokolohua photoemission a pau. ʻOi aku ka maikaʻi o ka ikehu a me ka hoʻonā angular i kā mākou mau hoʻokolohua ma mua o 30 meV a me 0.3 ° (e pili ana me 0.01 Å−1), i kēlā me kēia. Hana ʻia nā hoʻokolohua a pau ma ka lumi wela. ʻO ka ARPES kahi ʻenehana pili i ka ʻili. No ke kipaku ʻana i nā photoelectrons mai ka WS2 a me ka papa graphene, ua hoʻohana ʻia nā laʻana me kahi uhi WS2 piha ʻole o ~40%.
Hoʻokumu ʻia ka hoʻonohonoho tr-ARPES ma kahi 1-kHz Titanium: Sapphire amplifier (Coherent Legend Elite Duo). Ua hoʻohana ʻia ʻo 2 mJ o ka mana hoʻopuka no ka hoʻokumu ʻana i nā harmonics kiʻekiʻe ma argon. ʻO ka hopena o ke kukui ultraviolet loa i hele i loko o kahi monochromator grating e hana ana i 100-fs probe pulses ma 26-eV photon ikehu. Ua hoʻouna ʻia ʻo 8mJ o ka mana hoʻopuka amplifier i kahi mea hoʻonui parametric optical (HE-TOPAS mai Light Conversion). ʻO ka kukuna hōʻailona ma ka ikehu photon 1-eV ua pālua ʻia i loko o kahi aniani beta barium borate no ka loaʻa ʻana o nā pulu pulu 2-eV. Hana ʻia nā ana tr-ARPES me kahi mea hoʻoponopono hemispherical (SPECS PHOIBOS 100). ʻO 240 meV a me 200 fs ka nui o ka ikehu a me ka hoʻonā kino.
Loaʻa nā mea hoʻohui no kēia ʻatikala ma http://advances.sciencemag.org/cgi/content/full/6/20/eaay0761/DC1
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Na Sven Aeschlimann, Antonio Rossi, Mariana Chávez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Hōʻike mākou i ka hoʻokaʻawale ʻana i ka ultrafast charge i kahi WS2/graphene heterostructure e hiki ai ke hoʻokuʻi ʻia i loko o ka graphene.
Na Sven Aeschlimann, Antonio Rossi, Mariana Chávez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Hōʻike mākou i ka hoʻokaʻawale ʻana i ka ultrafast charge i kahi WS2/graphene heterostructure e hiki ai ke hoʻokuʻi ʻia i loko o ka graphene.
© 2020 ʻAhahui ʻAmelika no ka holomua o ka ʻepekema. Ua mālama ʻia nā kuleana āpau. He hoa pili ʻo AAAS no HINARI, AGORA, OARE, CHORUS, CLOCKSS, CrossRef a me COUNTER.Science Advances ISSN 2375-2548.
Ka manawa hoʻouna: Mei-25-2020