Hoʻohana mākou i ka spectroscopy photoemission i hoʻonā ʻia i ka manawa a me ke kihi (tr-ARPES) e noiʻi i ka hoʻoili hoʻoili wikiwiki loa i loko o kahi heterostructure epitaxial i hana ʻia me ka monolayer WS2 a me graphene. Hoʻohui kēia heterostructure i nā pono o kahi semiconductor direct-gap me ka hoʻopili spin-orbit ikaika a me ka pilina māmā ikaika me nā mea o kahi semimetal e hoʻokipa ana i nā mea lawe massless me ka neʻe kiʻekiʻe loa a me nā ola spin lōʻihi. ʻIke mākou, ma hope o ka photoexcitation ma ka resonance i ka A-exciton ma WS2, hoʻololi koke nā lua photoexcited i loko o ka papa graphene ʻoiai e noho ana nā electrons photoexcited i loko o ka papa WS2. ʻIke ʻia ka hopena o ka mokuʻāina transient i hoʻokaʻawale ʻia e ka hoʻouka he ola o ~1 ps. Hāʻawi mākou i kā mākou mau ʻike i nā ʻokoʻa i ka hakahaka phase scattering i hoʻokumu ʻia e ka alignment pili o WS2 a me nā hui graphene e like me ka hōʻike ʻana e nā ARPES hoʻonā 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 hoʻokomo spin optical maikaʻi i loko o graphene.
ʻO ka loaʻa ʻana o nā mea ʻelua-dimensional like ʻole ua wehe i ka hiki ke hana i nā heterostructures lahilahi hou me nā hana hou loa e pili ana i ka nānā ʻana o ka dielectric i hana ʻia a me nā hopena like ʻole i hoʻokomo ʻia e ka pili kokoke (1-3). Ua ʻike ʻia nā mea hōʻoia-o-kumumanaʻo no nā noi e hiki mai ana ma ke kahua o nā mea uila a me nā optoelectronics (4-6).
Maanei, ke kālele nei mākou i nā heterostructures epitaxial van der Waals i haku ʻia me ka monolayer WS2, kahi semiconductor direct-gap me ka hoʻopili spin-orbit ikaika a me ka māhele ʻana o ka spin nui o ke ʻano band ma muli o ka haʻihaʻi ʻana o ka symmetry inversion (7), a me ka monolayer graphene, kahi semimetal me ke ʻano band conical a me ka neʻe ʻana o ka mea lawe kiʻekiʻe loa (8), i ulu ʻia ma ka hydrogen-terminated SiC (0001). ʻO nā hōʻailona mua no ka hoʻoili hoʻoili ultrafast (9-15) a me nā hopena hoʻopili spin-orbit i hoʻokomo ʻia e ka proximity (16-18) e hoʻolilo iā WS2/graphene a me nā heterostructures like i mau moho no nā noi optoelectronic (19) a me optospintronic (20) e hiki mai ana.
Ua hoʻomaka mākou e hōʻike i nā ala hoʻomaha o nā hui electron-hole photogenerated ma WS2/graphene me ka spectroscopy photoemission i hoʻonā ʻia i ka manawa a me ke kihi (tr-ARPES). No kēlā kumu, hoʻonāukiuki mākou i ka heterostructure me nā pulse pump 2-eV e resonant ana i ka A-exciton ma WS2 (21, 12) a hoʻokuke i nā photoelectrons me ka pulse probe i hoʻopaneʻe ʻia i ka manawa ʻelua ma ka ikehu photon 26-eV. Hoʻoholo mākou i ka ikehu kinetic a me ke kihi hoʻokuʻu o nā photoelectrons me kahi mea kālailai hemispherical ma ke ʻano he hana o ka lohi pump-probe e loaʻa ai ke komo i ka momentum-, ikehu-, a me ka dynamics lawe i hoʻonā ʻia i ka manawa. ʻO ka ikehu a me ka hoʻonā manawa he 240 meV a me 200 fs, kēlā me kēia.
Hāʻawi kā mākou mau hopena i nā hōʻike pololei no ka hoʻoili ʻana o ka uku wikiwiki loa ma waena o nā papa i hoʻonohonoho ʻia epitaxially, e hōʻoia ana i nā hōʻailona mua e pili ana i nā ʻenehana optical āpau i nā heterostructures i hōʻuluʻulu lima ʻia me ka hoʻonohonoho azimuthal arbitrary o nā papa (9-15). Eia kekahi, hōʻike mākou he asymmetric loa kēia hoʻoili uku. Hōʻike kā mākou mau ana i kahi kūlana transient i hoʻokaʻawale ʻia me ka uku i ʻike ʻole ʻia ma mua me nā electrons photoexcited a me nā lua i loaʻa i ka papa WS2 a me graphene, kēlā me kēia, e ola ana no ~ 1 ps. Wehewehe mākou i kā mākou mau ʻike ma ke ʻano o nā ʻokoʻa i ka hakahaka pae scattering no ka hoʻoili electron a me ka lua i hoʻokumu ʻia e ka hoʻonohonoho pili o WS2 a me nā hui graphene e like me ka mea i hōʻike ʻia e nā ARPES hoʻonā kiʻekiʻe. I hui pū ʻia me ka spin- a me ke awāwa-selective optical excitation (22-25) hiki i nā WS2/graphene heterostructures ke hāʻawi i kahi kahua hou no ka hoʻokomo ʻana o ka optical spin ultrafast maikaʻi i loko o graphene.
Hōʻike ka Kiʻi 1A i kahi ana ARPES hoʻonā kiʻekiʻe i loaʻa me kahi kukui helium o ke ʻano hui ma ke kuhikuhi ΓK o ka epitaxial WS2/graphene heterostructure. Ua ʻike ʻia ka cone Dirac ua hole-doped me ka kiko Dirac i loaʻa ma kahi o 0.3 eV ma luna o ka equilibrium chemical potential. Ua ʻike ʻia ka piko o ka spin-split WS2 valence band ma kahi o 1.2 eV ma lalo o ka equilibrium chemical potential.
(A) ʻO ke au kiʻi kaulike i ana ʻia ma ke kuhikuhi ΓK me kahi kukui helium unpolarized. (B) ʻO ke au kiʻi no ka lohi pump-probe maikaʻi ʻole i ana ʻia me nā pulse ultraviolet koʻikoʻi p-polarized ma ka ikehu photon 26-eV. Hōʻailona nā laina hina hina a me ka ʻulaʻula i ke kūlana o nā ʻaoʻao laina i hoʻohana ʻia e unuhi i nā kūlana piko transient ma ke Kiʻi 2. (C) Nā loli i hoʻokomo ʻia e ka pump o ka photocurrent 200 fs ma hope o ka photoexcitation ma kahi ikehu photon pump o 2 eV me ka fluence pump o 2 mJ/cm2. Hōʻike ʻia ka loaʻa a me ka nalowale o nā photoelectrons ma ka ʻulaʻula a me ka uliuli, kēlā me kēia. Hōʻike nā pahu i kahi o ka hoʻohui ʻana no nā kaha pump-probe i hōʻike ʻia ma ke Kiʻi 3.
Hōʻike ka Kiʻi 1B i kahi kiʻi tr-ARPES o ke ʻano o ka hui kokoke i ka WS2 a me nā graphene K-points i ana ʻia me nā pulse ultraviolet koʻikoʻi 100-fs ma ka ikehu photon 26-eV ma ka lohi pump-probe maikaʻi ʻole ma mua o ka hiki ʻana mai o ka pulse pump. Maanei, ʻaʻole i hoʻoholo ʻia ka māhele ʻana o ka spin ma muli o ka hōʻino ʻana o ka laʻana a me ke alo o ka pulse pump 2-eV e hoʻonui ai i ka hoʻouka ākea o nā hiʻohiʻona spectral. Hōʻike ka Kiʻi 1C i nā loli i hoʻokomo ʻia e ka pump o ka photocurrent e pili ana i ka Kiʻi 1B ma kahi lohi pump-probe o 200 fs kahi i hiki ai ka hōʻailona pump-probe i kona kiʻekiʻe. Hōʻike nā kala ʻulaʻula a me ka uliuli i ka loaʻa a me ka nalowale o nā photoelectrons, kēlā me kēia.
No ka nānā ʻana i kēia dynamics waiwai me nā kikoʻī hou aku, hoʻoholo mua mākou i nā kūlana piko transient o ka hui valence WS2 a me ka graphene π-band ma nā laina dashed ma ke Kiʻi 1B e like me ka wehewehe kikoʻī ʻana ma nā Mea Hoʻohui. ʻIke mākou e neʻe ana ka hui valence WS2 i luna e 90 meV (Kiʻi 2A) a neʻe ana ka graphene π-band i lalo e 50 meV (Kiʻi 2B). ʻIke ʻia ke ola exponential o kēia mau neʻe ʻana he 1.2 ± 0.1 ps no ka hui valence o WS2 a me 1.7 ± 0.3 ps no ka graphene π-band. Hāʻawi kēia mau neʻe piko i ka hōʻike mua o ka hoʻouka ʻana transient o nā papa ʻelua, kahi e hoʻonui ai ka hoʻouka maikaʻi (maikaʻi ʻole) i ka ikehu hoʻopaʻa o nā kūlana uila. E hoʻomaopopo ʻo ka upshift o ka hui valence WS2 ke kuleana no ka hōʻailona pump-probe koʻikoʻi ma kahi i hōʻailona ʻia e ka pahu ʻeleʻele ma ke Kiʻi 1C.
Ka loli ʻana o ke kūlana kiʻekiʻe o ka hui valence WS2 (A) a me ka graphene π-band (B) ma ke ʻano he hana o ka hoʻopaneʻe pump-probe me nā exponential fits (nā laina mānoanoa). ʻO ke ola o ka neʻe ʻana o WS2 ma (A) he 1.2 ± 0.1 ps. ʻO ke ola o ka neʻe ʻana o graphene ma (B) he 1.7 ± 0.3 ps.
ʻO ka mea aʻe, hoʻohui mākou i ka hōʻailona pump-probe ma luna o nā wahi i hōʻike ʻia e nā pahu kala ma ke Kiʻi 1C a hoʻolālā i nā helu hopena ma ke ʻano he hana o ka hoʻopaneʻe pump-probe ma ke Kiʻi 3. Hōʻike ka Curve 1 ma ke Kiʻi 3 i ka dynamics o nā mea lawe photoexcited kokoke i ka lalo o ke kāʻei conduction o ka papa WS2 me ke ola o 1.1 ± 0.1 ps i loaʻa mai kahi exponential fit i ka ʻikepili (e ʻike i nā Mea Hoʻohui).
ʻO nā kaha o ka pump-probe ma ke ʻano he hana o ka lohi i loaʻa ma ka hoʻohui ʻana i ke kahe kiʻi ma luna o ka wahi i hōʻike ʻia e nā pahu ma ke Kiʻi 1C. ʻO nā laina mānoanoa he mau kūpono exponential i ka ʻikepili. Piʻo (1) Ka heluna lawe transient ma ke kāʻei conduction o WS2. Piʻo (2) Hōʻailona pump-probe o ka π-band o graphene ma luna o ka equilibrium chemical potential. Piʻo (3) Hōʻailona pump-probe o ka π-band o graphene ma lalo o ka equilibrium chemical potential. Piʻo (4) Hōʻailona pump-probe net ma ke kāʻei valence o WS2. ʻIke ʻia nā ola he 1.2 ± 0.1 ps ma (1), 180 ± 20 fs (loaʻa) a me ~2 ps (pohō) ma (2), a me 1.8 ± 0.2 ps ma (3).
Ma nā piʻo 2 a me 3 o ke Kiʻi 3, hōʻike mākou i ka hōʻailona pump-probe o ka graphene π-band. ʻIke mākou he pōkole loa ke ola o ka loaʻa ʻana o nā electrons ma luna o ka equilibrium chemical potential (piʻo 2 ma ke Kiʻi 3) (180 ± 20 fs) i hoʻohālikelike ʻia me ka nalowale o nā electrons ma lalo o ka equilibrium chemical potential (1.8 ± 0.2 ps ma ke piʻo 3 Kiʻi 3). Eia kekahi, ʻike ʻia ka loaʻa mua o ka photocurrent ma ke piʻo 2 o ke Kiʻi 3 e lilo i pohō ma t = 400 fs me ke ola o ~2 ps. ʻIke ʻia ʻaʻohe o ka asymmetry ma waena o ka loaʻa a me ka pohō i ka hōʻailona pump-probe o ka monolayer graphene i wehe ʻole ʻia (e ʻike i ke kiʻi S5 ma nā Mea Hoʻohui), e hōʻike ana he hopena ka asymmetry o ka interlayer coupling ma ka WS2/graphene heterostructure. ʻO ka nānā ʻana i ka loaʻa pōkole a me ka pohō lōʻihi ma luna a ma lalo o ka hiki kemika kaulike, kēlā me kēia, e hōʻike ana ua wehe pono ʻia nā electrons mai ka papa graphene ma luna o ka photoexcitation o ka heterostructure. ʻO ka hopena, lilo ka papa graphene i hoʻopiʻi maikaʻi ʻia, kahi e kūlike me ka hoʻonui ʻana o ka ikehu hoʻopaʻa o ka π-band i loaʻa ma ke Kiʻi 2B. ʻO ka downshift o ka π-band e wehe i ka huelo ikehu kiʻekiʻe o ka hoʻolaha Fermi-Dirac kaulike mai luna aʻe o ka hiki kemika kaulike, kahi e wehewehe hapa ai i ka loli o ka hōʻailona o ka hōʻailona pump-probe ma ka piʻo 2 o ke Kiʻi 3. E hōʻike mākou ma lalo nei ua hoʻonui hou ʻia kēia hopena e ka pohō transient o nā electrons ma ka π-band.
Kākoʻo ʻia kēia hiʻohiʻona e ka hōʻailona pump-probe net o ka hui valence WS2 ma ke kiʻikuhi 4 o ke Kiʻi 3. Ua loaʻa kēia mau ʻikepili ma ka hoʻohui ʻana i nā helu ma luna o ka ʻāpana i hāʻawi ʻia e ka pahu ʻeleʻele ma ke Kiʻi 1B e hopu ana i nā electrons i hoʻokuʻu ʻia mai ka hui valence ma nā lohi pump-probe āpau. I loko o nā kaha hewa hoʻokolohua, ʻaʻole mākou e ʻike i kahi hōʻailona no ke alo o nā lua i loko o ka hui valence o WS2 no kekahi lohi pump-probe. Hōʻike kēia, ma hope o ka photoexcitation, ua hoʻopiha hou ʻia kēia mau lua i kahi manawa pōkole i hoʻohālikelike ʻia me kā mākou hoʻonā manawa.
No ka hāʻawi ʻana i ka hōʻoia hope loa no kā mākou kuhiakau o ka hoʻokaʻawale ʻana o ka uku wikiwiki loa i loko o ka WS2/graphene heterostructure, hoʻoholo mākou i ka helu o nā lua i hoʻoili ʻia i ka papa graphene e like me ka mea i wehewehe kikoʻī ʻia ma nā Mea Hoʻohui. I ka pōkole, ua hoʻokomo ʻia ka hoʻolaha uila transient o ka π-band me kahi hoʻolaha Fermi-Dirac. A laila ua helu ʻia ka helu o nā lua mai nā waiwai i loaʻa no ka hiki kemika transient a me ka mahana uila. Hōʻike ʻia ka hopena ma ke Kiʻi 4. ʻIke mākou ua hoʻoili ʻia ka huina o ~5 × 1012 mau lua/cm2 mai WS2 a i graphene me kahi ola exponential o 1.5 ± 0.2 ps.
Ka loli ʻana o ka helu o nā lua i loko o ka π-band ma ke ʻano he hana o ka hoʻopaneʻe pump-probe me ka exponential fit e loaʻa ana kahi ola o 1.5 ± 0.2 ps.
Mai nā mea i loaʻa ma nā Kiʻi 2 a hiki i ka 4, ʻike ʻia ke kiʻi microscopic ma lalo nei no ka hoʻoili ʻana o ka uku wikiwiki loa i loko o ka WS2/graphene heterostructure (Kiʻi 5). ʻO ka photoexcitation o ka WS2/graphene heterostructure ma 2 eV e hoʻopiha nui ana i ka A-exciton ma WS2 (Kiʻi 5A). Hiki ke hoʻonui ʻia nā hoʻonāukiuki uila hou aʻe ma waena o ka Dirac point i loko o ka graphene a ma waena o nā kāʻei WS2 a me graphene akā ʻaʻole nui ka pono. Hoʻopiha hou ʻia nā lua photoexcited i loko o ka valence band o WS2 e nā electrons e puka mai ana mai ka graphene π-band ma kahi manawa pōkole i hoʻohālikelike ʻia me kā mākou hoʻonā manawa (Kiʻi 5A). ʻO ke ola o nā electrons photoexcited i loko o ka conduction band o WS2 he ~1 ps (Kiʻi 5B). Eia nō naʻe, pono ~2 ps e hoʻopiha hou i nā lua i loko o ka graphene π-band (Kiʻi 5B). Hōʻike kēia, ma waho aʻe o ka hoʻoili pololei ʻana o ka electron ma waena o ka hui hoʻoili WS2 a me ka hui graphene π-band, pono e noʻonoʻo ʻia nā ala hoʻomaha hou aʻe—hiki paha ma o nā kūlana kīnā (26)—e hoʻomaopopo i ka dinamika piha.
(A) Hoʻokomo ka Photoexcitation ma ke kani ʻana i ka WS2 A-exciton ma 2 eV i nā electrons i loko o ke kāʻei conduction o WS2. Hoʻopiha hou ʻia nā lua e pili ana i loko o ke kāʻei valence o WS2 e nā electrons mai ka graphene π-band. (B) ʻO ke ola o nā mea lawe photoexcited i loko o ke kāʻei conduction o WS2 he ~1 ps. Ola nā lua i loko o ka graphene π-band no ~2 ps, e hōʻike ana i ke koʻikoʻi o nā kahawai hoʻopuehu hou i hōʻike ʻia e nā pua dashed. Hōʻike nā laina ʻeleʻele dashed i loko o (A) a me (B) i nā neʻe ʻana o ke kāʻei a me nā loli i ka hiki kemika. (C) I ke kūlana transient, ua hoʻopiʻi maikaʻi ʻole ʻia ka papa WS2 ʻoiai ua hoʻopiʻi maikaʻi ʻia ka papa graphene. No ka hoʻonāukiuki spin-selective me ka mālamalama polarized circularly, manaʻo ʻia nā electrons photoexcited i loko o WS2 a me nā lua e pili ana i loko o graphene e hōʻike i ka polarization spin kū'ē.
I ke kūlana transient, noho nā electrons photoexcited i loko o ke kāʻei conduction o WS2 ʻoiai aia nā lua photoexcited i loko o ka π-band o graphene (Kiʻi 5C). ʻO ke ʻano kēia ua hoʻopiʻi maikaʻi ʻole ʻia ka papa WS2 a ua hoʻopiʻi maikaʻi ʻia ka papa graphene. Hoʻopili kēia i nā neʻe piko transient (Kiʻi 2), ka asymmetry o ka hōʻailona pump-probe graphene (nā piʻo 2 a me 3 o ke Kiʻi 3), ka ʻole o nā lua i loko o ke kāʻei valence o WS2 (piʻo 4 Kiʻi 3), a me nā lua hou i loko o ka graphene π-band (Kiʻi 4). ʻO ke ola o kēia kūlana i hoʻokaʻawale ʻia e ka hoʻopiʻi he ~1 ps (piʻo 1 Kiʻi 3).
Ua ʻike ʻia nā kūlana transient i hoʻokaʻawale ʻia e ka uku like ma nā heterostructures van der Waals pili i hana ʻia mai ʻelua semiconductors direct-gap me ke ʻano II band alignment a me ka staggered bandgap (27–32). Ma hope o ka photoexcitation, ua ʻike ʻia nā electrons a me nā lua e neʻe wikiwiki i ka lalo o ka conduction band a i ka piko o ka valence band, kēlā me kēia, aia ma nā papa like ʻole o ka heterostructure (27–32).
I ke ʻano o kā mākou WS2/graphene heterostructure, ʻo ka wahi ʻoi aku ka maikaʻi o ka ikehu no nā electrons a me nā lua ma ka pae Fermi i loko o ka papa graphene metala. No laila, e manaʻo ʻia e hoʻololi koke nā electrons a me nā lua i ka graphene π-band. Eia nō naʻe, hōʻike maopopo kā mākou mau ana ʻana he ʻoi aku ka maikaʻi o ka hoʻoili ʻana o ka lua (<200 fs) ma mua o ka hoʻoili ʻana o ka uila (∼1 ps). Hoʻopili mākou i kēia i ka hoʻonohonoho ikehu pili o ka WS2 a me nā hui graphene e like me ka mea i hōʻike ʻia ma ke Kiʻi 1A e hāʻawi ana i kahi helu nui o nā mokuʻāina hope loa no ka hoʻoili ʻana o ka lua i hoʻohālikelike ʻia me ka hoʻoili uila e like me ka mea i manaʻo ʻia e (14, 15). I kēia hihia, me ka manaʻo he ~2 eV WS2 bandgap, aia ka kiko graphene Dirac a me ka equilibrium chemical potential ma ~0.5 a me ~0.2 eV ma luna o ka waena o ka WS2 bandgap, kēlā me kēia, e uhaʻi ana i ka symmetry electron-hole. ʻIke mākou ʻo ka helu o nā kūlana hope loa i loaʻa no ka hoʻoili ʻana o ka lua he ~6 mau manawa ʻoi aku ka nui ma mua o ka hoʻoili ʻana o ka uila (e ʻike i nā Mea Hoʻohui), ʻo ia ke kumu e manaʻo ʻia ai ka wikiwiki o ka hoʻoili ʻana o ka lua ma mua o ka hoʻoili ʻana o ka uila.
ʻO kahi kiʻi microscopic piha o ka hoʻoili hoʻoili asymmetric ultrafast i ʻike ʻia, akā naʻe, e noʻonoʻo pū i ka overlap ma waena o nā orbitals e hana ana i ka hana nalu A-exciton ma WS2 a me ka graphene π-band, kēlā me kēia, nā kahawai electron-electron a me nā electron-phonon scattering like ʻole me nā palena i kau ʻia e ka momentum, ikehu, spin, a me ka pseudospin conservation, ka mana o nā oscillations plasma (33), a me ke kuleana o kahi hoʻonāukiuki displacive o nā oscillations phonon coherent e hiki ke hoʻoponopono i ka hoʻoili hoʻoili (34, 35). Eia kekahi, hiki i kekahi ke kuhi inā loaʻa i ka mokuʻāina hoʻoili hoʻoili i ʻike ʻia nā excitons hoʻoili hoʻoili a i ʻole nā hui electron-hole manuahi (e ʻike i nā Mea Hoʻohui). Pono nā noiʻi theoretical hou aʻe e hele ma mua o ka laulā o ka pepa o kēia manawa e wehewehe i kēia mau pilikia.
I ka hōʻuluʻulu manaʻo, ua hoʻohana mākou iā tr-ARPES e aʻo i ka hoʻoili uku interlayer ultrafast i loko o kahi heterostructure epitaxial WS2/graphene. Ua ʻike mākou, i ka wā i hoʻonāukiuki ʻia ai ma ka resonance i ka A-exciton o WS2 ma 2 eV, hoʻololi koke nā lua photoexcited i loko o ka papa graphene ʻoiai e noho ana nā electrons photoexcited i loko o ka papa WS2. Ua hoʻopili mākou i kēia i ka ʻoiaʻiʻo ʻoi aku ka nui o nā mokuʻāina hope loa no ka hoʻoili lua ma mua o ka hoʻoili electron. Ua ʻike ʻia ke ola o ke kūlana transient i hoʻokaʻawale ʻia e ka uku he ~1 ps. I ka hui pū ʻana me ka spin-selective optical excitation me ka hoʻohana ʻana i ka mālamalama polarized circularly (22-25), hiki ke hele pū ʻia ka hoʻoili uku ultrafast i ʻike ʻia me ka hoʻoili spin. I kēia hihia, hiki ke hoʻohana ʻia ka heterostructure WS2/graphene i noiʻi ʻia no ka hoʻokomo spin optical maikaʻi i loko o ka graphene e hopena ana i nā mea hana optospintronic hou.
Ua ulu ʻia nā laʻana graphene ma nā wafers semiconducting 6H-SiC (0001) kalepa mai SiCrystal GmbH. Aia nā wafers N-doped ma ke axis me kahi miscut ma lalo o 0.5°. Ua hydrogen-etched ka substrate SiC e wehe i nā ʻōpala a loaʻa nā terraces pālahalaha maʻamau. A laila ua graphitized ka ʻili Si-terminated maʻemaʻe a atomically pālahalaha ma ka annealing ʻana i ka laʻana ma ka lewa Ar ma 1300°C no 8 min (36). Ma kēia ʻano, ua loaʻa iā mākou kahi papa kalapona hoʻokahi kahi i hoʻokumu ai kēlā me kēia atom kalapona ʻekolu i kahi pilina covalent i ka substrate SiC (37). A laila ua hoʻololi ʻia kēia papa i graphene hole-doped quasi free-standing sp2-hybridized piha ma o ka hydrogen intercalation (38). Ua kapa ʻia kēia mau laʻana he graphene/H-SiC (0001). Ua hana ʻia ke kaʻina holoʻokoʻa ma kahi keʻena ulu Black Magic kalepa mai Aixtron. Ua hoʻokō ʻia ka ulu ʻana o WS2 i loko o kahi reactor paia wela maʻamau ma o ka waiho ʻana o ka mahu kemika haʻahaʻa haʻahaʻa (39, 40) me ka hoʻohana ʻana i nā pauka WO3 a me S me ka lakio nui o 1:100 ma ke ʻano he precursors. Ua mālama ʻia nā pauka WO3 a me S ma 900 a me 200°C, kēlā me kēia. Ua kau ʻia ka pauka WO3 kokoke i ka substrate. Ua hoʻohana ʻia ʻo Argon ma ke ʻano he kinoea lawe me ke kahe o 8 sccm. Ua mālama ʻia ke kaomi i loko o ka reactor ma 0.5 mbar. Ua wehewehe ʻia nā laʻana me ka microscopy electron lua, ka microscopy ikaika atomika, Raman, a me ka spectroscopy photoluminescence, a me ka diffraction electron ikehu haʻahaʻa. Ua hōʻike kēia mau ana i ʻelua mau kikowaena WS2 single-crystalline like ʻole kahi e kūlike ai ke kuhikuhi ΓK- a i ʻole ke kuhikuhi ΓK' me ke kuhikuhi ΓK o ka papa graphene. Ua ʻokoʻa ka lōʻihi o nā ʻaoʻao kikowaena ma waena o 300 a me 700 nm, a ua hoʻokokoke ʻia ka huina o ka uhi ʻana o WS2 i kahi o 40%, kūpono no ka loiloi ARPES.
Ua hana ʻia nā hoʻokolohua ARPES static me kahi mea kālailai hemispherical (SPECS PHOIBOS 150) me ka hoʻohana ʻana i kahi ʻōnaehana mea hoʻopili-hoʻouka no ka ʻike ʻana i ka ikehu electron a me ka momentum ʻelua-dimensional. Ua hoʻohana ʻia ka radiation He Iα monochromatic Unpolarized (21.2 eV) o kahi kumu hoʻokuʻu He flux kiʻekiʻe (VG Scienta VUV5000) no nā hoʻokolohua photoemission āpau. 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 like me 0.01 Å−1), kēlā me kēia. Ua hana ʻia nā hoʻokolohua āpau ma ka mahana o ka lumi. He ʻenehana koʻikoʻi loa ka ARPES i ka ʻili. No ka hoʻokuke ʻana i nā photoelectrons mai ka WS2 a me ka papa graphene, ua hoʻohana ʻia nā laʻana me ka uhi WS2 piha ʻole o ~40%.
Ua hoʻokumu ʻia ka hoʻonohonoho ʻana o tr-ARPES ma luna o kahi amplifier Titanium:Sapphire 1-kHz (Coherent Legend Elite Duo). Ua hoʻohana ʻia he 2 mJ o ka mana hoʻopuka no ka hana ʻana i nā harmonics kiʻekiʻe ma argon. Ua hala ka mālamalama ultraviolet koʻikoʻi ma o kahi monochromator grating e hana ana i nā pulse probe 100-fs ma ka ikehu photon 26-eV. Ua hoʻouna ʻia he 8mJ o ka mana hoʻopuka amplifier i loko o kahi amplifier parametric optical (HE-TOPAS mai ka Light Conversion). Ua pāpālua ʻia ke kukuna hōʻailona ma ka ikehu photon 1-eV i loko o kahi kristal beta barium borate e loaʻa ai nā pulse pump 2-eV. Ua hana ʻia nā ana tr-ARPES me kahi mea kālailai hemispherical (SPECS PHOIBOS 100). ʻO ka ikehu holoʻokoʻa a me ka hoʻonā manawa he 240 meV a me 200 fs, kēlā me kēia.
Loaʻa nā mea kōkua no kēia ʻatikala ma http://advances.sciencemag.org/cgi/content/full/6/20/eaay0761/DC1
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ʻO kēia nīnau no ka hoʻāʻo ʻana inā he malihini kanaka ʻoe a ʻaʻole paha a no ka pale ʻana i nā hoʻouna spam aunoa.
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 o ka hoʻouka wikiwiki loa i loko o kahi heterostructure WS2/graphene e hiki ai ke hoʻokomo i ka optical spin 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 o ka hoʻouka wikiwiki loa i loko o kahi heterostructure WS2/graphene e hiki ai ke hoʻokomo i ka optical spin 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