Timagwiritsa ntchito nthawi ndi ngodya photoemission spectroscopy (tr-ARPES) kuti tifufuze kusamutsa kwa charge mwachangu mu epitaxial heterostructure yopangidwa ndi monolayer WS2 ndi graphene. Heterostructure iyi imaphatikiza zabwino za direct-gap semiconductor yokhala ndi spin-orbit coupling yamphamvu komanso kulumikizana kwamphamvu kwa light-matter ndi zomwe zimapangidwa ndi semimetal hosting massless carriers zomwe zimakhala ndi kuyenda kwakukulu komanso nthawi yayitali yozungulira. Tapeza kuti, pambuyo pa photoexcitation pa resonance ku A-exciton mu WS2, mabowo a photoexcited amasamutsidwa mwachangu mu graphene layer pomwe ma electron a photoexcited amakhalabe mu WS2 layer. Mkhalidwe wosinthika womwe umaseweredwa ndi charge umapezeka kuti uli ndi moyo wa ~1 ps. Timapereka zomwe tapeza chifukwa cha kusiyana kwa malo ogawa chifukwa cha kuyanjana kwa WS2 ndi graphene bands monga momwe zawululidwira ndi high-resolution ARPES. Kuphatikiza ndi spin-selective optical excitation, WS2/graphene heterostructure yomwe yafufuzidwa ikhoza kupereka nsanja yolumikizira bwino optical spin mu graphene.
Kupezeka kwa zinthu zambiri zosiyanasiyana zamitundu iwiri kwatsegula mwayi wopanga mapangidwe atsopano amitundu yosiyanasiyana okhala ndi magwiridwe antchito atsopano kutengera kuwunikira kwa dielectric koyenera komanso zotsatira zosiyanasiyana zoyandikira (1-3). Zipangizo zotsimikizira mfundo zogwiritsira ntchito mtsogolo m'munda wa zamagetsi ndi ma optoelectronics zapezeka (4-6).
Pano, tikuyang'ana kwambiri pa epitaxial van der Waals heterostructures zomwe zili ndi monolayer WS2, semiconductor yolunjika yokhala ndi spin-orbit coupling yamphamvu komanso kugawanika kwakukulu kwa spin structure ya band chifukwa cha kusweka kwa inversion symmetry (7), ndi monolayer graphene, semimetal yokhala ndi conical band structure komanso highly carrier mobility (8), yomwe imakula pa hydrogen-terminated SiC(0001). Zizindikiro zoyamba za ultrafast charge transfer (9-15) ndi zotsatira za spin-orbit coupling zomwe zimayambitsidwa ndi proximity (16-18) zimapangitsa WS2/graphene ndi heterostructures zofanana kukhala ndi chiyembekezo chogwiritsa ntchito mtsogolo mwa optoelectronic (19) ndi optospintronic (20).
Tinayamba kuulula njira zopumulira za ma electron-hole awiriawiri opangidwa ndi photogenerated mu WS2/graphene pogwiritsa ntchito nthawi ndi angle-resolved photoemission spectroscopy (tr-ARPES). Pachifukwa chimenecho, timasangalatsa heterostructure ndi 2-eV pump pulses resonant to A-exciton mu WS2 (21, 12) ndikutulutsa ma photoelectron ndi nthawi yachiwiri yochedwa probe pulse pa 26-eV photon energy. Timazindikira mphamvu ya kinetic ndi emission angle ya ma photoelectron pogwiritsa ntchito hemispherical analyzer ngati ntchito ya pump-probe delay kuti tipeze mwayi wopeza mphamvu, mphamvu, ndi nthawi yokhazikika. Mphamvu ndi nthawi ndi 240 meV ndi 200 fs, motsatana.
Zotsatira zathu zimapereka umboni wolunjika wa kusamutsa mphamvu mwachangu pakati pa zigawo za epitaxially, kutsimikizira zizindikiro zoyambirira kutengera njira zonse zowunikira m'ma heterostructures ofanana ndi manja omwe ali ndi azimuthal alignment ya zigawo (9-15). Kuphatikiza apo, tikuwonetsa kuti kusamutsa mphamvu kumeneku sikuli kofanana kwambiri. Miyeso yathu ikuwonetsa mkhalidwe wa transient womwe sunawonedwepo kale wokhala ndi ma electron ndi mabowo omwe ali mu WS2 ndi graphene layer, motsatana, omwe amakhala kwa ∼1 ps. Timatanthauzira zomwe tapeza potengera kusiyana kwa malo ogawa magetsi a electron ndi mabowo omwe amayambitsidwa ndi kuyanjana kwa WS2 ndi graphene bands monga momwe zawululidwira ndi ARPES yapamwamba. Kuphatikiza ndi spin- ndi valley-selective optical excitation (22-25) WS2/graphene heterostructures zitha kupereka nsanja yatsopano yolumikizira bwino ultrafast optical spin mu graphene.
Chithunzi 1A chikuwonetsa muyeso wa ARPES wapamwamba kwambiri womwe wapezeka ndi nyali ya helium ya kapangidwe ka gulu motsatira njira ya ΓK ya epitaxial WS2/graphene heterostructure. Khoni ya Dirac imapezeka kuti ili ndi dzenje ndipo mfundo ya Dirac ili pa ∼0.3 eV pamwamba pa mphamvu ya mankhwala yofanana. Pamwamba pa gulu la valence la spin-split WS2 valence pakupezeka kuti ndi ∼1.2 eV pansi pa mphamvu ya mankhwala yofanana.
(A) Mphamvu yofanana yoyezedwa motsatira njira ya ΓK ndi nyali ya helium yosaponderezedwa. (B) Mphamvu yooneka ngati ya pompu-probe delay yoyezedwa ndi ma pulse a ultraviolet oponderezedwa ndi p-polarized extreme ultraviolet pa mphamvu ya photon ya 26-eV. Mizere yofiira ndi imvi yofiira imawonetsa malo a ma profiles omwe amagwiritsidwa ntchito kuchotsa malo a transient peak mu Chithunzi 2. (C) Kusintha kwa mphamvu yooneka ngati ya pompu kwa 200 fs pambuyo pa photoexcitation pa mphamvu ya photon ya pompu ya 2 eV yokhala ndi fluence ya pompu ya 2 mJ/cm2. Kuchuluka ndi kutayika kwa ma photoelectron akuwonetsedwa mu ofiira ndi abuluu, motsatana. Mabokosiwo akuwonetsa malo ophatikizika a ma trace a pompu-probe omwe akuwonetsedwa mu Chithunzi 3.
Chithunzi 1B chikuwonetsa chithunzi cha tr-ARPES cha kapangidwe ka gulu pafupi ndi WS2 ndi graphene K-points zoyesedwa ndi ma pulse a ultraviolet a 100-fs pa mphamvu ya photon ya 26-eV pa kuchedwa kwa pump-probe kusanafike kwa pump. Pano, kugawanika kwa spin sikuthetsedwa chifukwa cha kuwonongeka kwa zitsanzo ndi kukhalapo kwa pulse ya pump ya 2-eV komwe kumapangitsa kuti mawonekedwe a spectral ayambe kufalikira. Chithunzi 1C chikuwonetsa kusintha kwa photocurrent komwe kumachitika chifukwa cha pump poyerekeza ndi Chithunzi 1B pa kuchedwa kwa pump-probe kwa 200 fs pomwe chizindikiro cha pump-probe chimafika pachimake. Mitundu yofiira ndi yabuluu imasonyeza kuwonjezeka ndi kutayika kwa ma photoelectron, motsatana.
Kuti tiwunikenso bwino za mphamvu zimenezi, choyamba tipeza malo a peak osakhalitsa a gulu la valence la WS2 ndi gulu la graphene π motsatira mizere yodulidwa mu Chithunzi 1B monga momwe tafotokozera mwatsatanetsatane mu Zowonjezera. Tikupeza kuti gulu la valence la WS2 limasuntha ndi 90 meV (Chithunzi 2A) ndipo gulu la graphene π limasuntha ndi 50 meV (Chithunzi 2B). Nthawi yowonjezereka ya kusinthaku ikupezeka kuti ndi 1.2 ± 0.1 ps pa gulu la valence la WS2 ndi 1.7 ± 0.3 ps pa gulu la graphene π. Kusintha kumeneku kumapereka umboni woyamba wa kuyitanitsa kosakhalitsa kwa zigawo ziwirizi, komwe mphamvu yowonjezera (yoipa) imawonjezera (imachepetsa) mphamvu yomangira yamagetsi. Dziwani kuti kukwera kwa gulu la valence la WS2 ndiko komwe kumayambitsa chizindikiro chodziwika bwino cha pump-probe m'dera lomwe lalembedwa ndi bokosi lakuda mu Chithunzi 1C.
Kusintha kwa malo ofunikira kwambiri a gulu la valence la WS2 (A) ndi gulu la graphene π (B) chifukwa cha kuchedwa kwa pump-probe pamodzi ndi kufalikira kwa exponential (mizere yokhuthala). Nthawi ya moyo wa WS2 shift mu (A) ndi 1.2 ± 0.1 ps. Nthawi ya moyo wa graphene shift mu (B) ndi 1.7 ± 0.3 ps.
Kenako, timaphatikiza chizindikiro cha pump-probe pamwamba pa madera omwe awonetsedwa ndi mabokosi amitundu mu Chithunzi 1C ndikuwonetsa ziwerengero zomwe zapezeka ngati ntchito ya kuchedwa kwa pump-probe mu Chithunzi 3. Curve 1 mu Chithunzi 3 ikuwonetsa mphamvu za zonyamulira za photoexcited pafupi ndi pansi pa conduction band ya WS2 layer ndi moyo wa 1.1 ± 0.1 ps wopezeka kuchokera ku exponential fit to the data (onani Zowonjezera).
Ma trace a pomp-probe ngati ntchito ya kuchedwa komwe kumapezeka pophatikiza photocurrent pamalo omwe akuwonetsedwa ndi mabokosi omwe ali pa Chithunzi 1C. Mizere yokhuthala ikugwirizana ndi deta. Curve (1) Chiwerengero cha anthu onyamula zinthu m'gulu loyendetsa la WS2. Curve (2) Chizindikiro cha pomp-probe cha π-band ya graphene pamwamba pa mphamvu ya mankhwala yofanana. Curve (3) Chizindikiro cha pomp-probe cha π-band ya graphene pansi pa mphamvu ya mankhwala yofanana. Curve (4) Chizindikiro cha pomp-probe cha Net mu gulu la valence la WS2. Nthawi ya moyo imapezeka kuti ndi 1.2 ± 0.1 ps mu (1), 180 ± 20 fs (gain) ndi ∼2 ps (loss) mu (2), ndi 1.8 ± 0.2 ps mu (3).
Mu ma curve 2 ndi 3 a Chithunzi 3, tikuwonetsa chizindikiro cha pump-probe cha graphene π-band. Tapeza kuti phindu la ma elekitironi pamwamba pa equilibrium chemical potential (curve 2 mu Chithunzi 3) lili ndi moyo waufupi kwambiri (180 ± 20 fs) poyerekeza ndi kutayika kwa ma elekitironi pansi pa equilibrium chemical potential (1.8 ± 0.2 ps mu curve 3 Chithunzi 3). Kuphatikiza apo, phindu loyamba la photocurrent mu curve 2 ya Chithunzi 3 likupezeka kuti lasanduka kutayika pa t = 400 fs ndi moyo wa ∼2 ps. Kusagwirizana pakati pa phindu ndi kutayika kumapezeka kuti kulibe mu chizindikiro cha pump-probe cha monolayer graphene yosaphimbidwa (onani chithunzi S5 mu Zowonjezera), zomwe zikusonyeza kuti asymmetry ndi zotsatira za kuyanjana kwa interlayer mu heterostructure ya WS2/graphene. Kuwona kukwera kwa nthawi yochepa komanso kutayika kwa nthawi yayitali pamwamba ndi pansi pa mphamvu ya equilibrium chemical, motsatana, kumasonyeza kuti ma elekitironi amachotsedwa bwino kuchokera ku graphene layer pambuyo pa photoexcitation ya heterostructure. Zotsatira zake, graphene layer imakhala ndi positive charge, zomwe zikugwirizana ndi kuwonjezeka kwa mphamvu yomangirira ya π-band yomwe yapezeka pa Chithunzi 2B. Kutsika kwa π-band kumachotsa mchira wamphamvu kwambiri wa equilibrium Fermi-Dirac distribution kuchokera pamwamba pa mphamvu ya equilibrium chemical, zomwe zimafotokoza pang'ono kusintha kwa chizindikiro cha pump-probe signal mu curve 2 ya Chithunzi 3. Tiwonetsa pansipa kuti zotsatirazi zimakulitsidwanso ndi kutayika kwakanthawi kwa ma elekitironi mu π-band.
Izi zikuthandizidwa ndi chizindikiro cha net pump-probe cha WS2 valence band mu curve 4 ya Chithunzi 3. Deta iyi idapezeka pophatikiza ziwerengero pa dera lomwe laperekedwa ndi bokosi lakuda mu Chithunzi 1B lomwe limagwira ma elekitironi omwe amatulutsidwa kuchokera ku valence band nthawi zonse zochedwa za pump-probe. Mkati mwa mipiringidzo yoyesera, sitipeza chizindikiro chilichonse cha kukhalapo kwa mabowo mu valence band ya WS2 pakuchedwa kulikonse kwa pump-probe. Izi zikusonyeza kuti, pambuyo pa photoexcitation, mabowo awa amadzazidwanso mwachangu pamlingo wanthawi yochepa poyerekeza ndi nthawi yathu yokhazikika.
Kuti tipereke umboni womaliza wa lingaliro lathu la kulekanitsidwa kwa mphamvu mwachangu kwambiri mu WS2/graphene heterostructure, timapeza kuchuluka kwa mabowo omwe adasamutsidwira ku graphene layer monga momwe tafotokozera mwatsatanetsatane mu Supplementary Materials. Mwachidule, kugawa kwamagetsi kwa transient electronic kwa π-band kunayikidwa ndi Fermi-Dirac distribution. Chiwerengero cha mabowo kenako chinawerengedwa kuchokera ku ma values omwe adapezeka a transient chemical potential ndi electronic temperature. Zotsatira zake zikuwonetsedwa mu Chithunzi 4. Tapeza kuti chiwerengero chonse cha mabowo ∼5 × 1012/cm2 amasamutsidwa kuchokera ku WS2 kupita ku graphene ndi moyo wa exponential wa 1.5 ± 0.2 ps.
Kusintha kwa chiwerengero cha mabowo mu gulu la π ngati ntchito ya kuchedwa kwa pompu-probe pamodzi ndi kukwanira kwa exponential komwe kumabweretsa moyo wa 1.5 ± 0.2 ps.
Kuchokera pa zomwe zapezeka mu Zithunzi 2 mpaka 4, chithunzi chotsatira cha microscopic cha kusamutsa mphamvu mwachangu kwambiri mu heterostructure ya WS2/graphene chatuluka (Chithunzi 5). Kutulutsa kuwala kwa WS2/graphene heterostructure pa 2 eV kumadzaza kwambiri A-exciton mu WS2 (Chithunzi 5A). Zowonjezera zamagetsi kudutsa point ya Dirac mu graphene komanso pakati pa WS2 ndi graphene bands ndizotheka mwamphamvu koma sizogwira ntchito bwino. Mabowo otulutsa kuwala mu valence band ya WS2 amadzazidwanso ndi ma elekitironi ochokera ku graphene π-band pamlingo wa nthawi yochepa poyerekeza ndi nthawi yathu (Chithunzi 5A). Ma elekitironi otulutsa kuwala mu conduction band ya WS2 amakhala ndi moyo wa ∼1 ps (Chithunzi 5B). Komabe, zimatengera ∼2 ps kuti mudzazenso mabowo mu graphene π-band (Chithunzi 5B). Izi zikusonyeza kuti, kupatula kusamutsa ma elekitironi mwachindunji pakati pa gulu loyendetsa ma WS2 ndi gulu la graphene π, njira zina zopumulira—mwina kudzera m'magawo a defect states (26)—ziyenera kuganiziridwa kuti zimvetsetse mphamvu zonse.
(A) Kutulutsa kuwala kwa dzuwa (Photoexcitation) pa resonance ku WS2 A-exciton pa 2 eV kumalowetsa ma elekitironi mu gulu loyendetsa magetsi la WS2. Mabowo ofanana mu gulu loyendetsa magetsi la WS2 amadzazidwanso nthawi yomweyo ndi ma elekitironi ochokera ku gulu loyendetsa magetsi la graphene π. (B) Zonyamula kuwala kwa dzuwa zomwe zili mu gulu loyendetsa magetsi la WS2 zimakhala ndi moyo wa ∼1 ps. Mabowo omwe ali mu gulu loyendetsa magetsi la graphene π amakhala ndi moyo wa ∼2 ps, zomwe zikusonyeza kufunika kwa njira zina zofalikira zomwe zimawonetsedwa ndi mivi yodulidwa. Mizere yakuda yodulidwa mu (A) ndi (B) imasonyeza kusintha kwa mphamvu yamagetsi. (C) Mu mkhalidwe wodutsa, gawo la WS2 limakhala ndi mphamvu yoipa pomwe gawo la graphene limakhala ndi mphamvu yokhazikika. Pa kusuntha kosankha kwa spin ndi kuwala kozungulira, ma elekitironi omwe ali mu WS2 ndi mabowo ofanana mu graphene akuyembekezeka kuwonetsa polarization yozungulira yozungulira.
Mu mkhalidwe wa transient state, ma electron a photoexcited amakhala mu conduction band ya WS2 pomwe mabowo a photoexcited ali mu π-band ya graphene (Chithunzi 5C). Izi zikutanthauza kuti WS2 layer ili ndi negative charge ndipo graphene layer ili ndi positive charge. Izi zikutanthauza kusintha kwa transient peak (Chithunzi 2), asymmetry ya graphene pump-probe signal (ma curve 2 ndi 3 a Chithunzi 3), kusowa kwa mabowo mu valence band ya WS2 (ma curve 4 Chithunzi 3), komanso mabowo owonjezera mu graphene π-band (Chithunzi 4). Nthawi ya moyo wa mkhalidwe wolekanitsidwa ndi charge uwu ndi ∼1 ps (ma curve 1 Chithunzi 3).
Ma transient states ofanana ndi omwe amasemphana ndi mphamvu awonedwanso mu ma heterostructures ofanana a van der Waals opangidwa ndi ma semiconductor awiri a direct-gap okhala ndi mtundu wa II band alignment ndi staggered bandgap (27-32). Pambuyo pa photoexcitation, ma electron ndi mabowo adapezeka kuti akuyenda mofulumira pansi pa conduction band ndi pamwamba pa valence band, motsatana, omwe ali m'magawo osiyanasiyana a heterostructure (27-32).
Pankhani ya heterostructure yathu ya WS2/graphene, malo abwino kwambiri a ma elekitironi ndi mabowo ndi pamlingo wa Fermi mu graphene layer yachitsulo. Chifukwa chake, munthu angayembekezere kuti ma elekitironi ndi mabowo onse amasamukira mwachangu ku graphene π-band. Komabe, miyeso yathu ikuwonetsa momveka bwino kuti kusamutsa mabowo (<200 fs) ndikothandiza kwambiri kuposa kusamutsa ma elekitironi (∼1 ps). Tikunena izi chifukwa cha kulinganiza kwa mphamvu kwa WS2 ndi ma graphene band monga momwe zasonyezedwera mu Chithunzi 1A komwe kumapereka kuchuluka kwa mikhalidwe yomaliza yomwe ilipo yotumizira mabowo poyerekeza ndi kusamutsa ma elekitironi monga momwe tayembekezera posachedwapa ndi (14, 15). Pankhaniyi, poganiza kuti pali bandgap ya ∼2 eV WS2, graphene Dirac point ndi equilibrium chemical potential zili pa ∼0.5 ndi ∼0.2 eV pamwamba pa bandgap ya WS2, motsatana, kuswa electron-hole symmetry. Tapeza kuti chiwerengero cha mikhalidwe yomaliza yomwe ilipo yotumizira mabowo ndi yokulirapo nthawi ∼6 kuposa yotumizira ma elekitironi (onani Zowonjezera), ndichifukwa chake kutumiza mabowo kukuyembekezeka kukhala kofulumira kuposa kutumiza ma elekitironi.
Komabe, chithunzi chathunthu cha microscopic cha kusamutsa kwa charge kosasinthasintha komwe kwawonedwa kuyeneranso kuganizira za kuyanjana pakati pa ma orbitals omwe amapanga ntchito ya A-exciton wave mu WS2 ndi graphene π-band, motsatana, njira zosiyanasiyana zofalitsira ma electron-electron ndi ma electron-phonon kuphatikiza zoletsa zomwe zimayikidwa ndi momentum, energy, spin, ndi pseudospin conservation, mphamvu ya plasma oscillations (33), komanso ntchito ya displacitive excitation ya coherent phonon oscillations yomwe ingayambitse kusamutsa kwa charge (34, 35). Komanso, munthu angaganize ngati mkhalidwe wosamutsa charge womwe wawonedwa uli ndi ma exciton osamutsa charge kapena ma free electron-hole pairs (onani Zowonjezera). Kafukufuku wina wokhudza chiphunzitso womwe umapitirira zomwe zili mu pepalali ukufunika kuti ufotokoze bwino nkhaniyi.
Mwachidule, tagwiritsa ntchito tr-ARPES kuti tiphunzire kusamutsa mphamvu ya ultrafast interlayer mu epitaxial WS2/graphene heterostructure. Tapeza kuti, pamene tikulimbikitsidwa ndi resonance ku A-exciton ya WS2 pa 2 eV, mabowo a photoexcited amasamutsidwa mwachangu mu graphene layer pomwe ma electron a photoexcited amakhalabe mu WS2 layer. Tinaganiza izi chifukwa cha mfundo yakuti chiwerengero cha mikhalidwe yomaliza yomwe ilipo yotumizira mabowo ndi yayikulu kuposa kusamutsa ma electron. Nthawi ya moyo wa charge-separated transient state inapezeka kuti ndi ∼1 ps. Kuphatikiza ndi spin-selective optical excitation pogwiritsa ntchito circularly polarized light (22-25), kusamutsa mphamvu ya ultrafast komwe kwawonedwa kungaphatikizepo kusamutsa kwa spin. Pankhaniyi, WS2/graphene heterostructure yomwe yafufuzidwa ingagwiritsidwe ntchito polowetsa bwino optical spin mu graphene zomwe zimapangitsa kuti pakhale zida zatsopano za optospintronic.
Zitsanzo za graphene zinalimidwa pa ma wafer a 6H-SiC(0001) opangidwa ndi semiconducting ochokera ku SiCrystal GmbH. Ma wafer opangidwa ndi N anali pa-axis ndi miscut yolakwika pansi pa 0.5°. SiC substrate inadulidwa ndi hydrogen kuti ichotse mikwingwirima ndikupeza malo osalala okhazikika. Kenako pamwamba pa Si-yoyera komanso yathyathyathya ya atomiki inasinthidwa ndi graphit mwa kuyika chitsanzocho mumlengalenga wa Ar pa 1300°C kwa mphindi 8 (36). Mwanjira imeneyi, tinapeza gawo limodzi la carbon komwe atomu iliyonse yachitatu ya carbon inapanga covalent bond ku SiC substrate (37). Kenako gawoli linasanduka graphene yosakanikirana ndi sp2-yokhazikika quasi free-standing hole-doped graphene kudzera mu hydrogen intercalation (38). Zitsanzozi zimatchedwa graphene/H-SiC(0001). Njira yonseyi inachitika mu chipinda chokulirapo cha Black Magic chamalonda kuchokera ku Aixtron. Kukula kwa WS2 kunachitika mu reactor yokhazikika ya khoma lotentha pogwiritsa ntchito mpweya wochepa wa mankhwala (39, 40) pogwiritsa ntchito ufa wa WO3 ndi S wokhala ndi chiŵerengero cha kulemera cha 1:100 ngati zoyambira. Ufa wa WO3 ndi S unasungidwa pa 900 ndi 200°C, motsatana. Ufa wa WO3 unayikidwa pafupi ndi substrate. Argon idagwiritsidwa ntchito ngati mpweya wonyamula wokhala ndi kuyenda kwa 8 sccm. Kupanikizika mu reactor kunasungidwa pa 0.5 mbar. Zitsanzozo zidawonetsedwa ndi microscopy yachiwiri ya electron, microscopy ya atomic force, Raman, ndi photoluminescence spectroscopy, komanso low-energy electron diffraction. Miyeso iyi idawulula madera awiri osiyana a WS2 single-crystalline komwe ΓK- kapena ΓK'-direction imagwirizana ndi ΓK-direction ya graphene layer. Kutalika kwa mbali ya domain kunali kosiyana pakati pa 300 ndi 700 nm, ndipo kufalikira konse kwa WS2 kunayerekezeredwa kufika pa ∼40%, koyenera kusanthula kwa ARPES.
Kuyesa kwa static ARPES kunachitika ndi hemispherical analyzer (SPECS PHOIBOS 150) pogwiritsa ntchito charge-coupled device-detector system kuti azindikire mphamvu ya ma elekitironi ndi mphamvu. Unpolarized, monochromatic He Iα radiation (21.2 eV) ya high-flux He discharge source (VG Scienta VUV5000) idagwiritsidwa ntchito pa kuyesa konse kwa photoemission. Mphamvu ndi angular resolution mu kuyesa kwathu zinali zabwino kuposa 30 meV ndi 0.3° (zofanana ndi 0.01 Å−1), motsatana. Kuyesa konse kunachitika pa kutentha kwa chipinda. ARPES ndi njira yodziwika bwino kwambiri pamwamba. Kutulutsa ma photoelectron kuchokera ku WS2 ndi graphene layer, zitsanzo zokhala ndi WS2 coverage yosakwanira ya ∼40% zidagwiritsidwa ntchito.
Kukhazikitsa kwa tr-ARPES kunachokera pa 1-kHz Titanium:Sapphire amplifier (Coherent Legend Elite Duo). 2 mJ ya mphamvu yotulutsa idagwiritsidwa ntchito popanga ma harmonics ambiri mu argon. Kuwala kwakukulu kwa ultraviolet komwe kunatsatira kunadutsa mu grating monochromator yopanga ma pulses a probe a 100-fs pa 26-eV photon energy. 8mJ ya mphamvu yotulutsa ya amplifier idatumizidwa mu optical parametric amplifier (HE-TOPAS kuchokera ku Light Conversion). Chizindikiro cha mphamvu ya 1-eV photon chinawirikiza kawiri mu beta barium borate crystal kuti chipeze ma pulses a 2-eV pump. Kuyeza kwa tr-ARPES kunachitika ndi hemispherical analyzer (SPECS PHOIBOS 100). Mphamvu yonse ndi nthawi yake zinali 240 meV ndi 200 fs, motsatana.
Nkhani yowonjezera ya nkhaniyi ikupezeka pa http://advances.sciencemag.org/cgi/content/full/6/20/eaay0761/DC1
Iyi ndi nkhani yotseguka yogawidwa motsatira malamulo a chilolezo cha Creative Commons Attribution-NonCommercial, chomwe chimalola kugwiritsa ntchito, kufalitsa, ndi kubwerezanso munjira iliyonse, bola ngati kugwiritsa ntchito komwe kukubwera sikuli kopindulitsa pamalonda ndipo bola ngati ntchito yoyambirira yatchulidwa bwino.
ZINDIKIRANI: Timangopempha imelo yanu kuti munthu amene mukumulimbikitsa tsamba lanu adziwe kuti mukufuna kuti aione, komanso kuti si imelo yosayenera. Sitilemba imelo iliyonse.
Funso ili ndi loti muyese ngati ndinu mlendo weniweni kapena ayi komanso kuti mupewe kutumiza ma sipamu okha.
Ndi Sven Aeschlimann, Antonio Rossi, Mariana Chávez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Tikuwonetsa kulekanitsidwa kwa charge yofulumira kwambiri mu WS2/graphene heterostructure yomwe ingalole kuti kuwala kulowe mu graphene.
Ndi Sven Aeschlimann, Antonio Rossi, Mariana Chávez-Cervantes, Razvan Krause, Benito Arnoldi, Benjamin Stadtmüller, Martin Aeschlimann, Stiven Forti, Filippo Fabbri, Camilla Coletti, Isabella Gierz
Tikuwonetsa kulekanitsidwa kwa charge yofulumira kwambiri mu WS2/graphene heterostructure yomwe ingalole kuti kuwala kulowe mu graphene.
© 2020 American Association for the Advancement of Science. Maumwini onse ndi otetezedwa. AAAS ndi mnzake wa HINARI, AGORA, OARE, CHORUS, CLOCKSS, CrossRef ndi COUNTER.Science Advances ISSN 2375-2548.
Nthawi yotumizira: Meyi-25-2020