Umhlaba osizungezile uwumphumela ohlanganyelwe wezigigaba eziningi nezinqubo ezivela ezinhlobonhlobo zesayensi, cishe akunakwenzeka ukusho okubaluleke kakhulu. Naphezu kwezinga elithile lokuncintisana, izici eziningi zesayensi ethile zinezici ezifanayo. Ake sithathe i-geometry njengesibonelo: yonke into esiyibonayo inomumo othile, okunye okuvame kakhulu emvelweni kuyindilinga, indilinga, imbulunga, ibhola (umkhuba ebusweni). Isifiso sokuba yindilinga sibonakala kuwo womabili amaplanethi namaqoqo e-athomu. Kodwa kuhlale kukhona okuhlukile emithethweni. Ososayensi baseNyuvesi yaseLeuven (eBelgium) bathola ukuthi ama-athomu egolide awakhe amaqoqo ayindilinga, kodwa amaphiramidi. Yini ebangela lokhu kuziphatha okungavamile kwama-athomu egolide, imibhoshongo eyigugu inaziphi izici, futhi lokhu okutholakele kungasetshenziswa kanjani ekusebenzeni? Sifunda ngalokhu embikweni wososayensi. Hamba.
Isisekelo socwaningo
Ukuba khona kwamaqoqo angavamile ama-athomu egolide kwaziwa isikhathi eside. Lezi zakhiwo zinezakhiwo ezingavamile zamakhemikhali neze-elekthronikhi, yingakho isithakazelo kuzo siye sanda kuphela phakathi neminyaka. Ucwaningo oluningi lugxile ocwaningweni lokuncika kobukhulu, kodwa ucwaningo olunjalo ludinga ukuhlanganisa okulawulwayo kanye nezilinganiso zokunemba okuphezulu.
Ngokwemvelo, kunezinhlobo ezahlukene zamaqoqo, kodwa ethandwa kakhulu ocwaningweni yi-Au20, okungukuthi, iqoqo lama-athomu egolide angama-20. Ukuthandwa kwayo kungenxa yokulinganisa kwayo okuphezulu i-tetrahedral* isakhiwo futhi sikhulu ngokumangalisayo HOMO-LUMO (HL) ngegebe (gap)*.
I-Tetrahedron* - i-polyhedron enonxantathu abane njengobuso. Uma sibheka ubuso obunye njengesisekelo, i-tetrahedron ingabizwa ngokuthi iphiramidi engunxantathu.
Igebe le-HOMO-LUMO (igebe)* - I-HOMO ne-LUMO yizinhlobo ze-orbitals yamangqamuzana (umsebenzi wezibalo ochaza ukuziphatha kwamagagasi kwama-electron ku-molecule). I-HOMO imele i-molecular orbital ematasa kakhulu, futhi i-LUMO imele i-orbital ye-molecular orbital ephansi kunazo zonke. Ama-electron e-molecule endaweni engaphansi agcwalisa wonke ama-orbitals ngamandla aphansi kakhulu. I-orbital enamandla amakhulu phakathi kwalawo agcwalisiwe ibizwa nge-HOMO. Ngokulandelayo, i-LUMO iyi-orbital yamandla aphansi kakhulu. Umehluko wamandla phakathi kwalezi zinhlobo ezimbili zama-orbital ubizwa ngokuthi igebe le-HOMO-LUMO.
I-Photoelectron spectroscopy ye-Au20 ibonise ukuthi igebe le-HOMO-LUMO liyi-1.77 eV.
Ukulingisa okwenziwa ngesisekelo sethiyori yokusebenza kwabantu (indlela yokubala ukwakheka kwezinhlelo ze-elekthronikhi) kubonise ukuthi lo mehluko wamandla ungafinyelelwa kuphela ngephiramidi ye-tetrahedral ye-Td symmetry (i-tetrahedral symmetry), okuyijiyomethri ezinzile kakhulu iqoqo le-Au20.
Ososayensi bayaqaphela ukuthi ucwaningo lwangaphambilini lwe-Au20 lunikeze imiphumela enemba kakhulu ngenxa yobunkimbinkimbi benqubo. Ngaphambilini, kwakusetshenziswa isibonakhulu se-electron yokuskena, amandla aphezulu e-beam ahlanekezela imiphumela yokubuka: ukuguquguquka okuqhubekayo kwe-Au20 kwabonwa phakathi kokucushwa kwesakhiwo okuhlukile. Ku-5% wezithombe ezitholiwe, iqoqo le-Au20 laliyi-tetrahedral, kanti kokunye ijometri yalo yayiphazamisekile ngokuphelele. Ngakho-ke, ukuba khona kwesakhiwo se-tetrahedral Au20 ku-substrate eyenziwe, isibonelo, ikhabhoni ye-amorphous ngeke kuthiwe ifakazelwe nge-XNUMX%.
Ocwaningweni esilubuyekezayo namuhla, ososayensi banqume ukusebenzisa indlela emnene yokufunda i-Au20, okuyi-scanning tunnel microscopy (STM) kanye ne-scan tunnel spectroscopy (STS). Izinto zokubukwa bekungamaqoqo e-Au20 kumafilimu e-NaCl e-ultrathin. I-STM isivumele ukuthi siqinisekise ukulinganisa kukanxantathu kwesakhiwo se-pyramidal, futhi idatha ye-STS yenza kwaba nokwenzeka ukubala igebe le-HOMO-LUMO, elalilingana ne-2.0 eV.
Ukulungiselela ucwaningo
Isendlalelo se-NaCl satshalwa endaweni engaphansi ye-Au(111) kusetshenziswa umhwamuko wamakhemikhali ofakwa ku-800 K ekamelweni le-STM ngaphansi kwezimo ze-vacuum eziphezulu kakhulu.
Ama-ion e-Au20 cluster akhiqizwa ngokusetha kwe-magnetron sputtering kanye nosayizi okhethwe kusetshenziswa isihlungi se-quadrupole mass. Umthombo we-sputtering usebenze ngemodi eqhubekayo futhi ukhiqize ingxenye enkulu yamaqoqo ashajiwe, abese efaka isihlungi se-quadrupole mass. Amaqoqo akhethiwe afakwe ku-substrate ye-NaCl/Au(111). Ngokufakwa kwe-low-density, i-cluster flux yayiyi-30 pA (picoamps) futhi isikhathi sokubeka sasiyimizuzu engu-9; ekufakweni okuphezulu kakhulu, kwakuyi-1 nA (nanoamps) nemizuzu engu-15. Ukucindezela ekamelweni kwakungu-10-9 mbar.
Imiphumela yocwaningo
Amaqoqo e-anionic Au20 akhethwe ngobuningi anomthamo ophansi kakhulu wokumbozwa afakwe endaweni yokushisa yegumbi eziqhingini ze-Ultrathin NaCl, okuhlanganisa i-2L, 3L, kanye ne-4L (izendlalelo ze-athomu).
Isithombe #1
In I-1A Kuyabonakala ukuthi iningi le-NaCl esekhulile inezingqimba ezintathu, izindawo ezinezingqimba ezimbili nezine zithatha indawo encane, kanti izindawo ezingu-5L azikho ngempela.
Amaqoqo e-Au20 atholwe ezifundeni ezinezendlalelo ezintathu nezine, kodwa abengekho ku-2L. Lokhu kuchazwa ukuthi i-Au20 ingadlula ku-2L NaCl, kodwa esimweni se-3L ne-4L NaCl, igcinwa ebusweni bayo. Lapho kuminyene ukunamathela okuphansi esifundeni esingu-200 x 200 nm, kusuka ku-0 kuya ku-4 amaqoqo abonwa ngaphandle kwezimpawu ze-Au20 agglomeration (ukuqoqwa).
Ngenxa yokumelana okuphezulu kakhulu kwe-4L NaCl kanye nokungazinzi lapho kuthwetshulwa i-Au20 eyodwa ku-4L NaCl, ososayensi bagxile ekutadisheni amaqoqo ku-3L NaCl.
Isithombe #2
I-Microscopy yamaqoqo ku-3L NaCl ibonise ukuthi ukuphakama kwawo kungu-0.88 ± 0.12 nm. Lesi sibalo sivumelana kahle kakhulu nemiphumela yokumodela, ebikezele ukuphakama okungu-0.94 ± 0.01 nm (I-2A). I-Microscopy iphinde yabonisa ukuthi amanye amaqoqo anomumo ongunxantathu one-athomu eyodwa egqagqene phezulu, okuqinisekisa ucwaningo lwethiyori mayelana nokuma kwephiramidi yesakhiwo se-Au20 (2B).
Ososayensi bayaqaphela ukuthi lapho bebona ngeso lengqondo izinto ezincane kakhulu ezinezinhlangothi ezintathu, njengamaqoqo e-Au20, kunzima kakhulu ukugwema ukungalungi okuthile. Ukuze kutholwe izithombe ezinembe kakhulu (zombili ngokubuka kwe-athomu nejiyomethri), bekudingeka ukuthi kusetshenziswe ithiphu le-Cl-functionalized microscope ecijile ngokufanelekile. Umumo wephiramidi uhlonzwe ngamaqoqo amabili (I-1B и I-1С), izithombe ezinezinhlangothi ezintathu ezikhonjiswe ku 1D и 1E, ngokulandelana.
Nakuba ukuma kukanxantathu nokuphakama kokusabalalisa kubonisa ukuthi amaqoqo adiphozithi agcina umumo wephiramidi, izithombe ze-STM (I-1B и I-1С) azibonisi izakhiwo eziphelele ze-tetrahedral. I-engeli enkulu esithombeni I-1B cishe 78°. Futhi lokhu kungu-30% ngaphezu kuka-60° nge-tetrahedron ekahle enokulinganisa kwe-Td.
Kungase kube nezizathu ezimbili zalokhu. Okokuqala, kukhona ukungalungi emfanekisweni ngokwawo, okubangelwa kokubili ubunzima bale nqubo kanye neqiniso lokuthi ichopho lenaliti ye-microscope ayiqinile, futhi lokhu kungaphinde kuhlanekezele izithombe. Isizathu sesibili kungenxa yokuhlanekezelwa kwangaphakathi kwe-Au20 esekelwe. Lapho amaqoqo e-Au20 ane-Td symmetry ehlala endaweni eyisikwele ye-NaCl lattice, ukungafani kwe-symmetry kuhlanekezela ukwakheka kwe-tetrahedral efanelekile ye-Au20.
Ukuze kutholwe isizathu salokho kuchezuka ezithombeni, ososayensi bahlaziya idatha ngokulingana kwezakhiwo ezintathu ezithuthukisiwe ze-Au20 ku-NaCl. Ngenxa yalokho, kwatholakala ukuthi amaqoqo ahlanekezelwe kancane kuphela esakhiweni se-tetrahedral esifanelekile esinokulinganisa kwe-Td ngokuchezuka okukhulu ezindaweni ze-athomu ezingu-0.45. Ngakho-ke, ukuhlanekezela ezithombeni kuwumphumela wokungalungi enqubweni yezithombe ngokwayo, futhi hhayi wanoma yikuphi ukuphambuka ekubekweni kwamaqoqo ku-substrate kanye/noma ukusebenzisana phakathi kwawo.
Akuyona nje idatha ye-topographic eyizimpawu ezicacile zesakhiwo se-pyramidal seqoqo le-Au20, kodwa futhi negebe elikhulu kakhulu le-HL (cishe i-1.8 eV) uma liqhathaniswa ne-Au20 ama-isomer* ngamandla aphansi (ngokwethiyori engaphansi kuka-0.5 eV).
Isomers* - izakhiwo ezifanayo ngokwakheka kwe-athomu nesisindo se-molecule, kodwa ezihlukile ngesakhiwo noma ukuhlelwa kwama-athomu.
Ukuhlaziywa kwezakhiwo ze-elekthronikhi zamaqoqo afakwe ku-substrate kusetshenziswa i-scanning tunnel spectroscopy (1F) kwenze kwaba nokwenzeka ukuthola i-different conductivity spectrum (dI/dV) yeqoqo le-Au20, elibonisa igebe elikhulu lebhendi (Isb) elilingana no-3.1 eV.
Njengoba iqoqo lihlukaniswa ngogesi ngokufaka insulate yamafilimu e-NaCl, kwakheka umhubhe we-double-barrier junction (DBTJ), obangela imiphumela ye-electron-tunneling eyodwa. Ngakho-ke, ukungaqhubeki ku-spectrum ye-dI/dV kuwumphumela womsebenzi ohlanganyelwe we-quantum HL discontinuity (EHL) kanye ne-classical Coulomb energy (Ec). Izilinganiso zamakhefu ku-spectrum zibonisiwe ukusuka ku-2.4 ukuya ku-3.1 eV kumaqoqo ayisikhombisa (1F). Ukungaqhubeki okuphawuliwe kukhulu kunokunqanyulwa kwe-HL (1.8 eV) esigabeni segesi ye-Au20.
Ukuhlukahluka kwamakhefu kumaqoqo ahlukene kungenxa yenqubo yokulinganisa ngokwayo (indawo yenaliti ehlobene neqoqo). Igebe elikhulukazi elikalwe ku-spectra ye-dI/dV lalingu-3.1 eV. Kulesi simo, ithiphu ibibekwe kude neqoqo, okwenze amandla kagesi phakathi kwethiphu neqoqo abe ngaphansi kwalokho okuphakathi kweqoqo ne-Au(111) substrate.
Okulandelayo, senze izibalo zokugqashuka kwe-HL kwamaqoqo amahhala e-Au20 nalawo atholakala ku-3L NaCl.
Igrafu 2C ibonisa ukuminyana okulingiswayo kwejika lezifunda lesigaba segesi i-Au20 tetrahedron lapho igebe layo le-HL lingu-1.78 eV. Uma iqoqo liku-3L NaCl/Au(111), ukuhlanekezela kuyanda futhi igebe le-HL liyehla lisuka ku-1.73 liye ku-1.51 eV, eliqhathaniseka negebe le-HL lika-2.0 eV elitholwe phakathi nezilinganiso zokuhlola.
Ocwaningweni lwangaphambilini, kutholwe ukuthi ama-isomers e-Au20 anesakhiwo se-Cs-symmetric anegebe le-HL elingaba ngu-0.688 eV, kanye nezakhiwo ezine-amorphous symmetry - 0.93 eV. Ngokucabangela lokhu okubonwayo kanye nemiphumela yezilinganiso, ososayensi bafinyelela esiphethweni sokuthi igebe elikhulu lebhande lingenzeka kuphela ngaphansi kwezimo ze-tetrahedral pyramidal structure.
Isigaba esilandelayo socwaningo bekuwucwaningo lokusebenzisana kweqoqo, lapho i-Au3 eyengeziwe (ukuminyana ekhulisiwe) yafakwa ku-111L NaCl/Au(20) substrate.
Isithombe #3
Esithombeni I-3A isithombe se-STM se-topographic yamaqoqo afakiwe siyaboniswa. Cishe amaqoqo angama-100 abonwa endaweni yokuskena (100 nm x 30 nm). Osayizi bamaqoqo asebenzisanayo ku-3L NaCl makhulu noma alingana nosayizi balawo afundwe ekuhlolweni ngamaqoqo angawodwa. Lokhu kungachazwa ngokusatshalaliswa kanye nokuhlangana (clumping) ebusweni be-NaCl ekamelweni lokushisa.
Ukuqoqwa nokukhula kwamaqoqo kungachazwa ngezindlela ezimbili: Ukuvuthwa kwe-Ostwald (ukubuyisela kabusha) kanye nokuvuthwa kwe-Smoluchowski (ukwandiswa kweziqhingi). Endabeni yokuvuthwa kwe-Ostwald, amaqoqo amakhulu akhula ngezindleko zama-athomu amancane, lapho ama-athomu akamuva ehlukaniswa nawo futhi asakazeke komakhelwane. Ngesikhathi sokuvuthwa kwe-Smoluchowski, izinhlayiya ezinkulu ziyakhiwa ngenxa yokufuduka kanye nokuhlangana kwamaqoqo wonke. Olunye uhlobo lokuvuthwa lungahlukaniswa kolunye ngale ndlela elandelayo: ngokuvuthwa kwe-Ostwald, ukusatshalaliswa kosayizi bamaqoqo kuyakhula futhi kuyaqhubeka, futhi ngokuvuthwa kwe-Smoluchowski, usayizi usatshalaliswa ngokusobala.
Emashadini I-3B и I-3С imiphumela yokuhlaziywa kwamaqoqo angaphezu kuka-300 ikhonjisiwe, i.e. ukusatshalaliswa kosayizi. Ububanzi bokuphakama kweqoqo elibukiwe bubanzi kakhulu, kepha amaqembu amathathu ajwayelekile angahlukaniswa (I-3С): 0.85, 1.10 kanye no-1.33 nm.
Njengoba kungabonakala kugrafu I-3B, kukhona ukuhlobana phakathi kwevelu yobude nobubanzi beqoqo. Izakhiwo zeqoqo eziqashiwe zibonisa izici zokuvuthwa kwe-Smoluchowski.
Kukhona futhi ukuhlobana phakathi kwamaqoqo ekuhlolweni kokuminyana kwe-deposition ephezulu nephansi. Ngakho-ke, iqembu lamaqoqo anobude obungu-0.85 nm lihambisana neqoqo ngalinye elinobude obungu-0.88 nm ekuhlolweni ngobuningi obuphansi. Ngakho-ke, amaqoqo avela eqenjini lokuqala anikezwe inani le-Au20, futhi amaqoqo asuka kwelesibili (1.10 nm) neyesithathu (1.33 nm) anikezwa amanani e-Au40 ne-Au60, ngokulandelana.
Isithombe #4
Esithombeni I-4A singabona umehluko obonakalayo phakathi kwezigaba ezintathu zamaqoqo, i-spectra ye-dI/dV eboniswa kugrafu I-4B.
Njengoba amaqoqo e-Au20 ehlangana abe igebe elikhudlwana lamandla ku-spectrum, i-dI/dV iyehla. Ngakho, eqenjini ngalinye amanani alandelayo okuyekisa atholwe: Au20—3.0 eV, Au40—2.0 eV, and Au60—1.2 eV. Ngokucabangela le datha, kanye nezithombe ze-topographic zamaqembu afundwayo, kungaphikiswana ngokuthi i-geometry ye-cluster agglomerates iseduze ne-spherical noma i-hemispherical.
Ukuze ulinganisele inani lama-athomu kumaqoqo ayindilinga ne-hemispherical, ungasebenzisa i-Ns = [(h/2)/r]3 kanye no-Nh = 1/2 (h/r)3, lapho h и r umele ubude beqoqo kanye nerediyasi ye-athomu eyodwa ye-Au. Uma sicabangela irediyasi ye-Wigner-Seitz ye-athomu yegolide (r = 0.159 nm), singabala inombolo yabo ngokusondelana okuyindilinga: iqembu lesibili (Au40) - ama-athomu angu-41, iqembu lesithathu (Au60) - ama-athomu angu-68. Ekulinganisweni kwe-hemispherical, inani elilinganisiwe lama-athomu angu-166 no-273 liphezulu kakhulu kune-Au40 ne-Au60 ekulinganisweni kwe-spherical. Ngakho-ke, kungaphethwa ngokuthi i-geometry ye-Au40 ne-Au60 iyindilinga kune-hemispherical.
Ukuze uthole ukubheka okuningiliziwe kwama-nuances ocwaningo, ngincoma ukuthi ubheke и kuyena.
Epilogue
Kulolu cwaningo, ososayensi bahlanganisa i-spectroscopy yokuskena kanye ne-microscopy, okubavumela ukuthi bathole idatha enembe kakhulu mayelana nejometri yamaqoqo ama-athomu egolide. Kutholwe ukuthi iqoqo le-Au20 elifakwe ku-3L NaCl/Au(111) substrate ligcina isakhiwo sephiramidi yesigaba segesi esinegebe elikhulu le-HL. Kuphinde kwatholakala ukuthi indlela eyinhloko yokukhula nokuhlanganisa amaqoqo abe ngamaqembu ukuvuthwa kwe-Smoluchowski.
Ososayensi babiza enye yezimpumelelo eziyinhloko zomsebenzi wabo hhayi kakhulu imiphumela yocwaningo ngamaqoqo e-athomu, kodwa kunalokho indlela yokwenza lolu cwaningo. Ngaphambili, kwakusetshenziswa isibonakhulu se-electron yokudlulisela ukuskena, okwathi, ngenxa yezakhiwo zayo, kuhlanekezela imiphumela yokubuka. Nokho, indlela entsha echazwe kulo msebenzi isivumela ukuthi sithole idatha enembile.
Phakathi kwezinye izinto, ukutadisha izakhiwo zeqoqo kusivumela ukuthi siqonde izici zazo ze-catalytic ne-optical, ezibaluleke kakhulu ekusebenziseni kwazo kuma-cluster catalysts kanye namadivayisi abonakalayo. Njengamanje, amaqoqo asevele asetshenziswa kumaseli kaphethiloli nasekuthwebuleni ikhabhoni. Nokho, ngokososayensi ngokwabo, lokhu akuwona umkhawulo.
Siyabonga ngokufunda, hlalani nelukuluku futhi nibe neviki elihle bafana. 🙂
Ezinye izikhangiso 🙂
Siyabonga ngokuhlala nathi. Uyazithanda izindatshana zethu? Ufuna ukubona okuqukethwe okuthakaselayo okwengeziwe? Sisekele ngokufaka i-oda noma ngokuncoma kubangani, , i-analogue ehlukile yamaseva ezinga lokungena, esungulwe yithi ngenxa yakho: (itholakala nge-RAID1 kanye ne-RAID10, kufika kuma-cores angu-24 kuze kufike ku-40GB DDR4).
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Source: www.habr.com