Nyika yakatitenderedza ndiyo mhedzisiro yakabatana yezviitiko zvakawanda uye maitiro kubva kune akasiyana sainzi, hazvigoneke kusarudza iyo inonyanya kukosha. Pasinei nemwero wakati wekukwikwidzana, zvakawanda zveimwe sainzi zvine maitiro akafanana. Ngatitorei geometry semuenzaniso: zvese zvatinoona zvine chimiro chakati, icho chimwe chezvakajairika mune zvakasikwa denderedzwa, denderedzwa, denderedzwa, bhora (maitiro kumeso). Chishuvo chekuva denderedzwa chinoratidzwa mumapuraneti uye masumbu emaatomu. Asi pane nguva dzose kunze kwemitemo. Masayendisiti kubva kuYunivhesiti yeLeuven (Belgium) akawana kuti maatomu egoridhe anoumba kwete denderedzwa, asi mapoka emapiramidhi. Chii chinoparira kuita uku kusina kujairika kwemaatomu endarama, zvimiro zvipi zvine mapiramidhi anokosha, uye kuwana uku kungashandiswa sei mukuita? Tinodzidza nezveizvi kubva mushumo revasayendisiti. Enda.
Hwaro hwechidzidzo
Kuvapo kwemasumbu asina kujairika emaatomu egoridhe kwave kuchizivikanwa kwenguva yakati rebei. Aya maumbirwo ane makemikari asina kujairika uye emagetsi zvinhu, ndosaka kufarira mazviri kwakangowedzera nekufamba kwemakore. Zvidzidzo zvizhinji zvakanangana nekudzidza kwedimensional dependence, asi chidzidzo chakadaro chinoda kudzorwa synthesis uye kuyerwa kwepamusoro-soro.
Sezvingatarisirwa, kune marudzi akasiyana emasumbu, asi anonyanya kufarirwa pakudzidza ndiAu20, kureva, sumbu remaatomu egoridhe makumi maviri. Kukurumbira kwayo kunokonzerwa nekuenzana kwayo zvakanyanya tetrahedral* chimiro uye zvinoshamisa zvikuru HOMO-LUMO (HL) разрывом (щелью)*.
Tetrahedron* - polyhedron ine makona matatu sezviso. Kana tikafunga chimwe chezviso kuva nheyo, ipapo tetrahedron inogona kunzi piramidi yetatu.
HOMO-LUMO gap (gap)* - HOMO uye LUMO imhando dzemamorekuru orbitals (basa remasvomhu rinotsanangura mafambiro emagetsi emagetsi mumorekuru). HOMO inomirira yakanyanya kugariswa molecular orbital, uye LUMO inomiririra yakaderera isingagadzirwe molecular orbital. Maerekitironi emorekuru ari pasi pasi anozadza orbitals ese ane simba rakaderera. Iyo orbital ine simba guru pakati pevakazadzwa inonzi HOMO. Nekudaro, LUMO ndiyo yakaderera simba orbital. Musiyano wesimba pakati pemhando mbiri idzi dze orbitals unonzi HOMO-LUMO gap.
Photoelectron spectroscopy yeAu20 yakaratidza kuti HOMO-LUMO gap iri 1.77 eV.
Simulations yakaitwa pahwaro hwe density functional theory (nzira yekuverenga iyo yemagetsi chimiro chemasisitimu) yakaratidza kuti mutsauko wesimba wakadaro unogona kuwanikwa chete kuburikidza nepiramidhi yeTetrahedral yeTd symmetry (tetrahedral symmetry), inova iyo yakanyanya kugadzikana geometry ye iyo Au20 cluster.
Masayendisiti anocherekedza kuti tsvakiridzo yapfuura paAu20 yakapa zvakanyanya zvisizvo mhedzisiro nekuda kwekuoma kwemaitiro. Kare, kutapurirana scanning electron maikorosikopu yaishandiswa, simba repamusoro redanda rakakanganisa mibairo yekutarisa: kuchinjika kunogara kuripo kweAu20 kwakaonekwa pakati pezvimiro zvakasiyana. Mu5% yemifananidzo yakawanikwa, iyo Au20 cluster yaive tetrahedral, uye mune yakasara geometry yayo yakanga isina kurongeka zvachose. Naizvozvo, kuvepo kweiyo tetrahedral Au20 chimiro pane substrate yakagadzirwa, semuenzaniso, amorphous kabhoni haigone kunzi XNUMX% inopupurirwa.
Muchidzidzo chatiri kutarisa nhasi, masayendisiti akafunga kushandisa imwe nzira yakapfava yekudzidza Au20, inoti scanning tunneling microscopy (STM) uye scanning tunneling spectroscopy (STS). Zvinhu zvekucherechedzwa zvaive Au20 masumbu pamafirimu ekupedzisira eNaCl. STM yakatibvumira kuti tisimbise symmetry yetriangular yechimiro chepiramidi, uye STS data yakaita kuti zvikwanise kuverenga iyo HOMO-LUMO gap, iyo yaive yakawanda se2.0 eV.
Kugadzirira kudzidza
Iyo NaCl layer yakakurira paAu(111) substrate ichishandisa kemikari vapor deposition pa800 K mukamuri yeSTM pasi pemamiriro ekupedzisira ekutsvaira.
Au20 cluster ions yakagadzirwa kuburikidza nemagnetron sputtering setup uye saizi yakasarudzwa uchishandisa quadrupole mass sefa. Iyo sputtering sosi yakashanda muinoenderera uye yakagadzira chikamu chikuru chechaji masumbu, ayo akazopinda muquadrupole mass sefa. Masumbu akasarudzwa akaiswa paNaCl/Au(111) substrate. Kune yakaderera-density deposition, iyo cluster flux yaive 30 pA (picoamps) uye deposition nguva yaive 9 maminetsi; kune yakakwira-density deposition, yaive 1 nA (nanoamps) uye 15 maminetsi. Kumanikidza mukamuri kwaive 10-9 mbar.
Mhedzisiro yekutsvaga
Misa-yakasarudzwa anionic Au20 masumbu ane yakaderera kuvharika density akaiswa pakamuri tembiricha pane ultrathin NaCl zvitsuwa, kusanganisira 2L, 3L, uye 4L (atomic layers).
Mufananidzo #1
pamusoro 1A Zvinogona kuonekwa kuti mazhinji eNaCl akakura ane matatu akaturikidzana, nzvimbo dzine maviri uye mana akaturikidzana anotora nzvimbo diki, uye 5L nzvimbo dzinenge dzisipo.
Au20 masumbu akawanikwa munzvimbo nhatu- uye ina-matanho, asi aive asipo mu2L. Izvi zvinotsanangurwa nenyaya yekuti Au20 inogona kupfuura ne2L NaCl, asi mune iyo 3L uye 4L NaCl, inochengetwa pamusoro pavo. Pane yakaderera coating density munharaunda 200 x 200 nm, kubva 0 kusvika 4 masumbu akaonekwa pasina zviratidzo Au20 agglomeration (kuunganidza).
Nekuda kwekunyanya kupikisa kwe4L NaCl uye kusagadzikana paunenge uchitsvaga imwe Au20 pa4L NaCl, masayendisiti akanyanya kudzidza masumbu pa3L NaCl.
Mufananidzo #2
Microscopy yemasumbu mu3L NaCl yakaratidza kuti kureba kwavo 0.88 ± 0.12 nm. Huwandu uhu huri muchibvumirano chakanakisa nemhedzisiro yekuenzanisira, iyo yakafanotaura kureba kwe0.94 ± 0.01 nm (2A) Microscopy yakaratidzawo kuti mamwe masumbu ane chimiro chetriangular ane atomu imwe inobuda kumusoro, iyo inosimbisa tsvakiridzo yedzidziso maererano neiyo piramidi chimiro cheAu20 chimiro (2B).
Masayendisiti anocherekedza kuti kana uchiona zvinhu zvidiki-diki-mativi matatu, senge masumbu eAu20, zvakanyanya kuoma kudzivirira kumwe kusarongeka. Kuti uwane mifananidzo yakanyatsojeka (zvose kubva paatomu uye geometric poindi yekuona), zvaive zvakafanira kushandisa yakapinza atomu yakapinza Cl-functionalized maikorosikopu tip. Chimiro chepiramidi chakaonekwa mumasumbu maviri (1B и 1С), mifananidzo yemativi matatu ayo anoratidzwa mukati 1D и 1E, zvichiteerana.
Kunyangwe chimiro chetriangular uye kureba kugovera kunoratidza kuti masumbu akaiswa anochengetedza chimiro chepiramidhi, mifananidzo yeSTM (1B и 1С) usaratidze zvakakwana tetrahedral zvimiro. Yakakura kona mumufananidzo 1B inenge 78°. Uye iyi i30% inodarika 60° kune yakanaka tetrahedron ine Td symmetry.
Panogona kuva nezvikonzero zviviri zveizvi. Kutanga, pane zvisiri izvo mukufungidzira pachako, kunokonzerwa nekuoma kweiyi nzira uye nenyaya yekuti iyo muromo weiyo microscope tsono haina kuomarara, uye izvi zvinogona zvakare kukanganisa mifananidzo. Chikonzero chechipiri chinokonzerwa nekukanganiswa kwemukati kweAu20 inotsigirwa. Kana maAu20 masumbu ane Td symmetry pasi pane sikweya NaCl lattice, symmetry mismatch inokanganisa yakanakira tetrahedral chimiro cheAu20.
Kuti uwane chikonzero chekutsauka kwakadaro mumifananidzo, masayendisiti akaongorora dhata pane symmetry yematatu akagadziridzwa Au20 zvimiro paNaCl. Nekuda kweizvozvo, zvakaonekwa kuti masumbu acho anongotsveyamiswa zvishoma kubva kune yakakodzera tetrahedral chimiro neTd symmetry ine kutsauka kwakanyanya munzvimbo dzeatomu dze0.45. Naizvozvo, kukanganisa mumifananidzo imhaka yekusarurama mukuita kwekufungidzira pachayo, uye kwete yekukanganisa kupi mukuiswa kwemasumbu pane substrate uye / kana kudyidzana pakati pavo.
Kwete chete iyo topographic data zviratidzo zvakajeka zveiyo piramidhi chimiro cheAu20 cluster, asiwo yakakura kwazvo HL gap (inenge 1.8 eV) kana ichienzaniswa nedzimwe Au20. isomers* nesimba rakaderera (muchirevo pasi pe 0.5 eV).
Isomers* - zvimiro zvakafanana mukuumbwa kweatomu uye huremu hwemamorekuru, asi akasiyana muchimiro chazvo kana kuronga kwemaatomu.
Ongororo yezvigadzirwa zvemagetsi zvemasumbu akaiswa pane substrate uchishandisa scanning tunneling spectroscopy (1F) yakaita kuti zvikwanisike kuwana kusiyana kwemaitiro ekugadzirisa (dI / dV) yeAu20 cluster, iyo inoratidza bhendi guru (Eg) rakaenzana ne3.1 eV.
Sezvo sumbu racho rakapatsanurwa nemagetsi nekuvharisa NaCl mafirimu, kaviri-barriers tunnel junction (DBTJ) inoumbwa, iyo inokonzera single-electron tunneling mhedzisiro. Nokudaro, kusaenderera mberi mumutsara weDI / dV ndiwo mugumisiro webasa rakabatanidzwa re quantum HL discontinuity (EHL) uye classical Coulomb energy (Ec). Zviyero zvekuputsika mune zvakaratidzwa kubva ku2.4 kusvika ku3.1 eV kumasumbu manomwe (1F) Iwo akacherechedzwa discontinuities akakura kupfuura iyo HL discontinuities (1.8 eV) muchikamu cheAu20 gasi.
Kusiyana kwezvimedu mumasumbu akasiyana-siyana kunokonzerwa nechiyero chekuyera pachako (nzvimbo yetsono maererano nesumbu). Mukaha mukuru wakayerwa mudI/dV spectra waiva 3.1 eV. Muchiitiko ichi, muromo wacho wakanga uri kure neboka, izvo zvakaita kuti simba remagetsi pakati pechiputi uye sumbu rive shoma pane iro pakati pesumbu uye Au (111) substrate.
Tevere, takaita kuverenga kweHL kuputika kwemahara Au20 masumbu uye ayo ari pa3L NaCl.
Girafu 2C inoratidza kufananidzwa kudzikana kwematunhu curve yegasi-phase Au20 tetrahedron ine HL gap iri 1.78 eV. Kana iyo cluster iri pa3L NaCl/Au(111), kukanganisa kunowedzera uye HL gap inoderera kubva pa1.73 kusvika 1.51 eV, iyo inofananidzwa neHL gap ye2.0 eV yakawanikwa panguva yekuyerwa kuyerwa.
Muzvidzidzo zvakapfuura, zvakaonekwa kuti Au20 isomers ine Cs-symmetric chimiro ine HL gap inosvika 0.688 eV, uye zvimiro zvine amorphous symmetry - 0.93 eV. Tichifunga nezvekutarisa uku uye mhedzisiro yezviyero, masayendisiti akasvika pakugumisa kuti bhendi rakakura rinogoneka chete pasi pemamiriro eiyo tetrahedral pyramidal structure.
Nhanho inotevera yetsvagiridzo yaive yekudzidza kwekubatana-masumbu kupindirana, iyo yakawanda Au3 (yakawedzera density) yakaiswa pa111L NaCl/Au(20) substrate.
Mufananidzo #3
Mumufananidzo 3A iyo topographic STM mufananidzo wemasumbu akaiswa anoratidzwa. Anenge makumi matatu masumbu anoonekwa munzvimbo yekuongorora (100 nm x 100 nm). Saizi dzemasumbu anodyidzana pa30L NaCl anogona kunge akakura kupfuura kana kuenzana nesaizi yeaya akadzidzwa mukuyedza nemasumbu mamwechete. Izvi zvinogona kutsanangurwa nekupararira uye agglomeration (clumping) pamusoro peNaCl pamhepo tembiricha.
Kuunganidza uye kukura kwemasumbu kunogona kutsanangurwa nenzira mbiri: Ostwald ripening (recondensation) uye Smoluchowski ripening (kuwedzera kwezvitsuwa). Panyaya yekuibva kweOstwald, masumbu makuru anokura achibhadhara madiki, apo maatomu ekupedzisira anoparadzaniswa kubva kwavari uye anopararira kune akavakidzana. Munguva yekuibva kweSmoluchowski, zvimedu zvakakura zvinoumbwa semugumisiro wekutama uye kuungana kwemasumbu ose. Imwe mhando yekuibva inogona kusiyaniswa kubva kune imwe seinotevera: neOstwald kuibva, kugoverwa kwehukuru hwemasumbu kunowedzera uye kunoenderera, uye nekuibva kweSmoluchowski, saizi inogoverwa zvakapusa.
Pamachati 3B и 3С mhedzisiro yekuongororwa kweanopfuura masumbu e300 anoratidzwa, i.e. saizi kugovera. Huwandu hwemasumbu akacherechedzwa hurefu hwakafara, asi mapoka matatu eanonyanya kuzivikanwa anogona kusiyaniswa (3С): 0.85, 1.10 uye 1.33 nm.
Sezvinoonekwa mugirafu 3B, pane kuwirirana pakati pekukosha kwehurefu nehupamhi hwesumbu. Iwo akacherechedzwa masumbu zvimiro anoratidza maficha eSmoluchowski maturation.
Pane zvakare kuwirirana pakati pemasumbu mune yakakwirira uye yakaderera deposition density miedzo. Nokudaro, boka remasumbu ane urefu hwe 0.85 nm rinopindirana neboka rega rega rine urefu hwe 0.88 nm mukuedza nekuderera kwepasi. Naizvozvo, masumbu kubva kuboka rekutanga akapihwa kukosha kweAu20, uye masumbu kubva kune yechipiri (1.10 nm) uye yechitatu (1.33 nm) akapihwa kukosha Au40 uye Au60, zvichiteerana.
Mufananidzo #4
Mumufananidzo 4A tinogona kuona misiyano yekuona pakati pemapoka matatu emasumbu, iyo dI/dV spectra inoratidzwa mugirafu. 4B.
Sezvo masumbu eAu20 anobatana kuita gaka rakakura resimba mune spectrum, dI/dV inodzikira. Saka, kuboka rega rega maitiro anotevera ekusiya akawanikwa: Au20—3.0 eV, Au40—2.0 eV, uye Au60—1.2 eV. Tichifunga nezve data iyi, pamwe chete nemifananidzo yenzvimbo dzemapoka akadzidzwa, zvinogona kupokana kuti geometry ye cluster agglomerates iri padyo nedenderedzwa kana hemispherical.
Kuti ufungidzire huwandu hwemaatomu mumapoka espherical uye hemispherical, unogona kushandisa Ns = [(h/2)/r]3 uye Nh = 1/2 (h/r)3, apo h и r inomiririra kureba kwesumbu uye radius yeimwe Au atomu. Tichifunga nezve Wigner-Seitz radius yeatomu yegoridhe (r = 0.159 nm), tinogona kuverenga nhamba yavo ye spherical approximation: boka rechipiri (Au40) - 41 maatomu, boka rechitatu (Au60) - 68 maatomu. Mukuenzanisa kwehemispherical, huwandu hunofungidzirwa hwemaatomu 166 uye 273 hwakakwira zvakanyanya kupfuura muAu40 neAu60 mukuenzanisa kwedenderedzwa. Naizvozvo, zvinogona kugumiswa kuti iyo geometry yeAu40 uye Au60 ndeye spherical kwete hemispherical.
Kuti uwane rumwe ruzivo nezve nuances yechidzidzo, ini ndinokurudzira kutarisa и kwaari.
Epilogue
В данном исследовании ученые объединили сканирующую туннельную спектроскопию и микроскопию, что позволило им получить более точные данные касательно геометрии кластеров атомов золота. Было установлено, что кластер Au20, нанесенный на подложку 3L NaCl / Au (111), сохраняет свою газофазную пирамидальную структуру с большим HL разрывом. Также было установлено, что основным механизмом роста и объединения кластеров в группы является созревание Смолуховского.
Vesainzi vanodana chimwe chebudiriro huru dzebasa ravo kwete zvakanyanya mhedzisiro yetsvakiridzo pamasumbu eatomu, asi kuti nzira yekuitisa tsvagiridzo iyi. Kare, transmission scanning electron microscope yakashandiswa, iyo, nekuda kwehupfumi hwayo, yakakanganisa migumisiro yekucherechedza. Zvisinei, nzira itsva inotsanangurwa mubasa iri inotibvumira kuwana data yakarurama.
Pakati pezvimwe zvinhu, kudzidza zvimiro zvemasumbu kunotitendera kuti tinzwisise iwo catalytic uye optical zvimiro, izvo zvakakosha zvakanyanya pakushandisa kwavo mu cluster catalysts uye optical zvishandiso. Parizvino, masumbu atoshandiswa mumaseru emafuta uye kubatwa kwekabhoni. Zvisinei, maererano nemasayendisiti pachavo, iyi haisi iyo muganhu.
Ndatenda nekuverenga, garai muchida kuziva uye muve nevhiki yakanaka vakomana. 🙂
Dzimwe ads 🙂
Ndinokutendai nekugara nesu. Unoda zvinyorwa zvedu here? Unoda kuona zvimwe zvinonakidza zvemukati? Titsigire nekuisa odha kana kukurudzira kushamwari, , yakasarudzika analogue yekupinda-level maseva, iyo yakagadzirwa nesu kuti iwe: (inowanikwa neRAID1 uye RAID10, kusvika ku24 cores uye kusvika ku40GB DDR4).
Dell R730xd 2 nguva yakachipa muEquinix Tier IV data center muAmsterdam? Chete pano muNetherlands! Dell R420 - 2x E5-2430 2.2Ghz 6C 128GB DDR3 2x960GB SSD 1Gbps 100TB - kubva pamadhora makumi mapfumbamwe nemapfumbamwe! Verenga nezve
Source: www.habr.com