ʻO ka honua a puni mākou ka hopena hui o nā hanana a me nā kaʻina hana mai nā ʻano ʻepekema like ʻole, aneane hiki ʻole ke koho i ka mea nui loa. ʻOiai ke ʻano o ka hoʻokūkū, nui nā ʻano o kekahi mau ʻepekema i loaʻa nā hiʻohiʻona like. E lawe kākou i ka geometry ma ke ʻano he laʻana: ʻo nā mea a pau a mākou e ʻike ai he ʻano like ʻole, ʻo ia kekahi o nā mea maʻamau i ke ʻano he pōʻai, pōʻai, pōʻai, pōpō (he ʻano ma ka maka). Hōʻike ʻia ka makemake e lilo i spherical ma nā hōkūhele a me nā pūʻulu atomika. Akā, aia mau ka ʻokoʻa i nā lula. Ua ʻike nā kānaka ʻepekema mai ke Kulanui o Leuven (Belgium) ʻaʻole i spherical nā ʻātoma gula, akā nā puʻupuʻu pyramidal. He aha ke kumu o kēia ʻano maʻamau o nā atom gula, he aha nā waiwai i loaʻa i nā pyramids makamae, a pehea e hoʻohana ʻia ai kēia ʻike i ka hana? Aʻo mākou e pili ana i kēia mai ka hōʻike a nā ʻepekema. Hele.
Kumu noiʻi
Ua ʻike ʻia ke ola ʻana o nā pūʻulu maʻamau o nā ʻātoma gula no kekahi manawa. Loaʻa kēia mau hale i nā mea kemika a me nā waiwai uila, ʻo ia ke kumu i hoʻonui wale ʻia ai ka hoihoi iā lākou i nā makahiki. ʻO ka hapa nui o nā haʻawina i kālele ʻia i ke aʻo ʻana i nā hilinaʻi dimensional, akā ʻo ia ʻano noiʻi e koi i ka synthesis hoʻomalu a me nā ana kiʻekiʻe.
Ma keʻano maʻamau, aia nā ʻano hui like ʻole, akā ʻo ka mea kaulana loa no ke aʻo ʻana ʻo Au20, ʻo ia hoʻi, kahi hui o 20 mau ʻāpana gula. ʻO kona kaulana ma muli o kāna symmetrical nui tetrahedral* hale a kāhāhā nui HOMO-LUMO (HL) ma ke ākea (ākea)*.
Tetrahedron* - he polyhedron me nā huinakolu ʻehā e like me nā maka. Inā mākou e noʻonoʻo i kekahi o nā maka i ke kumu, a laila hiki ke kapa ʻia ka tetrahedron he pyramid triangular.
HOMO-LUMO āwaha (ākea)* — ʻO HOMO a me LUMO nā ʻano orbital molecular (he hana makemakika e wehewehe ana i ka ʻano nalu o nā electrons i loko o kahi mole). Kū ʻo HOMO no ka orbital molecular kiʻekiʻe i noho ʻia, a ʻo LUMO no ka orbital molecular haʻahaʻa loa. Hoʻopiha nā electrons o kahi mole ma ka ʻāina honua i nā orbital āpau me ka ikaika haʻahaʻa. ʻO ka orbital i loaʻa ka ikehu kiʻekiʻe ma waena o nā mea i hoʻopiha ʻia ʻo HOMO. ʻO ka LUMO ka orbital ikehu haʻahaʻa loa. ʻO ka ʻokoʻa ikehu ma waena o kēia mau ʻano orbital ʻelua i kapa ʻia ʻo ka HOMO-LUMO gap.
Ua hōʻike ʻo Photoelectron spectroscopy o Au20 he 1.77 eV ka lua HOMO-LUMO.
Ua hōʻike ʻia nā hoʻohālikelike i hana ʻia ma ke kumu o ka manaʻo hana hoʻopaʻapaʻa (he ʻano no ka helu ʻana i ka ʻōnaehana uila o nā ʻōnaehana) i hōʻike ʻia e hiki ke hoʻokō ʻia kēlā ʻokoʻa ikehu ma o ka pyramid tetrahedral o Td symmetry (tetrahedral symmetry), ʻo ia ka geometry paʻa loa no ka hui Au20.
Hoʻomaopopo ka poʻe ʻepekema ʻo ka noiʻi mua ma Au20 i hāʻawi i nā hopena pololei ʻole ma muli o ka paʻakikī o ke kaʻina hana. Ma mua, ua hoʻohana ʻia kahi microscope electron scanning transmission, ʻo ka ikehu kiʻekiʻe o ka kukuna i hoʻololi i nā hopena nānā: ʻike ʻia kahi loli mau o Au20 ma waena o nā hoʻonohonoho hoʻonohonoho like ʻole. Ma ka 5% o nā kiʻi i loaʻa, ʻo ka hui Au20 he tetrahedral, a ma ke koena, ua hoʻopilikia loa ʻia kona geometry. No laila, ʻaʻole hiki ke kapa ʻia ke ʻano o ka tetrahedral Au20 ma kahi substrate, no ka laʻana, ʻaʻole hiki ke kapa ʻia ke kalapona amorphous he XNUMX% hōʻoia.
Ma ke aʻo ʻana a mākou e loiloi nei i kēia lā, ua hoʻoholo nā ʻepekema e hoʻohana i kahi ala maʻalahi no ke aʻo ʻana iā Au20, ʻo ia hoʻi ka scanning tunneling microscopy (STM) a me ka scanning tunneling spectroscopy (STS). ʻO nā mea i nānā ʻia, ʻo ia nā pūʻulu Au20 ma nā kiʻi ʻoniʻoni ultrathin NaCl. Ua ʻae ʻo STM iā mākou e hōʻoia i ka symmetry triangular o ka hale pyramidal, a ua hiki i ka ʻikepili STS ke helu i ka ʻāpana HOMO-LUMO, ʻo ia ka nui o 2.0 eV.
Nā hoʻomākaukau no ka noi
Hoʻoulu ʻia ka papa NaCl ma kahi pānaʻi Au(111) me ka hoʻohana ʻana i ka hoʻoheheʻe ʻana i ka mahu ma 800 K i loko o kahi keʻena STM ma lalo o nā kūlana ʻūhā ultrahigh.
Ua hana ʻia nā ion hui Au20 ma o ka hoʻonohonoho ʻana i ka magnetron sputtering a me ka nui i koho ʻia me ka hoʻohana ʻana i kahi kānana quadrupole mass. Hoʻohana ʻia ke kumu sputtering ma ke ʻano hoʻomau a hoʻohua i kahi hapa nui o nā puʻupuʻu i hoʻopaʻa ʻia, a ma hope iho ua komo i ka kānana quadrupole mass. Ua waiho ʻia nā pūʻulu i koho ʻia ma luna o kahi substrate NaCl/Au(111). No ka haʻahaʻa haʻahaʻa haʻahaʻa, ʻo ka puʻupuʻu puʻupuʻu he 30 pA (picoamps) a ʻo ka manawa deposition he 9 mau minuke; no ka hoʻopaʻa ʻana kiʻekiʻe, ʻo ia ka 1 nA (nanoamps) a me 15 mau minuke. ʻO ke kaomi i loko o ke keʻena he 10-9 mbar.
Nā hopena noiʻi
Ua waiho ʻia nā pūʻulu anionic Au20 i koho ʻia me ka haʻahaʻa haʻahaʻa loa ma ka lumi wela ma nā mokupuni ultrathin NaCl, me 2L, 3L, a me 4L (nā papa ʻātoma).
Kiʻi #1
maluna o 1A Hiki ke ʻike ʻia ʻo ka hapa nui o ka NaCl i ulu ʻia he ʻekolu papa, ʻo nā wahi me ʻelua a me ʻehā mau ʻāpana e noho i kahi wahi liʻiliʻi, a ʻaʻole i loaʻa nā wahi 5L.
Ua loaʻa nā pūʻulu Au20 ma nā ʻāpana ʻekolu a me ʻehā, akā ʻaʻole i loaʻa ma 2L. Ua wehewehe ʻia kēia e ka mea hiki iā Au20 ke hele ma 2L NaCl, akā i ka hihia o 3L a me 4L NaCl, ua paʻa ia ma ko lākou ʻili. Ma ka haʻahaʻa haʻahaʻa coating density i loko o ka māhele o 200 x 200 nm, mai 0 a hiki i 4 mau puʻupuʻu i ʻike ʻia me ka ʻole o nā hōʻailona o Au20 agglomeration (accumulation).
Ma muli o ke kūpale kiʻekiʻe loa o ka 4L NaCl a me ka paʻa ʻole i ka nānā ʻana i ka Au20 hoʻokahi ma 4L NaCl, ua ʻike nā ʻepekema i ke aʻo ʻana i nā pūʻulu ma 3L NaCl.
Kiʻi #2
Ua hōʻike ʻia ka microscopy o nā pūʻulu ma 3L NaCl i ko lākou kiʻekiʻe he 0.88 ± 0.12 nm. Kūlike maikaʻi kēia helu me nā hopena hoʻohālike, i wānana i ke kiʻekiʻe o 0.94 ± 0.01 nm (2A). Ua hōʻike pū ʻia ʻo Microscopy he ʻano triangular kekahi mau puʻupuʻu me hoʻokahi atom e puka ana ma luna, a ma ka hoʻomaʻamaʻa e hōʻoia i ka noiʻi ʻana e pili ana i ke ʻano pyramidal o ka hale Au20 (2B).
Hoʻomaopopo ka poʻe ʻepekema i ka nānā ʻana i nā mea liʻiliʻi liʻiliʻi ʻekolu-dimensional, e like me nā pūʻulu Au20, he mea paʻakikī loa ke pale aku i kekahi mau hemahema. I mea e loaʻa ai nā kiʻi pololei loa (mai ka manaʻo atomic a me ka geometric), pono e hoʻohana i ka piko microscope Cl-functionalized atomically koi. Ua ʻike ʻia kahi ʻano pyramidal i ʻelua pūʻulu (1B и 1С), hōʻike ʻia nā kiʻi ʻekolu ʻāpana i loko 1D и 1E, pakahi.
ʻOiai ke hōʻike nei ke ʻano triangular a me ke kiʻekiʻe i ka mālama ʻana o nā puʻupuʻu i waiho ʻia i kahi ʻano pyramidal, nā kiʻi STM (1B и 1С) ʻaʻole hōʻike i nā hale tetrahedral maikaʻi loa. ʻO ka huina nui loa ma ke kiʻi 1B ma kahi o 78°. A he 30% ʻoi aku kēia ma mua o 60° no kahi tetrahedron kūpono me Td symmetry.
ʻElua paha kumu no kēia. ʻO ka mea mua, aia nā hewa i ke kiʻi ponoʻī, ma muli o ka paʻakikī o kēia kaʻina hana a me ka ʻoiaʻiʻo ʻaʻole paʻa ka piko o ka nila microscope, a hiki i kēia ke hoʻololi i nā kiʻi. ʻO ke kumu ʻelua ma muli o ka distortion kūloko o ka Au20 i kākoʻo ʻia. I ka hui ana o Au20 me ka Td symmetry aina ma ka huinahalike NaCl lattice, hoololi ka like ole o ka hoano i ka hana tetrahedral maikai o Au20.
I mea e ʻike ai i ke kumu o ia ʻano hoʻokaʻawale ʻana i nā kiʻi, ua kālailai nā ʻepekema i ka ʻikepili e pili ana i ka symmetry o ʻekolu mau hale Au20 i hoʻopaʻa ʻia ma NaCl. ʻO ka hopena, ua ʻike ʻia ua hoʻokaʻawale iki ʻia nā pūʻulu mai ka hale tetrahedral maikaʻi loa me ka symmetry Td me ka ʻokiʻoki loa i nā kūlana atomika o 0.45. No laila, ʻo nā distortions i loko o nā kiʻi ka hopena o nā hemahema i ke kaʻina hana kiʻi ponoʻī, a ʻaʻole i kekahi deviations i ka waiho ʻana o nā puʻupuʻu ma ka substrate a / a i ʻole ka pilina ma waena o lākou.
ʻAʻole wale ka ʻikepili topographic i nā hōʻailona maopopo o ke ʻano pyramidal o ka hui Au20, akā he ʻāpana HL nui loa (ma kahi o 1.8 eV) i hoʻohālikelike ʻia me nā Au20 ʻē aʻe. isomers* me ka ikehu haʻahaʻa (ma ke kumumanaʻo ma lalo o 0.5 eV).
Isomers* - nā hale e like me ka haku mele a me ke kaumaha mole, akā ʻokoʻa ko lākou ʻano a i ʻole ka hoʻonohonoho ʻana o nā mana.
Ka nānā ʻana i nā waiwai uila o nā puʻupuʻu i waiho ʻia ma kahi substrate me ka scanning tunneling spectroscopy (1F) ua hiki ke kiʻi i ka ʻokoʻa conductivity spectrum (dI/dV) o ka hui Au20, e hōʻike ana i kahi ʻāpana kaha nui (Eg) like me 3.1 eV.
Ma muli o ka hoʻokaʻawale ʻana o ka puʻupuʻu ma o ka hoʻokaʻawale ʻana i nā kiʻiʻoniʻoni NaCl, ua hoʻokumu ʻia kahi hui tunnel pālua ʻelua (DBTJ), kahi e hoʻoulu ai i nā hopena tunneling electron hoʻokahi. No laila, ʻo ka hoʻopau ʻana i ka spectrum dI/dV ka hopena o ka hana hui o ka quantum HL discontinuity (EHL) a me ka ikehu Coulomb maʻamau (Ec). Ua hōʻike ʻia nā ana o nā haʻihaʻi i ka spectrum mai ka 2.4 a i ka 3.1 eV no ʻehiku puʻupuʻu (1F). ʻOi aku ka nui o nā discontinuities i ʻike ʻia ma mua o ka HL discontinuities (1.8 eV) ma ka pae kinoea Au20.
ʻO ka ʻokoʻa o nā haʻihaʻi ma nā ʻāpana like ʻole ma muli o ke kaʻina ana ponoʻī (ke kūlana o ka nila e pili ana i ka hui). ʻO ka ʻāpana nui loa i ana ʻia ma ka spectra dI/dV he 3.1 eV. I kēia hihia, aia ka piko ma kahi mamao loa mai ka pūʻulu, kahi i hana ai ka capacitance uila ma waena o ka piko a me ka hui ʻoi aku ka liʻiliʻi ma waena o ka hui a me ka substrate Au (111).
Ma hope aʻe, ua hana mākou i ka helu ʻana o nā HL ruptures o nā pūʻulu Au20 manuahi a me nā mea i loaʻa ma 3L NaCl.
Hōʻike ka pakuhi 2C i ka mānoanoa hoʻohālikelike o nā ʻāpana mokuʻāina no kahi tetrahedron Au20 ma ke kinoea nona ka HL he 1.78 eV. Ke loaʻa ka pūʻulu ma 3L NaCl/Au(111), piʻi ka distortions a emi ka HL mai ka 1.73 a i ka 1.51 eV, e like me ka HL āpau o 2.0 eV i loaʻa i ka wā hoʻokolohua.
Ma nā haʻawina mua, ua ʻike ʻia ʻo Au20 isomers me kahi Cs-symmetric ʻano he HL āpau o kahi 0.688 eV, a me nā hale me ka amorphous symmetry - 0.93 eV. I ka noʻonoʻo ʻana i kēia mau ʻike a me nā hopena o nā ana, ua hiki mai nā ʻepekema i ka hopena e hiki ke loaʻa kahi ākea nui ma lalo o nā kūlana o kahi ʻano pyramidal tetrahedral.
ʻO ka pae aʻe o ka noiʻi ʻana, ʻo ia ke aʻo ʻana i nā hui puʻupuʻu puʻupuʻu, kahi i waiho ʻia ai ka Au3 (hoʻonui nui ʻia) ma ka substrate 111L NaCl/Au(20).
Kiʻi #3
Ma ke kiʻi 3A hōʻike ʻia kahi kiʻi topographic STM o nā pūʻulu i waiho ʻia. Ma kahi o 100 mau puʻupuʻu i ʻike ʻia ma ka wahi nānā (100 nm x 30 nm). ʻOi aku ka nui a i ʻole like me ka nui o nā puʻupuʻu pili ma 3L NaCl i nā nui o nā mea i aʻo ʻia ma nā hoʻokolohua me nā pūʻulu hoʻokahi. Hiki ke wehewehe ʻia kēia e ka diffusion a me ka agglomeration (clumping) ma luna o ka ʻili o NaCl i ka lumi wela.
Hiki ke wehewehe ʻia ka hōʻiliʻili a me ka ulu ʻana o nā puʻupuʻu e nā ʻano hana ʻelua: Ostwald ripening (recondensation) a me Smoluchowski ripening (enlargement of islands). I ke ʻano o ka oʻo ʻana o Ostwald, ulu nā ʻōpala nui ma ke kumukūʻai o nā mea liʻiliʻi, i ka wā e hoʻokaʻawale ʻia ai nā ʻātoma o ka hope mai iā lākou a hoʻopuehu i nā mea kokoke. I ka wā e oʻo ai ʻo Smoluchowski, ua hoʻokumu ʻia nā ʻāpana nui ma muli o ka neʻe ʻana a me ka hoʻohui ʻana o nā pūpū holoʻokoʻa. Hiki ke ho'oka'awale 'ia kekahi 'ano o ka 'o'o 'ana mai kekahi 'ē a'e penei: me ka o'o 'ana o Ostwald, ho'onui a ho'omau 'ia ka ho'olaha 'ana o ka nui pu'upu'u, a me ka o'o 'ana o Smoluchowski, puunaue 'ia ka nui.
Ma nā pakuhi 3B и 3С ua hōʻike ʻia nā hopena o ka loiloi ʻana ma mua o 300 mau pūʻulu, ʻo ia hoʻi. mahele nui. He ākea ka laulā o nā kiʻekiʻe puʻupuʻu i ʻike ʻia, akā hiki ke ʻike ʻia ʻekolu mau pūʻulu o nā mea maʻamau (3С): 0.85, 1.10 a me 1.33 nm.
E like me ka mea i ʻike ʻia ma ka pakuhi 3B, aia ka pilina ma waena o ka waiwai o ke kiʻekiʻe a me ka laula o ka hui. Hōʻike ʻia nā hiʻohiʻona o ka hui ʻana o Smoluchowski.
Aia kekahi pilina ma waena o nā pūʻulu i nā hoʻokolohua kiʻekiʻe a haʻahaʻa. No laila, ʻo kahi hui o nā pūʻulu me ke kiʻekiʻe o 0.85 nm e kūlike me kahi pūʻulu pākahi me ke kiʻekiʻe o 0.88 nm i nā hoʻokolohua me ka haʻahaʻa haʻahaʻa. No laila, ua hāʻawi ʻia nā pūʻulu mai ka hui mua i ka waiwai Au20, a ua hāʻawi ʻia nā pūʻulu mai ka lua (1.10 nm) a me ke kolu (1.33 nm) i nā waiwai Au40 a me Au60.
Kiʻi #4
Kiʻi ʻia 4A hiki iā mākou ke ʻike i nā ʻokoʻa ʻike ma waena o nā ʻāpana ʻekolu o nā pūʻulu, ʻo ka spectra dI/dV o ia mea i hōʻike ʻia ma ka pakuhi. 4B.
I ka hui ʻana o nā pūʻulu Au20 i kahi ākea ikehu ʻoi aku ka nui o ka spectrum, emi iho ka dI/dV. No laila, no kēlā me kēia pūʻulu ua loaʻa nā helu discontinuity penei: Au20—3.0 eV, Au40—2.0 eV, a me Au60—1.2 eV. Ma ka noʻonoʻo ʻana i kēia mau ʻikepili, a me nā kiʻi topographic o nā pūʻulu i aʻo ʻia, hiki ke hoʻopaʻapaʻa ʻia ʻo ka geometry o nā agglomerates puʻupuʻu ua kokoke i ka spherical a i ʻole hemispherical.
No ka hoʻohālikelike ʻana i ka helu o nā ʻātoma ma nā pūʻulu spherical a me nā hemispherical, hiki iā ʻoe ke hoʻohana i Ns = [(h/2)/r]3 a me Nh = 1/2 (h/r)3, kahi h и r hōʻike i ke kiʻekiʻe puʻupuʻu a me ka radius o hoʻokahi Au atom. I ka noʻonoʻo ʻana i ka radius Wigner-Seitz no ka atom gula (r = 0.159 nm), hiki iā mākou ke helu i kā lākou helu no ka spherical approximation: ʻo ka lua o ka hui (Au40) - 41 mau ʻāpana, ʻo ke kolu o ka hui (Au60) - 68 mau mana. Ma ka hemispherical approximation, ua oi loa aku ka nui o ka helu o na atoms 166 a me 273 ma mua o Au40 a me Au60 ma ka spherical approximation. No laila, hiki ke hoʻoholo ʻia he spherical ka geometry o Au40 a me Au60 ma mua o ka hemispherical.
No ka ʻike kikoʻī i nā nuances o ke aʻo ʻana, manaʻo wau e nānā и iāia.
Epilogue
I loko o kēia noiʻi ʻana, ua hoʻohui nā ʻepekema i ka scanning tunneling spectroscopy a me ka microscopy, i hiki ai iā lākou ke loaʻa i ka ʻikepili pololei e pili ana i ka geometry o nā pūpū o nā mana gula. Ua ʻike ʻia ʻo ka puʻupuʻu Au20 i waiho ʻia ma kahi substrate 3L NaCl/Au(111) e paʻa i kona ʻano pyramidal kinoea me kahi ākea HL nui. Ua ʻike ʻia ʻo ke kumu nui o ka ulu ʻana a me ka hui ʻana o nā puʻupuʻu i loko o nā hui ʻo Smoluchowski maturation.
Kāhea ka poʻe ʻepekema i kekahi o nā hana nui o kā lākou hana ʻaʻole i ka hopena o ka noiʻi ʻana i nā pūʻulu atomic, akā ke ʻano o ka hana ʻana i kēia noiʻi. Ma mua, ua hoʻohana ʻia kahi microscope electron scanning transmission, ma muli o kāna mau waiwai, hoʻololi i nā hopena o ka nānā ʻana. Eia naʻe, ʻo ke ala hou i wehewehe ʻia ma kēia hana e hiki ai iā mākou ke loaʻa ka ʻikepili pololei.
Ma waena o nā mea ʻē aʻe, ʻo ke aʻo ʻana i nā hale cluster e hiki ai iā mākou ke hoʻomaopopo i kā lākou catalytic a me nā waiwai optical, he mea nui loa ia no kā lākou hoʻohana ʻana i nā catalysts cluster a me nā mea optical. I kēia manawa, ua hoʻohana ʻia nā pūʻulu i loko o nā wahie a me ka hopu kalapona. Eia naʻe, e like me ka poʻe ʻepekema ponoʻī, ʻaʻole kēia ka palena.
Mahalo no ka heluhelu ʻana, noʻonoʻo a hauʻoli maikaʻi nā kāne. 🙂
Kekahi mau hoʻolaha 🙂
Mahalo no kou noho pū ʻana me mākou. Makemake ʻoe i kā mākou ʻatikala? Makemake ʻoe e ʻike i nā mea hoihoi hou aʻe? E kākoʻo iā mākou ma ke kau ʻana i kahi kauoha a i ʻole ka ʻōlelo ʻana i nā hoaaloha, , he analogue kū hoʻokahi o nā kikowaena hoʻokomo-level, i hana ʻia e mākou no ʻoe: (loaʻa me RAID1 a me RAID10, a hiki i 24 cores a hiki i 40GB DDR4).
ʻO Dell R730xd 2 mau manawa maʻalahi ma Equinix Tier IV kikowaena data ma Amsterdam? Eia wale nō ma Netherlands! Dell R420 - 2x E5-2430 2.2Ghz 6C 128GB DDR3 2x960GB SSD 1Gbps 100TB - mai $99! Heluhelu e pili ana
Source: www.habr.com