Chemistry at the Interface of α-Sexithiophene and Vapor-Deposited Ag, Al, Mg, and Ca: A Molecular View

Abstract

Interfacial chemistry of thiophene-based polymers and oligomers in contact with low work function metals is of interest for organic electronic devices. Herein, interfacial reactions of the model thiophene-based oligomer, α-sexithiophene (α-6T), in ultrathin (5 ML) films with vapor-deposited Ag, Al, Mg, and Ca are investigated using surface Raman spectroscopy and X-ray photoelectron spectroscopy under ultrahigh vacuum conditions. Although typically considered an electron donor, results indicate that α-6T is reduced by Al and Ca. The reduction product with Al is the tetrahydrothiophene, whereas complete degradation of the thiophene cores occurs with Ca with the formation of calcium sulfide. In contrast, for the higher work function Ag, contact doping from α-6T to Ag nanoparticles is observed, inducing the formation of polaron states at the interface. Inter-ring torsion by the C–C bond rotation is also induced by electron sharing between α-6T and Ag. Mg, which is expected to undergo electron transfer in a manner similar to Ca based on the work function, instead diffuses through these 5 ML films and deposits on or alloys with the Ag substrate beneath; however, electron transfer from Mg to α-6T is observed in thicker α-6T films suggesting that nucleation into structures with electronic characteristics that resemble those of bulk Mg metal occurs. Overall, the evolution of α-6T interfaces with these low work function metals alters the interfacial energetics through the formation of “gap” states, which ultimately impact the device performance.

Spinterface Formation at α-Sexithiophene/Ferromagnetic Conducting Oxide

“…57−59 The lower binding energy peak at 162.7 eV (S1) is typical of sulfide which is presumably S linked to the metal atoms of LSMO surface. 60,61 This feature is also consistent with partial charge transfer, as observed for aluminum deposition on 6T. 61 Higher binding-energy components (S2 and S3) can be attributed to the thiophene groups not directly interacting with the substrate because their photoemission-induced core holes are not well screened by valence electrons of the substrate.…”

“…After a Shirley background subtraction, spectra were decomposed into three multiple doublet components with a 1.2 eV spin–orbit splitting reflecting the nonequivalent S atom in the molecule . Considering that 6T adsorbs on LSMO with its long axis upright to the surface, three such S components can be assigned to the central thiol sulfur atoms from the main chain and the two sulfur atoms at the sides, the one close to the surface and the one that is free. − The lower binding energy peak at 162.7 eV (S1) is typical of sulfide which is presumably S linked to the metal atoms of LSMO surface. , This feature is also consistent with partial charge transfer, as observed for aluminum deposition on 6T . Higher binding-energy components (S2 and S3) can be attributed to the thiophene groups not directly interacting with the substrate because their photoemission-induced core holes are not well screened by valence electrons of the substrate .…”

Penetration and Reaction Depths of Vapor Deposited Ag, Mg, Al, and Ca on Oligothiophene Thin Films

“…XPS spectra in the S 2p binding energy region from 5 ML α-6T films before and after deposition of small coverages of metal have been described previously . For Al and Ca, new S 2p peaks with binding energies lower than the original S 2p peaks are observed, indicating formation of reduced α-6T forms.…”

“…Following our recent spectroscopic studies of metal–organic interfacial molecular processes between Ag, Al, Mg, and Ca and oligothiophenes, including 2,2′:5′,2″-terthiophene (α-3T) and α-sexithiophene (α-6T), this work describes estimation of both the penetration depth of different metals as well as the impact depth of the reaction chemistry of these oliogthiophenes (OTs) using spectroscopic methods. These two oligothiophenes have very similar spectroscopic and materials properties and both are well-accepted as models for polythiophene-based active layer materials. − Here, Raman spectroscopy is combined with depth sensitive, angle-dependent X-ray photoelectron spectroscopy (XPS) to explore OT reduction chemistry as a function of metal coverage.…”

Нанокластеры Серебра В Биохимии И Медицине (Обзор)

“… òî aeå âðåìÿ âåñüìà âûñîêàÿ ñêëîííîñòü òèîëàòîâ çîëîòà ê îáðàçîâàíèþ ðàçíîîáðàçíûõ ñóïåðìîëåêóëÿðíûõ êîìáèíàöèé îòêðûâàåò íîâûå ïóòè äëÿ âîçíèêíîâåíèÿ òàêèõ ìàòåðèàëîâ, ñòðóêòóðà êîòîðûõ íåïîñðåäñòâåííî ñâÿçàíà ñ èõ îïòè÷åñêèìè ñâîéñòâàìè; ñâåaeèì ïðèìåðîì ïîäîáíûõ ìàòåðèàëîâ ÿâëÿþòñÿ 100 íì-ðàçìåðà ñâåðõìîëåêóëÿðíûå àíñàìáëè Au-C, â òîì ÷èñëå èõ îáëåïëåííûé êëàñòåðàìè Ag áèìåòàëëè-÷åñêèé âàðèàíò [49] 18 (x ³ 2) òàêaeå çàâèñåëî íå òîëüêî îò ìåòîäà ñèíòåçà, íî è îò âðåìåíè èõ íàõîaeäåíèÿ â ðàñòâîðå [51]. Ìåaeäó òåì äàaeå â òîíêèõ, âêëþ÷àâøèõ íàïû-ë¸ííûå ÷àñòèöû ñåðåáðà ïë¸íêàõ ìîäåëüíîãî îëèãîìåðà, äëÿ êîòîðîãî õàðàêòåðíà ñòðóêòóðà òèîôåíàa-ñåêñèòèîôåíà, áûëè çàðåãèñòðèðîâàíû èíòåíñèâíûå ìåaeïîâåðõíîñòíûå ðåàêöèè; ïî äåôîðìàöèè åãî êîëüöà, âûçâàííîãî âðàùåíèåì s-ñâÿçè, ñäåëàí âûâîä î ïðîíèêíîâåíèè îëèãîìåðà â ñàìè ÷àñòèöû âî âðåìÿ ùàäÿùåãî ðåaeèìà ðàáîòû äåâàéñà [52].…”