Abstract
We have investigated the influence of the structure of oxide surfaces on the thermal stability of anchored phthalic acid (PA) thin films. Specifically, we have performed temperature programmed infrared reflection absorption spectroscopy (TP-IRAS) of PA films deposited by physical vapor deposition (PVD) in ultra-high vacuum (UVH) onto three well-ordered surfaces: Co3O4(111), CoO(111) and CoO(100), all grown on Ir(100). Restructuring and desorption of PA were monitored in situ by TP-IRAS. Upon annealing of PA multilayers, co-adsorbed phthalic anhydride (PAA) desorbs at 200 K and a structural transition to a flat-lying adsorption geometry occurs at 250 K, before the PA multilayer desorbs at 300 K. At temperatures up to 400 K co-adsorbed mono-carboxylates partially desorb and partially convert to bis-carboxylates. Pronounced structure dependencies are observed regarding the thermal stability of the anchored bis-carboxylate monolayers. From Co3O4(111) the anchored PA desorbs over a wide range of temperatures centered at around 540 K. Weaker binding is observed for CoO(111) with desorption temperatures centered around 490 K. The strongest binding occurs on CoO(100), where the anchored PA films are found to be perfectly stable up to 510 K, before desorption starts and centers at around 580 K. The differences in binding strength are rationalized based on the density and the accessibility of the surface Co(2+) ions. The findings show that the atomic structure of the oxide surface plays an important role in the stability of organic hybrid interfaces.
Highlights
Organic thin films on oxide surfaces play a key role in hybrid materials for molecular electronics[1,2] or photovoltaics.[3,4,5] To design stable and functional interfaces, the organic molecules often need to be immobilized on the oxide surface
We previously investigated the influence of the surface structure on the binding geometry and mechanism of phthalic acid by time-resolved isothermal infrared reflection absorption spectroscopy (IRAS).[18]
The peaks at 1775, 1790 and 1853 cmÀ1 cannot be assigned to any vibrational mode of phthalic acid (PA), but correspond to phthalic anhydride (PAA).[28,29,30]
Summary
Organic thin films on oxide surfaces play a key role in hybrid materials for molecular electronics[1,2] or photovoltaics.[3,4,5] To design stable and functional interfaces, the organic molecules often need to be immobilized on the oxide surface. The binding mechanism, the kinetics and the energetics of the immobilized organic films are essential factors that control the growth and structure formation of the film and, thereby, its electronic and physico-chemical properties.[6,7,8,9,10,11,12] To address this challenge we follow a surface science approach under ultrahigh vacuum (UHV) conditions. Based on the systematic work of Heinz, Hammer and coworkers (see their review[17] and references therein), we have prepared Co3O4(111), CoO(111) and CoO(100) thin films on Ir(100) Using these structures, we previously investigated the influence of the surface structure on the binding geometry and mechanism of phthalic acid by time-resolved isothermal infrared reflection absorption spectroscopy (IRAS).[18]. It is found that thermal behavior and stability of the anchored films is very different on the three surfaces
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
